WorldWideScience

Sample records for atomic scale study

  1. Atomic-scale studies on the effect of boundary coherency on stability in twinned Cu

    Energy Technology Data Exchange (ETDEWEB)

    Niu, Rongmei; Han, Ke, E-mail: han@magnet.fsu.edu; Su, Yi-Feng; Salters, Vincent J. [National High Magnetic Field Laboratory, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310 (United States)

    2014-01-06

    The stored energy and hardness of nanotwinned (NT) Cu are related to interaction between dislocations and (111)-twin boundaries (TBs) studied at atomic scales by high-angle annular dark-field scanning transmission electron microscope. Lack of mobile dislocations at coherent TBs (CTBs) provides as-deposited NT Cu a rare combination of stability and hardness. The introduction of numerous incoherent TBs (ITBs) reduces both the stability and hardness. While storing more energy in their ITBs than in the CTBs, deformed NT Cu also exhibits high dislocation density and TB mobility and therefore has increased the driving force for recovery, coarsening, and recrystallization.

  2. Atomic-scale studies on the effect of boundary coherency on stability in twinned Cu

    Science.gov (United States)

    Niu, Rongmei; Han, Ke; Su, Yi-Feng; Salters, Vincent J.

    2014-01-01

    The stored energy and hardness of nanotwinned (NT) Cu are related to interaction between dislocations and {111}-twin boundaries (TBs) studied at atomic scales by high-angle annular dark-field scanning transmission electron microscope. Lack of mobile dislocations at coherent TBs (CTBs) provides as-deposited NT Cu a rare combination of stability and hardness. The introduction of numerous incoherent TBs (ITBs) reduces both the stability and hardness. While storing more energy in their ITBs than in the CTBs, deformed NT Cu also exhibits high dislocation density and TB mobility and therefore has increased the driving force for recovery, coarsening, and recrystallization.

  3. Interaction of primary cascades with different atomic grain boundaries in α-Zr: An atomic scale study

    Energy Technology Data Exchange (ETDEWEB)

    Hatami, F.; Feghhi, S.A.H., E-mail: a.feghhi@gmail.com; Arjhangmehr, A., E-mail: ms.arjangmehr@gmail.com; Esfandiarpour, A.

    2016-11-15

    In this paper, we investigate interaction of primary cascades with grain boundaries (GBs) in α-Zr using the atomistic-scale simulations, and intend to study the influence of different GB structures on production and evolution of defects on picosecond timescale. We observe that, contrary to the previous results in cubic metals, GBs in α-Zr are not necessarily biased toward interstitials, and can preferentially absorb vacancies. Further, in terms of energetic and kinetic behavior, we find that GBs act as defect sinks due to the substantial reduction of defect formation energies and migration barriers in close vicinity of the GB center, with either a preference toward interstitials or vacancies which depends on the atomic structure of the boundaries. Finally, using continuous ion bombardment, we investigate the stability of GBs in sever irradiation environment. The results indicate that the sink strength and efficiency of boundaries varies with increasing accumulated defects in GB region. - Highlights: • GBs in hcp Zr are not necessarily biased toward interstitials. • Defect content within bulk depends on PKA energy, PKA distance, and GB texture. • Defect formation energies and diffusion barriers decrease in close vicinity of GBs. • GBs become locally unstable due to absorption of excess defects in ion bombardment.

  4. Influence of atomic force microscope tip-sample interaction on the study of scaling behavior

    NARCIS (Netherlands)

    Aue, J.; de Hosson, J.T.M.

    1997-01-01

    Images acquired with atomic force microscopy are based on tip-sample interaction. It is shown that using scanning probe techniques for determining scaling parameters of a surface leads to an underestimate of the actual scaling dimension, due to the dilation of tip and surface. How much we

  5. Copper atomic-scale transistors.

    Science.gov (United States)

    Xie, Fangqing; Kavalenka, Maryna N; Röger, Moritz; Albrecht, Daniel; Hölscher, Hendrik; Leuthold, Jürgen; Schimmel, Thomas

    2017-01-01

    We investigated copper as a working material for metallic atomic-scale transistors and confirmed that copper atomic-scale transistors can be fabricated and operated electrochemically in a copper electrolyte (CuSO 4 + H 2 SO 4 ) in bi-distilled water under ambient conditions with three microelectrodes (source, drain and gate). The electrochemical switching-on potential of the atomic-scale transistor is below 350 mV, and the switching-off potential is between 0 and -170 mV. The switching-on current is above 1 μA, which is compatible with semiconductor transistor devices. Both sign and amplitude of the voltage applied across the source and drain electrodes ( U bias ) influence the switching rate of the transistor and the copper deposition on the electrodes, and correspondingly shift the electrochemical operation potential. The copper atomic-scale transistors can be switched using a function generator without a computer-controlled feedback switching mechanism. The copper atomic-scale transistors, with only one or two atoms at the narrowest constriction, were realized to switch between 0 and 1 G 0 ( G 0 = 2e 2 /h; with e being the electron charge, and h being Planck's constant) or 2 G 0 by the function generator. The switching rate can reach up to 10 Hz. The copper atomic-scale transistor demonstrates volatile/non-volatile dual functionalities. Such an optimal merging of the logic with memory may open a perspective for processor-in-memory and logic-in-memory architectures, using copper as an alternative working material besides silver for fully metallic atomic-scale transistors.

  6. Visions of Atomic Scale Tomography

    International Nuclear Information System (INIS)

    Kelly, T.F.; Miller, Michael K.; Rajan, Krishna; Ringer, S.P.

    2012-01-01

    A microscope, by definition, provides structural and analytical information about objects that are too small to see with the unaided eye. From the very first microscope, efforts to improve its capabilities and push them to ever-finer length scales have been pursued. In this context, it would seem that the concept of an ultimate microscope would have received much attention by now; but has it really ever been defined? Human knowledge extends to structures on a scale much finer than atoms, so it might seem that a proton-scale microscope or a quark-scale microscope would be the ultimate. However, we argue that an atomic-scale microscope is the ultimate for the following reason: the smallest building block for either synthetic structures or natural structures is the atom. Indeed, humans and nature both engineer structures with atoms, not quarks. So far as we know, all building blocks (atoms) of a given type are identical; it is the assembly of the building blocks that makes a useful structure. Thus, would a microscope that determines the position and identity of every atom in a structure with high precision and for large volumes be the ultimate microscope? We argue, yes. In this article, we consider how it could be built, and we ponder the answer to the equally important follow-on questions: who would care if it is built, and what could be achieved with it?

  7. Atomic scale study of grain boundary segregation before carbide nucleation in Ni–Cr–Fe Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hui, E-mail: huili@shu.edu.cn [Key Laboratory for Microstructures, Shanghai University, Shanghai 200444 (China); Institute of Materials, Shanghai University, Shanghai 200072 (China); Xia, Shuang [Institute of Materials, Shanghai University, Shanghai 200072 (China); Liu, Wenqing [Key Laboratory for Microstructures, Shanghai University, Shanghai 200444 (China); Liu, Tingguang; Zhou, Bangxin [Institute of Materials, Shanghai University, Shanghai 200072 (China)

    2013-08-15

    Highlights: • Impurities segregated at grain boundaries were observed by atom probe tomography. • The comparison of segregation features in two Ni–Cr–Fe alloys was studied by APT. • C and Cr atoms co-segregated at grain boundaries before carbide precipitation. -- Abstract: Three dimensional chemical information concerning grain boundary segregation before carbide nucleation was characterized by atom probe tomography in two Ni–Cr–Fe alloys which were aged at 500 °C for 0.5 h after homogenizing treatment. B, C and Si atoms segregation at grain boundary in Alloy 690 was observed. B, C, N and P atoms segregation at grain boundary in 304 austenitic stainless steel was observed. C atoms co-segregation with Cr atoms at the grain boundaries both in Alloy 690 and 304 austenitic stainless steel was found, and its effect on the carbide nucleation was discussed. The amount of each segregated element at grain boundaries in the two Ni–Cr–Fe alloys were analyzed quantitatively. Comparison of the grain boundary segregation features of the two Ni–Cr–Fe alloys were carried out based on the experimental results.

  8. Atomic scale study of grain boundary segregation before carbide nucleation in Ni-Cr-Fe Alloys

    Science.gov (United States)

    Li, Hui; Xia, Shuang; Liu, Wenqing; Liu, Tingguang; Zhou, Bangxin

    2013-08-01

    Three dimensional chemical information concerning grain boundary segregation before carbide nucleation was characterized by atom probe tomography in two Ni-Cr-Fe alloys which were aged at 500 °C for 0.5 h after homogenizing treatment. B, C and Si atoms segregation at grain boundary in Alloy 690 was observed. B, C, N and P atoms segregation at grain boundary in 304 austenitic stainless steel was observed. C atoms co-segregation with Cr atoms at the grain boundaries both in Alloy 690 and 304 austenitic stainless steel was found, and its effect on the carbide nucleation was discussed. The amount of each segregated element at grain boundaries in the two Ni-Cr-Fe alloys were analyzed quantitatively. Comparison of the grain boundary segregation features of the two Ni-Cr-Fe alloys were carried out based on the experimental results. The impurity and solute atoms segregate inhomogeneously in the same grain boundary both in 304 SS and Alloy 690. The grain boundary segregation tendencies (Sav) are B (11.8 ± 1.4) > P (5.4 ± 1.4) > N (4.7 ± 0.3) > C (3.7 ± 0.4) in 304 SS, and B (6.9 ± 0.9) > C (6.7 ± 0.4) > Si (1.5 ± 0.2) in Alloy 690. Cr atoms may co-segregate with C atoms at grain boundaries before carbide nucleation at the grain boundaries both in 304 SS and Alloy 690. Ni atoms generally deplete at grain boundary both in 304 SS and Alloy 690. The literature shows that the Ni atoms may co-segregate with P atoms at grain boundaries [28], but the P atoms segregation do not leads to Ni segregation in the current study. In the current study, Fe atoms may segregate or deplete at grain boundary in Alloy 690. But Fe atoms generally deplete at grain boundary in 304 SS. B atoms have the strongest grain boundary segregation tendency both in 304 SS and Alloy 690. The grain boundary segregation tendency and Gibbs free energy of B in 304 SS is higher than in Alloy 690. C atoms are easy to segregate at grain boundaries both in 304 SS and Alloy 690. The grain boundary segregation

  9. Atomic-scale friction : thermal effects and capillary condensation

    NARCIS (Netherlands)

    Jinesh, Kochupurackal Balakrishna Pillai

    2006-01-01

    This work entitled as "Atomic-scale friction: thermal effects and capillary condensation" is a study on the fundamental aspects of the origin of friction from the atomic-scale. We study two realistic aspects of atomic-scale friction, namely the effect of temperature and the effect of relative

  10. Simulations of atomic-scale sliding friction

    DEFF Research Database (Denmark)

    Sørensen, Mads Reinholdt; Jacobsen, Karsten Wedel; Stoltze, Per

    1996-01-01

    Simulation studies of atomic-scale sliding friction have been performed for a number of tip-surface and surface-surface contacts consisting of copper atoms. Both geometrically very simple tip-surface structures and more realistic interface necks formed by simulated annealing have been studied....... Kinetic friction is observed to be caused by atomic-scale Stick and slip which occurs by nucleation and subsequent motion of dislocations preferably between close-packed {111} planes. Stick and slip seems ro occur in different situations. For single crystalline contacts without grain boundaries...... pinning of atoms near the boundary of the interface and is therefore more easily observed for smaller contacts. Depending on crystal orientation and load, frictional wear can also be seen in the simulations. In particular, for the annealed interface-necks which model contacts created by scanning tunneling...

  11. Laboratory studies on tropospheric iodine chemistry: bridging the atomic, molecular and particle scale

    Science.gov (United States)

    Gomez Martin, J.; Saunders, R. W.; Blitz, M. A.; Mahajan, A. S.; Plane, J. M.

    2008-12-01

    High mixing ratios of the iodine oxides IO and OIO have been observed in the polar, mid-latitude and tropical marine boundary layer (MBL). The impact of the iodine chemistry on the oxidizing capacity of the MBL is well documented. Moreover, there is evidence showing that the bursts of new particles measured in coastal regions are produced by the biogenic emission of iodine containing precursors, followed by the photochemical production and condensation of iodine oxide vapours. Airborne measurements of particle growth rates show that these particles can reach significant sizes where they can contribute to the regional aerosol loading, thus suggesting a potential impact on climate on a regional or global scale. Within the frame of the INSPECT project (INorganic Secondary Particle Evolution, Chemistry and Transport) we wish to understand at a fundamental level the tendency for the iodine oxides formed from IO and OIO recombination to condense into particles. Elemental analysis of iodine oxide particles (IOP) made in the laboratory shows that they have the empirical formula I2O5. The major question is how this happens: through formation of I2O5 in the gas phase, followed by polymerization, or by condensation of various IxOy to form amorphous iodine oxides, which subsequently rearrange to I2O5. We are studying the gas phase photochemistry leading to nucleation of IOP, their growth kinetics, aspects of their heterogeneous chemistry, and their properties as ice condensation nuclei. In order to bridge the molecular and the particle scales, a wide variety of techniques are being used, including CRDS, ARAS, LIF, UV-VIS spectroscopy, PI-TOF-MS and mobility particle size scanning. The results obtained so far provide new and interesting insights to the problem. From the gas phase point of view, a unit iodine atom quantum yield from OIO photolysis has been now established across its strong visible spectral bands. This result implies a short lifetime of OIO and explains why in

  12. STM studies of an atomic-scale gate electrode formed by a single charged vacancy in GaAs

    Science.gov (United States)

    Lee, Donghun; Daughton, David; Gupta, Jay

    2009-03-01

    Electric-field control of spin-spin interactions at the atomic level is desirable for the realization of spintronics and spin-based quantum computation. Here we demonstrate the realization of an atomic-scale gate electrode formed by a single charged vacancy on the GaAs(110) surface[1]. We can position these vacancies with atomic precision using the tip of a home-built, low temperature STM. Tunneling spectroscopy of single Mn acceptors is used to quantify the electrostatic field as a function of distance from the vacancy. Single Mn acceptors are formed by substituting Mn adatoms for Ga atoms in the first layer of the p-GaAs(110) surface[2]. Depending on the distance, the in-gap resonance of single Mn acceptors can shift as much as 200meV. Our data indicate that the electrostatic field decays according to a screened Coulomb potential. The charge state of the vacancy can be switched to neutral, as evidenced by the Mn resonance returning to its unperturbed position. Reversible control of the local electric field as well as charged states of defects in semiconductors can open new insights such as realizing an atomic-scale gate control and studying spin-spin interactions in semiconductors. http://www.physics.ohio-state.edu/sim jgupta [1] D. Lee and J.A. Gupta (in preparation) [2] D. Kitchen et al., Nature 442, 436-439 (2006)

  13. Spin-Polarized Scanning Tunneling Microscope for Atomic-Scale Studies of Spin Transport, Spin Relaxation, and Magnetism in Graphene

    Science.gov (United States)

    2017-11-09

    Polarized Scanning Tunneling Microscope for Atomic-Scale Studies of Spin Transport, Spin Relaxation, and Magnetism in Graphene Report Term: 0-Other Email ...Principal: Y Name: Jay A Gupta Email : gupta.208@osu.edu Name: Roland K Kawakami Email : kawakami.15@osu.edu RPPR Final Report as of 13-Nov-2017...studies on films and devices. Optimization of the Cr tip will be the next important step to establish this technique. We are writing up these early

  14. Atomic-scale simulation study of some bulk and interfacial properties of iron aluminium ordered alloys

    International Nuclear Information System (INIS)

    Besson, Remy

    1997-01-01

    A semi-empirical potential was designed for B 2 and DO 3 iron aluminides and used to study point defects and grain boundaries in these compounds. At low temperature, departure from B 2 stoichiometry is accommodated with antisite defects; when T increases, iron vacancies appear and defects have a trend to form clusters, the structure of which is very sensitive to this departure. Our calculations, relying on T = 0 K formation energies, predict the nature of major defects, but lead to underestimated quantitative results, which may point out the essential role of atomic vibrations. In the stoichiometric B 2 compound, the diffusion of both species is induced by four-jump cycles involving iron vacancies. Although the agreement between our calculated activation energies and other experiments is good, the calculated diffusion coefficients are below the experimental ones. Here again, this discrepancy may be put down to the overlooking of phonon contributions. The second application concerns the atomic structures of the [001] (310) symmetric tilt grain boundary in the B 2 and DO 3 compounds. At low temperature, in the stoichiometric B 2 compound, we obtain an iron-rich single stable structure (pseudo-symmetric), whose structure is strongly influenced by the bulk composition (with intergranular segregation of the major element). In the stoichiometric DO 3 compound, many energetically equivalent structures exist, all being systematically aluminium-rich. The study of the B 2 grain boundary structure at high temperature shows a phase transition favouring a symmetric structure. Its high excess energy at low temperature emphasizes the influence of atomic vibrations in the interfacial properties of B 2 Fe-Al compounds. (author) [fr

  15. Atomic scale numerical simulation study of elementary mechanisms of plasticity in aluminium and copper

    International Nuclear Information System (INIS)

    Aslanides, Antoine

    1998-01-01

    This study deals with elementary mechanisms of plasticity, such as the dissociation of a perfect edge dislocation into Shockley partials, the annihilation of dislocation dipoles and the interaction between a dislocation and an interface (free surface and grain boundary). Dislocation core effects are expected to influence crucially these interactions. A deeper understanding of these situations is thus achieved by resorting to an atomistic numerical approach, the application of the elastic theory of dislocations being no longer justified. Two FCC metals are considered: aluminium and copper, with respectively a small and a large dissociation width. An empirical potential for aluminium was designed to study the perfect as well as the dissociated states of the dislocation. The results are compared to the ones obtained with the interaction model for copper, for both the edge and the screw characters. The obtained core radius value ensures the continuity between the atomic and the elastic treatments. The calculations concerning edge dislocation dipole configurations show that there exists a critical distance between the glide planes of the two constitutive dislocations under which a spontaneous recombination occurs. We then compute the variation of the excess energy associated to the gradual approach of an edge dislocation toward the free surface of a crystal. An estimation of the energy required for the introduction of a dislocation in a thin film is obtained. The study of the interaction between a dislocation and a tilt grain boundary shows that the dislocation is absorbed in the interface, the stress required for its extraction being rather large. Finally, by proceeding to the simulation of a tensile test, we demonstrate that the surface steps constitute favoured sites for the nucleation of the dislocations. (author) [fr

  16. Atomic scale study of intrinsic and Mn doped quantum dots in III-V semiconductors

    NARCIS (Netherlands)

    Bozkurt, M.

    2011-01-01

    In this thesis, a Cross Sectional Scanning Tunneling Microscope (X-STM) is used to investigate nanostructures in IIIV semiconductors and single Mn impurities in bulk GaAs. The atomic resolution which can be achieved with X-STM makes it possible to link structural properties of nanostructures to

  17. Atomic scale study of vacancies in Earth's inner core: effect of pressure and chemistry

    Science.gov (United States)

    Ritterbex, S.; Tsuchiya, T.

    2017-12-01

    Seismic observations of the Earth's inner core [1] remain ambiguously related to mineral physics studies of the inner core stable crystalline iron phase [2,3,4,5]. This makes it difficult to clarify the role of plastic deformation as one of the primary candidates responsible for the observed seismic anisotropy of Earth's inner core. Nonetheless, atomic self-diffusion mechanisms provide a direct link between plastic deformation and the mechanical properties of Earth's inner core stable iron phase(s). Using first-principles density functional based calculation techniques, we have studied the conjugate effect of pressure and chemistry on vacancy diffusion in HCP-, BCC- and FCC-iron by taking into account potential light alloying elements as hydrogen, silicon and sulfur. Our results show that inner core pressure highly inhibits the rate of intrinsic self-diffusion by suppressing defect concentration rather than by effecting the mobility of the defects. Moreover, we found light elements to be able to affect metallic bonding which allows for extrinsic diffusion mechanisms in iron under inner core conditions. The latter clearly enables to enhance defect concentration and hence to enhance the rate of plastic deformation. This suggests that inner core chemistry affects the rheological properties (e.g.viscosity) of iron alloys which finally should match with seismic observations. references: [1] Deuss, A., 2014. Heterogeneity and Anisotropy of Earth's inner core. An. Rev. Earth Planet. Sci. 42, 103-126. [2] Anzellini, S., Dewaele, A., Mezouar, M., Loubeyre, P., Morard, G., 2013. Melting of iron at Earth's inner core boundary based on fast X-ray diffraction. Science 340, 464-466. [3] Godwal, B.K., Gonzales-Cataldo, F., Verma, A.K., Stixrude, L., Jeanloz, R., 2015. Stability of iron crystal structures at 0.3-1.5 TPa. [4] Vocadlo, L., 2007. Ab initio calculations of the elasticity of iron and iron alloys at inner core conditions: evidence for a partially molten inner core

  18. Atomic scale study of the chemistry of oxygen, hydrogen and water at SiC surfaces

    International Nuclear Information System (INIS)

    Amy, Fabrice

    2007-01-01

    Understanding the achievable degree of homogeneity and the effect of surface structure on semiconductor surface chemistry is both academically challenging and of great practical interest to enable fabrication of future generations of devices. In that respect, silicon terminated SiC surfaces such as the cubic 3C-SiC(1 0 0) 3 x 2 and the hexagonal 6H-SiC(0 0 0 1) 3 x 3 are of special interest since they give a unique opportunity to investigate the role of surface morphology on oxygen or hydrogen incorporation into the surface. In contrast to silicon, the subsurface structure plays a major role in the reactivity, leading to unexpected consequences such as the initial oxidation starting several atomic planes below the top surface or the surface metallization by atomic hydrogen. (review article)

  19. Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour

    OpenAIRE

    T. L. Martin; C. Coe; P. A. J. Bagot; P. Morrall; G. D. W Smith; T. Scott; M. P. Moody

    2016-01-01

    Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (∼5 nm) interfacia...

  20. Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy.

    Science.gov (United States)

    Loquet, Antoine; Tolchard, James; Berbon, Melanie; Martinez, Denis; Habenstein, Birgit

    2017-09-17

    Supramolecular protein assemblies play fundamental roles in biological processes ranging from host-pathogen interaction, viral infection to the propagation of neurodegenerative disorders. Such assemblies consist in multiple protein subunits organized in a non-covalent way to form large macromolecular objects that can execute a variety of cellular functions or cause detrimental consequences. Atomic insights into the assembly mechanisms and the functioning of those macromolecular assemblies remain often scarce since their inherent insolubility and non-crystallinity often drastically reduces the quality of the data obtained from most techniques used in structural biology, such as X-ray crystallography and solution Nuclear Magnetic Resonance (NMR). We here present magic-angle spinning solid-state NMR spectroscopy (SSNMR) as a powerful method to investigate structures of macromolecular assemblies at atomic resolution. SSNMR can reveal atomic details on the assembled complex without size and solubility limitations. The protocol presented here describes the essential steps from the production of 13 C/ 15 N isotope-labeled macromolecular protein assemblies to the acquisition of standard SSNMR spectra and their analysis and interpretation. As an example, we show the pipeline of a SSNMR structural analysis of a filamentous protein assembly.

  1. Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour.

    Science.gov (United States)

    Martin, T L; Coe, C; Bagot, P A J; Morrall, P; Smith, G D W; Scott, T; Moody, M P

    2016-07-12

    Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (~5 nm) interfacial layer of uranium hydride was observed at the oxide-metal interface. Exposure to deuterated water vapour produced an equivalent deuteride signal at the metal-oxide interface, confirming the hydride as originating via the water vapour oxidation mechanism. Hydroxide ions were detected uniformly throughout the oxide, yet showed reduced prominence at the metal interface. These results support a proposed mechanism for the oxidation of uranium in water vapour environments where the transport of hydroxyl species and the formation of hydride are key to understanding the observed behaviour.

  2. Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour

    Science.gov (United States)

    Martin, T. L.; Coe, C.; Bagot, P. A. J.; Morrall, P.; Smith, G. D. W.; Scott, T.; Moody, M. P.

    2016-07-01

    Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (~5 nm) interfacial layer of uranium hydride was observed at the oxide-metal interface. Exposure to deuterated water vapour produced an equivalent deuteride signal at the metal-oxide interface, confirming the hydride as originating via the water vapour oxidation mechanism. Hydroxide ions were detected uniformly throughout the oxide, yet showed reduced prominence at the metal interface. These results support a proposed mechanism for the oxidation of uranium in water vapour environments where the transport of hydroxyl species and the formation of hydride are key to understanding the observed behaviour.

  3. Inhomogeneous thermal expansion of metallic glasses in atomic-scale studied by in-situ synchrotron X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Taghvaei, Amir Hossein, E-mail: amirtaghvaei@gmail.com [Department of Materials Science and Engineering, Shiraz University of Technology, Shiraz (Iran, Islamic Republic of); Shakur Shahabi, Hamed [IFW Dresden, Institute for Complex Materials, Helmholtzstr. 20, 01069 Dresden (Germany); Bednarčik, Jozef [Photon Science DESY, Notkestraße 85, 22603 Hamburg (Germany); Eckert, Jürgen [IFW Dresden, Institute for Complex Materials, Helmholtzstr. 20, 01069 Dresden (Germany); TU Dresden, Institute of Materials Science, 01062 Dresden (Germany)

    2015-01-28

    Numerous investigations have demonstrated that the elastic strain in metallic glasses subjected to mechanical loading could be inhomogeneous in the atomic-scale and it increases with distance from an average atom and eventually reaches the macroscopic strain at larger inter-atomic distances. We have observed a similar behavior for the thermal strain imposed by heating of Co{sub 40}Fe{sub 22}Ta{sub 8}B{sub 30} glassy particles below the glass transition temperature by analysis of the scattering data obtained by in-situ high-energy synchrotron X-ray diffraction (XRD). The results imply that the volumetric thermal strains calculated from the shift in position of the principal diffraction maximum and reduced pair correlation function (PDF) peaks are in good agreement for the length scales beyond 0.6 nm, corresponding to the atoms located over the third near-neighbor shell. However, smaller and even negative volumetric thermal strains have been calculated based on the shifts in the positions of the second and first PDF peaks, respectively. The structural changes of Co{sub 40}Fe{sub 22}Ta{sub 8}B{sub 30} glassy particles are accompanied by decreasing the average coordination number of the first near-neighbor shell, which manifests the occurrence of local changes in the short-range order upon heating. It is believed that the detected length-scale dependence of the volumetric thermal strain is correlated with the local atomic rearrangements taking place in the topologically unstable regions of the glass governed by variations in the atomic-level stresses.

  4. Atomic scale study of thermal reduction of nano goethite coexisting with magnetite

    Science.gov (United States)

    singh, L. Herojit; Govindaraj, R.; Mythili, R.; Amarendra, G.; Sundar, C. S.

    2013-02-01

    Evolution of the local structure and magnetic properties of nano particles of goethite having magnetite as a composite due to controlled annealing treatments in vacuum has been studied using Mossbauer spectroscopy. Importance of size, defect associated with structural OH- for the observed structural and magnetic properties of goethite has been emphasized in this study. Present Mossbauer results show that thermal annealing at low temperatures (420-550 K) lead to a partial conversion / reduction of orthorhombic goethite to cubic spinel oxides such as maghemite and off-stochiometric magnetite. This study further establishes that annealing treatments beyond 650 K predominantly results in topotactic conversion of goethite to haematite. Underlying physics of the transitions of goethite to iron oxides and the important role of desorbed hydrogen for the orthorhombic to cubic structural transitions has been elucidated in this study.

  5. Atomic scale study of thermal reduction of nano goethite coexisting with magnetite

    Directory of Open Access Journals (Sweden)

    L. Herojit singh

    2013-02-01

    Full Text Available Evolution of the local structure and magnetic properties of nano particles of goethite having magnetite as a composite due to controlled annealing treatments in vacuum has been studied using Mossbauer spectroscopy. Importance of size, defect associated with structural OH- for the observed structural and magnetic properties of goethite has been emphasized in this study. Present Mossbauer results show that thermal annealing at low temperatures (420-550 K lead to a partial conversion / reduction of orthorhombic goethite to cubic spinel oxides such as maghemite and off-stochiometric magnetite. This study further establishes that annealing treatments beyond 650 K predominantly results in topotactic conversion of goethite to haematite. Underlying physics of the transitions of goethite to iron oxides and the important role of desorbed hydrogen for the orthorhombic to cubic structural transitions has been elucidated in this study.

  6. Ab-initio study of thermodynamic properties of boron nanowire at atomic scale

    Science.gov (United States)

    Bhuyan, Prabal D.; Gupta, Sanjeev K.; Sonvane, Y.; Gajjar, P. N.

    2018-04-01

    In the present work, we have optimized ribbon like zigzag structure of boron (B) nanowire (NW) and investigated vibrational and thermodynamic properties using quasi-harmonic approximations (QHA). All positive phonon in the phonon dispersive curve have confirmed dynamical stability of ribbon B-NW. The thermodynamic properties, like Debye temperature, internal energy and specific heat, are calculated as a function of temperature. The variation of specific heat is proportional to T3 Debye law at lower temperature for B-NW, while it becomes constant above room temperature at 1200K; obeys Dulong-Petit's law. The high Debye temperature of 1120K is observed at ambient temperature, which can be attributed to high thermal conductivity. Our study shows that B-NW with high thermal conductivity could be the next generation electron connector for nanoscale electronic devices.

  7. Alignment control and atomically-scaled heteroepitaxial interface study of GaN nanowires.

    Science.gov (United States)

    Liu, Qingyun; Liu, Baodan; Yang, Wenjin; Yang, Bing; Zhang, Xinglai; Labbé, Christophe; Portier, Xavier; An, Vladimir; Jiang, Xin

    2017-04-20

    Well-aligned GaN nanowires are promising candidates for building high-performance optoelectronic nanodevices. In this work, we demonstrate the epitaxial growth of well-aligned GaN nanowires on a [0001]-oriented sapphire substrate in a simple catalyst-assisted chemical vapor deposition process and their alignment control. It is found that the ammonia flux plays a key role in dominating the initial nucleation of GaN nanocrystals and their orientation. Typically, significant improvement of the GaN nanowire alignment can be realized at a low NH 3 flow rate. X-ray diffraction and cross-sectional scanning electron microscopy studies further verified the preferential orientation of GaN nanowires along the [0001] direction. The growth mechanism of GaN nanowire arrays is also well studied based on cross-sectional high-resolution transmission electron microscopy (HRTEM) characterization and it is observed that GaN nanowires have good epitaxial growth on the sapphire substrate following the crystallographic relationship between (0001) GaN ∥(0001) sapphire and (101[combining macron]0) GaN ∥(112[combining macron]0) sapphire . Most importantly, periodic misfit dislocations are also experimentally observed in the interface region due to the large lattice mismatch between the GaN nanowire and the sapphire substrate, and the formation of such dislocations will favor the release of structural strain in GaN nanowires. HRTEM analysis also finds the existence of "type I" stacking faults and voids inside the GaN nanowires. Optical investigation suggests that the GaN nanowire arrays have strong emission in the UV range, suggesting their crystalline nature and chemical purity. The achievement of aligned GaN nanowires will further promote the wide applications of GaN nanostructures toward diverse high-performance optoelectronic nanodevices including nano-LEDs, photovoltaic cells, photodetectors etc.

  8. The structure of poly(carbonsuboxide) on the atomic scale: a solid-state NMR study.

    Science.gov (United States)

    Schmedt auf der Günne, Jörn; Beck, Johannes; Hoffbauer, Wilfried; Krieger-Beck, Petra

    2005-07-18

    In this contribution we present a study of the structure of amorphous poly(carbonsuboxide) (C3O2)x by 13C solid-state NMR spectroscopy supported by infrared spectroscopy and chemical analysis. Poly(carbonsuboxide) was obtained by polymerization of carbonsuboxide C3O2, which in turn was synthesized from malonic acid bis(trimethylsilylester). Two different 13C labeling schemes were applied to probe inter- and intramonomeric bonds in the polymer by dipolar solid-state NMR methods and also to allow quantitative 13C MAS NMR spectra. Four types of carbon environments can be distinguished in the NMR spectra. Double-quantum and triple-quantum 2D correlation experiments were used to assign the observed peaks using the through-space and through-bond dipolar coupling. In order to obtain distance constraints for the intermonomeric bonds, double-quantum constant-time experiments were performed. In these experiments an additional filter step was applied to suppress contributions from not directly bonded 13C,13C spin pairs. The 13C NMR intensities, chemical shifts, connectivities and distances gave constraints for both the polymerization mechanism and the short-range order of the polymer. The experimental results were complemented by bond lengths predicted by density functional theory methods for several previously suggested models. Based on the presented evidence we can unambiguously exclude models based on gamma-pyronic units and support models based on alpha-pyronic units. The possibility of planar ladder- and bracelet-like alpha-pyronic structures is discussed.

  9. Atomic-scale study of the adsorption of calcium fluoride on Si(100) at low-coverage regime

    International Nuclear Information System (INIS)

    Chiaravalloti, Franco; Dujardin, Gerald; Riedel, Damien; Pinto, Henry P.; Foster, Adam S.

    2011-01-01

    We investigate, experimentally and theoretically, the initial stage of the formation of Ca/Si and Si/F structures that occurs during the adsorption of CaF 2 molecules onto a bare Si(100) surface heated to 1000 K in a low-coverage regime (0.3 monolayer). A low-temperature (5 K) scanning tunneling microscope (STM) is used to observe the topographies and the electronic properties of the exposed silicon surfaces. Our atomic-scale study reveals that several chemical reactions arise during CaF 2 deposition, such as dissociation of the CaF 2 molecules and etching of the surface silicon dimers. The experimental and calculated STM topographies are compared using the density functional theory, and this comparison enables us to identify two types of reacted structures on the Si(100) surface. The first type of observed complex surface structure consists of large islands formed with a semiperiodic sequence of 3 x 2 unit cells. The second one is made of isolated Ca adatoms adsorbed at specific sites on the Si(100)-2 x 1 surface.

  10. Atomic scale chemical tomography of human bone

    Science.gov (United States)

    Langelier, Brian; Wang, Xiaoyue; Grandfield, Kathryn

    2017-01-01

    Human bone is a complex hierarchical material. Understanding bone structure and its corresponding composition at the nanometer scale is critical for elucidating mechanisms of biomineralization under healthy and pathological states. However, the three-dimensional structure and chemical nature of bone remains largely unexplored at the nanometer scale due to the challenges associated with characterizing both the structural and chemical integrity of bone simultaneously. Here, we use correlative transmission electron microscopy and atom probe tomography for the first time, to our knowledge, to reveal structures in human bone at the atomic level. This approach provides an overlaying chemical map of the organic and inorganic constituents of bone on its structure. This first use of atom probe tomography on human bone reveals local gradients, trace element detection of Mg, and the co-localization of Na with the inorganic-organic interface of bone mineral and collagen fibrils, suggesting the important role of Na-rich organics in the structural connection between mineral and collagen. Our findings provide the first insights into the hierarchical organization and chemical heterogeneity in human bone in three-dimensions at its smallest length scale - the atomic level. We demonstrate that atom probe tomography shows potential for new insights in biomineralization research on bone.

  11. Mn doped InSb studied at the atomic scale by cross-sectional scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Mauger, S. J. C.; Bocquel, J.; Koenraad, P. M.; Feeser, C. E.; Parashar, N. D.; Wessels, B. W.

    2015-01-01

    We present an atomically resolved study of metal-organic vapor epitaxy grown Mn doped InSb. Both topographic and spectroscopic measurements have been performed by cross-sectional scanning tunneling microscopy (STM). The measurements on the Mn doped InSb samples show a perfect crystal structure without any precipitates and reveal that Mn acts as a shallow acceptor. The Mn concentration of the order of ∼10 20  cm −3 obtained from the cross-sectional STM data compare well with the intended doping concentration. While the pair correlation function of the Mn atoms showed that their local distribution is uncorrelated beyond the STM resolution for observing individual dopants, disorder in the Mn ion location giving rise to percolation pathways is clearly noted. The amount of clustering that we see is thus as expected for a fully randomly disordered distribution of the Mn atoms and no enhanced clustering or second phase material was observed

  12. The atomic scale structure of CXV carbon: wide-angle x-ray scattering and modeling studies.

    Science.gov (United States)

    Hawelek, L; Brodka, A; Dore, J C; Honkimaki, V; Burian, A

    2013-11-13

    The disordered structure of commercially available CXV activated carbon produced from finely powdered wood-based carbon has been studied using the wide-angle x-ray scattering technique, molecular dynamics and density functional theory simulations. The x-ray scattering data has been converted to the real space representation in the form of the pair correlation function via the Fourier transform. Geometry optimizations using classical molecular dynamics based on the reactive empirical bond order potential and density functional theory at the B3LYP/6-31g* level have been performed to generate nanoscale models of CXV carbon consistent with the experimental data. The final model of the structure comprises four chain-like and buckled graphitic layers containing a small percentage of four-fold coordinated atoms (sp(3) defects) in each layer. The presence of non-hexagonal rings in the atomic arrangement has been also considered.

  13. The fission time scale measured with an atomic clock

    NARCIS (Netherlands)

    Kravchuk, VL; Wilschut, HW; Hunyadi, M; Kopecky, S; Lohner, H; Rogachevskiy, A; Siemssen, RH; Krasznahorkay, A; Hamilton, JH; Ramayya, AV; Carter, HK

    2003-01-01

    We present a new direct method of measuring the fission absolute time scale using an atomic clock based on the lifetime of a vacancy in the atomic K-shell. We studied the reaction Ne-20 + Th-232 -> O-16 + U-236* at 30 MeV/u. The excitation energy of about 115 MeV in such a reaction is in the range

  14. The atomic-scale nucleation mechanism of NiTi metallic glasses upon isothermal annealing studied via molecular dynamics simulations.

    Science.gov (United States)

    Li, Yang; Li, JiaHao; Liu, BaiXin

    2015-10-28

    Nucleation is one of the most essential transformation paths in phase transition and exerts a significant influence on the crystallization process. Molecular dynamics simulations were performed to investigate the atomic-scale nucleation mechanisms of NiTi metallic glasses upon devitrification at various temperatures (700 K, 750 K, 800 K, and 850 K). Our simulations reveal that at 700 K and 750 K, nucleation is polynuclear with high nucleation density, while at 800 K it is mononuclear. The underlying nucleation mechanisms have been clarified, manifesting that nucleation can be induced either by the initial ordered clusters (IOCs) or by the other precursors of nuclei evolved directly from the supercooled liquid. IOCs and other precursors stem from the thermal fluctuations of bond orientational order in supercooled liquids during the quenching process and during the annealing process, respectively. The simulation results not only elucidate the underlying nucleation mechanisms varied with temperature, but also unveil the origin of nucleation. These discoveries offer new insights into the devitrification mechanism of metallic glasses.

  15. Dislocation glide in Ni-Al solid solutions from the atomic scale up: a molecular dynamics study

    International Nuclear Information System (INIS)

    Rodary, E.

    2003-01-01

    The glide of an edge dislocation in solid solutions is studied by molecular dynamics, at fixed temperature and imposed external stress. We have optimized an EAM potential for Ni(1 a 8% A1): it well reproduces the lattice expansion, local atomic order, stacking fault energy as a function of composition, as well as the elastic properties of the γ' phase with L1 2 structure. On increasing the stress, the dislocation is first immobile, then glides with a velocity proportional to the stress and the velocity saturates on reaching the transverse sound velocity. However, only beyond a static threshold stress, σ s , does the dislocation glide a distance large enough to allow macroscopic shear; the linear part of the velocity-stress curve extrapolates to zero at a dynamical threshold stress, σ d , The friction coefficient, and the threshold stresses (σ s and σ d ), increase with the A1 concentration and decrease with temperature (300 and 500 K). Close to the critical shear stress, σ s , the dislocation glide is analysed with a 'stop and go' model. The latter yields the flight velocity between obstacles, the mean obstacle density and the distribution of the waiting time on each obstacle as a function of stress, composition and temperature. The obstacle to the glide is proposed to be the strong repulsion between Al atoms brought into nearest neighbour position by the glide process, and not the dislocation-solute interaction. The microscopic parameters so defined are introduced into a micro-mechanical model, which well reproduces the known behaviour of nickel base solid solutions. (author)

  16. Polarized atomic orbitals for linear scaling methods

    Science.gov (United States)

    Berghold, Gerd; Parrinello, Michele; Hutter, Jürg

    2002-02-01

    We present a modified version of the polarized atomic orbital (PAO) method [M. S. Lee and M. Head-Gordon, J. Chem. Phys. 107, 9085 (1997)] to construct minimal basis sets optimized in the molecular environment. The minimal basis set derives its flexibility from the fact that it is formed as a linear combination of a larger set of atomic orbitals. This approach significantly reduces the number of independent variables to be determined during a calculation, while retaining most of the essential chemistry resulting from the admixture of higher angular momentum functions. Furthermore, we combine the PAO method with linear scaling algorithms. We use the Chebyshev polynomial expansion method, the conjugate gradient density matrix search, and the canonical purification of the density matrix. The combined scheme overcomes one of the major drawbacks of standard approaches for large nonorthogonal basis sets, namely numerical instabilities resulting from ill-conditioned overlap matrices. We find that the condition number of the PAO overlap matrix is independent from the condition number of the underlying extended basis set, and consequently no numerical instabilities are encountered. Various applications are shown to confirm this conclusion and to compare the performance of the PAO method with extended basis-set calculations.

  17. pH in atomic scale simulations of electrochemical interfaces

    DEFF Research Database (Denmark)

    Rossmeisl, Jan; Chan, Karen; Ahmed, Rizwan

    2013-01-01

    Electrochemical reaction rates can strongly depend on pH, and there is increasing interest in electrocatalysis in alkaline solution. To date, no method has been devised to address pH in atomic scale simulations. We present a simple method to determine the atomic structure of the metal......|solution interface at a given pH and electrode potential. Using Pt(111)|water as an example, we show the effect of pH on the interfacial structure, and discuss its impact on reaction energies and barriers. This method paves the way for ab initio studies of pH effects on the structure and electrocatalytic activity...

  18. Dynamic strain-induced transformation: An atomic scale investigation

    International Nuclear Information System (INIS)

    Zhang, H.; Pradeep, K.G.; Mandal, S.; Ponge, D.; Springer, H.; Raabe, D.

    2015-01-01

    Phase transformations provide the most versatile access to the design of complex nanostructured alloys in terms of grain size, morphology, local chemical constitution etc. Here we study a special case of deformation induced phase transformation. More specifically, we investigate the atomistic mechanisms associated with dynamic strain-induced transformation (DSIT) in a dual-phased multicomponent iron-based alloy at high temperatures. DSIT phenomena and the associated secondary phase nucleation were observed at atomic scale using atom probe tomography. The obtained local chemical composition was used for simulating the nucleation process which revealed that DSIT, occurring during load exertion, proceeds by a diffusion-controlled nucleation process

  19. Physically representative atomistic modeling of atomic-scale friction

    Science.gov (United States)

    Dong, Yalin

    Nanotribology is a research field to study friction, adhesion, wear and lubrication occurred between two sliding interfaces at nano scale. This study is motivated by the demanding need of miniaturization mechanical components in Micro Electro Mechanical Systems (MEMS), improvement of durability in magnetic storage system, and other industrial applications. Overcoming tribological failure and finding ways to control friction at small scale have become keys to commercialize MEMS with sliding components as well as to stimulate the technological innovation associated with the development of MEMS. In addition to the industrial applications, such research is also scientifically fascinating because it opens a door to understand macroscopic friction from the most bottom atomic level, and therefore serves as a bridge between science and engineering. This thesis focuses on solid/solid atomic friction and its associated energy dissipation through theoretical analysis, atomistic simulation, transition state theory, and close collaboration with experimentalists. Reduced-order models have many advantages for its simplification and capacity to simulating long-time event. We will apply Prandtl-Tomlinson models and their extensions to interpret dry atomic-scale friction. We begin with the fundamental equations and build on them step-by-step from the simple quasistatic one-spring, one-mass model for predicting transitions between friction regimes to the two-dimensional and multi-atom models for describing the effect of contact area. Theoretical analysis, numerical implementation, and predicted physical phenomena are all discussed. In the process, we demonstrate the significant potential for this approach to yield new fundamental understanding of atomic-scale friction. Atomistic modeling can never be overemphasized in the investigation of atomic friction, in which each single atom could play a significant role, but is hard to be captured experimentally. In atomic friction, the

  20. Atomic scale modelling of materials of the nuclear fuel cycle

    International Nuclear Information System (INIS)

    Bertolus, M.

    2011-10-01

    This document written to obtain the French accreditation to supervise research presents the research I conducted at CEA Cadarache since 1999 on the atomic scale modelling of non-metallic materials involved in the nuclear fuel cycle: host materials for radionuclides from nuclear waste (apatites), fuel (in particular uranium dioxide) and ceramic cladding materials (silicon carbide). These are complex materials at the frontier of modelling capabilities since they contain heavy elements (rare earths or actinides), exhibit complex structures or chemical compositions and/or are subjected to irradiation effects: creation of point defects and fission products, amorphization. The objective of my studies is to bring further insight into the physics and chemistry of the elementary processes involved using atomic scale modelling and its coupling with higher scale models and experimental studies. This work is organised in two parts: on the one hand the development, adaptation and implementation of atomic scale modelling methods and validation of the approximations used; on the other hand the application of these methods to the investigation of nuclear materials under irradiation. This document contains a synthesis of the studies performed, orientations for future research, a detailed resume and a list of publications and communications. (author)

  1. Ageing effects on polymeric track detectors: studies of etched tracks at nano size scale using atomic force microscope

    International Nuclear Information System (INIS)

    Espinosa, G.; Golzarri, J. I.; Fragoso, R.; Vazquez L, C.; Saad, A. F.; El-Namrouty, A. A.; Fujii, M.

    2012-01-01

    Among several different techniques to analyze material surface, the use of Atomic Force Microscope is one of the finest method. As we know, the sensitivity to detect energetic ions is extremely affected during the storage time and conditions of the polymeric material used as a nuclear track detector. On the basis of the surface analysis of several track detector materials, we examined the detection sensitivity of these detectors exposed to alpha particles. The preliminary results revealed that the ageing effect on its sensitivity is very strong, that need to be considered on the routine applications or research experiments. The results are consistent with the experimental data in the literature. (Author)

  2. Study on laser atomic spectroscopy

    International Nuclear Information System (INIS)

    Lee, Jong Min; Song, Kyu Seok; Jeong, Do Young; Kim, Chul Joong; Han, Phil Soon

    1992-01-01

    Electric discharge type atomic vaporizer is developed for the spectroscopic study on actinide elements. Laser induced fluorescence study on actinide elements is performed by using this high temperature type atomizer. For the effective photoionization of elements, copper vapor laser pumped dye laser and electron beam heating type atomic vaporizer are built and their characteristics are measured. In addition, resonance ionization mass spectroscopic analysis for lead sample as well as laser induced fluorescence study on uranium sample in solution phase is made. (Author)

  3. The Chip-Scale Atomic Clock - Recent Development Progress

    Science.gov (United States)

    2004-09-01

    35th Annual Precise Time and Time Interval (PTTI) Meeting 467 THE CHIP-SCALE ATOMIC CLOCK – RECENT DEVELOPMENT PROGRESS R. Lutwak ...1] R. Lutwak , et al., 2003, “The Chip-Scale Atomic Clock – Coherent Population Trapping vs. Conventional Interrogation,” in

  4. Atomic scale resolution with correlation holography

    International Nuclear Information System (INIS)

    Csonka, P.L.

    1979-01-01

    For many atoms (including atoms of interest in biology) the elastic and inelastic photon scattering cross sections (denoted respectively by sigma/sub el/ and sigma/sub inel/) for photons in the wavelength region of interest, satisfy sigma/sub el/ << sigma/sub inel/. Therefore, the probability is high that when illuminated with photons, such an atom will decay before a holographic picture of it can be taken. On the other hand, if certain nonlinear phenomena: correlations between photons are taken into account, a hologram of such atoms can nevertheless be generated. Observation of small objects is compatible with the principles of quantum mechanics, even if the probability of disturbing the object as a result of observation is arbitrarily small

  5. Chemical inhomogeneity in In{sub x}Ga{sub 1-x}N and ZnO. A HRTEM study on atomic scale clustering

    Energy Technology Data Exchange (ETDEWEB)

    Bartel, T.P.

    2008-10-08

    Nanostructuration as well as the nucleation and growth of nanoparticles pervades the development of modern materials and devices. Quantitative high resolution transmission electron microscopy (HRTEM) is currently being developed for a structural and chemical analysis at an atomic scale. It is used in this thesis to study the chemical inhomogeneity and clustering in In{sub x}Ga{sub 1-x}N, InN and ZnO. A methodology for reliable quantitative HRTEM is rst de ned: it necessitates a damage free sample, the avoidance of electron beam damage and the control of microscope instabilities. With these conditions satis ed, the reliability of quantitative HRTEM is demonstrated by an accurate measurement of lattice relaxation in a thin TEM sample. Clustering in an alloy can then be distinguished from a random distribution of atoms. In In{sub x}Ga{sub 1-x}N for instance, clustering is detected for concentrations x>0.1. The sensitivity is insufficient to determine whether clustering is present for lower concentrations. HRTEM allows to identify the amplitude and the spatial distribution of the decomposition which is attributed to a spinodal decomposition. In InN, nanometer scale metallic indium inclusions are detected. With decreasing size of the metallic clusters, the photoluminescence of the sample shifts towards the infrared. This indicates that the inclusions may be responsible for the infrared activity of InN. Finally, ZnO grown homoepitaxially on zinc-face and oxygen-face substrates is studied. The O-face epilayer is strained whereas the Zn-face epilayer is almost strain free and has a higher crystalline quality. Quantitative analysis of exit wave phases is in good agreement with simulations, but the signal to noise ratio needs to be improved for the detection of single point defects. (orig.)

  6. Chemical inhomogeneity in InxGa1-xN and ZnO. A HRTEM study on atomic scale clustering

    International Nuclear Information System (INIS)

    Bartel, T.P.

    2008-01-01

    Nanostructuration as well as the nucleation and growth of nanoparticles pervades the development of modern materials and devices. Quantitative high resolution transmission electron microscopy (HRTEM) is currently being developed for a structural and chemical analysis at an atomic scale. It is used in this thesis to study the chemical inhomogeneity and clustering in In x Ga 1-x N, InN and ZnO. A methodology for reliable quantitative HRTEM is rst de ned: it necessitates a damage free sample, the avoidance of electron beam damage and the control of microscope instabilities. With these conditions satis ed, the reliability of quantitative HRTEM is demonstrated by an accurate measurement of lattice relaxation in a thin TEM sample. Clustering in an alloy can then be distinguished from a random distribution of atoms. In In x Ga 1-x N for instance, clustering is detected for concentrations x>0.1. The sensitivity is insufficient to determine whether clustering is present for lower concentrations. HRTEM allows to identify the amplitude and the spatial distribution of the decomposition which is attributed to a spinodal decomposition. In InN, nanometer scale metallic indium inclusions are detected. With decreasing size of the metallic clusters, the photoluminescence of the sample shifts towards the infrared. This indicates that the inclusions may be responsible for the infrared activity of InN. Finally, ZnO grown homoepitaxially on zinc-face and oxygen-face substrates is studied. The O-face epilayer is strained whereas the Zn-face epilayer is almost strain free and has a higher crystalline quality. Quantitative analysis of exit wave phases is in good agreement with simulations, but the signal to noise ratio needs to be improved for the detection of single point defects. (orig.)

  7. Significant improvements in stability and reproducibility of atomic-scale atomic force microscopy in liquid

    International Nuclear Information System (INIS)

    Akrami, S M R; Nakayachi, H; Fukuma, T; Watanabe-Nakayama, T; Asakawa, H

    2014-01-01

    Recent advancement of dynamic-mode atomic force microscopy (AFM) for liquid-environment applications enabled atomic-scale studies on various interfacial phenomena. However, instabilities and poor reproducibility of the measurements often prevent systematic studies. To solve this problem, we have investigated the effect of various tip treatment methods for atomic-scale imaging and force measurements in liquid. The tested methods include Si coating, Ar plasma, Ar sputtering and UV/O 3 cleaning. We found that all the methods provide significant improvements in both the imaging and force measurements in spite of the tip transfer through the air. Among the methods, we found that the Si coating provides the best stability and reproducibility in the measurements. To understand the origin of the fouling resistance of the cleaned tip surface and the difference between the cleaning methods, we have investigated the tip surface properties by x-ray photoelectron spectroscopy and contact angle measurements. The results show that the contaminations adsorbed on the tip during the tip transfer through the air should desorb from the surface when it is immersed in aqueous solution due to the enhanced hydrophilicity by the tip treatments. The tip surface prepared by the Si coating is oxidized when it is immersed in aqueous solution. This creates local spots where stable hydration structures are formed. For the other methods, there is no active mechanism to create such local hydration sites. Thus, the hydration structure formed under the tip apex is not necessarily stable. These results reveal the desirable tip properties for atomic-scale AFM measurements in liquid, which should serve as a guideline for further improvements of the tip treatment methods. (paper)

  8. Photonic and Quantum Interactions of Atomic-Scale Junctions

    Data.gov (United States)

    National Aeronautics and Space Administration — In this proposal, the fundamental quantum and photonic interactions of bimetallic atomic-scale junctions (ASJs) will be explored, with three major space...

  9. Atomic scale characterization of mismatched graphene layers

    International Nuclear Information System (INIS)

    Luican-Mayer, Adina; Li, Guohong; Andrei, Eva Y.

    2017-01-01

    Highlights: • Review of STM/STS of graphene with various degree of coupling. • Review of vertically twisted graphene with respect with each other. • Review of Landau levels in graphene layers weakly decoupled electronically. • Review of laterally twisted graphene forming grain boundaries. - Abstract: In the bourgeoning field of two dimensional layered materials and their atomically thin counterparts, it has been established that the electronic coupling between the layers of the material plays a key role in determining its properties [1,2]. We are just beginning to understand how each material is unique in that respect while working our way up to building new materials with functionalities enabled by interlayer interactions. In this review, we will focus on a system that despite its apparent simplicity possesses a wealth of intriguing physics: layers of graphene with various degree of coupling. The situations discussed here are graphene layers vertically twisted with respect with each other, weakly decoupled electronically and laterally twisted forming grain boundaries. We emphasize experiments that atomically resolve the electronic properties.

  10. Atomic force microscopy and scanning electron microscopy evaluation of efficacy of scaling and root planing using magnification: A randomized controlled clinical study

    Directory of Open Access Journals (Sweden)

    Ranjana Mohan

    2013-01-01

    Full Text Available Aim: A randomized controlled clinical study was undertaken to evaluate the effectiveness of scaling and root planing (SRP by using Magnifying Loupes (ML and dental operating microscope (DOM. Materials and Methods: A total of 90 human teeth scheduled for extraction from 18 patients aged between 25 and 65 years suffering from generalized chronic severe periodontitis were randomly assigned to three treatment groups. Group 1 consisted SRP performed without using magnification (unaided, Group 2-SRP with ML and Group 3-SRP with DOM. Following extractions, samples were prepared for (i evaluation of surface topography by atomic force microscopy, (ii presence of smear layer, debris by scanning electron microscopy (iii elemental analysis by energy dispersive X-ray analysis. Data was subjected to statistical analysis using analysis of variance, post-hoc (Tukey-HSD and Chi-square test. Results: Statistically significant (P < 0.001 difference was found among the different treatment groups. Group 3 was the best while Group 1 was the least effective technique for SRP. Order of efficacy in terms of the surface was found to be - Palatal < Lingual < Distal ≅ Mesial < Buccal. Efficiency in mandibular to maxillary teeth was found to be significant (P < 0.05, also anterior to posterior teeth (P < 0.05. Conclusion: Magnification tools significantly enhance the efficacy of supragingival and subgingival SRP.

  11. Photocatalytic mechanism of high-activity anatase TiO2 with exposed (001) facets from molecular-atomic scale: HRTEM and Raman studies

    Science.gov (United States)

    Wu, Jun; Shi, Chentian; Zhang, Yupeng; Fu, Qiang; Pan, Chunxu

    2017-12-01

    Anatase TiO2 with a variant percentage of exposed (001) facets was prepared under hydrothermal processes by adjusting the volume of HF, and the photocatalytic mechanism was studied from atomic-molecular scale by HRTEM and Raman spectroscopy. It was revealed that: 1) From HRTEM observations, the surface of original TiO2 with exposed (001) facets was clean without impurity, and the crystal lattice was clear and completed; however, when mixed with methylene blue (MB) solution, there were many 1 nm molecular absorbed at the surface of TiO2; after the photocatalytic experiment, MB molecules disappeared and the TiO2 lattice image became fuzzy. 2) The broken path of the MB chemical bond was obtained by Raman spectroscopy, i.e., after the irradiation of the light, the vibrational mode of C-N-C disappeared due to the chemical bond breakage, and the groups containing C-N bond and carbon rings were gradually decomposed. Accordingly, we propose that the driving force for breaking the chemical bond and the disappearance of groups is from the surface lattice distortion of TiO2 during photocatalyzation.

  12. Multiple atomic scale solid surface interconnects for atom circuits and molecule logic gates

    International Nuclear Information System (INIS)

    Joachim, C; Martrou, D; Gauthier, S; Rezeq, M; Troadec, C; Jie Deng; Chandrasekhar, N

    2010-01-01

    The scientific and technical challenges involved in building the planar electrical connection of an atomic scale circuit to N electrodes (N > 2) are discussed. The practical, laboratory scale approach explored today to assemble a multi-access atomic scale precision interconnection machine is presented. Depending on the surface electronic properties of the targeted substrates, two types of machines are considered: on moderate surface band gap materials, scanning tunneling microscopy can be combined with scanning electron microscopy to provide an efficient navigation system, while on wide surface band gap materials, atomic force microscopy can be used in conjunction with optical microscopy. The size of the planar part of the circuit should be minimized on moderate band gap surfaces to avoid current leakage, while this requirement does not apply to wide band gap surfaces. These constraints impose different methods of connection, which are thoroughly discussed, in particular regarding the recent progress in single atom and molecule manipulations on a surface.

  13. First-principles studies on vacancy-modified interstitial diffusion mechanism of oxygen in nickel, associated with large-scale atomic simulation techniques

    International Nuclear Information System (INIS)

    Fang, H. Z.; Shang, S. L.; Wang, Y.; Liu, Z. K.; Alfonso, D.; Alman, D. E.; Shin, Y. K.; Zou, C. Y.; Duin, A. C. T. van; Lei, Y. K.; Wang, G. F.

    2014-01-01

    This paper is concerned with the prediction of oxygen diffusivities in fcc nickel from first-principles calculations and large-scale atomic simulations. Considering only the interstitial octahedral to tetrahedral to octahedral minimum energy pathway for oxygen diffusion in fcc lattice, greatly underestimates the migration barrier and overestimates the diffusivities by several orders of magnitude. The results indicate that vacancies in the Ni-lattice significantly impact the migration barrier of oxygen in nickel. Incorporation of the effect of vacancies results in predicted diffusivities consistent with available experimental data. First-principles calculations show that at high temperatures the vacancy concentration is comparable to the oxygen solubility, and there is a strong binding energy and a redistribution of charge density between the oxygen atom and vacancy. Consequently, there is a strong attraction between the oxygen and vacancy in the Ni lattice, which impacts diffusion

  14. Atomic scale studies of La/Sr ordering in La2-2xSr1+2xMn2O7 single crystals

    KAUST Repository

    Roldan, Manuel

    2016-12-21

    Many fascinating properties of materials depend strongly on the local chemical environment. This is the case for many complex oxides, such as materials with colossal magnetoresistance, where small variations of composition at the atomic scale can affect drastically the macroscopic properties. The main objective of the present work is to analyze the local chemical composition with atomic resolution and to find out if any underlying chemical order is in any way connected to the magnetic properties of double perovskite La2-2xSr1+2xMn2O7 (LSMO) manganite oxides. For these compounds, charge and orbital ordering are observed for some doping values near x = 0.50 [1, 2]. For this purpose, we have use aberration corrected scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) measurements and also theoretical simulations. We have compared different compositions within three distinct magnetic regions of the phase diagram: a ferromagnetic metallic sample with x=0.36, an insulating, antiferromagnetic (AF) x=0.56 and an additional AF x=0.50 sample which also exhibits charge ordering. High angle annular dark-field (HAADF) images, also known as Z-contrast, confirm that our single crystals exhibit high crystal quality. No secondary phases or defects are observed. Figure 1 displays an atomic resolution image obtained with the c-axis perpendicular to the electron beam of a x=0.50 sample. The perovskite (P)-like planes and the rock salt (R)-like planes are clearly observed, highlighted in green and red, respectively, on the image. The P-like planes exhibit a slightly high contrast, suggesting a possible La enrichment. EELS atomic resolution maps (inset) support a high degree of La segregation on those planes, while R-like planes are Sr rich. However, due to dechanneling of the beam, detailed image simulations are essential to accurately quantify the local chemical composition in an atomic column-by-atomic column fashion. For all our

  15. Atomic-scale observation of hydrogen-induced crack growth by atom-probe FIM

    International Nuclear Information System (INIS)

    Kuk, Y.; Pickering, H.W.; Sakurai, T.

    1980-01-01

    Formation and propagation of a microcrack due to hydrogen in a Fe-0.29 wt.% Ti alloy was observed at the atomic scale by field ion microscopy. A microcrack (-20 nm in length) formed and became noticeably large when the tip was heated at 950 0 C in the presence of about 1 torr of Hg. Propagation was reported several times by reheating, until a portion of the tip ruptured and became detached from the tip. Compositional analysis, performed in situ using a high performance atom-probe, identified atomic hydrogen in quantity and some hydrogen molecules and FEH in the crack, but not elsewhere on the surface

  16. Atomic-scale modeling of cellulose nanocrystals

    Science.gov (United States)

    Wu, Xiawa

    Cellulose nanocrystals (CNCs), the most abundant nanomaterials in nature, are recognized as one of the most promising candidates to meet the growing demand of green, bio-degradable and sustainable nanomaterials for future applications. CNCs draw significant interest due to their high axial elasticity and low density-elasticity ratio, both of which are extensively researched over the years. In spite of the great potential of CNCs as functional nanoparticles for nanocomposite materials, a fundamental understanding of CNC properties and their role in composite property enhancement is not available. In this work, CNCs are studied using molecular dynamics simulation method to predict their material' behaviors in the nanoscale. (a) Mechanical properties include tensile deformation in the elastic and plastic regions using molecular mechanics, molecular dynamics and nanoindentation methods. This allows comparisons between the methods and closer connectivity to experimental measurement techniques. The elastic moduli in the axial and transverse directions are obtained and the results are found to be in good agreement with previous research. The ultimate properties in plastic deformation are reported for the first time and failure mechanism are analyzed in details. (b) The thermal expansion of CNC crystals and films are studied. It is proposed that CNC film thermal expansion is due primarily to single crystal expansion and CNC-CNC interfacial motion. The relative contributions of inter- and intra-crystal responses to heating are explored. (c) Friction at cellulose-CNCs and diamond-CNCs interfaces is studied. The effects of sliding velocity, normal load, and relative angle between sliding surfaces are predicted. The Cellulose-CNC model is analyzed in terms of hydrogen bonding effect, and the diamond-CNC model compliments some of the discussion of the previous model. In summary, CNC's material properties and molecular models are both studied in this research, contributing to

  17. The Chip-Scale Atomic Clock - Prototype Evaluation

    Science.gov (United States)

    2007-11-01

    39th Annual Precise Time and Time Interval (PTTI) Meeting THE CHIP-SCALE ATOMIC CLOCK – PROTOTYPE EVALUATION R. Lutwak *, A. Rashed...been supported by the Defense Advanced Research Projects Agency, Contract # NBCHC020050. REFERENCES [1] R. Lutwak , D. Emmons, W. Riley, and...D.C.), pp. 539-550. [2] R. Lutwak , D. Emmons, T. English, W. Riley, A. Duwel, M. Varghese, D. K. Serkland, and G. M. Peake, 2004, “The Chip-Scale

  18. Microsecond atomic-scale molecular dynamics simulations of polyimides

    NARCIS (Netherlands)

    Lyulin, S.V.; Gurtovenko, A.A.; Larin, S.V.; Nazarychev, V.M.; Lyulin, A.V.

    2013-01-01

    We employ microsecond atomic-scale molecular dynamics simulations to get insight into the structural and thermal properties of heat-resistant bulk polyimides. As electrostatic interactions are essential for the polyimides considered, we propose a two-step equilibration protocol that includes long

  19. Atomic and close-to-atomic scale manufacturing—A trend in manufacturing development

    Science.gov (United States)

    Fang, Fengzhou

    2016-12-01

    Manufacturing is the foundation of a nation's economy. It is the primary industry to promote economic and social development. To accelerate and upgrade China's manufacturing sector from "precision manufacturing" to "high-performance and high-quality manufacturing", a new breakthrough should be found in terms of achieving a "leap-frog development". Unlike conventional manufacturing, the fundamental theory of "Manufacturing 3.0" is beyond the scope of conventional theory; rather, it is based on new principles and theories at the atomic and/or closeto- atomic scale. Obtaining a dominant role at the international level is a strategic move for China's progress.

  20. RF Shot Noise Measurements in Au Atomic-scale Junctions

    Science.gov (United States)

    Chen, Ruoyu

    Conduction electrons are responsible for many physical or chemical phenomena in condensed matter systems, and their behavior can be directly studied by electronic transport measurements. In conventional transport measurements, conductance or resistance is usually the focus. Such a measurement can be as simple as a quick two terminal DC check by a multi-meter, or a more sophisticated lock-in measurement of multiple higher harmonic signals synchronized to different frequencies. Conductance carries direct information about the quasi-particle density of states and the local electronic distributions, which are usually Fermi-Dirac distribution. Conductance is modified or dominated by scattering from defacts or interfaces, and could also reflect the spin-spin exchange interactions or inelastic couplings with phonons and photons. Naturally one can ask the question: is there anything else we can measure electronically, which carries extra information that a conductance measurement does not provide? One answer to this question is the electronic noise. While the conductance reflects the average charge conduction ability of a system, noise describes how the physical quantities fluctuate around their average values. Some of the fluctuations carry information about their physical origins. This thesis will focus on one particular type of the electronic noise shot noise, but other types of noise will also be introduced and discussed. We choose to measure the radio frequency component of shot noise, combining with a modulated lock-in detection technique, which provides a method to largely get rid of other unwanted low-frequency noise signals. Au atomic-scale junctions are the systems we studied here. Au is relatively well understood and will not generate too many complications, so it's ideal as the first platform for us to understand both shot noise itself and our RF technique. On the other hand, the atomic scale raises fundamental questions about electronic transport and local

  1. Variable scaling method and Stark effect in hydrogen atom

    International Nuclear Information System (INIS)

    Choudhury, R.K.R.; Ghosh, B.

    1983-09-01

    By relating the Stark effect problem in hydrogen-like atoms to that of the spherical anharmonic oscillator we have found simple formulas for energy eigenvalues for the Stark effect. Matrix elements have been calculated using 0(2,1) algebra technique after Armstrong and then the variable scaling method has been used to find optimal solutions. Our numerical results are compared with those of Hioe and Yoo and also with the results obtained by Lanczos. (author)

  2. Simulating atomic-scale phenomena on surfaces of unconventional superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kreisel, Andreas; Andersen, Brian [Niels Bohr Institute (Denmark); Choubey, Peayush; Hirschfeld, Peter [Univ. of Florida (United States); Berlijn, Tom [CNMS and CSMD, Oak Ridge National Laboratory (United States)

    2016-07-01

    Interest in atomic scale effects in superconductors has increased because of two general developments: First, the discovery of new materials as the cuprate superconductors, heavy fermion and Fe-based superconductors where the coherence length of the cooper pairs is as small to be comparable to the lattice constant, rendering small scale effects important. Second, the experimental ability to image sub-atomic features using scanning-tunneling microscopy which allows to unravel numerous physical properties of the homogeneous system such as the quasi particle excitation spectra or various types of competing order as well as properties of local disorder. On the theoretical side, the available methods are based on lattice models restricting the spatial resolution of such calculations. In the present project we combine lattice calculations using the Bogoliubov-de Gennes equations describing the superconductor with wave function information containing sub-atomic resolution obtained from ab initio approaches. This allows us to calculate phenomena on surfaces of superconductors as directly measured in scanning tunneling experiments and therefore opens the possibility to identify underlying properties of these materials and explain observed features of disorder. It will be shown how this method applies to the cuprate material Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and a Fe based superconductor.

  3. Probing Efimov discrete scaling in an atom-molecule collision

    Science.gov (United States)

    Shalchi, M. A.; Yamashita, M. T.; Hadizadeh, M. R.; Garrido, E.; Tomio, Lauro; Frederico, T.

    2018-01-01

    The discrete Efimov scaling behavior, well known in the low-energy spectrum of three-body bound systems for large scattering lengths (unitary limit), is identified in the energy dependence of an atom-molecule elastic cross section in mass-imbalanced systems. That happens in the collision of a heavy atom with mass mH with a weakly bound dimer formed by the heavy atom and a lighter one with mass mL≪mH . Approaching the heavy-light unitary limit, the s -wave elastic cross section σ will present a sequence of zeros or minima at collision energies following closely the Efimov geometrical law. Our results, obtained with Faddeev calculations and supplemented by a Born-Oppenheimer analysis, open a perspective to detecting the discrete scaling behavior from low-energy scattering data, which is timely in view of the ongoing experiments with ultracold binary mixtures having strong mass asymmetries, such as lithium and cesium or lithium and ytterbium.

  4. The self-breaking mechanism of atomic scale Au nanocontacts

    International Nuclear Information System (INIS)

    Nakazumi, Tomoka; Kiguchi, Manabu; Wada, Yasuo

    2012-01-01

    We have investigated the self-breaking mechanism of atomic scale Au nanocontacts at room temperature in air. In the conductance traces, we frequently observed traces showing both a 1G 0 (2e 2 /h) and 3G 0 plateaux, or only a 2G 0 plateau in the conductance regime below 3G 0 . The statistical analysis showed a negative correlation between the appearance of 1G 0 and 2G 0 peaks, and a positive correlation between 1G 0 and 3G 0 peaks. This conductance behavior suggested that the symmetric triple atomic rows changed into a symmetric single row, while the asymmetric double rows broke without changing into a symmetric single row. The regular self-breaking process can be explained by the breaking of the thermodynamically stable Au nanocontacts which were formed during the self-breaking of the contacts. (paper)

  5. Gravitational theory in atomic scale units in Dirac cosmology

    International Nuclear Information System (INIS)

    Davidson, W.

    1984-01-01

    The implication of Dirac's large numbers hypothesis (LNH) that there are two cosmological space-time metrics, gravitational (E) and atomic (A), is used to formulate the gravitational laws for a general mass system in atomic scale units within such a cosmology. The gravitational laws are illustrated in application to the case of a single spherical mass immersed in the smoothed out expanding universe. The condition is determined for such a metric to apply approximately just outside a typical member of a cosmic distribution of such masses. Conversely, the condition is given when the influence of the universe as a whole can be neglected outside such a mass. In the latter situation, which applies in particular to stars, a Schwarzschild-type metric is derived which incorporates variable G in accordance with the LNH. The dynamics of freely moving particles and photons in such a metric are examined according to the theory and observational tests are formulated. (author)

  6. Studies of x-ray localization and thickness dependence in atomic-scale elemental mapping by STEM energy-dispersive x-ray spectroscopy using single-frame scanning method.

    Science.gov (United States)

    Lu, Ping; Moya, Jaime M; Yuan, Renliang; Zuo, Jian Min

    2018-03-01

    The delocalization of x-ray signals limits the spatial resolution in atomic-scale elemental mapping by scanning transmission electron microscopy (STEM) using energy-dispersive x-ray spectroscopy (EDS). In this study, using a SrTiO 3 [001] single crystal, we show that the x-ray localization to atomic columns is strongly dependent on crystal thickness, and a thin crystal is critical for improving the spatial resolution in atomic-scale EDS mapping. A single-frame scanning technique is used in this study instead of the multiple-frame technique to avoid peak broadening due to tracking error. The strong thickness dependence is realized by measuring the full width at half maxima (FWHM) as well as the peak-to-valley (P/V) ratio of the EDS profiles for Ti K and Sr K + L, obtained at several crystal thicknesses. A FWHM of about 0.16 nm and a P/V ratio of greater than 7.0 are obtained for Ti K for a crystal thickness of less than 20 nm. With increasing crystal thickness, the FWHM and P/V ratio increases and decreases, respectively, indicating the advantage of using a thin crystal for high-resolution EDS mapping. Published by Elsevier B.V.

  7. Atomic-scale dislocation dynamics in radiation damage environment

    International Nuclear Information System (INIS)

    Osetsky, Y.; Stoller, R.; Bacon, D.J.

    2007-01-01

    Full text of publication follows: The dynamics behavior of dislocations determines mechanical properties of crystalline materials. Long-range interactions between a moving dislocation and other defects can be treated within a continuum approach via interaction of their stress and strain fields. However, a vast contribution to mechanical properties depends on the direct interaction between dislocations and other defects and depends very much on the particular atomic scale structure of the both moving dislocation core and the obstacle. In this work we review recent progress in large-scale modeling of dislocation dynamics in metals at the atomic level by molecular dynamics and statics. We review the modem techniques used to simulate dynamics of dislocations in different lattice structures, the dependence on temperature, strain rate and obstacle size. Examples are given for bcc, fcc and hcp metals where edge and screw dislocations interact with vacancy (loops, voids, stacking fault tetrahedra, etc), self-interstitial clusters and secondary phase precipitates. Attention is paid to interpretation of atomistic results from the point of view of parameterization of continuum models. The latter is vitally necessary for further application in 3-dimensional dislocation dynamics within the multi-scale materials modeling approach. Research sponsored by the Division of Materials Sciences and Engineering and the Office of Fusion Energy Sciences, U.S. Department of Energy, under contract DE-AC0S-00OR22725 with UT-Battelle, LLC. (authors)

  8. Modelling atomic scale manipulation with the non-contact atomic force microscope

    International Nuclear Information System (INIS)

    Trevethan, T; Watkins, M; Kantorovich, L N; Shluger, A L; Polesel-Maris, J; Gauthier, S

    2006-01-01

    We present the results of calculations performed to model the process of lateral manipulation of an oxygen vacancy in the MgO(001) surface using the non-contact atomic force microscope (NC-AFM). The potential energy surfaces for the manipulation as a function of tip position are determined from atomistic modelling of the MgO(001) surface interacting with a Mg terminated MgO tip. These energies are then used to model the dynamical evolution of the system as the tip oscillates and at a finite temperature using a kinetic Monte Carlo method. The manipulation process is strongly dependent on the lateral position of the tip and the system temperature. It is also found that the expectation value of the point at which the vacancy jumps depends on the trajectory of the oscillating cantilever as the surface is approached. The effect of the manipulation on the operation of the NC-AFM is modelled with a virtual dynamic AFM, which explicitly simulates the entire experimental instrumentation and control loops. We show how measurable experimental signals can result from a single controlled atomic scale event and suggest the most favourable conditions for achieving successful atomic scale manipulation experimentally

  9. Tuning magnetotransport in a compensated semimetal at the atomic scale

    Science.gov (United States)

    Wang, Lin; Gutiérrez-Lezama, Ignacio; Barreteau, Céline; Ubrig, Nicolas; Giannini, Enrico; Morpurgo, Alberto F.

    2015-11-01

    Either in bulk form, or in atomically thin crystals, layered transition metal dichalcogenides continuously reveal new phenomena. The latest example is 1T'-WTe2, a semimetal found to exhibit the largest known magnetoresistance in the bulk, and predicted to become a topological insulator in strained monolayers. Here we show that reducing the thickness through exfoliation enables the electronic properties of WTe2 to be tuned, which allows us to identify the mechanisms responsible for the observed magnetotransport down to the atomic scale. The longitudinal resistance and the unconventional magnetic field dependence of the Hall resistance are reproduced quantitatively by a classical two-band model for crystals as thin as six monolayers, whereas a crossover to an Anderson insulator occurs for thinner crystals. Besides establishing the origin of the magnetoresistance of WTe2, our results represent a complete validation of the classical theory for two-band electron-hole transport, and indicate that atomically thin WTe2 layers remain gapless semimetals.

  10. Iron phosphate glasses: Bulk properties and atomic scale structure

    Energy Technology Data Exchange (ETDEWEB)

    Joseph, Kitheri; Stennett, Martin C.; Hyatt, Neil C.; Asuvathraman, R.; Dube, Charu L.; Gandy, Amy S.; Govindan Kutty, K. V.; Jolley, Kenny; Vasudeva Rao, P. R.; Smith, Roger

    2017-10-01

    Bulk properties such as glass transition temperature, density and thermal expansion of iron phosphate glass compositions, with replacement of Cs by Ba, are investigated as a surrogate for the transmutation of 137Cs to 137Ba, relevant to the immobilisation of Cs in glass. These studies are required to establish the appropriate incorporation rate of 137Cs in iron phosphate glass. Density and glass transition temperature increases with the addition of BaO indicating the shrinkage and reticulation of the iron phosphate glass network. The average thermal expansion coefficient reduces from 19.8 × 10-6 K-1 to 13.4 × 10-6 K-1, when 25 wt. % of Cs2O was replaced by 25 wt. % of BaO in caesium loaded iron phosphate glass. In addition to the above bulk properties, the role of Ba as a network modifier in the structure of iron phosphate glass is examined using various spectroscopic techniques. The FeII content and average coordination number of iron in the glass network was estimated using Mössbauer spectroscopy. The FeII content in the un-doped iron phosphate glass and barium doped iron phosphate glasses was 20, 21 and 22 ± 1% respectively and the average Fe coordination varied from 5.3 ± 0.2 to 5.7 ± 0.2 with increasing Ba content. The atomic scale structure was further probed by Fe K-edge X-ray absorption spectroscopy. The average coordination number provided by extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure was in good agreement with that given by the Mössbauer data.

  11. EON: software for long time simulations of atomic scale systems

    Science.gov (United States)

    Chill, Samuel T.; Welborn, Matthew; Terrell, Rye; Zhang, Liang; Berthet, Jean-Claude; Pedersen, Andreas; Jónsson, Hannes; Henkelman, Graeme

    2014-07-01

    The EON software is designed for simulations of the state-to-state evolution of atomic scale systems over timescales greatly exceeding that of direct classical dynamics. States are defined as collections of atomic configurations from which a minimization of the potential energy gives the same inherent structure. The time evolution is assumed to be governed by rare events, where transitions between states are uncorrelated and infrequent compared with the timescale of atomic vibrations. Several methods for calculating the state-to-state evolution have been implemented in EON, including parallel replica dynamics, hyperdynamics and adaptive kinetic Monte Carlo. Global optimization methods, including simulated annealing, basin hopping and minima hopping are also implemented. The software has a client/server architecture where the computationally intensive evaluations of the interatomic interactions are calculated on the client-side and the state-to-state evolution is managed by the server. The client supports optimization for different computer architectures to maximize computational efficiency. The server is written in Python so that developers have access to the high-level functionality without delving into the computationally intensive components. Communication between the server and clients is abstracted so that calculations can be deployed on a single machine, clusters using a queuing system, large parallel computers using a message passing interface, or within a distributed computing environment. A generic interface to the evaluation of the interatomic interactions is defined so that empirical potentials, such as in LAMMPS, and density functional theory as implemented in VASP and GPAW can be used interchangeably. Examples are given to demonstrate the range of systems that can be modeled, including surface diffusion and island ripening of adsorbed atoms on metal surfaces, molecular diffusion on the surface of ice and global structural optimization of nanoparticles.

  12. Nano-scale study of phase separation in ferrite of long term thermally aged Mo-bearing duplex stainless steels - Atom probe tomography and Monte Carlo simulation

    International Nuclear Information System (INIS)

    Pareige, C.; Emo, J.; Pareige, P.; Saillet, S.; Domain, C.

    2015-01-01

    Duplex stainless steels (DSS), used in primary circuit of Pressurised Water Reactor (PWR), are prone to thermal ageing at service temperature, typically between 286 and 323 C. degrees. This ageing is due to the ferrite decomposition via two kinds of phase transformations: spinodal decomposition into Fe rich α zones and Cr rich α' zones and precipitation of G-phase enriched in Ni, Si, Mn and Mo. It has been shown by atom probe tomography (APT) that the G-phase particles form at the interface between α and α' regions thereby demonstrating that α-α' decomposition and G-phase precipitation are highly dependent. The synergy between the two decomposition processes should be related to both the thermodynamics of the system and the diffusion mechanisms active during ageing. This can be studied by atomistic kinetic Monte Carlo (AKMC) with a model that can reproduce the phase transformations which take place in ferrite of duplex stainless steels. This paper presents the first simulations of the kinetics of spinodal decomposition and G-phase precipitation occurring in ferrite of duplex stainless steels. The kinetics was simulated using a simple but effective atomic kinetic Monte Carlo model in a ternary alloy. The simulations reproduced the α/α' spinodal structure with precipitates at the α/α' interface. The comparison of simulated results with experiments shows that the simulations quantitatively reproduce the kinetics of phase transformation and the synergy observed experimentally between the spinodal decomposition and G-phase precipitation: the time evolution of the wavelength of the spinodal decomposition and the radius of G-phase precipitates were quantitatively reproduced. The simulations endorse the assumption that G-phase precipitation mainly results from the rejection of G-formers from α and α' domains. By following the vacancy pathway during simulation, we show that coarsening of the G-phase precipitates must proceed via

  13. Recent advances in atomic-scale spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    Smith, Arthur R; Yang, Rong; Yang, Haiqiang; Dick, Alexey; Neugebauer, Joerg; Lambrecht, Walter R L

    2005-02-01

    The Mn3N2 (010) surface has been studied using spin-polarized scanning tunneling microscopy at the atomic scale. The principle objective of this work is to elucidate the properties and potential of this technique to measure atomic-scale magnetic structures. The experimental approach involves the use of a combined molecular beam epitaxy/scanning tunneling microscopy system that allows the study of atomically clean magnetic surfaces. Several key findings have been obtained. First, both magnetic and non-magnetic atomic-scale information has been obtained in a single spin-polarized image. Magnetic modulation of the height profile having an antiferromagnetic super-period of c = 12.14 A (6 atomic rows) together with a non-magnetic superstructure having a period of c/2 = 6.07 A (3 atomic rows) was observed. Methods of separation of magnetic and non-magnetic profiles are presented. Second, bias voltage-dependent spin-polarized images show a reversal of the magnetic modulation at a particular voltage. This reversal is clearly due to a change in the sign of the magnetic term in the tunnel current. Since this term depends on both the tip's as well as the sample's magnetic local density of states, the reversal can be caused by either the sample or the tip. Third, the shape of the line profile was found to vary with the bias voltage, which is related to the energy-dependent spin contribution from the 2 chemically inequivalent Mn sites on the surface. Overall, the results shown here expand the application of the method of spin-polarized scanning tunneling microscopy to measure atomic-scale magnetic structures. (c) 2005 Wiley-Liss, Inc.

  14. Semiempirical studies of atomic structure

    International Nuclear Information System (INIS)

    Curtis, L.J.

    1992-01-01

    The energy level structure, transition probabilities, and general spectroscopic properties of highly ionized many-electron systems are studied through the combined use of sensitive semiempirical data systematizations, selected precision experimental measurements, and specialized theoretical computations. Measurements are made primarily through the use of fast ion beam excitation methods, which are combined with available data from laser-and tokamak-produced plasmas, astrophysical sources, and conventional light sources. The experimental studies are strengthened through large-scale ab initio calculations. Typical examples are the following: lifetime measurements in the neon isoelectronic sequence; multiplexed decay curve measurements of Li-like Si XII; and isoelectronic specification of intershell resonance and intercombination decay rates using measured transition probabilities and spectroscopically determined singlet-mixing amplitudes

  15. Atomic-scale structure of single-layer MoS2 nanoclusters

    DEFF Research Database (Denmark)

    Helveg, S.; Lauritsen, J. V.; Lægsgaard, E.

    2000-01-01

    We have studied using scanning tunneling microscopy (STM) the atomic-scale realm of molybdenum disulfide (MoS2) nanoclusters, which are of interest as a model system in hydrodesulfurization catalysis. The STM gives the first real space images of the shape and edge structure of single-layer MoS2...

  16. Atomic scale studies of La/Sr ordering in La2-2xSr1+2xMn2O7 single crystals

    KAUST Repository

    Roldan, Manuel; Oxley, Mark; Li, Qiang; Gray, Kenneth; Mitchell, John; Pennycook, Stephen; Varela, Maria

    2016-01-01

    quality. No secondary phases or defects are observed. Figure 1 displays an atomic resolution image obtained with the c-axis perpendicular to the electron beam of a x=0.50 sample. The perovskite (P)-like planes and the rock salt (R)-like planes are clearly

  17. Nano Scale Mechanical Analysis of Biomaterials Using Atomic Force Microscopy

    Science.gov (United States)

    Dutta, Diganta

    The atomic force microscope (AFM) is a probe-based microscope that uses nanoscale and structural imaging where high resolution is desired. AFM has also been used in mechanical, electrical, and thermal engineering applications. This unique technique provides vital local material properties like the modulus of elasticity, hardness, surface potential, Hamaker constant, and the surface charge density from force versus displacement curve. Therefore, AFM was used to measure both the diameter and mechanical properties of the collagen nanostraws in human costal cartilage. Human costal cartilage forms a bridge between the sternum and bony ribs. The chest wall of some humans is deformed due to defective costal cartilage. However, costal cartilage is less studied compared to load bearing cartilage. Results show that there is a difference between chemical fixation and non-chemical fixation treatments. Our findings imply that the patients' chest wall is mechanically weak and protein deposition is abnormal. This may impact the nanostraws' ability to facilitate fluid flow between the ribs and the sternum. At present, AFM is the only tool for imaging cells' ultra-structure at the nanometer scale because cells are not homogeneous. The first layer of the cell is called the cell membrane, and the layer under it is made of the cytoskeleton. Cancerous cells are different from normal cells in term of cell growth, mechanical properties, and ultra-structure. Here, force is measured with very high sensitivity and this is accomplished with highly sensitive probes such as a nano-probe. We performed experiments to determine ultra-structural differences that emerge when such cancerous cells are subject to treatments such as with drugs and electric pulses. Jurkat cells are cancerous cells. These cells were pulsed at different conditions. Pulsed and non-pulsed Jurkat cell ultra-structures were investigated at the nano meter scale using AFM. Jurkat cell mechanical properties were measured under

  18. Atom-scale molecular interactions in lipid raft mixtures

    DEFF Research Database (Denmark)

    Niemelä, Perttu S; Hyvönen, Marja T; Vattulainen, Ilpo

    2009-01-01

    We review the relationship between molecular interactions and the properties of lipid environments. A specific focus is given on bilayers which contain sphingomyelin (SM) and sterols due to their essential role for the formation of lipid rafts. The discussion is based on recent atom-scale molecular...... dynamics simulations, complemented by extensive comparison to experimental data. The discussion is divided into four sections. The first part investigates the properties of one-component SM bilayers and compares them to bilayers with phosphatidylcholine (PC), the focus being on a detailed analysis...... examples of this issue. The third part concentrates on the specificity of intermolecular interactions in three-component mixtures of SM, PC and cholesterol (CHOL) under conditions where the concentrations of SM and CHOL are dilute with respect to that of PC. The results show how SM and CHOL favor one...

  19. Large-scale atomic calculations using variational methods

    Energy Technology Data Exchange (ETDEWEB)

    Joensson, Per

    1995-01-01

    Atomic properties, such as radiative lifetimes, hyperfine structures and isotope shift, have been studied both theoretically and experimentally. Computer programs which calculate these properties from multiconfiguration Hartree-Fock (MCHF) and configuration interaction (CI) wave functions have been developed and tested. To study relativistic effects, a program which calculates hyperfine structures from multiconfiguration Dirac-Fock (MCDF) wave functions has also been written. A new method of dealing with radial non-orthogonalities in transition matrix elements has been investigated. This method allows two separate orbital sets to be used for the initial and final states, respectively. It is shown that, once the usual orthogonality restrictions have been overcome, systematic MCHF calculations are able to predict oscillator strengths in light atoms with high accuracy. In connection with recent high-power laser experiments, time-dependent calculations of the atomic response to intense laser fields have been performed. Using the frozen-core approximation, where the atom is modeled as an active electron moving in the average field of the core electrons and the nucleus, the active electron has been propagated in time under the influence of the laser field. Radiative lifetimes and hyperfine structures of excited states in sodium and silver have been experimentally determined using time-resolved laser spectroscopy. By recording the fluorescence light decay following laser excitation in the vacuum ultraviolet spectral region, the radiative lifetimes and hyperfine structures of the 7p{sup 2}P states in silver have been measured. The delayed-coincidence technique has been used to make very accurate measurements of the radiative lifetimes and hyperfine structures of the lowest 2P states in sodium and silver. 77 refs, 2 figs, 14 tabs.

  20. Large-scale atomic calculations using variational methods

    International Nuclear Information System (INIS)

    Joensson, Per.

    1995-01-01

    Atomic properties, such as radiative lifetimes, hyperfine structures and isotope shift, have been studied both theoretically and experimentally. Computer programs which calculate these properties from multiconfiguration Hartree-Fock (MCHF) and configuration interaction (CI) wave functions have been developed and tested. To study relativistic effects, a program which calculates hyperfine structures from multiconfiguration Dirac-Fock (MCDF) wave functions has also been written. A new method of dealing with radial non-orthogonalities in transition matrix elements has been investigated. This method allows two separate orbital sets to be used for the initial and final states, respectively. It is shown that, once the usual orthogonality restrictions have been overcome, systematic MCHF calculations are able to predict oscillator strengths in light atoms with high accuracy. In connection with recent high-power laser experiments, time-dependent calculations of the atomic response to intense laser fields have been performed. Using the frozen-core approximation, where the atom is modeled as an active electron moving in the average field of the core electrons and the nucleus, the active electron has been propagated in time under the influence of the laser field. Radiative lifetimes and hyperfine structures of excited states in sodium and silver have been experimentally determined using time-resolved laser spectroscopy. By recording the fluorescence light decay following laser excitation in the vacuum ultraviolet spectral region, the radiative lifetimes and hyperfine structures of the 7p 2 P states in silver have been measured. The delayed-coincidence technique has been used to make very accurate measurements of the radiative lifetimes and hyperfine structures of the lowest 2P states in sodium and silver. 77 refs, 2 figs, 14 tabs

  1. Electronic transport properties of copper and gold at atomic scale

    Energy Technology Data Exchange (ETDEWEB)

    Mohammadzadeh, Saeideh

    2010-11-23

    The factors governing electronic transport properties of copper and gold atomic-size contacts are theoretically examined in the present work. A two-terminal conductor using crystalline electrodes is adopted. The non-equilibrium Green's function combined with the density functional tight-binding method is employed via gDFTB simulation tool to calculate the transport at both equilibrium and non-equilibrium conditions. The crystalline orientation, length, and arrangement of electrodes have very weak influence on the electronic characteristics of the considered atomic wires. The wire width is found to be the most effective geometric aspect determining the number of conduction channels. The obtained conductance oscillation and linear current-voltage curves are interpreted. To analyze the conduction mechanism in detail, the transmission channels and their decomposition to the atomic orbitals are calculated in copper and gold single point contacts. The presented results offer a possible explanation for the relation between conduction and geometric structure. Furthermore, the results are in good agreement with available experimental and theoretical studies. (orig.)

  2. Studies in Composing Hydrogen Atom Wavefunctions

    DEFF Research Database (Denmark)

    Putnam, Lance Jonathan; Kuchera-Morin, JoAnn; Peliti, Luca

    2015-01-01

    We present our studies in composing elementary wavefunctions of a hydrogen-like atom and identify several relationships between physical phenomena and musical composition that helped guide the process. The hydrogen-like atom accurately describes some of the fundamental quantum mechanical phenomen...

  3. Atomic-scale nanowires: physical and electronic structure

    International Nuclear Information System (INIS)

    Bowler, D R

    2004-01-01

    The technology to build and study nanowires with sizes ranging from individual atoms to tens of nanometres has been developing rapidly over the last few years. We survey the motivation behind these developments, and summarize the basics behind quantized conduction. Several of the different experimental techniques and materials systems used in the creation of nanowires are examined, and the range of theoretical methods developed both for examining open systems (especially their conduction properties) and for modelling large systems are considered. We present various noteworthy example results from the field, before concluding with a look at future directions. (topical review)

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

    International Nuclear Information System (INIS)

    Osetsky, Yu.N.; Bacon, D.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

  5. Effect of deposition rate on melting point of copper film catalyst substrate at atomic scale

    Science.gov (United States)

    Marimpul, Rinaldo; Syuhada, Ibnu; Rosikhin, Ahmad; Winata, Toto

    2018-03-01

    Annealing process of copper film catalyst substrate was studied by molcular dynamics simulation. This copper film catalyst substrate was produced using thermal evaporation method. The annealing process was limited in nanosecond order to observe the mechanism at atomic scale. We found that deposition rate parameter affected the melting point of catalyst substrate. The change of crystalline structure of copper atoms was observed before it had been already at melting point. The optimum annealing temperature was obtained to get the highest percentage of fcc structure on copper film catalyst substrate.

  6. Development of indigenous laboratory scale gas atomizer for producing metal powders

    International Nuclear Information System (INIS)

    Khan, K.K.; Qasim, A.M.; Ahmed, P.

    2011-01-01

    Gas atomization is one of the methods for production of clean metal powders at relatively moderate cost. A laboratory scale gas atomizer was designed and fabricated indigenously to produce metal powders with a batch capacity of 500 g of copper (Cu). The design includes several features regarding fabrication and operation to provide optimum conditions for atomization. The inner diameter of atomizing chamber is 440 mm and its height is 1200 mm. The atomizing nozzle is of annular confined convergent type with an angle of 25 degree. Argon gas at desired pressure has been used for atomizing the metals to produce relatively clean powders. A provision has also been made to view the atomization process. The indigenous laboratory scale gas atomizer was used to produce tin (Sn) and copper (Cu) powders with different atomizing gas pressures ranging from 2 to 10 bar. The particle size of different powders produced ranges from 40 to 400 im. (author)

  7. Case studies in atomic collision physics

    CERN Document Server

    McDaniel, E W

    1974-01-01

    Case Studies in Atomic Physics III focuses on case studies on atomic and molecular physics, including atomic collisions, transport properties of electrons, ions, molecules, and photons, interaction potentials, spectroscopy, and surface phenomena. The selection first discusses detailed balancing in the time-dependent impact parameter method, as well as time-reversal in the impact parameter method and coupled state approximation. The text also examines the mechanisms of electron production in ion. Topics include measurement of doubly differential cross sections and electron spectra, direct Coul

  8. Dislocations and elementary processes of plasticity in FCC metals: atomic scale simulations

    International Nuclear Information System (INIS)

    Rodney, D.

    2000-01-01

    We present atomic-scale simulations of two elementary processes of FCC crystal plasticity. The first study consists in the simulation by molecular dynamics, in a nickel crystal, of the interactions between an edge dislocation and glissile interstitial loops of the type that form under irradiation in displacement cascades. The simulations show various atomic-scale interaction processes leading to the absorption and drag of the loops by the dislocation. These reactions certainly contribute to the formation of the 'clear bands' observed in deformed irradiated materials. The simulations also allow to study quantitatively the role of the glissile loops in irradiation hardening. In particular, dislocation unpinning stresses for certain pinning mechanisms are evaluated from the simulations. The second study consists first in the generalization in three dimensions of the quasi-continuum method (QCM), a multi-scale simulation method which couples atomistic techniques and the finite element method. In the QCM, regions close to dislocation cores are simulated at the atomic-scale while the rest of the crystal is simulated with a lower resolution by means of a discretization of the displacement fields using the finite element method. The QCM is then tested on the simulation of the formation and breaking of dislocation junctions in an aluminum crystal. Comparison of the simulations with an elastic model of dislocation junctions shows that the structure and strength of the junctions are dominated by elastic line tension effects, as is assumed in classical theories. (author)

  9. Atomic-scale epitaxial aluminum film on GaAs substrate

    Directory of Open Access Journals (Sweden)

    Yen-Ting Fan

    2017-07-01

    Full Text Available Atomic-scale metal films exhibit intriguing size-dependent film stability, electrical conductivity, superconductivity, and chemical reactivity. With advancing methods for preparing ultra-thin and atomically smooth metal films, clear evidences of the quantum size effect have been experimentally collected in the past two decades. However, with the problems of small-area fabrication, film oxidation in air, and highly-sensitive interfaces between the metal, substrate, and capping layer, the uses of the quantized metallic films for further ex-situ investigations and applications have been seriously limited. To this end, we develop a large-area fabrication method for continuous atomic-scale aluminum film. The self-limited oxidation of aluminum protects and quantizes the metallic film and enables ex-situ characterizations and device processing in air. Structure analysis and electrical measurements on the prepared films imply the quantum size effect in the atomic-scale aluminum film. Our work opens the way for further physics studies and device applications using the quantized electronic states in metals.

  10. Atomic level characterization in corrosion studies

    Science.gov (United States)

    Marcus, Philippe; Maurice, Vincent

    2017-06-01

    Atomic level characterization brings fundamental insight into the mechanisms of self-protection against corrosion of metals and alloys by oxide passive films and into how localized corrosion is initiated on passivated metal surfaces. This is illustrated in this overview with selected data obtained at the subnanometre, i.e. atomic or molecular, scale and also at the nanometre scale on single-crystal copper, nickel, chromium and stainless steel surfaces passivated in well-controlled conditions and analysed in situ and/or ex situ by scanning tunnelling microscopy/spectroscopy and atomic force microscopy. A selected example of corrosion modelling by ab initio density functional theory is also presented. The discussed aspects include the surface reconstruction induced by hydroxide adsorption and formation of two-dimensional (hydr)oxide precursors, the atomic structure, orientation and surface hydroxylation of three-dimensional ultrathin oxide passive films, the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at grain boundaries of passive films and the role of step edges at the exposed surface of oxide grains on the dissolution of the passive film. This article is part of the themed issue 'The challenges of hydrogen and metals'.

  11. Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene.

    Science.gov (United States)

    Choi, Jin Sik; Chang, Young Jun; Woo, Sungjong; Son, Young-Woo; Park, Yeonggu; Lee, Mi Jung; Byun, Ik-Su; Kim, Jin-Soo; Choi, Choon-Gi; Bostwick, Aaron; Rotenberg, Eli; Park, Bae Ho

    2014-12-01

    Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzag directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. The correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene.

  12. Thermovoltage in scanning tunnelling microscopy. Study of heterogeneous metal surfaces on atomic scale; Thermospannung in der Rastertunnelmikroskopie. Untersuchung heterogener Metalloberflaechen auf atomarer Skala

    Energy Technology Data Exchange (ETDEWEB)

    Weyers, B.

    2005-07-01

    In this thesis the thermovoltage has been studied via a tunnel barrier under different aspects. Au(111) has been chosen as substrate. The mean free path of the electrons on the Au(111) surface was determined by a comparison of the standing waves on stage edges with the theoretical prediction. The measurements were performed at different temperatures. Detailed studies were performed on Au(111), Cu(111), and Cu(110) in order to examine the question whether the cause for strong signal on the stage edges lies in the surface state itself or in the band gap. The mani theme of this thesis is the study of a binary metal system, in this case silver on Au(111).

  13. Atomic scale mass delivery driven by bend kink in single walled carbon nanotube

    International Nuclear Information System (INIS)

    Kan Biao; Ding Jianning; Ling Zhiyong; Yuan Ningyi; Cheng Guanggui

    2010-01-01

    The possibility of atomic scale mass delivery by bend kink in single walled carbon nanotube was investigated with the aid of molecular dynamics simulation. By keeping the bending angle while moving the tube end, the encapsulated atomic scale mass such as atom, molecule and atom group were successfully delivered through the nanotube. The van der Waals interaction between the encapsulated mass and the tube wall provided the driving force for the delivery. There were no dramatic changes in the van der Waals interaction, and a smooth and steady delivery was achieved when constant loading rate was applied. The influence of temperature on the atom group delivery was also analyzed. It is found raising temperature is harmful to the smooth movement of the atom group. However, the delivery rate can be promoted under higher temperature when the atom group is situated before the kink during the delivery.

  14. Case studies in atomic collision physics

    CERN Document Server

    McDaniel, Earl Wadsworth

    1972-01-01

    Case Studies in Atomic Collision Physics II focuses on studies on the role of atomic collision processes in astrophysical plasmas, including ionic recombination, electron transport, and position scattering. The book first discusses three-body recombination of positive and negative ions, as well as introduction to ionic recombination, calculation of the recombination coefficient, ions recombining in their parent gas, and three-body recombination at moderate and high gas-densities. The manuscript also takes a look at precision measurements of electron transport coefficients and differential cr

  15. Static and Dynamic Electron Microscopy Investigations at the Atomic and Ultrafast Scales

    Science.gov (United States)

    Suri, Pranav Kumar

    Advancements in the electron microscopy capabilities - aberration-corrected imaging, monochromatic spectroscopy, direct-electron detectors - have enabled routine visualization of atomic-scale processes with millisecond temporal resolutions in this decade. This, combined with progress in the transmission electron microscopy (TEM) specimen holder technology and nanofabrication techniques, allows comprehensive experiments on a wide range of materials in various phases via in situ methods. The development of ultrafast (sub-nanosecond) time-resolved TEM with ultrafast electron microscopy (UEM) has further pushed the envelope of in situ TEM to sub-nanosecond temporal resolution while maintaining sub-nanometer spatial resolution. A plethora of materials phenomena - including electron-phonon coupling, phonon transport, first-order phase transitions, bond rotation, plasmon dynamics, melting, and dopant atoms arrangement - are not yet clearly understood and could be benefitted with the current in situ TEM capabilities having atomic-level and ultrafast precision. Better understanding of these phenomena and intrinsic material dynamics (e.g. how phonons propagate in a material, what time-scales are involved in a first-order phase transition, how fast a material melts, where dopant atoms sit in a crystal) in new-generation and technologically important materials (e.g. two-dimensional layered materials, semiconductor and magnetic devices, rare-earth-element-free permanent magnets, unconventional superconductors) could bring a paradigm shift in their electronic, structural, magnetic, thermal and optical applications. Present research efforts, employing cutting-edge static and dynamic in situ electron microscopy resources at the University of Minnesota, are directed towards understanding the atomic-scale crystallographic structural transition and phonon transport in an iron-pnictide parent compound LaFeAsO, studying the mechanical stability of fast moving hard-drive heads in heat

  16. Atomic-scale friction on stepped surfaces of ionic crystals.

    Science.gov (United States)

    Steiner, Pascal; Gnecco, Enrico; Krok, Franciszek; Budzioch, Janusz; Walczak, Lukasz; Konior, Jerzy; Szymonski, Marek; Meyer, Ernst

    2011-05-06

    We report on high-resolution friction force microscopy on a stepped NaCl(001) surface in ultrahigh vacuum. The measurements were performed on single cleavage step edges. When blunt tips are used, friction is found to increase while scanning both up and down a step edge. With atomically sharp tips, friction still increases upwards, but it decreases and even changes sign downwards. Our observations extend previous results obtained without resolving atomic features and are associated with the competition between the Schwöbel barrier and the asymmetric potential well accompanying the step edges.

  17. A method optimization study for atomic absorption ...

    African Journals Online (AJOL)

    A sensitive, reliable and relative fast method has been developed for the determination of total zinc in insulin by atomic absorption spectrophotometer. This designed study was used to optimize the procedures for the existing methods. Spectrograms of both standard and sample solutions of zinc were recorded by measuring ...

  18. Microparticle adhesion studies by atomic force microscopy

    NARCIS (Netherlands)

    Segeren, L.H.G.J.; Siebum, B.; Karssenberg, F.G.; Berg, van den J.W.A.; Vancso, G.J.

    2002-01-01

    Atomic force microscopy (AFM) is one of the most flexible and simple techniques for probing surface interactions. This article reviews AFM studies on particle adhesion. Special attention is paid to the characterization of roughness and its effect on adhesion. This is of importance when comparing the

  19. Atomic-Scale Control of Electron Transport through Single Molecules

    DEFF Research Database (Denmark)

    Wang, Y. F.; Kroger, J.; Berndt, R.

    2010-01-01

    Tin-phthalocyanine molecules adsorbed on Ag(111) were contacted with the tip of a cryogenic scanning tunneling microscope. Orders-of-magnitude variations of the single-molecule junction conductance were achieved by controllably dehydrogenating the molecule and by modifying the atomic structure...

  20. Nanometer-scale optical traps using atomic state localization

    International Nuclear Information System (INIS)

    Yavuz, D. D.; Proite, N. A.; Green, J. T.

    2009-01-01

    We suggest a scheme where a laser beam forms an optical trap with a spatial size that is much smaller than the wavelength of light. The key idea is to combine a far-off-resonant dipole trap with a scheme that localizes an atomic excitation.

  1. Evolution of the Contact Area with Normal Load for Rough Surfaces: from Atomic to Macroscopic Scales.

    Science.gov (United States)

    Huang, Shiping

    2017-11-13

    The evolution of the contact area with normal load for rough surfaces has great fundamental and practical importance, ranging from earthquake dynamics to machine wear. This work bridges the gap between the atomic scale and the macroscopic scale for normal contact behavior. The real contact area, which is formed by a large ensemble of discrete contacts (clusters), is proven to be much smaller than the apparent surface area. The distribution of the discrete contact clusters and the interaction between them are key to revealing the mechanism of the contacting solids. To this end, Green's function molecular dynamics (GFMD) is used to study both how the contact cluster evolves from the atomic scale to the macroscopic scale and the interaction between clusters. It is found that the interaction between clusters has a strong effect on their formation. The formation and distribution of the contact clusters is far more complicated than that predicted by the asperity model. Ignorance of the interaction between them leads to overestimating the contacting force. In real contact, contacting clusters are smaller and more discrete due to the interaction between the asperities. Understanding the exact nature of the contact area with the normal load is essential to the following research on friction.

  2. Ultrafast, laser-based, x-ray science: the dawn of atomic-scale cinematography

    International Nuclear Information System (INIS)

    Barty, C.P.J.

    2000-01-01

    The characteristics of ultrafast chirped pulse amplification systems are reviewed. Application of ultrafast chirped pulse amplification to the generation of femtosecond, incoherent, 8-keV line radiation is outlined and the use of femtosecond laser-based, x-rays for novel time-resolved diffraction studies of crystalline dynamics with sub-picosecond temporal resolution and sub-picometer spatial resolution is reviewed in detail. Possible extensions of laser-based, x-ray technology and evaluation of alternative x-ray approaches for time-resolved studies of the atomic scale dynamics are given. (author)

  3. Ultrafast, laser-based, x-ray science: the dawn of atomic-scale cinematography

    Energy Technology Data Exchange (ETDEWEB)

    Barty, C.P.J. [University of California, Department of Applied Mechanics and Engineering Science, Urey Hall, Mali Code 0339, San Diego, La Jolla, CA (United States)

    2000-03-01

    The characteristics of ultrafast chirped pulse amplification systems are reviewed. Application of ultrafast chirped pulse amplification to the generation of femtosecond, incoherent, 8-keV line radiation is outlined and the use of femtosecond laser-based, x-rays for novel time-resolved diffraction studies of crystalline dynamics with sub-picosecond temporal resolution and sub-picometer spatial resolution is reviewed in detail. Possible extensions of laser-based, x-ray technology and evaluation of alternative x-ray approaches for time-resolved studies of the atomic scale dynamics are given. (author)

  4. Atomic and molecular dynamics triggered by ultrashort light pulses on the atto- to picosecond time scale

    Science.gov (United States)

    Pabst, Stefan

    2013-04-01

    Time-resolved investigations of ultrafast electronic and molecular dynamics were not possible until recently. The typical time scale of these processes is in the picosecond to attosecond realm. The tremendous technological progress in recent years made it possible to generate ultrashort pulses, which can be used to trigger, to watch, and to control atomic and molecular motion. This tutorial focuses on experimental and theoretical advances which are used to study the dynamics of electrons and molecules in the presence of ultrashort pulses. In the first part, the rotational dynamics of molecules, which happens on picosecond and femtosecond time scales, is reviewed. Well-aligned molecules are particularly suitable for angle-dependent investigations like x-ray diffraction or strong-field ionization experiments. In the second part, the ionization dynamics of atoms is studied. The characteristic time scale lies, here, in the attosecond to few-femtosecond regime. Although a one-particle picture has been successfully applied to many processes, many-body effects do constantly occur. After a broad overview of the main mechanisms and the most common tools in attosecond physics, examples of many-body dynamics in the attosecond world (e.g., in high-harmonic generation and attosecond transient absorption spectroscopy) are discussed.

  5. Atomic-scale properties of Ni-based FCC ternary, and quaternary alloys

    International Nuclear Information System (INIS)

    Tamm, Artur; Aabloo, Alvo; Klintenberg, Mattias; Stocks, Malcolm; Caro, Alfredo

    2015-01-01

    The aim of this study is to characterize some atomic-scale properties of Ni-based FCC multicomponent alloys. For this purpose, we use Monte Carlo method combined with density functional theory calculations to study short-range order (SRO), atomic displacements, electronic density of states, and magnetic moments in equimolar ternary NiCrCo, and quaternary NiCrCoFe alloys. According to our study, the salient features for the ternary alloy are a negative SRO parameter between Ni–Cr and a positive between Cr–Cr pairs as well as a weakly magnetic state. For the quaternary alloy we predict negative SRO parameter for Ni–Cr and Ni–Fe pairs and positive for Cr–Cr and Fe–Fe pairs. Atomic displacements for both ternary and quaternary alloys are negligible. In contrast to the ternary, the quaternary alloy shows a complex magnetic structure. The electronic structure of the ternary and quaternary alloys shows differences near the Fermi energy between a random solid solution and the predicted structure with SRO. Despite that, the calculated EXAFS spectra does not show enough contrast to discriminate between random and ordered structures. The predicted SRO has an impact on point-defect energetics, electron–phonon coupling and thermodynamic functions and thus, SRO should not be neglected when studying properties of these two alloys

  6. Molecular beam studies and hot atom chemistry

    International Nuclear Information System (INIS)

    Continetti, R.E.; Lee, Y.T.

    1993-01-01

    The application of the crossed molecular beam technique to the study of hot atom chemistry has provided significant insights into the dynamics of hot atom reaction. To illustrate this, two recent studies are discussed. Those are the study on the influence of translational energy in 0.6 to 1.5 eV range on endoergic reaction, and the experimental study on the detailed dynamics of elementary reaction at translational energy of 0.53 and 1.01 eV. The first example illustrates the contribution that molecular beam experiment can make in the understanding of the dynamics of endoergic substitution reaction. The second example illustrates the role that such studies can play in evaluating exact three-dimensional quantum scattering calculation and ab initio potential energy surfaces for chemical reaction. In the case of endoergic reaction of halogen substitution, it was observed that the reactive collision involved short lived collision complexes. It is suggested that energetic effect alone cannot account for the difference in cross sections, and dynamic effect most play a large role. In atom-diatom reaction, the differential cross section measurement of D+H 2 →DH+H reaction was carried out, and the results are discussed. (K.I.)

  7. Fundamental Challenges for Modeling Electrochemical Energy Storage Systems at the Atomic Scale.

    Science.gov (United States)

    Groß, Axel

    2018-04-23

    There is a strong need to improve the efficiency of electrochemical energy storage, but progress is hampered by significant technological and scientific challenges. This review describes the potential contribution of atomic-scale modeling to the development of more efficient batteries, with a particular focus on first-principles electronic structure calculations. Numerical and theoretical obstacles are discussed, along with ways to overcome them, and some recent examples are presented illustrating the insights into electrochemical energy storage that can be gained from quantum chemical studies.

  8. Femtosecond structural dynamics on the atomic length scale

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Dongfang

    2014-03-15

    This thesis reports on the development and application of two different but complementary ultrafast electron diffraction setups built at the Max Planck Research Department for Structural Dynamics. One is an ultra-compact femtosecond electron diffraction (FED) setup (Egun300), which is currently operational (with a maximum electron energy of 150 keV) and provides ultrashort (∝300 fs) and bright (∝10 e/μm{sup 2}) electron bunches. The other one, named as Relativistic Electron Gun for Atomic Exploration (REGAE) is a radio frequency driven 2 to 5 MeV FED setup built in collaboration with different groups from DESY. REGAE was developed as a facility that will provide high quality diffraction with sufficient coherence to even address structural protein dynamics and with electron pulses as short as 20 fs (FWHM). As one of the first students in Prof. R.J. Dwayne Miller's group, I led the femtosecond (fs) laser sub-group at REGAE being responsible for the construction of different key optical elements required to drive both of aforementioned FED systems. A third harmonic generation (THG) and a nonlinear optical parametric amplifier (NOPA) have been used for the photo-generation of ultrashort electron bursts as well as sample laser excitation. Different diagnostic tools have been constructed to monitor the performance of the fs optical system. A fast autocorrelator was developed to provide on the fly pulse duration correction. A transient-grating frequency-resolved optical gating (TG-FROG) was built to obtain detail information about the characteristics of fs optical pulse, i.e. phase and amplitude of its spectral components. In addition to these optical setups, I developed a fs optical pump-probe system, which supports broadband probe pulses. This setup was successfully applied to investigate the semiconductor-to-metal photoinduced phase transition in VO{sub 2} and the ultrafast photo-reduction mechanism of graphene oxide. In regard to FED setups, I have been

  9. Femtosecond structural dynamics on the atomic length scale

    International Nuclear Information System (INIS)

    Zhang, Dongfang

    2014-03-01

    This thesis reports on the development and application of two different but complementary ultrafast electron diffraction setups built at the Max Planck Research Department for Structural Dynamics. One is an ultra-compact femtosecond electron diffraction (FED) setup (Egun300), which is currently operational (with a maximum electron energy of 150 keV) and provides ultrashort (∝300 fs) and bright (∝10 e/μm 2 ) electron bunches. The other one, named as Relativistic Electron Gun for Atomic Exploration (REGAE) is a radio frequency driven 2 to 5 MeV FED setup built in collaboration with different groups from DESY. REGAE was developed as a facility that will provide high quality diffraction with sufficient coherence to even address structural protein dynamics and with electron pulses as short as 20 fs (FWHM). As one of the first students in Prof. R.J. Dwayne Miller's group, I led the femtosecond (fs) laser sub-group at REGAE being responsible for the construction of different key optical elements required to drive both of aforementioned FED systems. A third harmonic generation (THG) and a nonlinear optical parametric amplifier (NOPA) have been used for the photo-generation of ultrashort electron bursts as well as sample laser excitation. Different diagnostic tools have been constructed to monitor the performance of the fs optical system. A fast autocorrelator was developed to provide on the fly pulse duration correction. A transient-grating frequency-resolved optical gating (TG-FROG) was built to obtain detail information about the characteristics of fs optical pulse, i.e. phase and amplitude of its spectral components. In addition to these optical setups, I developed a fs optical pump-probe system, which supports broadband probe pulses. This setup was successfully applied to investigate the semiconductor-to-metal photoinduced phase transition in VO 2 and the ultrafast photo-reduction mechanism of graphene oxide. In regard to FED setups, I have been deeply involved in

  10. Solid-state electrochemistry on the nanometer and atomic scales: the scanning probe microscopy approach

    Science.gov (United States)

    Strelcov, Evgheni; Yang, Sang Mo; Jesse, Stephen; Balke, Nina; Vasudevan, Rama K.; Kalinin, Sergei V.

    2016-01-01

    Energy technologies of the 21st century require understanding and precise control over ion transport and electrochemistry at all length scales – from single atoms to macroscopic devices. This short review provides a summary of recent works dedicated to methods of advanced scanning probe microscopy for probing electrochemical transformations in solids at the meso-, nano- and atomic scales. Discussion presents advantages and limitations of several techniques and a wealth of examples highlighting peculiarities of nanoscale electrochemistry. PMID:27146961

  11. Effect of interlayer bonding strength and bending stiffness on 2-dimensional materials’ frictional properties at atomic-scale steps

    International Nuclear Information System (INIS)

    Lang, Haojie; Peng, Yitian; Zeng, Xingzhong

    2017-01-01

    Highlights: • Bending of uncovered step edge of 2-dimensional materials could be a common phenomenon during friction processes. • 2-dimensional materials with large interlayer bonding strength possess good frictional properties at step. • Increased bending stiffness of step edge could be the major reason that lateral force increased with step height. - Abstract: Atomic-scale steps generally presented in 2-dimensional materials have important influence on the overall nanotribological properties of surface. Frictional properties at atomic-scale steps of two types of 2-dimensional materials are studied using calibrated atomic force microscopy (AFM) tip sliding against the steps. The lateral force at uncovered step is larger than covered step due to the bending of step edge. The lateral force at monolayer uncovered step edge of h-BN is lower than graphene because h-BN possesses higher interlayer bonding strength than graphene and the bending of h-BN step edge is suppressed to some extent. The high uncovered step exhibits much larger lateral force than low uncovered step, which could be mainly induced by increased bending stiffness of step edge rather than increased step height. The results revealed that interlayer bonding strength and bending stiffness have great influence on the lateral force at atomic-scale steps. The studies can provide a further understanding of frictional properties at atomic scale steps and could be helpful for the applications of 2-dimensional materials as lubricant coating.

  12. Effect of interlayer bonding strength and bending stiffness on 2-dimensional materials’ frictional properties at atomic-scale steps

    Energy Technology Data Exchange (ETDEWEB)

    Lang, Haojie; Peng, Yitian, E-mail: yitianpeng@dhu.edu.cn; Zeng, Xingzhong

    2017-07-31

    Highlights: • Bending of uncovered step edge of 2-dimensional materials could be a common phenomenon during friction processes. • 2-dimensional materials with large interlayer bonding strength possess good frictional properties at step. • Increased bending stiffness of step edge could be the major reason that lateral force increased with step height. - Abstract: Atomic-scale steps generally presented in 2-dimensional materials have important influence on the overall nanotribological properties of surface. Frictional properties at atomic-scale steps of two types of 2-dimensional materials are studied using calibrated atomic force microscopy (AFM) tip sliding against the steps. The lateral force at uncovered step is larger than covered step due to the bending of step edge. The lateral force at monolayer uncovered step edge of h-BN is lower than graphene because h-BN possesses higher interlayer bonding strength than graphene and the bending of h-BN step edge is suppressed to some extent. The high uncovered step exhibits much larger lateral force than low uncovered step, which could be mainly induced by increased bending stiffness of step edge rather than increased step height. The results revealed that interlayer bonding strength and bending stiffness have great influence on the lateral force at atomic-scale steps. The studies can provide a further understanding of frictional properties at atomic scale steps and could be helpful for the applications of 2-dimensional materials as lubricant coating.

  13. Energy loading effects in the scaling of atomic xenon lasers

    International Nuclear Information System (INIS)

    Ohwa, M.; Kushner, M.J.

    1990-01-01

    The intrinsic power efficiency of the atomic xenon (5d → 6p) infrared (1.73--3.65 μm) laser is sensitive to the rate of pumping due to electron collision mixing of the laser levels. Long duration pumping at moderate power deposition may therefore result in higher energy efficiencies than pumping at higher powers. In this paper the authors examine the consequences of high energy deposition (100's J/1 atm) during long pumping pulses (100's μs) on the intrinsic power and energy efficiency and optimum power deposition of the atomic xenon laser. The dominant effect of high energy loading, gas heating, causes an increase in the electron density and therefore an increase in the electron collision mixing of the laser levels. The optimum power deposition for a given gas density therefore shifts to lower values with increasing gas temperature. For sufficiently long pumping pulses, nonuniform gas heating results in convection and rarification of highly pumped regions. The optimum power deposition therefore shifts to even lower values as the length of the pumping pulse increases. As a result, laser efficiency depends on the spatial distribution of power deposition as well as its magnitude

  14. Atoms

    International Nuclear Information System (INIS)

    Fuchs, Alain; Villani, Cedric; Guthleben, Denis; Leduc, Michele; Brenner, Anastasios; Pouthas, Joel; Perrin, Jean

    2014-01-01

    Completed by recent contributions on various topics (atoms and the Brownian motion, the career of Jean Perrin, the evolution of atomic physics since Jean Perrin, relationship between scientific atomism and philosophical atomism), this book is a reprint of a book published at the beginning of the twentieth century in which the author addressed the relationship between atomic theory and chemistry (molecules, atoms, the Avogadro hypothesis, molecule structures, solutes, upper limits of molecular quantities), molecular agitation (molecule velocity, molecule rotation or vibration, molecular free range), the Brownian motion and emulsions (history and general features, statistical equilibrium of emulsions), the laws of the Brownian motion (Einstein's theory, experimental control), fluctuations (the theory of Smoluchowski), light and quanta (black body, extension of quantum theory), the electricity atom, the atom genesis and destruction (transmutations, atom counting)

  15. A study of atomic interaction between suspended nanoparticles and sodium atoms in liquid sodium

    International Nuclear Information System (INIS)

    Saito, Jun-ichi; Ara, Kuniaki

    2010-01-01

    A feasibility study of suppression of the chemical reactivity of sodium itself using an atomic interaction between nanoparticles and sodium atoms has been carried out. We expected that the atomic interaction strengthens when the nanoparticle metal is the transition element which has a major difference in electronegativity from sodium. We also calculated the atomic interaction between nanoparticle and sodium atoms. It became clear that the atomic bond between the nanoparticle atom and the sodium atom is larger than that between sodium atoms, and the charge transfer takes place to the nanoparticle atom from the sodium atom. Using sodium with suspended nanoparticles, the fundamental physical properties related to the atomic interaction were investigated to verify the atomic bond. The surface tension of sodium with suspended nanoparticles increased, and the evaporation rate of sodium with suspended nanoparticles also decreased compared with that of sodium. Therefore the presence of the atomic interaction between nanoparticles and sodium was verified from these experiments. Because the fundamental physical property changes by the atomic interaction, we expected changes in the chemical reactivity characteristics. The chemical reaction properties of sodium with suspended nanoparticles with water were investigated experimentally. The released reaction heat and the reaction rate of sodium with suspended nanoparticles were reduced than those of sodium. The influence of the charge state of nanoparticle on the chemical process with water was theoretically investigated to speculate on the cause of reaction suppression. The potential energy in both primary and side reactions changed by the charge transfer, and the free energy of activation of the reaction with water increased. Accordingly, the reaction barrier also increased. This suggests there is a possibility of the reduction in the reaction of sodium by the suspension of nanoparticles. Consequently the possibility of the

  16. Atomic scale simulations of hydrogen implantation defects in hydrogen implanted silicon - smart Cut technology

    International Nuclear Information System (INIS)

    Bilteanu, L.

    2010-12-01

    The topic of this thesis is related to the implantation step of the SmartCut TM technology. This technology uses hydrogen in order to transfer silicon layers on insulating substrates. The transfer is performed through a fracture induced by the formation of bidimensional defects well known in literature as 'platelets'. More exactly, we have studied within this thesis work the defects appearing in the post implant state and the evolution of the implantation damage towards a state dominated by platelets. The study is organised into two parts: in the first part we present the results obtained by atomic scale simulations while in the second part we present an infrared spectroscopy study of the evolution of defects concentrations after annealing at different temperatures. The atomic scale simulations have been performed within the density functional theory and they allowed us to compute the formation energies and the migration and recombination barriers. The defects included in our study are: the atomic and diatomic interstitials, the hydrogenated vacancies and multi-vacancies and the several platelets models. The obtained energies allowed us to build a stability hierarchy for these types of defects. This scheme has been confronted with some infrared analysis on hydrogen implanted silicon samples (37 keV) in a sub-dose regime which does not allow usually the formation of platelets during the implantation step. The analysis of the infrared data allowed the detailed description of the defects concentration based on the behaviour of peaks corresponding to the respective defects during annealing. The comparison between these evolutions and the energy scheme obtained previously allowed the validation of an evolution scenario of defects towards the platelet state. (author)

  17. The Scales of Time, Length, Mass, Energy, and Other Fundamental Physical Quantities in the Atomic World and the Use of Atomic Units in Quantum Mechanical Calculations

    Science.gov (United States)

    Teo, Boon K.; Li, Wai-Kee

    2011-01-01

    This article is divided into two parts. In the first part, the atomic unit (au) system is introduced and the scales of time, space (length), and speed, as well as those of mass and energy, in the atomic world are discussed. In the second part, the utility of atomic units in quantum mechanical and spectroscopic calculations is illustrated with…

  18. Atomic scale simulations for improved CRUD and fuel performance modeling

    Energy Technology Data Exchange (ETDEWEB)

    Andersson, Anders David Ragnar [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Cooper, Michael William Donald [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-01-06

    A more mechanistic description of fuel performance codes can be achieved by deriving models and parameters from atomistic scale simulations rather than fitting models empirically to experimental data. The same argument applies to modeling deposition of corrosion products on fuel rods (CRUD). Here are some results from publications in 2016 carried out using the CASL allocation at LANL.

  19. NATO Advanced Study Institute on Atoms in Strong Fields

    CERN Document Server

    Clark, Charles; Nayfeh, Munir

    1990-01-01

    This book collects the lectures given at the NATO Advanced Study Institute on "Atoms in Strong Fields", which took place on the island of Kos, Greece, during the two weeks of October 9-21,1988. The designation "strong field" applies here to an external electromagnetic field that is sufficiently strong to cause highly nonlinear alterations in atomic or molecular struc­ ture and dynamics. The specific topics treated in this volume fall into two general cater­ gories, which are those for which strong field effects can be studied in detail in terrestrial laboratories: the dynamics of excited states in static or quasi-static electric and magnetic fields; and the interaction of atoms and molecules with intense laser radiation. In both areas there exist promising opportunities for research of a fundamental nature. An electric field of even a few volts per centimeter can be very strong on the atom­ ic scale, if it acts upon a weakly bound state. The study of Rydberg states with high reso­ lution laser spectroscop...

  20. Atomic Scale Imaging of Nucleation and Growth Trajectories of an Interfacial Bismuth Nanodroplet.

    Science.gov (United States)

    Li, Yingxuan; Bunes, Benjamin R; Zang, Ling; Zhao, Jie; Li, Yan; Zhu, Yunqing; Wang, Chuanyi

    2016-02-23

    Because of the lack of experimental evidence, much confusion still exists on the nucleation and growth dynamics of a nanostructure, particularly of metal. The situation is even worse for nanodroplets because it is more difficult to induce the formation of a nanodroplet while imaging the dynamic process with atomic resolution. Here, taking advantage of an electron beam to induce the growth of Bi nanodroplets on a SrBi2Ta2O9 platelet under a high resolution transmission electron microscope (HRTEM), we directly observed the detailed growth pathways of Bi nanodroplets from the earliest stage of nucleation that were previously inaccessible. Atomic scale imaging reveals that the dynamics of nucleation involves a much more complex trajectory than previously predicted based on classical nucleation theory (CNT). The monatomic Bi layer was first formed in the nucleation process, which induced the formation of the prenucleated clusters. Following that, critical nuclei for the nanodroplets formed both directly from the addition of atoms to the prenucleated clusters by the classical growth process and indirectly through transformation of an intermediate liquid film based on the Stranski-Krastanov growth mode, in which the liquid film was induced by the self-assembly of the prenucleated clusters. Finally, the growth of the Bi nanodroplets advanced through the classical pathway and sudden droplet coalescence. This study allows us to visualize the critical steps in the nucleation process of an interfacial nanodroplet, which suggests a revision of the perspective of CNT.

  1. Atomic oxygen production scaling in a nanosecond-pulsed externally grounded dielectric barrier plasma jet

    Science.gov (United States)

    Sands, Brian; Schmidt, Jacob; Ganguly, Biswa; Scofield, James

    2014-10-01

    Atomic oxygen production is studied in a capillary dielectric barrier plasma jet that is externally grounded and driven with a 20-ns risetime positive unipolar pulsed voltage at pulse repetition rates up to 25 kHz. The power coupled to the discharge can be easily increased by increasing the pulse repetition rate. At a critical turnover frequency, determined by the net energy density coupled to the discharge, the plasma chemistry abruptly changes. This is indicated by increased plasma conductance and a transition in reactive oxygen species production from an ozone-dominated production regime below the turnover frequency to atomic-oxygen-dominated production at higher pulse rates. Here, we characterize atomic oxygen production scaling using spatially- and temporally-resolved two-photon absorption laser-induced-fluorescence (TALIF). Quantitative results are obtained via calibration with xenon using a similar laser excitation and collection system. These results are compared with quantitative ozone and discharge power measurements using a helium gas flow with oxygen admixtures up to 3%.

  2. Evolution of atomic-scale surface structures during ion bombardment: A fractal simulation

    International Nuclear Information System (INIS)

    Shaheen, M.A.; Ruzic, D.N.

    1993-01-01

    Surfaces of interest in microelectronics have been shown to exhibit fractal topographies on the atomic scale. A model utilizing self-similar fractals to simulate surface roughness has been added to the ion bombardment code TRIM. The model has successfully predicted experimental sputtering yields of low energy (less then 1000 eV) Ar on Si and D on C using experimentally determined fractal dimensions. Under ion bombardment the fractal surface structures evolve as the atoms in the collision cascade are displaced or sputtered. These atoms have been tracked and the evolution of the surface in steps of one monolayer of flux has been determined. The Ar--Si system has been studied for incidence energies of 100 and 500 eV, and incidence angles of 0 degree, 30 degree, and 60 degree. As expected, normally incident ion bombardment tends to reduce the roughness of the surface, whereas large angle ion bombardment increases the degree of surface roughness. Of particular interest though, the surfaces are still locally self-similar fractals after ion bombardment and a steady state fractal dimension is reached, except at large angles of incidence

  3. Atomic-scale origin of dynamic viscoelastic response and creep in disordered solids

    Science.gov (United States)

    Milkus, Rico; Zaccone, Alessio

    2017-02-01

    Viscoelasticity has been described since the time of Maxwell as an interpolation of purely viscous and purely elastic response, but its microscopic atomic-level mechanism in solids has remained elusive. We studied three model disordered solids: a random lattice, the bond-depleted fcc lattice, and the fcc lattice with vacancies. Within the harmonic approximation for central-force lattices, we applied sum rules for viscoelastic response derived on the basis of nonaffine atomic motions. The latter motions are a direct result of local structural disorder, and in particular, of the lack of inversion symmetry in disordered lattices. By defining a suitable quantitative and general atomic-level measure of nonaffinity and inversion symmetry, we show that the viscoelastic responses of all three systems collapse onto a master curve upon normalizing by the overall strength of inversion-symmetry breaking in each system. Close to the isostatic point for central-force lattices, power-law creep G (t ) ˜t-1 /2 emerges as a consequence of the interplay between soft vibrational modes and nonaffine dynamics, and various analytical scalings, supported by numerical calculations, are predicted by the theory.

  4. Platinum clusters with precise numbers of atoms for preparative-scale catalysis.

    Science.gov (United States)

    Imaoka, Takane; Akanuma, Yuki; Haruta, Naoki; Tsuchiya, Shogo; Ishihara, Kentaro; Okayasu, Takeshi; Chun, Wang-Jae; Takahashi, Masaki; Yamamoto, Kimihisa

    2017-09-25

    Subnanometer noble metal clusters have enormous potential, mainly for catalytic applications. Because a difference of only one atom may cause significant changes in their reactivity, a preparation method with atomic-level precision is essential. Although such a precision with enough scalability has been achieved by gas-phase synthesis, large-scale preparation is still at the frontier, hampering practical applications. We now show the atom-precise and fully scalable synthesis of platinum clusters on a milligram scale from tiara-like platinum complexes with various ring numbers (n = 5-13). Low-temperature calcination of the complexes on a carbon support under hydrogen stream affords monodispersed platinum clusters, whose atomicity is equivalent to that of the precursor complex. One of the clusters (Pt 10 ) exhibits high catalytic activity in the hydrogenation of styrene compared to that of the other clusters. This method opens an avenue for the application of these clusters to preparative-scale catalysis.The catalytic activity of a noble metal nanocluster is tied to its atomicity. Here, the authors report an atom-precise, fully scalable synthesis of platinum clusters from molecular ring precursors, and show that a variation of only one atom can dramatically change a cluster's reactivity.

  5. An atomic-scale model of fcc crystal-growth

    Energy Technology Data Exchange (ETDEWEB)

    Waal, B.W. van de (Technische Hogeschool Twente, Enschede (Netherlands). Dept. of Physics)

    1991-01-01

    Nearly perfect fcc growth may be simulated by the application of a simple growth-algorithm - only sites that are at least 4-coordinated are occupied - to a selected seed. The seed is a 22-atom cluster, being the smallest close-packed structure with two crossing stacking-faults. The stacking-faults produce active surface-sites, that can not be exhausted by occupation; they are arranged in non-vanishing steps, similar to those produced by screw-dislocations. The algorithm prevents further stacking-faults, and ensures ABC-stacking of close-packed (111)-layers, characteristic of the fcc structure. The same algorithm would not produce further growth of perfect fcc clusters or of Mackay icosahedra. It is proposed that the ability to grow fast under near-equilibrium conditions is a better criterion to select clusters as precursors of the bulk-structure than their cohesive energy. The crystal structure problem of the rare gases - why fcc, not hcp - is discussed in connection with the apparent impossibility to simulate hcp growth by an analogous procedure. (orig.).

  6. The atomic-scale origins of grain boundary superconducting properties

    International Nuclear Information System (INIS)

    Pennycook, S.J.; Chisholm, M.F.; Buban, J.; Browning, N.D.; Prouteau, C.; Univ. of Illinois, Chicago, IL; Nellist, P.D.

    1998-02-01

    Due to the extremely short coherence lengths of the high-T c superconductors, defects such as grain boundaries are obvious barriers to the flow of supercurrent. Within a few months of the discovery of these materials, it was shown how the critical current dropped four orders of magnitude as the grain boundary misorientation increased from zero to 45 degree. Even today, there is no quantitative understanding of this behavior. A qualitative understanding is however possible through atomic resolution Z-contrast imaging on YBa 2 Cu 3 O 7-δ and SrTiO 3 bicrystal grain boundaries, combined with bond-valence-sum analysis. The Z-contrast image of a YBa 2 Cu 3 O 7-δ low angle grain boundary shows the same kind of reconstructed dislocation cores as seen in SrTiO 3 , containing reconstructions on both the Cu and Y/Ba sublattices. An image of an asymmetric 30 degree boundary in YBa 2 Cu 3 O 7-δ shows the same units and unit sequence as expected for SrTiO 3 . YBa 2 Cu 3 O 7-δ boundaries are wavy because of their non-equilibrium growth process, and therefore mostly asymmetric in nature, although small segments have the symmetric structure. It seems reasonable to assume that boundaries of other angles will also have similar structures in these two materials

  7. Semiconductor studies by radioactive probe atoms

    International Nuclear Information System (INIS)

    Wichert, Thomas

    2003-01-01

    There are a growing number of experimental techniques that have in common the usage of radioactive isotopes for the characterization of semiconductors. These techniques deliver atomistic information about identity, formation, lattice environment, and electronic structure, as well as dynamics of defects and defect complexes. The results obtained by different hyperfine techniques are discussed in context with the study of intrinsic and extrinsic defects, i.e. of vacancies or self-interstitials and dopant or impurity atoms, respectively. In addition, the employment of electrical and optical techniques in combination with radioactive isotopes is presented

  8. Antiprotonic Radioactive Atom for Nuclear Structure Studies

    International Nuclear Information System (INIS)

    Wada, M.; Yamazaki, Y.

    2005-01-01

    A future experiment to synthesize antiprotonic radioactive nuclear ions is proposed for nuclear structure studies. Antiprotonic radioactive nuclear atom can be synthesized in a nested Penning trap where a cloud of antiprotons is prestored and slow radioactive nuclear ions are bunch-injected into the trap. By observing of the ratio of π+ and π- produced in the annihilation process, we can deduce the different abundance of protons and neutrons at the surface of the nuclei. The proposed method would provide a unique probe for investigating the nuclear structure of unstable nuclei

  9. Max Auwaerter symposium: spin mapping and spin manipulation on the atomic scale

    International Nuclear Information System (INIS)

    Wiesendanger, R.

    2008-01-01

    Full text: A fundamental understanding of magnetic and spin-dependent phenomena requires the determination of spin structures and spin excitations down to the atomic scale. The direct visualization of atomic-scale spin structures has first been accomplished for magnetic metals by combining the atomic resolution capability of Scanning Tunnelling Microscopy (STM) with spin sensitivity, based on vacuum tunnelling of spin-polarized electrons. The resulting technique, Spin-Polarized Scanning Tunnelling Microscopy (SP-STM), nowadays provides unprecedented insight into collinear and non-collinear spin structures at surfaces of magnetic nanostructures and has already led to the discovery of new types of magnetic order at the nanoscale. More recently, the development of subkelvin SP-STM has allowed studies of ground-state magnetic properties of individual magnetic adatoms on non-magnetic substrates as well as the magnetic interactions between them. Based on SP-STM experiments performed at temperatures of 300 mK, indirect magnetic exchange interactions at the sub-milli-electronvolt energy scale between individual paramagnetic adatoms as well as between adatoms and nearby magnetic nanostructures could directly be revealed in real space up to distances of several nanometers. In both cases we have observed an oscillatory behavior of the magnetic exchange coupling, alternating between ferromagnetic and antiferromagnetic, as a function of distance. Moreover, the detection of spin-dependent exchange and correlation forces has allowed a first direct real-space observation of spin structures at surfaces of antiferromagnetic insulators. This new type of scanning probe microscopy, called Magnetic Exchange Force Microscopy (MExFM), offers a powerful new tool to investigate different types of spin-spin interactions based on direct-, super-, or RKKY-type exchange down to the atomic level. By combining MExFM with high-precision measurements of damping forces, localized or confined spin

  10. Pharao: study of an atomic clock using laser-cooled atoms and realization of a prototype

    International Nuclear Information System (INIS)

    Lemonde, P.

    1997-01-01

    Thermal jets and atomic fountains are two different principles on which atomic clocks are based. In atomic fountains the velocity of atoms can be reduced to a few cm/s so the classical limitations of thermal jets such as phase shift between two Ramsey impulses, second order Doppler effect become negligible. The new limitations set by atomic fountain clocks are now collisions between cold atoms and the radiation emitted by the black body. Weightlessness leads to a different running of the atomic clock and can imply an enhancement of its performances. In micro-gravity an interatomic interaction time of several seconds can be reached. The application of such atomic clocks can go beyond time or frequency metrology. This work is dedicated to the development of a spatial atomic clock to fully use the extremely low velocity of laser-cooled atoms and to quantify what can be expected of weightlessness. This study has involved the realization of a prototype and its testing in a zero-g plane. The experimental results are presented and it is highlighted that an accuracy and a one-day stability of 10 -16 are within reach with an optimized version of this atomic clock. (A.C.)

  11. New atom probe approaches to studying segregation in nanocrystalline materials

    International Nuclear Information System (INIS)

    Samudrala, S.K.; Felfer, P.J.; Araullo-Peters, V.J.; Cao, Y.; Liao, X.Z.; Cairney, J.M.

    2013-01-01

    Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping. - Highlights: ► New data treatment methods allow delineation of grain boundaries, even without segregation. ► Proxigrams calculated from the surfaces accurately show the extent of segregation. ► Tessellation of the data volume can be used to map the Gibbsian interfacial excess

  12. New atom probe approaches to studying segregation in nanocrystalline materials

    Energy Technology Data Exchange (ETDEWEB)

    Samudrala, S.K.; Felfer, P.J.; Araullo-Peters, V.J. [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); The Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia); Cao, Y.; Liao, X.Z. [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); Cairney, J.M., E-mail: julie.cairney@sydney.edu.au [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); The Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia)

    2013-09-15

    Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping. - Highlights: ► New data treatment methods allow delineation of grain boundaries, even without segregation. ► Proxigrams calculated from the surfaces accurately show the extent of segregation. ► Tessellation of the data volume can be used to map the Gibbsian interfacial excess.

  13. New atom probe approaches to studying segregation in nanocrystalline materials.

    Science.gov (United States)

    Samudrala, S K; Felfer, P J; Araullo-Peters, V J; Cao, Y; Liao, X Z; Cairney, J M

    2013-09-01

    Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping. Copyright © 2013 Elsevier B.V. All rights reserved.

  14. The l-mixing cross section of Rydberg states of atomic Rb and the scaling LAW

    International Nuclear Information System (INIS)

    Liu Hong; Chen Aiqiu; Li Baiwen

    1991-01-01

    On the basis of impulse approximate method, a kind of analytical wavefunctions based on a potential model was used to calculate the l mixing cross section of thermal collision of Rydberg states of atomic Rb with rare gas (He, Ne). The results were compared with the experimental results and other theoretical values. These results show that there exists a kind of scaling law for the l mixing cross section of Rydberg alkali atoms

  15. Ion-atom collisions for materials study

    International Nuclear Information System (INIS)

    Loaiza S, N.S.

    1976-01-01

    The diffusion process of silver in aluminium was studied in thin films as a function of temperature, the most important characteristics of dispersor atoms that technique permits us to study are the atomic mass and depth into the solid. This is possible because when a sample is bombarded with ions of a given energy, the ions are dispersed with different energies for different masses and depths, hence this technique is a useful instrument for research into the physical processes which ocurr in thin films up to depths of several microns, one of the results obtained after the bombardment of the target with protons having an energy of 650 KeV was that when the target reached a temperature of approximately 40 0 C, 80 0 C, 110 0 C and 160 0 C during 15 minutes and the spectra of heated and unheated targets were compared it was found that the aluminium peak, the valley, the silver peak and the peak over the silver peak change with the increase of temperature and tend to get mixed, that is to say that silver and the aluminium are diffusing themselves. The analysis is essentially qualitative with this technique we ca also measure the thickness of thin films, the silver thickness was measured (3320A). (author)

  16. Atomic-scale simulations of the mechanical deformation of nanocrystalline metals

    DEFF Research Database (Denmark)

    Schiøtz, Jakob; Vegge, Tejs; Di Tolla, Francesco

    1999-01-01

    that the main deformation mode is sliding in the grain boundaries through a large number of uncorrelated events, where a few atoms (or a few tens of atoms) slide with respect to each other. Little dislocation activity is seen in the grain interiors. The localization of the deformation to the grain boundaries......Nanocrystalline metals, i.e., metals in which the grain size is in the nanometer range, have a range of technologically interesting properties including increased hardness and yield strength. We present atomic-scale simulations of the plastic behavior of nanocrystalline copper. The simulations show...

  17. Physical essence of the multibody contact-sliding at atomic scale

    Science.gov (United States)

    Han, Xuesong

    2014-01-01

    Investigation the multibody contact-sliding occurred at atomic discrete contact spot will play an important role in determine the origin of tribology behavior and evaluates the micro-mechanical property of nanomaterials and thus optimizing the design of surface texture. This paper carries out large scale parallel molecular dynamics simulation on contact-sliding at atomic scale to uncover the special physical essence. The research shows that some kind of force field exists between nanodot pair and the interaction can be expressed by the linear combination of exponential function while the effective interaction distance limited in 1 angstrom for nanodot with several tens of nanometer diameter. The variation tendency about the interaction force between nanodot array is almost the same between nanodot pairs and thus the interaction between two nanodot array can be characterized by parallel mechanical spring. Multibody effect which dominates the interaction between atoms or molecules will gradually diminish with the increasing of length scales.

  18. Point defects and irradiation in oxides: simulations at the atomic scale

    International Nuclear Information System (INIS)

    Crocombette, J.P.

    2005-12-01

    The studies done by Jean-Paul Crocombette between 1996 and 2005 in the Service de Recherches de Metallurgie Physique of the Direction de l'Energie Nucleaire in Saclay are presented in this Habilitation thesis. These works were part of the material science researches on the ageing, especially under irradiation, of oxides of interest for the nuclear industry. In this context simulation studies at the atomic scale were performed on two elementary components of ageing under irradiation : point defects and displacement cascades ; using two complementary simulation techniques : ab initio electronic structure calculations and empirical potential molecular dynamics. The first part deals with point defects : self defects (vacancies or interstitials) or hetero-atomic dopants. One first recalls the energetics of such defects in oxides, the specific features of defects calculations and the expected accuracy of these calculations. Then one presents the results obtained on uranium dioxide, oxygen in silver and amorphous silica. The second part tackles the modelling of disintegration recoil nuclei in various?displacement cascades created by crystalline matrices for actinide waste disposal. Cascade calculations give access to the amorphization mechanisms under irradiation of these materials. One thus predicts that the amorphization in zircon takes place directly in the tracks whereas in lanthanum zirconate, the amorphization proceeds through the accumulation of point defects. Finally the prospects of these studies are discussed. (author)

  19. Atomic Scale Modulation of Self-Rectifying Resistive Switching by Interfacial Defects

    KAUST Repository

    Wu, Xing; Yu, Kaihao; Cha, Dong Kyu; Bosman, Michel; Raghavan, Nagarajan; Zhang, Xixiang; Li, Kun; Liu, Qi; Sun, Litao; Pey, Kinleong

    2018-01-01

    Higher memory density and faster computational performance of resistive switching cells require reliable array‐accessible architecture. However, selecting a designated cell within a crossbar array without interference from sneak path currents through neighboring cells is a general problem. Here, a highly doped n++ Si as the bottom electrode with Ni‐electrode/HfOx/SiO2 asymmetric self‐rectifying resistive switching device is fabricated. The interfacial defects in the HfOx/SiO2 junction and n++ Si substrate result in the reproducible rectifying behavior. In situ transmission electron microscopy is used to quantitatively study the properties of the morphology, chemistry, and dynamic nucleation–dissolution evolution of the chains of defects at the atomic scale. The spatial and temporal correlation between the concentration of oxygen vacancies and Ni‐rich conductive filament modifies the resistive switching effect. This study has important implications at the array‐level performance of high density resistive switching memories.

  20. Atomic Scale Modulation of Self-Rectifying Resistive Switching by Interfacial Defects

    KAUST Repository

    Wu, Xing

    2018-04-14

    Higher memory density and faster computational performance of resistive switching cells require reliable array‐accessible architecture. However, selecting a designated cell within a crossbar array without interference from sneak path currents through neighboring cells is a general problem. Here, a highly doped n++ Si as the bottom electrode with Ni‐electrode/HfOx/SiO2 asymmetric self‐rectifying resistive switching device is fabricated. The interfacial defects in the HfOx/SiO2 junction and n++ Si substrate result in the reproducible rectifying behavior. In situ transmission electron microscopy is used to quantitatively study the properties of the morphology, chemistry, and dynamic nucleation–dissolution evolution of the chains of defects at the atomic scale. The spatial and temporal correlation between the concentration of oxygen vacancies and Ni‐rich conductive filament modifies the resistive switching effect. This study has important implications at the array‐level performance of high density resistive switching memories.

  1. Aging studies in atomic bomb survivors

    International Nuclear Information System (INIS)

    Belsky, J.L.; Moriyama, I.M.; Fujita, Shoichiro; Kawamoto, Sadahisa.

    1979-07-01

    Although the studies of the effect of ionizing radiation on atomic bomb survivors have not produced any evidence of radiation-induced aging, there have been studies on experimental animals and man which suggest accelerated aging after exposure to ionizing radiation. To determine if certain physiologic functions could be related to exposure to ionizing radiation, a battery of age-related tests was given at the time of the physical examinations at ABCC. Some 11,351 persons were given these non-invasive age-related tests. The results were essentially negative. Until a satisfactory operational definition of biologic or physiologic age is developed, the administration of functional tests as a measure of aging does not seem justified. (author)

  2. Atom

    International Nuclear Information System (INIS)

    Auffray, J.P.

    1997-01-01

    The atom through centuries, has been imagined, described, explored, then accelerated, combined...But what happens truly inside the atom? And what are mechanisms who allow its stability? Physicist and historian of sciences, Jean-Paul Auffray explains that these questions are to the heart of the modern physics and it brings them a new lighting. (N.C.)

  3. The Chip-Scale Atomic Clock - Low-Power Physics Package

    Science.gov (United States)

    2004-12-01

    36th Annual Precise Time and Time Interval (PTTI) Meeting 339 THE CHIP-SCALE ATOMIC CLOCK – LOW-POWER PHYSICS PACKAGE R. Lutwak ...pdf/documents/ds-x72.pdf [2] R. Lutwak , D. Emmons, W. Riley, and R. M. Garvey, 2003, “The Chip-Scale Atomic Clock – Coherent Population Trapping vs...2002, Reston, Virginia, USA (U.S. Naval Observatory, Washington, D.C.), pp. 539-550. [3] R. Lutwak , D. Emmons, T. English, and W. Riley, 2004

  4. Dye-sensitized solar cells: Atomic scale investigation of interface structure and dynamics

    International Nuclear Information System (INIS)

    Ma Wei; Zhang Fan; Meng Sheng

    2014-01-01

    Recent progress in dye-sensitized solar cells (DSC) research is reviewed, focusing on atomic-scale investigations of the interface electronic structures and dynamical processes, including the structure of dye adsorption onto TiO 2 , ultrafast electron injection, hot-electron injection, multiple-exciton generation, and electron—hole recombination. Advanced experimental techniques and theoretical approaches are briefly summarized, and then progressive achievements in photovoltaic device optimization based on insights from atomic scale investigations are introduced. Finally, some challenges and opportunities for further improvement of dye solar cells are presented. (invited review — international conference on nanoscience and technology, china 2013)

  5. Atomic Scale Structure-Chemistry Relationships at Oxide Catalyst Surfaces and Interfaces

    Science.gov (United States)

    McBriarty, Martin E.

    Oxide catalysts are integral to chemical production, fuel refining, and the removal of environmental pollutants. However, the atomic-scale phenomena which lead to the useful reactive properties of catalyst materials are not sufficiently understood. In this work, the tools of surface and interface science and electronic structure theory are applied to investigate the structure and chemical properties of catalytically active particles and ultrathin films supported on oxide single crystals. These studies focus on structure-property relationships in vanadium oxide, tungsten oxide, and mixed V-W oxides on the surfaces of alpha-Al2O3 and alpha-Fe2O 3 (0001)-oriented single crystal substrates, two materials with nearly identical crystal structures but drastically different chemical properties. In situ synchrotron X-ray standing wave (XSW) measurements are sensitive to changes in the atomic-scale geometry of single crystal model catalyst surfaces through chemical reaction cycles, while X-ray photoelectron spectroscopy (XPS) reveals corresponding chemical changes. Experimental results agree with theoretical calculations of surface structures, allowing for detailed electronic structure investigations and predictions of surface chemical phenomena. The surface configurations and oxidation states of V and W are found to depend on the coverage of each, and reversible structural shifts accompany chemical state changes through reduction-oxidation cycles. Substrate-dependent effects suggest how the choice of oxide support material may affect catalytic behavior. Additionally, the structure and chemistry of W deposited on alpha-Fe 2O3 nanopowders is studied using X-ray absorption fine structure (XAFS) measurements in an attempt to bridge single crystal surface studies with real catalysts. These investigations of catalytically active material surfaces can inform the rational design of new catalysts for more efficient and sustainable chemistry.

  6. Fragmentation of atomic clusters: A theoretical study

    International Nuclear Information System (INIS)

    Lopez, M.J.; Jellinek, J.

    1994-01-01

    Collisionless fragmentation of nonrotating model n-atom metal clusters (n=12, 13, and 14) is studied using isoergic molecular-dynamics simulations. Minimum-energy paths for fragmentation are mapped out as functions of the distance between the centers of mass of the fragments. These paths provide information on the fragmentation energies for the different fragmentation channels. Fragmentation patterns (distributions of the fragmentation channel probabilities) and global and channel-specific fragmentation rate constants are computed and analyzed as functions of the internal energy and of the size of the clusters. The trends derived from the dynamics are compared with those obtained using the RRK and TST statistical approaches. The dynamics of the fragmentation process is analyzed in terms of characteristic quantities such as the distance between the centers of mass of the fragments, their relative translational energy, and their interaction energy, all considered as functions of time

  7. A Study of Confined Helium Atom

    International Nuclear Information System (INIS)

    Xie Wenfang

    2007-01-01

    The helium atom confined by a spherical parabolic potential well is studied employing the adiabatic hyperspherical approach method. Total energies of the ground and three low-excited states are obtained as a function of the confined potential radii. We find that the energies of a spherical parabolic potential well are in good agreement with those of an impenetrable spherical box for the larger confined potential radius. We find also that the confinement may cause accidental degeneracies between levels with different low-excited states and the inversion of the energy values. The results for the three-dimensional spherical potential well and the two-dimensional disc-like potential well are compared with each other. We find that the energy difference between states in a two-dimensional parabolic potential is also obviously larger than the corresponding levels for a spherical parabolic potential.

  8. Atomic Scale Picture of the Ion Conduction Mechanism in Tetrahedral Network of Lanthanum Barium Gallate

    Energy Technology Data Exchange (ETDEWEB)

    Jalarvo, Niina H [ORNL; Gourdon, Olivier [ORNL; Bi, Zhonghe [ORNL; Gout, Delphine J [ORNL; Ohl, Michael E [ORNL; Paranthaman, Mariappan Parans [ORNL

    2013-01-01

    Combined experimental study of impedance spectroscopy, neutron powder diffraction and quasielastic neutron scattering was performed to shed light into the atomic scale ion migration processes in proton and oxide ion conductor; La0.8Ba1.2GaO3.9 . This material consist of tetrahedral GaO4 units, which are rather flexible and rocking motion of these units promotes the ionic migration process. The oxide ion (vacancy) conduction takes place on channels along c axis, involving a single elementary step, which occurs between adjacent tetrahedron (inter-tetrahedron jump). The proton conduction mechanism consists of intra-tetrahedron and inter-tetrahedron elementary processes. The intra-tetrahedron proton transport is the rate-limiting process, with activation energy of 0.44 eV. The rocking motion of the GaO4 tetrahedron aids the inter-tetrahedral proton transport, which has the activation energy of 0.068 eV.

  9. Atomic-Scale Simulation of Electrochemical Processes at Electrode/Water Interfaces under Referenced Bias Potential.

    Science.gov (United States)

    Bouzid, Assil; Pasquarello, Alfredo

    2018-04-19

    Based on constant Fermi-level molecular dynamics and a proper alignment scheme, we perform simulations of the Pt(111)/water interface under variable bias potential referenced to the standard hydrogen electrode (SHE). Our scheme yields a potential of zero charge μ pzc of ∼0.22 eV relative to the SHE and a double layer capacitance C dl of ≃19 μF cm -2 , in excellent agreement with experimental measurements. In addition, we study the structural reorganization of the electrical double layer for bias potentials ranging from -0.92 eV to +0.44 eV and find that O down configurations, which are dominant at potentials above the pzc, reorient to favor H down configurations as the measured potential becomes negative. Our modeling scheme allows one to not only access atomic-scale processes at metal/water interfaces, but also to quantitatively estimate macroscopic electrochemical quantities.

  10. Dielectric discontinuity at interfaces in the atomic-scale limit: permittivity of ultrathin oxide films on silicon.

    Science.gov (United States)

    Giustino, Feliciano; Umari, Paolo; Pasquarello, Alfredo

    2003-12-31

    Using a density-functional approach, we study the dielectric permittivity across interfaces at the atomic scale. Focusing on the static and high-frequency permittivities of SiO2 films on silicon, for oxide thicknesses from 12 A down to the atomic scale, we find a departure from bulk values in accord with experiment. A classical three-layer model accounts for the calculated permittivities and is supported by the microscopic polarization profile across the interface. The local screening varies on length scales corresponding to first-neighbor distances, indicating that the dielectric transition is governed by the chemical grading. Silicon-induced gap states are shown to play a minor role.

  11. Atomic-scaled characterization of graphene PN junctions

    Science.gov (United States)

    Zhou, Xiaodong; Wang, Dennis; Dadgar, Ali; Agnihotri, Pratik; Lee, Ji Ung; Reuter, Mark C.; Ross, Frances M.; Pasupathy, Abhay N.

    Graphene p-n junctions are essential devices for studying relativistic Klein tunneling and the Veselago lensing effect in graphene. We have successfully fabricated graphene p-n junctions using both lithographically pre-patterned substrates and the stacking of vertical heterostructures. We then use our 4-probe STM system to characterize the junctions. The ability to carry out scanning electron microscopy (SEM) in our STM instrument is essential for us to locate and measure the junction interface. We obtain both the topography and dI/dV spectra at the junction area, from which we track the shift of the graphene chemical potential with position across the junction interface. This allows us to directly measure the spatial width and roughness of the junction and its potential barrier height. We will compare the junction properties of devices fabricated by the aforementioned two methods and discuss their effects on the performance as a Veselago lens.

  12. Atomic-scale origin of piezoelectricity in wurtzite ZnO.

    Science.gov (United States)

    Lee, Jung-Hoon; Lee, Woo-Jin; Lee, Sung-Hoon; Kim, Seong Min; Kim, Sungjin; Jang, Hyun Myung

    2015-03-28

    ZnO has been extensively studied by virtue of its remarkably high piezoelectric responses, especially in nanowire forms. Currently, the high piezoelectricity of wurtzite ZnO is understood in terms of the covalent-bonding interaction between Zn 3d and O 2p orbitals. However, the Zn 3d orbitals are not capable of forming hybridized orbitals with the O 2pz orbitals since the Zn ion is characterized by fully filled non-interacting 3d orbitals. To resolve this puzzling problem, we have investigated the atomic-scale origin of piezoelectricity by exploiting density-functional theory calculations. On the basis of the computed orbital-resolved density of states and the band structure over the Γ-M first Brillouin zone, we propose an intriguing bonding mechanism that accounts for the observed high piezoelectricity - intra-atomic 3dz(2)-4pz orbital self-mixing of Zn, followed by asymmetric hybridization between the Zn 3dz(2)-4pz self-mixed orbital and the O 2pz orbital along the polar c-axis of the wurtzite ZnO.

  13. Atomic scale imaging of competing polar states in a Ruddlesden–Popper layered oxide

    Science.gov (United States)

    Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J.; Schlom, Darrell G.; Alem, Nasim; Gopalan, Venkatraman

    2016-01-01

    Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden–Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure. PMID:27578622

  14. Atomic scale imaging of competing polar states in a Ruddlesden-Popper layered oxide.

    Science.gov (United States)

    Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J; Schlom, Darrell G; Alem, Nasim; Gopalan, Venkatraman

    2016-08-31

    Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden-Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.

  15. Molecular dynamics modeling of bonding two materials by atomic scale friction stir welding

    Science.gov (United States)

    Konovalenko S., Iv.; Konovalenko, Ig. S.; Psakhie, S. G.

    2017-12-01

    Molecular dynamics model of atomic scale friction stir welding has been developed. Formation of a butt joint between two crystallites was modeled by means of rotating rigid conical tool traveling along the butt joint line. The formed joint had an intermixed atomic structure composed of atoms initially belonged to the opposite mated piece of metal. Heat removal was modeled by adding the extra viscous force to peripheral atomic layers. This technique provides the temperature control in the tool-affected zone during welding. Auxiliary vibration action was added to the rotating tool. The model provides the variation of the tool's angular velocity, amplitude, frequency and direction of the auxiliary vibration action to provide modeling different welding modes.

  16. RF-Interrogated End-State Chip-Scale Atomic Clock

    Science.gov (United States)

    2007-11-01

    coherent population trapping,” Electronics Letters 37, (24), 1449-1451. [2] R. Lutwak , P. Vlitas, M. Varghese, M. Mescher, D. K. Serkland, and G. M...367. [9] R. Lutwak , D. Emmons, T. English, W. Riley, A. Duwel, M. Varghese, D. K. Serland, and G. M. Peake, 2003, “Chip-Scale Atomic Clock, Recent

  17. Visible Light Emission from Atomic Scale Patterns Fabricated by the Scanning Tunneling Microscope

    DEFF Research Database (Denmark)

    Thirstrup, C.; Sakurai, M.; Stokbro, Kurt

    1999-01-01

    Scanning tunneling microscope (STM) induced light emission from artificial atomic scale structures comprising silicon dangling bonds on hydrogen-terminated Si(001) surfaces has been mapped spatially and analyzed spectroscopically in the visible spectral range. The light emission is based on a novel...

  18. Role of cardiolipins in the inner mitochondrial membrane: insight gained through atom-scale simulations

    DEFF Research Database (Denmark)

    Róg, Tomasz; Martinez-Seara, Hector; Munck, Nana

    2009-01-01

    , the exceptional nature of cardiolipins is characterized by their small charged head group connected to typically four hydrocarbon chains. In this work, we present atomic-scale molecular dynamics simulations of the inner mitochondrial membrane modeled as a mixture of cardiolipins (CLs), phosphatidylcholines (PCs...

  19. Atomic-scale structure and electrostatics of anionic palmitoyloleoylphosphatidylglycerol lipid bilayers with Na+ counterions

    NARCIS (Netherlands)

    Zhao, W.; Róg, T.; Gurtovenko, A.A.; Vattulainen, I.; Karttunen, M.E.J.

    2007-01-01

    Anionic palmitoyloleoylphosphatidylglycerol (POPG) is one of the most abundant lipids in nature, yet its atomic-scale properties have not received significant attention. Here we report extensive 150-ns molecular dynamics simulations of a pure POPG lipid membrane with sodium counterions. It turns out

  20. Recurrence spectroscopy of atoms in electric fields: Failure of classical scaling laws near bifurcations

    International Nuclear Information System (INIS)

    Shaw, J.A.; Robicheaux, F.

    1998-01-01

    The photoabsorption spectra of atoms in a static external electric field shows modulations from recurrences: electron waves that go out from and return to the vicinity of the atomic core. Closed-orbit theory predicts the amplitudes and phases of these modulations in terms of closed classical orbits. A classical scaling law relates the properties of a closed orbit at one energy and field strength to its properties at another energy and field strength at fixed scaled energy ε=EF -1/2 . The scaling law states that the recurrence strength of orbits along the electric field axis scale as F 1/4 . We show how this law fails near bifurcations when the effective Planck constant ℎ≡ℎF 1/4 increases with increasing field at fixed ε. The recurrences of orbits away from the axis scale as F 1/8 in accordance with the classical prediction. These deviations from the classical scaling law are important in interpreting the recurrence spectra of atoms in current experiments. This leads to an extension of the uniform approximation developed by Gao and Delos [Phys. Rev. A 56, 356 (1997)] to complex momenta. copyright 1998 The American Physical Society

  1. Atomic-scale structural signature of dynamic heterogeneities in metallic liquids

    Science.gov (United States)

    Pasturel, Alain; Jakse, Noel

    2017-08-01

    With sufficiently high cooling rates, liquids will cross their equilibrium melting temperatures and can be maintained in a metastable undercooled state before solidifying. Studies of undercooled liquids reveal several intriguing dynamic phenomena and because explicit connections between liquid structure and liquids dynamics are difficult to identify, it remains a major challenge to capture the underlying structural link to these phenomena. Ab initio molecular dynamics (AIMD) simulations are yet especially powerful in providing atomic-scale details otherwise not accessible in experiments. Through the AIMD-based study of Cr additions in Al-based liquids, we evidence for the first time a close relationship between the decoupling of component diffusion and the emergence of dynamic heterogeneities in the undercooling regime. In addition, we demonstrate that the origin of both phenomena is related to a structural heterogeneity caused by a strong interplay between chemical short-range order (CSRO) and local fivefold topology (ISRO) at the short-range scale in the liquid phase that develops into an icosahedral-based medium-range order (IMRO) upon undercooling. Finally, our findings reveal that this structural signature is also captured in the temperature dependence of partial pair-distribution functions which opens up the route to more elaborated experimental studies.

  2. Microstructural investigation of Sr-modified Al-15 wt%Si alloys in the range from micrometer to atomic scale.

    Science.gov (United States)

    Timpel, M; Wanderka, N; Vinod Kumar, G S; Banhart, J

    2011-05-01

    Strontium-modified Al-15 wt%Si casting alloys were investigated after 5 and 60 min of melt holding. The eutectic microstructures were studied using complementary methods at different length scales: focused ion beam-energy selective backscattered tomography, transmission electron microscopy and 3D atom probe. Whereas the samples after 5 min of melt holding show that the structure of eutectic Si changes into a fine fibrous morphology, the increase of prolonged melt holding (60 min) leads to the loss of Sr within the alloy with an evolution of an unmodified eutectic microstructure displaying coarse interconnected Si plates. Strontium was found at the Al/Si eutectic interfaces on the side of the eutectic Al region, measured by 3D atom probe. The new results obtained using 3D atom probe shed light on the location of Sr within the Al-Si eutectic microstructure. Copyright © 2010 Elsevier B.V. All rights reserved.

  3. Molecular beam studies of hot atom chemical reactions: Reactive scattering of energetic deuterium atoms

    International Nuclear Information System (INIS)

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

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H 2 /minus/> DH + H and the substitution reaction D + C 2 H 2 /minus/> C 2 HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible. 18 refs., 9 figs

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

    Science.gov (United States)

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

    1989-02-01

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

  5. Theoretical study of adsorption of lithium atom on carbon nanotube

    Directory of Open Access Journals (Sweden)

    Masato Senami

    2011-12-01

    Full Text Available We investigate the adsorption of lithium atoms on the surface of the (12,0 single wall carbon nanotube (SWCNT by using ab initio quantum chemical calculations. The adsorption of one lithium atom on the inside of this SWCNT is favored compared to the outside. We check this feature by charge transfer and regional chemical potential density. The adsorption of multiple lithium atoms on the interior of the SWCNT is studied in terms of adsorption energy and charge transfer. We show that repulsive force between lithium atoms destabilizes a system for the large number of lithium atoms.

  6. Implementation of exterior complex scaling in B-splines to solve atomic and molecular collision problems

    International Nuclear Information System (INIS)

    McCurdy, C William; MartIn, Fernando

    2004-01-01

    B-spline methods are now well established as widely applicable tools for the evaluation of atomic and molecular continuum states. The mathematical technique of exterior complex scaling has been shown, in a variety of other implementations, to be a powerful method with which to solve atomic and molecular scattering problems, because it allows the correct imposition of continuum boundary conditions without their explicit analytic application. In this paper, an implementation of exterior complex scaling in B-splines is described that can bring the well-developed technology of B-splines to bear on new problems, including multiple ionization and breakup problems, in a straightforward way. The approach is demonstrated for examples involving the continuum motion of nuclei in diatomic molecules as well as electronic continua. For problems involving electrons, a method based on Poisson's equation is presented for computing two-electron integrals over B-splines under exterior complex scaling

  7. New theoretical approaches to atomic and molecular dynamics triggered by ultrashort light pulses on the atto- to picosecond time scale

    International Nuclear Information System (INIS)

    Pabst, Stefan Ulf

    2013-04-01

    The concept of atoms as the building blocks of matter has existed for over 3000 years. A revolution in the understanding and the description of atoms and molecules has occurred in the last century with the birth of quantum mechanics. After the electronic structure was understood, interest in studying the dynamics of electrons, atoms, and molecules increased. However, time-resolved investigations of these ultrafast processes were not possible until recently. The typical time scale of atomic and molecular processes is in the picosecond to attosecond realm. Tremendous technological progress in recent years makes it possible to generate light pulses on these time scales. With such ultrashort pulses, atomic and molecular dynamics can be triggered, watched, and controlled. Simultaneously, the need rises for theoretical models describing the underlying mechanisms. This doctoral thesis focuses on the development of theoretical models which can be used to study the dynamical behavior of electrons, atoms, and molecules in the presence of ultrashort light pulses. Several examples are discussed illustrating how light pulses can trigger and control electronic, atomic, and molecular motions. In the first part of this work, I focus on the rotational motion of asymmetric molecules, which happens on picosecond and femtosecond time scales. Here, the aim is to align all three axes of the molecule as well as possible. To investigate theoretically alignment dynamics, I developed a program that can describe alignment motion ranging from the impulsive to the adiabatic regime. The asymmetric molecule SO 2 is taken as an example to discuss strategies of optimizing 3D alignment without the presence of an external field (i.e., field-free alignment). Field-free alignment is particularly advantageous because subsequent experiments on the aligned molecule are not perturbed by the aligning light pulse. Wellaligned molecules in the gas phase are suitable for diffraction experiments. From the

  8. New theoretical approaches to atomic and molecular dynamics triggered by ultrashort light pulses on the atto- to picosecond time scale

    Energy Technology Data Exchange (ETDEWEB)

    Pabst, Stefan Ulf

    2013-04-15

    The concept of atoms as the building blocks of matter has existed for over 3000 years. A revolution in the understanding and the description of atoms and molecules has occurred in the last century with the birth of quantum mechanics. After the electronic structure was understood, interest in studying the dynamics of electrons, atoms, and molecules increased. However, time-resolved investigations of these ultrafast processes were not possible until recently. The typical time scale of atomic and molecular processes is in the picosecond to attosecond realm. Tremendous technological progress in recent years makes it possible to generate light pulses on these time scales. With such ultrashort pulses, atomic and molecular dynamics can be triggered, watched, and controlled. Simultaneously, the need rises for theoretical models describing the underlying mechanisms. This doctoral thesis focuses on the development of theoretical models which can be used to study the dynamical behavior of electrons, atoms, and molecules in the presence of ultrashort light pulses. Several examples are discussed illustrating how light pulses can trigger and control electronic, atomic, and molecular motions. In the first part of this work, I focus on the rotational motion of asymmetric molecules, which happens on picosecond and femtosecond time scales. Here, the aim is to align all three axes of the molecule as well as possible. To investigate theoretically alignment dynamics, I developed a program that can describe alignment motion ranging from the impulsive to the adiabatic regime. The asymmetric molecule SO{sub 2} is taken as an example to discuss strategies of optimizing 3D alignment without the presence of an external field (i.e., field-free alignment). Field-free alignment is particularly advantageous because subsequent experiments on the aligned molecule are not perturbed by the aligning light pulse. Wellaligned molecules in the gas phase are suitable for diffraction experiments. From the

  9. Determination of Krypton Diffusion Coefficients in Uranium Dioxide Using Atomic Scale Calculations.

    Science.gov (United States)

    Vathonne, Emerson; Andersson, David A; Freyss, Michel; Perriot, Romain; Cooper, Michael W D; Stanek, Christopher R; Bertolus, Marjorie

    2017-01-03

    We present a study of the diffusion of krypton in UO 2 using atomic scale calculations combined with diffusion models adapted to the system studied. The migration barriers of the elementary mechanisms for interstitial or vacancy assisted migration are calculated in the DFT+U framework using the nudged elastic band method. The attempt frequencies are obtained from the phonon modes of the defect at the initial and saddle points using empirical potential methods. The diffusion coefficients of Kr in UO 2 are then calculated by combining this data with diffusion models accounting for the concentration of vacancies and the interaction of vacancies with Kr atoms. We determined the preferred mechanism for Kr migration and the corresponding diffusion coefficient as a function of the oxygen chemical potential μ O or nonstoichiometry. For very hypostoichiometric (or U-rich) conditions, the most favorable mechanism is interstitial migration. For hypostoichiometric UO 2 , migration is assisted by the bound Schottky defect and the charged uranium vacancy, V U 4- . Around stoichiometry, migration assisted by the charged uranium-oxygen divacancy (V UO 2- ) and V U 4- is the favored mechanism. Finally, for hyperstoichiometric or O-rich conditions, the migration assisted by two V U 4- dominates. Kr migration is enhanced at higher μ O , and in this regime, the activation energy will be between 4.09 and 0.73 eV depending on nonstoichiometry. The experimental values available are in the latter interval. Since it is very probable that these values were obtained for at least slightly hyperstoichiometric samples, our activation energies are consistent with the experimental data, even if further experiments with precisely controlled stoichiometry are needed to confirm these results. The mechanisms and trends with nonstoichiometry established for Kr are similar to those found in previous studies of Xe.

  10. Quantitative atom probe analysis of nanostructure containing clusters and precipitates with multiple length scales

    International Nuclear Information System (INIS)

    Marceau, R.K.W.; Stephenson, L.T.; Hutchinson, C.R.; Ringer, S.P.

    2011-01-01

    A model Al-3Cu-(0.05 Sn) (wt%) alloy containing a bimodal distribution of relatively shear-resistant θ' precipitates and shearable GP zones is considered in this study. It has recently been shown that the addition of the GP zones to such microstructures can lead to significant increases in strength without a decrease in the uniform elongation. In this study, atom probe tomography (APT) has been used to quantitatively characterise the evolution of the GP zones and the solute distribution in the bimodal microstructure as a function of applied plastic strain. Recent nuclear magnetic resonance (NMR) analysis has clearly shown strain-induced dissolution of the GP zones, which is supported by the current APT data with additional spatial information. There is significant repartitioning of Cu from the GP zones into the solid solution during deformation. A new approach for cluster finding in APT data has been used to quantitatively characterise the evolution of the sizes and shapes of the Cu containing features in the solid solution solute as a function of applied strain. -- Research highlights: → A new approach for cluster finding in atom probe tomography (APT) data has been used to quantitatively characterise the evolution of the sizes and shapes of the Cu containing features with multiple length scales. → In this study, a model Al-3Cu-(0.05 Sn) (wt%) alloy containing a bimodal distribution of relatively shear-resistant θ' precipitates and shearable GP zones is considered. → APT has been used to quantitatively characterise the evolution of the GP zones and the solute distribution in the bimodal microstructure as a function of applied plastic strain. → It is clearly shown that there is strain-induced dissolution of the GP zones with significant repartitioning of Cu from the GP zones into the solid solution during deformation.

  11. Probing Local Ionic Dynamics in Functional Oxides: From Nanometer to Atomic Scale

    Science.gov (United States)

    Kalinin, Sergei

    2014-03-01

    Vacancy-mediated electrochemical reactions in oxides underpin multiple applications ranging from electroresistive memories, to chemical sensors to energy conversion systems such as fuel cells. Understanding the functionality in these systems requires probing reversible (oxygen reduction/evolution reaction) and irreversible (cathode degradation and activation, formation of conductive filaments) electrochemical processes. In this talk, I summarize recent advances in probing and controlling these transformations locally on nanometer level using scanning probe microscopy. The localized tip concentrates the electric field in the nanometer scale volume of material, inducing local transition. Measured simultaneously electromechanical response (piezoresponse) or current (conductive AFM) provides the information on the bias-induced changes in material. Here, I illustrate how these methods can be extended to study local electrochemical transformations, including vacancy dynamics in oxides such as titanates, LaxSr1-xCoO3, BiFeO3, and YxZr1-xO2. The formation of electromechanical hysteresis loops and their bias-, temperature- and environment dependences provide insight into local electrochemical mechanisms. In materials such as lanthanum-strontium cobaltite, mapping both reversible vacancy motion and vacancy ordering and static deformation is possible, and can be corroborated by post mortem STEM/EELS studies. In ceria, a broad gamut of electrochemical behaviors is observed as a function of temperature and humidity. The possible strategies for elucidation ionic motion at the electroactive interfaces in oxides using high-resolution electron microscopy and combined ex-situ and in-situ STEM-SPM studies are discussed. In the second part of the talk, probing electrochemical phenomena on in-situ grown surfaces with atomic resolution is illustrated. I present an approach based on the multivariate statistical analysis of the coordination spheres of individual atoms to reveal

  12. Scaling studies - PWR

    International Nuclear Information System (INIS)

    Sonneck, G.

    1983-05-01

    A RELAP 4/MOD 6 study was made based on the blowdown phase of the intermediate break experiment LOFT L5-1. The method was to set up a base model and to vary parametrically some areas where it is known or suspected that LOFT differs from a commercial PWR. The aim was not to simulate LOFT or a PWR exactly but to understand the influence of the following parameters on the thermohydraulic behaviour of the system and the clad temperature: stored heat in the downcomer (LOFT has rather large filler blocks in this part of the pressure vessel); bypass between downcomer and upper plenum; and core length. The results show that LOFT is prototypical for all calculated blowdowns. As the clad temperatures decrease with decreasing stored energy in the downcomer, increased bypass and increased core length, LOFT results seem to be realistic as long as realistic bypass sizes are considered; they are conservative in the two other areas. (author)

  13. A method optimization study for atomic absorption ...

    African Journals Online (AJOL)

    Sadia Ata

    2014-04-24

    Apr 24, 2014 ... Manufacturer brand Win 2.1 software was used for data inte- gration and processing. ... reagents and analyst) is suitable for the intended application. The % relative standard deviation for absorbance ... flame atomic absorption spectrometry. Table 2 Linearity data for analysis of zinc in insulin using AAS.

  14. Study on the fine control of atoms by coherent interaction

    International Nuclear Information System (INIS)

    Han, Jae Min; Rho, S. P.; Park, H. M.; Lee, K. S.; Rhee, Y. J.; Yi, J. H.; Jeong, D. Y.; Ko, K. H.; Lee, J. M.; Kim, M.K.

    2000-01-01

    Study on one dimensional atom cooling and trapping process which is basic to the development of atom manipulation technology has been performed. A Zeeman slower has been designed and manufactured for efficient cooling of atoms. The speed of atoms finally achieved is as slow as 15 m/s with proper cooling conditions. By six circularly-polarized laser beams and quadrupole magnetic field, the atoms which have been slowed down by zeeman slower have been trapped in a small spatial region inside MOT. The higher the intensity of the slowing laser is the more is the number of atoms slowed and the maximum number of atoms trapped has been 10 8 . The atoms of several tens of μK degree have been trapped by controlling the intensity of trapping laser and intensity gradient of magnetic field. EIT phenomena caused by atomic coherent interaction has been studied for the development of atom optical elements. For the investigation of the focusing phenomena induced by the coherent interaction, experimental measurements and theoretical analysis have been performed. Spatial dependency of spectrum and double distribution signal of coupling laser have been obtained. The deflection of laser beams utilizing the EIT effects has also been considered. (author)

  15. Implementation of atomic layer etching of silicon: Scaling parameters, feasibility, and profile control

    Energy Technology Data Exchange (ETDEWEB)

    Ranjan, Alok, E-mail: alok.ranjan@us.tel.com; Wang, Mingmei; Sherpa, Sonam D.; Rastogi, Vinayak [TEL Technology Center, America LLC, 255 Fuller Road, Suite 214, Albany, New York 12203 (United States); Koshiishi, Akira [Tokyo Electron Miyagi, Ltd., 1 Techno-Hills, Taiwa-cho, Kurokawa-gun, Miyagi, 9813629 (Japan); Ventzek, Peter L. G. [Tokyo Electron America, Inc., 2400 Grove Blvd., Austin, Texas 78741 (United States)

    2016-05-15

    Atomic or layer by layer etching of silicon exploits temporally segregated self-limiting adsorption and material removal steps to mitigate the problems associated with continuous or quasicontinuous (pulsed) plasma processes: selectivity loss, damage, and profile control. Successful implementation of atomic layer etching requires careful choice of the plasma parameters for adsorption and desorption steps. This paper illustrates how process parameters can be arrived at through basic scaling exercises, modeling and simulation, and fundamental experimental tests of their predictions. Using chlorine and argon plasma in a radial line slot antenna plasma source as a platform, the authors illustrate how cycle time, ion energy, and radical to ion ratio can be manipulated to manage the deviation from ideality when cycle times are shortened or purges are incomplete. Cell based Monte Carlo feature scale modeling is used to illustrate profile outcomes. Experimental results of atomic layer etching processes are illustrated on silicon line and space structures such that iso-dense bias and aspect ratio dependent free profiles are produced. Experimental results also illustrate the profile control margin as processes move from atomic layer to multilayer by layer etching. The consequence of not controlling contamination (e.g., oxygen) is shown to result in deposition and roughness generation.

  16. Sensing Noncollinear Magnetism at the Atomic Scale Combining Magnetic Exchange and Spin-Polarized Imaging.

    Science.gov (United States)

    Hauptmann, Nadine; Gerritsen, Jan W; Wegner, Daniel; Khajetoorians, Alexander A

    2017-09-13

    Storing and accessing information in atomic-scale magnets requires magnetic imaging techniques with single-atom resolution. Here, we show simultaneous detection of the spin-polarization and exchange force with or without the flow of current with a new method, which combines scanning tunneling microscopy and noncontact atomic force microscopy. To demonstrate the application of this new method, we characterize the prototypical nanoskyrmion lattice formed on a monolayer of Fe/Ir(111). We resolve the square magnetic lattice by employing magnetic exchange force microscopy, demonstrating its applicability to noncollinear magnetic structures for the first time. Utilizing distance-dependent force and current spectroscopy, we quantify the exchange forces in comparison to the spin-polarization. For strongly spin-polarized tips, we distinguish different signs of the exchange force that we suggest arises from a change in exchange mechanisms between the probe and a skyrmion. This new approach may enable both nonperturbative readout combined with writing by current-driven reversal of atomic-scale magnets.

  17. Assessment of the Scales of Gilthead Seabream (Sparus aurata L. by Image Analysis and Atomic Force Microscopy

    Directory of Open Access Journals (Sweden)

    Francisco Casado

    2018-01-01

    Full Text Available Understanding the protective role of fish skin is critical to improving the development of aquaculture, since skin is the main surface that separates the animal from its always hazardous environment. Many techniques have been used for its study, but certain structural characteristics of fish skin still remain not clearly understood. That is the case with scales, which have always been attributed a mere protective role, but which are proving to have more functions than it was traditionally thought. To acquire a deeper knowledge, scales from six different regions of gilthead seabream (Sparus aurata L. were studied and measured by image analysis. Results prove that scales from the base of the dorsal fin are larger than those in other parts of the fish body while scales from the peduncle are the smallest of the skin. Furthermore, a technique relatively new in this field, known as atomic force microscopy (AFM, was used to obtain representations of the ultrastructure of the scales and measure certain features such as the circuli and the lines in the basal layer. The data obtained allowed us to compare the height of circuli among the different scales, showing that they were higher in scales from the dorsum and the operculum. The present results introduce a nanostructural model of the scales of gilthead seabream that might serve as a useful guideline for future studies.

  18. Dislocation glide in Ni-Al solid solutions from the atomic scale up: a molecular dynamics study; Etude du glissement des dislocations dans la solution solide Ni-Al par simulation a l'echelle atomique

    Energy Technology Data Exchange (ETDEWEB)

    Rodary, E

    2003-01-01

    The glide of an edge dislocation in solid solutions is studied by molecular dynamics, at fixed temperature and imposed external stress. We have optimized an EAM potential for Ni(1 a 8% A1): it well reproduces the lattice expansion, local atomic order, stacking fault energy as a function of composition, as well as the elastic properties of the {gamma}' phase with L1{sub 2} structure. On increasing the stress, the dislocation is first immobile, then glides with a velocity proportional to the stress and the velocity saturates on reaching the transverse sound velocity. However, only beyond a static threshold stress, {sigma}{sub s}, does the dislocation glide a distance large enough to allow macroscopic shear; the linear part of the velocity-stress curve extrapolates to zero at a dynamical threshold stress, {sigma}{sub d}, The friction coefficient, and the threshold stresses ({sigma}{sub s} and {sigma}{sub d}), increase with the A1 concentration and decrease with temperature (300 and 500 K). Close to the critical shear stress, {sigma}{sub s}, the dislocation glide is analysed with a 'stop and go' model. The latter yields the flight velocity between obstacles, the mean obstacle density and the distribution of the waiting time on each obstacle as a function of stress, composition and temperature. The obstacle to the glide is proposed to be the strong repulsion between Al atoms brought into nearest neighbour position by the glide process, and not the dislocation-solute interaction. The microscopic parameters so defined are introduced into a micro-mechanical model, which well reproduces the known behaviour of nickel base solid solutions. (author)

  19. Reaction studies of hot silicon, germanium and carbon atoms

    International Nuclear Information System (INIS)

    Gaspar, P.P.

    1990-01-01

    The goal of this project was to increase the authors understanding of the interplay between the kinetic and electronic energy of free atoms and their chemical reactivity by answering the following questions: (1) what is the chemistry of high-energy carbon silicon and germanium atoms recoiling from nuclear transformations; (2) how do the reactions of recoiling carbon, silicon and germanium atoms take place - what are the operative reaction mechanisms; (3) how does the reactivity of free carbon, silicon and germanium atoms vary with energy and electronic state, and what are the differences in the chemistry of these three isoelectronic atoms? This research program consisted of a coordinated set of experiments capable of achieving these goals by defining the structures, the kinetic and internal energy, and the charge states of the intermediates formed in the gas-phase reactions of recoiling silicon and germanium atoms with silane, germane, and unsaturated organic molecules, and of recoiling carbon atoms with aromatic molecules. The reactions of high energy silicon, germanium, and carbon atoms created by nuclear recoil were studied with substrates chosen so that their products illuminated the mechanism of the recoil reactions. Information about the energy and electronic state of the recoiling atoms at reaction was obtained from the variation in end product yields and the extent of decomposition and rearrangement of primary products (usually reactive intermediates) as a function of total pressure and the concentration of inert moderator molecules that remove kinetic energy from the recoiling atoms and can induce transitions between electronic spin states. 29 refs

  20. Spectroscopic studies of hydrogen atom and molecule collisions: Performance report

    International Nuclear Information System (INIS)

    Kielkopf, J.

    1986-01-01

    This research is concerned with spectroscopic measurements of collisions in atomic and molecular hydrogen in order to clarify the basic physical processes that take place during radiative collisions and to provide experimental values for systems where the theoretical analysis is tractable. To this end, we proposed to measure from the cores to the far wings the profiles of the spectral lines of atomic hydrogen broadened by molecular hydrogen and noble gases, and to study energy transfer in the atom and molecule

  1. Theoretical study of adsorption of lithium atom on carbon nanotube

    OpenAIRE

    Senami, Masato; Ikeda, Yuji; Fukushima, Akinori; Tachibana, Akitomo

    2011-01-01

    We investigate the adsorption of lithium atoms on the surface of the (12, 0) single wall carbon nanotube (SWCNT) by using ab initio quantum chemical calculations. The adsorption of one lithium atom on the inside of this SWCNT is favored compared to the outside. We check this feature by charge transfer and regional chemical potential density. The adsorption of multiple lithium atoms on the interior of the SWCNT is studied in terms of adsorption energy and charge transfer. We show that repulsiv...

  2. Capillary condensation in atomic scale friction: how water acts like a glue.

    Science.gov (United States)

    Jinesh, K B; Frenken, J W M

    2006-04-28

    We present atomic-scale friction force measurements that strongly suggest that the capillary condensation of water between a tungsten tip and a graphite surface leads to the formation of ice at room temperature. This phenomenon increases the friction force, introduces a short-term memory in the form of an elastic response against shearing, and allows us to "write" a temporary line of ice on a hydrophobic surface. Rearrangements of the condensate are shown to take place on a surprisingly slow time scale of seconds.

  3. Quantifying the Hierarchical Order in Self-Aligned Carbon Nanotubes from Atomic to Micrometer Scale.

    Science.gov (United States)

    Meshot, Eric R; Zwissler, Darwin W; Bui, Ngoc; Kuykendall, Tevye R; Wang, Cheng; Hexemer, Alexander; Wu, Kuang Jen J; Fornasiero, Francesco

    2017-06-27

    Fundamental understanding of structure-property relationships in hierarchically organized nanostructures is crucial for the development of new functionality, yet quantifying structure across multiple length scales is challenging. In this work, we used nondestructive X-ray scattering to quantitatively map the multiscale structure of hierarchically self-organized carbon nanotube (CNT) "forests" across 4 orders of magnitude in length scale, from 2.0 Å to 1.5 μm. Fully resolved structural features include the graphitic honeycomb lattice and interlayer walls (atomic), CNT diameter (nano), as well as the greater CNT ensemble (meso) and large corrugations (micro). Correlating orientational order across hierarchical levels revealed a cascading decrease as we probed finer structural feature sizes with enhanced sensitivity to small-scale disorder. Furthermore, we established qualitative relationships for single-, few-, and multiwall CNT forest characteristics, showing that multiscale orientational order is directly correlated with number density spanning 10 9 -10 12 cm -2 , yet order is inversely proportional to CNT diameter, number of walls, and atomic defects. Lastly, we captured and quantified ultralow-q meridional scattering features and built a phenomenological model of the large-scale CNT forest morphology, which predicted and confirmed that these features arise due to microscale corrugations along the vertical forest direction. Providing detailed structural information at multiple length scales is important for design and synthesis of CNT materials as well as other hierarchically organized nanostructures.

  4. Further localization studies of Co atoms diffused into silicon

    International Nuclear Information System (INIS)

    Dezsi, I.; Feher, S.; Forgacs, G.; Horvath, D.; Kotai, E.; Manuaba, A.; Mezey, G.; Molnar, B.; Nagy, D.L.; Zsoldos, E.

    1982-01-01

    57 Co atoms diffused at 1270 K for 1 h into single crystals of Si have a single Moessbauer line at (-0.059 +- 0.001) mm/s. Channelling studies show that 77% of the Co atoms occupy some substitutional sites. It is found that Co forms epitaxial CoSi 2 clusters in the Si lattice. (orig.)

  5. Further localization studies of Co atoms diffused into silicon

    International Nuclear Information System (INIS)

    Dezsi, I.; Feher, S.; Forgacs, Gy.; Horvath, D.; Kotai, E.; Manuaba, A.; Mezey, G.; Molnar, B.; Nagy, D.L.; Zsoldos, E.

    1981-01-01

    57 Co atoms diffused at 1270 K for 1 hour into single crystals of Si have a single Moessbauer line at -0.059+-0.001 mm/s. Channelling studies show 77 per cent of the Co atoms to occupy substitutional sites. It is found that Co forms epitaxial CoSi 2 clusters in the Si lattice. (author)

  6. Evidence for atomic scale disorder in indium nitride from perturbed angular correlation spectroscopy

    International Nuclear Information System (INIS)

    Dogra, R; Shrestha, S K; Byrne, A P; Ridgway, M C; Edge, A V J; Vianden, R; Penner, J; Timmers, H

    2005-01-01

    The crystal lattice of bulk grains and state-of-the-art films of indium nitride was investigated at the atomic scale with perturbed angular correlation spectroscopy using the 111 In/Cd radioisotope probe. The probe was introduced during sample synthesis, by diffusion and by ion implantation. The mean quadrupole interaction frequency ν Q = 28 MHz was observed at the indium probe site in all types of indium nitride samples with broad frequency distributions. The observed small, but non-zero, asymmetry parameter indicates broken symmetry around the probe atoms. Results have been compared with theoretical calculations based on the point charge model. The consistency of the experimental results and their independence of the preparation technique suggest that the origin of the broad frequency distribution is inherent to indium nitride, indicating a high degree of disorder at the atomic scale. Due to the low dissociation temperature of indium nitride, furnace and rapid thermal annealing at atmospheric pressure reduce the lattice disorder only marginally

  7. Implementation of highly parallel and large scale GW calculations within the OpenAtom software

    Science.gov (United States)

    Ismail-Beigi, Sohrab

    The need to describe electronic excitations with better accuracy than provided by band structures produced by Density Functional Theory (DFT) has been a long-term enterprise for the computational condensed matter and materials theory communities. In some cases, appropriate theoretical frameworks have existed for some time but have been difficult to apply widely due to computational cost. For example, the GW approximation incorporates a great deal of important non-local and dynamical electronic interaction effects but has been too computationally expensive for routine use in large materials simulations. OpenAtom is an open source massively parallel ab initiodensity functional software package based on plane waves and pseudopotentials (http://charm.cs.uiuc.edu/OpenAtom/) that takes advantage of the Charm + + parallel framework. At present, it is developed via a three-way collaboration, funded by an NSF SI2-SSI grant (ACI-1339804), between Yale (Ismail-Beigi), IBM T. J. Watson (Glenn Martyna) and the University of Illinois at Urbana Champaign (Laxmikant Kale). We will describe the project and our current approach towards implementing large scale GW calculations with OpenAtom. Potential applications of large scale parallel GW software for problems involving electronic excitations in semiconductor and/or metal oxide systems will be also be pointed out.

  8. Atomic-Scale Nuclear Spin Imaging Using Quantum-Assisted Sensors in Diamond

    Directory of Open Access Journals (Sweden)

    A. Ajoy

    2015-01-01

    Full Text Available Nuclear spin imaging at the atomic level is essential for the understanding of fundamental biological phenomena and for applications such as drug discovery. The advent of novel nanoscale sensors promises to achieve the long-standing goal of single-protein, high spatial-resolution structure determination under ambient conditions. In particular, quantum sensors based on the spin-dependent photoluminescence of nitrogen-vacancy (NV centers in diamond have recently been used to detect nanoscale ensembles of external nuclear spins. While NV sensitivity is approaching single-spin levels, extracting relevant information from a very complex structure is a further challenge since it requires not only the ability to sense the magnetic field of an isolated nuclear spin but also to achieve atomic-scale spatial resolution. Here, we propose a method that, by exploiting the coupling of the NV center to an intrinsic quantum memory associated with the nitrogen nuclear spin, can reach a tenfold improvement in spatial resolution, down to atomic scales. The spatial resolution enhancement is achieved through coherent control of the sensor spin, which creates a dynamic frequency filter selecting only a few nuclear spins at a time. We propose and analyze a protocol that would allow not only sensing individual spins in a complex biomolecule, but also unraveling couplings among them, thus elucidating local characteristics of the molecule structure.

  9. Quantitative characterization of the atomic-scale structure of oxyhydroxides in rusts formed on steel surfaces

    International Nuclear Information System (INIS)

    Saito, M.; Suzuki, S.; Kimura, M.; Suzuki, T.; Kihira, H.; Waseda, Y.

    2005-01-01

    Quantitative X-ray structural analysis coupled with anomalous X-ray scattering has been used for characterizing the atomic-scale structure of rust formed on steel surfaces. Samples were prepared from rust layers formed on the surfaces of two commercial steels. X-ray scattered intensity profiles of the two samples showed that the rusts consisted mainly of two types of ferric oxyhydroxide, α-FeOOH and γ-FeOOH. The amounts of these rust components and the realistic atomic arrangements in the components were estimated by fitting both the ordinary and the environmental interference functions with a model structure calculated using the reverse Monte Carlo simulation technique. The two rust components were found to be the network structure formed by FeO 6 octahedral units, the network structure itself deviating from the ideal case. The present results also suggest that the structural analysis method using anomalous X-ray scattering and the reverse Monte Carlo technique is very successful in determining the atomic-scale structure of rusts formed on the steel surfaces

  10. Structure and transport at grain boundaries in polycrystalline olivine: An atomic-scale perspective

    Science.gov (United States)

    Mantisi, Boris; Sator, Nicolas; Guillot, Bertrand

    2017-12-01

    Structure and transport properties at grain boundaries in polycrystalline olivine have been investigated at the atomic scale by molecular dynamics simulation (MD) using an empirical ionocovalent interaction potential. On the time scale of the simulation (a few tens of nanoseconds for a system size of ∼650,000 atoms) grain boundaries and grain interior were identified by mapping the atomic displacements along the simulation run. In the investigated temperature range (1300-1700 K) the mean thickness of the grain boundary phase is evaluated between 0.5 and 2 nm, a value which depends on temperature and grain size. The structure of the grain boundary phase is found to be disordered (amorphous-like) and is different from the one exhibited by the supercooled liquid. The self-diffusion coefficients of major elements in the intergranular region range from ∼10-13 to 10-10 m2/s between 1300 and 1700 K (with DSigb Kubo relation expressing the viscosity as function of the stress tensor time correlation function. In spite of a slow convergence of the calculation by MD, the grain boundary viscosity was estimated about ∼105 Pa s at 1500 K, a value in agreement with high-temperature viscoelastic relaxation data. An interesting information gained from MD is that sliding at grain boundaries is essentially controlled by the internal friction between the intergranular phase and the grain edges.

  11. Aging study on atomic bomb survivors

    International Nuclear Information System (INIS)

    Okajima, Shunzo; Aoyama, Takashi; Norimura, Toshiyuki; Nishimori, Issei; Shiomi, Toshio

    1976-01-01

    This is an ad interim report on the survey which is being performed at the Atomic Disease Institute, Nagasaki University School of Medicine for the acceleration of aging in atomic bomb survivors. The survivors group consisted of 50 females between 40 and 49 years of age who were exposed somewhere within 1.4 km where exposure dose could be estimated accurately and whose mean estimated exposure dose was 225.9+-176.8 rads. The control group consisted of females of the same age group who were exposed at sites more than 2.5 km apart (atmospheric dose 2.9 rads). The items for the judgement of aging included physical measurements, external findings, functional findings, and special tests (urine, blood, pattern of serum protein fraction, and chromosome aberrations). As far as chromosome aberrations were concerned, the number of cells with stable aberrations, Cs, showed differences between the two groups, and the number of cells with exchange-type aberrations was large in the survivors group. No significant differences were observed in the other tests. (Serizawa, K.)

  12. Dislocation-stacking fault tetrahedron interaction: what can we learn from atomic-scale modelling

    International Nuclear Information System (INIS)

    Osetsky, Yu.N.; Stoller, R.E.; Matsukawa, Y.

    2004-01-01

    The high number density of stacking fault tetrahedra (SFTs) observed in irradiated fcc metals suggests that they should contribute to radiation-induced hardening and, therefore, taken into account when estimating mechanical properties changes of irradiated materials. The central issue is describing the individual interaction between a moving dislocation and an SFT, which is characterized by a very fine size scale, ∼100 nm. This scale is amenable to both in situ TEM experiments and large-scale atomic modelling. In this paper we present results of an atomistic simulation of dislocation-SFT interactions using molecular dynamics (MD). The results are compared with observations from in situ deformation experiments. It is demonstrated that in some cases the simulations and experimental observations are quite similar, suggesting a reasonable interpretation of experimental observations

  13. Review of chip-scale atomic clocks based on coherent population trapping

    International Nuclear Information System (INIS)

    Wang Zhong

    2014-01-01

    Research on chip-scale atomic clocks (CSACs) based on coherent population trapping (CPT) is reviewed. The background and the inspiration for the research are described, including the important schemes proposed to improve the CPT signal quality, the selection of atoms and buffer gases, and the development of micro-cell fabrication. With regard to the reliability, stability, and service life of the CSACs, the research regarding the sensitivity of the CPT resonance to temperature and laser power changes is also reviewed, as well as the CPT resonance's collision and light of frequency shifts. The first generation CSACs have already been developed but its characters are still far from our expectations. Our conclusion is that miniaturization and power reduction are the most important aspects calling for further research. (review)

  14. Analysis of Carbon Nanotubes on the Mechanical Properties at Atomic Scale

    Directory of Open Access Journals (Sweden)

    Xiaowen Lei

    2011-01-01

    Full Text Available This paper aims at developing a mathematic model to characterize the mechanical properties of single-walled carbon nanotubes (SWCNTs. The carbon-carbon (C–C bonds between two adjacent atoms are modeled as Euler beams. According to the relationship of Tersoff-Brenner force theory and potential energy acting on C–C bonds, material constants of beam element are determined at the atomic scale. Based on the elastic deformation energy and mechanical equilibrium of a unit in graphite sheet, simply form ED equations of calculating Young's modulus of armchair and zigzag graphite sheets are derived. Following with the geometrical relationship of SWCNTs in cylindrical coordinates and the structure mechanics approach, Young's modulus and Poisson's ratio of armchair and zigzag SWCNTs are also investigated. The results show that the approach to research mechanical properties of SWCNTs is a concise and valid method. We consider that it will be useful technique to progress on this type of investigation.

  15. Photoionization studies of atoms and molecules using synchrotron radiation

    International Nuclear Information System (INIS)

    Lindle, D.W.

    1988-01-01

    Photoionization studies of free atoms and molecules have undergone considerable development in the past decade, in large part due to the use of synchrotron radiation. The tunability of synchrotron radiation has permitted the study of photoionization processes near valence-and core-level ionization thresholds for atoms and molecules throught the Periodic Table. A general illustration of these types of study will be presented, with emphasis on a few of the more promising new directions in atomic and molecular physics being pursued with synchrotron radiation. (author) [pt

  16. Atomic-Scale Simulations of Cascade Overlap and Damage Evolution in Silicon Carbide

    International Nuclear Information System (INIS)

    Gao, Fei; Weber, William J.

    2003-01-01

    In a previous computer simulation experiment, the accumulation of damage in SiC from the overlap of 10 keV Si displacement cascades at 200 K was investigated, and the damage states produced following each cascade were archived for further analysis. In the present study, interstitial clustering, system energy, and volume changes are investigated as the damage states evolve due to cascade overlap. An amorphous state is achieved at a damage energy density of 27.5 eV/atom (0.28 displacements per atom). At low dose levels, most defects are produced as isolated Frenkel pairs, with a small number of defect clusters involving only 4 to 6 atoms; however, after the overlap of 5 cascades (0.0125 displacements per atom), the size and number of interstitial clusters increases with increasing dose. The average energy per atom increases linearly with increasing short-range (or chemical) disorder. The volume change exhibits two regimes of linear dependence on system energy and increases more rapidly with dose than either the energy or the disorder, which indicate a significant contribution to swelling of isolated interstitials and anti-site defects. The saturation volume change for the cascade-amorphized state in these simulations is 8.2%, which is in reasonable agreement with the experimental value of 10.8% in neutron-irradiated SiC

  17. Atomic-scale simulation of dust grain collisions: Surface chemistry and dissipation beyond existing theory

    Science.gov (United States)

    Quadery, Abrar H.; Doan, Baochi D.; Tucker, William C.; Dove, Adrienne R.; Schelling, Patrick K.

    2017-10-01

    The early stages of planet formation involve steps where submicron-sized dust particles collide to form aggregates. However, the mechanism through which millimeter-sized particles aggregate to kilometer-sized planetesimals is still not understood. Dust grain collision experiments carried out in the environment of the Earth lead to the prediction of a 'bouncing barrier' at millimeter-sizes. Theoretical models, e.g., Johnson-Kendall-Roberts and Derjaguin-Muller-Toporov theories, lack two key features, namely the chemistry of dust grain surfaces, and a mechanism for atomic-scale dissipation of energy. Moreover, interaction strengths in these models are parameterized based on experiments done in the Earth's environment. To address these issues, we performed atomic-scale simulations of collisions between nonhydroxylated and hydroxylated amorphous silica nanoparticles. We used the ReaxFF approach which enables modeling chemical reactions using an empirical potential. We found that nonhydroxylated nanograins tend to adhere with much higher probability than suggested by existing theories. By contrast, hydroxylated nanograins exhibit a strong tendency to bounce. Also, the interaction between dust grains has the characteristics of a strong chemical force instead of weak van der Waals forces. This suggests that the formation of strong chemical bonds and dissipation via internal atomic vibration may result in aggregation beyond what is expected based on our current understanding. Our results also indicate that experiments should more carefully consider surface conditions to mimic the space environment. We also report results of simulations with molten silica nanoparticles. It is found that molten particles are more likely to adhere due to viscous dissipation, which supports theories that suggest aggregation to kilometer scales might require grains to be in a molten state.

  18. Multiple microflame quartz tube atomizer: Study and minimization of interferences in quartz tube atomizers in hydride generation atomic absorption spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Moraes Flores, Erico Marlon de [Departamento de Quimica, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS (Brazil)], E-mail: flores@quimica.ufsm.br; Medeiros Nunes, Adriane; Luiz Dressler, Valderi [Departamento de Quimica, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS (Brazil); Dedina, Jiri [Institute of Analytical Chemistry of the ASCR, v.v.i., Videnska 1083, CZ-142 20 Prague (Czech Republic)

    2009-02-15

    A systematic study was performed to evaluate the performance of a multiple microflame (MM) quartz tube atomizer (QTA) for minimizing interferences and to improve the extent of the calibration range using a batch system for hydride generation atomic absorption spectrometry (HG AAS). A comparison of the results with conventional QTA on the determination of antimony, arsenic, bismuth and selenium was performed. The interference of As, Bi, Se, Pb, Sn and Sb was investigated using QTA and MMQTA atomizers. Better performance was found for MMQTA, and no loss of linearity was observed up to 160 ng for Se and Sb and 80 ng for As, corresponding to an enhancement of two times for both analytes when compared to QTA (analyte mass refers to a volume of 200 {mu}l). For Bi, the linear range was the same for QTA and MMQTA (140 ng). With the exception of Bi, the tolerance limits for hydride-forming elements were improved more than 50% in comparison to the conventional QTA system, especially for the interferences of As, Sb and Se. However, for Sn as an interferent, no difference was observed in the determination of Se and Sb using the MMQTA system. The use of MMQTA-HG AAS complied with the relatively high sensitivity of conventional QTA and also provided better performance for interferences and the linear range of calibration.

  19. Mechanical deformation of atomic-scale metallic contacts: Structure and mechanisms

    DEFF Research Database (Denmark)

    Sørensen, Mads Reinholdt; Brandbyge, Mads; Jacobsen, Karsten Wedel

    1998-01-01

    We have simulated the mechanical deformation of atomic-scale metallic contacts under tensile strain using molecular dynamics and effective medium theory potentials. The evolution of the structure of the contacts and the underlying deformation mechanisms are described along with the calculated......, but vacancies can be permanently present. The transition states and energies for slip mechanisms have been determined using the nudged elastic band method, and we find a size-dependent crossover from a dislocation-mediated slip to a homogeneous slip when the contact diameter becomes less than a few nm. We show...

  20. General Atomic Reprocessing Pilot Plant: engineering-scale dissolution system description

    International Nuclear Information System (INIS)

    Yip, H.H.

    1979-04-01

    In February 1978, a dissolver-centrifuge system was added to the cold reprocessing pilot plant at General Atomic Company, which completed the installation of an HTGR fuel head-end reprocessing pilot plant. This report describes the engineering-scale equipment in the pilot plant and summarizes the design features derived from development work performed in the last few years. The dissolver operating cycles for both thorium containing BISO and uranium containinng WAR fissile fuels are included. A continuous vertical centrifuge is used to clarify the resultant dissolver product solution. Process instrumentation and controls for the system reflect design philosophy suitable for remote operation

  1. Molecular dynamics modeling of bonding two materials by atomic scale friction stir welding at different process parameters

    Science.gov (United States)

    Konovalenko S., Iv.; Psakhie, S. G.

    2017-12-01

    Using the molecular dynamics method, we simulated the atomic scale butt friction stir welding on two crystallites and varied the onset FSW tool plunge depth. The effects of the plunge depth value on the thermomechanical evolution of nanosized crystallites and mass transfer in the course of FSW have been studied. The increase of plunge depth values resulted in more intense heating and reducing the plasticized metal resistance to the tool movement. The mass transfer intensity was hardly dependent on the plunge depth value. The plunge depth was recommended to be used as a FSW process control parameter in addition to the commonly used ones.

  2. Atomic-Scale Characterization and Manipulation of Freestanding Graphene Using Adapted Capabilities of a Scanning Tunneling Microscope

    Science.gov (United States)

    Barber, Steven

    Graphene was the first two-dimensional material ever discovered, and it exhibits many unusual phenomena important to both pure and applied physics. To ensure the purest electronic structure, or to study graphene's elastic properties, it is often suspended over holes or trenches in a substrate. The aim of the research presented in this dissertation was to develop methods for characterizing and manipulating freestanding graphene on the atomic scale using a scanning tunneling microscope (STM). Conventional microscopy and spectroscopy techniques must be carefully reconsidered to account for movement of the extremely flexible sample. First, the acquisition of atomic-scale images of freestanding graphene using the STM and the ability to pull the graphene perpendicular to its plane by applying an electrostatic force with the STM tip are demonstrated. The atomic-scale images contained surprisingly large corrugations due to the electrostatic attractive force varying in registry with the local density of states. Meanwhile, a large range of control over the graphene height at a point was obtained by varying the tip bias voltage, and the application to strain engineering of graphene's so-called pseudomagnetic field is examined. Next, the effect of the tunneling current was investigated. With increasing current, the graphene sample moves away from the tip rather than toward it. It was determined that this must be due to local heating by the electric current, causing the graphene to contract because it has a negative coefficient of thermal expansion. Finally, by imaging a very small area, the STM can monitor the height of one location over long time intervals. Results sometimes exhibit periodic behavior, with a frequency and amplitude that depend on the tunneling current. These fluctuations are interpreted as low-frequency flexural phonon modes within elasticity theory. All of these findings set the foundation for employing a STM in the study of freestanding graphene.

  3. Numerical atomic scale simulations of the microstructural evolution of ferritic alloys under irradiation

    International Nuclear Information System (INIS)

    Vincent, E.

    2006-12-01

    In this work, we have developed a model of point defect (vacancies and interstitials) diffusion whose aim is to simulate by kinetic Monte Carlo (KMC) the formation of solute rich clusters observed experimentally in irradiated FeCuNiMnSi model alloys and in pressure vessel steels. Electronic structure calculations have been used to characterize the interactions between point defects and the different solute atoms. Each of these solute atoms establishes an attractive bond with the vacancy. As for Mn, which is the element which has the weakest bond with the vacancy, it establishes more favourable bonds with interstitials. Binding energies, migration energies as well as other atomic scale properties, determined by ab initio calculations, have led to a parameter set for the KMC code. Firstly, these parameters have been optimised on thermal ageing experiments realised on the FeCu binary alloy and on complex alloys, described in the literature. The vacancy diffusion thermal annealing simulations show that when a vacancy is available, all the solutes migrate and form clusters, in agreement with the observed experimental tendencies. Secondly, to simulate the microstructural evolution under irradiation, we have introduced interstitials in the KMC code. Their presence leads to a more efficient transport of Mn. The first simulations of electron and neutron irradiations show that the model results are globally qualitatively coherent with the experimentally observed tendencies. (author)

  4. Atom probe characterization of nano-scaled features in irradiated Eurofer and ODS Eurofer steel

    International Nuclear Information System (INIS)

    Rogozkin, S.; Aleev, A.; Nikitin, A.; Zaluzhnyi, A.; Vladimirov, P.; Moeslang, A.; Lindau, R.

    2009-01-01

    Outstanding performance of oxide dispersion strengthened (ODS) steels at high temperatures and up to high doses allowed to consider them as potential candidates for fusion and fission power plants. At the same time their mechanical parameters strongly correlate with number density of oxide particles and their size. It is believed that fine particles are formed at the last stage of sophisticated production procedures and play a crucial role in higher heat- and radiation resistance in comparison with conventional materials. However, due to their small size - only few nanometers, characterization of such objects requires considerable efforts. Recent study of ODS steel by tomographic atom probe, the most appropriate technique in this case, shown considerable stability of these particles under high temperatures and ion-irradiation. However, these results were obtained for 12/14% Cr with addition of 0.3% Y 2 O 3 and titanium which is inappropriate in case of ODS Eurofer 97 and possibility to substitute neutron by ion irradiation is still under consideration. In this work effect of neutron irradiation on nanostructure behaviour of ODS Eurofer are investigated. Irradiation was performed on research reactor BOR-60 in SSC RF RIAR (Dimitrovgrad, Russia) up to 30 dpa at 280 deg. C and 580 deg. C. Recent investigation of unirradiated state revealed high number density of nano-scaled features (nano-clusters) even without addition of Ti in steel. It was shown that vanadium played significant role in nucleation process and core of nano-clusters was considerably enriched with it. In irradiated samples solution of vanadium in matrix was observed while the size of particles stayed practically unchanged. Also no nitrogen was detected in these particles in comparison with unirradiated state where bond energy of N with V was considered to be high as VN 2+ ions were detected on mass-spectra. (author)

  5. Fabrication Of Atomic-scale Gold Junctions By Electrochemical Plating Technique Using A Common Medical Disinfectant

    Science.gov (United States)

    Umeno, Akinori; Hirakawa, Kazuhiko

    2005-06-01

    Iodine tincture, a medical liquid familiar as a disinfectant, was introduced as an etching/deposition electrolyte for the fabrication of nanometer-separated gold electrodes. In the gold dissolved iodine tincture, the gold electrodes were grown or eroded slowly in atomic scale, enough to form quantum point contacts. The resistance evolution during the electrochemical deposition showed plateaus at integer multiples of the resistance quantum, (2e2/h)-1, at the room temperature. The iodine tincture is a commercially available common material, which makes the fabrication process to be the simple and cost effective. Moreover, in contrast to the conventional electrochemical approaches, this method is free from highly toxic cyanide compounds or extraordinary strong acid. We expect this method to be a useful interface between single-molecular-scale structures and macroscopic opto-electronic devices.

  6. Communication: An effective linear-scaling atomic-orbital reformulation of the random-phase approximation using a contracted double-Laplace transformation

    International Nuclear Information System (INIS)

    Schurkus, Henry F.; Ochsenfeld, Christian

    2016-01-01

    An atomic-orbital (AO) reformulation of the random-phase approximation (RPA) correlation energy is presented allowing to reduce the steep computational scaling to linear, so that large systems can be studied on simple desktop computers with fully numerically controlled accuracy. Our AO-RPA formulation introduces a contracted double-Laplace transform and employs the overlap-metric resolution-of-the-identity. First timings of our pilot code illustrate the reduced scaling with systems comprising up to 1262 atoms and 10 090 basis functions. 

  7. Atomic scale 0-π transition and pairing symmetry in a Josephson junction with a ferromagnetic insulator

    International Nuclear Information System (INIS)

    Kawabata, S.; Kashiwaya, S.; Tanaka, Y.; Golubov, A. A.; Asano, Y.

    2011-01-01

    Full text: A superconducting ring with a π-junction made from superconductor (S) / ferromagnetic- metal (FM) / superconductor (S) exhibits a spontaneous current without an external magnetic field and the corresponding magnetic flux is half a flux quantum in the ground state. Such a π-ring provides so-called 'quiet qubit' that can be efficiently decoupled from the fluctuation of the external field. However, the usage of FM gives rise to strong Ohmic dissipation. Therefore, the realization of π-junctions without FM is highly desired for qubit applications. We theoretically consider the possibility of the π-junction formation in the mesoscopic Josephson junctions with ferromagnetic insulators (FI) by taking into account the band structure of such materials explicitly. In the case of the fully polarized FIs, e.g., La 2 BaCuO 5 (LBCO) and K 2 CuF 4 , we found the formation of a π-junction and a novel atomic-scale 0-π transition induced by increasing the FI thickness LF. In this talk, I will discuss a thermal stability and material-parameter dependences of the atomic-scale 0-π transition as well as possibility of the odd-frequency pairing in such systems. (author)

  8. Quantitative atomic resolution elemental mapping via absolute-scale energy dispersive X-ray spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Z. [School of Physics and Astronomy, Monash University, Clayton, Victoria 3800 (Australia); Weyland, M. [Monash Centre for Electron Microscopy, Monash University, Clayton, Victoria 3800 (Australia); Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800 (Australia); Sang, X.; Xu, W.; Dycus, J.H.; LeBeau, J.M. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695 (United States); D' Alfonso, A.J.; Allen, L.J. [School of Physics, University of Melbourne, Parkville, Victoria 3010 (Australia); Findlay, S.D., E-mail: scott.findlay@monash.edu [School of Physics and Astronomy, Monash University, Clayton, Victoria 3800 (Australia)

    2016-09-15

    Quantitative agreement on an absolute scale is demonstrated between experiment and simulation for two-dimensional, atomic-resolution elemental mapping via energy dispersive X-ray spectroscopy. This requires all experimental parameters to be carefully characterized. The agreement is good, but some discrepancies remain. The most likely contributing factors are identified and discussed. Previous predictions that increasing the probe forming aperture helps to suppress the channelling enhancement in the average signal are confirmed experimentally. It is emphasized that simple column-by-column analysis requires a choice of sample thickness that compromises between being thick enough to yield a good signal-to-noise ratio while being thin enough that the overwhelming majority of the EDX signal derives from the column on which the probe is placed, despite strong electron scattering effects. - Highlights: • Absolute scale quantification of 2D atomic-resolution EDX maps is demonstrated. • Factors contributing to remaining small quantitative discrepancies are identified. • Experiment confirms large probe-forming apertures suppress channelling enhancement. • The thickness range suitable for reliable column-by-column analysis is discussed.

  9. Fast Atomic-Scale Elemental Mapping of Crystalline Materials by STEM Energy-Dispersive X-Ray Spectroscopy Achieved with Thin Specimens.

    Science.gov (United States)

    Lu, Ping; Yuan, Renliang; Zuo, Jian Min

    2017-02-01

    Elemental mapping at the atomic-scale by scanning transmission electron microscopy (STEM) using energy-dispersive X-ray spectroscopy (EDS) provides a powerful real-space approach to chemical characterization of crystal structures. However, applications of this powerful technique have been limited by inefficient X-ray emission and collection, which require long acquisition times. Recently, using a lattice-vector translation method, we have shown that rapid atomic-scale elemental mapping using STEM-EDS can be achieved. This method provides atomic-scale elemental maps averaged over crystal areas of ~few 10 nm2 with the acquisition time of ~2 s or less. Here we report the details of this method, and, in particular, investigate the experimental conditions necessary for achieving it. It shows, that in addition to usual conditions required for atomic-scale imaging, a thin specimen is essential for the technique to be successful. Phenomenological modeling shows that the localization of X-ray signals to atomic columns is a key reason. The effect of specimen thickness on the signal delocalization is studied by multislice image simulations. The results show that the X-ray localization can be achieved by choosing a thin specimen, and the thickness of less than about 22 nm is preferred for SrTiO3 in [001] projection for 200 keV electrons.

  10. Comparative Criticality Analysis of Two Monte Carlo Codes on Centrifugal Atomizer: MCNPS and SCALE

    International Nuclear Information System (INIS)

    Kang, H-S; Jang, M-S; Kim, S-R; Park, J-M; Kim, K-N

    2015-01-01

    There are two well-known Monte Carlo codes for criticality analysis, MCNP5 and SCALE. MCNP5 is a general-purpose Monte Carlo N-Particle code that can be used for neutron, photon, electron or coupled neutron / photon / electron transport, including the capability to calculate eigenvalues for critical system as a main analysis code. SCALE provides a comprehensive, verified and validated, user-friendly tool set for criticality safety, reactor physics, radiation shielding, radioactive source term characterization, and sensitivity and uncertainty analysis. SCALE was conceived and funded by US NRC to perform standardized computer analysis for licensing evaluation and is used widely in the world. We performed a validation test of MCNP5 and a comparative analysis of Monte Carlo codes, MCNP5 and SCALE, in terms of the critical analysis of centrifugal atomizer. In the criticality analysis using MCNP5 code, we obtained the statistically reliable results by using a large number of source histories per cycle and performing of uncertainty analysis

  11. Comparative Criticality Analysis of Two Monte Carlo Codes on Centrifugal Atomizer: MCNPS and SCALE

    Energy Technology Data Exchange (ETDEWEB)

    Kang, H-S; Jang, M-S; Kim, S-R [NESS, Daejeon (Korea, Republic of); Park, J-M; Kim, K-N [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    There are two well-known Monte Carlo codes for criticality analysis, MCNP5 and SCALE. MCNP5 is a general-purpose Monte Carlo N-Particle code that can be used for neutron, photon, electron or coupled neutron / photon / electron transport, including the capability to calculate eigenvalues for critical system as a main analysis code. SCALE provides a comprehensive, verified and validated, user-friendly tool set for criticality safety, reactor physics, radiation shielding, radioactive source term characterization, and sensitivity and uncertainty analysis. SCALE was conceived and funded by US NRC to perform standardized computer analysis for licensing evaluation and is used widely in the world. We performed a validation test of MCNP5 and a comparative analysis of Monte Carlo codes, MCNP5 and SCALE, in terms of the critical analysis of centrifugal atomizer. In the criticality analysis using MCNP5 code, we obtained the statistically reliable results by using a large number of source histories per cycle and performing of uncertainty analysis.

  12. Atomic-scale structure of dislocations revealed by scanning tunneling microscopy and molecular dynamics

    DEFF Research Database (Denmark)

    Christiansen, Jesper; Morgenstern, K.; Schiøtz, Jakob

    2002-01-01

    The intersection between dislocations and a Ag(111) surface has been studied using an interplay of scanning tunneling microscopy (STM) and molecular dynamics. Whereas the STM provides atomically resolved information about the surface structure and Burgers vectors of the dislocations, the simulati......The intersection between dislocations and a Ag(111) surface has been studied using an interplay of scanning tunneling microscopy (STM) and molecular dynamics. Whereas the STM provides atomically resolved information about the surface structure and Burgers vectors of the dislocations......, the simulations can be used to determine dislocation structure and orientation in the near-surface region. In a similar way, the subsurface structure of other extended defects can be studied. The simulations show dislocations to reorient the partials in the surface region leading to an increased splitting width...

  13. Tetragonal fcc-Fe induced by κ -carbide precipitates: Atomic scale insights from correlative electron microscopy, atom probe tomography, and density functional theory

    Science.gov (United States)

    Liebscher, Christian H.; Yao, Mengji; Dey, Poulumi; Lipińska-Chwalek, Marta; Berkels, Benjamin; Gault, Baptiste; Hickel, Tilmann; Herbig, Michael; Mayer, Joachim; Neugebauer, Jörg; Raabe, Dierk; Dehm, Gerhard; Scheu, Christina

    2018-02-01

    Correlative scanning transmission electron microscopy, atom probe tomography, and density functional theory calculations resolve the correlation between elastic strain fields and local impurity concentrations on the atomic scale. The correlative approach is applied to coherent interfaces in a κ -carbide strengthened low-density steel and establishes a tetragonal distortion of fcc-Fe. An interfacial roughness of ˜1 nm and a localized carbon concentration gradient extending over ˜2 -3 nm is revealed, which originates from the mechano-chemical coupling between local strain and composition.

  14. Experimental and theoretical studies of metal vapor atoms

    International Nuclear Information System (INIS)

    Whitfield, S.B.; Wehlitz, Ralf; Martins, Michael

    2004-01-01

    Employing electron spectrometry in conjunction with tuneable synchrotron radiation, we will present a detailed examination of the photoionization dynamics of selected metal vapor atoms. In particular, this paper will focus on the relative partial cross sections of the atomic Li K-shell main and satellite (ionization with excitation) photoelectron lines in the region of the strong 1snln'l' autoionizing transitions, the atomic Sc 3d, 4s main and satellite photoelectron lines in the region of the 3p→3d giant resonance, and also the atomic Fe 3d, 4s main and satellite photoelectron lines in the same resonance region. Our experimental data for Sc and Fe will be compared to our state-of-the-art calculations based on the superposition of configuration method developed by Cowan (The Theory of Atomic Structure and Spectra. University of California Berkeley Press, Berkeley and Los Angeles, 1981). Our partial cross section measurements for Li and Sc will be complemented with measurements of the angular distribution parameter, β. In addition, our Li data will also be compared with recent R-matrix calculations (Phys. Rev. 57 (1998) 1045). In the case of Fe, we will also address the term dependent behavior of the partial cross sections on resonance. These results will highlight what can be achieved with today's technology and point the way towards future endeavors in the study of the photoionization dynamics of open-shell metal vapor atoms

  15. Study on high density multi-scale calculation technique

    International Nuclear Information System (INIS)

    Sekiguchi, S.; Tanaka, Y.; Nakada, H.; Nishikawa, T.; Yamamoto, N.; Yokokawa, M.

    2004-01-01

    To understand degradation of nuclear materials under irradiation, it is essential to know as much about each phenomenon observed from multi-scale points of view; they are micro-scale in atomic-level, macro-level in structural scale and intermediate level. In this study for application to meso-scale materials (100A ∼ 2μm), computer technology approaching from micro- and macro-scales was developed including modeling and computer application using computational science and technology method. And environmental condition of grid technology for multi-scale calculation was prepared. The software and MD (molecular dynamics) stencil for verifying the multi-scale calculation were improved and their movement was confirmed. (A. Hishinuma)

  16. Calculations of recombination rates for cold 4He atoms from atom-dimer phase shifts and determination of universal scaling functions

    International Nuclear Information System (INIS)

    Shepard, J. R.

    2007-01-01

    Three-body recombination rates for cold 4 He are calculated with a method which exploits the simple relationship between the imaginary part of the atom-dimer elastic scattering phase shift and the S-matrix for recombination. The elastic phase shifts are computed above breakup threshold by solving a three-body Faddeev equation in momentum space with inputs based on a variety of modern atom-atom potentials. Recombination coefficients for the HFD-B3-FCII potential agree very well with the only previously published results. Since the elastic scattering and recombination processes for 4 He are governed by 'Efimov physics', they depend on universal functions of a scaling variable. The computed recombination coefficients for potentials other than HFD-B3-FCII make it possible to determine these universal functions

  17. ARECIBO MULTI-EPOCH H I ABSORPTION MEASUREMENTS AGAINST PULSARS: TINY-SCALE ATOMIC STRUCTURE

    International Nuclear Information System (INIS)

    Stanimirovic, S.; Weisberg, J. M.; Pei, Z.; Tuttle, K.; Green, J. T.

    2010-01-01

    We present results from multi-epoch neutral hydrogen (H I) absorption observations of six bright pulsars with the Arecibo telescope. Moving through the interstellar medium (ISM) with transverse velocities of 10-150 AU yr -1 , these pulsars have swept across 1-200 AU over the course of our experiment, allowing us to probe the existence and properties of the tiny-scale atomic structure (TSAS) in the cold neutral medium (CNM). While most of the observed pulsars show no significant change in their H I absorption spectra, we have identified at least two clear TSAS-induced opacity variations in the direction of B1929+10. These observations require strong spatial inhomogeneities in either the TSAS clouds' physical properties themselves or else in the clouds' galactic distribution. While TSAS is occasionally detected on spatial scales down to 10 AU, it is too rare to be characterized by a spectrum of turbulent CNM fluctuations on scales of 10 1 -10 3 AU, as previously suggested by some work. In the direction of B1929+10, an apparent correlation between TSAS and interstellar clouds inside the warm Local Bubble (LB) indicates that TSAS may be tracing the fragmentation of the LB wall via hydrodynamic instabilities. While similar fragmentation events occur frequently throughout the ISM, the warm medium surrounding these cold cloudlets induces a natural selection effect wherein small TSAS clouds evaporate quickly and are rare, while large clouds survive longer and become a general property of the ISM.

  18. Two-dimensional nanowires on homoepitaxial interfaces: Atomic-scale mechanism of breakdown and disintegration

    Science.gov (United States)

    Michailov, Michail; Ranguelov, Bogdan

    2018-03-01

    We present a model for hole-mediated spontaneous breakdown of ahomoepitaxial two-dimensional (2D) flat nanowire based exclusively on random, thermally-activated motion of atoms. The model suggests a consecutive three-step mechanism driving the rupture and complete disintegration of the nanowire on a crystalline surface. The breakdown scenario includes: (i) local narrowing of a part of the stripe to a monatomic chain, (ii) formation of a recoverable single vacancy or a 2D vacancy cluster that causes temporary nanowire rupture, (iii) formation of a non-recoverable 2D hole leading to permanent nanowire breakdown. These successive events in the temporal evolution of the nanowire morphology bring the nanowire stripe into an irreversible unstable state, leading to a dramatic change in its peculiar physical properties and conductivity. The atomistic simulations also reveal a strong increase of the nanowire lifetime with an enlargement of its width and open up a way for a fine atomic-scale control of the nanowire lifetime and structural, morphological and thermodynamic stability.

  19. Fabrication of atomic-scale gold junctions by electrochemical plating using a common medical liquid

    Science.gov (United States)

    Umeno, A.; Hirakawa, K.

    2005-04-01

    Fabrication of nanometer-separated gold junctions has been performed using "iodine tincture," a medical liquid known as a disinfectant, as an etching/deposition electrolyte. In the gold-dissolved iodine tincture, gold electrodes were grown or eroded slowly enough to form quantum point contacts in an atomic scale. The resistance evolution during the electrochemical deposition showed plateaus at integer multiples of the resistance quantum, (2e2/h)-1, at room temperature (e: the elementary charge, h: the Planck constant). Iodine tincture is a commercially available common material, which makes the fabrication process to be simple and cost effective. Moreover, in contrast to the conventional electrochemical approaches, this method is free from highly toxic cyanide compounds or extraordinarily strong acids.

  20. Atomic-scale Ge diffusion in strained Si revealed by quantitative scanning transmission electron microscopy

    Science.gov (United States)

    Radtke, G.; Favre, L.; Couillard, M.; Amiard, G.; Berbezier, I.; Botton, G. A.

    2013-05-01

    Aberration-corrected scanning transmission electron microscopy is employed to investigate the local chemistry in the vicinity of a Si0.8Ge0.2/Si interface grown by molecular-beam epitaxy. Atomic-resolution high-angle annular dark field contrast reveals the presence of a nonuniform diffusion of Ge from the substrate into the strained Si thin film. On the basis of multislice calculations, a model is proposed to quantify the experimental contrast, showing that the Ge concentration in the thin film reaches about 4% at the interface and decreases monotonically on a typical length scale of 10 nm. Diffusion occurring during the growth process itself therefore appears as a major factor limiting the abruptness of interfaces in the Si-Ge system.

  1. High frequency measurements of shot noise suppression in atomic-scale metal contacts

    Science.gov (United States)

    Wheeler, Patrick J.; Evans, Kenneth; Russom, Jeffrey; King, Nicholas; Natelson, Douglas

    2009-03-01

    Shot noise provides a means of assessing the number and transmission coefficients of transmitting channels in atomic- and molecular-scale junctions. Previous experiments at low temperatures in metal and semiconductor point contacts have demonstrated the expected suppression of shot noise when junction conductance is near an integer multiple of the conductance quantum, G0≡2e^2/h. Using high frequency techniques, we demonstrate the high speed acquisition of such data at room temperature in mechanical break junctions. In clean Au contacts conductance histograms with clear peaks at G0, 2G0, and 3G0 are acquired within hours, and histograms of simultaneous measurements of the shot noise show clear suppression at those conductance values. We describe the dependence of the noise on bias voltage and analyze the noise vs. conductance histograms in terms of a model that averages over transmission coefficients.

  2. Atomic scale properties of magnetic Mn-based alloys probed by emission Mössbauer spectroscopy

    CERN Multimedia

    Mn-based alloys are characterized by a wealth of properties, which are of interest both from fundamental physics point of view and particularly attractive for different applications in modern technology: from magnetic storage to sensing and spin-based electronics. The possibility to tune their magnetic properties through post-growth thermal processes and/or stoichiometry engineering is highly important in order to target different applications (i.e. Mn$_{x}$Ga) or to increase their Curie temperature above room temperature (i.e. off-stoichiometric MnSi). In this project, the Mössbauer effect will be applied at $^{57}$Fe sites following implantation of radioactive $^{57}$Mn, to probe the micro-structure and magnetism of Mn-based alloys on the atomic-scale. The proposed experimental plan is devoted to establish a direct correlation between the local structure and bulk magnetism (and other physical properties) of Mn-based alloys.

  3. Hydrogen atom temperature measured with wavelength-modulated laser absorption spectroscopy in large scale filament arc negative hydrogen ion source

    International Nuclear Information System (INIS)

    Nakano, H.; Goto, M.; Tsumori, K.; Kisaki, M.; Ikeda, K.; Nagaoka, K.; Osakabe, M.; Takeiri, Y.; Kaneko, O.; Nishiyama, S.; Sasaki, K.

    2015-01-01

    The velocity distribution function of hydrogen atoms is one of the useful parameters to understand particle dynamics from negative hydrogen production to extraction in a negative hydrogen ion source. Hydrogen atom temperature is one of the indicators of the velocity distribution function. To find a feasibility of hydrogen atom temperature measurement in large scale filament arc negative hydrogen ion source for fusion, a model calculation of wavelength-modulated laser absorption spectroscopy of the hydrogen Balmer alpha line was performed. By utilizing a wide range tunable diode laser, we successfully obtained the hydrogen atom temperature of ∼3000 K in the vicinity of the plasma grid electrode. The hydrogen atom temperature increases as well as the arc power, and becomes constant after decreasing with the filling of hydrogen gas pressure

  4. Quantum Mechanical Study of Atoms and Molecules

    Science.gov (United States)

    Sahni, R. C.

    1961-01-01

    This paper, following a brief introduction, is divided into five parts. Part I outlines the theory of the molecular orbital method for the ground, ionized and excited states of molecules. Part II gives a brief summary of the interaction integrals and their tabulation. Part III outlines an automatic program designed for the computation of various states of molecules. Part IV gives examples of the study of ground, ionized and excited states of CO, BH and N2 where the program of automatic computation and molecular integrals have been utilized. Part V enlists some special problems of Molecular Quantum Mechanics are being tackled at New York University.

  5. Fine structure studies of terbium atoms

    International Nuclear Information System (INIS)

    Abhay Kumar; Bandyopadhyay, Krishnanath; Niraj Kumar

    2012-01-01

    Terbium (Z = 65) is a typical rare-earth element. Fine structure of spectural lines of terbium (Tb) are presented using the laser optogalvanic spectroscopic technique. Altogether eighty transitions in the 5686-6367 A range have been observed in the fine structure spectrum of 159 Tb. Wavelengths of all the observed transitions have been determined. Out of 80 transitions of Tb, a total of 59 transitions are being reported for the first time. Classifications of 39 new transitions have been provided using the known energy levels, Doppler-limited optogalvanic spectroscopic technique is employed to study the fine structure (fs) 159 Tb. (author)

  6. Atomic-scale investigations of grain boundary segregation in astrology with a three dimensional atom-probe

    Energy Technology Data Exchange (ETDEWEB)

    Blavette, D. [Rouen Univ., 76 - Mont-Saint-Aignan (France). Lab. de Microscopie Electronique]|[Institut Universitaire de France (France); Letellier, L. [Rouen Univ., 76 - Mont-Saint-Aignan (France). Lab. de Microscopie Electronique; Duval, P. [Rouen Univ., 76 - Mont-Saint-Aignan (France). Lab. de Microscopie Electronique; Guttmann, M. [Rouen Univ., 76 - Mont-Saint-Aignan (France). Lab. de Microscopie Electronique]|[Institut de Recherches de la Siderurgie Francaise (IRSID), 57 - Maizieres-les-Metz (France)

    1996-08-01

    Both conventional and 3D atom-probes were applied to the investigation of grain-boundary (GB) segregation phenomena in two-phase nickel base superalloys Astroloy. 3D images as provided by the tomographic atom-probe reveal the presence of a strong segregation of both boron and molybdenum at grain-boundaries. Slight carbon enrichment is also detected. Considerable chromium segregation is exhibited at {gamma}`-{gamma}` grain-boundaries. All these segregants are distributed in a continuous manner along the boundary over a width close to 0.5 nm. Experiments show that segregation occurs during cooling and more probably between 1000 C and 800 C. Boron and molybdenum GB enrichments are interpreted as due to an equilibrium type-segregation while chromium segregation is thought to be induced by {gamma}` precipitation at GB`s and stabilised by the presence of boron. No segregation of zirconium is detected. (orig.)

  7. Aging studies in atomic bomb survivors

    International Nuclear Information System (INIS)

    Belsky, J.L.; Moriyama, I.M.; Fujita, Seiichiro; Kawamoto, Sadahisa.

    1980-01-01

    Though acceleration of aging induced by radiation could not be demonstrated in many investigations on delayed effects of ionizing radiation on a-bomb survivors, studies on acceleration of aging after the exposure to ionizing radiation in human and animals have been carried out. To investigate whether physiological function was related to the exposure to ionizing radiation, a series of examinations concerning age was carried out at the time of general health examinations at ABCC. Simple examinations concerning aging were carried out on 11,351 a-bomb survivors, but the result was essentially negative. If biological or physiological age was defined clearly, the results of functional test would be used as criterion of aging. (Tsunoda, M.)

  8. How grain boundaries affect the efficiency of poly-CdTe solar-cells: A fundamental atomic-scale study of grain boundary dislocation cores using CdTe bi-crystal thin films.

    Energy Technology Data Exchange (ETDEWEB)

    Klie, Robert [Univ. of Illinois, Chicago, IL (United States)

    2016-10-25

    It is now widely accepted that grain boundaries in poly-crystalline CdTe thin film devices have a detrimental effect on the minority carrier lifetimes, the open circuit voltage and therefore the overall solar-cell performance. The goal of this project was to develop a fundamental understanding of the role of grain boundaries in CdTe on the carrier life-time, open-circuit voltage, Voc, and the diffusion of impurities. To achieve this goal, i) CdTe bi-crystals were fabricated with various misorientation angels, ii) the atomic- and electronic structures of the grain boundaries were characterized using scanning transmission electron microscopy (STEM), and iii) first-principles density functional theory modeling was performed on the structures determined by STEM to predict the grain boundary potential. The transport properties and minority carrier lifetimes of the bi-crystal grain boundaries were measured using a variety of approaches, including TRPL, and provided feedback to the characterization and modeling effort about the effectiveness of the proposed models.

  9. The softness of an atom in a molecule and a functional group softness definition; an LCAO scale

    International Nuclear Information System (INIS)

    Giambiagi, M.; Giambiagi, M.S. de; Pires, J.M.; Pitanga, P.

    1987-01-01

    We introduce a scale for the softness of an atom in different molecules and we similarly define a functional group softness. These definitions, unlike previous ones, are not tied to the finite difference approximation neither, hence, to valence state ionization potentials and electron affinities; they result from the LCAO calculation itself. We conclude that a) the softness of an atom in a molecule shows wide variations; b) the geometric average of the softnesses of the atoms in the molecule gives the most consistent results for the molecular softnesses; c) the functional group softness is transferable within a homologous series. (Author) [pt

  10. Atomic scale imaging of structural changes in solid electrolyte lanthanum lithium niobate upon annealing

    International Nuclear Information System (INIS)

    Hu, Xiaobing; Fisher, Craig A.J.; Kobayashi, Shunsuke; Ikuhara, Yumi H.; Fujiwara, Yasuyuki; Hoshikawa, Keigo; Moriwake, Hiroki; Kohama, Keiichi; Iba, Hideki; Ikuhara, Yuichi

    2017-01-01

    La (1-x)/3 Li x NbO 3 (LLNbO) is a promising electrolyte material for solid-state lithium-ion batteries because it is stable in contact with Li metal and contains a high concentration of intrinsic Li-ion vacancies. One strategy for improving its ionic conductivity and making it more competitive with other solid-state Li-ion electrolytes is to disorder the Li-ion vacancies by appropriate post-synthesis heat treatment, e.g., annealing. In this study, we examine the effects of annealing on single crystals of LLNbO with Li contents x = 0.07 and 0.13 based on simultaneous atomic resolution high angle annular dark field and annular bright field imaging methods using state-of-the-art aberration corrected scanning transmission electron microscopes. It is found that La modulation within A1 layers of the cation-deficient layered perovskite structure becomes more diffuse after annealing. In addition, some La atoms move to A-site positions and O4 window positions in the nominally vacant A2 layer, while O atom columns in this layer become rumpled in the [001] p direction, indicating that the NbO 6 octahedra are more heavily distorted after annealing. The observed crystal structure differences between as-prepared and annealed single crystals explain the drop in Li-ion conductivities of LLNbO single crystals after heat treatment.

  11. An Atomic Force Microscopical Study of the Synaptonemal Complex

    NARCIS (Netherlands)

    Putman, C.A.J.; Putman, C.A.J.; Dietrich, A.J.J.; de Grooth, B.G.; van Marle, J.; Heyting, C.; van Hulst, N.F.; Greve, Jan

    1993-01-01

    The chromosomal structure which is specific for meiosis, the synaptonemal complex (SC), plays a major role in chromosome pairing and the recombination of genetic material. The SC was studied using atomic force microscopy (AFM). The results of this study confirm the results of light and electron

  12. GRASP92: a package for large-scale relativistic atomic structure calculations

    Science.gov (United States)

    Parpia, F. A.; Froese Fischer, C.; Grant, I. P.

    2006-12-01

    of CSFs sharing the same quantum numbers is determined using the configuration-interaction (CI) procedure that results upon varying the expansion coefficients to determine the extremum of a variational functional. Radial functions may be determined by numerically solving the multiconfiguration Dirac-Fock (MCDF) equations that result upon varying the orbital radial functions or some subset thereof so as to obtain an extremum of the variational functional. Radial wavefunctions may also be determined using a screened hydrogenic or Thomas-Fermi model, although these schemes generally provide initial estimates for MCDF self-consistent-field (SCF) calculations. Transition properties for pairs of ASFs are computed from matrix elements of multipole operators of the electromagnetic field. All matrix elements of CSFs are evaluated using the Racah algebra. Reasons for the new version: During recent studies using the general relativistic atomic structure package (GRASP92), several errors were found, some of which might have been present already in the earlier GRASP92 version (program ABJN_v1_0, Comput. Phys. Comm. 55 (1989) 425). These errors were reported and discussed by Froese Fischer, Gaigalas, and Ralchenko in a separate publication [C. Froese Fischer, G. Gaigalas, Y. Ralchenko, Comput. Phys. Comm. 175 (2006) 738-744. [7

  13. Towards the atomic-scale characterization of isolated iron sites confined in a nitrogen-doped graphene matrix

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Qingfei; Liu, Yun; Li, Haobo [State Key Laboratory of Catalysis, CAS Center for Excellence in Nanoscience, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China); University of Chinese Academy of Sciences, Beijing, 100039 (China); Li, Lulu [College of Chemistry, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian, 116023 (China); Deng, Dehui [State Key Laboratory of Catalysis, CAS Center for Excellence in Nanoscience, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China); Yang, Fan, E-mail: fyang@dicp.ac.cn [State Key Laboratory of Catalysis, CAS Center for Excellence in Nanoscience, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China); Bao, Xinhe, E-mail: xhbao@dicp.ac.cn [State Key Laboratory of Catalysis, CAS Center for Excellence in Nanoscience, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China)

    2017-07-15

    Highlights: • Local atomic and electronic structure of the Fe-N-C catalyst characterized by STM and STS. • The combination of air-AFM, UHV-STM and DFT calculations for the characterization of powder catalysts. • The selection of solvent is vital to the homogeneous dispersion of powder catalyst on a planar support. - Abstract: Atomic scale characterization of the surface structure of powder catalysts is essential to the identification of active sites, but remains a major challenge in catalysis research. We described here a procedure that combines atomic force microscopy (AFM), operated in air, and scanning tunneling microscopy (STM), operated in UHV, to obtain the atomic structure and local electronic properties of powder catalysts. The atomically dispersed Fe-N-C catalyst was used as an example, which was synthesized by low temperature ball milling methods. We discussed the effect of solvents in the dispersion of powder catalysts on a planar support, which is key to the subsequent atomic characterization. From the morphology, atomic structure and local electronic properties of the Fe-N-C catalyst, our combined measurements also provide an insight for the effect of ball milling in the preparation of atomically dispersed metal catalysts.

  14. Large scale nuclear structure studies

    International Nuclear Information System (INIS)

    Faessler, A.

    1985-01-01

    Results of large scale nuclear structure studies are reported. The starting point is the Hartree-Fock-Bogoliubov solution with angular momentum and proton and neutron number projection after variation. This model for number and spin projected two-quasiparticle excitations with realistic forces yields in sd-shell nuclei similar good results as the 'exact' shell-model calculations. Here the authors present results for a pf-shell nucleus 46 Ti and results for the A=130 mass region where they studied 58 different nuclei with the same single-particle energies and the same effective force derived from a meson exchange potential. They carried out a Hartree-Fock-Bogoliubov variation after mean field projection in realistic model spaces. In this way, they determine for each yrast state the optimal mean Hartree-Fock-Bogoliubov field. They apply this method to 130 Ce and 128 Ba using the same effective nucleon-nucleon interaction. (Auth.)

  15. Assessment of current atomic scale modelling methods for the investigation of nuclear fuels under irradiation: Example of uranium dioxide

    International Nuclear Information System (INIS)

    Bertolus, M.; Freyss, M.; Krack, M.; Devanathan, R.

    2015-01-01

    We focus here on the assessment of the description of interatomic interactions in uranium dioxide using, on the one hand, electronic structure methods, in particular in the Density Functional Theory (DFT) framework, and on the other hand, empirical potential methods. These two types of methods are complementary, the former enabling results to be obtained from a minimal amount of input data and further insight into the electronic and magnetic properties to be achieved, while the latter are irreplaceable for studies where a large number of atoms need to be considered. We consider basic properties as well as specific ones, which are important for the description of nuclear fuel under irradiation. These are especially energies, which are the main data passed on to higher scale models. For this exercise, we limit ourselves to uranium dioxide (UO 2 ) because of the extensive amount of studies available on this system. (authors)

  16. Near relativistic study of binded levels in atoms. Application to alkaline atoms

    International Nuclear Information System (INIS)

    Varade, A.; Delgado-Barrio, G.; Villarreal, P.

    1985-01-01

    A model is described for the calculation of the atomic binding energies. The Pauli equation has been solved with a local potential. The results for alkaline atoms are reported here and compared with the perturbative calculation and experimental data. (author)

  17. Molecular dynamics study of atomic displacements in disordered solid alloys

    Science.gov (United States)

    Puzyrev, Yevgeniy S.

    The effects of atomic displacements on the energetics of alloys plays important role in the determining the properties of alloys. We studied the atomic displacements in disordered solid alloys using molecular dynamics and Monte-Carlo methods. The diffuse scattering of pure materials, copper, gold, nickel, and palladium was calculated. The experimental data for pure Cu was obtained from diffuse scattering intensity of synchrotron x-ray radiation. The comparison showed the advantages of molecular dynamics method for calculating the atomic displacements in solid alloys. The individual nearest neighbor separations were calculated for Cu 50Au50 alloy and compared to the result of XAFS experiment. The molecular dynamics method provided theoretical predictions of nearest neighbor pair separations in other binary alloys, Cu-Pd and Cu-Al for wide range of the concentrations. We also experimentally recovered the diffuse scattering maps for the Cu47.3Au52.7 and Cu85.2Al14.8 alloy.

  18. Detection and control of broken symmetries with Andreev bound state tunneling spectroscopy: effects of atomic-scale disorder

    International Nuclear Information System (INIS)

    Greene, L.H.; Hentges, P.J.; Aubin, H.; Aprili, M.; Badica, E.; Covington, M.; Pafford, M.M.; Westwood, G.; Klemperer, W.G.; Jian, Sha; Hinks, D.G.

    2004-01-01

    Quasiparticle planar tunneling spectroscopy is used to study unconventional superconductivity in YBa 2 Cu 3 O 7 (YBCO) thin films and Bi 2 Sr 2 CaCu 2 O 8 (BSCCO) single crystals. Tunneling conductances are obtained as a function of crystallographic orientation, applied magnetic field (magnitude and orientation), atomic substitution and surface damage. Our systematic studies confirm that the observed zero-bias conductance peak (ZBCP), a measure of the near-surface quasiparticle (QP) density of states (DoS), is comprised of Andreev bound states (ABS) resulting directly from the sign change of the d-wave order parameter (OP) at the Fermi surface. Our data, plus a literature search, reveals a consistency in the observation of the splitting of the ZBCP in optimally-doped materials. We note that the splitting of the ZBCP observed in applied field, and the spontaneous splitting observed at lower temperatures in zero field, occur concomitantly in a given junction, and that observation of this splitting is dependent upon two parameters: (1) the magnitude of the tunneling cone and (2) the degree of atomic-scale disorder at the interface

  19. [Study on lead absorption in pumpkin by atomic absorption spectrophotometry].

    Science.gov (United States)

    Li, Zhen-Xia; Sun, Yong-Dong; Chen, Bi-Hua; Li, Xin-Zheng

    2008-07-01

    A study was carried out on the characteristic of lead absorption in pumpkin via atomic absorption spectrophotometer. The results showed that lead absorption amount in pumpkin increased with time, but the absorption rate decreased with time; And the lead absorption amount reached the peak in pH 7. Lead and cadmium have similar characteristic of absorption in pumpkin.

  20. Consequences of atomic layer etching on wafer scale uniformity in inductively coupled plasmas

    Science.gov (United States)

    Huard, Chad M.; Lanham, Steven J.; Kushner, Mark J.

    2018-04-01

    Atomic layer etching (ALE) typically divides the etching process into two self-limited reactions. One reaction passivates a single layer of material while the second preferentially removes the passivated layer. As such, under ideal conditions the wafer scale uniformity of ALE should be independent of the uniformity of the reactant fluxes onto the wafers, provided all surface reactions are saturated. The passivation and etch steps should individually asymptotically saturate after a characteristic fluence of reactants has been delivered to each site. In this paper, results from a computational investigation are discussed regarding the uniformity of ALE of Si in Cl2 containing inductively coupled plasmas when the reactant fluxes are both non-uniform and non-ideal. In the parameter space investigated for inductively coupled plasmas, the local etch rate for continuous processing was proportional to the ion flux. When operated with saturated conditions (that is, both ALE steps are allowed to self-terminate), the ALE process is less sensitive to non-uniformities in the incoming ion flux than continuous etching. Operating ALE in a sub-saturation regime resulted in less uniform etching. It was also found that ALE processing with saturated steps requires a larger total ion fluence than continuous etching to achieve the same etch depth. This condition may result in increased resist erosion and/or damage to stopping layers using ALE. While these results demonstrate that ALE provides increased etch depth uniformity, they do not show an improved critical dimension uniformity in all cases. These possible limitations to ALE processing, as well as increased processing time, will be part of the process optimization that includes the benefits of atomic resolution and improved uniformity.

  1. Previsions of the microstructural evolution of ferritic alloys under irradiation by numerical atomic scale simulations

    International Nuclear Information System (INIS)

    Ngayam Happy, R.

    2010-01-01

    In this work, we have improved a diffusion model for point defects (vacancies and self-interstitials) by introducing hetero-interstitials. The model has been used to simulate by Kinetic Monte Carlo (KMC) the formation of solute rich clusters that are observed experimentally in irradiated ferritic model alloys of type Fe - CuMnNiSiP - C.Electronic structure calculations have been used to characterize the interactions between self-interstitials and all solute atoms, and also carbon. P interacts with vacancies and strongly with self-interstitials. Mn also interacts with self-interstitials to form mixed dumbbells. C, with occupies octahedral sites, interacts strongly with vacancies and less with self-interstitials. Binding and migration energies, as well as others atomic scale properties, obtained by ab initio calculations, have been used as parameters for the KMC code. Firstly, these parameters have been optimized over isochronal annealing experiments, in the literature, of binary alloys that have been electron-irradiated. Isochronal annealing simulations, by reproducing experimental results, have allowed us to link each mechanism to a single evolution of the resistivity during annealing. Moreover, solubility limits of all the elements have been determined by Metropolis Monte Carlo. Secondly, we have simulated the evolution at 300 C of the microstructure under irradiation of different alloys of increasing complexity: pure Fe, binary alloys, ternaries, quaternaries, and finally complex alloys which compositions are close to those of pressure vessel steels. The results show that the model globally reproduces all the experimental tendencies, what has led us to propose mechanisms to explain the behaviours observed. (author)

  2. Plasticity analysis of nano-grain-sized NiAl alloy in an atomic scale

    International Nuclear Information System (INIS)

    Wang Jingyang; Wang Xiaowei; Rifkin, J.; Li Douxing

    2001-12-01

    The molecular dynamics method is used to simulate a uniaxial tensile deformation of 3.8nm nano-NiAl alloy with curved amorphous-like interfaces at 0K. Plastic deformation behaviour is studied by examining the strain-stress relationship and the microstructural evolution characteristic. Atomic level analysis showed that the micro-strain is essentially heterogeneous in simulated nano-phase samples. The plastic deformation is not only attributed to the plasticity of interfaces, but also accompanied with the plastic shear strain mechanism inside lattice distortion regions and grains. (author)

  3. The Atomic Energy of Canada Limited (AECL) employee health study

    International Nuclear Information System (INIS)

    Weeks, J.L.

    1985-01-01

    The Atomic Energy Health Study formally began in April 1980. The purpose of the study is to determine the causes of death among a population of radiation workers and to compare this information with data available for the causes of death in the general population. The study population and the implementation are briefly discussed. The aim of the study is to determine the real occupational risk of being a radiation worker. 3 refs

  4. Nanometer-scale isotope analysis of bulk diamond by atom probe tomography

    NARCIS (Netherlands)

    Schirhagl, R.; Raatz, N.; Meijer, J.; Markham, M.; Gerstl, S. S. A.; Degen, C. L.

    2015-01-01

    Atom-probe tomography (APT) combines field emission of atoms with mass spectrometry to reconstruct three-dimensional tomograms of materials with atomic resolution and isotope specificity. Despite significant recent progress in APT technology, application to wide-bandgap materials with strong

  5. Phonon interference control of atomic-scale metamirrors, meta-absorbers, and heat transfer through crystal interfaces

    Science.gov (United States)

    Kosevich, Yu. A.; Potyomina, L. G.; Darinskii, A. N.; Strelnikov, I. A.

    2018-03-01

    The paper theoretically studies the possibility of using the effects of phonon interference between paths through different interatomic bonds for the control of phonon heat transfer through internal crystal interfaces and for the design of phonon metamirrors and meta-absorbers. These metamirrors and meta-absorbers are considered to be defect nanolayers of atomic-scale thicknesses embedded in a crystal. Several analytically solvable three-dimensional lattice-dynamics models of the phonon metamirrors and meta-absorbers at the internal crystal planes are described. It is shown that due to destructive interference in the two or more phonon paths, the internal crystal planes, fully or partially filled with weakly bound or heavy-isotope defect atoms, can completely reflect or completely absorb phonons at the transmission antiresonances, whose wavelengths are larger than the effective thickness of the metamirror or meta-absorber. Due to cooperative superradiant effect, the spectral widths of the two-path interference antiresonances for the plane waves are given by the square of partial filling fraction in the defect crystal plane. Our analysis reveals that the presence of two or more phonon paths plays the dominant role in the emergence of the transmission antiresonances in phonon scattering at the defect crystal planes and in reduction of the thermal interface conductance in comparison with the Fano-resonance concept. We study analytically phonon transmission through internal crystal plane in a model cubic lattice of Si-like atoms, partially filled with Ge-like defect atoms. Such a plane can serve as interference phonon metamirror with the transmission antiresonances in the vicinities of eigenmode frequencies of Ge-like defect atoms in the terahertz frequency range. We predict the extraordinary phonon transmission induced by the two-path constructive interference of the lattice waves in resonance with the vibrations of rare host atoms, periodically distributed in the

  6. Modeling the effects of cohesive energy for single particle on the material removal in chemical mechanical polishing at atomic scale

    International Nuclear Information System (INIS)

    Wang Yongguang; Zhao Yongwu; An Wei; Wang Jun

    2007-01-01

    This paper proposes a novel mathematical model for chemical mechanical polishing (CMP) based on interface solid physical and chemical theory in addition to energy equilibrium knowledge. And the effects of oxidation concentration and particle size on the material removal in CMP are investigated. It is shown that the mechanical energy and removal cohesive energy couple with the particle size, and being a cause of the non-linear size-removal rate relation. Furthermore, it also shows a nonlinear dependence of removal rate on removal cohesive energy. The model predictions are in good qualitative agreement with the published experimental data. The current study provides an important starting point for delineating the micro-removal mechanism in the CMP process at atomic scale

  7. Atomic and nano-scale characterization of a 50-year-old hydrated C3S paste

    KAUST Repository

    Geng, Guoqing

    2015-07-15

    This paper investigates the atomic and nano-scale structures of a 50-year-old hydrated alite paste. Imaged by TEM, the outer product C-S-H fibers are composed of particles that are 1.5-2 nm thick and several tens of nanometers long. 29Si NMR shows 47.9% Q1 and 52.1% Q2, with a mean SiO4 tetrahedron chain length (MCL) of 4.18, indicating a limited degree of polymerization after 50 years\\' hydration. A Scanning Transmission X-ray Microscopy (STXM) study was conducted on this late-age paste and a 1.5 year old hydrated C3S solution. Near Edge X-ray Absorption Fine Structure (NEXAFS) at Ca L3,2-edge indicates that Ca2 + in C-S-H is in an irregular symmetric coordination, which agrees more with the atomic structure of tobermorite than that of jennite. At Si K-edge, multi-scattering phenomenon is sensitive to the degree of polymerization, which has the potential to unveil the structure of the SiO44 - tetrahedron chain. © 2015 Elsevier Ltd. All rights reserved.

  8. Atomic and nano-scale characterization of a 50-year-old hydrated C3S paste

    KAUST Repository

    Geng, Guoqing; Taylor, Rae; Bae, Sungchul; Herná ndez-Cruz, Daniel; Kilcoyne, David A.; Emwas, Abdul-Hamid M.; Monteiro, Paulo J M

    2015-01-01

    This paper investigates the atomic and nano-scale structures of a 50-year-old hydrated alite paste. Imaged by TEM, the outer product C-S-H fibers are composed of particles that are 1.5-2 nm thick and several tens of nanometers long. 29Si NMR shows 47.9% Q1 and 52.1% Q2, with a mean SiO4 tetrahedron chain length (MCL) of 4.18, indicating a limited degree of polymerization after 50 years' hydration. A Scanning Transmission X-ray Microscopy (STXM) study was conducted on this late-age paste and a 1.5 year old hydrated C3S solution. Near Edge X-ray Absorption Fine Structure (NEXAFS) at Ca L3,2-edge indicates that Ca2 + in C-S-H is in an irregular symmetric coordination, which agrees more with the atomic structure of tobermorite than that of jennite. At Si K-edge, multi-scattering phenomenon is sensitive to the degree of polymerization, which has the potential to unveil the structure of the SiO44 - tetrahedron chain. © 2015 Elsevier Ltd. All rights reserved.

  9. Probing and Manipulating the Interfacial Defects of InGaAs Dual-Layer Metal Oxides at the Atomic Scale.

    Science.gov (United States)

    Wu, Xing; Luo, Chen; Hao, Peng; Sun, Tao; Wang, Runsheng; Wang, Chaolun; Hu, Zhigao; Li, Yawei; Zhang, Jian; Bersuker, Gennadi; Sun, Litao; Pey, Kinleong

    2018-01-01

    The interface between III-V and metal-oxide-semiconductor materials plays a central role in the operation of high-speed electronic devices, such as transistors and light-emitting diodes. The high-speed property gives the light-emitting diodes a high response speed and low dark current, and they are widely used in communications, infrared remote sensing, optical detection, and other fields. The rational design of high-performance devices requires a detailed understanding of the electronic structure at this interface; however, this understanding remains a challenge, given the complex nature of surface interactions and the dynamic relationship between the morphology evolution and electronic structures. Herein, in situ transmission electron microscopy is used to probe and manipulate the structural and electrical properties of ZrO 2 films on Al 2 O 3 and InGaAs substrate at the atomic scale. Interfacial defects resulting from the spillover of the oxygen-atom conduction-band wavefunctions are resolved. This study unearths the fundamental defect-driven interfacial electric structure of III-V semiconductor materials and paves the way to future high-speed and high-reliability devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Atomic and nano-scale characterization of a 50-year-old hydrated C3S paste

    International Nuclear Information System (INIS)

    Geng, Guoqing; Taylor, Rae; Bae, Sungchul; Hernández-Cruz, Daniel; Kilcoyne, David A.; Emwas, Abdul-Hamid; Monteiro, Paulo J.M.

    2015-01-01

    This paper investigates the atomic and nano-scale structures of a 50-year-old hydrated alite paste. Imaged by TEM, the outer product C–S–H fibers are composed of particles that are 1.5–2 nm thick and several tens of nanometers long. 29 Si NMR shows 47.9% Q 1 and 52.1% Q 2 , with a mean SiO 4 tetrahedron chain length (MCL) of 4.18, indicating a limited degree of polymerization after 50 years' hydration. A Scanning Transmission X-ray Microscopy (STXM) study was conducted on this late-age paste and a 1.5 year old hydrated C 3 S solution. Near Edge X-ray Absorption Fine Structure (NEXAFS) at Ca L 3,2 -edge indicates that Ca 2+ in C–S–H is in an irregular symmetric coordination, which agrees more with the atomic structure of tobermorite than that of jennite. At Si K-edge, multi-scattering phenomenon is sensitive to the degree of polymerization, which has the potential to unveil the structure of the SiO 4 4− tetrahedron chain.

  11. Comparative studies of atomic independent-particle potentials

    International Nuclear Information System (INIS)

    Talman, J.D.; Ganas, P.S.; Green, A.E.S.

    1979-01-01

    A number of atomic properties are compared in various independent-particle models for atoms. The models studied are the Hartree-Fock method, a variationally optimized potential model, a parametrized analytic form of the same model, parametrized analytic models constructed to fit atomic energy levels, the so-called Hartree-Fock-Slater model, and the Xα model. The physical properties compared are single-particle energy levels, total energies, and dipole polarizabilities. The extent to which the virial theorem is satisfied in the different models is also considered. The atoms Be, Ne, Ar, Kr, and Xe and ions O v and Al iv hav been compared. The results show that the experimental properties can be well represented by several of the independent-particle models. Since it has been shown that the optimized potential models yield wavefunctions that are almost the same as Hartree-Fock wavefunctions, they provide a natural solution to the problem of extending the Hartree-Fock method to excited states

  12. Periodic order and defects in Ni-based inverse opal-like crystals on the mesoscopic and atomic scale

    NARCIS (Netherlands)

    Chumakova, A. V.; Valkovskiy, G. A.; Mistonov, A. A.; Dyadkin, V. A.; Grigoryeva, N. A.; Sapoletova, N. A.; Napolskii, K. S.; Eliseev, A. A.; Petukhov, Andrei V.; Grigoriev, S. V.

    2014-01-01

    The structure of inverse opal crystals based on nickel was probed on the mesoscopic and atomic levels by a set of complementary techniques such as scanning electron microscopy and synchrotron microradian and wide-angle diffraction. The microradian diffraction revealed the mesoscopic-scale

  13. Atomic-scale structure of self-assembled In(Ga)As quantum rings in GaAs

    NARCIS (Netherlands)

    Offermans, P.; Koenraad, P.M.; Wolter, J.H.; Granados, D.; Garcia, J.M.; Fomin, V.; Gladilin, V.N.; Devreese, J.T.

    2005-01-01

    We present an atomic-scale analysis of the indium distribution of self-assembled In(Ga)As quantum rings (QRs) which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. We find that the size and shape of QRs as observed by cross-sectional scanning

  14. The geopotential value W 0 for specifying the relativistic atomic time scale and a global vertical reference system

    Czech Academy of Sciences Publication Activity Database

    Burša, Milan; Kenyon, S.; Kouba, J.; Šíma, Zdislav; Vatrt, V.; Vítek, V.; Vojtíšková, M.

    2007-01-01

    Roč. 81, č. 2 (2007), s. 103-110 ISSN 0949-7714 R&D Projects: GA ČR GA205/05/2381 Institutional research plan: CEZ:AV0Z10030501 Keywords : geopotential * vertical datum unification * relativistic atomic time scale Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.636, year: 2007

  15. SOME SPECIATION STUDIES IN FOODSTUFF BY ATOMIC ABSORPTION SPECTROMETRY

    OpenAIRE

    Gücer, S

    2000-01-01

    There has been increasing interest in speciation studies of essentialelements in foods. The main limitation of this studies, their levels in foodsamples and the difficulties for the determination in their own differentforms without any changes in their original forms.Atomic Absorption Spectrometry (AAS) coupled with separation methodswould be outline in this presentation. Analytical scheme was given for tea, olive and garlic samples forManganese, Magnesium and Selenium respectively. Activated...

  16. Approximate symmetries in atomic nuclei from a large-scale shell-model perspective

    Science.gov (United States)

    Launey, K. D.; Draayer, J. P.; Dytrych, T.; Sun, G.-H.; Dong, S.-H.

    2015-05-01

    In this paper, we review recent developments that aim to achieve further understanding of the structure of atomic nuclei, by capitalizing on exact symmetries as well as approximate symmetries found to dominate low-lying nuclear states. The findings confirm the essential role played by the Sp(3, ℝ) symplectic symmetry to inform the interaction and the relevant model spaces in nuclear modeling. The significance of the Sp(3, ℝ) symmetry for a description of a quantum system of strongly interacting particles naturally emerges from the physical relevance of its generators, which directly relate to particle momentum and position coordinates, and represent important observables, such as, the many-particle kinetic energy, the monopole operator, the quadrupole moment and the angular momentum. We show that it is imperative that shell-model spaces be expanded well beyond the current limits to accommodate particle excitations that appear critical to enhanced collectivity in heavier systems and to highly-deformed spatial structures, exemplified by the second 0+ state in 12C (the challenging Hoyle state) and 8Be. While such states are presently inaccessible by large-scale no-core shell models, symmetry-based considerations are found to be essential.

  17. Universal scaling relations for the energies of many-electron Hooke atoms

    Science.gov (United States)

    Odriazola, A.; Solanpää, J.; Kylänpää, I.; González, A.; Räsänen, E.

    2017-04-01

    A three-dimensional harmonic oscillator consisting of N ≥2 Coulomb-interacting charged particles, often called a (many-electron) Hooke atom, is a popular model in computational physics for, e.g., semiconductor quantum dots and ultracold ions. Starting from Thomas-Fermi theory, we show that the ground-state energy of such a system satisfies a nontrivial relation: Eg s=ω N4 /3fg s(β N1 /2) , where ω is the oscillator strength, β is the ratio between Coulomb and oscillator characteristic energies, and fg s is a universal function. We perform extensive numerical calculations to verify the applicability of the relation. In addition, we show that the chemical potentials and addition energies also satisfy approximate scaling relations. In all cases, analytic expressions for the universal functions are provided. The results have predictive power in estimating the key ground-state properties of the system in the large-N limit, and can be used in the development of approximative methods in electronic structure theory.

  18. Direct imaging of atomic-scale ripples in few-layer graphene.

    Science.gov (United States)

    Wang, Wei L; Bhandari, Sagar; Yi, Wei; Bell, David C; Westervelt, Robert; Kaxiras, Efthimios

    2012-05-09

    Graphene has been touted as the prototypical two-dimensional solid of extraordinary stability and strength. However, its very existence relies on out-of-plane ripples as predicted by theory and confirmed by experiments. Evidence of the intrinsic ripples has been reported in the form of broadened diffraction spots in reciprocal space, in which all spatial information is lost. Here we show direct real-space images of the ripples in a few-layer graphene (FLG) membrane resolved at the atomic scale using monochromated aberration-corrected transmission electron microscopy (TEM). The thickness of FLG amplifies the weak local effects of the ripples, resulting in spatially varying TEM contrast that is unique up to inversion symmetry. We compare the characteristic TEM contrast with simulated images based on accurate first-principles calculations of the scattering potential. Our results characterize the ripples in real space and suggest that such features are likely common in ultrathin materials, even in the nanometer-thickness range.

  19. Quantized edge modes in atomic-scale point contacts in graphene

    Science.gov (United States)

    Kinikar, Amogh; Phanindra Sai, T.; Bhattacharyya, Semonti; Agarwala, Adhip; Biswas, Tathagata; Sarker, Sanjoy K.; Krishnamurthy, H. R.; Jain, Manish; Shenoy, Vijay B.; Ghosh, Arindam

    2017-07-01

    The zigzag edges of single- or few-layer graphene are perfect one-dimensional conductors owing to a set of gapless states that are topologically protected against backscattering. Direct experimental evidence of these states has been limited so far to their local thermodynamic and magnetic properties, determined by the competing effects of edge topology and electron-electron interaction. However, experimental signatures of edge-bound electrical conduction have remained elusive, primarily due to the lack of graphitic nanostructures with low structural and/or chemical edge disorder. Here, we report the experimental detection of edge-mode electrical transport in suspended atomic-scale constrictions of single and multilayer graphene created during nanomechanical exfoliation of highly oriented pyrolytic graphite. The edge-mode transport leads to the observed quantization of conductance close to multiples of G0 = 2e2/h. At the same time, conductance plateaux at G0/2 and a split zero-bias anomaly in non-equilibrium transport suggest conduction via spin-polarized states in the presence of an electron-electron interaction.

  20. Numerical studies of the g-hartree density functional in the Thomas-Fermi scaling limit

    International Nuclear Information System (INIS)

    Millack, T.; Weymans, G.

    1986-02-01

    Methods of finite temperature quantum field theory are used to construct the g-Hartree density functional for atoms. Low and high temperature expansions are discussed in detail. Numerical studies for atomic ground-state configurations are presented in the Thomas-Fermi-Scaling limit. (orig.)

  1. Hydride generation – in-atomizer collection of Pb in a quartz trap-and-atomizer device for atomic absorption spectrometry – an interference study

    Energy Technology Data Exchange (ETDEWEB)

    Novotný, Pavel [Institute of Analytical Chemistry of the ASCR, v.v.i., Veveří 97, 602 00 Brno (Czech Republic); High School in Hořice, Husova 1414, 508 01 Hořice (Czech Republic); Kratzer, Jan, E-mail: jkratzer@biomed.cas.cz [Institute of Analytical Chemistry of the ASCR, v.v.i., Veveří 97, 602 00 Brno (Czech Republic)

    2013-01-01

    Interferences of selected hydride forming elements (As, Sb, Bi, Se and Sn) on lead determination by hydride generation atomic absorption spectrometry were extensively studied in both on-line atomization and preconcentration (collection) modes. The commonly used on-line atomization mode was found free of significant interferences, whereas strong interference from Bi was observed when employing the preconcentration mode with plumbane collection in a quartz trap-and-atomizer device. Interference of Bi seems to take place in the preconcentration step. Interference of Bi in the collection mode cannot be reduced by increased hydrogen radical amount in the trap and/or the atomizer. - Highlights: ► Interference study on Pb determination by in-atomizer trapping was performed for the first time. ► Bi was found as a severe interferent in the preconcentration mode (Pb:Bi ratio 1:100). ► No interference was found in the on-line atomization (no preconcentration). ► Bi interference occurs during preconcentration.

  2. Studying the effect of Ruthenium on High Temperature Mechanical Properties of Nickel Based Superalloys and Determining the Universal Behavior of Ruthenium at Atomic Scale with respect to alloying elements, Stress and Temperature

    Directory of Open Access Journals (Sweden)

    Sriswaroop Dasari

    2016-10-01

    Full Text Available Any property of a material is a function of its microstructure and microstructure is a function of material composition. So, to maximize the desired properties of a material, one has to understand the evolution of microstructure which in turn is nothing but the reflection of the role of alloying elements. Research has not been done to understand the universal behavior of a certain base/alloying element. Let’s take the example of Cl- ion in HCl, we all know that in general, chloride ion can only be replaced by Fluoride or oxygen ion and that no other ion can replace it. But when you consider a metal like Ni, Co, Cr, Fe etc. there is no establishment that it behaves only in a certain way. Though I concord to the fact that discovery of universal behavior of Ni is lot complex than chloride ion, I think that future research should be focused in this direction also. Superalloys are the candidate materials required to improve thermal efficiency of a gas turbine by allowing higher turbine inlet gas temperatures. Gas turbines are the heart of local power systems, next generation jet engines and high performance space rockets. Recent research in superalloys showed that addition of some alloying elements in minor quantities can result in drastic change in properties. Such an alloying element is Ruthenium (Ru. Addition of Ruthenium to superalloys has shown improvement in mechanical properties by an order of magnitude. However reasons for such improvement are not known yet. Hence, there is a need to identify its role and discover the universal behavior of ruthenium to utilize it efficiently. In this proposal, we study materials with different compositions that are derived based on one ruthenium containing superalloy, and different thermomechanical history. Based on the evolution of microstructures and results of mechanical testing, we plan to determine the exact role of Ruthenium and prediction of its behavior with respect to other elements in the material

  3. Atomic photoelectron-spectroscopy studies using synchrotron radiation

    International Nuclear Information System (INIS)

    Kobrin, P.H.

    1983-02-01

    Photoelectron spectroscopy combined with tunable synchrotron radiation has been used to study the photoionization process in several atomic systems. The time structure of the synchrotron radiation source at the Stanford Synchrotron Radiation Laboratory (SSRL) was used to record time-of-flight (TOF) photoelectron spectra of gaseous Cd, Hg, Ne, Ar, Ba, and Mn. The use of two TOF analyzers made possible the measurement of photoelectron angular distributions as well as branching ratios and partial cross sections

  4. Visualisation and orbital-free parametrisation of the large-Z scaling of the kinetic energy density of atoms

    Science.gov (United States)

    Cancio, Antonio C.; Redd, Jeremy J.

    2017-03-01

    The scaling of neutral atoms to large Z, combining periodicity with a gradual trend to homogeneity, is a fundamental probe of density functional theory, one that has driven recent advances in understanding both the kinetic and exchange-correlation energies. Although research focus is normally upon the scaling of integrated energies, insights can also be gained from energy densities. We visualise the scaling of the positive-definite kinetic energy density (KED) in closed-shell atoms, in comparison to invariant quantities based upon the gradient and Laplacian of the density. We notice a striking fit of the KED within the core of any atom to a gradient expansion using both the gradient and the Laplacian, appearing as an asymptotic limit around which the KED oscillates. The gradient expansion is qualitatively different from that derived from first principles for a slowly varying electron gas and is correlated with a nonzero Pauli contribution to the KED near the nucleus. We propose and explore orbital-free meta-GGA models for the kinetic energy to describe these features, with some success, but the effects of quantum oscillations in the inner shells of atoms make a complete parametrisation difficult. We discuss implications for improved orbital-free description of molecular properties.

  5. Study of the electrons elastic scattering by atoms through pseudopotentials

    International Nuclear Information System (INIS)

    Bettega, M.H.F.

    1990-01-01

    Pseudopotentials allow an extraordinary simplification in the calculation of the electronic structure of atoms, molecules and crystals. Though they have been used extensively for electronic structure calculations, little is known of their applicability to scattering. A study of the pseudopotentials of Bachelet, Hamann and Schuter in the electron scattering by atoms was made, calculating phase-shifts and cross sections for angular momenta 1=0,1 and 2 and energy up to 5 R y. The results for the pseudopotential were compared all-electron calculations. The agreement is very good in a broad energy band. A simplification of the calculation of scattering by complex molecules where an all-electron calculation is impossible is aimed. (author)

  6. Magnetic resonance studies of atomic hydrogen gas at low temperatures

    International Nuclear Information System (INIS)

    Hardy, W.N.; Morrow, M.; Jochemsen, R.; Statt, B.W.; Kubik, P.R.; Marsolais, R.M.; Berlinsky, A.J.; Landesman, A.

    1980-01-01

    Using a pulsed low temperature discharge in a closed cell containing H 2 and 4 He, we have been able to store a low density (approximately 10 12 atoms/cc) gas of atomic hydrogen for periods of order one hour in zero magnetic field and T=1 K. Pulsed magnetic resonance at the 1420 MHz hyperfine transition has been used to study a number of the properties of the gas, including the recombination rate H + H + 4 He→H 2 + 4 He, the hydrogen spin-exchange relaxation rates, the diffusion coefficient of H in 4 He gas and the pressure shift of the hyperfine frequency due to the 4 He buffer gas. Here we discuss the application of hyperfine frequency shifts as a probe of the H-He potential, and as a means for determining the binding energy of H on liquid helium

  7. The Atomic Energy of Canada Limited (AECL) employee health study

    International Nuclear Information System (INIS)

    Myers, D.K.; Werner, M.M.

    1985-01-01

    A preliminary examination of records relating to past Chalk River employees provides some reassurance that large numbers of cancer deaths that might be related to occupational radiation exposure do not exist in the groups of employees studied to the end of 1982. The lack of reliable information on deaths of ex-employees who left AECL for other employment prevented the inclusion of this group in this preliminary study. This information will presumably be obtained during the course of the more comprehensive Atomic Energy of Canada Ltd. employee health study. 6 refs

  8. Comparative study of low-energy neutral atom imaging techniques

    International Nuclear Information System (INIS)

    Funsten, H.O.; McComas, D.J.; Scime, E.E.

    1994-01-01

    Low-energy neutral atom (LENA) imaging promise to be a revolutionary tool for global imaging of space plasmas. The technical challenges of LENA detection include separating them from the intense ambient UV without losing information about their incident trajectories, quantifying their trajectories, and obtaining high-sensitivity measurements. Two techniques that have been proposed for this purpose are based on fundamentally different atomic interaction mechanisms between LENAs and a solid; LENA transmission through an ultra thin foil and LENA reflection from a solid surface. Both of these methods provide LENA ionization (for subsequent removal from the UV by electrostatic deflection) and secondary electron emission (for time-of-flight start pulse generation and/or coincidence). They present a comparative study of the transmission and reflection techniques based on differences in atomic interactions with solids and surfaces. Transmission methods are shown to be superior for secondary electron emission rather than reflection methods. Furthermore, transmission methods are shown to be a sufficient for LENA imaging at LENA energies of approximately 1 keV to greater than 30 keV. A hybrid instrument using reflection from a low work function surface for LENA ionization and transmission for secondary electron emission is optimal for imaging of LENAs with energies less than approximately 1 keV

  9. Molecular beam studies of oxide reduction by atomic hydrogen

    International Nuclear Information System (INIS)

    Olander, D.R.

    1978-01-01

    The graphite and oxide internals of a CTR are susceptible to chemical corrosion as well as to physical degradation by high-energy particles. Reactions of thermal atomic hydrogen with oxides are being studied. The hydrogen used is at thermal energy (0.22 eV). Typical data are reported for the H/UO 2 system. The reaction probability is plotted as a function of solid temperature at fixed beam intensity and moculation frequency. The reaction probability increases from low temperature to a high-temperature plateau at about 1300 0 C. Here the reaction rate is limited solely by the sticking probability of H on the surface; about one in seven of the incident atoms is chemisorbed by the surface and ultimately returns to the gas phase as water vapor. A reaction model comprising sticking, recombination to H 2 , solution and diffusion of H in the bulk of the UO 2 , surface reaction of adsorbed H with lattice oxygen atoms to produce the hydroxyl radical, and production of water is constructed. The rate constants for the elementary steps in the mechanism are tabulated. 2 figures, 2 tables

  10. Model study in chemisorption: atomic hydrogen on beryllium clusters

    International Nuclear Information System (INIS)

    Bauschlicher, C.W. Jr.

    1976-08-01

    The interaction between atomic hydrogen and the (0001) surface of Be metal has been studied by ab initio electronic structure theory. Self-consistent-field (SCF) calculations have been performed using minimum, optimized minimum, double zeta and mixed basis sets for clusters as large as 22 Be atoms. The binding energy and equilibrium geometry (the distance to the surface) were determined for 4 sites. Both spatially restricted (the wavefunction was constrained to transform as one of the irreducible representations of the molecular point group) and unrestricted SCF calculations were performed. Using only the optimized minimum basis set, clusters containing as many as 22 beryllium atoms have been investigated. From a variety of considerations, this cluster is seen to be nearly converged within the model used, providing the most reliable results for chemisorption. The site dependence of the frequency is shown to be a geometrical effect depending on the number and angle of the bonds. The diffusion of atomic hydrogen through a perfect beryllium crystal is predicted to be energetically unfavorable. The cohesive energy, the ionization energy and the singlet-triplet separation were computed for the clusters without hydrogen. These quantities can be seen as a measure of the total amount of edge effects. The chemisorptive properties are not related to the total amount of edge effects, but rather the edge effects felt by the adsorbate bonding berylliums. This lack of correlation with the total edge effects illustrates the local nature of the bonding, further strengthening the cluster model for chemisorption. A detailed discussion of the bonding and electronic structure is included. The remaining edge effects for the Be 22 cluster are discussed

  11. xGASS: total cold gas scaling relations and molecular-to-atomic gas ratios of galaxies in the local Universe

    Science.gov (United States)

    Catinella, Barbara; Saintonge, Amélie; Janowiecki, Steven; Cortese, Luca; Davé, Romeel; Lemonias, Jenna J.; Cooper, Andrew P.; Schiminovich, David; Hummels, Cameron B.; Fabello, Silvia; Geréb, Katinka; Kilborn, Virginia; Wang, Jing

    2018-05-01

    We present the extended GALEX Arecibo SDSS Survey (xGASS), a gas fraction-limited census of the atomic hydrogen (H I) gas content of 1179 galaxies selected only by stellar mass (M⋆ = 109-1011.5 M⊙) and redshift (0.01 new Arecibo observations of 208 galaxies, for which we release catalogues and H I spectra. In addition to extending the GASS H I scaling relations by one decade in stellar mass, we quantify total (atomic+molecular) cold gas fractions and molecular-to-atomic gas mass ratios, Rmol, for the subset of 477 galaxies observed with the IRAM 30 m telescope. We find that atomic gas fractions keep increasing with decreasing stellar mass, with no sign of a plateau down to log M⋆/M⊙ = 9. Total gas reservoirs remain H I-dominated across our full stellar mass range, hence total gas fraction scaling relations closely resemble atomic ones, but with a scatter that strongly correlates with Rmol, especially at fixed specific star formation rate. On average, Rmol weakly increases with stellar mass and stellar surface density μ⋆, but individual values vary by almost two orders of magnitude at fixed M⋆ or μ⋆. We show that, for galaxies on the star-forming sequence, variations of Rmol are mostly driven by changes of the H I reservoirs, with a clear dependence on μ⋆. Establishing if galaxy mass or structure plays the most important role in regulating the cold gas content of galaxies requires an accurate separation of bulge and disc components for the study of gas scaling relations.

  12. Atomic scale modeling of twinning in hexagonal metals: germination and migration of disconnections in zirconium, titanium and magnesium

    International Nuclear Information System (INIS)

    Mackain, Olivier

    2017-01-01

    We perform an atomic scale study of twinning in three hexagonal close packed metals: zirconium, titanium and magnesium. For that, we use two energetic models, an empirical potential suited for the study of zirconium and ab initio calculations in order to compare the three metals. The study of perfect twin boundaries shows that their surface energies are not relevant to predict which twin system is going to activate experimentally. We study nucleation and then migration of disconnections, that is to say interfacial dislocations whose glide along twin plane leads to twin thickening. We show that disconnections nucleation, rather than their migration, is the rate limiting step of twin thickening. In particular, by developing a coupling with elastic theory, we extract the core energies of each disconnection. With this method we prove that for a given twin system, the disconnection with the lowest formation energy is always the one compatible with twin mode observed experimentally, even if its elastic energy is higher. Finally, we construct the preliminary elements of a model considering the effect of stress on nucleation of disconnection. (author) [fr

  13. Study of atomic and condensed atomic indices for reactive sites of ...

    Indian Academy of Sciences (India)

    Unknown

    function indices in the framework of the AIM method of Bader.15 The atomic and group ... P Kolandaivel et al. 592. FF values. One of the reasons, they have argued, is that according to the analytic definition of FF it is valid only when ∆N → 0. In that case, the fluctuation in ..... In their work, they have concluded that the N atom ...

  14. Analogue studies at the french atomic commission (CEA)

    International Nuclear Information System (INIS)

    Petit, J.C.

    1986-06-01

    The different research activities of the French Atomic Energy Commission in the analogue study field are presented. Most of them are conducted in collaboration with major research organisations, both french and international. In fact, the scientific community has been associated to these programmes at different steps of their realisation. The brief description presented illustrates the great diversity and complementarity of actions conducted by CEA for better understanding, through the study of natural analogues, the basic processes that will rule the long term behaviour of high level radwaste materials in a repository and hence contributing to hopefully guaranty disposal safety

  15. Atomic-scale Visualization of Electronic Nematicity and Cooper Pairing in Iron-based Superconductors

    Science.gov (United States)

    Allan, Milan P.

    2013-03-01

    The mechanism of high-temperature superconductivity in the relatively novel iron-based high-Tc superconductors is unresolved, both in terms of how the phases evolve with doping, and in terms of the actual Cooper pairing process. To explore these issues, we used spectroscopic-imaging scanning tunneling microscopy to study the electronic structure of CaFe2As2 in the antiferromagnetic-orthorhombic `parent' state from which the superconductivity emerges. We discovered and visualized the now widely studied electronic `nematicity' of this phase, whose suppression is associated with the emergence of superconductivity (Science 327, 181, 2010). As subsequent transport experiments discovered a related anisotropic conductance which increases with dopant concentration, the interplay between the electronic structure surrounding each dopant atom, quasiparticle scattering therefrom, and the transport nematicity has become a pivotal focus of research. We find that substituting Co for Fe atoms in underdoped Ca(Fe1-xCox)2As2 generates a dense population of identical and strongly anisotropic impurity states that are distributed randomly but aligned with the antiferromagnetic a-axis. We also demonstrate, by imaging their surrounding interference patterns, that these impurity states scatter quasiparticles and thus influence transport in a highly anisotropic manner (M.P. Allan et al., 2013). Next, we studied the momentum dependence of the energy gaps of iron-based superconductivity, now focusing on LiFeAs. If strong electron-electron interactions mediate the Cooper pairing, then momentum-space anisotropic superconducting energy gaps Δi (k) were predicted by multiple techniques to appear on the different electronic bands i. We introduced intraband Bogoliubov quasiparticle scattering interference (QPI) techniques for the determination of anisotropic energy gaps to test these hypotheses and discovered the anisotropy, magnitude, and relative orientations of the energy gaps on multiple

  16. Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies.

    Science.gov (United States)

    Petkov, Valeri; Prasai, Binay; Shan, Shiyao; Ren, Yang; Wu, Jinfang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian

    2016-05-19

    Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum.

  17. Quantum interference between two phonon paths and reduced heat transport in diamond lattice with atomic-scale planar defects

    Science.gov (United States)

    Kosevich, Yu. A.; Strelnikov, I. A.

    2018-02-01

    Destructive quantum interference between the waves propagating through laterally inhomogeneous layer can result in their total reflection, which in turn reduces energy flux carried by these waves. We consider the systems of Ge atoms, which fully or partly, in the chequer-wise order, fill a crystal plane in diamond-like Si lattice. We have revealed that a single type of the atomic defects, which are placed in identical positions in different unit cells in the defect crystal plane, can result in double transmission antiresonances of phonon wave packets. This new effect we relate with the complex structure of the diamond-like unit cell, which comprises two atoms in different positions and results in two distinct vibration resonances in two interfering phonon paths. We also consider the propagation of phonon wave packets in the superlatticies made of the defect planes, half-filled in the chequer-wise order with Ge atoms. We have revealed relatively broad phonon stop bands with center frequencies at the transmission antiresonances. We elaborate the equivalent analytical quasi-1D lattice model of the two phonon paths through the complex planar defect in the diamond-like lattice and describe the reduction of phonon heat transfer through the atomic-scale planar defects.

  18. Resiliency Scale (RS): Scale Development, Reliability and Validity Study

    OpenAIRE

    GÜRGAN, Uğur

    2003-01-01

    The purpose of this study was to develop a new Resiliency Scale (RS) for Turkish samples. Various items from some major resiliency scales, most of them with some partial change, were collected and a pool of 228 items containing almost all possible resilience areas were obtained. This item-pool was administered to a college sample of 419. Resulting of analysis 50 item RS were obtained and administered to a new college sample of 112 participants. This second sample has also received the Rosenba...

  19. Studies on preparation of the database system for clinical records of atomic bomb survivors

    International Nuclear Information System (INIS)

    Nakamura, Tsuyoshi

    1981-01-01

    Construction of the database system aimed at multipurpose application of data on clinical medicine was studied through the preparation of database system for clinical records of atomic bomb survivors. The present database includes the data about 110,000 atomic bomb survivors in Nagasaki City. This study detailed: (1) Analysis of errors occurring in a period from generation of data in the clinical field to input into the database, and discovery of a highly precise, effective method of input. (2) Development of a multipurpose program for uniform processing of data on physical examinations from many organizations. (3) Development of a record linkage method for voluminous files which are essential in the construction of a large-scale medical information system. (4) A database model suitable for clinical research and a method for designing a segment suitable for physical examination data. (Chiba, N.)

  20. Understanding the Atomic Scale Mechanisms that Control the Attainment of Ultralow Friction and Wear in Carbon-Based Materials

    Science.gov (United States)

    2016-01-16

    materials to applications such as vibrating joints1,2, contacting and sliding surfaces in micro- and nanoelectromechanical systems for sensors and...Friction and Wear. R.W. Carpick, Midwest Mechanics 2014/2015 Invited Speaker , Iowa State University, Feb. 2015. 4. Invited. Atomic-Scale Processes...in Single Asperity Friction and Wear. R.W. Carpick, Midwest Mechanics 2014/2015 Invited Speaker , University of Minnesota, Feb. 2015. 5. Invited

  1. Site-specific atomic-scale characterisation of retained austenite in a strip cast TRIP steel

    International Nuclear Information System (INIS)

    Xiong, Z.P.; Saleh, A.A.; Marceau, R.K.W.; Taylor, A.S.; Stanford, N.E.; Kostryzhev, A.G.; Pereloma, E.V.

    2017-01-01

    Knowledge of carbon content in retained austenite (RA) with different neighbouring phases is essential to understand the chemical stability of RA, which is useful for microstructure tuning of transformation-induced plasticity (TRIP) steels. The present study investigates different morphologies and chemical compositions of RA by correlating electron backscattering diffraction, transmission electron microscopy and atom probe tomography. The effect of neighbouring phases, such as polygonal ferrite, bainitic ferrite lath, ferrite in granular bainite and carbides, on the carbon content in the RA is investigated. The results reveal that the film RA morphology does not always have a higher carbon content than the blocky RA; as coarse RA sometimes displays a higher carbon content than the fine RA films or islands depending on the neighbouring phases. The diffusion of carbon and manganese between austenite and ferrite in bainitic ferrite/granular bainite has been explained according to either diffusionless and/or diffusional mechanism of bainitic ferrite formation followed by tempering. -- Highlights: •The effect of neighbouring phases on retained austenite (RA) features was investigated. •A lower carbon content in fine/film RA compared to coarse/blocky RA was experimentally demonstrated. •At least locally controlled diffusion of substitutional solutes across the RA/bainitic ferrite lath interface was suggested.

  2. Atomic scale observation of phase transformation in long term thermally aged duplex stainless steels

    International Nuclear Information System (INIS)

    Novy, St.

    2009-01-01

    Embrittlement study of duplex stainless steels is a very important in order to predict the lifetime of primary circuits of nuclear power plant. Ferrite steels aged over 20 years, on-site, in laboratory and at different temperatures was analyzed by tomographic probe atom to assess the trend of aging of these materials with very long times. A more prospective work was also carried out, the aim was to model the decomposition of ferrite from austenitic-ferritic steels. The simulation of the decomposition of these steels are very complex, we initiated preliminary work in modelling the Fe-Cr alloys, because the decomposition of Fe and Cr in these steels is the main cause of their fragility. To validate the parameters used in simulation, an experimental study of the decomposition of an alloy Fe-20% at. Cr aged at 500 C was performed. This experimental study has shown that a non-classical germination (NCG) is involved in this alloy. The performed simulations on the same alloy at the same temperature, did not reproduce the progressive enrichment of precipitated phase a' (characteristic of NCG). The study of steels, aged over 20 years, has confirmed that the steel aged in laboratory are representative to steel aged in site ( T ≤350 C). Moreover, it has been shown that the G-phase (intermetallic precipitation at the interface a/a' phases) does not influence the embrittlement of the ferrite and the difference of thermo-mechanical treatment is not determinant of the variance decomposition observed in these steels. (author)

  3. 2nd International Symposium "Atomic Cluster Collisions : Structure and Dynamics from the Nuclear to the Biological Scale"

    CERN Document Server

    Solov'yov, Andrey; ISACC 2007; Latest advances in atomic cluster collisions

    2008-01-01

    This book presents a 'snapshot' of the most recent and significant advances in the field of cluster physics. It is a comprehensive review based on contributions by the participants of the 2nd International Symposium on Atomic Cluster Collisions (ISACC 2007) held in July 19-23, 2007 at GSI, Darmstadt, Germany. The purpose of the Symposium is to promote the growth and exchange of scientific information on the structure and properties of nuclear, atomic, molecular, biological and complex cluster systems studied by means of photonic, electronic, heavy particle and atomic collisions. Particular attention is devoted to dynamic phenomena, many-body effects taking place in cluster systems of a different nature - these include problems of fusion and fission, fragmentation, collective electron excitations, phase transitions, etc.Both the experimental and theoretical aspects of cluster physics, uniquely placed between nuclear physics on the one hand and atomic, molecular and solid state physics on the other, are discuss...

  4. Determination of trace elements in atomic absorption spectrophotometry. Study of the atomic cloud and atom generator. Application to the measurement of physical quantities

    International Nuclear Information System (INIS)

    Hircq, Bernard.

    1976-06-01

    After the description of the absorption cell the principal parameters are studied: argon flow rate in the cell, atomization temperature, cell geometry etc. The technique is applied to the measurement of impurities in uranium after deposition on a carbon filament. The atomic concentration distribution and the dimensions of the cloud generated by a graphite filament are then studied along the axes parallel to the filament and as a function of the various experimental parameters. From the determination of the cloud elevation rate it is possible to calculate the absolute atomic concentration, which allows certain physical quantities to be evaluated: oscillator force, Lorentz Widening, diffusion coefficient... The size and penetration depth of the deposit are then determined with an ionic microprobe and the distribution with a Castaing microprobe. The chemical transformations undergone by the uranium matrix during the heat cycles are studied by the X-ray method [fr

  5. Study of Adhesion Interaction Using Atomic Force Microscopy

    Science.gov (United States)

    Grybos, J.; Pyka-Fosciak, G.; Lebed, K.; Lekka, M.; Stachura, Z.; Styczeñ, J.

    2003-05-01

    An atomic force microscope is a useful tool to study the interaction forces at molecular level. In particular the atomic force microscope can measure an unbinding force needed to separate the two single molecule complexes. Recent studies have shown that such unbinding force depends linearly on the logarithm of the applied loading rate, defined as a product of scanning velocity and the spring constant characterizing the investigated system (cantilever vs. surface). This dependence can be used to study the energy landscape shape of a molecular complex by the estimation of energy barrier locations and the related dissociation rates. In the present work the complex consisting of ethylene(di)aminetetraacetic acid and the bovine serum albumin was measured. The dependence between the unbinding force and the logarithm of the loading rate was linear. Using the Bell model describing the dissociation of the above molecules caused by the action of the external bond breaking force, two parameters were estimated: the dissociation rate and the position of the energy barrier needed to overcome during a transition from a bound to unbound state. The obtained results are similar to those obtained for a typical ligand--receptor interaction.

  6. Josephson current at atomic scale: Tunneling and nanocontacts using a STM

    International Nuclear Information System (INIS)

    Rodrigo, J.G.; Crespo, V.; Vieira, S.

    2006-01-01

    Using a scanning tunneling microscope, STM, with a superconducting tip, we have measured the Josephson current in atomic size tunnel junctions and contacts with a small number of quantum channels of conduction. We analyze our results in terms of the Ivanchenko and Zil'berman model for phase diffusion. The effect of the thermal energy and the electromagnetic environment on the Josephson current is discussed in terms of the transmissions of the individual quantum channels. These results suppose an initial step to the control of Scanning Josephson Spectroscopy at atomic level

  7. Atomic-scale processes revealing dynamic twin boundary strengthening mechanisms in face-centered cubic materials

    International Nuclear Information System (INIS)

    Yang, Z.Q.; Chisholm, M.F.; He, L.L.; Pennycook, S.J.; Ye, H.Q.

    2012-01-01

    We report experimental investigations on interactions/reactions between dislocations and twin boundaries in Al. The absorption of screw dislocations via cross-slip and the production of stair-rods via reactions with non-screw dislocations were verified by atomic resolution imaging. Importantly, the resulting partial dislocations moving along twin boundaries can produce secondary sessile defects. These immobile defects act as obstacles to other dislocations and also serve to pin the twin boundaries. These findings show the atomic-level dynamics of the dislocation–twin boundary processes and the unique strengthening mechanism of twin boundaries in face-centered cubic metals.

  8. Atomic Scale Simulation on the Anti-Pressure and Friction Reduction Mechanisms of MoS2 Monolayer

    Directory of Open Access Journals (Sweden)

    Yang Liu

    2018-04-01

    Full Text Available MoS2 nanosheets can be used as solid lubricants or additives of lubricating oils to reduce friction and resist wear. However, the atomic scale mechanism still needs to be illustrated. Herein, molecular simulations on the indentation and scratching process of MoS2 monolayer supported by Pt(111 surface were conducted to study the anti-pressure and friction reduction mechanisms of the MoS2 monolayer. Three deformation stages of Pt-supported MoS2 monolayer were found during the indentation process: elastic deformation, plastic deformation and finally, complete rupture. The MoS2 monolayer showed an excellent friction reduction effect at the first two stages, as a result of enhanced load bearing capacity and reduced deformation degree of the substrate. Unlike graphene, rupture of the Pt-supported MoS2 monolayer was related primarily to out-of-plane compression of the monolayer. These results provide a new insight into the relationship between the mechanical properties and lubrication properties of 2D materials.

  9. Periodic order and defects in Ni-based inverse opal-like crystals on the mesoscopic and atomic scale

    Science.gov (United States)

    Chumakova, A. V.; Valkovskiy, G. A.; Mistonov, A. A.; Dyadkin, V. A.; Grigoryeva, N. A.; Sapoletova, N. A.; Napolskii, K. S.; Eliseev, A. A.; Petukhov, A. V.; Grigoriev, S. V.

    2014-10-01

    The structure of inverse opal crystals based on nickel was probed on the mesoscopic and atomic levels by a set of complementary techniques such as scanning electron microscopy and synchrotron microradian and wide-angle diffraction. The microradian diffraction revealed the mesoscopic-scale face-centered-cubic (fcc) ordering of spherical voids in the inverse opal-like structure with unit cell dimension of 750±10nm. The diffuse scattering data were used to map defects in the fcc structure as a function of the number of layers in the Ni inverse opal-like structure. The average lateral size of mesoscopic domains is found to be independent of the number of layers. 3D reconstruction of the reciprocal space for the inverse opal crystals with different thickness provided an indirect study of original opal templates in a depth-resolved way. The microstructure and thermal response of the framework of the porous inverse opal crystal was examined using wide-angle powder x-ray diffraction. This artificial porous structure is built from nickel crystallites possessing stacking faults and dislocations peculiar for the nickel thin films.

  10. Atomic-scale observation of structural and electronic orders in the layered compound α-RuCl3

    Science.gov (United States)

    Ziatdinov, M.; Banerjee, A.; Maksov, A.; Berlijn, T.; Zhou, W.; Cao, H. B.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Baddorf, A. P.; Kalinin, S. V.

    2016-12-01

    A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, α-RuCl3. Our local crystallography analysis reveals considerable variations in the geometry of the ligand sublattice in thin films of α-RuCl3 that opens a way to realization of a spatially inhomogeneous magnetic ground state at the nanometre length scale. Using scanning tunnelling techniques, we observe the electronic energy gap of ~0.25 eV and intra-unit cell symmetry breaking of charge distribution in individual α-RuCl3 surface layer. The corresponding charge-ordered pattern has a fine structure associated with two different types of charge disproportionation at Cl-terminated surface.

  11. Atomic-scale structure of GeSe2 glass revisited: a continuous or broken network of Ge-(Se1/2)4 tetrahedra?

    International Nuclear Information System (INIS)

    Petkov, V; Le Messurier, D

    2010-01-01

    The atomic-scale structure of germanium diselenide (GeSe 2 ) glass has been revisited using a combination of high-energy x-ray diffraction and constrained reverse Monte Carlo simulations. The study shows that the glass structure may be very well described in terms of a continuous network of corner- and edge-sharing Ge-Se 4 tetrahedra. The result is in contrast to other recent studies asserting that the chemical order and, hence, network integrity in GeSe 2 glass are intrinsically broken. It is suggested that more elaborate studies are necessary to resolve the controversy.

  12. Rubidium distribution at atomic scale in high efficient Cu(In,Ga)Se2 thin-film solar cells

    Science.gov (United States)

    Vilalta-Clemente, Arantxa; Raghuwanshi, Mohit; Duguay, Sébastien; Castro, Celia; Cadel, Emmanuel; Pareige, Philippe; Jackson, Philip; Wuerz, Roland; Hariskos, Dimitrios; Witte, Wolfram

    2018-03-01

    The introduction of a rubidium fluoride post deposition treatment (RbF-PDT) for Cu(In,Ga)Se2 (CIGS) absorber layers has led to a record efficiency up to 22.6% for thin-film solar cell technology. In the present work, high efficiency CIGS samples with RbF-PDT have been investigated by atom probe tomography (APT) to reveal the atomic distribution of all alkali elements present in CIGS layers and compared with non-treated samples. A Scanning Electron Microscopy Dual beam station (Focused Ion Beam-Gas Injection System) as well as Transmission Kikuchi diffraction is used for atom probe sample preparation and localization of the grain boundaries (GBs) in the area of interest. The analysis of the 3D atomic scale APT reconstructions of CIGS samples with RbF-PDT shows that inside grains, Rb is under the detection limit, but the Na concentration is enhanced as compared to the reference sample without Rb. At the GBs, a high concentration of Rb reaching 1.5 at. % was found, and Na and K (diffusing from the glass substrate) are also segregated at GBs but at lower concentrations as compared to Rb. The intentional introduction of Rb leads to significant changes in the chemical composition of CIGS matrix and at GBs, which might contribute to improve device efficiency.

  13. First-principles study on silicon atom doped monolayer graphene

    Science.gov (United States)

    Rafique, Muhammad; Shuai, Yong; Hussain, Nayyar

    2018-01-01

    This paper illustrates the structural, electronic and optical properties of individual silicon (Si) atom-doped single layer graphene using density functional theory method. Si atom forms tight bonding with graphene layer. The effect of doping has been investigated by varying the concentration of Si atoms from 3.125% to 9.37% (i.e. From one to three Si atoms in 4 × 4 pure graphene supercell containing 32 carbon atoms), respectively. Electronic structure, partial density of states (PDOS) and optical properties of pure and Si atom-doped graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with Si atom doped graphene. It is revealed that upon Si doping in graphene, a finite band gap appears at the high symmetric K-point, thereby making graphene a direct band gap semiconductor. Moreover, the band gap value is directly proportional to the concentration of impurity Si atoms present in graphene lattice. Upon analyzing the optical properties of Si atom-doped graphene structures, it is found that, there is significant change in the refractive index of the graphene after Si atom substitution in graphene. In addition, the overall absorption spectrum of graphene is decreased after Si atom doping. Although a significant red shift in absorption is found to occur towards visible range of radiation when Si atom is substituted in its lattice. The reflectivity of graphene improves in low energy region after Si atom substitution in graphene. These results can be useful for tuning the electronic structure and to manipulate the optical properties of graphene layer in the visible region.

  14. Environmental studies and clearance compliance of Kudankulam Atomic Power Project

    International Nuclear Information System (INIS)

    Agarwal, S.K.; Singh, Jitendra

    2002-01-01

    Full text: Nuclear industry has played a leading role in evolving proper and effective environmental management impact from development practices right form inception thus minimizing the environmental impact from developmental activities of man. In the engineering design of nuclear power plant, safety is further enhanced considerably by providing double back-upped engineered safety systems. Besides the engineered safety, the other factors considered for ensuring environmental impact minimization are siting criteria, conservative rad-waste management, effluent treatment, application of stringent environmental protection standards for limiting waste discharges, an elaborate environmental surveillance program and an on site and off site emergency preparedness plan. Recently, nuclear power industry has taken a drive to develop and implement Environmental Management System (EMS) to all its operating stations in line with ISO-14001 standards. For Kudankulam atomic power project, a number of studies specifically for environmental protection are carried out to meet the requirements of Russian Federation, new guidelines of Ministry of environment and Forests (MOEF) and Atomic Energy Regulatory Board (AERB). In the present paper an attempt has been made to present the environmental management plan and clearance compliance status of the project

  15. Micrometeorological study of the emplacement at the Ezeiza Atomic Center

    International Nuclear Information System (INIS)

    Berri, G.J.; Robbio, C.A.

    1986-01-01

    An evaluation of meteorological conditions searched at the Ezeiza Atomic Center is presented by means of the data obtained at the micrometeorological station of the Atomic Center during the period January-December 1979. The daily and yearly mean behaviour of the temperature, humidity and wind's directions and speed is shown as well as extreme values persistence of temperature and humidity, the annual behaviour of the precipitation and its relation with the wind's direction. Special attention is given to the atmospheric dispersion characteristic through the study of the low-wind-speed persistence, wind direction persistence and wind's direction distribution confronted with the stability classes. An evaluation of the dispersion factor or normalized concentration, both for short term releases (1 hour), as well as long term releases (time integrated concentration annual factor) is shown. Those factors are representative for mean situations; they can not be employed for isolated situations. Finally, it is emphasized that although the results were obtained by means of 1979 data, significative differences are no expected for other years. (M.E.L.) [es

  16. Theoretical studies of the reactions of HCN with atomic hydrogen

    International Nuclear Information System (INIS)

    Bair, R.A.; Dunning, T.H. Jr.

    1985-01-01

    A comprehensive theoretical study has been made of the energetics of the important pathways involved in the reaction of hydrogen atoms with hydrogen cyanide. For each reaction ab initio GVB-CI calculations were carried out to determine the structures and vibrational frequencies of the reactants, transition states, and products; then POL-CI calculations were carried out to more accurately estimate the electronic contribution to the energetics of the reactions. The hydrogen abstraction reaction is calculated to be endoergic by 24 kcal/mol [expt. ΔH (0 K) = 16--19 kcal/mol] with a barrier of 31 kcal/mol in the forward direction and 6 kcal/mol in the reverse direction. For the hydrogen addition reactions, addition to the carbon atom is calculated to be exoergic by 19 kcal/mol with a barrier of 11 kcal/mol, while addition to the nitrogen center is essentially thermoneutral with a barrier of 17 kcal/mol. Calculations were also carried out on the isomerization reactions of the addition products. The cis→trans isomerization of HCNH has a barrier of only 10 kcal/mol with the trans isomer being more stable by 5 kcal/mol. The (1,2)-hydrogen migration reaction, converting H 2 CN to trans-HCNH, is endoergic by only 14 kcal/mol, but the calculated barrier for the transfer is 52 kcal/mol. The energy of the migration pathway thus lies above that of the dissociation--recombination pathway

  17. Predicting scattering properties of ultracold atoms : Adiabatic accumulated phase method and mass scaling

    NARCIS (Netherlands)

    Verhaar, B.J.; Kempen, van E.G.M.; Kokkelmans, S.J.J.M.F.

    2009-01-01

    Ultracold atoms are increasingly used for high-precision experiments that can be utilized to extract accurate scattering properties. This results in a stronger need to improve on the accuracy of interatomic potentials, and in particular the usually rather inaccurate inner-range potentials. A

  18. Finite Bias Calculations to Model Interface Dipoles in Electrochemical Cells at the Atomic Scale

    DEFF Research Database (Denmark)

    Hansen, Martin Hangaard; Jin, Chengjun; Thygesen, Kristian Sommer

    2016-01-01

    The structure of an electrochemical interface is not determined by any external electrostatic field, but rather by external chemical potentials. This paper demonstrates that the electric double layer should be understood fundamentally as an internal electric field set up by the atomic structure...

  19. True atomic-scale imaging of a spinel Li{sub 4}Ti{sub 5}O{sub 12}(111) surface in aqueous solution by frequency-modulation atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kitta, Mitsunori, E-mail: m-kitta@aist.go.jp; Kohyama, Masanori [Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577 (Japan); Onishi, Hiroshi [Department of Chemistry, Graduate School of Science, Kobe University 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan)

    2014-09-15

    Spinel-type lithium titanium oxide (LTO; Li{sub 4}Ti{sub 5}O{sub 12}) is a negative electrode material for lithium-ion batteries. Revealing the atomic-scale surface structure of LTO in liquid is highly necessary to investigate its surface properties in practical environments. Here, we reveal an atomic-scale image of the LTO(111) surface in LiCl aqueous solution using frequency-modulation atomic force microscopy. Atomically flat terraces and single steps having heights of multiples of 0.5 nm were observed in the aqueous solution. Hexagonal bright spots separated by 0.6 nm were also observed on the flat terrace part, corresponding to the atomistic contrast observed in the ultrahigh vacuum condition, which suggests that the basic atomic structure of the LTO(111) surface is retained without dramatic reconstruction even in the aqueous solution.

  20. Studies on low energy ion-atom collisions by means of electron-spectroscopy

    International Nuclear Information System (INIS)

    Hirosi Suzuki

    1991-01-01

    The typical results of studies on autoionization processes produced by low energy ion-atom collisions are given by means of the ejected electron spectroscopy, which have been performed by Atomic Physics Group of Sophia University

  1. Atomic scale engineering of HfO2-based dielectrics for future DRAM applications

    International Nuclear Information System (INIS)

    Dudek, Piotr

    2011-01-01

    Modern dielectrics in combination with appropriate metal electrodes have a great potential to solve many difficulties associated with continuing miniaturization process in the microelectronic industry. One significant branch of microelectronics incorporates dynamic random access memory (DRAM) market. The DRAM devices scaled for over 35 years starting from 4 kb density to several Gb nowadays. The scaling process led to the dielectric material thickness reduction, resulting in higher leakage current density, and as a consequence higher power consumption. As a possible solution for this problem, alternative dielectric materials with improved electrical and material science parameters were intensively studied by many research groups. The higher dielectric constant allows the use of physically thicker layers with high capacitance but strongly reduced leakage current density. This work focused on deposition and characterization of thin insulating layers. The material engineering process was based on Si cleanroom compatible HfO 2 thin films deposited on TiN metal electrodes. A combined materials science and dielectric characterization study showed that Ba-added HfO 2 (BaHfO 3 ) films and Ti-added BaHfO 3 (BaHf 0.5 Ti 0.5 O 3 ) layers are promising candidates for future generation of state-of-the-art DRAMs. In especial a strong increase of the dielectric permittivity k was achieved for thin films of cubic BaHfO 3 (k∝38) and BaHf 0.5 Ti 0.5 O 3 (k∝90) with respect to monoclinic HfO 2 (k∝19). Meanwhile the CET values scaled down to 1 nm for BaHfO 3 and ∝0.8 nm for BaHf 0.5 Ti 0.5 O 3 with respect to HfO 2 (CET=1.5 nm). The Hf 4+ ions substitution in BaHfO 3 by Ti 4+ ions led to a significant decrease of thermal budget from 900 C for BaHfO 3 to 700 C for BaHf 0.5 Ti 0.5 O 3 . Future studies need to focus on the use of appropriate metal electrodes (high work function) and on film deposition process (homogeneity) for better current leakage control. (orig.)

  2. Atomic scale engineering of HfO{sub 2}-based dielectrics for future DRAM applications

    Energy Technology Data Exchange (ETDEWEB)

    Dudek, Piotr

    2011-02-14

    Modern dielectrics in combination with appropriate metal electrodes have a great potential to solve many difficulties associated with continuing miniaturization process in the microelectronic industry. One significant branch of microelectronics incorporates dynamic random access memory (DRAM) market. The DRAM devices scaled for over 35 years starting from 4 kb density to several Gb nowadays. The scaling process led to the dielectric material thickness reduction, resulting in higher leakage current density, and as a consequence higher power consumption. As a possible solution for this problem, alternative dielectric materials with improved electrical and material science parameters were intensively studied by many research groups. The higher dielectric constant allows the use of physically thicker layers with high capacitance but strongly reduced leakage current density. This work focused on deposition and characterization of thin insulating layers. The material engineering process was based on Si cleanroom compatible HfO{sub 2} thin films deposited on TiN metal electrodes. A combined materials science and dielectric characterization study showed that Ba-added HfO{sub 2} (BaHfO{sub 3}) films and Ti-added BaHfO{sub 3} (BaHf{sub 0.5}Ti{sub 0.5}O{sub 3}) layers are promising candidates for future generation of state-of-the-art DRAMs. In especial a strong increase of the dielectric permittivity k was achieved for thin films of cubic BaHfO{sub 3} (k{proportional_to}38) and BaHf{sub 0.5}Ti{sub 0.5}O{sub 3} (k{proportional_to}90) with respect to monoclinic HfO{sub 2} (k{proportional_to}19). Meanwhile the CET values scaled down to 1 nm for BaHfO{sub 3} and {proportional_to}0.8 nm for BaHf{sub 0.5}Ti{sub 0.5}O{sub 3} with respect to HfO{sub 2} (CET=1.5 nm). The Hf{sup 4+} ions substitution in BaHfO{sub 3} by Ti{sup 4+} ions led to a significant decrease of thermal budget from 900 C for BaHfO{sub 3} to 700 C for BaHf{sub 0.5}Ti{sub 0.5}O{sub 3}. Future studies need to focus

  3. Mechanisms of defect production and atomic mixing in high energy displacement cascades: A molecular dynamics study

    International Nuclear Information System (INIS)

    Diaz de la Rubia, T.; Guinan, M.W.

    1991-01-01

    We have performed molecular dynamics computer simulation studies of displacement cascades in Cu at low temperature. For 25 keV recoils we observe the splitting of a cascade into subcascades and show that cascades in Cu may lead to the formation of vacancy and interstitial dislocation loops. We discuss a new mechanism of defect production based on the observation of interstitial prismatic dislocation loop punching from cascades at 10 K. We also show that below the subcascade threshold, atomic mixing in the cascade is recoil-energy dependent and obtain a mixing efficiency that scales as the square root of the primary recoil energy. 44 refs., 12 figs

  4. Atomic-scale nanoindentation: detection and identification of single glide events in three dimensions by force microscopy

    International Nuclear Information System (INIS)

    Egberts, P; Bennewitz, R

    2011-01-01

    Indentation experiments on the nanometre scale have been performed by means of atomic force microscopy in ultra-high vacuum on KBr(100) surfaces. The surfaces yield in the form of discrete surface displacements with a typical length scale of 1 A. These surface displacements are detected in both normal and lateral directions. Measurement of the lateral tip displacement requires a load-dependent calibration due to the load dependence of the effective lateral compliance. Correlation of the lateral and normal displacements for each glide event allow identification of the activated slip system. The results are discussed in terms of the resolved shear stress in indentation experiments and of typical results in atomistic simulations of nanometre-scale indentation.

  5. Study of confined many electron atoms by means of the POEP method

    International Nuclear Information System (INIS)

    Sarsa, A; Buendía, E; Gálvez, F J

    2014-01-01

    The electronic structure of confined atoms under impenetrable spherical walls is studied by means of the parameterized optimized effective potential method. A cut-off factor is employed to account for Dirichlet boundary conditions. Two atomic basis sets commonly used for describing free atoms have been analyzed within this scheme. The accuracy of the method is similar to that achieved for the free atoms. The ground state electrostatic multiplet of the carbon atom as well as the ground state and both the [Ar]4s3d 7 5 F and [Ar]3d 8 3 F excited states of the iron atom are studied. The behaviour of the energy levels with the confinement has been analyzed in terms of the different contributions to the total energy of the atom. For the iron atom, the effect of confinement on the outermost orbitals is studied. (paper)

  6. Theoretical studies of atomic transitions. Progress report, March 15, 1985-March 14, 1986

    International Nuclear Information System (INIS)

    Fischer, C.F.

    1986-01-01

    A brief description of the research program for atomic studies is given. The program includes an effort to combine the Multi-Configuration Hartree-Fock (MCHF) method with Many-Body Perturbation Theory and the development of a database system for atomic data generated by the atomic structure package. 6 refs

  7. Studies on the life spans of atom-bomb survivors

    International Nuclear Information System (INIS)

    Kato, Hiroo

    1975-01-01

    A shortening of whole life as late injuries of atom-bomb survivors was discussed from the aspects of aging and the studies on the causes of leukemia and cancers. Twenty-one thousands four hundreds and forty-seven of 109000 subjects died during the period between 1950 and 1970. Mortality by exposure doses presented a high value with exposure doses. Mortality of subjects which had received exposure doses of more than 200 rads rose to a level which was 1.27 times in all causes of deaths of the control which had received exposure doses of 0 to 9 rads, and it showed 1.32 times in all deaths of sickness, 18.3 times in leukemia, and 1.48 times in death from cancer. Mortality due to leukemia decreases after 1950-1954, but in the group which had received exposure doses over 100 rads, the mortality was significantly higher than that in all districts in Japan. The shape of dose-reaction curve in Hiroshima was different from that in Nagasaki. In the same dose, mortality due to leukemia in Hiroshima was higher than that in Nagasaki. The younger the age at exposure was, the higher the risk rate of occurring cancer was. Especially, the risk rate of cancer was high in the patients who were exposed to atomic bomb during the age of 0 to 9 years old. Mortality due to cancer increased with the dose. Cancers which statistically showed higher mortality than that in the control group are lung cancer, cancer of the breast (100-199 rad), carcinoma of the esophagus, cancer of the urinary organ (200-299 rad) and gastric cancer (over 300 rads). There are not so clear difference in the mortality due to cancer between Hiroshima and Nagasaki, comparing with the mortality due to leukemia. (Kanao, N.)

  8. Studies on the life spans of atom-bomb survivors

    Energy Technology Data Exchange (ETDEWEB)

    Kato, H [Radiation Effect Research Foundation, Hiroshima (Japan)

    1975-12-01

    A shortening of whole life as late injuries of atom-bomb survivors was discussed from the aspects of aging and the studies on the causes of leukemia and cancers. Twenty-one thousands four hundreds and forty-seven of 109000 subjects died during the period between 1950 and 1970. Mortality by exposure doses presented a high value with exposure doses. Mortality of subjects which had received exposure doses of more than 200 rads rose to a level which was 1.27 times in all causes of deaths of the control which had received exposure doses of 0 to 9 rads, and it showed 1.32 times in all deaths of sickness, 18.3 times in leukemia, and 1.48 times in death from cancer. Mortality due to leukemia decreases after 1950-1954, but in the group which had received exposure doses over 100 rads, the mortality was significantly higher than that in all districts in Japan. The shape of dose-reaction curve in Hiroshima was different from that in Nagasaki. In the same dose, mortality due to leukemia in Hiroshima was higher than that in Nagasaki. The younger the age at exposure was, the higher the risk rate of occurring cancer was. Especially, the risk rate of cancer was high in the patients who were exposed to atomic bomb during the age of 0 to 9 years old. Mortality due to cancer increased with the dose. Cancers which statistically showed higher mortality than that in the control group are lung cancer, cancer of the breast (100-199 rad), carcinoma of the esophagus, cancer of the urinary organ (200-299 rad) and gastric cancer (over 300 rads). There are not so clear difference in the mortality due to cancer between Hiroshima and Nagasaki, comparing with the mortality due to leukemia.

  9. Macro-mechanics controls quantum mechanics: mechanically controllable quantum conductance switching of an electrochemically fabricated atomic-scale point contact.

    Science.gov (United States)

    Staiger, Torben; Wertz, Florian; Xie, Fangqing; Heinze, Marcel; Schmieder, Philipp; Lutzweiler, Christian; Schimmel, Thomas

    2018-01-12

    Here, we present a silver atomic-scale device fabricated and operated by a combined technique of electrochemical control (EC) and mechanically controllable break junction (MCBJ). With this EC-MCBJ technique, we can perform mechanically controllable bistable quantum conductance switching of a silver quantum point contact (QPC) in an electrochemical environment at room temperature. Furthermore, the silver QPC of the device can be controlled both mechanically and electrochemically, and the operating mode can be changed from 'electrochemical' to 'mechanical', which expands the operating mode for controlling QPCs. These experimental results offer the perspective that a silver QPC may be used as a contact for a nanoelectromechanical relay.

  10. Atomic-scale investigation of interface-facilitated deformation twinning in severely deformed Ag-Cu nanolamellar composites

    International Nuclear Information System (INIS)

    An, X. H.; Cao, Y.; Liao, X. Z.; Zhu, S. M.; Nie, J. F.; Kawasaki, M.; Ringer, S. P.; Langdon, T. G.; Zhu, Y. T.

    2015-01-01

    We report an atomic-scale investigation of interface-facilitated deformation twinning behaviour in Ag-Cu nanolamellar composites. Profuse twinning activities in Ag supply partial dislocations to directly transmit across the Ag-Cu lamellar interface that promotes deformation twinning in the neighbouring Cu lamellae although the interface is severely deformed. The trans-interface twin bands change the local structure at the interface. Our analysis suggests that the orientation relationship and interfacial structure between neighbouring Ag-Cu lamellae play a crucial role in such special interface-facilitated twinning behaviour

  11. Atomic-scale insight into the origin of pyridine inhibition of MoS2-based hydrotreating catalysts

    DEFF Research Database (Denmark)

    Temel, Burcin; Tuxen, Anders K.; Kibsgaard, Jakob

    2010-01-01

    in earlier IR experiments on high surface alumina-supported MoS2 catalyst. The adsorption sites appear to be very similar to the brim sites involved in hydrogenation reactions in HDS. Thus, the combined STM and DFT results provide new atomic-scale insight into the inhibition effect of basic N......-compounds in HDS and the first direct observation of the adsorption mode of basic N-compounds on the catalytically active MoS2 edges. Our results lend further support to previously reported correlations between inhibiting strength and proton affinity for the N-containing compounds....

  12. Periodic order and defects in Ni-based inverse opal-like crystals on the mesoscopic and atomic scale

    OpenAIRE

    Chumakova, A. V.; Valkovskiy, G. A.; Mistonov, A. A.; Dyadkin, V. A.; Grigoryeva, N. A.; Sapoletova, N. A.; Napolskii, K. S.; Eliseev, A. A.; Petukhov, Andrei V.; Grigoriev, S. V.

    2014-01-01

    The structure of inverse opal crystals based on nickel was probed on the mesoscopic and atomic levels by a set of complementary techniques such as scanning electron microscopy and synchrotron microradian and wide-angle diffraction. The microradian diffraction revealed the mesoscopic-scale face-centered-cubic (fcc) ordering of spherical voids in the inverse opal-like structure with unit cell dimension of 750±10nm. The diffuse scattering data were used to map defects in the fcc structure as a f...

  13. Macro-mechanics controls quantum mechanics: mechanically controllable quantum conductance switching of an electrochemically fabricated atomic-scale point contact

    Science.gov (United States)

    Staiger, Torben; Wertz, Florian; Xie, Fangqing; Heinze, Marcel; Schmieder, Philipp; Lutzweiler, Christian; Schimmel, Thomas

    2018-01-01

    Here, we present a silver atomic-scale device fabricated and operated by a combined technique of electrochemical control (EC) and mechanically controllable break junction (MCBJ). With this EC-MCBJ technique, we can perform mechanically controllable bistable quantum conductance switching of a silver quantum point contact (QPC) in an electrochemical environment at room temperature. Furthermore, the silver QPC of the device can be controlled both mechanically and electrochemically, and the operating mode can be changed from ‘electrochemical’ to ‘mechanical’, which expands the operating mode for controlling QPCs. These experimental results offer the perspective that a silver QPC may be used as a contact for a nanoelectromechanical relay.

  14. Direct characterization of spin-transfer switching of nano-scale magnetic tunnel junctions using a conductive atomic force microscope

    International Nuclear Information System (INIS)

    Lee, Jia-Mou; Yang, Dong-Chin; Lee, Ching-Ming; Ye, Lin-Xiu; Chang, Yao-Jen; Wu, Te-ho; Lee, Yen-Chi; Wu, Jong-Ching

    2013-01-01

    We present an alternative method of spin-transfer-induced magnetization switching for magnetic tunnel junctions (MTJs) using a conductive atomic force microscope (CAFM) with pulsed current. The nominal MTJ cells' dimensions were 200 × 400 nm 2 . The AFM probes were coated with a Pt layer via sputtering to withstand up to several milliamperes. The pulsed current measurements, with pulse duration varying from 5 to 300 ms, revealed a magnetoresistance ratio of up to 120%, and an estimated intrinsic switching current density, based on the thermal activation model, of 3.94 MA cm −2 . This method demonstrates the potential skill to characterize nanometre-scale magnetic devices. (paper)

  15. A perfect wetting of Mg monolayer on Ag(111) under atomic scale investigation: First principles calculations, scanning tunneling microscopy, and Auger spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Migaou, Amani; Guiltat, Mathilde; Payen, Kevin; Landa, Georges; Hémeryck, Anne, E-mail: anne.hemeryck@laas.fr [LAAS-CNRS, Université de Toulouse, CNRS, UPS, Toulouse (France); Sarpi, Brice; Daineche, Rachid; Vizzini, Sébastien [Aix Marseille University, IM2NP, Fac Sci St. Jérôme, F-13397 Marseille (France)

    2016-05-21

    First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally.

  16. LABORATORY SCALE STEAM INJECTION TREATABILITY STUDIES

    Science.gov (United States)

    Laboratory scale steam injection treatability studies were first developed at The University of California-Berkeley. A comparable testing facility has been developed at USEPA's Robert S. Kerr Environmental Research Center. Experience has already shown that many volatile organic...

  17. Nanometer-Scale Dissection of Chromosomes by Atomic Force Microscopy Combined with Heat-Denaturing Treatment

    Science.gov (United States)

    Tsukamoto, Kazumi; Kuwazaki, Seigo; Yamamoto, Kimiko; Shichiri, Motoharu; Yoshino, Tomoyuki; Ohtani, Toshio; Sugiyama, Shigeru

    2006-03-01

    We have developed a method for dissecting chromosome fragments with a size of a few hundred nanometers by atomic force microscopy (AFM). By using this method, we demonstrated reproducible dissections of silkworm chromosomes in the pachytene phase. The dissected fragments were successfully recovered on the cantilever tips, as confirmed by fluorescent microscopy using fluorescent stained chromosomes. To recover dissected chromosome fragments from a larger chromosome, such as the human metaphase chromosome of a somatic cell, heat denaturation was found to be effective. Further improvements in this method may lead to a novel tool for isolating valuable genes and/or investigating local genome structures in the near future.

  18. Atomic-Scale Visualization of Quasiparticle Interference on a Type-II Weyl Semimetal Surface.

    Science.gov (United States)

    Zheng, Hao; Bian, Guang; Chang, Guoqing; Lu, Hong; Xu, Su-Yang; Wang, Guangqiang; Chang, Tay-Rong; Zhang, Songtian; Belopolski, Ilya; Alidoust, Nasser; Sanchez, Daniel S; Song, Fengqi; Jeng, Horng-Tay; Yao, Nan; Bansil, Arun; Jia, Shuang; Lin, Hsin; Hasan, M Zahid

    2016-12-23

    We combine quasiparticle interference simulation (theory) and atomic resolution scanning tunneling spectromicroscopy (experiment) to visualize the interference patterns on a type-II Weyl semimetal Mo_{x}W_{1-x}Te_{2} for the first time. Our simulation based on first-principles band topology theoretically reveals the surface electron scattering behavior. We identify the topological Fermi arc states and reveal the scattering properties of the surface states in Mo_{0.66}W_{0.34}Te_{2}. In addition, our result reveals an experimental signature of the topology via the interconnectivity of bulk and surface states, which is essential for understanding the unusual nature of this material.

  19. Neutral-helium-atom diffraction from a micron-scale periodic structure: Photonic-crystal-membrane characterization

    Science.gov (United States)

    Nesse, Torstein; Eder, Sabrina D.; Kaltenbacher, Thomas; Grepstad, Jon Olav; Simonsen, Ingve; Holst, Bodil

    2017-06-01

    Surface scattering of neutral helium beams created by supersonic expansion is an established technique for measuring structural and dynamical properties of surfaces on the atomic scale. Helium beams have also been used in Fraunhofer and Fresnel diffraction experiments. Due to the short wavelength of the atom beams of typically 0.1 nm or less, Fraunhofer diffraction experiments in transmission have so far been limited to grating structures with a period (pitch) of up to 200 nm. However, larger periods are of interest for several applications, for example, for the characterization of photonic-crystal-membrane structures, where the period is typically in the micron to high submicron range. Here we present helium atom diffraction measurements of a photonic-crystal-membrane structure with a two-dimensional square lattice of 100 ×100 circular holes. The nominal period and the hole radius were 490 and 100 nm, respectively. To our knowledge this is the largest period that has been measured with helium diffraction. The helium diffraction measurements are interpreted using a model based on the helium beam characteristics. It is demonstrated how to successfully extract values from the experimental data for the average period of the grating, the hole diameter, and the width of the virtual source used to model the helium beam.

  20. Shannon entropy: A study of confined hydrogenic-like atoms

    Science.gov (United States)

    Nascimento, Wallas S.; Prudente, Frederico V.

    2018-01-01

    The Shannon entropy in the atomic, molecular and chemical physics context is presented by using as test cases the hydrogenic-like atoms Hc, Hec+ and Lic2 + confined by an impenetrable spherical box. Novel expressions for entropic uncertainty relation and Shannon entropies Sr and Sp are proposed to ensure their physical dimensionless characteristic. The electronic ground state energy and the quantities Sr,Sp and St are calculated for the hydrogenic-like atoms to different confinement radii by using a variational method. The global behavior of these quantities and different conjectures are analyzed. The results are compared, when available, with those previously published.

  1. Atomic scale Monte Carlo simulations of BF3 plasma immersion ion implantation in Si

    International Nuclear Information System (INIS)

    La Magna, Antonino; Fisicaro, Giuseppe; Nicotra, Giuseppe; Spiegel, Yohann; Torregrosa, Frank

    2014-01-01

    We present a numerical model aimed to accurately simulate the plasma immersion ion implantation (PIII) process in micro and nano-patterned Si samples. The code, based on the Monte Carlo approach, is designed to reproduce all the relevant physical phenomena involved in the process. The particle based simulation technique is fundamental to efficiently compute the material modifications promoted by the plasma implantation at the atomic resolution. The accuracy in the description of the process kinetic is achieved linking (one to one) each virtual Monte Carlo event to each possible atomic phenomenon (e.g. ion penetration, neutral absorption, ion induced surface modification, etc.). The code is designed to be coupled with a generic plasma status, characterized by the particle types (ions and neutrals), their flow rates and their energy/angle distributions. The coupling with a Poisson solver allows the simulation of the correct trajectories of charged particles in the void regions of the micro-structures. The implemented model is able to predict the implantation 2D profiles and significantly support the process design. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Very large-scale structures in sintered silica aerogels as evidenced by atomic force microscopy and ultra-small angle X-ray scattering experiments

    CERN Document Server

    Marliere, C; Etienne, P; Woignier, T; Dieudonné, P; Phalippou, J

    2001-01-01

    During the last few years the bulk structure of silica aerogels has been extensively studied mainly by scattering techniques (neutrons, X-rays, light). It has been shown that small silica particles aggregate to constitute a fractal network. Its spatial extension and fractal dimension are strongly dependent on the synthesis conditions (e.g., pH of gelifying solutions). These typical lengths range from 1 to 10 nm. Ultra-small angle X-ray scattering (USAXS) and atomic force microscopy (AFM) experiments have been carried out on aerogels at different steps of densification. The results presented in this paper reveal the existence of a spatial arrangement of the solid part at a very large length scale. The evolution of this very large-scale structure during the densification process has been studied and reveals a contraction of this macro-structure made of aggregates of clusters. (16 refs).

  3. Detection of atomic scale changes in the free volume void size of three-dimensional colorectal cancer cell culture using positron annihilation lifetime spectroscopy.

    Science.gov (United States)

    Axpe, Eneko; Lopez-Euba, Tamara; Castellanos-Rubio, Ainara; Merida, David; Garcia, Jose Angel; Plaza-Izurieta, Leticia; Fernandez-Jimenez, Nora; Plazaola, Fernando; Bilbao, Jose Ramon

    2014-01-01

    Positron annihilation lifetime spectroscopy (PALS) provides a direct measurement of the free volume void sizes in polymers and biological systems. This free volume is critical in explaining and understanding physical and mechanical properties of polymers. Moreover, PALS has been recently proposed as a potential tool in detecting cancer at early stages, probing the differences in the subnanometer scale free volume voids between cancerous/healthy skin samples of the same patient. Despite several investigations on free volume in complex cancerous tissues, no positron annihilation studies of living cancer cell cultures have been reported. We demonstrate that PALS can be applied to the study in human living 3D cell cultures. The technique is also capable to detect atomic scale changes in the size of the free volume voids due to the biological responses to TGF-β. PALS may be developed to characterize the effect of different culture conditions in the free volume voids of cells grown in vitro.

  4. Atomic-scale investigation of ε and θ precipitates in bainite in 100Cr6 bearing steel by atom probe tomography and ab initio calculations

    International Nuclear Information System (INIS)

    Song, W.; Appen, J. von; Choi, P.; Dronskowski, R.; Raabe, D.; Bleck, W.

    2013-01-01

    Carbide precipitation during upper and lower bainite formation in high-carbon bearing steel 100Cr6 is characterized using transmission electron microscopy and atom probe tomography. The results reveal that both ε and θ carbides precipitate in lower bainite isothermally held at 260 °C and only θ precipitates form in upper bainite isothermally held at 500 °C. ε and θ precipitate under paraequilibrium condition at 260 °C in lower bainite and θ precipitates under negligible partitioning local equilibrium condition in upper bainite at 500 °C. In order to theoretically study ε and θ precipitation and the ε → θ transition in bainite, thermodynamic calculations have been carried out using ab initio techniques. We find that ε and θ carbides in ferrite have almost identical thermodynamic stability, and hence have similar formation probability. In austenite, however, cementite formation is clearly preferred: it is favored by 5 kJ mol −1 at room temperature and still by 4 kJ mol −1 at 500 °C. Hence, the thermodynamic predictions agree well with the atom probe tomography results

  5. Fundamental symmetries studies with cold trapped francium atoms at ISAC

    International Nuclear Information System (INIS)

    Gwinner, G.; Gomez, E.; Orozco, L. A.; Perez Galvan, A.; Sheng, D.; Zhao, Y.; Sprouse, G. D.; Behr, J. A.; Jackson, K. P.; Pearson, M. R.; Aubin, S.; Flambaum, V. V.

    2006-01-01

    Francium combines a heavy nucleus (Z = 87) with the simple atomic structure of alkalis and is a very promising candidate for precision tests of fundamental symmetries such as atomic parity non-conservation measurements. Fr has no stable isotopes, and the ISAC radioactive beam facility at TRIUMF, equipped with an actinide target, promises to provide record quantities of Fr atoms, up to 10 10 /s for some isotopes. We discuss our plans for a Fr on-line laser trapping facility at ISAC and experiments with samples of cold Fr atoms. We outline our plans for a measurement of the nuclear anapole moment - a parity non-conserving, time-reversal conserving moment that arises from weak interactions between nucleons - in a chain of Fr isotopes. Its measurement is a unique probe for neutral weak interactions inside the nucleus.

  6. Contribution to viscosity from the structural relaxation via the atomic scale Green-Kubo stress correlation function

    Science.gov (United States)

    Levashov, V. A.

    2017-11-01

    We studied the connection between the structural relaxation and viscosity for a binary model of repulsive particles in the supercooled liquid regime. The used approach is based on the decomposition of the macroscopic Green-Kubo stress correlation function into the correlation functions between the atomic level stresses. Previously we used the approach to study an iron-like single component system of particles. The role of vibrational motion has been addressed through the demonstration of the relationship between viscosity and the shear waves propagating over large distances. In our previous considerations, however, we did not discuss the role of the structural relaxation. Here we suggest that the contribution to viscosity from the structural relaxation can be taken into account through the consideration of the contribution from the atomic stress auto-correlation term only. This conclusion, however, does not mean that only the auto-correlation term represents the contribution to viscosity from the structural relaxation. Previously the role of the structural relaxation for viscosity has been addressed through the considerations of the transitions between inherent structures and within the mode-coupling theory by other authors. In the present work, we study the structural relaxation through the considerations of the parent liquid and the atomic level stress correlations in it. The comparison with the results obtained on the inherent structures also is made. Our current results suggest, as our previous observations, that in the supercooled liquid regime, the vibrational contribution to viscosity extends over the times that are much larger than the Einstein's vibrational period and much larger than the times that it takes for the shear waves to propagate over the model systems. Besides addressing the atomic level shear stress correlations, we also studied correlations between the atomic level pressure elements.

  7. Atomic nuclei: a laboratory for the study of complexity

    International Nuclear Information System (INIS)

    Abe, Y.; Suraud, E.

    1993-01-01

    The nucleus is a mandatory step in the understanding of nature, between elementary particles and atoms and molecules. To what extent might it be understood with the help of complexity viewpoints. Conversely, could the atomic nucleus provide a laboratory for understanding the behaviour of 'complex' systems. The purpose of this note is to capitalize on the fad for complexity and claim that nuclear physics is an excellent choice to do physics of complex systems...without getting lost

  8. Studying atomic-resolution by X-ray fluorescence holography

    International Nuclear Information System (INIS)

    Gao Hongyi; Chen Jianwen; Xie Honglan; Zhu Huafeng; Li Ruxin; Xu Zhizhan

    2005-01-01

    In this work, the results of numerical simulations of X-ray fluorescence holograms and the reconstructed atomic images for Fe single crystal are given. The influences of the recording angles ranges and the polarization effect on the reconstruction of the atomic images are discussed. The process for removing twin images by multiple energy fluorescence holography and expanding the energy range of the incident X-rays to improve the resolution of the reconstructed images is presented

  9. A study on development strategy of atomic safety organization for atomic environment

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sung Bok; Jeong, Ji Hun; Kim Tae Hee; Lee, Seung Hyuk; Woo, Eun Jung [Konkuk Univ., Seoul (Korea, Republic of)

    2005-02-15

    The objective of this research is to suggest some strategies which can make the safety of atomic power possible and reinforce the nuclear regulatory system. It will contribute to the expansion and settlement of nuclear safety culture by making the public understand well about the safety of nuclear energy, and searching public relations and incentive strategies. In addition, since the nuclear environment is changing rapidly, the necessity of cooperation between the public and the private has veen mostly required. So we need to develop the effective administrative system based on their cooperation. Therefore, it will examine the function of organization established, operation system, and also social network closely connected with the nuclear safety. Moreover, by analyzing the change of regulatory environment and present safety confirmation of nuclear energy, it will devise the new safety confirmation system of nuclear energy.

  10. NATO Advanced Study Institute on Atoms in Unusual Situations

    CERN Document Server

    1986-01-01

    Atomic Physics is certainly the oldest field in which Quantum Mechanics has been used and has provided the most significant proofs of this new theory. Most of the basic concepts, except those more recently developed in field quantization, have been understood for quite a time. Atomic Physics began to serve as a basis for other fields such as molecu­ lar, solid state or nuclear physics. A renewal of interest in Atomic Physics began in the sixties, after the discovery of Quantum Electro­ dynamics, and later when it provided some basic tests of fundamental questions like parity violation, time reversal or Dirac theory. More recently the development of new technologies led to the ex­ ploration of very extreme cases in which the most secrete aspects of atoms have been observed. - Rydberg states where the atoms are so big that they can be described by classical theories; - Heavy or super-heavy ions or exotic atoms where unknown QED or relativistic effects can be observed (very heavy hydrogenlike or heliu...

  11. Atomic scale modeling of defect production and microstructure evolution in irradiated metals

    Energy Technology Data Exchange (ETDEWEB)

    Diaz de la Rubia, T.; Soneda, N.; Shimomura, Y. [Lawrence Livermore National Lab., CA (United States)] [and others

    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.

  12. Atomic scale modeling of defect production and microstructure evolution in irradiated metals

    International Nuclear Information System (INIS)

    Diaz de la Rubia, T.; Soneda, N.; Shimomura, Y.

    1997-01-01

    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 αFe during irradiation at 600 K

  13. Atomic-scale observation of lithiation reaction front in nanoscale SnO2 materials

    KAUST Repository

    Nie, Anmin; Gan, Liyong; Cheng, Yingchun; Asayesh-Ardakani, Hasti; Li, Qianqian; Dong, Cezhou; Tao, Runzhe; Mashayek, Farzad; Wang, Hongtao; Schwingenschlö gl, Udo; Klie, Robert F.; Yassar, Reza Shahbazian

    2013-01-01

    In the present work, taking advantage of aberration-corrected scanning transmission electron microscopy, we show that the dynamic lithiation process of anode materials can be revealed in an unprecedented resolution. Atomically resolved imaging of the lithiation process in SnO2 nanowires illustrated that the movement, reaction, and generation of b = [1Ì...1Ì...1] mixed dislocations leading the lithiated stripes effectively facilitated lithium-ion insertion into the crystalline interior. The geometric phase analysis and density functional theory simulations indicated that lithium ions initial preference to diffuse along the [001] direction in the {200} planes of SnO2 nanowires introduced the lattice expansion and such dislocation behaviors. At the later stages of lithiation, the Li-induced amorphization of rutile SnO2 and the formation of crystalline Sn and LixSn particles in the Li2O matrix were observed. © 2013 American Chemical Society.

  14. Revealing the correlation between real-space structure and chiral magnetic order at the atomic scale

    Science.gov (United States)

    Hauptmann, Nadine; Dupé, Melanie; Hung, Tzu-Chao; Lemmens, Alexander K.; Wegner, Daniel; Dupé, Bertrand; Khajetoorians, Alexander A.

    2018-03-01

    We image simultaneously the geometric, the electronic, and the magnetic structures of a buckled iron bilayer film that exhibits chiral magnetic order. We achieve this by combining spin-polarized scanning tunneling microscopy and magnetic exchange force microscopy (SPEX) to independently characterize the geometric as well as the electronic and magnetic structures of nonflat surfaces. This new SPEX imaging technique reveals the geometric height corrugation of the reconstruction lines resulting from strong strain relaxation in the bilayer, enabling the decomposition of the real-space from the electronic structure at the atomic level and the correlation with the resultant spin-spiral ground state. By additionally utilizing adatom manipulation, we reveal the chiral magnetic ground state of portions of the unit cell that were not previously imaged with spin-polarized scanning tunneling microscopy alone. Using density functional theory, we investigate the structural and electronic properties of the reconstructed bilayer and identify the favorable stoichiometry regime in agreement with our experimental result.

  15. Atomic-scale observation of lithiation reaction front in nanoscale SnO2 materials

    KAUST Repository

    Nie, Anmin

    2013-07-23

    In the present work, taking advantage of aberration-corrected scanning transmission electron microscopy, we show that the dynamic lithiation process of anode materials can be revealed in an unprecedented resolution. Atomically resolved imaging of the lithiation process in SnO2 nanowires illustrated that the movement, reaction, and generation of b = [1Ì...1Ì...1] mixed dislocations leading the lithiated stripes effectively facilitated lithium-ion insertion into the crystalline interior. The geometric phase analysis and density functional theory simulations indicated that lithium ions initial preference to diffuse along the [001] direction in the {200} planes of SnO2 nanowires introduced the lattice expansion and such dislocation behaviors. At the later stages of lithiation, the Li-induced amorphization of rutile SnO2 and the formation of crystalline Sn and LixSn particles in the Li2O matrix were observed. © 2013 American Chemical Society.

  16. Atomic Scale Chemical and Structural Characterization of Ceramic Oxide Heterostructure Interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Singh, R. K.

    2003-04-16

    The research plan was divided into three tasks: (a) growth of oxide heterostructures for interface engineering using standard thin film deposition techniques, (b) atomic level characterization of oxide heterostructure using such techniques as STEM-2 combined with AFM/STM and conventional high-resolution microscopy (HRTEM), and (c) property measurements of aspects important to oxide heterostructures using standard characterization methods, including dielectric properties and dynamic cathodoluminescence measurements. Each of these topics were further classified on the basis of type of oxide heterostructure. Type I oxide heterostructures consisted of active dielectric layers, including the materials Ba{sub x}Sr{sub 1-x}TiO{sub 3} (BST), Y{sub 2}O{sub 3} and ZrO{sub 2}. Type II heterostructures consisted of ferroelectric active layers such as lanthanum manganate and Type III heterostructures consist of phosphor oxide active layers such as Eu-doped Y{sub 2}O{sub 3}.

  17. Atomic scale simulations of pyrochlore oxides with a tight-binding variable-charge model: implications for radiation tolerance

    International Nuclear Information System (INIS)

    Sattonnay, G; Tétot, R

    2014-01-01

    Atomistic simulations with new interatomic potentials derived from a tight-binding variable-charge model were performed in order to investigate the lattice properties and the defect formation energies in Gd 2 Ti 2 O 7 and Gd 2 Zr 2 O 7 pyrochlores. The main objective was to determine the role played by the defect stability on the radiation tolerance of these compounds. Calculations show that the titanate has a more covalent character than the zirconate. Moreover, the properties of oxygen Frenkel pairs, cation antisite defects and cation Frenkel pairs were studied. In Gd 2 Ti 2 O 7 the cation antisite defect and the Ti-Frenkel pair are not stable: they evolve towards more stable defect configurations during the atomic relaxation process. This phenomenon is driven by a decrease of the Ti coordination number down to five which leads to a local atomic reorganization and strong structural distortions around the defects. These kinds of atomic rearrangements are not observed around defects in Gd 2 Zr 2 O 7 . Therefore, the defect stability in A 2 B 2 O 7 depends on the ability of B atoms to accommodate high coordination number (higher than six seems impossible for Ti). The accumulation of structural distortions around Ti-defects due to this phenomenon could drive the Gd 2 Ti 2 O 7 amorphization induced by irradiation. (paper)

  18. High temperature facility for atomic physics studies. Final report

    International Nuclear Information System (INIS)

    1978-01-01

    The results of a program designed to develop a laser heated plasma sample for atomic physics studies in the 30 to 100 eV range of electron temperature and the 3 x 10 17 to 10 18 cm -3 range in electron density are presented. The approach used was discussed in detail in Mathematical Sciences Northwest, Inc., (MSNW) Proposal 1660, that is, the laser breakdown mode of heating in a slow solenoid. An extensive rework of the plasma sample facility was done in order to use this mode of heating. Specifically, a new solenoid magnet was constructed to allow higher field operation and the plasma chamber was modified to allow the use of puff filling orifices and small bore tube liners. The vacuum system and focussing optics were changed to allow the use of an on-axis Cassagranian system capable of focussing the laser radiation to a nearly diffraction limited spot as is necessary when heating through a small aperture. The 10 liter CO 2 laser optics were charged to an unstable oscillator configuration and additional windows were provided into the optical cavity for alignment purposes

  19. Kaonic atomsstudies of the strong interaction with strangeness

    Directory of Open Access Journals (Sweden)

    Marton J.

    2014-01-01

    Full Text Available The strong interaction of charged antikaons (K− with nucleons and nuclei in the low-energy regime is a fascinating topic. The antikaon plays a peculiar role in hadron physics due to the strong attraction antikaon-nucleon which is a key question for possible kaonic nuclear bound states. A rather direct experimental access to the antikaon-nucleon scattering lengths is provided by precision X-ray spectroscopy of transitions to low-lying states in light kaonic atoms like kaonic hydrogen and deuterium. After the successful completion of precision measurements on kaonic hydrogen and helium isotopes by SIDDHARTA at DAΦNE/LNF, new X-ray studies with the focus on kaonic deuterium are in preparation (SIDDHARTA2. In the future with kaonic deuterium data the antikaon-nucleon isospin-dependent scattering lengths can be extracted for the first time. An overview of the experimental results of SIDDHARTA and an outlook to future perspectives in the SIDDHARTA2 experiments in this frontier research field will be given.

  20. Experimental studies of ions and atoms interaction with insulating surface

    International Nuclear Information System (INIS)

    Villette, J.

    2000-10-01

    Grazing collisions ( + , Ne + , Ne 0 , Na + on LiF (001) single crystal, an ionic insulator, are investigated by a time of flight technique. The incident beam is chopped and the scattered particles are collected on a position sensitive detector providing differential cross section while the time of flight gives the energy loss. Deflection plates allow the charge state analysis. Secondary electrons are detected in coincidence allowing direct measurements of electron emission yield, angular and energetic distribution through time of flight measurements. The target electronic structure characterized by a large band gap, governs the collisional processes: charge exchange, electronic excitations and electron emission. In particular, these studies show that the population of local target excitations surface excitons is the major contribution to the kinetic energy transfer (stopping power). Auger neutralization of Ne + and He + ions reveals the population of quasi-molecular excitons, an exciton bound on two holes. Referenced in the literature as trion. A direct energy balance determines the binding energy associated with these excited states of the surface. Besides these electronic energy loss processes, two nuclear energy loss mechanisms are characterized. These processes imply momentum transfer to individual target atoms during close binary collisions or, if the projectile is charged, to collective mode of optical phonons induced by the projectile coulomb field. The effect of the temperature on the scattering profile, the contribution of topological surface defects to the energy loss profile and to skipping motion on the surface are analyzed in view of classical trajectory simulations. (author)

  1. Atomic-scale structure and formation of self-assembled In(Ga)As quantum rings

    NARCIS (Netherlands)

    Offermans, P.; Koenraad, P.M.; Wolter, J.H.; Granados, D.; Garcia, J.M.; Fomin, V.; Gladilin, V.N.; Devreese, J.T.

    2006-01-01

    The authors present an at.-scale anal. of the In distribution of self-assembled (In,Ga)As quantum rings (QRs), which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. The size and shape of QRs as obsd. by cross-sectional scanning tunneling microscopy

  2. Studying the Atomic Nucleus - A New Era in Nuclear Structure Studies

    International Nuclear Information System (INIS)

    Casten, R. F.

    2011-01-01

    The study of atomic nuclei is part of the fascinating quest to understand the fundamental nature and origins of matter. This field, nuclear structure, is undergoing a revolutionary transformation that is breaking cherished paradigms, opening new vistas of nuclear matter for study, and which has the promise of leading to a new comprehensive understanding. The advent of new facilities for the production and study of exotic nuclei provides access to an entirely new territory of nuclei, and advances in extreme computing are enabling similar advances in the theory of atomic nuclei.

  3. Atomic scale simulations of arsenic ion implantation and annealing in silicon

    International Nuclear Information System (INIS)

    Caturla, M.J.; Diaz de la Rubia, T.; Jaraiz, M.

    1995-01-01

    We present results of multiple-time-scale simulations of 5, 10 and 15 keV low temperature ion implantation of arsenic on silicon (100), followed by high temperature anneals. The simulations start with a molecular dynamics (MD) calculation of the primary state of damage after 10ps. The results are then coupled to a kinetic Monte Carlo (MC) simulation of bulk defect diffusion and clustering. Dose accumulation is achieved considering that at low temperatures the damage produced in the lattice is stable. After the desired dose is accumulated, the system is annealed at 800 degrees C for several seconds. The results provide information on the evolution for the damage microstructure over macroscopic length and time scales and affords direct comparison to experimental results. We discuss the database of inputs to the MC model and how it affects the diffusion process

  4. Visualizing pair formation on the atomic scale in high-Tc superconductors

    International Nuclear Information System (INIS)

    Pasupathy, A.

    2008-01-01

    Full text: Unlike traditional superconductors, the density of states (DOS) of the high-T c superconductor Bi-2212 shows large nanoscale variations that have been detected using scanning tunneling microscopy (STM). Such variations are seen in the low temperature superconducting gap and in features associated with the coupling of pairs to boson modes. In order to understand these variations in the spectra, we perform atomic resolution STM measurements of Bi-2212 as a function of temperature. Using newly developed experimental techniques, we measure the evolution of the DOS from low temperature (T c ) to temperatures where all gaps in the spectrum have disappeared (T>T*). Such measurements show that the pairing gap nucleates in nanoscale regions at temperatures between T c and T*. By normalizing the low temperature DOS (T c ) to the DOS at high temperature, we are able to fit the superconducting DOS to the d-wave BCS form. We find that the experimental spectrum deviations from a simple d-wave fit indicating a strong coupling between electrons and bosonic modes. We will discuss the temperature evolution of these as well as other features in the DOS and correlate such measurements with the inhomogeneity seen in the gap magnitude at low temperature

  5. Ultrafast atomic-scale visualization of acoustic phonons generated by optically excited quantum dots

    Directory of Open Access Journals (Sweden)

    Giovanni M. Vanacore

    2017-07-01

    Full Text Available Understanding the dynamics of atomic vibrations confined in quasi-zero dimensional systems is crucial from both a fundamental point-of-view and a technological perspective. Using ultrafast electron diffraction, we monitored the lattice dynamics of GaAs quantum dots—grown by Droplet Epitaxy on AlGaAs—with sub-picosecond and sub-picometer resolutions. An ultrafast laser pulse nearly resonantly excites a confined exciton, which efficiently couples to high-energy acoustic phonons through the deformation potential mechanism. The transient behavior of the measured diffraction pattern reveals the nonequilibrium phonon dynamics both within the dots and in the region surrounding them. The experimental results are interpreted within the theoretical framework of a non-Markovian decoherence, according to which the optical excitation creates a localized polaron within the dot and a travelling phonon wavepacket that leaves the dot at the speed of sound. These findings indicate that integration of a phononic emitter in opto-electronic devices based on quantum dots for controlled communication processes can be fundamentally feasible.

  6. Cometary dust at the smallest scale - latest results of the MIDAS Atomic Force Microscope onboard Rosetta

    Science.gov (United States)

    Bentley, Mark; Torkar, Klaus; Jeszenszky, Harald; Romstedt, Jens; Schmied, Roland; Mannel, Thurid

    2015-04-01

    The MIDAS instrument onboard the Rosetta orbit is a unique combination of a dust collection and handling system and a high resolution Atomic Force Microscope (AFM). By building three-dimensional images of the dust particle topography, MIDAS addresses a range of fundamental questions in Solar System and cometary science. The first few months of dust collection and scanning revealed a deficit of smaller (micron and below) particles but eventually several 10 µm-class grains were discovered. In fact these were unexpectedly large and close to the limit of what is observable with MIDAS. As a result the sharp tip used by the AFM struck the particles from the side, causing particle breakage and distortion. Analyses so far suggest that the collected particles are fluffy aggregates of smaller sub-units, although determination of the size of these sub-units and high resolution re-imaging remains to be done. The latest findings will be presented here, including a description of the particles collected and the implications of these observations for cometary science and the Rosetta mission at comet 67P.

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

    Science.gov (United States)

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

    2016-08-23

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

  8. The study of multiphoton ionization processes in hydrogen atoms

    International Nuclear Information System (INIS)

    Mohammad, M.A.

    1981-01-01

    In this thesis we investigate theoretically the multiphoton ionization of hydrogen atoms based on perturbation theory.The main problem in the numorical evaluation is the appearance of infinite summation over the matrix element and energy denominators of the intermediate state in the formula for ionization cross section.Our numerical result is in excellent agreement with other workers.In the last part of the thesis we have again calculated the two photon ionization of hydrogen atoms using momentum translation approximation of Reiss.The method in general is in fair agreement with other calculations but dose not show the resonance behaviour.(2 tabs., 1 fig., 45 refs.)

  9. Atomic-scale observation of structural and electronic orders in the layered compound ?-RuCl3

    OpenAIRE

    Ziatdinov, M.; Banerjee, A.; Maksov, A.; Berlijn, T.; Zhou, W.; Cao, H. B.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Baddorf, A. P.; Kalinin, S. V.

    2016-01-01

    A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, ?-RuCl3. Our local crystal...

  10. Elemental and Isotopic Tomography at Single-Atom-Scale in 4.0 and 2.4 Ga Zircons

    Science.gov (United States)

    Valley, J. W.; Reinhard, D. A.; Snoeyenbos, D.; Lawrence, D.; Martin, I.; Kelly, T. F.; Ushikubo, T.; Strickland, A.; Cavosie, A. J.

    2012-12-01

    Atom probe tomography can determine identity (mass/charge ratio) and 3-D position of individual atoms in minerals such as zircon. These data provide unique information for understanding the thermal history and mechanisms of mineral reaction and exchange, including radiation damage. Nine needle-shaped specimens ~100 nm in diameter (at the apex) were sampled from 2 zircons by FIB and analyzed with a local-electrode atom probe (LEAP), CAMECA LEAP 4000X HR. The LEAP uses pulsed-laser heating to field evaporate the tip of a zircon needle and accelerates the ions into a position-sensitive TOF-MS. With due care for complex isobaric interferences (molecules, multiple ionizations) and background correction, it is possible to individually identify up to 10E8 atoms/needle (36% detection efficiency) by mass/charge (MRP ~ 1000@ m/n=16Da) and position (X-Y-Z coordinates on 0.2 nm scale) (Kelly & Larson 2012). The 3-D distribution of Pb and Y differ at atom-scale in the 2 zircons. Zircon #1 (4007 Ma, Jack Hills, W. Australia, Cavosie 2005, Ushikubo et al. 2008, Bouvier et al. 2011) is homogeneous in Pb and Y. In contrast, incompatible elements, including Pb and Y, are concentrated in equant 5-10 nm dia. domains, spaced ~50 nm apart in zircon #2 (2438 Ma, Albion-Raft R-Grouse Ck core complex, Utah, Strickland et al. 2011). U is homogeneously distributed in both zircons. The analyzed domains suffered 4-8 x 10E15 α-decay events/mg due to U and Th decay and yet both zircons yield >97% concordant U-Pb ages by SIMS, suggesting annealing of radiation damage during the life of the zircons. The 207-Pb/206-Pb ratios for these nm-scale domains, as measured by LEAP, average 0.17 for the 2.4 Ga Zrc2 (3 needles) and 0.43 for the 4.0 Ga Zrc1 (5 needles). These ratios are less precise (±40% 2σ) due to ultra-small sample size, but are in excellent agreement with values measured by SIMS, 0.1684 and 0.4269, respectively. Thus Pb in both zircons is radiogenic. The Pb-Y-rich domains and lack of

  11. Photoionization and cold collision studies using trapped atoms

    International Nuclear Information System (INIS)

    Gould, P.L.

    1996-01-01

    The authors have used laser cooling and trapping techniques to investigate photoionization and cold collisions. With laser-trapped Rb, they have measured the photoionization cross section from the first excited (5P) level by observing the photoionization-induced loss rate of neutral atoms from the trap. This technique has the advantage that it directly measures the photoionization rate per atom. Knowing the ionizing laser intensity and the excited-state fraction, the measured loss rate gives the absolute cross section. Using this technique, the Rb 5P photoionization cross section at ∼400 nm has been determined with an uncertainty of 9%. The authors are currently attempting to extend this method to the 5D level. Using time-ordered pulses of diode-laser light (similar to the STIRAP technique), they have performed very efficient two-photon excitation of trapped Rb atoms to 5D. Finally, they will present results from a recent collaboration which combines measurements form conventional molecular spectroscopy (single photon and double resonance) with photoassociation collisions of ultracold Na atoms to yield a precise (≤1 ppm) value for the dissociation energy of the X Σ g+ ground state of the Na 2 molecule

  12. Self-referenced coherent diffraction x-ray movie of Ångstrom- and femtosecond-scale atomic motion

    International Nuclear Information System (INIS)

    Glownia, J. M.; Natan, A.; Cryan, J. P.; Hartsock, R.; Kozina, M.

    2016-01-01

    Time-resolved femtosecond x-ray diffraction patterns from laser-excited molecular iodine are used to create a movie of intramolecular motion with a temporal and spatial resolution of 30 fs and 0.3 Å. This high fidelity is due to interference between the nonstationary excitation and the stationary initial charge distribution. The initial state is used as the local oscillator for heterodyne amplification of the excited charge distribution to retrieve real-space movies of atomic motion on ångstrom and femtosecond scales. This x-ray interference has not been employed to image internal motion in molecules before. In conclusion, coherent vibrational motion and dispersion, dissociation, and rotational dephasing are all clearly visible in the data, thereby demonstrating the stunning sensitivity of heterodyne methods.

  13. Interlayer Exchange Coupling: A General Scheme Turning Chiral Magnets into Magnetic Multilayers Carrying Atomic-Scale Skyrmions.

    Science.gov (United States)

    Nandy, Ashis Kumar; Kiselev, Nikolai S; Blügel, Stefan

    2016-04-29

    We report on a general principle using interlayer exchange coupling to extend the regime of chiral magnetic films in which stable or metastable magnetic Skyrmions can appear at a zero magnetic field. We verify this concept on the basis of a first-principles model for a Mn monolayer on a W(001) substrate, a prototype chiral magnet for which the atomic-scale magnetic texture is determined by the frustration of exchange interactions, impossible to unwind by laboratory magnetic fields. By means of ab initio calculations for the Mn/W_{m}/Co_{n}/Pt/W(001) multilayer system we show that for certain thicknesses m of the W spacer and n of the Co reference layer, the effective field of the reference layer fully substitutes the required magnetic field for Skyrmion formation.

  14. Quantitative compositional analysis and field-evaporation behavior of ordered Ni4Mo on an atomic plane-by-plane basis: an atom-probe field-ion microscope study. MSC report No. 4802

    International Nuclear Information System (INIS)

    Yamamoto, M.; Seidman, D.N.

    1982-10-01

    The (211) fundamental and (101) superlattice planes, of the bct lattice, were analysed chemically on an atomic plane-by-plane basis. It was demonstrated that the composition of each individual plane can be determined as a function of depth without any ambiguity. The overall average Mo concentration was measured to be 17.1 at. % for the (211) fundamental plane. Details of the field evaporation behavior of the (211) fundamental and (101) superlattice planes were studied. The field-evaporation behavior is described in terms of the field-evaporation rate, the order of the field evaporated ions, etc. Each individual atomic plane field evaporated on an atomic plane-by-plane basis for the (211) fundamental plane. While for (101) superlattice plane a group of planes consisting of one plane of Mo atoms and four planes of Ni atoms field-evaporated as a unit. An abnormal increase in the number of Mo atoms was found in the central portion of the (211) fundamental plane. Possible mechanisms for the abnormal field evaporation rate are discussed. It is concluded that the atom probe technique can be used to follow the physics and chemistry of the field-evaporation process and the chemistry of the alloy as a function of position, on a subnanometer scale, throughout the specimen. 13 figures

  15. Clinical Music Study Quality Assessment Scale (MUSIQUAS)

    NARCIS (Netherlands)

    Jaschke, A.C.; Eggermont, L.H.P.; Scherder, E.J.A.; Shippton, M.; Hiomonides, I.

    2013-01-01

    AIMS Quality assessment of studies is essential for the understanding and application of these in systematic reviews and meta analyses, the two “gold standards” of medical sciences. Publications in scientific journals have extensively used assessment scales to address poor methodological quality,

  16. Finite size scaling and spectral density studies

    International Nuclear Information System (INIS)

    Berg, B.A.

    1991-01-01

    Finite size scaling (FSS) and spectral density (SD) studies are reported for the deconfining phase transition. This talk concentrates on Monte Carlo (MC) results for pure SU(3) gauge theory, obtained in collaboration with Alves and Sanielevici, but the methods are expected to be useful for full QCD as well. (orig.)

  17. Theoretical studies of atomic and quasiatomic excitations by electron and ion impact

    International Nuclear Information System (INIS)

    Kam, K.F.

    1999-09-01

    Electron emission from ion induced excitations of Ca, Sc, Ti and V metal surfaces and from electron impact on transition metal oxides CoO and TiO 2 has been studied in this thesis. Both the autoionising emission from sputtered atoms and the 3p→3d and 3s→3d excitations in the oxides reveal strong atomic features. The work has involved explaining these spectra in an atomic approach, via the use of atomic structure calculations, cross section studies and empirical/semi-empirical analyses. The other aspect of this work involves extension of current theories of electron-atom scattering in the high electron energy impact regime. Overall it is shown that much can be learned about some solid-state spectra by relating them to atomic phenomena. (author)

  18. Growth of centimeter-scale atomically thin MoS2 films by pulsed laser deposition

    Directory of Open Access Journals (Sweden)

    Gene Siegel

    2015-05-01

    Full Text Available We are reporting the growth of single layer and few-layer MoS2 films on single crystal sapphire substrates using a pulsed-laser deposition technique. A pulsed KrF excimer laser (wavelength: 248 nm; pulse width: 25 ns was used to ablate a polycrystalline MoS2 target. The material thus ablated was deposited on a single crystal sapphire (0001 substrate kept at 700 °C in an ambient vacuum of 10−6 Torr. Detailed characterization of the films was performed using atomic force microscopy (AFM, Raman spectroscopy, UV-Vis spectroscopy, and photoluminescence (PL measurements. The ablation of the MoS2 target by 50 laser pulses (energy density: 1.5 J/cm2 was found to result in the formation of a monolayer of MoS2 as shown by AFM results. In the Raman spectrum, A1g and E12g peaks were observed at 404.6 cm−1 and 384.5 cm−1 with a spacing of 20.1 cm−1, confirming the monolayer thickness of the film. The UV-Vis absorption spectrum exhibited two exciton absorption bands at 672 nm (1.85 eV and 615 nm (2.02 eV, with an energy split of 0.17 eV, which is in excellent agreement with the theoretically predicted value of 0.15 eV. The monolayer MoS2 exhibited a PL peak at 1.85 eV confirming the direct nature of the band-gap. By varying the number of laser pulses, bi-layer, tri-layer, and few-layer MoS2 films were prepared. It was found that as the number of monolayers (n in the MoS2 films increases, the spacing between the A1g and E12g Raman peaks (Δf increases following an empirical relation, Δ f = 26 . 45 − 15 . 42 1 + 1 . 44 n 0 . 9 cm − 1 .

  19. Atomic-scale details of dislocation-stacking fault tetrahedra interaction

    International Nuclear Information System (INIS)

    Osetsky, Yu. N.; Stoller, R.E.; Rodney, D.; Bacon, D.J.

    2005-01-01

    Stacking fault tetrahedra (SFTs) are formed during irradiation of f.c.c. metals and alloys with low stacking fault energy. The high number density of SFTs observed suggests that they should contribute to radiation-induced hardening and, therefore, be taken into account when estimating mechanical property changes of irradiated materials. Key issue is to describe the interaction between a moving dislocation and an individual SFT, which is characterized by a small physical scale of about 100 nm. In this paper we present results of an atomistic simulation of edge and screw dislocations interacting with small SFTs at different temperatures and strain rates and present mechanisms which can explain the formation of defect-free channels observed experimentally

  20. Atomic structure of machined semiconducting chips: An x-ray absorption spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Paesler, M.; Sayers, D.

    1988-12-01

    X-ray absorption spectroscopy (XAS) has been used to examine the atomic structure of chips of germanium that were produced by single point diamond machining. It is demonstrated that although the local (nearest neighbor) atomic structure is experimentally quite similar to that of single crystal specimens information from more distant atoms indicates the presence of considerable stress. An outline of the technique is given and the strength of XAS in studying the machining process is demonstrated.

  1. Study on the GaAs(110) surface using emitted atom spectrometry

    International Nuclear Information System (INIS)

    Gayone, J.E.; Sanchez, E.A.; Grizzi, O.; Universidad Nacional de Cuyo, Mendoza

    1998-01-01

    The facilities implemented at Bariloche for the ion scattering spectrometry is described, and recent examples of the technique application to determine the atomic structure and the composition of metallic and semiconductor surfaces, pure and with different adsorbates. The surface analysis technique using emitted atom spectrometry is discussed. The sensitivity to the GaAs(110) surface atomic relaxation is presented, and the kinetic of hydrogen adsorption by the mentioned surface is studied

  2. Ultrastrong Carbon Thin Films from Diamond to Graphene under Extreme Conditions: Probing Atomic Scale Interfacial Mechanisms to Achieve Ultralow Friction and Wear

    Science.gov (United States)

    2016-12-08

    tribological behavior of hard carbon materials during initial sliding contact, in order to understand what controls and enables the transition from high to...publication. Our goal is to characterize and understand the atomic-scale mechanisms governing the tribological behavior (friction and wear) of hard carbon...affecting the sliding behavior of these materials, including: rehybridization from sp3 to sp2-bonding of the C atoms20, formation of bonds across the

  3. Atomic Scale Investigation of Structural Properties and Glass Forming Ability of Ti100- x Al x Metallic Glasses

    Science.gov (United States)

    Tahiri, M.; Hasnaoui, A.; Sbiaai, K.

    2018-06-01

    In this work, we employed molecular dynamics (MD) simulations to study Ti-Al metallic glasses (MGs) using the embedded atom method (EAM) potential to model the atomic interaction with different compositions. The results showed evidence of the metallic glass formation induced by the split occurring in the second peak of the radial distribution function (RDF) curves implying both Ti and Al atoms. The common neighbor analysis (CNA) method confirmed the presence of the icosahedral clusters with a maximum amount observed for an alloy with 75 pct of Al. Analysis of coordination numbers (CNs) indicated that the total CNs are nearly unchanged in these systems. Finally, Voronoi tessellation analyses (VTA) showed a higher value of the number of icosahedral units at Ti25Al75 composition. This specific composition represents a nearby peritectic point localized at a low melting point in the Ti-Al binary phase diagram. The glass forming ability (GFA) becomes important when the fraction of Al increases by forming and connecting "icosahedral-like" clusters (12-coordinated and 13-coordinated ) and by playing a main role in the structure stability of the Ti-Al MGs.

  4. Atomic Scale Investigation of Structural Properties and Glass Forming Ability of Ti100-x Al x Metallic Glasses

    Science.gov (United States)

    Tahiri, M.; Hasnaoui, A.; Sbiaai, K.

    2018-03-01

    In this work, we employed molecular dynamics (MD) simulations to study Ti-Al metallic glasses (MGs) using the embedded atom method (EAM) potential to model the atomic interaction with different compositions. The results showed evidence of the metallic glass formation induced by the split occurring in the second peak of the radial distribution function (RDF) curves implying both Ti and Al atoms. The common neighbor analysis (CNA) method confirmed the presence of the icosahedral clusters with a maximum amount observed for an alloy with 75 pct of Al. Analysis of coordination numbers (CNs) indicated that the total CNs are nearly unchanged in these systems. Finally, Voronoi tessellation analyses (VTA) showed a higher value of the number of icosahedral units at Ti25Al75 composition. This specific composition represents a nearby peritectic point localized at a low melting point in the Ti-Al binary phase diagram. The glass forming ability (GFA) becomes important when the fraction of Al increases by forming and connecting "icosahedral-like" clusters (12-coordinated and 13-coordinated ) and by playing a main role in the structure stability of the Ti-Al MGs.

  5. Study on the fine control of atoms by coherent interaction

    Energy Technology Data Exchange (ETDEWEB)

    Min, Han Jae; Rho, S. P.; Park, H. M.; Lee, K. S.; Rhee, Y. J.; Yi, J. H.; Jeong, D. Y.; Jung, E. C.; Choe, A. S.; Lee, J. M

    1999-01-01

    The doppler-free saturation spectroscopy of Na atoms has been performed and the proper conditions for the frequency stabilization of narrow band cw dye lasers, which was used as laser sources for the laser cooling and trapping, have been obtained as follows : a) optimum pressure of a Na vapor cell: 10 mTorr b) intensity of a pump laser : a few {mu}W c) intensity of a probe laser : 1/10 of that of a pump laser. EIT (Electromagnetically Induced Transparency) generated by coherent laser-atom interactions was investigated experimentally and analyzed theoretically. The absorption of a probe laser could be remarkably reduced more than 90 % due to EIT effect. The EIT spectrum as narrow as 6 MHz which is even narrower than the natural linewidth of an excited state could be obtained under proper conditions.

  6. Study on the fine control of atoms by coherent interaction

    International Nuclear Information System (INIS)

    Min, Han Jae; Rho, S. P.; Park, H. M.; Lee, K. S.; Rhee, Y. J.; Yi, J. H.; Jeong, D. Y.; Jung, E. C.; Choe, A. S.; Lee, J. M.

    1999-01-01

    The doppler-free saturation spectroscopy of Na atoms has been performed and the proper conditions for the frequency stabilization of narrow band cw dye lasers, which was used as laser sources for the laser cooling and trapping, have been obtained as follows : a) optimum pressure of a Na vapor cell: 10 mTorr b) intensity of a pump laser : a few μW c) intensity of a probe laser : 1/10 of that of a pump laser. EIT (Electromagnetically Induced Transparency) generated by coherent laser-atom interactions was investigated experimentally and analyzed theoretically. The absorption of a probe laser could be remarkably reduced more than 90 % due to EIT effect. The EIT spectrum as narrow as 6 MHz which is even narrower than the natural linewidth of an excited state could be obtained under proper conditions

  7. Supplementary plasma heating studies in the Atomic Energy Commission France

    International Nuclear Information System (INIS)

    Consoli, T.

    1976-01-01

    The research on supplementary heating of toroidal plasma made in France at the Atomic Energy Commission and in the European Community are described (with special reference to the J.E.T. project) in the frame of the national programs. A non exhaustive description of the world effort in this topic is also presented: (neutral injection heating, TTMP (transit time magnetic pumping) heating, electron and ion cyclotron resonance, and lower hybrid resonance heating)

  8. Tuberculosis among atomic bomb survivors. Study of autopsy cases

    Energy Technology Data Exchange (ETDEWEB)

    Hamada, T [H.ma Atomic Bomb Hospital (Japan); Matsushita, Hiroshi

    1980-03-01

    Effects of atomic bomb on tuberculosis among atomic bomb survivors necropsied after 1956 when Atomic Bomb Hospital was opened were observed statistically and the following results were obtained. The morbidity of tuberculosis in the group exposed within 2 km from the hypocenter was higher than that of the control group, but there was not a significant difference between the groups. The morbidity of all types of tuberculosis was significantly higher in the group exposed within 2 km from the hypocenter than in the control group. The morbidity of tuberculosis tended to decrease in both exposed and non-exposed groups with time. However, the morbidity of miliary or active tuberculosis has tended to rise in the exposed since 1975. The morbidity in young a-bomb survivors exposed within 2 km was higher than that in those of other groups, but there was not a difference in the morbidity among the aged. The higher the rate of complication of active tuberculosis with stomach cancer or acute myelocytic leukemia or liver cirrhosis, the nearer the places of exposure were to the hypocenter. Out of 26 patients with miliary tuberculosis, 6 were suspected to have leukemia while they were alive and were suggested to have leukemoid reaction by autopsy. They all were a-bomb survivors, and 4 of them were exposed within 2 km from the hypocenter.

  9. Atomic Force Microscopy Application in Biological Research: A Review Study

    Directory of Open Access Journals (Sweden)

    Surena Vahabi

    2013-06-01

    Full Text Available Atomic force microscopy (AFM is a three-dimensional topographic technique with a high atomic resolution to measure surface roughness. AFM is a kind of scanning probe microscope, and its near-field technique is based on the interaction between a sharp tip and the atoms of the sample surface. There are several methods and many ways to modify the tip of the AFM to investigate surface properties, including measuring friction, adhesion forces and viscoelastic properties as well as determining the Young modulus and imaging magnetic or electrostatic properties. The AFM technique can analyze any kind of samples such as polymers, adsorbed molecules, films or fibers, and powders in the air whether in a controlled atmosphere or in a liquid medium. In the past decade, the AFM has emerged as a powerful tool to obtain the nanostructural details and biomechanical properties of biological samples, including biomolecules and cells. The AFM applications, techniques, and -in particular- its ability to measure forces, are not still familiar to most clinicians. This paper reviews the literature on the main principles of the AFM modality and highlights the advantages of this technique in biology, medicine, and- especially- dentistry. This literature review was performed through E-resources, including Science Direct, PubMed, Blackwell Synergy, Embase, Elsevier, and Scholar Google for the references published between 1985 and 2010.

  10. Atomic force microscopy study of anion intercalation into highly oriented pyrolytic graphite

    Energy Technology Data Exchange (ETDEWEB)

    Alliata, D; Haering, P; Haas, O; Koetz, R [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Siegenthaler, H [University of Berne (Switzerland)

    1999-08-01

    In the context of ion transfer batteries, we studied highly oriented pyrolytic graphite (HOPG) in perchloric acid, as a model to elucidate the mechanism of electrochemical intercalation in graphite. Aim of the work is the local and time dependent investigation of dimensional changes of the host material during electrochemical intercalation processes on the nanometer scale. We used atomic force microscopy (AFM), combined with cyclic voltammetry, as in-situ tool of analysis during intercalation and expulsion of perchloric anions into the HOPG electrodes. According to the AFM measurements, the HOPG interlayer spacing increases by 32% when perchloric anions intercalate, in agreement with the formation of stage IV of graphite intercalation compounds. (author) 3 figs., 3 refs.

  11. Adsorption and manipulation of carbon onions on highly oriented pyrolytic graphite studied with atomic force microscopy

    International Nuclear Information System (INIS)

    Zhou Jianfeng; Shen Ziyong; Hou Shimin; Zhao Xingyu; Xue Zengquan; Shi Zujin; Gu Zhennan

    2007-01-01

    Carbon onions produced by DC arc discharge method were deposited on highly oriented pyrolytic graphite (HOPG) surface and their adsorption and manipulation was studied using an atomic force microscopy (AFM). Well-dispersed adsorption of carbon onions on HOPG surface was obtained and aggregations of onions were not observed. The van der Waals interaction between the onion and HOPG surface and that between two onions, were calculated and discussed using Hamaker's theory. The manipulation of adsorbed onions on HOPG surface was realized using the AFM in both the raster mode and the vector mode. The controllability and precision of two manipulation modes were compared and the vector mode manipulation was found superior, and is a useful technique for the construction of nano-scale devices based on carbon onions

  12. Surface kinetic roughening caused by dental erosion: An atomic force microscopy study

    Science.gov (United States)

    Quartarone, Eliana; Mustarelli, Piercarlo; Poggio, Claudio; Lombardini, Marco

    2008-05-01

    Surface kinetic roughening takes place both in case of growth and erosion processes. Teeth surfaces are eroded by contact with acid drinks, such as those used to supplement mineral salts during sporting activities. Calcium-phosphate based (CPP-ACP) pastes are known to reduce the erosion process, and to favour the enamel remineralization. In this study we used atomic force microscopy (AFM) to investigate the surface roughening during dental erosion, and the mechanisms at the basis of the protection role exerted by a commercial CPP-ACP paste. We found a statistically significant difference (p<0.01) in the roughness of surfaces exposed and not exposed to the acid solutions. The treatment with the CPP-ACP paste determined a statistically significant reduction of the roughness values. By interpreting the AFM results in terms of fractal scaling concepts and continuum stochastic equations, we showed that the protection mechanism of the paste depends on the chemical properties of the acid solution.

  13. Electron - atom bremsstrahlung

    International Nuclear Information System (INIS)

    Kim, L.

    1986-01-01

    Features of bremsstrahlung radiation from neutral atoms and atoms in hot dense plasmas are studied. Predictions for the distributions of electron-atom bremsstrahlung radiation for both the point-Coulomb potential and screened potentials are obtained using a classical numerical method. Results agree with exact quantum-mechanical partial-wave results for low incident electron energies in both the point-Coulomb and screened potentials. In the screened potential, the asymmetry parameter of a spectrum is reduced from the Coulomb values. The difference increases with decreasing energy and begins to oscillate at very low energies. The scaling properties of bremsstrahlung spectra and energy losses were also studied. It was found that the ratio of the radiative energy loss for positrons to that for electrons obeys a simple scaling law, being expressible fairly accurately as a function only of the quantity T 1 /Z 2 . This scaling is exact in the case of the point-Coulomb potential, both for classical bremsstrahlung and for the nonrelativistic dipole Sommerfeld formula. Bremsstrahlung from atoms in hot dense plasmas were also studied describing the atomic potentials by the temperature-and-density dependent Thomas-Fermi mode. Gaunt factors were obtained with the relativistic partial-wave method for atoms in plasmas of various densities and temperatures

  14. Theoretical study on the ultra-narrow bandwidth tunable atomic filter with electromagnetically induced transparency

    Science.gov (United States)

    Liu, Yang; Li, Shu-qing; Feng, Zhong-ying; Liu, Xiao-fei; Gao, Jin-yue

    2016-12-01

    To obtain the weak signal light detection from the high background noise, we present a theoretical study on the ultra-narrow bandwidth tunable atomic filter with electromagnetically induced transparency. In a three-level Λ -type atomic system in the rubidium D1 line, the bandwidth of the EIT atomic filter is narrowed to ~6.5 \\text{MHz} . And the single peak transmission of the filter can be up to 86% . Moreover, the transmission wavelength can be tuned by changing the coupling light frequency. This theoretical scheme can also be applied to other alkali atomic systems.

  15. Point defects and irradiation in oxides: simulations at the atomic scale; Defauts ponctuels et irradiation dans les oxydes: simulation a l'echelle atomique

    Energy Technology Data Exchange (ETDEWEB)

    Crocombette, J.P

    2005-12-15

    The studies done by Jean-Paul Crocombette between 1996 and 2005 in the Service de Recherches de Metallurgie Physique of the Direction de l'Energie Nucleaire in Saclay are presented in this Habilitation thesis. These works were part of the material science researches on the ageing, especially under irradiation, of oxides of interest for the nuclear industry. In this context simulation studies at the atomic scale were performed on two elementary components of ageing under irradiation : point defects and displacement cascades ; using two complementary simulation techniques : ab initio electronic structure calculations and empirical potential molecular dynamics. The first part deals with point defects : self defects (vacancies or interstitials) or hetero-atomic dopants. One first recalls the energetics of such defects in oxides, the specific features of defects calculations and the expected accuracy of these calculations. Then one presents the results obtained on uranium dioxide, oxygen in silver and amorphous silica. The second part tackles the modelling of disintegration recoil nuclei in various?displacement cascades created by crystalline matrices for actinide waste disposal. Cascade calculations give access to the amorphization mechanisms under irradiation of these materials. One thus predicts that the amorphization in zircon takes place directly in the tracks whereas in lanthanum zirconate, the amorphization proceeds through the accumulation of point defects. Finally the prospects of these studies are discussed. (author)

  16. Application of atomic force microscopy to the study of natural and model soil particles.

    Science.gov (United States)

    Cheng, S; Bryant, R; Doerr, S H; Rhodri Williams, P; Wright, C J

    2008-09-01

    The structure and surface chemistry of soil particles has extensive impact on many bulk scale properties and processes of soil systems and consequently the environments that they support. There are a number of physiochemical mechanisms that operate at the nanoscale which affect the soil's capability to maintain native vegetation and crops; this includes soil hydrophobicity and the soil's capacity to hold water and nutrients. The present study used atomic force microscopy in a novel approach to provide unique insight into the nanoscale properties of natural soil particles that control the physiochemical interaction of material within the soil column. There have been few atomic force microscopy studies of soil, perhaps a reflection of the heterogeneous nature of the system. The present study adopted an imaging and force measurement research strategy that accounted for the heterogeneity and used model systems to aid interpretation. The surface roughness of natural soil particles increased with depth in the soil column a consequence of the attachment of organic material within the crevices of the soil particles. The roughness root mean square calculated from ten 25 microm(2) images for five different soil particles from a Netherlands soil was 53.0 nm, 68.0 nm, 92.2 nm and 106.4 nm for the respective soil depths of 0-10 cm, 10-20 cm, 20-30 cm and 30-40 cm. A novel analysis method of atomic force microscopy phase images based on phase angle distribution across a surface was used to interpret the nanoscale distribution of organic material attached to natural and model soil particles. Phase angle distributions obtained from phase images of model surfaces were found to be bimodal, indicating multiple layers of material, which changed with the concentration of adsorbed humic acid. Phase angle distributions obtained from phase images of natural soil particles indicated a trend of decreasing surface coverage with increasing depth in the soil column. This was consistent with

  17. (113) Facets of Si-Ge/Si Islands; Atomic Scale Simulation

    Science.gov (United States)

    Kassem, Hassan

    We have studied, by computer simulation, some static and vibrationnal proprieties of SiGe/Si islands. We have used a Valence Force Field combined to Monte Carlo technique to study the growth of Ge and SiGe on (001)Si substrates. We have focalised on the case of large pyramidal islands presenting (113) facets on the free (001)Si surface with various non uniform composition inside the islands. The deformation inside the islands and Raman spectroscopy are discussed.

  18. Molecular structure of dipalmitoylphospatidylcholine Langmuir-Blodgett monolayers studied by atomic force microscopy.

    NARCIS (Netherlands)

    Zhai, X.; Kleijn, J.M.

    1997-01-01

    Monolayers of dipalmitoylphosphatidylcholine (DPPC) on the air-water interface have been transferred at various surface pressures onto quartz substrates using the Langmuir-Blodgett (LB) technique. The topography of these layers, on a molecular scale, has been examined by atomic force microscopy

  19. Study of e-+ alkaline atom inelastic collisions with the Glauber approxmation

    International Nuclear Information System (INIS)

    Bielschowsky, C.E.

    1984-01-01

    Glauber's approximation is used to study discrete excitations in alkali atoms by electron impact. The interaction between the incident electron and the core electrons and (N-1) nuclear charges is described through an Yukawa-like potential. Analitical expressions for m 2 S and m 2 P excitations are obtained, as well as numerical results for several excitations processes in alkali atoms. (Author) [pt

  20. Studies on atom deceleration process by using the Zeeman-tuned technique

    International Nuclear Information System (INIS)

    Bagnato, V.S.

    1990-01-01

    The Zeeman-tuned technique to slow an atomic beam of sodium atoms was detailed studied. A new technique to study the deceleration which consists in monitoring the fluorescence along the deceleration path is used. This allows a direct observation of the process and open possibilities to investigate the adiabatic following of atoms in the magnetic field, and others very important aspects of the process. With a single laser and some modification of the magnetic field profile it is possible stop atoms outside the slower solenoid, which make a lot of experiments much simpler. A systematic study of the optical pumping effects and adiabatic following conditions allow to produce a very strong slow motion atomic beam. (author)

  1. Modelization of nanospace interaction involving a ferromagnetic atom: a spin polarization effect study by thermogravimetric analysis.

    Science.gov (United States)

    Santhanam, K S V; Chen, Xu; Gupta, S

    2014-04-01

    Ab initio studies of ferromagnetic atom interacting with carbon nanotubes have been reported in the literature that predict when the interaction is strong, a higher hybridization with confinement effect will result in spin polarization in the ferromagnetic atom. The spin polarization effect on the thermal oxidation to form its oxide is modeled here for the ferromagnetic atom and its alloy, as the above studies predict the 4s electrons are polarized in the atom. The four models developed here provide a pathway for distinguishing the type of interaction that exists in the real system. The extent of spin polarization in the ferromagnetic atom has been examined by varying the amount of carbon nanotubes in the composites in the thermogravimetric experiments. In this study we report the experimental results on the CoNi alloy which appears to show selective spin polarization. The products of the thermal oxidation has been analyzed by Fourier Transform Infrared Spectroscopy.

  2. A visualized investigation at the atomic scale of the antitumor effect of magnetic nanomedicine on gastric cancer cells.

    Science.gov (United States)

    Liu, Xiaokang; Deng, Xia; Li, Xinghua; Xue, Desheng; Zhang, Haoli; Liu, Tao; Liu, Qingfang; Mellors, Nigel J; Li, Yumin; Peng, Yong

    2014-07-01

    Discovering which anticancer drugs attack which organelle(s) of cancer cells is essential and significant, not only for understanding their therapeutic and adverse effects, but also to enable the development of new-generation therapeutics. Here, we show that novel Fe3O4-carboxymethyl cellulose-5-fluorouracil (Fe3O4-CMC-5FU) nanomedicine can apparently enhance the antitumor effect on gastric cancer cells, and its mechanism of killing the SGC-7901 gastric cancer cells can be directly observed at the atomic scale. The novel nanomedicine was prepared using the traditional antitumor drug 5FU to chemically bond onto the functionalized Fe3O4 nanoparticles (Fe3O4-CMC-5FU nanomedicine), and then was fed into SGC-7901 gastric cancer cells. The inorganic Fe3O4 nanoparticles were used to track the distribution and antitumor effect of the nanomedicine within individual SGC-7901 gastric cancer cells. Atomic-level observation and tracking the elemental distribution inside individual cells proved that the magnetic nanomedicine killed the gastric cells mainly by attacking their mitochondria. The enhanced therapeutic efficacy derives from the localized high concentration and poor mobility of the aggregated Fe3O4-CMC-5FU nanomedicine in the cytoplasm. A brand new mechanism of Fe3O4-CMC-5FU nanomedicine killing SGC-7901 gastric cancer cells by attacking their mitochondria was discovered, which is different from the classical mechanism utilized by traditional medicine 5FU, which kills gastric cancer cells by damaging their DNA. Our work might provide a partial solution in nanomedicines or even modern anticancer medicine for the visualized investigation of their antitumor effect.

  3. Normal Contacts of Lubricated Fractal Rough Surfaces at the Atomic Scale

    NARCIS (Netherlands)

    Solhjoo, Soheil; Vakis, Antonis I.

    The friction of contacting interfaces is a function of surface roughness and applied normal load. Under boundary lubrication, this frictional behavior changes as a function of lubricant wettability, viscosity, and density, by practically decreasing the possibility of dry contact. Many studies on

  4. Atomic-scale structures of interfaces between phyllosilicate edges and water

    NARCIS (Netherlands)

    Liu, X.; Lu, X.; Meijer, E.J.; Wang, R.; Zhou, H.

    2012-01-01

    We report first-principles molecular dynamics (FPMD) studies on the structures of interfaces between phyllosilicate edges and water. Using FPMD, the substrates and solvents are simulated at the same first-principles level, and the thermal motions are sampled via molecular dynamics. Both the neutral

  5. Real-Time Atomic Scale Imaging of Nanostructural Evolution in Aluminum Alloys

    NARCIS (Netherlands)

    Malladi, S.K.; Xu, X.; van Huis, M.A.; Tichelaar, F.D.; Batenburg, K.J.; Yücelen, E.; Dubiel, B.; Czyrska-Filemonowicz, A.; Zandbergen, H.W.

    2014-01-01

    We present a new approach to study the three- dimensional compositional and structural evolution of metal alloys during heat treatments such as commonly used for improving overall material properties. It relies on in situ heating in a high-resolution scanning transmission electron microscope (STEM).

  6. Atomic-scale effects of chromium-doping on defect behaviour in uranium dioxide fuel

    International Nuclear Information System (INIS)

    Guo, Zhexi; Ngayam-Happy, Raoul; Krack, Matthias; Pautz, Andreas

    2017-01-01

    The effects of doping conventional UO 2 fuel with chromium are studied through atomistic simulations using empirical force field methods. We first analyse the stable structures of unirradiated doped fuel by determining the preferred lattice configuration of chromium ions and oxygen vacancies within the matrix. In order to understand the physical effects of the dopants, we investigate the energy change upon inserting isolated defects and Frenkel pairs in the vicinity of chromium. The behaviour of point defects is then studied with collision cascade simulations and relaxation of doped simulation cells containing Frenkel pairs. The defective structures are analysed using an in-house tool named ASTRAM. Results indicate definite effects of chromium-doping on the ease with which defects are formed. Moreover, the extent of Cr effects on the residual damage following a displacement cascade is dependent on the dopant distribution and concentration in the fuel matrix.

  7. Atomic-scale effects of chromium-doping on defect behaviour in uranium dioxide fuel

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Zhexi; Ngayam-Happy, Raoul, E-mail: raoul.ngayam-happy@psi.ch; Krack, Matthias; Pautz, Andreas

    2017-05-15

    The effects of doping conventional UO{sub 2} fuel with chromium are studied through atomistic simulations using empirical force field methods. We first analyse the stable structures of unirradiated doped fuel by determining the preferred lattice configuration of chromium ions and oxygen vacancies within the matrix. In order to understand the physical effects of the dopants, we investigate the energy change upon inserting isolated defects and Frenkel pairs in the vicinity of chromium. The behaviour of point defects is then studied with collision cascade simulations and relaxation of doped simulation cells containing Frenkel pairs. The defective structures are analysed using an in-house tool named ASTRAM. Results indicate definite effects of chromium-doping on the ease with which defects are formed. Moreover, the extent of Cr effects on the residual damage following a displacement cascade is dependent on the dopant distribution and concentration in the fuel matrix.

  8. Atomic polarizabilities

    International Nuclear Information System (INIS)

    Safronova, M. S.; Mitroy, J.; Clark, Charles W.; Kozlov, M. G.

    2015-01-01

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed

  9. Atomic polarizabilities

    Energy Technology Data Exchange (ETDEWEB)

    Safronova, M. S. [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Mitroy, J. [School of Engineering, Charles Darwin University, Darwin NT 0909 (Australia); Clark, Charles W. [Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, Gaithersburg, Maryland 20899-8410 (United States); Kozlov, M. G. [Petersburg Nuclear Physics Institute, Gatchina 188300 (Russian Federation)

    2015-01-22

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed.

  10. Size effects and strain localization in atomic-scale cleavage modeling

    International Nuclear Information System (INIS)

    Elsner, B A M; Müller, S

    2015-01-01

    In this work, we study the adhesion and decohesion of Cu(1 0 0) surfaces using density functional theory (DFT) calculations. An upper stress to surface decohesion is obtained via the universal binding energy relation (UBER), but the model is limited to rigid separation of bulk-terminated surfaces. When structural relaxations are included, an unphysical size effect arises if decohesion is considered to occur as soon as the strain energy equals the energy of the newly formed surfaces. We employ the nudged elastic band (NEB) method to show that this size effect is opposed by a size-dependency of the energy barriers involved in the transition. Further, we find that the transition occurs via a localization of bond strain in the vicinity of the cleavage plane, which resembles the strain localization at the tip of a sharp crack that is predicted by linear elastic fracture mechanics. (paper)

  11. A comprehensive picture in the view of atomic scale on piezoelectricity of ZnO tunnel junctions: The first principles simulation

    Directory of Open Access Journals (Sweden)

    Genghong Zhang

    2016-06-01

    Full Text Available Piezoelectricity is closely related with the performance and application of piezoelectric devices. It is a crucial issue to understand its detailed fundamental for designing functional devices with more peculiar performances. Basing on the first principles simulations, the ZnO piezoelectric tunnel junction is taken as an example to systematically investigate its piezoelectricity (including the piezopotential energy, piezoelectric field, piezoelectric polarization and piezocharge and explore their correlation. The comprehensive picture of the piezoelectricity in the ZnO tunnel junction is revealed at atomic scale and it is verified to be the intrinsic characteristic of ZnO barrier, independent of its terminated surface but dependent on its c axis orientation and the applied strain. In the case of the ZnO c axis pointing from right to left, an in-plane compressive strain will induce piezocharges (and a piezopotential energy drop with positive and negative signs (negative and positive signs emerging respectively at the left and right terminated surfaces of the ZnO barrier. Meanwhile a piezoelectric polarization (and a piezoelectric field pointing from right to left (from left to right are also induced throughout the ZnO barrier. All these piezoelectric physical quantities would reverse when the applied strain switches from compressive to tensile. This study provides an atomic level insight into the fundamental behavior of the piezoelectricity of the piezoelectric tunnel junction and should have very useful information for future designs of piezoelectric devices.

  12. A comprehensive picture in the view of atomic scale on piezoelectricity of ZnO tunnel junctions: The first principles simulation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Genghong; Zhu, Jia; Jiang, Gelei; Sheng, Qiang; Zheng, Yue, E-mail: zhengy35@mail.sysu.edu.cn [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Micro& Nano Physics and Mechanics Research Laboratory, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Chen, Weijin [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Micro& Nano Physics and Mechanics Research Laboratory, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082 (China); Wang, Biao, E-mail: wangbiao@mail.sysu.edu.cn [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082 (China)

    2016-06-15

    Piezoelectricity is closely related with the performance and application of piezoelectric devices. It is a crucial issue to understand its detailed fundamental for designing functional devices with more peculiar performances. Basing on the first principles simulations, the ZnO piezoelectric tunnel junction is taken as an example to systematically investigate its piezoelectricity (including the piezopotential energy, piezoelectric field, piezoelectric polarization and piezocharge) and explore their correlation. The comprehensive picture of the piezoelectricity in the ZnO tunnel junction is revealed at atomic scale and it is verified to be the intrinsic characteristic of ZnO barrier, independent of its terminated surface but dependent on its c axis orientation and the applied strain. In the case of the ZnO c axis pointing from right to left, an in-plane compressive strain will induce piezocharges (and a piezopotential energy drop) with positive and negative signs (negative and positive signs) emerging respectively at the left and right terminated surfaces of the ZnO barrier. Meanwhile a piezoelectric polarization (and a piezoelectric field) pointing from right to left (from left to right) are also induced throughout the ZnO barrier. All these piezoelectric physical quantities would reverse when the applied strain switches from compressive to tensile. This study provides an atomic level insight into the fundamental behavior of the piezoelectricity of the piezoelectric tunnel junction and should have very useful information for future designs of piezoelectric devices.

  13. Atomic force microscopy studies of native photosynthetic membranes.

    Science.gov (United States)

    Sturgis, James N; Tucker, Jaimey D; Olsen, John D; Hunter, C Neil; Niederman, Robert A

    2009-05-05

    In addition to providing the earliest surface images of a native photosynthetic membrane at submolecular resolution, examination of the intracytoplasmic membrane (ICM) of purple bacteria by atomic force microscopy (AFM) has revealed a wide diversity of species-dependent arrangements of closely packed light-harvesting (LH) antennae, capable of fulfilling the basic requirements for efficient collection, transmission, and trapping of radiant energy. A highly organized architecture was observed with fused preparations of the pseudocrystalline ICM of Blastochloris viridis, consiting of hexagonally packed monomeric reaction center light-harvesting 1 (RC-LH1) core complexes. Among strains which also form a peripheral LH2 antenna, images of ICM patches from Rhodobacter sphaeroides exhibited well-ordered, interconnected networks of dimeric RC-LH1 core complexes intercalated by rows of LH2, coexisting with LH2-only domains. Other peripheral antenna-containing species, notably Rhodospirillum photometricum and Rhodopseudomonas palustris, showed a less regular organization, with mixed regions of LH2 and RC-LH1 cores, intermingled with large, paracrystalline domains. The ATP synthase and cytochrome bc(1) complex were not observed in any of these topographs and are thought to be localized in the adjacent cytoplasmic membrane or in inaccessible ICM regions separated from the flat regions imaged by AFM. The AFM images have served as a basis for atomic-resolution modeling of the ICM vesicle surface, as well as forces driving segregation of photosynthetic complexes into distinct domains. Docking of atomic-resolution molecular structures into AFM topographs of Rsp. photometricum membranes generated precise in situ structural models of the core complex surrounded by LH2 rings and a region of tightly packed LH2 complexes. A similar approach has generated a model of the highly curved LH2-only membranes of Rba. sphaeroides which predicts that sufficient space exists between LH2 complexes

  14. Effective Electrostatic Interactions Between Two Overall Neutral Surfaces with Quenched Charge Heterogeneity Over Atomic Length Scale

    Science.gov (United States)

    Zhou, S.

    2017-12-01

    Using Monte Carlo results as a reference, a classical density functional theory ( CDFT) is shown to reliably predict the forces between two heterogeneously charged surfaces immersed in an electrolyte solution, whereas the Poisson-Boltzmann ( PB) theory is demonstrated to deteriorate obviously for the same system even if the system parameters considered fall within the validity range of the PB theory in the homogeneously charged surfaces. By applying the tested CDFT, we study the effective electrostatic potential of mean force ( EPMF) between two face-face planar and hard surfaces of zero net charge on which positive and negative charges are separated and considered to present as discontinuous spots on the inside edges of the two surfaces. Main conclusions are summarized as follows: (i) strength of the EPMF in the surface charge separation case is very sensitively and positively correlated with the surface charge separation level and valency of the salt ion. Particularly, the charge separation level and the salt ion valency have a synergistic effect, which makes high limit of the EPMF strength in the surface charge separation case significantly go beyond that of the ideal homogeneously charged surface counterpart at average surface charge density similar to the average surface positive or negative charge density in the charge separation case. (ii) The surface charge distribution patterns mainly influence sign of the EPMF: symmetrical and asymmetrical patterns induce repulsive and attractive (at small distances) EPMF, respectively; but with low valency salt ions and low charge separation level the opposite may be the case. With simultaneous presence of both higher valency cation and anion, the EPMF can be repulsive at intermediate distances for asymmetrical patterns. (iii) Salt ion size has a significant impact, which makes the EPMF tend to become more and more repulsive with the ion diameter regardless of the surface charge distribution patterns and the valency of

  15. Directed Atom-by-Atom Assembly of Dopants in Silicon.

    Science.gov (United States)

    Hudak, Bethany M; Song, Jiaming; Sims, Hunter; Troparevsky, M Claudia; Humble, Travis S; Pantelides, Sokrates T; Snijders, Paul C; Lupini, Andrew R

    2018-05-17

    The ability to controllably position single atoms inside materials is key for the ultimate fabrication of devices with functionalities governed by atomic-scale properties. Single bismuth dopant atoms in silicon provide an ideal case study in view of proposals for single-dopant quantum bits. However, bismuth is the least soluble pnictogen in silicon, meaning that the dopant atoms tend to migrate out of position during sample growth. Here, we demonstrate epitaxial growth of thin silicon films doped with bismuth. We use atomic-resolution aberration-corrected imaging to view the as-grown dopant distribution and then to controllably position single dopants inside the film. Atomic-scale quantum-mechanical calculations corroborate the experimental findings. These results indicate that the scanning transmission electron microscope is of particular interest for assembling functional materials atom-by-atom because it offers both real-time monitoring and atom manipulation. We envision electron-beam manipulation of atoms inside materials as an achievable route to controllable assembly of structures of individual dopants.

  16. Epidemiologic study of skin cancer in Nagasaki atomic bomb survivors

    Energy Technology Data Exchange (ETDEWEB)

    Sadamori, Naoki; Mine, Mariko (Nagasaki Univ. (Japan). School of Medicine)

    1989-01-01

    Data from 140 A-bomb survivors with skin cancer were analyzed with the purpose of elucidating the relationship between atomic bombing and skin cancer. The incidence of skin cancer was significantly correlated with the distance from the hypocenter (p<0.01), regardless of sex. Basal cell epithelioma was the most predominant, followed by squamous cell carcinoma. Histology of skin cancer seemed independent of the distance. Since 1965, the incidence of skin cancer has been increased with aging in A-bomb survivors exposed at le2500 m from the hypocenter. It has been significantly higher since 1975 in the le2500 m group than in the ge3000 m group. (N.K.).

  17. In situ electrochemical atomic force microscope study on graphite electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Hirasawa, K.A.; Sato, Tomohiro; Asahina, Hitoshi; Yamaguchi, Shoji; Mori, Shoichiro [Mitsubishi Chemical Corp., Inashiki, Ibaraki (Japan). Tsukuba Research Center

    1997-04-01

    Interest in the formation of the solid electrolyte interphase (SEI) film on graphite electrodes has increased recently in the quest to improve the performance of lithium-ion batteries. Topographic and frictional changes on the surface of a highly oriented pyrolytic graphite electrode in 1 M LiCiO{sub 4} ethylene carbonate/ethylmethyl carbonate (1:1) electrolyte were examined during charge and discharge by in situ electrochemical atomic force microscopy and friction force microscopy simultaneously in real-time. Solid electrolyte interphase film formation commenced at approximately 2 V vs. Li/Li{sup +} and stable film formation with an island-like morphology was observed below approximately 0.9 V vs. Li/Li{sup +}. Further experiments on a KS-44 graphite/polyvinylidene difluoride binder composite electrode showed similar phenomena.

  18. Epidemiologic study of skin cancer in Nagasaki atomic bomb survivors

    International Nuclear Information System (INIS)

    Sadamori, Naoki; Mine, Mariko

    1989-01-01

    Data from 140 A-bomb survivors with skin cancer were analyzed with the purpose of elucidating the relationship between atomic bombing and skin cancer. The incidence of skin cancer was significantly correlated with the distance from the hypocenter (p<0.01), regardless of sex. Basal cell epithelioma was the most predominant, followed by squamous cell carcinoma. Histology of skin cancer seemed independent of the distance. Since 1965, the incidence of skin cancer has been increased with aging in A-bomb survivors exposed at ≤2500 m from the hypocenter. It has been significantly higher since 1975 in the ≤2500 m group than in the ≥3000 m group. (N.K.)

  19. Atomic physics

    International Nuclear Information System (INIS)

    Armbruster, P.; Beyer, H.; Bosch, F.; Dohmann, H.D.; Kozhuharov, C.; Liesen, D.; Mann, R.; Mokler, P.H.

    1984-01-01

    The heavy ion accelerator UNILAC is well suited to experiments in the field of atomic physics because, with the aid of high-energy heavy ions atoms can be produced in exotic states - that is, heavy atoms with only a few electrons. Also, in close collisions of heavy ions (atomic number Z 1 ) and heavy target atoms (Z 2 ) short-lived quasi-atomic 'superheavy' systems will be formed - huge 'atoms', where the inner electrons are bound in the field of the combined charge Z 1 + Z 2 , which exceeds by far the charge of the known elements (Z <= 109). Those exotic or transient superheavy atoms delivered from the heavy ion accelerator make it possible to study for the first time in a terrestrial laboratory exotic, but fundamental, processes, which occur only inside stars. Some of the basic research carried out with the UNILAC is discussed. This includes investigation of highly charged heavy atoms with the beam-foil method, the spectroscopy of highly charged slow-recoil ions, atomic collision studies with highly ionised, decelerated ions and investigations of super-heavy quasi-atoms. (U.K.)

  20. Molecular dynamics simulation study of the influence of the lattice atom potential function upon atom ejection processes

    International Nuclear Information System (INIS)

    Harrison, D.E. Jr.; Webb, R.P.

    1982-01-01

    A molecular dynamics simulation has been used to investigate the sensitivity of atom ejection processes from a single-crystal target to changes in the atom-atom potential function. Four functions, three constructed from the Gibson potentials with Anderman's attractive well, and a fouth specifically developed for this investigation, were investigated in the Cu/Ar/sup +/ system over a range of ion energies from 1.0 to 10.0 kev with the KSE-B ion-atom potential. Well depths and widths also were varied. The calculations were done at normal incidence on the fcc (111) crystal orientation. Computed values were compared with experimental data where they exist. Sputtering yields, multimer yield ratios, layer yield ratios, and the ejected atom energy distribution vary systematically with the parameters of the atom-atom potential function. Calculations also were done with the modified Moliere function. Yields and other properties fall exactly into the positions predicted from the Born-Mayer function analysis. Simultaneous analysis of the ejected atom energy distribution and the ion energy dependence of the sputtering yield curve provides information about the parameters of both the wall and well portions of the atom-atom potential function

  1. Atomic-Scale Structure of the Tin DX Center and Other Related Defects in Aluminum Gallium Arsenide Semiconductors Using Moessbauer Spectroscopy.

    Science.gov (United States)

    Greco, Luigi Alessandro

    The DX center in III-V alloys has limited the use of these materials for electronic devices since the defect acts as an electron trap. To be able to control or eliminate the DX center, its atomic scale structure should be understood. Mossbauer spectroscopy has proven to be a valuable technique in probing the atomic-scale structure of certain atomic species. The dopant studied here is ^{119}Sn. The thermal diffusion of Sn in Al_ {rm x}Ga_{rm 1-x }As using different temperatures, times, sample geometries and As_4 overpressures in evacuated and sealed fused silica ampoules was studied by x-ray diffraction (XRD), secondary ion mass spectroscopy and electrochemical capacitance versus voltage measurements. The AlGaAs surfaces decomposed into various Sn, Si, Ga and As oxides when an As_4 overpressure was introduced during annealing. However, annealing under ambient As_4 and furnace cooling eliminated surface decomposition although the Sn diffusion depth was less than that for a 0.5 atm As_4 overpressure. SiO_{rm x} and Si_{rm x }N_{rm y} RF-sputtered thin film capping layers deposited on AlGaAs were studied by XRD and Auger electron spectroscopy. For the annealed SiO_{rm x} films the AlGaAs surface was preserved, independent of the cooling technique used. Mossbauer spectroscopy was conducted on ^{rm 119m} Sn-implanted Al_ {rm x } Ga_{rm 1-x} As (x = 0.22 and 0.25) used for the source experiments and ^{119}Sn-doped Al _{rm x}Ga _{rm 1-x}As (x = 0.15, N _{rm Sn} ~2 times 10 ^{18} cm^{ -3}) for the absorber experiment. The source samples were capped with 120 nm of SiO_ {rm x} to preserve the surface during the systematic study of annealing temperature versus site occupation and electrical activation via Mossbauer spectroscopy at 76 K and 4 K in the dark and in the light (to observe persistent photoconductivity (PPC) due to the DX center). For all of the annealing conditions used the x = 0.22 sample showed little evidence of PPC possibly due to compensating defects and

  2. Dislocations and elementary processes of plasticity in FCC metals: atomic scale simulations; Dislocations et processus elementaires de la plasticite dans les metaux CFC: apports des simulations a l'echelle atomique

    Energy Technology Data Exchange (ETDEWEB)

    Rodney, D

    2000-07-01

    We present atomic-scale simulations of two elementary processes of FCC crystal plasticity. The first study consists in the simulation by molecular dynamics, in a nickel crystal, of the interactions between an edge dislocation and glissile interstitial loops of the type that form under irradiation in displacement cascades. The simulations show various atomic-scale interaction processes leading to the absorption and drag of the loops by the dislocation. These reactions certainly contribute to the formation of the 'clear bands' observed in deformed irradiated materials. The simulations also allow to study quantitatively the role of the glissile loops in irradiation hardening. In particular, dislocation unpinning stresses for certain pinning mechanisms are evaluated from the simulations. The second study consists first in the generalization in three dimensions of the quasi-continuum method (QCM), a multi-scale simulation method which couples atomistic techniques and the finite element method. In the QCM, regions close to dislocation cores are simulated at the atomic-scale while the rest of the crystal is simulated with a lower resolution by means of a discretization of the displacement fields using the finite element method. The QCM is then tested on the simulation of the formation and breaking of dislocation junctions in an aluminum crystal. Comparison of the simulations with an elastic model of dislocation junctions shows that the structure and strength of the junctions are dominated by elastic line tension effects, as is assumed in classical theories. (author)

  3. Effective atomic numbers of some tissue substitutes by different methods: A comparative study

    Directory of Open Access Journals (Sweden)

    Vishwanath P Singh

    2014-01-01

    Full Text Available Effective atomic numbers of some human organ tissue substitutes such as polyethylene terephthalate, red articulation wax, paraffin 1, paraffin 2, bolus, pitch, polyphenylene sulfide, polysulfone, polyvinylchloride, and modeling clay have been calculated by four different methods like Auto-Z eff, direct, interpolation, and power law. It was found that the effective atomic numbers computed by Auto-Z eff , direct and interpolation methods were in good agreement for intermediate energy region (0.1 MeV < E < 5 MeV where the Compton interaction dominates. A large difference in effective atomic numbers by direct method and Auto-Z eff was observed in photo-electric and pair-production regions. Effective atomic numbers computed by power law were found to be close to direct method in photo-electric absorption region. The Auto-Z eff , direct and interpolation methods were found to be in good agreement for computation of effective atomic numbers in intermediate energy region (100 keV < E < 10 MeV. The direct method was found to be appropriate method for computation of effective atomic numbers in photo-electric region (10 keV < E < 100 keV. The tissue equivalence of the tissue substitutes is possible to represent by any method for computation of effective atomic number mentioned in the present study. An accurate estimation of Rayleigh scattering is required to eliminate effect of molecular, chemical, or crystalline environment of the atom for estimation of gamma interaction parameters.

  4. Absolute fragmentation cross sections in atom-molecule collisions : Scaling laws for non-statistical fragmentation of polycyclic aromatic hydrocarbon molecules

    NARCIS (Netherlands)

    Chen, T.; Gatchell, M.; Stockett, M. H.; Alexander, J. D.; Zhang, Y.; Rousseau, P.; Domaracka, A.; Maclot, S.; Delaunay, R.; Adoui, L.; Huber, B. A.; Schlathölter, T.; Schmidt, H. T.; Cederquist, H.; Zettergren, H.

    2014-01-01

    We present scaling laws for absolute cross sections for non-statistical fragmentation in collisions between Polycyclic Aromatic Hydrocarbons (PAH/PAH+) and hydrogen or helium atoms with kinetic energies ranging from 50 eV to 10 keV. Further, we calculate the total fragmentation cross sections

  5. Structural atomic-scale analysis of GaAs/AlGaAs quantum wires and quantum dots grown by droplet epitaxy on a (311)A substrate

    NARCIS (Netherlands)

    Keizer, J.G.; Jo, M.; Mano, T.; Noda, T.; Sakoda, K.; Koenraad, P.M.

    2011-01-01

    We report the structural analysis at the atomic scale of GaAs/AlGaAs quantum wires and quantum dots grown by droplet epitaxy on a (311)A-oriented substrate. The shape, interfaces, and composition of these nanostructures and their surrounding matrix are investigated. We show that quantum wires can be

  6. Local elasticity and adhesion of nanostructures on Drosophila melanogaster wing membrane studied using atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, Ryan, E-mail: rbwagner@purdue.edu [School of Mechanical Engineering, Purdue University, West Lafayette (United States); Brick Nanotechnology Center, Purdue University, West Lafayette (United States); Pittendrigh, Barry R. [Department of Entomology, University of Illinois, Champaign (United States); Raman, Arvind, E-mail: raman@purdue.edu [School of Mechanical Engineering, Purdue University, West Lafayette (United States); Brick Nanotechnology Center, Purdue University, West Lafayette (United States)

    2012-10-15

    Highlights: Black-Right-Pointing-Pointer We studied the wing membrane of Drosophila melanogaster with atomic force microscopy. Black-Right-Pointing-Pointer We report the structure, elasticity, and adhesion on the wing membrane in air and nitrogen environments. Black-Right-Pointing-Pointer Results provide insight into the nature of the wing membrane enabling the development of biomimetic surface and micro air vehicles. - Abstract: Insect wings have a naturally occurring, complex, functional, hierarchical microstructure and nanostructure, which enable a remarkably water-resistant and self-cleaning surface. Insect wings are used as a basis for engineering biomimetic materials; however, the material properties of these nanostructures such as local elastic modulus and adhesion are poorly understood. We studied the wings of the Canton-S strain of Drosophila melanogaster (hereafter referred to as Drosophila) with atomic force microscopy (AFM) to quantify the local material properties of Drosophila wing surface nanostructures. The wings are found to have a hierarchical structure of 10-20 {mu}m long, 0.5-1 {mu}m diameter hair, and at a much smaller scale, 100 nm diameter and 30-60 nm high bumps. The local properties of these nanoscale bumps were studied under ambient and dry conditions with force-volume AFM. The wing membrane was found to have a elastic modulus on the order of 1000 MPa and the work of adhesion between the probe and wing membrane surface was found to be on the order of 100 mJ/m{sup 2}, these properties are the same order of magnitude as common thermoplastic polymers such as polyethylene. The difference in work of adhesion between the nanoscale bump and membrane does not change significantly between ambient (relative humidity of 30%) or dry conditions. This suggests that the nanoscale bumps and the surrounding membrane are chemically similar and only work to increase hydrophobicity though surface roughening or the geometric lotus effect.

  7. Local elasticity and adhesion of nanostructures on Drosophila melanogaster wing membrane studied using atomic force microscopy

    International Nuclear Information System (INIS)

    Wagner, Ryan; Pittendrigh, Barry R.; Raman, Arvind

    2012-01-01

    Highlights: ► We studied the wing membrane of Drosophila melanogaster with atomic force microscopy. ► We report the structure, elasticity, and adhesion on the wing membrane in air and nitrogen environments. ► Results provide insight into the nature of the wing membrane enabling the development of biomimetic surface and micro air vehicles. - Abstract: Insect wings have a naturally occurring, complex, functional, hierarchical microstructure and nanostructure, which enable a remarkably water-resistant and self-cleaning surface. Insect wings are used as a basis for engineering biomimetic materials; however, the material properties of these nanostructures such as local elastic modulus and adhesion are poorly understood. We studied the wings of the Canton-S strain of Drosophila melanogaster (hereafter referred to as Drosophila) with atomic force microscopy (AFM) to quantify the local material properties of Drosophila wing surface nanostructures. The wings are found to have a hierarchical structure of 10–20 μm long, 0.5–1 μm diameter hair, and at a much smaller scale, 100 nm diameter and 30–60 nm high bumps. The local properties of these nanoscale bumps were studied under ambient and dry conditions with force-volume AFM. The wing membrane was found to have a elastic modulus on the order of 1000 MPa and the work of adhesion between the probe and wing membrane surface was found to be on the order of 100 mJ/m 2 , these properties are the same order of magnitude as common thermoplastic polymers such as polyethylene. The difference in work of adhesion between the nanoscale bump and membrane does not change significantly between ambient (relative humidity of 30%) or dry conditions. This suggests that the nanoscale bumps and the surrounding membrane are chemically similar and only work to increase hydrophobicity though surface roughening or the geometric lotus effect.

  8. Atomic-scale structure of irradiated GaN compared to amorphised GaP and GaAs

    International Nuclear Information System (INIS)

    Ridgway, M.C.; Everett, S.E.; Glover, C.J.; Kluth, S.M.; Kluth, P.; Johannessen, B.; Hussain, Z.S.; Llewellyn, D.J.; Foran, G.J.; Azevedo, G. de M.

    2006-01-01

    We have compared the atomic-scale structure of ion irradiated GaN to that of amorphised GaP and GaAs. While continuous and homogenous amorphised layers were easily achieved in GaP and GaAs, ion irradiation of GaN yielded both structural and chemical inhomogeneities. Transmission electron microscopy revealed GaN crystallites and N 2 bubbles were interspersed within an amorphous GaN matrix. The crystallite orientation was random relative to the unirradiated epitaxial structure, suggesting their formation was irradiation-induced, while the crystallite fraction was approximately constant for all ion fluences beyond the amorphisation threshold, consistent with a balance between amorphisation and recrystallisation processes. Extended X-ray absorption fine structure measurements at the Ga K-edge showed short-range order was retained in the amorphous phase for all three binary compounds. For ion irradiated GaN, the stoichiometric imbalance due to N 2 bubble formation was not accommodated by Ga-Ga bonding in the amorphous phase or precipitation of metallic Ga but instead by a greater reduction in Ga coordination number

  9. Lorentz-Symmetry Test at Planck-Scale Suppression With a Spin-Polarized 133Cs Cold Atom Clock.

    Science.gov (United States)

    Pihan-Le Bars, H; Guerlin, C; Lasseri, R-D; Ebran, J-P; Bailey, Q G; Bize, S; Khan, E; Wolf, P

    2018-06-01

    We present the results of a local Lorentz invariance (LLI) test performed with the 133 Cs cold atom clock FO2, hosted at SYRTE. Such a test, relating the frequency shift between 133 Cs hyperfine Zeeman substates with the Lorentz violating coefficients of the standard model extension (SME), has already been realized by Wolf et al. and led to state-of-the-art constraints on several SME proton coefficients. In this second analysis, we used an improved model, based on a second-order Lorentz transformation and a self-consistent relativistic mean field nuclear model, which enables us to extend the scope of the analysis from purely proton to both proton and neutron coefficients. We have also become sensitive to the isotropic coefficient , another SME coefficient that was not constrained by Wolf et al. The resulting limits on SME coefficients improve by up to 13 orders of magnitude the present maximal sensitivities for laboratory tests and reach the generally expected suppression scales at which signatures of Lorentz violation could appear.

  10. Atomic-scale microstructures of Zr2Al3C4 and Zr3Al3C5 ceramics

    International Nuclear Information System (INIS)

    Lin, Z.J.; Zhuo, M.J.; He, L.F.; Zhou, Y.C.; Li, M.S.; Wang, J.Y.

    2006-01-01

    The microstructures of bulk Zr 2 Al 3 C 4 and Zr 3 Al 3 C 5 ceramics have been investigated using transmission electron microscopy and scanning transmission electron microscopy. These two carbides were determined to have a point group 6/mmm and a space group P6 3 /mmc using selected-area electron diffraction and convergent beam electron diffraction. The atomic-scale microstructures of Zr 2 Al 3 C 4 and Zr 3 Al 3 C 5 were investigated through high-resolution imaging and Z-contrast imaging. Furthermore, intergrowth between Zr 2 Al 3 C 4 and Zr 3 Al 3 C 5 was identified. Stacking faults in Zr 3 Al 3 C 5 were found to result from the insertion of an additional Zr-C layer. Cubic ZrC was occasionally identified to be incorporated in elongated Zr 3 Al 3 C 5 grains. In addition, Al may induce a twinned ZrC structure and lead to the formation of ternary zirconium aluminum carbides

  11. Atomic scale images of acceptors in III-V semiconductors. Band bending, tunneling paths and wave functions

    Energy Technology Data Exchange (ETDEWEB)

    Loth, S.

    2007-10-26

    This thesis reports measurements of single dopant atoms in III-V semiconductors with low temperature Scanning Tunneling Microscopy (STM) and Scanning Tunneling Spectroscopy (STS). It investigates the anisotropic spatial distribution of acceptor induced tunneling processes at the {l_brace}110{r_brace} cleavage planes. Two different tunneling processes are identified: conventional imaging of the squared acceptor wave function and resonant tunneling at the charged acceptor. A thorough analysis of the tip induced space charge layers identifies characteristic bias windows for each tunnel process. The symmetry of the host crystal's band structure determines the spatial distribution of the tunneling paths for both processes. Symmetry reducing effects at the surface are responsible for a pronounced asymmetry of the acceptor contrasts along the principal [001] axis. Uniaxial strain fields due to surface relaxation and spin orbit interaction of the tip induced electric field are discussed on the basis of band structure calculations. High-resolution STS studies of acceptor atoms in an operating p-i-n diode confirm that an electric field indeed changes the acceptor contrasts. In conclusion, the anisotropic contrasts of acceptors are created by the host crystal's band structure and concomitant symmetry reduction effects at the surface. (orig.)

  12. Scaling studies of solar pumped lasers

    Science.gov (United States)

    Christiansen, W. H.; Chang, J.

    1985-01-01

    A progress report of scaling studies of solar pumped lasers is presented. Conversion of blackbody radiation into laser light has been demonstrated in this study. Parametric studies of the variation of laser mixture composition and laser gas temperature were carried out for CO2 and N2O gases. Theoretical analysis and modeling of the system have been performed. Reasonable agreement between predictions in the parameter variation and the experimental results have been obtained. Almost 200 mW of laser output at 10.6 micron was achieved by placing a small sapphire laser tube inside an oven at 1500 K the tube was filled with CO2 laser gas mixture and cooled by longitudinal nitrogen gas flow.

  13. Cold atoms in singular potentials

    International Nuclear Information System (INIS)

    Denschlag, J. P.

    1998-09-01

    We studied both theoretically and experimentally the interaction between cold Li atoms from a magnetic-optical trap (MOT) and a charged or current-carrying wire. With this system, we were able to realize 1/r 2 and 1/r potentials in two dimensions and to observe the motion of cold atoms in both potentials. For an atom in an attractive 1/r 2 potential, there exist no stable trajectories, instead there is a characteristic class of trajectories for which atoms fall into the singularity. We were able to observe this falling of atoms into the center of the potential. Moreover, by probing the singular 1/r 2 potential with atomic clouds of varying size and temperature we extracted scaling properties of the atom-wire interaction. For very cold atoms, and very thin wires the motion of the atoms must be treated quantum mechanically. Here we predict that the absorption cross section for the 1/r 2 potential should exhibit quantum steps. These quantum steps are a manifestation of the quantum mechanical decomposition of plane waves into partial waves. For the second part of this work, we realized a two dimensional 1/r potential for cold atoms. If the potential is attractive, the atoms can be bound and follow Kepler-like orbits around the wire. The motion in the third dimension along the wire is free. We were able to exploit this property and constructed a novel cold atom guide, the 'Kepler guide'. We also demonstrated another type of atom guide (the 'side guide'), by combining the magnetic field of the wire with a homogeneous offset magnetic field. In this case, the atoms are held in a potential 'tube' on the side of the wire. The versatility, simplicity, and scaling properties of this guide make it an interesting technique. (author)

  14. Recent progress in the studies of atomic spectra and transition probabilities by beam-foil spectroscopy

    International Nuclear Information System (INIS)

    Martinson, I.

    1982-01-01

    A review is given of recent studies of atomic structure (in particular atomic spectra, energy levels and transition probabilities) using fast beams from ion accelerators. Thanks to improved spectral resolution detailed and quite accurate studies of energy levels are now possible, a number of such results will be discussed. The non-autoionizing, multiply excited levels in atoms and ions (including negative ions) are being vigorously investigated at present, some new results will be reported. The accuracy in lifetime determinations continues to improve, and several new ways for reduction of cascading effects have been developed. Some selected examples of recent progress in lifetime measurements are also included. (orig.)

  15. On the extension of (e,2e) theory to coincidence studies of ion-atom collisions

    International Nuclear Information System (INIS)

    Godunov, A.L.; Kampp, Marco; Sulik, B.; Walters, H.R.J.; Whelan, Colm T.

    2007-01-01

    The extension of (e,2e) theory to the coincidence studies of ion-atom collisions is considered. The simultaneous ionization of projectile and target is discussed and results are presented for transfer ionization

  16. The molecular-scale arrangement and mechanical strength of phospholipid/cholesterol mixed bilayers investigated by frequency modulation atomic force microscopy in liquid

    International Nuclear Information System (INIS)

    Asakawa, Hitoshi; Fukuma, Takeshi

    2009-01-01

    Cholesterols play key roles in controlling molecular fluidity in a biological membrane, yet little is known about their molecular-scale arrangements in real space. In this study, we have directly imaged lipid-cholesterol complexes in a model biological membrane consisting of dipalmitoylphosphatidylcholine (DPPC) and cholesterols by frequency modulation atomic force microscopy (FM-AFM) in phosphate buffer solution. FM-AFM images of a DPPC/cholesterol bilayer in the liquid-ordered phase showed higher energy dissipation values compared to those measured on a nanoscale DPPC domain in the gel phase, reflecting the increased molecular fluidity due to the insertion of cholesterols. Molecular-resolution FM-AFM images of a DPPC/cholesterol bilayer revealed the existence of a rhombic molecular arrangement (lattice constants: a = 0.46 nm, b = 0.71 nm) consisting of alternating rows of DPPC and cholesterols as well as the increased defect density and reduced molecular ordering. The mechanical strength of a DPPC/cholesterol bilayer was quantitatively evaluated by measuring a loading force required to penetrate the membrane with an AFM tip. The result revealed the significant decrease of mechanical strength upon insertion of cholesterols. Based on the molecular-scale arrangement found in this study, we propose a model to explain the reduced mechanical strength in relation to the formation of lipid-ion networks.

  17. The molecular-scale arrangement and mechanical strength of phospholipid/cholesterol mixed bilayers investigated by frequency modulation atomic force microscopy in liquid

    Energy Technology Data Exchange (ETDEWEB)

    Asakawa, Hitoshi; Fukuma, Takeshi [Frontier Science Organization, Kanazawa University, Kakuma-machi, 920-1192 Kanazawa (Japan)], E-mail: hi_asa@staff.kanazawa-u.ac.jp, E-mail: fukuma@staff.kanazawa-u.ac.jp

    2009-07-01

    Cholesterols play key roles in controlling molecular fluidity in a biological membrane, yet little is known about their molecular-scale arrangements in real space. In this study, we have directly imaged lipid-cholesterol complexes in a model biological membrane consisting of dipalmitoylphosphatidylcholine (DPPC) and cholesterols by frequency modulation atomic force microscopy (FM-AFM) in phosphate buffer solution. FM-AFM images of a DPPC/cholesterol bilayer in the liquid-ordered phase showed higher energy dissipation values compared to those measured on a nanoscale DPPC domain in the gel phase, reflecting the increased molecular fluidity due to the insertion of cholesterols. Molecular-resolution FM-AFM images of a DPPC/cholesterol bilayer revealed the existence of a rhombic molecular arrangement (lattice constants: a = 0.46 nm, b = 0.71 nm) consisting of alternating rows of DPPC and cholesterols as well as the increased defect density and reduced molecular ordering. The mechanical strength of a DPPC/cholesterol bilayer was quantitatively evaluated by measuring a loading force required to penetrate the membrane with an AFM tip. The result revealed the significant decrease of mechanical strength upon insertion of cholesterols. Based on the molecular-scale arrangement found in this study, we propose a model to explain the reduced mechanical strength in relation to the formation of lipid-ion networks.

  18. Emotional Presence in Online Learning Scale: A Scale Development Study

    Science.gov (United States)

    Sarsar, Firat; Kisla, Tarik

    2016-01-01

    Although emotions are not a new topic in learning environments, the emerging technologies have changed not only the type of learning environments but also the perspectives of emotions in learning environments. This study designed to develop a survey to assist online instructors to understand students' emotional statement in online learning…

  19. Application of fundamental principles to mineral scale reduction : case studies

    Science.gov (United States)

    Peter W. Hart; Alan W. Rudie

    2005-01-01

    This paper will present several successful case studies where scale has been eliminated in mills including calcium carbonate scale in a white liquor strainer, calcium oxalate scale in the D0 stage, enzymatic treatment of brown stock to eliminate oxalate scale, and control of barium sulfate scale.

  20. Study of structural colour of Hebomoia glaucippe butterfly wing scales

    Science.gov (United States)

    Shur, V. Ya; Kuznetsov, D. K.; Pryakhina, V. I.; Kosobokov, M. S.; Zubarev, I. V.; Boymuradova, S. K.; Volchetskaya, K. V.

    2017-10-01

    Structural colours of Hebomoia glaucippe butterfly wing scales have been studied experimentally using high resolution scanning electron microscopy. Visualization of scales structures and computer simulation allowed distinguishing correlation between nanostructures on the scales and their colour.

  1. Structural Dynamics and Activity of Nanocatalysts Inside Fuel Cells by in-operando Atomic Pair Distribution Studies

    Science.gov (United States)

    Prasai, Binay

    We present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). Using in-operando high-energy X-ray diffraction we tracked the evolution of the atomic structure and activity of noble metal-transition metal(NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Data were analyzed in terms of atomic pair distribution functions and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore, we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation.

  2. Initial studies of a competition agressivity scale

    Directory of Open Access Journals (Sweden)

    Daniel Bartholomeu

    2008-12-01

    Full Text Available This article describes the development of an aggressivity measure among athletes. Participants included 172 athletes, from five different sports, ranging in age from 14 to 58 years old (mean age 21 years, DP=5,99. The scale was composed of 54 items (on a three-point Likert scale that described various aggressive behaviors. The subjects were asked to indicate the frequency of the behaviors from “always” to “sometimes” and “never.”. The differential item functioning results by sex pointed to six items favoring one of the groups. The data were analyzed by means of principal components analysis with a varimax rotation and suggested a three factor structure explaining 44,31% of the variance. The dimensions were, Intimidation, External Aggression and Internal Aggression. Chronbach’s alphas ranged from 0,74 to 0,90. No significant differences of the dimensions were observed between the studied sports. These data enables the instrument to be used in future research.   Keywords: aggressivity; psychological assessment; sport psychology; factorial analysis; differential item functioning.

  3. Precipitation in an Al-Zn-Mg-Cu alloy during isothermal aging: Atomic-scale HAADF-STEM investigation

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Xuesong; Zheng, Jingxu; Li, Zhi; Luo, Ruichun [School of Materials Science and Engineering, Shanghai Jiao Tong University (China); Frontier Research Center for Materials Structure, Shanghai Jiao Tong University (China); Chen, Bin, E-mail: steelboy@sjtu.edu.cn [School of Materials Science and Engineering, Shanghai Jiao Tong University (China); Frontier Research Center for Materials Structure, Shanghai Jiao Tong University (China)

    2017-04-13

    The present study, using advanced Cs-corrected high-angle annular dark field – scanning transmission electron microscopy (HAADF-STEM), reports on a comprehensive investigation into the precipitate structures in an Al-Zn-Mg-Cu alloy aged at 150 ℃, including GP zones, η’ and η precipitates. In the nucleation stage, Zn atoms enrich on the {111}{sub Al}-planes abutting spherical Mg clusters that are approximately 3–6 nm in diameter. In the subsequent growth, the as-nucleated structures extend with an increasing diameter and a constant width along [111]{sub Al} and grow into platelet precipitates. η’ is proved to be a group of metastable structures existing in the transition from FCC Al to HCP MgZn{sub 2} (η). Some metastable structures are assembled by local-ordered rhombohedral units and orthorhombic units as building blocks. Subsequently, the precipitates evolve into η phases with stacking faults.

  4. Ion cyclotron resonance study of reactions of ions with hydrogen atoms

    International Nuclear Information System (INIS)

    Karpas, Z.; Anicich, V.; Huntress, W.T. Jr.

    1979-01-01

    Reactions of H 2 + , HeH + , and CO 2 + ions with hydrogen atoms, and the reactions of D 2 + , CO 2 + , CO + , N 2 + and HCN + with deuterium atoms, were studied using ion cyclotron resonance techniques. These reactions proceed predominantly via a charge transfer mechanism. The rate constants measured are: 6.4, 9.1, 1.1, 5.0, 0.84, 0.90, 1.2, and 0.37 x 10 -10 cm 3 /sec, respectively. Hydrocarbon ions of the types CH/sub n/ + and C 2 H/sub n/ + , where n=2--4, do not react with H or D atoms

  5. Towards high-energy and durable lithium-ion batteries via atomic layer deposition: elegantly atomic-scale material design and surface modification

    International Nuclear Information System (INIS)

    Meng, Xiangbo

    2015-01-01

    Targeted at fueling future transportation and sustaining smart grids, lithium-ion batteries (LIBs) are undergoing intensive investigation for improved durability and energy density. Atomic layer deposition (ALD), enabling uniform and conformal nanofilms, has recently made possible many new advances for superior LIBs. The progress was summarized by Liu and Sun in their latest review [1], offering many insightful views, covering the design of nanostructured battery components (i.e., electrodes and solid electrolytes), and nanoscale modification of electrode/electrolyte interfaces. This work well informs peers of interesting research conducted and it will also further help boost the applications of ALD in next-generation LIBs and other advanced battery technologies. (viewpoint)

  6. LETTER TO THE EDITOR: Quantum manifestations of closed orbits in the photoexcitation scaled spectrum of the hydrogen atom in crossed fields

    Science.gov (United States)

    Rao, Jianguo; Delande, D.; Taylor, K. T.

    2001-06-01

    The scaled photoexcitation spectrum of the hydrogen atom in crossed electric and magnetic fields has been obtained by means of accurate quantum mechanical calculation using a new algorithm. Closed orbits in the corresponding classical system have also been obtained, using a new, efficient and practical searching procedure. Two new classes of closed orbit have been identified. Fourier transforming each photoexcitation quantum spectrum to yield a plot against scaled action has allowed direct comparison between peaks in such plots and the scaled action values of closed orbits. Excellent agreement has been found with all peaks assigned.

  7. On the thermodynamic efficiency of a nickel-based multiferroic thermomagnetic generator: From bulk to atomic scale

    Energy Technology Data Exchange (ETDEWEB)

    Sandoval, Samuel M., E-mail: samuel.m.sandoval@gmail.com; Sepulveda, Abdon E., E-mail: abdon.sepulveda@gmail.com; Keller, Scott M., E-mail: smkeller@ucla.edu [Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, California 90095 (United States)

    2015-04-28

    A model is developed to correlate the effects of size on the thermodynamic efficiency for a nickel-based multiferroic thermomagnetic generator device. Three existing models are combined in order to estimate this correlation, they are (1) thermodynamic efficiency relations, (2) a model of ferromagnetic transition behavior, and (3) the bond-order length strength correlation. At the smallest size considered, a monolayer of nickel atoms shows a reduction in Curie temperature from its bulk value of T{sub c,Bulk}=630 K to T{sub c,ML}=240 K. This difference is analytically shown to affect the thermodynamic efficiency values when compared to bulk. Various nickel nanofilms are considered as a working body, such that the combined model predicts relative efficiency values that are comparable to the bulk scale, but operating closer to room-temperature when compared to bulk form. This result is unexpected since the absolute efficiency is shown to increase as a function of decreasing size, this discrepancy is explained as a consequence of Curie point suppression. The combined model is also applied to a hypothetical composite made of separated layers of nickel with distinct thicknesses. This composite material is predicted to spread the ferromagnetic transition across a much larger temperature range as compared to bulk nickel, such that this material may be better suited for different applications; for example, as a sensor or thermal switch. Moreover, this combined model is also shown to give a lower-bound estimate for thermodynamic efficiency, since the actual performance depends on material characterizations that have yet to be determined.

  8. Evidencing `Tight Bound States' in the Hydrogen Atom:. Empirical Manipulation of Large-Scale XD in Violation of QED

    Science.gov (United States)

    Amoroso, Richard L.; Vigier, Jean-Pierre

    2013-09-01

    In this work we extend Vigier's recent theory of `tight bound state' (TBS) physics and propose empirical protocols to test not only for their putative existence, but also that their existence if demonstrated provides the 1st empirical evidence of string theory because it occurs in the context of large-scale extra dimensionality (LSXD) cast in a unique M-Theoretic vacuum corresponding to the new Holographic Anthropic Multiverse (HAM) cosmological paradigm. Physicists generally consider spacetime as a stochastic foam containing a zero-point field (ZPF) from which virtual particles restricted by the quantum uncertainty principle (to the Planck time) wink in and out of existence. According to the extended de Broglie-Bohm-Vigier causal stochastic interpretation of quantum theory spacetime and the matter embedded within it is created annihilated and recreated as a virtual locus of reality with a continuous quantum evolution (de Broglie matter waves) governed by a pilot wave - a `super quantum potential' extended in HAM cosmology to be synonymous with the a `force of coherence' inherent in the Unified Field, UF. We consider this backcloth to be a covariant polarized vacuum of the (generally ignored by contemporary physicists) Dirac type. We discuss open questions of the physics of point particles (fermionic nilpotent singularities). We propose a new set of experiments to test for TBS in a Dirac covariant polarized vacuum LSXD hyperspace suggestive of a recently tested special case of the Lorentz Transformation put forth by Kowalski and Vigier. These protocols reach far beyond the recent battery of atomic spectral violations of QED performed through NIST.

  9. Atom probe, AFM and STM study on vacuum fired stainless steel

    International Nuclear Information System (INIS)

    Stupnik, A.; Frank, P.; Leisch, M.

    2008-01-01

    Full text: Stainless steel is one of the most commonly used structural materials for vacuum equipment. An efficient method to reduce the outgassing rate from stainless steel is a high temperature bakeout in vacuum (vacuum firing). This procedure reduces significantly the amount of dissolved hydrogen in the bulk. For the outgassing process the recombination rate of hydrogen atoms to the molecules plays the determining role and recombination is strongly related to the surface structure and composition. To get more detailed information about the surface morphology and composition AFM, STM and atom probe studies were carried out. Experiments on AISI 304L stainless steel samples show that the surface reconstructs completely during vacuum firing and large atomically flat terraces bounded by bunched steps and facets are formed. The large flat terraces can be assigned to (111) planes. The bunched steps and facets are corresponding in orientation almost to (110) planes and (100) planes. Surface inspection after vacuum firing by Auger electron spectroscopy (AES) gives reason for a composition change indicated by a reduction of the chromium signal in relation to the iron and nickel signal. Since the information depth of AES covers several atomic layers not only the top atomic layer of the sample surface is probed. For this reason 3D atom probe was used as well suited tool to investigate the segregation behavior of this alloy with the goal to examine the change in local chemical composition due to the high temperature treatment. As a result of vacuum firing the atom probe experiments show a significant enrichment of nickel at the top surface layer. In the second atomic layer chromium enrichment is detected. After vacuum firing the average composition below the second atomic layer shows certain chromium depletion up to 2 nm in depth. The observed changes in surface chemistry influence recombination and desorption probability from the surface and may contribute to the present

  10. Study of the Dissociative Processes in O_2 Discharges. Development of an Atomic Oxygen Beam Source

    International Nuclear Information System (INIS)

    Pagnon, Daniel

    1992-01-01

    The first part of this work is devoted to the study of dissociative processes in an oxygen glow discharge at low pressure (0,1-5 Torr, 1-80 mA). The kinetics of oxygen atoms has been determined supported by the measurements of atomic concentrations by VUV absorption spectroscopy and actinometry. The reaction coefficients for dissociative excitation and direct excitation of oxygen atoms have been calculated using the cross sections of the literature and a previously calculated EEDF. It has been demonstrated that dissociative excitation is negligible in respect with direct excitation for dissociation rates smaller than 2,5 %. An upper limit of 20 % for dissociative rates is observed. This limit has been explained by the increase of the atomic recombination at the discharge wall with increasing wall temperature. Using all these results, we have designed and optimized a source of oxygen atoms which has then been adapted on a MBE device. The spatial distribution of the atomic density has been measured in molecular jet by laser induced fluorescence (LIF) and Resonant Multi-Photon Ionization (RMPI). A stimulated emission has been evidenced and the coefficient for this process evaluated. A model for the effusion of atoms has been developed from which the flow of atoms on the sample can be predicted. This source has already been used in industrial MBE devices for in-situ oxidation of copper films, superconductors, and substrates for VLSI high speed applications. The methodology of this work and the diagnostics developed can be applied to other kinds of discharges, of other molecular gases, to design sources of atoms for the treatment of large area samples. (author) [fr

  11. Cellulose fibril aggregation studies of eucalyptus dissolving pulps using atomic force microscopy

    CSIR Research Space (South Africa)

    Chunilall, Viren

    2006-11-01

    Full Text Available STUDIES OF Eucalyptus DISSOLVING PULPS USING ATOMIC FORCE MICROSCOPY V. Chunilall1, J.Wesley-Smith2, T. Bush1 1CSIR, Forestry and Forest Product Research Centre, P.O. Box 17001, Congella, 4013, South Africa. 2Electron Microscope Unit, University of Kwa... pulp using atomic force microscopy (AFM) have reported increased cellulose fibril aggregation during processing, and a concomitant decrease in surface area available for chemical reaction1,2. These findings were subsequently confirmed...

  12. Studies of photoionization processes from ground-state and excited-state atoms and molecules

    International Nuclear Information System (INIS)

    Ederer, D.L.; Parr, A.C.; West, J.B.

    1982-01-01

    Recent triply-differential photoelectron spectroscopy experiments designed for the study of correlation effects in atoms and molecules are described. Final-state symmetry of the n=2 state of helium has been determined. The non-Franck-Condon behavior of vibrational branching ratios and large variations of the angular asymmetry parameter has been observed for shape resonances and autoionizing resonances in CO and other molecules. Recent observations of the photoionization of excited sodium atoms are also described

  13. Atomic physics

    International Nuclear Information System (INIS)

    Anon.

    1976-01-01

    Research activities in atomic physics at Lawrence Berkeley Laboratory during 1976 are described. Topics covered include: experiments on stored ions; test for parity violation in neutral weak currents; energy conservation and astrophysics; atomic absorption spectroscopy, atomic and molecular detectors; theoretical studies of quantum electrodynamics and high-z ions; atomic beam magnetic resonance; radiative decay from the 2 3 Po, 2 levels of helium-like argon; quenching of the metastable 2S/sub 1/2/ state of hydrogen-like argon in an external electric field; and lifetime of the 2 3 Po level of helium-like krypton

  14. Study of atomic and molecular emission spectra of Sr by laser induced breakdown spectroscopy (LIBS).

    Science.gov (United States)

    Bhatt, Chet R; Alfarraj, Bader; Ayyalasomayajula, Krishna K; Ghany, Charles; Yueh, Fang Y; Singh, Jagdish P

    2015-12-01

    Laser Induced Breakdown Spectroscopy (LIBS) is an ideal analytical technique for in situ analysis of elemental composition. We have performed a comparative study of the quantitative and qualitative analysis of atomic and molecular emission from LIBS spectra. In our experiments, a mixture of SrCl2 and Al2O3 in powder form was used as a sample. The atomic emission from Sr and molecular emission from SrCl and SrO observed in LIBS spectra were analyzed. The optimum laser energies, gate delays, and gate widths for selected atomic lines and molecular bands were determined from spectra recorded at various experimental parameters. These optimum experimental conditions were used to collect calibration data, and the calibration curves were used to predict the Sr concentration. Limits of detection (LODs) for selected atomic and molecular emission spectra were determined.

  15. Studying nearest neighbor correlations by atom probe tomography (APT) in metallic glasses as exemplified for Fe40Ni40B20 glassy ribbons

    KAUST Repository

    Shariq, Ahmed

    2012-01-01

    A next nearest neighbor evaluation procedure of atom probe tomography data provides distributions of the distances between atoms. The width of these distributions for metallic glasses studied so far is a few Angstrom reflecting the spatial resolution of the analytical technique. However, fitting Gaussian distributions to the distribution of atomic distances yields average distances with statistical uncertainties of 2 to 3 hundredth of an Angstrom. Fe 40Ni40B20 metallic glass ribbons are characterized this way in the as quenched state and for a state heat treated at 350 °C for 1 h revealing a change in the structure on the sub-nanometer scale. By applying the statistical tool of the χ2 test a slight deviation from a random distribution of B-atoms in the as quenched sample is perceived, whereas a pronounced elemental inhomogeneity of boron is detected for the annealed state. In addition, the distance distribution of the first fifteen atomic neighbors is determined by using this algorithm for both annealed and as quenched states. The next neighbor evaluation algorithm evinces a steric periodicity of the atoms when the next neighbor distances are normalized by the first next neighbor distance. A comparison of the nearest neighbor atomic distribution for as quenched and annealed state shows accumulation of Ni and B. Moreover, it also reveals the tendency of Fe and B to move slightly away from each other, an incipient step to Ni rich boride formation. © 2011 Elsevier B.V.

  16. Laser-Assisted Atom Probe Tomography of Deformed Minerals: A Zircon Case Study.

    Science.gov (United States)

    La Fontaine, Alexandre; Piazolo, Sandra; Trimby, Patrick; Yang, Limei; Cairney, Julie M

    2017-04-01

    The application of atom probe tomography to the study of minerals is a rapidly growing area. Picosecond-pulsed, ultraviolet laser (UV-355 nm) assisted atom probe tomography has been used to analyze trace element mobility within dislocations and low-angle boundaries in plastically deformed specimens of the nonconductive mineral zircon (ZrSiO4), a key material to date the earth's geological events. Here we discuss important experimental aspects inherent in the atom probe tomography investigation of this important mineral, providing insights into the challenges in atom probe tomography characterization of minerals as a whole. We studied the influence of atom probe tomography analysis parameters on features of the mass spectra, such as the thermal tail, as well as the overall data quality. Three zircon samples with different uranium and lead content were analyzed, and particular attention was paid to ion identification in the mass spectra and detection limits of the key trace elements, lead and uranium. We also discuss the correlative use of electron backscattered diffraction in a scanning electron microscope to map the deformation in the zircon grains, and the combined use of transmission Kikuchi diffraction and focused ion beam sample preparation to assist preparation of the final atom probe tip.

  17. Study on the performances of an absolute atomic gravimeter: limit sensitivity and preliminary accuracy

    International Nuclear Information System (INIS)

    Le Gouet, J.

    2008-02-01

    Atom interferometry is applied to absolute measurement of gravity acceleration g, to provide an accurate value for the realization of the LNE watt balance. The atomic source is obtained from a cloud of cold 87 Rubidium atoms. Two vertical counter-propagating are used to generate stimulated Raman transitions, that separate the wave-packets and make them interfere. During the transitions, the phase difference between the beams is printed on the phase of the free-falling atoms. Then the atomic phase shift between the two vertical paths becomes sensitive to the atom acceleration and allows obtaining an accurate value of g. A part of this manuscript is dedicated to the study of noise sources which deteriorate the measurement sensitivity. In particular, we detail the vibrations contribution, which we are able to reduce by a factor of 3 to 10, depending on the configurations, thanks to the measurement of a seismometer and to its analog processing. The best reported sensitivity, in optimal environment, is 1.4*10 -8 g/Hz 1/2 . The study of the measurement accuracy also represents an important part of this work. Although the vacuum chamber was only temporary, we started to list the systematic shifts. According to two comparisons with well-known absolute gravimeters based on optical interferometry, our measurement shows a residual bias of 16*10 -9 g. (author)

  18. Theoretical study on the photocatalytic properties of graphene oxide with single Au atom adsorption

    Science.gov (United States)

    Ju, Lin; Dai, Ying; Wei, Wei; Li, Mengmeng; Jin, Cui; Huang, Baibiao

    2018-03-01

    The photocatalytic properties of graphene oxide (GO) with single Au atom adsorption are studied via the first-principles calculations based on the density functional theory. The present study addresses the origin of enhancement in photocatalytic efficiency of GO derived from single Au atom depositing. Compared with the clean one, the work function of the single Au atom adsorbed GO is lowered due to the charge transfer from Au to GO, indicating enhanced surface activity. The Au atom plays as an electron trapping center and a mediating role in charge transfer from photon excited GO to target species. The photogenerated electron-hole pairs can be separated effectively. For the GO configuration with atomic Au dispersion, there are some states introduced in the band gap, which are predominantly composed of Au 6s states. Through the in-gap state, the photo-generated electron transfer from the valence band of clean GO to the conductive band more easily. In addition, the reduction of the gap in the system is also presented in the current work, which indicates that the single Au atom adsorption improves light absorption for the GO based photocatalyst. These theoretical results are valuable for the future applications of GO materials as photocatalyst for water splitting.

  19. Infrared studies of ortho-para conversion at Cl-atom and H-atom impurity centers in cryogenic solid hydrogen

    International Nuclear Information System (INIS)

    Raston, P.L.; Kettwich, S.C.; Anderson, D.T.

    2010-01-01

    We report infrared spectroscopic studies of H 2 ortho-para (o/p) conversion in solid hydrogen doped with Cl-atoms at 2 K while the Cl + H 2 (υ = 1) → HCl + H infrared-induced chemical reaction is occurring. The Cl-atom doped hydrogen crystals are synthesized using 355 nm in situ photodissociation of Cl 2 precursor molecules. For hydrogen solids with high ortho-H 2 fractional concentrations (X o = 0.55), the o/p conversion kinetics is dominated by Cl-atom catalyzed conversion with a catalyzed conversion rate constant K cc = 1.16(11) min -1 and the process is rate-limited by ortho-H 2 quantum diffusion. For hydrogen crystals with low ortho-H2 concentrations (X o = 0.03), single-exponential decay of the ortho-H 2 concentration with time is observed which is attributed to H-atom catalyzed o/p conversion by the H-atoms produced during the infrared-induced Cl + H 2 reaction. The measured H-atom catalyzed o/p conversion kinetics indicates the H-atoms are mobile under these conditions in agreement with previous ESR measurements.

  20. Atomic and molecular manipulation

    CERN Document Server

    Mayne, Andrew J

    2011-01-01

    Work with individual atoms and molecules aims to demonstrate that miniaturized electronic, optical, magnetic, and mechanical devices can operate ultimately even at the level of a single atom or molecule. As such, atomic and molecular manipulation has played an emblematic role in the development of the field of nanoscience. New methods based on the use of the scanning tunnelling microscope (STM) have been developed to characterize and manipulate all the degrees of freedom of individual atoms and molecules with an unprecedented precision. In the meantime, new concepts have emerged to design molecules and substrates having specific optical, mechanical and electronic functions, thus opening the way to the fabrication of real nano-machines. Manipulation of individual atoms and molecules has also opened up completely new areas of research and knowledge, raising fundamental questions of "Optics at the atomic scale", "Mechanics at the atomic scale", Electronics at the atomic scale", "Quantum physics at the atomic sca...

  1. Pulse radiolysis studies of the reactions of bromine atoms and dimethyl sulfoxide bromine atom complexes with alcohols

    Science.gov (United States)

    Sumiyoshi, Takashi; Fujiyoshi, Ryoko; Katagiri, Miho; Sawamura, Sadashi

    2007-05-01

    Dimethylsulfoxide (DMSO)-Br complexes were generated by pulse radiolysis of DMSO/bromomethane mixtures and the formation mechanism and spectral characteristics of the formed complexes were investigated in detail. The rate constant for the reaction of bromine atoms with DMSO and the extinction coefficient of the complex were obtained to be 4.6×10 9 M -1 s -1 and 6300 M -1 cm -1 at the absorption maximum of 430 nm. Rate constants for the reaction of bromine atoms with a series of alcohols were determined in CBrCl 3 solutions applying a competitive kinetic method using the DMSO-Br complex as the reference system. The obtained rate constants were ˜10 8 M -1 s -1, one or two orders larger than those reported for highly polar solvents. Rate constants of DMSO-Br complexes with alcohols were determined to be ˜ 10 7 M -1 s -1. A comparison of the reactivities of Br atoms and DMSO-Br complexes with those of chlorine atoms and chlorine atom complexes which are ascribed to hydrogen abstracting reactants strongly indicates that hydrogen abstraction from alcohols is not the rate determining step in the case of Br atoms and DMSO-Br complexes.

  2. A theoretical study of dopant atom detection and probe behavior in STEM

    Science.gov (United States)

    Mittal, Anudha

    Very detailed information about the atomic and electronic structure of materials can be obtained via atomic-scale resolution scanning transmission electron microscopy (STEM). These experiments reach the limits of current microscopes, which means that optimal experimental design is a key ingredient in success. The step following experiment, extraction of information from experimental data is also complex. Comprehension of experimental data depends on comparison with simulated data and on fundamental understanding of aspects of scattering behavior. The research projects discussed in this thesis are formulated within three large concepts. 1. Usage of simulation to suggest experimental technique for observation of a particular structural feature.. Two specific structural features are explored. One is the characterization of a substitutional dopant atom in a crystal. Annular dark field scanning transmission electron microscope (ADF-STEM) images allow detection of individual dopant atoms in a crystal based on contrast between intensities of doped and non-doped column in the image. The magnitude of the said contrast is heavily influenced by specimen and microscope parameters. Analysis of multislice-based simulations of ADF-STEM images of crystals doped with one substitutional dopant atom for a wide range of crystal thicknesses, types and locations of dopant atom inside the crystal, and crystals with different atoms revealed trends and non-intuitive behaviors in visibility of the dopant atom. The results provide practical guidelines for the optimal experimental setup regarding both the microscope and specimen conditions in order to characterize the presence and location of a dopant atom. Furthermore, the simulations help in recognizing the cases where detecting a single dopant atom via ADF-STEM imaging is not possible. The second is a more specific case of detecting intrinsic twist in MoS2 nanotubes. Objective molecular dynamics simulations coupled with a density

  3. Atom-surface potentials and atom interferometry

    International Nuclear Information System (INIS)

    Babb, J.F.

    1998-01-01

    Long-range atom-surface potentials characterize the physics of many actual systems and are now measurable spectroscopically in deflection of atomic beams in cavities or in reflection of atoms in atomic fountains. For a ground state, spherically symmetric atom the potential varies as -1/R 3 near the wall, where R is the atom-surface distance. For asymptotically large distances the potential is weaker and goes as -1/R 4 due to retardation arising from the finite speed of light. This diminished interaction can also be interpreted as a Casimir effect. The possibility of measuring atom-surface potentials using atomic interferometry is explored. The particular cases studied are the interactions of a ground-state alkali-metal atom and a dielectric or a conducting wall. Accurate descriptions of atom-surface potentials in theories of evanescent-wave atomic mirrors and evanescent wave-guided atoms are also discussed. (author)

  4. Atomic-scale investigation of point defects and hydrogen-solute atmospheres on the edge dislocation mobility in alpha iron

    Energy Technology Data Exchange (ETDEWEB)

    Bhatia, M. A.; Solanki, K. N., E-mail: kiran.solanki@asu.edu [School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287 (United States); Groh, S. [Institute of Mechanics and Fluid Dynamics, TU Bergakademie Freiberg, Freiberg 09556 (Germany)

    2014-08-14

    In this study, we present atomistic mechanisms of 1/2 [111](11{sup ¯}0) edge dislocation interactions with point defects (hydrogen and vacancies) and hydrogen solute atmospheres in body centered cubic (bcc) iron. In metals such as iron, increases in hydrogen concentration can increase dislocation mobility and/or cleavage-type decohesion. Here, we first investigate the dislocation mobility in the presence of various point defects, i.e., change in the frictional stress as the edge dislocation interacts with (a) vacancy, (b) substitutional hydrogen, (c) one substitutional and one interstitial hydrogen, (d) interstitial hydrogen, (e) vacancy and interstitial hydrogen, and (f) two interstitial hydrogen. Second, we examine the role of a hydrogen-solute atmosphere on the rate of local dislocation velocity. The edge dislocation simulation with a vacancy in the compression side of the dislocation and an interstitial hydrogen atom at the tension side exhibit the strongest mechanical response, suggesting a higher potential barrier and hence, the higher frictional stress (i.e., ∼83% higher than the pure iron Peierls stress). In the case of a dislocation interacting with a vacancy on the compressive side, the vacancy binds with the edge dislocation, resulting in an increase in the friction stress of about 28% when compared with the Peierls stress of an edge dislocation in pure iron. Furthermore, as the applied strain increases, the vacancy migrates through a dislocation transportation mechanism by attaining a velocity of the same order as the dislocation velocity. For the case of the edge dislocation interacting with interstitial hydrogen on the tension side, the hydrogen atom jumps through one layer perpendicular to the glide plane during the pinning-unpinning process. Finally, our simulation of dislocation interactions with hydrogen show first an increase in the local dislocation velocity followed by a pinning of the dislocation core in the atmosphere, resulting in

  5. Brunel mood scale: South African norm study

    Directory of Open Access Journals (Sweden)

    Charles H Van Wijk

    2011-06-01

    Full Text Available Objective: The Brunel Mood Scale (BRUMS has proved useful to assess mood states in a range of clinical settings. Its local utility is restricted by the lack of normative data from South Africa. This paper presents preliminary normative data for the use of the BRUMS in the South African health care setting. Method: Participants (N=2200, ranging from 18 to 59 years, employed in the public sector, and were recruited during routine occupational health surveillance, completed the 24-item self-report BRUMS. They came from all South African race and language groups, and from all nine provinces. Results: Significant differences were found between the scores of women and men, and their results are reported separately. Due to the language dependant nature of the BRUMS, results are also reported separately for respondents with English as first language, and those who have other South African languages as mother tongue. Norm tables with T-scores are presented for the full sample, and per gender X language groups. Conclusion: This study presents normative data for a sample of educated and employed South Africans from various backgrounds. Its brevity, and provisionally language friendly nature makes it a useful measure for screening psychological distress in the SA clinical health care context.

  6. On the random cascading model study of anomalous scaling in multiparticle production with continuously diminishing scale

    International Nuclear Information System (INIS)

    Liu Lianshou; Zhang Yang; Wu Yuanfang

    1996-01-01

    The anomalous scaling of factorial moments with continuously diminishing scale is studied using a random cascading model. It is shown that the model currently used have the property of anomalous scaling only for descrete values of elementary cell size. A revised model is proposed which can give good scaling property also for continuously varying scale. It turns out that the strip integral has good scaling property provided the integral regions are chosen correctly, and that this property is insensitive to the concrete way of self-similar subdivision of phase space in the models. (orig.)

  7. The development of high-resolution spectroscopic methods and their use in atomic structure studies

    International Nuclear Information System (INIS)

    Poulsen, O.

    1984-01-01

    This thesis discusses work performed during the last nine years in the field of atomic spectroscopy. Several high-resolution techniques, ranging from quantum beats, level crossings, rf-laser double resonances to nonlinear field atom interactions, have been employed. In particular, these methods have been adopted and developed to deal with fast accelerated atomic or ionic beams, allowing studies of problems in atomic-structure theory. Fine- and hyperfine-structure determinations in the He I and Li I isoelectronic sequences, in 51 V I, and in 235 U I, II have permitted a detailed comparison with ab initio calculations, demonstrating the change in problems when going towards heavier elements or higher ionization stage. The last part of the thesis is concerned with the fundamental question of obtaining very high optical resolution in the interaction between a fast accelerated atom or ion beam and a laser field, this problem being the core in the continuing development of atomic spectroscopy necessary to challenge the more precise and sophisticated theories advanced. (Auth.)

  8. A study of public acceptance of construction of atomic power plant

    International Nuclear Information System (INIS)

    Harada, Kazunori; Matsuhashi, Ryuji; Yoshida, Yoshikuni

    2011-01-01

    In June 2010, Basic Energy Plan was approved in a Cabinet meeting. It says that Japan aims to construct more than 14 atomic power plants by 2030. Today, there are 12 plans of construction of atomic power plant, but it is hard to say that their plans easily come off. That's because public acceptance of atomic power plant is low in Japan, for example local residents wage opposition campaigns. This study conducts a survey in the form of a questionnaire and analyzes it by Analytical Hierarchical Process (AHP). Analytic Hierarchy Process is a structured technique for dealing with complex decisions. A questionnaire using AHP is very easy to answer and analyze. This survey was conducted in 2 areas. First area is Hohoku-cho, Yamaguchi Pref. that had a plan of construction of atomic power plant and the plan was demolished by opposition campaigns. Second area is Kaminoseki-cho, Yamaguchi Pref. that has a plan of construction of atomic power plant now and the plan is working order. Public acceptance can be calculated from survey data of 2 areas, and it helps to understand why first area disapproved a plan of atomic power plant and second area approves it. We consider a model to analyze public acceptance. (author)

  9. Adsorption of alkali and alkaline-earth metal atoms on stanene: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Kadioglu, Yelda; Ersan, Fatih [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Gökoğlu, Gökhan [Department of Physics, Karabük University, 78050 Karabük (Turkey); Aktürk, Olcay Üzengi [Department of Electrical & Electronics Engineering, Adnan Menderes University, 09100 Aydın (Turkey); Nanotechnology Application and Research Center, Adnan Menderes University, 09100 Aydın (Turkey); Aktürk, Ethem, E-mail: ethem.akturk@adu.edu.tr [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Nanotechnology Application and Research Center, Adnan Menderes University, 09100 Aydın (Turkey)

    2016-09-01

    This paper presents a study on the adsorption of alkali and alkaline-earth metal atoms on single-layer stanene with different levels of coverage using first-principles plane wave calculations within spin-polarized density functional theory. The most favorable adsorption site for alkali atoms (Li, Na, K) were found to be the hollow site similar to other group IV single-layers, but the case of alkaline-earths on stanene is different from silicene and germanene. Whereas Mg and Ca are bound to stanene at hollow site, the bridge site is found to be energetically favorable for Be adatom. All adsorbed atoms are positively charged due to the charge transfer from adatom to stanene single-layer. The semimetallic bare stanene become metallic except for Be adsorption. The Beryllium adsorption give rise to non-magnetic semiconducting ground state. Our results illustrate that stanene has a reactive and functionalizable surface similar to graphene or silicene. - Highlights: • Alkali and alkaline-earth metal atoms form stronger bonds with stanene compared to other group IV monolayers. • Semi-metallic stanene becomes nonmagnetic metal for Li, Na, K, Mg, and Ca atoms adsorption. • Semi-metallic stanene becomes nonmagnetic semiconductor with 94 meV band gap for Be atom adsorption.

  10. Quantitative study of two- and three-dimensional strong localization of matter waves by atomic scatterers

    International Nuclear Information System (INIS)

    Antezza, Mauro; Castin, Yvan; Hutchinson, David A. W.

    2010-01-01

    We study the strong localization of atomic matter waves in a disordered potential created by atoms pinned at the nodes of a lattice, for both three-dimensional (3D) and two-dimensional (2D) systems. The localization length of the matter wave, the density of localized states, and the occurrence of energy mobility edges (for the 3D system), are numerically investigated as a function of the effective scattering length between the atomic matter wave and the pinned atoms. Both positive and negative matter wave energies are explored. Interesting features of the density of states are discovered at negative energies, where maxima in the density of bound states for the system can be interpreted in terms of bound states of a matter wave atom with a few pinned atomic scatterers. In 3D we found evidence of up to three mobility edges, one at positive energies, and two at negative energies, the latter corresponding to transitions between extended and localized bound states. In 2D, no mobility edge is found, and a rapid exponential-like increase of the localization length is observed at high energy.

  11. Atomic-scale microstructures, Raman spectra and dielectric properties of cubic pyrochlore-typed Bi1.5MgNb1.5O7 dielectric ceramics

    KAUST Repository

    Li, Yangyang

    2014-07-01

    Single-phase cubic pyrochlore-typed Bi1.5MgNb 1.5O7 (BMN) dielectric ceramics were synthesized at temperatures of 1050-1200 °C by solid-state reaction method. Their atomic-scale microstructures and dielectric properties were investigated. X-ray diffraction patterns revealed that the BMN ceramics had an average cubic pyrochlore structure, whereas the Raman spectra indicated that they had an essentially cubic symmetry with small local deviations at the A and O\\' sites of the cubic pyrochlore structure. This was confirmed by selected electron area diffraction (SAED) patterns, where the reflections of {442} (not allowed in the cubic pyrochlore with Fd3̄m symmetry) were clearly observed. SEM and TEM images revealed that the average grain size was increased with the sintering temperature, and an un-homogeneous grain growth was observed at high temperatures. HRTEM images and SAED patterns revealed the single-crystalline nature of the BMN ceramic grains. Energy dispersive spectroscopy (EDS) elemental mapping studies indicated that the compositional distributions of Bi, Mg, Nb and O elements in the ceramic grains were homogenous, and no elemental precipitation was observed at the grain boundary. Quantitative EDS data on ceramic grains revealed the expected cationic stoichiometry based on the initial composition of Bi1.5MgNb1.5O7. Dielectric constants of all the BMN samples exhibited almost frequency independent characteristic in the frequency range of 102-106 Hz, and the highest value was 195 for the BMN ceramics sintered at sintered at 1150 °C with the highest bulk density. The dielectric losses were stable and less than 0.002 in the frequency range of 102-105 Hz. The high dielectric constants of the present BMN samples can be ascribed to the local atomic deviations at the A and O\\' sites from the ideal atomic positions of the pyrochlore structure, which affect the different polarization mechanisms in the BMN ceramics, and which in turn enhance the dielectric

  12. Atomic-scale microstructures, Raman spectra and dielectric properties of cubic pyrochlore-typed Bi1.5MgNb1.5O7 dielectric ceramics

    KAUST Repository

    Li, Yangyang; Zhu, Xinhua; Al-Kassab, Talaat

    2014-01-01

    Single-phase cubic pyrochlore-typed Bi1.5MgNb 1.5O7 (BMN) dielectric ceramics were synthesized at temperatures of 1050-1200 °C by solid-state reaction method. Their atomic-scale microstructures and dielectric properties were investigated. X-ray diffraction patterns revealed that the BMN ceramics had an average cubic pyrochlore structure, whereas the Raman spectra indicated that they had an essentially cubic symmetry with small local deviations at the A and O' sites of the cubic pyrochlore structure. This was confirmed by selected electron area diffraction (SAED) patterns, where the reflections of {442} (not allowed in the cubic pyrochlore with Fd3̄m symmetry) were clearly observed. SEM and TEM images revealed that the average grain size was increased with the sintering temperature, and an un-homogeneous grain growth was observed at high temperatures. HRTEM images and SAED patterns revealed the single-crystalline nature of the BMN ceramic grains. Energy dispersive spectroscopy (EDS) elemental mapping studies indicated that the compositional distributions of Bi, Mg, Nb and O elements in the ceramic grains were homogenous, and no elemental precipitation was observed at the grain boundary. Quantitative EDS data on ceramic grains revealed the expected cationic stoichiometry based on the initial composition of Bi1.5MgNb1.5O7. Dielectric constants of all the BMN samples exhibited almost frequency independent characteristic in the frequency range of 102-106 Hz, and the highest value was 195 for the BMN ceramics sintered at sintered at 1150 °C with the highest bulk density. The dielectric losses were stable and less than 0.002 in the frequency range of 102-105 Hz. The high dielectric constants of the present BMN samples can be ascribed to the local atomic deviations at the A and O' sites from the ideal atomic positions of the pyrochlore structure, which affect the different polarization mechanisms in the BMN ceramics, and which in turn enhance the dielectric constants of

  13. Adatom Bond Dissociation in the Collision Between an Adsorbed Atom and Incident Diatomic Molecule: A Classical Trajectory Study

    International Nuclear Information System (INIS)

    Bayhan, U.

    2004-01-01

    The collisional dissociation of the Atom-Surface bond in the diatomic molecule (gas) / atom (ads) collision taking place on a bcc-structure surface have been studied by classical trajectory methods over the collision energy ranges and the attractive well depth of the diatomic molecule (gas) / atom (ads) interactions

  14. Molecular-scale noncontact atomic force microscopy contrasts in topography and energy dissipation on c(4x2) superlattice structures of alkanethiol self-assembled monolayers

    OpenAIRE

    Fukuma, Takeshi; Ichii, Takashi; Kobayashi, Kei; Yamada, Hirofumi; Matsushige, Kazumi

    2004-01-01

    Alkanethiol self-assembledmonolayers formed on Au(111) surfaces were investigated by noncontact atomic force microscopy (NC-AFM). Dodecanethiol monolayers prepared at 78 °C were imaged by NC-AFM, which revealed that the film is composed predominantly of two different phases of c(4×2)superlattice structures. The obtained molecular-scale NC-AFM contrasts are discussed in comparison with previously reported scanning tunneling microscopy images. We found that the energy dissipation image exhibits...

  15. Atomic-Scale Imaging of Surfaces and Interfaces. Materials Research Society Symposium Proceedings Held in Boston, Massachusetts on November 30-December 2, 1992. Volume 295

    Science.gov (United States)

    1992-01-01

    ofrindi idual siruxtural ui.inix cn. hoes er, be atitntcdiru Aith current comnputer hardwa~e A firsit oi Xr Model for the detect structure max be...02115 ABSTRACT Atomic force microscopy (AFM) has been used to image the surface atomic structure of hydroxyapatite lCaI0(PO4 )6 (Oll)2 1, HA. and...The structure and chemical nature of the minerals hydroxyapatite and brushite have been studied extensively in biological researchf-t0 HA is found

  16. BENCH SCALE SALTSTONE PROCESS DEVELOPMENT MIXING STUDY

    Energy Technology Data Exchange (ETDEWEB)

    Cozzi, A.; Hansen, E.

    2011-08-03

    The Savannah River National Laboratory (SRNL) was requested to develop a bench scale test facility, using a mixer, transfer pump, and transfer line to determine the impact of conveying the grout through the transfer lines to the vault on grout properties. Bench scale testing focused on the effect the transfer line has on the rheological property of the grout as it was processed through the transfer line. Rheological and other physical properties of grout samples were obtained prior to and after pumping through a transfer line. The Bench Scale Mixing Rig (BSMR) consisted of two mixing tanks, grout feed tank, transfer pump and transfer hose. The mixing tanks were used to batch the grout which was then transferred into the grout feed tank. The contents of the feed tank were then pumped through the transfer line (hose) using a progressive cavity pump. The grout flow rate and pump discharge pressure were monitored. Four sampling stations were located along the length of the transfer line at the 5, 105 and 205 feet past the transfer pump and at 305 feet, the discharge of the hose. Scaling between the full scale piping at Saltstone to bench scale testing at SRNL was performed by maintaining the same shear rate and total shear at the wall of the transfer line. The results of scaling down resulted in a shorter transfer line, a lower average velocity, the same transfer time and similar pressure drops. The condition of flow in the bench scale transfer line is laminar. The flow in the full scale pipe is in the transition region, but is more laminar than turbulent. The resulting plug in laminar flow in the bench scale results in a region of no-mixing. Hence mixing, or shearing, at the bench scale should be less than that observed in the full scale, where this plug is non existent due to the turbulent flow. The bench scale tests should be considered to be conservative due to the highly laminar condition of flow that exists. Two BSMR runs were performed. In both cases, wall

  17. Atomic collisions involving pulsed positrons

    DEFF Research Database (Denmark)

    Merrison, J. P.; Bluhme, H.; Field, D.

    2000-01-01

    Conventional slow positron beams have been widely and profitably used to study atomic collisions and have been instrumental in understanding the dynamics of ionization. The next generation of positron atomic collision studies are possible with the use of charged particle traps. Not only can large...... instantaneous intensities be achieved with in-beam accumulation, but more importantly many orders of magnitude improvement in energy and spatial resolution can be achieved using positron cooling. Atomic collisions can be studied on a new energy scale with unprecedented precion and control. The use...

  18. Atomic-Scale Structure of Al2O3-ZrO2 Mixed Oxides Prepared by Laser Ablation

    International Nuclear Information System (INIS)

    Yang Xiuchun; Dubiel, M.; Hofmeister, H.; Riehemann, W.

    2007-01-01

    By means of x-ray diffractometry (XRD) and X-ray absorption fine structure spectroscopy, the phase composition and atomic structure of laser evaporated ZrO2 and ZrO2-Al2O3 nanopowders have been studied. The results indicate that pure ZrO2 exists in the form of tetragonal structure, Al2O3 doped ZrO2 nanoparticles, however, have cubic structure. Compared to bulk tetragonal ZrO2, pure tetragonal ZrO2 nanoparticles have a shorter Zr-O- and Zr-Zr shell, indicating that the lattice contracts with decreasing particle size. For Al2O3 doped ZrO2 solid solution, the distances of first Zr-O and Zr-Zr (Al) coordination decrease with increasing solid solubility. The disorder degree of the ZrO2 lattice increases with increasing solid solubility. The coevaporated ZrO2-Al2O3 is quickly solidified into amorphous phase when it is ablated in a higher pressure. The amorphous phase contains Zr-O-Zr (Al) clusters and has shorter Zr-O distance and tower Zr-O coordination number

  19. Energy-related atomic and molecular structure and scattering studies: Final report

    International Nuclear Information System (INIS)

    1987-01-01

    The general goals of the DOE research concerned the use of molecular beams techniques in the study of atomic and molecular polarizabilities and the study of the interactions between electrons and highly polar molecules. Both of these goals are directly relevant to the general problem of the role played by long-range forces in atomic and molecular physics. Details related to this motivation can be found in the published literature. Here we will describe in general terms the work performed under DOE sponsorship in the atomic beams laboratory at NYU. Our original intent was to exploit techniques developed at NYU, mainly in the study of simple atomic systems, to the more complex atomic and molecular systems that are related to DOE interests. These included the developing understanding of the structure of molecular systems, particularly of alkali halide molecules, and the study of the interactions of electrons with such molecules. The structure experiments would serve as critical experimental benchmarks for computational techniques on molecular properties, including both molecular wave functions and derivative properties of them, such as vibrational and rotational constants, but in particular of molecular electric dipole polarizabilities. We believe that we have at least to some extent fulfilled these goals. 16 refs., 1 fig

  20. Combined short scale roughness and surface dielectric function gradient effects on the determination of tip-sample force in atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Gusso, André, E-mail: gusso@metal.eeimvr.uff.br [Departamento de Ciências Exatas-EEIMVR, Universidade Federal Fluminense, Volta Redonda, RJ 27255-125 (Brazil)

    2013-11-11

    The contribution of tip roughness to the van der Waals force between an atomic force microscopy probe tip and the sample is calculated using the multilayer effective medium model, which allows us to consider the relevant case of roughness characterized by correlation length and amplitude in the nanometer scale. The effect of the surface dielectric function gradient is incorporated in the tip-sample force model. It is concluded that for rms roughness in the few nanometers range the effect of short scale tip roughness is quite significant.

  1. Applications of atomic force microscopy to the studies of biomaterials in biomolecular systems

    Science.gov (United States)

    Ma, Xiang

    Atomic force microscopy (AFM) is a unique tool for the studies of nanoscale structures and interactions. In this dissertation, I applied AFM to study transitions among multiple states of biomaterials in three different microscopic biomolecular systems: MukB-dependent DNA condensation, holdfast adhesion, and virus elasticity. To elucidate the mechanism of MukB-dependent DNA condensation, I have studied the conformational changes of MukB proteins as indicators for the strength of interactions between MukB, DNA and other molecular factors, such as magnesium and ParC proteins, using high-resolution AFM imaging. To determine the physical origins of holdfast adhesion, I have investigated the dynamics of adhesive force development of the holdfast, employing AFM force spectroscopy. By measuring rupture forces between the holdfast and the substrate, I showed that the holdfast adhesion is strongly time-dependent and involves transformations at multiple time scales. Understanding the mechanisms of adhesion force development of the holdfast will be critical for future engineering of holdfasts properties for various applications. Finally, I have examined the elasticity of self-assembled hepatitis B virus-like particles (HBV VLPs) and brome mosaic virus (BMV) in response to changes of pH and salinity, using AFM nanoindentation. The distributions of elasticity were mapped on a single particle level and compared between empty, RNA- and gold-filled HBV VLPs. I found that a single HBV VLP showed heterogeneous distribution of elasticity and a two-step buckling transition, suggesting a discrete property of HBV capsids. For BMV, I have showed that viruses containing different RNA molecules can be distinguished by mechanical measurements, while they are indistinguishable by morphology. I also studied the effect of pH on the elastic behaviors of three-particle BMV and R3/4 BMV. This study can yield insights into RNA presentation/release mechanisms, and could help us to design novel drug

  2. Intersegmental interactions in supercoiled DNA: atomic force microscope study

    Energy Technology Data Exchange (ETDEWEB)

    Shlyakhtenko, Luda S.; Miloseska, Lela; Potaman, Vladimir N.; Sinden, Richard R.; Lyubchenko, Yuri L

    2003-10-15

    Intersegmental interactions in DNA facilitated by the neutralization of electrostatic repulsion was studied as a function of salt concentration and DNA supercoiling. DNA samples with defined superhelical densities were deposited onto aminopropyl mica at different ionic conditions and imaged in air after drying of the samples. Similar to hydrodynamic data, we did not observe a collapse of supercoiled DNA, as proposed earlier by cryo-EM studies. Instead, the formation of the contacts between DNA helices within supercoiled loops with no visible space between the duplexes was observed. The length of such close contacts increased upon increasing NaCl concentration. DNA supercoiling was a critical factor for the stabilization of intersegmental contacts. Implications of the observed effect for understanding DNA compaction in the cell and for regulation DNA transactions via interaction of distantly separated DNA regions are discussed.

  3. Basic Equations Interrelate Atomic and Nuclear Properties to Patterns at the Size Scales of the Cosmos, Extended Clusters of Galaxies, Galaxies, and Nebulae

    Science.gov (United States)

    Allen, Rob

    2016-09-01

    Structures within molecules and nuclei have relationships to astronomical patterns. The COBE cosmic scale plots, and large scale surveys of galaxy clusters have patterns also repeating and well known at atomic scales. The Induction, Strong Force, and Nuclear Binding Energy Periods within the Big Bang are revealed to have played roles in the formation of these large scale distributions. Equations related to the enormous patterns also model chemical bonds and likely nucleus and nucleon substructures. ratios of the forces that include gravity are accurately calculated from the distributions and shapes. In addition, particle masses and a great many physical constants can be derived with precision and accuracy from astrophysical shapes. A few very basic numbers can do modelling from nucleon internals to molecules to super novae, and up to the Visible Universe. Equations are also provided along with possible structural configurations for some Cold Dark Matter and Dark Energy.

  4. Light scattering studies of solids and atomic vapors

    International Nuclear Information System (INIS)

    Chiang, T.C.

    1978-09-01

    The general technique of light scattering and luminescence was used to study the properties of a number of material systems. First, multi-phonon resonant Raman scattering up to four phonons in GaSe and one- and two-phonon resonant Raman scattering in the mixed GaS/sub x/Se/sub 1-x/ crystals with x 2 is reported. The result is used to determine the position of the direct gap of HfS 2 . Third, the first observation of the π-polarized one-magnon luminescence sideband of the 4 T/sub lg/ ( 4 G) → 6 A/sub lg/( 6 S) excitonic transition in antiferromagnetic MnF 2 is presented. An effective temperature of the crystal is deduced from the simultaneously observed anti-Stokes sideband emission. Multi-magnon ( 2 , KMnF 2 , and RbMnF 3 using pulsed excitation and detection. A simple model based on two-ion local exchange is proposed to explain the results qualitatively. Fourth, the first observation of two-magnon resonant Raman scattering in MnF 2 around the magnon sidebands is reported. A simple theoretical description explains the experimental observations. Fifth, a detailed theory of exciton-exciton interaction in MnF 2 is developed to explain and to predict the experimental results on two-exciton absorption, high level excitation, and exciton--exciton scattering. Sixth, Brillouin scattering was used to obtain the five independent elastic constants of the layered compound GaSe. The results show clear elastic anisotropy of the crystal. Resonant Brillouin scattering near the absorption edge was also studied, but no resonant enhancement was found. Seventh, two-photon parametric scattering in sodium vapor was studied. Phase matching angles and scattering cross sections are calculated for a given set of experimental conditions

  5. The potentials and challenges of electron microscopy in the study of atomic chains

    Science.gov (United States)

    Banhart, Florian; Torre, Alessandro La; Romdhane, Ferdaous Ben; Cretu, Ovidiu

    2017-04-01

    The article is a brief review on the potential of transmission electron microscopy (TEM) in the investigation of atom chains which are the paradigm of a strictly one-dimensional material. After the progress of TEM in the study of new two-dimensional materials, microscopy of free-standing one-dimensional structures is a new challenge with its inherent potentials and difficulties. In-situ experiments in the TEM allowed, for the first time, to generate isolated atomic chains consisting of metals, carbon or boron nitride. Besides having delivered a solid proof for the existence of atomic chains, in-situ TEM studies also enabled us to measure the electrical properties of these fundamental linear structures. While ballistic quantum conductivity is observed in chains of metal atoms, electrical transport in chains of sp1-hybridized carbon is limited by resonant states and reflections at the contacts. Although substantial progress has been made in recent TEM studies of atom chains, fundamental questions have to be answered, concerning the structural stability of the chains, bonding states at the contacts, and the suitability for applications in nanotechnology. Contribution to the topical issue "The 16th European Microscopy Congress (EMC 2016)", edited by Richard Brydson and Pascale Bayle-Guillemaud

  6. Single-collision studies of hot atom energy transfer and chemical reaction

    International Nuclear Information System (INIS)

    Valentini, J.J.

    1991-01-01

    This report discusses research in the collision dynamics of translationally hot atoms, with funding with DOE for the project ''Single-Collision Studies of Hot Atom Energy Transfer and Chemical Reaction,'' Grant Number DE-FG03-85ER13453. The work reported here was done during the period September 9, 1988 through October 31, 1991. During this period this DOE-funded work has been focused on several different efforts: (1) experimental studies of the state-to-state dynamics of the H + RH → H 2 R reactions where RH is CH 4 , C 2 H 6 , or C 3 H 8 , (2) theoretical (quasiclassical trajectory) studies of hot hydrogen atom collision dynamics, (3) the development of photochemical sources of translationally hot molecular free radicals and characterization of the high resolution CARS spectroscopy of molecular free radicals, (4) the implementation of stimulated Raman excitation (SRE) techniques for the preparation of vibrationally state-selected molecular reactants

  7. An experimental study on atomizing formation process of diesel spray

    International Nuclear Information System (INIS)

    Kim, Ki Bong

    2000-02-01

    In this study, the experiment has, been conducted to investigate the spray characteristics under the parameter of an ambient pressure with a single hole nozzle having aspect ratio(L/D) of 5 and diameter of 0.45mm. Under the condition of the injection pressure of 14Mpa, the initial disintegrating process of a diesel spray is investigated and analysized according to change of the ambient pressures, 0.1, 1, 2 and 3Mpa. The double flash method has been employed to visualize the process of the diesel sprays. The results obtained in this study are as follows: 1) After spray starts, the spray is shown as non-disturbance liquid column within about 1∼2mm from the nozzle tip, whose diameter is similar to that of a nozzle. For the same injection pressure, the increase of the ambient pressure makes the length of the non-disturbance liquid column become short. 2) Due to the surface wave, ligaments of the shape thread appear at the boundary of liquid column right after spray. The more developed wave together the progress of spray transforms ligaments into droplets that have generally the uniformed size. 3) In case spraying into chambers having different ambient pressures, 1, 2, and 3Mpa, the spray tip velocities reach up to 1.5, 1.2, and 0.6ms, respectively, and decrease with lapse of time. The spray angle keeps increasing for 0.6, 1.2, and 1.4ms after spray under the various ambient pressures, 3, 2, and 1Mpa, respectively, and begins to decrease and maintains the constant value. Therefore, the transition points appear near the point where the velocity decreases and the spray angle increases, simultaneously. The higher ambient pressure leads to fast appearance of transition under the same spray pressure. 4) The disintegrating mechanism of the liquid spray is two combined effects: a) friction forces between the surface waves generated at the surface of the liquid column and the ambient gas, b) the collisions of liquid droplets and ligaments by spray were overtaking

  8. Atomic Scale coexistence of Periodic and quasiperiodic order in a2-fold A1-Ni-Co decagonal quasicrystal surface

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jeong Young; Ogletree, D. Frank; Salmeron, Miquel; Ribeiro,R.A.; Canfield, P.C.; Jenks, C.J.; Thiel, P.A.

    2005-11-14

    Decagonal quasicrystals are made of pairs of atomic planes with pentagonal symmetry periodically stacked along a 10-fold axis. We have investigated the atomic structure of the 2-fold surface of a decagonal Al-Ni-Co quasicrystal using scanning tunneling microscopy (STM). The surface consists of terraces separated by steps of heights 1.9, 4.7, 7.8, and 12.6{angstrom} containing rows of atoms parallel to the 10-fold direction with an internal periodicity of 4{angstrom}. The rows are arranged aperiodically, with separations that follow a Fibonacci sequence and inflation symmetry. The results indicate that the surfaces are preferentially Al-terminated and in general agreement with bulk models.

  9. Precise atomic-scale investigations of material sputtering process by light gas ions in pre-threshold energy region

    CERN Document Server

    Suvorov, A L

    2002-01-01

    Foundation and prospects of the new original technique of the sputtering yield determination of electro-conducting materials and sub-atomic layers on their surface by light gas ions the pre-threshold energy region (from 10 to 500 eV) are considered. The technique allows to identify individual surface vacancies, i.e., to count individual sputtered atoms directly. A short review of the original results obtained by using the developed techniques is given. Data are presented and analyzed concerning energy thresholds of the sputtering onset and energy dependences of sputtering yield in the threshold energy region for beryllium, tungsten, tungsten oxide, alternating tungsten-carbon layers, three carbon materials as well as for sub-atomic carbon layers on surface of certain metals at their bombardment by hydrogen, deuterium and/or helium ions

  10. Theoretical Study of Triatomic Systems Involving Helium Atoms

    International Nuclear Information System (INIS)

    Suno, H.; Hiyama, E.; Kamimura, M.

    2013-01-01

    The triatomic 4 He system and its isotopic species 4 He 2 3 He are theoretically investigated. By adopting the best empirical helium interaction potentials, we calculate the bound state energy levels as well as the rates for the three-body recombination processes: 4 He + 4 He + 4 He → 4 He 2 + 4 He and 4 He + 4 He + 3 He → 4 He 2 + 3 He. We consider not only zero total angular momentum J = 0 states, but also J > 0 states. We also extend our study to mixed helium-alkali triatomic systems, that is 4 He 2 X with X = 7 Li, 23 Na, 39 K, 85 Rb, and 133 Cs. The energy levels of all the J ≥ 0 bound states for these species are calculated as well as the rates for three-body recombination processes such as 4 He + 4 He + 7 Li → 4 He 2 + 7 Li and 4 He + 4 He + 7 Li → 4 He 7 Li + 4 He. In our calculations, the adiabatic hyperspherical representation is employed but we also obtain preliminary results using the Gaussian expansion method. (author)

  11. Studies for aseismatic design of atomic power equipment

    International Nuclear Information System (INIS)

    Uchiyama, Yuichi; Takayanagi, Masaaki; Moriyama, Takeo; Mizuno, Sadao

    1976-01-01

    The social requirements for the safety of nuclear power stations are very severe, and especially in Japan where earthquakes occur frequently, the safety against earthquakes is regarded as an important matter. The numerous machinery and equipments composing nuclear power plants have largely different roles in the safety, accordingly it is important to maintain effectively the safety as a whole. The design is carried out by classifying buildings, machinery and equipments, pipings and electric appliances according to the importance, and so that the aseismatic property corresponding to the importance is given to each. In most cases, the aseismatic design is carried out with computing codes, but it is necessary to forward the design by proving the propriety of analysis models and calculated results. Efforts are exerted in Hitachi Ltd. to improve the accuracy of the aseismatic analysis by carrying out basic experiment, the demonstration test in actual plants and the study on analytical method as many as possible. The measurement of the vibration of actual pipings in order to confirm the supporting conditions, the comparison of multi-input analysis and SRSS method for piping analysis, and the vibration tests of a model containment vessel and a fuel assembly were carried out, and the results are reported in this paper. It is important to improve the accuracy of earthquake response analysis further. (Kako, I.)

  12. Study of gastric cancer in atomic bomb survivors

    International Nuclear Information System (INIS)

    Takayama, Sadamatsu; Tadehara, Futoshi; Okusaki, Ken; Ito, Yoshiko; Ogawa, Junichiro; Kato, Masafumi; Ito, Chikako; Oyama, Hiroko; Mito, Kazuyo.

    1990-01-01

    Ten gastric cancer A-bomb survivors who had been false negative in mass screening for gastric cancer one year before the diagnosis were entered in a study determining an adequate interval of gastric mass screening for A-bomb survivors. Doubling time of cancer was determined on X-ray films. Of the 10 A-bomb survivors, 8 had entered the city after the bombing and the other two had been exposed at 1,700 m and 2,500 m, respectively, from the hypocenter. Six had early gastric cancer and the other 4 had advanced cancer. Doubling time averaged 19.1 months for early cancer and 7.6 months for advanced cancer. Three measurements of tumor diameter available for 4 A-bomb survivors revealed a very rapid increase in doubling time during the progression period from early to advanced cancer. An interval of one year seems to be adequate in mass screening to detect early cancer. (N.K.)

  13. Study of thyroid tumors in atomic bomb survivors in Nagasaki

    International Nuclear Information System (INIS)

    Sekine, Ichiro; Shichijo, Kazuko; Ito, Masahiro; Kishikawa, Masao; Mine, Mariko; Ikeda, Takayoshi; Ooya, Seiichi.

    1992-01-01

    Thyroid tumors, which were registered during 16 years from 1973 through 1988 in the Nagasaki tumor tissue registration committee, were examined with the purpose of searching for the relationship between thyroid tumors and A-bombing. One hundred and three A-bomb survivors having an A-bomb survivors 'handbook and 89 non-exposed persons born before August 9, 1945 in Nagasaki City were enrolled in the present study. The A-bomb survivors were divided into three groups: people exposed at >2,000 m from the hypocenter (n=20), those exposed at ≤2,000 m (n=68), and those entered the city early after A-bombing (n=15). Thyroid tumors examined were: thyroid carcinoma, nodular goiter, thyroid adenoma and malignant lymphoma. Crude incidence rate and relative risk of thyroid cancer were higher in all exposed groups, except for the ≤2,000 m group of males, than the non-exposed group. In particular, the >2,000 m group had significantly higher incidence of thyroid cancer, irrespective of sex. These findings confirmed the previous data for the higher incidence of thyroid cancer in A-bomb survivors exposed to higher doses of radiation. According to age, thyroid cancer was the most common in their sixth decade of life in the exposed group and in their fifth decade of life in the non-exposed group. Histologically, follicular carcinoma occupied higher incidence in the exposed group (19.2%) than the non-exposed group (8.7%). (N.K.)

  14. Studies in hot atom and radiation chemistry. Progress report, December 1, 1979-November 30, 1980

    International Nuclear Information System (INIS)

    Koski, W.S.

    1980-09-01

    /sub nThe results on the reactive scattering of B + ( 3 P/sub u/) by D 2 has been published and a corresponding study on the ground state ( 1 S/sub g/) of B + has been submitted for publication. The ionic aspect of the Br-ethane hot atom system is being investigated using beam techniques. It is found that there is no direct reaction of Br + with ethane which can explain the thermal ionic yield of CH 3 Br reported by hot atom chemists for the Br-ethane hot atom system. Likewise, no satisfactory explanation exists for the dependence of the thermal ionic yield of CH 3 Br on moderator mole fraction. Studies of the collisions of Br + with Kr (which is used as a moderator in hot atom systems) shows that ions such as BrKr + are formed. Electron irradiation of CH 3 Br-Kr mixtures shows that CH 3 BrKr + is formed in good yield. Electron irradiation of Br 2 -Kr mixtures shows that ions such as Br(Kr)/sub n/ + are formed. Such ions can be produced in the Kr moderated Br-ethane hot atom system and can explain the thermal ionic yield of CH 3 Br and its dependence on Kr pressure

  15. Epidemiological studies of employees of the United Kingdom Atomic Energy Authority

    International Nuclear Information System (INIS)

    Fraser, P.; Beral, V.; Booth, M.; Inskip, H.; Carpenter, L.

    1987-01-01

    The Epidemiological Monitoring Unit at the London School of Hygiene and Tropical Medicine is carrying out several epidemiological studies of employees of the United Kingdom Atomic Energy Authority (UKAEA) in which mortality is being investigated in relation to radiation exposure. This paper summarises the results obtained so far and describes briefly studies currently in progress. (author)

  16. Disordered Nanohole Patterns in Metal-Insulator Multilayer for Ultra-broadband Light Absorption: Atomic Layer Deposition for Lithography Free Highly repeatable Large Scale Multilayer Growth.

    Science.gov (United States)

    Ghobadi, Amir; Hajian, Hodjat; Dereshgi, Sina Abedini; Bozok, Berkay; Butun, Bayram; Ozbay, Ekmel

    2017-11-08

    In this paper, we demonstrate a facile, lithography free, and large scale compatible fabrication route to synthesize an ultra-broadband wide angle perfect absorber based on metal-insulator-metal-insulator (MIMI) stack design. We first conduct a simulation and theoretical modeling approach to study the impact of different geometries in overall stack absorption. Then, a Pt-Al 2 O 3 multilayer is fabricated using a single atomic layer deposition (ALD) step that offers high repeatability and simplicity in the fabrication step. In the best case, we get an absorption bandwidth (BW) of 600 nm covering a range of 400 nm-1000 nm. A substantial improvement in the absorption BW is attained by incorporating a plasmonic design into the middle Pt layer. Our characterization results demonstrate that the best configuration can have absorption over 0.9 covering a wavelength span of 400 nm-1490 nm with a BW that is 1.8 times broader compared to that of planar design. On the other side, the proposed structure retains its absorption high at angles as wide as 70°. The results presented here can serve as a beacon for future performance enhanced multilayer designs where a simple fabrication step can boost the overall device response without changing its overall thickness and fabrication simplicity.

  17. Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

    International Nuclear Information System (INIS)

    Cabon, J.Y.; Giamarchi, P.; Le Bihan, A.

    2010-01-01

    Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L -1 (20 μL, 3σ) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3σ) of 3 ng L -1 (i.e. 54 pM) for total Fe concentration with the use a 20 μL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 μg L -1 ) seawater sample were in good agreement with the certified values.

  18. Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: a comparative study.

    Science.gov (United States)

    Cabon, J Y; Giamarchi, P; Le Bihan, A

    2010-04-07

    Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L(-1) (20 microL, 3sigma) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3sigma) of 3 ng L(-1) (i.e. 54 pM) for total Fe concentration with the use a 20 microL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 microg L(-1)) seawater sample were in good agreement with the certified values. Copyright 2010 Elsevier B.V. All rights reserved.

  19. In situ surface X-ray diffraction studies of the copper-electrolyte interface. Atomic structure and homoepitaxial grwoth

    Energy Technology Data Exchange (ETDEWEB)

    Golks, Frederik

    2011-05-19

    Copper electrodeposition is the predominantly used technique for on-chip wiring in the fabrication of ultra-large scale integrated (ULSI) microchips. In this 'damascene copper electroplating' process, multicomponent electrolytes containing organic additives realize void-free filling of trenches with high aspect ratio ('superconformal deposition'). Despite manifold studies, motivated by the continuous trend to shrink wiring dimensions and thus the demand of optimized plating baths, detailed knowledge on the growth mechanism - in presence and absence of additives - is still lacking. Using a recently developed hanging meniscus X-ray transmission cell, brilliant synchrotron x-rays and a fast, one-dimensional detector system, unique real-time in situ surface X-ray diffraction studies of copper electrodeposition were performed under realistic reaction conditions, approaching rates of technological relevance. Preparatory measurements of the electrochemical dissolution of Au(001) in chloride-containing electrolyte demonstrated the capability of this powerful technique, specifically the possibility to follow atomic-scale deposition or dissolution processes with a time resolution down to five milliseconds. The electrochemical as well as structural characterization of the Cu(001)- and Cu(111)-electrolyte interfaces provided detailed insight into the complex atomic-scale structures in presence of specifically adsorbed chloride on these surfaces. The interface of Cu(001) in chloride-containing electrolyte exhibits a continuous surface phase transition of a disordered Cl adlayer to a c(2 x 2) Cl adlayer with increasing potential. The latter was found to induce a small vertical corrugation of substrate atoms, which can be ascribed to lattice relaxations induced by the presence of coadsorbed water molecules and cations in the outer part of the electrochemical double layer. The study of the specific adsorption of chloride on Cu(111) from acidic aqueous

  20. In situ surface X-ray diffraction studies of the copper-electrolyte interface. Atomic structure and homoepitaxial grwoth

    Energy Technology Data Exchange (ETDEWEB)

    Golks, Frederik

    2011-05-19

    Copper electrodeposition is the predominantly used technique for on-chip wiring in the fabrication of ultra-large scale integrated (ULSI) microchips. In this 'damascene copper electroplating' process, multicomponent electrolytes containing organic additives realize void-free filling of trenches with high aspect ratio ('superconformal deposition'). Despite manifold studies, motivated by the continuous trend to shrink wiring dimensions and thus the demand of optimized plating baths, detailed knowledge on the growth mechanism - in presence and absence of additives - is still lacking. Using a recently developed hanging meniscus X-ray transmission cell, brilliant synchrotron x-rays and a fast, one-dimensional detector system, unique real-time in situ surface X-ray diffraction studies of copper electrodeposition were performed under realistic reaction conditions, approaching rates of technological relevance. Preparatory measurements of the electrochemical dissolution of Au(001) in chloride-containing electrolyte demonstrated the capability of this powerful technique, specifically the possibility to follow atomic-scale deposition or dissolution processes with a time resolution down to five milliseconds. The electrochemical as well as structural characterization of the Cu(001)- and Cu(111)-electrolyte interfaces provided detailed insight into the complex atomic-scale structures in presence of specifically adsorbed chloride on these surfaces. The interface of Cu(001) in chloride-containing electrolyte exhibits a continuous surface phase transition of a disordered Cl adlayer to a c(2 x 2) Cl adlayer with increasing potential. The latter was found to induce a small vertical corrugation of substrate atoms, which can be ascribed to lattice relaxations induced by the presence of coadsorbed water molecules and cations in the outer part of the electrochemical double layer. The study of the specific adsorption of chloride on Cu(111) from acidic aqueous electrolyte revealed a

  1. Section of Atomic Collisions

    International Nuclear Information System (INIS)

    Berenyi, D.; Biri, S.; Gulyas, L.; Juhasz, Z.; Kover, A.; Orban, A.; Palinkas, J.; Papp, T.; Racz, R.; Ricz, S.

    2009-01-01

    The Section of Atomic Collisions is a research unit with extended activity in the field of atomic and molecular physics. Starting from the study of atomic processes at the beamlines of nuclear physics accelerators in the seventies, our research community became one of the centers of fundamental research in Atomki. We also have a strong connection to materials sciences especially along the line of electron and ion spectroscopy methods. Our present activity covers a wide range of topics from atomic collision mechanisms of fundamental interest, to the complex interactions of electrons, ions, photons and antiparticles with atoms, molecules, surfaces, and specific nanostructures. In the last few years, an increasing fraction of our present topics has become relevant for applications, e.g., molecular collision studies for the radiation therapy methods of tumors, or ion-nanostructure interactions for the future construction of small ion-focusing elements. Our section belongs to the Division of Atomic Physics. The other unit of the Division is the Section of Electron Spectroscopy and Materials Sciences. There are traditionally good connections and a strong collaboration between the groups of the two sections in many fields. From the very beginning of our research work in atomic collisions, external collaborations were of vital importance for us. We regularly organize international workshops in the field of fast ion-atom collisions and related small conferences in Debrecen from 1981. Recently, we organized the Conference on Radiation Damage in Biomolecular Systems (RADAM 2008, Debrecen), and coorganized the Conference on Elementary Processes in Atomic Systems (CEPAS 2008, Cluj). We have access to several large scale facilities in Europe within the framework of formal and informal collaborations. The next themes are in this article: Forward electron emission from energetic atomic collisions; Positron-atom collisions; Photon-atom interactions; Interference effects in electron

  2. Studies on population change of atomic bomb survivors in Hiroshima prefecture 1965-1979

    International Nuclear Information System (INIS)

    Ueoka, Hiroshi; Munaka, Masaki; Kurihara, Minoru

    1984-01-01

    Studies of population change of Japanese Atomic Bomb Survivors from 1965 to 1979 in Hiroshima prefecture of which registered in Data Base of Atomic Bomb Survivors of RINMB were conducted, and following were obtained: 1. Population change of Japanese Atomic Bomb Survivors showed increasing trend until 1976 and diminishing trend from 1977. It would be estimated that reason of increasing trend of Atomic Bomb Survivors was correlated the same trend to get register card of ''Atomic Bomb Treatment Law'', and decreasing trend of them was related so much death of the elderly generations. 2. Analysing by residential place the survivors who make a living in Hiroshima city was almost 110,000, and those who make a living in Hiroshima prefecture (except Hiroshima city) was 65,000. Considering exposed distance of the survivors in Hiroshima city, those survivors exposed within 2 km showed diminishing trend; and those who make a living in Hiroshima prefecture (except Hiroshima city), exposed within 2 km showed increasing trend. 3. In 1979, the ratio of male and female survivors by age level showed difference. Those male survivors over 50 years old in Hiroshima city showed much lower percentage than female. 4. In 1979, the population trends of survivors who get the ''card'' before 1964 showed rapid decrease, and those who get the ''card'' after 1965 showed mild decrease. (author)

  3. Resonance studies of H atoms adsorbed on frozen H2 surfaces

    International Nuclear Information System (INIS)

    Crampton, S.B.

    1980-01-01

    Observations are reported of the ground state hyperfine resonance of hydrogen atoms stored in a 5 cm. diameter bottle coated with frozen molecular hydrogen. Dephasing of the hyperfine resonance while the atoms are adsorbed produces frequency shifts which vary by a factor of two over the temperature range 3.7 K to 4.6 K and radiative decay rates which vary by a factor of five over this range. The magnitudes and temperature dependences of the frequency shifts and decay rates are consistent with a non-uniform distribution of surface adsorption energies with mean about 38(8) K, in agreement with theoretical estimates for a smooth surface. Extrapolation of the 30 nanosec. mean adsorption times at 4.2 K predicts very long adsorption times for H on H 2 below 1 K. Studies of level population recovery rates provide evidence for surface electron spin exchange collisions between adsorbed atoms with collision duration long compared to the hyperfine period, suggesting that the atoms are partially mobile on the surface. The lowest rates observed for level population recovery set a lower limit of about 500 atom-surface collisions at 4.2 K without recombination

  4. Long-term outcome of the adjustable transobturator male system (ATOMS): results of a European multicentre study.

    Science.gov (United States)

    Friedl, Alexander; Mühlstädt, Sandra; Zachoval, Roman; Giammò, Alessandro; Kivaranovic, Danijel; Rom, Maximilian; Fornara, Paolo; Brössner, Clemens

    2017-05-01

    To evaluate the long-term effectiveness and safety of the adjustable transobturator male system (ATOMS ® , Agency for Medical Innovations A.M.I., Feldkirch, Austria) in a European-wide multicentre setting. In all, 287 men with stress urinary incontinence (SUI) were treated with the ATOMS device between June 2009 and March 2016. Continence parameters (daily pad test/pad use), urodynamics (maximum urinary flow rate, voiding volume, residual urine), and pain/quality of life (QoL) ratings (visual analogue scale/Leeds Assessment of Neuropathic Symptoms and Signs, International Consultation on Incontinence Questionnaire-Short Form [ICIQ-SF]/Patient Global Impression of Improvement [PGI-I]) were compared preoperatively and after intermediate (12 months) as well as after individual maximum follow-up. Overall success rate, dry rate (ATOMS devices are still functioning; 56 (20%) were removed, the most common reason being local titanium intolerance (41%) and leak/dysfunction (30%). The operating time and continence outcome varied between port generations. In this regard the latest port generation (silicone-covered scrotal port) was superior to its predecessors. Primary implantation (P = 0.002), good physical health (P = 0.001), and no history of radiotherapy (P ATOMS device is safe and shows high treatment efficacy and patient satisfaction in the largest cohort study to date. The latest generation, with its pre-attached silicone-covered scrotal port, is superior to its predecessors. Significantly better results were achieved with primary implantation and in those without a history of radiotherapy. © 2016 The Authors BJU International © 2016 BJU International Published by John Wiley & Sons Ltd.

  5. Atom Skimmers and Atom Lasers Utilizing Them

    Science.gov (United States)

    Hulet, Randall; Tollett, Jeff; Franke, Kurt; Moss, Steve; Sackett, Charles; Gerton, Jordan; Ghaffari, Bita; McAlexander, W.; Strecker, K.; Homan, D.

    2005-01-01

    Atom skimmers are devices that act as low-pass velocity filters for atoms in thermal atomic beams. An atom skimmer operating in conjunction with a suitable thermal atomic-beam source (e.g., an oven in which cesium is heated) can serve as a source of slow atoms for a magneto-optical trap or other apparatus in an atomic-physics experiment. Phenomena that are studied in such apparatuses include Bose-Einstein condensation of atomic gases, spectra of trapped atoms, and collisions of slowly moving atoms. An atom skimmer includes a curved, low-thermal-conduction tube that leads from the outlet of a thermal atomic-beam source to the inlet of a magneto-optical trap or other device in which the selected low-velocity atoms are to be used. Permanent rare-earth magnets are placed around the tube in a yoke of high-magnetic-permeability material to establish a quadrupole or octupole magnetic field leading from the source to the trap. The atoms are attracted to the locus of minimum magnetic-field intensity in the middle of the tube, and the gradient of the magnetic field provides centripetal force that guides the atoms around the curve along the axis of the tube. The threshold velocity for guiding is dictated by the gradient of the magnetic field and the radius of curvature of the tube. Atoms moving at lesser velocities are successfully guided; faster atoms strike the tube wall and are lost from the beam.

  6. SMR Re-Scaling and Modeling for Load Following Studies

    Energy Technology Data Exchange (ETDEWEB)

    Hoover, K.; Wu, Q.; Bragg-Sitton, S.

    2016-11-01

    This study investigates the creation of a new set of scaling parameters for the Oregon State University Multi-Application Small Light Water Reactor (MASLWR) scaled thermal hydraulic test facility. As part of a study being undertaken by Idaho National Lab involving nuclear reactor load following characteristics, full power operations need to be simulated, and therefore properly scaled. Presented here is the scaling analysis and plans for RELAP5-3D simulation.

  7. Ophthalmologic survey of atomic bomb survivors in Japan, 1949. Atomic bomb radiation cataract case report with histopathologic study. Medical examination of Hiroshima patients with radiation cataracts

    Energy Technology Data Exchange (ETDEWEB)

    Cogan, D.G.; Martin, S.F.; Kimura, S.J.; Ikui, Hiroshi; Fillmore, P.G.

    1959-01-01

    This document contains 3 reports dealing with the delayed effects of radiation on the eyes of survivors of the atomic explosions in Hiroshima and Nagasaki. In the first study, 1000 persons who were listed as having been in the open and within two kilometers of the hypocenter at the time of the explosion were selected at random from the census files of the Atomic Bomb Casualty Commission for study. In addition, 231 others, comprising the total available number of surviving persons listed at present in the census files as having been within one kilometer of the hypocenter, were examined, as were several hundred others who were contacted through newspaper publicity, referrals from local ophthalmologists, or through hearsay. The survey resulted in bringing in persons having, or having had, a variety of ocular conditions. Those connected with the atomic bomb included the following diagnoses; multiple injuries of eyes and eyelids; keratoconjunctivitis from ultraviolet and ionizing radiations; thermal burn of the cornea and of the retina; retinitis proliferans; and radiation cataracts. The cataracts were the only delayed manifestations of ocular injury from the atomic bomb. The second paper is a case report of a histopathologic study of atomic bomb radiation cataract. The third paper presents the results of medical examinations of survivors having radiation induced cataracts. 32 references, 8 figures. (DMC)

  8. Atomic Force Microscopy Study on the Stiffness of Nanosized Liposomes Containing Charged Lipids.

    Science.gov (United States)

    Takechi-Haraya, Yuki; Goda, Yukihiro; Sakai-Kato, Kumiko

    2018-06-18

    It has recently been recognized that the mechanical properties of lipid nanoparticles play an important role during in vitro and in vivo behaviors such as cellular uptake, blood circulation, and biodistribution. However, there have been no quantitative investigations of the effect of commonly used charged lipids on the stiffness of nanosized liposomes. In this study, by means of atomic force microscopy (AFM), we quantified the stiffness of nanosized liposomes composed of neutrally charged lipids combined with positively or negatively charged lipids while simultaneously imaging the liposomes in aqueous medium. Our results showed that charged lipids, whether negatively or positively charged, have the effect of reducing the stiffness of nanosized liposomes, independently of the saturation degree of the lipid acyl chains; the measured stiffness values of liposomes containing charged lipids are 30-60% lower than those of their neutral counterpart liposomes. In addition, we demonstrated that the Laurdan generalized polarization values, which are related to the hydration degree of the liposomal membrane interface and often used as a qualitative indicator of liposomal membrane stiffness, do not directly correlate with the physical stiffness values of the liposomes prepared in this study. However, our results indicate that direct quantitative AFM measurement is a valuable method to gain molecular-scale information about how the hydration degree of liposomal interfaces reflects (or does not reflect) liposome stiffness as a macroscopic property. Our AFM method will contribute to the quantitative characterization of the nano-bio interaction of nanoparticles and to the optimization of the lipid composition of liposomes for clinical use.

  9. Impact parameter sensitive study of inner-shell atomic processes in the experimental storage ring

    Science.gov (United States)

    Gumberidze, A.; Kozhuharov, C.; Zhang, R. T.; Trotsenko, S.; Kozhedub, Y. S.; DuBois, R. D.; Beyer, H. F.; Blumenhagen, K.-H.; Brandau, C.; Bräuning-Demian, A.; Chen, W.; Forstner, O.; Gao, B.; Gassner, T.; Grisenti, R. E.; Hagmann, S.; Hillenbrand, P.-M.; Indelicato, P.; Kumar, A.; Lestinsky, M.; Litvinov, Yu. A.; Petridis, N.; Schury, D.; Spillmann, U.; Trageser, C.; Trassinelli, M.; Tu, X.; Stöhlker, Th.

    2017-10-01

    In this work, we present a pilot experiment in the experimental storage ring (ESR) at GSI devoted to impact parameter sensitive studies of inner shell atomic processes for low-energy (heavy-) ion-atom collisions. The experiment was performed with bare and He-like xenon ions (Xe54+, Xe52+) colliding with neutral xenon gas atoms, resulting in a symmetric collision system. This choice of the projectile charge states was made in order to compare the effect of a filled K-shell with the empty one. The projectile and target X-rays have been measured at different observation angles for all impact parameters as well as for the impact parameter range of ∼35-70 fm.

  10. Combination of lasers and synchrotron radiation in studies of atomic photoionization

    International Nuclear Information System (INIS)

    Meyer, M.

    2009-01-01

    Recent experiments using the combination of conventional lasers and synchrotron radiation are presented and discussed. The controlled laser-manipulation of atoms prior to ionization by the synchrotron radiation provides an ideal experimental basis for detailed investigations of atomic photoionization. Due to the recent advances in high-resolution electron spectroscopy, it has become possible to analyze the J-resolved fine structure of the final ionic states in the photoionization of laser-excited atoms enabling thereby the determination of the specific influence of the outer electron to the ionization from inner subshells. Especially, the analysis of photoemission satellites and their relative intensities bring out directly the importance of electron correlations. Furthermore, it is shown through some examples of experiments using linearly and circularly polarized radiations, how the study of magnetic dichroisms in the photoionization opens the access to a complete description of the photoionization process, in particular to the determination of partial photoionization cross-sections.

  11. Use of analytical Born amplitude representation in studies of dispersion potentials and electron-atom scattering

    International Nuclear Information System (INIS)

    Carvalho, I.L. de.

    1985-01-01

    Two distinct problems have been studied using simplifield Born's Amplitude Analitical Expressions. The first problem deals with the dispersion energy between the constituent members of the systems He - Ne, - He and H 2 - H 2 . In the second problem second order Born Aproximation has been used for the Electron - Atom Inelastic Scattering for the transitions 1 1 S → 2 1 S and 1 1 S → 2 1 P of helium atom and 1 S → 1 s 2 ([3s' {1/2} sup(o) 1; M sub(j)>) of neon atom (in the case of neon we have used the coupling scheme proposed by Cowan and Andrew). The results obtained by us have been compared with the theoretical and experimental results available in the literature. (author) [pt

  12. A review of 40 years studies of Hiroshima and Nagasaki atomic bomb survivors

    International Nuclear Information System (INIS)

    Itsuzo Shigematsu

    1993-01-01

    The late health effects of ionizing radiation have been studied by the Atomic Bomb Casualty Commission (ABCC) and its successor, the Radiation Effects Research Foundation (RERF) based on a fixed population of atomic bomb survivors in Hiroshima and Nagasaki which had been established in 1950. The results thus far obtained up to the present can be classified into the following three categories: (1) The effects for which a strong association with atomic bomb radiation has been found include malignant neoplasms, cataracts, chromosomal aberrations, small head size and mental retardation among the in utero exposed. (2) A weak association has been found in the several sites of cancers, some non-cancer mortalities and immunological abnormalities. (3) No association has been observed in some types of leukemia, osteosarcoma, accelerated aging, sterility and hereditary effects

  13. Experimental study of single-electron loss by Ar+ ions in rare-gas atoms

    Science.gov (United States)

    Reyes, P. G.; Castillo, F.; Martínez, H.

    2001-04-01

    Absolute differential and total cross sections for single-electron loss were measured for Ar+ ions on rare-gas atoms in the laboratory energy range of 1.5 to 5.0 keV. The electron loss cross sections for all the targets studied are found to be in the order of magnitude between 10-19 and 10-22 cm2, and show a monotonically increasing behaviour as a function of the incident energy. The behaviour of the total single-electron loss cross sections with the atomic target number, Zt, shows different dependences as the collision energy increases. In all cases the present results display experimental evidence of saturation in the single-electron loss cross section as the atomic number of the target increases.

  14. Observation of isolated carbon atoms and the study of their mobility on Pt clusters by NMR

    International Nuclear Information System (INIS)

    Wang, P.; Ansermet, J.; Slichter, C.P.; Sinfelt, J.H.

    1985-01-01

    The authors have used NMR to determine the structure of surface species after the C-C bond scission of adsorbed acetylene and ethylene on Pt clusters produced by heating the samples to 690 K. They have found the species to be predominantly isolated carbon atoms adsorbed on Pt surfaces. They have studied the mobility of adsorbed carbon atoms from motional narrowing of the 13 C line shapes and motion-induced shortening of the spin-lattice relaxation times. They have found that the carbon atoms on Pt clusters are very mobile, their activation energy of 7 +- 1 kcal/mole for translational motion being less than half that of CO on Pt clusters

  15. Atomic defects in monolayer WSe2 tunneling FETs studied by systematic ab initio calculations

    Science.gov (United States)

    Wu, Jixuan; Fan, Zhiqiang; Chen, Jiezhi; Jiang, Xiangwei

    2018-05-01

    Atomic defects in monolayer WSe2 tunneling FETs (TFETs) are studied through systematic ab initio calculations aiming at performance predictions and enhancements. The effects of various defect positions and different passivation atoms are characterized in WSe2 TFETs by rigorous ab initio quantum transport simulations. It is suggested that the Se vacancy (VSe) defect located in the gate-controlled channel region tends to increase the OFF current (I off), whereas it can be well suppressed by oxygen passivation. It is demonstrated that chlorine (Cl) passivation at the source-side tunneling region can largely suppress I off, leading to an impressively improved on–off ratio (I on/I off) compared with that without any defect. However, it is also observed that randomly positioned atomic defects tend to induce significant fluctuation of the TFET output. Further discussions are made with focus on the performance-variability trade-off for robust circuit design.

  16. Atomic structure of Fe thin-films on Cu(0 0 1) studied with stereoscopic photography

    International Nuclear Information System (INIS)

    Hattori, Azusa N.; Fujikado, M.; Uchida, T.; Okamoto, S.; Fukumoto, K.; Guo, F.Z.; Matsui, F.; Nakatani, K.; Matsushita, T.; Hattori, K.; Daimon, H.

    2004-01-01

    The complex magnetic properties of Fe films epitaxially grown on Cu(0 0 1) have been discussed in relation to their atomic structure. We have studied the Fe films on Cu(0 0 1) by a new direct method for three-dimensional (3D) atomic structure analysis, so-called 'stereoscopic photography'. The forward-focusing peaks in the photoelectron angular distribution pattern excited by the circularly polarized light rotate around the light axis in either clockwise or counterclockwise direction depending on the light helicity. By using a display-type spherical mirror analyzer for this phenomenon, we can obtain stereoscopic photographs of atomic structure. The photographs revealed that the iron structure changes from bcc to fcc and almost bcc structure with increasing iron film thickness

  17. Monte-Carlo study on primary knock-on atom energy spectrum produced by neutron radiation

    International Nuclear Information System (INIS)

    Zhou Wei; Liu Yongkang; Deng Yongjun; Ma Jimin

    2012-01-01

    Computational method on energy distribution of primary knock-on atom (PKA) produced by neutron radiation was built in the paper. Based on the DBCN card in MCNP, reaction position, reaction type and energy transfer between neutrons and atoms were recorded. According to statistic of these data, energy and space distributions of PKAs were obtained. The method resolves preferably randomicity of random number and efficiency of random sampling computation. The results show small statistical fluctuation and well statistical. Three-dimensional figure of energy and space distribution of PKAs were obtained, which would be important to evaluate radiation capability of materials and study radiation damage by neutrons. (authors)

  18. H atom kinetics in superheated water studied by muon spin spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Percival, Paul W. [Department of Chemistry and TRIUMF, Simon Fraser University, 8888 University Drive, Burnaby BC, V5A 1S6 (Canada)]. E-mail: percival@sfu.ca; Brodovitch, Jean-Claude [Department of Chemistry and TRIUMF, Simon Fraser University, 8888 University Drive, Burnaby BC, V5A 1S6 (Canada); Ghandi, Khashayar [Department of Chemistry and TRIUMF, Simon Fraser University, 8888 University Drive, Burnaby BC, V5A 1S6 (Canada); McCollum, Brett M. [Department of Chemistry and TRIUMF, Simon Fraser University, 8888 University Drive, Burnaby BC, V5A 1S6 (Canada); McKenzie, Iain [Department of Chemistry and TRIUMF, Simon Fraser University, 8888 University Drive, Burnaby BC, V5A 1S6 (Canada)

    2007-08-15

    It is possible to study H atom chemistry in aqueous systems over a wide range of conditions, from standard to supercritical, using the exotic atom muonium (Mu) as an effective light isotope of hydrogen. The Mu rate constants exhibit marked non-Arrhenius behaviour, going through a maximum and fall-off as the density is reduced in the neighbourhood of the critical point, and subsequent recovery as the medium becomes more gas-like. This is illustrated with new kinetic data for the reaction of Mu with methanol.

  19. H atom kinetics in superheated water studied by muon spin spectroscopy

    International Nuclear Information System (INIS)

    Percival, Paul W.; Brodovitch, Jean-Claude; Ghandi, Khashayar; McCollum, Brett M.; McKenzie, Iain

    2007-01-01

    It is possible to study H atom chemistry in aqueous systems over a wide range of conditions, from standard to supercritical, using the exotic atom muonium (Mu) as an effective light isotope of hydrogen. The Mu rate constants exhibit marked non-Arrhenius behaviour, going through a maximum and fall-off as the density is reduced in the neighbourhood of the critical point, and subsequent recovery as the medium becomes more gas-like. This is illustrated with new kinetic data for the reaction of Mu with methanol

  20. Quadrupole type mass spectrometric study of the abstraction reaction between hydrogen atoms and ethane.

    Science.gov (United States)

    Bayrakçeken, Fuat

    2008-02-01

    The reactions of photochemically generated deuterium atoms of selected initial translational energy with ethane have been investigated. At each initial energy the relative probability of the atoms undergoing reaction or energy loss on collision with ethane was investigated, and the phenomenological threshold energy was measured as 30+/-5kJmol(-1) for the abstraction from the secondary C-H bonds. The ratio of relative yields per bond, secondary:primary was approximately 3 at the higher energies studied. The correlation of threshold energies with bond dissociation energies, heats of reaction and activation energies is discussed for abstraction reactions with several hydrocarbons.