WorldWideScience

Sample records for atomic clusters

  1. Determination of atomic cluster structure with cluster fusion algorithm

    DEFF Research Database (Denmark)

    Obolensky, Oleg I.; Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters.......We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters....

  2. Atomic mobility in energetic cluster deposition

    Institute of Scientific and Technical Information of China (English)

    PAN Zheng-Ying; WANG Yue-Xia; WEI Qi; LI Zhi-Jie; ZHOU Liang; ZHANG Liang-Kun

    2004-01-01

    This paper tries to outline the influence of atomic mobility on the initial fabrication of thin films formed by LECBD. Based on our recent studies on low-energy cluster beam deposition (LECBD) by molecular dynamics simulation, two examples, the deposition of small carbon clusters on Si and diamond surfaces and Al clusters on Ni substrate, were mainly discussed. The impact energy of the cluster ranges from 0.1 eV to 100 eV. In the former case,the mobility and the lateral migration of surface atoms, especially the recoil atoms, are enhanced with increasing the impact energy, which promote the film to be smoother and denser. For the latter case, the transverse kinetic energy of cluster atoms, caused mainly by the collision between moving cluster atoms, dominates the lateral spread of cluster atoms on the surface, which is contributive to layer-by-layer growth of thin films. Our result is consistent with the experimental observations that the film structure is strongly dependent on the impact energy. In addition, it elucidates that the atomic mobility takes a leading role in the structure characteristic of films formed by LECBD.

  3. On clusters and clustering from atoms to fractals

    CERN Document Server

    Reynolds, PJ

    1993-01-01

    This book attempts to answer why there is so much interest in clusters. Clusters occur on all length scales, and as a result occur in a variety of fields. Clusters are interesting scientifically, but they also have important consequences technologically. The division of the book into three parts roughly separates the field into small, intermediate, and large-scale clusters. Small clusters are the regime of atomic and molecular physics and chemistry. The intermediate regime is the transitional regime, with its characteristics including the onset of bulk-like behavior, growth and aggregation, a

  4. Collisional process involving atomic cluster ions

    International Nuclear Information System (INIS)

    Collision of Ar cluster ions, Ar+n (n = 3-16), with He and Ne atoms was investigated by use of mass spectroscopic techniques. The cross sections for the production of Ar+n' (n' < n) were measured as functions of the size of the parent cluster ion and the collision energy (0.1-10 eV in the center-of-mass frame). These results were analyzed in the scheme of hard-sphere spectator collision with RRK theory. It was concluded that the reaction proceeds via collisional excitation of the parent cluster ion and following sequential loss of the constituent Ar atoms. (orig.)

  5. Clusters: systems between atoms and solids

    International Nuclear Information System (INIS)

    Atomic and molecular clusters will be discussed here. These are aggregates of atoms and molecules so large that one cannot describe them properly as large molecules. But they are small enough, that the condensed phase properties, if present at all, are not fully developed. This field forms the bridge between the traditional disciplines of atomic or molecular physics on one side and the physics and chemistry of condensed matter on the other side. The number of groups working in this field has increased tremendously in recent years. (Author)

  6. Beyond organic chemistry: aromaticity in atomic clusters.

    Science.gov (United States)

    Boldyrev, Alexander I; Wang, Lai-Sheng

    2016-04-28

    We describe joint experimental and theoretical studies carried out collaboratively in the authors' labs for understanding the structures and chemical bonding of novel atomic clusters, which exhibit aromaticity. The concept of aromaticity was first discovered to be useful in understanding the square-planar unit of Al4 in a series of MAl4(-) bimetallic clusters that led to discoveries of aromaticity in many metal cluster systems, including transition metals and similar cluster motifs in solid compounds. The concept of aromaticity has been found to be particularly powerful in understanding the stability and bonding in planar boron clusters, many of which have been shown to be analogous to polycyclic aromatic hydrocarbons in their π bonding. Stimulated by the multiple aromaticity in planar boron clusters, a design principle has been proposed for stable metal-cerntered aromatic molecular wheels of the general formula, M@Bn(k-). A series of such borometallic aromatic wheel complexes have been produced in supersonic cluster beams and characterized experimentally and theoretically, including Ta@B10(-) and Nb@B10(-), which exhibit the highest coordination number in two dimensions. PMID:26864511

  7. Quantum Monte Carlo methods and lithium cluster properties. [Atomic clusters

    Energy Technology Data Exchange (ETDEWEB)

    Owen, R.K.

    1990-12-01

    Properties of small lithium clusters with sizes ranging from n = 1 to 5 atoms were investigated using quantum Monte Carlo (QMC) methods. Cluster geometries were found from complete active space self consistent field (CASSCF) calculations. A detailed development of the QMC method leading to the variational QMC (V-QMC) and diffusion QMC (D-QMC) methods is shown. The many-body aspect of electron correlation is introduced into the QMC importance sampling electron-electron correlation functions by using density dependent parameters, and are shown to increase the amount of correlation energy obtained in V-QMC calculations. A detailed analysis of D-QMC time-step bias is made and is found to be at least linear with respect to the time-step. The D-QMC calculations determined the lithium cluster ionization potentials to be 0.1982(14) (0.1981), 0.1895(9) (0.1874(4)), 0.1530(34) (0.1599(73)), 0.1664(37) (0.1724(110)), 0.1613(43) (0.1675(110)) Hartrees for lithium clusters n = 1 through 5, respectively; in good agreement with experimental results shown in the brackets. Also, the binding energies per atom was computed to be 0.0177(8) (0.0203(12)), 0.0188(10) (0.0220(21)), 0.0247(8) (0.0310(12)), 0.0253(8) (0.0351(8)) Hartrees for lithium clusters n = 2 through 5, respectively. The lithium cluster one-electron density is shown to have charge concentrations corresponding to nonnuclear attractors. The overall shape of the electronic charge density also bears a remarkable similarity with the anisotropic harmonic oscillator model shape for the given number of valence electrons.

  8. Genetic algorithm optimization of atomic clusters

    International Nuclear Information System (INIS)

    The authors have been using genetic algorithms to study the structures of atomic clusters and related problems. This is a problem where local minima are easy to locate, but barriers between the many minima are large, and the number of minima prohibit a systematic search. They use a novel mating algorithm that preserves some of the geometrical relationship between atoms, in order to ensure that the resultant structures are likely to inherit the best features of the parent clusters. Using this approach, they have been able to find lower energy structures than had been previously obtained. Most recently, they have been able to turn around the building block idea, using optimized structures from the GA to learn about systematic structural trends. They believe that an effective GA can help provide such heuristic information, and (conversely) that such information can be introduced back into the algorithm to assist in the search process

  9. Clusters of atoms and molecules theory, experiment, and clusters of atoms

    CERN Document Server

    1994-01-01

    Clusters of Atoms and Molecules is devoted to theoretical concepts and experimental techniques important in the rapidly expanding field of cluster science. Cluster properties are dicussed for clusteres composed of alkali metals, semiconductors, transition metals, carbon, oxides and halides of alkali metals, rare gases, and neutral molecules. The book is composed of several well-integrated treatments all prepared by experts. Each contribution starts out as simple as possible and ends with the latest results so that the book can serve as a text for a course, an introduction into the field, or as a reference book for the expert.

  10. Magnetic anisotropies of late transition metal atomic clusters

    OpenAIRE

    Fernández-Seivane, Lucas; Ferrer, Jaime

    2006-01-01

    We analyze the impact of the magnetic anisotropy on the geometric structure and magnetic ordering of small atomic clusters of palladium, iridium, platinum and gold, using Density Functional Theory. Our results highlight the absolute need to include self-consistently the spin orbit interaction in any simulation of the magnetic properties of small atomic clusters, and a complete lack of universality in the magnetic anisotropy of small-sized atomic clusters.

  11. Quantum algebraic symmetries in atomic clusters and nuclei

    International Nuclear Information System (INIS)

    Atomic clusters are known to exhibit magic numbers analogous to but different from the magic numbers of atomic nuclei. In addition, atomic clusters offer the opportunity for observing supershells, which in nuclei cannot be seen because of the small number of particles present. It is shown that magic numbers and supershells in alkali clusters can be described well in terms of the 3-dimensional q-deformed harmonic oscillator, characterized by the uq(3) including soq(3) quantum algebraic symmetry

  12. Reaction of tungsten anion clusters with molecular and atomic nitrogen

    OpenAIRE

    Kim, Young Dok; Stolcic, Davor; Fischer, Matthias; Ganteför, Gerd

    2003-01-01

    Ultraviolet photoelectron spectra for WnN-2 (n=1 8) clusters produced by addition of atomic and molecular nitrogen on W anion clusters are presented. Evidence is provided that molecular chemisorption of N2 is more stable than the dissociative one on tungsten anion clusters consisting of eight atoms or less, which is completely different from the results on tungsten bulk surfaces. A general tendency toward molecular chemisorption for small clusters can be explained by reduced charge transfer f...

  13. Atomically precise cluster catalysis towards quantum controlled catalysts

    International Nuclear Information System (INIS)

    Catalysis of atomically precise clusters supported on a substrate is reviewed in relation to the type of reactions. The catalytic activity of supported clusters has generally been discussed in terms of electronic structure. Several lines of evidence have indicated that the electronic structure of clusters and the geometry of clusters on a support, including the accompanying cluster-support interaction, are strongly correlated with catalytic activity. The electronic states of small clusters would be easily affected by cluster–support interactions. Several studies have suggested that it is possible to tune the electronic structure through atomic control of the cluster size. It is promising to tune not only the number of cluster atoms, but also the hybridization between the electronic states of the adsorbed reactant molecules and clusters in order to realize a quantum-controlled catalyst. (review)

  14. Sequential oxygen atom chemisorption on surfaces of small iron Clusters

    International Nuclear Information System (INIS)

    We report photoelectron spectra of iron oxide clusters, FexOy- (x=1 endash 4, y=1 endash 6). For a given x, we find that the electron affinity increases with the number of O atoms, consistent with an increasing degree of oxidation. The results are interpreted based on charge transfer interactions between the Fex clusters and the O atoms, and provide key information about the oxide cluster structures, in which each O atom is suggested to locate on the surface of the clusters for the x=3 and 4 series. These clusters provide novel model systems to understand the electronic structure of bulk iron oxides. copyright 1996 The American Physical Society

  15. Nanophase materials assembled from atomic clusters

    Energy Technology Data Exchange (ETDEWEB)

    Siegel, R.W.

    1989-09-01

    The preparation of atomic clusters of metals and ceramics by means of the gas-condensation method, followed by their in situ consolidation under high-vacuum conditions, has recently led to the synthesis of a new class of ultrafine-grained materials for which their physics is intimately coupled with their application. These nanophase materials, with 2 to 20 nm grain sizes, appear to have properties that are often rather different from conventional materials, and also processing characteristics that are greatly improved. The nanophase synthesis method described here should enable the design of materials heretofore unavailable, with improved or unique properties, based upon an understanding of the physics of these new materials. 23 refs., 8 figs.

  16. Nanophase materials assembled from atomic clusters

    International Nuclear Information System (INIS)

    The preparation of atomic clusters of metals and ceramics by means of the gas-condensation method, followed by their in situ consolidation under high-vacuum conditions, has recently led to the synthesis of a new class of ultrafine-grained materials for which their physics is intimately coupled with their application. These nanophase materials, with 2 to 20 nm grain sizes, appear to have properties that are often rather different from conventional materials, and also processing characteristics that are greatly improved. The nanophase synthesis method described here should enable the design of materials heretofore unavailable, with improved or unique properties, based upon an understanding of the physics of these new materials. 23 refs., 8 figs

  17. Quantum fluctuation effects on nuclear fragment and atomic cluster formation

    Energy Technology Data Exchange (ETDEWEB)

    Ohnishi, Akira [Hokkaido Univ., Sapporo (Japan). Dept. of Physics; Randrup, J.

    1997-05-01

    We investigate the nuclear fragmentation and atomic cluster formation by means of the recently proposed quantal Langevin treatment. It is shown that the effect of the quantal fluctuation is in the opposite direction in nuclear fragment and atomic cluster size distribution. This tendency is understood through the effective classical temperature for the observables. (author)

  18. Unraveling the atomic structure of ultrafine iron clusters

    KAUST Repository

    Wang, Hongtao

    2012-12-18

    Unraveling the atomic structures of ultrafine iron clusters is critical to understanding their size-dependent catalytic effects and electronic properties. Here, we describe the stable close-packed structure of ultrafine Fe clusters for the first time, thanks to the superior properties of graphene, including the monolayer thickness, chemical inertness, mechanical strength, electrical and thermal conductivity. These clusters prefer to take regular planar shapes with morphology changes by local atomic shuffling, as suggested by the early hypothesis of solid-solid transformation. Our observations differ from observations from earlier experimental study and theoretical model, such as icosahedron, decahedron or cuboctahedron. No interaction was observed between Fe atoms or clusters and pristine graphene. However, preferential carving, as observed by other research groups, can be realized only when Fe clusters are embedded in graphene. The techniques introduced here will be of use in investigations of other clusters or even single atoms or molecules.

  19. Clustering in atomic nuclei: a mean field perspective

    International Nuclear Information System (INIS)

    In this paper the physics of clustering in atomic nucleus as seen from a mean field perspective will be discussed. Special attention is paid to phenomena involving octupole deformation like the α structure of 20Ne or the emission of heavy clusters. The stabilizing role of spin for cluster-like highly deformed states is also discussed in the case of 36 Ar

  20. Spectroscopy and Dynamics of K Atoms on Argon Clusters.

    Science.gov (United States)

    Douady, J; Awali, S; Poisson, L; Soep, B; Mestdagh, J M; Gervais, B

    2015-06-11

    We present a combined experimental and simulation study of the 4s → 4p photoexcitation of the K atom trapped at the surface of ArN clusters made of a few hundred Ar atoms. Our experimental method based on photoelectron spectroscopy allows us to firmly establish that one single K atom is trapped at the surface of the cluster. The absorption spectrum is characterized by the splitting of the atomic absorption line into two broad bands, a Π band associated with p orbitals parallel to the cluster surface and a Σ band associated with the perpendicular orientation. The spectrum is consistent with observations reported for K atoms trapped on lighter inert gas clusters, but the splitting between the Π and Σ bands is significantly larger. We show that a large amount of K atoms are transiently stuck and eventually lost by the Ar cluster, in contrast with previous observations reported for alkaline earth metal systems. The excitation in the Σ band leads systematically to the ejection of the K atom from the Ar cluster. On the contrary, excitation in the Π band leads to the formation of a bound state. In this case, the analysis of the experimental photoelectron spectrum by means of nonadiabatic molecular dynamics simulation shows that the relaxation drives the system toward a basin where the coordination of the K atom is 2.2 Ar atoms on the average, in a poorly structured surface. PMID:25854161

  1. Effects on energetic impact of atomic clusters with surfaces

    International Nuclear Information System (INIS)

    A brief state-of-the-art review in the field of cluster ion interaction with surface is presented. Cluster beams are efficient tools for manipulating agglomerates of atoms providing control over the synthesis as well as modification of surfaces on the nm-scale. The application of cluster beams for technological purposes requires knowledge of the physics of cluster-surface impact. This has some significant differences compared to monomer ion - surface interactions. The main effects of cluster-surface collisions are discussed. Recent results obtained in experiments on silicon surface nanostructuring using keV-energy implantation of inert gas cluster ions are presented and compared with molecular dynamics simulations. (authors)

  2. Sputtering from spherical Au clusters by energetic atom bombardment

    International Nuclear Information System (INIS)

    Using molecular-dynamics simulation, we study the effect of 100 keV Au atom bombardment of spherical Au clusters (radius R=40 A), containing 15,784 atoms. Results range from projectile transmission with only few atoms sputtered to more or less complete cluster disintegration. During disintegration, besides major fragments of the original cluster, monatomics and a large number of clusters with sizes up to 100 atoms, and even beyond, are created. Angular and energy spectra of sputtered atoms show features of both collisional sputtering and evaporation: particle emission is isotropic with an additional contribution of preferential emission along [1 1 0] directions. Energy spectra show the high-energy E-2 fall-off typical of linear-cascade sputtering plus an additional low-energy thermal component

  3. Structures of 38-atom gold-platinum nanoalloy clusters

    Energy Technology Data Exchange (ETDEWEB)

    Ong, Yee Pin; Yoon, Tiem Leong [School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Lim, Thong Leng [Faculty of Engineering and Technology, Multimedia University, Melaka Campus, 75450 Melaka (Malaysia)

    2015-04-24

    Bimetallic nanoclusters, such as gold-platinum nanoclusters, are nanomaterials promising wide range of applications. We perform a numerical study of 38-atom gold-platinum nanoalloy clusters, Au{sub n}Pt{sub 38−n} (0 ≤ n ≤ 38), to elucidate the geometrical structures of these clusters. The lowest-energy structures of these bimetallic nanoclusters at the semi-empirical level are obtained via a global-minimum search algorithm known as parallel tempering multi-canonical basin hopping plus genetic algorithm (PTMBHGA), in which empirical Gupta many-body potential is used to describe the inter-atomic interactions among the constituent atoms. The structures of gold-platinum nanoalloy clusters are predicted to be core-shell segregated nanoclusters. Gold atoms are observed to preferentially occupy the surface of the clusters, while platinum atoms tend to occupy the core due to the slightly smaller atomic radius of platinum as compared to gold’s. The evolution of the geometrical structure of 38-atom Au-Pt clusters displays striking similarity with that of 38-atom Au-Cu nanoalloy clusters as reported in the literature.

  4. Structures of 38-atom gold-platinum nanoalloy clusters

    International Nuclear Information System (INIS)

    Bimetallic nanoclusters, such as gold-platinum nanoclusters, are nanomaterials promising wide range of applications. We perform a numerical study of 38-atom gold-platinum nanoalloy clusters, AunPt38−n (0 ≤ n ≤ 38), to elucidate the geometrical structures of these clusters. The lowest-energy structures of these bimetallic nanoclusters at the semi-empirical level are obtained via a global-minimum search algorithm known as parallel tempering multi-canonical basin hopping plus genetic algorithm (PTMBHGA), in which empirical Gupta many-body potential is used to describe the inter-atomic interactions among the constituent atoms. The structures of gold-platinum nanoalloy clusters are predicted to be core-shell segregated nanoclusters. Gold atoms are observed to preferentially occupy the surface of the clusters, while platinum atoms tend to occupy the core due to the slightly smaller atomic radius of platinum as compared to gold’s. The evolution of the geometrical structure of 38-atom Au-Pt clusters displays striking similarity with that of 38-atom Au-Cu nanoalloy clusters as reported in the literature

  5. Atomic cluster and graph states. An engineering proposal

    International Nuclear Information System (INIS)

    We suggest a simple method to generate cluster states of two-level atoms. The protocol utilizes minimum cavity/atomic resources and is based upon standard cavity QED tools along with Ramsey technique. Two identical atoms, each initially prepared in coherent superposition, interact simultaneously with an initially vacuum state cavity for a specified time. One atom has resonant interactions while at the same time the other one interacts dispersively. When, after completion of the interaction, cavity is again left into vacuum then atoms are shown to be entangled in bipartite cluster state. The method is also generalized to generate multi-partite linear cluster states as well as the atomic graph states. (author)

  6. Quantum Algebraic Symmetries in Nuclei, Molecules and Atomic Clusters

    OpenAIRE

    Bonatsos, Dennis; Daskaloyannis, C.

    1999-01-01

    Various applications of quantum algebraic techniques in nuclear structure physics and in molecular physics are briefly reviewed and a recent application of these techniques to the structure of atomic clusters is discussed in more detail.

  7. Cluster Structure of Atomic Nuclei and Nucleosynthesis

    International Nuclear Information System (INIS)

    It is shown that the static and dynamic α-cluster models of nuclei, which describe an elastic electron scattering, photodisintegration reactions and pion double charge exchange reactions on α-cluster nuclei are in favor of the α-capture and α process of the formation of these nuclei

  8. SASP - Symposium on atomic, cluster and surface physics '94

    International Nuclear Information System (INIS)

    This international symposium (Founding Chairman: W. Lindinger, Innsbruck) is one in a continuing biennial series of conferences which seeks to promote the growth of scientific knowledge and its effective exchange among scientists in the field of atomic, molecular, cluster and surface physics and related areas. The symposium deals in particular with interactions between ions, electrons, photons, atoms, molecules, and clusters and their interactions with surfaces. (author)

  9. Fusion and fission of atomic clusters: recent advances

    DEFF Research Database (Denmark)

    Obolensky, Oleg I.; Solov'yov, Ilia; Solov'yov, Andrey V.;

    2005-01-01

    We review recent advances made by our group in finding optimized geometries of atomic clusters as well as in description of fission of charged small metal clusters. We base our approach to these problems on analysis of multidimensional potential energy surface. For the fusion process we have...... developed an effective scheme of adding new atoms to stable cluster geometries of larger clusters in an efficient way. We apply this algorithm to finding geometries of metal and noble gas clusters. For the fission process the analysis of the potential energy landscape calculated on the ab initio level...... of theory allowed us to obtain very detailed information on energetics and pathways of the different fission channels for the Na^2+_10 clusters....

  10. Hydrogen atom adsorption on aluminum icosahedral clusters: A DFT study

    International Nuclear Information System (INIS)

    Graphical abstract: Energy barriers for H atom migrating from the interstitial sites to surface adsorption sites for f.c.c. Al(1 1 1) surface and icosahedral surface. The icosahedral surface lowers the migration barriers of H atom both within the subsurface and between the surface and the subsurface. Research highlights: → Energetic properties of aluminum clusters absorbed with hydrogen atoms were investigated for the 'magic' clusters with icosahedral symmetry based on the first-principles calculation. → The slab model is made for representing the surface of icosahedral clusters by deforming the f.c.c. surface model. → The hydrogen diffusion barriers are calculated for interstitial sites of aluminum clusters and compared to those of bulk aluminum system. → The icosahedral surface lowers the migration barriers to H atoms between the surface and subsurface compared to the f.c.c. surface. - Abstract: Properties of hydrogenated, icosahedral aluminum clusters were investigated using density functional theory in comparison with those of aluminum bulk systems. The most stable site for H adsorption to Al13 was the hollow HCP site. The H binding energy suggests that the top and the bridge configurations are transition states. Results for Al13H were compared with those obtained for two surface models simulating f.c.c. and icosahedral (1 1 1) surfaces. Results show that the H atom interacts weakly with surface of clusters when the cluster size is increased. The migration energy of H atom between neighboring T and O sites becomes smaller for icosahedral subsurface than for either bulk material or the f.c.c. subsurface. A similar relation between the two surface models was found for the migration energy between surface and subsurface sites. These results indicate that the icosahedral surface lowers the migration barriers of H atom both within the subsurface and between the surface and the subsurface.

  11. Chemisorption and reactions on clusters of nickel atoms

    Science.gov (United States)

    Waber, J. T.; Adachi, H.; Yu, T.

    1982-01-01

    The nucleation and growth of metallic clusters on a substantially amorphous substrate are discussed with emphasis on the geometrical and electronic structure of the clusters. Several clusters of different symmetry containing five to nine nickel atoms were studied. It was found that the energy range of primary d-like states is not significantly different from the width of the d-band states in nickel metal, as long as the interatomic distance is comparable to that in the bulk metal. The approach of one or more molecules to the cluster is examined using at the hydrogenation of acetylene and the dehydrogenation of ethylene as examples.

  12. Electronic excitations in atomic clusters: beyond dipole plasmon

    CERN Document Server

    Nesterenko, V O; Reinhard, P G

    2005-01-01

    Multipole electron modes beyond the Mie plasmon in atomic clusters are investigated within the time-dependent local density approximation theory (TDLDA). We consider the origin of the modes, their connection with basic cluster properties and possible routes of experimental observation. Particular attention is paid to infrared magnetic orbital modes, scissors and twist, and electric quadrupole mode. The scissors and twist modes determine orbital magnetism of clusters while the electric quadrupole mode provides direct access to the single electron spectra of the cluster. We examine two-photon processes (Raman scattering, stimulated emission pumping and stimulated adiabatic Raman passage) as the most promising tools for experimental investigation of the modes.

  13. Atom-Precise Organometallic Zinc Clusters.

    Science.gov (United States)

    Banh, Hung; Dilchert, Katharina; Schulz, Christine; Gemel, Christian; Seidel, Rüdiger W; Gautier, Régis; Kahlal, Samia; Saillard, Jean-Yves; Fischer, Roland A

    2016-03-01

    The bottom-up synthesis of organometallic zinc clusters is described. The cation {[Zn10 ](Cp*)6 Me}(+) (1) is obtained by reacting [Zn2 Cp*2 ] with [FeCp2 ][BAr4 (F) ] in the presence of ZnMe2 . In the presence of suitable ligands, the high reactivity of 1 enables the controlled abstraction of single Zn units, providing access to the lower-nuclearity clusters {[Zn9 ](Cp*)6 } (2) and {[Zn8 ](Cp*)5 ((t) BuNC)3 }(+) (3). According to DFT calculations, 1 and 2 can be described as closed-shell species that are electron-deficient in terms of the Wade-Mingos rules because the apical ZnCp* units that constitute the cluster cage do not have three, but only one, frontier orbitals available for cluster bonding. Zinc behaves flexibly in building the skeletal metal-metal bonds, sometimes providing one major frontier orbital (like Group 11 metals) and sometimes providing three frontier orbitals (like Group 13 elements). PMID:26846901

  14. Cluster variation method in the atomic ordering theory

    International Nuclear Information System (INIS)

    A brief review is presented of the history of the origin, generalization, and the application of one of modern methods for the examination of cooperative phenomena to the theory of atomic ordering. The method has been named ''cluster variation method''. Using a computer, mathematical difficulties have been overcome; and the interest to the cluster variation method has considerarably increased. The results are discussed, which have been obtained by the above method for binary alloys with a face-centered cubic lattice or with space-centered one. Considered is the theory of atomic ordering in ternary alloys according to the type of binary superstructures, L12 and L10. The cluster variation method is applicable to a new model of the alloy, too. The method allows the range of problems to be expanded, which are solved in the statistical theory of atomic ordering

  15. Super-atom properties of 13 atom clusters of group 13 elements

    Energy Technology Data Exchange (ETDEWEB)

    Varns, Rebecca; Strange, Paul [School of Physical Sciences, University of Kent, SEPnet, Canterbury, Kent, CT2 7NH (United Kingdom)

    2012-11-15

    We report first principles calculations of the geometry and electronic structure of 13 atom clusters of boron, aluminium, gallium and indium. These density functional theory calculations support the jellium model in the energy levels and molecular orbitals of the cluster and enable us to discuss the relevance of the superatom concept. We go on to examine a number of cluster symmetries in detail as a function of charge and comment on the successes and limitations of the jellium and superatom models in describing these clusters. In particular we find that the monovalent anionic cluster is the most stable and has the most symmetric structure. As charge changes the symmetry of the clusters decreases in a way that is dependent on symmetry and charge, but not atomic species. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Dynamics of excess electrons in atomic and molecular clusters

    OpenAIRE

    Young, Ryan Michael

    2011-01-01

    Femtosecond time-resolved photoelectron imaging (TRPEI) is applied to the study of excess electrons in clusters as well as to microsolvated anion species. This technique can be used to perform explicit time-resolved as well as one-color (single- or multiphoton) studies on gas phase species. The first part of this dissertation details time-resolved studies done on atomic clusters with an excess electron, the excited-state dynamics of solvated molecular anions, and charge-transfer dynamics to...

  17. Ab initio calculations and modelling of atomic cluster structure

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Lyalin, Andrey G.; Solov'yov, Andrey V.;

    2004-01-01

    framework for modelling the fusion process of noble gas clusters is presented. We report the striking correspondence of the peaks in the experimentally measured abundance mass spectra with the peaks in the size-dependence of the second derivative of the binding energy per atom calculated for the chain...

  18. Thermodynamics of small clusters of atoms: A molecular dynamics simulation

    DEFF Research Database (Denmark)

    Damgaard Kristensen, W.; Jensen, E. J.; Cotterill, Rodney M J

    1974-01-01

    The thermodynamic properties of clusters containing 55, 135, and 429 atoms have been calculated using the molecular dynamics method. Structural and vibrational properties of the clusters were examined at different temperatures in both the solid and the liquid phase. The nature of the melting...... transition was investigated, and a number of properties, such as melting temperature, latent heat of melting, and premelting phenomena, were found to vary with cluster size. These properties were also found to depend on the structure of the solid phase. In this phase the configuration of lowest free energy...... was found to be icosahedral in the 55-atom system and face centered cubic for the two larger systems. ©1974 American Institute of Physics...

  19. Photoelectron imaging, probe of the dynamics: from atoms... to clusters

    International Nuclear Information System (INIS)

    This thesis concerns the study of the deexcitation of clusters and atoms by photoelectron imaging. The first part is dedicated to thermionic emission of a finite size system. A 3-dimensional imaging setup allows us to measure the time evolution of the kinetic energy spectrum of electrons emitted from different clusters (Wn-, Cn-, C60). Then we have a direct access to the fundamental quantities which characterize this statistical emission: the temperature of the finite heat bath and the decay rate. The second part concerns the ionization of atomic Rydberg states placed in a static electric field. We performed the first experiment of photoionization microscopy which allows us to obtain a picture which is the macroscopic projection of the electronic wave function. Then we have access to the detail of the photoionization and particularly to the quantum properties of the electron usually confined at the atomic scale. (author)

  20. Deposition of size-selected atomic clusters on surfaces

    CERN Document Server

    Carroll, S J

    1999-01-01

    implant into the surface. For Ag sub 2 sub 0 -Ag sub 2 sub 0 sub 0 clusters, the implantation depth is found to scale linearly with the impact energy and inversely with the cross-sectional area of the cluster, with an offset due to energy lost to the elastic compression of the surface (Paper VI). For smaller (Ag sub 3) clusters the orientation of the cluster with respect to the surface and the precise impact site play an important role; the impact energy has to be 'focused' in order for cluster implantation to occur (Paper VII). The application of deposited clusters for the creation of Si nanostructures by plasma etching is explored in Paper VIII. This dissertation presents technical developments and experimental and computational investigations concerned with the deposition of atomic clusters onto surfaces. It consists of a collection of papers, in which the main body of results are contained, and four chapters presenting a subject review, computational and experimental techniques and a summary of the result...

  1. Probabilistic Teleportation of Three-Atom State via Five-Atom Cluster State

    International Nuclear Information System (INIS)

    A scheme for probabilistic teleportation of an unknown three-atom entangled state via a five-atom non-maximally entangled cluster state as quantum channel is proposed. In this scheme, the sender performs two Bell state and a single-atom measurements on the atoms, the receiver can reconstruct the original state with a certain probability by introducing an auxiliary atom and operating appropriate unitary transformations and controlled-not (C-not) operations according to the sender Alice's measurement results. As a result, the probability of successful teleportation is determined by the smallest two of the coefficients' absolute values of the cluster state. The considerable advantage of our scheme is that we employ a non-maximally entangled cluster state as quantum channel in the scheme, which can greatly reduce the amount of entanglement resources and need less classical bits. If we employ a maximally entangled cluster state as quantum channel, the probabilistic teleportation scheme becomes usual teleportation, the successful probability being 100%. (general)

  2. High-accuracy coupled cluster calculations of atomic properties

    International Nuclear Information System (INIS)

    The four-component Fock-space coupled cluster and intermediate Hamiltonian methods are implemented to evaluate atomic properties. The latter include the spectra of nobelium and lawrencium (elements 102 and 103) in the range 20000-30000 cm−1, the polarizabilities of elements 112-114 and 118, required for estimating their adsorption enthalpies on surfaces used to separate them in accelerators, and the nuclear quadrupole moments of some heavy atoms. The calculations on superheavy elements are supported by the very good agreement with experiment obtained for the lighter homologues

  3. Electronically excited rubidium atom in a helium cluster or film

    Science.gov (United States)

    Leino, Markku; Viel, Alexandra; Zillich, Robert E.

    2008-11-01

    We present theoretical studies of helium droplets and films doped with one electronically excited rubidium atom Rb∗ (P2). Diffusion and path integral Monte Carlo approaches are used to investigate the energetics and the structure of clusters containing up to 14 helium atoms. The surface of large clusters is approximated by a helium film. The nonpair additive potential energy surface is modeled using a diatomic in molecule scheme. Calculations show that the stable structure of Rb∗Hen consists of a seven helium atom ring centered at the rubidium, surrounded by a tirelike second solvation shell. A very different structure is obtained when performing a "vertical Monte Carlo transition." In this approach, a path integral Monte Carlo equilibration starts from the stable configuration of a rubidium atom in the electronic ground state adsorbed to the helium surface after switching to the electronically excited surface. In this case, Rb∗Hen relaxes to a weakly bound metastable state in which Rb∗ sits in a shallow dimple. The interpretation of the results is consistent with the recent experimental observations [G. Auböck et al., Phys. Rev. Lett. 101, 035301 (2008)].

  4. Atom scattering off superfluid 4He clusters and films

    International Nuclear Information System (INIS)

    In this work, the HNC-Euler-Lagrange theory is applied to the many-body scattering problem. We use time-dependent variational correlated wave functions in excitation calculations in order to describe atom scattering off nanoclusters and microscopically thin films of superfluid helium-4. Apart from elastic processes, the level of implementation of the method includes dissipation, i.e. processes in which the atom imparts energy to the cluster/film, such as direct inelastic scattering and sticking. From the cross sections/probabilities for elastic and dissipative processes, information about the energetic structure (excitation energies, dispersion relations) of the helium-4 system can be gleaned, and, for scattering off a helium-4 film, about the strength of Van der Waal forces between atom and the substrate, on which the film is adsorbed. For the determination of inelastic scattering cross sections, we develop a method based on the expansion of the expectation value of the probability current to second order in correlation fluctuations which leads to a formulation which allows to identify the decay probability into open scattering channels. Various differential cross sections are calculated such as the probability for energy- and momentum-transfer to the helium cluster which is the analogon to the dynamic structure function measured by inelastic neutron scattering and which allows the determination of the surface wave (ripplons) dispersion relation. The effect of particle statistics on identical particle scattering is studied by comparing helium-4 scattering to impurity (helium-3) scattering off helium-4 clusters; e.g. we show how the elastic conversion process from helium-4 atom to roton and back can be understood as a resonance phenomenon at the excitation energy of the roton in helium clusters. The connection between resonances in the elastic scattering channel to their counterpart in inelastic channels is highlighted in the example of our results for quantum

  5. Atom scattering off superfluid4He clusters and films

    International Nuclear Information System (INIS)

    In this work, the HNC-Euler-Lagrange theory is applied to the many-body scattering problem. We use time-dependent variational correlated wave functions in excitation calculations in order to describe atom scattering off nanoclusters and microscopically thin films of superfluid helium-4. Apart from elastic processes, the level of implementation of the method includes dissipation, i.e. processes in which the atom imparts energy to the cluster/film, such as direct inelastic scattering and sticking. From the cross sections/probabilities for elastic and dissipative processes, information about the energetic structure (excitation energies, dispersion relations) of the helium-4 system can be gleaned, and, for scattering off a helium-4 film, about the strength of Van der Waal forces between atom and the substrate, on which the film is adsorbed. For the determination of inelastic scattering cross sections, we develop a method based on the expansion of the expectation value of the probability current to second order in correlation fluctuations which leads to a formulation which allows to identify the decay probability into open scattering channels. Various differential cross sections are calculated such as the probability for energy- and momentum-transfer to the helium cluster which is the analogon to the dynamic structure function measured by inelastic neutron scattering and which allows the determination of the surface wave (ripplons) dispersion relation. The effect of particle statistics on identical particle scattering is studied by comparing helium-4 scattering to impurity (helium-3) scattering off helium-4 clusters; e.g. we show how the elastic conversion process from helium-4 atom to roton and back can be understood as a resonance phenomenon at the excitation energy of the roton in helium clusters. The connection between resonances in the elastic scattering channel to their counterpart in inelastic channels is highlighted in the example of our results for quantum

  6. Alkali atoms, dimers, exciplexes and clusters in 4He crystals

    International Nuclear Information System (INIS)

    Full text: A closed-shell He atom and a single-electron alkali atom strongly repel each other because of the Pauli principle. As a consequence, an alkali atom immersed into condensed (superfluid or solid) 4He forms a spherical bubble state, in which the alkali repels the He quantum fluid/solid by imposing its own symmetry on the local He environment. For 15 years we have investigated such atomic bubbles in solid 4He using optical and magnetic resonance spectroscopy. In this talk I will first review our high resolution magnetic resonance studies performed on solid He matrix-isolated alkali atoms in the radio-frequency and microwave domains with special emphasis on their sensitive dependence on the crystalline structure (body-centered cubic, bcc, versus hexagonally close-packed, hcp) of the helium matrix. In recent years we have extended the purely atomic studies to larger bound complexes, such as exciplexes, dimers and clusters. I will present some of our intriguing recent results: in their respective ground states, alkali and He atoms are the worst enemies in the periodic table and strongly repel each other. Excited alkali atoms, however, attract He atoms and form bound states (so-called exciplexes), in which up to 7 He atoms can be attached to one alkali atom. Cs2 and Rb2 dimers in solid He can be excited via a large variety of absorption bands, and the deexcitation proceeds either by photodissociation or by emission of radiation. We made the strange observation that, irrespective of the excitation band, dimer fluorescence is only emitted on the (1)3Πu → X1Σg triplet-singlet transition which is forbidden in the free dimer. When the first excited P1/2 state of an alkali atom is populated by direct atomic excitation, it fluoresces at 879 nm (1.7 % blueshifted from the free atomic transition at 894 nm), a quantitatively well explained fact. However, when the same state is populated by photodissociation of the dimer, the emission wavelength is 885 nm. We attribute

  7. Plasmon excitations in two-dimensional atomic cluster systems

    Science.gov (United States)

    Yu, Yan-Qin; Yu, Ya-Bin; Xue, Hong-Jie; Wang, Ya-Xin; Chen, Jie

    2016-09-01

    Properties of plasmon excitations in two-dimensional (2D) atomic cluster systems are theoretically studied within an extended Hubbard model. The collective oscillation equations of charge, plasmon eigen-equations and the energy-absorption spectrum formula are presented. The calculated results show that different symmetries of plasmons exist in the cluster systems, and the symmetry of charge distribution in the plasmon resonance originate from the intrinsic symmetry of the corresponding eigen-plasmon modes, but not from the symmetry of applied external fields; however, the plasmon excitation with a certain polarization direction should be excited by the field in this direction, the dipole mode of plasmons can be excited by both uniform and non-uniform fields, but multipole ones cannot be excited by an uniform field. In addition, we show that for a given electron density, plasmon spectra are red-shifted with increasing size of the systems.

  8. Properties of light atomic nuclei in the potential cluster model

    CERN Document Server

    Dubovichenko, S B

    2010-01-01

    Monograph includes the results of the scientific work of the author for approximately 10 years and it is dedicated to theoretical studies of the structure of light atomic nuclei on the basis of potential cluster model with the forbidden states. Are examined questions of the single-valued construction of the intercluster potentials, which contain the forbidden states and simultaneously applied in the continuous and discrete spectra for the light nuclear systems with a mass of from 2 to 16. Is presented the mathematical apparatus and some calculation methods, utilized in the cluster model. Many questions, until now, considered here did not be reflected in the monographic literature. The book can represent interest for the students of elder courses, probationers, graduate students and scientific workers, who work in the field of theoretical nuclear physics. This Book is written in Russian, but will perhaps present certain interest.

  9. The Physics Cluster for Atomic and Subatomic Physics

    International Nuclear Information System (INIS)

    Full text: It is planned to bring together the Institute of High Energy Physics (HEPHY) and the Stefan- Meyer Institute (SMI), forming a new Institute of Particle Physics which will be in close scientific, technological and geographic location to the Atominstitut (ATI) of the Univ. of Technology, Vienna . Together, these institutes would form the Physics Cluster for Atomic and Subatomic Physics. At the Physics Cluster we will develop a unique research programme comprising a threefold approach to fundamental problems in particle physics: (1) accelerator-based high-energy physics for direct discoveries, (2) precision studies of the strong interaction searching for new exotic hadronic excitations (3) ultra high precision experiments at low energies with discovery potential not accessible with the conventional methods of particle physics. In the coming decade research will focus on exploiting the discovery potential at accelerators, LHC and KEK, with emphasis on Physics beyond the Standard Model and on studies of exotic nuclear matter at Frascati, at J-PARC and FAIR. The new research line of ultra high precision experiments will start from present expertise with precision experiments with cold and ultracold neutrons at the ILL or at FRMII, atoms, molecules or nuclear transition. It will focus on observables, which are sensitive to physics beyond the Standard Model, such as the breaking of fundamental symmetries (e.g. C, P and T), the variability of fundamental constants, aspects of gravity and ultra weak interactions or Supersymmetry. We will describe the research aims and the potential this Cluster for Atomic and Subatomic Physics will bring to particle physics. (author)

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

    Science.gov (United States)

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

    2016-03-01

    Field evaporation of metallic glasses is a stochastic process combined with spatially and temporally correlated events, which are referred to as clustered evaporation (CE). This phenomenon is investigated by studying the distance between consecutive detector hits. CE is found to be a strongly localized phenomenon (up to 3nm in range) which also depends on the type of evaporating ions. While a similar effect in crystals is attributed to the evaporation of crystalline layers, CE of metallic glasses presumably has a different - as yet unknown - physical origin. The present work provides new perspectives on quantification methods for atom probe tomography of metallic glasses. PMID:26724469

  11. Clustering of ions at atomic dimensions in quantum plasmas

    Science.gov (United States)

    Shukla, Padma K.; Eliasson, Bengt; Eliasson

    2013-08-01

    By means of particle simulations of the equations of motion for ions interacting among themselves under the influence of newly discovered Shukla-Eliasson attractive force (SEAF) in a dense quantum plasma, we demonstrate that the SEAF can bring ions closer at atomic dimensions. We present simulation results of the dynamics of an ensemble of ions in the presence of the SEAF without and with confining external potentials and collisions between ions and degenerate electrons. Our particle simulations reveal that under the SEAF, ions attract each other, come closer, and form ionic clusters in the bath of degenerate electrons that shield ions. Furthermore, an external confining potential produces robust ion clusters that can have cigar- and ball-like shapes, which remain stable when the confining potential is removed. The stability of ion clusters is discussed. Our results may have applications to solid density plasmas (density exceeding 1023 per cm3), where the electrons will be degenerate and quantum forces due to the electron recoil effect caused by the overlapping of electron wave functions and electron tunneling through the Bohm potential, electron-exchange and electron-exchange and electron correlations associated with electron-1/2 spin effect, and the quantum statistical pressure of the degenerate electrons play a decisive role.

  12. Clustering of Ions at Atomic-Dimensions in Quantum Plasmas

    CERN Document Server

    Shukla, P K

    2012-01-01

    By means of particle simulations of the equations of motion for ions interacting with the newly discovered Shukla-Eliasson (SE) force in a dense quantum plasma, we demonstrate that the SE force is powerful to bring ions closer at atomic dimensions. Specifically, we present simulation results on the dynamics of an ensemble of ions in the presence of the SE force without and with confining external potentials and collisions between the ions and degenerate electrons. Our particle simulations reveal that under the SE force, ions attract each other, come closer and form ionic clusters in the bath of degenerate electrons that shield the ions. Furthermore, an external confining potential produces robust ion clusters that can have cigar-like and ball-like shapes. The binding between the ions on account of the SE force may provide possibility of non-Coulombic explosions of ionic clusters for inertial confined fusion (ICF) schemes when high-energy density plasmas (density exceeding $10^{23}$ per cubic centimeters) are ...

  13. Ternary and quaternary Lennard-Jones atomic clusters: The effects of atomic sizes on the compositions, geometries, and relative stability

    Energy Technology Data Exchange (ETDEWEB)

    Takeuchi, Hiroshi, E-mail: takehi@sci.hokudai.ac.jp

    2015-08-18

    Highlights: • Geometry optimization of ternary and quaternary Lennard-Jones clusters. • Elucidation of atomic compositions, growth sequence, and relative stability. • Pronounced effects of the atom-size difference on the features of the clusters. • High efficiency of atom-type conversions in the geometry optimization. - Abstract: Global-minimum geometries of ternary and quaternary Lennard-Jones clusters have been calculated with constraints on atomic compositions of the clusters. In the present study, the constraints were removed to obtain optimal compositions. The size ratios of the largest-sized atom to the smallest-sized one ranged from 1.1 to 1.6 whereas the depths of the interatomic potentials were constant. The heuristic method combined with the geometrical perturbations and atom-type conversion was used to search for the global minima of the clusters with up to 50 atoms. The smallest-sized and largest-sized atoms usually occupy cores and outer shells, respectively, and the atoms with intermediate sizes are often lacking. The size ratio has pronounced effects on the compositions, structures, and relative stability of the clusters.

  14. Ternary and quaternary Lennard-Jones atomic clusters: The effects of atomic sizes on the compositions, geometries, and relative stability

    International Nuclear Information System (INIS)

    Highlights: • Geometry optimization of ternary and quaternary Lennard-Jones clusters. • Elucidation of atomic compositions, growth sequence, and relative stability. • Pronounced effects of the atom-size difference on the features of the clusters. • High efficiency of atom-type conversions in the geometry optimization. - Abstract: Global-minimum geometries of ternary and quaternary Lennard-Jones clusters have been calculated with constraints on atomic compositions of the clusters. In the present study, the constraints were removed to obtain optimal compositions. The size ratios of the largest-sized atom to the smallest-sized one ranged from 1.1 to 1.6 whereas the depths of the interatomic potentials were constant. The heuristic method combined with the geometrical perturbations and atom-type conversion was used to search for the global minima of the clusters with up to 50 atoms. The smallest-sized and largest-sized atoms usually occupy cores and outer shells, respectively, and the atoms with intermediate sizes are often lacking. The size ratio has pronounced effects on the compositions, structures, and relative stability of the clusters

  15. Aerosol cluster impact and break-up : II. Atomic and Cluster Scale Models.

    Energy Technology Data Exchange (ETDEWEB)

    Lechman, Jeremy B.; Takato, Yoichi (State University of New York at Buffalo, Buffalo, NY)

    2010-09-01

    Understanding the interaction of aerosol particle clusters/flocs with surfaces is an area of interest for a number of processes in chemical, pharmaceutical, and powder manufacturing as well as in steam-tube rupture in nuclear power plants. Developing predictive capabilities for these applications involves coupled phenomena on multiple length and timescales from the process macroscopic scale ({approx}1m) to the multi-cluster interaction scale (1mm-0.1m) to the single cluster scale ({approx}1000 - 10000 particles) to the particle scale (10nm-10{micro}m) interactions, and on down to the sub-particle, atomic scale interactions. The focus of this report is on the single cluster scale; although work directed toward developing better models of particle-particle interactions by considering sub-particle scale interactions and phenomena is also described. In particular, results of mesoscale (i.e., particle to single cluster scale) discrete element method (DEM) simulations for aerosol cluster impact with rigid walls are presented. The particle-particle interaction model is based on JKR adhesion theory and is implemented as an enhancement to the granular package in the LAMMPS code. The theory behind the model is outlined and preliminary results are shown. Additionally, as mentioned, results from atomistic classical molecular dynamics simulations are also described as a means of developing higher fidelity models of particle-particle interactions. Ultimately, the results from these and other studies at various scales must be collated to provide systems level models with accurate 'sub-grid' information for design, analysis and control of the underlying systems processes.

  16. Controllable irregular melting induced by atomic segregation in bimetallic clusters with fabricating different initial configurations

    International Nuclear Information System (INIS)

    The melting process of Co, Co-Cu and Co-Ni clusters with different initial configurations is studied in molecular dynamics by a general embedded atom method. An irregular melting, at which energy decreases as the temperature increase near the melting point, is found in the onion-like Co-Cu-Co clusters, but not in the mixed Co-Cu and onion-like Co-Ni-Co clusters. From the analysis of atomic distributions and energy variation, the results indicate the irregular melting is induced by Cu atomic segregation. Furthermore, this melting can be controlled by doping hetero atoms with different surface energies and controlling their distributions.

  17. Atomic characterization of Au clusters in vapor-liquid-solid grown silicon nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Wanghua; Roca i Cabarrocas, Pere [Laboratoire de Physique des Interfaces et Couches Minces (LPICM), UMR 7647, CNRS, Ecole Polytechnique, 91128 Palaiseau (France); Pareige, Philippe; Castro, Celia [Groupe de Physique des Matériaux (GPM), Université et INSA de Rouen, UMR 6634, CNRS, Av. de l' Université, BP 12, 76801 Saint Etienne du Rouvray (France); Xu, Tao; Grandidier, Bruno; Stiévenard, Didier [Institut d' Electronique et de Microélectronique et de Nanotechnologies (IEMN), UMR 8520, CNRS, Département ISEN, 41 bd Vauban, 59046 Lille Cedex (France)

    2015-09-14

    By correlating atom probe tomography with other conventional microscope techniques (scanning electron microscope, scanning transmission electron microscope, and scanning tunneling microscopy), the distribution and composition of Au clusters in individual vapor-liquid-solid grown Si nanowires is investigated. Taking advantage of the characteristics of atom probe tomography, we have developed a sample preparation method by inclining the sample at certain angle to characterize the nanowire sidewall without using focused ion beam. With three-dimensional atomic scale reconstruction, we provide direct evidence of Au clusters tending to remain on the nanowire sidewall rather than being incorporated into the Si nanowires. Based on the composition measurement of Au clusters (28% ± 1%), we have demonstrated the supersaturation of Si atoms in Au clusters, which supports the hypothesis that Au clusters are formed simultaneously during nanowire growth rather than during the cooling process.

  18. Atomic characterization of Au clusters in vapor-liquid-solid grown silicon nanowires

    International Nuclear Information System (INIS)

    By correlating atom probe tomography with other conventional microscope techniques (scanning electron microscope, scanning transmission electron microscope, and scanning tunneling microscopy), the distribution and composition of Au clusters in individual vapor-liquid-solid grown Si nanowires is investigated. Taking advantage of the characteristics of atom probe tomography, we have developed a sample preparation method by inclining the sample at certain angle to characterize the nanowire sidewall without using focused ion beam. With three-dimensional atomic scale reconstruction, we provide direct evidence of Au clusters tending to remain on the nanowire sidewall rather than being incorporated into the Si nanowires. Based on the composition measurement of Au clusters (28% ± 1%), we have demonstrated the supersaturation of Si atoms in Au clusters, which supports the hypothesis that Au clusters are formed simultaneously during nanowire growth rather than during the cooling process

  19. Meta-atom cluster acoustic metamaterial with broadband negative effective mass density

    International Nuclear Information System (INIS)

    We design a resonant meta-atom cluster, via which a two-dimensional (2D) acoustic metamaterial (AM) with broadband negative effective mass density from 1560 Hz to 5580 Hz is fabricated. Experimental results confirm that there is only weak interaction among the meta-atoms in the cluster. And then the meta-atoms in the cluster independently resonate, resulting in the cluster becoming equivalent to a broadband resonance unit. Extracted effective refractive indices from reflection and transmission measurements of the 2D AM appear to be negative from 1500 Hz to 5480 Hz. The broadband negative refraction has also been demonstrated by our further experiments. We expect that this meta-atom cluster AM will significantly contribute to the design of broadband negative effective mass density AM

  20. Inter-atomic Coulombic Decay (ICD) of clusters upon electron impact

    International Nuclear Information System (INIS)

    Full text: ICD is proposed to be a universal ionization mechanism in clusters, where one atom absorbs energy, becomes inner valence ionized and the excess energy is transferred to a neighboring atom via a virtual photon, leading to its ionization. Thus the cluster ends up with two positively charged particles exploding due to the Coulombic force. In the present study mass spectrometry is used to investigate the presence of ICD relaxation mechanisms in neon clusters. This is done by measuring the initial kinetic energy of product ions after electron impact of the clusters. (author)

  1. Detecting and extracting clusters in atom probe data: A simple, automated method using Voronoi cells

    Energy Technology Data Exchange (ETDEWEB)

    Felfer, P., E-mail: peter.felfer@sydney.edu.au [Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia); School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006 (Australia); Ceguerra, A.V., E-mail: anna.ceguerra@sydney.edu.au [Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia); School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006 (Australia); Ringer, S.P., E-mail: simon.ringer@sydney.edu.au [Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia); School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006 (Australia); Cairney, J.M., E-mail: julie.cairney@sydney.edu.au [Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia); School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006 (Australia)

    2015-03-15

    The analysis of the formation of clusters in solid solutions is one of the most common uses of atom probe tomography. Here, we present a method where we use the Voronoi tessellation of the solute atoms and its geometric dual, the Delaunay triangulation to test for spatial/chemical randomness of the solid solution as well as extracting the clusters themselves. We show how the parameters necessary for cluster extraction can be determined automatically, i.e. without user interaction, making it an ideal tool for the screening of datasets and the pre-filtering of structures for other spatial analysis techniques. Since the Voronoi volumes are closely related to atomic concentrations, the parameters resulting from this analysis can also be used for other concentration based methods such as iso-surfaces. - Highlights: • Cluster analysis of atom probe data can be significantly simplified by using the Voronoi cell volumes of the atomic distribution. • Concentration fields are defined on a single atomic basis using Voronoi cells. • All parameters for the analysis are determined by optimizing the separation probability of bulk atoms vs clustered atoms.

  2. Detecting and extracting clusters in atom probe data: A simple, automated method using Voronoi cells

    International Nuclear Information System (INIS)

    The analysis of the formation of clusters in solid solutions is one of the most common uses of atom probe tomography. Here, we present a method where we use the Voronoi tessellation of the solute atoms and its geometric dual, the Delaunay triangulation to test for spatial/chemical randomness of the solid solution as well as extracting the clusters themselves. We show how the parameters necessary for cluster extraction can be determined automatically, i.e. without user interaction, making it an ideal tool for the screening of datasets and the pre-filtering of structures for other spatial analysis techniques. Since the Voronoi volumes are closely related to atomic concentrations, the parameters resulting from this analysis can also be used for other concentration based methods such as iso-surfaces. - Highlights: • Cluster analysis of atom probe data can be significantly simplified by using the Voronoi cell volumes of the atomic distribution. • Concentration fields are defined on a single atomic basis using Voronoi cells. • All parameters for the analysis are determined by optimizing the separation probability of bulk atoms vs clustered atoms

  3. Study on structures and electronic properties of NaxV (x = 1-12) atomic clusters

    International Nuclear Information System (INIS)

    Superatoms, novel entities being studied extensively in recent years, can be stabilized by mixing with transition metal atoms. The aim of this paper is to present some recent theoretical results on the application of quantum calculations for examining the atomic clusters NaxV (x = 1-12) made from the mixing of Nax superatoms with vanadium transition metal atom. Optimized structures of NaxV, NaxV+ and NaxV- are determined by using the TPSSTPSS/DZVP DFT calculations. Characteristics of optimized structures, as point group symmetry, chemical hardness (η), absolute electronegativity (χ), electrophilicity index (ω), fragmentation energy (Ef), secondary energy (∆2E), are calculated. The obtained results point out that among different structures of an atomic cluster, the more negative total energy the more stable structure and the Na8V cluster is the most stable in NaxV (x = 1-12) clusters. (author)

  4. Fock space relativistic coupled-Cluster calculations of Two-Valence Atoms

    OpenAIRE

    Mani, B. K.; Angom, D.

    2010-01-01

    We have developed an all particle Fock-space relativistic coupled-cluster method for two-valence atomic systems. We then describe a scheme to employ the coupled-cluster wave function to calculate atomic properties. Based on these developments we calculate the excitation energies, magnetic hyperfine constants and electric dipole matrix elements of Sr, Ba and Yb. Further more, we calculate the electric quadrupole HFS constants and the electric dipole matrix elements of Sr$^+$, Ba$^+$ and Yb$^+$...

  5. A nine-atom rhodium–aluminum oxide cluster oxidizes five carbon monoxide molecules

    Science.gov (United States)

    Li, Xiao-Na; Zhang, Hua-Min; Yuan, Zhen; He, Sheng-Gui

    2016-01-01

    Noble metals can promote the direct participation of lattice oxygen of very stable oxide materials such as aluminum oxide, to oxidize reactant molecules, while the fundamental mechanism of noble metal catalysis is elusive. Here we report that a single atom of rhodium, a powerful noble metal catalyst, can promote the transfer of five oxygen atoms to oxidize carbon monoxide from a nine-atom rhodium–aluminum oxide cluster. This is a sharp improvement in the field of cluster science where the transfer of at most two oxygen atoms from a doped cluster is more commonly observed. Rhodium functions not only as the preferred trapping site to anchor and oxidize carbon monoxide by the oxygen atoms in direct connection with rhodium but also the primarily oxidative centre to accumulate the large amounts of electrons and the polarity of rhodium is ultimately transformed from positive to negative. PMID:27094921

  6. A nine-atom rhodium-aluminum oxide cluster oxidizes five carbon monoxide molecules.

    Science.gov (United States)

    Li, Xiao-Na; Zhang, Hua-Min; Yuan, Zhen; He, Sheng-Gui

    2016-01-01

    Noble metals can promote the direct participation of lattice oxygen of very stable oxide materials such as aluminum oxide, to oxidize reactant molecules, while the fundamental mechanism of noble metal catalysis is elusive. Here we report that a single atom of rhodium, a powerful noble metal catalyst, can promote the transfer of five oxygen atoms to oxidize carbon monoxide from a nine-atom rhodium-aluminum oxide cluster. This is a sharp improvement in the field of cluster science where the transfer of at most two oxygen atoms from a doped cluster is more commonly observed. Rhodium functions not only as the preferred trapping site to anchor and oxidize carbon monoxide by the oxygen atoms in direct connection with rhodium but also the primarily oxidative centre to accumulate the large amounts of electrons and the polarity of rhodium is ultimately transformed from positive to negative. PMID:27094921

  7. Structure and stability of a silicon cluster on sequential doping with carbon atoms

    Science.gov (United States)

    AzeezullaNazrulla, Mohammed; Joshi, Krati; Israel, S.; Krishnamurty, Sailaja

    2016-02-01

    SiC is a highly stable material in bulk. On the other hand, alloys of silicon and carbon at nanoscale length are interesting from both technological as well fundamental view point and are being currently synthesized by various experimental groups (Truong et. al., 2015 [26]). In the present work, we identify a well-known silicon cluster viz., Si10 and dope it sequentially with carbon atoms. The evolution of electronic structure (spin state and the structural properties) on doping, the charge redistribution and structural properties are analyzed. It is interesting to note that the ground state SiC clusters prefer to be in the lowest spin state. Further, it is seen that carbon atoms are the electron rich centres while silicon atoms are electron deficient in every SiC alloy cluster. The carbon-carbon bond lengths in alloy clusters are equivalent to those seen in fullerene molecules. Interestingly, the carbon atoms tend to aggregate together with silicon atoms surrounding them by donating the charge. As a consequence, very few Si-Si bonds are noted with increasing concentrations of C atoms in a SiC alloy. Physical and chemical stability of doped clusters is studied by carrying out finite temperature behaviour and adsorbing O2 molecule on Si9C and Si8C2 clusters, respectively.

  8. Helium clusters as cold, liquid matrix for the laser spectroscopy of silver atoms, silver clusters and C60 fullerenes

    International Nuclear Information System (INIS)

    One of the main obstacles in the study of gas phase metal clusters is their high temperature. Even cooling in a seeded beam is only of limited used, since the condensation continuously releases energy into the system. As a consequence, spectroscopic studies of free metal clusters typically yield broad structures, which are interpreted as plasma resonances of a free electron gas. An experiment on ionic sodium clusters has shown that low temperatures lead to a narrowing of the absorption bands and the appearance of additional structure, that can not be explained within the free electron model. Thus the need for cold clusters is evident. In principle the deposition of metal clusters into inert matrices eliminates the temperature problem but it can also inflict strong changes on the electronic spectra. Droplets of liquid helium serve as a much more gentle matrix that avoids many of the above problems. In this thesis the new technique of helium droplet spectroscopy is presented as a tool for the study of extremely cold metal clusters. Clusters of silver up to a mass greater than 7000 amu have been produced by pickup of single atoms by a beam of helium droplets. The droplets are formed in a supersonic expansion. The cluster's binding energy is removed by evaporative cooling and the system remains at 0.4 K. The doped droplets are probed by laser spectroscopy with a depletion technique or resonant two photon ionization. We were able to measure the first UV absorption spectrum of metal atoms (silver) inside helium droplets. Another experiment shows that a small fraction of the captured silver atoms resides on the surface of the droplet like alkali atoms. In a two photon process previously unobserved s- and d-Rydberg states of the free silver atom (20 left angle n left angle 80) were excited. The silver atoms, initially embedded in the helium droplets, are found to move to the surface and desorb when excited to the broadened 5p level. This is the first result showing laser

  9. Fragmentation of neutral carbon clusters formed by high velocity atomic collision

    International Nuclear Information System (INIS)

    The aim of this work is to understand the fragmentation of small neutral carbon clusters formed by high velocity atomic collision on atomic gas. In this experiment, the main way of deexcitation of neutral clusters formed by electron capture with ionic species is the fragmentation. To measure the channels of fragmentation, a new detection tool based on shape analysis of current pulse delivered by semiconductor detectors has been developed. For the first time, all branching ratios of neutral carbon clusters are measured in an unambiguous way for clusters size up to 10 atoms. The measurements have been compared to a statistical model in microcanonical ensemble (Microcanonical Metropolis Monte Carlo). In this model, various structural properties of carbon clusters are required. These data have been calculated with Density Functional Theory (DFT-B3LYP) to find the geometries of the clusters and then with Coupled Clusters (CCSD(T)) formalism to obtain dissociation energies and other quantities needed to compute fragmentation calculations. The experimental branching ratios have been compared to the fragmentation model which has allowed to find an energy distribution deposited in the collision. Finally, specific cluster effect has been found namely a large population of excited states. This behaviour is completely different of the atomic carbon case for which the electron capture in the ground states predominates. (author)

  10. Bound electron states in clusters of inert atoms in magnetic field

    International Nuclear Information System (INIS)

    Electron states in inert gas clusters placed into the magnetic field are considered. It is shown that the external magnetic field leads to two important consequences: first, is leads to electron level deepening and consequently, to stabilization of charged cluster; second, the magnetic field leads to much lower values of atom critical numbers, under which the production of electron and cluster bound state is possible. 6 refs., 1 tab

  11. van der Waals interaction of finite metallic systems: A study of cluster-atom scattering

    International Nuclear Information System (INIS)

    Absolute integral cross sections for elastic collisions of neutral sodium clusters Nan (n=2--20) with sodium atoms have been measured and the van der Waals interaction constants determined. The center-of-mass cross sections are very large (up to thousands of square angstroms), reflecting high cluster polarizabilities. It is found that the dispersion theory based on measured response parameters of alkali-metal clusters tends to overestimate the interaction strength

  12. Picosecond multiphoton ionization of atomic and molecular clusters

    International Nuclear Information System (INIS)

    High peak-power picosecond laser pulses have been used for the first time to effect nonresonant or resonant multiphoton ionization (MPI) of clusters generated in a supersonic nozzle expansion. The resulting ions are subsequently detected and characterized by time-of-flight mass spectroscopy. Specifically, we present results involving MPI of clusters of xenon and nitric oxide. Previous MPI studies of many molecular clusters using nanosecond lasers have not been successful in observing the parent ion, presumably due to fast dissociation channels. It is proposed that the present technique is a new and rather general ionization source for cluster studies which is complementary to electron impact but may, in addition, provide unique spectroscopic or dynamical information. 23 refs., 5 figs

  13. Manipulation of magnetic anisotropy in Irn+1 clusters by Co atom

    Science.gov (United States)

    Ge, Gui-Xian; Yan, Hong-Xia; Yang, Jue-Ming; Zhou, Long; Wan, Jian-Guo; Zhao, Ji-Jun; Wang, Guang-Hou

    2016-07-01

    Based on the first principles calculations, we have investigated the magnetic properties of Irn+1 clusters modulated by Co atoms. The research conclusions show that the amplitude of magnetic anisotropy energy (MAE) and magnetization direction of the small Irn+1 can be manipulated by Co atom if we can control the size very precisely. Such regulatory mechanism of MAE is ascribed to the distributing variation of Ir-5d orbits around the Fermi level induced by Co atom. More importantly, the colossal MAE values, 67.4 meV/atom, 40.26 meV/atom and 91.37 meV/atom, can be obtained for Ir2, Ir4, and CoIr clusters, respectively. Such high values provide a promising avenue for developing high-density magnetic storage units at sub-nanometer size.

  14. Generation of microscale current loops, atom rings, and cubic clusters using twisted optical molasses

    International Nuclear Information System (INIS)

    We propose a scheme for a viable and highly flexible all-optical atomic cooling and trapping using twisted light. In particular, we explain how one-dimensional twisted optical molasses should lead to a microscale atomic ring or a picoampere ionic current. Two-dimensional and three-dimensional molasses lead, respectively, to the creation of atom or ion loops and discrete atom clusters positioned at the eight corners of a microcube. These features at the microscale should find applications in physics and in quantum information processing using optically trapped atoms and ions

  15. Electronic and atomic structure of the AlnHn+2 clusters

    DEFF Research Database (Denmark)

    Martinez, Jose Ignacio; Alonso, J.A.

    2008-01-01

    polyhedron of n vertices and n H atoms form strong H-Al terminal bonds; one pair of electrons is involved in each of those bonds. The remaining n+1 electron pairs form a delocalized cloud over the surface of the Al cage. The clusters fulfilling the Wade-Mingos rule have wider HOMO-LUMO gaps and are......The electronic and atomic structure of the family of hydrogenated Al clusters AlnHn+2 with n=4-11 has been studied using the density functional theory with the generalized gradient approximation (GGA) for exchange and correlation. All these clusters have substantial gaps between the highest...

  16. Cluster Fusion: Face-Fused Nine-Atom Deltahedral Clusters in [Sn14 Ni(CO)](4.).

    Science.gov (United States)

    Perla, Luis G; Sevov, Slavi C

    2016-06-01

    The title anion was synthesized by heating dimethylformamide (DMF) solution of the known Ni-centered and Ni(CO)-capped tin clusters [Ni@Sn9 Ni(CO)](3-) . The new anion represents the first example of face-fused nine-atom molecular clusters. The two clusters are identical elongated tricapped trigonal prisms of nido-[Sn8 Ni(CO)](6-) with nickel at one of the capping positions. They are fused along a triangular face adjacent to a trigonal prismatic base and made of two Sn and one Ni atoms. The new anion is structurally characterized by single-crystal X-ray diffraction in the compound (K[222-crypt])4 [Sn14 Ni(CO)]⋅DMF. Its presence in solution is corroborated by electrospray mass spectrometry. PMID:27098199

  17. Self-diffusion dynamic behavior of atomic clusters on Re(0 0 0 1) surface

    International Nuclear Information System (INIS)

    Using molecular dynamics simulations and a modified analytic embedded atom potential, the self-diffusion dynamics of rhenium atomic clusters up to seven atoms on Re(0 0 0 1) surface have been studied in the temperature ranges from 600 K to 1900 K. The simulation time varies from 20 ns to 200 ns according to the cluster sizes and the temperature. The heptamer and trimer are more stable comparing to other neighboring non-compact clusters. The diffusion coefficients of clusters are derived from the mean square displacement of cluster's mass-center, and diffusion prefactors D0 and activation energies Ea are derived from the Arrhenius relation. It is found that the Arrhenius relation of the adatom can be divided into two parts at different temperature range. The activation energy of clusters increases with the increasing of the atom number in clusters. The prefactor of the heptamer is 2-3 orders of magnitude higher than a usual prefactor because of a large number of nonequivalent diffusion processes. The trimer and heptamer are the nuclei at different temperature range according to the nucleation theory.

  18. Atomic and electronic structure of clusters from car-Parrinello method

    International Nuclear Information System (INIS)

    With the development of ab-initio molecular dynamics method, it has now become possible to study the static and dynamical properties of clusters containing up to a few tens of atoms. Here I present a review of the method within the framework of the density functional theory and pseudopotential approach to represent the electron-ion interaction and discuss some of its applications to clusters. Particular attention is focussed on the structure and bonding properties of clusters as a function of their size. Applications to clusters of alkali metals and Al, non-metal - metal transition in divalent metal clusters, molecular clusters of carbon and Sb are discussed in detail. Some results are also presented on mixed clusters. (author). 121 refs, 24 ifigs

  19. Migration mechanisms of self-interstitial atoms and their clusters in Fe-Cr alloys

    International Nuclear Information System (INIS)

    The mobility of self-interstitial atoms (SIAs) and their clusters in pure iron and iron-chromium alloys was studied by atomic scale modelling techniques. Molecular dynamics (MD) was used to simulate thermally activated motion, i.e. diffusion, and its mechanisms whereas molecular statics was used to estimate energies of interactions of SIA and SIA clusters with Cr-impurities. It is shown that the presence of Cr atoms reduces the diffusivity of SIAs and their clusters in a non monotonic way with increasing Cr concentration. The main reason for this reduction is the presence of a long-range attractive interaction between self-interstitials in the crowdion configuration and Cr atoms. The migration mechanisms behind this effect are discussed relying on the results obtained from the MD simulations. (author)

  20. Dynamics simulation on the interaction of intense laser pulses with atomic clusters

    Institute of Scientific and Technical Information of China (English)

    Du Hong-Chuan; Zhu Peng-Jia; Sun Shao-Hua; Liu Zuo-Ye; Li Lu; Ma Ling-Ling; Hu Bi-Tao

    2009-01-01

    Under classical particle dynamics, the interaction process between intense femtosecond laser pulses and icosahedral noble-gas atomic clusters was studied. Our calculated results show that ionization proceeds mainly through tunnel ionization in the combined field from ions, electrons and laser, rather than the electron-impact ionization. With increasing cluster size, the average and maximum kinetic energy of the product ion increases. According to our calculation, the expansion process of the clusters after laser irradiation is dominated by Coulomb explosion and the expansion scale increases with increasing cluster size. The dependence of average kinetic energy and average charge state of the product ions on laser wavelength is also presented and discussed. The dependence of average kinetic energy on the number of atoms inside the cluster was studied and compared with the experimental data. Our results agree with the experimental results reasonably well.

  1. Atomic-scale observation of dynamical fluctuation and three-dimensional structure of gold clusters

    Energy Technology Data Exchange (ETDEWEB)

    Li, Junjie [Engineering Research Center for Nanophotonics and Advanced Instrument, Ministry of Education, Department of Physics, East China Normal University, North Zhongshan Road 3663, Shanghai 200062 (China); Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Yin, Deqiang [School of Manufacturing Science and Engineering, Sichuan University, Chengdu 610064 (China); Chen, Chunlin; Lin, Liyang; Wang, Zhongchang, E-mail: zcwang@wpi-aimr.tohoku.ac.jp [Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Li, Qiang [School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093 (China); Sun, Rong [Institute of Engineering Innovation, The University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Huang, Sumei, E-mail: smhuang@phy.ecnu.edu.cn [Engineering Research Center for Nanophotonics and Advanced Instrument, Ministry of Education, Department of Physics, East China Normal University, North Zhongshan Road 3663, Shanghai 200062 (China)

    2015-02-28

    Unravelling three-dimensional structures and dynamical fluctuation of metal nanoclusters is critical to understanding reaction process and the origin of catalytic activity in many heterogeneous catalytic systems. We obtain three-dimensional structures of ultra-small Au clusters by combining aberration-corrected scanning transmission electron microscopy, density functional theory calculations, and imaging simulations. The configurations of unique Au clusters are revealed at the atomic scale and the corresponding electronic states are given. The sequential observations reveal a transition of ultra-small Au clusters with about 25 atoms from a near-square to an elongated structure. We also find a transition from two dimensions to three dimensions for the Au clusters. The obtained three-dimensional geometry and associated electronic states help to clarify atomistic mechanism of shape- and number-dependent catalytic activities of Au clusters.

  2. Functionalization of atomic cobalt clusters obtained by electrochemical methods

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez Cobo, Eldara [Laboratorio de Magnetismo y Tecnologia, Instituto Tecnoloxico, Pabillon de Servicios, Campus Sur, 15782 Santiago de Compostela (Spain); Departamento de Quimica Organica y Unidad Asociada al CSIC, Universidad de Santiago de Compostela, 15782 Santiago de Compostela (Spain); Rivas Rey, Jose; Blanco Varela, M. Carmen; Lopez Quintela, M. Arturo [Laboratorio de Magnetismo y Tecnologia, Instituto Tecnoloxico, Pabillon de Servicios, Campus Sur, 15782 Santiago de Compostela (Spain); Mourino Mosquera, Antonio; Torneiro Abuin, Mercedes [Departamento de Quimica Organica y Unidad Asociada al CSIC, Universidad de Santiago de Compostela, 15782 Santiago de Compostela (Spain)

    2006-05-15

    Functionalization of magnetic nanoparticles with appropriate organic molecules is very important for many applications. In the present study, cobalt nanoparticles, with an average diameter of 2 nm corresponding to Co{sub 309} clusters were synthesised by an electrochemical method, and then coated with ADCB (4-(9-deceniloxi)benzoic acid), in order to protect the clusters against oxidation and to obtain a final nanostructure, which can be attached later on to many different materials, like drugs, proteins or some other biological molecules. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Electron exchange between an H{sup -} ion and a spherical cluster of aluminum atoms

    Energy Technology Data Exchange (ETDEWEB)

    Shestakov, D.K.; Polivnikova, T.Yu. [Department of Physics, Moscow State University, Moscow 119992 (Russian Federation); Gainullin, I.K. [Department of Physics, Moscow State University, Moscow 119992 (Russian Federation)], E-mail: Ivan.Gainullin@gmail.com; Urazgildin, I.F. [Department of Physics, Moscow State University, Moscow 119992 (Russian Federation)

    2009-08-15

    The resonant charge transfer (RCT) between a hydrogen anion and a cluster of aluminum atoms is investigated by means of the wave-packet propagation method that does not exploit the perturbation theory. The RCT on a spherical cluster is found to exhibit quantum size effects due to the finite size of the cluster. The survival amplitude of an ion state has been calculated as a function of the distance to the ion-surface in a normal collision. It is shown that depending on the velocity of the impinging particle, the cluster can behave either as a bulk metal or as a quantum structure with discrete energy states existing over two coordinates.

  4. Electron exchange between an H- ion and a spherical cluster of aluminum atoms

    International Nuclear Information System (INIS)

    The resonant charge transfer (RCT) between a hydrogen anion and a cluster of aluminum atoms is investigated by means of the wave-packet propagation method that does not exploit the perturbation theory. The RCT on a spherical cluster is found to exhibit quantum size effects due to the finite size of the cluster. The survival amplitude of an ion state has been calculated as a function of the distance to the ion-surface in a normal collision. It is shown that depending on the velocity of the impinging particle, the cluster can behave either as a bulk metal or as a quantum structure with discrete energy states existing over two coordinates.

  5. First principles investigation of cluster consisting of hydrogen–helium atoms interstitially-trapped in tungsten

    International Nuclear Information System (INIS)

    We evaluate the binding energies of mixed helium and hydrogen clusters consisted of interstitially trapped atoms in bcc tungsten by first-principles calculations based on density functional theories. It is shown that helium-rich interstitially-trapped clusters have the positive binding energies and the low electron-density region expand as the number of helium in the cluster increase. Thus, the helium-rich interstitially trapped clusters can act as a trapping site for hydrogen, and interstitially trapped helium interrupts or disturbs the hydrogen diffusion in tungsten

  6. Kr atoms and their clustering in zeolite A

    CERN Document Server

    Lim, W T; Jung, K J; Heo, N H

    2001-01-01

    The positions of Kr atoms encapsulated in the molecular-dimensioned cavities of fully dehydrated zeolite A of unit-cell composition Cs sub 3 Na sub 8 HSi sub 1 sub 2 Al sub 1 sub 2 O sub 4 sub 8 (Cs sub 3 -A) have been determined. Cs sub 3 -A was exposed to 1025 atm of krypton gas at 400 .deg. C for four days, followed by cooling at pressure to encapsulate Kr atoms. The resulting crystal structure of Cs sub 3 -A(6Kr) (a=12.247(2) A, R sub 1 =0.078, and R sub 2 =0.085) has been determined by single-crystal X-ray diffraction techniques in the cubic space group Pm3m at 21(1) .deg. C and 1 atm. In the crystal structure of Cs sub 3 -A(6Kr), six Kr atoms per unit cell are distributed over three crystallographically distinct positions: each unit cell contains one Kr atom at Kr(1) on a threefold axis in the sodalite unit, three at Kr(2) opposite four-rings in the large cavity , and two at Kr(3) on threefold axes in the large cavity . Relatively strong interactions of Kr atoms at Kr(1) and Kr(3) with Na sup + ions of ...

  7. Electronic properties of ordered and disordered linear clusters of atoms and molecules

    International Nuclear Information System (INIS)

    The electronic properties of one-dimensional clusters of N atoms or molecules have been studied. The model used is similar to the Kronig-Penney model with the potential offered by each ion being approximated by an attractive δ-function. The energy eigenvalues, the eigenstates and the density of states are calculated exactly for a linear cluster of N atoms or molecules. The dependence of these quantities on the various parameters of the problem show interesting behavior. Effects of random distribution of the positions of the atoms and random distribution of the strengths of the potential have also been studied. The results obtained in this paper can have direct applications for linear chains of atoms produced on metal surfaces or for artificially created chains of atoms using scanning tunneling microscope or in studying molecular conduction of electrons across one-dimensional barriers

  8. Atom clusters and vibrational excitations in chemically-disordered Pt357Fe

    International Nuclear Information System (INIS)

    Inelastic nuclear resonant scattering spectra of 57Fe atoms were measured on crystalline alloys of Pt357Fe that were chemically disordered, partially ordered, and L12 ordered. Phonon partial density of states curves for 57Fe were obtained from these spectra. Upon disordering, about 10% of the spectral intensity underwent a distinct shift from 25 to 19 meV. This change in optical modes accounted for most of the change of the vibrational entropy of disordering contributed by Fe atoms, which was (+0.10 ± 0.03) kB (Fe atom)-1. Prospects for parametrizing the vibrational entropy with low-order cluster variables were assessed. To calculate the difference in vibrational entropy of the disordered and ordered alloys, the clusters must be large enough to account for the abundances of several of the atom configurations of the first-nearest-neighbor shell about the 57Fe atoms. (c) 2000 The American Physical Society

  9. Adsorption of a single gold or silver atom on vanadium oxide clusters.

    Science.gov (United States)

    Ding, Xun-Lei; Wang, Dan; Li, Rui-Jie; Liao, Heng-Lu; Zhang, Yan; Zhang, Hua-Yong

    2016-03-30

    The bonding properties between a single atom and its support have a close relationship with the stability and reactivity of single-atom catalysts. As a model system, the structural and electronic properties of bimetallic oxide clusters MV3Oy(q) (M = Au or Ag, q = 0, ±1, and y = 6-8) are systematically studied using density functional theory. The single noble metal atom Au or Ag tends to be adsorbed on the periphery of the V oxide clusters. Au prefers V sites for oxygen-poor clusters and O sites for oxygen-rich clusters, while Ag prefers O sites for most cases. According to natural population analysis, Au may possess positive or negative charges in the bimetallic oxide clusters, while Ag usually possesses positive charges. The bonding between Au and V has relatively high covalent character according to the bond order analysis. This work may provide some clues for understanding the bonding properties of single noble metal atoms on the support in practical single-atom catalysts, and serve as a starting point for further theoretical studies on the reaction mechanisms of related catalytic systems. PMID:26984782

  10. Light-induced processes on atoms and clusters confined in nanoporous silica and organic films

    Science.gov (United States)

    Moi, L.; Burchianti, A.; Bogi, A.; Marinelli, C.; Maibohm, C.; Mariotti, E.

    2007-03-01

    The study of light induced processes on atoms and nanoparticles confined in organic films or in dielectric structures is motivated both by fundamental interest and applications in optics and photonics. Depending on the light intensity and frequency and the kind of confinement, different processes can be activated. Among them photodesorption processes have a key role. Non thermal light induced atomic desorption has been observed from siloxane and paraffin films previously exposed to alkali vapors. This effect has been extensively investigated and used both to develop photo-atom sources and to load magneto-optical traps. Recently we observed huge photodesorption of alkali atoms embedded in nanoporous silica. In this case the atomic photodesorption causes, by properly tuning the light frequency, either formation or evaporation of clusters inside the silica matrix. Green-blue light desorbs isolated adatoms from the glass surface eventually producing clusters, whereas red-near infrared (NIR) light causes cluster evaporation due to direct excitation of surface plasmon oscillations. Green-blue light induces cluster formation taking advantage of the dense atomic vapor, which diffuses through the glass nano-cavities. Both processes are reversible and even visible to the naked eye. By alternatively illuminating the porous glass sample with blue-green and red-NIR light we demonstrate that the glass remembers the illumination sequences behaving as an effective rereadable and rewritable optical medium.

  11. Quantum Cloning of an Unknown 2-Atom State via Entangled Cluster States

    Science.gov (United States)

    Yu, L.-z.; Zhong, F.

    2016-06-01

    This paper presented a scheme for cloning a 2-atom state in the QED cavity with the help of Victor who is the state's preparer. The cloning scheme has two steps. In the first step, the scheme requires probabilistic teleportation of a 2-atom state that is unknown in advance, and uses a 4-atom cluster state as quantum channel. In the second step, perfect copies of the 2-atom entangled state may be realized with the assistance of Victor. The finding is that our scheme has two outstanding advantages: it is not sensitive to the cavity decay, and Bell state is easy to identify.

  12. Quantum Cloning of an Unknown 2-Atom State via Entangled Cluster States

    Science.gov (United States)

    Yu, L.-z.; Zhong, F.

    2016-01-01

    This paper presented a scheme for cloning a 2-atom state in the QED cavity with the help of Victor who is the state's preparer. The cloning scheme has two steps. In the first step, the scheme requires probabilistic teleportation of a 2-atom state that is unknown in advance, and uses a 4-atom cluster state as quantum channel. In the second step, perfect copies of the 2-atom entangled state may be realized with the assistance of Victor. The finding is that our scheme has two outstanding advantages: it is not sensitive to the cavity decay, and Bell state is easy to identify.

  13. A numerical study of spin-dependent organization of alkali-metal atomic clusters using density-functional method

    International Nuclear Information System (INIS)

    We calculate the different geometric isomers of spin clusters composed of a small number of alkali-metal atoms using the UB3LYP density-functional method. The electron density distribution of clusters changes according to the value of total spin. Steric structures as well as planar structures arise when the number of atoms increases. The lowest spin state is the most stable and Lin, Nan, Kn, Rbn, and Csn with n = 2–8 can be formed in higher spin states. In the highest spin state, the preparation of clusters depends on the kind and the number of constituent atoms. The interaction energy between alkali-metal atoms and rare-gas atoms is smaller than the binding energy of spin clusters. Consequently, it is possible to self-organize the alkali-metal-atom clusters on a non-wetting substrate coated with rare-gas atoms.

  14. Atomic-scale study of the role of carbon on boron clustering

    International Nuclear Information System (INIS)

    Boron (BF2, 20 keV, 3.14/cm2) and carbon (13 keV, 1015/cm2) implanted silicon annealed at 800 oC during 30 min or at 1000 oC during 10 s has been investigated using a laser-assisted wide-angle tomographic atom probe (LaWaTAP) instrument. Boron-silicon clusters containing ∼ 1.3 at.% of boron atoms have been observed in boron implanted silicon with a concentration exceeding the solubility limit. Often identified as BICs, they are interpreted as a metastable phase. Furthermore, addition of carbon clearly reduced the clustering of boron. This was interpreted as a diminution of boron diffusion or as an increase of the solubility limit of boron. Carbon-silicon clusters containing ∼ 1.5 at.% of carbon atoms were observed, maybe the precursors of the SiC phase.

  15. Recent studies of kaonic atoms and nuclear clusters

    International Nuclear Information System (INIS)

    Recent studies of kaonic atoms, few-body kaonic quasibound states and kaonic nuclei are reviewed, with emphasis on implementing the subthreshold energy dependence of the K¯N interaction in chiral interaction models that are consistent with the SIDDHARTA K− hydrogen data. Remarks are made on the possible role of the p-wave Σ(1385) resonance with respect to that of the s-wave Λ(1405) resonance in searches for strangeness S=−1 dibaryons

  16. Clustering Effects Under Irradiation in Fe-0.1%Cu Alloy : An Atomic Scale Investigation with the Tomographic Atom Probe

    OpenAIRE

    Pareige, P.; Welzel, S; Auger, P.

    1996-01-01

    In order to understand the effect of displacement cascades on the evolution of the microstructure of ferritic low copper supersaturated materials, analyses by 3D atomic tomography of neutron, electron and self ion irradiated Fe-0.1%Cu, were performed. This alloy was chosen because of its low copper concentration, close to that of french pressure vessel steels. The comparison of the microstructure evolutions in these irradiated specimens reveals the appearance of tiny copper "clusters" or "agg...

  17. Energy absorption, ionization, and harmonic emission in laser-irradiated atomic clusters

    OpenAIRE

    Kundu, M.

    2007-01-01

    The excellent coupling of laser light to atomic clusters is a known, experimentally established fact. However, the physical mechanism of laser absorption is still controversially discussed. Linear resonance (LR) absorption occurs for sufficiently long laser pulses of optical or longer wavelengths. Here the Mie-plasma frequency initially rises above the laser frequency, then drops due to cluster expansion and therefore meets the laser frequency at some point. Instead, in few-cycle laser pulses...

  18. Photoabsorption spectra in the continuum of molecules and atomic clusters

    CERN Document Server

    Nakatsukasa, T; Nakatsukasa, Takashi; Yabana, Kazuhiro

    2001-01-01

    We present linear response theories in the continuum capable of describing photoionization spectra and dynamic polarizabilities of finite systems with no spatial symmetry. Our formulations are based on the time-dependent local density approximation with uniform grid representation in the three-dimensional Cartesian coordinate. Effects of the continuum are taken into account either with a Green's function method or with a complex absorbing potential in a real-time method. The two methods are applied to a negatively charged cluster in the spherical jellium model and to some small molecules (silane, acetylene and ethylene).

  19. Chemisorption of hydrogen and oxygen atoms on a cobalt surface: A quantum chemical cluster model study

    International Nuclear Information System (INIS)

    The chemisorption of atomic hydrogen and oxygen on a cobalt surface has been studied on a five-atom cluster model using one-electron effective core potential (le- ECP) and all-electron calculations at the ab initio SCF and MCPF levels. Also, density functional calculations have been carried out. The different approaches are evaluated. The le- ECP has been compared to similar ECPS for nickel and copper. Our results indicate that this approach is valid also for cobalt. Different contributions to the cluster-adsorbate bonding energy are discussed. 31 refs., 1 fig., 1 tab

  20. Atomic structure of Ag(111) saturated with chlorine: Formation of Ag3Cl7 clusters

    Science.gov (United States)

    Andryushechkin, B. V.; Cherkez, V. V.; Gladchenko, E. V.; Zhidomirov, G. M.; Kierren, B.; Fagot-Revurat, Y.; Malterre, D.; Eltsov, K. N.

    2011-08-01

    The structure of saturated chlorine layer on Ag(111) has been studied with low temperature scanning tunneling microscopy and density functional theory. For the first time atomic-resolution STM images of saturated chlorine coverage have been obtained. STM images demonstrate coexistence of the domain with (3 × 3)-like reconstruction and numerous bright objects identified as Ag3Cl7 clusters. According to our model supported by DFT calculations, clusters are formed on the boundaries between the adjacent (3×3) antiphase domains. These boundaries have a characteristic triangular shape and are formed by six chlorine atoms chemisorbed on the triangular silver island with local periodicity (1 × 1).

  1. Structural fluctuation and atom-permutation in transition-metal clusters

    International Nuclear Information System (INIS)

    The atomic structure and thermodynamic properties of transition-metal clusters containing N atoms are investigated for N=6 and 7 using the method of molecular dynamics, where Gupta's potential taking into account many-body interaction is employed. The caloric curve (total energy-temperature curve) and the structural fluctuations are studied. The 'fluctuating state' is found for N=6 in the region of the temperature near below the melting point, where clusters undergo structural transition from one isomer to others without making any topological change. The fluctuating state differs from the coexistence state in that the former involves no atomic diffusion, and goes to a structural phase transition of the bulk when N is increased. On the other hand, the motion of atom-permutation is found in the low-temperature region of the liquid state, being induced by the cooperative motion of two atoms. It is discussed that such a motion easily occurs along the surface and may be considered to be one of the characteristics of small clusters. The fluctuating state is discussed in relation to the structural fluctuation of gold clusters observed experimentally. (orig.)

  2. Chemisorption of atomic and molecular oxygen on Au and Ag cluster anions : discrimination of different isomers

    OpenAIRE

    Kim, Young Dok; Ganteför, Gerd; Sun, Qiang; Jena, Purusottam

    2004-01-01

    Structures of coinage metal clusters reacted with atomic and molecular oxygen were studied using Ultraviolet Photoelectron Spectroscopy and Density Functional Theory calculations. We show that O2 partially dissociates on Ag-2, and this dissociative chemisorption is a kinetically hindered step. For Au4O-2, in addition to the previously observed molecularly adsorbed oxygen, we are now able to synthesize a second isomer using atomic oxygen reagents, in which oxygen adsorbs dissociatively. We dem...

  3. Structural and Magnetic Evolution of Bimetallic MnAu Clusters Driven by Asymmetric Atomic Migration

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Xiaohui; Zhou, Rulong; Lefebvre, Williams; He, Kai; Le Roy, Damien; Skomski, Ralph; Li, Xingzhong; Shield, Jeffrey E; Kramer, Matthew J; Chen, Shuang; Zeng, Xiao Cheng; Sellmyer, David J

    2014-03-12

    The nanoscale structural, compositional, and magnetic properties are examined for annealed MnAu nanoclusters. The MnAu clusters order into the L10 structure, and monotonic size-dependences develop for the composition and lattice parameters, which are well reproduced by our density functional theory calculations. Simultaneously, Mn diffusion forms 5 Å nanoshells on larger clusters inducing significant magnetization in an otherwise antiferromagnetic system. The differing atomic mobilities yield new cluster nanostructures that can be employed generally to create novel physical properties.

  4. Mobility of self-interstitial atom clusters in vanadium, tantalum and copper

    International Nuclear Information System (INIS)

    Molecular dynamics (MD) simulations were performed to investigate the mobility of isolated self-interstitial atoms (SIAs) and their clusters in V, Ta and Cu. The migration of an isolated SIA is accompanied by rotation of a dumbbell axis to the close-packed direction of metals. The migration of an SIA cluster strongly depends on its structure. A relatively smaller-size cluster can migrate with simultaneous rotation of the axes of SIA pairs in the cluster to the same close-packed direction, which is the glissile configuration of the cluster. The transformation to the glissile configuration takes place more frequently than the dumbbell rotation of an isolated SIA in V and Ta, while it takes place less frequently in Cu. The smaller cluster can still change its diffusion direction. A greater-size cluster in the bcc metals, on the other hand, has the thermally stable form of densely-packed, parallel crowdions. It migrates without any changes of diffusion direction. The migration behavior of 7-SIAs clusters in Ta was also evaluated as a function of tensile and compressive strains

  5. Coupled-cluster theory for atoms and molecules in strong magnetic fields

    International Nuclear Information System (INIS)

    An implementation of coupled-cluster (CC) theory to treat atoms and molecules in finite magnetic fields is presented. The main challenges for the implementation stem from the magnetic-field dependence in the Hamiltonian, or, more precisely, the appearance of the angular momentum operator, due to which the wave function becomes complex and which introduces a gauge-origin dependence. For this reason, an implementation of a complex CC code is required together with the use of gauge-including atomic orbitals to ensure gauge-origin independence. Results of coupled-cluster singles–doubles–perturbative-triples (CCSD(T)) calculations are presented for atoms and molecules with a focus on the dependence of correlation and binding energies on the magnetic field

  6. Acceleration of atomic clusters in the MeV energy range by the 1 MV Tandetron accelerator

    International Nuclear Information System (INIS)

    Atomic clusters of Bn, Cn, Aln, Sin and Cun can be accelerated in the MeV energy range by using the 1 MV Tandetron accelerator at the University of Tsukuba. The negative cluster ions are generated by a Cesium sputtering ion source and extracted by the energy of 20 keV. The charge exchange from negative to positive cluster ion is achieved by collision with stripper gas in a gas cell at the high voltage terminal. It is necessary to accelerate cluster ions as the same energy ratio (MeV/atom) for the interaction experiment between cluster ions and the target. The terminal voltage of the 1 MV Tandetron accelerator is possible to be varied from 0.1 to 1.0 MV. We select the accelerating energy to 0.24 MeV/atom for small cluster ions (n ≤ 8). Experimental results obtained with accelerating Cn cluster ions are reported. (author)

  7. Electronic relaxation dynamics of a metal atom deposited on argon cluster

    International Nuclear Information System (INIS)

    This thesis is a study on the interaction between electronically excited atomic states and a non-reactive environment. We have theoretically and experimentally studied situations where a metal atom (Ba or K) is placed in a finite size environment (argon cluster). The presence of the medium affects the electronic levels of the atom. On the other side, the excitation of the atom induces a relaxation dynamics of the electronic energy through the deformation of the cluster. The experimental part of this work focuses on two aspects: the spectroscopy and the dynamics. In both cases a first laser electronically excites the metal atom and the second ionizes the excited system. The observable is the photoelectron spectrum recorded after photoionization and possibly information on the photoion which are also produced. This pump/probe technique, with also two lasers, provide the ultrafast dynamic when the lasers pulses used are of ultrashort (60 fs). The use of nanosecond lasers leads to resonance spectroscopic measurement, unresolved temporally, which give information on the position of the energy levels of the studied system. From a theoretical point-of-view, the excited states of M-Arn were calculated at the ab initio level, using large core pseudo-potential to limit the active electrons of the metal to valence electrons. The study of alkali metals (potassium) is especially well adapted to this method since only one electron is active. The ab-initio calculation and a Monte-Carlo simulation where coupled to optimize the geometry of the KArn (n = 1-10) cluster when K is in the ground state of the neutral and the ion, or excited in the 4p or 5s state. Calculations were also conducted in collaboration with B. Gervais (CIMAP, Caen) on KArn clusters having several tens of argon atoms. Absorption spectra were also calculated. From an experimental point-of-view, we were able to characterize the excited states of potassium and barium perturbed by the clusters. In both cases a

  8. Molecular cluster theory for chemisorption of first row atoms on nickel /100/ surfaces

    Science.gov (United States)

    Ellis, D. E.; Adachi, H.; Averill, F. W.

    1976-01-01

    Self-consistent Hartree-Fock-Slater molecular cluster models for the chemisorption of first-row atoms on Ni(100) surfaces are presented. Energy levels and ground-state charge distributions are given for XNi5 clusters with the adatom X = H, C, N, O located in C4V symmetry at a fixed height of 2.0 au above the surface. The variation of properties with height was studied in detail for the case of oxygen. Theoretical results compare rather well with experimental photoelectron and energy-loss data. Local-densities-of-states diagrams are used to clarify the interaction between adsorbate levels and metal conduction bands.

  9. Plasmon Enhanced Electron and Atom Emission from a Spherical Sodium Cluster: Na91-

    International Nuclear Information System (INIS)

    The photoabsorption cross section of the negatively charged, spherical Na91- cluster shows a broad collective resonance at ℎω=2.65 eV, the decay of which can lead to two final channels: atom and electron emission. The branching ratio between the two channels was measured to increase linearly with photon energy over the unexpectedly broad energy range of 1.2 eV, which is attributed to the cluster close-quote s incipient valence band width. The femtosecond time scales of the processes involved are discussed. copyright 1996 The American Physical Society

  10. Investigation of energy thresholds of atomic and cluster sputtering of some elements under ion bombardment

    CERN Document Server

    Atabaev, B G; Lifanova, L F

    2002-01-01

    Threshold energies of sputtering of negative cluster ions from the Si(111) surface were measured at bombardment by Cs sup + , Rb sup + , and Na sup + ions with energy of 0.1-3.0 keV. These results are compared with the calculations of the similar thresholds by Bohdansky etc. formulas (3) for clusters Si sub n sup - and Cu sub n sup - with n=(1-5) and also for B, C, Al, Si, Fe, Cu atoms. Threshold energies of sputtering for the above elements were also estimated using the data from (5). Satisfactory agreement between the experimental and theoretical results was obtained. (author)

  11. Role of interstitial silicon atoms in the configuration restructuring divacancies in the defect clusters

    International Nuclear Information System (INIS)

    The behavior of the mobility of electrons as they diffuse movement in the high-resistivity silicon, grown by floating zone melting (Fz) and Czochralski (Cz), after irradiation with fast neutrons reactor and subsequent annealing at room temperature was described. As part of the revised model of defect clusters was calculated temperature dependence of the electrons density in the conductive matrix of silicon samples n-type. The energy levels of radiation defects in n-Si defined. It is substantiates the role of interstitial silicon atoms in the hysteresis of the temperature dependence of the electron mobility and their participation in the restructuring of the configuration divacancy defects in clusters

  12. Negative ion productions in high velocity collision between small carbon clusters and Helium atom target

    International Nuclear Information System (INIS)

    We measured absolute double capture cross section of Cn+ ions (n=1,5) colliding, at 2.3 and 2.6 a.u velocities, with an Helium target atom and the branching ratios of fragmentation of the so formed electronically excited anions Cn−*. We also measured absolute cross section for the electronic attachment on neutral Cn clusters colliding at same velocities with He atom. This is to our knowledge the first measurement of neutral-neutral charge exchange in high velocity collision.

  13. 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...

  14. Characterization of atom clusters in irradiated pressure vessel steels and model alloys

    International Nuclear Information System (INIS)

    In order to characterize the microstructural evolution of the iron solid solution under irradiation, two pressure vessel steels irradiated in service conditions and, for comparison, low copper model alloys irradiated with neutrons and electrons have been studied. The characterization has been carried out mainly thanks to small angle neutron scattering and atom probe experiments. Both techniques lead to the conclusion that clusters develop with irradiations. In Fe-Cu model alloys, copper clusters are formed containing uncertain proportions of iron. In the low copper industrial steels, the feature is more complex. Solute atoms like Ni, Mn and Si, sometimes associated with Cu, segregate as ''clouds'' more or less condensed in the iron solid solution. These silicides, or at least Si, Ni, Mn association, may facilitate the copper segregation although the initial iron matrix contains a low copper concentration. (authors). 24 refs., 3 figs., 2 tabs

  15. The Production of Strong Blast Waves through Intense Laser Irradiation of Atomic Clusters

    International Nuclear Information System (INIS)

    An understanding of radiation effects on the evolution of shock waves is of great importance to many problems in astrophysics. Shock waves driven by a laser-heated plasma are attractive for laboratory investigation of these phenomena. Recent studies of intense short-pulse laser interactions with gases of atomic clusters indicate a potential avenue to access this regime of radiative hydrodynamics. We have measured the energy absorption efficiency of high-intensity, picosecond laser pulses in low-density gases composed of large atomic clusters and find that the energy absorption can be very high (>95%), producing a high-temperature plasma filament which consequently produces a strong blast wave. Interferometric characterization of these shock waves indicates that in high-Z gases such as Xe, radiation transport plays an important role in the evolution of the shock wave. (c) 2000 The American Astronomical Society

  16. Transport, dissociation and rotation of small self-interstitial atom clusters in tungsten

    International Nuclear Information System (INIS)

    Numerical calculations have been performed to study the thermal motion of self-interstitial atom (SIA) clusters in tungsten (W). Molecular dynamics simulations show that SIA clusters exhibit a fast one-dimensional (1D) motion along the close packed 〈1 1 1〉 direction accompanied by a significant mass transport in this direction. A low frequency vibration mode is identified and considered to assist the motion of SIAs. The migration energy of SIA clusters are weakly dependent on their size in the average value of 0.019 eV, which is due to the strong interaction between SIAs revealed by calculating the potential energy curve of artificially moving the SIAs along 〈1 1 1〉 direction as well as nudged elastic band (NEB) method. The rotation process of SIA cluster is studied by activation–relaxation technique and the results show that SIA cluster presents complex rotation process. Our results on the motion SIA cluster may provide updated understanding on the performance decay of materials related to SIA defects

  17. Fabrication and atomic structure of size-selected, layered MoS2 clusters for catalysis.

    Science.gov (United States)

    Cuddy, Martin J; Arkill, Kenton P; Wang, Zhi Wei; Komsa, Hannu-Pekka; Krasheninnikov, Arkady V; Palmer, Richard E

    2014-11-01

    Well defined MoS2 nanoparticles having a layered structure and abundant edges would be of considerable interest for applications including photocatalysis. We report the atomic structure of MoS2 size-selected clusters with mass in a range all the way from 50 to ∼2000 MoS2 units. The clusters were prepared by magnetron sputtering and gas condensation prior to size selection and soft landing on carbon supports. Aberration-corrected scanning transmission electron microscopy (STEM) in high-angle annular dark-field (HAADF) mode reveals a layered structure and Mo-Mo spacing similar to the bulk material. The mean number of layers in these lamellar clusters increases from one to three with increasing mass, consistent with density functional theory calculations of the balance between edge energies and interlayer binding. PMID:25226541

  18. Electric dipole polarizability of alkaline-Earth-metal atoms from perturbed relativistic coupled-cluster theory with triples

    CERN Document Server

    Chattopadhyay, S; Angom, D

    2014-01-01

    The perturbed relativistic coupled-cluster (PRCC) theory is applied to calculate the electric dipole polarizabilities of alkaline Earth metal atoms. The Dirac-Coulomb-Breit atomic Hamiltonian is used and we include the triple excitations in the relativistic coupled-cluster (RCC) theory. The theoretical issues related to the triple excitation cluster operators are described in detail and we also provide details on the computational implementation. The PRCC theory results are in good agreement with the experimental and previous theoretical results. We, then, highlight the importance of considering the Breit interaction for alkaline Earth metal atoms.

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

    Energy Technology Data Exchange (ETDEWEB)

    Steinberg, Simon; Zimmermann, Sina; Brühmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd, E-mail: gerd.meyer@uni-koeln.de

    2014-11-15

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

  20. Medium polarization dynamics with atomic cluster formation in radioactive lutetium oxide

    International Nuclear Information System (INIS)

    Full text: The study of processes in a material of a radioactive sources was begun by us in connection with our work directed to the accuracy increase of electron-spectroscopy researches of nucleus decays. It was necessary to draw large attention to the form of electronic spectra and separate conversion lines, their dynamics and to research explanations of their anomalies with use for this purpose not only nuclear-spectroscopy methods, but also opportunities of auto-emission and Auger-spectroscopy. The analysis of all experimental results of our long-time research (∼ 13 years) of the radioactive lutetium oxide, deposited on a platinum support, as a radioactive source, has resulted us in the following assumptions of processes occurring in the source material. The lutetium oxide is a dielectric, having spontaneous polarization varying in the radiation field of the radioactive decay. The polarization is determined by domains - areas with various directions of polarization. Under action of an electrical field the volumes of the polarized along the field domains are increased at the expense of the ones, polarized against the field. The domain borders fixed on inhomogeneities move, for example, under action of internal conversion electrons accompanying the decay of radioactive nuclei. The experimentally observable energy losses of such electrons achieve 500 eV. In the cluster formation process the multipole character of nucleus decay electron radiation causing transfer of the angular moment by the electrons to atoms with collision with them plays a significant role. The auto-emission and Auger-spectra specify a determining role of the M4- and M5-subshells of ytterbium atoms in the cluster formation. It is possible to assume, that in the lutetium oxide electrical dipole medium at first the metal ytterbium clusters are formed. Their valent electrons are not located in space and are conducting electrons, for example, the electrons of the destroyed N-shell. It is possible

  1. The multi-scattering-Xα method for analysis of the electronic structure of atomic clusters

    International Nuclear Information System (INIS)

    A computer program, MSXALPHA, has been developed to carry out a quantum-mechanical analysis of the electronic structure of molecules and atomic clusters using the Multi-Scattering-Xα (MSXα) method. The MSXALPHA program is based on a code obtained from the University of Alberta; several improvements and new features were incorporated to increase generality and efficiency. The major ones are: (1) minimization of core memory usage, (2) reduction of execution time, (3) introduction of a dynamic core allocation scheme for a large number of arrays, (4) incorporation of an atomic program to generate numerical orbitals used to construct the initial molecular potential, and (5) inclusion of a routine to evaluate total energy. This report is divided into three parts. The first discusses the theory of the MSXα method. The second gives a detailed description of the program, MSXALPHA. The third discusses the results of calculations carried out for the methane molecule (CH4) and a four-atom zirconium cluster (Zr4)

  2. Damage creation in silicon single crystals irradiated with 200 keV/atom Aun+ clusters

    International Nuclear Information System (INIS)

    Silicon wafers of (1 0 0) orientation were irradiated with Aun cluster beams (1≤n≤7) produced by the 2.5 MV Van de Graaff accelerator of the Institut de Physique Nucleaire de Lyon equipped with a liquid metal source. The incident energy was of 200 keV per gold atom, which corresponds to a slowing-down mainly governed by elastic processes (nuclear energy loss of Au+ ions: 3 keV nm-1). All the irradiations were performed at room temperature with fluences up to 5x1014 Au (at. cm-2). The typical beam currents varied from 1.5 nA for Au+ down to 20 pA for Au7+. The radiation-induced disorder was measured by means of Rutherford backscattering spectrometry in channeling geometry (RBS-C), using a 4He+ beam accelerated at 2 MV. From the fluence evolution of the lattice disorder at the target surface, we evidence that polyatomic projectiles produce more defects per incident atom than single Au+ ions. As an example we measured damage cross-sections per incident Au atom of 12.5 and 2.7 nm2 for Au7+ and Au+ projectiles, respectively. This cluster effect was ascribed to the high density of nuclear energy deposited within the cascade. Transmission electron microscopy (TEM) was performed on samples irradiated at low fluences (109 at. cm-2) in order to visualize each projectile impact

  3. Generalized boson model and α-cluster states of 44Ti atomic nucleus

    International Nuclear Information System (INIS)

    At present some rotational bands for the 44Ti atomic nucleus with a sequence of spins and parities are discovered. For an analysis of these bands the generalized boson model U(6) direct X U(4) including the collective (quadrupole) degree of freedom and cluster (dipole) variable as well as an inter-relation of quadrupole and dipole degrees of freedom is used. Different collective bands of U(6) direct X SU(3) model reduction are considered as well. Parameter of SU(3) symmetrical Hamiltonian are equal to k=0.0016 MeV. (3/4k-k')=0.085 MeV. The U(4)contains U(3)-symmetry, caused by dipole clusterization of nucleons, describes bands of α-cluster states kπ=04+,02-, with theoretical parameters E0=-11 MeV, εp=0.1 MeV, β=0.15 MeV. An interaction of the cluster (dipole) degree with he quadrupole one allows to explain the band of parity, kπ=01-, beginning with E=6.22 MeV by values of parameters of kp=0, γ=6.2 MeV

  4. Asymptotical approximation of interconnection of nucleons' quadrupole and cluster motion in atomic nucleus

    International Nuclear Information System (INIS)

    Atomic nuclei display different kinds of collective motion. The well known example - is the collective model arising from valent nucleons motion. The other a special kind of collective motion is cluster mode. If a collective model has quadrupole character, then cluster one has dipole character. In the boson formalism this model is describing by dynamic symmetry U(6) direct X U(4). The common Hamiltonian symmetrical to U(6) direct X U(4) group has a form H=Hd+Hp+Vpd. In the paper the asymptotical wave function for dipole states connected with (N-1) bosons of s- and d-types is presented. In this case the problem for Hamiltonian eigenvalues is solving by analytical way. With use Elliot method and wave functions asymptotical form the operators for matrix elements of E2-, E1-, M1-transitions are cited

  5. Cluster ions from keV-energy ion and atom bombardment of frozen gases

    Science.gov (United States)

    David, Donald E.; Magnera, Thomas F.; Tian, Rujiang; Stulik, Dusan; Michl, Josef

    1986-04-01

    A brief survey is given of the mass spectra obtained from frozen gases by bombardment with keV-energy ions and atoms. The internal chemical constitution of the observed secondary cluster ions, which bears no simple relation to the molecular structure of the solid, has been established by observations of collision-induced dissociation, laser-induced dissociation and metastable decay. It has been correlated with the chemical composition of the residual bombarded solid, deduced from spectroscopic observations. These results, as well as preliminary results on sputtering yields for impact of 1-4 keV rare gas ions on solid argon, are compatible with the previously proposed mechanistic model for the formation of the cluster ions based on the flow of supercritical gas from the elastic collision spike region.

  6. Monte Carlo simulation of atomic short range order and cluster formation in two dimensional model alloys

    International Nuclear Information System (INIS)

    Using monte Carlo simulation have been carried out an atomistic description of the structure and ordering processes in the system Cu-Au in a two-dimensional model. The ABV model of the alloy is a system of N atoms A and B, located in rigid lattice with some vacant sites. In the model we assume pair wise interactions between nearest neighbors with constant ordering energy J = 0,03 eV. The dynamics was introduced by means of a vacancy that exchanges of place with any atom of its neighbors. The simulations were carried out in a square lattice with 1024 and 4096 particles, using periodic boundary conditions to avoid border effects. We calculate the first two parameters of short range order of Warren-Cowley as function of the concentration and temperature. It was also studied the probabilities of formation of different atomic clusters that consist of 9 atoms as function of the concentration of the alloy and temperatures in a wide range of values. In some regions of temperature and concentration it was observed compositional and thermal polymorphism

  7. Dynamics of atomic clusters in intense optical fields of ultrashort duration

    Indian Academy of Sciences (India)

    Deepak Mathur; Firoz A Rajgara

    2012-01-01

    Intense laser pulses have been generated that last for only 10 fs, long enough to accommodate only 3 optical cycles of 800 nm light. Upon focussing such pulses, intensities in the 1015 W cm−2 range are readily generated. At such intensities, the magnitude of the optical field begins to match intra-atomic Coulombic fields. Consequently, exposure of atoms and molecules to such intense pulses inevitably leads to single and multiple ionization. We report here results of experiments that we have conducted that involve irradiation of gas-phase Ar15,000 clusters by such intense, few-cycle laser pulses. The clusters become multiply ionized and undergo Coulomb explosion, giving rise to ejection of fast Ar-ions. Results show that the strong-field dynamics in the few-cycle domain differ significantly from those that occur in the longer pulse (> 30 fs) regime. Manifestations of these differences are presented in the form of angle-dependent ion energy and ion yield functions.

  8. Density functional theory investigation of 3d, 4d, and 5d 13-atom metal clusters

    International Nuclear Information System (INIS)

    The knowledge of the atomic structure of clusters composed by few atoms is a basic prerequisite to obtain insights into the mechanisms that determine their chemical and physical properties as a function of diameter, shape, surface termination, as well as to understand the mechanism of bulk formation. Due to the wide use of metal systems in our modern life, the accurate determination of the properties of 3d, 4d, and 5d metal clusters poses a huge problem for nanoscience. In this work, we report a density functional theory study of the atomic structure, binding energies, effective coordination numbers, average bond lengths, and magnetic properties of the 3d, 4d, and 5d metal (30 elements) clusters containing 13 atoms, M13. First, a set of lowest-energy local minimum structures (as supported by vibrational analysis) were obtained by combining high-temperature first-principles molecular-dynamics simulation, structure crossover, and the selection of five well-known M13 structures. Several new lower energy configurations were identified, e.g., Pd13, W13, Pt13, etc., and previous known structures were confirmed by our calculations. Furthermore, the following trends were identified: (i) compact icosahedral-like forms at the beginning of each metal series, more opened structures such as hexagonal bilayerlike and double simple-cubic layers at the middle of each metal series, and structures with an increasing effective coordination number occur for large d states occupation. (ii) For Au13, we found that spin-orbit coupling favors the three-dimensional (3D) structures, i.e., a 3D structure is about 0.10 eV lower in energy than the lowest energy known two-dimensional configuration. (iii) The magnetic exchange interactions play an important role for particular systems such as Fe, Cr, and Mn. (iv) The analysis of the binding energy and average bond lengths show a paraboliclike shape as a function of the occupation of the d states and hence, most of the properties can be explained

  9. Experimental search of discrete symmetry violations when atomic cluster formation in thin radioactive films

    International Nuclear Information System (INIS)

    The ways of transformation (self-organization) of nano-clusters into nano-structures depend not only on properties insulated nano-clusters and inter-cluster interplays, but also from methods of nano-cluster making. Our outcomes of searches of influencing of clustering on nuclear decay electron spectra in thin radioactive films are also endorsement to this. Radioactive sources can be produced by different methods: by the evaporation of radioactive solution drop on a platinum support, wetted insulin; by irradiation of mono-isotope vapor-deposited film in vacuo on aluminium support with neutrons; by vapor-deposition of certain radioactive isotope on aluminium support. Most neatly displays of atomic clusters (in the nanometre range) formation in a radioactive source solid-state matrix and nanostructures with a closed magnetic flux, i.e. in the form of toroids, were watched in the Lu→Yb and Lu→Hf decays. The radioactivity represented the Lu isotope fraction, isolated from the tantalum target, irradiated with protons with energy 660 MeV, and deposited by an electrolysis on platinum support (thickness 10 μm). Briefly our experimental data, their dynamic features are reduced to the following The internal conversion electron lines have composite structure varying with time. The M4- and M5-Auger-electron quantity exceeds (in tens of times) that, which one is conditioned by nuclear decay. This ratio shows time function. The auto emission spectrum electron line scission shows composite time function also. In the electron spectrum the display of the certain interference figure and asymmetrical satellite lines (having multipole dependence and varying with time) is watched. It testifies to the formation of toroids with inversely directional toroidal moments and interplay of angular momentums of ordered electrons with an external electromagnetic field. The experimental outcomes indicate the very significant role (during the cluster formation) of multipole electron radiation

  10. Remote preparation of atomic and field cluster states from a pair of tri-partite GHZ states

    International Nuclear Information System (INIS)

    We propose two simple and resource-economical schemes for remote preparation of four-partite atomic as well as cavity field cluster states. In the case of atomic state generation, we utilize simultaneous resonant and dispersive interactions of the two two-level atoms at the preparation station. Atoms involved in these interactions are individually pair-wise entangled into two different tri-partite GHZ states. After interaction, the passage of the atoms through a Ramsey zone and their subsequent detection completes the protocol. However, for field state generation we first copy the quantum information in the cavities to the atoms by resonant interactions and then adapt the same method as in the case of atomic state generation. The method can be generalised to remotely generate any arbitrary graph states in a straightforward manner. (general)

  11. Photoelectron imaging, probe of the dynamics: from atoms... to clusters; Imagerie de photoelectrons, sonde de la dynamique: des atomes... aux agregats

    Energy Technology Data Exchange (ETDEWEB)

    Lepine, F

    2003-06-15

    This thesis concerns the study of the deexcitation of clusters and atoms by photoelectron imaging. The first part is dedicated to thermionic emission of a finite size system. A 3-dimensional imaging setup allows us to measure the time evolution of the kinetic energy spectrum of electrons emitted from different clusters (W{sub n}{sup -}, C{sub n}{sup -}, C{sub 60}). Then we have a direct access to the fundamental quantities which characterize this statistical emission: the temperature of the finite heat bath and the decay rate. The second part concerns the ionization of atomic Rydberg states placed in a static electric field. We performed the first experiment of photoionization microscopy which allows us to obtain a picture which is the macroscopic projection of the electronic wave function. Then we have access to the detail of the photoionization and particularly to the quantum properties of the electron usually confined at the atomic scale. (author)

  12. The effect of doped Pd atoms on the geometries and optical adsorption properties of Au cluster: Au32−nPdn (n = 1, 2, 4 and 6)

    International Nuclear Information System (INIS)

    The geometries and optical adsorption properties of Au32−nPdn (n = 1, 2, 4, 6) alloy clusters were investigated within the static and time-dependent density functional theory. Our results confirm that Pd atoms favor to replace the inner Au atoms rather than the surface Au atoms of the cluster, which agrees well with previous reports. The optical adsorption property of the Au32 cluster is significantly changed by the Pd doping. Our calculations show that the optical adsorption of Pd-doped alloy cluster in the visible light region is remarkably enhanced compared to the pure Au32 cluster, especially in the lower energy sections. The analysis of the electronic structures of Au26Pd6, Au32 and Pd32 were performed to reveal the roles of doped Pd atoms. It is found that the doped Pd atoms increase the density of state around the Fermi level of the alloy clusters, which causes the enhanced optical adsorption of the Au–Pd alloy cluster in the visible light region. - Highlights: • The optical adsorption property of Au–Pd alloy cluster were investigated by TDDFT calculations. • Pd atoms favor the inner site in the Au–Pd alloy cluster. • The orbitals of Pd atoms substantively involve the states around the Fermi level of the alloy cluster. • Pd doping can enhance the optical adsorption of Au cluster under the visible light

  13. Relativistic Equation of Motion Coupled-Cluster Method: Application to the closed-shell atomic systems

    CERN Document Server

    Pathak, Himadri; Das, B P; Vaval, Nayana; Pal, Sourav

    2014-01-01

    We report our successful implementation of the full fledged relativistic equation of motion coupled cluster (EOMCC) method. This method is employed to compute the principal ionization potentials (IPs) of closed-shell rare gas atoms, He-like ions, Be-like ions along with Na+, Al+, K+, Be, and Mg. Four component Dirac spinors are used in the calculations and the one and two electron integrals are evaluated using the Dirac Coulomb Hamiltonian. Our results are in excellent agreement with those available measurements, which are taken from the National Institute of Science and Technology database (NIST). We also present results using the second order many-body perturbation theory (MBPT(2)) and random phase approximation (RPA) in the EOMCC framework. These results are compared with those of EOMCC at the level of single and double excitations in order to assess the role of the electron correlation effects in the intermediate schemes considered in our calculations .

  14. Computer-simulated images of icosahedral, pentagonal and decagonal clusters of atoms

    International Nuclear Information System (INIS)

    The aim of this work was to assess, by computer-simulation the sensitivity of high-resolution electron microscopy (HREM) images for a set of icosahedral and decagonal clusters, containing 50-400 atoms. An experimental study of both crystalline and quasy-crystalline alloys of A1(Si)Mn is presented, in which carefully-chosen electron optical conditions were established by computer simulation then used to obtain high quality images. It was concluded that while there is a very significant degree of model sensitiveness available, direct inversion from image to structure is not at realistic possibility. A reasonable procedure would be to record experimental images of known complex icosahedral alloys, in a crystalline phase, then use the computer-simulations to identify fingerprint imaging conditions whereby certain structural elements could be identified in images of quasi-crystalline or amorphous specimens. 27 refs., 12 figs., 1 tab

  15. Effective cluster interactions using the generalized perturbation method in the atomic-sphere approximation

    International Nuclear Information System (INIS)

    We describe the generalized perturbation method in the atomic-sphere approximation (ASA) for calculating the effective cluster interactions. Based on our development of Korringa-Kohn-Rostoker coherent-potential approximation in the ASA [Singh et al., Phys. Rev. B 44, 8578 (1991)], the present approach is the next step towards developing a first-principles method that can be easily applied to describe substitutionally disordered alloys based on simple lattice structures as well as complex lattice structures with low symmetry. To test the accuracy of the ASA results, we have calculated the effective pair interactions (EPI) up to fourth-nearest neighbors for the substitutionally disordered Pd0.5V0.5 and Pd0.75Rh0.25 alloys. Our calculated EPI's are in good agreement with the respective muffin-tin results

  16. Atomic-scale magnetometry of distant nuclear spin clusters via nitrogen-vacancy spin in diamond.

    Science.gov (United States)

    Zhao, Nan; Hu, Jian-Liang; Ho, Sai-Wah; Wan, Jones T K; Liu, R B

    2011-04-01

    The detection of single nuclear spins is an important goal in magnetic resonance spectroscopy. Optically detected magnetic resonance can detect single nuclear spins that are strongly coupled to an electron spin, but the detection of distant nuclear spins that are only weakly coupled to the electron spin has not been considered feasible. Here, using the nitrogen-vacancy centre in diamond as a model system, we numerically demonstrate that it is possible to detect two or more distant nuclear spins that are weakly coupled to a centre electron spin if these nuclear spins are strongly bonded to each other in a cluster. This cluster will stand out from other nuclear spins by virtue of characteristic oscillations imprinted onto the electron spin decoherence profile, which become pronounced under dynamical decoupling control. Under many-pulse dynamical decoupling, the centre electron spin coherence can be used to measure nuclear magnetic resonances of single molecules. This atomic-scale magnetometry should improve the performance of magnetic resonance spectroscopy for applications in chemical, biological, medical and materials research, and could also have applications in solid-state quantum computing. PMID:21358646

  17. Effect of the clusters of disordered atoms on thermal conductivity of Bi0.85Sb0.15 alloys

    International Nuclear Information System (INIS)

    Bi0.85Sb0.15 nano powders were prepared by mechanical alloying and then pressed to form bulk material under 6 GPa. Thermal conductivity was investigated in the temperature range of 4-300 K. It has lower thermal conductivity compared to single crystal in measured temperature. It was fitted using Debye phonon model. High-resolution transmission electron micrographs showed that there were clusters of disordered atoms which were homogeneously distributed in grains and each cluster size is in a order of about 1-3 nm. The cluster scattering to phonon was the key reason to great decrease of thermal conductivity

  18. Computer simulation of reactions between self-interstitial atom clusters in BCC-FE

    International Nuclear Information System (INIS)

    Irradiation with high-energy particles, such as neutrons, ions and electrons, produces microstructural changes in materials. This happens because point defects, i.e. SIA (self-interstitial atoms) and vacancies, are generated in quantities well above the thermodynamic equilibrium concentration and aggregate to form clusters (dislocation loops and small cavities) and then more complex structures (dislocation networks, ...) or interact with impurities and solute atoms, thereby enhancing or inducing phenomena such as precipitation and phase segregation. These microstructural changes will in turn affect the macroscopic properties of the material. It is therefore of fundamental importance, in order to understand and possibly predict the behaviour of materials under irradiation, to be able to model the corresponding microstructural evolution. This evolution is driven mainly by processes taking place at the atomic level, thus at the scale of nanometers and pico- or nanoseconds, and in many cases it is experimentally impossible to obtain detailed information about them. For the study of these processes atomistic computer simulation is therefore a powerful tool and in fact often the only one that can be used. The most important class of structural materials for nuclear applications are iron alloys and for this reason atomistic computer simulation has been extensively applied to the study of radiation damage in these materials. Yet, there are still features of their microstructural evolution under irradiation that are not fully understood. As a matter of fact, TEM (transmission electron microscopy) studies of irradiated iron, both pure and alloyed, revealed already 40 years ago that two types of dislocation loops can be created in these materials

  19. Interaction of intense VUV radiation from a free-electron laser with rare gas atoms and clusters

    International Nuclear Information System (INIS)

    At DESY, the short wavelength free-electron laser of the TESLA test facility (TTF1-FEL) showed in September 2001 the production of vacuum-ultraviolet radiation, whose peak power exceeded that of existing light-sources by a factor of more than thousand. Thus it opened the way to studies of matter with intense, short wavelength radiation. First experiments on the interaction of intense, short wavelength radiation with rare gas atom and cluster beams have been conducted. Atomic and cluster beams are produced by a supersonic nozzle expansion. The ionisation products are detected by time-of-flight techniques. At 98 nm wavelength the ionisation of rare gas atoms is attributed to a stepwise multiphoton ionisation. Compared to the atomic beam the absorption in the cluster beam is strongly enhanced. At a power density of ∝ 3 x 1013 W/cm2 each atom in a Xe2500 cluster absorbs on average ∝600 eV, corresponding to ∝50 VUV photons. As a result of the strong absorption multiply charged atomic ions up to Xe8+ are produced. Finally, the cluster completely disintegrates by Coulomb explosion, causing high kinetic energies of the ejected ions up to 3 keV. Coulomb explosion begins at a power density approximately two orders of magnitude lower than the threshold for such processes in optical laser experiments. A comparison is made with classical models describing quantitatively the energy absorption at optical wavelengths. It appears that quantum mechanical processes have to be included, in order to explain the energy absorption in the present FEL experiment at short wavelengths. (orig.)

  20. Some consequences of a Universal Tension arising from Dark Energy for structures from Atomic Nuclei to Galaxy Clusters

    CERN Document Server

    Sivaram, C; V., Kiren O

    2013-01-01

    In recent work, a new cosmological paradigm implied a mass-radius relation, suggesting a universal tension related to the background dark energy (cosmological constant), leading to an energy per unit area that holds for structures from atomic nuclei to clusters of galaxies. Here we explore some of the consequences that arise from such a universal tension.

  1. Statistical analysis of atom probe data: Detecting the early stages of solute clustering and/or co-segregation

    International Nuclear Information System (INIS)

    Statistical analysis of atom probe data has improved dramatically in the last decade and it is now possible to determine the size, the number density and the composition of individual clusters or precipitates such as those formed in reactor pressure vessel (RPV) steels during irradiation. However, the characterisation of the onset of clustering or co-segregation is more difficult and has traditionally focused on the use of composition frequency distributions (for detecting clustering) and contingency tables (for detecting co-segregation). In this work, the authors investigate the possibility of directly examining the neighbourhood of each individual solute atom as a means of identifying the onset of solute clustering and/or co-segregation. The methodology involves comparing the mean observed composition around a particular type of solute with that expected from the overall composition of the material. The methodology has been applied to atom probe data obtained from several irradiated RPV steels. The results show that the new approach is more sensitive to fine scale clustering and co-segregation than that achievable using composition frequency distribution and contingency table analyses.

  2. Electron correlation in the interacting quantum atoms partition via coupled-cluster lagrangian densities.

    Science.gov (United States)

    Holguín-Gallego, Fernando José; Chávez-Calvillo, Rodrigo; García-Revilla, Marco; Francisco, Evelio; Pendás, Ángel Martín; Rocha-Rinza, Tomás

    2016-07-15

    The electronic energy partition established by the Interacting Quantum Atoms (IQA) approach is an important method of wavefunction analyses which has yielded valuable insights about different phenomena in physical chemistry. Most of the IQA applications have relied upon approximations, which do not include either dynamical correlation (DC) such as Hartree-Fock (HF) or external DC like CASSCF theory. Recently, DC was included in the IQA method by means of HF/Coupled-Cluster (CC) transition densities (Chávez-Calvillo et al., Comput. Theory Chem. 2015, 1053, 90). Despite the potential utility of this approach, it has a few drawbacks, for example, it is not consistent with the calculation of CC properties different from the total electronic energy. To improve this situation, we have implemented the IQA energy partition based on CC Lagrangian one- and two-electron orbital density matrices. The development presented in this article is tested and illustrated with the H2 , LiH, H2 O, H2 S, N2 , and CO molecules for which the IQA results obtained under the consideration of (i) the CC Lagrangian, (ii) HF/CC transition densities, and (iii) HF are critically analyzed and compared. Additionally, the effect of the DC in the different components of the electronic energy in the formation of the T-shaped (H2 )2 van der Waals cluster and the bimolecular nucleophilic substitution between F(-) and CH3 F is examined. We anticipate that the approach put forward in this article will provide new understandings on subjects in physical chemistry wherein DC plays a crucial role like molecular interactions along with chemical bonding and reactivity. © 2016 Wiley Periodicals, Inc. PMID:27237084

  3. Ab initio study of the structural, magnetic, and electronic properties of copper and silver clusters and their alloys with one palladium atom

    Directory of Open Access Journals (Sweden)

    S. J Hashemifar

    2015-01-01

    Full Text Available In this paper, the structural, magnetic, and electronic properties of two- to nine-atom copper and silver clusters and their alloys with one palladium atom are investigated by using full-potential all-electron density functional computations. After calculating minimized energy of several structural isomers of every nanocluster, it is argued that the small size nanoclusters (up to size of 6, ‎ prefer planar structures, while by increasing size a 2D-3D structural transformation is observed. The structural transformation of pure and copper-palladium clusters occurs in the size of seven and that of silver-palladium cluster in happens at the size of six. The calculated second difference and dissociation energies confirm that the two- and eight- atom pure clusters and three- and seven- atom alloyed clusters are magic clusters. The electronic and magnetic properties of stable isomers are calculated and considered after applying many body based GW correction.

  4. Exploration of electronic quadrupole states in atomic clusters by two-photon processes

    CERN Document Server

    Nesterenko, V O; Halfmann, T; Suraud, E; Halfmann, Th.

    2006-01-01

    We analyze particular two-photon processes as possible means to explore electronic quadrupole states in free small deformed atomic clusters. The analysis is done in the time-dependent local density approximation (TDLDA). It is shown that the direct two-photon population (DTP) and off-resonant stimulated Raman (ORSR) scattering can be effectively used for excitation of the quadrupole states in high-frequency (quadrupole plasmon) and low-frequency (infrared) regions, respectively. In ORSR, isolated dipole particle-hole states as well as the tail of the dipole plasmon can serve as an intermediate state. A simultaneous study of low- and high-frequency quadrupoles, combining DTP and ORSR, is most effective. Femtosecond pulses with intensities $I = 2\\cdot 10^{10} - 2\\cdot 10^{11} W/cm^2$ and pulse durations $T = 200 - 500$ fs are found to be optimal. Since the low-lying quadrupole states are dominated by one single electron-hole pair, their energies, being combined with the photoelectron data for hole states, allow...

  5. Quantitative Z-Contrast Imaging of Supported Metal Complexes and Clusters - A Gateway to Understanding Catalysis on the Atomic Scale

    Energy Technology Data Exchange (ETDEWEB)

    Browning, Nigel D.; Aydin, C.; Lu, Jing; Kulkarni, Apoorva; Okamoto, Norihiko L.; Ortalan, V.; Reed, Bryan W.; Uzun, Alper; Gates, Bruce C.

    2013-09-01

    Z-contrast imaging in an aberration-corrected scanning transmission electron microscope can be used to observe and quantify the sizes, shapes, and compositions of the metal frames in supported mono-, bi-, and multimetallic metal clusters and can even detect the metal atoms in single-metal-atom complexes, as well as providing direct structural information characterizing the metal-support interface. Herein, we assess the major experimental challenges associated with obtaining atomic resolution Z-contrast images of the materials that are highly beam-sensitive, that is, the clusters readily migrate and sinter on support surfaces, and the support itself can drastically change in structure if the experiment is not properly controlled. Calibrated and quantified Z-contrast images are used in conjunction with exsitu analytical measurements and larger-scale characterization methods such as extended X-ray absorption fine structure spectroscopy to generate an atomic-scale understanding of supported catalysts and their function. Examples of the application of these methods include the characterization of a wide range of sizes and compositions of supported clusters, primarily those incorporating Ir, Os, and Au, on highly crystalline supports (zeolites and MgO).

  6. Atoms

    Institute of Scientific and Technical Information of China (English)

    刘洪毓

    2007-01-01

    Atoms(原子)are all around us.They are something like the bricks (砖块)of which everything is made. The size of an atom is very,very small.In just one grain of salt are held millions of atoms. Atoms are very important.The way one object acts depends on what

  7. Atoms

    International Nuclear Information System (INIS)

    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)

  8. Herschel observations of extended atomic gas in the core of the Perseus cluster

    Science.gov (United States)

    Mittal, Rupal; Oonk, J. B. Raymond; Ferland, Gary J.; Edge, Alastair C.; O'Dea, Christopher P.; Baum, Stefi A.; Whelan, John T.; Johnstone, Roderick M.; Combes, Francoise; Salomé, Philippe; Fabian, Andy C.; Tremblay, Grant R.; Donahue, Megan; Russell, Helen

    2012-11-01

    We present Herschel observations of the core of the Perseus cluster of galaxies. Especially intriguing is the network of filaments that surround the brightest cluster galaxy, NGC 1275, previously imaged extensively in Hα and CO. In this work, we report detections of far-infrared (FIR) lines, in particular, [C II] 158, [O I] 63, [N II] 122, [O IB] 145 and [O III] 88 μm, with Herschel. All lines are spatially extended, except [O III], with the [C II] line emission extending up to 25 kpc from the core. [C II] emission is found to be co-spatial with Hα and CO. Furthermore, [C II] shows a similar velocity distribution to CO, which has been shown in previous studies to display a close association with the Hα kinematics. The spatial and kinematical correlation among [C II], Hα and CO gives us confidence to model the different components of the gas with a common heating model. With the help of FIR continuum Herschel measurements, together with a suite of coeval radio, sub-millimetre and IR data from other observatories, we performed a spectral energy distribution fitting of NGC 1275 using a model that contains contributions from dust emission as well as synchrotron active galactic nucleus emission. This has allowed us to accurately estimate the dust parameters. The data indicate a low dust emissivity index, β ≈ 1, a total dust mass close to 107 M⊙, a cold dust component with temperature 38 ± 2 K and a warm dust component with temperature 116 ± 9 K. The FIR-derived star formation rate is 24 ± 1 M⊙ yr-1, which is in agreement with the far-ultraviolet-derived star formation rate in the core, determined after applying corrections for both Galactic and internal reddening. The total IR luminosity in the range 8-1000 μm is inferred to be 1.5 × 1011 L⊙, making NGC 1275 a luminous IR galaxy. We investigated in detail the source of the Herschel FIR and Hα emissions emerging from a core region 4 kpc in radius. Based on simulations conducted using the radiative

  9. Clustering

    Directory of Open Access Journals (Sweden)

    Jinfei Liu

    2013-04-01

    Full Text Available DBSCAN is a well-known density-based clustering algorithm which offers advantages for finding clusters of arbitrary shapes compared to partitioning and hierarchical clustering methods. However, there are few papers studying the DBSCAN algorithm under the privacy preserving distributed data mining model, in which the data is distributed between two or more parties, and the parties cooperate to obtain the clustering results without revealing the data at the individual parties. In this paper, we address the problem of two-party privacy preserving DBSCAN clustering. We first propose two protocols for privacy preserving DBSCAN clustering over horizontally and vertically partitioned data respectively and then extend them to arbitrarily partitioned data. We also provide performance analysis and privacy proof of our solution..

  10. Caging of Cl atoms from photodissociation of CF2Cl2 in clusters

    Czech Academy of Sciences Publication Activity Database

    Poterya, Viktoriya; Kočišek, Jaroslav; Pysanenko, Andriy; Fárník, Michal

    2014-01-01

    Roč. 16, č. 2 (2014), s. 421-429. ISSN 1463-9076 R&D Projects: GA ČR GAP208/11/0161 EU Projects: European Commission(XE) 238671 - ICONIC Institutional support: RVO:61388955 Keywords : AR-N CLUSTERS * (HBR)(N) CLUSTERS * HYDROGEN HALIDES Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.493, year: 2014

  11. Density functional calculations on 13-atom Pd12M (M=Sc-Ni) bimetallic clusters

    Institute of Scientific and Technical Information of China (English)

    Tang Chun-Mei; Chen Sheng-Wei; Zhu Wei-Hua; Tao Cheng-Jun; Zhang Ai-Mei; Gong Jiang-Feng; Zou Hua; Liu Ming-Yi; Zhu Feng

    2012-01-01

    The geometric structures,electronic and magnetic properties of the 3d transition metal doped clusters Pd12M (M =Sc Ni) are studied using the semi-core pseudopots density functional theory.The groundstate geometric structure of the Pd12M cluster is probably of pseudoicosahedron.The Ih-Pd12M cluster has the most thermodynamic stability in five different symmetric isomers.The energy gap shows that Pd12M cluster is partly metallic.Both the absolutely predominant metal bond and very weak covalent bond might exist in the Pd12M cluster.The magnetic moment of Pd12M varies from 0 to 5 μB' implying that it has a potential application in new nanomaterials with tunable magnetic properties.

  12. Fragmentation of neutral carbon clusters formed by high velocity atomic collision; Fragmentation d'agregats de carbone neutres formes par collision atomique a haute vitesse

    Energy Technology Data Exchange (ETDEWEB)

    Martinet, G

    2004-05-01

    The aim of this work is to understand the fragmentation of small neutral carbon clusters formed by high velocity atomic collision on atomic gas. In this experiment, the main way of deexcitation of neutral clusters formed by electron capture with ionic species is the fragmentation. To measure the channels of fragmentation, a new detection tool based on shape analysis of current pulse delivered by semiconductor detectors has been developed. For the first time, all branching ratios of neutral carbon clusters are measured in an unambiguous way for clusters size up to 10 atoms. The measurements have been compared to a statistical model in microcanonical ensemble (Microcanonical Metropolis Monte Carlo). In this model, various structural properties of carbon clusters are required. These data have been calculated with Density Functional Theory (DFT-B3LYP) to find the geometries of the clusters and then with Coupled Clusters (CCSD(T)) formalism to obtain dissociation energies and other quantities needed to compute fragmentation calculations. The experimental branching ratios have been compared to the fragmentation model which has allowed to find an energy distribution deposited in the collision. Finally, specific cluster effect has been found namely a large population of excited states. This behaviour is completely different of the atomic carbon case for which the electron capture in the ground states predominates. (author)

  13. Influence of oxygen impurity atoms on defect clusters and radiation hardening in neutron-irradiated vanadium

    International Nuclear Information System (INIS)

    Single crystal TEM samples and polycrystalline tensile samples of vanadium containing 60-640 wt ppm oxygen were irradiated at about 1000C to about 1.3 x 1019 neutrons/cm2 (E greater than 1 MeV) and post-irradiation annealed up to 8000C. The defect cluster density increased and the average size decreased with increasing oxygen concentration. Higher oxygen concentrations caused the radiation hardening and radiation-anneal hardening to increase. The observations are consistent with the nucleation of defect clusters by small oxygen or oxygen-point defect complexes and the trapping of oxygen at defect clusters upon post-irradiation annealing

  14. Formation of globular clusters in atomic-cooling halos via rapid gas condensation and fragmentation during the epoch of reionization

    CERN Document Server

    Kimm, Taysun; Rosdahl, Joakim; Yi, Sukyoung

    2015-01-01

    We investigate the formation of metal-poor globular clusters (GCs) at the center of two dark matter halos with $M_{halo}\\sim4\\times10^7\\,M_\\odot$ at $z>10$ using cosmological radiation-hydrodynamics simulations. We find that very compact ($\\lesssim$ 1 pc) and massive ($\\sim6\\times10^5\\,M_\\odot$) clusters form rapidly when pristine gas collapses isothermally with the aid of efficient Ly$\\alpha$ emission during the transition from molecular-cooling halos to atomic-cooling halos. Because the local free-fall time of dense star-forming gas is very short ($\\ll 1\\,{\\rm Myr}$), a large fraction of the collapsed gas is turned into stars before stellar feedback processes blow out the gas and shut down star formation. Although the early stage of star formation is limited to a small region of the central star-forming disk, we find that the disk quickly fragments due to metal enrichment from supernovae. Sub-clusters formed in the fragmented clouds eventually merge with the main cluster at the center. We estimate using a s...

  15. Ultrafast photoinduced enhancement of nonlinear optical response in 15-atom gold clusters on indium tin oxide conducting film.

    Science.gov (United States)

    Kumar, Sunil; Shibu, E S; Pradeep, T; Sood, A K

    2013-04-01

    We show that the third order optical nonlinearity of 15-atom gold clusters is significantly enhanced when in contact with indium tin oxide (ITO) conducting film. Open and close aperture z-scan experiments together with non-degenerate pump-probe differential transmission experiments were done using 80 fs laser pulses centered at 395 nm and 790 nm on gold clusters encased inside cyclodextrin cavities. We show that two photon absorption coefficient is enhanced by an order of magnitude as compared to that when the clusters are on pristine glass plate. The enhancement for the nonlinear optical refraction coefficient is ~3 times. The photo-induced excited state absorption using pump-probe experiments at pump wavelength of 395 nm and probe at 790 nm also show an enhancement by an order of magnitude. These results attributed to the excited state energy transfer in the coupled gold cluster-ITO system are different from the enhancement seen so far in charge donor-acceptor complexes and nanoparticle-conjugate polymer composites. PMID:23571938

  16. Charge transfer, excitation and evaporation in low energy collisions of simple metal clusters and fullerenes with atomic targets

    International Nuclear Information System (INIS)

    We present charge transfer, excitation and evaporation cross sections in low energy collisions of small and medium-size metal clusters (Nanq+, Linq+) and C60 with atomic targets (H+, He2+ and Cs) using a molecular close-coupling formalism and a post-collision rate equation model. The theoretical model benefits from different time scales associated with the collision and the internal motion of the cluster nuclei. The collision description includes the many-electron aspect of the problem and makes use of a realistic cluster potential obtained with density functional theory and a spherical jellium model. The evaporation model takes into account the non-harmonic effects of the ionic motion and describes sequential evaporation to any order within the framework of the microcanonical statistical model of Weisskopf. We show that the relative abundance of different fragments depends critically on the cluster temperature and the spectrometer time of flight window. We have found good agreement with recent experimental results [Eur. Phys. J. D 12 (2000) 185

  17. Conductance of Ag atoms and clusters on Ag(111): Spectroscopic and time-resolved data

    Energy Technology Data Exchange (ETDEWEB)

    Sperl, A.; Kroeger, J.; Berndt, R. [Institut fuer Experimentelle und Angewandte Physik, Christian-Albrechts-Universitaet zu Kiel (Germany)

    2010-05-15

    The evolution of the electronic structure of linear atomic Ag chains on Ag(111) has been explored atom by atom using low-temperature scanning tunnelling microscopy and spectroscopy. Electronic states confined to the linear chains are well described within a particle-in-a-box model. The evolution of an unoccupied Ag monomer resonance during the synthesis of an Ag dimer reveals that the Ag-Ag interaction is predominantly direct owing to the large spatial extension of p wave functions of the adsorbed atoms. The hopping dynamics of a single Ag atom adsorbed on Ag(111) have been monitored by time-resolved two-level conductance fluctuations of the tunnel junctions. Effective temperatures of the junction and diffusion barrier heights in the presence of the tip were extracted from a voltage-dependent analysis of the fluctuation rate. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  18. Density functional theory study of the adsorption of hydrogen atoms on Cu2X (X = 3d) clusters

    Science.gov (United States)

    Li, Jiao; Liu, Yanqi; Zhang, Jingjing; Liang, Xiaogang; Duan, Haiming

    2016-05-01

    Density functional theory is carried out to calculate the ground-state structures and electronic properties of Cu2X (X = Sc-Zn) and Cu2X-nH (n = 1-6) clusters. It is found that the dissociation adsorption of H2 molecules of Cu2Ti has obvious advantages over the other mixed clusters. Variations of adsorption energies of Cu2X-nH (n = 1-6) are almost opposite to the energy gaps of Cu2X-(n - 1)H (n = 1-6), which is especially evident in Cu and Zn. Odd-even variations of the distribution of d electrons near the Fermi energy in Cu3-nH and Cu2Zn-nH are opposite, which are strongly correlated to the number of H atoms.

  19. Phase changes in 38 atom Lennard-Jones clusters; 1, A parallel tempering study in the canonical ensemble

    CERN Document Server

    Neirotti, J P; Freeman, D L; Doll, J D; Freeman, David L.

    2000-01-01

    The heat capacity and isomer distributions of the 38 atom Lennard-Jones cluster have been calculated in the canonical ensemble using parallel tempering Monte Carlo methods. A distinct region of temperature is identified that corresponds to equilibrium between the global minimum structure and the icosahedral basin of structures. This region of temperatures occurs below the melting peak of the heat capacity and is accompanied by a peak in the derivative of the heat capacity with temperature. Parallel tempering is shown to introduce correlations between results at different temperatures. A discussion is given that compares parallel tempering with other related approaches that ensure ergodic simulations.

  20. Production of intense beams of mass-selected water cluster ions and theoretical study of atom-water interactions

    CERN Document Server

    Wang, Z P; Reinhard, P -G; Suraud, E; Bruny, G; Montano, C; Feil, S; Eden, S; Abdoul-Carime, H; Farizon, B; Farizon, M; Ouaskit, S; Maerk, T D

    2009-01-01

    The influences of water molecules surrounding biological molecules during irradiation with heavy particles (atoms,ions) are currently a major subject in radiation science on a molecular level. In order to elucidate the underlying complex reaction mechanisms we have initiated a joint experimental and theoretical investigation with the aim to make direct comparisons between experimental and theoretical results. As a first step, studies of collisions of a water molecule with a neutral projectile (C atom) at high velocities (> 0.1 a.u.), and with a charged projectile (proton) at low velocities (< 0.1 a.u.) have been studied within the microscopic framework. In particular, time-dependent density functional theory (TDDFT) was applied to the valence electrons and coupled non-adiabatically to Molecular dynamics (MD) for ionic cores. Complementary experimental developments have been carried out to study projectile interactions with accelerated (< 10 keV) and mass-selected cluster ions. The first size distributio...

  1. Relativistic equation-of-motion coupled-cluster method for the double ionization potentials of the closed-shell atoms

    CERN Document Server

    Pathak, Himadri; Sahoo, B K; Das, B P; Vaval, Nayana; Pal, Sourav

    2014-01-01

    We report the implementation of the relativistic equation-of-motion coupled-cluster method to calculate double ionization spectra (DI-EOMCC) of the closed-shell atomic systems. This method is employed to calculate principal valence double ionization potential values of He and alkaline earth metal (Be, Mg, Ca, Sr and Ba) atoms. Our results are compared with the results available from the national institute of science and technology (NIST) database and other ab initio calculations. We have achieved an accuracy of ~ 0.1%, which is an improvement over the first principles T-matrix calculations [J. Chem. Phys. 123, 144112 (2005)]. We also present results using the second-order many-body perturbation theory and the random -phase approximation in the equation-of-motion framework and these results are compared with the DI-EOMCC results.

  2. Intense deuterium nuclear fusion of pycnodeuterium-lumps coagulated locally within highly deuterated atom clusters

    International Nuclear Information System (INIS)

    Embedded nano-Pd particles of 5 nm in size instantly abundant D-atoms more than 250% in the atomic ratio against Pd-atoms at room temperature when they are kept in D2 gas pressurized to less than 10 atm. In such ultrahigh densities, 2-4 D-atoms can be coagulated inside each octahedral space of Pd lattice (pycnodeuterium-lump). When a stimulation energy such as latticequake causing by ultrasonic wave was supplied to those highly deuterated Pd particles, intense deuterium nuclear fusion (''solid fusion'') was generated there and both excess heat and 4He gas were abundantly produced. Naturally, these facts can not be realized at all in bulk Pd. The results show that the nuclear fusion occurs without any hazardous rays in pycnodeuterium-lumps coagulated locally inside the each cell of the host metal lattice. These unit cells correspond to minimum unit of the solid fusion reactor as a ''Lattice Reactor''. (author)

  3. Intense deuterium nuclear fusion of pycnodeuterium-lumps coagulated locally within highly deuterated atom clusters

    CERN Document Server

    Yoshiaki, A; Zhang, Y C

    2002-01-01

    Embedded nano-Pd particles of 5 nm in size instantly abundant D-atoms more than 250% in the atomic ratio against Pd-atoms at room temperature when they are kept in D sub 2 gas pressurized to less than 10 atm. In such ultrahigh densities, 2-4 D-atoms can be coagulated inside each octahedral space of Pd lattice (pycnodeuterium-lump). When a stimulation energy such as latticequake causing by ultrasonic wave was supplied to those highly deuterated Pd particles, intense deuterium nuclear fusion (''solid fusion'') was generated there and both excess heat and sup 4 He gas were abundantly produced. Naturally, these facts can not be realized at all in bulk Pd. The results show that the nuclear fusion occurs without any hazardous rays in pycnodeuterium-lumps coagulated locally inside the each cell of the host metal lattice. These unit cells correspond to minimum unit of the solid fusion reactor as a ''Lattice Reactor''. (author)

  4. Statistical distribution of single atoms and clusters of supported Au catalyst analyzed by global high-resolution HAADF-STEM observation with morphological image-processing operation.

    Science.gov (United States)

    Yamamoto, Yuta; Arai, Shigeo; Esaki, Akihiko; Ohyama, Junya; Satsuma, Atsushi; Tanaka, Nobuo

    2014-06-01

    We have developed a quantitative particle size analytical method at the single atomic level employing electron microscopy and image processing for the investigation of supported metal catalysts. In the present study, a supported gold (Au) catalyst containing sub-nano clusters and individual atoms was globally observed by high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) using spherical aberration (Cs)-corrected TEM. To fully extract structural information of the Au clusters and individual atoms from the HAADF-STEM images, a morphological image-processing operation was applied. The resulting mean particle size was in good agreement with particle sizes estimated from average information provided by X-ray absorption fine structure analysis. It is demonstrated that the present HAADF-STEM image analysis gives a quantitative particle size distribution measurement of supported Au clusters and individual atoms. PMID:24489113

  5. Electrical properties of amorphous and epitaxial Si-rich silicide films composed of W-atom-encapsulated Si clusters

    International Nuclear Information System (INIS)

    We investigated the electrical properties and derived the energy band structures of amorphous Si-rich W silicide (a-WSin) films and approximately 1-nm-thick crystalline WSin epitaxial films (e-WSin) on Si (100) substrates with composition n = 8–10, both composed of Sin clusters each of which encapsulates a W atom (WSin clusters). The effect of annealing in the temperature range of 300–500 °C was also investigated. The Hall measurements at room temperature revealed that a-WSin is a nearly intrinsic semiconductor, whereas e-WSin is an n-type semiconductor with electron mobility of ∼8 cm2/V s and high sheet electron density of ∼7 × 1012 cm−2. According to the temperature dependence of the electrical properties, a-WSin has a mobility gap of ∼0.1 eV and mid gap states in the region of 1019 cm−3 eV−1 in an optical gap of ∼0.6 eV with considerable band tail states; e-WSin has a donor level of ∼0.1 eV with sheet density in the region of 1012 cm−2 in a band gap of ∼0.3 eV. These semiconducting band structures are primarily attributed to the open band-gap properties of the constituting WSin cluster. In a-WSin, the random network of the clusters generates the band tail states, and the formation of Si dangling bonds results in the generation of mid gap states; in e-WSin, the original cluster structure is highly distorted to accommodate the Si lattice, resulting in the formation of intrinsic defects responsible for the donor level

  6. First-principles determination of the structure of NaN and NaN- clusters with up to 80 atoms.

    Science.gov (United States)

    Aguado, Andrés; Kostko, Oleg

    2011-04-28

    We have performed an extensive computational search for the global minimum (GM) structures of both neutral and anionic sodium clusters with up to 80 atoms. The theoretical framework combines basin hopping unbiased optimizations based on a Gupta empirical potential (EP) and subsequent reoptimization of many candidate structures at the density functional theory level. An important technical point is that the candidates are selected based on cluster shape descriptors rather than the relative stabilities of the EP model. An explicit comparison of the electronic density of states of cluster anions to experimental photoemission spectra suggests that the correct GM structures have been identified for all but two sizes (N = 47 and 70). This comparison validates the accuracy of the proposed methodology. Furthermore, our GM structures either match or improve over the results of previous works for all sizes. Sodium clusters are seen to accommodate strain very efficiently because: (a) many structures are based on polyicosahedral packing; (b) others are based on Kasper polyhedra and show polytetrahedral order; (c) finally, some (N + 1)-atom structures are obtained by incorporating one adatom into the outermost atomic shell of a compact N-atom cluster, at the cost of increasing the bond strain. GM structures of neutrals and anions differ for most sizes. Cluster stabilities are analyzed and shown to be dominated by electron shell closing effects for the smaller clusters and by geometrical packing effects for the larger clusters. The critical size separating both regimes is around 55 atoms. Some implications for the melting behavior of sodium clusters are discussed. PMID:21528957

  7. Herschel observations of extended atomic gas in the core of the Perseus cluster

    OpenAIRE

    Mittal, Rupal; Oonk, J. B. Raymond; Ferland, Gary J.; Edge, Alastair C.; O'Dea, Christopher P.; Baum, Stefi A.; Whelan, John T.; Johnstone, Roderick M.; Combes, Francoise; Salomé, Philippe; Fabian, Andy C.; Tremblay, Grant R.; Donahue, Megan; Russell, Helen

    2012-01-01

    We present Herschel observations of the core of the Perseus cluster of galaxies. Especially intriguing is the network of filaments that surround the brightest cluster galaxy, NGC 1275, previously imaged extensively in Hα and CO. In this work, we report detections of far-infrared (FIR) lines, in particular, [C ii] 158, [O i] 63, [N ii] 122, [O ib] 145 and [O iii] 88  μm, with Herschel. All lines are spatially extended, except [O iii], with the [C ii] line emission extending up to 25 kpc from t...

  8. Application of cluster-plus-glue-atom model to barrierless Cu–Ni–Ti and Cu–Ni–Ta films

    International Nuclear Information System (INIS)

    To improve the thermal stability of copper and avoid its diffusion into surrounding dielectrics or interfacial reactions with them, the authors applied the cluster-plus-glue-atom model to investigate barrierless Cu–Ni–M (M = Ti or Ta) seed layers. The dissolution of the third element (Ti or Ta) in the Cu lattice with the aid of Ni significantly improved the thermal stability of the Cu seed layer. The appropriate M/Ni (M = Ti or Ta) ratio was selected to obtain a low resistivity: the resistivity was as low as 2.5 μΩ cm for the (Ti1.5/13.5Ni12/13.5)0.3Cu99.7 film and 2.8 μΩ cm for the (Ta1.1/13.1Ni12/13.1)0.4Cu99.6 film after annealing at 500 °C for 1 h. After annealing at 500 °C for 40 h, the two films remained stable without forming a Cu3Si compound. The authors confirmed that the range of applications of the cluster-plus-glue-atom model could be extended. Therefore, a third element M with negative enthalpies of mixing with both Cu and Ni could be selected, under the premise that the mixing enthalpy of M–Ni is more negative than that of M–Cu

  9. Photoionization and Velocity Map Imaging spectroscopy of atoms, molecules and clusters with Synchrotron and Free Electron Laser radiation at Elettra

    Science.gov (United States)

    Di Fraia, M.; Sergo, R.; Stebel, L.; Giuressi, D.; Cautero, G.; Tudor, M.; Callegari, C.; O'Keeffe, P.; Ovcharenko, Y.; Lyamayev, V.; Feyer, V.; Moise, A.; Devetta, M.; Piseri, P.; Grazioli, C.; Coreno, M.

    2015-12-01

    Advances in laser and Synchrotron Radiation instrumentation are continuously boosting fundamental research on the electronic structure of matter. At Elettra the collaboration between several groups active in the field of atomic, molecular and cluster physics and the Instrumentation and Detector Laboratory has resulted in an experimental set-up that successfully tackles the challenges posed by the investigation of the electronic structure of isolated species in the gas phase. The use of Synchrotron Radiation (SR) and Free Electron Laser (FEL) light, allows to cover a wide spectrum of targets from energetic to dynamics. We developed a Velocity Map Imaging (VMI) spectrometer that allows to perform as well SR as FEL experiments, just by changing part of the detection system. In SR experiments, at the Gasphase beamline of Elettra, a cross delay line detector is used, coupled to a 4-channel time-to-digital converter that reconstructs the position of the electrons. Simultaneously, a Time-of-Flight (TOF) mass spectrometer is used to acquire photoion spectra. Such a system allows PhotoElectron-PhotoIon-Coincidence (PEPICO) spectroscopy of atoms, molecules and clusters. In FEL experiments (notably differing from SR experiments in the much higher rate of events produced and detected, which forces one to forfeit coincidence detection), at the Low Density Matter (LDM) beamline of FERMI, a Micro Channel Plate (MCP) a phosphor screen and a CCD camera are used instead, capable of shot-by-shot collection of practically all events, albeit without time resolution.

  10. Star-forming dwarf galaxies in the Virgo cluster: the link between molecular gas, atomic gas, and dust

    Science.gov (United States)

    Grossi, M.; Corbelli, E.; Bizzocchi, L.; Giovanardi, C.; Bomans, D.; Coelho, B.; De Looze, I.; Gonçalves, T. S.; Hunt, L. K.; Leonardo, E.; Madden, S.; Menéndez-Delmestre, K.; Pappalardo, C.; Riguccini, L.

    2016-05-01

    We present 12CO(1-0) and 12CO(2-1) observations of a sample of 20 star-forming dwarfs selected from the Herschel Virgo Cluster Survey, with oxygen abundances ranging from 12 + log (O / H) ~ 8.1 to 8.8. CO emission is observed in ten galaxies and marginally detected in another one. CO fluxes correlate with the FIR 250 μm emission, and the dwarfs follow the same linear relation that holds for more massive spiral galaxies extended to a wider dynamical range. We compare different methods to estimate H2 molecular masses, namely a metallicity-dependent CO-to-H2 conversion factor and one dependent on H-band luminosity. The molecular-to-stellar mass ratio remains nearly constant at stellar masses ≲ 109 M⊙, contrary to the atomic hydrogen fraction, MHI/M∗, which increases inversely with M∗. The flattening of the MH2/M∗ ratio at low stellar masses does not seem to be related to the effects of the cluster environment because it occurs for both Hi-deficient and Hi-normal dwarfs. The molecular-to-atomic ratio is more tightly correlated with stellar surface density than metallicity, confirming that the interstellar gas pressure plays a key role in determining the balance between the two gaseous components of the interstellar medium. Virgo dwarfs follow the same linear trend between molecular gas mass and star formation rate as more massive spirals, but gas depletion timescales, τdep, are not constant and range between 100 Myr and 6 Gyr. The interaction with the Virgo cluster environment is removing the atomic gas and dust components of the dwarfs, but the molecular gas appears to be less affected at the current stage of evolution within the cluster. However, the correlation between Hi deficiency and the molecular gas depletion time suggests that the lack of gas replenishment from the outer regions of the disc is lowering the star formation activity. Based on observations carried out with the IRAM 30-m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany

  11. mutation3D: Cancer Gene Prediction Through Atomic Clustering of Coding Variants in the Structural Proteome.

    Science.gov (United States)

    Meyer, Michael J; Lapcevic, Ryan; Romero, Alfonso E; Yoon, Mark; Das, Jishnu; Beltrán, Juan Felipe; Mort, Matthew; Stenson, Peter D; Cooper, David N; Paccanaro, Alberto; Yu, Haiyuan

    2016-05-01

    A new algorithm and Web server, mutation3D (http://mutation3d.org), proposes driver genes in cancer by identifying clusters of amino acid substitutions within tertiary protein structures. We demonstrate the feasibility of using a 3D clustering approach to implicate proteins in cancer based on explorations of single proteins using the mutation3D Web interface. On a large scale, we show that clustering with mutation3D is able to separate functional from nonfunctional mutations by analyzing a combination of 8,869 known inherited disease mutations and 2,004 SNPs overlaid together upon the same sets of crystal structures and homology models. Further, we present a systematic analysis of whole-genome and whole-exome cancer datasets to demonstrate that mutation3D identifies many known cancer genes as well as previously underexplored target genes. The mutation3D Web interface allows users to analyze their own mutation data in a variety of popular formats and provides seamless access to explore mutation clusters derived from over 975,000 somatic mutations reported by 6,811 cancer sequencing studies. The mutation3D Web interface is freely available with all major browsers supported. PMID:26841357

  12. Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters - A kinetic in situ study.

    Science.gov (United States)

    Jendrzej, Sandra; Gökce, Bilal; Amendola, Vincenzo; Barcikowski, Stephan

    2016-02-01

    Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions. PMID:26555960

  13. Atomic layer deposition of platinum clusters on titania nanoparticles at atmospheric pressure

    NARCIS (Netherlands)

    Goulas, A.; Van Ommen, J.R.

    2013-01-01

    We report the fabrication of platinum nanoclusters with a narrow size distribution on TiO2 nanoparticles using atomic layer deposition. With MeCpPtMe3 and ozone as reactants, the deposition can be carried out at a relatively low temperature of 250 degrees C. Our approach of working with suspended na

  14. Characterizing the network topology of the energy landscapes of atomic clusters

    OpenAIRE

    Doye, Jonathan P. K.; Massen, Claire P.

    2004-01-01

    By dividing potential energy landscapes into basins of attractions surrounding minima and linking those basins that are connected by transition state valleys, a network description of energy landscapes naturally arises. These networks are characterized in detail for a series of small Lennard-Jones clusters and show behaviour characteristic of small-world and scale-free networks. However, unlike many such networks, this topology cannot reflect the rules governing the dynamics of network growth...

  15. Atomic scale modelling of nanosize Ni3Al cluster beam deposition on Al, Ni and Ni3Al (1 1 1) surfaces

    International Nuclear Information System (INIS)

    The slowing down of Ni3Al clusters on a Al, Ni and Ni3Al (1 1 1) surfaces is studied by atomic scale modelling. The semi-grand canonical metropolis Monte Carlo is used for the preparation of isolated clusters at thermodynamic equilibrium. The cluster deposition on the surface is studied in detail by classical Molecular Dynamics simulations that include a model to account for electron-phonon coupling. Long- and short-range orders in the cluster are evaluated as functions of temperature in an impact energy range between 0 and 1.5 eV/atom. The interaction between the Ni3Al cluster and an Al surface is characterised low short range (chemical) disorder. No sizeable epitaxy is found, subsequent to the impact. In contrast, in the case of Ni and Ni3Al substrates, which are harder materials than aluminium, the chemical disorder is higher and epitaxial accommodation is possible. With these substrates, chemical disorder in the cluster is an increasing function of the impact energy, as well as of temperature when the impact energy is low enough. The cluster epitaxy is enhanced by both the temperature and the impact energy. A direct correlation between epitaxy and chemical disordering is found during the accommodation of the cluster with the surface

  16. Rydberg Matter clusters of alkali metal atoms: the link between meteoritic matter, polar mesosphere summer echoes (PMSE), sporadic sodium layers, polar mesospheric clouds (PMCs, NLCs), and ion chemistry

    CERN Document Server

    Olofson, Frans; Holmlid, Leif

    2010-01-01

    A material exists which links together the influx of meteoritic matter from interplanetary space, the polar mesosphere summer echoes (PMSE), the sporadic sodium layers, the polar mesospheric clouds (PMCs, NLCs), and the observed ion chemistry in the mesosphere. The evidence in these research fields is here analyzed and found to agree well with the properties of Rydberg Matter (RM). This material has been studied with numerous methods in the laboratory. Alkali atoms, mainly Na, reach the mesosphere in the form of interplanetary (meteoritic, cometary) dust. The planar RM clusters NaN usually contain N = 19, 37 or 61 atoms, and have the density of air at 90 km altitude where they float. The diameters of the clusters are 10-100 nm from laboratory high precision radio frequency spectroscopic studies. Such experiments show that RM clusters interact strongly with radar frequencies: this explains the radio frequency heating and reflection studies of PMSE layers. The clusters give the low temperature in the mesosphere...

  17. Sensing and atomic-scale structure analysis of single nuclear spin clusters in diamond

    OpenAIRE

    Shi, Fazhan; Kong, Xi; Wang, Pengfei; Kong, Fei; Zhao, Nan; Liu, Ren-Bao; Du, Jiangfeng

    2013-01-01

    Single-molecule nuclear magnetic resonance (NMR) is a crown-jewel challenge in the field of magnetic resonance spectroscopy and has important applications in chemical analysis and in quantum computing. Recently, it becomes possible to tackle this grand challenge thanks to experimental advances in preserving quantum coherence of nitrogen-vacancy (NV) center spins in diamond as a sensitive probe and theoretical proposals on atomic-scale magnetometry via dynamical decoupling control. Through dec...

  18. Dual squeezed states in an atom-photon cluster and their manifestations

    International Nuclear Information System (INIS)

    The general kinetic equation for an isolated two-level atom and a high-Q cavity mode in a heat bath exhibiting quantum correlations (entangled bath) is applied to the analysis of the squeezed states of the collective system. Two types of collective operators are introduced for the analysis: one is based on bosonic commutation relations, and the other, on the commutation relations of the algebra obtained by a polynomial deformation of the angular momentum algebra. On the basis of these relations, formulas for observables are constructed that identify squeezed states in the system. It is shown that, under certain conditions, the collective system exhibits dual squeezing within the relations for boson operators, as well as for the operators constructed from the angular momentum algebra. Such squeezing is demonstrated under a projective measurement of an atom and for an entanglement swapping protocol. In the latter case, when measuring two initially independent atomic systems, depending on the type of measurement, two cavity modes collapse into a nonseparable state, which is described either by a nonseparability relation based on boson operators or by a relation based on the operators of the algebra of the quasimomentum of the collective system consisting of these two modes.

  19. Isolation of atomically precise mixed ligand shell PdAu24 clusters

    Science.gov (United States)

    Sels, Annelies; Barrabés, Noelia; Knoppe, Stefan; Bürgi, Thomas

    2016-05-01

    Exposure of PdAu24(2-PET)18 (2-PET: 2-phenylethylthiolate) to BINAS (1,1-binaphthyl-2,2-dithiol) leads to species of composition PdAu24(2-PET)18-2x(BINAS)x due to ligand exchange reactions. The BINAS adsorbs in a specific mode that bridges the apex and one core site of two adjacent S(R)-Au-S(R)-Au-S(R) units. Species with different compositions of the ligand shell can be separated by HPLC. Furthermore, site isomers can be separated. For the cluster with exactly one BINAS in its ligand shell only one isomer is expected due to the symmetry of the cluster, which is confirmed by High-Performance Liquid Chromatography (HPLC). Addition of a second BINAS to the ligand shell leads to several isomers. In total six distinguishable isomers are possible for PdAu24(2-PET)14(BINAS)2 including two pairs of enantiomers concerning the adsorption pattern. At least four distinctive isomers are separated by HPLC. Calculations indicate that one of the six possibilities is energetically disfavoured. Interestingly, diastereomers, which have an enantiomeric relationship concerning the adsorption pattern of chiral BINAS, have significantly different stabilities. The relative intensity of the observed peaks in the HPLC does not reflect the statistical weight of the different isomers. This shows, as supported by the calculations, that the first adsorbed BINAS molecule influences the adsorption of the second incoming BINAS ligand. In addition, experiments with the corresponding Pt doped gold cluster reveal qualitatively the same behaviour, however with slightly different relative abundances of the corresponding isomers. This finding points towards the influence of electronic effects on the isomer distribution. Even for clusters containing more than two BINAS ligands a limited number of isomers were found, which is in contrast to the corresponding situation for monothiols, where the number of possible isomers is much larger.Exposure of PdAu24(2-PET)18 (2-PET: 2-phenylethylthiolate) to BINAS (1

  20. Herschel observations of extended atomic gas in the core of the Perseus cluster

    CERN Document Server

    Mittal, Rupal; Ferland, Gary J; Edge, Alastair C; O'Dea, Christopher P; Baum, Stefi A; Whelan, John T; Johnstone, Roderick M; Combes, Francoise; Salome, Philippe; Fabian, Andy C; Tremblay, Grant R; Donahue, Megan; Russell, Helen

    2012-01-01

    We present Herschel observations of the core of the Perseus cluster of galaxies. The brightest cluster galaxy, NGC 1275, is surrounded by a network of filaments previously imaged extensively in H{\\alpha} and CO. In this work, we report detections of FIR lines with Herschel. All but one of the lines are spatially extended, with the [CII] line emission extending up to 25 kpc from the core. There is spatial and kinematical correlation among [CII], H{\\alpha} and CO, which gives us confidence to model the different components of the gas with a common heating model. With the help of FIR continuum Herschel measurements, together with a suite of coeval radio, submm and infrared data, we performed a SED fitting of NGC 1275 using a model that contains contributions from dust emission as well as synchrotron AGN emission. The data indicate a low dust emissivity index, beta ~ 1, a total dust mass close to 10^7 solar mass, a cold dust component with temperature 38 \\pm 2 K and a warm dust component with temperature of 116 \\...

  1. Electrical properties of amorphous and epitaxial Si-rich silicide films composed of W-atom-encapsulated Si clusters

    Energy Technology Data Exchange (ETDEWEB)

    Okada, Naoya, E-mail: okada-naoya@aist.go.jp [Japan Science and Technology Agency, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan); Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Uchida, Noriyuki [Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan); Kanayama, Toshihiko [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

    2015-03-07

    We investigated the electrical properties and derived the energy band structures of amorphous Si-rich W silicide (a-WSi{sub n}) films and approximately 1-nm-thick crystalline WSi{sub n} epitaxial films (e-WSi{sub n}) on Si (100) substrates with composition n = 8–10, both composed of Si{sub n} clusters each of which encapsulates a W atom (WSi{sub n} clusters). The effect of annealing in the temperature range of 300–500 °C was also investigated. The Hall measurements at room temperature revealed that a-WSi{sub n} is a nearly intrinsic semiconductor, whereas e-WSi{sub n} is an n-type semiconductor with electron mobility of ∼8 cm{sup 2}/V s and high sheet electron density of ∼7 × 10{sup 12 }cm{sup −2}. According to the temperature dependence of the electrical properties, a-WSi{sub n} has a mobility gap of ∼0.1 eV and mid gap states in the region of 10{sup 19 }cm{sup −3} eV{sup −1} in an optical gap of ∼0.6 eV with considerable band tail states; e-WSi{sub n} has a donor level of ∼0.1 eV with sheet density in the region of 10{sup 12 }cm{sup −2} in a band gap of ∼0.3 eV. These semiconducting band structures are primarily attributed to the open band-gap properties of the constituting WSi{sub n} cluster. In a-WSi{sub n}, the random network of the clusters generates the band tail states, and the formation of Si dangling bonds results in the generation of mid gap states; in e-WSi{sub n}, the original cluster structure is highly distorted to accommodate the Si lattice, resulting in the formation of intrinsic defects responsible for the donor level.

  2. Star-forming dwarf galaxies in the Virgo cluster: the link between molecular gas, atomic gas, and dust

    CERN Document Server

    Grossi, M; Bizzocchi, L; Giovanardi, C; Bomans, D; Coelho, B; De Looze, I; Gonçalves, T S; Hunt, L K; Leonardo, E; Madden, S; Menéndez-Delmestre, K; Pappalardo, C; Riguccini, L

    2016-01-01

    We present $^{12}$CO(1-0) and $^{12}$CO(2-1) observations of a sample of 20 star-forming dwarfs selected from the Herschel Virgo Cluster Survey, with oxygen abundances ranging from 12 + log(O/H) ~ 8.1 to 8.8. CO emission is observed in ten galaxies and marginally detected in another one. CO fluxes correlate with the FIR 250 $\\mu$m emission, and the dwarfs follow the same linear relation that holds for more massive spiral galaxies extended to a wider dynamical range. We compare different methods to estimate H2 molecular masses, namely a metallicity-dependent CO-to-H2 conversion factor and one dependent on H-band luminosity. The molecular-to-stellar mass ratio remains nearly constant at stellar masses <~ 10$^9$ M$_{\\odot}$, contrary to the atomic hydrogen fraction, M$_{HI}$/M$_*$, which increases inversely with M$_*$. The flattening of the M$_{H_2}$/M$_*$ ratio at low stellar masses does not seem to be related to the effects of the cluster environment because it occurs for both HI-deficient and HI-normal dwa...

  3. Lateral manipulation of small clusters on the Cu and Ag(1 1 1) surfaces with the single-atom and trimer-apex tips: Reliability study

    International Nuclear Information System (INIS)

    We study the reliability of the lateral manipulation of small Cu clusters (dimer and trimer) on the flat Cu(1 1 1) surface with both the single-atom and trimer-apex tips and that for the Ag/Ag(1 1 1) system, and compare the results between the two systems as well as with the single-atom manipulation on these surfaces. Manipulations are simulated using molecular statics method with semi-empirical potentials. The dependence of the manipulation reliability on the tip height and tip orientation are investigated. Overall, the manipulation reliability increases with decreasing tip height although it depends obviously on the tip orientation. For the Cu/Cu(1 1 1) system, the manipulation of the dimmer and trimer can be successful with both tips. The manipulation reliability can be improved by the trimer-apex tip, and the tip-height range for the successful manipulation is also broader, as compared to the single-atom apex tip. Differently from the single-atom manipulation, the tip orientation has a noticeable influence on the manipulation reliability even for the single-atom tip due to the stronger tip-cluster and surface-adatom interactions in cluster manipulation. For the Ag/Ag(1 1 1) system, successful manipulations only be achieved with the trimer-apex tip, and the manipulation reliability is worse than that of the Cu/Cu(1 1 1) system, indicating the difference in mechanic properties between the two surfaces at the atomic level.

  4. Ion-irradiation-induced clustering in W–Re and W–Re–Os alloys: A comparative study using atom probe tomography and nanoindentation measurements

    International Nuclear Information System (INIS)

    This study examines clustering and hardening in W–2 at.% Re and W–1 at.% Re–1 at.% Os alloys induced by 2 MeV W+ ion irradiation at 573 and 773 K. Such clusters are known precursors to the formation of embrittling precipitates, a potentially life-limiting phenomenon in the operation of fusion reactor components. Increases in hardness were studied using nanoindentation. The presence of osmium significantly increased post-irradiation hardening. Atom probe tomography analysis revealed clustering in both alloys, with the size and number densities strongly dependent on alloy composition and irradiation temperature. The highest cluster number density was found in the ternary alloy irradiated at 773 K. In the ternary alloy, Os was found to cluster preferentially compared to Re. The implications of this result for the structural integrity of fusion reactor components are discussed

  5. First principle study of magnetic and electronic properties of single X (X = Al, Si) atom added to small carbon clusters (C n X, n = 2-10)

    Science.gov (United States)

    Afshar, M.; Hoseini, S. S.; Sargolzaei, M.

    2016-07-01

    In this paper, the magnetic and electronic properties of single aluminum and silicon atom added to small carbon clusters (C n X; X = Al, Si; n = 2-10) are studied in the framework of generalized-gradient approximation using density functional theory. The calculations were performed for linear, two dimensional and three dimensional clusters based on full-potential local-orbital (FPLO) method. The total energies, HOMO-LUMO energy gap and total magnetic moments of the most stable structures are presented in this work. The calculations show that C n Si clusters have more stability compared to C n Al clusters. In addition, our magnetic calculations were shown that the C n Al isomers are magnetic objects whereas C n Si clusters are nonmagnetic objects.

  6. Metals on graphene and carbon nanotube surfaces: From mobile atoms to atomtronics to bulk metals to clusters and catalysts

    KAUST Repository

    Sarkar, Santanu C.

    2014-01-14

    In this Perspective, we present an overview of recent fundamental studies on the nature of the interaction between individual metal atoms and metal clusters and the conjugated surfaces of graphene and carbon nanotube with a particular focus on the electronic structure and chemical bonding at the metal-graphene interface. We discuss the relevance of organometallic complexes of graphitic materials to the development of a fundamental understanding of these interactions and their application in atomtronics as atomic interconnects, high mobility organometallic transistor devices, high-frequency electronic devices, organometallic catalysis (hydrogen fuel generation by photocatalytic water splitting, fuel cells, hydrogenation), spintronics, memory devices, and the next generation energy devices. We touch on chemical vapor deposition (CVD) graphene grown on metals, the reactivity of its surface, and its use as a template for asymmetric graphene functionalization chemistry (ultrathin Janus discs). We highlight some of the latest advances in understanding the nature of interactions between metals and graphene surfaces from the standpoint of metal overlayers deposited on graphene and SWNT thin films. Finally, we comment on the major challenges facing the field and the opportunities for technological applications. © 2013 American Chemical Society.

  7. Atomic Diffusion and Mixing in Old Stars V: A deeper look into the Globular Cluster NGC 6752

    CERN Document Server

    Gruyters, Pieter; Korn, Andreas J

    2014-01-01

    Abundance trends in heavier elements with evolutionary phase have been shown to exist in the globular cluster NGC 6752 [Fe/H]=-1.6. These trends are a result of atomic diffusion and additional (non-convective) mixing. Studying such trends can provide us with important constraints on the extent to which diffusion modifies the internal structure and surface abundances of solar-type, metal-poor stars. Taking advantage of a larger data sample, we investigate the reality and the size of these abundance trends and address questions and potential biases associated with the various stellar populations that make up NGC6752. Based on uvby Str\\"omgren photometry, we are able to separate three stellar populations in NGC 6752 along the evolutionary sequence from the base of the red giant branch down to the turnoff point. We find weak systematic abundance trends with evolutionary phase for Ca, Ti, and Fe which are best explained by stellar-structure models including atomic diffusion with efficient additional mixing. We der...

  8. Revision of single atom local density and capture number varying with coverage in uniform depletion approximation and its effect on coalescence and number of stable clusters

    Institute of Scientific and Technical Information of China (English)

    Shao Qing-Yi; Zhang Juan

    2011-01-01

    In vapour deposition,single atoms(adatoms)on the substrate surface are the main source of growth.The change in its density plays a decisive role in the growth of thin films and quantum size islands.In the nucleation and cluster coalescence stages of vapour deposition,the growth of stable clusters occurs on the substrate surface covered by stable clusters.Nucleation occurs in the non-covered part,while the total area covered by stable clusters on the substrate surface will gradually increase.Carefully taking into account the coverage effect,a revised single atom density rate equation is given for the famous and widely used thin-film rate equation theory,but the work of solving the revised equation has not been done.In this paper,we solve the equation and obtain the single-atom density and capture number by using a uniform depletion approximation.We determine that the single atom density is much lower than that evaluated from the single atom density rate equation in the traditional rate equation theory when the stable cluster coverage fraction is large,and it goes down very fast with an increase in the coverage fraction.The revised equation gives a higher value for the 'average' capture number than the present equation. It also increases with increasing coverage.That makes the preparation of single crystalline thin film materials difficult and the size control of quantum size islands complicated.We also discuss the effect of the revision on coalescence and the number of stable clusters in vapour deposition.

  9. Application of a convergent, composite coupled cluster approach to bound state, adiabatic electron affinities in atoms and small molecules.

    Science.gov (United States)

    Feller, David

    2016-01-01

    Benchmark quality adiabatic electron affinities for a collection of atoms and small molecules were obtained with the Feller-Peterson-Dixon composite coupled cluster theory method. Prior applications of this method demonstrated its ability to accurately predict atomization energies/heats of formation for more than 170 molecules. In the current work, the 1-particle expansion involved very large correlation consistent basis sets, ranging up to aug-cc-pV9Z (aug-cc-pV10Z for H and H2), with the goal of minimizing the residual basis set truncation error that must otherwise be approximated with extrapolation formulas. The n-particle expansion begins with coupled cluster calculations through iterative single and double excitations plus a quasiperturbative treatment of "connected" triple excitations (CCSD(T)) pushed to the complete basis set limit followed by CCSDT, CCSDTQ, or CCSDTQ5 corrections. Due to the small size of the systems examined here, it was possible in many cases to extend the n-particle expansion to the full configuration interaction wave function limit. Additional, smaller corrections associated with core/valence correlation, scalar relativity, anharmonic zero point vibrational energies, and non-adiabatic effects were also included. The overall root mean square (RMS) deviation was 0.005 eV (0.12 kcal/mol). This level of agreement was comparable to what was found with molecular heats of formation. A 95% confidence level corresponds to roughly twice the RMS value or 0.01 eV. While the atomic electron affinities are known experimentally to high accuracy, the molecular values are less certain. This contributes to the difficulty of gauging the accuracy of the theoretical results. A limited number of electron affinities were determined with the explicitly correlated CCSD(T)-F12b method. After extending the VnZ-F12 orbital basis sets with additional diffuse functions, the F12b method was found to accurately reproduce the best F/F(-) value obtained with standard

  10. Application of a convergent, composite coupled cluster approach to bound state, adiabatic electron affinities in atoms and small molecules

    Science.gov (United States)

    Feller, David

    2016-01-01

    Benchmark quality adiabatic electron affinities for a collection of atoms and small molecules were obtained with the Feller-Peterson-Dixon composite coupled cluster theory method. Prior applications of this method demonstrated its ability to accurately predict atomization energies/heats of formation for more than 170 molecules. In the current work, the 1-particle expansion involved very large correlation consistent basis sets, ranging up to aug-cc-pV9Z (aug-cc-pV10Z for H and H2), with the goal of minimizing the residual basis set truncation error that must otherwise be approximated with extrapolation formulas. The n-particle expansion begins with coupled cluster calculations through iterative single and double excitations plus a quasiperturbative treatment of "connected" triple excitations (CCSD(T)) pushed to the complete basis set limit followed by CCSDT, CCSDTQ, or CCSDTQ5 corrections. Due to the small size of the systems examined here, it was possible in many cases to extend the n-particle expansion to the full configuration interaction wave function limit. Additional, smaller corrections associated with core/valence correlation, scalar relativity, anharmonic zero point vibrational energies, and non-adiabatic effects were also included. The overall root mean square (RMS) deviation was 0.005 eV (0.12 kcal/mol). This level of agreement was comparable to what was found with molecular heats of formation. A 95% confidence level corresponds to roughly twice the RMS value or 0.01 eV. While the atomic electron affinities are known experimentally to high accuracy, the molecular values are less certain. This contributes to the difficulty of gauging the accuracy of the theoretical results. A limited number of electron affinities were determined with the explicitly correlated CCSD(T)-F12b method. After extending the VnZ-F12 orbital basis sets with additional diffuse functions, the F12b method was found to accurately reproduce the best F/F- value obtained with standard

  11. Embedded-cluster calculations in a numeric atomic orbital density-functional theory framework

    International Nuclear Information System (INIS)

    We integrate the all-electron electronic structure code FHI-aims into the general ChemShell package for solid-state embedding quantum and molecular mechanical (QM/MM) calculations. A major undertaking in this integration is the implementation of pseudopotential functionality into FHI-aims to describe cations at the QM/MM boundary through effective core potentials and therewith prevent spurious overpolarization of the electronic density. Based on numeric atomic orbital basis sets, FHI-aims offers particularly efficient access to exact exchange and second order perturbation theory, rendering the established QM/MM setup an ideal tool for hybrid and double-hybrid level density functional theory calculations of solid systems. We illustrate this capability by calculating the reduction potential of Fe in the Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for (photo-)catalytic water oxidation at TiO2(110)

  12. FRACTAL PATTERN GROWTH OF METAL ATOM CLUSTERS IN ION IMPLANTED POLYMERS

    Institute of Scientific and Technical Information of China (English)

    ZHANG TONG-HE; WU YU-GUANG; SANG HAI-BO; ZHOU GU

    2001-01-01

    The fractal and multi-fractal patterns of metal atoms are observed in the surface layer and cross section of a metal ion implanted polymer using TEM and SEM for the first time. The surface structure in the metal ion implanted polyethylene terephthalane (PET) is the random fractal. Certain average quantities of the random geometric patterns contain self-similarity. Some growth origins appeared in the fractal pattern which has a dimension of 1.67. The network structure of the fractal patterns is formed in cross section, having a fractal dimension of 1.87. So it can be seen that the fractal pattern is three-dimensional space fractal. We also find the collision cascade fractal in the cross section of implanted nylon, which is similar to the collision cascade pattern in transverse view calculated by the TRIM computer program. Finally, the mechanism for the formation and growth of the fractal patterns during ion implantation is discussed.

  13. Application of the explicitly correlated coupled-cluster models CCSD(F12*) and CC3(F12*) to the hyperpolarizability of the Ne atom

    International Nuclear Information System (INIS)

    This work demonstrates the performance of the recently proposed explicitly correlated coupled-cluster method CCSD(F12*) and a new method using explicitly correlated triple excitations, CC3(F12*), in the calculation of the static ESHG hyperpolarizability of the Ne atom

  14. Ultracold few fermionic atoms in needle-shaped double wells: spin chains and resonating spin clusters from microscopic Hamiltonians emulated via antiferromagnetic Heisenberg and t–J models

    Science.gov (United States)

    Yannouleas, Constantine; Brandt, Benedikt B.; Landman, Uzi

    2016-07-01

    Advances with trapped ultracold atoms intensified interest in simulating complex physical phenomena, including quantum magnetism and transitions from itinerant to non-itinerant behavior. Here we show formation of antiferromagnetic ground states of few ultracold fermionic atoms in single and double well (DW) traps, through microscopic Hamiltonian exact diagonalization for two DW arrangements: (i) two linearly oriented one-dimensional, 1D, wells, and (ii) two coupled parallel wells, forming a trap of two-dimensional, 2D, nature. The spectra and spin-resolved conditional probabilities reveal for both cases, under strong repulsion, atomic spatial localization at extemporaneously created sites, forming quantum molecular magnetic structures with non-itinerant character. These findings usher future theoretical and experimental explorations into the highly correlated behavior of ultracold strongly repelling fermionic atoms in higher dimensions, beyond the fermionization physics that is strictly applicable only in the 1D case. The results for four atoms are well described with finite Heisenberg spin-chain and cluster models. The numerical simulations of three fermionic atoms in symmetric DWs reveal the emergent appearance of coupled resonating 2D Heisenberg clusters, whose emulation requires the use of a t–J-like model, akin to that used in investigations of high T c superconductivity. The highly entangled states discovered in the microscopic and model calculations of controllably detuned, asymmetric, DWs suggest three-cold-atom DW quantum computing qubits.

  15. Implementation and Application of the Relativistic Equation of Motion Coupled-cluster Method for the Excited States of Closed-shell Atomic Systems

    CERN Document Server

    Nandy, D K; Sahoo, B K

    2014-01-01

    We report the implementation of equation-of-motion coupled-cluster (EOMCC) method in the four-component relativistic framework with the spherical atomic potential to generate the excited states from a closed-shell atomic configuration. This theoretical development will be very useful to carry out high precision calculations of varieties of atomic properties in many atomic systems. We employ this method to calculate excitation energies of many low-lying states in a few Ne-like highly charged ions, such as Cr XV, Fe XVII, Co XVIII and Ni XIX ions, and compare them against their corresponding experimental values to demonstrate the accomplishment of the EOMCC implementation. The considered ions are apt to substantiate accurate inclusion of the relativistic effects in the evaluation of the atomic properties and are also interesting for the astrophysical studies. Investigation of the temporal variation of the fine structure constant (\\alpha) from the astrophysical observations is one of the modern research problems...

  16. Post-irradiation annealing of Ni–Mn–Si-enriched clusters in a neutron-irradiated RPV steel weld using Atom Probe Tomography

    International Nuclear Information System (INIS)

    Highlights: • Characterisation of high Ni neutron irradiated RPV surveillance samples at high fluence. • Post-irradiation annealing performed to give insight into the formation mechanisms of Ni–Mn–Si precipitates. • Dissolution of Ni–Mn–Si clusters appears to be lead by the removal of Mn. - Abstract: Atom Probe Tomography has been performed on as-irradiated and post-irradiation annealed surveillance weld samples from Ringhals Unit 3. The weld contains low Cu (0.07 at.%) and high Ni (1.5 at.%). A high number density (∼4 × 1023 m−3) of Ni–Mn–Si-enriched clusters was observed in the as-irradiated material. The onset of recovery was observed during the annealing for 30 min at 450 °C. Much more significant dissolution of clusters occurred during the 10 min 500 °C anneal, resulting in a reduction in mean cluster size and a halving of their volume fraction. Detailed analyses of the changes in microstructure demonstrate that the dissolution process is driven by migration of Mn atoms from the clusters. This may indicate a strong correlation between Mn and point defects. Dissolution of the clusters is shown to correlate with recovery of mechanical properties in this material

  17. Atomic scale modelling of nanosize Ni sub 3 Al cluster beam deposition on Al, Ni and Ni sub 3 Al (1 1 1) surfaces

    CERN Document Server

    Kharlamov, V S; Hou, M

    2002-01-01

    The slowing down of Ni sub 3 Al clusters on a Al, Ni and Ni sub 3 Al (1 1 1) surfaces is studied by atomic scale modelling. The semi-grand canonical metropolis Monte Carlo is used for the preparation of isolated clusters at thermodynamic equilibrium. The cluster deposition on the surface is studied in detail by classical Molecular Dynamics simulations that include a model to account for electron-phonon coupling. Long- and short-range orders in the cluster are evaluated as functions of temperature in an impact energy range between 0 and 1.5 eV/atom. The interaction between the Ni sub 3 Al cluster and an Al surface is characterised low short range (chemical) disorder. No sizeable epitaxy is found, subsequent to the impact. In contrast, in the case of Ni and Ni sub 3 Al substrates, which are harder materials than aluminium, the chemical disorder is higher and epitaxial accommodation is possible. With these substrates, chemical disorder in the cluster is an increasing function of the impact energy, as well as of ...

  18. Post-irradiation annealing of Ni–Mn–Si-enriched clusters in a neutron-irradiated RPV steel weld using Atom Probe Tomography

    Energy Technology Data Exchange (ETDEWEB)

    Styman, P.D., E-mail: paul.styman@materials.ox.ac.uk [National Nuclear Laboratory, 168 Harwell Business Centre, Didcot, Oxon OX11 0QT (United Kingdom); Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Hyde, J.M. [National Nuclear Laboratory, 168 Harwell Business Centre, Didcot, Oxon OX11 0QT (United Kingdom); Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom); Parfitt, D.; Wilford, K. [Rolls-Royce, PO BOX 2000, Raynesway, Derby DE21 7XX (United Kingdom); Burke, M.G. [School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom); English, C.A. [National Nuclear Laboratory, 168 Harwell Business Centre, Didcot, Oxon OX11 0QT (United Kingdom); Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom); Efsing, P. [Vattenfall Ringhals AB, Väröbacka (Sweden)

    2015-04-15

    Highlights: • Characterisation of high Ni neutron irradiated RPV surveillance samples at high fluence. • Post-irradiation annealing performed to give insight into the formation mechanisms of Ni–Mn–Si precipitates. • Dissolution of Ni–Mn–Si clusters appears to be lead by the removal of Mn. - Abstract: Atom Probe Tomography has been performed on as-irradiated and post-irradiation annealed surveillance weld samples from Ringhals Unit 3. The weld contains low Cu (0.07 at.%) and high Ni (1.5 at.%). A high number density (∼4 × 10{sup 23} m{sup −3}) of Ni–Mn–Si-enriched clusters was observed in the as-irradiated material. The onset of recovery was observed during the annealing for 30 min at 450 °C. Much more significant dissolution of clusters occurred during the 10 min 500 °C anneal, resulting in a reduction in mean cluster size and a halving of their volume fraction. Detailed analyses of the changes in microstructure demonstrate that the dissolution process is driven by migration of Mn atoms from the clusters. This may indicate a strong correlation between Mn and point defects. Dissolution of the clusters is shown to correlate with recovery of mechanical properties in this material.

  19. Adsorption of carbon monoxide on small aluminum oxide clusters: Role of the local atomic environment and charge state on the oxidation of the CO molecule

    International Nuclear Information System (INIS)

    We present extensive density functional theory (DFT) calculations dedicated to analyze the adsorption behavior of CO molecules on small AlxOy± clusters. Following the experimental results of Johnson et al. [J. Phys. Chem. A 112, 4732 (2008)], we consider structures having the bulk composition Al2O3, as well as smaller Al2O2 and Al2O units. Our electron affinity and total energy calculations are consistent with aluminum oxide clusters having two-dimensional rhombus-like structures. In addition, interconversion energy barriers between two- and one-dimensional atomic arrays are of the order of 1 eV, thus clearly defining the preferred isomers. Single CO adsorption on our charged AlxOy± clusters exhibits, in general, spontaneous oxygen transfer events leading to the production of CO2 in line with the experimental data. However, CO can also bind to both Al and O atoms of the clusters forming aluminum oxide complexes with a CO2 subunit. The vibrational spectra of AlxOy + CO2 provides well defined finger prints that may allow the identification of specific isomers. The AlxOy+ clusters are more reactive than the anionic species and the final Al2O+ + CO reaction can result in the production of atomic Al and carbon dioxide as observed from experiments. We underline the crucial role played by the local atomic environment, charge density distribution, and spin-multiplicity on the oxidation behavior of CO molecules. Finally, we analyze the importance of coadsorption and finite temperature effects by performing DFT Born-Oppenheimer molecular dynamics. Our calculations show that CO oxidation on AlxOy+ clusters can be also promoted by the binding of additional CO species at 300 K, revealing the existence of fragmentation processes in line with the ones experimentally inferred

  20. Displaying of formation of atomic clusters in radioactive lutetium oxide films

    International Nuclear Information System (INIS)

    We earlier reported the results of our investigations of electron spectra of radioactive lutetium oxide films on the magnetic β-spectrometer π√2 with momentum resolution 0.04-0.1 %. The researches were conducted many times during ≅15 years, and a lot of the data has resulted us in the conclusion about possible formation of toroidal structures in these films. It is impossible to consider a radioactive oxide layer, deposited on metallic foil support having the electric potential of its foil support on all its depth because of its high dielectric properties. There is the potential gradient (≅106-107 V/c) on its depth because of constant outflow of electrons from its surface. Our experiments included in itself also giving a potential, accelerating for electrons, to the metallic foil support. In this case we received a capability to watch the segments of auto emission and low energy Auger electrons. The analysis of the threshold relations and behavior (in time) of the M4NN and M5NN Auger electron intensities have resulted us in the conclusion that the greatest contribution to structure formations of these oxide films is introduced by electrons of M4-, M5- and N-sub-shell of ytterbium atoms (being formed as the result of radioactive decay of the lutetium fraction with half-times from 140 to 1200 days). The auto emission electron spectrum testifies to composite scission of M4 and M5 stationary states of the atom. It is possible to offer as the explanation a quantum flat rotator. If the particle orbit un-compresses the solenoid with a magnetic flux Φ, power condition of a rotator Em=h2(m-Φ/Φ0)2/(8πmeR02), where me - electron mass, R0 - an electron orbit radius; m - a magnetic quantum number, a Φ0=h c/e - a quantum of magnetic flux. At a quantum flow Φ=nΦ0 (n - integer) and the power spectrum does not differ from a spectrum without the solenoid. The behavior (in time) of the experimental auto emission electron spectrum responds the supposition that the main

  1. On the use of big-bang method to generate low-energy structures of atomic clusters modeled with pair potentials of different ranges.

    Science.gov (United States)

    Marques, J M C; Pais, A A C C; Abreu, P E

    2012-02-01

    The efficiency of the so-called big-bang method for the optimization of atomic clusters is analysed in detail for Morse pair potentials with different ranges; here, we have used Morse potentials with four different ranges, from long- ρ = 3) to short-ranged ρ = 14) interactions. Specifically, we study the efficacy of the method in discovering low-energy structures, including the putative global minimum, as a function of the potential range and the cluster size. A new global minimum structure for long-ranged ρ = 3) Morse potential at the cluster size of n= 240 is reported. The present results are useful to assess the maximum cluster size for each type of interaction where the global minimum can be discovered with a limited number of big-bang trials. PMID:22131287

  2. Coordination-resolved local bond strain and 3p energy entrapment of K atomic clusters and K(1 1 0) skin

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Coordination environment resolves electron binding-energy shift of K44, K46, K55 clusters. • Predict the effective coordination number of K nanoclusters when we get the atomic number N. • Atomic under coordination shortens the local bonds and entrapment. • XPS derives core level of an isolated atom and its bulk shift. - Abstract: We have examined the atomic coordination effect on the local bond strain and the 3p core-level shift of K(1 1 0) skin and nanoclusters using a combination of the bond order–length–strength correlation notion, tight-binding approach, density functional theory calculations, and photoelectron spectroscopy measurements. It turns out that: (i) the 3p core-level shifts from 15.595 ± 0.003 eV for an isolated K atom by 2.758 eV to the bulk value of 18.353 eV; (ii) the effective atomic coordination number reduces from the bulk value of 12 to 3.93 for the first layer and to 5.81 for the second layer of K(1 1 0) skin associated with the local lattice strain of 12.76%, a binding energy density 72.67%, and atomic cohesive energy −62.46% for the skin; and (iii) K cluster size reduction lowers the effective atomic coordination number and enhances further the skin electronic attribution. Results have revealed that the 3p core-level shifts of K(1 1 0) and nanoclusters originate from perturbation of the Hamiltonian by under-coordination induced charge densification and quantum entrapment

  3. Coordination-resolved local bond strain and 3p energy entrapment of K atomic clusters and K(1 1 0) skin

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Ting; Bo, Maolin; Guo, Yongling [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Chen, Hefeng [United Superconductive Institution, Shanghai Jiaotong University, Shanghai 200240 (China); Wang, Yan [School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Huang, Yongli, E-mail: huangyongli@xtu.edu.cn [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Chang Q., E-mail: ecqsun@ntu.edu.sg [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore)

    2015-09-15

    Graphical abstract: - Highlights: • Coordination environment resolves electron binding-energy shift of K{sub 44}, K{sub 46}, K{sub 55} clusters. • Predict the effective coordination number of K nanoclusters when we get the atomic number N. • Atomic under coordination shortens the local bonds and entrapment. • XPS derives core level of an isolated atom and its bulk shift. - Abstract: We have examined the atomic coordination effect on the local bond strain and the 3p core-level shift of K(1 1 0) skin and nanoclusters using a combination of the bond order–length–strength correlation notion, tight-binding approach, density functional theory calculations, and photoelectron spectroscopy measurements. It turns out that: (i) the 3p core-level shifts from 15.595 ± 0.003 eV for an isolated K atom by 2.758 eV to the bulk value of 18.353 eV; (ii) the effective atomic coordination number reduces from the bulk value of 12 to 3.93 for the first layer and to 5.81 for the second layer of K(1 1 0) skin associated with the local lattice strain of 12.76%, a binding energy density 72.67%, and atomic cohesive energy −62.46% for the skin; and (iii) K cluster size reduction lowers the effective atomic coordination number and enhances further the skin electronic attribution. Results have revealed that the 3p core-level shifts of K(1 1 0) and nanoclusters originate from perturbation of the Hamiltonian by under-coordination induced charge densification and quantum entrapment.

  4. Energetics and kinetics of Cu atoms and clusters on the Si(111)-7 × 7 surface: first-principles calculations.

    Science.gov (United States)

    Ren, Xiao-Yan; Niu, Chun-Yao; Chen, Wei-Guang; Tang, Ming-Sheng; Cho, Jun-Hyung

    2016-07-21

    Exploring the properties of noble metal atoms and nano- or subnano-clusters on the semiconductor surface is of great importance in many surface catalytic reactions, self-assembly processes, crystal growth, and thin film epitaxy. Here, the energetics and kinetic properties of a single Cu atom and previously reported Cu magic clusters on the Si(111)-(7 × 7) surface are re-examined by the state-of-the-art first-principles calculations based on density functional theory. First of all, the diffusion path and high diffusion rate of a Cu atom on the Si(111)-(7 × 7) surface are identified by mapping out the total potential energy surface of the Cu atom as a function of its positions on the surface, supporting previous experimental hypothesis that the apparent triangular light spots observed by scanning tunneling microscopy (STM) are resulted from a single Cu atom frequently hopping among adjacent adsorption sites. Furthermore, our findings confirm that in the low coverage of 0.15 monolayer (ML) the previously proposed hexagonal ring-like Cu6 cluster configuration assigned to the STM pattern is considerably unstable. Importantly, the most stable Cu6/Si(111) complex also possesses a distinct simulated STM pattern with the experimentally observed ones. Instead, an energetically preferred solid-centered Cu7 structure exhibits a reasonable agreement between the simulated STM patterns and the experimental images. Therefore, the present findings convincingly rule out the tentative six-atom model and provide new insights into the understanding of the well-defined Cu nanocluster arrays on the Si(111)-(7 × 7) surface. PMID:27341196

  5. Migration of Single Iridium Atoms and Tri-iridium Clusters on MgO Surfaces. Aberration-Corrected STEM Imaging and ab-initio Calculations

    Energy Technology Data Exchange (ETDEWEB)

    Han, Chang W. [Purdue Univ., West Lafayette, IN (United States); Iddir, Hakim [Argonne National Lab. (ANL), Argonne, IL (United States); Uzun, Alper [Koc Univ., Instanbul (Turkey); Curtiss, Larry A. [Argonne National Lab. (ANL), Argonne, IL (United States); Browning, Nigel D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Gates, Bruce C. [Univ. of California, Davis, CA (United States); Ortalan, Volkan [Purdue Univ., West Lafayette, IN (United States)

    2015-11-06

    To address the challenge of fast, direct atomic-scale visualization of the diffusion of atoms and clusters on surfaces, we used aberration-corrected scanning transmission electron microscopy (STEM) with high scan speeds (as little as ~0.1 s per frame) to visualize the diffusion of (1) a heavy atom (Ir) on the surface of a support consisting of light atoms, MgO(100), and (2) an Ir3 cluster on MgO(110). Sequential Z-contrast images elucidate the diffusion mechanisms, including the hopping of Ir1 and the rotational migration of Ir3 as two Ir atoms remain anchored to the surface. Density functional theory (DFT) calculations provided estimates of the diffusion energy barriers and binding energies of the iridium species to the surfaces. The results show how the combination of fast-scan STEM and DFT calculations allow real-time visualization and fundamental understanding of surface diffusion phenomena pertaining to supported catalysts and other materials.

  6. Relative yields, mass distributions and energy spectra of cluster ions sputtered from niobium under keV atomic and polyatomic gold ion bombardment

    Energy Technology Data Exchange (ETDEWEB)

    Belykh, S.F. E-mail: serbel@ariel.tashkent.su; Habets, B.; Rasulev, U.Kh.; Samartsev, A.V.; Stroev, L.V.; Veryovkin, I.V

    2000-04-01

    In the present work, the comparative studies of relative yields, mass distributions and kinetic energy spectra of secondary Nb{sub n}{sup +} ions (n=1-16) sputtered from niobium target by atomic and polyatomic Au{sub m}{sup -} projectiles (m=1-3) with the energy E{sub 0}=6-18 keV/atom have been carried out. The strong effect of anomalously high non-additivity of metal sputtering as positive large cluster ions under polyatomic ion bombardment was found. The comparison and discussion of the results obtained for Nb and for Ta are presented.

  7. Multireference Equation of Motion Coupled Cluster study of atomic excitation spectra of first-row transition metal atoms Cr, Mn, Fe and Co

    Czech Academy of Sciences Publication Activity Database

    Liu, Z.; Demel, Ondřej; Nooijen, M.

    2015-01-01

    Roč. 311, SI (2015), s. 54-63. ISSN 0022-2852 Institutional support: RVO:61388955 Keywords : multireference * coupled cluster * electronic excited states Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.482, year: 2014

  8. Recombination radius of a Frenkel pair and capture radius of a self-interstitial atom by vacancy clusters in bcc Fe

    International Nuclear Information System (INIS)

    The recombination radius of a Frenkel pair is a fundamental parameter for the object kinetic Monte Carlo (OKMC) and mean field rate theory (RT) methods that are used to investigate irradiation damage accumulation in irradiated materials. The recombination radius in bcc Fe has been studied both experimentally and numerically, however there is no general consensus about its value. The detailed atomistic processes of recombination also remain uncertain. Values from 1.0a0 to 3.3a0 have been employed as a recombination radius in previous studies using OKMC and RT. The recombination process of a Frenkel pair is investigated at the atomic level using the self-evolved atomistic kinetic Monte Carlo (SEAKMC) method in this paper. SEAKMC calculations reveal that a self-interstitial atom recombines with a vacancy in a spontaneous reaction from several nearby sites following characteristic pathways. The recombination radius of a Frenkel pair is estimated to be 2.26a0 by taking the average of the recombination distances from 80 simulation cases. In addition, we apply these procedures to the capture radius of a self-interstitial atom by a vacancy cluster. The capture radius is found to gradually increase with the size of the vacancy cluster. The fitting curve for the capture radius is obtained as a function of the number of vacancies in the cluster. (paper)

  9. Atomic Diffusion in Cu/Si (111) and Cu/SiO2/Si (111) Systems by Neutral Cluster Beam Deposition

    Institute of Scientific and Technical Information of China (English)

    CAO Bo; LI Gong-Ping; CHEN Xi-Meng; CHO Seong-Jin; KIM Hee

    2008-01-01

    @@ The Cu films are deposited on two kinds of p-type Si (111) substrates by ionized cluster beam (ICB) technique.The interface reaction and atomic diffusion of Cu/Si (111) and Cu/SiO2/Si (111) systems are studied at different annealing temperatures by x-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Some significant results are obtained: For the Cu/Si (111) samples prepared by neutral clusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃and 500℃ are 8.5 × 10-15 cm2.s-1 and 3.0 × 10-14 cm2.s-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2/Si (111) samples prepared by neutral clusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 × 10-16 cm2.s-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.

  10. Structures of Mn clusters

    Indian Academy of Sciences (India)

    Tina M Briere; Marcel H F Sluiter; Vijay Kumar; Yoshiyuki Kawazoe

    2003-01-01

    The geometries of several Mn clusters in the size range Mn13–Mn23 are studied via the generalized gradient approximation to density functional theory. For the 13- and 19-atom clusters, the icosahedral structures are found to be most stable, while for the 15-atom cluster, the bcc structure is more favoured. The clusters show ferrimagnetic spin configurations.

  11. ''Hidden'' world of virtually excited clusters in atomic nuclei and its possible observation in quasielastic knockout of clusters by 1 GeV protons

    International Nuclear Information System (INIS)

    A new kind of cluster quasieleastic knockout experiment is proposed based on the generalized distorted wave impulse approximation calculation which uses Glauber-Sitenko multiple scattering theory and takes into account deexcitation of virtual excited clusters in the nucleus. Elements of general formalism are presented, including the discussion of the difference between ''fast'' and ''slow'' cluster processes. The reaction 12C(p,pα)8Be is considered in detail. It shows a strong dependence of the ''effective momentum distribution'' of knocked-out cluster on both the scattering angle of fast proton and orientation angles of recoil momentum q with respect to the direction of the incident beam and to the scattering plane of a fast proton (i.e., Θq and cphiq anisotropies). Experiments of this kind are desirable also for electron-induced cluster knockout. Finally, the possibility of observing Θq and cphiq anisotropies in 2H(e,e'p)N* and 1H(e,e'π+)n reactions at a few GeV energies due to the quark deexcitation effects is discussed

  12. 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.)

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

    International Nuclear Information System (INIS)

    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 InxGa1-xN, 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 InxGa1-xN 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.)

  14. Cluster generator

    Science.gov (United States)

    Donchev, Todor I.; Petrov, Ivan G.

    2011-05-31

    Described herein is an apparatus and a method for producing atom clusters based on a gas discharge within a hollow cathode. The hollow cathode includes one or more walls. The one or more walls define a sputtering chamber within the hollow cathode and include a material to be sputtered. A hollow anode is positioned at an end of the sputtering chamber, and atom clusters are formed when a gas discharge is generated between the hollow anode and the hollow cathode.

  15. Cross section measurements of the processes occurring in the fragmentation of Hn+ (3 ≤ n ≤ 35) hydrogen clusters induced by high speed (60 keV/u) collisions on helium atoms

    International Nuclear Information System (INIS)

    Different processes involved in the fragmentation of ionised hydrogen clusters H3 + (H2)(n-3)/2 (n = 5-35) have been studied in the same experiment: the fragmentation of the cluster is induced by the collision with an helium atom at high velocity (≅ c/100). The collision is realised in reversed kinematic - clusters are accelerated - which allows the detection of neutral and charged fragments. The different channels of fragmentation are identified by using coincidence techniques. For all the cluster sizes studied the capture cross sections of one electron of the target by the cluster is equal to the capture cross section of the H3+ ion. In the same way, the dissociation cross section of the H3+ core of the cluster does not depend on cluster size. These fragmentation processes are due to the interaction of H3+ core of the cluster and the helium atom without ionization of another component of the cluster. On the contrary, the cross sections of loss of one, two and three molecules by the cluster and the dissociation cross section of the cluster in all its molecular components depends strongly on the cluster size. This dependence is different from the one measured for the metastable decay of the cluster. Thus, the process of loss of molecules induced by a collision should correspond to a different dissociation mechanism. In regard of the singularities observed for the size dependence, the H9+, H15+, H19+ and H29+ clusters could be the 'core' of the biggest clusters. These observation are in agreement with the size effects of smaller magnitude observed for the dissociation cross section (all the processes). The values of the cross section for the process of at least one ionization of the cluster indicate that about 80% of the fragmentation events result from this process. (author)

  16. 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.

  17. Atomic polarizabilities

    International Nuclear Information System (INIS)

    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

  18. An ab initio cluster study of atomic oxygen chemisorption on Ga-rich GaAs(100) (2x1) and beta(4x2) surfaces

    OpenAIRE

    Mayo, Michael L.; Ray, Asok K.

    2003-01-01

    Ab initio self-consistent total energy calculations using second order Moller-Plesset perturbation theory and Hay-Wadt effective core potentials for gallium and arsenic have been used to investigate the chemisorption of atomic oxygen on the Ga-rich GaAs (100) (2 x 1) and beta(4 x 2) surfaces. Finite sized hydrogen saturated clusters with the experimental zinc-blende lattice constant of 5.654 angstroms and the energy optimized surface Ga dimer bond length of 2.758 angstroms have been used to m...

  19. An {\\it ab initio} relativistic coupled-cluster theory of dipole and quadrupole polarizabilities: Applications to a few alkali atoms and alkaline earth ions

    CERN Document Server

    Sahoo, B K

    2006-01-01

    We present a general approach within the relativistic coupled-cluster theory framework to calculate exactly the first order wave functions due to any rank perturbation operators. Using this method, we calculate the static dipole and quadrupole polarizabilities in some alkali atoms and alkaline earth-metal ions. This may be a good test of the present theory for different rank and parity interaction operators. This shows a wide range of applications including precise calculations of both parity and CP violating amplitudes due to rank zero and rank one weak interaction Hamiltonians. We also give contributions from correlation effects and discuss them in terms of lower order many-body perturbation theory.

  20. Statistical disordering of chalcogen atoms in cluster fragments of K4[Re6(μ3-S)8-y(μ3-Te)y(CN)6

    International Nuclear Information System (INIS)

    X-ray diffraction investigation is conducted for three types of crystals of K4[Re6(μ3-S)8-y(μ3-Te)y(CN)6] - representatives of the continuous series of solid solutions prepared by high temperature reactions with the use of different initial substances. Syngony of the crystals is cubic, space group is Ia3. Statistical disordering of chalcogen atoms in cluster fragments [Re6(μ3-S)8-y(μ3-Te)y(CN)6] is investigated on data for three crystals. Results obtained show different effect of statistical disordering degree of Te and S on metric characteristics of the structures

  1. Coupled-cluster response theory for near-edge x-ray-absorption fine structure of atoms and molecules

    DEFF Research Database (Denmark)

    Coriani, Sonia; Christiansen, Ove; Fransson, Thomas;

    2012-01-01

    Based on an asymmetric Lanczos-chain subspace algorithm, damped coupled cluster linear response functions have been implemented for the hierarchy of coupled cluster (CC) models including CC with single excitations (CCS), CC2, CC with single and double excitations (CCSD), and CCSD with noniterativ...... electronic relaxation and correlation that amount to 1–2 eV. With inclusion of triple excitations, errors in energetics are less than 0.9 eV and thereby capturing 90%, 95%, and 98% of the relaxation-correlation energies for C, O, and Ne, respectively....

  2. H/C atomic ratio as a smart linkage between pyrolytic temperatures, aromatic clusters and sorption properties of biochars derived from diverse precursory materials

    Science.gov (United States)

    Xiao, Xin; Chen, Zaiming; Chen, Baoliang

    2016-03-01

    Biochar is increasingly gaining attention due to multifunctional roles in soil amelioration, pollution mitigation and carbon sequestration. It is a significant challenge to compare the reported results from world-wide labs regarding the structure and sorption of biochars derived from various precursors under different pyrolytic conditions due to a lack of a simple linkage. By combining the published works on various biochars, we established a quantitative relationship between H/C atomic ratio and pyrolytic temperature (T), aromatic structure, and sorption properties for naphthalene and phenanthrene. A reverse sigmoid shape between T and the H/C ratio was observed, which was independent of the precursors of biochars, including the ash contents. Linear correlations of Freundlich parameters (N, log Kf) and sorption amount (log Qe, log QA) with H/C ratios were found. A rectangle-like model was proposed to predict the aromatic cluster sizes of biochars from their H/C ratios, and then a good structure-sorption relationship was derived. These quantitative relationships indicate that the H/C atomic ratio is a universal linkage to predict pyrolytic temperatures, aromatic cluster sizes, and sorption characteristics. This study would guide the global study of biochars toward being comparable, and then the development of the structure-sorption relationships will benefit the structural design and environmental application of biochars.

  3. Enhanced intra- and interlayer mass transport on Pt(111) via 5-50 eV Pt atom impacts on two-dimensional Pt clusters

    International Nuclear Information System (INIS)

    Embedded-atom molecular dynamics simulations were used to investigate the effects of low-energy (5-50 eV) normally-incident self-ion irradiation of two-dimensional compact Pt3, Pt7, Pt19, and Pt37 clusters on Pt(111). We follow atomistic pathways leading to bombardment-induced intra- and interlayer mass transport. The results can be described in terms of three impact energy regimes. With E ≤ 20 eV, we observe an increase in 2D island dimensions and negligible residual point defect formation. As the impact energy is raised above 20 eV, we observe an increase in irradiation-induced lateral mass transport, a decrease in island size, and the activation of interlayer processes. For E ≥ 35 eV, this trend continues, but point defects, in the form of surface vacancies, are also formed. The results illustrate the richness of the dynamical interaction mechanisms occurring among incident energetic species, target clusters, and substrate atoms, leading to island preservation, reconfiguration, disruption and/or residual point defects formation. We discuss the significance of these results in terms of thin film growth

  4. Enhanced intra- and interlayer mass transport on Pt(111) via 5-50 eV Pt atom impacts on two-dimensional Pt clusters

    Energy Technology Data Exchange (ETDEWEB)

    Adamovic, D. [Department of Physics and Measurement, IFM, Linkoeping University, SE - 581 83 Linkoeping (Sweden)]. E-mail: draad@ifm.liu.se; Chirita, V. [Department of Physics and Measurement, IFM, Linkoeping University, SE - 581 83 Linkoeping (Sweden); Muenger, E.P. [Department of Physics and Measurement, IFM, Linkoeping University, SE - 581 83 Linkoeping (Sweden); Hultman, L. [Department of Physics and Measurement, IFM, Linkoeping University, SE - 581 83 Linkoeping (Sweden); Greene, J.E. [Materials Science Department and the Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States)

    2006-12-05

    Embedded-atom molecular dynamics simulations were used to investigate the effects of low-energy (5-50 eV) normally-incident self-ion irradiation of two-dimensional compact Pt{sub 3}, Pt{sub 7}, Pt{sub 19}, and Pt{sub 37} clusters on Pt(111). We follow atomistic pathways leading to bombardment-induced intra- and interlayer mass transport. The results can be described in terms of three impact energy regimes. With E {<=} 20 eV, we observe an increase in 2D island dimensions and negligible residual point defect formation. As the impact energy is raised above 20 eV, we observe an increase in irradiation-induced lateral mass transport, a decrease in island size, and the activation of interlayer processes. For E {>=} 35 eV, this trend continues, but point defects, in the form of surface vacancies, are also formed. The results illustrate the richness of the dynamical interaction mechanisms occurring among incident energetic species, target clusters, and substrate atoms, leading to island preservation, reconfiguration, disruption and/or residual point defects formation. We discuss the significance of these results in terms of thin film growth.

  5. Three-Dimensional Structural Analysis of MgO-Supported Osmium Clusters by Electron Microscopy with Single-Atom Sensitivity

    Energy Technology Data Exchange (ETDEWEB)

    Aydin, C.; Kulkarni, Apoorva; Chi, Miaofang; Browning, Nigel D.; Gates, Bruce C.

    2013-05-10

    Size, shape, nuclearity: Aberration-corrected scanning transmission electron microscopy was used to determine the 3D structures of MgO-supported Os3, Os4, Os5, and Os10 clusters, which have structures nearly matching those of osmium carbonyl compounds with known crystal structures. The samples are among the best-defined supported catalysts.

  6. Benchmark calculations of excess electrons in water cluster cavities: balancing the addition of atom-centered diffuse functions versus floating diffuse functions.

    Science.gov (United States)

    Zhang, Changzhe; Bu, Yuxiang

    2016-09-14

    Diffuse functions have been proved to be especially crucial for the accurate characterization of excess electrons which are usually bound weakly in intermolecular zones far away from the nuclei. To examine the effects of diffuse functions on the nature of the cavity-shaped excess electrons in water cluster surroundings, both the HOMO and LUMO distributions, vertical detachment energies (VDEs) and visible absorption spectra of two selected (H2O)24(-) isomers are investigated in the present work. Two main types of diffuse functions are considered in calculations including the Pople-style atom-centered diffuse functions and the ghost-atom-based floating diffuse functions. It is found that augmentation of atom-centered diffuse functions contributes to a better description of the HOMO (corresponding to the VDE convergence), in agreement with previous studies, but also leads to unreasonable diffuse characters of the LUMO with significant red-shifts in the visible spectra, which is against the conventional point of view that the more the diffuse functions, the better the results. The issue of designing extra floating functions for excess electrons has also been systematically discussed, which indicates that the floating diffuse functions are necessary not only for reducing the computational cost but also for improving both the HOMO and LUMO accuracy. Thus, the basis sets with a combination of partial atom-centered diffuse functions and floating diffuse functions are recommended for a reliable description of the weakly bound electrons. This work presents an efficient way for characterizing the electronic properties of weakly bound electrons accurately by balancing the addition of atom-centered diffuse functions and floating diffuse functions and also by balancing the computational cost and accuracy of the calculated results, and thus is very useful in the relevant calculations of various solvated electron systems and weakly bound anionic systems. PMID:27522987

  7. Structure and properties of atomic nanoclusters

    CERN Document Server

    Alonso, Julio A

    2011-01-01

    Atomic clusters are aggregates of atoms containing a few to several thousand atoms. Due to the small size of these pieces of matter, the properties of atomic clusters in general are different from those of the corresponding material in the macroscopic bulk phase. This monograph presents the main developments of atomic clusters and the current status of the field. The book treats different types of clusters with very different properties: clusters in which the atoms or molecules are tied by weak van der Waals interactions, metallic clusters, clusters of ionic materials, and network clusters mad

  8. Structure-reactivity relation, optical properties and real-time study of ultrafast processes in atomic clusters

    OpenAIRE

    MITRIC, Roland

    2003-01-01

    Die Untersuchungen der nichtskalierbaren Eigenschaften von Clustern in dem Größenregime, in dem jedes Atom zählt, zeigten, daß hier neuartige Phänomene und Funktionalität entstehen können. Dadurch motiviert wurden in dieser Arbeit: i) strukturelle und elektronische Eigenschaften sowie die Reaktivität von Metall Clustern, ii) stationäre optische Eigenschaften und iii) zeitabhängige Eigenschaften und optimale Kontrolle von ultraschnellen Prozessen in Edelmetallcluster und in nonstoichiome...

  9. β Zr–Nb–Ti–Mo–Sn alloys with low Young's modulus and low magnetic susceptibility optimized via a cluster-plus-glue-atom model

    International Nuclear Information System (INIS)

    The multi-element Zr-based bio-alloys are optimized for reaching lower Young's modulus and magnetic susceptibility by introducing the cluster-plus-glue-atom model to realize the composition design. A general cluster formulas of [(Mo,Sn)–(Zr,Ti)14]Nbx (x=1, 3) was obtained from the model and alloy rods with a diameter of 3 mm were prepared by copper-mold suction-casting processing. The β structural stabilities of the designed alloys were studied by the valence electron concentration (VEC). Among the β-Zr alloys, the [(Mo0.5Sn0.5)–Zr14]Nb1 (Zr87.5Nb6.25Mo3.13Sn3.13 at%) and [(Mo0.5Sn0.5)–(Zr13Ti)]Nb1 (Zr81.25Nb6.25Ti6.25Mo3.13Sn3.13 at%) alloys, corresponding to the lower β stability limit, display lower Young's moduli (77–79 GPa), lowest magnetic susceptibilities (2.12×10−6–2.13×10−6 cm3 g−1), as well as higher Vickers hardness (288–311 HV)

  10. Basis set limit electronic excitation energies, ionization potentials, and electron affinities for the 3d transition metal atoms: Coupled cluster and multireference methods

    Science.gov (United States)

    Balabanov, Nikolai B.; Peterson, Kirk A.

    2006-08-01

    Recently developed correlation consistent basis sets for the first row transition metal elements Sc-Zn have been utilized to determine complete basis set (CBS) scalar relativistic electron affinities, ionization potentials, and 4s23dn -2-4s1dn -1 electronic excitation energies with single reference coupled cluster methods [CCSD(T), CCSDT, and CCSDTQ] and multireference configuration interaction with three reference spaces: 3d4s, 3d4s4p, and 3d4s4p3d'. The theoretical values calculated with the highest order coupled cluster techniques at the CBS limit, including extrapolations to full configuration interaction, are well within 1kcal/mol of the corresponding experimental data. For the early transition metal elements (Sc-Mn) the internally contracted multireference averaged coupled pair functional method yielded excellent agreement with experiment; however, the atomic properties for the late transition metals (Mn-Zn) proved to be much more difficult to describe with this level of theory, even with the largest reference function of the present work.

  11. Long term simulation of point defect cluster size distributions from atomic displacement cascades in Fe{sub 70}Cr{sub 20}Ni{sub 10}

    Energy Technology Data Exchange (ETDEWEB)

    Souidi, A., E-mail: aek_souidi@yahoo.fr [Université Dr. Tahar Moulay de Saida, Faculté des Sciences, Département de physique, En-nasr BP138, Saida 20000 (Algeria); Hou, M. [Université Libre de Bruxelles, Faculté des Sciences, CP 223, Bd du Triomphe, B-1050 Bruxelles (Belgium); Becquart, C.S. [Unité Matériaux et Transformations (UMET), UMR 8207 Université Lille-1, F-59655 Villeneuve d’Ascq Cédex (France); Domain, C. [EDF-R& D Département MMC, Les renardières, F-77818 Moret sur Loing Cédex (France); De Backer, A. [CCFE, Culham Centre for Fusion Energy, Abingdon (United Kingdom)

    2015-06-01

    We have used an Object Kinetic Monte Carlo (OKMC) model to simulate the long term evolution of the primary damage in Fe{sub 70}Cr{sub 20}Ni{sub 10} alloys. The mean number of Frenkel pairs created by different Primary Knocked on Atoms (PKA) was estimated by Molecular Dynamics using a ternary EAM potential developed in the framework of the PERFORM-60 European project. This number was then used to obtain the vacancy–interstitial recombination distance required in the calculation of displacement cascades in the Binary Collision Approximation (BCA) with code MARLOWE (Robinson, 1989). The BCA cascades have been generated in the 10–100 keV range with the MARLOWE code and two different screened Coulomb potentials, namely, the Molière approximation to the Thomas–Fermi potential and the so-called “Universal” potential by Ziegler, Biersack and Littmark (ZBL). These cascades have been used as input to the OKMC code LAKIMOCA (Domain et al., 2004), with a set of parameters for describing the mobility of point defect clusters based on ab initio calculations and experimental data. The cluster size distributions have been estimated for irradiation doses of 0.1 and 1 dpa, and a dose rate of 10{sup −7} dpa/s at 600 K. We demonstrate that, like in the case of BCC iron, cluster size distributions in the long term are independent of the cascade energy and that the recursive cascade model suggested for BCC iron in Souidi et al. (2011) also applies to FCC Fe{sub 70}Cr{sub 20}Ni{sub 10.} The results also show that the influence of the BCA potential is sizeable but the qualitative correspondence in the predicted long term evolution is excellent.

  12. CMOS-compatible dense arrays of Ge quantum dots on the Si(001 surface: hut cluster nucleation, atomic structure and array life cycle during UHV MBE growth

    Directory of Open Access Journals (Sweden)

    Arapkina Larisa

    2011-01-01

    Full Text Available Abstract We report a direct observation of Ge hut nucleation on Si(001 during UHV molecular beam epitaxy at 360°C. Nuclei of pyramids and wedges were observed on the wetting layer (WL (M × N patches starting from the coverage of 5.1 Å and found to have different structures. Atomic models of nuclei of both hut species have been built as well as models of the growing clusters. The growth of huts of each species has been demonstrated to follow generic scenarios. The formation of the second atomic layer of a wedge results in rearrangement of its first layer. Its ridge structure does not repeat the nucleus. A pyramid grows without phase transitions. A structure of its vertex copies the nucleus. Transitions between hut species turned out to be impossible. The wedges contain point defects in the upper corners of the triangular faces and have preferential growth directions along the ridges. The derived structure of the {105} facet follows the paired dimer model. Further growth of hut arrays results in domination of wedges, and the density of pyramids exponentially drops. The second generation of huts arises at coverages >10 Å; new huts occupy the whole WL at coverages ~14 Å. Nanocrystalline Ge 2D layer begins forming at coverages >14 Å.

  13. Atomic-scale Modeling of Interactions of Helium, Vacancies and Helium-vacancy Clusters with Screw Dislocations in Alpha-Iron

    Energy Technology Data Exchange (ETDEWEB)

    Heinisch, Howard L.; Gao, Fei; Kurtz, Richard J.

    2010-05-01

    The interactions of He and vacancy defects with <111> screw dislocations in alpha-Fe are modeled using molecular statics, molecular dynamics and transition state energy determinations. The formation energies and binding energies of interstitial He atoms, vacancies and He-vacancy clusters near and within dislocations in alpha-Fe are determined at various locations relative to the dislocation core. Using the dimer transition state method the migration energies and trajectories of the He and vacancy defects near and within the screw dislocation are also determined. Both interstitial He atoms and single vacancies are attracted to and trapped in the dislocation core region, and they both migrate along the dislocation line with a migration energy of about 0.4 eV, which is about half the migration energy of vacancies in the perfect crystal and about five times the migration energy for interstitial He in the perfect crystal. Divacancies and He-divacancy complexes have migration properties within the dislocation core that are similar to those in the perfect crystal, although the stability of these defects within the dislocation may be somewhat less than in the perfect crystal.

  14. Ethanol and Water Adsorption on Transition-Metal 13-Atom Clusters: A Density Functional Theory Investigation within van der Waals Corrections.

    Science.gov (United States)

    Zibordi-Besse, Larissa; Tereshchuk, Polina; Chaves, Anderson S; Da Silva, Juarez L F

    2016-06-23

    Transition-metal (TM) nanoparticles supported on oxides or carbon black have attracted much attention as potential catalysts for ethanol steam reforming reactions for hydrogen production. To improve the performance of nanocatalysts, a fundamental understanding of the interaction mechanism between water and ethanol with finite TM particles is required. In this article, we employed first-principles density functional theory with van der Waals (vdW) corrections to investigate the interaction of ethanol and water with TM13 clusters, where TM = Ni, Cu, Pd, Ag, Pt, and Au. We found that both water and ethanol bind via the anionic O atom to onefold TM sites, while at higher-energy structures, ethanol binds also via the H atom from the CH2 group to the TM sites, which can play an important role at real catalysts. The putative global minimum TM13 configurations are only slightly affected upon the adsorption of water or ethanol; however, for few systems, the compact higher-energy icosahedron structure changes its configuration upon ethanol or water adsorption. That is, those configurations are only shallow local minimums in the phase space. Except few deviations, we found similar trends for the magnitude of the adsorption energies of water and ethanol, that is, Ni13 > Pt13 > Pd13 and Cu13 > Au13 > Ag13, which is enhanced by the addition of the vdW correction (i.e., from 4% to 62%); however, the trend is the same. We found that the magnitude of the adsorption energy increases by shifting the center of gravity of the d-states toward the highest occupied molecular orbital. On the basis of the Mulliken and Hirshfeld charge analysis, as well as electron density differences, we identified the location of the charge redistribution and a tiny charge transfer (from 0.01 e to 0.19 e) from the molecules to the TM13 clusters. Our vibrational analysis indicates the red shifts in the OH modes upon binding of both water and ethanol molecules to the TM13 clusters, suggesting a weakening of

  15. Atomic scale observation of phase separation and formation of silicon clusters in Hf higk-{kappa} silicates

    Energy Technology Data Exchange (ETDEWEB)

    Talbot, E.; Roussel, M.; Genevois, C.; Pareige, P. [Groupe de Physique des Materiaux (GPM), Universite et INSA de Rouen, UMR CNRS 6634, Av. de l' Universite, BP 12, 76801 Saint Etienne du Rouvray (France); Khomenkova, L.; Portier, X.; Gourbilleau, F. [Centre de Recherche sur les Ions, les Materiaux et la Photonique (CIMAP), CEA/CNRS/ENSICAEN/UCBN, 6 Bd. Marechal Juin, 14050 Caen Cedex 4 (France)

    2012-05-15

    Hafnium silicate films were fabricated by RF reactive magnetron sputtering technique. Fine microstructural analyses of the films were performed by means of high-resolution transmission electron microscopy and atom probe tomography. A thermal treatment of as-grown homogeneous films leads to a phase separation process. The formation of SiO{sub 2} and HfO{sub 2} phases as well as pure Si one was revealed. This latter was found to be amorphous Si nanoclusters, distributed uniformly in the film volume. Their mean diameter and density were estimated to be about 2.8 nm and (2.9 {+-} 0.4) x 10{sup 17} Si-ncs/cm{sup 3}, respectively. The mechanism of the decomposition process was proposed. The obtained results pave the way for future microelectronic and photonic applications of Hf-based high-{kappa} dielectrics with embedded Si nanoclusters.

  16. Atomic scale observation of phase separation and formation of silicon clusters in Hf higk-κ silicates

    Science.gov (United States)

    Talbot, E.; Roussel, M.; Genevois, C.; Pareige, P.; Khomenkova, L.; Portier, X.; Gourbilleau, F.

    2012-05-01

    Hafnium silicate films were fabricated by RF reactive magnetron sputtering technique. Fine microstructural analyses of the films were performed by means of high-resolution transmission electron microscopy and atom probe tomography. A thermal treatment of as-grown homogeneous films leads to a phase separation process. The formation of SiO2 and HfO2 phases as well as pure Si one was revealed. This latter was found to be amorphous Si nanoclusters, distributed uniformly in the film volume. Their mean diameter and density were estimated to be about 2.8 nm and (2.9 ± 0.4) × 1017 Si-ncs/cm3, respectively. The mechanism of the decomposition process was proposed. The obtained results pave the way for future microelectronic and photonic applications of Hf-based high-κ dielectrics with embedded Si nanoclusters.

  17. Atomic scale observation of phase separation and formation of silicon clusters in Hf higk-κ silicates

    International Nuclear Information System (INIS)

    Hafnium silicate films were fabricated by RF reactive magnetron sputtering technique. Fine microstructural analyses of the films were performed by means of high-resolution transmission electron microscopy and atom probe tomography. A thermal treatment of as-grown homogeneous films leads to a phase separation process. The formation of SiO2 and HfO2 phases as well as pure Si one was revealed. This latter was found to be amorphous Si nanoclusters, distributed uniformly in the film volume. Their mean diameter and density were estimated to be about 2.8 nm and (2.9 ± 0.4) x 1017 Si-ncs/cm3, respectively. The mechanism of the decomposition process was proposed. The obtained results pave the way for future microelectronic and photonic applications of Hf-based high-κ dielectrics with embedded Si nanoclusters.

  18. Change in magnetic and structural properties of FeRh thin films by gold cluster ion beam irradiation with the energy of 1.67 MeV/atom

    International Nuclear Information System (INIS)

    The effect of energetic cluster ion beam irradiation on magnetic and structural properties of FeRh thin films have been investigated. The cluster ions used in the present studies consist of a few gold atoms with the energy of 1.67 MeV/gold atom. Saturation magnetization of the sample irradiated with Au3 cluster ion beam (280 emu/cc) is larger than that for the irradiated sample with Au1 ion beam (240 emu/cc) for the same irradiation ion fluence. These results can also be confirmed by the X-ray magnetic circular dichroism (XMCD) measurement; the XMCD signal for Au3 cluster ion irradiation is larger than that for Au1 ion irradiation. Since the ion beam irradiation induced magnetization of FeRh is significantly correlated with the amount of the lattice defects in the samples, cluster ion beam irradiation can be considered to effectively introduce the lattice defects in B2-type FeRh rather than the single ion beam. Consequently, cluster ion irradiation is better than single ion irradiation for the viewpoint of saturation magnetization, even if the same irradiation energy is deposited in the samples

  19. Change in magnetic and structural properties of FeRh thin films by gold cluster ion beam irradiation with the energy of 1.67 MeV/atom

    Science.gov (United States)

    Koide, T.; Saitoh, Y.; Sakamaki, M.; Amemiya, K.; Iwase, A.; Matsui, T.

    2014-05-01

    The effect of energetic cluster ion beam irradiation on magnetic and structural properties of FeRh thin films have been investigated. The cluster ions used in the present studies consist of a few gold atoms with the energy of 1.67 MeV/gold atom. Saturation magnetization of the sample irradiated with Au3 cluster ion beam (280 emu/cc) is larger than that for the irradiated sample with Au1 ion beam (240 emu/cc) for the same irradiation ion fluence. These results can also be confirmed by the X-ray magnetic circular dichroism (XMCD) measurement; the XMCD signal for Au3 cluster ion irradiation is larger than that for Au1 ion irradiation. Since the ion beam irradiation induced magnetization of FeRh is significantly correlated with the amount of the lattice defects in the samples, cluster ion beam irradiation can be considered to effectively introduce the lattice defects in B2-type FeRh rather than the single ion beam. Consequently, cluster ion irradiation is better than single ion irradiation for the viewpoint of saturation magnetization, even if the same irradiation energy is deposited in the samples.

  20. Change in magnetic and structural properties of FeRh thin films by gold cluster ion beam irradiation with the energy of 1.67 MeV/atom

    Energy Technology Data Exchange (ETDEWEB)

    Koide, T.; Iwase, A. [Department of Materials Science, Osaka Prefecture University, Sakai, Osaka 599-8531 (Japan); Saitoh, Y. [Japan Atomic Energy Agency, Takasaki, Gunma 370-1292 (Japan); Sakamaki, M.; Amemiya, K. [High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801 (Japan); Matsui, T., E-mail: t-matsui@21c.osakafu-u.ac.jp [Research Organization for the 21st Century, Osaka Prefecture University Sakai, Osaka 599-8531 (Japan)

    2014-05-07

    The effect of energetic cluster ion beam irradiation on magnetic and structural properties of FeRh thin films have been investigated. The cluster ions used in the present studies consist of a few gold atoms with the energy of 1.67 MeV/gold atom. Saturation magnetization of the sample irradiated with Au3 cluster ion beam (280 emu/cc) is larger than that for the irradiated sample with Au1 ion beam (240 emu/cc) for the same irradiation ion fluence. These results can also be confirmed by the X-ray magnetic circular dichroism (XMCD) measurement; the XMCD signal for Au3 cluster ion irradiation is larger than that for Au1 ion irradiation. Since the ion beam irradiation induced magnetization of FeRh is significantly correlated with the amount of the lattice defects in the samples, cluster ion beam irradiation can be considered to effectively introduce the lattice defects in B2-type FeRh rather than the single ion beam. Consequently, cluster ion irradiation is better than single ion irradiation for the viewpoint of saturation magnetization, even if the same irradiation energy is deposited in the samples.

  1. β Zr–Nb–Ti–Mo–Sn alloys with low Young's modulus and low magnetic susceptibility optimized via a cluster-plus-glue-atom model

    Energy Technology Data Exchange (ETDEWEB)

    Pang, Chang [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Wang, Qing, E-mail: wangq@dlut.edu.cn [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Zhang, Ruiqian [Science and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu 610041 (China); Li, Qun [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Dai, Xun [Science and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu 610041 (China); Dong, Chuang [Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Liaw, Peter K. [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996 (United States)

    2015-02-25

    The multi-element Zr-based bio-alloys are optimized for reaching lower Young's modulus and magnetic susceptibility by introducing the cluster-plus-glue-atom model to realize the composition design. A general cluster formulas of [(Mo,Sn)–(Zr,Ti){sub 14}]Nb{sub x} (x=1, 3) was obtained from the model and alloy rods with a diameter of 3 mm were prepared by copper-mold suction-casting processing. The β structural stabilities of the designed alloys were studied by the valence electron concentration (VEC). Among the β-Zr alloys, the [(Mo{sub 0.5}Sn{sub 0.5})–Zr{sub 14}]Nb{sub 1} (Zr{sub 87.5}Nb{sub 6.25}Mo{sub 3.13}Sn{sub 3.13} at%) and [(Mo{sub 0.5}Sn{sub 0.5})–(Zr{sub 13}Ti)]Nb{sub 1} (Zr{sub 81.25}Nb{sub 6.25}Ti{sub 6.25}Mo{sub 3.13}Sn{sub 3.13} at%) alloys, corresponding to the lower β stability limit, display lower Young's moduli (77–79 GPa), lowest magnetic susceptibilities (2.12×10{sup −6}–2.13×10{sup −6} cm{sup 3} g{sup −1}), as well as higher Vickers hardness (288–311 HV)

  2. Melting of clusters

    Energy Technology Data Exchange (ETDEWEB)

    Haberland, H. [Freiburg Univ., Facultat fur Physik (Germany)

    2001-07-01

    An experiment is described which allows to measure the caloric curve of size selected sodium cluster ions. This allows to determine rather easily the melting temperatures, and latent heats in the size range between 55 and 340 atoms per cluster. A more detailed analysis is necessary to show that the cluster Na{sub 147}{sup +} has a negative microcanonical heat capacity, and how to determine the entropy of the cluster from the data. (authors)

  3. Cluster fusion algorithm: application to Lennard-Jones clusters

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2008-01-01

    We present a new general theoretical framework for modelling the cluster structure and apply it to description of the Lennard-Jones clusters. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing ...

  4. Cluster fusion algorithm: application to Lennard-Jones clusters

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2006-01-01

    We present a new general theoretical framework for modelling the cluster structure and apply it to description of the Lennard-Jones clusters. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing ...

  5. A DFT study on CO oxidation on Pd4 and Rh4 clusters and adsorbed Pd and Rh atoms on CeO2 and Ce0.75Zr0.25O2 supports for TWC applications

    International Nuclear Information System (INIS)

    CO oxidation reaction mechanisms and energetics are examined on adsorbed Pd4 and Rh4 clusters and adsorbed Pd and Rh atoms on CeO2 and Ce0.75Zr0.25O2 support structures using DFT methods. Activation barriers and TS structures are computed with CI-NEB method. On cluster adsorbed systems, Zr affects CO binding position and O2 adsorption mode. Energetically, formation of two CO2 molecules without barrier and surface regeneration is possible only on Pd4-CeO2 surface. With metal atom substituted surfaces, Pd substituted Ce0.75Zr0.25O2 and CeO2 supports are found to be capable of completing catalytic cycle with consecutive CO oxidations by creating and filling surface oxygen vacancies.

  6. Cool Cluster Correctly Correlated

    Energy Technology Data Exchange (ETDEWEB)

    Sergey Aleksandrovich Varganov

    2005-12-17

    Atomic clusters are unique objects, which occupy an intermediate position between atoms and condensed matter systems. For a long time it was thought that physical and chemical properties of atomic dusters monotonically change with increasing size of the cluster from a single atom to a condensed matter system. However, recently it has become clear that many properties of atomic clusters can change drastically with the size of the clusters. Because physical and chemical properties of clusters can be adjusted simply by changing the cluster's size, different applications of atomic clusters were proposed. One example is the catalytic activity of clusters of specific sizes in different chemical reactions. Another example is a potential application of atomic clusters in microelectronics, where their band gaps can be adjusted by simply changing cluster sizes. In recent years significant advances in experimental techniques allow one to synthesize and study atomic clusters of specified sizes. However, the interpretation of the results is often difficult. The theoretical methods are frequently used to help in interpretation of complex experimental data. Most of the theoretical approaches have been based on empirical or semiempirical methods. These methods allow one to study large and small dusters using the same approximations. However, since empirical and semiempirical methods rely on simple models with many parameters, it is often difficult to estimate the quantitative and even qualitative accuracy of the results. On the other hand, because of significant advances in quantum chemical methods and computer capabilities, it is now possible to do high quality ab-initio calculations not only on systems of few atoms but on clusters of practical interest as well. In addition to accurate results for specific clusters, such methods can be used for benchmarking of different empirical and semiempirical approaches. The atomic clusters studied in this work contain from a few atoms

  7. Tuning the charge state of Ag and Au atoms and clusters deposited on oxide surfaces by doping: a DFT study of the adsorption properties of nitrogen- and niobium-doped TiO2 and ZrO2.

    Science.gov (United States)

    Schlexer, Philomena; Ruiz Puigdollers, Antonio; Pacchioni, Gianfranco

    2015-09-14

    The charge state of Ag and Au atoms and clusters (Ag4 and Au4, Ag5 and Au5) adsorbed on defective TiO2 anatase(101) and tetragonal ZrO2(101) has been systematically investigated as a function of oxide doping and defectivity using a DFT+U approach. As intrinsic defects, we have considered the presence of oxygen vacancies. As extrinsic defects, substitutional nitrogen- and niobium-doping have been investigated, respectively. Both surface and sub-surface defects and dopants have been considered. Whereas on surfaces with oxygen vacancies or Nb-doping, atoms and clusters may become negatively charged, N-doping always leads to the formation of positively charged adsorbates, independently of the supporting material (TiO2 or ZrO2). This suggests the possibility to tune the electronic properties of supported metal clusters by selective doping of the oxide support, an effect that may result in complete changes in chemical reactivity. PMID:26248205

  8. Extending DFT-based genetic algorithms by atom-to-place re-assignment via perturbation theory: A systematic and unbiased approach to structures of mixed-metallic clusters

    International Nuclear Information System (INIS)

    Energy surfaces of metal clusters usually show a large variety of local minima. For homo-metallic species the energetically lowest can be found reliably with genetic algorithms, in combination with density functional theory without system-specific parameters. For mixed-metallic clusters this is much more difficult, as for a given arrangement of nuclei one has to find additionally the best of many possibilities of assigning different metal types to the individual positions. In the framework of electronic structure methods this second issue is treatable at comparably low cost at least for elements with similar atomic number by means of first-order perturbation theory, as shown previously [F. Weigend, C. Schrodt, and R. Ahlrichs, J. Chem. Phys. 121, 10380 (2004)]. In the present contribution the extension of a genetic algorithm with the re-assignment of atom types to atom sites is proposed and tested for the search of the global minima of PtHf12 and [LaPb7Bi7]4−. For both cases the (putative) global minimum is reliably found with the extended technique, which is not the case for the “pure” genetic algorithm

  9. Extending DFT-based genetic algorithms by atom-to-place re-assignment via perturbation theory: A systematic and unbiased approach to structures of mixed-metallic clusters

    Science.gov (United States)

    Weigend, Florian

    2014-10-01

    Energy surfaces of metal clusters usually show a large variety of local minima. For homo-metallic species the energetically lowest can be found reliably with genetic algorithms, in combination with density functional theory without system-specific parameters. For mixed-metallic clusters this is much more difficult, as for a given arrangement of nuclei one has to find additionally the best of many possibilities of assigning different metal types to the individual positions. In the framework of electronic structure methods this second issue is treatable at comparably low cost at least for elements with similar atomic number by means of first-order perturbation theory, as shown previously [F. Weigend, C. Schrodt, and R. Ahlrichs, J. Chem. Phys. 121, 10380 (2004)]. In the present contribution the extension of a genetic algorithm with the re-assignment of atom types to atom sites is proposed and tested for the search of the global minima of PtHf12 and [LaPb7Bi7]4-. For both cases the (putative) global minimum is reliably found with the extended technique, which is not the case for the "pure" genetic algorithm.

  10. Deposition of Small Clusters on Surface: a Molecular Dynamics Simulation

    Institute of Scientific and Technical Information of China (English)

    DUAN Xiang-Mei; GONG Xin-Gao

    2000-01-01

    By using the molecular dynamics simulation, we have studied the dynamic behaviors of small energetic clusters deposited on the surface. We find that, at incident energy as low as 1.0eV/atom, the structure of the cluster is destroyed and cluster atoms form an epitaxial layer above the surface. At high energy incidence, the site exchange between cluster atom and surface atom is observed. The effects of the cluster size and orientation are discussed.

  11. Atomic and electronic structures of neutral and charged Pbn clusters (n=2-15): Theoretical investigation based on density functional theory

    Science.gov (United States)

    Rajesh, Chinagandham; Majumder, Chiranjib

    2007-06-01

    The geometric and electronic structures of the Pbn+ clusters (n=2-15) have been investigated and compared with neutral clusters. The search for several low-lying isomers was carried out under the framework of the density functional theory formalism using the generalized gradient approximation for the exchange correlation energy. The wave functions were expanded using a plane wave basis set and the electron-ion interactions have been described by the projector augmented wave method. The ground state geometries of the singly positively charged Pbn+ clusters showed compact growth pattern as those observed for neutrals with small local distortions. Based on the total energy of the lowest energy isomers, a systematic analysis was carried out to obtain the physicochemical properties, viz., binding energy, second order difference in energy, and fragmentation behavior. It is found that n =4, 7, 10, and 13 clusters are more stable than their neighbors, reflecting good agreement with experimental observation. The chemical stability of these clusters was analyzed by evaluating their energy gap between the highest occupied and lowest unoccupied molecular orbitals and adiabatic ionization potentials. The results revealed that, although Pb13 showed higher stability from the total energy analysis, its energy gap and ionization potential do not follow the trend. Albeit of higher stability in terms of binding energy, the lower ionization potential of Pb13 is interesting which has been explained based on its electronic structure through the density of states and electron shell filling model of spherical clusters.

  12. Introduction to cluster dynamics

    CERN Document Server

    Reinhard, Paul-Gerhard

    2008-01-01

    Clusters as mesoscopic particles represent an intermediate state of matter between single atoms and solid material. The tendency to miniaturise technical objects requires knowledge about systems which contain a ""small"" number of atoms or molecules only. This is all the more true for dynamical aspects, particularly in relation to the qick development of laser technology and femtosecond spectroscopy. Here, for the first time is a highly qualitative introduction to cluster physics. With its emphasis on cluster dynamics, this will be vital to everyone involved in this interdisciplinary subje

  13. Silicon clusters: Chemistry and structure

    Energy Technology Data Exchange (ETDEWEB)

    Jarrold, M.F.; Ray, U.; Ijiri, Y. (AT and T Bell Labs., Murray Hill, NJ (USA))

    1991-01-01

    The chemical reactions of size selected silicon cluster ions (containing up to 70 atoms) have been studied with a number of different reagents using injected ion drift tube techniques. Both kinetic and equilibrium measurements have been performed as a function of temperature, and the influence of cluster annealing on chemical reactivity explored. Unlike metal clusters, where bulk behavior appears to be approached with around 30 atoms, large silicon clusters (n up to 70) are much less reactive than bulk silicon surfaces. These results suggest that the clusters in the size range examined here are not small crystals of bulk silicon, but have compact, high coordination number structures with few dangling bonds. (orig.).

  14. Tracking Rh atoms in Zeolite HY: First Steps of Metal Cluster Formation and Influence of Metal Nuclearity on Catalysis of Ethylene Hydrogenation and Ethylene Dimerization

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Dong; Xu, Pinghong; Browning, Nigel D.; Gates, Bruce C.

    2016-07-07

    The initial steps of rhodium cluster formation from zeolite-supported mononuclear Rh(C2H4)2 complexes in H2 at 373 K and 1 bar were investigated by infrared and extended X-ray absorption fine structure spectroscopies and scanning transmission electron microscopy (STEM). The data show that ethylene ligands on the rhodium react with H2 to give supported rhodium hydrides and trigger the formation of rhodium clusters. STEM provided the first images of the smallest rhodium clusters (Rh2) and their further conversion into larger clusters. The samples were investigated in a plug-flow reactor as catalysts for the conversion of ethylene + H2 in a molar ratio of 4:1 at 1 bar and 298 K, with the results showing how the changes in catalyst structure affect the activity and selectivity; the rhodium clusters are more active for hydrogenation of ethylene than the single-site complexes, which are more selective for dimerization of ethylene to give butenes

  15. Tracking Rh Atoms in Zeolite HY: First Steps of Metal Cluster Formation and Influence of Metal Nuclearity on Catalysis of Ethylene Hydrogenation and Ethylene Dimerization.

    Science.gov (United States)

    Yang, Dong; Xu, Pinghong; Browning, Nigel D; Gates, Bruce C

    2016-07-01

    The initial steps of rhodium cluster formation from zeolite-supported mononuclear Rh(C2H4)2 complexes in H2 at 373 K and 1 bar were investigated by infrared and extended X-ray absorption fine structure spectroscopies and scanning transmission electron microscopy (STEM). The data show that ethylene ligands on the rhodium react with H2 to give supported rhodium hydrides and trigger the formation of rhodium clusters. STEM provided the first images of the smallest rhodium clusters (Rh2) and their further conversion into larger clusters. The samples were investigated in a plug-flow reactor as catalysts for the conversion of ethylene + H2 in a molar ratio of 4:1 at 1 bar and 298 K, with the results showing how the changes in catalyst structure affect the activity and selectivity; the rhodium clusters are more active for hydrogenation of ethylene than the single-site complexes, which are more selective for dimerization of ethylene to give butenes. PMID:27315020

  16. Cross section measurements of the processes occurring in the fragmentation of H{sub n}{sup +} (3 {<=} n {<=} 35) hydrogen clusters induced by high speed (60 keV/u) collisions on helium atoms; Mesure des sections efficaces des differents processus intervenant dans la fragmentation d`agregats d`hydrogene H{sub n}{sup +} (3 {<=} n {<=} 35) induite par collision a haute vitesse (60 keV/u) sur un atome d`helium

    Energy Technology Data Exchange (ETDEWEB)

    Louc, Sandrine [Inst. de Physique Nucleaire, Lyon-1 Univ., 69 - Villeurbanne (France)

    1997-09-15

    Different processes involved in the fragmentation of ionised hydrogen clusters H{sub 3} + (H{sub 2}){sub (n-3)/2} (n = 5-35) have been studied in the same experiment: the fragmentation of the cluster is induced by the collision with an helium atom at high velocity ({approx_equal} c/100). The collision is realised in reversed kinematic - clusters are accelerated - which allows the detection of neutral and charged fragments. The different channels of fragmentation are identified by using coincidence techniques. For all the cluster sizes studied the capture cross sections of one electron of the target by the cluster is equal to the capture cross section of the H{sub 3}{sup +} ion. In the same way, the dissociation cross section of the H{sub 3}{sup +} core of the cluster does not depend on cluster size. These fragmentation processes are due to the interaction of H{sub 3}{sup +} core of the cluster and the helium atom without ionization of another component of the cluster. On the contrary, the cross sections of loss of one, two and three molecules by the cluster and the dissociation cross section of the cluster in all its molecular components depends strongly on the cluster size. This dependence is different from the one measured for the metastable decay of the cluster. Thus, the process of loss of molecules induced by a collision should correspond to a different dissociation mechanism. In regard of the singularities observed for the size dependence, the H{sub 9}{sup +}, H{sub 15}{sup +}, H{sub 19}{sup +} and H{sub 29}{sup +} clusters could be the `core` of the biggest clusters. These observation are in agreement with the size effects of smaller magnitude observed for the dissociation cross section (all the processes). The values of the cross section for the process of at least one ionization of the cluster indicate that about 80% of the fragmentation events result from this process. (author) 114 refs., 74 figs., 9 tabs.

  17. Cluster growing process and a sequence of magic numbers

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter; Koshelev, Andrey; Shutovich, Andrey

    2003-01-01

    We present a new theoretical framework for modeling the cluster growing process. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system, and absorbing its energy at each step, we find cluster growing paths up to the cluster sizes of more than 100 atoms. We...... demonstrate that in this way all known global minimum structures of the Lennard-Jones (LJ) clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic cluster structure. With its use we justify the magic number sequence for the clusters of noble gas atoms and...

  18. Chemisorption of O and H on an Al-13 cluster

    Science.gov (United States)

    Patridge, H.; Bauschlicher, C. W., Jr.

    1986-01-01

    Chemisorption of oxygen and hydrogen atoms onto a 13 atom aluminum cluster is investigated theoretically. Oxygen atoms are found to remain on the outside of the cluster, and at low coverage, to expand the Al-Al bond length by 0.42 bohr. Hydrogen atoms penetrate into the cluster resulting in a sizeable, 0.57 bohr expansion at high coverage. The difference between chemisorption on aluminum and beryllium clusters is discussed.

  19. Coupled cluster calculations of mean excitation energies of the noble gas atoms He, Ne and Ar and of the H2 molecule

    DEFF Research Database (Denmark)

    Sauer, Stephan P. A.; Haq, Inam U.; Sabin, John R.;

    2013-01-01

    Using an asymmetric-Lanczos-chain algorithm for the calculation of the coupled cluster linear response functions at the CCSD and CC2 levels of approximation, we have calculated the mean excitation energies of the noble gases He, Ne and Ar, and of the hydrogen molecule H2. Convergence with respect...... for the mean excitation energy of these two systems within the Bethe theory for the chosen basis set and, in the case of H2, at the experimental equilibrium geometry....

  20. Blue emitting undecaplatinum clusters

    Science.gov (United States)

    Chakraborty, Indranath; Bhuin, Radha Gobinda; Bhat, Shridevi; Pradeep, T.

    2014-07-01

    A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents.A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents. Electronic supplementary information (ESI) available: Details of experimental procedures, instrumentation, chromatogram of the crude cluster; SEM/EDAX, DLS, PXRD, TEM, FT-IR, and XPS of the isolated Pt11 cluster; UV/Vis, MALDI MS and SEM/EDAX of isolated 2 and 3; and 195Pt NMR of the K2PtCl6 standard. See DOI: 10.1039/c4nr02778g

  1. Theoretical study on ground-state proton/H-atom exchange in formic acid clusters through different H-bonded bridges

    Indian Academy of Sciences (India)

    HUA FANG

    2016-09-01

    The ground-state triple proton/H-atom transfer (GSTPT/GSTHAT) reactions in HCOOH complexed cyclically with H₂O, CH₃OH, NH₃ and mixed solvents H₂O-NH₃/CH₃ OH-NH₃ were studied byquantum mechanical methods in heptane. The GSTPT/GSTHAT in HCOOH-(H₂O) ₂, HCOOH-(CH₃OH)₂, HCOOH-(NH₃)₂, HCOOH-H₂O-NH₃, HCOOH-NH₃-H₂O, HCOOH-CH₃OH-NH₃ and HCOOH-NH₃-CH₃ OH systems all occurred in an asynchronous but concerted protolysis mechanism. The formation pattern of the H-bonded chain was important to reduce the proton/H-atom transfer barrier. For the HCOOH-S₁-S₂ (S₁, S₂: H₂O, CH₃OH, NH₃) complex, the GSTPT/GSTHAT barrier height of the HCOOH-S₁-S₂ complex, in which the H-bonded chain was formed with different solvent molecules, was lower than that of HCOOH-S₁-S₂ complex, in which the H-bonded chain was composed of same solvent molecules. H-bonded chain consisting of mixed solvent molecules can accumulate their proton-accepting abilities and then speed up proton/H-atom transfer. When the less-basic H₂O or CH₃OH is connected to O-H group of HCOOH directly and the PT/HAT process is started by accepting a proton/H-atom from HCOOH, the PT/HAT reaction would be pulled by the more basic NH₃ along the H-bonded chain from the front. On the contrary, when the more-basic NH₃ is bonded to O-H group of HCOOH directly, the less-basic H₂O or CH₃OH hardly pulled PT/HAT process from the front. A good correlation between the proton-accepting ability (basicity) of the H-bonded chain and the GSTPT/GSTHAT barrier height was obtained.

  2. Structure and stability of small H clusters on graphene

    DEFF Research Database (Denmark)

    Sljivancanin, Zeljko; Andersen, Mie; Hammer, Bjørk

    2011-01-01

    The structure and stability of small hydrogen clusters adsorbed on graphene is studied by means of density functional theory (DFT) calculations. Clusters containing up to six H atoms are investigated systematically, with the clusters having either all H atoms on one side of the graphene sheet (cis......-clusters) or having the H atoms on both sides in an alternating manner (trans-clusters). The most stable cis-clusters found have H atoms in ortho- and para-positions with respect to each other (two H’s on neighboring or diagonally opposite carbon positions within one carbon hexagon), while the most stable...... trans-clusters found have H atoms in ortho-trans-positions with respect to each other (two H’s on neighboring carbon positions, but on opposite sides of the graphene). Very stable trans-clusters with 13–22 H atoms were identified by optimizing the number of H atoms in ortho-trans-positions and thereby...

  3. Imaging with Mass Spectrometry: A SIMS and VUV-Photoionization Study of Ion-Sputtered Atoms and Clusters from GaAs and Au

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Lynelle; Zhou, Jia; Wilson, Kevin R.; Leone, Stephen R.; Ahmed, Musahid

    2008-12-05

    A new mass spectrometry surface imaging method is presented in which ion-sputtered neutrals are postionized by wavelength-tunable vacuum ultraviolet (VUV) light from a synchrotron source. Mass spectra and signal counts of the photoionized neutrals from GaAs (100) and Au are compared to those of the secondary ions. While clusters larger than dimers are more efficiently detected as secondary ions, certain species, such as As2, Au and Au2, are more efficiently detected through the neutral channel. Continuously tuning the photon wavelength allows photoionization efficiency (PIE) curves to be obtained for sputtered Asm (m=1,2) and Aun (n=1-4). From the observed ionization thresholds, sputtered neutral As and Au show no clear evidence of electronic excitation, while neutral clusters have photoionization onsets shifted to lower energies by ~;;0.3 eV. These shifts are attributed to unresolved vibrational and rotational excitations. High-spatial resolution chemical imaging with synchrotron VUV postionization is demonstrated at two different photon energies using a copper TEM grid embedded in indium. The resulting images are used to illustrate the use of tunable VUV light for verifying mass peak assignments by exploiting the unique wavelength-dependent PIE of each sputtered neutral species. This capability is valuable for identifying compounds when imaging chemically complex systems with mass spectrometry-based techniques.

  4. Cluster Automorphisms

    OpenAIRE

    Assem, Ibrahim; Schiffler, Ralf; Shramchenko, Vasilisa

    2010-01-01

    In this article, we introduce the notion of cluster automorphism of a given cluster algebra as a $\\ZZ$-automorphism of the cluster algebra that sends a cluster to another and commutes with mutations. We study the group of cluster automorphisms in detail for acyclic cluster algebras and cluster algebras from surfaces, and we compute this group explicitly for the Dynkin types and the Euclidean types.

  5. Generation of Cluster States in Cavity QED

    Institute of Scientific and Technical Information of China (English)

    ZHOU Yan-Li; YANG Li-Jia; DAI Hong-Yi

    2007-01-01

    We propose two schemes for the generation of cluster states in the context of cavity quantum electrodynamics (QED).In the first scheme,we prepare multi-cavity cluster states with information encoded in the coherent states.The second scheme is to generate multi-atom cluster states,where qubits are represented by the states of cascade Rydberg atoms.Both the schemes are based on the atom-cavity interaction and the atomic spontaneous radiation can be effciently reduced since the cavity frequency is largely detuned from the atomic transition frequency.

  6. Cluster ion beam evaporation

    International Nuclear Information System (INIS)

    Cluster ions can be made by the supercooling due to adiabatic expansion of substances to be vaporized which are ejected from a nozzle. This paper is described on the recent progress of studies concerning the cluster beam. The technique of cluster ion beam has been applied for the studies of thermonuclear plasma, the fabrication of thin films, crystal growth and electronic devices. The density of cluster ion beam is larger than that of atomic ion beam, and the formation of thin films can be easily done in high vacuum. This method is also useful for epitaxial growth. Metallic vapour cluster beam was made by the help of jetting rare gas beam. Various beam sources were developed. The characteristics of these sources were measured and analyzed. (Kato, T.)

  7. Electron attachment to HCl clusters

    International Nuclear Information System (INIS)

    Negatively charged cluster ions of hydrogen chloride are formed by electron attachment to HCl clusters, which are produced in a seeded supersonic beam traversing a sustained gas discharge. Cluster ions of (HCl)n-, with n = 2, and tentatively with n = 3 and 4 are observed. Cluster ions like Cln-, Cln- (HCl)m, and with Ar attached to them are also seen. The relevance to radiation chemistry of HCl is briefly discussed. Atoms evaporating from the hot, thoriated tungsten filament of the glow discharge lead to clusters such as Thn- and its oxides. (orig.)

  8. Structure and bonding in clusters

    International Nuclear Information System (INIS)

    We review here the recent progress made in the understanding of the electronic and atomic structure of small clusters of s-p bonded materials using the density functional molecular dynamics technique within the local density approximation. Starting with a brief description of the method, results are presented for alkali metal clusters, clusters of divalent metals such as Mg and Be which show a transition from van der Waals or weak chemical bonding to metallic behaviour as the cluster size grows and clusters of Al, Sn and Sb. In the case of semiconductors, we discuss results for Si, Ge and GaAs clusters. Clusters of other materials such as P, C, S, and Se are also briefly discussed. From these and other available results we suggest the possibility of unique structures for the magic clusters. (author). 69 refs, 7 figs, 1 tab

  9. Time-of-flight mass spectrometry with desorption-ionization multiprobes (UV photons and KeV and MeV particles). Cluster atoms are used as projectiles

    International Nuclear Information System (INIS)

    A new time-of-flight mass spectrometer, Super-Depil, is used to study secondary ion emission from solid surfaces bombarded by various kinds of primary particles. Three different desorption probes were set up on this machine: a 252 californium source, providing by spontaneous fission about 1 MeV/u energy heavy ions, a 5 to 30 keV energy pulsed caesium ion gun and a pulsed nitrogen laser, which wavelength is 337 mm. A two stages electrostatic mirror was added to the spectrometer. The time spread due to the initial kinetic energy of secondary ions leaving the surface was minimized. The mass resolution is greater than 5000. The analysis of glycosidic terpenes showed the complementarity of the three probes. The study of such metastable ions, with the electrostatic mirror, showed that some fragment ions may conserve the memory of the stereochemistry of the neutral lost. Clusters ions were used as projectiles in the energy range 5-60 keV. A strong non linear enhancement was observed in the secondary ion yield from various targets

  10. Cu cluster shell structure at elevated temperatures

    DEFF Research Database (Denmark)

    Christensen, Ole Bøssing; Jacobsen, Karsten Wedel; Nørskov, Jens Kehlet;

    1991-01-01

    Equilibrium structures of small (3–29)-atom Cu clusters are determined by simulated annealing, and finite-temperature ensembles are simulated by Monte Carlo techniques using the effective-medium theory for the energy calculation. Clusters with 8, 18, and 20 atoms are found to be particularly stable...

  11. Strontium clusters: electronic and geometry shell effects

    DEFF Research Database (Denmark)

    Lyalin, Andrey G.; Solov'yov, Ilia; Solov'yov, Andrey V.;

    2008-01-01

    charged strontium clusters consisting of up to 14 atoms, average bonding distances, electronic shell closures, binding energies per atom, and spectra of the density of electronic states (DOS). It is demonstrated that the size-evolution of structural and electronic properties of strontium clusters is...

  12. ''Anomalous'' properties of technetium clusters

    International Nuclear Information System (INIS)

    The authors show how some properties of technetium clusters can be explained on the basis of a qualitative model of the electrostatic repulsion of the metal atoms in the clusters. The position of technetium in the periodic table, as well as the experimentally recently discovered ability of technetium to lower the effective charge on its atoms when M-M bonds are formed by them, impart a high capacity to this element to form clusters with both weak-field ligands and strong field ligands

  13. Optical response of small magnesium clusters

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2004-01-01

    We predict strong enhancement in the photoabsorption of small Mg clusters in the region of 4–5 eV due to the resonant excitation of the plasmon oscillations of cluster electrons. Photoabsorption spectra for neutral Mg clusters consisting of up to N = 11 atoms have been calculated using an ab init...

  14. Photoabsorption of small sodium and magnesium clusters

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2004-01-01

    We predict the strong enhancement in the photoabsorption of small Mg clusters in the region of 4-5 eV due to the resonant excitation of the plasmon oscillations of cluster electrons. The photoabsorption spectra for neutral Mg clusters consisting of up to N=11 atoms have been calculated using it a...

  15. Melting and boiling of clusters

    International Nuclear Information System (INIS)

    Clusters properties depends on their size, the transition from the atom / molecule to the bulk is often smooth and the asymptotic behaviour well understood, but for cluster melting is not the case, where irregular fluctuations are found even for clusters containing more than hundred atoms. A method to measure caloric curves for size selected cluster ions is provided. A plot of the cluster energy as a function of cluster temperature gives the caloric curve and contains all its basic thermodynamic properties. The method consists of two steps: in the first, sodium clusters ions are produced and thermalized. The heat bath was a helium gas of known temperature T, where clusters make so many collisions that they reach thermal equilibrium. Then, the thermalized clusters are extracted, transferred to high vacuum, and mass analysed. In the second step, the internal dominantly vibrational energy E of the cluster is measured by a photofragmentation technique, knowing E and T, the caloric curve E= E(T) can be plotted. As an example the Na 139+ and Na+n study is presented. (nevyjel)

  16. Weighted Clustering

    DEFF Research Database (Denmark)

    Ackerman, Margareta; Ben-David, Shai; Branzei, Simina;

    2012-01-01

    We investigate a natural generalization of the classical clustering problem, considering clustering tasks in which different instances may have different weights.We conduct the first extensive theoretical analysis on the influence of weighted data on standard clustering algorithms in both the...... partitional and hierarchical settings, characterizing the conditions under which algorithms react to weights. Extending a recent framework for clustering algorithm selection, we propose intuitive properties that would allow users to choose between clustering algorithms in the weighted setting and classify...

  17. Cluster Headache

    OpenAIRE

    Frederick G Freitag

    1985-01-01

    Learning Objectives: Review the current understanding of the pathophysiology of cluster headache Be able to recognize the clinical features of cluster headache Be able to develop a strategy for treatment of cluster headache Cluster headache is divided into multiple subtypes under the IHC classification criteria. The vast majority of patients present with episodic cluster headache (3.1.1). This will be the focus of the presentation. The syndrome is characterized by repeated at...

  18. Structure and physical properties of silicon clusters and of vacancy clusters in bulk silicon

    International Nuclear Information System (INIS)

    In this thesis the growth-pattern of free silicon clusters and vacancy clusters in bulk silicon is investigated. The aim is to describe and to better understand the cluster to bulk transition. Silicon structures in between clusters and solids feature new interesting physical properties. The structure and physical properties of silicon clusters can be revealed by a combination of theory and experiment, only. Low-energy clusters are determined with different optimization techniques and a density-functional based tight-binding method. Additionally, infrared and Raman spectra, and polarizabilities calculated within self-consistent field density-functional theory are provided for the smaller clusters. For clusters with 25 to 35 atoms an analysis of the shape of the clusters and the related mobilities in a buffer gas is given. Finally, the clusters observed in low-temperature experiments are identified via the best match between calculated properties and experimental data. Silicon clusters with 10 to 15 atoms have a tricapped trigonal prism as a common subunit. Clusters with up to about 25 atoms follow a prolate growth-path. In the range from 24 to 30 atoms the geometry of the clusters undergoes a transition towards compact spherical structures. Low-energy clusters with up to 240 atoms feature a bonding pattern strikingly different from the tetrahedral bonding in the solid. It follows that structures with dimensions of several Angstroem have electrical and optical properties different from the solid. The calculated stabilities and positron-lifetimes of vacancy clusters in bulk silicon indicate the positron-lifetimes of about 435 ps detected in irradiated silicon to be related to clusters of 9 or 10 vacancies. The vacancies in these clusters form neighboring hexa-rings and, therefore, minimize the number of dangling bonds. (orig.)

  19. Atom Chips

    CERN Document Server

    Folman, R; Cassettari, D; Hessmo, B; Maier, T; Schmiedmayer, J; Folman, Ron; Krüger, Peter; Cassettari, Donatella; Hessmo, Björn; Maier, Thomas

    1999-01-01

    Atoms can be trapped and guided using nano-fabricated wires on surfaces, achieving the scales required by quantum information proposals. These Atom Chips form the basis for robust and widespread applications of cold atoms ranging from atom optics to fundamental questions in mesoscopic physics, and possibly quantum information systems.

  20. Cluster headache

    Science.gov (United States)

    Histamine headache; Headache - histamine; Migrainous neuralgia; Headache - cluster; Horton's headache ... Doctors do not know exactly what causes cluster headaches. They ... (chemical in the body released during an allergic response) or ...

  1. Isotopic clusters

    International Nuclear Information System (INIS)

    Spectra of isotopically mixed clusters (dimers of SF6) are calculated as well as transition frequencies. The result leads to speculations about the suitability of the laser-cluster fragmentation process for isotope separation. (Auth.)

  2. Geometry, chemical reactivity and Raman spectra of gold clusters

    OpenAIRE

    Ngangbam Bedamani Singh; Utpal Sarkar

    2015-01-01

    Structures, stability, and chemical reactivity of Aun (n = 2-10) clusters are investigated using density functional theory (DFT). We have studied the reactivity parameters of the clusters in terms of relevant electronic structure principles. It is observed that stability and properties are strongly dependent on the cluster size. Clusters with an even number of atoms are found to be energetically and chemically more stable than odd-numbered clusters. Electronic structure of clusters has been i...

  3. Weighted Clustering

    OpenAIRE

    Ackerman, Margareta; Ben-David, Shai; Branzei, Simina; Loker, David

    2012-01-01

    We investigate a natural generalization of the classical clusteringproblem, considering clustering tasks in which differentinstances may have different weights.We conduct the firstextensive theoretical analysis on the influence of weighteddata on standard clustering algorithms in both the partitionaland hierarchical settings, characterizing the conditions underwhich algorithms react to weights. Extending a recent frameworkfor clustering algorithm selection, we propose intuitiveproperties that...

  4. Meaningful Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Sanfilippo, Antonio P.; Calapristi, Augustin J.; Crow, Vernon L.; Hetzler, Elizabeth G.; Turner, Alan E.

    2004-05-26

    We present an approach to the disambiguation of cluster labels that capitalizes on the notion of semantic similarity to assign WordNet senses to cluster labels. The approach provides interesting insights on how document clustering can provide the basis for developing a novel approach to word sense disambiguation.

  5. Formation of global energy minimim structures in the growth process of Lennard-Jones clusters

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Koshelev, Andrey; Shutovich, Andrey; Solov'yov, Andrey V.; Greiner, Walter

    2003-01-01

    We present a new theoretical framework for modelling the cluster growing process. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing paths up to the cluster sizes of 150 atoms. We demonstrate...... that in this way all known global minimum structures of the Lennard-Jones (LJ) clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic cluster structure. With its use we justify the magic numbers sequence for the clusters of noble gases atoms and compare...

  6. On the applicability of jellium model to the description of alkali clusters

    DEFF Research Database (Denmark)

    Matveentsev, Anton; Lyalin, Andrey G.; Solov'yov, Ilia;

    2003-01-01

    -density approximations we have calculated the binding energies per atom, ionization potentials, deformation parameters and optimized values of the Wigner–Seitz radii for neutral and singly charged sodium clusters with the number of atoms N<=20. The characteristics calculated within the framework of the deformed jellium...... role of the cluster shape deformations in the formation cluster properties and quite reasonable level of applicability of the deformed jellium model. This elucidates the similarities of atomic cluster physics with the physics of atomic nuclei....

  7. Cluster Effects during High Pressure Supersonic Molecular Beam Injection into Plasma

    Institute of Scientific and Technical Information of China (English)

    YAOLianghua; FENGBeibin; DONGJiafu; LIWenzhong; FENGZhen; HONGWenyu; LIBo

    2001-01-01

    When we speak of clusters, we have in mind entities which have neither the well-defined compositions, geometries, and strong bonds of conventional molecules northe boundary-independent properties of bulk matter. For example, an aggregate of a few atoms held together by Van der Waals forces constitutes a cluster. But clusters need not be weakly bound, several metal atoms bound together also constitute a cluster. Clusters need not be composed of a single kind of chemical entity, either atomic or molecular,

  8. Cluster Lenses

    CERN Document Server

    Kneib, Jean-Paul; 10.1007/s00159-011-0047-3

    2012-01-01

    Clusters of galaxies are the most recently assembled, massive, bound structures in the Universe. As predicted by General Relativity, given their masses, clusters strongly deform space-time in their vicinity. Clusters act as some of the most powerful gravitational lenses in the Universe. Light rays traversing through clusters from distant sources are hence deflected, and the resulting images of these distant objects therefore appear distorted and magnified. Lensing by clusters occurs in two regimes, each with unique observational signatures. The strong lensing regime is characterized by effects readily seen by eye, namely, the production of giant arcs, multiple-images, and arclets. The weak lensing regime is characterized by small deformations in the shapes of background galaxies only detectable statistically. Cluster lenses have been exploited successfully to address several important current questions in cosmology: (i) the study of the lens(es) - understanding cluster mass distributions and issues pertaining...

  9. Relaxation channels of multi-photon excited xenon clusters

    Energy Technology Data Exchange (ETDEWEB)

    Serdobintsev, P. Yu.; Melnikov, A. S. [Institute of Nanobiotechnologies, Peter the Great St.Petersburg Polytechnic University, Saint Petersburg 195251 (Russian Federation); Department of Physics, St. Petersburg State University, Saint Petersburg 198904 (Russian Federation); Rakcheeva, L. P., E-mail: lida@nanobio.spbstu.ru; Murashov, S. V.; Khodorkovskii, M. A. [Institute of Nanobiotechnologies, Peter the Great St.Petersburg Polytechnic University, Saint Petersburg 195251 (Russian Federation); Lyubchik, S. [REQUIMTE, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica 2829-516 (Portugal); Timofeev, N. A.; Pastor, A. A. [Department of Physics, St. Petersburg State University, Saint Petersburg 198904 (Russian Federation)

    2015-09-21

    The relaxation processes of the xenon clusters subjected to multi-photon excitation by laser radiation with quantum energies significantly lower than the thresholds of excitation of atoms and ionization of clusters were studied. Results obtained by means of the photoelectron spectroscopy method showed that desorption processes of excited atoms play a significant role in the decay of two-photon excited xenon clusters. A number of excited states of xenon atoms formed during this process were discovered and identified.

  10. Atomic bonding between metal and graphene

    KAUST Repository

    Wang, Hongtao

    2013-03-07

    To understand structural and chemical properties of metal-graphene composites, it is crucial to unveil the chemical bonding along the interface. We provide direct experimental evidence of atomic bonding between typical metal nano structures and graphene, agreeing well with density functional theory studies. Single Cr atoms are located in the valleys of a zigzag edge, and few-atom ensembles preferentially form atomic chains by self-assembly. Low migration barriers lead to rich dynamics of metal atoms and clusters under electron irradiation. We demonstrate no electron-instigated interaction between Cr clusters and pristine graphene, though Cr has been reported to be highly reactive to graphene. The metal-mediated etching is a dynamic effect between metal clusters and pre-existing defects. The resolved atomic configurations of typical nano metal structures on graphene offer insight into modeling and simulations on properties of metal-decorated graphene for both catalysis and future carbon-based electronics. © 2013 American Chemical Society.

  11. Statistical evaporation of rotating clusters

    CERN Document Server

    Calvo, F

    2003-01-01

    Unimolecular evaporation in rotating atomic clusters is investigated using phase space theory (PST) and molecular dynamics simulations. The rotational densities of states are calculated in the sphere+atom approximation, and analytical expressions are given for a radial interaction potential with the form -C/r^p. The vibrational densities of states are calculated using Monte Carlo simulations, and the average radial potential at finite temperature is obtained using a recent extension of the multiple range random-walk algorithm. These ideas are tested on simple argon clusters modelled with the Lennard-Jones (LJ) interaction potential, at several total energies and angular momenta of the parent cluster. Our results show that PST successfully reproduces the simulation data, not only the average KER but its probability distribution, for dissociations from LJ_14, for which the product cluster can effectively be considered as spherical. Even for dissociations from the nonspherical LJ_8, simulation results remain ver...

  12. Kinetic approach to the cluster liquid-gas transition

    CERN Document Server

    Calvo, F

    2004-01-01

    The liquid-gas transition in free atomic clusters is investigated theoretically based on simple unimolecular rate theories and assuming sequential evaporations. A kinetic Monte Carlo scheme is used to compute the time-dependent properties of clusters undergoing multiple dissociations, and two possible definitions of the boiling point are proposed, relying on the cluster or gas temperature. This numerical approach is supported by molecular dynamics simulations of clusters made of sodium atoms or C60 molecules, as well as simplified rate equation.

  13. Interfacial reaction rates and free energy of cubic clusters

    OpenAIRE

    Lepinoux, Joel

    2004-01-01

    Abstract A new formulation of interfacial reaction rates for clusters in binary alloys is presented. It accounts for the matrix structure and the topological properties of cluster at the atomic scale. It is shown that the probabilities per unit time that a solute atom be captured or released by a cluster are functions of the partition function but also of a transition function. The principles of calculation of these functions are general but only the case of cubic clusters is treat...

  14. Fusion process of Lennard-Jones clusters: global minima and magic numbers formation

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2004-01-01

    We present a new theoretical framework for modeling the fusion process of Lennard–Jones (LJ) clusters. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing paths up to the cluster size of 150 atoms...

  15. Atomic energy

    CERN Multimedia

    1996-01-01

    Interviews following the 1991 co-operation Agreement between the Department of Atomic Energy (DAE) of the Government of India and the European Organization for Nuclear Research (CERN) concerning the participation in the Large Hadron Collider Project (LHC) . With Chidambaram, R, Chairman, Atomic Energy Commission and Secretary, Department of Atomic Energy, Department of Atomic Energy (DAE) of the Government of India and Professor Llewellyn-Smith, Christopher H, Director-General, CERN.

  16. Atom chips

    CERN Document Server

    Reichel, Jakob

    2010-01-01

    This book provides a stimulating and multifaceted picture of a rapidly developing field. The first part reviews fundamentals of atom chip research in tutorial style, while subsequent parts focus on the topics of atom-surface interaction, coherence on atom chips, and possible future directions of atom chip research. The articles are written by leading researchers in the field in their characteristic and individual styles.

  17. Retarded and nonretarded van der Waals interactions between a cluster and a second cluster or a conducting surface

    OpenAIRE

    Calbi, M. M.; Gatica, S. M.; Velegol, D.; Cole, M. W.

    2002-01-01

    In some respects, a cluster consisting of many atoms may be regarded as a single large atom. Knowing the dielectric properties of such a cluster permits one to evaluate the form of the van der Waals (dispersion) interactions between two clusters or between one cluster and a surface. In this paper, we derive these interactions in two extreme opposite regimes of separation: fully retarded and nonretarded. In the fully retarded regime (very large separation), the magnitude of the interaction is ...

  18. Cluster ion impacts on solids

    International Nuclear Information System (INIS)

    Experimental methods for the production of cluster ions by expansion of weakly ionized plasmas through a supersonic nozzle and skimmer were described. Techniques for the production of relatively narrow mass distributions of singly charged ions containing as many as thousands of molecules of Hydrogen, Argon, Water, Alcohols and Hydrocarbons were reviewed with an explanation of the dependence of the mean cluster ion size on stagnation conditions in the ion source and the orifice geometry in nozzle or free jet expansions. Diagnostic techniques for the mass analysis and detection of these high molecule weight cluster ions were reviewed. A description of the BNL 400 kilovolt post-acceleration detection system and the advantages of secondary electron pulse distributions were presented and discussed. The application of energetic cluster ion impacts for deposition of large amounts of translational energy in thin films and solid surfaces was the main topic of the presentation. Cluster ions can be used to generate assemblies of atoms in solid surfaces with energies determined by available acceleration facilities. The production of assemblies of thousands of atoms with energies of in excess of several hundred volts per atom is readily achieved. The consequence of the ability of generate high energy densities is among other things the production of craters, cavities and in thin films holes of sizes that are smaller than those achievable by atomic ion bombardment and wet etching techniques. Examples of such results were presented showing holes in thin carbon films obtained by transmissions electron microscopy

  19. Data Clustering

    Science.gov (United States)

    Wagstaff, Kiri L.

    2012-03-01

    On obtaining a new data set, the researcher is immediately faced with the challenge of obtaining a high-level understanding from the observations. What does a typical item look like? What are the dominant trends? How many distinct groups are included in the data set, and how is each one characterized? Which observable values are common, and which rarely occur? Which items stand out as anomalies or outliers from the rest of the data? This challenge is exacerbated by the steady growth in data set size [11] as new instruments push into new frontiers of parameter space, via improvements in temporal, spatial, and spectral resolution, or by the desire to "fuse" observations from different modalities and instruments into a larger-picture understanding of the same underlying phenomenon. Data clustering algorithms provide a variety of solutions for this task. They can generate summaries, locate outliers, compress data, identify dense or sparse regions of feature space, and build data models. It is useful to note up front that "clusters" in this context refer to groups of items within some descriptive feature space, not (necessarily) to "galaxy clusters" which are dense regions in physical space. The goal of this chapter is to survey a variety of data clustering methods, with an eye toward their applicability to astronomical data analysis. In addition to improving the individual researcher’s understanding of a given data set, clustering has led directly to scientific advances, such as the discovery of new subclasses of stars [14] and gamma-ray bursts (GRBs) [38]. All clustering algorithms seek to identify groups within a data set that reflect some observed, quantifiable structure. Clustering is traditionally an unsupervised approach to data analysis, in the sense that it operates without any direct guidance about which items should be assigned to which clusters. There has been a recent trend in the clustering literature toward supporting semisupervised or constrained

  20. Experimental study of multicharged sodium clusters stability generated by collision of neutral clusters with ions

    International Nuclear Information System (INIS)

    The aim of this thesis is to study the stability of a sodium cluster with respect to a positive charge excess. In the experiment, clusters of several atoms to about a thousand of atoms were obtained using a gaseous thermalization type source. A two stages Wiley-McLaren type time-of-flight mass spectrometer was built for the experiment but with a better focalization. A mass resolution above 2000 is obtained around the 1100 u ma mass, and mono-charged sodium clusters up to 700 atoms can be separated. The sequential ionization of a neutral clusters with a laser pulse can lead to hot multicharged clusters (with atom evaporation). The maximum cluster charge is limited by the photon energy. The interaction between neutral clusters and ions shows the coexistence of two ionization processes: the remote capture of electrons by the ion coulomb field and the statistical electron emission following the electronic excitation of the cluster when an ion goes through it. When the ion charge increases, the first process becomes predominant and corresponds to a diminution of multicharged clusters temperature and critical size. In conclusion, the interaction between neutral clusters with ions allows to produce multicharged clusters with variable charge, size and temperature. This method seems to be of prime importance for fragmentation study of unstable structures. (J.S.). 72 refs., 90 figs., 16 tabs

  1. Cluster Chemistry

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    @@ Cansisting of eight scientists from the State Key Laboratory of Physical Chemistry of Solid Surfaces and Xiamen University, this creative research group is devoted to the research of cluster chemistry and creation of nanomaterials.After three-year hard work, the group scored a series of encouraging progresses in synthesis of clusters with special structures, including novel fullerenes, fullerene-like metal cluster compounds as well as other related nanomaterials, and their properties study.

  2. Atomic Physics

    CERN Document Server

    Foot, Christopher J

    2007-01-01

    This text will thoroughly update the existing literature on atomic physics. Intended to accompany an advanced undergraduate course in atomic physics, the book will lead the students up to the latest advances and the applications to Bose-Einstein Condensation of atoms, matter-wave inter-ferometry and quantum computing with trapped ions. The elementary atomic physics covered in the early chapters should be accessible to undergraduates when they are first introduced to the subject. To complement. the usual quantum mechanical treatment of atomic structure the book strongly emphasizes the experimen

  3. Atom interferometry

    International Nuclear Information System (INIS)

    We will first present a development of the fundamental principles of atom interferometers. Next we will discuss a few of the various methods now available to split and recombine atomic De Broglie waves, with special emphasis on atom interferometers based on optical pulses. We will also be particularly concerned with high precision interferometers with long measurement times such those made with atomic fountains. The application of atom interferometry to the measurement of the acceleration due to gravity will be detailed. We will also develop the atom interferometry based on adiabatic transfer and we will apply it to the measurement of the photon recoil in the case of the Doppler shift of an atomic resonance caused by the momentum recoil from an absorbed photon. Finally the outlook of future developments will be given. (A.C.)

  4. Electronic state of helium atoms in nickel metal

    International Nuclear Information System (INIS)

    The molecular orbital calculations are carried out for model clusters to investigate the electronic state of the interstitial helium atoms implanted into nickel metal. The computational method used is the discrete variational Xα (DV-Xα) method. In order to study the difference in the electronic structures of helium atoms between at the tetrahedral site and at the octahedral one, the computations are performed using model clusters, Ni4He and Ni6He. The bond strength is evaluated by the use of Mulliken population analysis. The computations are also carried out for the larger cluster Ni14He to investigate the size effect of the cluster model. Furthermore, the electronic structure of the He9 cluster in Ni metal is studied, using the Ni14He9 cluster model which includes both of tetrehedral and octahedral interstitial He atoms. This paper discusses the interactions between He and Ni atoms when both interstitial He atoms coexist. (orig.)

  5. Sixteenth International Conference on the physics of electronic and atomic collisions

    International Nuclear Information System (INIS)

    This report contains abstracts of papers on the following topics: photons, electron-atom collisions; electron-molecule collisions; electron-ion collisions; collisions involving exotic species; ion- atom collisions, ion-molecule or atom-molecule collisions; atom-atom collisions; ion-ion collisions; collisions involving rydberg atoms; field assisted collisions; collisions involving clusters and collisions involving condensed matter

  6. Sixteenth International Conference on the physics of electronic and atomic collisions

    Energy Technology Data Exchange (ETDEWEB)

    Dalgarno, A.; Freund, R.S.; Lubell, M.S.; Lucatorto, T.B. (eds.)

    1989-01-01

    This report contains abstracts of papers on the following topics: photons, electron-atom collisions; electron-molecule collisions; electron-ion collisions; collisions involving exotic species; ion- atom collisions, ion-molecule or atom-molecule collisions; atom-atom collisions; ion-ion collisions; collisions involving rydberg atoms; field assisted collisions; collisions involving clusters and collisions involving condensed matter.

  7. Cancer Clusters

    Science.gov (United States)

    ... of cancer. Cancer clusters can help scientists identify cancer-causing substances in the environment. For example, in the early 1970s, a cluster ... the area and time period over which the cancers were diagnosed. They also ask about specific environmental hazards or concerns in the affected area. If ...

  8. Rearrangement of cluster structure during fission processes

    DEFF Research Database (Denmark)

    Lyalin, Andrey G.; Obolensky, Oleg I.; Solov'yov, Andrey V.;

    2004-01-01

    groups of atoms from the parent cluster is largely independent of the isomer form of the parent cluster. The importance of rearrangement of the cluster structure during the fission process is elucidated. This rearrangement may include transition to another isomer state of the parent cluster before actual......Results of molecular dynamics simulations of fission reactions $Na_10^2+ -->Na_7^++ Na_3^+ and Na_18^2+--> 2Na_9^+ are presented. The dependence of the fission barriers on the isomer structure of the parent cluster is analysed. It is demonstrated that the energy necessary for removing homothetic...

  9. Phase-transitions and nuclear clusterization

    International Nuclear Information System (INIS)

    After reviewing some basic features of the temperature-governed phase-transitions in macroscopic systems and in atomic nuclei we consider non-thermal phase-transitions of nuclear structure in the example of cluster states. Phenomenological and semimicroscopical algebraic cluster models with identical interactions are applied to binary cluster systems of closed and non-closed shell clusters. Phase-transitions are observed in each case between the rotational (rigid molecule-like) and vibrational (shell-like) cluster states. The phase of this finite quantum system shows a quasi-dynamical symmetry. (author)

  10. Clustering processes

    CERN Document Server

    Ryabko, Daniil

    2010-01-01

    The problem of clustering is considered, for the case when each data point is a sample generated by a stationary ergodic process. We propose a very natural asymptotic notion of consistency, and show that simple consistent algorithms exist, under most general non-parametric assumptions. The notion of consistency is as follows: two samples should be put into the same cluster if and only if they were generated by the same distribution. With this notion of consistency, clustering generalizes such classical statistical problems as homogeneity testing and process classification. We show that, for the case of a known number of clusters, consistency can be achieved under the only assumption that the joint distribution of the data is stationary ergodic (no parametric or Markovian assumptions, no assumptions of independence, neither between nor within the samples). If the number of clusters is unknown, consistency can be achieved under appropriate assumptions on the mixing rates of the processes. (again, no parametric ...

  11. Schroedinger atom

    International Nuclear Information System (INIS)

    Features of an electrodynamical interpretation suggested by Schroedinger for the wave function are discribed. According to this conception electron charges are continuously distributed all over the volume of an atomic system. The proof is given that classical electrodynamics keeps its action inside atom. Schroedinger's atom has been shown to be the only model in which electrones do not lose their energy for emission when they move around nucleus. A significance of the distributed electron charge self-field is estimated. Practical applications of this conception have been noted including the new trend in quantum electrodynamics. Experimental and theoretical corroborations of the atom model with a continuous electron charge are adduced

  12. Atomic physics

    International Nuclear Information System (INIS)

    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 23Po,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 23Po level of helium-like krypton

  13. Palladium clusters deposited on the heterogeneous substrates

    Science.gov (United States)

    Wang, Kun; Liu, Juanfang; Chen, Qinghua

    2016-07-01

    To improve the performance of the Pd composite membrane prepared by the cold spraying technology, it is extremely essential to give insights into the deposition process of the cluster and the heterogeneous deposition of the big Pd cluster at the different incident velocities on the atomic level. The deposition behavior, morphologies, energetic and interfacial configuration were examined by the molecular dynamic simulation and characterized by the cluster flattening ratio, the substrate maximum local temperature, the atom-embedded layer number and the surface-alloy formation. According to the morphology evolution, three deposition stages and the corresponding structural and energy evolution were clearly identified. The cluster deformation and penetrating depth increased with the enhancement of the incident velocity, but the increase degree also depended on the substrate hardness. The interfacial interaction between the cluster and the substrate can be improved by the higher substrate local temperature. Furthermore, it is found that the surface alloys were formed by exchanging sites between the cluster and substrate atoms, and the cluster atoms rearranged following as the substrate lattice arrangement from bottom to up in the deposition course. The ability and scope of the structural reconstruction are largely determined by both the size and incident energy of the impacted cluster.

  14. Sputtered Clusters from Niobium-Vanadium Alloys

    DEFF Research Database (Denmark)

    Schou, Jørgen; Hofer, W. O.

    1982-01-01

    A series of Nb&z.sbnd;V alloys have been irradiated by 6 keV argon ions. Homonuclear and heteronuclear clusters emitted from these alloys have been studied by means of post-ionization and/or secondary ion mass spectrometry. The intensity of clusters of atomic masses up to approximately 300 amu wa...

  15. Clusters in strong laser fields: Comparison between carbon, platinum, and lead clusters

    Science.gov (United States)

    Schumacher, M.; Teuber, S.; Köller, L.; Köhn, J.; Tiggesbäumker, J.; Meiwes-Broer, K. H.

    Carbon and metal clusters are excited by strong femtosecond laser pulses with up to 1016 W/cm2, yielding ionized clusters and highly charged atomic ions. For small carbon clusters and fullerenes the abundance of charged species correlates with the laser power, while for metal clusters the ionization efficiency is additionally strongly affected by the chosen laser pulse width which may result in an enhanced up-charging of the metal particle. In the case of platinum atomic charge states up to z=20 are detected at a pulse duration of about 600 fs. This observation is in accordance with a model based on a multi-plasmon excitation process.

  16. Emergence of antiferromagnetic ordering in Mn clusters

    International Nuclear Information System (INIS)

    First-principles density-functional-theory investigations of small Mnn (n=2-7,13) clusters reveal a competition between ferromagnetic and antiferromagnetic ordering of atomic magnetic moments. For smaller sizes (n≤6), this competition results in a near degeneracy between the two types of orderings, whereas AF arrangements are clearly favored for larger clusters. The calculations thus predict a size-dependent transition in the magnetic ordering of Mn clusters

  17. Clustering analysis

    International Nuclear Information System (INIS)

    Cluster analysis is the name of group of multivariate techniques whose principal purpose is to distinguish similar entities from the characteristics they process.To study this analysis, there are several algorithms that can be used. Therefore, this topic focuses to discuss the algorithms, such as, similarity measures, and hierarchical clustering which includes single linkage, complete linkage and average linkage method. also, non-hierarchical clustering method, which is popular name K-mean method' will be discussed. Finally, this paper will be described the advantages and disadvantages of every methods

  18. Cluster editing

    DEFF Research Database (Denmark)

    Böcker, S.; Baumbach, Jan

    2013-01-01

    The Cluster Editing problem asks to transform a graph into a disjoint union of cliques using a minimum number of edge modifications. Although the problem has been proven NP-complete several times, it has nevertheless attracted much research both from the theoretical and the applied side. The...... algorithms for biological problems. © 2013 Springer-Verlag....... problem has been the inspiration for numerous algorithms in bioinformatics, aiming at clustering entities such as genes, proteins, phenotypes, or patients. In this paper, we review exact and heuristic methods that have been proposed for the Cluster Editing problem, and also applications of these...

  19. Cluster analysis

    CERN Document Server

    Everitt, Brian S; Leese, Morven; Stahl, Daniel

    2011-01-01

    Cluster analysis comprises a range of methods for classifying multivariate data into subgroups. By organizing multivariate data into such subgroups, clustering can help reveal the characteristics of any structure or patterns present. These techniques have proven useful in a wide range of areas such as medicine, psychology, market research and bioinformatics.This fifth edition of the highly successful Cluster Analysis includes coverage of the latest developments in the field and a new chapter dealing with finite mixture models for structured data.Real life examples are used throughout to demons

  20. Spitzer Clusters

    Science.gov (United States)

    Krick, Kessica

    This proposal is a specific response to the strategic goal of NASA's research program to "discover how the universe works and explore how the universe evolved into its present form." Towards this goal, we propose to mine the Spitzer archive for all observations of galaxy groups and clusters for the purpose of studying galaxy evolution in clusters, contamination rates for Sunyaev Zeldovich cluster surveys, and to provide a database of Spitzer observed clusters to the broader community. Funding from this proposal will go towards two years of support for a Postdoc to do this work. After searching the Spitzer Heritage Archive, we have found 194 unique galaxy groups and clusters that have data from both the Infrared array camera (IRAC; Fazio et al. 2004) at 3.6 - 8 microns and the multiband imaging photometer for Spitzer (MIPS; Rieke et al. 2004) at 24microns. This large sample will add value beyond the individual datasets because it will be a larger sample of IR clusters than ever before and will have sufficient diversity in mass, redshift, and dynamical state to allow us to differentiate amongst the effects of these cluster properties. An infrared sample is important because it is unaffected by dust extinction while at the same time is an excellent measure of both stellar mass (IRAC wavelengths) and star formation rate (MIPS wavelengths). Additionally, IRAC can be used to differentiate star forming galaxies (SFG) from active galactic nuclei (AGN), due to their different spectral shapes in this wavelength regime. Specifically, we intend to identify SFG and AGN in galaxy groups and clusters. Groups and clusters differ from the field because the galaxy densities are higher, there is a large potential well due mainly to the mass of the dark matter, and there is hot X-ray gas (the intracluster medium; ICM). We will examine the impact of these differences in environment on galaxy formation by comparing cluster properties of AGN and SFG to those in the field. Also, we will

  1. Growth mechanisms for doped clusters

    International Nuclear Information System (INIS)

    Structural growth mechanisms for metal doped nanoclusters are investigated in combined experimental and theoretical studies. In particular, silicon, copper and gold clusters incorporating a transition metal dopant atom are investigated: SinX (X=Cu, V), CunSc+ and AunY+ with n < 20. The doped clusters are produced with a dual-target dual-laser vaporization source. Structural information about the doped nanoclusters is provided by infrared multi-photon dissociation spectroscopy. Their size and composition dependent stability is studied with photofragmentation and mass spectrometry. A detailed understanding of the role of the dopant atom in the structural growth and in the electronic structure of the clusters is obtained by comparison with quantum chemical computations using density functional theory. (review)

  2. Indication of a size-dependent transition from molecular to dissociative chemisorption on clusters

    OpenAIRE

    Burkart, Stefan; Blessing, Nico; Ganteför, Gerd

    1999-01-01

    We report experimental indications for a size-dependent change of the chemical nature of chemisorption on small atomic clusters. We studied chemisorption of atomic hydrogen on negatively charged Tin- clusters using mass and photoelectron spectroscopy. Our experimental data support the assumption that for clusters with up to four Ti atoms, adsorption of intact H2 molecules is the energetically preferred configuration. For larger Tin clusters with n>4, dissociative hydrogen chemisorption is the...

  3. Atomic physics

    CERN Document Server

    Born, Max

    1989-01-01

    The Nobel Laureate's brilliant exposition of the kinetic theory of gases, elementary particles, the nuclear atom, wave-corpuscles, atomic structure and spectral lines, electron spin and Pauli's principle, quantum statistics, molecular structure and nuclear physics. Over 40 appendices, a bibliography, numerous figures and graphs.

  4. Structure and properties of small sodium clusters

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2002-01-01

    and the results of other theoretical work. We have systematically calculated the optimized geometries of neutral and singly charged sodium clusters having up to 20 atoms, their multipole moments (dipole and quadrupole), static polarizabilities, binding energies per atom, ionization potentials, and...

  5. Cluster Bulleticity

    OpenAIRE

    Massey, Richard; Kitching, Thomas D.; Nagai, Daisuke

    2010-01-01

    The unique properties of dark matter are revealed during collisions between clusters of galaxies, like the bullet cluster (1E 0657-56) and baby bullet (MACSJ0025-12). These systems provide evidence for an additional, invisible mass in the separation between the distribution of their total mass, measured via gravitational lensing, and their ordinary 'baryonic' matter, measured via its X-ray emission. Unfortunately, the information available from these systems is limited by th...

  6. Cluster Bulleticity

    OpenAIRE

    Massey, R; Kitching, T.; Nagai, D.

    2010-01-01

    The unique properties of dark matter are revealed during collisions between clusters of galaxies, such as the bullet cluster (1E 0657−56) and baby bullet (MACS J0025−12). These systems provide evidence for an additional, invisible mass in the separation between the distributions of their total mass, measured via gravitational lensing, and their ordinary ‘baryonic’ matter, measured via its X-ray emission. Unfortunately, the information available from these systems is limited by their rarity. C...

  7. Molecular dynamics simulation of melting behaviours of supported cobalt cluster

    International Nuclear Information System (INIS)

    The molecular dynamics simulation combined with the simulated annealing method are used to study the melting behaviors of free cobalt clusters and two kinds of supported cobalt clusters with cluster size ranging from 400 to 2000 atoms. Gupta potential is used for the cobalt - cobalt interactions in Co clusters. Influences on the melting properties are discussed with two kinds of supported potentials: the Lennard-Jones potential and the Morse potential. Our results reveal that with the same number of cobalt atoms and the same cobalt-substrate interation stength, the melting points and pre-melting intervals of the two kinds of supported Co clusters are all in reasonable agreement with each other. With increasing the depth of supported potential, the melting points increase for the supported cluster. Similar to the case of free clusters, the linear relation between the melting point and the inverse of cluster's size cube root is also found for the two kinds of supported clusters. (authors)

  8. Sequential desorption energy of hydrogen from nickel clusters

    Energy Technology Data Exchange (ETDEWEB)

    Deepika,; Kumar, Rakesh, E-mail: rakesh@iitrpr.ac.in [Department of Physics, Indian Institute of Technology Ropar, Rupnagar-140001 (India); R, Kamal Raj. [Indian Institute of Science Education and Research Kolkata, Mohanpur-741246 (India); Kumar, T. J. Dhilip [Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar-140001 (India)

    2015-06-24

    We report reversible Hydrogen adsorption on Nickel clusters, which act as a catalyst for solid state storage of Hydrogen on a substrate. First-principles technique is employed to investigate the maximum number of chemically adsorbed Hydrogen molecules on Nickel cluster. We observe a maximum of four Hydrogen molecules adsorbed per Nickel atom, but the average Hydrogen molecules adsorbed per Nickel atom decrease with cluster size. The dissociative chemisorption energy per Hydrogen molecule and sequential desorption energy per Hydrogen atom on Nickel cluster is found to decrease with number of adsorbed Hydrogen molecules, which on optimization may help in economical storage and regeneration of Hydrogen as a clean energy carrier.

  9. Sequential desorption energy of hydrogen from nickel clusters

    International Nuclear Information System (INIS)

    We report reversible Hydrogen adsorption on Nickel clusters, which act as a catalyst for solid state storage of Hydrogen on a substrate. First-principles technique is employed to investigate the maximum number of chemically adsorbed Hydrogen molecules on Nickel cluster. We observe a maximum of four Hydrogen molecules adsorbed per Nickel atom, but the average Hydrogen molecules adsorbed per Nickel atom decrease with cluster size. The dissociative chemisorption energy per Hydrogen molecule and sequential desorption energy per Hydrogen atom on Nickel cluster is found to decrease with number of adsorbed Hydrogen molecules, which on optimization may help in economical storage and regeneration of Hydrogen as a clean energy carrier

  10. Electronic excitation processes in rare gas clusters studied by electron energy loss spectroscopy

    International Nuclear Information System (INIS)

    We present the electron energy loss spectra for Ar clusters as a function of incident electron energy and of cluster size. In spectra measured with 100 eV incident electron energy the bulk excitation peak becomes visible for a mean cluster size above 170 atoms per cluster. For 250 eV incident electron energy the bulk excitation peak is clearly observable even for a mean cluster size of 120 atoms per cluster. These experimental results are qualitatively reproduced by a simple calculation that accounts for the mean free path of electrons in Ar clusters; i.e., the penetration depth of incident electrons into the cluster.

  11. Atomic level analysis of biomolecules by the scanning atom probe

    International Nuclear Information System (INIS)

    Utilizing the unique features of the scanning atom probe (SAP) the binding states of the biomolecules, leucine and methionine, are investigated at atomic level. The molecules are mass analyzed by detecting a single atom and/or clustering atoms field evaporated from a specimen surface. Since the field evaporation is a static process, the evaporated clustering atoms are closely related with the binding between atoms forming the molecules. For example, many thiophene radicals are detected when polythiophene is mass analyzed by the SAP. In the present study the specimens are prepared by immersing a micro cotton ball of single walled carbon nanotubes (SWCNT) in the leucine or methionine solution. The mass spectra obtained by analyzing the cotton balls exhibit singly and doubly ionized carbon ions of SWCNT and the characteristic fragments of the molecules, CH3, CHCH3, C4H7, CHNH2 and COOH for leucine and CH3, SCH3, C2H4, C4H7, CHNH2 and COOH for methionine.

  12. Composite-cluster states and alternative architectures for one-way quantum computation

    OpenAIRE

    Milne, Darran F.; Korolkova, Natalia V.

    2012-01-01

    We propose a new architecture for the measurement-based quantum computation model. The new design relies on small composite light-atom primary clusters. These are then assembled into cluster arrays using ancillary light modes and the actual computation is run on such a cellular cluster. We show how to create the primary clusters, which are Gaussian cluster states composed of both light and atomic modes. These are entangled via QND interactions and beamsplitters and the scheme is well describe...

  13. Electron motion enhanced high harmonic generation in xenon clusters

    CERN Document Server

    Li, Na; Bai, Ya; Peng, Peng; Li, Ruxin; Xu, Zhizhan

    2016-01-01

    Atomic clusters presents an isolated system that models the bulk materials whose mechanism of HHG remains uncertain, and a promising medium to produce HHG beyond the limited conversion efficiency for gaseous atoms. Here we reveal that the oscillation of collective electron motion within clusters develops after the interaction of intense laser fields, and it significantly enhances the harmonic dipole and increases the quantum phase of the harmonics. Experimentally, the phase matching conditions of HHG from nanometer xenon clusters and atoms are distinguished, which confirms the enhanced internal field that was proposed theoretically a decade ago. The separation of HHG from atoms and clusters allows the determination of the amplitude of the HHG for clusters to be 5 orders higher, corresponding to 4 times higher conversion efficiency for atomic response. The finding provides an insight on the HHG mechanism of bulk materials and a means by which an efficient coherent X-ray source can be developed.

  14. Superposition of Fragment Excitations for Excited States of Large Clusters with Application to Helium Clusters.

    Science.gov (United States)

    Closser, Kristina D; Ge, Qinghui; Mao, Yuezhi; Shao, Yihan; Head-Gordon, Martin

    2015-12-01

    We develop a local excited-state method, based on the configuration interaction singles (CIS) wave function, for large atomic and molecular clusters. This method exploits the properties of absolutely localized molecular orbitals (ALMOs), which strictly limits the total number of excitations, and results in formal scaling with the third power of the system size for computing the full spectrum of ALMO-CIS excited states. The derivation of the equations and design of the algorithm are discussed in detail, with particular emphasis on the computational scaling. Clusters containing ∼500 atoms were used in evaluating the scaling, which agrees with the theoretical predictions, and the accuracy of the method is evaluated with respect to standard CIS. A pioneering application to the size dependence of the helium cluster spectrum is also presented for clusters of 25-231 atoms, the largest of which results in the computation of 2310 excited states per sampled cluster geometry. PMID:26609558

  15. Metal Clusters and Nuclei: some Similarities and Differences

    CERN Document Server

    Haberland, H

    1999-01-01

    Atomic nuclei and simple metal clusters exhibit several surprising similarities. Some of the cluster properties are discussed, which have an analogue in nuclear physics, such as magic numbers, single and collective excitations, higher excitations of the Giant Dipole Resonance, etc. As an example of a difference the solid to liquid phase transitions of clusters is described.

  16. Metal Clusters and Nuclei: some Similarities and Differences

    International Nuclear Information System (INIS)

    Atomic nuclei and simple metal clusters exhibit several surprising similarities. Some of the cluster properties are discussed, which have an analogue in nuclear physics, such as magic numbers, single and collective excitations, higher excitations of the Giant Dipole Resonance, etc. As an example of a difference the solid to liquid phase transitions of clusters is described

  17. Formation and stability of sputtered clusters

    International Nuclear Information System (INIS)

    Current theory for the formation of sputtered clusters states that either atoms are sputtered individually and aggregate after having left the surface or they are sputtered as complete clusters. There is no totally sharp boundary between the two interpretations, but experimental evidence is mainly thought to favour the latter model. Both theories demand a criterion for the stability of the clusters. In computer simulations of sputtering, the idea has been to use the same interaction potential as in the lattice computations to judge the stability. More qualitatively, simple geometrical shapes have also been looked for. It is found here, that evidence for 'magic numbers' and electron parity effects in clusters have existed in the sputtering literature for a long time, making more sophisticated stability criteria necessary. The breakdown of originally sputtered metastable clusters into stable clusters gives strong support to the 'sputtered as clusters' hypothesis. (author)

  18. Gold-cluster ranges in aluminium, silicon and copper

    Energy Technology Data Exchange (ETDEWEB)

    Andersen, H.H. E-mail: nimb@fys.ku.dk; Johansen, A.; Olsen, M.; Touboltsev, V

    2003-12-01

    Single atom Au and Au{sub 2}, Au{sub 3} and Au{sub 7} clusters with energies of 10-100 keV/atom have been implanted at low fluence into Al, Si and Cu targets, the Au{sub 7} clusters only at 44.3 keV/atom into Si. The range distributions were analyzed by oblique (15 deg. ) incidence RBS. In no case was the range found to be different for the cluster implant from that of the atomic implant at equal velocity, implying the nuclear stopping to be identical, but the 10 keV/atom implant in Cu showed the cluster distributions to be substantially broader than those of the atomic implants. The energies were thus too high to observe a possible 'clearing the way' effect, but the Cu results hint at a 'within spike' diffusion mechanism.

  19. Denominators of cluster variables

    OpenAIRE

    Buan, Aslak Bakke; Marsh, Robert J.; Reiten, Idun

    2007-01-01

    Associated to any acyclic cluster algebra is a corresponding triangulated category known as the cluster category. It is known that there is a one-to-one correspondence between cluster variables in the cluster algebra and exceptional indecomposable objects in the cluster category inducing a correspondence between clusters and cluster-tilting objects. Fix a cluster-tilting object T and a corresponding initial cluster. By the Laurent phenomenon, every cluster variable can be written as a Laurent...

  20. Enhanced magnetocrystalline anisotropy in deposited cobalt clusters

    International Nuclear Information System (INIS)

    The magnetic properties of nanomaterials made by embedding cobalt nanocrystals in a copper matrix have been studied using a SQUID magnetometer. The remanent magnetization at temperatures down to 1.8 K and the RT (room temperature) field-dependent magnetization of 1000- and 8000-atom (average-size) cobalt cluster samples have been measured. In all cases it has been possible to relate the morphology of the material to the magnetic properties. However, it is found that the deposited cluster samples contain a majority of sintered clusters even at cobalt concentrations as low as 5% by volume. The remanent magnetization of the 8000-atom samples was found to be bimodal, consisting of one contribution from spherical particles and one from touching (sintered) clusters. Using a Monte Carlo calculation to simulate the sintering it has been possible to calculate a size distribution which fits the RT superparamagnetic behaviour of the 1000-atom samples. The remanent magnetization for this average size of clusters could then be fitted to a simple model assuming that all the nanoparticles are spherical and have a size distribution which fits the superparamagnetic behaviour. This gives a value for the potential energy barrier height (for reversing the spin direction) of 2.0 μeV/atom which is almost four times the accepted value for face-centred-cubic bulk cobalt. The remanent magnetization for the spherical component of the large-cluster sample could not be fitted with a single barrier height and it is conjectured that this is because the barriers change as a function of cluster size. The average value is 1.5 μeV/atom but presumably this value tends toward the bulk value (0.5 μeV/atom) for the largest clusters in this sample. (author)

  1. Cluster size and substrate temperature affecting thin film formation during copper cluster deposition on a Si (001) surface

    Institute of Scientific and Technical Information of China (English)

    Gong Heng-Feng; Lü Wei; Wang Lu-Min; Li Gong-Ping

    2012-01-01

    The soft deposition of Cu clusters on a Si (001) surface was studied by molecular dynamics simulations.The embedded atom method,the Stillinger-Weber and the Lennar Jones potentials were used to describe the interactions between the cluster atoms,between the substrate atoms,and between the cluster and the substrate atoms,respectively.The Cu13,Cu55,and Cu147 clusters were investigated at different substrate temperatures.We found that the substrate temperature had a significant effect on the Cu147 cluster.For smaller Cu13 and Cu55 clusters,the substrate temperature in the range of study appeared to have little effect on the mean center-of-mass height.The clusters showed better degrees of epitaxy at 800 K.With the same substrate temperature,the Cu55 cluster demonstrated the highest degree of epitaxy,followed by Cu147 and then Cu13 clusters.In addition,the Cu55 cluster showed the lowest mean center-of-mass height.These results suggested that the Cu55 cluster is a better choice for the thin-film formation among the clusters considered.Our studies may provide insight into the formation of desired Cu thin films on a Si substrate.

  2. Study of aluminum-doped silicon clusters

    International Nuclear Information System (INIS)

    Using full-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have investigated the effect of aluminum heteroatoms on the geometric structures and bond characteristics of Si n (n=5-10) clusters in detail. It is found that the geometric framework of the ground state structures for Si n (n=5-10) clusters change to some extent upon the substitution of Al atoms in some Si atoms. The effect of aluminum doping on the silicon clusters depends on the geometric structures of Si n (n=5-10) clusters. In particular, the calculations suggest that the aluminum doping would improve the bond strength of some Si-Si bonds in the mixed Si n-m Al m clusters

  3. Non-nearest neighbour ICD in clusters

    Science.gov (United States)

    Fasshauer, E.

    2016-04-01

    Interatomic Coulombic decay (ICD) is an electronic decay process of excited, ionized systems. It has been shown to occur in a multitude of small and large systems. The effects of more than one possible decay partner are discussed in detail illustrated by simulated ICD electron spectra of NeAr clusters and pure Ne clusters. Hereby, the mostly underestimated contribution of decay with non-nearest neighbours is highlighted. In the neon clusters, the lifetime of the bulk atoms is found to be in excellent agreement with experiment (Jahnke et al 2004 Phys. Rev. Lett. 93 173401) while the lifetimes of the surface atoms differ significantly. Hence, the experimental lifetime can not purely be explained by the effect of the number of neighbours. We propose the possibility to investigate the transition from small clusters to the solid state by using the ICD electron spectra to distinguish between icosahedral and cuboctahedral cluster structures.

  4. Cluster Bulleticity

    CERN Document Server

    Massey, Richard; Nagai, Daisuke

    2010-01-01

    The unique properties of dark matter are revealed during collisions between clusters of galaxies, like the bullet cluster (1E 0657-56) and baby bullet (MACSJ0025-12). These systems provide evidence for an additional, invisible mass in the separation between the distribution of their total mass, measured via gravitational lensing, and their ordinary 'baryonic' matter, measured via its X-ray emission. Unfortunately, the information available from these systems is limited by their rarity. Constraints on the properties of dark matter, such as its interaction cross-section, are therefore restricted by uncertainties in the individual systems' impact velocity, impact parameter and orientation with respect to the line of sight. Here we develop a complementary, statistical measurement in which every piece of substructure falling into every massive cluster is treated as a bullet. We define 'bulleticity' as the mean separation between dark matter and ordinary matter, and we measure a positive signal in hydrodynamical si...

  5. Re4As6S3, a thio-spinel-related cluster system

    DEFF Research Database (Denmark)

    Besnard, Celine; Svensson, Christer; Ståhl, Kenny;

    2003-01-01

    rhenium atoms form tetrahedral clusters linked via tetrahedral arsenic clusters to produce an NaCl-type arrangement. The oxidation state of rhenium is IV and the number of electrons shared by the rhenium atoms in the cluster is 12. The structure is based on an ordered defect thio-spinel A((1-x))B(2)X(4...

  6. Anion photoelectron spectroscopy of germanium and tin clusters containing a transition- or lanthanide-metal atom; MGe(n)- (n = 8-20) and MSn(n)- (n = 15-17) (M = Sc-V, Y-Nb, and Lu-Ta).

    Science.gov (United States)

    Atobe, Junko; Koyasu, Kiichirou; Furuse, Shunsuke; Nakajima, Atsushi

    2012-07-14

    The electronic properties of germanium and tin clusters containing a transition- or lanthanide-metal atom from group 3, 4, or 5, MGe(n) (M = Sc, Ti, V, Y, Zr, Nb, Lu, Hf, and Ta) and MSn(n) (M = Sc, Ti, Y. Zr, and Hf), were investigated by anion photoelectron spectroscopy at 213 nm. In the case of the group 3 elements Sc, Y, and Lu, the threshold energy of electron detachment of MGe(n)(-) exhibits local maxima at n = 10 and 16, while in the case of the group 4 elements Ti, Zr, and Hf, it exhibits a local minimum only at n = 16, associated with the presence of a small bump in the spectrum. A similar behavior is observed for MSn(n)(-) around n = 16, and these electronic characteristics of MGe(n) and MSn(n) are closely related to those of MSi(n). Compared to MSi(n), however, the larger cavity size of a Ge(n) cage allows metal atom encapsulation at a smaller size n. A cooperative effect between the electronic and geometric structures of clusters with a large cavity of Ge(16) or Sn(16) is discussed together with the results of experiments that probe their geometric stability via their reactivity to H(2)O adsorption. PMID:22333909

  7. Chemical Reactions of Silicon Clusters

    CERN Document Server

    Ramakrishna, M V; Ramakrishna, Mushti V.; Pan, Jun

    1994-01-01

    Smalley and co-workers discovered that chemisorption reactivities of silicon clusters vary over three orders of magnitude as a function of cluster size. In particular, they found that \\Si{33}, \\Si{39}, and \\Si{45} clusters are least reactive towards various reagents compared to their immediate neighbors in size. We explain these observations based on our stuffed fullerene model. This structural model consists of bulk-like core of five atoms surrounded by fullerene-like surface. Reconstruction of the ideal fullerene geometry gives rise to four-fold coordinated crown atoms and $\\pi$-bonded dimer pairs. This model yields unique structures for \\Si{33}, \\Si{39}, and \\Si{45} clusters without any dangling bonds and thus explains their lowest reactivity towards chemisorption of closed shell reagents. This model is also consistent with the experimental finding of Jarrold and Constant that silicon clusters undergo a transition from prolate to spherical shapes at \\Si{27}. We justify our model based on an in depth analys...

  8. Cluster-surface interaction: from soft landing to implantation

    DEFF Research Database (Denmark)

    Popok, Vladimir; Barke, Ingo; Campbell, Eleanor E.B.;

    2011-01-01

    . For cluster-surface interactions, one of the important scenarios is the low-energy regime where the kinetic energy per atom of the accelerated cluster stays well below the binding (cohesive) energy of the cluster constituents. This case is often called soft landing: the deposition typically does not......The current paper presents a state-of-the-art review in the field of interaction of atomic and molecular clusters with solids. We do not attempt to overview the entire broad field but rather concentrate on impact phenomena: how the physics of the cluster-surface interaction depends on the kinetic...... deposition and implantation, i.e. slight cluster embedding into the surface – otherwise known as cluster pinning. At higher impact energies, cluster structure is lost and the impact results in local damage of the surface and often in crater and hillock formation. We consider both experimental data and...

  9. Atomic secrecy

    International Nuclear Information System (INIS)

    An article, The H-Bomb Secret: How We Got It, Why We're Telling It, by Howard Morland was to be published in The Progressive magazine in February, 1979. The government, after learning of the author's and the editors' intention to publish the article and failing to persuade them to voluntarily delete about 20% of the text and all of the diagrams showing how an H-bomb works, requested a court injunction against publication. Acting under the Atomic Energy Act of 1954, US District Court Judge Robert W. Warren granted the government's request on March 26. Events dealing with the case are discussed in this publication. Section 1, Progressive Hydrogen Bomb Case, is discussed under the following: Court Order Blocking Magazine Report; Origins of the Howard Morland Article; Author's Motives, Defense of Publication; and Government Arguments Against Disclosure. Section 2, Access to Atomic Data Since 1939, contains information on need for secrecy during World War II; 1946 Atomic Energy Act and its effects; Soviet A-Bomb and the US H-Bomb; and consequences of 1954 Atomic Energy Act. Section 3, Disputed Need for Atomic Secrecy, contains papers entitled: Lack of Studies on H-Bomb Proliferation; Administration's Position on H-Bombs; and National Security Needs vs Free Press

  10. Fuzzy Clustering

    DEFF Research Database (Denmark)

    Berks, G.; Keyserlingk, Diedrich Graf von; Jantzen, Jan;

    2000-01-01

    and clustering are the basic concerns in medicine. Classification depends on definitions of the classes and their required degree of participant of the elements in the cases' symptoms. In medicine imprecise conditions are the rule and therefore fuzzy methods are much more suitable than crisp ones...

  11. Quotients of cluster categories

    OpenAIRE

    Jorgensen, Peter

    2007-01-01

    Higher cluster categories were recently introduced as a generalization of cluster categories. This paper shows that in Dynkin types A and D, half of all higher cluster categories are actually just quotients of cluster categories. The other half can be obtained as quotients of 2-cluster categories, the "lowest" type of higher cluster categories. Hence, in Dynkin types A and D, all higher cluster phenomena are implicit in cluster categories and 2-cluster categories. In contrast, the same is not...

  12. Thermal stability of helium-vacancy clusters in iron

    International Nuclear Information System (INIS)

    Molecular dynamics calculations were performed to evaluate the thermal stability of helium-vacancy clusters (HenVm) in Fe using the Ackland Finnis-Sinclair potential, the Wilson-Johnson potential and the Ziegler-Biersack-Littmark-Beck potential for describing the interactions of Fe-Fe, Fe-He and He-He, respectively. Both the calculated numbers of helium atoms, n, and vacancies, m, in clusters ranged from 0 to 20. The binding energies of an interstitial helium atom, an isolated vacancy and a self-interstitial iron atom to a helium-vacancy cluster were obtained from the calculated formation energies of clusters. All the binding energies do not depend much on cluster size, but they primarily depend on the helium-to-vacancy ratio (n/m) of clusters. The binding energy of a vacancy to a helium-vacancy cluster increases with the ratio, showing that helium increases cluster lifetime by dramatically reducing thermal vacancy emission. On the other hand, both the binding energies of a helium atom and an iron atom to a helium-vacancy cluster decrease with increasing the ratio, indicating that thermal emission of self-interstitial atoms (SIAs) (i.e. Frenkel-pair production), as well as thermal helium emission, may take place from the cluster of higher helium-to-vacancy ratios. The thermal stability of clusters is decided by the competitive processes among thermal emission of vacancies, SIAs and helium, depending on the helium-to-vacancy ratio of clusters. The calculated thermal stability of clusters is consistent with the experimental observations of thermal helium desorption from α-Fe during post-He-implantation annealing

  13. Universal four-boson system: dimer-atom-atom Efimov effect and recombination reactions

    OpenAIRE

    Deltuva, A.

    2013-01-01

    Recent theoretical developments in the four-boson system with resonant interactions are described. Momentum-space scattering equations for the four-particle transition operators are used. The properties of unstable tetramers with approximate dimer-atom-atom structure are determined. In addition, the three- and four-cluster recombination processes in the four-boson system are studied.

  14. Size Determination of Argon Clusters from a Rayleigh Scattering Experiment

    Institute of Scientific and Technical Information of China (English)

    LEI An-Le; ZHAI Hua-Jin; LIU Bing-Chen; LI Zhong; NI Guo-Yuan; XU Zhi-Zhan

    2000-01-01

    Argon clusters are produced in the process of adiabatic expansion of a high backing pressure gas into vacuum through a nozzle. The cluster size is determined by a Rayleigh scattering measurement. The scattered signal measured is proportional to the 2.78th power of gas stagnation pressure. The average cluster sizes vary from 100 to more than 12000 atoms/cluster with the argon gas backing pressures ranging between 3 to 45 atm.

  15. Cluster fission from the standpoint of nuclear fission

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sangmoo [Tsukuba Univ., Ibaraki (Japan). Inst. of Physics

    1996-03-01

    Atomic nucleus belongs to a quantal finite many body system. Nucleus shows great resemblance to cluster, above all metal cluster, although the strength of interaction is different. The works of Brechignac group, Saunder, Martin and P. Froeblich are explained by the critical size Nc as the central term. The differences between cluster and nucleus are investigated and a future view of cluster fission is explained. (S.Y.)

  16. Regional Innovation Clusters

    Data.gov (United States)

    Small Business Administration — The Regional Innovation Clusters serve a diverse group of sectors and geographies. Three of the initial pilot clusters, termed Advanced Defense Technology clusters,...

  17. Atomic theories

    CERN Document Server

    Loring, FH

    2014-01-01

    Summarising the most novel facts and theories which were coming into prominence at the time, particularly those which had not yet been incorporated into standard textbooks, this important work was first published in 1921. The subjects treated cover a wide range of research that was being conducted into the atom, and include Quantum Theory, the Bohr Theory, the Sommerfield extension of Bohr's work, the Octet Theory and Isotopes, as well as Ionisation Potentials and Solar Phenomena. Because much of the material of Atomic Theories lies on the boundary between experimentally verified fact and spec

  18. Atoms as Qed bound atoms

    International Nuclear Information System (INIS)

    The relevance of Quantum Electrodynamics (Qed) in contemporary atomic structure theory is reviewed. Recent experimental advances allow both the production of heavy ions of high charge as well as the measurement of atomic properties with a precision never achieved before. The description of heavy atoms with few electrons via the successive incorporation of one, two, etcetera photons in a rigorous manner and within the bound state Furry representation of Qed is technically feasible. For many-electron atoms the many-body (correlation) effects are very important and it is practically impossible to evaluate all the relevant Feynman diagrams to the required accuracy. Thus, it is necessary to develop a theoretical scheme in which the radiative and nonradiative effects are taken into account in an effective way making emphasis in electronic correlation. Preserving gauge invariance, and avoiding both continuum dissolution and variational collapse are basic problems that must be solved when using effective potential methods and finite-basis representations of them. In this context, we shall discuss advances and problems in the description of atoms as Qed bound states. (Author)

  19. Reactive cluster model of metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Travis E. [Molecular Theory Group, Colorado School of Mines, Golden, Colorado 80401 (United States); School of Physics, The University of Sydney, Sydney, New South Wales 2006 (Australia); Miorelli, Jonathan; Eberhart, Mark E. [Molecular Theory Group, Colorado School of Mines, Golden, Colorado 80401 (United States)

    2014-02-28

    Though discovered more than a half century ago metallic glasses remain a scientific enigma. Unlike crystalline metals, characterized by short, medium, and long-range order, in metallic glasses short and medium-range order persist, though long-range order is absent. This fact has prompted research to develop structural descriptions of metallic glasses. Among these are cluster-based models that attribute amorphous structure to the existence of clusters that are incommensurate with crystalline periodicity. Not addressed, however, are the chemical factors stabilizing these clusters and promoting their interconnections. We have found that glass formers are characterized by a rich cluster chemistry that above the glass transformation temperature promotes exchange as well as static and vibronic sharing of atoms between clusters. The vibronic mechanism induces correlated motions between neighboring clusters and we hypothesize that the distance over which these motions are correlated mediates metallic glass stability and influences critical cooling rates.

  20. Configurations and magnetic properties of Mn-B binary clusters

    Science.gov (United States)

    Cui-Ju, FENG; Bin-Zhou, MI

    2016-05-01

    We investigate the structures and magnetic properties of boron-doped manganese clusters using first-principle density functional theory. We arrive at the lowest energy structures for clusters by simultaneously optimizing the cluster geometries, total spins, and relative orientations of individual atomic moments. For MnnB (n=2-12) clusters, the theoretical results indicate that the B atom prefers the surface site for all the lowest-energy structures except Mn10B cluster. The doped B atom enhances the stability of pure Mnn cluster. We also have studied the magnetic behavior of Mn-B clusters in the size range. Based on the analysis of the different magnetic behavior of boron-doped manganese clusters, we have further studied Mn9B2 and Mn8B3 clusters and it indicates that the doping of non-magnetism B element can induce all the Mn atoms align ferromagnetic coupling. Furthermore, a stable pearl necklace nanowire ([Mn8B3]n→∞) which retains the ferromagnetic ordering of all the manganese atoms has been predicted.

  1. Structure and dynamics of Lennard-Jones clusters with impurities

    International Nuclear Information System (INIS)

    Molecular dynamics simulations and Lennard-Jones potentials have been used to study binary mixed clusters. The low temperature structures, impurity solvation and the melting and freezing transitions for different values of the relative atomic size and interaction energy have been studied for A13B, A12B, A55B and A13B13 clusters. For A13B large impurities do not solvate even for high interaction energy. For A55B larger impurities remain on the surface for low interaction energies but solvate as the energy of interaction increases. The presence of the impurity very strongly affects the solid-liquid transition. Icosahedral structures remain as the minimum energy configurations for A13B13 clusters with atoms of the same size and different interaction energies. For A13B13 clusters with atoms of the same interaction energy and different size, smaller atoms go inside surrounded by the bigger surface atoms. (orig.)

  2. Rotation of small clusters in sheared metallic glasses

    International Nuclear Information System (INIS)

    Graphical abstract: When a Cu50Ti50 metallic glass is shear-deformed, the irreversible rearrangement of local structures allows the rigid body rotation of clusters. Highlights: → A shear-deformed Cu50Ti50 metallic glass was studied by molecular dynamics. → Atomic displacements occur at irreversible rearrangements of local structures. → The dynamics of such events includes the rigid body rotation of clusters. → Relatively large clusters can undergo two or more complete rotations. - Abstract: Molecular dynamics methods were used to simulate the response of a Cu50Ti50 metallic glass to shear deformation. Attention was focused on the atomic displacements taking place during the irreversible rearrangement of local atomic structures. It is shown that the apparently disordered dynamics of such events hides the rigid body rotation of small clusters. Cluster rotation was investigated by evaluating rotation angle, axis and lifetimes. This permitted to point out that relatively large clusters can undergo two or more complete rotations.

  3. Static dipole polarizabilities of Scn (n ≤ 15) clusters

    International Nuclear Information System (INIS)

    The static dipole polarizabilities of scandium clusters with up to 15 atoms are determined by using the numerically finite field method in the framework of density functional theory. The electronic effects on the polarizabilities are investigated for the scandium clusters. We examine a large highest occupied molecular orbital — the lowest occupied molecular orbital (HOMO–LUMO) gap of a scandium cluster usually corresponds to a large dipole moment. The static polarizability per atom decreases slowly and exhibits local minimum with increasing cluster size. The polarizability anisotropy and the ratio of mean static polarizability to the HOMO–LUMO gap can also reflect the cluster stability. The polarizability of the scandium cluster is partially related to the HOMO–LUMO gap and is also dependent on geometrical characteristics. A strong correlation between the polarizability and ionization energy is observed. (atomic and molecular physics)

  4. Sputtering of clusters from copper-gold alloys

    International Nuclear Information System (INIS)

    Polycrystalline Cu, Cu20Au80, Cu40Au60, Cu80Au20 and Au samples were bombarded with 15 keV Ar+, and the resulting secondary neutral yield distribution was studied by non-resonant laser post-ionisation mass spectrometry. Neutral clusters containing up to 15 atoms were observed for the targets. The yield of neutral clusters, CumAun-m, containing n atoms, Yn, was found to follow a power in n, i.e. Yn∝n-δ, where the exponent δ varied from 5.2 to 10.1. For a fixed n, the cluster yields showed a variation with number of copper atoms, m, much greater than expected for a binomial distribution suggesting that the clusters are not formed randomly above the surface and a component of preformed cluster emission occurs. In addition, the cluster compositions from the sputtered alloys were indicative of sputtering from a copper rich surface.

  5. Clustering experiments

    CERN Document Server

    Wang, Zhengwei; Tan, Ken; Di, Zengru; Roehner, Bertrand M

    2011-01-01

    It is well known that bees cluster together in cold weather, in the process of swarming (when the ``old'' queen leaves with part of the colony) or absconding (when the queen leaves with all the colony) and in defense against intruders such as wasps or hornets. In this paper we describe a fairly different clustering process which occurs at any temperature and independently of any special stimulus or circumstance. As a matter of fact, this process is about four times faster at 28 degree Celsius than at 15 degrees. Because of its simplicity and low level of ``noise'' we think that this phenomenon can provide a means for exploring the strength of inter-individual attraction between bees or other living organisms. For instance, and at first sight fairly surprisingly, our observations showed that this attraction does also exist between bees belonging to different colonies. As this study is aimed at providing a comparative perspective, we also describe a similar clustering experiment for red fire ants.

  6. Cerium Oxyhydroxide Clusters: Formation, Structure and Reactivity

    Energy Technology Data Exchange (ETDEWEB)

    Frederic Aubriet; Jean-Jacques Gaumet; Wibe A de Jong; Groenewold, Gary S (058000); Gianotto, Anita K (057404); McIlwain, Michael E (051783); Michael J. Van Stipdonk; Christopher M. Leavitt

    2009-06-01

    Cerium oxyhydroxide cluster anions were produced by irradiating ceric oxide particles using 355 nm laser pulses that were synchronized with pulses of nitrogen gas admitted to the irradiation chamber. The gas pulse stabilized the nascent clusters that are largely anhydrous [CexOy] ions and neutrals. These initially-formed species react with water, principally forming closed-shell (c-s) oxohydroxy species that are described by the general formula [CexOy(OH)z]-. In general, the extent of hydroxylation varies from a value of 3 OH per Ce atom when x = 1 to a value slightly greater than 1 for x > 8. The Ce3 and Ce6 species deviate significantly from this trend: the x = 3 cluster accommodates more hydroxyl moieties compared to neighboring congeners at x = 2 and x = 4. Conversely, the x = 6 cluster is significantly less hydroxylated. Density functional theory (DFT) modeling of the cluster structures show that the hydrated clusters are hydrolyzed, and contain one-to-multiple hydroxide moieties, but not datively bound water. DFT also predicts an energetic preference for formation of highly symmetric structures as the size of the clusters increases. The calculated structures indicate that the ability of the Ce3 oxyhydroxide to accommodate more extensive hydroxylation is due to a more open, hexagonal structure in which the Ce atoms can participate in multiple hydrolysis reactions. Conversely the Ce6 oxyhydroxide has an octahedral structure that is not conducive to hydrolysis. In addition to the c-s clusters, open-shell (o-s) oxyhydroxides and superoxides are also formed, and they become more prominent as the size of the clusters increases, suggesting that the larger ceria clusters have an increased ability to stabilize a non-bonding electron. The overall intensity of the clusters tends to monotonically decrease as the cluster size increases, however this trend is interrupted at Ce13, which is significantly more stable compared to neighboring congeners, suggesting formation of

  7. Cerium Oxyhydroxide Clusters: Formation, Structure and Reactivity

    Energy Technology Data Exchange (ETDEWEB)

    Aubriet, F.; Gaumet, Jean-Jacques; De Jong, Wibe A.; Groenewold, G. S.; Gianotto, Anita K.; McIIwain, Michael E.; Van Stipdonk, Michael J.; Leavitt, Christopher M.

    2009-05-11

    Cerium oxyhydroxide cluster anions were produced by irradiating ceric oxide particles using 355 nm laser pulses that were synchronized with pulses of nitrogen gas admitted to the irradiation chamber. The gas pulse stabilized the nascent clusters that are largely anhydrous [CexOy] ions and neutrals. These initially-formed species react with water, principally forming closed-shell (c-s) oxohydroxy species that are described by the general formula [CexOy(OH)z]-. In general, the extent of hydroxylation varies from a value of 3 OH per Ce atom when x = 1 to a value slightly greater than 1 for x > 8. The Ce3 and Ce6 species deviate significantly from this trend: the x = 3 cluster accommodates more hydroxyl moieties compared to neighboring congeners at x = 2 and x = 4. Conversely, the x = 6 cluster is significantly less hydroxylated. Density functional theory (DFT) modeling of the cluster structures show that the hydrated clusters are hydrolyzed, and contain one-to-multiple hydroxide moieties, but not datively bound water. DFT also predicts an energetic preference for formation of highly symmetric structures as the size of the clusters increases. The calculated structures indicate that the ability of the Ce3 oxyhydroxide to accommodate more extensive hydroxylation is due to a more open, hexagonal structure in which the Ce atoms can participate in multiple hydrolysis reactions. Conversely the Ce6 oxyhydroxide has an octahedral structure that is not conducive to hydrolysis. In addition to the c-s clusters, open-shell (o-s) oxyhydroxides and superoxides are also formed, and they become more prominent as the size of the clusters increases, suggesting that the larger ceria clusters have an increased ability to stabilize a non-bonding electron. The overall intensity of the clusters tends to monotonically decrease as the cluster size increases, however this trend is interrupted at Ce13, which is significantly more stable compared to neighboring congeners, suggesting formation of

  8. Photofragmentation and photoabsorption cross sections for mass selected argon cluster ions, n = 3 to 108

    International Nuclear Information System (INIS)

    A tandem time-of-flight mass spectrometer is used to measure photofragmentation mass spectra and optical absorption spectra of mass selected argon cluster ions in the n=3 to 108 atoms per cluster range. (orig.)

  9. Factor PD-Clustering

    OpenAIRE

    Gettler Summa, Mireille; Palumbo, Francesco; Tortora, Cristina

    2012-01-01

    Factorial clustering methods have been developed in recent years thanks to the improving of computational power. These methods perform a linear transformation of data and a clustering on transformed data optimizing a common criterion. Factorial PD-clustering is based on Probabilistic Distance clustering (PD-clustering). PD-clustering is an iterative, distribution free, probabilistic, clustering method. Factor PD-clustering make a linear transformation of original variables into a reduced numb...

  10. Ionic recoil energies in the Coulomb explosion of metal clusters

    Science.gov (United States)

    Teuber, S.; Döppner, T.; Fennel, T.; Tiggesbäumker, J.; Meiwes-Broer, K. H.

    The photoionization of metal clusters in intense femtosecond laser fields has been studied. In contrast to an experiment on atoms, the interaction in this case leads to a very efficient and high charging of the particle where tens of electrons per atom are ejected from the cluster. The recoil energy distribution of the atomic fragment ions was measured which in the case of lead clusters exceeds 180 keV. Enhanced charging efficiency which we observed earlier for specific pulse conditions is not reflected in the recoil energy spectra. Both the average and the maximum energies decrease with increasing laser pulse width. This is in good agreement with molecular dynamics calculations.

  11. CO dissociation on magnetic Fen clusters

    KAUST Repository

    Jedidi, Abdesslem

    2014-01-01

    This work theoretically investigates the CO dissociation on Fen nanoparticles, for n in the range of 1-65, focusing on size dependence in the context of the initial step of the Fischer-Tropsch reaction. CO adsorbs molecularly through its C-end on a triangular facet of the nanoparticle. Dissociation becomes easier when the cluster size increases. Then, the C atom is bonded to a square facet that is generated as a result of the adsorption if it does not yet exist in the bare cluster, while the O atom is adsorbed on a triangular facet. In the most stable situation, the two adsorbed atoms remain close together, both having in common one shared first-neighbor iron atom. There is a partial spin quenching of the neighboring Fe atoms, which become more positively charged than the other Fe atoms. The shared surface iron atom resembles a metal-cation from a complex. Despite the small size of the iron cluster considered, fluctuations due to specific configurations do not influence properties for n > 25 and global trends seem significant.

  12. Molecular dynamics simulation of gas clusters impact on solid targets

    International Nuclear Information System (INIS)

    The interaction of a cluster of Arn (n=87-300) on a gold and silicon substrate was simulated by use of ordinary and Langevin Molecular Dynamics. The cluster was prepared by cutting out of a spherical f.c.c. block of Dynamics. The Buckingham potential was used for an interaction between the argon atoms. The excitation of the argon atoms due to high temperature and/or high pressure inside the cluster have been taken into account by use of a Monte-Carlo procedure. The N-body potential proposed by Rosato for gold and Axilrod-Teller 3-body potential for silicon was used, which describes well equilibrium properties of bulk material. The substrate was modeled using a b.c.c. lattice (for gold) and diamond (for silicon) of about 30000 atoms. These atoms were separated into three regions, depending on how near they are the impact zone. The atoms of central impact zone are being described by NM. The next zone consists of several semi-spherical layers of a thermal bath, for which the LMD was used. All the other atoms represent the movable (in radial direction) or rigid framework. The kinetic energy of the clusters is varied from 10 to 100 eV/atom. It has been shown that the impact of energetic Ar cluster with the kinetic energy of 100 eV/atom on a gold target sputters not only single atoms but also small gold clusters in the 10 atoms range. Lateral sputtering of gold target material has been predicted. Preliminary results for argon clusters implantation into the silicon (111) shows that this process seems to be quite small due to the very weak bond energy between argon and silicon atoms

  13. Influence of Dynamics on Magic Numbers for Silicon Clusters

    CERN Document Server

    Porter, A R

    1997-01-01

    We present the results of over 90 tight-binding molecular-dynamics simulations of collisions between three- and five-atom silicon clusters, at a system temperature of 2000K. Much the most likely products are found to be two 'magic' four-atom clusters. We show that previous studies, which focused on the equilibrium binding energies of clusters of different sizes, are of limited relevance, and introduce a new effective binding energy which incorporates the highly anharmonic dynamics of the clusters. The inclusion of dynamics enhances the magic nature of both Si4 and Si6 and destroys that of Si7.

  14. Molecular dynamical simulations of melting behaviors of metal clusters

    International Nuclear Information System (INIS)

    The melting behaviors of metal clusters are studied in a wide range by molecular dynamics simulations. The calculated results show that there are fluctuations in the heat capacity curves of some metal clusters due to the strong structural competition; For the 13-, 55- and 147-atom clusters, variations of the melting points with atomic number are almost the same; It is found that for different metal clusters the dynamical stabilities of the octahedral structures can be inferred in general by a criterion proposed earlier by F. Baletto et al. [J. Chem. Phys. 116 3856 (2002)] for the statically stable structures

  15. Small rare gas clusters in XUV laser pulses

    CERN Document Server

    Bauer, D

    2003-01-01

    Semi-classical molecular dynamics simulations of small rare gas clusters in short laser pulses of 100 nm wavelength were performed. For comparison, the cluster response to 800 nm laser pulses was investigated as well. The inner ionization dynamics of the multi-electron atoms inside the cluster was treated explicitly. The simulation results underpin that at XUV wavelengths collisions play an important role in the energy absorption and the generation of the surprisingly high charge states of Xe atoms inside clusters, as they were observed in the free-electron laser experiment at DESY, Hamburg, Germany [Wabnitz et al., Nature 420, 482 (2002)].

  16. Computer simulation structure and vibrations of small metal cluster on the Cu (111) surface

    International Nuclear Information System (INIS)

    Vibrational properties of the small tetrahedral cluster of Co on the Cu (111) surface are studied by using tight-binding second moment approximation interatomic interaction potentials. It was shown that interaction of the clusters with substrate leads to arising of frustrated translation and frustrated rotation in-plane polarized vibrational modes localized on the cluster atoms. The Co4 cluster on the surface the high frequency modes remain strongly localized and mixed with the nearest neighbor atoms vibrations

  17. Magnetic properties of icosahedral MRu12 clusters

    International Nuclear Information System (INIS)

    The magnetic properties of icosahedral MRu12 clusters are studied using the discrete-variational local-spin-density-functional method, where M = V, Cr, Mn, Fe, Co, and Ni. The results show that all of the Ih MRu12 clusters, just like the case for the Ih Ru13 cluster, have double magnetic solutions. In contrast to the moment of 4 μB for the Ih Ru13 cluster, the total magnetic moments of the Ih MRu12 clusters, ranging from 1 μB to 20 μB, have been changed greatly by the substitution of the central Ru atom with M. Among them, the NiRu12 cluster has a giant moment of 20 μB. Furthermore, the NiRu12 cluster has nondegenerate ground state and could be expected to be remarkably stable. Therefore, for the purpose of enhancing the magnetic moment of the Ih Ru13 cluster, Ni is a promising candidate as a dopant. Finally, we predict that all the Ih MRu12 clusters except NiRu12 might belong to the class in which the magnetization of the cluster increases with temperature. (author)

  18. Theoretical Study of Hydrogenated Tetrahedral Aluminum Clusters

    CERN Document Server

    Ichikawa, Kazuhide; Wagatsuma, Ayumu; Watanabe, Kouhei; Szarek, Pawel; Tachibana, Akitomo

    2011-01-01

    We report on the structures of aluminum hydrides derived from a tetrahedral aluminum Al4 cluster using ab initio quantum chemical calculation. Our calculation of binding energies of the aluminum hydrides reveals that stability of these hydrides increases as more hydrogen atoms are adsorbed, while stability of Al-H bonds decreases. We also analyze and discuss the chemical bonds of those clusters by using recently developed method based on the electronic stress tensor.

  19. Cluster automorphisms and compatibility of cluster variables

    OpenAIRE

    Assem, Ibrahim; Schiffler, Ralf; Shramchenko, Vasilisa

    2013-01-01

    In this paper, we introduce a notion of unistructural cluster algebras, for which the set of cluster variables uniquely determines the clusters. We prove that cluster algebras of Dynkin type and cluster algebras of rank 2 are unistructural, then prove that if $\\mathcal{A}$ is unistructural or of Euclidean type, then $f: \\mathcal{A}\\to \\mathcal{A}$ is a cluster automorphism if and only if $f$ is an automorphism of the ambient field which restricts to a permutation of the cluster variables. In ...

  20. Globular Cluster Formation in the Virgo Cluster

    CERN Document Server

    Moran, C Corbett; Lake, G

    2014-01-01

    Metal poor globular clusters (MPGCs) are a unique probe of the early universe, in particular the reionization era. Systems of globular clusters in galaxy clusters are particularly interesting as it is in the progenitors of galaxy clusters that the earliest reionizing sources first formed. Although the exact physical origin of globular clusters is still debated, it is generally admitted that globular clusters form in early, rare dark matter peaks (Moore et al. 2006; Boley et al. 2009). We provide a fully numerical analysis of the Virgo cluster globular cluster system by identifying the present day globular cluster system with exactly such early, rare dark matter peaks. A popular hypothesis is that that the observed truncation of blue metal poor globular cluster formation is due to reionization (Spitler et al. 2012; Boley et al. 2009; Brodie & Strader 2006); adopting this view, constraining the formation epoch of MPGCs provides a complementary constraint on the epoch of reionization. By analyzing both the l...

  1. DNA templates silver clusters with magic sizes and colors for multi-cluster fluorescent assemblies

    Science.gov (United States)

    Copp, Stacy

    2015-03-01

    The natural inclusion of information in DNA, a vital part of life's rich complexity, can also be exploited to create diverse structures with multiple scales of complexity. Now emerging in novel photonic applications, DNA-stabilized silver clusters (AgN-DNA) are compelling examples of multi-scale DNA-directed assembly: individual fluorescent clusters, each templated by specific DNA base motifs, can then be arranged together in DNA-mediated multi-cluster assemblies with nanoscale precision. We discuss how DNA imbues AgN-DNA with unique features. Our optical data on pure AgN-DNA show that DNA base-cationic silver ligands impose rod-like shapes for neutral silver clusters, whose length primarily determines fluorescence color. This shape anisotropy leads to the aspherical AgN-DNA magic number cluster sizes and ``magic color'' groupings. We exploit DNA's sequence properties to extract multi-base motifs that select certain magic cluster sizes, using machine learning algorithms applied to large data sets. With these base motifs, we design DNA scaffolds to arrange multiple atomically precise AgN together in nanoscale proximity. We demonstrate that clusters are stable when held at separations below 10 nm, both in bicolor, dual cluster DNA clamp assemblies and in one-dimensional assemblies of atomically precise clusters arrayed on DNA nanotubes. Supported by NSF-CHE-1213895 and NSF-DMR-1309410. SMC acknowledges NSF-DGE-1144085, a NSF GRFP.

  2. Adaptive Evolutionary Clustering

    OpenAIRE

    Xu, Kevin S.; Kliger, Mark; Hero III, Alfred O.

    2011-01-01

    In many practical applications of clustering, the objects to be clustered evolve over time, and a clustering result is desired at each time step. In such applications, evolutionary clustering typically outperforms traditional static clustering by producing clustering results that reflect long-term trends while being robust to short-term variations. Several evolutionary clustering algorithms have recently been proposed, often by adding a temporal smoothness penalty to the cost function of a st...

  3. Relational visual cluster validity

    OpenAIRE

    Ding, Y.; Harrison, R F

    2007-01-01

    The assessment of cluster validity plays a very important role in cluster analysis. Most commonly used cluster validity methods are based on statistical hypothesis testing or finding the best clustering scheme by computing a number of different cluster validity indices. A number of visual methods of cluster validity have been produced to display directly the validity of clusters by mapping data into two- or three-dimensional space. However, these methods may lose too much information to corre...

  4. Exotic atoms

    International Nuclear Information System (INIS)

    The experiments use a solid hydrogen layer to form muonic hydrogen isotopes that escape into vacuum. The method relies on transfer of the muon from protium to either a deuteron or a triton. The resulting muonic deuterium or muonic tritium will not immediately thermalize because of the very low elastic cross sections, and may be emitted from the surface of the layer. Measurements which detect decay electrons, muonic x-rays, and fusion products have been used to study the processes. A target has been constructed which exploits muonic atom emission in order to learn more about the energy dependence of transfer and muon molecular formation

  5. Atomic Clocks

    Science.gov (United States)

    Wynands, Robert

    Time is a strange thing. On the one hand it is arguably the most inaccessible physical phenomenon of all: both in that it is impossible to manipulate or modify—for all we know—and in that even after thousands of years mankind's philosophers still have not found a fully satisfying way to understand it. On the other hand, no other quantity can be measured with greater precision. Today's atomic clocks allow us to reproduce the length of the second as the SI unit of time with an uncertainty of a few parts in 1016—orders of magnitude better than any other quantity. In a sense, one can say [1

  6. Single atom measurement and atomic manipulation using atomic force microscope

    International Nuclear Information System (INIS)

    This paper explains studies to measure atomic force as the force linking an atom and atom, using an atomic force microscope (AFM). First, it describes the principle and device configuration of AFM, and as an example of the atomic force measurement of Si atoms on the surface of Si(111)-(7x7), it describes the technique to measure atomic force using AFM, as well as the uncertainty of probe tip against atomic force. In addition, it describes the following items on the measurement results of chemical bonding force: (1) chemical bonding force vs physical force and chemical bonding force vs current on the surface of Si(111)-(7x7), (2) chemical bonding force and element dependence on the surface of Si/Sn(111)-(√3x√3), (3) atomic manipulation based on AMF, and (4) relationship between atomic manipulation and the size of chemical bonding force with a probe. (A.O.)

  7. Sputtered Clusters from Niobium-Vanadium Alloys

    DEFF Research Database (Denmark)

    Schou, Jørgen; Hofer, W. O.

    1982-01-01

    A series of Nb&z.sbnd;V alloys have been irradiated by 6 keV argon ions. Homonuclear and heteronuclear clusters emitted from these alloys have been studied by means of post-ionization and/or secondary ion mass spectrometry. The intensity of clusters of atomic masses up to approximately 300 amu was...... related to the concentrations of Nb and V in the alloys. In addition, the behaviour of polyatomic cluster yields as a function of partial oxygen pressure was studied. At partial pressures larger than approximately 10 6Torr, the yields decreased with increasing partial pressures. By inclusion of the post...

  8. Density functional theory study on geometrical structure and magnetisms of RhnBe(n=1∼7) clusters

    International Nuclear Information System (INIS)

    Geometrical structures and magnetisms of RhnBe(n=1∼7) clusters were studied by using generalized gradient approximation in the density functional theory. The results show that the structures of Rhn in RhnBe clusters are similar to that of the corresponding Rhn cluster. The bond length between Rh atoms connected with Be atom in RhnBe clusters is larger than that between Rh atoms in Rhn cluster. The changes of stability in RhnBe and Rhn clusters with cluster size are similar to each other, but RhnBe clusters are more stable. Be atoms lose electrons and the magnetic moments become smaller in all RhnBe clusters. All Rh atoms connected with Be atom receive electrons. Magnetic moments of RhnBe clusters are due mainly to Rh atoms. If Be atom has positive magnetic moment, the magnetic moment of RhnBe cluster is larger than that of Rhn cluster, else it is smaller. (authors)

  9. Electronic and magnetic properties of CrGen (15 ⩽ n ⩽ 29) clusters: A DFT study

    Science.gov (United States)

    Mahtout, Sofiane; Tariket, Yacine

    2016-06-01

    We report ab initio calculations of electronic and magnetic properties of medium-sized CrGen (15 ⩽ n ⩽ 29) clusters using density functional theory. The encapsulation of Cr atoms within Gen clusters leads to stable Cr encapsulated Gen clusters. The binding energies generally increase while the differences between the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO gaps) generally decrease with the increasing of cluster size. The clusters of CrGen at size 16, 17, 19, 22, 24 and 29 exhibit high stabilities when compared to their neighbors. This has been discussed in terms of their structures, energies and the effect of the position of doping atom. Doping of Gen clusters with one Cr atom leads to CrGen clusters with magnetic moment depending on the structure of the clusters and the position of Cr atom in the clusters. Moreover, vertical ionization potential, vertical electronic affinity, and chemical hardness are also analyzed.

  10. The Density Functional Theory Study of Structural and Electronical Properties of ZnO Clusters

    Directory of Open Access Journals (Sweden)

    O.V. Bovgyra

    2013-03-01

    Full Text Available Density functional theory studies of structural and electronic properties of small clusters were performed. For each cluster an optimization of structure and the basic properties of the band structure were conducted. It was determined that with increasing (n energetically more efficient in the small clusters is stabilization from the ring to fulleren-like structures containing tetragonal and hexagonal faces and all atoms have coordination number equal three. Among the clusters (ZnO12 with doped atoms most stable are clusters where Zn was replaced by Mn, Cu and Co atoms. Band gap in the electronic spectrum of doped clusters decreases due to p-d hybridization orbitals of the impurity atom with the orbitals of the oxygen atom.

  11. Optical response of small magnesium clusters

    CERN Document Server

    Solovyov, I A; Greiner, W; Solovyov, Ilia A.; Solovyov, Andrey V.; Greiner, Walter

    2004-01-01

    We predict the strong enhancement in the photoabsorption of small Mg clusters in the region of 4-5 eV due to the resonant excitation of the plasmon oscillations of cluster electrons. The photoabsorption spectra for neutral Mg clusters consisting of up to N=11 atoms have been calculated using ab initio framework based on the time dependent density functional theory (TDDFT). The nature of predicted resonances has been elucidated by comparison of the results of the ab initio calculations with the results of the classical Mie theory. The splitting of the plasmon resonances caused by the cluster deformation is analysed. The reliability of the used calculation scheme has been proved by performing the test calculation for a number of sodium clusters and the comparison of the results obtained with the results of other methods and experiment.

  12. CdS clusters in pores of zeolite X

    International Nuclear Information System (INIS)

    The crystal structures of the hydrated and dehydrated forms of zeolites involving CdS clusters are determined by X-ray diffraction. Crystals with the CdS clusters obtained by repeated exchanges in a Na2S solution or treatment with H2S vapor are investigated. It is found that only the CdS molecules are located in the large cavities of the CdX(Na2S) crystals. The CdX(H2S) crystals contain the [Cd20S13]14+ clusters in the large cavities. It is shown that these clusters are built up around the S atoms, which are situated at the centers of the large cavities of zeolite and coordinated tetrahedrally by Cd atoms. These atoms are bound through sulfur atoms with Cd cations situated near the walls of the cavity in the environment of the aluminosilicate framework oxygens

  13. Atomistic studies of nucleation of He clusters and bubbles in bcc iron

    Science.gov (United States)

    Yang, L.; Deng, H. Q.; Gao, F.; Heinisch, H. L.; Kurtz, R. J.; Hu, S. Y.; Li, Y. L.; Zu, X. T.

    2013-05-01

    Atomistic simulations of the nucleation of He clusters and bubbles in bcc iron at 800 K have been carried out using the newly developed Fe-Fe interatomic potential, along with Ackland potential for the Fe-Fe interactions. Microstructure changes were analyzed in detail. We found that a He cluster with four He atoms is able to push out an iron interstitial from the cluster, creating a Frenkel pair. Small He clusters and self-interstitial atom (SIA) can migrate in the matrix, but He-vacancy (He-V) clusters are immobile. Most SIAs form clusters, and only the dislocation loops with a Burgers vector of b = 1/2 appear in the simulations. SIA clusters (or loops) are attached to He-V clusters for He implantation up to 1372 appm, while the He-V cluster-loop complexes with more than one He-V cluster are formed at the He concentration of 2057 appm and larger.

  14. 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.

  15. Noble Gas Clusters and Nanoplasmas in High Harmonic Generation

    CERN Document Server

    Aladi, M; Rácz, P; Földes, I B

    2015-01-01

    We report a study of high harmonic generation from noble gas clusters of xenon atoms in a gas jet. Harmonic spectra were investigated as a function of backing pressure, showing spectral shifts due to the nanoplasma electrons in the clusters. At certain value of laser intensity this process may oppose the effect of the well-known ionization-induced blueshift. In addition, these cluster-induced harmonic redshifts may give the possibility to estimate cluster density and cluster size in the laser-gas jet interaction range.

  16. What is the ground-state structure of intermediate-sized carbon clusters?

    OpenAIRE

    Yu, Ming; Chaudhuri, Indira; Leahy, C.; Jayanthi, C. S.; Wu, S Y

    2008-01-01

    A comprehensive study on the relative structural stability of various nanostructures of carbon clusters (including fullerenes, cages, onions, icosahedral clusters, bucky-diamond clusters, spherically bulk terminated clusters, and clusters with faceted termination) in the range of d < 5 nm has been carried out using a semi-empirical method based on a self-consistent and environment-dependent/linear combination of atomic orbital (SCED-LCAO) Hamiltonian. It was found that among these nanostructu...

  17. Geometry, chemical reactivity and Raman spectra of gold clusters

    Directory of Open Access Journals (Sweden)

    Ngangbam Bedamani Singh

    2015-12-01

    Full Text Available Structures, stability, and chemical reactivity of Aun (n = 2-10 clusters are investigated using density functional theory (DFT. We have studied the reactivity parameters of the clusters in terms of relevant electronic structure principles. It is observed that stability and properties are strongly dependent on the cluster size. Clusters with an even number of atoms are found to be energetically and chemically more stable than odd-numbered clusters. Electronic structure of clusters has been investigated using partial density of states (PDOS. PDOS analysis clearly shows that energy states of highest occupied molecular orbital and lowest unoccupied molecular orbital are predominantly contributed by s orbital. From time-dependent DFT calculations, it is shown that absorption spectra of even-numbered clusters are more intense and are observed at lower wavelength region than the odd-sized gold clusters.

  18. Molecular dynamics simulations of cluster fission and fusion processes

    DEFF Research Database (Denmark)

    Lyalin, Andrey G.; Obolensky, Oleg I.; Solov'yov, Ilia;

    2004-01-01

    groups of atoms from the parent cluster is largely independent of the isomer form of the parent cluster. The importance of rearrangement of the cluster structure during the fission process is elucidated. This rearrangement may include transition to another isomer state of the parent cluster before actual......Results of molecular dynamics simulations of fission reactions Na_10^2+ --> Na_7^+ +Na_3^+ and Na_18^2+ --> 2Na_9^+ are presented. The dependence of the fission barriers on the isomer structure of the parent cluster is analyzed. It is demonstrated that the energy necessary for removing homothetic...... separation of the daughter fragments begins and/or forming a "neck" between the separating fragments. A novel algorithm for modeling the cluster growth process is described. This approach is based on dynamic search for the most stable cluster isomers and allows one to find the optimized cluster geometries...

  19. Laser-Cluster interaction in Mid-IR range

    Science.gov (United States)

    Park, Hyunwook; Wang, Zhou; Agostini, Pierre; Dimauro, Louis

    2015-05-01

    We report an experimental study on high harmonic generation (HHG) from inert gas clusters in direct comparison with atomic gases. In the experiment, noble gas clusters, which are produced by a supersonic pulsed jet, interact with infrared lasers at moderate intensity and generate high-order harmonics. Harmonic yields are recorded as a function of cluster size in an optical spectrometer, and group delay measurements are conducted with RABBITT method. In the HHG amplitude measurements, we observed a fast increase of the yield with the size of the clusters, and slowdown when clusters are larger than a critical size. In the HHG phase measurements, we observed almost identical group delay of harmonics from the cluster comparing with the monomer, which supports three step model in harmonic generation from noble gas clusters. A 1D Lewenstein's model in a cluster is constructed with an assumption of partially delocalized electron behavior. Army Res Office.

  20. Cluster Deposition and Implantation on/in Graphite

    DEFF Research Database (Denmark)

    Popok, Vladimir

    2013-01-01

    chosen for surface experiments because it is a good model material; it has an atomically smooth surface that makes it easy to resolve very small deposited clusters or damaged areas. Layered structure of graphite with strong covalent bonds in the graphene sheets and very week van der Waals interactions......Cluster ion beam technique is a versatile tool which can be used for controllable formation of nanosize objects on the surface, modification and processing of surfaces and shallow layers on an atomic scale. In this chapter an overview of research on cluster interaction with graphite is presented....... One of the emphases is put on pinning of metal clusters on graphite with a possibility of following selective etching of graphene layers. The other topic of concern is related to the phenomenon of cluster stopping and the development of scaling law for cluster implantation in graphite. Graphite is...

  1. Partitional clustering algorithms

    CERN Document Server

    2015-01-01

    This book summarizes the state-of-the-art in partitional clustering. Clustering, the unsupervised classification of patterns into groups, is one of the most important tasks in exploratory data analysis. Primary goals of clustering include gaining insight into, classifying, and compressing data. Clustering has a long and rich history that spans a variety of scientific disciplines including anthropology, biology, medicine, psychology, statistics, mathematics, engineering, and computer science. As a result, numerous clustering algorithms have been proposed since the early 1950s. Among these algorithms, partitional (nonhierarchical) ones have found many applications, especially in engineering and computer science. This book provides coverage of consensus clustering, constrained clustering, large scale and/or high dimensional clustering, cluster validity, cluster visualization, and applications of clustering. Examines clustering as it applies to large and/or high-dimensional data sets commonly encountered in reali...

  2. Magnetic behavior of clusters of ferromagnetic transition metals

    DEFF Research Database (Denmark)

    Khanna, S. N.; Linderoth, Søren

    1991-01-01

    The effective magnetic moments of small iron and cobalt clusters have been calculated by assuming that the clusters undergo superparamagnetic relaxation. The effective moments per atom are found to be much below the bulk values, even at low temperatures (100 K). They increase with particle size a...

  3. Thermal stability of helium-vacancy clusters in iron

    CERN Document Server

    Morishita, K; Wirth, B D; Díaz de la Rubia, T

    2003-01-01

    Molecular dynamics calculations were performed to evaluate the thermal stability of helium-vacancy clusters (He sub n V sub m) in Fe using the Ackland Finnis-Sinclair potential, the Wilson-Johnson potential and the Ziegler-Biersack-Littmark-Beck potential for describing the interactions of Fe-Fe, Fe-He and He-He, respectively. Both the calculated numbers of helium atoms, n, and vacancies, m, in clusters ranged from 0 to 20. The binding energies of an interstitial helium atom, an isolated vacancy and a self-interstitial iron atom to a helium-vacancy cluster were obtained from the calculated formation energies of clusters. All the binding energies do not depend much on cluster size, but they primarily depend on the helium-to-vacancy ratio (n/m) of clusters. The binding energy of a vacancy to a helium-vacancy cluster increases with the ratio, showing that helium increases cluster lifetime by dramatically reducing thermal vacancy emission. On the other hand, both the binding energies of a helium atom and an iron ...

  4. Cluster Evaluation of Density Based Subspace Clustering

    OpenAIRE

    Sembiring, Rahmat Widia; Zain, Jasni Mohamad

    2010-01-01

    Clustering real world data often faced with curse of dimensionality, where real world data often consist of many dimensions. Multidimensional data clustering evaluation can be done through a density-based approach. Density approaches based on the paradigm introduced by DBSCAN clustering. In this approach, density of each object neighbours with MinPoints will be calculated. Cluster change will occur in accordance with changes in density of each object neighbours. The neighbours of each object ...

  5. Clustering with Spectral Methods

    OpenAIRE

    Gaertler, Marco

    2002-01-01

    Grouping and sorting are problems with a great tradition in the history of mankind. Clustering and cluster analysis is a small aspect in the wide spectrum. But these topics have applications in most scientific disciplines. Graph clustering is again a little fragment in the clustering area. Nevertheless it has the potential for new pioneering and innovative methods. One such method is the Markov Clustering presented by van Dongen in 'Graph Clustering by Flow Simulation'. We investigated the qu...

  6. Sparse Convex Clustering

    OpenAIRE

    Wang, Binhuan; Zhang, Yilong; Sun, Wei; Fang, Yixin

    2016-01-01

    Convex clustering, a convex relaxation of k-means clustering and hierarchical clustering, has drawn recent attentions since it nicely addresses the instability issue of traditional nonconvex clustering methods. Although its computational and statistical properties have been recently studied, the performance of convex clustering has not yet been investigated in the high-dimensional clustering scenario, where the data contains a large number of features and many of them carry no information abo...

  7. Cluster Ion Implantation in Graphite and Diamond

    DEFF Research Database (Denmark)

    Popok, Vladimir

    2014-01-01

    Cluster ion beam technique is a versatile tool which can be used for controllable formation of nanosize objects as well as modification and processing of surfaces and shallow layers on an atomic scale. The current paper present an overview and analysis of data obtained on a few sets of graphite and...

  8. Interplay between experiments and calculations for organometallic clusters and caged clusters

    International Nuclear Information System (INIS)

    Clusters consisting of 10-1000 atoms exhibit size-dependent electronic and geometric properties. In particular, composite clusters consisting of several elements and/or components provide a promising way for a bottom-up approach for designing functional advanced materials, because the functionality of the composite clusters can be optimized not only by the cluster size but also by their compositions. In the formation of composite clusters, their geometric symmetry and dimensionality are emphasized to control the physical and chemical properties, because selective and anisotropic enhancements for optical, chemical, and magnetic properties can be expected. Organometallic clusters and caged clusters are demonstrated as a representative example of designing the functionality of the composite clusters. Organometallic vanadium-benzene forms a one dimensional sandwich structure showing ferromagnetic behaviors and anomalously large HOMO-LUMO gap differences of two spin orbitals, which can be regarded as spin-filter components for cluster-based spintronic devices. Caged clusters of aluminum (Al) are well stabilized both geometrically and electronically at Al12X, behaving as a “superatom”

  9. Interplay between experiments and calculations for organometallic clusters and caged clusters

    Science.gov (United States)

    Nakajima, Atsushi

    2015-12-01

    Clusters consisting of 10-1000 atoms exhibit size-dependent electronic and geometric properties. In particular, composite clusters consisting of several elements and/or components provide a promising way for a bottom-up approach for designing functional advanced materials, because the functionality of the composite clusters can be optimized not only by the cluster size but also by their compositions. In the formation of composite clusters, their geometric symmetry and dimensionality are emphasized to control the physical and chemical properties, because selective and anisotropic enhancements for optical, chemical, and magnetic properties can be expected. Organometallic clusters and caged clusters are demonstrated as a representative example of designing the functionality of the composite clusters. Organometallic vanadium-benzene forms a one dimensional sandwich structure showing ferromagnetic behaviors and anomalously large HOMO-LUMO gap differences of two spin orbitals, which can be regarded as spin-filter components for cluster-based spintronic devices. Caged clusters of aluminum (Al) are well stabilized both geometrically and electronically at Al12X, behaving as a "superatom".

  10. Interplay between experiments and calculations for organometallic clusters and caged clusters

    Energy Technology Data Exchange (ETDEWEB)

    Nakajima, Atsushi [Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama 223-8522 (Japan); Nakajima Designer Nanocluster Assembly Project, ERATO, JST, KSP, 3-2-1 Sakado, Kawasaki 213-0012 (Japan); Keio Institute of Pure and Applied Sciences (KiPAS), Keio University, 3-14-1 Hiyoshi, Yokohama 223-8522 (Japan)

    2015-12-31

    Clusters consisting of 10-1000 atoms exhibit size-dependent electronic and geometric properties. In particular, composite clusters consisting of several elements and/or components provide a promising way for a bottom-up approach for designing functional advanced materials, because the functionality of the composite clusters can be optimized not only by the cluster size but also by their compositions. In the formation of composite clusters, their geometric symmetry and dimensionality are emphasized to control the physical and chemical properties, because selective and anisotropic enhancements for optical, chemical, and magnetic properties can be expected. Organometallic clusters and caged clusters are demonstrated as a representative example of designing the functionality of the composite clusters. Organometallic vanadium-benzene forms a one dimensional sandwich structure showing ferromagnetic behaviors and anomalously large HOMO-LUMO gap differences of two spin orbitals, which can be regarded as spin-filter components for cluster-based spintronic devices. Caged clusters of aluminum (Al) are well stabilized both geometrically and electronically at Al{sub 12}X, behaving as a “superatom”.

  11. Multiply-negatively charged aluminium clusters and fullerenes

    Energy Technology Data Exchange (ETDEWEB)

    Walsh, Noelle

    2008-07-15

    Multiply negatively charged aluminium clusters and fullerenes were generated in a Penning trap using the 'electron-bath' technique. Aluminium monoanions were generated using a laser vaporisation source. After this, two-, three- and four-times negatively charged aluminium clusters were generated for the first time. This research marks the first observation of tetra-anionic metal clusters in the gas phase. Additionally, doubly-negatively charged fullerenes were generated. The smallest fullerene dianion observed contained 70 atoms. (orig.)

  12. Structure of overheated metal clusters: MD simulation study

    International Nuclear Information System (INIS)

    The structure of overheated metal clusters appeared in condensation process was studied by computer simulation techniques. It was found that clusters with size larger than several tens of atoms have three layers: core part, intermediate dense packing layer and a gas- like shell with low density. The change of the size and structure of these layers with the variation of internal energy and the size of cluster is discussed

  13. The Herschel Virgo Cluster Survey XVI: a cluster inventory

    CERN Document Server

    Davies, J I; Baes, M; Bendo, G J; Clemens, M; De Looze, I; Alighieri, S di Serego; Fritz, J; Fuller, C; Pappalardo, C; Hughes, T M; Madden, S; Smith, M W L; Verstappen, J; Vlahakis, C

    2013-01-01

    Herschel FIR observations are used to construct Virgo cluster galaxy luminosity functions and to show that the cluster lacks the very bright and the numerous faint sources detected in field galaxy surveys. The far-infrared SEDs are fitted to obtain dust masses and temperatures and the dust mass function. The cluster is over dense in dust by about a factor of 100 compared to the field. The same emissivity (beta) temperature relation applies for different galaxies as that found for different regions of M31. We use optical and HI data to show that Virgo is over dense in stars and atomic gas by about a factor of 100 and 20 respectively. Metallicity values are used to measure the mass of metals in the gas phase. The mean metallicity is about 0.7 solar and 50% of the metals are in the dust. For the cluster as a whole the mass density of stars in galaxies is 8 times that of the gas and the gas mass density is 130 times that of the metals. We use our data to consider the chemical evolution of the individual galaxies,...

  14. Low energy Cu clusters slow deposition on a Fe (001) surface investigated by molecular dynamics simulation

    International Nuclear Information System (INIS)

    Highlights: • We study the deposition of low energy Cu clusters on Fe (001) surface by molecular dynamics. • The interaction between low energy cluster and substrate can be divided to the landing and the thermal diffusion phases. • The phenomenon of contact epitaxy of cluster occurred. • The thermal diffusion of cluster atoms was analyzed. - Abstract: The slow deposition of low energy Cu clusters on a Fe (001) surface was investigated by molecular dynamics simulation. A many-body potential based on Finnis–Sinclair model was used to describe the interactions among atoms. Three clusters comprising of 13, 55 and 147 atoms, respectively, were deposited with incident energies ranging from 0.0 to 1.0 eV/atom at various substrate temperatures (0, 300 and 800 K). The rearrangement and the diffusion of cluster can occur, only when the cluster atoms are activated and obtained enough migration energy. The interaction between low energy cluster and substrate can be divided to the landing and the thermal diffusion phases. In the former, the migration energy originates from the latent heat of binding energy for the soft deposition regime and primarily comes from the incident energy of cluster for the energetic cluster deposition regime. In the latter, the thermal vibration would result in some cluster atoms activated again at medium and high substrate temperatures. Also, the effects of incident energy, cluster size and substrate temperature on the interaction potential energy between cluster and substrate, the final deposition morphology of cluster, the spreading index and the structure parameter of cluster are analyzed

  15. Evolution of ConAl clusters and chemisorption of hydrogen on ConAl clusters

    International Nuclear Information System (INIS)

    The growth behavior of ConAl (n = 1–15) and the chemisorptions of hydrogen on the ground state geometries have been studied using the density functional theory (DFT) within the generalized gradient approximation (GGA). The growth pattern for ConAl is Al-substituted Con+1 clusters, and it keeps the similar frameworks of the most stable Con+1 clusters except for n = 2, 3, and 6. The Al atom substitutes the surface atom of the Con+1 clusters for n ≤ 13. Starting from n = 14, the Al atom completely falls into the center of the Co-frame. The dissociation energy, the second-order energy differences, and the HOMO–LUMO gaps indicate that the magic numbers of the calculated ConAl clusters are 7, 9, and 13, corresponding to the high symmetrical structures. To my knowledge, this is the first time that a systematic study of chemisorption of hydrogen on cobalt aluminum clusters. The twofold bridge site is identified to be the most favorable chemisorptions site for one hydrogen adsorption on ConAl (n = 1–6, 8, 10), and two hydrogen adsorption on ConAl (n = 1–7), while threefold hollow site is preferred for one hydrogen adsorption on ConAl (n = 7, 9, 11–15) and two hydrogen adsorption on ConAl (n = 8–10, 12–15) clusters. The ground state structure of two hydrogen adsorption on Co11Al is exceptional. In general, the binding energy of both H and 2H of ConAl (n = 1–12) is found to increase with the cluster size. And the result shows that large binding energies of the hydrogen atoms and large fragmentation energies for Co11AlH and Co12AlH make these species behaving like magic clusters.

  16. Mass distribution of products of cluster impacts

    International Nuclear Information System (INIS)

    Mass distributions of ionic atomic and molecular fragments sputtered from carbon surfaces by singly charged positive cluster ions containing 80 water molecules have been determined. With cluster kinetic energy of 240 keV significant yields of molecular fragments containing up to 21 carbon atoms were observed. Ion yields were used to estimate relative yields of neutral fragments with the assumption that relative yields of the respective ionic and neutral sputtering processes were determined by kinetic factors which could be evaluated independently. The derived neutral yields were then used to estimate the fraction of total projectile energy utilized in evaporative cooling, i.e., sputtering. The results indicate a major fraction of the energy available is used in the cluster sputtering process. 9 refs., 1 tab

  17. Cluster optimization simplified by interaction modification

    Science.gov (United States)

    Stillinger, Frank H.; Stillinger, Dorothea K.

    1990-10-01

    Even when interactions are known exactly, it is generally very difficult to determine the lowest-energy configuration (a global potential energy minimum) for clusters with more than very few atoms or molecules. In mathematical parlance this is an NP-complete problem. A nonlinear optimization strategy, the ``ant-lion method,'' has been proposed to accelerate the search for global minima, and works by adroitly deforming the potential surface to produce overwhelming dominance by global minimum potential energy basins. This strategy is illustrated by application to clusters of 13 noble gas atoms. Monte Carlo results demonstrate that reduction of p in the pair potential 4(r-2p-r-p) below the ``physical'' value 6 produces a dramatic rise to essentially unity in probability of random encounter with the global minimum basins (icosahedral clusters).

  18. Density functional theory study on the structural and electronic properties of Ag-adsorbed (MgO)_n clusters

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Equilibrium geometries, charge distributions, stabilities and electronic properties of the Ag-adsorbed (MgO)n (n = 1-8) clusters have been investigated by density functional theory (DFT) with generalized gradient approximation (GGA) for exchange-correlation functional. The results show that hollow site is energetically preferred for n≥4, and the incoming Ag atoms tend to cluster on the existing Ag cluster. The Mulliken populations indicate that the interaction between the Ag atom and Magnesia clusters is mainly induced by a weak atomic polarization. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of Magnesia clusters is minor. Furthermore, the investigations on the first energy difference, fragmentation energies and electron affinities show that the Ag(MgO)4 and Ag(MgO)6 are the most stable among studied clusters.

  19. Density functional theory study on the structural and electronic properties of Ag-adsorbed (MgO)n clusters

    Institute of Scientific and Technical Information of China (English)

    GE GuiXian; JING Qun; LUO YouHua

    2009-01-01

    Equilibrium geometries, charge distributions, stabilities and electronic properties of the Ag-adsorbed (MgO)n(n=1-8) clusters have been investigated by density functional theory (DFT)with generalized gradient approximation (GGA) for exchange-correlation functional. The results show that hollow site is energetically preferred for n≥4, and the incoming Ag atoms tend to cluster on the existing Ag cluster.The Mulliken populations indicate that the interaction between the Ag atom and Magnesia clusters is mainly induced by a weak atomic polarization. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of Magnesia clusters is minor. Furthermore, the investigations on the first energy difference,fragmentation energies and electron affinities show that the Ag(MgO)4 and Ag(MgO)6 are the most stable among studied clusters.

  20. Computer studies on reflection and sputtering due to low-energy cluster impacts

    International Nuclear Information System (INIS)

    In order to study the reflection and sputtering by low-energy cluster impact, we have performed the molecular dynamics (MD) simulations of (Cu)55 cluster impact on a Pt (1 1 1) surface with an energy of 100 eV/atom, and compared with those of monatomic Cu ion bombardment with the same energy per atom. As to the reflection, the lower-part cluster atoms are more reflected than the upper-part cluster atoms at the very-early stage of cluster impact. This is the high-density effect on the reflection by cluster impact. However, the upper-part cluster atoms are more reflected than the lower-part cluster atoms after all. As to the sputtering, the sputtering yield for cluster impact is by far larger than that for monatomic ion bombardment. In the case of monatomic ion bombardment, Pt atoms tend to be sputtered in the close-packed directions of the Pt (1 1 1) target. In the case of cluster impact, Pt atoms are fairly sputtered in the normal and lateral directions as well as the close-packed directions. These results for sputtering agree with experimental observations and other simulation results. The sputtering in the normal and lateral directions is certainly enhanced due to cluster impact, but the high-density effect on the sputtering by cluster impact is not clearly observed. The high-density effect is not the main effect on the reflection and sputtering by cluster impact, and it does not seem to be observable experimentally

  1. Stability of uncommon interstitial clusters in Fe

    International Nuclear Information System (INIS)

    We present empirical potential and Density Functional Theory calculations on small interstitial clusters of unconventional shape in Fe. Empirical potential simulations of displacement cascades and subsequent annealing resulted in the formation of a number of interstitial clusters with nonstandard configurations which are characterized by non-parallel dumbbells and di-interstitials consisting of three atoms sharing one lattice site. Such clusters were found to be essentially immobile as compared to the clusters of conventional shapes (i.e. platelets of dumbbells or crowdions) and be able to grow by absorbing other interstitials. Both empirical potential and Density Functional Theory calculations indicate that the formation energies of these alternative structures are not much higher than or as high as those of the conventional configurations. The interstitial clusters were observed to remain in these alternative configurations for substantial periods of time remaining immobile during empirical-potential molecular dynamics simulations and the process of transformation from an immobile state into a regular cluster was found to be thermally activated. Therefore the presence of such immobile states may have an impact on the interstitial cluster mobility. The energetics of found immobile clusters and transformation mechanisms between immobile and mobile states are discussed. (authors)

  2. Cluster categories and cluster-tilted algebras

    OpenAIRE

    Torkildsen, Hermund Andre

    2006-01-01

    We have given an introduction to the theory of cluster categories and cluster-tilted algebras, and this was one of our main objectives in this thesis. We have seen that cluster-tilted algebras are relation-extension algebras, and this gave us a way of constructing the quiver of a cluster-tilted algebra from a tilted algebra. A cluster-tilted algebra of finite representation type is determined by its quiver, and this raised questions about the generality of this result. We defined a new class...

  3. Thermodynamics of confined gallium clusters

    International Nuclear Information System (INIS)

    We report the results of ab initio molecular dynamics simulations of Ga13 and Ga17 clusters confined inside carbon nanotubes with different diameters. The cluster-tube interaction is simulated by the Lennard–Jones (LJ) potential. We discuss the geometries, the nature of the bonding and the thermodynamics under confinement. The geometries as well as the isomer spectra of both the clusters are significantly affected. The degree of confinement decides the dimensionality of the clusters. We observe that a number of low-energy isomers appear under moderate confinement while some isomers seen in the free space disappear. Our finite-temperature simulations bring out interesting aspects, namely that the heat capacity curve is flat, even though the ground state is symmetric. Such a flat nature indicates that the phase change is continuous. This effect is due to the restricted phase space available to the system. These observations are supported by the mean square displacement of individual atoms, which are significantly smaller than in free space. The nature of the bonding is found to be approximately jellium-like. Finally we note the relevance of the work to the problem of single file diffusion for the case of the highest confinement. (paper)

  4. Ion-Induced Reactivity in Pyrene Clusters

    International Nuclear Information System (INIS)

    We report experimental indications of chemical reactions inside clusters of pyrene (C16H10) molecules following collisions with 11.25 keV He+ - and 12.0 keV Ar2+ ions. It appears that bond-forming reactions are more likely with the heavier projectile. We have also performed classical molecular dynamics simulations of these processes where we treat the interaction between the projectiles and all atoms in the cluster as well as non-dispersive and dispersive forces between all atoms in the cluster before, during and after the collision. The time step is typically 10−17 s and the total simulation time 1 picosecond. The simulations were performed for a fixed cluster size with 36 pyrene molecules, although there is a broad range of cluster sizes in the experiment. Still, there is good qualitative agreement between the experimental and the simulated mass spectra exhibiting reaction products with masses between those of the C16H10- monomer and dimer in both cases. Additional studies of the influence of the projectile charge and mass is planned as well as simulations on longer time scales and as functions of cluster size

  5. Simulation of interaction of circular clusters C7, C12, C13 with nanographene

    International Nuclear Information System (INIS)

    Interaction of circular carbon clusters C7, C12 and C13 with graphene consisting of 272 atoms has been studied by computer simulation based on the Monte Carlo method. The mutual arrangement of the cluster atoms and graphene and their cohesive energy before and after their interaction have been investigated. (author)

  6. The structure of small nickel clusters. II. Ni16--Ni28

    International Nuclear Information System (INIS)

    The molecular adsorption of nitrogen on nickel clusters is used to probe the clusters' geometrical structures. The application of nitrogen binding rules derived from earlier studies of both larger and smaller nickel clusters allows a determination of structure from nitrogen uptake patterns. In the 16- and 28-atom size region cluster structure is dominated by local pentagonal symmetry, a consequence of a preference for close packing of atoms on clusters with curved surfaces. In most cases, the structures that result can be derived from the 13-atom icosahedron, the polyicosahedral 19-, 23-, and 26-atom clusters, and the 55-atom icosahedron, by adding or removing atoms. Icosahedral and polyicosahedral clusters often have substantial surface strain, which in some cases is relieved by deviations from the ideal geometry. Structures are proposed for all clusters in the Ni16 to Ni28 size range, with the exception of Ni27. Generally, there is no evidence for structural changes as a consequence of nitrogen binding, so that the proposed structures are those of the bare as well as the nitrogenated clusters. Where possible, comparison with existing theoretical calculations of nickel cluster structure is made

  7. Structures, stabilities, and magnetic properties of CoRu binary clusters

    International Nuclear Information System (INIS)

    Highlights: • The doped Ru atoms prefer a planar structure. • The doping of the Ru atoms enhances the stability of alloy clusters. • The magnetic moments of monatomic impurity clusters do not dramatically change. • The magnetic moments of polyatomic impurity clusters sharply decrease. • The decreasing magnetic moment results from the formation of Ru–Ru bonds. - Abstract: The geometries, stabilities, and magnetic properties of binary clusters CoN-mRum (N = 2–13, m = 1–5) are explored by density functional theory calculations. The ground-state structures of CoN-mRum alloy clusters are similar to those of corresponding pure CoN or RuN clusters, except for Co3Ru, Co2Ru2, and Co6Ru. Calculations show that when one Co atom is replaced by one Ru atom, the total magnetic moments of the CoN−1Ru (N = 2–13) clusters do not dramatically change and only deviate from those of pure CoN clusters by ±1 μB. On the other hand, when the number of doped Ru atoms is increased to 3, the calculated magnetic moments of CoN-mRum (N = 4–6) clusters sharply decrease. The partial density of states analysis demonstrates that the formation of Ru–Ru bond weakens the spin exchange splitting effect of Ru atoms and thus reduces the magnetism of clusters

  8. A curved line search algorithm for atomic structure relaxation

    OpenAIRE

    Chen, Zhanghui; Wang, Linwang; Li, Jingbo; Li, Shushen

    2015-01-01

    Ab initio atomic relaxations often take large numbers of steps and long times to converge. An atomic relaxation method based on on-the-flight force learning and a corresponding new curved line minimization algorithm is presented to dramatically accelerate this process. Results for metal clusters demonstrate the significant speedup of this method compared with conventional conjugate-gradient method.

  9. Minimal mass-size of a stable 3He cluster

    OpenAIRE

    Guardiola Barcena, Rafael; Navarro Faus, Jesús

    2004-01-01

    The minimal number of 3He atoms required to form a bound cluster has been estimated by means of a Diffusion Monte Carlo procedure within the fixed-node approximation. Several importance sampling wave functions have been employed in order to consider different shell-model configurations. The resulting upper bound for the minimal number is 32 atoms.

  10. Change of Energy of the Cubic Subnanocluster of Iron Under Influence of Interstitial and Substitutional Atoms.

    Science.gov (United States)

    Nedolya, Anatoliy V; Bondarenko, Natalya V

    2016-12-01

    Energy change of an iron face-centred cubic subnanocluster was evaluated using molecular mechanics method depending on the position of a carbon interstitial atom and substitutional atoms of nickel. Calculations of all possible positions of impurity atoms show that the energy change of the system are discrete and at certain positions of the atoms are close to continuous.In terms of energy, when all impurity atoms are on the same edge of an atomic cluster, their positions are more advantageous. The presence of nickel atoms on the edge of a cubic cluster resulted in decrease of potential barrier for a carbon atom and decrease in energy in the whole cluster. A similar drift of a carbon atom from central octahedral interstitial site to the surface in the direction occurred under the influence of surface factors.Such configuration corresponds to decreasing symmetry and increasing the number of possible energy states of a subnanocluster, and it corresponds to the condition of spontaneous crystallization process in an isolated system.Taking into account accidental positions of the nickel atom in the iron cluster, such behaviour of the carbon atom can explain the mechanism of growth of a new phase and formation of new clusters in the presence of other kind of atoms because of surface influence. PMID:26754941

  11. Calculation of Al-Zn diagram from central atoms model

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    A slightly modified central atoms model was proposed. The probabilities of various clusters with the central atoms and their nearest neighboring shells can be calculated neglecting the assumption of the param eter of energy in the central atoms model in proportion to the number of other atoms i (referred with the central atom). A parameter Pα is proposed in this model, which equals to reciprocal of activity coefficient of a component, therefore, the new model can be understood easily. By this model, the Al-Zn phase diagram and its thermodynamic properties were calculated, the results coincide with the experimental data.

  12. Photoelectron spectroscopy of boron aluminum hydride cluster anions

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Haopeng; Zhang, Xinxing; Ko, Yeon Jae; Gantefoer, Gerd; Bowen, Kit H., E-mail: kbowen@jhu.edu, E-mail: kiran@mcneese.edu [Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Li, Xiang [Center for Space Science and Technology, University of Maryland–Baltimore County, Baltimore, Maryland 21250 (United States); Kiran, Boggavarapu, E-mail: kbowen@jhu.edu, E-mail: kiran@mcneese.edu [Department of Chemistry and Physics, McNeese State University, Lake Charles, Louisiana 70609 (United States); Kandalam, Anil K. [Department of Physics, West Chester University, West Chester, Pennsylvania 19383 (United States)

    2014-04-28

    Boron aluminum hydride clusters are studied through a synergetic combination of anion photoelectron spectroscopy and density functional theory based calculations. Boron aluminum hydride cluster anions, B{sub x}Al{sub y}H{sub z}{sup −}, were generated in a pulsed arc cluster ionization source and identified by time-of-flight mass spectrometry. After mass selection, their photoelectron spectra were measured by a magnetic bottle-type electron energy analyzer. The resultant photoelectron spectra as well as calculations on a selected series of stoichiometries reveal significant geometrical changes upon substitution of aluminum atoms by boron atoms.

  13. Fluorescent Thiol-Derivatized Gold Clusters Embedded in Polymers

    Directory of Open Access Journals (Sweden)

    G. Carotenuto

    2013-01-01

    Full Text Available Owing to aurophilic interactions, linear and/or planar Au(I-thiolate molecules spontaneously aggregate, leading to molecular gold clusters passivated by a thiolate monolayer coating. Differently from the thiolate precursors, such cluster compounds show very intensive visible fluorescence characteristics that can be tuned by alloying the gold clusters with silver atoms or by conjugating the electronic structure of the metallic core with unsaturated electronic structures in the organic ligand through the sulphur atom. Here, the photoluminescence features of some examples of these systems are shortly described.

  14. Size-dependent mobility of gold nano-clusters during growth on chemically modified graphene

    International Nuclear Information System (INIS)

    Gold nano-clusters were grown on chemically modified graphene by direct sputter deposition. Transmission electron microscopy of the nano-clusters on these electron-transparent substrates reveals an unusual bimodal island size distribution (ISD). A kinetic Monte Carlo model of growth incorporating a size-dependent cluster mobility rule uniquely reproduces the bimodal ISD, providing strong evidence for the mobility of large clusters during surface growth. The cluster mobility exponent of −5/3 is consistent with cluster motion via one-dimensional diffusion of gold atoms around the edges of the nano-clusters

  15. Size-dependent mobility of gold nano-clusters during growth on chemically modified graphene

    Directory of Open Access Journals (Sweden)

    Gavin R. Bell

    2014-01-01

    Full Text Available Gold nano-clusters were grown on chemically modified graphene by direct sputter deposition. Transmission electron microscopy of the nano-clusters on these electron-transparent substrates reveals an unusual bimodal island size distribution (ISD. A kinetic Monte Carlo model of growth incorporating a size-dependent cluster mobility rule uniquely reproduces the bimodal ISD, providing strong evidence for the mobility of large clusters during surface growth. The cluster mobility exponent of −5/3 is consistent with cluster motion via one-dimensional diffusion of gold atoms around the edges of the nano-clusters.

  16. First-principle study of silicon cluster doped with rhodium: Rh2Sin (n = 1–11) clusters

    International Nuclear Information System (INIS)

    The geometries, stabilities and electronic properties of rhodium-doped silicon clusters Rh2Sin (n = 1–11) have been systematically studied by using density functional calculations at the B3LYP/GENECP level. The optimized results show that the lowest-energy isomers of Rh2Sin clusters favor three-dimensional structures for n = 2–11. Based on the averaged binding energy, fragmentation energy, second-order energy difference and HOMO-LUMO energy gap, the stabilities of Rh2Sin (n = 1–11) clusters have been analyzed. The calculated results suggest that the Rh2Si6 cluster has the strongest relative stability and the doping with rhodium atoms can reduce the chemical stabilities of Sin clusters. The natural population and natural electron configuration analysis indicate that there is charge transfer from the Si atoms and 5s orbital of the Rh atoms to the 4d and 5p orbitals of Rh atoms. The analysis of electron localization function reveal that the Si–Si bonds are mainly covalent bonds and the Si–Rh bonds are almost ionic bonds. Moreover, the vertical ionization potential, vertical electron affinity, chemical hardness, chemical potential, vibrational spectrum and polarizability are also discussed. - Highlights: • The geometric structures of Rh2Sin (n = 1–11) clusters are determined. • The stabilities and electronic properties of Rh2Sin clusters are discussed. • The Rh2Si6 cluster has the higher stability than other clusters. • The doped rhodium atoms can reduce the chemical stabilities of Sin clusters

  17. Nanophase materials assembled from clusters

    Energy Technology Data Exchange (ETDEWEB)

    Siegel, R.W.

    1992-02-01

    The preparation of metal and ceramic atom clusters by means of the gas-condensation method, followed by their in situ collection and consolidation under high-vacuum conditions, has recently led to the synthesis of a new class of ultrafine-grained materials. These nanophase materials, with typical average grain sizes of 5 to 50 nm and, hence, a large fraction of their atoms in interfaces, exhibit properties that are often considerably improved relative to those of conventional materials. Furthermore, their synthesis and processing characteristics should enable the design of new materials with unique properties. Some examples are ductile ceramics that can be formed and sintered to full density at low temperatures without the need for binding or sintering aids, and metals with dramatically increased strength. The synthesis of these materials is briefly described along with what is presently known of their structure and properties. Their future impact on materials science and technology is also considered.

  18. Geometries, stabilities, and electronic properties of Be-doped gold clusters: a density functional theory study

    International Nuclear Information System (INIS)

    We have systematically investigated the geometrical structures, relative stabilities and electronic properties of small bimetallic AunBe (n = 1, 2, ..., 8) clusters using a density functional method at BP86 level. The optimized geometries reveal that the impurity beryllium atom dramatically affects the structures of the Aun clusters. The averaged binding energies, fragmentation energies, second-order difference of energies, the highest occupied-lowest unoccupied molecular orbital energy gaps and chemical hardness are investigated. All of them exhibit a pronounced odd—even alternation, manifesting that the clusters with even number of gold atoms possess relatively higher stabilities. Especially, the linear Au2Be cluster is magic cluster with the most stable chemical stability. According to the natural population analysis, it is found that charge-transferring direction between Au atom and Be atom changes at the size of n = 4. (atomic and molecular physics)

  19. Learning predictive clustering rules

    OpenAIRE

    Ženko, Bernard; Džeroski, Sašo; Struyf, Jan

    2005-01-01

    The two most commonly addressed data mining tasks are predictive modelling and clustering. Here we address the task of predictive clustering, which contains elements of both and generalizes them to some extent. We propose a novel approach to predictive clustering called predictive clustering rules, present an initial implementation and its preliminary experimental evaluation.

  20. Clustering of correlated networks

    OpenAIRE

    Dorogovtsev, S. N.

    2003-01-01

    We obtain the clustering coefficient, the degree-dependent local clustering, and the mean clustering of networks with arbitrary correlations between the degrees of the nearest-neighbor vertices. The resulting formulas allow one to determine the nature of the clustering of a network.

  1. Foodservice Occupations Cluster Guide.

    Science.gov (United States)

    Oregon State Dept. of Education, Salem.

    Intended to assist vocational teachers in developing and implementing a cluster program in food service occupations, this guide contains sections on cluster organization and implementation and instructional emphasis areas. The cluster organization and implementation section covers goal-based planning and includes a proposed cluster curriculum, a…

  2. "Bohr's Atomic Model."

    Science.gov (United States)

    Willden, Jeff

    2001-01-01

    "Bohr's Atomic Model" is a small interactive multimedia program that introduces the viewer to a simplified model of the atom. This interactive simulation lets students build an atom using an atomic construction set. The underlying design methodology for "Bohr's Atomic Model" is model-centered instruction, which means the central model of the…

  3. Relevant Subspace Clustering

    DEFF Research Database (Denmark)

    Müller, Emmanuel; Assent, Ira; Günnemann, Stephan; Krieger, Ralph; Seidl, Thomas

    Subspace clustering aims at detecting clusters in any subspace projection of a high dimensional space. As the number of possible subspace projections is exponential in the number of dimensions, the result is often tremendously large. Recent approaches fail to reduce results to relevant subspace...... clusters. Their results are typically highly redundant, i.e. many clusters are detected multiple times in several projections. In this work, we propose a novel model for relevant subspace clustering (RESCU). We present a global optimization which detects the most interesting non-redundant subspace clusters...... achieves top clustering quality while competing approaches show greatly varying performance....

  4. Molecular dynamics study on different melting behaviors of Cu{sub N} (N = 51-53) clusters

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Lin; Sun, Haixia [Institute of Materials Physics and Chemistry, College of Science, Northeastern University, Shenyang 110004 (China)

    2010-05-15

    The structural changes of three Cu clusters containing 51-53 atoms during their melting processes have been studied by employing molecular dynamics simulations. The local structures in the atomic density shells are presented according to the pair index of Honeycutt and Andersen. Structural transformation temperatures of the three clusters are increased on increasing the cluster size. Owing to structural differences in these three clusters, their different melting behaviors can be observed. The simulations provide the implications for us to understand the effect of atomic packing in these clusters with icosahedron-based geometries on causing the structural change differences at elevated temperature. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  5. Tilting theory and cluster algebras

    OpenAIRE

    Reiten, Idun

    2010-01-01

    We give an introduction to the theory of cluster categories and cluster tilted algebras. We include some background on the theory of cluster algebras, and discuss the interplay with cluster categories and cluster tilted algebras.

  6. Seniority-based coupled cluster theory

    CERN Document Server

    Henderson, Thomas M; Stein, Tamar; Scuseria, Gustavo E

    2014-01-01

    Doubly occupied configuration interaction (DOCI) with optimized orbitals often accurately describes strong correlations while working in a Hilbert space much smaller than that needed for full configuration interaction. However, the scaling of such calculations remains combinatorial with system size. Pair coupled cluster doubles (pCCD) is very successful in reproducing DOCI energetically, but can do so with low polynomial scaling ($N^3$, disregarding the two-electron integral transformation from atomic to molecular orbitals). We show here several examples illustrating the success of pCCD in reproducing both the DOCI energy and wave function, and show how this success frequently comes about. What DOCI and pCCD lack are an effective treatment of dynamic correlations, which we here add by including higher-seniority cluster amplitudes which are excluded from pCCD. This frozen pair coupled cluster approach is comparable in cost to traditional closed-shell coupled cluster methods with results that are competitive fo...

  7. Cluster radioactivities — past, present and future

    International Nuclear Information System (INIS)

    The half-lives of cluster emitters predicted by the analytical superasymmetric fission model have been experimentally confirmed. Potential energy surfaces of cluster emitters are showing deep valleys due to the strong shell effect of the doubly magic daughter 208Pb. Cluster radioactivities allow us to study transitions from a deformed parent nucleus, with a complex structure resulted from mixing of several single-particle states, to a spherical daughter possessing a pure well known state. Recently, preliminary data concerning the 14C radioactivity of 223Ac were reported. The following modes have been experimentally confirmed: 14C, 20O, 24,25Ne, 28,30Mg, and 32,34Si; lower limits for 18O, 23F and 26Ne are available. We give a list of some other experiments which have a good chance to be performed in the future. Applications for true ternary fission, 2α-accompanied fission, and atomic clusters are outlined. (author)

  8. Structure and magnetic properties of Fe12X clusters

    International Nuclear Information System (INIS)

    Highlights: • A DFT-GGA approach is used. • Binary clusters Fe12X are optimized. • The considered X dopants are Al, 3d-, 4d-, and Gd atoms. • Gd and Mn do increase the total spin magnetic moment. • 4d-metal atoms form more stable clusters. - Abstract: The electronic and geometrical structures of a Fe12X family of binary clusters Fe12Al, Fe12Sc, Fe12Ti, Fe12V, Fe12Cr, Fe12Mn, Fe12Co, Fe12Ni, Fe12Cu, Fe12Zn, Fe12Y, Fe12Zr, Fe12Nb, Fe12Mo, Fe12Tc, Fe12Ru, Fe12Rh, Fe12Pd, Fe12Ag, Fe12Cd, and Fe12Gd are studied using density functional theory within generalized gradient approximation. It is found that the geometrical structures corresponding to the lowest total energy states found for the Fe12X clusters possess icosahedral shape with the substituent atom occupying the central or a surface site. The only exception presents Fe12Nb where a squeezed cage structure is the energetically most favorable. The substitution of an atom in the Fe13 cluster results in the decrease of its total spin magnetic moment of 44 μB, except for Fe12Mn and Fe12Gd. The Fe12X clusters are more stable than the parent Fe13 cluster when X = Al, Sc, Ti, V, Co, Y, Zr, Nb, Mo, Tc, Ru, and Rh

  9. Molecular Dynamics Simulation of Icosahedral Transformations in Solid Cu-Co Clusters

    Institute of Scientific and Technical Information of China (English)

    LI Guo-Jian; WANG Qiang; LIU Tie; LI Dong-Gang; LU Xiao; HE Ji-Cheng

    2009-01-01

    We study the icosahedral transformations of solid Cu-Co clusters with different initial configurations by using molecular dynamics with the embedded atom method.It is found that the formation of symmetric icosahedral cluster is strongly related to the atomic number and initial configuration.The transformation originates from the surface into the interior of the cluster and is a structural change which is rapid and diffusionless.The icosahedral clusters with any composition and configuration,such as core-shell or three-shell cluster,can be prepared by the means of solid-solid phase transition in bimetallic dusters.

  10. Beams of mass-selected clusters: realization and first experiments

    International Nuclear Information System (INIS)

    The main objective of this work concerns the production of beams of mass-selected clusters of metallic and semiconductor materials. Clusters are produced in magnetron sputtering source combined with a gas aggregation chamber, cooled by liquid nitrogen circulation. Downstream of the cluster source, a Wiley-McLaren time-of-flight setup allows to select a given cluster size or a narrow size range. The pulsed mass-selected cluster ion beam is separated from the continuous neutral one by an electrostatic 90-quadrupole deflector. After the deflector, the density of the pulsed beam amounts to about 103 particles/cm3. Preliminary deposition experiments of mass-selected copper clusters with a deposition energy of about 0.5 eV/atom have ben performed on highly oriented pyrolytic graphite (HOPG) substrates, indicating that copper clusters are evidently mobile on the HOPG-surface until they reach cleavage steps, dislocation lines or other surface defects. In order to lower the cluster mobility on the HOPG-surface, we have first irradiated HOPG samples with slow highly charged ions (high dose) in order to create superficial defects. In a second step we have deposited mass-selected copper clusters on these pre-irradiated samples. The first analysis by AFM (Atomic Force Microscopy) techniques showed that the copper clusters are trapped on the defects produced by the highly charged ions. (author)

  11. Photoionization profiles of metal clusters and the Fowler formula

    CERN Document Server

    Prem, Abhinav; 10.1103/PhysRevA.85.025201

    2012-01-01

    Metal cluster ionization potentials are important characteristics of these "artificial atoms," but extracting these quantities from cluster photoabsorption spectra, especially in the presence of thermal smearing, remains a big challenge. Here we demonstrate that the classic Fowler theory of surface photoemission does an excellent job of fitting the photoabsorption profile shapes of neutral In_{n=3-34} clusters [Wucher et al., New J. Phys. 10, 103007 (2008)]. The deduced ionization potentials extrapolate precisely to the bulk work function, and the internal cluster temperatures are in close agreement with values expected for an ensemble of freely evaporating clusters. Supplementing an earlier application to potassium clusters, these results suggest that the Fowler formalism, which is straightforward and physical, may be of significant utility in metal cluster spectroscopy. It is hoped also that the results will encourage a comprehensive theoretical analysis of the applicability of bulk-derived models to cluste...

  12. Ground state structures and properties of small hydrogenated silicon clusters

    Indian Academy of Sciences (India)

    R Prasad

    2003-01-01

    We present results for ground state structures and properties of small hydrogenated silicon clusters using the Car–Parrinello molecular dynamics with simulated annealing. We discuss the nature of bonding of hydrogen in these clusters. We find that hydrogen can form a bridge like Si–H–Si bond connecting two silicon atoms. We find that in the case of a compact and closed silicon cluster hydrogen bonds to the silicon cluster from outside. To understand the structural evolutions and properties of silicon cluster due to hydrogenation, we have studied the cohesive energy and first excited electronic level gap of clusters as a function of hydrogenation. We find that first excited electronic level gap of Si and SiH fluctuates as function of size and this may provide a first principle basis for the short-range potential fluctuations in hydrogenated amorphous silicon. The stability of hydrogenated silicon clusters is also discussed.

  13. Application of fractals and kinetic equations to cluster formation

    Science.gov (United States)

    Villarica, M.; Casey, M. J.; Goodisman, J.; Chaiken, J.

    1993-03-01

    The log normal distribution is shown to be useful for characterizing cluster distributions produced by coalescence growth mechanisms. The Smoluchowski equation and variations thereof produce cluster size distributions very similar to those produced using nozzle beam expansions and laser chemistry of organometallics. The model provides a statistically unbiased basis for interpreting cluster size distributions produced using a wide variety of synthetic methods. It also provides a unified chemical and physical basis for discussing and rationalizing the results of a wide range of gas phase cluster experiments. Under certain conditions, size distributions can be produced in which there is an alteration in the number of odd and even clusters produced. In addition to some inferences regarding fullerene chemistry, data gleaned from the literature are rationalized on the basis of the kinematics of cluster formation, the fractal dimension of clusters composed of different atoms, the Periodic Table, and the degree to which the translational motion of the coalescing species is diffusional or ballistic.

  14. Magnetic Properties of Iron Clusters in Silver

    Energy Technology Data Exchange (ETDEWEB)

    Elzain, M., E-mail: elzain@squ.edu.om; Al Rawas, A.; Yousif, A.; Gismelseed, A.; Rais, A.; Al-Omari, I.; Bouziane, K. [College of Science, Department of Physics (Oman); Widatallah, H. [Khartoum University, Department of Physics, Faculty of Science (Sudan)

    2004-12-15

    The discrete variational method is used to study the effect of interactions of iron impurities on the magnetic moments, hyperfine fields and isomer shifts at iron sites in silver. We study small clusters of iron atoms as they grow to form FCC phase that is coherent with the silver lattice. The effects of the lattice relaxation and the ferromagnetic and antiferromagnetic couplings are also considered. When Fe atoms congregate around a central Fe atom in an FCC arrangement under ferromagnetic coupling, the local magnetic moment and the contact charge density at the central atom hardly change as the cluster builds up, whereas the hyperfine field increases asymptotically as the number of Fe nearest neighbors increases. Introduction of antiferromagnetic coupling has minor effect on the local magnetic moments and isomer shifts, however it produces large reduction in the hyperfine field. The lattice relaxation of the surrounding Fe atoms towards a BCC phase around a central Fe atom leads to reduction in the magnetic moment accompanied by increase in the magnetic hyperfine field.

  15. Parallel Local Graph Clustering

    OpenAIRE

    Shun, Julian; Roosta-Khorasani, Farbod; Fountoulakis, Kimon; Mahoney, Michael W.

    2016-01-01

    Graph clustering has many important applications in computing, but due to growing sizes of graph, even traditionally fast clustering methods such as spectral partitioning can be computationally expensive for real-world graphs of interest. Motivated partly by this, so-called local algorithms for graph clustering have received significant interest due to the fact that they can find good clusters in a graph with work proportional to the size of the cluster rather than that of the entire graph. T...

  16. Clustering and classification

    CERN Document Server

    Arabie, Phipps

    1996-01-01

    At a moderately advanced level, this book seeks to cover the areas of clustering and related methods of data analysis where major advances are being made. Topics include: hierarchical clustering, variable selection and weighting, additive trees and other network models, relevance of neural network models to clustering, the role of computational complexity in cluster analysis, latent class approaches to cluster analysis, theory and method with applications of a hierarchical classes model in psychology and psychopathology, combinatorial data analysis, clusterwise aggregation of relations, review

  17. Cluster ion beam facilities

    International Nuclear Information System (INIS)

    A brief state-of-the-art review in the field of cluster-surface interactions is presented. Ionised cluster beams could become a powerful and versatile tool for the modification and processing of surfaces as an alternative to ion implantation and ion assisted deposition. The main effects of cluster-surface collisions and possible applications of cluster ion beams are discussed. The outlooks of the Cluster Implantation and Deposition Apparatus (CIDA) being developed in Guteborg University are shown

  18. Graded cluster algebras

    OpenAIRE

    Grabowski, Jan

    2015-01-01

    In the cluster algebra literature, the notion of a graded cluster algebra has been implicit since the origin of the subject. In this work, we wish to bring this aspect of cluster algebra theory to the foreground and promote its study. We transfer a definition of Gekhtman, Shapiro and Vainshtein to the algebraic setting, yielding the notion of a multi-graded cluster algebra. We then study gradings for finite type cluster algebras without coefficients, giving a full classification. Translating ...

  19. A simulation of the cluster structures in Ge-Se vitreous chalcogenide semiconductors

    OpenAIRE

    Gurin, V.; Shpotyuk, O.; Boyko, V

    2013-01-01

    A structure of germanium selenide glasses is simulated by the featured clusters built from the tetrahedral GeSe4 units up to the clusters with six germanium atoms (Ge6Se16H4 and Ge6Se16H8). Quantum chemical calculations at the DFT level with effective core potentials for Ge and Se atoms for the clusters of different composition reveal their relative stability and optical properties.

  20. Atomic Energy Basics, Understanding the Atom Series.

    Science.gov (United States)

    Atomic Energy Commission, Oak Ridge, TN. Div. of Technical Information.

    This booklet is part of the "Understanding the Atom Series," though it is a later edition and not included in the original set of 51 booklets. A basic survey of the principles of nuclear energy and most important applications are provided. These major topics are examined: matter has molecules and atoms, the atom has electrons, the nucleus,…

  1. Ligand-protected gold clusters: the structure, synthesis and applications

    Science.gov (United States)

    Pichugina, D. A.; Kuz'menko, N. E.; Shestakov, A. F.

    2015-11-01

    Modern concepts of the structure and properties of atomic gold clusters protected by thiolate, selenolate, phosphine and phenylacetylene ligands are analyzed. Within the framework of the superatom theory, the 'divide and protect' approach and the structure rule, the stability and composition of a cluster are determined by the structure of the cluster core, the type of ligands and the total number of valence electrons. Methods of selective synthesis of gold clusters in solution and on the surface of inorganic composites based, in particular, on the reaction of Aun with RS, RSe, PhC≡C, Hal ligands or functional groups of proteins, on stabilization of clusters in cavities of the α-, β and γ-cyclodextrin molecules (Au15 and Au25) and on anchorage to a support surface (Au25/SiO2, Au20/C, Au10/FeOx) are reviewed. Problems in this field are also discussed. Among the methods for cluster structure prediction, particular attention is given to the theoretical approaches based on the density functional theory (DFT). The structures of a number of synthesized clusters are described using the results obtained by X-ray diffraction analysis and DFT calculations. A possible mechanism of formation of the SR(AuSR)n 'staple' units in the cluster shell is proposed. The structure and properties of bimetallic clusters MxAunLm (M=Pd, Pt, Ag, Cu) are discussed. The Pd or Pt atom is located at the centre of the cluster, whereas Ag and Cu atoms form bimetallic compounds in which the heteroatom is located on the surface of the cluster core or in the 'staple' units. The optical properties, fluorescence and luminescence of ligand-protected gold clusters originate from the quantum effects of the Au atoms in the cluster core and in the oligomeric SR(AuSR)x units in the cluster shell. Homogeneous and heterogeneous reactions catalyzed by atomic gold clusters are discussed in the context of the reaction mechanism and the nature of the active sites. The bibliography includes 345 references.

  2. Catalysis applications of size-selected cluster deposition.

    Energy Technology Data Exchange (ETDEWEB)

    Vajda, Stefan; White, Michael G.

    2015-12-01

    In this Perspective, we review recent studies of size-selected cluster deposition for catalysis applications performed at the U.S. DOE National Laboratories, with emphasis on work at Argonne National Laboratory (ANL) and Brookhaven National Laboratory (BNL). The focus is on the preparation of model supported catalysts in which the number of atoms in the deposited clusters is precisely controlled using a combination of gas-phase cluster ion sources, mass spectrometry, and soft-landing techniques. This approach is particularly effective for investigations of small nanoclusters, 0.5-2 nm (<200 atoms), where the rapid evolution of the atomic and electronic structure makes it essential to have precise control over cluster size. Cluster deposition allows for independent control of cluster size, coverage, and stoichiometry (e.g., the metal-to-oxygen ratio in an oxide cluster) and can be used to deposit on any substrate without constraints of nucleation and growth. Examples are presented for metal, metal oxide, and metal sulfide cluster deposition on a variety of supports (metals, oxides, carbon/diamond) where the reactivity, cluster-support electronic interactions, and cluster stability and morphology are investigated. Both UHV and in situ/operando studies are presented that also make use of surface-sensitive X-ray characterization tools from synchrotron radiation facilities. Novel applications of cluster deposition to electrochemistry and batteries are also presented. This review also highlights the application of modern ab initio electronic structure calculations (density functional theory), which can essentially model the exact experimental system used in the laboratory (i.e., cluster and support) to provide insight on atomic and electronic structure, reaction energetics, and mechanisms. As amply demonstrated in this review, the powerful combination of atomically precise cluster deposition and theory is able to address fundamental aspects of size-effects, cluster

  3. Cluster Evaluation of Density Based Subspace Clustering

    CERN Document Server

    Sembiring, Rahmat Widia

    2010-01-01

    Clustering real world data often faced with curse of dimensionality, where real world data often consist of many dimensions. Multidimensional data clustering evaluation can be done through a density-based approach. Density approaches based on the paradigm introduced by DBSCAN clustering. In this approach, density of each object neighbours with MinPoints will be calculated. Cluster change will occur in accordance with changes in density of each object neighbours. The neighbours of each object typically determined using a distance function, for example the Euclidean distance. In this paper SUBCLU, FIRES and INSCY methods will be applied to clustering 6x1595 dimension synthetic datasets. IO Entropy, F1 Measure, coverage, accurate and time consumption used as evaluation performance parameters. Evaluation results showed SUBCLU method requires considerable time to process subspace clustering; however, its value coverage is better. Meanwhile INSCY method is better for accuracy comparing with two other methods, altho...

  4. Teach us atom structure

    International Nuclear Information System (INIS)

    This book is written to teach atom structure in very easy way. It is divided into nine chapters, which indicates what is the components of matter? when we divide matter continuously, it becomes atom, what did atom look like? particles comprised of matter is not only atom, discover of particles comprised of atom, symbol of element, various radiation, form alchemy to nuclear transmutation, shape of atom is evolving. It also has various pictures in each chapters to explain easily.

  5. Teach us atom structure

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Suh Yeon

    2006-08-15

    This book is written to teach atom structure in very easy way. It is divided into nine chapters, which indicates what is the components of matter? when we divide matter continuously, it becomes atom, what did atom look like? particles comprised of matter is not only atom, discover of particles comprised of atom, symbol of element, various radiation, form alchemy to nuclear transmutation, shape of atom is evolving. It also has various pictures in each chapters to explain easily.

  6. Media Clusters and Media Cluster Policies

    OpenAIRE

    Karlsson, Charlie; Picard, Robert

    2011-01-01

    Large media clusters have emerged in a limited number of large cities, characterizing the geographical concentration of the global media industry. This paper explores the reasons behind the localization patterns of media industries, the effect of the rapid advancement of Information and Communication Technologies (ICT) on media clusters and the role of media cluster policies. One might draw the conclusion that with the developments of the ICT sector and the fact that there are no raw material...

  7. Size-selected Au clusters deposited on SiO2/Si: Stability of clusters under ambient pressure and elevated temperatures

    International Nuclear Information System (INIS)

    This study examined the oxidation and reduction behavior of mass-selected Au clusters consisting of 2-13 atoms deposited on silica. An atomic oxygen environment was used for the oxidation of Au. X-ray photoelectron spectroscopy (XPS) was used to identify Au(III) and Au(O). Au5, Au7 and Au13 clusters deposited on the as-prepared SiO2/Si substrates were highly inert towards oxidation, whereas the other clusters could be oxidized, i.e. the chemical property drastically changed with the number of atoms in a cluster. The size-selectivity in chemical reactivity remained unchanged upon air-exposure. The chemical properties of the deposited Au clusters were unchanged after annealing at 250 deg. C. Annealing at higher temperatures caused structural changes to the surface, as determined by the oxidation behavior. XPS of the deposited Au clusters upon annealing indicated charge transfer from Au to silica.

  8. Cluster selection in divisive clustering algorithms

    OpenAIRE

    Savaresi, Sergio,; Boley, Daniel L.; Bittanti, Sergio; Gazzaniga, Giovanna

    2002-01-01

    This paper deals with the problem of clustering a data-set. In particular, the bisecting divisive approach is here considered. This approach can be naturally divided into two sub-problems: the problem of choosing which cluster must be divided, and the problem of splitting the selected cluster. The focus here is on the first problem. The contribution of this work is to propose a new technique for the selection of the cluster to split. This technique is based upon the shape of...

  9. Structural, electronic and magnetic properties of Cr-doped (ZnTe)12 clusters

    International Nuclear Information System (INIS)

    We have studied the energetics and magnetism in Cr-doped (ZnTe)12 clusters by first principles density functional calculations. Total energy calculations suggest that it is energetically most favourable for Cr atoms to substitute at Zn sites. Both ferromagnetic and anti-ferromagnetic coupling between the Cr atoms exist depending on the Cr-Cr distance in the clusters. The magnetic exchange coupling between Cr atoms is short-ranged

  10. Atomic phase diagram

    Institute of Scientific and Technical Information of China (English)

    LI Shichun

    2004-01-01

    Based on the Thomas-Fermi-Dirac-Cheng model, atomic phase diagram or electron density versus atomic radius diagram describing the interaction properties of atoms of different kinds in equilibrium state is developed. Atomic phase diagram is established based on the two-atoms model. Besides atomic radius, electron density and continuity condition for electron density on interfaces between atoms, the lever law of atomic phase diagram involving other physical parameters is taken into account, such as the binding energy, for the sake of simplicity.

  11. Atomizer design for viscous-melt atomization

    Energy Technology Data Exchange (ETDEWEB)

    Czisch, C. [Chemical Engineering Department, University Bremen, Badgasteiner Str. 3, 28359 Bremen (Germany); Fritsching, U. [Chemical Engineering Department, University Bremen, Badgasteiner Str. 3, 28359 Bremen (Germany)], E-mail: ufri@iwt.uni-bremen.de

    2008-03-25

    The development of a gas atomization unit is introduced, which utilizes characteristic flow effects for efficient fragmentation of viscous liquids and melts. The proposed device combines a classical rotary atomizer with an external mixing gas atomizer. Here, the liquid stream is first transformed into a thin liquid sheet before disintegration. Thereby the specific surface energy is increased without breakup. The movement of the free flowing liquid film is controlled by the local gas flow field in order to transport the film into the most effective atomization region. The fragmentation process itself is caused by a perpendicular impinging gas stream. Numerical flow simulations are used for the development of the hybrid atomizer construction. Experiments using viscous model liquids show that for constant air-to-liquid mass-flow ratio the particle size is reduced using the hybrid atomizer compared with a conventional gas atomizer. Results of model experiments as well as of experiments with a viscous mineral melt are discussed.

  12. Atomizer design for viscous-melt atomization

    International Nuclear Information System (INIS)

    The development of a gas atomization unit is introduced, which utilizes characteristic flow effects for efficient fragmentation of viscous liquids and melts. The proposed device combines a classical rotary atomizer with an external mixing gas atomizer. Here, the liquid stream is first transformed into a thin liquid sheet before disintegration. Thereby the specific surface energy is increased without breakup. The movement of the free flowing liquid film is controlled by the local gas flow field in order to transport the film into the most effective atomization region. The fragmentation process itself is caused by a perpendicular impinging gas stream. Numerical flow simulations are used for the development of the hybrid atomizer construction. Experiments using viscous model liquids show that for constant air-to-liquid mass-flow ratio the particle size is reduced using the hybrid atomizer compared with a conventional gas atomizer. Results of model experiments as well as of experiments with a viscous mineral melt are discussed

  13. Cold Matter Assembled Atom-by-Atom

    CERN Document Server

    Endres, Manuel; Keesling, Alexander; Levine, Harry; Anschuetz, Eric R; Krajenbrink, Alexandre; Senko, Crystal; Vuletic, Vladan; Greiner, Markus; Lukin, Mikhail D

    2016-01-01

    The realization of large-scale fully controllable quantum systems is an exciting frontier in modern physical science. We use atom-by-atom assembly to implement a novel platform for the deterministic preparation of regular arrays of individually controlled cold atoms. In our approach, a measurement and feedback procedure eliminates the entropy associated with probabilistic trap occupation and results in defect-free arrays of over 50 atoms in less than 400 ms. The technique is based on fast, real-time control of 100 optical tweezers, which we use to arrange atoms in desired geometric patterns and to maintain these configurations by replacing lost atoms with surplus atoms from a reservoir. This bottom-up approach enables controlled engineering of scalable many-body systems for quantum information processing, quantum simulations, and precision measurements.

  14. Properties of small Ar sub N-1 K/+/ ionic clusters

    Science.gov (United States)

    Etters, R. D.; Danilowicz, R.; Dugan, J.

    1977-01-01

    A self-consistent formalism is developed that, based upon a many-body potential, dynamically determines the thermodynamic properties of ionic clusters without an a priori designation of the equilibrium structures. Aggregates consisting of a single closed shell K(+) ion and N-1 isoelectronic argon atoms were studied. The clusters form crystallites at low temperatures, and melting transitions and spontaneous dissociations are indicated. The results confirm experimental evidence that shows that ionic clusters become less stable with increasing N. The crystallite structures formed by four different clusters are isosceles triangle, skewed form, octahedron with ion in the middle, and icosahedron with the ion in the middle.

  15. Surface reconstruction precursor to melting in Au309 clusters

    Directory of Open Access Journals (Sweden)

    Fuyi Chen

    2011-09-01

    Full Text Available The melting of gold cluster is one of essential properties of nanoparticles and revisited to clarify the role played by the surface facets in the melting transition by molecular dynamics simulations. The occurrence of elaborate surface reconstruction is observed using many-body Gupta potential as energetic model for 309-atom (2.6 nm decahedral, cuboctahedral and icosahedral gold clusters. Our results reveal for the first time a surface reconstruction as precursor to the melting transitions. The surface reconstruction lead to an enhanced melting temperature for (100 faceted decahedral and cuboctahedral cluster than (111 faceted icosahedral gold cluster, which form a liquid patch due to surface vacancy.

  16. Nuclear clustering in the energy density functional approach

    International Nuclear Information System (INIS)

    Nuclear Energy Density Functionals (EDFs) are a microscopic tool of choice extensively used over the whole chart to successfully describe the properties of atomic nuclei ensuing from their quantum liquid nature. In the last decade, they also have proved their ability to deal with the cluster phenomenon, shedding a new light on its fundamental understanding by treating on an equal footing both quantum liquid and cluster aspects of nuclei. Such a unified microscopic description based on nucleonic degrees of freedom enables to tackle the question pertaining to the origin of the cluster phenomenon and emphasizes intrinsic mechanisms leading to the emergence of clusters in nuclei

  17. Determining the properties of gas-phase clusters

    Science.gov (United States)

    Hopkins, W. Scott

    2015-11-01

    As our understanding of clusters has improved, we have found that rather than being models for surface and condensed phase phenomena, clusters often display chemical and physical properties that are quite distinct from those of their atomic constituents or associated bulk materials. Indeed, identifying and utilising the unique properties of dimensionally confined species is a major theme in nanotechnology. Consequently, numerous experimental and computational methods have been employed to investigate the structures and properties of cluster systems. In this article, the techniques of infrared multiple photon dissociation and differential mobility spectrometry are discussed using the examples of [Ag.B12F12]- and tetraalkylammonium/solvent ionic clusters, respectively.

  18. Nuclear clustering in the energy density functional approach

    Energy Technology Data Exchange (ETDEWEB)

    Ebran, J.-P., E-mail: jean-paul.ebran@cea.fr [CEA,DAM,DIF, F-91297 Arpajon (France); Khan, E. [Institut de Physique Nucléaire, Université Paris-Sud CEA, IN2P3 CNRS, F-91406 Orsay Cedex (France); Nikšić, T.; Vretenar, D. [Physics Department, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia)

    2015-10-15

    Nuclear Energy Density Functionals (EDFs) are a microscopic tool of choice extensively used over the whole chart to successfully describe the properties of atomic nuclei ensuing from their quantum liquid nature. In the last decade, they also have proved their ability to deal with the cluster phenomenon, shedding a new light on its fundamental understanding by treating on an equal footing both quantum liquid and cluster aspects of nuclei. Such a unified microscopic description based on nucleonic degrees of freedom enables to tackle the question pertaining to the origin of the cluster phenomenon and emphasizes intrinsic mechanisms leading to the emergence of clusters in nuclei.

  19. Electronic and Magnetic Properties of Small Iridium Clusters

    Institute of Scientific and Technical Information of China (English)

    KUANG Xiang-jun

    2004-01-01

    The electronic and magnetic properties of small IrN clusters (N=5, 6, 9, 13, and 19 ) are studied by using the discrete-variational local-spin-density-functional method. The equilibrium bond length in the chosen geometry for IrN clusters are determined and show bond contraction compared with the bulk interatomic spacing. The clusters with magnetic ground state have ferromagnetic interaction and their average magnetic moment per atom has a complex size dependence. At last, the reactivity of IrN clusters toward H2, N2 and CO molecules is predicted.

  20. Young massive star clusters

    CERN Document Server

    Zwart, Simon Portegies; Gieles, Mark

    2010-01-01

    Young massive clusters are dense aggregates of young stars that form the fundamental building blocks of galaxies. Several examples exist in the Milky Way Galaxy and the Local Group, but they are particularly abundant in starburst and interacting galaxies. The few young massive clusters that are close enough to resolve are of prime interest for studying the stellar mass function and the ecological interplay between stellar evolution and stellar dynamics. The distant unresolved clusters may be effectively used to study the star-cluster mass function, and they provide excellent constraints on the formation mechanisms of young cluster populations. Young massive clusters are expected to be the nurseries for many unusual objects, including a wide range of exotic stars and binaries. So far only a few such objects have been found in young massive clusters, although their older cousins, the globular clusters, are unusually rich in stellar exotica. In this review we focus on star clusters younger than $\\sim100$\\,Myr, m...

  1. Photonic, Electronic and Atomic Collisions

    Science.gov (United States)

    Fainstein, Pablo D.; Lima, Marco Aurelio P.; Miraglia, Jorge E.; Montenegro, Eduardo C.; Rivarola, Roberto D.

    2006-11-01

    Plenary. Electron collisions - past, present and future / J. W. McConkey. Collisions of slow highly charged ions with surfaces / J. Burgdörfer ... [et al.]. Atomic collisions studied with "reaction-microscopes" / R. Moshammer ... [et al.]. Rydberg atoms: a microscale laboratory for studying electron-molecule tnteractions / F. B. Dunning -- Collisions involvintg photons. Quantum control of photochemical reaction dynamics and molecular functions / M. Yamaki ... [et al.]. Manipulating and viewing Rydberg wavepackets / R. R. Jones. Angle-resolved photoelectrons as a probe of strong-field interactions / M. Vrakking. Ultracold Rydberg atoms in a structured environment / I. C. H. Liu and J. M. Rost. Synchrotron-radiation-based recoil ion momentum spectroscopy of laser cooled and trapped cesium atoms / L. H. Coutinho. Reconstruction of attosecond pulse trains / Y. Mairesse ... [et al.]. Selective excitation of metastable atomic states by Femto- and attosecond laser pulses / A. D. Kondorskiy. Accurate calculations of triple differential cross sections for double photoionization of the hygrogen molecule / W. Vanroose ... [et al.]. Double and triple photoionization of Li and Be / J. Colgan, M. S. Pindzola and F. Robicheaux. Few/many body dynamics in strong laser fields / J. Zanghellini and T. Brabec. Rescattering-induced effects in electron-atom scattering in the presence of a circularly polarized laser field / A. V. Flegel ... [et al.]. Multidimensional photoelectron spectroscopy / P. Lablanquie ... [et al.]. Few photon and strongly driven transitions in the XUV and beyond / P. Lambropoulos, L. A. A. Nikolopoulos and S. I. Themelis. Ionization dynamics of atomic clusters in intense laser pulses / U. Saalmann and J. M. Rost. On the second order autocorrelation of an XUV attosecond pulse train / E. P. Benis ... [et al.]. Evidence for rescattering in molecular dissociation / I. D. Williams ... [et al.]. Photoionizing ions using synchrotron radiation / R. Phaneuf. Photo double

  2. Density functional study on structural and electronic properties of bimetallic gold-yttrium clusters: comparison with pure gold and yttrium clusters

    Institute of Scientific and Technical Information of China (English)

    Mao Hua-Ping; Wang Hong-Yan; Sheng Yong

    2008-01-01

    Employing first-principles methods, based on the density functional theory, this paper investigates the ground state geometric and electronic properties of pure gold clusters, pure yttrium clusters and gold clusters doped each with one yttrium atom. It is shown that the average bond lengths in the Aun-lY(n ≤9) bimetallic clusters are shorter than those in the corresponding pure gold and yttrium clusters. The most stable isomers of the yttrium-doped gold clusters tend to equally delocalize valence s, p and d electrons of the constituent atoms over the entire structure. The Y atom has maximum number of neighbouring Au atom, which tends to be energetically favourable in the lowest-energy equilibrium structures, because the Au-Y bond is stronger than the Au-Au bond. The three-dimensional isomers of Aun-1Y structures are found in an early appearance starting at n=5 (Au4Y). Calculated vertical ionization potential and electron affinities as a function of the cluster size show odd-even oscillatory behaviour, and resemble pure gold clusters. However, one of the most striking feature of pure yttrium clusters is the absence of odd-even alternation, in agreement with mass spectrometric observations. The HOMO-LUMO gap of Au3Y is the biggest in all the doped Aun-1Y(n≤9) bimetallic clusters.

  3. Cluster automorphism groups of cluster algebras with coefficients

    OpenAIRE

    Chang, Wen; Zhu, Bin

    2015-01-01

    We study the cluster automorphism group of a skew-symmetric cluster algebra with geometric coefficients. For this, we introduce the notion of gluing free cluster algebra, and show that under a weak condition the cluster automorphism group of a gluing free cluster algebra is a subgroup of the cluster automorphism group of its principal part cluster algebra (i.e. the corresponding cluster algebra without coefficients). We show that several classes of cluster algebras with coefficients are gluin...

  4. Structures and Melting of Cu38 Clusters

    International Nuclear Information System (INIS)

    Using Molecular Dynamics and thermal quenching simulations the stable geometrical structures and energies of the Cu38 clusters are identified. The interaction between the cluster atoms is modeled by an Embedded-Atom Potential Surface, Voter and Chen's version. For the most stable isomers of Cu38 cluster, independent 500 phase space coordinates are generated along high-energy trajectories, which are used as the initial configurations for thermal quenching. The energies of the first and second isomers are -108.62 eV and -108.36 eV, respectively. The lowest energy structure of the Cu38 cluster has a fcc-like truncated octahedron form which is different from those of the other sizes, i.e., the second isomer has a truncated icosahedral form. The average bond lengths, of the first and second isomers' of the Cu38 cluster are 2.4914 A A and 2.4994 A A respectively. The melting dynamics of these isomers are being studied. In addition, the following most stable three isomers are identified

  5. Atomic model of liquid pure Fe

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Using a θ-θX-ray diffractometer, the liquid structure of pure Fewas investigated and the diffraction intensity, structure factor, pair distribution function as well as the coordination number and atomic distance were obtained. The experimental results showed that there was also a pre-peak on the curve of the structure factor of liquid pure Fe. The pre-peak is a mark of medium-range order in melts. According to the characteristics of pre-peak, an atomic model of liquid pure Fe is constructed, namely, the structure of liquid pure Fe is a combination of clusters consisting of bcc cells with shared vertexes and other atoms with random dense atom distribution.

  6. What Makes Clusters Decline?

    DEFF Research Database (Denmark)

    Østergaard, Christian Richter; Park, Eun Kyung

    2015-01-01

    Most studies on regional clusters focus on identifying factors and processes that make clusters grow. However, sometimes technologies and market conditions suddenly shift, and clusters decline. This paper analyses the process of decline of the wireless communication cluster in Denmark. The...... longitudinal study on the high-tech cluster reveals that technological lock-in and exit of key firms have contributed to decline. Entrepreneurship has a positive effect on the cluster’s adaptive capabilities, while multinational companies have contradicting effects by bringing in new resources to the cluster...

  7. New projectiles: multicharged metal clusters and biopolymers

    International Nuclear Information System (INIS)

    Metal clusters and molecules are the one mean to realize simultaneous impacts of several atoms on a reduced surface(∼100A). The interaction characteristics is the non-linearity of energy deposition; the perturbation that the cluster produces, is above than the sum of the perturbation induced by its components, taken separately. The purpose of ORION project is to accelerate these new projectiles at ORSAY Tandem. The considered mass range is from 100 Daltons to 100 000 Daltons and energy range from MeV to GeV

  8. Identification of TiO2 clusters present during synthesis of sol-gel derived TiO2 nano-particles

    DEFF Research Database (Denmark)

    Simonsen, Morten Enggrob; Søgaard, Erik Gydesen

    -MS) and dynamic light scattering (DLS). Depending on the involved precursor TiO2 clusters of different sizes were identified (TTIP ~ 11-12 Ti atoms, TTB ~ 10-11 Ti atoms, and TTE ~ 5-7 Ti atoms).4 The Ti-O-Ti backbone/core of the titanium clusters were found to be quite stable after formation and do not...

  9. Research briefing on selected opportunities in atomic, molecular, and optical sciences

    International Nuclear Information System (INIS)

    This report discusses research on the following topics: The Laser-Atom Revolution; Controlling Dynamical Pathways; Nonclassical States of Light; Transient States of Atomic Systems; New Light Generation and Handling; Clusters; Atomic Physics at User Facilities; and Impacts of AMO Sciences on Modern Technologies

  10. Analysis of Various Clustering Algorithms

    OpenAIRE

    Asst Prof. Sunila Godara,; Ms. Amita Verma,

    2013-01-01

    Data clustering is a process of putting similar data into groups. A clustering algorithm partitions a data set into several groups such that the similarity within a group is larger than among groups. This paper reviews four types of clustering techniques- k-Means Clustering, Farther first clustering, Density Based Clustering, Filtered clusterer. These clustering techniques are implemented and analyzed using a clustering tool WEKA. Performance of the 4 techniques are presented and compared.

  11. Infrared Multiple Photon Dissociation Spectroscopy Of Metal Cluster-Adducts

    Science.gov (United States)

    Cox, D. M.; Kaldor, A.; Zakin, M. R.

    1987-01-01

    Recent development of the laser vaporization technique combined with mass-selective detection has made possible new studies of the fundamental chemical and physical properties of unsupported transition metal clusters as a function of the number of constituent atoms. A variety of experimental techniques have been developed in our laboratory to measure ionization threshold energies, magnetic moments, and gas phase reactivity of clusters. However, studies have so far been unable to determine the cluster structure or the chemical state of chemisorbed species on gas phase clusters. The application of infrared multiple photon dissociation IRMPD to obtain the IR absorption properties of metal cluster-adsorbate species in a molecular beam is described here. Specifically using a high power, pulsed CO2 laser as the infrared source, the IRMPD spectrum for methanol chemisorbed on small iron clusters is measured as a function of the number of both iron atoms and methanols in the complex for different methanol isotopes. Both the feasibility and potential utility of IRMPD for characterizing metal cluster-adsorbate interactions are demonstrated. The method is generally applicable to any cluster or cluster-adsorbate system dependent only upon the availability of appropriate high power infrared sources.

  12. A molecular dynamics simulation study of small cluster formation and migration in metals

    International Nuclear Information System (INIS)

    Molecular dynamics (MD) simulations were performed to investigate the kinetics and energetics of self-interstitial atom (SIA) clusters in vanadium, tantalum and copper. The formation energies of the SIA clusters in all the metals are well represented by a power function with a 0.75 exponent of the cluster size. The cluster diffusivities strongly depend on their structure. In vanadium and tantalum, all the SIA pairs in clusters are located along the direction rather than the direction. The clusters can migrate one-dimensionally in the direction with a small activation energy of around 0.1 eV. In copper, the collective orientation preference of the SIA pairs is not observed indicating that rotation of several pairs in the cluster is required for the cluster to migrate. The activation energy for the rotation is not so high as the cluster migration energy itself. The difference in the SIA cluster migration behavior between bcc and fcc metals is discussed

  13. FY 1997 research and development of fusion domains. Part 1. Studies on cluster science; 1997 nendo seika hokokusho (yugo ryoiki kenkyu kaihatsu). 1. Cluster Science no kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-03-01

    Studies were made on clusters which are thought to play important roles in status changes in substances (coagulation, crystallization and phase segregation) and chemical reactions (combustion, aqueous solution reaction and catalytic reaction). In the study of clusters by using infrared spectra, a method was developed to detect by using mass analyzer the cluster ion amount produced by dual resonance between resonantly enhanced multiphoton ionization (REMPI) and infrared lights. Fabrication of a Terahertz spectrometer was planned to enable high-resolution and high-accuracy observation on molecular clusters. Clusters consisting of silver atoms and ammonia molecules were successfully observed. A method was developed to investigate size dependence of cluster reactivity by using a Fourier converted ion cyclotron resonant mass analyzer. In addition, studies were conducted on clusters in liquids and aqueous solutions, clusters frozen in surface and matrix, and clusters stabilized in micro-space. 96 refs., 34 figs., 2 tabs.

  14. Optimum Metallic-Bond Scheme: A Quantitative Analysis of Mass Spectra of Sodium Clusters

    Institute of Scientific and Technical Information of China (English)

    苏长荣; 李家明

    2001-01-01

    Based on the results of the optimum metallic-bond scheme for sodium clusters, we present a quantitative analysis of the detailed features of the mass spectra of sodium clusters. We find that, in the generation of sodium clusters with various abundances, the quasi-steady processes through adding or losing a sodium atom dominate. The quasi-steady processes through adding or losing a sodium dimer are also important to understand the detailed features of mass spectra for small clusters.

  15. Magnetron sputtering cluster apparatus for formation and deposition of size-selected metal nanoparticles

    OpenAIRE

    Hanif, Muhammad; Popok, Vladimir

    2015-01-01

    The experimental setup utilizing a DC magnetron sputtering source for production of metal clusters, their size (mass) selection and following deposition in high vacuum is described. The source is capable to form clusters of various metals, for example, copper, silver, gold etc. Cluster size selection is achieved using an electrostatic quadrupole mass selector. The deposited silver clusters are studied using atomic force microscopy. The height distributions show typical relative standard size ...

  16. Mass Spectrometric Developments and a Study of Lithium Doped Silicon and Germanium Clusters.

    OpenAIRE

    Haeck, Jorg de

    2011-01-01

    Clusters, consisting of a few up to several thousands of atoms, exhibit size-dependent physical and chemical properties linking the nanoscale to bulk matter in a non-trivial way. The careful design of clusters of two different elements (binary clusters) allows the synthesis of particularly stable species with tailored properties that eventually could be used as building blocks for novel nanomaterials. However, the continuation of our experimental research of binary clusters in the gas phase o...

  17. Secondary cluster ion distributions produced by MeV ion impacts on Group IIA oxides and nitrates

    Science.gov (United States)

    Ferrell, W. R.; von Heimburg, S. L.; van Stipdonk, M. J.; Schweikert, E. A.

    1996-10-01

    Cluster ion distributions from MeV atomic ion impacts (fission fragments from 252Cf on divalent Group IIA (GIIA) oxides and nitrates have been examined. The two predominant positive cluster species observed from both solids, (MO)nH+ and (MO)n M+ (M denotes metal atom) are evidence of a localized plasma state thought to be created by discrete MeV ion impacts. Cluster intensities and extent of clustering from nitrates were generally greater than those from oxides. The enhanced abundances at certain "magic numbers" of n observed in the mass spectra are believed to arise during the actual cluster production process. These periodic enhancements in cluster stabilities are attributed to the adoption by size-specific clusters of atomic arrangements analogous to segments of the rock salt lattice of the GIIA oxides. Cluster stabilities for the GIIA oxides and nitrates are influenced by the ionicity of M-O bonds, formal valence of metal and radius of cation.

  18. Electronic and magnetic properties of small rhodium clusters

    Energy Technology Data Exchange (ETDEWEB)

    Soon, Yee Yeen; Yoon, Tiem Leong [School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Lim, Thong Leng [Faculty of Engineering and Technology, Multimedia University, Melaka Campus, 75450 Melaka (Malaysia)

    2015-04-24

    We report a theoretical study of the electronic and magnetic properties of rhodium-atomic clusters. The lowest energy structures at the semi-empirical level of rhodium clusters are first obtained from a novel global-minimum search algorithm, known as PTMBHGA, where Gupta potential is used to describe the atomic interaction among the rhodium atoms. The structures are then re-optimized at the density functional theory (DFT) level with exchange-correlation energy approximated by Perdew-Burke-Ernzerhof generalized gradient approximation. For the purpose of calculating the magnetic moment of a given cluster, we calculate the optimized structure as a function of the spin multiplicity within the DFT framework. The resultant magnetic moments with the lowest energies so obtained allow us to work out the magnetic moment as a function of cluster size. Rhodium atomic clusters are found to display a unique variation in the magnetic moment as the cluster size varies. However, Rh{sub 4} and Rh{sub 6} are found to be nonmagnetic. Electronic structures of the magnetic ground-state structures are also investigated within the DFT framework. The results are compared against those based on different theoretical approaches available in the literature.

  19. Electronic and magnetic properties of small rhodium clusters

    International Nuclear Information System (INIS)

    We report a theoretical study of the electronic and magnetic properties of rhodium-atomic clusters. The lowest energy structures at the semi-empirical level of rhodium clusters are first obtained from a novel global-minimum search algorithm, known as PTMBHGA, where Gupta potential is used to describe the atomic interaction among the rhodium atoms. The structures are then re-optimized at the density functional theory (DFT) level with exchange-correlation energy approximated by Perdew-Burke-Ernzerhof generalized gradient approximation. For the purpose of calculating the magnetic moment of a given cluster, we calculate the optimized structure as a function of the spin multiplicity within the DFT framework. The resultant magnetic moments with the lowest energies so obtained allow us to work out the magnetic moment as a function of cluster size. Rhodium atomic clusters are found to display a unique variation in the magnetic moment as the cluster size varies. However, Rh4 and Rh6 are found to be nonmagnetic. Electronic structures of the magnetic ground-state structures are also investigated within the DFT framework. The results are compared against those based on different theoretical approaches available in the literature

  20. Cluster-enhanced sparse approximation of overlapping ultrasonic echoes.

    Science.gov (United States)

    Mor, Etai; Aladjem, Mayer; Azoulay, Amnon

    2015-02-01

    Ultrasonic pulse-echo methods have been used extensively in non-destructive testing of layered structures. In acoustic measurements on thin layers, the resulting echoes from two successive interfaces overlap in time, making it difficult to assess the individual echo parameters. Over the last decade sparse approximation methods have been extensively used to address this issue. These methods employ a large dictionary of elementary functions (atoms) and attempt to select the smallest subset of atoms (sparsest approximation) that represent the ultrasonic signal accurately. In this paper we propose the cluster-enhanced sparse approximation (CESA) method for estimating overlapping ultrasonic echoes. CESA is specifically adapted to deal with a large number of signals acquired during an ultrasonic scan. It incorporates two principal algorithms. The first is a clustering algorithm, which divides a set of signals comprising an ultrasonic scan into groups of signals that can be approximated by the same set of atoms. The second is a two-stage iterative algorithm, which alternates between update of the atoms associated with each cluster, and re-clustering of the signals according to the updated atoms. Because CESA operates on clusters of signals, it achieves improved results in terms of approximation error and computation time compared with conventional sparse methods, which operate on each signal separately. The superior ability of CESA to approximate highly overlapping ultrasonic echoes is demonstrated through simulation and experiments on adhesively bonded structures. PMID:25643086