Koopmans' theorem in the Hartree-Fock method. General formulation

NASA Astrophysics Data System (ADS)

Plakhutin, Boris N.

2018-03-01

This work presents a general formulation of Koopmans' theorem (KT) in the Hartree-Fock (HF) method which is applicable to molecular and atomic systems with arbitrary orbital occupancies and total electronic spin including orbitally degenerate (OD) systems. The new formulation is based on the full set of variational conditions imposed upon the HF orbitals by the variational principle for the total energy and the conditions imposed by KT on the orbitals of an ionized electronic shell [B. N. Plakhutin and E. R. Davidson, J. Chem. Phys. 140, 014102 (2014)]. Based on these conditions, a general form of the restricted open-shell HF method is developed, whose eigenvalues (orbital energies) obey KT for the whole energy spectrum. Particular attention is paid to the treatment of OD systems, for which the new method gives a number of unexpected results. For example, the present method gives four different orbital energies for the triply degenerate atomic level 2p in the second row atoms B to F. Based on both KT conditions and a parallel treatment of atoms B to F within a limited configuration interaction approach, we prove that these four orbital energies, each of which is triply degenerate, are related via KT to the energies of different spin-dependent ionization and electron attachment processes (2p)N → (2p ) N ±1. A discussion is also presented of specific limitations of the validity of KT in the HF method which arise in OD systems. The practical applicability of the theory is verified by comparing KT estimates of the ionization potentials I2s and I2p for the second row open-shell atoms Li to F with the relevant experimental data.

Magnetic spherical cores partly coated with periodic mesoporous organosilica single crystals.

PubMed

Li, Jing; Wei, Yong; Li, Wei; Deng, Yonghui; Zhao, Dongyuan

2012-03-07

Core-shell structured materials are of special significance in various applications. Until now, most reported core-shell structures have polycrystalline or amorphous coatings as their shell layers, with popular morphologies of microspheres or quasi-spheres. However, the single crystals, either mesoscale or atomic ones, are still rarely reported as shell layers. If single crystals can be coated on core materials, it would result in a range of new type core-shell structures with various morphologies, and probably more potential applications. In this work, we demonstrate that periodic mesoporous organosilica (PMO) single crystals can partly grow on magnetic microspheres to form incomplete Fe(3)O(4)@nSiO(2)@PMO core-shell materials in aqueous solution, which indeed is the first illustration that mesoporous single-crystal materials can be used as shell layers for preparation of core-shell materials. The achieved materials have advantages of high specific surface areas, good magnetic responses, embedded functional groups and cubic mesopore channels, which might provide them with various application conveniences. We suppose the partial growth is largely decided by the competition between growing tendency of single crystals and the resistances to this tendency. In principle, other single crystals, including a range of atomic single crystals, such as zeolites, are able to be developed into such core-shell structures.

Tuning optical properties of magic number cluster (SiO2)4O2H4 by substitutional bonding with gold atoms.

PubMed

Cai, Xiulong; Zhang, Peng; Ma, Liuxue; Zhang, Wenxian; Ning, Xijing; Zhao, Li; Zhuang, Jun

2009-04-30

By bonding gold atoms to the magic number cluster (SiO(2))(4)O(2)H(4), two groups of Au-adsorbed shell-like clusters Au(n)(SiO(2))(4)O(2)H(4-n) (n = 1-4) and Au(n)(SiO(2))(4)O(2) (n = 5-8) were obtained, and their spectral properties were studied. The ground-state structures of these clusters were optimized by density functional theory, and the results show that in despite of the different numbers and types of the adsorbed Au atoms, the cluster core (SiO(2))(4)O(2) of T(d) point-group symmetry keeps almost unchanged. The absorption spectra were obtained by time-dependent density functional theory. From one group to the other, an extension of absorption wavelength from the UV-visible to the NIR region was observed, and in each group the absorption strengths vary linearly with the number of Au atoms. These features indicate their advantages for exploring novel materials with easily controlled tunable optical properties. Furthermore, due to the weak electronic charge transfer between the Au atoms, the clusters containing Au(2) dimers, especially Au(8)(SiO(2))(4)O(2), absorb strongly NIR light at 900 approximately 1200 nm. Such strong absorption suggests potential applications of these shell-like clusters in tumor cells thermal therapy, like the gold-coated silica nanoshells with larger sizes.

Coaxial metal-oxide-semiconductor (MOS) Au/Ga2O3/GaN nanowires.

PubMed

Hsieh, Chin-Hua; Chang, Mu-Tung; Chien, Yu-Jen; Chou, Li-Jen; Chen, Lih-Juann; Chen, Chii-Dong

2008-10-01

Coaxial metal-oxide-semiconductor (MOS) Au-Ga2O3-GaN heterostructure nanowires were successfully fabricated by an in situ two-step process. The Au-Ga2O3 core-shell nanowires were first synthesized by the reaction of Ga powder, a mediated Au thin layer, and a SiO2 substrate at 800 degrees C. Subsequently, these core-shell nanowires were nitridized in ambient ammonia to form a GaN coating layer at 600 degrees C. The GaN shell is a single crystal, an atomic flat interface between the oxide and semiconductor that ensures that the high quality of the MOS device is achieved. These novel 1D nitride-based MOS nanowires may have promise as building blocks to the future nitride-based vertical nanodevices.

A new near-linear scaling, efficient and accurate, open-shell domain-based local pair natural orbital coupled cluster singles and doubles theory.

PubMed

Saitow, Masaaki; Becker, Ute; Riplinger, Christoph; Valeev, Edward F; Neese, Frank

2017-04-28

The Coupled-Cluster expansion, truncated after single and double excitations (CCSD), provides accurate and reliable molecular electronic wave functions and energies for many molecular systems around their equilibrium geometries. However, the high computational cost, which is well-known to scale as O(N 6 ) with system size N, has limited its practical application to small systems consisting of not more than approximately 20-30 atoms. To overcome these limitations, low-order scaling approximations to CCSD have been intensively investigated over the past few years. In our previous work, we have shown that by combining the pair natural orbital (PNO) approach and the concept of orbital domains it is possible to achieve fully linear scaling CC implementations (DLPNO-CCSD and DLPNO-CCSD(T)) that recover around 99.9% of the total correlation energy [C. Riplinger et al., J. Chem. Phys. 144, 024109 (2016)]. The production level implementations of the DLPNO-CCSD and DLPNO-CCSD(T) methods were shown to be applicable to realistic systems composed of a few hundred atoms in a routine, black-box fashion on relatively modest hardware. In 2011, a reduced-scaling CCSD approach for high-spin open-shell unrestricted Hartree-Fock reference wave functions was proposed (UHF-LPNO-CCSD) [A. Hansen et al., J. Chem. Phys. 135, 214102 (2011)]. After a few years of experience with this method, a few shortcomings of UHF-LPNO-CCSD were noticed that required a redesign of the method, which is the subject of this paper. To this end, we employ the high-spin open-shell variant of the N-electron valence perturbation theory formalism to define the initial guess wave function, and consequently also the open-shell PNOs. The new PNO ansatz properly converges to the closed-shell limit since all truncations and approximations have been made in strict analogy to the closed-shell case. Furthermore, given the fact that the formalism uses a single set of orbitals, only a single PNO integral transformation is necessary, which offers large computational savings. We show that, with the default PNO truncation parameters, approximately 99.9% of the total CCSD correlation energy is recovered for open-shell species, which is comparable to the performance of the method for closed-shells. UHF-DLPNO-CCSD shows a linear scaling behavior for closed-shell systems, while linear to quadratic scaling is obtained for open-shell systems. The largest systems we have considered contain more than 500 atoms and feature more than 10 000 basis functions with a triple-ζ quality basis set.

A new near-linear scaling, efficient and accurate, open-shell domain-based local pair natural orbital coupled cluster singles and doubles theory

NASA Astrophysics Data System (ADS)

Saitow, Masaaki; Becker, Ute; Riplinger, Christoph; Valeev, Edward F.; Neese, Frank

2017-04-01

The Coupled-Cluster expansion, truncated after single and double excitations (CCSD), provides accurate and reliable molecular electronic wave functions and energies for many molecular systems around their equilibrium geometries. However, the high computational cost, which is well-known to scale as O(N6) with system size N, has limited its practical application to small systems consisting of not more than approximately 20-30 atoms. To overcome these limitations, low-order scaling approximations to CCSD have been intensively investigated over the past few years. In our previous work, we have shown that by combining the pair natural orbital (PNO) approach and the concept of orbital domains it is possible to achieve fully linear scaling CC implementations (DLPNO-CCSD and DLPNO-CCSD(T)) that recover around 99.9% of the total correlation energy [C. Riplinger et al., J. Chem. Phys. 144, 024109 (2016)]. The production level implementations of the DLPNO-CCSD and DLPNO-CCSD(T) methods were shown to be applicable to realistic systems composed of a few hundred atoms in a routine, black-box fashion on relatively modest hardware. In 2011, a reduced-scaling CCSD approach for high-spin open-shell unrestricted Hartree-Fock reference wave functions was proposed (UHF-LPNO-CCSD) [A. Hansen et al., J. Chem. Phys. 135, 214102 (2011)]. After a few years of experience with this method, a few shortcomings of UHF-LPNO-CCSD were noticed that required a redesign of the method, which is the subject of this paper. To this end, we employ the high-spin open-shell variant of the N-electron valence perturbation theory formalism to define the initial guess wave function, and consequently also the open-shell PNOs. The new PNO ansatz properly converges to the closed-shell limit since all truncations and approximations have been made in strict analogy to the closed-shell case. Furthermore, given the fact that the formalism uses a single set of orbitals, only a single PNO integral transformation is necessary, which offers large computational savings. We show that, with the default PNO truncation parameters, approximately 99.9% of the total CCSD correlation energy is recovered for open-shell species, which is comparable to the performance of the method for closed-shells. UHF-DLPNO-CCSD shows a linear scaling behavior for closed-shell systems, while linear to quadratic scaling is obtained for open-shell systems. The largest systems we have considered contain more than 500 atoms and feature more than 10 000 basis functions with a triple-ζ quality basis set.

Correlation between the band gap expansion and melting temperature depression of nanostructured semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jianwei, E-mail: jwl189@163.com; Zhao, Xinsheng; Liu, Xinjuan

The band gap and melting temperature of a semiconductor are tunable with the size and shape of the specimen at the nanometer scale, and related mechanisms remain as yet unclear. In order to understand the common origin of the size and shape effect on these two seemingly irrelevant properties, we clarify, correlate, formulate, and quantify these two properties of GaAs, GaN, InP, and InN nanocrystals from the perspectives of bond order-length-strength correlation using the core-shell configuration. The consistency in the theoretical predictions, experimental observations, and numerical calculations verify that the broken-bond-induced local bond contraction and strength gain dictates the bandmore » gap expansion, while the atomic cohesive energy loss due to bond number reduction depresses the melting point. The fraction of the under-coordinated atoms in the skin shell quantitatively determines the shape and size dependency. The atomic under-coordination in the skin down to a depth of two atomic layers inducing a change in the local chemical bond is the common physical origin.« less

Following electron impact excitation of single (N, O, F, Ne, Na, Mg, Al, Si) atom L subshells ionization cross section calculations by using Lotz's equation

NASA Astrophysics Data System (ADS)

Aydinol, Mahmut

2017-02-01

L shell and L subshells ionization cross sections σL and σLi (i = 1, 2, 3) following electron impact on (N,O, F, Ne, Na, Mg, Al, Si) atoms calculated. By using Lotz' equation for nonrelativistic cases in Matlab σL and σLi cross section values obtained for ten electron impact(Eo) values in the range of ELi

Catalytic performance of M@Ni (M = Fe, Ru, Ir) core-shell nanoparticles towards ammonia decomposition for CO x -free hydrogen production

NASA Astrophysics Data System (ADS)

Chen, Xin; Zhou, Junwei; Chen, Shuangjing; Zhang, Hui

2018-06-01

To reduce the use of precious metals and maintain the catalytic activity for NH3 decomposition reaction, it is an effective way to construct bimetallic nanoparticles with special structures. In this paper, by using density functional theory methods, we investigated NH3 decomposition reaction on three types of core-shell nanoparticles M@Ni (M = Fe, Ru, Ir) with 13 core M atoms and 42 shell Ni atoms. The size of these three particles is about 1 nm. Benefit from alloying with Ru in this nanocluster, Ru@Ni core-shell nanoparticles exhibit catalytic activity comparable to that of single metal Ru, based on the analysis of the adsorption energy and potential energy diagram of NH3 decomposition, as well as N2 desorption processes. However, as for Fe@Ni and Ir@Ni core-shell nanoparticles, their catalytic activities are still unsatisfactory compared to the active metal Ru. In addition, in order to further explain the synergistic effect of bimetallic core-shell nanoparticles, the partial density of states were also calculated. The results show that d-band electrons provided by the core metal are the main factors affecting the entire catalytic process.

Transition energy and potential energy curves for ionized inner-shell states of CO, O2 and N 2 calculated by several inner-shell multiconfigurational approaches.

PubMed

Moura, Carlos E V de; Oliveira, Ricardo R; Rocha, Alexandre B

2013-05-01

Potential energy curves and inner-shell ionization energies of carbon monoxide, oxygen and nitrogen molecules were calculated using several forms of the inner-shell multiconfigurational self-consistent field (IS-MCSCF) method-a recently proposed protocol to obtain specifically converged inner-shell states at this level. The particular forms of the IS-MCSCF method designated IS-GVB-PP, IS-FVBL and IS-CASSCF stand for perfect pairing generalized valence bond, full valence bond-like MCSCF and complete active space self consistent field, respectively. A comparison of these different versions of the IS-MCSCF method was carried out for the first time. The results indicate that inner-shell states are described accurately even for the simplest version of the method (IS-GVB-PP). Dynamic correlation was recovered by multireference configuration interaction or multireference perturbation theory. For molecules not having equivalent atoms, all methods led to comparable and accurate transition energies. For molecules with equivalent atoms, the most accurate results were obtained by multireference perturbation theory. Scalar relativistic effects were accounted for using the Douglas-Kroll-Hess Hamiltonian.

Nanosized (mu12-Pt)Pd164-xPtx(CO)72(PPh3)20 (x approximately 7) containing Pt-centered four-shell 165-atom Pd-Pt core with unprecedented intershell bridging carbonyl ligands: comparative analysis of icosahedral shell-growth patterns with geometrically related Pd145(CO)x(PEt3)30 (x approximately 60) containing capped three-shell Pd145 core.

PubMed

Mednikov, Evgueni G; Jewell, Matthew C; Dahl, Lawrence F

2007-09-19

Presented herein are the preparation and crystallographic/microanalytical/magnetic/spectroscopic characterization of the Pt-centered four-shell 165-atom Pd-Pt cluster, (mu(12)-Pt)Pd(164-x)Pt(x)(CO)(72)(PPh(3))(20) (x approximately 7), 1, that replaces the geometrically related capped three-shell icosahedral Pd(145) cluster, Pd(145)(CO)(x)(PEt(3))(30) (x approximately 60), 2, as the largest crystallographically determined discrete transition metal cluster with direct metal-metal bonding. A detailed comparison of their shell-growth patterns gives rise to important stereochemical implications concerning completely unexpected structural dissimilarities as well as similarities and provides new insight concerning possible synthetic approaches for generation of multi-shell metal clusters. 1 was reproducibly prepared in small yields (<10%) from the reaction of Pd(10)(CO)(12)(PPh(3))(6) with Pt(CO)(2)(PPh(3))(2). Its 165-atom metal-core geometry and 20 PPh(3) and 72 CO ligands were established from a low-temperature (100 K) CCD X-ray diffraction study. The well-determined crystal structure is attributed largely to 1 possessing cubic T(h) (2/m3) site symmetry, which is the highest crystallographic subgroup of the noncrystallographic pseudo-icosahedral I(h) (2/m35) symmetry. The "full" four-shell Pd-Pt anatomy of 1 consists of: (a) shell 1 with the centered (mu(12)-Pt) atom encapsulated by the 12-atom icosahedral Pt(x)Pd(12-x) cage, x = 1.2(3); (b) shell 2 with the 42-atom nu(2) icosahedral Pt(x)Pd(42-x) cage, x = 3.5(5); (c) shell 3 with the anti-Mackay 60-atom semi-regular rhombicosidodecahedral Pt(x)Pd(60-x) cage, x = 2.2(6); (d) shell 4 with the 50-atom nu(2) pentagonal dodecahedral Pd(50) cage. The total number of crystallographically estimated Pt atoms, 8 +/- 3, which was obtained from least-squares (Pt(x)/Pd(1-x))-occupancy analysis of the X-ray data that conclusively revealed the central atom to be pure Pt (occupancy factor, x = 1.00(3)), is fortuitously in agreement with that of 7.6(7) found from an X-ray Pt/Pd microanalysis (WDS spectrometer) on three crystals of 1. Our utilization of this site-occupancy (Pt(x)Pd(1-x))-analysis for shells 1-3 originated from the microanalytical results; otherwise, the presumed metal-core composition would have been (mu(12)-Pt)Pd(164). [Alternatively, the (mu(12)-Pt)M(164) core-geometry of 1 may be viewed as a pseudo-Ih Pt-centered six-shell successive nu(1) polyhedral system, each with radially equivalent vertex atoms: Pt@M(12)(icosahedron)@M(30)(icosidodecahedron)@M(12)(icosahedron)@M(60)(rhombicosidodecahedron)@M(30)(icosidodecahedron)@M(20)(pentagonal dodecahedron)]. Completely surprising structural dissimilarities between 1 and 2 are: (1) to date 1 is only reproducibly isolated as a heterometallic Pd-Pt cluster with a central Pt instead of Pd atom; (2) the 50 atoms comprising the outer fourth nu(2) pentagonal dodecahedral shell in 1 are less than the 60 atoms of the inner third shell in 1, in contradistinction to shell-by-shell growth processes in all other known shell-based structures; (3) the 10 fewer PR3 ligands in 1 necessitate larger bulky PPh(3) ligands to protect the Pd-Pt core-geometry; (4) the 72 CO ligands consist of six bridging COs within each of the 12 pentagons in shell 4 that are coordinated to intershell metal atoms. SQUID magnetometry measurements showed a single-crystal sample of 1 to be diamagnetic over the entire temperature range of 10-300 K.

Microstructure of In x Ga1-x N nanorods grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Webster, R. F.; Soundararajah, Q. Y.; Griffiths, I. J.; Cherns, D.; Novikov, S. V.; Foxon, C. T.

2015-11-01

Transmission electron microscopy is used to examine the structure and composition of In x Ga1-x N nanorods grown by plasma-assisted molecular beam epitaxy. The results confirm a core-shell structure with an In-rich core and In-poor shell resulting from axial and lateral growth sectors respectively. Atomic resolution mapping by energy-dispersive x-ray microanalysis and high angle annular dark field imaging show that both the core and the shell are decomposed into Ga-rich and In-rich platelets parallel to their respective growth surfaces. It is argued that platelet formation occurs at the surfaces, through the lateral expansion of surface steps. Studies of nanorods with graded composition show that decomposition ceases for x ≥ 0.8 and the ratio of growth rates, shell:core, decreases with increasing In concentration.

Empirical mass formula with proton-neutron interaction

NASA Astrophysics Data System (ADS)

Tachibana, Takahiro; Uno, Masahiro; Yamada, So; Yamada, Masami

1987-12-01

An atomic mass formula consisting of a gross part, and averge even-odd part and an empirical shell part is studied. The gross part is, apart from a small atomic term, taken to be the sum of nucleon rest masses. Coulomb energies and a polynomial in A1/3 and ‖N-Z‖/A. The shell part includes, in addition to proton and neutron support of nuclear magicities and the cooperative deformation effect. After the first construction of such a formula, refinements have been made in two respects. One is a separate treatment of Z=N odd-odd nuclei suggested by a quartet model, and the other is an improvement of the proton neutron interaction term. By these refinements the root-mean-square deviation of calculated masses from the 1986 Audi-Wapstra masses has been reduced from 538 keV to 460 keV.

Lithography-Free Fabrication of Core-Shell GaAs Nanowire Tunnel Diodes.

PubMed

Darbandi, A; Kavanagh, K L; Watkins, S P

2015-08-12

GaAs core-shell p-n junction tunnel diodes were demonstrated by combining vapor-liquid-solid growth with gallium oxide deposition by atomic layer deposition for electrical isolation. The characterization of an ensemble of core-shell structures was enabled by the use of a tungsten probe in a scanning electron microscope without the need for lithographic processing. Radial tunneling transport was observed, exhibiting negative differential resistance behavior with peak-to-valley current ratios of up to 3.1. Peak current densities of up to 2.1 kA/cm(2) point the way to applications in core-shell photovoltaics and tunnel field effect transistors.

Reactions of Copper and Silver Cations with Carbon Dioxide: An Infrared Photodissociation Spectroscopic and Theoretical Study.

PubMed

Zhao, Zhi; Kong, Xiangtao; Yang, Dong; Yuan, Qinqin; Xie, Hua; Fan, Hongjun; Zhao, Jijun; Jiang, Ling

2017-05-04

The reaction of copper and silver cations with carbon dioxide was studied by mass-selected infrared photodissociation spectroscopy. Quantum chemical calculations were performed on these products, which aided the experimental assignments of the infrared spectra and helped to elucidate the geometrical and electronic structures. The Cu + and Ag + cations bind to an oxygen atom of CO 2 in an end-on configuration via a charge-quadrupole electrostatic interaction in the [M(CO 2 ) n ] + complexes. The formation of oxide-carbonyl and carbonyl-carbonate structures is not favored for the interaction of CO 2 with Cu + and Ag + . For n = 3 and 4, the n + 0 structure is preferred. [Note on the nomenclature: Using i + j, i denotes the number of CO 2 molecules in the first coordination shell, and j denotes the number of CO 2 molecules in the second coordination shell.] The two nearly energy-identical n + 0 and (n - 1) + 1 structures coexist in n = 5 and 6. While the six-coordinated structure is favored for [Cu(CO 2 ) n=7,8 ] + , the n + 0 configuration is dominated in [Ag(CO 2 ) n=7,8 ] + . The reaction of CO 2 with the cationic metal atoms has been compared to that with the neutral and anionic metal atoms, which would have important implications for understanding the interaction of CO 2 with reduction catalysts and rationally designing catalysts for CO 2 reduction based on cost-effective transition metals.

On the size and structure of helium snowballs formed around charged atoms and clusters of noble gases.

PubMed

Bartl, Peter; Leidlmair, Christian; Denifl, Stephan; Scheier, Paul; Echt, Olof

2014-09-18

Helium nanodroplets doped with argon, krypton, or xenon are ionized by electrons and analyzed in a mass spectrometer. HenNgx(+) ions containing up to seven noble gas (Ng) atoms and dozens of helium atoms are identified; the high resolution of the mass spectrometer combined with advanced data analysis make it possible to unscramble contributions from isotopologues that have the same nominal mass but different numbers of helium or Ng atoms, such as the magic He20(84)Kr2(+) and the isobaric, nonmagic He41(84)Kr(+). Anomalies in these ion abundances reveal particularly stable ions; several intriguing patterns emerge. Perhaps most astounding are the results for HenAr(+), which show evidence for three distinct, solid-like solvation shells containing 12, 20, and 12 helium atoms. This observation runs counter to the common notion that only the first solvation shell is solid-like but agrees with calculations by Galli et al. for HenNa(+) [J. Phys. Chem. A 2011, 115, 7300] that reveal three shells of icosahedral symmetry. HenArx(+) (2 ≤ x ≤ 7) ions appear to be especially stable if they contain a total of n + x = 19 atoms. A sequence of anomalies in the abundance distribution of HenKrx(+) suggests that rings of six helium atoms are inserted into the solvation shell each time a krypton atom is added to the ionic core, from Kr(+) to Kr3(+). Previously reported strong anomalies at He12Kr2(+) and He12Kr3(+) [Kim , J. H.; et al. J. Chem. Phys. 2006, 124, 214301] are attributed to a contamination. Only minor local anomalies appear in the distributions of HenXex(+) (x ≤ 3). The distributions of HenKr(+) and HenXe(+) show strikingly similar, broad features that are absent from the distribution of HenAr(+); differences are tentatively ascribed to the very different fragmentation dynamics of these ions.

On the Size and Structure of Helium Snowballs Formed around Charged Atoms and Clusters of Noble Gases

PubMed Central

2013-01-01

Helium nanodroplets doped with argon, krypton, or xenon are ionized by electrons and analyzed in a mass spectrometer. HenNgx+ ions containing up to seven noble gas (Ng) atoms and dozens of helium atoms are identified; the high resolution of the mass spectrometer combined with advanced data analysis make it possible to unscramble contributions from isotopologues that have the same nominal mass but different numbers of helium or Ng atoms, such as the magic He2084Kr2+ and the isobaric, nonmagic He4184Kr+. Anomalies in these ion abundances reveal particularly stable ions; several intriguing patterns emerge. Perhaps most astounding are the results for HenAr+, which show evidence for three distinct, solid-like solvation shells containing 12, 20, and 12 helium atoms. This observation runs counter to the common notion that only the first solvation shell is solid-like but agrees with calculations by Galli et al. for HenNa+ [J. Phys. Chem. A2011, 115, 730021568337] that reveal three shells of icosahedral symmetry. HenArx+ (2 ≤ x ≤ 7) ions appear to be especially stable if they contain a total of n + x = 19 atoms. A sequence of anomalies in the abundance distribution of HenKrx+ suggests that rings of six helium atoms are inserted into the solvation shell each time a krypton atom is added to the ionic core, from Kr+ to Kr3+. Previously reported strong anomalies at He12Kr2+ and He12Kr3+ [KimJ. H.; et al. J. Chem. Phys.2006, 124, 21430116774401] are attributed to a contamination. Only minor local anomalies appear in the distributions of HenXex+ (x ≤ 3). The distributions of HenKr+ and HenXe+ show strikingly similar, broad features that are absent from the distribution of HenAr+; differences are tentatively ascribed to the very different fragmentation dynamics of these ions. PMID:24128371

A beachhead on the island of stability

DOE PAGES

Oganessian, Yuri Ts.; Rykaczewski, Krzysztof P.

2015-01-01

Remember learning the periodic table of elements in high school? Our chemistry teachers explained that the chemical properties of elements come from the electronic shell structure of atoms. Furthermore, our physics teachers enriched that picture of the atomic world by introducing us to isotopes and the Segrè chart of nuclides, which arranges them by proton number Z and neutron number N.

Building Atoms Shell by Shell.

ERIC Educational Resources Information Center

Sussman, Beverly

1993-01-01

Describes an atom-building activity where students construct three-dimensional models of atoms using a styrofoam ball as the nucleus and pom-poms, gum drops, minimarshmallows, or other small items of two different colors to represent protons and neutrons attached. Rings of various sizes with pom-poms attached represent electron shells and…

Structural evolution of atomically precise thiolated bimetallic [Au(12+n)Cu₃₂(SR)(30+n)]⁴⁻ (n = 0, 2, 4, 6) nanoclusters.

PubMed

Yang, Huayan; Wang, Yu; Yan, Juanzhu; Chen, Xi; Zhang, Xin; Häkkinen, Hannu; Zheng, Nanfeng

2014-05-21

A series of all-thiol stabilized bimetallic Au-Cu nanoclusters, [Au(12+n)Cu32(SR)(30+n)](4-) (n = 0, 2, 4, 6 and SR = SPhCF3), are successfully synthesized and characterized by X-ray single-crystal analysis and density functional theory (DFT) calculations. Each cluster consists of a Keplerate two-shell Au12@Cu20 core protected by (6 - n) units of Cu2(SR)5 and n units of Cu2Au(SR)6 (n = 0, 2, 4, 6) motifs on its surface. The size and structural evolution of the clusters is atomically controlled by the Au precursors and countercations used in the syntheses. The clusters exhibit similar optical absorption properties that are not dependent on the number of surface Cu2Au(SR)6 units. Although DFT suggests an electronic structure with an 18-electron superatom shell closure, the clusters display different thermal stabilities. [Au(12+n)Cu32(SR)(30+n)](4-) clusters with n = 0 and 2 are more stable than those with n = 4 and 6. Moreover, an oxidation product of the clusters, [Au13Cu12(SR)20](4-), is structurally identified to gain insight into how the clusters are oxidized.

Angle-resolved studies of inner shell excitations for argon, krypton and xenon using third-generation synchrotron sources

NASA Astrophysics Data System (ADS)

Farhat, Ahmad H.

This dissertation, which is in the area of atomic physics, concentrates on the study of the interaction between VUV-soft X-ray radiation and atoms in the gas phase. The main area of interest is the study of Auger decay in atoms utilizing the process known as the resonance Auger effect, where an inner shell electron is excited to an unfilled orbital followed by the ejection of an Auger electron. The measurements in this thesis were performed by using the high resolution Atomic, Molecular and Optical Physics undulator beam line, which utilizes a spherical grating monochromator at the Advanced Light Source at Lawrence Berkeley National Laboratory. The research focused on three rare gases, argon, krypton and xenon. For argon, high resolution angular-resolved measurements of the 2p → 4s, 3d, 4d resonant Auger lines have been achieved. By measuring photoelectron spectra simultaneously at two different angles using efficient time of flight spectrometers, the angular distributions anisotropy parameters β have been measured, and relative intensities have been evaluated for each of the resolved final ionic states. For krypton, the resonant Auger decay of all the photoexcited Kr 3d3/2,5/2-1 nl (n = 5-9) states have been studied using an angle resolved two dimensional photoelectron spectroscopic technique, in which the electron yield was measured as a function of both photon energy and electron kinetic energy. Angular distributions, spectator and shake probabilities have been derived for the Kr 3d-1np/to4s- 14p-1mp + e/sp- (n = 5-9, m = 5-11) resonance Auger decay. The results show that the spectator-core coupling is strong at lower n (n = 5,6) but it lessens for higher n, with a shake up of m = n + 1 preferred. Finally for xenon, the autoionization resonances and angular distribution of the 4d → 6p decay spectrum were studied utilizing the Auger resonant Raman effect. Using this technique, β parameters of almost all 5p4/ (3P,/ 1D,/ 1S) 6p final ionic states were determined. These results contribute to our understanding of atomic structure and dynamics of inner shell processes and hopefully will stimulate further experimental and theoretical work.

Calculated gadolinium atomic electron energy levels and Auger electron emission probability as a function of atomic number Z

NASA Astrophysics Data System (ADS)

Miloshevsky, G. V.; Tolkach, V. I.; Shani, Gad; Rozin, Semion

2002-06-01

Auger electron interaction with matter is gaining importance in particular in medical application of radiation. The production probability and energy spectrum is therefore of great importance. A good source of Auger electrons is the 157Gd(n,γ) 158Gd reaction. The present article describes calculations of electron levels in Gd atoms and provides missing data of outer electron energy levels. The energy of these electron levels missing in published tables, was found to be in the 23-24 and 6-7 eV energy ranges respectively. The probability of Auger emission was calculated as an interaction of wave function of the initial and final electron states. The wave functions were calculated using the Hartree-Fock-Slater approximation with relativistic correction. The equations were solved using a spherical symmetry potential. The error for inner shell level is less than 10%, it is increased to the order of 10-15% for the outer shells. The width of the Auger process changes from 0.1 to 1.2 eV for atomic number Z from 5 to 70. The fluorescence yield width changes five orders of magnitude in this range. Auger electron emission width from the K shell changes from 10 -2 to ˜1 eV with Z changing from 10 to 64, depending on the final state. For the L shell it changes from 0 to 0.25 when it Z changes from 20 to 64.

Empirical mass formula with proton-neutron interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tachibana, T.; Uno, M.; Yamada, S.

An atomic mass formula consisting of a gross part, and averge even-odd part and an empirical shell part is studied. The gross part is, apart from a small atomic term, taken to be the sum of nucleon rest masses. Coulomb energies and a polynomial in A/sup 1/3/ and chemically bondN-Zchemically bond/A. The shell part includes, in addition to proton and neutron support of nuclear magicities and the cooperative deformation effect. After the first construction of such a formula, refinements have been made in two respects. One is a separate treatment of Z = N odd-odd nuclei suggested by a quartetmore » model, and the other is an improvement of the proton neutron interaction term. By these refinements the root-mean-square deviation of calculated masses from the 1986 Audi-Wapstra masses has been reduced from 538 keV to 460 keV.« less

Capsid expansion mechanism of bacteriophage T7 revealed by multistate atomic models derived from cryo-EM reconstructions

PubMed Central

Guo, Fei; Liu, Zheng; Fang, Ping-An; Zhang, Qinfen; Wright, Elena T.; Wu, Weimin; Zhang, Ci; Vago, Frank; Ren, Yue; Jakana, Joanita; Chiu, Wah; Serwer, Philip; Jiang, Wen

2014-01-01

Many dsDNA viruses first assemble a DNA-free procapsid, using a scaffolding protein-dependent process. The procapsid, then, undergoes dramatic conformational maturation while packaging DNA. For bacteriophage T7 we report the following four single-particle cryo-EM 3D reconstructions and the derived atomic models: procapsid (4.6-Å resolution), an early-stage DNA packaging intermediate (3.5 Å), a later-stage packaging intermediate (6.6 Å), and the final infectious phage (3.6 Å). In the procapsid, the N terminus of the major capsid protein, gp10, has a six-turn helix at the inner surface of the shell, where each skewed hexamer of gp10 interacts with two scaffolding proteins. With the exit of scaffolding proteins during maturation the gp10 N-terminal helix unfolds and swings through the capsid shell to the outer surface. The refolded N-terminal region has a hairpin that forms a novel noncovalent, joint-like, intercapsomeric interaction with a pocket formed during shell expansion. These large conformational changes also result in a new noncovalent, intracapsomeric topological linking. Both interactions further stabilize the capsids by interlocking all pentameric and hexameric capsomeres in both DNA packaging intermediate and phage. Although the final phage shell has nearly identical structure to the shell of the DNA-free intermediate, surprisingly we found that the icosahedral faces of the phage are slightly (∼4 Å) contracted relative to the faces of the intermediate, despite the internal pressure from the densely packaged DNA genome. These structures provide a basis for understanding the capsid maturation process during DNA packaging that is essential for large numbers of dsDNA viruses. PMID:25313071

Interpretation of two compact planetary nebulae, IC 4997 and NGC 6572, with aid of theoretical models.

PubMed Central

Hyung, S; Aller, L H

1993-01-01

Observations of two dense compact planetary nebulae secured with the Hamilton Echelle spectrograph at Lick Observatory combined with previously published UV spectra secured with the International Ultraviolet Explorer enable us to probe the electron densities and temperatures (plasma diagnostics) and ionic concentrations in these objects. The diagnostic diagrams show that no homogenous model will work for these nebulae. NGC 6572 may consist of an inner torordal ring of density 25,000 atoms/cm3 and an outer conical shell of density 10,000 atoms/cm3. The simplest model of IC 4997 suggests a thick inner shell with a density of about 107 atoms/cm3 and an outer envelope of density 10,000 atoms/cm3. The abundances of all elements heavier than He appear to be less than the solar values in NGC 6572, whereas He, C, N, and O may be more abundant in IC 4997 than in the sun. IC 4997 presents puzzling problems. PMID:11607347

Structures of 38-atom gold-platinum nanoalloy clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ong, Yee Pin; Yoon, Tiem Leong; Lim, Thong Leng

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 atomsmore » 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.« less

In-depth understanding of core-shell nanoarchitecture evolution of g-C3N4@C, N co-doped anatase/rutile: Efficient charge separation and enhanced visible-light photocatalytic performance

NASA Astrophysics Data System (ADS)

Mohamed, Mohamad Azuwa; Jaafar, Juhana; M. Zain, M. F.; Minggu, Lorna Jeffery; Kassim, Mohammad B.; Rosmi, Mohamad Saufi; Alias, Nur Hashimah; Mohamad Nor, Nor Azureen; W. Salleh, W. N.; Othman, Mohd Hafiz Dzarfan

2018-04-01

Herein, we demonstrated the simultaneous formation of multi-component heterojunction consisting graphitic carbon nitride (g-C3N4) and C, N co-doped anatase/rutile mixed phase by using facile sol-gel assisted heat treatment. The evolution of core-shell nanostructures heterojunction formation was elucidated by varying the temperature of heat treatment from 300 °C to 600 °C. Homogeneous heterojunction formation between g-C3N4 and anatase/rutile mixed phase was observed in gT400 with C and N doping into TiO2 lattice by O substitution. The core-shell nanoarchitectures between g-C3N4 as shell, and anatase/rutile mixed phase as core with C and N atoms are doped at the interstitial positions of TiO2 lattice was observed in gT500. The result indicated that core-shell nanoarchitectures photocatalyst (gT500) prepared at 500 ◦C exhibited the highest photocatalytic activity in the degradation of methyl orange under visible light irradiation. Meanwhile, the possible mechanisms of charge generation, migration, action species and reaction that probably occur at the gT500 sample were also proposed. The photodegradation results of gT500 correlated completely with the results of the PEC and photoluminescence analysis, which directly evidenced improved charge separation and migration as the crucial parameters governing photocatalysis. It is worthy to note that, the simultaneous formation of multicomponent heterojunction with core-shell structure provided an enormous impact in designing highly active photocatalyst with superior interfacial charge transfer.

Pancake π–π Bonding Goes Double: Unexpected 4e/All-Sites Bonding in Boron- and Nitrogen-Doped Phenalenyls

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Yong-Hui; Sumpter, Bobby G.; Du, Shiyu

Phenalenyl is an important neutral pi-radical due to its capability to form unconventional pancake pi-pi bonding interactions, whereas its analogues with graphitic boron (B) or nitrogen (N)-doping have been regarded as closed-shell systems and therefore received much less attention. By using high-level quantum chemistry calculations, we also show that the B- and N-doped closed-shell phenalenyls unexpectedly form open-shell singlet pi-dimers with diradicaloid character featuring 2e/all-sites double pi-pi bonding. Moreover, by proper substitutions, the doped phenalenyl derivatives can be made open-shell species that form closed shell singlet pi-dimers bound by stronger 4e/all-sites double pi-pi bonding. Moreover, covalent pi-pi bonding overlap ismore » distributed on all of the atomic sites giving robust and genuine pancake-shaped pi-dimers which, depending on the number of electrons available in the bonding interactions, are equally or more stable than the pi-dimers of the pristine phenalenyl.« less

Pancake π–π Bonding Goes Double: Unexpected 4e/All-Sites Bonding in Boron- and Nitrogen-Doped Phenalenyls

DOE PAGES

Tian, Yong-Hui; Sumpter, Bobby G.; Du, Shiyu; ...

2015-06-03

Phenalenyl is an important neutral pi-radical due to its capability to form unconventional pancake pi-pi bonding interactions, whereas its analogues with graphitic boron (B) or nitrogen (N)-doping have been regarded as closed-shell systems and therefore received much less attention. By using high-level quantum chemistry calculations, we also show that the B- and N-doped closed-shell phenalenyls unexpectedly form open-shell singlet pi-dimers with diradicaloid character featuring 2e/all-sites double pi-pi bonding. Moreover, by proper substitutions, the doped phenalenyl derivatives can be made open-shell species that form closed shell singlet pi-dimers bound by stronger 4e/all-sites double pi-pi bonding. Moreover, covalent pi-pi bonding overlap ismore » distributed on all of the atomic sites giving robust and genuine pancake-shaped pi-dimers which, depending on the number of electrons available in the bonding interactions, are equally or more stable than the pi-dimers of the pristine phenalenyl.« less

Interpretation of atomic mass systematics in terms of the valence shells and a simple scheme for predicting masses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haustein, P.E.; Brenner, D.S.; Casten, R.F.

1988-07-01

A new semiempirical method that significantly simplifies atomic mass systematics and which provides a method for making mass predictions by linear interpolation is discussed in the context of the nuclear valence space. In certain regions complicated patterns of mass systematics in traditional plots versus Z, N, or isospin are consolidated and transformed into linear ones extending over long isotopic and isotonic sequences.

Metal-Organic-Framework-Derived Hybrid Carbon Nanocages as a Bifunctional Electrocatalyst for Oxygen Reduction and Evolution.

PubMed

Liu, Shaohong; Wang, Zhiyu; Zhou, Si; Yu, Fengjiao; Yu, Mengzhou; Chiang, Chang-Yang; Zhou, Wuzong; Zhao, Jijun; Qiu, Jieshan

2017-08-01

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are cornerstone reactions for many renewable energy technologies. Developing cheap yet durable substitutes of precious-metal catalysts, especially the bifunctional electrocatalysts with high activity for both ORR and OER reactions and their streamlined coupling process, are highly desirable to reduce the processing cost and complexity of renewable energy systems. Here, a facile strategy is reported for synthesizing double-shelled hybrid nanocages with outer shells of Co-N-doped graphitic carbon (Co-NGC) and inner shells of N-doped microporous carbon (NC) by templating against core-shell metal-organic frameworks. The double-shelled NC@Co-NGC nanocages well integrate the high activity of Co-NGC shells into the robust NC hollow framework with enhanced diffusion kinetics, exhibiting superior electrocatalytic properties to Pt and RuO 2 as a bifunctional electrocatalyst for ORR and OER, and hold a promise as efficient air electrode catalysts in Zn-air batteries. First-principles calculations reveal that the high catalytic activities of Co-NGC shells are due to the synergistic electron transfer and redistribution between the Co nanoparticles, the graphitic carbon, and the doped N species. Strong yet favorable adsorption of an OOH* intermediate on the high density of uncoordinated hollow-site C atoms with respect to the Co lattice in the Co-NGC structure is a vital rate-determining step to achieve excellent bifunctional electrocatalytic activity. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interatomic interactions in M2(C8H4O4)2C6H12N2 (M = Zn, Cu, Co, Ni) metal-organic framework polymers: X-ray photoelectron spectroscopy, QTAIM and ELF study

NASA Astrophysics Data System (ADS)

Kozlova, S. G.; Ryzhikov, M. R.; Samsonenko, D. G.; Kalinkin, A. V.

2017-12-01

Interatomic interactions in M2(C8H4O4)2C6H12N2 (M = Co, Ni, Cu, Zn) metal-organic framework polymers have been studied with the methods of quantum chemistry and X-ray photoelectron spectroscopy. Interactions of C6H12N2 molecules and C8H4O42- anions with metal atoms are shown to be of closed-shell type. C6H12N2 molecules are positively charged, the value of the charge slightly depends on the type of the metal atoms. Msbnd M interactions are described as "intermediate interactions" with some covalence contribution which reaches maximum for the interactions between cobalt atoms. The obtained quantum-chemical data agree with those obtained from photoelectron spectroscopy measurements.

Atomic level characterization of cadmium selenide nanocrystal systems using atomic number contrast scanning transmission electron microscopy and Rutherford backscattering spectroscopy

NASA Astrophysics Data System (ADS)

McBride, James R.

This project involved the characterization of CdSe nanocrystals. Through the use of Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-STEM) and Rutherford Backscattering Spectroscopy (RBS), atomic level structure and chemical information was obtained. Specifically, CdSe nanocrystals produced using a mixture of hexadecylamine (HDA) and trioctylphosphine oxide (TOPO) were determined to be spherical compared to nanocrystals produced in TOPO only, which had elongated (101) facets. Additionally, the first Z-STEM images of CdSe/ZnS core/shell nanocrystals were obtained. From these images, the growth mechanism of the ZnS shell was determined and the existence of non-fluorescent ZnS particles was confirmed. Through collaboration with Quantum Dot Corp., core/shell nanocrystals with near unity quantum yield were developed. These core/shell nanocrystals included a US intermediate layer to improve shell coverage.

Scanning Tunneling Microscopy, Atomic Force Microscopy, and Related Techniques.

DTIC Science & Technology

1992-06-15

images of the heaoal ekdprotein monolayer pressed powder samples of pismO claim and sea urchin shells found ~ ~ sx inteotrcelwl fDincoccu radioduran...can be in- Semiconductor Substrates. The atomic structure of sem - vastigated using AFM but has not been as extensively re- iconductor-detal interfaces...from SEM mage (D99). Komaica and p-type Si(00) and p-n junctions formed by implantation of ANALYTICAL CHEMISTRY. VOL 84, NO. 12. JILNE 18. 1992 121R

Simulation study of 3–5 keV x-ray conversion efficiency from Ar K-shell vs. Ag L-shell targets on the National Ignition Facility laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kemp, G. E., E-mail: kemp10@llnl.gov; Colvin, J. D.; Fournier, K. B.

2015-05-15

Tailored, high-flux, multi-keV x-ray sources are desirable for studying x-ray interactions with matter for various civilian, space and military applications. For this study, we focus on designing an efficient laser-driven non-local thermodynamic equilibrium 3–5 keV x-ray source from photon-energy-matched Ar K-shell and Ag L-shell targets at sub-critical densities (∼n{sub c}/10) to ensure supersonic, volumetric laser heating with minimal losses to kinetic energy, thermal x rays and laser-plasma instabilities. Using HYDRA, a multi-dimensional, arbitrary Lagrangian-Eulerian, radiation-hydrodynamics code, we performed a parameter study by varying initial target density and laser parameters for each material using conditions readily achievable on the National Ignition Facilitymore » (NIF) laser. We employ a model, benchmarked against Kr data collected on the NIF, that uses flux-limited Lee-More thermal conductivity and multi-group implicit Monte-Carlo photonics with non-local thermodynamic equilibrium, detailed super-configuration accounting opacities from CRETIN, an atomic-kinetics code. While the highest power laser configurations produced the largest x-ray yields, we report that the peak simulated laser to 3–5 keV x-ray conversion efficiencies of 17.7% and 36.4% for Ar and Ag, respectively, occurred at lower powers between ∼100–150 TW. For identical initial target densities and laser illumination, the Ag L-shell is observed to have ≳10× higher emissivity per ion per deposited laser energy than the Ar K-shell. Although such low-density Ag targets have not yet been demonstrated, simulations of targets fabricated using atomic layer deposition of Ag on silica aerogels (∼20% by atomic fraction) suggest similar performance to atomically pure metal foams and that either fabrication technique may be worth pursuing for an efficient 3–5 keV x-ray source on NIF.« less

First-principles calculations of K-shell X-ray absorption spectra for warm dense nitrogen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zi; Zhang, Shen; Kang, Wei

2016-05-15

X-ray absorption spectrum is a powerful tool for atomic structure detection on warm dense matter. Here, we perform first-principles molecular dynamics and X-ray absorption spectrum calculations on warm dense nitrogen along a Hugoniot curve. From the molecular dynamics trajectory, the detailed atomic structures are examined for each thermodynamical condition. The K-shell X-ray absorption spectrum is calculated, and its changes with temperature and pressure along the Hugoniot curve are discussed. The warm dense nitrogen systems may contain isolated nitrogen atoms, N{sub 2} molecules, and nitrogen clusters, which show quite different contributions to the total X-ray spectrum due to their different electronmore » density of states. The changes of X-ray spectrum along the Hugoniot curve are caused by the different nitrogen structures induced by the temperature and the pressure. Some clear signatures on X-ray spectrum for different thermodynamical conditions are pointed out, which may provide useful data for future X-ray experiments.« less

Green Synthesis of Ag-Cu Nanoalloys Using Opuntia ficus- indica

NASA Astrophysics Data System (ADS)

Rocha-Rocha, O.; Cortez-Valadez, M.; Hernández-Martínez, A. R.; Gámez-Corrales, R.; Alvarez, Ramón A. B.; Britto-Hurtado, R.; Delgado-Beleño, Y.; Martinez-Nuñez, C. E.; Pérez-Rodríguez, A.; Arizpe-Chávez, H.; Flores-Acosta, M.

2017-02-01

Bimetallic Ag/Cu nanoparticles have been obtained by green synthesis using Opuntia ficus- indica plant extract. Two synthesis methods were applied to obtain nanoparticles with core-shell and Janus morphologies by reversing the order of precursors. Transmission electronic microscopy revealed size of 10 nm and 20 nm for the core-shell and Janus nanoparticles, respectively. Other small particles with size of up to 2 nm were also observed. Absorption bands attributed to surface plasmon resonance were detected at 440 nm and 500 nm for the core-shell and Janus nanoparticles, respectively. Density functional theory predicted a breathing mode type (BMT) located at low wavenumber due to small, low-energy clusters of (AgCu) n with n = 2 to 9, showing a certain correlation with the experimental one (at 220 cm-1). The dependence of the BMT on the number of atoms constituting the cluster is also studied.

Theoretical predictions of a bucky-diamond SiC cluster.

PubMed

Yu, Ming; Jayanthi, C S; Wu, S Y

2012-06-15

A study of structural relaxations of Si(n)C(m) clusters corresponding to different compositions, different relative arrangements of Si/C atoms, and different types of initial structure, reveals that the Si(n)C(m) bucky-diamond structure can be obtained for an initial network structure constructed from a truncated bulk 3C-SiC for a magic composition corresponding to n = 68 and m = 79. This study was performed using a semi-empirical Hamiltonian (SCED-LCAO) since it allowed an extensive search of different types of initial structures. However, the bucky-diamond structure predicted by this method was also confirmed by a more accurate density functional theory (DFT) based method. The bucky-diamond structure exhibited by a SiC-based system represents an interesting paradigm where a Si atom can form three-coordinated as well as four-coordinated networks with carbon atoms and vice versa and with both types of network co-existing in the same structure. Specifically, the bucky-diamond structure of the Si(68)C(79) cluster consists of a 35-atom diamond-like inner core (four-atom coordinations) suspended inside a 112-atom fullerene-like shell (three-atom coordinations).

The generator coordinate Dirac-Fock method for open-shell atomic systems

NASA Astrophysics Data System (ADS)

Malli, Gulzari L.; Ishikawa, Yasuyuki

1998-11-01

Recently we developed generator coordinate Dirac-Fock and Dirac-Fock-Breit methods for closed-shell systems assuming finite nucleus and have reported Dirac-Fock and Dirac-Fock-Breit energies for the atoms He through Nobelium (Z=102) [see Refs. Reference 10Reference 11Reference 12Reference 13]. In this paper, we generalize our earlier work on closed-shell systems and develop a generator coordinate Dirac-Fock method for open-shell systems. We present results for a number of representative open-shell heavy atoms (with nuclear charge Z>80) including the actinide and superheavy transactinide (with Z>103) atomic systems: Fr (Z=87), Ac (Z=89), and Lr (Z=103) to E113 (eka-thallium, Z=113). The high accuracy obtained in our open-shell Dirac-Fock calculations is similar to that of our closed-shell calculations, and we attribute it to the fact that the representation of the relativistic dynamics of an electron in a spherical ball finite nucleus near the origin in terms of our universal Gaussian basis set is as accurate as that provided by the numerical finite difference method. The DF SCF energies calculated by Desclaux [At. Data. Nucl. Data Tables 12, 311 (1973)] (apart from a typographic error for Fr pointed out here) are higher than those reported here for atoms of some of the superheavy transactinide elements by as much as 5 hartrees (136 eV). We believe that this is due to the use by Desclaux of much larger atomic masses than the currently accepted values for these elements.

Topology of charge density of flucytosine and related molecules and characteristics of their bond charge distributions.

PubMed

Murgich, Juan; Franco, Héctor J; San-Blas, Gioconda

2006-08-24

The molecular charge distribution of flucytosine (4-amino-5-fluoro-2-pyrimidone), uracil, 5-fluorouracil, and thymine was studied by means of density functional theory calculations (DFT). The resulting distributions were analyzed by means of the atoms in molecules (AIM) theory. Bonds were characterized through vectors formed with the charge density value, its Laplacian, and the bond ellipticity calculated at the bond critical point (BCP). Within each set of C=O, C-H, and N-H bonds, these vectors showed little dispersion. C-C bonds formed three different subsets, one with a significant degree of double bonding, a second corresponding to single bonds with a finite ellipticity produced by hyperconjugation, and a third one formed by a pure single bond. In N-C bonds, a decrease in bond length (an increase in double bond character) was not reflected as an increase in their ellipticity, as in all C-C bonds studied. It was also found that substitution influenced the N-C, C-O, and C-C bond ellipticity much more than density and its Laplacian at the BCP. The Laplacian of charge density pointed to the existence of both bonding and nonbonding maxima in the valence shell charge concentration of N, O, and F, while only bonding ones were found for the C atoms. The nonbonding maxima related to the sites for electrophilic attack and H bonding in O and N, while sites of nucleophilic attack were suggested by the holes in the valence shell of the C atoms of the carbonyl groups.

Experimental and theoretical studies of metal vapor atoms

NASA Astrophysics Data System (ADS)

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

2004-05-01

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

Quantum Tunneling Model of a P-N Junction in Silvaco

DTIC Science & Technology

2008-09-01

electrical characteristics of materials on a large scale. According to Niels Bohr, atoms are comprised of three subatomic particles: a negative...nucleus at a specific energy level known as an orbit or shell. The three subatomic particles are held together by the electrostatic force between the

Platinum-coated non-noble metal-noble metal core-shell electrocatalysts

DOEpatents

Adzic, Radoslav; Zhang, Junliang; Mo, Yibo; Vukmirovic, Miomir

2015-04-14

Core-shell particles encapsulated by a thin film of a catalytically active metal are described. The particles are preferably nanoparticles comprising a non-noble core with a noble metal shell which preferably do not include Pt. The non-noble metal-noble metal core-shell nanoparticles are encapsulated by a catalytically active metal which is preferably Pt. The core-shell nanoparticles are preferably formed by prolonged elevated-temperature annealing of nanoparticle alloys in an inert environment. This causes the noble metal component to surface segregate and form an atomically thin shell. The Pt overlayer is formed by a process involving the underpotential deposition of a monolayer of a non-noble metal followed by immersion in a solution comprising a Pt salt. A thin Pt layer forms via the galvanic displacement of non-noble surface atoms by more noble Pt atoms in the salt. The overall process is a robust and cost-efficient method for forming Pt-coated non-noble metal-noble metal core-shell nanoparticles.

First-principles study of the binding energy between nanostructures and its scaling with system size

NASA Astrophysics Data System (ADS)

Tao, Jianmin; Jiao, Yang; Mo, Yuxiang; Yang, Zeng-Hui; Zhu, Jian-Xin; Hyldgaard, Per; Perdew, John P.

2018-04-01

The equilibrium van der Waals binding energy is an important factor in the design of materials and devices. However, it presents great computational challenges for materials built up from nanostructures. Here we investigate the binding-energy scaling behavior from first-principles calculations. We show that the equilibrium binding energy per atom between identical nanostructures can scale up or down with nanostructure size, but can be parametrized for large N with an analytical formula (in meV/atom), Eb/N =a +b /N +c /N2+d /N3 , where N is the number of atoms in a nanostructure and a , b , c , and d are fitting parameters, depending on the properties of a nanostructure. The formula is consistent with a finite large-size limit of binding energy per atom. We find that there are two competing factors in the determination of the binding energy: Nonadditivities of van der Waals coefficients and center-to-center distance between nanostructures. To decode the detail, the nonadditivity of the static multipole polarizability is investigated from an accurate spherical-shell model. We find that the higher-order multipole polarizability displays ultrastrong intrinsic nonadditivity, no matter if the dipole polarizability is additive or not.

Disorders of metal metabolism

PubMed Central

Ferreira, Carlos R.; Gahl, William A.

2017-01-01

Trace elements are chemical elements needed in minute amounts for normal physiology. Some of the physiologically relevant trace elements include iodine, copper, iron, manganese, zinc, selenium, cobalt and molybdenum. Of these, some are metals, and in particular, transition metals. The different electron shells of an atom carry different energy levels, with those closest to the nucleus being lowest in energy. The number of electrons in the outermost shell determines the reactivity of such an atom. The electron shells are divided in sub-shells, and in particular the third shell has s, p and d sub-shells. Transition metals are strictly defined as elements whose atom has an incomplete d sub-shell. This incomplete d sub-shell makes them prone to chemical reactions, particularly redox reactions. Transition metals of biologic importance include copper, iron, manganese, cobalt and molybdenum. Zinc is not a transition metal, since it has a complete d sub-shell. Selenium, on the other hand, is strictly speaking a nonmetal, although given its chemical properties between those of metals and nonmetals, it is sometimes considered a metalloid. In this review, we summarize the current knowledge on the inborn errors of metal and metalloid metabolism. PMID:29354481

The Electronic Structure of Transition Metal Coated Fullerenes

NASA Astrophysics Data System (ADS)

Patton, David C.; Pederson, Mark R.; Kaxiras, Efthimios

1998-03-01

Clusters composed of fullerene molecules with an outer shell of transition metal atoms in the composition C_60M_62 (M being a transition metal) have been produced with laser vaporisation techniques(F. Tast, N. Malinowski, S. Frank, M. Heinebrodt, I.M.L. Billas, and T. P. Martin, Z. Phys D 40), 351 (1997).. We have studied several of these very large systems with a parallel version of the all-electron NRLMOL cluster code. Optimized geometries of the metal encased fullerenes C_60Ti_62 and C_60V_62 are presented along with their HOMO-LUMO gaps, electron affinities, ionization energies, and cohesive energies. We compare the stability of these clusters to relaxed met-car structures (e.g. Ti_8C_12) and to relaxed rocksalt metal-carbide fragments (TiC)n with n=8 and 32. In addition to metal-coated fullerenes we consider the possibility of a trilayered structure consisting of a small shell of metal atoms enclosed by a metal coated fullerene. The nature of bonding in these systems is analyzed by studying the electronic charge distributions.

Core excitation effects on oscillator strengths for transitions in four electron atomic systems

NASA Astrophysics Data System (ADS)

Chang, T. N.; Luo, Yuxiang

2007-06-01

By including explicitly the electronic configurations with two and three simultaneously excited electronic orbital, we have extended the BSCI (B-spline based configuration interaction) method [1] to estimate directly the effect of inner shell core excitation to oscillator strengths for transitions in four-electron atomic systems. We will present explicitly the change in oscillator strengths due to core excitations, especially for transitions involving doubly excited states and those with very small oscillator strengths. The length and velocity results are typically in agreement better than 1% or less. [1] Tu-nan Chang, in Many-body Theory of Atomic Structure and Photoionization, edited by T. N. Chang (World Scientific, Singapore, 1993), p. 213-47; and T. N. Chang and T. K. Fang, Elsevier Radiation Physics and Chemistry 70, 173-190 (2004).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eriksen, Janus J., E-mail: janusje@chem.au.dk; Jørgensen, Poul; Matthews, Devin A.

The accuracy at which total energies of open-shell atoms and organic radicals may be calculated is assessed for selected coupled cluster perturbative triples expansions, all of which augment the coupled cluster singles and doubles (CCSD) energy by a non-iterative correction for the effect of triple excitations. Namely, the second- through sixth-order models of the recently proposed CCSD(T–n) triples series [J. J. Eriksen et al., J. Chem. Phys. 140, 064108 (2014)] are compared to the acclaimed CCSD(T) model for both unrestricted as well as restricted open-shell Hartree-Fock (UHF/ROHF) reference determinants. By comparing UHF- and ROHF-based statistical results for a test setmore » of 18 modest-sized open-shell species with comparable RHF-based results, no behavioral differences are observed for the higher-order models of the CCSD(T–n) series in their correlated descriptions of closed- and open-shell species. In particular, we find that the convergence rate throughout the series towards the coupled cluster singles, doubles, and triples (CCSDT) solution is identical for the two cases. For the CCSD(T) model, on the other hand, not only its numerical consistency, but also its established, yet fortuitous cancellation of errors breaks down in the transition from closed- to open-shell systems. The higher-order CCSD(T–n) models (orders n > 3) thus offer a consistent and significant improvement in accuracy relative to CCSDT over the CCSD(T) model, equally for RHF, UHF, and ROHF reference determinants, albeit at an increased computational cost.« less

Structural, electronic, and magnetic properties of Y(n)O (n=2-14) clusters: Density functional study.

PubMed

Yang, Zhi; Xiong, Shi-Jie

2008-09-28

The geometries stability, electronic properties, and magnetism of Y(n)O clusters up to n=14 are systematically studied with density functional theory. In the lowest-energy structures of Y(n)O clusters, the equilibrium site of the oxygen atom gradually moves from an outer site of the cluster, via a surface site, and finally, to an interior site as the number of the Y atoms increases from 2 to 14. Starting from n=12, the O atom falls into the center of the cluster with the Y atoms forming the outer frame. The results show that clusters with n=2, 4, 8, and 12 are more stable than their respective neighbors, and that the total magnetic moments of Y(n)O clusters are all quite small except Y(12)O cluster. The lowest-energy structure of Y(12)O cluster is a perfect icosahedron with a large magnetic moment 6mu(B). In addition, we find that the total magnetic moments are quenched for n=2, 6, and 8 due to the closed-shell electronic configuration. The calculated ionization potentials and electron affinities are in good agreement with the experimental results, which imply that the present theoretical treatments are satisfactory.

The Periodic Pyramid

ERIC Educational Resources Information Center

Hennigan, Jennifer N.; Grubbs, W. Tandy

2013-01-01

The chemical elements present in the modern periodic table are arranged in terms of atomic numbers and chemical periodicity. Periodicity arises from quantum mechanical limitations on how many electrons can occupy various shells and subshells of an atom. The shell model of the atom predicts that a maximum of 2, 8, 18, and 32 electrons can occupy…

Study of lithium cation in water clusters: based on atom-bond electronegativity equalization method fused into molecular mechanics.

PubMed

Li, Xin; Yang, Zhong-Zhi

2005-05-12

We present a potential model for Li(+)-water clusters based on a combination of the atom-bond electronegativity equalization and molecular mechanics (ABEEM/MM) that is to take ABEEM charges of the cation and all atoms, bonds, and lone pairs of water molecules into the intermolecular electrostatic interaction term in molecular mechanics. The model allows point charges on cationic site and seven sites of an ABEEM-7P water molecule to fluctuate responding to the cluster geometry. The water molecules in the first sphere of Li(+) are strongly structured and there is obvious charge transfer between the cation and the water molecules; therefore, the charge constraint on the ionic cluster includes the charged constraint on the Li(+) and the first-shell water molecules and the charge neutrality constraint on each water molecule in the external hydration shells. The newly constructed potential model based on ABEEM/MM is first applied to ionic clusters and reproduces gas-phase state properties of Li(+)(H(2)O)(n) (n = 1-6 and 8) including optimized geometries, ABEEM charges, binding energies, frequencies, and so on, which are in fair agreement with those measured by available experiments and calculated by ab initio methods. Prospects and benefits introduced by this potential model are pointed out.

Energetic Nitrogen Ions within the Inner Magnetosphere of Saturn

NASA Astrophysics Data System (ADS)

Sittler, E. C.; Johnson, R. E.; Richardson, J. D.; Jurac, S.; Moore, M.; Cooper, J. F.; Mauk, B. H.; Smith, H. T.; Michael, M.; Paranicus, C.; Armstrong, T. P.; Tsurutani, B.; Connerney, J. E. P.

2003-05-01

Titan's interaction with Saturn's magnetosphere will result in the energetic ejection of atomic nitrogen atoms into Saturn's magnetosphere due to dissociation of N2 by electrons, ions, and UV photons. The ejection of N atoms into Saturn's magnetosphere will form a nitrogen torus around Saturn with mean density of about 4 atoms/cm3 with source strength of 4.5x1025 atoms/sec. These nitrogen atoms are ionized by photoionization, electron impact ionization and charge exchange reactions producing an N+ torus of 1-4 keV suprathermal ions centered on Titan's orbital position. We will show Voyager plasma observations that demonstrate presence of a suprathermal ion component within Saturn's outer magnetosphere. The Voyager LECP data also reported the presence of inward diffusing energetic ions from the outer magnetosphere of Saturn, which could have an N+ contribution. If so, when one conserves the first and second adiabatic invariant the N+ ions will have energies in excess of 100 keV at Dione's L shell and greater than 400 keV at Enceladus' L shell. Energetic charged particle radial diffusion coefficients are also used to constrain the model results. But, one must also consider the solar wind as another important source of keV ions, in the form of protons and alpha particles, for Saturn's outer magnetosphere. Initial estimates indicate that a solar wind source could dominate in the outer magnetosphere, but various required parameters for this estimate are highly uncertain and will have to await Cassini results for confirmation. We show that satellite sweeping and charged particle precipitation within the middle and outer magnetosphere will tend to enrich N+ ions relative to protons within Saturn's inner magnetosphere as they diffuse radially inward for radial diffusion coefficients that do not violate observations. Charge exchange reactions within the inner magnetosphere can be an important loss mechanism for O+ ions, but to a lesser degree for N+ ions. Initial LECP results using composition data at energies greater than 200 keV/nucl., showed that heavy ions within Saturn's inner magnetosphere dominated over protons, but that contrary to original suggestions that these ions were O+ , we now argue that they are instead N+ ions. With energetic N+ ions bombarding the icy satellite surfaces chemical reactions can occur at the end of the ion tracks and produce nitrogen oxides or other nitrogen containing molecules such that the radiology within the icy surfaces is driven by the impacting energetic nitrogen ions. These can accumulate over the lifetime of the Saturn system.

Controlled Synthesis of Pd/Pt Core Shell Nanoparticles Using Area-selective Atomic Layer Deposition

PubMed Central

Cao, Kun; Zhu, Qianqian; Shan, Bin; Chen, Rong

2015-01-01

We report an atomic scale controllable synthesis of Pd/Pt core shell nanoparticles (NPs) via area-selective atomic layer deposition (ALD) on a modified surface. The method involves utilizing octadecyltrichlorosilane (ODTS) self-assembled monolayers (SAMs) to modify the surface. Take the usage of pinholes on SAMs as active sites for the initial core nucleation, and subsequent selective deposition of the second metal as the shell layer. Since new nucleation sites can be effectively blocked by surface ODTS SAMs in the second deposition stage, we demonstrate the successful growth of Pd/Pt and Pt/Pd NPs with uniform core shell structures and narrow size distribution. The size, shell thickness and composition of the NPs can be controlled precisely by varying the ALD cycles. Such core shell structures can be realized by using regular ALD recipes without special adjustment. This SAMs assisted area-selective ALD method of core shell structure fabrication greatly expands the applicability of ALD in fabricating novel structures and can be readily applied to the growth of NPs with other compositions. PMID:25683469

Core-Shell Structure of Intermediate Precipitates in a Nb-Based Z-Phase Strengthened 12% Cr Steel.

PubMed

Rashidi, Masoud; Andrén, Hans-Olof; Liu, Fang

2017-04-01

In creep resistant Z-phase strengthened 12% Cr steels, MX (M=Nb, Ta, or V, and X=C and/or N) to Z-phase (CrMN, M=Ta, Nb, or V) transformation plays an important role in achieving a fine distribution of Z-phase precipitates for creep strengthening. Atom probe tomography was employed to investigate the phase transformation in a Nb-based Z-phase strengthened trial steel. Using iso-concentration surfaces with different concentration values, and subtracting the matrix contribution enabled us to reveal the core-shell structure of the transient precipitates between MX and Z-phase. It was shown that Z-phase forms by diffusion of Cr into NbN upon ageing, and Z-phase has a composition corresponding to Cr1+x Nb1-x N with x=0.08.

Atom Probe Tomographic Mapping Directly Reveals the Atomic Distribution of Phosphorus in Resin Embedded Ferritin

NASA Astrophysics Data System (ADS)

Perea, Daniel E.; Liu, Jia; Bartrand, Jonah; Dicken, Quinten; Thevuthasan, S. Theva; Browning, Nigel D.; Evans, James E.

2016-02-01

Here we report the atomic-scale analysis of biological interfaces within the ferritin protein using atom probe tomography that is facilitated by an advanced specimen preparation approach. Embedding ferritin in an organic polymer resin lacking nitrogen provided chemical contrast to visualise atomic distributions and distinguish the inorganic-organic interface of the ferrihydrite mineral core and protein shell, as well as the organic-organic interface between the ferritin protein shell and embedding resin. In addition, we definitively show the atomic-scale distribution of phosphorus as being at the surface of the ferrihydrite mineral with the distribution of sodium mapped within the protein shell environment with an enhanced distribution at the mineral/protein interface. The sample preparation method is robust and can be directly extended to further enhance the study of biological, organic and inorganic nanomaterials relevant to health, energy or the environment.

Atom Probe Tomographic Mapping Directly Reveals the Atomic Distribution of Phosphorus in Resin Embedded Ferritin

PubMed Central

Perea, Daniel E.; Liu, Jia; Bartrand, Jonah; Dicken, Quinten; Thevuthasan, S. Theva; Browning, Nigel D.; Evans, James E.

2016-01-01

Here we report the atomic-scale analysis of biological interfaces within the ferritin protein using atom probe tomography that is facilitated by an advanced specimen preparation approach. Embedding ferritin in an organic polymer resin lacking nitrogen provided chemical contrast to visualise atomic distributions and distinguish the inorganic-organic interface of the ferrihydrite mineral core and protein shell, as well as the organic-organic interface between the ferritin protein shell and embedding resin. In addition, we definitively show the atomic-scale distribution of phosphorus as being at the surface of the ferrihydrite mineral with the distribution of sodium mapped within the protein shell environment with an enhanced distribution at the mineral/protein interface. The sample preparation method is robust and can be directly extended to further enhance the study of biological, organic and inorganic nanomaterials relevant to health, energy or the environment. PMID:26924804

K-shell photoionization of O4 + and O5 + ions: experiment and theory

NASA Astrophysics Data System (ADS)

McLaughlin, B. M.; Bizau, J.-M.; Cubaynes, D.; Guilbaud, S.; Douix, S.; Shorman, M. M. Al; Ghazaly, M. O. A. El; Sakho, I.; Gharaibeh, M. F.

2017-03-01

Absolute cross-sections for the K-shell photoionization of Be-like (O4 +) and Li-like (O5 +) atomic oxygen ions were measured for the first time (in their respective K-shell regions) by employing the ion-photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/ΔE ≈ 3200 (≈170 meV, full width at half-maximum) was achieved with photon energy from 550 to 670 eV. Rich resonance structure observed in the experimental spectra is analysed using the R-matrix with pseudo-states (RMPS) method. Results are also compared with the screening constant by unit nuclear charge (SCUNC) calculations. We characterize and identify the strong 1s → 2p resonances for both ions and the weaker 1s → np resonances (n ≥ 3) observed in the K-shell spectra of O4 +.

Evidence for the Role of Proton Shell Closure in Quasifission Reactions from X-Ray Fluorescence of Mass-Identified Fragments

NASA Astrophysics Data System (ADS)

Morjean, M.; Hinde, D. J.; Simenel, C.; Jeung, D. Y.; Airiau, M.; Cook, K. J.; Dasgupta, M.; Drouart, A.; Jacquet, D.; Kalkal, S.; Palshetkar, C. S.; Prasad, E.; Rafferty, D.; Simpson, E. C.; Tassan-Got, L.; Vo-Phuoc, K.; Williams, E.

2017-12-01

The atomic numbers and the masses of fragments formed in quasifission reactions are simultaneously measured at scission in 48Ti + 238U reactions at a laboratory energy of 286 MeV. The atomic numbers are determined from measured characteristic fluorescence x rays, whereas the masses are obtained from the emission angles and times of flight of the two emerging fragments. For the first time, thanks to this full identification of the quasifission fragments on a broad angular range, the important role of the proton shell closure at Z =82 is evidenced by the associated maximum production yield, a maximum predicted by time-dependent Hartree-Fock calculations. This new experimental approach gives now access to precise studies of the time dependence of the N /Z (neutron over proton ratios of the fragments) evolution in quasifission reactions.

Nuclear Data Evaluation for Mass Chain A=217:Odd-Proton Nuclei

PubMed Central

Nafee, Sherif S.; Shaheen, Salem A.; Al-Ramady, Amir M.

2016-01-01

Thallium (Tl81217), Bismuth (Bi83217), Astatine (At85217), Francium (Fr87217), Actinium (Ac89217) and Protactinium (Pa91217) are of odd-proton numbers among the mass chain A = 217. In the present work, the half-lives and gamma transitions for the six nuclei have been studied and adopted based on the recently published interactions or unevaluated nuclear data sets XUNDL. The Q (α) has been updated based on the recent published work of the Atomic Mass Evaluation AME2012 as well. Moreover, the total conversion electrons as well as the K-Shell to L-Shell, L-Shell to M-Shell and L-Shell to N-Shell Conversion Electron Ratios have been calculated using BrIcc code v2.3. An updated skeleton decay scheme for each of the above nuclei has been presented here. The decay hindrance factors (HF) calculated using the ALPHAD program, which is available from Brookhaven National Laboratory’s website, have been calculated for the α- decay data sets for 221Fr-, 221Ac- and 221Pa- α-decays. PMID:26761207

C/sub 60/La: a deflated soccer ball

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cox, D.M.; Trevor, D.J.; Reichmann, K.C.

1986-04-30

A recent paper reported very exciting results; the production and detection of C/sub n/La complexes, n = 44, 46, 48,...76, with n = 60 the dominant species. For the dominant C/sub n/La species, C/sub 60/La, the metal atom was postulated, on the basis of the experimental photoionization mass spectroscopy data, to be strongly bound within a spheroidal carbon shell possessing unusually high stability. In this paper we present further experimental evidence which when added to the information presented by HOZLCKTS and Kroto et al. (KHOCS) seriously challenges this enticing conclusion.

Structures of small Pd Pt bimetallic clusters by Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Cheng, Daojian; Huang, Shiping; Wang, Wenchuan

2006-11-01

Segregation phenomena of Pd-Pt bimetallic clusters with icosahedral and decahedral structures are investigated by using Monte Carlo method based on the second-moment approximation of the tight-binding (TB-SMA) potentials. The simulation results indicate that the Pd atoms generally lie on the surface of the smaller clusters. The three-shell onion-like structures are observed in 55-atom Pd-Pt bimetallic clusters, in which a single Pd atom is located in the center, and the Pt atoms are in the middle shell, while the Pd atoms are enriched on the surface. With the increase of Pd mole fraction in 55-atom Pd-Pt bimetallic clusters, the Pd atoms occupy the vertices of clusters first, then edge and center sites, and finally the interior shell. It is noticed that some decahedral structures can be transformed into the icosahedron-like structure at 300 and 500 K. Comparisons are made with previous experiments and theoretical studies of Pd-Pt bimetallic clusters.

Lifetime of inner-shell hole states of Ar (2p) and Kr (3d) using equation-of-motion coupled cluster method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghosh, Aryya; Vaval, Nayana, E-mail: np.vaval@ncl.res.in; Pal, Sourav

2015-07-14

Auger decay is an efficient ultrafast relaxation process of core-shell or inner-shell excited atom or molecule. Generally, it occurs in femto-second or even atto-second time domain. Direct measurement of lifetimes of Auger process of single ionized and double ionized inner-shell state of an atom or molecule is an extremely difficult task. In this paper, we have applied the highly correlated complex absorbing potential-equation-of-motion coupled cluster (CAP-EOMCC) approach which is a combination of CAP and EOMCC approach to calculate the lifetime of the states arising from 2p inner-shell ionization of an Ar atom and 3d inner-shell ionization of Kr atom. Wemore » have also calculated the lifetime of Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}D, Ar{sup 2+}(2p{sup −1}3p{sup −1}) {sup 1}S, and Ar{sup 2+}(2p{sup −1}3s{sup −1}) {sup 1}P double ionized states. The predicted results are compared with the other theoretical results as well as experimental results available in the literature.« less

Shielding of longitudinal magnetic fields with thin, closely, spaced concentric cylindrical shells with applications to atomic clocks

NASA Technical Reports Server (NTRS)

Wolf, S. A.; Gubser, D. U.; Cox, J. E.

1978-01-01

A general formula is given for the longitudinal shielding effectiveness of N closed concentric cylinders. The use of these equations is demonstrated by application to the design of magnetic shields for hydrogen maser atomic clocks. Examples of design tradeoffs such as size, weight, and material thickness are discussed. Experimental results on three sets of shields fabricated by three manufacturers are presented. Two of the sets were designed employing the techniques described. Agreement between the experimental results and the design calculations is then demonstrated.

Neutron Diffraction Studies of the Atomic Vibrations of Bulk and Surface Atoms of Nanocrystalline SiC

NASA Technical Reports Server (NTRS)

Stelmakh, S.; Grzanka, E.; Zhao, Y.; Palosz, W.; Palosz, B.

2004-01-01

Thermal atomic motions of nanocrystalline Sic were characterized by two temperature atomic factors B(sub core), and B(sub shell). With the use of wide angle neutron diffraction data it was shown that at the diffraction vector above 15A(exp -1) the Wilson plots gives directly the temperature factor of the grain interior (B(sub core)). At lower Q values the slope of the Wilson plot provides information on the relative amplitudes of vibrations of the core and shell atoms.

Impact parameter sensitive study of inner-shell atomic processes in the experimental storage ring

NASA Astrophysics Data System (ADS)

Gumberidze, A.; Kozhuharov, C.; Zhang, R. T.; Trotsenko, S.; Kozhedub, Y. S.; DuBois, R. D.; Beyer, H. F.; Blumenhagen, K.-H.; Brandau, C.; Bräuning-Demian, A.; Chen, W.; Forstner, O.; Gao, B.; Gassner, T.; Grisenti, R. E.; Hagmann, S.; Hillenbrand, P.-M.; Indelicato, P.; Kumar, A.; Lestinsky, M.; Litvinov, Yu. A.; Petridis, N.; Schury, D.; Spillmann, U.; Trageser, C.; Trassinelli, M.; Tu, X.; Stöhlker, Th.

2017-10-01

In this work, we present a pilot experiment in the experimental storage ring (ESR) at GSI devoted to impact parameter sensitive studies of inner shell atomic processes for low-energy (heavy-) ion-atom collisions. The experiment was performed with bare and He-like xenon ions (Xe54+, Xe52+) colliding with neutral xenon gas atoms, resulting in a symmetric collision system. This choice of the projectile charge states was made in order to compare the effect of a filled K-shell with the empty one. The projectile and target X-rays have been measured at different observation angles for all impact parameters as well as for the impact parameter range of ∼35-70 fm.

Ag@ZnO core-shell nanoparticles study by first principle: The structural, magnetic and optical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Hai-Xia; Wang, Xiao-Xu; Beijing Computing Center, Beijing 100094

Ag@ZnO core-shell nanoparticles of around 72 atoms have been investigated by the density functional theory, revealing proving for the first time that the core-shell structure exhibits a shrinkage phenomenon from outer shell in agreement with the other studies in literatures. Our calculations predict that the Ag@ZnO core-shell structure is a ferromagnetic spin polarized state, and the magnetism mainly stems from the spin splitting of 2p electrons of O atoms. In addition, the total and partial DOS of Ag@ZnO indicate that the nanostructure is a half-metallic nanoparticle and has the characters of the p-type semiconductor. Furthermore, the optical properties calculations showmore » that the absorption edge of Ag@ZnO have a red shift and good photocatalysis compare to that of the bulk ZnO. These results of the Ag@ZnO core-shell structure obtain a well agreement with the experimental measurement. - Graphical abstract: Geometric structure of (a) Ag@ZnO core-shell nanostructure; (b) the core of Ag; (c) the shell of ZnO The core-shell nanoparticle Ag@ZnO contains Ag inner core of radius of 4 Å and ZnO outer shell with thickness of 2 Å. Ag@ZnO core-shell nanoparticles of around 72 atoms have been proved for the first time that the core-shell structure exhibit a shrinkage phenomenon from outer shell. Our calculations predict that the Ag@ZnO core-shell structure is a half-metallic nanoparticle and has the characters of the p-type semiconductor. The absorption edge of Ag@ZnO have a red shift and get good photo-catalysis compare to that of the bulk ZnO.« less

A Theoretical Investigation of the Infrared Spectroscopic Properties of Closed-Shell Polycyclic Aromatic Hydrocarbon Cations

NASA Technical Reports Server (NTRS)

Hudgins, Douglas M.; Bauschlicher, Charles W., Jr.; Allamandola, Louis J.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

Density functional theory has been employed to calculate the harmonic frequencies and intensities of a range of PAH cations which explore both size and electronic structure effects on the infrared spectroscopic of these species. The sample extends the size range of PAH species considered to more than 50 carbon atoms and includes several representatives from each of two heretofore unexplored categories of PAH cations: (1) fully benzenoid PAH cations whose carbon skeleton is composed of an odd number of carbon atoms and (2) protonated PAH cations. Unlike the radical electronic structures of the PAH cations that have been the subject of previous theoretical and experimental work, the species in these two classes have a closed-shell electronic configuration. The calculated spectra of circumcoronene, C54H18, in both neutral and (radical) cationic form are also reported and compared to those of the other species. Closed-shell species are inherently less reactive than radical (or open-shell) cations and are known to play a role in combustion chemistry. Since interstellar PAHs are typically exposed to abundant atomic hydrogen and are thought to originate under pseudo-combustion conditions in carbon-rich circumstellar shells, such species may represent an important component of the interstellar PAH population. Furthermore, species larger than 50 carbon atoms are more representative of the size of the typical interstellar PAH. Overall, as has been the case for previous studies of PAH radical cations, the general pattern of band positions and intensities are consistent with that of the interstellar infrared emission spectrum. In addition, the spectra of closed-shell and open-shell cations are found to converge with increasing molecular size and are found to be relatively similar for species containing about 50 carbon atoms.

The spectrum of the variable planetary nebula IC 4997

NASA Technical Reports Server (NTRS)

Hyung, Siek; Aller, Lawrence H.; Feibelman, Walter A.

1994-01-01

The compact, dusty, presumably young planetary nebula (PN) IC 4997 has been studied extensively since the variability of the lambda 4363/lambda 4340 ratio was established in 1956. Since 1938, other nebular lines have shown changes. IC 4997 is also unique because of the great density range revealed by its spectrum which goes in excitation from Mg I to (Ar IV). We present a detailed listing of spectral lines from 360 to 1005 nm. The diagnostic diagram shows that the spectrum can be interpreted only in terms of strata with a huge density gamut. Essential spectral features can be reproduced approximately by a model consisting of a geometrically thin shell of density around 10(exp 7) atoms cm(exp -3), surrounded by a much larger shell with a density of about 10(exp 4) atoms cm(exp -3). The actual, certainly more complex structure can be evaluated only when high resolution spatial imaging is at hand. The usual method of getting abundances from N(ion)/N(H(+)) and ionization correction factors (ICFs) cannot be applied here. It is argued that a reasonable theoretical model that represents the spectrum provides a valid initial approximation to nebular abundances. We propose that the chemical composition of IC 4997 does not differ greatly from that of the Sun. The finally adopted model suggests that the ejection of the material destined to form the inner shell occurred between 1900 and 1960, but observational evidence of such an ejection event is lacking. Perhaps the shell was accelerated. A need for further study is emphasized, especially the role of dust which appears to contribute 2% of the total mass. More attention to this object is recommended. An accurate measurement of its distance is especially desirable.

Vanadium fine-structure K-shell electron impact ionization cross sections for fast-electron diagnostic in laser–solid experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmeri, P., E-mail: patrick.palmeri@umons.ac.be; Quinet, P., E-mail: pascal.quinet@umons.ac.be; IPNAS, Université de Liège, B-4000 Liège

2015-09-15

The K-shell electron impact ionization (EII) cross section, along with the K-shell fluorescence yield, is one of the key atomic parameters for fast-electron diagnostic in laser–solid experiments through the K-shell emission cross section. In addition, in a campaign dedicated to the modeling of the K lines of astrophysical interest (Palmeri et al. (2012)), the K-shell fluorescence yields for the K-vacancy fine-structure atomic levels of all the vanadium isonuclear ions have been calculated. In this study, the K-shell EII cross sections connecting the ground and the metastable levels of the parent vanadium ions to the daughter ions K-vacancy levels considered in Palmerimore » et al. (2012) have been determined. The relativistic distorted-wave (DW) approximation implemented in the FAC atomic code has been used for the incident electron kinetic energies up to 20 times the K-shell threshold energies. Moreover, the resulting DW cross sections have been extrapolated at higher energies using the asymptotic behavior of the modified relativistic binary encounter Bethe model (MRBEB) of Guerra et al. (2012) with the density-effect correction proposed by Davies et al. (2013)« less

Abnormal elastic modulus behavior in a crystalline-amorphous core-shell nanowire system.

PubMed

Lee, Jeong Hwan; Choi, Su Ji; Kwon, Ji Hwan; Van Lam, Do; Lee, Seung Mo; Kim, An Soon; Baik, Hion Suck; Ahn, Sang Jung; Hong, Seong Gu; Yun, Yong Ju; Kim, Young Heon

2018-06-13

We investigated the elastic modulus behavior of crystalline InAs/amorphous Al2O3 core-shell heterostructured nanowires with shell thicknesses varying between 10 and 90 nm by conducting in situ tensile tests inside a transmission electron microscope (TEM). Counterintuitively, the elastic modulus behaviors of InAs/Al2O3 core-shell nanowires differ greatly from those of bulk-scale composite materials, free from size effects. According to our results, the elastic modulus of InAs/Al2O3 core-shell nanowires increases, peaking at a shell thickness of 40 nm, and then decreases in the range of 50-90 nm. This abnormal behavior is attributed to the continuous decrease in the elastic modulus of the Al2O3 shell as the thickness increases, which is caused by changes in the atomic/electronic structure during the atomic layer deposition process and the relaxation of residual stress/strain in the shell transferred from the interfacial mismatch between the core and shell materials. A novel method for estimating the elastic modulus of the shell in a heterostructured core-shell system was suggested by considering these two effects, and the predictions from the suggested method coincided well with the experimental results. We also found that the former and latter effects account for 89% and 11% of the change in the elastic modulus of the shell. This study provides new insight by showing that the size dependency, which is caused by the inhomogeneity of the atomic/electronic structure and the residual stress/strain, must be considered to evaluate the mechanical properties of heterostructured nanowires.

Copper fine-structure K-shell electron impact ionization cross sections for fast-electron diagnostic in laser-solid experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmeri, P., E-mail: patrick.palmeri@umons.ac.be; Quinet, P., E-mail: pascal.quinet@umons.ac.be; IPNAS, Université de Liège, B-4000 Liège

2015-03-15

The K-shell electron impact ionization (EII) cross section, along with the K-shell fluorescence yield, is one of the key atomic parameters for fast-electron diagnostic in laser-solid experiments through the K-shell emission cross section. In addition, copper is a material that has been often used in those experiments because it has a maximum total K-shell emission yield. Furthermore, in a campaign dedicated to the modeling of the K lines of astrophysical interest (Palmeri et al., 2012), the K-shell fluorescence yields for the K-vacancy fine-structure atomic levels of all the copper isonuclear ions have been calculated. In this study, the K-shell EII crossmore » sections connecting the ground and the metastable levels of the parent copper ions to the daughter ions K-vacancy levels considered in Palmeri et al. (2012) have been determined. The relativistic distorted-wave (DW) approximation implemented in the FAC atomic code has been used for the incident electron kinetic energies up to 10 times the K-shell threshold energies. Moreover, the resulting DW cross sections have been extrapolated at higher energies using the asymptotic form proposed by Davies et al. (2013)« less

Sonochemical Synthesis of a Zinc Oxide Core-Shell Nanorod Radial p-n Homojunction Ultraviolet Photodetector.

PubMed

Vabbina, Phani Kiran; Sinha, Raju; Ahmadivand, Arash; Karabiyik, Mustafa; Gerislioglu, Burak; Awadallah, Osama; Pala, Nezih

2017-06-14

We report for the first time on the growth of a homogeneous radial p-n junction in the ZnO core-shell configuration with a p-doped ZnO nanoshell structure grown around a high-quality unintentionally n-doped ZnO nanorod using sonochemistry. The simultaneous decomposition of phosphorous (P), zinc (Zn), and oxygen (O) from their respective precursors during sonication allows for the successful incorporation of P atoms into the ZnO lattice. The as-formed p-n junction shows a rectifying current-voltage characteristic that is consistent with a p-n junction with a threshold voltage of 1.3 V and an ideality factor of 33. The concentration of doping was estimated to be N A = 6.7 × 10 17 cm -3 on the p side from the capacitance-voltage measurements. The fabricated radial p-n junction demonstrated a record optical responsivity of 9.64 A/W and a noise equivalent power of 0.573 pW/√Hz under ultraviolet illumination, which is the highest for ZnO p-n junction devices.

Charge Radii of Neutron Deficient Fe,5352 Produced by Projectile Fragmentation

NASA Astrophysics Data System (ADS)

Minamisono, K.; Rossi, D. M.; Beerwerth, R.; Fritzsche, S.; Garand, D.; Klose, A.; Liu, Y.; Maaß, B.; Mantica, P. F.; Miller, A. J.; Müller, P.; Nazarewicz, W.; Nörtershäuser, W.; Olsen, E.; Pearson, M. R.; Reinhard, P.-G.; Saperstein, E. E.; Sumithrarachchi, C.; Tolokonnikov, S. V.

2016-12-01

Bunched-beam collinear laser spectroscopy is performed on neutron deficient Fe,5352 prepared through in-flight separation followed by a gas stopping. This novel scheme is a major step to reach nuclides far from the stability line in laser spectroscopy. Differential mean-square charge radii δ ⟨r2⟩ of Fe,5352 are determined relative to stable 56Fe as δ ⟨r2⟩56 ,52=-0.034 (13 ) fm2 and δ ⟨r2⟩56 ,53=-0.218 (13 ) fm2 , respectively, from the isotope shift of atomic hyperfine structures. The multiconfiguration Dirac-Fock method is used to calculate atomic factors to deduce δ ⟨r2⟩. The values of δ ⟨r2⟩ exhibit a minimum at the N =28 neutron shell closure. The nuclear density functional theory with Fayans and Skyrme energy density functionals is used to interpret the data. The trend of δ ⟨r2⟩ along the Fe isotopic chain results from an interplay between single-particle shell structure, pairing, and polarization effects and provides important data for understanding the intricate trend in the δ ⟨r2⟩ of closed-shell Ca isotopes.

Core-shell titanium dioxide-titanium nitride nanotube arrays with near-infrared plasmon resonances

NASA Astrophysics Data System (ADS)

Farsinezhad, Samira; Shanavas, Thariq; Mahdi, Najia; Askar, Abdelrahman M.; Kar, Piyush; Sharma, Himani; Shankar, Karthik

2018-04-01

Titanium nitride (TiN) is a ceramic with high electrical conductivity which in nanoparticle form, exhibits localized surface plasmon resonances (LSPRs) in the visible region of the solar spectrum. The ceramic nature of TiN coupled with its dielectric loss factor being comparable to that of gold, render it attractive for CMOS polarizers, refractory plasmonics, surface-enhanced Raman scattering and a whole host of sensing applications. We report core-shell TiO2-TiN nanotube arrays exhibiting LSPR peaks in the range 775-830 nm achieved by a simple, solution-based, low cost, large area-compatible fabrication route that does not involve laser-writing or lithography. Self-organized, highly ordered TiO2 nanotube arrays were grown by electrochemical anodization of Ti thin films on fluorine-doped tin oxide-coated glass substrates and then conformally coated with a thin layer of TiN using atomic layer deposition. The effects of varying the TiN layer thickness and thermal annealing on the LSPR profiles were also investigated. Modeling the TiO2-TiN core-shell nanotube structure using two different approaches, one employing effective medium approximations coupled with Fresnel coefficients, resulted in calculated optical spectra that closely matched the experimentally measured spectra. Modeling provided the insight that the observed near-infrared resonance was not collective in nature, and was mainly attributable to the longitudinal resonance of annular nanotube-like TiN particles redshifted due to the presence of the higher permittivity TiO2 matrix. The resulting TiO2-TiN core-shell nanotube structures also function as visible light responsive photocatalysts, as evidenced by their photoelectrochemical water-splitting performance under light emitting diode illumination using 400, 430 and 500 nm photons.

Population kinetics on K alpha lines of partially ionized Cl atoms.

PubMed

Kawamura, Tohru; Nishimura, Hiroaki; Koike, Fumihiro; Ochi, Yoshihiro; Matsui, Ryoji; Miao, Wen Yong; Okihara, Shinichiro; Sakabe, Shuji; Uschmann, Ingo; Förster, Eckhart; Mima, Kunioki

2002-07-01

A population kinetics code was developed to analyze K alpha emission from partially ionized chlorine atoms in hydrocarbon plasmas. Atomic processes are solved under collisional-radiative equilibrium for two-temperature plasmas. It is shown that the fast electrons dominantly contribute to ionize the K-shell bound electrons (i.e., inner-shell ionization) and the cold electrons to the outer-shell bound ones. Ratios of K alpha lines of partially ionized atoms are presented as a function of cold-electron temperature. The model was validated by observation of the K alpha lines from a chlorinated plastic target irradiated with 1 TW Ti:sapphire laser pulses at 1.5 x 10(17) W/cm(2), inferring a plasma temperature of about 100 eV on the target surface.

Simulation of angular-resolved RABBITT measurements in noble-gas atoms

NASA Astrophysics Data System (ADS)

Bray, Alexander W.; Naseem, Faiza; Kheifets, Anatoli S.

2018-06-01

We simulate angular-resolved RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) measurements on valence shells of noble-gas atoms (Ne, Ar, Kr, and Xe). Our nonperturbative numerical simulation is based on solution of the time-dependent Schrödinger equation (TDSE) for a target atom driven by an ionizing XUV and dressing IR fields. From these simulations we extract the angular-dependent magnitude and phase of the RABBITT oscillations and deduce the corresponding angular anisotropy β parameter and Wigner time delay τW for the single XUV photon absorption that initiates the RABBITT process. Said β and τW parameters are compared with calculations in the random-phase approximation with exchange (RPAE), which includes intershell correlation. This comparison is used to test various effective potentials employed in the one-electron TDSE. In lighter atoms (Ne and Ar), several effective potentials are found to provide accurate simulations of RABBITT measurements for a wide range of photon energies up to 100 eV above the valence-shell threshold. In heavier atoms (Kr and Xe), the onset of strong correlation with the d shell restricts the validity of the single active electron approximation to several tens of eV above the valence-shell threshold.

An extended N-H bond, driven by a conserved second-order interaction, orients the flavin N5 orbital in cholesterol oxidase

NASA Astrophysics Data System (ADS)

Golden, Emily; Yu, Li-Juan; Meilleur, Flora; Blakeley, Matthew P.; Duff, Anthony P.; Karton, Amir; Vrielink, Alice

2017-01-01

The protein microenvironment surrounding the flavin cofactor in flavoenzymes is key to the efficiency and diversity of reactions catalysed by this class of enzymes. X-ray diffraction structures of oxidoreductase flavoenzymes have revealed recurrent features which facilitate catalysis, such as a hydrogen bond between a main chain nitrogen atom and the flavin redox center (N5). A neutron diffraction study of cholesterol oxidase has revealed an unusual elongated main chain nitrogen to hydrogen bond distance positioning the hydrogen atom towards the flavin N5 reactive center. Investigation of the structural features which could cause such an unusual occurrence revealed a positively charged lysine side chain, conserved in other flavin mediated oxidoreductases, in a second shell away from the FAD cofactor acting to polarize the peptide bond through interaction with the carbonyl oxygen atom. Double-hybrid density functional theory calculations confirm that this electrostatic arrangement affects the N-H bond length in the region of the flavin reactive center. We propose a novel second-order partial-charge interaction network which enables the correct orientation of the hydride receiving orbital of N5. The implications of these observations for flavin mediated redox chemistry are discussed.

Visualization of Bacterial Microcompartment Facet Assembly Using High-Speed Atomic Force Microscopy

DOE PAGES

Sutter, Markus; Faulkner, Matthew; Aussignargues, Clément; ...

2015-11-30

Bacterial microcompartments (BMCs) are proteinaceous organelles widespread among bacterial phyla. They compartmentalize enzymes within a selectively permeable shell and play important roles in CO 2 fixation, pathogenesis, and microbial ecology. Here, we combine X-ray crystallography and high-speed atomic force microscopy to characterize, at molecular resolution, the structure and dynamics of BMC shell facet assembly. Our results show that preformed hexamers assemble into uniformly oriented shell layers, a single hexamer thick. We also observe the dynamic process of shell facet assembly. Shell hexamers can dissociate from and incorporate into assembled sheets, indicating a flexible intermolecular interaction. Furthermore, we demonstrate that themore » self-assembly and dynamics of shell proteins are governed by specific contacts at the interfaces of shell proteins. Our study provides novel insights into the formation, interactions, and dynamics of BMC shell facets, which are essential for the design and engineering of self-assembled biological nanoreactors and scaffolds based on BMC architectures.« less

Making sense of the conflicting magic numbers in WSi{sub n} clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abreu, Marissa Baddick; Reber, Arthur C.; Khanna, Shiv N.

2015-08-21

First principles studies on the geometric structure, stability, and electronic structure of WSi{sub n} clusters, n = 6-16, have been carried out to show that the observed differing “magic sizes” for WSi{sub n} clusters are associated with the nature of the growth processes. The WSi{sub 12} cluster, observed as a magic species in experiments reacting transition metal ions with silane, is not stable due to a filled shell of 18 electrons, as previously proposed, but due to its atomic structure that arrests further growth because of an endohedral transition metal site. In fact, it is found that all of thesemore » clusters, n = 6-16, have filled 5d shells except for WSi{sub 12}, which has a 5d{sup 8} configuration that is caused by crystal field splitting. The stability of WSi{sub 15}{sup +}, observed as highly stable in clusters generated by vaporizing silicon and metal carbonyls, is shown to be associated with a combination of geometric and electronic features. The findings are compared with previous results on CrSi{sub n} clusters.« less

Effect of energy transfer from atomic electron shell to an α particle emitted by decaying nucleus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Igashov, S. Yu., E-mail: igashov@theor.mephi.ru; Tchuvil’sky, Yu. M.

2016-12-15

The process of energy transfer from the electron shell of an atom to an α particle propagating through the shell is formulated mathematically. Using the decay of the {sup 226}Ra nucleus as an example, it is demonstrated that this phenomenon increases the α-decay intensity in contrast with other known effects of similar type. Moreover, the α decay of the nucleus is more strongly affected by the energy transfer than by all other effects taken together.

Freshwater mussel shells as environmental chronicles: Geochemical and taphonomic signatures of mercury-related extirpations in the North Fork Holston River, Virginia

USGS Publications Warehouse

Brown, M.E.; Kowalewski, M.; Neves, R.J.; Cherry, D.S.; Schreiber, M.E.

2005-01-01

This study utilized freshwater mussel shells to assess mercury (Hg) contamination in the North Fork Holston River that extirpated (caused local extinctions of) a diverse mussel fauna. Shells (n = 366) were collected from five sites situated upstream (two sites), just below (one site), and downstream (two sites) of the town of Saltville, Virginia, where Hg was used to produce chlorine and caustic soda from 1950 to 1972. Shell samples were used to test the (1) utility of geochemical signatures of shells for assessing the spatial variation in Hg levels in the river relative to the contamination source and (2) value of taphonomy (postmortem shell alteration) for distinguishing sites that differ in extirpation histories. Geochemical signatures of 40 shells, analyzed using atomic absorption spectroscopy, indicated a strong longitudinal pattern. All shells from the two upstream sites had low Hg concentrations (<5-31 ??g/kg), shells directly below Saltville had variable, but dramatically higher concentrations (23-4637 ??g/kg), and shells from the two downstream sites displayed intermediate Hg levels (<5-115 ??g/kg) that declined with distance from Saltville. Two pre-industrial shells, collected at Saltville in 1917, yielded very low Hg estimates (5-6 ??g/kg). Hg signatures were consistent among mussel species, suggesting that Hg concentrations were invariant to species type; most likely, highly variable Hg levels, both across sites and through time, overwhelmed any interspecific differences in Hg acquisition. Also, a notable postmortem incorporation of Hg in mussel shells seemed unlikely, as the Hg content was not correlated with shell taphonomy (r = 0.18; p = 0.28). The taphonomic analysis (n = 366) showed that the degree of shell alteration reliably distinguished sites with different extirpation histories. At Saltville, where live mussels have been absent for at least 30 years, shells were most heavily altered and fragmented. Conversely, fresh-looking shells abounded upstream, where reproducing mussel populations are still present. In summary, relic shells offered valuable spatiotemporal data on Hg concentrations in a polluted ecosystem, and shell taphonomic signatures discriminated sites with different extirpation histories. The shell-based strategies exemplified here do not require sampling live specimens and may augment more standard strategies applied to environmental monitoring. The approach should prove especially useful in areas with unknown extirpation and pollution histories. ?? 2005 American Chemical Society.

Proton - Neutron Interactions and The New Atomic Masses

NASA Astrophysics Data System (ADS)

Cakirli, R. B.; Casten, R. F.; Brenner, D. S.; Millman, E. A.

2005-04-01

Proton - neutron interactions determine structural evolution with N and Z including the onset of collectivity, deformation, and phase transitions. We have extracted the interaction of the last proton and the last neutron, called δVpn, from a specific double difference of binding energies using the new mass tabulation [1]. Striking variations are seen near closed shells. In the Pb region, these are interpreted using overlaps of shell model orbits, which are large when both protons and neutrons are in similar orbits, and small when they are not. Further, we used the idea that shell filling follows a typical systematic pattern to look at the correlation of δVpn values to the fractions of the proton and neutron shells that are filled. These results provide useful signatures of structure in exotic nuclei.This work was supported by US DOE Grant Nos. DE-FG02-91ER40609 and DE-FG02-88ER-40417. [1] G. Audi, A.H. Wapstra and C. Thibault, Nucl. Phys.A729, 337 (2003).

Sequential two-photon double ionization of noble gases by circularly polarized XUV radiation

NASA Astrophysics Data System (ADS)

Gryzlova, E. V.; Grum-Grzhimailo, A. N.; Kuzmina, E. I.; Strakhova, S. I.

2014-10-01

Photoelectron angular distributions (PADs) and angular correlations between two emitted electrons in sequential two-photon double ionization (2PDI) of atoms by circularly polarized radiation are studied theoretically. In particular, the sequential 2PDI of the valence n{{p}6} shell in noble gas atoms (neon, argon, krypton) is analyzed, accounting for the first-order corrections to the dipole approximation. Due to different selection rules in ionization transitions, the circular polarization of photons causes some new features of the cross sections, PADs and angular correlation functions in comparison with the case of linearly polarized photons.

Structural Evolution of Supercritical CO2 across the Frenkel Line.

PubMed

Bolmatov, Dima; Zav'yalov, D; Gao, M; Zhernenkov, Mikhail

2014-08-21

Here, we study structural properties of the supercritical carbon dioxide and discover the existence of persistent medium-range order correlations, which make supercritical carbon dioxide nonuniform and heterogeneous on an intermediate length scale. We report on the CO2 heterogeneity shell structure where, in the first shell, both carbon and oxygen atoms experience gas-like-type interactions with short-range order correlations while within the second shell, oxygen atoms essentially exhibit a liquid-like type of interactions due to localization of transverse-like phonon packets. Importantly, we highlight a catalytic role of atoms inside of the nearest-neighbor heterogeneity shell in providing a mechanism for diffusion and proving the existence of an additional thermodynamic boundary in the supercritical carbon dioxide on an intermediate length scale. Finally, we discuss important implications for answering the intriguing question whether Venus may have had CO2 oceans and urge for an experimental detection of this persistent local-order heterogeneity.

Reexamination of the interaction of atoms with a LiF(001) surface

NASA Astrophysics Data System (ADS)

Miraglia, J. E.; Gravielle, M. S.

2017-02-01

Pairwise additive potentials for multielectronic atoms interacting with a LiF(001) surface are revisited by including an improved description of the electron density associated with the different lattice sites, as well as nonlocal electron density contributions. Within this model, the electron distribution around each ionic site of the crystal is described by means of a so-called "onion" approach that accounts for the influence of the Madelung potential. From such densities, binary interatomic potentials are then derived by using well-known nonlocal functionals. Rumpling and long-range contributions due to projectile polarization and van der Waals forces are also included. We apply this pairwise additive approximation to evaluate the interaction potential between closed-shell (He, Ne, Ar, Kr, and Xe) and open-shell (N, S, and Cl) atoms and the LiF surface, analyzing the relative importance of the different contributions. The performance of the proposed potentials is assessed by contrasting angular positions of rainbow and supernumerary rainbow maxima produced by fast grazing incidence with available experimental data. One important result of our model is that both van der Waals contributions and thermal lattice vibrations play a negligible role for normal energies in the eV range.

Global optimization of additive potential energy functions: Predicting binary Lennard-Jones clusters

NASA Astrophysics Data System (ADS)

Kolossváry, István; Bowers, Kevin J.

2010-11-01

We present a method for minimizing additive potential-energy functions. Our hidden-force algorithm can be described as an intricate multiplayer tug-of-war game in which teams try to break an impasse by randomly assigning some players to drop their ropes while the others are still tugging until a partial impasse is reached, then, instructing the dropouts to resume tugging, for all teams to come to a new overall impasse. Utilizing our algorithm in a non-Markovian parallel Monte Carlo search, we found 17 new putative global minima for binary Lennard-Jones clusters in the size range of 90-100 particles. The method is efficient enough that an unbiased search was possible; no potential-energy surface symmetries were exploited. All new minima are comprised of three nested polyicosahedral or polytetrahedral shells when viewed as a nested set of Connolly surfaces (though the shell structure has previously gone unscrutinized, known minima are often qualitatively similar). Unlike known minima, in which the outer and inner shells are comprised of the larger and smaller atoms, respectively, in 13 of the new minima, the atoms are not as clearly separated by size. Furthermore, while some known minima have inner shells stabilized by larger atoms, four of the new minima have outer shells stabilized by smaller atoms.

Size effect on atomic structure in low-dimensional Cu-Zr amorphous systems.

PubMed

Zhang, W B; Liu, J; Lu, S H; Zhang, H; Wang, H; Wang, X D; Cao, Q P; Zhang, D X; Jiang, J Z

2017-08-04

The size effect on atomic structure of a Cu 64 Zr 36 amorphous system, including zero-dimensional small-size amorphous particles (SSAPs) and two-dimensional small-size amorphous films (SSAFs) together with bulk sample was investigated by molecular dynamics simulations. We revealed that sample size strongly affects local atomic structure in both Cu 64 Zr 36 SSAPs and SSAFs, which are composed of core and shell (surface) components. Compared with core component, the shell component of SSAPs has lower average coordination number and average bond length, higher degree of ordering, and lower packing density due to the segregation of Cu atoms on the shell of Cu 64 Zr 36 SSAPs. These atomic structure differences in SSAPs with various sizes result in different glass transition temperatures, in which the glass transition temperature for the shell component is found to be 577 K, which is much lower than 910 K for the core component. We further extended the size effect on the structure and glasses transition temperature to Cu 64 Zr 36 SSAFs, and revealed that the T g decreases when SSAFs becomes thinner due to the following factors: different dynamic motion (mean square displacement), different density of core and surface and Cu segregation on the surface of SSAFs. The obtained results here are different from the results for the size effect on atomic structure of nanometer-sized crystalline metallic alloys.

Ab initio effective core potentials including relativistic effects and their application to the electronic structure calculations of heavy atoms and molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Y.S.

1977-11-01

The effects of the 4f shell of electrons and the relativity of valence electrons are compared. The effect of 4f shell (lanthanide contraction) is estimated from the numerical Hartree-Fock (HF) calculations of pseudo-atoms corresponding to Hf, Re, Au, Hg, Tl, Pb and Bi without 4f electrons and with atomic numbers reduced by 14. The relativistic effect estimated from the numerical Dirac-Hartree-Fock (DHF) calculations of those atoms is comparable in the magnitude with that of the 4f shell of electrons. Both are larger for 6s than for 5d or 6p electrons. The various relativistic effects on valence electrons are discussed inmore » detail to determine the proper level of the approximation for the valence electron calculations of systems with heavy elements. An effective core potential system has been developed for heavy atoms in which relativistic effects are included in the effective potentials.« less

Advanced Kr Atomic Structure and Ionization Kinetics for Pinches on ZR

NASA Astrophysics Data System (ADS)

Dasgupta, Arati; Clark, Robert; Giuliani, John; Ouart, Nick; Davis, Jack; Jones, Brent; Ampleford, Dave; Hansen, Stephanie

2011-10-01

High fluence photon sources above 10 keV are a challenge for HED plasmas. This motivates Kr atomic modeling as its K-shell radiation starts at 13 keV. We have developed atomic structure and collisional-radiatve data for the full K-and L-shell and much of the M-shell using the the state-of-the-art Flexible Atomic Code. All relevant atomic collisional and radiative processes that affect ionization balance and are necessary to accurately model the pinch dynamics and the spectroscopic details of the emitted radiation are included in constructing the model. This non-LTE CRE model will be used to generate synthetic spectra for fixed densities and temperatures relevant for Kr gas-puff simulations in ZR. Work supported by DOE/NNSA. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Optical oscillator strengths of the valence-shell excitations of atoms and molecules determined by the dipole ( γ,γ) method

NASA Astrophysics Data System (ADS)

Xu, Long-Quan; Liu, Ya-Wei; Xu, Xin; Ni, Dong-Dong; Yang, Ke; Zhu, Lin-Fan

2017-07-01

The dipole (γ,γ) method, which is the inelastic X-ray scattering operated at a negligibly small momentum transfer, has been developed to determine the absolute optical oscillator strengths of the valence-shell excitations of atoms and molecules. This new method is free from the line saturation effect, and its Bethe-Born conversion factor varies much more slowly with the excitation energy than that of the dipole (e, e) method. Thus the dipole (γ,γ) method provides a reliable approach to obtain the benchmark optical oscillator strengths of the valence-shell excitations for gaseous atoms and molecules. In this paper, we give a review of the dipole (γ,γ) method and some recent measurements of absolute optical oscillator strengths of gaseous atoms and molecules. Contribution to the Topical Issue "Atomic and Molecular Data and their Applications", edited by Gordon W.F. Drake, Jung-Sik Yoon, Daiji Kato, Grzegorz Karwasz.

Ionic bonding of lanthanides, as influenced by d- and f-atomic orbitals, by core-shells and by relativity.

PubMed

Ji, Wen-Xin; Xu, Wei; Schwarz, W H Eugen; Wang, Shu-Guang

2015-03-15

Lanthanide trihalide molecules LnX3 (X = F, Cl, Br, I) were quantum chemically investigated, in particular detail for Ln = Lu (lutetium). We applied density functional theory (DFT) at the nonrelativistic and scalar and SO-coupled relativistic levels, and also the ab initio coupled cluster approach. The chemically active electron shells of the lanthanide atoms comprise the 5d and 6s (and 6p) valence atomic orbitals (AO) and also the filled inner 4f semivalence and outer 5p semicore shells. Four different frozen-core approximations for Lu were compared: the (1s(2) -4d(10) ) [Pd] medium core, the [Pd+5s(2) 5p(6) = Xe] and [Pd+4f(14) ] large cores, and the [Pd+4f(14) +5s(2) 5p(6) ] very large core. The errors of LuX bonding are more serious on freezing the 5p(6) shell than the 4f(14) shell, more serious upon core-freezing than on the effective-core-potential approximation. The LnX distances correlate linearly with the AO radii of the ionic outer shells, Ln(3+) -5p(6) and X(-) -np(6) , characteristic for dominantly ionic Ln(3+) -X(-) binding. The heavier halogen atoms also bind covalently with the Ln-5d shell. Scalar relativistic effects contract and destabilize the LuX bonds, spin orbit coupling hardly affects the geometries but the bond energies, owing to SO effects in the free atoms. The relativistic changes of bond energy BE, bond length Re , bond force k, and bond stretching frequency vs do not follow the simple rules of Badger and Gordy (Re ∼BE∼k∼vs ). The so-called degeneracy-driven covalence, meaning strong mixing of accidentally near-degenerate, nearly nonoverlapping AOs without BE contribution is critically discussed. © 2015 Wiley Periodicals, Inc.

Transition Quadrupole Collectivity of Ar and Cl Isotopes Near N = 28

NASA Astrophysics Data System (ADS)

Winkler, R.; Gade, A.; Brown, B. A.; Glasmacher, T.; Baugher, T. R.; Bazin, D.; Grinyer, G. F.; McDaniel, S.; Meharchand, R.; Ratkiewicz, A.; Stroberg, R.; Walsh, K.; Weisshaar, D.; Riley, L. A.

2010-11-01

Measurements of the reduced quadrupole transition strengths, B(E2; 0^+ -> 2^+) of even-even nuclei guide our understanding of the onset collectivity with the addition of valence nucleons beyond the known shell structure of the atomic nucleus. The study of the quadrupole collectivity of neutron-rich ^47,48Ar and ^45,46Cl via relativistic Coulomb excitation was performed using a cocktail of exotic beams produced by the coupled cyclotron facility at NSCL. Particle tracking and identification was achieved on an event-by-event basis using the S800 high-resolution spectrograph. Gamma rays emitted at the reaction target position in coincidence with the detection of scattered particles were observed with the segmented high-purity Germanium array SeGA, a vital tool for the Doppler reconstruction of each observed event. Results from the present work provide insight into the persistence of the N = 28 shell closure and will be discussed in the framework of the shell model utilizing modern effective interactions in the sdpf valence space. This work is supported by the National Science Foundation under Grants No. PHY-0606007 and PHY-0758099.

Photoionization cross sections for atomic chlorine using an open-shell random phase approximation

NASA Technical Reports Server (NTRS)

Starace, A. F.; Armstrong, L., Jr.

1975-01-01

The use of the Random Phase Approximation with Exchange (RPAE) for calculating partial and total photoionization cross sections and photoelectron angular distributions for open shell atoms is examined for atomic chlorine. Whereas the RPAE corrections in argon (Z=18) are large, it is found that those in chlorine (Z=17) are much smaller due to geometric factors. Hartree-Fock calculations with and without core relaxation are also presented. Sizable deviations from the close coupling results of Conneely are also found.

Evolution of L -shell photoabsorption of the molecular-ion series Si Hn + (n =1 ,2 ,3 ): Experimental and theoretical studies

NASA Astrophysics Data System (ADS)

Kennedy, E. T.; Mosnier, J.-P.; van Kampen, P.; Bizau, J.-M.; Cubaynes, D.; Guilbaud, S.; Carniato, S.; Puglisi, A.; Sisourat, N.

2018-04-01

We report on complementary laboratory and theoretical investigations of the 2 p photoexcitation cross sections for the molecular-ion series Si Hn + (n =1 ,2 ,3 ) near the L -shell threshold. The experiments used an electron cyclotron resonance (ECR) plasma molecular-ion source coupled with monochromatized synchrotron radiation in a merged-beam configuration. For all three molecular ions, the S i2 + decay channel appeared dominant, suggesting similar electronic and nuclear relaxation patterns involving resonant Auger and dissociation processes, respectively. The total yields of the S i2 + products were recorded and put on absolute cross-section scales by comparison with the spectrum of the S i+ parent atomic ion. Interpretation of the experimental spectra ensued from a comparison with total photoabsorption cross-sectional profiles calculated using ab initio configuration interaction theoretical methods inclusive of vibrational dynamics and contributions from inner-shell excitations in both ground and valence-excited electronic states. The spectra, while broadly similar for all three molecular ions, moved towards lower energies as the number of screening hydrogen atoms increased from one to three. They featured a wide and shallow region below ˜107 eV due to 2 p →σ* transitions to dissociative states, and intense and broadened peaks in the ˜107 -113 -eV region merging into sharp Rydberg series due to 2 p →n δ ,n π transitions converging on the LII ,III limits above ˜113 eV . This overall spectral shape is broadly replicated by theory in each case, but the level of agreement does not extend to individual resonance structures. In addition to the fundamental interest, the work should also prove useful for the understanding and modeling of astronomical and laboratory plasma sources where silicon hydride molecular species play significant roles.

Charge radii of neutron deficient Fe 52 , 53 produced by projectile fragmentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minamisono, K.; Rossi, D. M.; Beerwerth, R.

Bunched-beam collinear laser spectroscopy is performed on neutron deficient 52,53Fe prepared through in-flight separation followed by a gas stopping. This novel scheme is a major step to reach nuclides far from the stability line in laser spectroscopy. Differential mean-square charge radii δmore » $$\\langle$$r 2$$\\rangle$$ of 52,53Fe are determined relative to stable 56Fe as δ$$\\langle$$r2$$\\rangle$$ 56,52=$-$0.034(13) fm 2 and δ$$\\langle$$r 2$$\\rangle$$56,53=$-$0.218(13) fm 2, respectively, from the isotope shift of atomic hyperfine structures. The multiconfiguration Dirac-Fock method is used to calculate atomic factors to deduce δ$$\\langle$$r 2$$\\rangle$$. The values of δ$$\\langle$$r 2$$\\rangle$$ exhibit a minimum at the N=28 neutron shell closure. The nuclear density functional theory with Fayans and Skyrme energy density functionals is used to interpret the data. As a result, the trend of δ$$\\langle$$r 2$$\\rangle$$ along the Fe isotopic chain results from an interplay between single-particle shell structure, pairing, and polarization effects and provides important data for understanding the intricate trend in the δ$$\\langle$$r 2$$\\rangle$$ of closed-shell Ca isotopes« less

Charge radii of neutron deficient Fe 52 , 53 produced by projectile fragmentation

DOE PAGES

Minamisono, K.; Rossi, D. M.; Beerwerth, R.; ...

2016-12-15

Bunched-beam collinear laser spectroscopy is performed on neutron deficient 52,53Fe prepared through in-flight separation followed by a gas stopping. This novel scheme is a major step to reach nuclides far from the stability line in laser spectroscopy. Differential mean-square charge radii δmore » $$\\langle$$r 2$$\\rangle$$ of 52,53Fe are determined relative to stable 56Fe as δ$$\\langle$$r2$$\\rangle$$ 56,52=$-$0.034(13) fm 2 and δ$$\\langle$$r 2$$\\rangle$$56,53=$-$0.218(13) fm 2, respectively, from the isotope shift of atomic hyperfine structures. The multiconfiguration Dirac-Fock method is used to calculate atomic factors to deduce δ$$\\langle$$r 2$$\\rangle$$. The values of δ$$\\langle$$r 2$$\\rangle$$ exhibit a minimum at the N=28 neutron shell closure. The nuclear density functional theory with Fayans and Skyrme energy density functionals is used to interpret the data. As a result, the trend of δ$$\\langle$$r 2$$\\rangle$$ along the Fe isotopic chain results from an interplay between single-particle shell structure, pairing, and polarization effects and provides important data for understanding the intricate trend in the δ$$\\langle$$r 2$$\\rangle$$ of closed-shell Ca isotopes« less

Novel highly ordered core–shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dey, Sonal; Hossain, Mohammad D.; Mayanovic, Robert A.

2016-10-26

Core–shell nanoparticles have potential for a wide range of applications due to the tunability of their magnetic, catalytic, electronic, optical, and other physicochemical properties. A frequent drawback in the design of core–shell nanoparticles and nanocrystals is the lack of control over an extensive, disordered, and compositionally distinct interface that occurs due to the dissimilarity of structural and compositional phases of the core and shell. In this work, we demonstrate a new hydrothermal nanophase epitaxy (HNE) technique to synthesize highly structurally ordered α-Cr 2O 3@α-Co 0.38Cr 1.62O 2.92 inverted core–shell nanoparticles (CSNs) with evidence for the nanoscale growth of corundum structuremore » beginning from the core and extending completely into the shell of the CSNs with minimal defects at the interface. The high-resolution TEM results show a sharp interface exhibiting epitaxial atomic registry of shell atoms over highly ordered core atoms. The XPS and Co K-edge XANES analyses indicate the +2 oxidation state of cobalt is incorporated in the shell of the CSNs. Our XPS and EXAFS results are consistent with oxygen vacancy formation in order to maintain charge neutrality upon substitution of the Co 2+ ion for the Cr 3+ ion in the α-Co 0.38Cr 1.62O 2.92 shell. Furthermore, the CSNs exhibit the magnetic exchange bias effect, which is attributed to the exchange anisotropy at the interface made possible by the nanophase epitaxial growth of the α-Co 0.38Cr 1.62O 2.92 shell on the α-Cr 2O 3 core of the nanoparticles. The combination of a well-structured, sharp interface and novel nanophase characteristics is highly desirable for nanostructures having enhanced magnetic properties.« less

Ultrasonically synthesized organic liquid-filled chitosan microcapsules: part 2: characterization using AFM (atomic force microscopy) and combined AFM-confocal laser scanning fluorescence microscopy.

PubMed

Mettu, Srinivas; Ye, Qianyu; Zhou, Meifang; Dagastine, Raymond; Ashokkumar, Muthupandian

2018-04-25

Atomic Force Microscopy (AFM) is used to measure the stiffness and Young's modulus of individual microcapsules that have a chitosan cross-linked shell encapsulating tetradecane. The oil filled microcapsules were prepared using a one pot synthesis via ultrasonic emulsification of tetradecane and crosslinking of the chitosan shell in aqueous solutions of acetic acid. The concentration of acetic acid in aqueous solutions of chitosan was varied from 0.2% to 25% v/v. The effect of acetic acid concentration and size of the individual microcapsules on the strength was probed. The deformations and forces required to rupture the microcapsules were also measured. Three dimensional deformations of microcapsules under large applied loads were obtained by the combination of Laser Scanning Confocal Microscopy (LSCM) with Atomic Force Microscopy (AFM). The stiffness, and hence the modulus, of the microcapsules was found to decrease with an increase in size with the average stiffness ranging from 82 to 111 mN m-1 and average Young's modulus ranging from 0.4 to 6.5 MPa. The forces required to rupture the microcapsules varied from 150 to 250 nN with deformations of the microcapsules up to 62 to 110% relative to their radius, respectively. Three dimensional images obtained using laser scanning confocal microscopy showed that the microcapsules retained their structure and shape after being subjected to large deformations and subsequent removal of the loads. Based on the above observations, the oil filled chitosan crosslinked microcapsules are an ideal choice for use in the food and pharmaceutical industries as they would be able to withstand the process conditions encountered.

Imaging powders with the atomic force microscope: from biominerals to commercial materials.

PubMed

Friedbacher, G; Hansma, P K; Ramli, E; Stucky, G D

1991-09-13

Atomically resolved images of pressed powder samples have been obtained with the atomic force microscope (AFM). The technique was successful in resolving the particle, domain, and atomic structure of pismo clam (Tivela stultorum) and sea urchin (Strongylocentrotus purpuratus) shells and of commercially available calcium carbonate (CaCO(3)) and strontium carbonate (SrCO(3)) powders. Grinding and subsequent pressing of the shells did not destroy the microstructure of these materials. The atomic-resolution imaging capabilities of AFM can be applied to polycrystalline samples by means of pressing powders with a grain size as small as 50 micrometers. These results illustrate that the AFM is a promising tool for material science and the study of biomineralization.

Structure Analyses of Highly Symmetric Superstructures Formed by Rodlike Mesogen

NASA Astrophysics Data System (ADS)

Saito, Kazuya; Kutsumizu, Shoichi

Process of structure determination of liquid-crystalline superstructures formed in a mesogenic series, bis(n-alkoxybenzoyl)hydrazine[BABH(n) ; n, the number of carbon atoms in the alkoxy group], is described. The chain-length (n) dependence of relative diffraction intensities from the Ia3d phase resolves the phase problem, leading to the structural description that the molecular centers are on the rods forming two interpenetrating jungle gyms. Theoretical consideration on the stability of superstructures and systematic MEM analysis reveal the coexistence of two aggregation modes (rods forming an extending jungle gym and closed sheets forming spherical shells) for the Im3m phase.

Tunable Core-Shell Single-Walled Carbon Nanotube-Cu2S Networked Nanocomposites as High-Performance Cathodes for Lithium-ion Batteries

DOE PAGES

Meng, Xiangbo; Riha, Shannon C.; Libera, Joseph A.; ...

2015-01-24

In this study, nanoscale copper(I) sulfide (n-Cu2S) was deposited over networks of single-walled carbon nanotubes (SWCNTs) by atomic layer deposition (ALD). This synthetic route provides a high degree of control for tuning the materials properties. The resulting core shell SWCNT-n-Cu2S composite structure ensures an intimate contact between the two components while maintaining a high porosity for efficient transport of charges. Indeed, electrochemical testing demonstrates that these nanocomposites are promising as cathodes in lithium-ion batteries (LIBs), exhibiting excellent stability over 200 discharge-charge cycles with a sustainable, high capacity of 260 mAh g(-1) (92% of the theoretical value in terms of Cu2S)more » and >99% Coulombic efficiency. This work establishes a general strategy for developing high-performance nanoscale electrode materials.« less

Hohlraum-driven mid-Z (SiO2) double-shell implosions on the omega laser facility and their scaling to NIF.

PubMed

Robey, H F; Amendt, P A; Milovich, J L; Park, H-S; Hamza, A V; Bono, M J

2009-10-02

High-convergence, hohlraum-driven implosions of double-shell capsules using mid-Z (SiO2) inner shells have been performed on the OMEGA laser facility [T. R. Boehly, Opt. Commun. 133, 495 (1997)]. These experiments provide an essential extension of the results of previous low-Z (CH) double-shell implosions [P. A. Amendt, Phys. Rev. Lett. 94, 065004 (2005)] to materials of higher density and atomic number. Analytic modeling, supported by highly resolved 2D numerical simulations, is used to account for the yield degradation due to interfacial atomic mixing. This extended experimental database from OMEGA enables a validation of the mix model, and provides a means for quantitatively assessing the prospects for high-Z double-shell implosions on the National Ignition Facility [Paisner, Laser Focus World 30, 75 (1994)].

Quantitative measurement of solvation shells using frequency modulated atomic force microscopy

NASA Astrophysics Data System (ADS)

Uchihashi, T.; Higgins, M.; Nakayama, Y.; Sader, J. E.; Jarvis, S. P.

2005-03-01

The nanoscale specificity of interaction measurements and additional imaging capability of the atomic force microscope make it an ideal technique for measuring solvation shells in a variety of liquids next to a range of materials. Unfortunately, the widespread use of atomic force microscopy for the measurement of solvation shells has been limited by uncertainties over the dimensions, composition and durability of the tip during the measurements, and problems associated with quantitative force calibration of the most sensitive dynamic measurement techniques. We address both these issues by the combined use of carbon nanotube high aspect ratio probes and quantifying the highly sensitive frequency modulation (FM) detection technique using a recently developed analytical method. Due to the excellent reproducibility of the measurement technique, additional information regarding solvation shell size as a function of proximity to the surface has been obtained for two very different liquids. Further, it has been possible to identify differences between chemical and geometrical effects in the chosen systems.

A non-LTE kinetic model for quick analysis of K-shell spectra from Z-pinch plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, J., E-mail: s.duan@163.com; Huang, X. B., E-mail: s.duan@163.com; Cai, H. C., E-mail: s.duan@163.com

Analyzing and modeling K-shell spectra emitted by low-to moderate-atomic number plasma is a useful and effective way to retrieve temperature density of z-pinch plasmas. In this paper, a non-LTE population kinetic model for quick analysis of K-shell spectra was proposed. The model contains ionization stages from bare nucleus to neutral atoms and includes all the important atomic processes. In the present form of the model, the plasma is assumed to be both optically thin and homogeneous with constant temperature and density, and only steady-state situation is considered. According to the detailed calculations for aluminum plasmas, contours of ratios of certainmore » K-shell lines in electron temperature and density plane as well as typical synthesized spectra were presented and discussed. The usefulness of the model is demonstrated by analyzing the spectrum from a neon gas-puff Z-pinch experiment performed on a 1 MA pulsed-power accelerator.« less

Hund’s rule in superatoms with transition metal impurities

PubMed Central

Medel, Victor M.; Reveles, Jose Ulises; Khanna, Shiv N.; Chauhan, Vikas; Sen, Prasenjit; Castleman, A. Welford

2011-01-01

The quantum states in metal clusters bunch into supershells with associated orbitals having shapes resembling those in atoms, giving rise to the concept that selected clusters could mimic the characteristics of atoms and be classified as superatoms. Unlike atoms, the superatom orbitals span over multiple atoms and the filling of orbitals does not usually exhibit Hund’s rule seen in atoms. Here, we demonstrate the possibility of enhancing exchange splitting in superatom shells via a composite cluster of a central transition metal and surrounding nearly free electron metal atoms. The transition metal d states hybridize with superatom D states and result in enhanced splitting between the majority and minority sets where the moment and the splitting can be controlled by the nature of the central atom. We demonstrate these findings through studies on TMMgn clusters where TM is a 3d atom. The clusters exhibit Hund’s filling, opening the pathway to superatoms with magnetic shells. PMID:21646542

Investigation of rubidium(I) ion solvation in liquid ammonia using QMCF-MD simulation and NBO analysis of first solvation shell structure.

PubMed

Hidayat, Yuniawan; Armunanto, Ria; Pranowo, Harno Dwi

2018-04-27

Rb(I) ion solvation in liquid ammonia has been studied by an ab initio quantum mechanical charge field molecular dynamics simulation, and the first solvation shell structure has been analyzed using natural bond orbital. The simulation was performed for an ion and 593 ammonia molecules in a box with a length of 29.03 Å corresponding to a liquid ammonia density of 0.69 g/mL at 235.16 K. The quantum mechanical calculation was carried out for atomic interactions in the radius of 6.4 Å from the ion using LANL2DZ ECP and DZP (Dunning) basis sets for Rb(I) ion and ammonia respectively. The trajectories of the simulation were analyzed in terms of radial, angular, and coordination number distribution functions, vibration, and mean residence time (MRT). Two solvation shell regions are observed for the Rb(I)-N as well as the Rb(I)-H. The maximum distance of Rb(I)-N in the first solvation shell is in accordance with experimental data where a coordination number of 8 is favorable. A non-single coordination number of the first and second shell indicates dynamic solvation structure. It is confirmed by frequent exchange ligand processes observed within a simulation time of 15 ps. The low stabilization energy of donor acceptor ion-ligand interaction with a small Wiberg bond index affirms that the Rb(I)-NH 3 interaction is weak electrostatically.

Point Defects in Quenched and Mechanically-Milled Intermetallic Compounds

NASA Astrophysics Data System (ADS)

Sinha, Praveen

Investigations were made of structural and thermal point defects in the highly-ordered B2 compound PdIn and deformation-induced defects in PdIn and NiAl. The defects were detected through the quadrupole interactions they induce at nearby ^{111}In/Cd probe atoms using the technique of perturbed gamma-gamma angular correlations (PAC). Measurements on annealed PdIn on both sides of stoichiometry show structural defects that are the Pd vacancies on the Pd-poor side of the stoichiometry and Pd antisite atoms on the Pd-rich side. Signals were attributed to various defect configurations near the In/Cd probes. In addition to the first-shell Pd vacancy and second-shell Pd antisite atom configurations previously observed by Hahn and Muller, we observed two Pd-divacancy configurations in the first shell, a fourth-shell Pd vacancy, a second-shell In vacancy and the combination of a first -shell Pd vacancy and fourth-shell Pd vacancy. Vacancies on both the Pd and In sublattices were detected after quenching. Fractions of probe atoms having each type of neighboring vacancy defect were observed to increase monotonically with quenching temperature over the range 825-1500 K. For compositions very close to 50.15 at.% Pd, nearly equal site fractions were observed for Pd and In vacancies, indicating that the Schottky vacancy-pair defect is the thermal defect at high temperature. The formation enthalpy of the Schottky defect was determined from measurements of the Pd-vacancy site fraction to be 1.30(18) eV from analysis of quenching data in the range 825-1200 K, using the law of mass action and assuming a random distribution. Above 1200 K, the Pd-vacancy concentration was observed to be saturated at a value of 1.3(2) atomic percent. For more Pd-rich compositions, evidence was also obtained for a defect reaction in which a Pd antisite atom and Pd vacancy react to form an In vacancy, thereby increasing the In vacancy concentration and decreasing the Pd vacancy concentration. Analysis of defect concentrations allowed the conclusion that the In vacancy signal was due to second-shell and not third-shell defects. PAC spectroscopy was applied to study deformation -induced defects in PdIn and NiAl after mechanically milling in a SPEX 8000 vibrator mill for periods of up to four hours. For PdIn, the Pd vacancy concentration increased rapidly for short milling times and was observed to saturate at a value of 3.5(5) at.% after 10 minutes of milling when milling was carried out using a WC vial to avoid sample contamination. Such a large vacancy concentration accounts for 4.41(63) kJ mol-1 excess-stored energy in milled PdIn and implies a high density of "broken bonds" which may lead to mechanical instability of the lattice. Milling also produced In antisite atoms on the Pd sublattice. The antisite-atom concentration increased linearly with milling time, reaching a value of 4.0(7) at.% after 2 hours of milling. The Ni vacancy concentration in NiAl was also observed to increase with milling and to saturate after two hours of milling. Here, the "local" Ni vacancy concentration in the first-neighbor shell of the probe, deduced from the vacancy site fraction, was in excess of values that should occur if defects were located at random. This is attributed to binding between the Ni vacancy and the In/Cd probe, which is known from other work to be 0.22 eV.

BH3-Amine and B(CH3)3-Amine Adducts as Additives for Liquid/Gel Hypergols and Solid Hybrid Rocket Motor Fuels: Property and Performance Predictions

DTIC Science & Technology

2013-12-01

and Thermolysis of Lithium, Magnesium Calcium and Strontium Tetraborate Complex Compounds With Triethylenediamine-Crystal Structure of 2BH3•C6H12N2...of Closed-Shell Atoms and Hydrides of the 1st-Row Elements. Journal of Chemical Physics 1988, 89 , 2193-2218. Petersson, G. A.; Tensfeldt, T

Extreme ultraviolet and soft x-ray spectral lines in Rb XXIX

NASA Astrophysics Data System (ADS)

Indu, Khatri; Arun, Goyal; Sunny, Aggarwal; A, K. Singh; Man, Mohan

2016-03-01

An extensive theoretical set of atomic data for Rb XXIX in a wide range with L-shell electron excitations to the M-shell has been reported. We have computed energy levels for the lowest 113 fine structure levels of Rb XXIX. The fully relativistic multiconfigurational Dirac-Fock method (MCDF) within the framework of Dirac-Coulomb Hamiltonian taking quantum electrodynamics (QED) and Breit corrections into account has been adopted for calculations. Radiative data are reported for electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions from the ground level, although calculations have been performed for a much larger number of levels. To assess the accuracy of results, we performed analogous calculations using flexible atomic code (FAC). Comparisons are made with existing available results and a good agreement has been achieved. Most of the wavelengths calculated lie in the soft x-ray (SXR) region. Lifetimes for all 113 levels have also been provided for the first time. Additionally, we have provided the spectra for allowed transitions from n = 2 to n = 3 within the x-ray region and also compared our SXR photon wavelengths with experimentally recognized wavelengths. We hope that our results will be beneficial in fusion plasma research and astrophysical applications.

Confinement induced binding of noble gas atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khatua, Munmun; Pan, Sudip; Chattaraj, Pratim K., E-mail: pkc@chem.iitkgp.ernet.in

2014-04-28

The stability of Ng{sub n}@B{sub 12}N{sub 12} and Ng{sub n}@B{sub 16}N{sub 16} systems is assessed through a density functional study and ab initio simulation. Although they are found to be thermodynamically unstable with respect to the dissociation of individual Ng atoms and parent cages, ab initio simulation reveals that except Ne{sub 2}@B{sub 12}N{sub 12} they are kinetically stable to retain their structures intact throughout the simulation time (500 fs) at 298 K. The Ne{sub 2}@B{sub 12}N{sub 12} cage dissociates and the Ne atoms get separated as the simulation proceeds at this temperature but at a lower temperature (77 K) itmore » is also found to be kinetically stable. He-He unit undergoes translation, rotation and vibration inside the cavity of B{sub 12}N{sub 12} and B{sub 16}N{sub 16} cages. Electron density analysis shows that the He-He interaction in He{sub 2}@B{sub 16}N{sub 16} is of closed-shell type whereas for the same in He{sub 2}@B{sub 12}N{sub 12} there may have some degree of covalent character. In few cases, especially for the heavier Ng atoms, the Ng-N/B bonds are also found to have some degree of covalent character. But the Wiberg bond indices show zero bond order in He-He bond and very low bond order in cases of Ng-N/B bonds. The energy decomposition analysis further shows that the ΔE{sub orb} term contributes 40.9% and 37.3% towards the total attraction in the He{sub 2} dimers having the same distances as in He{sub 2}@B{sub 12}N{sub 12} and He{sub 2}@B{sub 16}N{sub 16}, respectively. Therefore, confinement causes some type of orbital interaction between two He atoms, which akins to some degree of covalent character.« less

Tailoring characteristic thermal stability of Ni-Au binary nanocrystals via structure and composition engineering: theoretical insights into structural evolution and atomic inter-diffusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Bangquan; Wang, Hailong; Xing, Guozhong

We report on the structural evolution and atomic inter-diffusion characteristics of the bimetallic Ni-Au nanocrystals (NCs) by molecular dynamics simulations studies. Our results reveal that the thermal stability dynamics of Ni-Au NCs strongly depends on the atomic configurations. By engineering the structural construction with Ni:Au = 1:1 atomic composition, compared with core-shell Au@Ni and alloy NCs, the melting point of core-shell Ni@Au NCs is significantly enhanced up to 1215 K. Unexpectedly, with atomic ratio of Au:Ni= 1:9, the melting process initiates from the atoms in the shell of Ni@Au and alloy NCs, while starts from the core of Au@Ni NCs.more » The corresponding features and evolution process of structural motifs, mixing and segregation are illustrated via a series of dynamic simulations videos. Moreover, our results revealed that the face centered cubic phase Au{sub 0.75}Ni{sub 0.25} favorably stabilizes in NCs form but does not exist in the bulk counterpart, which elucidates the anomalies of previously reported experimental results on such bimetallic NCs.« less

How the hydrophobic factor drives protein folding

PubMed Central

Baldwin, Robert L.; Rose, George D.

2016-01-01

How hydrophobicity (HY) drives protein folding is studied. The 1971 Nozaki–Tanford method of measuring HY is modified to use gases as solutes, not crystals, and this makes the method easy to use. Alkanes are found to be much more hydrophobic than rare gases, and the two different kinds of HY are termed intrinsic (rare gases) and extrinsic (alkanes). The HY values of rare gases are proportional to solvent-accessible surface area (ASA), whereas the HY values of alkanes depend on special hydration shells. Earlier work showed that hydration shells produce the hydration energetics of alkanes. Evidence is given here that the transfer energetics of alkanes to cyclohexane [Wolfenden R, Lewis CA, Jr, Yuan Y, Carter CW, Jr (2015) Proc Natl Acad Sci USA 112(24):7484–7488] measure the release of these shells. Alkane shells are stabilized importantly by van der Waals interactions between alkane carbon and water oxygen atoms. Thus, rare gases cannot form this type of shell. The very short (approximately picoseconds) lifetime of the van der Waals interaction probably explains why NMR efforts to detect alkane hydration shells have failed. The close similarity between the sizes of the opposing energetics for forming or releasing alkane shells confirms the presence of these shells on alkanes and supports Kauzmann's 1959 mechanism of protein folding. A space-filling model is given for the hydration shells on linear alkanes. The model reproduces the n values of Jorgensen et al. [Jorgensen WL, Gao J, Ravimohan C (1985) J Phys Chem 89:3470–3473] for the number of waters in alkane hydration shells. PMID:27791131

Analytical transition-matrix treatment of electric multipole polarizabilities of hydrogen-like atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kharchenko, V.F., E-mail: vkharchenko@bitp.kiev.ua

2015-04-15

The direct transition-matrix approach to the description of the electric polarization of the quantum bound system of particles is used to determine the electric multipole polarizabilities of the hydrogen-like atoms. It is shown that in the case of the bound system formed by the Coulomb interaction the corresponding inhomogeneous integral equation determining an off-shell scattering function, which consistently describes virtual multiple scattering, can be solved exactly analytically for all electric multipole polarizabilities. Our method allows to reproduce the known Dalgarno–Lewis formula for electric multipole polarizabilities of the hydrogen atom in the ground state and can also be applied to determinemore » the polarizability of the atom in excited bound states. - Highlights: • A new description for electric polarization of hydrogen-like atoms. • Expression for multipole polarizabilities in terms of off-shell scattering functions. • Derivation of integral equation determining the off-shell scattering function. • Rigorous analytic solving the integral equations both for ground and excited states. • Study of contributions of virtual multiple scattering to electric polarizabilities.« less

Equatorial and Apical Solvent Shells of the UO₂²⁺ Ion.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nichols, Pat; Bylaska, Eric J.; Schenter, Gregory K.

2008-03-08

First principles molecular dynamics simulations of the hydration shells surrounding UO₂²⁺ ions are reported for temperatures near 300 K. Most of the simulations were done with 64 solvating water molecules (22 ps). Simulations with 122 water molecules (9 ps) were also carried out. The hydration structure predicted from the simulations was found to agree very well known results from X-ray data. The average U=O bond length was found to be 1.77Å . The first hydration shell contained five trigonally coordinated water molecules that were equatorially oriented about the O-U-O axis with the hydrogen atoms oriented away from the uranium atom.more » The five waters in the first shell were located at an average distance of 2.44Å (2.46Å - 122 water simulation). The second hydration shell was composed of distinct equatorial and apical regions resulting in a peak in the U-O radial distribution function at 4.59Å. The equatorial second shell contained 10 water molecules hydrogen-bonded to the five first shell molecules. Above and below the UO₂²⁺ ion, the water molecules were found to be significantly less structured. In these apical regions, water molecules were found to sporadically hydrogen bond to the oxygen atoms of the UO₂²⁺; oriented in such way as to have their protons pointed towards the cation. While the number of apical waters varied greatly, an average of 5-6 waters was found in this region. Many water transfers into and out of the equatorial and apical second solvation shells were observed to occur on a picosecond (ps) time scale via dissociative mechanisms. Beyond these shells, the bonding pattern substantially returned to the tetrahedral structure of bulk water.« less

High Resolution X-Ray Spectroscopy and Imaging of Supernova Remnant N132D

NASA Technical Reports Server (NTRS)

Behar, Ehud; Rasmussen, Andrew; Griffiths, R. Gareth; Dennerl, Konrad; Audard, Marc; Aschenbach, Bernd

2000-01-01

The observation of the supernova remnant N132D by the scientific instruments on board the XMM-Newton satellite is presented. The X-rays from N132D are dispersed into a detailed line-rich spectrum using the Reflection Grating Spectrometers. Spectral lines of C, N, O, Ne, Mg, Si, S, and Fe are identified. Images of the remnant, in narrow wavelength bands, produced by the European Photon Imaging Cameras reveal a complex spatial structure of the ionic distribution. While K - shell Fe seems to originate near the centre, all of the other ions are observed along the shell. An emission excess of O(6+) over O(7+) is detected on the northeastern edge of the remnant. This can be a sign of hot ionising conditions, or it can reflect a relatively cool region. Spectral fitting of the CCD spectrum suggests high temperatures in this region, but a detailed analysis of the atomic processes involved in producing the O(6+) spectral lines leads to the conclusion that the intensities of these lines alone cannot provide a conclusive distinction between the two scenarios.

Atomic Layer-by-Layer Deposition of Platinum on Palladium Octahedra for Enhanced Catalysts toward the Oxygen Reduction Reaction

DOE PAGES

Park, Jinho; Zhang, Lei; Choi, Sang-Il; ...

2015-02-08

We systematically evaluated two different approaches to the syntheses of Pd@PtnL (n = 2–5) core–shell octahedra. We initially prepared the core–shell octahedra using a polyol-based route by titrating a Pt(IV) precursor into the growth solution containing Pd octahedral seeds at 200 °C through the use of a syringe pump. The number of Pt atomic layers could be precisely controlled from two to five by increasing the volume of the precursor solution while fixing the amount of seeds. We then demonstrated the synthesis of Pd@Pt nL octahedra using a water-based route at 95 °C through the one-shot injection of a Pt(II)more » precursor. Due to the large difference in reaction temperature, the Pd@Pt nL octahedra obtained via the water-based route showed sharper corners than their counterparts obtained through the polyol-based route. When compared to a commercial Pt/C catalyst based upon 3.2 nm Pt particles, the Pd@Pt nL octahedra prepared using both methods showed similar remarkable enhancement in terms of activity (both specific and mass) and durability toward the oxygen reduction reaction. These calculations based upon periodic, self-consistent density functional theory suggested that the enhancement in specific activity for the Pd@Pt nL octahedra could be attributed to the destabilization of OH on their Pt nL*/Pd(111) surface relative to the {111} and {100} facets exposed on the surface of Pt/C. Finally. the destabilization of OH facilitates its hydrogenation, which was found to be the rate-limiting step of the oxygen reduction reaction on all these surfaces.« less

Structural and electronic properties of Aun-xPtx (n = 2-14; x ⩽ n) clusters: The density functional theory investigation

NASA Astrophysics Data System (ADS)

Yuan, H. K.; Kuang, A. L.; Tian, C. L.; Chen, H.

2014-03-01

The structural evolutions and electronic properties of bimetallic Aun-xPtx (n = 2-14; x ⩽ n) clusters are investigated by using the density functional theory (DFT) with the generalized gradient approximation (GGA). The monatomic doping Aun-1Pt clusters are emphasized and compared with the corresponding pristine Aun clusters. The results reveal that the planar configurations are favored for both Aun-1Pt and Aun clusters with size up to n = 13, and the former often employ the substitution patterns based on the structures of the latter. The most stable clusters are Au6 and Au6Pt, which adopt regular planar triangle (D3h) and hexagon-ring (D6h) structures and can be regarded as the preferential building units in designing large clusters. For Pt-rich bimetallic clusters, their structures can be obtained from the substitution of Pt atoms by Au atoms from the Ptn structures, where Pt atoms assemble together and occupy the center yet Au atoms prefer the apex positions showing a segregation effect. With respect to pristine Au clusters, AunPt clusters exhibit somewhat weaker and less pronounced odd-even oscillations in the highest occupied and lowest unoccupied molecular-orbital gaps (HOMO-LUMO gap), electron affinity (EA), and ionization potential (IP) due to the partially released electron pairing effect. The analyses of electronic structure indicate that Pt atoms in AuPt clusters would delocalize their one 6s and one 5d electrons to contribute the electronic shell closure. The sp-d hybridizations as well as the d-d interactions between the host Au and dopant Pt atoms result in the enhanced stabilities of AuPt clusters.

Progress toward development of a platform for studying burn in the presence of mix on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Murphy, T. J.; Kyrala, G. A.; Bradley, P. A.; Krasheninnikova, N. S.; Cobble, J. A.; Tregillis, I. L.; Obrey, K. A. D.; Hsu, S. C.; Shah, R. C.; Hakel, P.; Kline, J. L.; Grim, G. P.; Baumgaertel, J. A.; Schmitt, M. J.; Kanzleiter, R. J.; Batha, S. H.

2013-10-01

Mix of shell material into ICF capsule fuel can degrade implosion performance through a number of mechanisms. One way is by dilution of the fusion fuel, which affects performance by an amount that is dependent on the degree of mix at the atomic level. Experiments are underway to quantify the mix of shell material into fuel using directly driven capsules on the National Ignition Facility. Deuterated plastic shells will be utilized with tritium fill so that the production of DT neutrons is indicative of mix at the atomic level. Neutron imaging will locate the burn region and spectroscopic imaging of the doped layers will reveal the location, temperature, and density of the shell material. Correlation of the two will be used to determine the degree of atomic mixing of the shell into the fuel and will be compared to models. This talk will review progress toward the development of an experimental platform to measure burn in the presence of measured mix. This work is supported by US DOE/NNSA, performed at LANL, operated by LANS LLC under contract DE-AC52-06NA25396.

Application of Powder Diffraction Methods to the Analysis of the Atomic Structure of Nanocrystals: The Concept of the Apparent Lattice Parameter (ALP)

NASA Technical Reports Server (NTRS)

Palosz, B.; Grzanka, E.; Gierlotka, S.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H.-P.; Palosz, W.; Curreri, Peter A. (Technical Monitor)

2002-01-01

The applicability of standard methods of elaboration of powder diffraction data for determination of the structure of nano-size crystallites is analysed. Based on our theoretical calculations of powder diffraction data we show, that the assumption of the infinite crystal lattice for nanocrystals smaller than 20 nm in size is not justified. Application of conventional tools developed for elaboration of powder diffraction data, like the Rietveld method, may lead to erroneous interpretation of the experimental results. An alternate evaluation of diffraction data of nanoparticles, based on the so-called 'apparent lattice parameter' (alp) is introduced. We assume a model of nanocrystal having a grain core with well-defined crystal structure, surrounded by a surface shell with the atomic structure similar to that of the core but being under a strain (compressive or tensile). The two structural components, the core and the shell, form essentially a composite crystal with interfering, inseparable diffraction properties. Because the structure of such a nanocrystal is not uniform, it defies the basic definitions of an unambiguous crystallographic phase. Consequently, a set of lattice parameters used for characterization of simple crystal phases is insufficient for a proper description of the complex structure of nanocrystals. We developed a method of evaluation of powder diffraction data of nanocrystals, which refers to a core-shell model and is based on the 'apparent lattice parameter' methodology. For a given diffraction pattem, the alp values are calculated for every individual Bragg reflection. For nanocrystals the alp values depend on the diffraction vector Q. By modeling different a0tomic structures of nanocrystals and calculating theoretically corresponding diffraction patterns using the Debye functions we showed, that alp-Q plots show characteristic shapes which can be used for evaluation of the atomic structure of the core-shell system. We show, that using a simple model of a nanocrystal with spherical shape and centro-symmetric strain at the surface shell we obtain theoretical alp-Q values which match very well the alp-Q plots determined experimentally for Sic, GaN, and diamond nanopowders. The theoretical models are defined by the lattice parameter of the grain core, thickness of the surface shell, and the magnitude and distribution of the strain field in the surface shell. According to our calculations, the part of the diffraction pattern measured at relatively low diffraction vectors Q (below 10/angstrom) provides information on the surface strain, whle determination of the lattice parameters in the grain core requires measurements at large Q-values (above 15 - 20/angstrom).

Atomic layer deposition of TiO2 shells on MoO3 nanobelts allowing enhanced lithium storage performance.

PubMed

Xie, Sanmu; Cao, Daxian; She, Yiyi; Wang, Hongkang; Shi, Jian-Wen; Leung, Micheal K H; Niu, Chunming

2018-06-26

Atomic layer deposition (ALD) of TiO2 shells on MoO3 nanobelts (denote as TiO2@MoO3) is realized using a home-made ALD system, which allows a controllable hydrolysis reaction of TiCl4-H2O on an atomic scale. When used as an anode material for lithium ion batteries, the TiO2@MoO3 electrode demonstrates much enhanced lithium storage performance including higher specific capacity, better cycling stability and rate capability.

Mass spectrometric identification of Au68(SR)34 molecular gold nanoclusters with 34-electron shell closing.

PubMed

Dass, Amala

2009-08-26

The molecular formula Au(68)(SCH(2)CH(2)Ph)(34) has been assigned to the 14 kDa nanocluster using MALDI-TOF mass spectrometry. The 34-electron shell closing in a macroscopically obtained thiolated gold nanocluster is demonstrated. The Au(68) nanocluster is predicted to have a 49 atom Marks decahedral core with 19 inner core atoms and 30 outer atoms chelating with the staple motifs. The nanoclusters' predicted formulation is [Au](19+30) [Au(SR)(2)](11) [Au(2)(SR)(3)](4).

On the atomic-number similarity of the binding energies of electrons in filled shells of elements of the periodic table

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karpov, V. Ya.; Shpatakovskaya, G. V., E-mail: shpagalya@yandex.ru

An expression for the binding energies of electrons in the ground state of an atom is derived on the basis of the Bohr–Sommerfeld quantization rule within the Thomas–Fermi model. The validity of this relation for all elements from neon to uranium is tested within a more perfect quantum-mechanical model with and without the inclusion of relativistic effects, as well as with experimental binding energies. As a result, the ordering of electronic levels in filled atomic shells is established, manifested in an approximate atomic-number similarity. It is proposed to use this scaling property to analytically estimate the binding energies of electronsmore » in an arbitrary atom.« less

Predicted trends of core-shell preferences for 132 late transition-metal binary-alloy nanoparticles.

PubMed

Wang, Lin-Lin; Johnson, Duane D

2009-10-07

Transition-metal alloyed nanoparticles with core-shell features (shell enrichment by one of the metals) are becoming ubiquitous, from (electro-)catalysis to biomedical applications, due to their size control, performance, biocompatibility, and cost. We investigate 132 binary-alloyed nanoparticle systems (groups 8 to 11 in the Periodic Table) using density functional theory (DFT) and systematically explore their segregation energies to determine core-shell preferences. We find that core-shell preferences are generally described by two independent factors: (1) cohesive energy (related to vapor pressure) and (2) atomic size (quantified by the Wigner-Seitz radius), and the interplay between them. These independent factors are shown to provide general trends for the surface segregation preference for atoms in nanoparticles, as well as semi-infinite surfaces, and give a simple correlation (a "design map") for the alloying and catalytic behavior. Finally, we provide a universal description of core-shell preference via tight-binding theory (band-energy differences) that (i) quantitatively reproduces the DFT segregation energies and (ii) confirms the electronic origins and correlations for core-shell behavior.

Nanomechanics of biocompatible hollow thin-shell polymer microspheres.

PubMed

Glynos, Emmanouil; Koutsos, Vasileios; McDicken, W Norman; Moran, Carmel M; Pye, Stephen D; Ross, James A; Sboros, Vassilis

2009-07-07

The nanomechanical properties of biocompatible thin-shell hollow polymer microspheres with approximately constant ratio of shell thickness to microsphere diameter were measured by nanocompression tests in aqueous conditions. These microspheres encapsulate an inert gas and are used as ultrasound contrast agents by releasing free microbubbles in the presence of an ultrasound field as a result of free gas leakage from the shell. The tests were performed using an atomic force microscope (AFM) employing the force-distance curve technique. An optical microscope, on which the AFM was mounted, was used to guide the positioning of tipless cantilevers on top of individual microspheres. We performed a systematic study using several cantilevers with spring constants varying from 0.08 to 2.3 N/m on a population of microspheres with diameters from about 2 to 6 microm. The use of several cantilevers with various spring constants allowed a systematic study of the mechanical properties of the microsphere thin shell at different regimes of force and deformation. Using thin-shell mechanics theory for small deformations, the Young's modulus of the thin wall material was estimated and was shown to exhibit a strong size effect: it increased as the shell became thinner. The Young's modulus of thicker microsphere shells converged to the expected value for the macroscopic bulk material. For high applied forces, the force-deformation profiles showed a reversible and/or irreversible nonlinear behavior including "steps" and "jumps" which were attributed to mechanical instabilities such as buckling events.

Dock 'n roll: folding of a silk-inspired polypeptide into an amyloid-like beta solenoid.

PubMed

Zhao, Binwu; Cohen Stuart, Martien A; Hall, Carol K

2016-04-20

Polypeptides containing the motif ((GA)mGX)n occur in silk and have a strong tendency to self-assemble. For example, polypeptides containing (GAGAGAGX)n, where X = G or H have been observed to form filaments; similar sequences but with X = Q have been used in the design of coat proteins (capsids) for artificial viruses. The structure of the (GAGAGAGX)m filaments has been proposed to be a stack of peptides in a β roll structure with the hydrophobic side chains pointing outwards (hydrophobic shell). Another possible configuration, a β roll or β solenoid structure which has its hydrophobic side chains buried inside (hydrophobic core) was, however, overlooked. We perform ground state analysis as well as atomic-level molecular dynamics simulations, both on single molecules and on two-molecule stacks of the silk-inspired sequence (GAGAGAGQ)10, to decide whether the hydrophobic core or the hydrophobic shell configuration is the most stable one. We find that a stack of two hydrophobic core molecules is energetically more favorable than a stack of two hydrophobic shell molecules. A shell molecule initially placed in a perfect β roll structure tends to rotate its strands, breaking in-plane hydrogen bonds and forming out-of-plane hydrogen bonds, while a core molecule stays in the β roll structure. The hydrophobic shell structure has type II' β turns whereas the core configuration has type II β turns; only the latter secondary structure agrees well with solid-state NMR experiments on a similar sequence (GA)15. We also observe that the core stack has a higher number of intra-molecular hydrogen bonds and a higher number of hydrogen bonds between stack and water than the shell stack. Hence, we conclude that the hydrophobic core configuration is the most likely structure. In the stacked state, each peptide has more intra-molecular hydrogen bonds than a single folded molecule, which suggests that stacking provides the extra stability needed for molecules to reach the folded state.

Growth Behavior and Electronic Structure of Noble Metal-Doped Germanium Clusters.

PubMed

Mahtout, Sofiane; Siouani, Chaouki; Rabilloud, Franck

2018-01-18

Structures, energetics, and electronic properties of noble metal-doped germanium (MGe n with M = Cu, Ag, Au; n = 1-19) clusters are systematically investigated by using the density functional theory (DFT) approach. The endohedral structures in which the metal atom is encapsulated inside of a germanium cage appear at n = 10 when the dopant is Cu and n = 12 for M = Ag and Au. While Cu doping enhances the stability of the corresponding germanium frame, the binding energies of AgGe n and AuGe n are always lower than those of pure germanium clusters. Our results highlight the great stability of the CuGe 10 cluster in a D 4d structure and, to a lesser extent, that of AgGe 15 and AuGe 15 , which exhibits a hollow cage-like geometry. The sphere-type geometries obtained for n = 10-15 present a peculiar electronic structure in which the valence electrons of the noble metal and Ge atoms are delocalized and exhibit a shell structure associated with the quasi-spherical geometry. It is found that the coinage metal is able to give both s- and d-type electrons to be reorganized together with the valence electrons of Ge atoms through a pooling of electrons. The cluster size dependence of the stability, the frontier orbital energy gap, the vertical ionization potentials, and electron affinities are given.

Properties of small Ar sub N-1 K/+/ ionic clusters

NASA Technical Reports Server (NTRS)

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.

Enabling liquid solvent structure analysis using hard x-ray absorption spectroscopy with a transferrable microfluidic reactor.

PubMed

Zheng, Jian; Zhang, Wei; Wang, Feng; Yu, Xiao-Ying

2018-05-10

In this paper, a vacuum compatible microfluidic device, system for analysis at the liquid vacuum interface, is integrated to hard x-ray absorption spectroscopy to obtain the local structure of K 3 [Fe(CN) 6 ] in aqueous solutions with three concentrations of 0.5 M, 0.05 M, and 0.005 M. The solutions were sealed in a microchannel 500 µm wide and 300 µm deep in a portable microfluidic device. The Fe K-edge x-ray absorption spectra indicate a presence of Fe(III) in the complex in water, with an octahedral geometry coordinated with 6 C atoms in the first shell with a distance of ~1.92 Å and 6 N atoms in the second shell with a distance of ~3.10 Å. Varying the concentration has no observable influence on the structure of K 3 [Fe(CN) 6 ]. Our results demonstrate the feasibility of using microfluidic based liquid cells in large synchrotron facilities. Using portable microfludic reactors provides a viable approach to enable multifaceted measurements of liquids in the future.

Enabling liquid solvent structure analysis using hard x-ray absorption spectroscopy with a transferrable microfluidic reactor

NASA Astrophysics Data System (ADS)

Zheng, Jian; Zhang, Wei; Wang, Feng; Yu, Xiao-Ying

2018-05-01

In this paper, a vacuum compatible microfluidic device, system for analysis at the liquid vacuum interface, is integrated to hard x-ray absorption spectroscopy to obtain the local structure of K3[Fe(CN)6] in aqueous solutions with three concentrations of 0.5 M, 0.05 M, and 0.005 M. The solutions were sealed in a microchannel 500 µm wide and 300 µm deep in a portable microfluidic device. The Fe K-edge x-ray absorption spectra indicate a presence of Fe(III) in the complex in water, with an octahedral geometry coordinated with 6 C atoms in the first shell with a distance of ~1.92 Å and 6 N atoms in the second shell with a distance of ~3.10 Å. Varying the concentration has no observable influence on the structure of K3[Fe(CN)6]. Our results demonstrate the feasibility of using microfluidic based liquid cells in large synchrotron facilities. Using portable microfludic reactors provides a viable approach to enable multifaceted measurements of liquids in the future.

Enabling liquid solvent structure analysis using hard x-ray absorption spectroscopy with a transferrable microfluidic reactor

DOE PAGES

Zheng, Jian; Zhang, Wei; Wang, Feng; ...

2018-04-11

In this study, a vacuum compatible microfluidic device, system for analysis at the liquid vacuum interface, is integrated to hard x-ray absorption spectroscopy to obtain the local structure of K 3[Fe(CN) 6] in aqueous solutions with three concentrations of 0.5 M, 0.05 M, and 0.005 M. The solutions were sealed in a microchannel 500 µm wide and 300 µm deep in a portable microfluidic device. The Fe K-edge x-ray absorption spectra indicate a presence of Fe(III) in the complex in water, with an octahedral geometry coordinated with 6 C atoms in the first shell with a distance of ~1.92 Åmore » and 6 N atoms in the second shell with a distance of ~3.10 Å. Varying the concentration has no observable influence on the structure of K 3[Fe(CN) 6]. Our results demonstrate the feasibility of using microfluidic based liquid cells in large synchrotron facilities. Using portable microfludic reactors provides a viable approach to enable multifaceted measurements of liquids in the future.« less

Enabling liquid solvent structure analysis using hard x-ray absorption spectroscopy with a transferrable microfluidic reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Jian; Zhang, Wei; Wang, Feng

In this study, a vacuum compatible microfluidic device, system for analysis at the liquid vacuum interface, is integrated to hard x-ray absorption spectroscopy to obtain the local structure of K 3[Fe(CN) 6] in aqueous solutions with three concentrations of 0.5 M, 0.05 M, and 0.005 M. The solutions were sealed in a microchannel 500 µm wide and 300 µm deep in a portable microfluidic device. The Fe K-edge x-ray absorption spectra indicate a presence of Fe(III) in the complex in water, with an octahedral geometry coordinated with 6 C atoms in the first shell with a distance of ~1.92 Åmore » and 6 N atoms in the second shell with a distance of ~3.10 Å. Varying the concentration has no observable influence on the structure of K 3[Fe(CN) 6]. Our results demonstrate the feasibility of using microfluidic based liquid cells in large synchrotron facilities. Using portable microfludic reactors provides a viable approach to enable multifaceted measurements of liquids in the future.« less

Enabling liquid solvent structure analysis using hard x-ray absorption spectroscopy with a transferrable microfluidic reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Jian; Zhang, Wei; Wang, Feng

In this paper, a vacuum compatible microfluidic device, System for Analysis at the Liquid Vacuum Interface (SALVI), is integrated to hard x-ray absorption spectroscopy (XAS) to obtain the local structure of K3[Fe(CN)6] in aqueous solutions with three concentrations of 0.5 M, 0.05 M, and 0.005 M. The solutions were sealed in a microchannel of 500 μm wide and 300 µm deep in a portable microfluidic device. The Fe K-edge x-ray absorption spectra show that the complex in water is Fe(III). The complex is present with octahedral geometry coordinated with 6 C atoms in the first shell with a distance ofmore » ~1.92 Å and 6 N atoms in the second shell with a distance of ~3.10 Å. Varying the concentration has no observable influence on the structure of K3[Fe(CN)6]. Our results demonstrate the feasibility of using microfluidic based liquid cells in large synchrotron facilities and it is a viable approach to enable multifaceted measurements of liquids in the future.« less

Study of clusters using negative ion photodetachment spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Yuexing

1995-12-01

The weak van der Waals interaction between an open-shell halogen atom and a closed-shell atom or molecule has been investigated using zero electron kinetic energy (ZEKE) spectroscopy. This technique is also applied to study the low-lying electronic states in GaAs and GaAs -. In addition, the spectroscopy and electron detachment dynamics of several small carbon cluster anions are studied using resonant multiphoton detachment spectroscopy.

Organic superalkalis with closed-shell structure and aromaticity

NASA Astrophysics Data System (ADS)

Srivastava, Ambrish Kumar

2018-06-01

Benzene (C6H6) and polycyclic hydrocarbons such as naphthalene (C10H8), anthracene (C14H10) and coronene (C24H12) are well known aromatic organic compounds. We study the substitution of Li replacing all H-atoms in these hydrocarbons using density functional method. The vertical ionisation energy of such lithiated species, i.e. C6Li6, C10Li8, C14Li10 and C24Li12 ranges 4.24-4.50 eV, which is lower than the ionisation energy (IE) of Li atom. Thus, these species may behave as superalkalis due to their lower IE than alkali metal. However, these lithiated species possess planar and closed-shell structure, unlike typical superalkalis. Furthermore, all Li-substituted species are aromatic although their degree of aromaticity is reduced as compared to corresponding hydrocarbon analogues. We have further explored the structure of C6Li6 as star-like, unlike its inorganic analogue B3N3Li6, which appears as fan-like structure. We have also demonstrated that the interaction of C6Li6 with a superhalogen (such as BF4) is similar to that of a typical superalkali (such as OLi3). This may further suggest that the proposed lithiated species may form a new class of closed-shell organic superalkalis with aromaticity.

Experimental artefacts occurring during atom probe tomography analysis of oxide nanoparticles in metallic matrix: Quantification and correction

NASA Astrophysics Data System (ADS)

Hatzoglou, C.; Radiguet, B.; Pareige, P.

2017-08-01

Oxide Dispersion Strengthened (ODS) steels are promising candidates for future nuclear reactors, partly due to the fine dispersion of the nanoparticles they contain. Until now, there was no consensus as to the nature of the nanoparticles because their analysis pushed the techniques to their limits and in consequence, introduced some artefacts. In this study, the artefacts that occur during atom probe tomography analysis are quantified. The artefacts quantification reveals that the particles morphology, chemical composition and atomic density are biased. A model is suggested to correct these artefacts in order to obtain a fine and accurate characterization of the nanoparticles. This model is based on volume fraction calculation and an analytical expression of the atomic density. Then, the studied ODS steel reveals nanoparticles, pure in Y, Ti and O, with a core/shell structure. The shell is rich in Cr. The Cr content of the shell is dependent on that of the matrix by a factor of 1.5. This study also shows that 15% of the atoms that were initially in the particles are not detected during the analysis. This only affects O atoms. The particle stoichiometry evolves from YTiO2 for the smallest observed (<2 nm) to Y2TiO5 for the biggest (>8 nm).

Report on the 18th International Conference on X-ray and Inner-Shell Processes (X99).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gemmell, D. S.; Physics

2000-01-01

The 18th conference of the series served as a forum for discussing fundamental issues in the field of x-ray and inner-shell processes and their application in various disciplines of science and technology. Special emphasis was given to the opportunities offered by modern synchrotron x-ray sources. The program included plenary talks, progress reports and poster presentations relating to new developments in the field of x-ray and inner-shell processes. The range of topics included: X-ray interactions with atoms, molecules, clusters, surfaces and solids; Decay processes for inner-shell vacancies; X-ray absorption and emission spectroscopy - Photoionization processes; Phenomena associated with highly charged ionsmore » and collisions with energetic particles; Electron-spin and -momentum spectroscopy; X-ray scattering and spectroscopy in the study of magnetic systems; Applications in materials science, biology, geosciences, and other disciplines; Elastic and inelastic x-ray scattering processes in atoms and molecules; Threshold phenomena (post-collision interaction, resonant Raman processes, etc.); Nuclear absorption and scattering of x-rays; 'Fourth-generation' x-ray sources; Processes exploiting the polarization and coherence properties of x-ray beams; Developments in experimental techniques (x-ray optics, temporal techniques, detectors); Microscopy, spectromicroscopy, and various imaging techniques; Non-linear processes and x-ray lasers; Ionization and excitation induced by charged particles and by x-rays; and Exotic atoms (including 'hollow' atoms and atoms that contain 'exotic' particles).« less

Measurement of K to L shell vacancy transfer probabilities for the elements 46≤ Z≤55 by photoionization

NASA Astrophysics Data System (ADS)

Şimşek, Ö.; Karagöz, D.; Ertugrul, M.

2003-10-01

The K to L shell vacancy transfer probabilities for nine elements in the atomic region 46≤ Z≤55 were determined by measuring the L X-ray yields from targets excited by 5.96 and 59.5 keV photons and using the theoretical K and L shell photoionization cross-sections. The L X-rays from different targets were detected with an Ultra-LEGe detector with very thin polymer window. Present experimental results were compared with the semi empirical values tabulated by Rao et al. [Atomic vacancy distributions product by inner shellionization, Phys. Rev. A 5 (1972) 997-1002] and theoretically calculated values using radiative and radiationless transitions. The radiative transitions of these elements were observed from the relativistic Hartree-Slater model, which was proposed by Scofield [Relativistic Hartree-Slater values for K and L shell X-ray emission rates, At. Data Nucl. Data Tables 14 (1974) 121-137]. The radiationless transitions were observed from the Dirac-Hartree-Slater model, which was proposed by Chen et al. [Relativistic radiationless transition probabilities for atomic K- and L-shells, At. Data Nucl. Data Tables 24 (1979) 13-37]. To the best of our knowledge, these vacancy transfer probabilities are reported for the first time.

Electrochemical oxygen reduction behavior of selectively deposited platinum atoms on gold nanoparticles.

PubMed

Sarkar, A; Kerr, J B; Cairns, E J

2013-07-22

Carbon-supported Pt@Au "core-shell" nanoparticles with varying surface concentration of platinum atoms have been synthesized using a novel redox-mediated synthesis approach. The synthesis technique allows for a selective deposition of platinum atoms on the surface of prefabricated gold nanoparticles. Energy dispersive spectroscopic analyses in a scanning electron microscope reveal that the platinum to gold atomic ratios are close to the nominal values, validating the synthesis scheme. X-ray diffraction data indicate an un-alloyed structure. The platinum to gold surface atomic ratio determined from cyclic voltammetry and copper under-potential deposition experiments reveal good agreement with the calculated values at low platinum concentration. However, there is an increase in non-uniformity in the deposition process upon increasing the platinum concentration. Koutecky-Levich analysis of the samples indicates a transition of the total number of electrons transferred (n) in the electrochemical oxygen reduction reaction from two to four electrons upon increasing the surface concentration of platinum atoms. Furthermore, the data indicate that isolated platinum atoms can reduce molecular oxygen but via a two-electron route. Moreover, successful four-electron reduction of molecular oxygen requires clusters of platinum atoms. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

PubMed

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

2014-07-28

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

Investigation of non-corrin cobalt(II)-containing sites in protein structures of the Protein Data Bank.

PubMed

Abriata, Luciano Andres

2013-04-01

Protein X-ray structures with non-corrin cobalt(II)-containing sites, either natural or substituting another native ion, were downloaded from the Protein Data Bank and explored to (i) describe which amino acids are involved in their first ligand shells and (ii) analyze cobalt(II)-donor bond lengths in comparison with previously reported target distances, CSD data and EXAFS data. The set of amino acids involved in Co(II) binding is similar to that observed for catalytic Zn(II) sites, i.e. with a large fraction of carboxylate O atoms from aspartate and glutamate and aromatic N atoms from histidine. The computed Co(II)-donor bond lengths were found to depend strongly on structure resolution, an artifact previously detected for other metal-donor distances. Small corrections are suggested for the target bond lengths to the aromatic N atoms of histidines and the O atoms of water and hydroxide. The available target distance for cysteine (Scys) is confirmed; those for backbone O and other donors remain uncertain and should be handled with caution in refinement and modeling protocols. Finally, a relationship between both Co(II)-O bond lengths in bidentate carboxylates is quantified.

Shannon entropies and Fisher information of K-shell electrons of neutral atoms

NASA Astrophysics Data System (ADS)

Sekh, Golam Ali; Saha, Aparna; Talukdar, Benoy

2018-02-01

We represent the two K-shell electrons of neutral atoms by Hylleraas-type wave function which fulfils the exact behavior at the electron-electron and electron-nucleus coalescence points and, derive a simple method to construct expressions for single-particle position- and momentum-space charge densities, ρ (r) and γ (p) respectively. We make use of the results for ρ (r) and γ (p) to critically examine the effect of correlation on bare (uncorrelated) values of Shannon information entropies (S) and of Fisher information (F) for the K-shell electrons of atoms from helium to neon. Due to inter-electronic repulsion the values of the uncorrelated Shannon position-space entropies are augmented while those of the momentum-space entropies are reduced. The corresponding Fisher information are found to exhibit opposite behavior in respect of this. Attempts are made to provide some plausible explanation for the observed response of S and F to electronic correlation.

The role of ion exchange in the passivation of In(Zn)P nanocrystals with ZnS

PubMed Central

Cho, Deok-Yong; Xi, Lifei; Boothroyd, Chris; Kardynal, Beata; Lam, Yeng Ming

2016-01-01

We have investigated the chemical state of In(Zn)P/ZnS core/shell nanocrystals (NCs) for color conversion applications using hard X-ray absorption spectroscopy (XAS) and photoluminescence excitation (PLE). Analyses of the edge energies as well as the X-ray absorption fine structure (XAFS) reveal that the Zn2+ ions from ZnS remain in the shell while the S2− ions penetrate into the core at an early stage of the ZnS deposition. It is further demonstrated that for short growth times, the ZnS shell coverage on the core was incomplete, whereas the coverage improved gradually as the shell deposition time increased. Together with evidence from PLE spectra, where there is a strong indication of the presence of P vacancies, this suggests that the core-shell interface in the In(Zn)P/ZnS NCs are subject to substantial atomic exchanges and detailed models for the shell structure beyond simple layer coverage are needed. This substantial atomic exchange is very likely to be the reason for the improved photoluminescence behavior of the core-shell particles compare to In(Zn)P-only NCs as S can passivate the NCs surfaces. PMID:26972936

Use of 41Ar production to measure ablator areal density in NIF beryllium implosions

DOE PAGES

Wilson, Douglas Carl; Cassata, W. S.; Sepke, S. M.; ...

2017-02-06

For the first time, 41Ar produced by the (n,Υ) reaction from 40Ar in the beryllium shell of a DT filled Inertial Confinement Fusion capsule has been measured. Ar is co-deposited with beryllium in the sputter deposition of the capsule shell. Combined with a measurement of the neutron yield, the radioactive 41Ar then quantifies the areal density of beryllium during the DT neutron production. Here, the measured 1.15 ± 0.17 × 10 +8 atoms of 41Ar are 2.5 times that from the best post-shot calculation, suggesting that the Ar and Be areal densities are correspondingly higher than those calculated. Possible explanationsmore » are that (1) the beryllium shell is compressed more than calculated, (2) beryllium has mixed into the cold DT ice, or more likely (3) less beryllium is ablated than calculated. Since only one DT filled beryllium capsule has been fielded at NIF, these results can be confirmed and expanded in the future.« less

Penning-trap mass measurements of the neutron-rich K and Ca isotopes: Resurgence of the N=28 shell strength

NASA Astrophysics Data System (ADS)

Lapierre, A.; Brodeur, M.; Brunner, T.; Ettenauer, S.; Finlay, P.; Gallant, A. T.; Simon, V. V.; Delheij, P.; Lunney, D.; Ringle, R.; Savajols, H.; Dilling, J.

2012-02-01

We present Penning-trap mass measurements of neutron-rich 44,47-50K and 49,50Ca isotopes carried out at the TITAN facility at TRIUMF-ISAC. The 44K mass measurement was performed with a charge-bred 4+ ion utilizing the TITAN electron beam ion trap and agrees with the literature. The mass excesses obtained for 47K and 49,50Ca are more precise and agree with the values published in the 2003 Atomic Mass Evaluation (AME’03). The 48,49,50K mass excesses are more precise than the AME’03 values by more than 1 order of magnitude. For 48,49K, we find deviations of 7σ and 10σ, respectively. The new 49K mass excess lowers significantly the two-neutron separation energy at the neutron number N=30 compared with the separation energy calculated from the AME’03 mass-excess values and thus increases the N=28 neutron-shell gap energy at Z=19 by approximately 1 MeV.

Magnetic Study of the Novel Polynuclear Compound [Cu(II)(6-Mercaptopurinolate 2-)] n

NASA Astrophysics Data System (ADS)

Acevedo-Chávez, Rodolfo; Costas, María. Eugenia; Escudero, Roberto

1997-08-01

Chemical reactions between Cu(II) and 6-mercaptopurine, both in aqueous and in methanolic media, yield the novel amorphous polynuclear compound [Cu(II)(6-mercaptopurinolate)2-]n, which is also obtained from diverse Cu(II)-heterocyclic ligand competitive reactions. The kinetic and thermodynamic stabilities associated with the formation of this compound are inferred as remarkable. The spectroscopic data let us suggest the involvement of the exocyclic S(6) donor site and the N atoms in the imidazolic moiety of the deprotonated heterocyclic ligand in the coordination to Cu(II) atoms, forming a distorted bidimensional metallic network. The magnetic studies show the existence of very weak antiferromagnetic coupling in the solid sample. This system represents the first example of a 1 : 1 metal : 6-mercaptopurinolate2-system with ad-type open shell metallic center. The magnetic study carried out also represents the first example of magnetic characterization for this type of polynuclear Cu(II) systems with the dianionic 6-mercaptopurine ligand.

The P-factor and atomic mass systematics: Application to medium mass nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brenner, D.S.; Haustein, P.E.; Casten, R.F.

1988-01-01

The P formalism was applied to atomic mass systematics for medium and heavy nuclei. The P-factor linearizes the structure-dependent part of the nuclear mass in those regions which are free from subshell effects indicating that the attractive quadrupole p-n force plays an important role in determining the binding of valence nucleons. Where marked non-linearities occur, the P-factor provides a means for recognizing subshell closures and/or other structural features not embodied in the simple assumptions of abrupt shell or subshell changes. These are thought to be regions where the monopole part of the p-n interaction is highly orbit dependent and altersmore » the underlying single-particle structure as a function of A, N or Z. Finally, in those regions where the systematics are smooth and subshells are absent, the P-factor provides a means for predicting masses of some nuclei far-from-stability by interpolation rather than by extrapolation. 5 figs.« less

Hydroxyl migration disorders the surface structure of hydroxyapatite nanoparticles

NASA Astrophysics Data System (ADS)

Cheng, Xiajie; Wu, Hong; Zhang, Li; Ma, Xingtao; Zhang, Xingdong; Yang, Mingli

2017-09-01

The surface structure of nano-hydroxyapatite (HAP) was investigated using a combined simulated annealing and molecular dynamics method. The stationary structures of nano-HAP with 4-7 nm in diameter and annealed under different temperatures were analyzed in terms of pair distribution function, structural factor, mean square displacement and atomic coordination number. The particles possess different structures from bulk crystal. A clear radial change in their atomic arrangements was noted. From core to surface the structures change from ordered to disordered. A three-shell model was proposed to describe the structure evolution of nano-HAP. Atoms in the core zone keep their arrangements as in crystal, while atoms in the surface shell are in short-range order and long-range disorder, adopting a typically amorphous structure. Atoms in the middle shell have small displacements and/or deflections but basically retain their original locations as in crystal. The disordered shell is about 1 nm in thickness, in agreement with experimental observations. The disordering mainly stems from hydroxyl migration during which hydroxyls move to the surface and bond with the exposed Ca ions, and their left vacancies bring about a rearrangement of nearby atoms. The disordering is to some extent different for particles unannealed under different temperatures, resulting from fewer number of migrated hydroxyls at lower temperatures. Particles with different sizes have similar surface structures, and their surface energy decreases with increasing size. Moreover, the surface energy is reduced by hydroxyl migration because the exposed Ca ions on the surface are ionically bonded with the migrated hydroxyls. Our calculations proposed a new structure model for nano-HAP, which indicates a surface structure with activities different from those without surface reorganization. This is particularly interesting because most bioactivities of biomaterials are dominated by their surface activity.

Lanthanum(III) and Lutetium(III) in Nitrate-Based Ionic Liquids: A Theoretical Study of Their Coordination Shell.

PubMed

Bodo, Enrico

2015-09-03

By using ab initio molecular dynamics, we investigate the solvent shell structure of La(3+) and Lu(3+) ions immersed in two ionic liquids, ethylammonium nitrate (EAN) and its hydroxy derivative (2-ethanolammonium nitrate, HOEAN). We provide the first study of the coordination properties of these heavy metal ions in such a highly charged nonacqueous environment. We find, as expected, that the coordination in the liquid is mainly due to nitrate anions and that, due to the bidentate nature of the ligand, the complexation shell of the central ion has a nontrivial geometry and a coordination number in terms of nitrate molecules that apparently violates the decrease of ionic radii along the lanthanides series, since the smaller Lu(3+) ion seems to coordinate six nitrate molecules and the La(3+) ion only five. A closer inspection of the structural features obtained from our calculations shows, instead, that the first shell of oxygen atoms is more compact for Lu(3+) than for La(3+) and that the former coordinates 8 oxygen atoms while the latter 10 in accord with the typical lanthanide's trend along the series and that their first solvation shells have a slight irregular and complex geometrical pattern. When moving to the HOEAN solutions, we have found that the solvation of the central ion is possibly also due to the cation itself through the oxygen atom on the side chain. Also, in this liquid, the coordination numbers in terms of oxygen atoms in both solvents is 10 for La(3+) and 8 for Lu(3+).

The study of dielectric properties of the endohedral fullerenes

NASA Astrophysics Data System (ADS)

Bhusal, Shusil

Dielectric response of the metal nitride fullerenes is studied using the density functional theory at the all-electron level using generalized gradient approximation. The dielectric response is studied by computing the static dipole polarizabilities using the finite field method, i.e. by numerically differentiating the dipole moments with respect to electric field. The endohedral fullerenes studied in this work are Sc3N C68(6140), Sc3N C68(6146), Sc3N C70(7854), Sc3N C70(7960), Sc3N C76(17490), Sc3N C78(22010), Sc3N C80(31923), Sc3N C80(31924), Sc3N C82(39663), Sc3N C90(43), Sc3N C90(44), Sc3N C92(85), Sc3N C94(121), Sc3N C96(186), Sc3N C98(166). Using the Voronoi and Hirschfield approaches as implemented in our NRLMOL code, we determine the atomic contributions to the total polarizability. The site-specific contributions to the polarizability of endohedral fullerenes allowed us to determine the polarizability of two subsystems: the fullerene shell and the encapsulated Sc3N unit. Our results showed that the contributions to the total polarizability from the encapsulated Sc3N units are vanishingly small. Thus, the total polarizability of the endohedral fullerene is almost entirely due to the outer fullerene shell. These fullerenes are excellent molecular models of a Faraday cage.

Fine structural features of nanoscale zero-valent iron characterized by spherical aberration corrected scanning transmission electron microscopy (Cs-STEM).

PubMed

Liu, Airong; Zhang, Wei-xian

2014-09-21

An angstrom-resolution physical model of nanoscale zero-valent iron (nZVI) is generated with a combination of spherical aberration corrected scanning transmission electron microscopy (Cs-STEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) on the Fe L-edge. Bright-field (BF), high-angle annular dark-field (HAADF) and secondary electron (SE) imaging of nZVI acquired by a Hitachi HD-2700 STEM show near atomic resolution images and detailed morphological and structural information of nZVI. The STEM-EDS technique confirms that the fresh nZVI comprises of a metallic iron core encapsulated with a thin layer of iron oxides or oxyhydroxides. SAED patterns of the Fe core suggest the polycrystalline structure in the metallic core and amorphous nature of the oxide layer. Furthermore, Fe L-edge of EELS shows varied structural features from the innermost Fe core to the outer oxide shell. A qualitative analysis of the Fe L(2,3) edge fine structures reveals that the shell of nZVI consists of a mixed Fe(II)/Fe(III) phase close to the Fe (0) interface and a predominantly Fe(III) at the outer surface of nZVI.

Alpha decay properties of the semi-magic nucleus 219Np

NASA Astrophysics Data System (ADS)

Yang, H. B.; Ma, L.; Zhang, Z. Y.; Yang, C. L.; Gan, Z. G.; Zhang, M. M.; Huang, M. H.; Yu, L.; Jiang, J.; Tian, Y. L.; Wang, Y. S.; Wang, J. G.; Liu, Z.; Liu, M. L.; Duan, L. M.; Zhou, S. G.; Ren, Z. Z.; Zhou, X. H.; Xu, H. S.; Xiao, G. Q.

2018-02-01

The semi-magic nucleus 219Np was produced in the fusion reaction 187Re(36Ar, 4n)219Np at the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). A fast electronics system based on waveform digitizers was used in the data acquisition and the sampled pulses were processed by digital algorithms. The reaction products were identified using spatial and time correlations between the implants and subsequent α decays. According to the observed α-decay chain, an energy of Eα = 9039 (40) keV and a half-life of T1/2 =0.15-0.07 + 0.72 ms were determined for 219Np. The deduced proton binding energy of 219Np fits well into the systematics, which gives another evidence of that there is no sub-shell closure at Z = 92. The influence of the N = 126 shell closure on the stability of Np isotopes is discussed within the framework of α-decay reduced widths.

Core-shell carbon nanosphere-TiO2 composite and hollow TiO2 nanospheres prepared by atomic layer deposition

NASA Astrophysics Data System (ADS)

Bakos, L. P.; Justh, N.; Hernádi, K.; Kiss, G.; Réti, B.; Erdélyi, Z.; Parditka, B.; Szilágyi, I. M.

2016-10-01

Core-shell carbon-TiO2 composite and hollow TiO2 nanospheres were prepared using carbon nanospheres as hard-templates, coating them with TiO2 using atomic layer deposition, and subsequent burning out of the carbon cores. The bare carbon, the composite carbon-TiO2 and the hollow TiO2 nanospheres were characterized with TG/DTA-MS, FTIR, XRD and SEM-EDX.

Shell- and subshell-resolved projectile excitation of hydrogenlike Au{sup 78+} ions in relativistic ion-atom collisions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gumberidze, A.; Frankfurt Institute for Advanced Studies FIAS, D-60438 Frankfurt am Main; Fritzsche, S.

2010-11-15

The projectile excitation of high-Z ions has been investigated in relativistic ion-atoms collisions by observing the subsequent x-ray emission. The x-ray spectra from the projectile excitation have been separated from the x-ray emission following electron capture into the excited states using a novel anticoincidence technique. For the particular case of hydrogenlike Au{sup 78+} ions colliding with Ar atoms, Coulomb excitation from the ground state into the fine-structure-resolved n=2 levels as well as into levels with principal quantum number n{>=}3 has been measured with excellent statistics. The observed spectra agree well with simulated spectra that are based on Dirac's relativistic equationmore » and the proper inclusion of the magnetic interaction into the amplitudes for projectile excitation. It is shown that a coherent inclusion of the magnetic part of the Lienard-Wiechert potential leads to the lowering of the excitation cross section by up to 35%. This effect is more pronounced for excitation into states with high angular momentum and is confirmed by our experimental data.« less

Realistic Gamow shell model for resonance and continuum in atomic nuclei

NASA Astrophysics Data System (ADS)

Xu, F. R.; Sun, Z. H.; Wu, Q.; Hu, B. S.; Dai, S. J.

2018-02-01

The Gamow shell model can describe resonance and continuum for atomic nuclei. The model is established in the complex-moment (complex-k) plane of the Berggren coordinates in which bound, resonant and continuum states are treated on equal footing self-consistently. In the present work, the realistic nuclear force, CD Bonn, has been used. We have developed the full \\hat{Q}-box folded-diagram method to derive the realistic effective interaction in the model space which is nondegenerate and contains resonance and continuum channels. The CD-Bonn potential is renormalized using the V low-k method. With choosing 16O as the inert core, we have applied the Gamow shell model to oxygen isotopes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hall, J.; Richard, P.; Gray, T.J.

The systematics of single and double K-shell-vacancy production in titanium has been investigated in the limit of zero target thickness (approx.1 ..mu..g/cm/sup 2/) for incident C, N, O, F, Mg, Al, Si, S, and Cl ions over a maximum energy range of 0.5 to 6.5 MeV/amu. This corresponds to collision systems with 0.27< or =Z/sub 1//Z/sub 2/< or =0.77 and 0.24< or =v/sub 1//vK< or =0.85, where v/sub 1/ is the projectile nuclear velocity and vK is the mean velocity of an electron in the target K shell. The present work is divided into four major sections. (1) Single K-shell-vacancymore » production has been investigated by measuring K..cap alpha.. and K..beta.. p satellite x-ray-production cross sections for projectiles incident with no K-shell vacancies. For incident ions with Z/sub 1/> or =9, the contribution due to electron-transfer processes from the target K shell to outer shells of the projectile has also been noted. (2) Single K-shell--to--K-shell electron-transfer cross sections have been obtained indirectly by the measuring of the enhancement in the Ti K x-ray production cross section for bare incident projectiles over ions incident with no initial K-shell vacancies. (3) Double K-vacancy production has been investigated by measuring the K..cap alpha.. hypersatellite intensity in ratio to the total K..cap alpha.. intensity. (4) Double K-shell--to--K-shell electron-transfer cross sections have been obtained indirectly with the use of a procedure similar to that used for single K to K transfer. The measured cross sections have been compared to theoretical models for direct Coulomb ionization and inner-shell electron transfer and have been used to investigate the relative importance of these mechanisms for K-vacancy production in heavy-ion--atom collisions.« less

Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory

ERIC Educational Resources Information Center

Talbot, Christopher; Neo, Choo Tong

2013-01-01

This "Science Note" looks at the way that the shapes of simple molecules can be explained in terms of the number of electron pairs in the valence shell of the central atom. This theory is formally known as valence shell electron pair repulsion (VSEPR) theory. The article explains the preferred shape of chlorine trifluoride (ClF3),…

SnO2@TiO2 double-shell nanotubes for a lithium ion battery anode with excellent high rate cyclability.

PubMed

Jeun, Jeong-Hoon; Park, Kyu-Young; Kim, Dai-Hong; Kim, Won-Sik; Kim, Hong-Chan; Lee, Byoung-Sun; Kim, Honggu; Yu, Woong-Ryeol; Kang, Kisuk; Hong, Seong-Hyeon

2013-09-21

SnO2@TiO2 double-shell nanotubes have been facilely synthesized by atomic layer deposition (ALD) using electrospun PAN nanofibers as templates. The double-shell nanotubes exhibited excellent high rate cyclability for lithium ion batteries. The retention of hollow structures during cycling was demonstrated.

Maria Goeppert Mayer, the Nuclear Shell Structure, and Magic Numbers

Science.gov Websites

dropdown arrow Site Map A-Z Index Menu Synopsis Maria Goeppert-Mayer, the Nuclear Shell Model, and Magic explanation of how neutrons and protons within atomic nuclei are structured. Called the "nuclear shell American husband, chemical physicist Joseph Mayer. At Argonne, Goeppert-Mayer learned most of her nuclear

Demonstration of Confined Electron Gas and Steep-Slope Behavior in Delta-Doped GaAs-AlGaAs Core-Shell Nanowire Transistors.

PubMed

Morkötter, S; Jeon, N; Rudolph, D; Loitsch, B; Spirkoska, D; Hoffmann, E; Döblinger, M; Matich, S; Finley, J J; Lauhon, L J; Abstreiter, G; Koblmüller, G

2015-05-13

Strong surface and impurity scattering in III-V semiconductor-based nanowires (NW) degrade the performance of electronic devices, requiring refined concepts for controlling charge carrier conductivity. Here, we demonstrate remote Si delta (δ)-doping of radial GaAs-AlGaAs core-shell NWs that unambiguously exhibit a strongly confined electron gas with enhanced low-temperature field-effect mobilities up to 5 × 10(3) cm(2) V(-1) s(-1). The spatial separation between the high-mobility free electron gas at the NW core-shell interface and the Si dopants in the shell is directly verified by atom probe tomographic (APT) analysis, band-profile calculations, and transport characterization in advanced field-effect transistor (FET) geometries, demonstrating powerful control over the free electron gas density and conductivity. Multigated NW-FETs allow us to spatially resolve channel width- and crystal phase-dependent variations in electron gas density and mobility along single NW-FETs. Notably, dc output and transfer characteristics of these n-type depletion mode NW-FETs reveal excellent drain current saturation and record low subthreshold slopes of 70 mV/dec at on/off ratios >10(4)-10(5) at room temperature.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lehmann, C. S.; Picón, A.; Bostedt, C.

The availability at x-ray free electron lasers of generating two intense, femtosecond x-ray pulses with controlled time delay opens the possibility of performing time-resolved experiments for x-ray induced phenomena. We have applied this capability to molecular dynamics. In diatomic molecules composed of low-Z elements, K-shell ionization creates a core-hole state in which the main decay is an Auger process involving two electrons in the valence shell. After Auger decay, the nuclear wavepackets of the transient two-valence-hole states continue evolving on the femtosecond timescale, leading either to separated atomic ions or long-lived quasi-bound states. By using an x-ray pump and anmore » x-ray probe pulse tuned above the K-shell ionization threshold of the nitrogen molecule, we are able to observe ion dissociation in progress by measuring the time-dependent kinetic energy releases of different breakup channels. We simulated the measurements on N2 with a molecular dynamics model that accounts for K-shell ionization, Auger decay, and time evolution of the nuclear wavepackets. In addition to explaining the time-dependent feature in the measured kinetic energy release distributions from the dissociative states, the simulation also reveals the contributions of quasi-bound states.« less

Site-specific recoil-induced effects on inner-shell photoionization of linear triatomic molecules: N 1 s photoelectron spectra of N2 O

NASA Astrophysics Data System (ADS)

Krivosenko, Yu. S.; Pavlychev, A. A.

2016-11-01

We investigate hard X-ray ionization of linear triatomic molecules accenting recoil-induced effects on the dynamics of molecular frame. This dynamics is studied within the two-springs and harmonic approximations. The mode-channel relationship connecting the excitations of vibrational, rotational and translational degrees of freedom with the Σ → Σ and Σ → Π photoionization channels is applied to compute the N 1s-1 photoelectron spectra of molecular N2 O for various photon energies. The distinct ionized-site- and molecular-orientation-specific changes in the vibration structure of the 1 s photoelectron lines of terminal and central nitrogen atoms are revealed and discussed.

Coherent Magnetic Response at Optical Frequencies Using Atomic Transitions

NASA Astrophysics Data System (ADS)

Brewer, Nicholas R.; Buckholtz, Zachary N.; Simmons, Zachary J.; Mueller, Eli A.; Yavuz, Deniz D.

2017-01-01

In optics, the interaction of atoms with the magnetic field of light is almost always ignored since its strength is many orders of magnitude weaker compared to the interaction with the electric field. In this article, by using a magnetic-dipole transition within the 4 f shell of europium ions, we show a strong interaction between a green laser and an ensemble of atomic ions. The electrons move coherently between the ground and excited ionic levels (Rabi flopping) by interacting with the magnetic field of the laser. By measuring the Rabi flopping frequency as the laser intensity is varied, we report the first direct measurement of a magnetic-dipole matrix element in the optical region of the spectrum. Using density-matrix simulations of the ensemble, we infer the generation of coherent magnetization with magnitude 5.5 ×10-3 A /m , which is capable of generating left-handed electromagnetic waves of intensity 1 nW /cm2 . These results open up the prospect of constructing left-handed materials using sharp transitions of atoms.

Some preliminary calculations of whole atom Compton scattering of unpolarized photons

NASA Astrophysics Data System (ADS)

Bergstrom, P. M.; Surić, T.; Pisk, K.; Pratt, R. H.

1992-07-01

This paper represents a preliminary attempt to develop a practical prescription for calculating whole atom cross sections for the Compton scattering of unpolarized photons from the bound electrons of an atom for the entire spectrum of scattered photon energies. We initially study the scattering of 2.94 keV photons from carbon. We make use of our new second order S-matrix computer code in this case to verify that, when our recently developed criterion for the validity of the relativistic impulse approximation (which concerns the average momentum contributing to the photon spectrum ( pav)) is satisfied, the spectrum is adequately described by the impulse approximation. This criterion is generally satisfied in the peak intensity region for scattering by the outer shells, which dominate at these scattered photon energies. For soft scattered photons, however, the spectrum, dominated by K shell contributions, is given by terms corresponding to the contribution of the " p· A" term in the nonrelativistic interaction Hamiltonian, not included in the impulse approximation. Here, the spectrum is adequately reproduced by the K shell contribution. We then consider scattering of 17.4 keV photons from aluminum and 279.1 keV photons from lead. In these cases we use the S-matrix for the K shell and the impulse approximation for the outer shells, and find good agreement with experiment.

Simulation study of 3-5 keV x-ray conversion efficiency from Ar K-shell vs. Ag L-shell targets on the National Ignition Facility laser

NASA Astrophysics Data System (ADS)

Kemp, G. E.; Colvin, J. D.; Fournier, K. B.; May, M. J.; Barrios, M. A.; Patel, M. V.; Scott, H. A.; Marinak, M. M.

2015-05-01

Tailored, high-flux, multi-keV x-ray sources are desirable for studying x-ray interactions with matter for various civilian, space and military applications. For this study, we focus on designing an efficient laser-driven non-local thermodynamic equilibrium 3-5 keV x-ray source from photon-energy-matched Ar K-shell and Ag L-shell targets at sub-critical densities (˜nc/10) to ensure supersonic, volumetric laser heating with minimal losses to kinetic energy, thermal x rays and laser-plasma instabilities. Using Hydra, a multi-dimensional, arbitrary Lagrangian-Eulerian, radiation-hydrodynamics code, we performed a parameter study by varying initial target density and laser parameters for each material using conditions readily achievable on the National Ignition Facility (NIF) laser. We employ a model, benchmarked against Kr data collected on the NIF, that uses flux-limited Lee-More thermal conductivity and multi-group implicit Monte-Carlo photonics with non-local thermodynamic equilibrium, detailed super-configuration accounting opacities from Cretin, an atomic-kinetics code. While the highest power laser configurations produced the largest x-ray yields, we report that the peak simulated laser to 3-5 keV x-ray conversion efficiencies of 17.7% and 36.4% for Ar and Ag, respectively, occurred at lower powers between ˜100-150 TW. For identical initial target densities and laser illumination, the Ag L-shell is observed to have ≳10× higher emissivity per ion per deposited laser energy than the Ar K-shell. Although such low-density Ag targets have not yet been demonstrated, simulations of targets fabricated using atomic layer deposition of Ag on silica aerogels (˜20% by atomic fraction) suggest similar performance to atomically pure metal foams and that either fabrication technique may be worth pursuing for an efficient 3-5 keV x-ray source on NIF.

Analyzing non-LTE Kr plasmas produced in high energy density experiments: from the Z machine to the National Ignition Facility

NASA Astrophysics Data System (ADS)

Dasgupta, Arati

2015-11-01

Designing high fluence photon sources above 10 keV are a challenge for High Energy Density plasmas. This has motivated radiation source development investigations of Kr with K-shell energies around 13 keV. Recent pulsed power driven gas-puff experiments on the refurbished Z machine at Sandia have produced intense X-rays in the multi-keV photon energy range. K-shell radiative yields and efficiencies are very high for Ar, but rapidly decrease for higher atomic number (ZA) elements such as Kr. It has been suggested that an optimum exists corresponding to a trade-off between the increase of photon energy for higher ZA elements and the corresponding fall off in radiative power. However the conversion efficiency on NIF, where the drive, energy deposition process, and target dynamics are different, does not fall off with higher ZA as rapidly as on Z. We have developed detailed atomic structure and collisional data for the full K-, L- and partial M-shell of Kr using the Flexible Atomic Code (FAC). Our non-LTE atomic model includes all collisional and recombination processes, including state-specific dielectronic recombination (DR), that significantly affect ionization balance and spectra of Kr plasmas at the temperatures and densities of concern. The model couples ionization physics, radiation production and transport, and magnetohydrodynamics. In this talk, I will give a detailed description of the model and discuss 1D Kr simulations employing a multifrequency radiation transport scheme. Synthetic K- and L-shell spectra will be compared with available experimental data. This talk will analyze experimental data indicative of the differences between Z and NIF experimental data and discuss how they affect the K-shell radiative output of Kr plasma. Work supported by DOE/NNSA.

Composition Formulas of Inorganic Compounds in Terms of Cluster Plus Glue Atom Model.

PubMed

Ma, Yanping; Dong, Dandan; Wu, Aimin; Dong, Chuang

2018-01-16

The present paper attempts to identify the molecule-like structural units in inorganic compounds, by applying the so-called "cluster plus glue atom model". This model, originating from metallic glasses and quasi-crystals, describes any structure in terms of a nearest-neighbor cluster and a few outer-shell glue atoms, expressed in the cluster formula [cluster](glue atoms). Similar to the case for normal molecules where the charge transfer occurs within the molecule to meet the commonly known octet electron rule, the octet state is reached after matching the nearest-neighbor cluster with certain outer-shell glue atoms. These kinds of structural units contain information on local atomic configuration, chemical composition, and electron numbers, just as for normal molecules. It is shown that the formulas of typical inorganic compounds, such as fluorides, oxides, and nitrides, satisfy a similar octet electron rule, with the total number of valence electrons per unit formula being multiples of eight.

Dock ’n Roll: Folding of a Silk-Inspired Polypeptide into an Amyloid-like Beta Solenoid

PubMed Central

Zhao, Binwu; Cohen Stuart, Martien A.; Hall, Carol K.

2016-01-01

Polypeptides containing the motif ((GA)mGX)n occur in silk (we refer to them as ‘silk-like’) and have a strong tendency to self-assemble. For example, polypeptides containing (GAGAGAGX)n, where X = G or H have been observed to form filaments; similar sequences but with X = Q have been used in the design of coat proteins (capsids) for artificial viruses. The structure of the (GAGAGAGX)m filaments has been proposed to be a stack of peptides in a β roll structure with the hydrophobic side chains pointing outwards (hydrophobic shell). Another possible configuration, a β roll or β solenoid structure which has its hydrophobic side chains buried inside (hydrophobic core) was, however, overlooked. We perform ground state analysis as well as atomic-level molecular dynamics simulations, both on single molecules and on two-molecule stacks of the silk-inspired sequence (GAGAGAGQ)10, to decide whether the hydrophobic core or the hydrophobic shell configuration is the most stable one. We find that a stack of two hydrophobic core molecules is energetically more favorable than a stack of two shell molecules. A shell molecule initially placed in a perfect β roll structure tends to rotate its strands, breaking in-plane hydrogen bonds and forming out-of-plane hydrogen bonds, while a core molecule stays in the β roll structure. The hydrophobic shell structure has type II’ β turns whereas the core configuration has type II β turns; only the latter secondary structure agrees well with solid-state NMR experiments on a similar sequence (GA)15. We also observe that the core stack has a higher number of intra-molecular hydrogen bonds and a higher number of hydrogen bonds between stack and water than the shell stack. Hence, we conclude that the hydrophobic core configuration is the most likely structure. In the stacked state, each peptide has more intra-molecular hydrogen bonds than a single folded molecule, which suggests that stacking provides the extra stability needed for molecules to reach the folded state. PMID:26947809

Hydrodynamic stability and Ti-tracer distribution in low-adiabat OMEGA direct-drive implosions

NASA Astrophysics Data System (ADS)

Joshi, Tirtha R.

We discuss the hydrodynamic stability of low-adiabat OMEGA direct-drive implosions based on results obtained from simultaneous emission and absorption spectroscopy of a titanium tracer added to the target. The targets were deuterium filled, warm plastic shells of varying thicknesses and filling gas pressures with a submicron Ti-doped tracer layer initially located on the inner surface of the shell. The spectral features from the titanium tracer are observed during the deceleration and stagnation phases of the implosion, and recorded with a time integrated spectrometer (XRS1), streaked crystal spectrometer (SSCA) and three gated, multi-monochromatic X-ray imager (MMI) instruments fielded along quasi-orthogonal lines-of-sight. The time-integrated, streaked and gated data show simultaneous emission and absorption spectral features associated with titanium K-shell line transitions but only the MMI data provides spatially resolved information. The arrays of gated spectrally resolved images recorded with MMI were processed to obtain spatially resolved spectra characteristic of annular contour regions on the image. A multi-zone spectroscopic analysis of the annular spatially resolved spectra permits the extraction of plasma conditions in the core as well as the spatial distribution of tracer atoms. In turn, the titanium atom distribution provides direct evidence of tracer penetration into the core and thus of the hydrodynamic stability of the shell. The observations, timing and analysis indicate that during fuel burning the titanium atoms have migrated deep into the core and thus shell material mixing is likely to impact the rate of nuclear fusion reactions, i.e. burning rate, and the neutron yield of the implosion. We have found that the Ti atom number density decreases towards the center in early deceleration phase, but later in time the trend is just opposite, i.e., it increases towards the center of the implosion core. This is in part a consequence of the convergent effect of spherical geometry. The spatial profiles of Ti areal densities in the implosion core are extracted from space-resolved spectra and also evaluated using 1D spherical scaling. The trends are similar to the Ti number density spatial profiles. The areal densities extracted from data and 1D spherical scaling are very comparable in the outer spherical zones of the implosion core but significantly deviate in the innermost zone. We have observed that approximately 85% of the Ti atoms migrate into the hot core, while 15% of the atoms are still on the shell-fuel interface and contributing to the absorption. In addition, a method to extract the hot spot size based on the formation of the absorption feature in a sequence of annular spectra will be discussed. Results and trends are discussed as a function of target shell thickness and filling pressure, and laser pulse shape.

Two-photon decay of K-shell vacancies in silver atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mokler, P.H.; University of Giessen, Giessen; Schaeffer, H.W.

2004-09-01

The spectral distributions for the two-photon decay modes of singly K-shell ionized silver atoms are determined by x-ray-x-ray coincidence measurements. Ag K-shell vacancies were induced by nuclear electron capture decay of radioactive cadmium isotopes {sup 109}Cd and two-photon coincidences were taken back to back (180 deg.) and at a 90 deg. opening angle for the emission. Each of the two-photon transitions from the 2s, 3s, and 3d states exhibits unique angular and spectral distributions. The measurements agree nicely with relativistic self-consistent field calculations of Tong et al. Our results also confirm and extend the earlier experimental data of Ilakovac andmore » co-workers with improved accuracy.« less

Two-dimensional membrane as elastic shell with proof on the folds revealed by three-dimensional atomic mapping

NASA Astrophysics Data System (ADS)

Zhao, Jiong; Deng, Qingming; Ly, Thuc Hue; Han, Gang Hee; Sandeep, Gorantla; Rümmeli, Mark H.

2015-11-01

The great application potential for two-dimensional (2D) membranes (MoS2, WSe2, graphene and so on) aroused much effort to understand their fundamental mechanical properties. The out-of-plane bending rigidity is the key factor that controls the membrane morphology under external fields. Herein we provide an easy method to reconstruct the 3D structures of the folded edges of these 2D membranes on the atomic scale, using high-resolution (S)TEM images. After quantitative comparison with continuum mechanics shell model, it is verified that the bending behaviour of the studied 2D materials can be well explained by the linear elastic shell model. And the bending rigidities can thus be derived by fitting with our experimental results. Recall almost only theoretical approaches can access the bending properties of these 2D membranes before, now a new experimental method to measure the bending rigidity of such flexible and atomic thick 2D membranes is proposed.

Ignition and combustion characteristics of metallized propellants

NASA Technical Reports Server (NTRS)

Mueller, D. C.; Turns, Stephen R.

1991-01-01

Over the past six months, experimental investigations were continued and theoretical work on the secondary atomization process was begun. Final shakedown of the sizing/velocity measuring system was completed and the aluminum combustion detection system was modified and tested. Atomizer operation was improved to allow steady state operation over long periods of time for several slurries. To validate the theoretical modeling, work involving carbon slurry atomization and combustion was begun and qualitative observations were made. Simultaneous measurements of aluminum slurry droplet size distributions and detection of burning aluminum particles were performed at several axial locations above the burner. The principle theoretical effort was the application of a rigid shell formation model to aluminum slurries and an investigation of the effects of various parameters on the shell formation process. This shell formation model was extended to include the process leading up to droplet disruption, and previously developed analytical models were applied to yield theoretical aluminum agglomerate ignition and combustion times. The several theoretical times were compared with the experimental results.

Measurement of local structural configurations associated with reversible photostructural changes in arsenic trisulfide films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, C.Y.; Paesler, M.A.; Sayers, D.E.

1987-12-15

Extended x-ray-absorption fine-structure measurements have been made on three reversible and reproducible cycles of thermally annealed and light-soaked amorphous As/sub 2/S/sub 3/ films. Associated with the light-soaked material are (1) a very small increase in the population of wrong bonds in the first shell, (2) an enlarged As: S: As bond angle with an expansion of As: As distance in the second shell, (3) a larger spread in the distribution of As: S: As bond angles, and (4) an absence of any change in the third As: S shell. From these data, we present the first quantitative correlation between observedmore » local atomic structural changes and measured macroscopic properties that are associated with photodarkening. Our data demonstrate that the photoinduced structural changes mainly involve bonding alterations at S atoms as well as a change in the dihedral angle relationship between adjacent AsS/sub 3/ pyramids joined at S atoms.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilchen, M.; Hartmann, G.; Rupprecht, P.

The angle-resolved inner-shell photoionization of R-trifluoromethyloxirane, C 3H 3F 3O, is studied experimentally and theoretically. Thereby, we investigate the photoelectron circular dichroism (PECD) for nearly symmetric O 1s and F 1s electronic orbitals, which are localized on different molecular sites. The respective dichroic β 1 and angular distribution β 2 parameters are measured at the photoelectron kinetic energies from 1 to 16 eV by using variably polarized synchrotron radiation and velocity map imaging spectroscopy. The present experimental results are in good agreement with the outcome of ab initio electronic structure calculations. We report a sizable chiral asymmetry β 1 ofmore » up to about 9% for the K -shell photoionization of oxygen atom. For the individual fluorine atoms, the present calculations predict asymmetries of similar size. However, being averaged over all fluorine atoms, it drops down to about 2%, as also observed in the present experiment. Our study demonstrates a strong emitter and site sensitivity of PECD in the one-photon inner-shell ionization of this chiral molecule.« less

Comparative XAFS studies of some Cobalt complexes of (3-N- phenyl -thiourea-pentanone-2)

NASA Astrophysics Data System (ADS)

soni, Namrata; Parsai, Neetu; Mishra, Ashutosh

2016-10-01

XAFS spectroscopy is a useful method for determining the local structure around a specific atom in disordered systems. XAFS study of some cobalt complexes of (3-N-phenyle- thiourea-pentanon-2) is carried out using the latest XAFS analysis software Demeter with Strawberry Perl. The same study is also carried out theoretically using Mathcad software. It is found that the thiourea has significant influence in the spectra and the results obtained experimentally and theoretically are in agreement. Fourier transform of the experimental and theoretically generated XAFS have been taken to obtain first shell radial distance. The values so obtained are in agreement with each other.

Organic Stable Isotopes in Ancient Oyster Shell Trace Pre-colonial Nitrogen Sources

NASA Astrophysics Data System (ADS)

Darrow, E. S.; Carmichael, R. H.; Andrus, C. F. T.; Jackson, H. E.

2016-02-01

Oysters (Crassostrea virginica) were an important food resource for native peoples of the northern Gulf of Mexico, who harvested oysters and deposited waste shell and other artifacts in middens. Shell δ15N is a proxy for oyster tissue δ15N that reflects nitrogen (N) in food sources of bivalves. We tested the use of shell δ15N as a paleo proxy of ancient N sources, which to our knowledge has not been previously done for archeological bivalve specimens. To determine δ15N of the very low-N and high-carbonate ancient specimens, we tested established and modified acidification techniques developed for modern clams and oysters to decalcify organic shell matrix and extract sufficient N for analyses. Centrifugation following acidification better concentrated N from ancient shells for stable isotope analysis. Careful screening was required to detect effects of diagenesis, incomplete acidification, and sample contamination. Modern oyster shells did not require acidification and bulk shell material was directly analyzed for δ15N using an EA-IRMS coupled to a CO2 trap. δ15N values in ancient oyster shells did not differ from modern oyster shells from the same sites, but %N and % organic carbon (C) were lower in ancient than in modern shells. Organic δ13C in ancient shells had a significant negative relationship with shell age, possibly due to an effect of sea level rise increasing marine suspended particulate matter (SPM) sources to oysters. In modern oysters, δ15N had a significant relationship with soft tissue δ15N, and predicted by SPM δ15N, water column nitrate, and water column dissolved organic nitrogen (DON) concentrations, demonstrating the effectiveness of oyster shell δ15N to identify N sources to bivalves such as oysters. Our study has demonstrated the usefulness of δ15N from midden oyster shells as a proxy for N sources in an estuary that has undergone relatively light impacts from human land-use change through the past 2000 years.

Following electron impact excitations of Rn, Ra, Th, U and Pu single atom L sub-shells ionization cross section calculations by using Lotz’s equation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ayinol, M., E-mail: aydinolm@dicle.edu.tr; Aydeniz, D., E-mail: daydeniz@hotmail.com

L shell ionization cross section and L{sub i} subshells ionization cross sections of Rn, Ra, Th, U, Pu atoms calculated. For each of atoms, ten different electron impact energy values (E{sub o}) are used. Calculations carried out by using Lotz equation in Matlab. First, calculations done for non-relativistic case by using non-relativistic Lotz equation then repeated with relativistic Lotz equation. σ{sub L} total and σ{sub Li}(i = 1,2,3) subshells ionisation cross section values obtained for E{sub o} values in the energy range of E{sub Li}

Direct observation of the transition from calcite to aragonite growth as induced by abalone shell proteins.

PubMed Central

Thompson, J B; Paloczi, G T; Kindt, J H; Michenfelder, M; Smith, B L; Stucky, G; Morse, D E; Hansma, P K

2000-01-01

The mixture of EDTA-soluble proteins found in abalone nacre are known to cause the nucleation and growth of aragonite on calcite seed crystals in supersaturated solutions of calcium carbonate. Past atomic force microscope studies of the interaction of these proteins with calcite crystals did not observe this transition because no information about the crystal polymorph on the surface was obtained. Here we have used the atomic force microscope to directly observe changes in the atomic lattice on a calcite seed crystal after the introduction of abalone shell proteins. The observed changes are consistent with a transition to (001) aragonite growth on a (1014) calcite surface. PMID:11106633

Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness

NASA Astrophysics Data System (ADS)

Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E.; Huang, Yu

2012-01-01

Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications.Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications. Electronic supplementary information (ESI) available: Supplementary TEM, EELS, EDS, Electro-chemical measurement data can be found. See DOI: 10.1039/c1nr11374g

Energy and charge transfer in ionized argon coated water clusters.

PubMed

Kočišek, J; Lengyel, J; Fárník, M; Slavíček, P

2013-12-07

We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H2O)n clusters resulting in the ionization threshold above ≈15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar(+) and water occurs above the threshold; at higher electron energies above ~28 eV, an excitonic transfer process between Ar(+)* and water opens leading to new products Ar(n)H(+) and (H2O)(n)H(+). On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H2O)(n)H2(2+) and (H2O)(n)(2+) ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent.

Density-functional theory study of ionic inhomogeneity in metal clusters using SC-ISJM

NASA Astrophysics Data System (ADS)

Payami, Mahmoud; Mahmoodi, Tahereh

2017-12-01

In this work we have applied the recently formulated self-compressed inhomogeneous stabilized jellium model [51] to describe the equilibrium electronic and geometric properties of atomic-closed-shell simple metal clusters of AlN (N = 13, 19, 43, 55, 79, 87, 135, 141), NaN, and CsN (N = 9, 15, 27, 51, 59, 65, 89, 113). To validate the results, we have also performed first-principles pseudo-potential calculations and used them as our reference. In the model, we have considered two regions consisting of ;surface; and ;inner; ones, the border separating them being sharp. This generalization makes possible to decouple the relaxations of different parts of the system. The results show that the present model correctly predicts the size reductions seen in most of the clusters. It also predicts increase in size of some clusters, as observed from first-principles results. Moreover, the changes in inter-layer distances, being as contractions or expansions, are in good agreement with the atomic simulation results. For a more realistic description of the properties, it is possible to improve the method of choosing the surface thicknesses or generalize the model to include more regions than just two.

Atomic radii for atoms with the 6s shell outermost: The effective atomic radius and the van der Waals radius from {sub 55}Cs to {sub 80}Hg

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tatewaki, Hiroshi, E-mail: htatewak@nsc.nagoya-cu.ac.jp; Institute of Advanced Studies in Artificial Intelligence, Chukyo University, Toyota, Aichi 470-0393; Hatano, Yasuyo

We consider, for atoms from {sub 55}Cs to {sub 80}Hg, the effective atomic radius (r{sub ear}), which is defined as the distance from the nucleus at which the magnitude of the electric field is equal to that in He at one half of the equilibrium bond length of He{sub 2}. The values of r{sub ear} are about 50% larger than the mean radius of the outermost occupied orbital of 6s, . The value of r{sub ear} decreases from {sub 55}Cs to {sub 56}Ba and undergoes increases and decreases with rising nuclear charge from {sub 57}La to {sub 70}Y b. Inmore » fact r{sub ear} is understood as comprising two interlaced sequences; one consists of {sub 57}La, {sub 58}Ce, and {sub 64}Gd, which have electronic configuration (4f{sup n−1})(5d{sup 1})(6s{sup 2}), and the remaining atoms have configuration (4f{sup n})(6s{sup 2}). The sphere defined by r{sub ear} contains 85%–90% of the 6s electrons. From {sub 71}Lu to {sub 80}Hg the radius r{sub ear} also involves two sequences, corresponding to the two configurations 5d{sup n+1}6s{sup 1} and 5d{sup n}6s{sup 2}. The radius r{sub ear} according to the present methodology is considerably larger than r{sub vdW} obtained by other investigators, some of who have found values of r{sub vdW} close to .« less

Snoek Relaxation in Fe-Cr Alloys and Interstitial-Substitutional Interaction

NASA Astrophysics Data System (ADS)

Golovin, I. S.; Blanter, M. S.; Schaller, R.

1997-03-01

The internal friction (IF) spectra of -Fe, Fe-Cr ferritic alloys and Cr have been investigated in a frequency range of 0.01 to 10 Hz. A Snoek-type relaxation was found in all the investigated C doped Fe-Cr alloys, starting from pure Fe and finishing with pure Cr. The temperature location of the Snoek peak (Tmax) in -Fe was found to be 315 K (1 Hz). The activation energy deduced from the T - f shift was 0.81 eV. Tmax in Cr was 433 K with an activation energy of 1.11 eV. The Snoek-type peaks in Fe-Cr alloys are much wider than in pure Fe or pure Cr. The temperature location of the peak versus chromium content curve exhibits a maximum in the vicinity of 35 wt% Cr (Tmax was 573 to 578 K, f 1.2 Hz and the activation energy was about 1.45 eV). It is important that Cr atoms in α-Fe have a more pronounced influence on the temperature location of the peak than Fe atoms have in chromium. A new model based on the atomic interactions is proposed to explain the influence of composition on Snoek peak location. The internal friction has been simulated by a Monte Carlo method, using C-C and C-substitutional atom (s) interaction energies. A model of long-range strain-induced (elastic) interaction supplemented by the chemical interaction in the two nearest coordination shells around an immobile substitutional atom was used for the C-s interaction. The interatomic interaction was supposed to affect IF by changing both the carbon atom arrangement (short-range order) and the energy of C atoms in octahedral interstices, and therefore the activation energy of IF. The peak temperatue calculated coincides well with the experimental ones if the value for the chemical interaction in the first coordination shell (Hchem) for C-Cr in Fe is - 0.15 eV and for C-Fe in Cr +0.15 eV. The difference in the influence of Cr in α-Fe and Fe in Cr is accounted for by a difference in the elastic and chemical interaction both between the carbon atoms and the substitutional atoms. The relaxation process in chromium Fe-based alloys is due to the carbon atom diffusion under stress between octahedral interstices of first and second coordination shells around the Cr atoms, and in Cr-based alloys, between second and third shells around the Fe atoms.

Increasing Stability and Activity of Core-Shell Catalysts by Preferential Segregation of Oxide on Edges and Vertexes: Oxygen Reduction on Ti-Au@Pt/C

DOE PAGES

Hu, J.; Wu, L.; Kuttiyiel, K.; ...

2016-06-30

We describe a new class of core-shell nanoparticle catalysts having edges and vertexes covered by refractory metal oxide that preferentially segregates onto these catalyst sites. The monolayer shell is deposited on the oxidefree core atoms. The oxide on edges and vertexes induces high catalyst’s stability and activity. The catalyst and synthesis are exemplified by fabrication of Au nanoparticles doped by Ti atoms that segregate as oxide onto low–coordination sites of edges and vertexes. Pt monolayer shell deposited on Au sites has the mass and specific activities for the oxygen reduction reaction about 13 and 5 times higher than those ofmore » commercial Pt/C catalysts. The durability tests show no activity loss after 10000 potential cycles from 0.6 to 1.0V. The superior activity and durability of the Ti-Au@Pt catalyst originate from protective Ti oxide located at the most dissolution-prone edge and vertex sites, and Au-supported active and stable Pt shell.« less

Characterization of 3D Voronoi Tessellation Nearest Neighbor Lipid Shells Provides Atomistic Lipid Disruption Profile of Protein Containing Lipid Membranes

PubMed Central

Cheng, Sara Y.; Duong, Hai V.; Compton, Campbell; Vaughn, Mark W.; Nguyen, Hoa; Cheng, Kwan H.

2015-01-01

Quantifying protein-induced lipid disruptions at the atomistic level is a challenging problem in membrane biophysics. Here we propose a novel 3D Voronoi tessellation nearest-atom-neighbor shell method to classify and characterize lipid domains into discrete concentric lipid shells surrounding membrane proteins in structurally heterogeneous lipid membranes. This method needs only the coordinates of the system and is independent of force fields and simulation conditions. As a proof-of-principle, we use this multiple lipid shell method to analyze the lipid disruption profiles of three simulated membrane systems: phosphatidylcholine, phosphatidylcholine/cholesterol, and beta-amyloid/phosphatidylcholine/cholesterol. We observed different atomic volume disruption mechanisms due to cholesterol and beta-amyloid Additionally, several lipid fractional groups and lipid-interfacial water did not converge to their control values with increasing distance or shell order from the protein. This volume divergent behavior was confirmed by bilayer thickness and chain orientational order calculations. Our method can also be used to analyze high-resolution structural experimental data. PMID:25637891

K-shell excitation studied for H- and He-like bismuth ions in collisions with low-Z target atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoehlker, T.; Ionescu, D.C.; Rymuza, P.

1998-02-01

The formation of excited projectile states via Coulomb excitation is investigated for hydrogenlike and heliumlike bismuth projectiles (Z=83) in relativistic ion-atom collisions. The excitation process was unambiguously identified by observing the radiative decay of the excited levels to the vacant 1s shell in coincidence with ions that did not undergo charge exchange in the reaction target. In particular, owing to the large fine-structure splitting of Bi, the excitation cross sections to the various L-shell sublevels are determined separately. The results are compared with detailed relativistic calculations, showing that both the relativistic character of the bound-state wave functions and the magneticmore » interaction are of considerable importance for the K-shell excitation process in high-Z ions such as Bi. The experimental data confirm the result of the complete relativistic calculations, namely, that the magnetic part of the Li{acute e}nard-Wiechert interaction leads to a significant reduction of the K-shell excitation cross section. {copyright} {ital 1998} {ital The American Physical Society}« less

Application of Powder Diffraction Methods to the Analysis of Short- and Long-Range Atomic Order in Nanocrystalline Diamond and SiC: The Concept of the Apparent Lattice Parameter (alp)

NASA Technical Reports Server (NTRS)

Palosz, B.; Grzanka, E.; Gierlotka, S.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H.-P.; Palosz, W.

2003-01-01

Two methods of the analysis of powder diffraction patterns of diamond and SiC nanocrystals are presented: (a) examination of changes of the lattice parameters with diffraction vector Q ('apparent lattice parameter', alp) which refers to Bragg scattering, and (b), examination of changes of inter-atomic distances based on the analysis of the atomic Pair Distribution Function, PDF. Application of these methods was studied based on the theoretical diffraction patterns computed for models of nanocrystals having (i) a perfect crystal lattice, and (ii), a core-shell structure, i.e. constituting a two-phase system. The models are defined by the lattice parameter of the grain core, thickness of the surface shell, and the magnitude and distribution of the strain field in the shell. X-ray and neutron experimental diffraction data of nanocrystalline SiC and diamond powders of the grain diameter from 4 nm up to micrometers were used. The effects of the internal pressure and strain at the grain surface on the structure are discussed based on the experimentally determined dependence of the alp values on the Q-vector, and changes of the interatomic distances with the grain size determined experimentally by the atomic Pair Distribution Function (PDF) analysis. The experimental results lend a strong support to the concept of a two-phase, core and the surface shell structure of nanocrystalline diamond and SiC.

Structure and Formation Mechanism of Black TiO 2 Nanoparticles

DOE PAGES

Tian, Mengkun; Mahjouri-Samani, Masoud; Eres, Gyula; ...

2015-10-27

The remarkable properties of black TiO 2 are due to its disordered surface shell surrounding a crystalline core. However, the chemical composition and the atomic and electronic structure of the disordered shell and its relationship to the core remain poorly understood. Using advanced transmission electron microscopy methods, we show that the outermost layer of black TiO 2 nanoparticles consists of a disordered Ti 2O 3 shell. The measurements show a transition region that connects the disordered Ti 2O 3 shell to the perfect rutile core consisting first of four to five monolayers of defective rutile, containing clearly visible Ti interstitialmore » atoms, followed by an ordered reconstruction layer of Ti interstitial atoms. Our data suggest that this reconstructed layer presents a template on which the disordered Ti 2O 3 layers form by interstitial diffusion of Ti ions. In contrast to recent reports that attribute TiO 2 band-gap narrowing to the synergistic action of oxygen vacancies and surface disorder of nonspecific origin, our results point to Ti 2O 3, which is a narrow-band-gap semiconductor. In conclusion, as a stoichiometric compound of the lower oxidation state Ti 3+ it is expected to be a more robust atomic structure than oxygen-deficient TiO 2 for preserving and stabilizing Ti 3+ surface species that are the key to the enhanced photocatalytic activity of black TiO 2.« less

From middens to modern estuaries, oyster shells sequester source-specific nitrogen

NASA Astrophysics Data System (ADS)

Darrow, Elizabeth S.; Carmichael, Ruth H.; Andrus, C. Fred T.; Jackson, H. Edwin

2017-04-01

Oysters (Crassostrea virginica) were an important food resource for native peoples of the northern Gulf of Mexico, who deposited waste shells in middens. Nitrogen (N) stable isotopes (δ15N) in bivalve shells have been used as modern proxies for estuarine N sources because they approximate δ15N in suspended particulate matter. We tested the use of midden shell δ15N as a proxy for ancient estuarine N sources. We hypothesized that isotopic signatures in ancient shells from coastal Mississippi would differ from modern shells due to increased anthropogenic N sources, such as wastewater, through time. We decalcified shells using an acidification technique previously developed for modern bivalves, but modified to determine δ15N, δ13C, %N, and % organic C of these low-N, high-C specimens. The modified method resulted in the greatest percentage of usable data from midden shells. Our results showed that oyster shell δ15N did not significantly differ between ancient (500-2100 years old) and modern oysters from the same locations where the sites had undergone relatively little land-use change. δ15N values in modern shells, however, were positively correlated with water column nitrate concentrations associated with urbanization. When N content and total shell mass were combined, we estimated that middens sequestered 410-39,000 kg of relic N, buried at a rate of up to 5 kg N m-2 yr-1. This study provides a relatively simple technique to assess baseline conditions in ecosystems over long time scales by demonstrating that midden shells can be an indicator of pre-historic N source to estuaries and are a potentially significant but previously uncharacterized estuarine N sink.

Catalyst-free fabrication of novel ZnO/CuO core-Shell nanowires heterojunction: Controlled growth, structural and optoelectronic properties

NASA Astrophysics Data System (ADS)

Khan, Muhammad Arif; Wahab, Yussof; Muhammad, Rosnita; Tahir, Muhammad; Sakrani, Samsudi

2018-03-01

Development of controlled growth and vertically aligned ZnO/CuO core-shell heterojunction nanowires (NWs) with large area by a catalyst free vapor deposition and oxidation approach has been investigated. Structural characterization reveals successful fabrication of a core ZnO nanowire having single crystalline hexagonal wurtzite structure along [002] direction and CuO nanostructure shell with thickness (8-10 nm) having polycrystalline monoclinic structure. The optical property analysis suggests that the reflectance spectrum of ZnO/CuO heterostructure nanowires is decreased by 18% in the visible range, which correspondingly shows high absorption in this region as compared to pristine ZnO nanowires. The current-voltage (I-V) characteristics of core-shell heterojunction nanowires measured by conductive atomic force microscopy (C-AFM) shows excellent rectifying behavior, which indicates the characteristics of a good p-n junction. The high-resolution transmission electron microscopy (HRTEM) has confirmed the sharp junction interface between the core-shell heterojunction nanowire arrays. The valence band offset and conduction band offset at ZnO/CuO heterointerfaces are measured to be 2.4 ± 0.05 and 0.23 ± 0.005 eV respectively, using X-ray photoelectron spectroscopy (XPS) and a type-II band alignment structure is found. The results of this study contribute to the development of new advanced device heterostructures for solar energy conversion and optoelectronics applications.

Fabrication of a transparent ultraviolet detector by using n-type Ga2O3 and p-type Ga-doped SnO2 core-shell nanowires.

PubMed

Hsu, Cheng-Liang; Lu, Ying-Ching

2012-09-21

This study investigates the feasibility of synthesizing high-density transparent Ga(2)O(3)/SnO(2):Ga core-shell nanowires on a sapphire substrate at 1000 °C by VLS. The doping Ga concentrations are 0.46, 1.07, 2.30 and 17.53 atomic%. The XRD spectrum and HR-TEM reveal Ga(2)O(3) and SnO(2) as having monoclinic and tetragonal rutile structures, respectively. Experimental results indicate that the XRD peak shift of SnO(2) to a larger angle increases with the increasing amount of Ga doping. According to the CL spectrum, SnO(2) and Ga(2)O(3) peak at approximately 528-568 nm and 422-424 nm, respectively. The maximum quantum efficiency of Ga(2)O(3)/SnO(2):Ga core-shell nanowires is around 0.362%. The UV light on-off current contrast ratio of Ga(2)O(3)/SnO(2):Ga core-shell nanowires is around 1066.7 at a bias of 5 V. Moreover, the dynamic response of Ga(2)O(3)/SnO(2):Ga core-shell nanowires has an on-off current contrast ratio of around 16. Furthermore, the Ga(2)O(3) region functions similar to a capacitor and continues to accumulate SnO(2):Ga excited electrons under UV light exposure.

Surface passivation and self-regulated shell growth in selective area-grown GaN-(Al,Ga)N core-shell nanowires.

PubMed

Hetzl, Martin; Winnerl, Julia; Francaviglia, Luca; Kraut, Max; Döblinger, Markus; Matich, Sonja; Fontcuberta I Morral, Anna; Stutzmann, Martin

2017-06-01

The large surface-to-volume ratio of GaN nanowires implicates sensitivity of the optical and electrical properties of the nanowires to their surroundings. The implementation of an (Al,Ga)N shell with a larger band gap around the GaN nanowire core is a promising geometry to seal the GaN surface. We investigate the luminescence and structural properties of selective area-grown GaN-(Al,Ga)N core-shell nanowires grown on Si and diamond substrates. While the (Al,Ga)N shell allows a suppression of yellow defect luminescence from the GaN core, an overall intensity loss due to Si-related defects at the GaN/(Al,Ga)N interface has been observed in the case of Si substrates. Scanning transmission electron microscopy measurements indicate a superior crystal quality of the (Al,Ga)N shell along the nanowire side facets compared to the (Al,Ga)N cap at the top facet. A nucleation study of the (Al,Ga)N shell reveals a pronounced bowing of the nanowires along the c-direction after a short deposition time which disappears for longer growth times. This is assigned to an initially inhomogeneous shell nucleation. A detailed study of the proceeding shell growth allows the formulation of a strain-driven self-regulating (Al,Ga)N shell nucleation model.

Structural determination of Bi-doped magnetite multifunctional nanoparticles for contrast imaging.

PubMed

Laguna-Marco, M A; Piquer, C; Roca, A G; Boada, R; Andrés-Vergés, M; Veintemillas-Verdaguer, S; Serna, C J; Iadecola, A; Chaboy, J

2014-09-14

To determine with precision how Bi atoms are distributed in Bi-doped iron oxide nanoparticles their structural characterization has been carried out by X-ray absorption spectroscopy (XAS) recorded at the K edge of Fe and at the L3 edge of Bi. The inorganic nanoparticles are nominally hybrid structures integrating an iron oxide core and a bismuth oxide shell. Fe K-edge XAS indicates the formation of a structurally ordered, non-stoichiometric magnetite (Fe3-δO4) phase for all the nanoparticles. The XAS spectra show that, in the samples synthesized by precipitation in aqueous media and laser pyrolysis, the Bi atoms neither enter into the iron oxide spinel lattice nor form any other mixed Bi-Fe oxides. No modification of the local structure around the Fe atoms induced by the Bi atoms is observed at the Fe K edge. In addition, contrary to expectations, our results indicate that the Bi atoms do not form a well-defined Bi oxide structure. The XAS study at the Bi L3 edge indicates that the environment around Bi atoms is highly disordered and only a first oxygen coordination shell is observed. Indefinite [BiO6-x(OH)x] units (isolated or aggregated forming tiny amorphous clusters) bonded through hydroxyl bridges to the nanoparticle, rather than a well defined Bi2O3 shell, surround the nanoparticle. On the other hand, the XAS study indicates that, in the samples synthesized by thermal decomposition, the Bi atoms are embedded in a longer range ordered structure showing the first and second neighbors.

Multiple-collision analysis of characteristic X-rays from low-energy Ar 2+ travelling in solid targets

NASA Astrophysics Data System (ADS)

Cipolla, Sam J.; Mildebrath, Mark E.

1983-12-01

The density of atoms in a solid target fosters a multiple-collision mechanism that leads to the production of an equilibrium fraction of L-shell vacancies in an incident heavy ion. It is then possiblein a subsequent ion-atom collision in the solid for an L-vacancy to be transferred to the K-shell of a target atom via rotational coupling of the 2p π-2p σ molecular orbitals formed in the ion-atom quasimolecule. The vacancy-transfer cross section and the equilibrium fraction and lifetime of the vacancies can be found by using an appropriate multiple-collision analysis of the characteristic target and projectile X-rays. Results will be presented for 160-380 keV Ar 2+ incident of targets of Mg, Al, and Si.

EXAFS study of some coordination polymers of copper

NASA Astrophysics Data System (ADS)

Deshpande, A. P.

1995-02-01

The EXAFS spectra for (1) azelaic acid bis phenyl hydrazide, (2) azelaic acid bis 2,4 dinitro phenyl hydrazide and (3) sebacic acid bis phenyl hydrazide coordination polymers of copper were obtained using the EXAFS facility of the Daresbury Laboratory. The EXAFS analysis revealed that copper is surrounded by four nitrogen and two oxygen atoms in the first coordination shell, while the second coordination shell consists of two carbon atoms. This information suggests the octahedral geometry for the repeating units of polymeric complexes, in contrast to the square planar geometry previously proposed.

Crystal Structure of Faradaurate-279: Au279(SPh-tBu)84 Plasmonic Nanocrystal Molecules.

PubMed

Sakthivel, Naga Arjun; Theivendran, Shevanuja; Ganeshraj, Vigneshraja; Oliver, Allen G; Dass, Amala

2017-11-01

We report the discovery of an unprecedentedly large, 2.2 nm diameter, thiolate protected gold nanocrystal characterized by single crystal X-ray crystallography (sc-XRD), Au 279 (SPh-tBu) 84 named Faradaurate-279 (F-279) in honor of Michael Faraday's (1857) pioneering work on nanoparticles. F-279 nanocrystal has a core-shell structure containing a truncated octahedral core with bulk face-centered cubic-like arrangement, yet a nanomolecule with a precise number of metal atoms and thiolate ligands. The Au 279 S 84 geometry was established from a low-temperature 120 K sc-XRD study at 0.90 Å resolution. The atom counts in core-shell structure of Au 279 follows the mathematical formula for magic number shells: Au@Au 12 @Au 42 @Au 92 @Au 54 , which is further protected by a final shell of Au 48 . Au 249 core is protected by three types of staple motifs, namely: 30 bridging, 18 monomeric, and 6 dimeric staple motifs. Despite the presence of such diverse staple motifs, Au 279 S 84 structure has a chiral pseudo-D 3 symmetry. The core-shell structure can be viewed as nested, concentric polyhedra, containing a total of five forms of Archimedean solids. A comparison between the Au 279 and Au 309 cuboctahedral superatom model in shell-wise growth is illustrated. F-279 can be synthesized and isolated in high purity in milligram quantities using size exclusion chromatography, as evidenced by mass spectrometry. Electrospray ionization-mass spectrometry independently verifies the X-ray diffraction study based heavy atoms formula, Au 279 S 84 , and establishes the molecular formula with the complete ligands, namely, Au 279 (SPh-tBu) 84 . It is also the smallest gold nanocrystal to exhibit metallic behavior, with a surface plasmon resonance band around 510 nm.

Structural Characterization of CO-Inhibited Mo-Nitrogenase by Combined Application of Nuclear Resonance Vibrational Spectroscopy, Extended X-ray Absorption Fine Structure, and Density Functional Theory: New Insights into the Effects of CO Binding and the Role of the Interstitial Atom

DOE PAGES

Scott, Aubrey D.; Pelmenschikov, Vladimir; Guo, Yisong; ...

2014-10-02

The properties of CO-inhibited Azotobacter vinelandii (Av) Mo-nitrogenase (N 2ase) have been examined by the combined application of nuclear resonance vibrational spectroscopy (NRVS), extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT). Dramatic changes in the NRVS are seen under high-CO conditions, especially in a 188 cm –1 mode associated with symmetric breathing of the central cage of the FeMo-cofactor. Similar changes are reproduced with the α-H195Q N 2ase variant. In the frequency region above 450 cm –1, additional features are seen that are assigned to Fe-CO bending and stretching modes (confirmed by 13CO isotope shifts). The EXAFSmore » for wild-type N 2ase shows evidence for a significant cluster distortion under high-CO conditions, most dramatically in the splitting of the interaction between Mo and the shell of Fe atoms originally at 5.08 Å in the resting enzyme. A DFT model with both a terminal ₋CO and a partially reduced ₋CHO ligand bound to adjacent Fe sites is consistent with both earlier FT-IR experiments, and the present EXAFS and NRVS observations for the wild-type enzyme. Another DFT model with two terminal CO ligands on the adjacent Fe atoms yields Fe-CO bands consistent with the α-H195Q variant NRVS. The calculations also shed light on the vibrational “shake” modes of the interstitial atom inside the central cage, and their interaction with the Fe-CO modes. We discuss implications for the CO and N 2 reactivity of N 2ase.« less

Structural characterization of CO-inhibited Mo-nitrogenase by combined application of nuclear resonance vibrational spectroscopy, extended X-ray absorption fine structure, and density functional theory: new insights into the effects of CO binding and the role of the interstitial atom.

PubMed

Scott, Aubrey D; Pelmenschikov, Vladimir; Guo, Yisong; Yan, Lifen; Wang, Hongxin; George, Simon J; Dapper, Christie H; Newton, William E; Yoda, Yoshitaka; Tanaka, Yoshihito; Cramer, Stephen P

2014-11-12

The properties of CO-inhibited Azotobacter vinelandii (Av) Mo-nitrogenase (N2ase) have been examined by the combined application of nuclear resonance vibrational spectroscopy (NRVS), extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT). Dramatic changes in the NRVS are seen under high-CO conditions, especially in a 188 cm(-1) mode associated with symmetric breathing of the central cage of the FeMo-cofactor. Similar changes are reproduced with the α-H195Q N2ase variant. In the frequency region above 450 cm(-1), additional features are seen that are assigned to Fe-CO bending and stretching modes (confirmed by (13)CO isotope shifts). The EXAFS for wild-type N2ase shows evidence for a significant cluster distortion under high-CO conditions, most dramatically in the splitting of the interaction between Mo and the shell of Fe atoms originally at 5.08 Å in the resting enzyme. A DFT model with both a terminal -CO and a partially reduced -CHO ligand bound to adjacent Fe sites is consistent with both earlier FT-IR experiments, and the present EXAFS and NRVS observations for the wild-type enzyme. Another DFT model with two terminal CO ligands on the adjacent Fe atoms yields Fe-CO bands consistent with the α-H195Q variant NRVS. The calculations also shed light on the vibrational "shake" modes of the interstitial atom inside the central cage, and their interaction with the Fe-CO modes. Implications for the CO and N2 reactivity of N2ase are discussed.

Electrophobic interaction induced impurity clustering in metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Hong-Bo; Wang, Jin-Long; Jiang, W.

2016-10-01

We introduce the concept of electrophobic interaction, analogous to hydrophobic interaction, for describing the behavior of impurity atoms in a metal, a 'solvent of electrons'. We demonstrate that there exists a form of electrophobic interaction between impurities with closed electron shell structure, which governs their dissolution behavior in a metal. Using He, Be and Ar as examples, we predict by first-principles calculations that the electrophobic interaction drives He, Be or Ar to form a close-packed cluster with a clustering energy that follows a universal power-law scaling with the number of atoms (N) dissolved in a free electron gas, as wellmore » as W or Al lattice, as Ec is proportional to (N2/3-N). This new concept unifies the explanation for a series of experimental observations of close-packed inert-gas bubble formation in metals, and significantly advances our fundamental understanding and capacity to predict the solute behavior of impurities in metals, a useful contribution to be considered in future material design of metals for nuclear, metallurgical, and energy applications.« less

Contribution of inner shell Compton ionization to the X-ray fluorescence line intensity

NASA Astrophysics Data System (ADS)

Fernández, Jorge E.; Scot, Viviana; Di Giulio, Eugenio

2016-10-01

The Compton effect is a potential ionization mechanism of atoms. It produces vacancies in inner shells that are filled with the same mechanism of atomic relaxation as the one following photo-absorption. This contribution to X-ray fluorescence emission is frequently neglected because the total Compton cross-section is apparently much lower than the photoelectric one at useful X-ray energies. However, a more careful analysis suggests that is necessary to consider single shell cross sections (instead of total cross sections) as a function of energy. In this article these Compton cross sections are computed for the shells K, L1-L3 and M1-M5 in the framework of the impulse approximation. By comparing the Compton and the photoelectric cross-section for each shell it is then possible to determine the extent of the Compton correction to the intensity of the corresponding characteristic lines. It is shown that for the K shell the correction becomes relevant for excitation energies which are too high to be influent in X-ray spectrometry. In contrast, for L and M shells the Compton contribution is relevant for medium-Z elements and medium energies. To illustrate the different grades of relevance of the correction, for each ionized shell, the energies for which the Compton contribution reaches the extent levels of 1, 5, 10, 20, 50 and 100% of the photoelectric one are determined for all the elements with Z = 11-92. For practical applications it is provided a simple formula and fitting coefficients to compute average correction levels for the shells considered.

Planar CoB18- Cluster: a New Motif for - and Metallo-Borophenes

NASA Astrophysics Data System (ADS)

Chen, Teng-Teng; Jian, Tian; Lopez, Gary; Li, Wan-Lu; Chen, Xin; Li, Jun; Wang, Lai-Sheng

2016-06-01

Combined Photoelectron Spectroscopy (PES) and theoretical calculations have found that anion boron clusters (Bn-) are planar and quasi-planar up to B25-. Recent works show that anion pure boron clusters continued to be planar at B27-,B30-,B35- and B36-. B35- and B36- provide the first experimental evidence for the viability of the two-dimensional (2D) boron sheets (Borophene). The 2D to three-dimensional (3D) transitions are shown to happen at B40-,B39- and B28-, which possess cage-like structures. These fullerene-like boron cage clusters are named as Borospherene. Recently, borophenes or similar structures are claimed to be synthesized by several groups. Following an electronic design principle, a series of transition-metal-doped boron clusters (M©Bn-, n=8-10) are found to possess the monocyclic wheel structures. Meanwhile, CoB12- and RhB12- are revealed to adopt half-sandwich-type structures with the quasi-planar B12 moiety similar to the B12- cluster. Very lately, we show that the CoB16- cluster possesses a highly symmetric Cobalt-centered drum-like structure, with a new record of coordination number at 16. Here we report the CoB18- cluster to possess a unique planar structure, in which the Co atom is doped into the network of a planar boron cluster. PES reveals that the CoB18- cluster is a highly stable electronic system with the first adiabatic detachment energy (ADE) at 4.0 eV. Global minimum searches along with high-level quantum calculations show the global minimum for CoB18- is perfectly planar and closed shell (1A1) with C2v symmetry. The Co atom is bonded with 7 boron atoms in the closest coordination shell and the other 11 boron atoms in the outer coordination shell. The calculated vertical detachment energy (VDE) values match quite well with our experimental results. Chemical bonding analysis by the Adaptive Natural Density Partitioning (AdNDP) method shows the CoB18- cluster is π-aromatic with four 4-centered-2-electron (4c-2e) π bonds and one 19-centered-2-electron (19c-2e) π bond, 10 π electrons in total. This perfectly planar structure reveals the viability of creating a new class of hetero-borophenes and metallo-borophenes by doping metal atoms into the plane of monolayer boron atoms. This gives a new approach to design perspective hetero-borophenes and metallo-borophenes materials with tunable chemical, magnetic and optical properties.

Structure of RNA polymerase complex and genome within a dsRNA virus provides insights into the mechanisms of transcription and assembly.

PubMed

Wang, Xurong; Zhang, Fuxian; Su, Rui; Li, Xiaowu; Chen, Wenyuan; Chen, Qingxiu; Yang, Tao; Wang, Jiawei; Liu, Hongrong; Fang, Qin; Cheng, Lingpeng

2018-06-25

Most double-stranded RNA (dsRNA) viruses transcribe RNA plus strands within a common innermost capsid shell. This process requires coordinated efforts by RNA-dependent RNA polymerase (RdRp) together with other capsid proteins and genomic RNA. Here we report the near-atomic resolution structure of the RdRp protein VP2 in complex with its cofactor protein VP4 and genomic RNA within an aquareovirus capsid using 200-kV cryoelectron microscopy and symmetry-mismatch reconstruction. The structure of these capsid proteins enabled us to observe the elaborate nonicosahedral structure within the double-layered icosahedral capsid. Our structure shows that the RdRp complex is anchored at the inner surface of the capsid shell and interacts with genomic dsRNA and four of the five asymmetrically arranged N termini of the capsid shell proteins under the fivefold axis, implying roles for these N termini in virus assembly. The binding site of the RNA end at VP2 is different from the RNA cap binding site identified in the crystal structure of orthoreovirus RdRp λ3, although the structures of VP2 and λ3 are almost identical. A loop, which was thought to separate the RNA template and transcript, interacts with an apical domain of the capsid shell protein, suggesting a mechanism for regulating RdRp replication and transcription. A conserved nucleoside triphosphate binding site was localized in our RdRp cofactor protein VP4 structure, and interactions between the VP4 and the genomic RNA were identified.

Recent Livermore Excitation and Dielectronic Recombination Measurements for Laboratory and Astrophysical Spectral Modeling

NASA Technical Reports Server (NTRS)

Beiersdorfer, P.; Brown, G. V.; Gu, M.-F.; Harris, C. L.; Kahn, S. M.; Kim, S.-H.; Neill, P. A.; Savin, D. W.; Smith, A. J.; Utter, S. B.

2000-01-01

Using the EBIT facility in Livermore we produce definitive atomic data for input into spectral synthesis codes. Recent measurements of line excitation and dielectronic recombination of highly charged K-shell and L-shell ions are presented to illustrate this point.

Production and decay of K -shell hollow krypton in collisions with 52-197-MeV/u bare xenon ions

NASA Astrophysics Data System (ADS)

Shao, Caojie; Yu, Deyang; Cai, Xiaohong; Chen, Xi; Ma, Kun; Evslin, Jarah; Xue, Yingli; Wang, Wei; Kozhedub, Yury S.; Lu, Rongchun; Song, Zhangyong; Zhang, Mingwu; Liu, Junliang; Yang, Bian; Guo, Yipan; Zhang, Jianming; Ruan, Fangfang; Wu, Yehong; Zhang, Yuezhao; Dong, Chenzhong; Chen, Ximeng; Yang, Zhihu

2017-07-01

X-ray spectra of K -shell hollow krypton atoms produced in single collisions with 52-197-MeV/u X e54 + ions are measured in a heavy-ion storage ring equipped with an internal gas-jet target. Energy shifts of the K α1,2 s , K α1,2 h ,s , and K β1,3 s transitions are obtained. Thus the average number of the spectator L vacancies presented during the x-ray emission is deduced. From the relative intensities of the K α1,2 s and K α1,2 h ,s transitions, the ratio of K -shell hollow krypton to singly K -shell ionized atoms is determined to be 14 %-24 % . In the considered collisions, the K vacancies are mainly created by the direct ionization which cannot be calculated within the perturbation descriptions. The experimental results are compared with a relativistic coupled-channel calculation performed within the independent particle approximation.

Spectroscopic Investigations of Highly Charged Tungsten Ions - Atomic Spectroscopy and Fusion Plasma Diagnostics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clementson, Joel

2010-05-01

The spectra of highly charged tungsten ions have been investigated using x-ray and extreme ultraviolet spectroscopy. These heavy ions are of interest in relativistic atomic structure theory, where high-precision wavelength measurements benchmark theoretical approaches, and in magnetic fusion research, where the ions may serve to diagnose high-temperature plasmas. The work details spectroscopic investigations of highly charged tungsten ions measured at the Livermore electron beam ion trap (EBIT) facility. Here, the EBIT-I and SuperEBIT electron beam ion traps have been employed to create, trap, and excite tungsten ions of M- and L-shell charge states. The emitted spectra have been studied inmore » high resolution using crystal, grating, and x-ray calorimeter spectrometers. In particular, wavelengths of n = 0 M-shell transitions in K-like W 55+ through Ne-like W 64+, and intershell transitions in Zn-like W 44+ through Co-like W 47+ have been measured. Special attention is given to the Ni-like W46+ ion, which has two strong electric-dipole forbidden transitions that are of interest for plasma diagnostics. The EBIT measurements are complemented by spectral modeling using the Flexible Atomic Code (FAC), and predictions for tokamak spectra are presented. The L-shell tungsten ions have been studied at electron-beam energies of up to 122 keV and transition energies measured in Ne-like W 64+ through Li-like W 71+. These spectra constitute the physics basis in the design of the ion-temperature crystal spectrometer for the ITER tokamak. Tungsten particles have furthermore been introduced into the Sustained Spheromak Physics Experiment (SSPX) spheromak in Livermore in order to investigate diagnostic possibilities of extreme ultraviolet tungsten spectra for the ITER divertor. The spheromak measurement and spectral modeling using FAC suggest that tungsten ions in charge states around Er-like W 6+ could be useful for plasma diagnostics.« less

An atomic-force-microscopy study of the structure of surface layers of intact fibroblasts

NASA Astrophysics Data System (ADS)

Khalisov, M. M.; Ankudinov, A. V.; Penniyaynen, V. A.; Nyapshaev, I. A.; Kipenko, A. V.; Timoshchuk, K. I.; Podzorova, S. A.; Krylov, B. V.

2017-02-01

Intact embryonic fibroblasts on a collagen-treated substrate have been studied by atomic-force microscopy (AFM) using probes of two types: (i) standard probes with tip curvature radii of 2-10 nm and (ii) special probes with a calibrated 325-nm SiO2 ball radius at the tip apex. It is established that, irrespective of probe type, the average maximum fibroblast height is on a level of 1.7 μm and the average stiffness of the probe-cell contact amounts to 16.5 mN/m. The obtained AFM data reveal a peculiarity of the fibroblast structure, whereby its external layers move as a rigid shell relative to the interior and can be pressed inside to a depth dependent on the load only.

REVIEWS OF TOPICAL PROBLEMS: Helium-isotope mass-spectrometric method for studying tritium beta decay (idea, experiment, nuclear and molecular physics applications)

NASA Astrophysics Data System (ADS)

Akulov, Yuii A.; Mamyrin, Boris A.

2003-11-01

Experimental data on the variation of tritium nucleus beta decay constant caused by the interaction of the resulting beta-electron with orbital electrons and shell vacancies are reviewed for free atomic tritium and molecular tritium and used to obtain the half-life of atomic tritium (T1/2)a=(12.264±0.018) y, the half-life of the free triton (T1/2)t=(12.238±0.020) y, the axial-vector-to-vector weak-interaction coupling constant ratio (GA/GV)t=-1.2646 ± 0.0035 for beta decay of the triton, and an independent estimate of the free neutron lifetime τn= (890.3 ± 3.9stat ± 1.4syst) s.

Experimental binding energies for the metal complexes [Mg(CH3OH)n](2+), [Ca(CH3OH)n](2+), and [Sr(CH3OH)n](2+) for n in the range 4-20.

PubMed

Bruzzi, E; Stace, A J

2014-10-09

A supersonic source of clusters has been used to prepare neutral complexes of methanol in association with an alkaline earth metal atom. From these complexes the following metal-containing dications have been generated through electron ionization: [Mg(CH3OH)n](2+), [Ca(CH3OH)n](2+), and [Sr(CH3OH)n](2+), and for n in the range 4-20, kinetic energy release measurements following the evaporation of a single molecule have been undertaken using a high resolution mass spectrometer. Using finite heat bath theory, these data have been transformed into binding energies for individual methanol molecules attached to each of the three cluster systems. In the larger complexes (n > 6) the results exhibit a consistent trend, whereby the experimental binding energy data for all three metal ions are similar, suggesting that the magnitude of the charge rather than charge density influences the strength of the interaction. From a comparison with data recorded previously for (CH3OH)nH(+) it is found that the 2+ charge on a metal ion has an effect on the binding energy of molecules in complexes containing up to 20 solvent molecules. The results recorded for [Ca(CH3OH)n](2+) show evidence of a very marked transition between n = 6 and 7, which is thought to coincide with the completion of a primary solvation shell and the onset of molecules starting to occupy a second and most probably a third shell.

Atomic x-ray production by relativistic heavy ions. [Cross sections, K and L shells, ionization 3 and 4. 88 GEV holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ioannou, J.G.

1977-12-01

The interaction of heavy ion projectiles with the electrons of target atoms gives rise to the production, in the target, of K-, L- or higher shell vacancies which are in turn followed by the emission of characteristic x-rays. The calculation of the theoretical value of the K- and L-shells vacancy production cross section was carried out for heavy ion projectiles of any energy. The transverse component of the cross section is calculated for the first time in detail and extensive tables of its numerical value as a function of its parameters are also given. Experimental work for 4.88 GeV protonsmore » and 3 GeV carbon ions is described. The K vacancy cross section has been measured for a variety of targets from Ti to U. The agreement between the theoretical predictions and experimental results for the 4.88 GeV protons is rather satisfactory. For the 3 GeV carbon ions, however, it is observed that the deviation of the theoretical and experimental values of the K vacancy production becomes larger with the heavier target element. Consequently, the simple scaling law of Z/sub 1//sup 2/ for the cross section of the heavy ion with atomic number Z/sub 1/ to the proton cross section is not true, for the K-shell at least. A dependence on the atomic number Z/sub 2/ of the target of the form (Z/sub 1/ - ..cap alpha..Z/sub 2/)/sup 2/, instead of Z/sub 1//sup 2/, is found to give extremely good agreement between theory and experiment. Although the exact physical meaning of such dependence is not yet clearly understood, it is believed to be indicative of some sort of screening effect of the incoming fast projectile by the fast moving in Bohr orbits K-shell electrons of the target. The enhancement of the K-shell ionization cross section by relativistic heavy ions on heavy targets is also discussed in terms of its practical applications in various branches of science and technology.« less

Shell biofilm-associated nitrous oxide production in marine molluscs: processes, precursors and relative importance.

PubMed

Heisterkamp, Ines M; Schramm, Andreas; Larsen, Lone H; Svenningsen, Nanna B; Lavik, Gaute; de Beer, Dirk; Stief, Peter

2013-07-01

Emission of the greenhouse gas nitrous oxide (N2 O) from freshwater and terrestrial invertebrates has exclusively been ascribed to N2 O production by ingested denitrifying bacteria in the anoxic gut of the animals. Our study of marine molluscs now shows that also microbial biofilms on shell surfaces are important sites of N2 O production. The shell biofilms of Mytilus edulis, Littorina littorea and Hinia reticulata contributed 18-94% to the total animal-associated N2 O emission. Nitrification and denitrification were equally important sources of N2 O in shell biofilms as revealed by (15) N-stable isotope experiments with dissected shells. Microsensor measurements confirmed that both nitrification and denitrification can occur in shell biofilms due to a heterogeneous oxygen distribution. Accordingly, ammonium, nitrite and nitrate were important drivers of N2 O production in the shell biofilm of the three mollusc species. Ammonium excretion by the animals was found to be sufficient to sustain N2 O production in the shell biofilm. Apparently, the animals provide a nutrient-enriched microenvironment that stimulates growth and N2 O production of the shell biofilm. This animal-induced stimulation was demonstrated in a long-term microcosm experiment with the snail H. reticulata, where shell biofilms exhibited the highest N2 O emission rates when the animal was still living inside the shell. © 2012 John Wiley & Sons Ltd and Society for Applied Microbiology.

X-ray natural widths, level widths and Coster-Kronig transition probabilities

NASA Astrophysics Data System (ADS)

Papp, T.; Campbell, J. L.; Varga, D.

1997-01-01

A critical review is given for the K-N7 atomic level widths. The experimental level widths were collected from x-ray photoelectron spectroscopy (XPS), x-ray emission spectroscopy (XES), x-ray spectra fluoresced by synchrotron radiation, and photoelectrons from x-ray absorption (PAX). There are only limited atomic number ranges for a few atomic levels where data are available from more than one source. Generally the experimental level widths have large scatter compared to the reported error bars. The experimental data are compared with the recent tabulation of Perkins et al. and of Ohno et al. Ohno et al. performed a many body approach calculation for limited atomic number ranges and have obtained reasonable agreement with the experimental data. Perkins et al. presented a tabulation covering the K-Q1 shells of all atoms, based on extensions of the Scofield calculations for radiative rates and extensions of the Chen calculations for non-radiative rates. The experimental data are in disagreement with this tabulation, in excess of a factor of two in some cases. A short introduction to the experimental Coster-Kronig transition probabilities is presented. It is our opinion that the different experimental approaches result in systematically different experimental data.

State-specific transport properties of electronically excited Ar and C

NASA Astrophysics Data System (ADS)

Istomin, V. A.; Kustova, E. V.

2018-05-01

In the present study, a theoretical model of state-resolved transport properties in electronically excited atomic species developed earlier is applied to argon and carbon atomic species. It is shown that for Ar and C, similarly to the case of atomic nitrogen and oxygen, the Slater-like models can be applied to calculate diameters of electronically excited atoms. Using the Slater-like model it is shown that for half-filled N (2 px1py1pz1) and full-filled Ar (3 px2py2pz2) electronic shells the growth of atomic radius goes slowly compared to C (2 px1py1) and O (2 px2py1pz1). The effect of collision diameters on the transport properties of Ar and C is evaluated. The influence of accounted number of electronic levels on the transport coefficients is examined for the case of Boltzmann distributions over electronic energy levels. It is emphasized that in the temperature range 1000-14000 K, for Boltzmann-like distributions over electronic states the number of accounted electronic levels do not influence the transport coefficients. Contrary to this, for higher temperatures T > 14000 K this effect becomes of importance, especially for argon.

Emitter-site-selective photoelectron circular dichroism of trifluoromethyloxirane

DOE PAGES

Ilchen, M.; Hartmann, G.; Rupprecht, P.; ...

2017-05-30

The angle-resolved inner-shell photoionization of R-trifluoromethyloxirane, C 3H 3F 3O, is studied experimentally and theoretically. Thereby, we investigate the photoelectron circular dichroism (PECD) for nearly symmetric O 1s and F 1s electronic orbitals, which are localized on different molecular sites. The respective dichroic β 1 and angular distribution β 2 parameters are measured at the photoelectron kinetic energies from 1 to 16 eV by using variably polarized synchrotron radiation and velocity map imaging spectroscopy. The present experimental results are in good agreement with the outcome of ab initio electronic structure calculations. We report a sizable chiral asymmetry β 1 ofmore » up to about 9% for the K -shell photoionization of oxygen atom. For the individual fluorine atoms, the present calculations predict asymmetries of similar size. However, being averaged over all fluorine atoms, it drops down to about 2%, as also observed in the present experiment. Our study demonstrates a strong emitter and site sensitivity of PECD in the one-photon inner-shell ionization of this chiral molecule.« less

Patched bimetallic surfaces are active catalysts for ammonia decomposition.

PubMed

Guo, Wei; Vlachos, Dionisios G

2015-10-07

Ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material's structure. Core-shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core-shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.

First determination of ground state electromagnetic moments of Fe 53

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, A. J.; Minamisono, K.; Rossi, D. M.

Here, the hyperfine coupling constants of neutron deficient 53Fe were deduced from the atomic hyperfine spectrum measured using the bunched-beam collinear laser spectroscopy technique. The low-energy 53Fe beam was produced by projectile-fragmentation reactions followed by gas stopping, and used for the first time for laser spectroscopy. Ground state magnetic-dipole and electric-quadrupole moments were determined as μ= –0.65(1)μ N and Q=+35(15)e 2fm 2, respectively. The multiconfiguration Dirac-Fock method was used to calculate the electric field gradient to deduce Q from the quadrupole hyperfine coupling constant, since the quadrupole coupling constant has not been determined for any Fe isotopes. Both experimental valuesmore » agree well with nuclear shell model calculations using the GXPF1A effective interaction performed in a full fp shell model space, which support the soft nature of the 56Ni nucleus.« less

Hierarchical Petascale Simulation Framework for Stress Corrosion Cracking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vashishta, Priya

2014-12-01

Reaction Dynamics in Energetic Materials: Detonation is a prototype of mechanochemistry, in which mechanically and thermally induced chemical reactions far from equilibrium exhibit vastly different behaviors. It is also one of the hardest multiscale physics problems, in which diverse length and time scales play important roles. The CACS group has performed multimillion-atom reactive MD simulations to reveal a novel two-stage reaction mechanism during the detonation of cyclotrimethylenetrinitramine (RDX) crystal. Rapid production of N2 and H2O within ~10 ps is followed by delayed production of CO molecules within ~ 1 ns. They found that further decomposition towards the final products ismore » inhibited by the formation of large metastable C- and O-rich clusters with fractal geometry. The CACS group has also simulated the oxidation dynamics of close-packed aggregates of aluminum nanoparticles passivated by oxide shells. Their simulation results suggest an unexpectedly active role of the oxide shell as a nanoreactor.« less

First determination of ground state electromagnetic moments of Fe 53

DOE PAGES

Miller, A. J.; Minamisono, K.; Rossi, D. M.; ...

2017-11-16

Here, the hyperfine coupling constants of neutron deficient 53Fe were deduced from the atomic hyperfine spectrum measured using the bunched-beam collinear laser spectroscopy technique. The low-energy 53Fe beam was produced by projectile-fragmentation reactions followed by gas stopping, and used for the first time for laser spectroscopy. Ground state magnetic-dipole and electric-quadrupole moments were determined as μ= –0.65(1)μ N and Q=+35(15)e 2fm 2, respectively. The multiconfiguration Dirac-Fock method was used to calculate the electric field gradient to deduce Q from the quadrupole hyperfine coupling constant, since the quadrupole coupling constant has not been determined for any Fe isotopes. Both experimental valuesmore » agree well with nuclear shell model calculations using the GXPF1A effective interaction performed in a full fp shell model space, which support the soft nature of the 56Ni nucleus.« less

Patched bimetallic surfaces are active catalysts for ammonia decomposition

NASA Astrophysics Data System (ADS)

Guo, Wei; Vlachos, Dionisios G.

2015-10-01

Ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material's structure. Core-shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core-shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.

Determination of K shell absorption jump factors and jump ratios in the elements between Tm( Z = 69) and Os( Z = 76) by measuring K shell fluorescence parameters

NASA Astrophysics Data System (ADS)

Kaya, N.; Tıraşoğlu, E.; Apaydın, G.

2008-04-01

The K shell absorption jump factors and jump ratios have been measured in the elements between Tm ( Z = 69) and Os( Z = 76) without having any mass attenuation coefficient at the upper and lower energy branch of the K absorption edge. The jump factors and jump ratios for these elements have been determined by measuring K shell fluorescence parameters such as the total atomic absorption cross-sections, the K α X-ray production cross-sections, the intensity ratio of the K β and K α X-rays and the K shell fluorescence yields. We have performed the measurements for the calculations of these values in attenuation and direct excitation experimental geometry. The K X-ray photons are excited in the target using 123.6 keV gamma-rays from a strong 57Co source, and detected with an Ultra-LEGe solid state detector with a resolution 0.15 keV at 5.9 keV. The measured values have been compared with theoretical and others' experimental values. The results have been plotted versus atomic number.

Evaluation of the Mechanical Properties and Effectiveness of Countermine Boots.

DTIC Science & Technology

1998-03-01

regarding comfort except that the 60 shanks overall length of approximately 5.7 in should allow normal flexure of the forefoot . Weight, however, is...When the electron beam strikes an element in the sample, electrons are ejected from inner atomic shells to outer shells resulting in ions in the

Ligand-protected gold clusters: the structure, synthesis and applications

NASA Astrophysics Data System (ADS)

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.

Electronic stopping in oxides beyond Bragg additivity

NASA Astrophysics Data System (ADS)

Sigmund, P.; Schinner, A.

2018-01-01

We present stopping cross sections calculated by our PASS code for several ions in metal oxides and SiO2 over a wide energy range. Input takes into account changes in the valence structure by assigning two additional electrons to the 2p shell of oxygen and removing the appropriate number of electrons from the outer shells of the metal atom. Results are compared with tabulated experimental values and with two versions of Bragg's additivity rule. Calculated stopping cross sections are applied in testing a recently-proposed scaling rule, which relates the stopping cross section to the number of oxygen atoms per molecule.

O-shell emission of heavy atoms in an optically thin tokamak plasma

NASA Astrophysics Data System (ADS)

Finkenthal, M.; Lippmann, S.; Huang, L. K.; Zwicker, A.; Moos, H. W.; Goldstein, W. H.; Osterheld, A. L.

1992-04-01

Heavy atoms Au (Z=79), Pb (Z=82), Bi (Z=83), and U (Z=92) have been introduced in the low-density (ne~1013 cm-3) high-temperature (Te>=1 keV) TEXT tokamak (Fusion Research Center, University of Texas at Austin) plasma. The emission has been measured in the 50-200-Å range using a photometrically calibrated, time-resolving grazing-incidence spectrometer. The O-shell ion emission has been identified by comparison with ab initio energy-level calculations and line-intensity predictions of collisional radiative models for various charge states with 5p65dk ground-state configurations.

Co-axial Electrospun Polyacrylonitrile-Poly(methylmethacrylate) Nanofibers: Atomic Force Microscopy and Compositional Characterization

PubMed Central

Zander, N.E.; Strawhecker, K.E.; Orlicki, J.A.; Rawlett, A.M.; Beebe, T.P.

2011-01-01

Poly(methylmethacrylate) (PMMA)- Polyacrylonitrile (PAN) fibers were prepared using a conventional single-nozzle electrospinning technique. The as-spun fibers exhibited core-shell morphology as verified by transmission electron microscopy (TEM) and atomic force microscopy (AFM). AFM-phase and modulus mapping images of the fiber cross-section and x-ray photoelectron spectroscopy (XPS) analysis indicated PAN formed the shell and PMMA the core material. XPS, thermal gravimetric analysis (TGA), and elemental analysis were used to determine fiber compositional information. Soaking the fibers in solvent demonstrated removal of the core material, generating hollow PAN fibers. PMID:21928836

Modified Activated Carbon Prepared from Acorn Shells as a New Solid-Phase Extraction Sorbent for the Preconcentration and Determination of Trace Amounts of Nickel in Food Samples Prior to Flame Atomic Absorption Spectrometry.

PubMed

Ebrahimi, Bahram

2017-03-01

A new solid-phase extraction (SPE) sorbent was introduced based on acidic-modified (AM) activated carbon (AC) prepared from acorn shells of native oak trees in Kurdistan. Hydrochloric acid (15%, w/w) and nitric acid (32.5%, w/w) were used to condition and modify AC. The IR spectra of AC and AM-AC showed that AM lead to the formation of increasing numbers of acidic functional groups on AM-AC. AM-AC was used in the SPE method for the extraction and preconcentration of Ni+2 prior to flame atomic absorption spectrometric determination at ng/mL levels in model and real food samples. Effective parameters of the SPE procedure, such as the pH of the solutions, sorbent dosage, extraction time, sample volume, type of eluent, and matrix ions, were considered and optimized. An enrichment factor of 140 was obtained. The calibration curve was linear with an R2 of 0.997 in the concentration range of 1-220 ng/mL. The RSD was 5.67% (for n = 7), the LOD was 0.352 ng/mL, and relative recoveries in vegetable samples ranged from 96.7 to 103.7%.

Tuning the synthesis of platinum-copper nanoparticles with a hollow core and porous shell for the selective hydrogenation of furfural to furfuryl alcohol

NASA Astrophysics Data System (ADS)

Huang, Shuangshuang; Yang, Nating; Wang, Shibin; Sun, Yuhan; Zhu, Yan

2016-07-01

Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol.Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03894h

Global molecular identification from graphs. Neutral and ionized main-group diatomic molecules.

PubMed

James, Bryan; Caviness, Ken; Geach, Jonathan; Walters, Chris; Hefferlin, Ray

2002-01-01

Diophantine equations and inequalities are presented for main-group closed-shell diatomic molecules. Specifying various bond types (covalent, dative, ionic, van der Waals) and multiplicities, it becomes possible to identify all possible molecules. While many of the identified species are probably unstable under normal conditions, they are interesting and present a challenge for computational or experimental analysis. Ionized molecules with net charges of -1, 1, and 2 are also identified. The analysis applies to molecules with atoms from periods 2 and 3 but can be generalized by substituting isovalent atoms. When closed-shell neutral diatomics are positioned in the chemical space (with axes enumerating the numbers of valence electrons of the free atoms), it is seen that they lie on a few parallel isoelectronic series.

Fermi orbital derivatives in self-interaction corrected density functional theory: Applications to closed shell atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pederson, Mark R., E-mail: mark.pederson@science.doe.gov

2015-02-14

A recent modification of the Perdew-Zunger self-interaction-correction to the density-functional formalism has provided a framework for explicitly restoring unitary invariance to the expression for the total energy. The formalism depends upon construction of Löwdin orthonormalized Fermi-orbitals which parametrically depend on variational quasi-classical electronic positions. Derivatives of these quasi-classical electronic positions, required for efficient minimization of the self-interaction corrected energy, are derived and tested, here, on atoms. Total energies and ionization energies in closed-shell singlet atoms, where correlation is less important, using the Perdew-Wang 1992 Local Density Approximation (PW92) functional, are in good agreement with experiment and non-relativistic quantum-Monte-Carlo results albeitmore » slightly too low.« less

Electron Impact K-shell Ionization Cross Sections at high energies

NASA Astrophysics Data System (ADS)

Haque, A. K. F.; Sarker, M. S. I.; Patoary, M. A. R.; Shahjahan, M.; Ismail Hossain, M.; Alfaz Uddin, M.; Basak, A. K.; Saha, Bidhan

2008-10-01

A simple modification of the empirical model of Deutsh et. al. [1] by incorporating both the ionic [2] and relativistic corrections [3] is proposed for evaluating the electron impact K -shell ionization cross sections of neutral atomic targets. Present results for 30 atomic targets with atomic number Z=1 -- 92 for incident energies up to E=2 GeV, agree well with available experimental cross sections. Comparisons with other theoretical findings will also be presented at the conference. [1] H. Deutsh, K. Becker, T. D. Mark, Int. J. Mass Spect. 177, 47 (1998). [2] M. A. Uddin, A. K. F. Haque, M. M. Billah, A. K. Basak, K. R. Karim, B. C. Saha, Phys. Rev. A 71, 032715 (2005).; Phys. Rev. A 73, 012708 (2006). [3] M. Gryzinski, Phys. Rev 138, 336 (1965).

Why K, L, M. . .?

NASA Astrophysics Data System (ADS)

Hayn, Carl H.

2000-09-01

The innermost atomic shells received the designations K, L, M in a circuitious way. Barkla had assigned these letters to the x-ray series that he observed. Later Kossel introduced these same names to the atomic levels at which the various x-ray transitions terminated.

Defect-Induced Nucleation and Epitaxy: A New Strategy toward the Rational Synthesis of WZ-GaN/3C-SiC Core-Shell Heterostructures.

PubMed

Liu, Baodan; Yang, Bing; Yuan, Fang; Liu, Qingyun; Shi, Dan; Jiang, Chunhai; Zhang, Jinsong; Staedler, Thorsten; Jiang, Xin

2015-12-09

In this work, we demonstrate a new strategy to create WZ-GaN/3C-SiC heterostructure nanowires, which feature controllable morphologies. The latter is realized by exploiting the stacking faults in 3C-SiC as preferential nucleation sites for the growth of WZ-GaN. Initially, cubic SiC nanowires with an average diameter of ∼100 nm, which display periodic stacking fault sections, are synthesized in a chemical vapor deposition (CVD) process to serve as the core of the heterostructure. Subsequently, hexagonal wurtzite-type GaN shells with different shapes are grown on the surface of 3C-SiC wire core. In this context, it is possible to obtain two types of WZ-GaN/3C-SiC heterostructure nanowires by means of carefully controlling the corresponding CVD reactions. Here, the stacking faults, initially formed in 3C-SiC nanowires, play a key role in guiding the epitaxial growth of WZ-GaN as they represent surface areas of the 3C-SiC nanowires that feature a higher surface energy. A dedicated structural analysis of the interfacial region by means of high-resolution transmission electron microscopy (HRTEM) revealed that the disordering of the atom arrangements in the SiC defect area promotes a lattice-matching with respect to the WZ-GaN phase, which results in a preferential nucleation. All WZ-GaN crystal domains exhibit an epitaxial growth on 3C-SiC featuring a crystallographic relationship of [12̅10](WZ-GaN) //[011̅](3C-SiC), (0001)(WZ-GaN)//(111)(3C-SiC), and d(WZ-GaN(0001)) ≈ 2d(3C-SiC(111)). The approach to utilize structural defects of a nanowire core to induce a preferential nucleation of foreign shells generally opens up a number of opportunities for the epitaxial growth of a wide range of semiconductor nanostructures which are otherwise impossible to acquire. Consequently, this concept possesses tremendous potential for the applications of semiconductor heterostructures in various fields such as optics, electrics, electronics, and photocatalysis for energy harvesting and environment processing.

Tailoring the surface chemical bond states of the NbN films by doping Ag: Achieving hard hydrophobic surface

NASA Astrophysics Data System (ADS)

Ren, Ping; Zhang, Kan; Du, Suxuan; Meng, Qingnan; He, Xin; Wang, Shuo; Wen, Mao; Zheng, Weitao

2017-06-01

Robust hydrophobic surfaces based on ceramics capable of withstanding harsh conditions such as abrasion, erosion and high temperature, are required in a broad range of applications. The metal cations with coordinative saturation or low electronegativity are commonly chosen to achieve the intrinsically hydrophobic ceramic by reducing Lewis acidity, and thus the ceramic systems are limited. In this work, we present a different picture that robust hydrophobic surface with high hardness (≥20 GPa) can be fabricated through doping Ag atoms into intrinsically hydrophilic ceramic film NbN by reactive co-sputtering. The transition of wettability from hydrophilic to hydrophobic of Nb-Ag-N films induced by Ag doping results from the appearance of Ag2O groups on the films surfaces through self-oxidation, because Ag cations (Ag+) in Ag2O are the filled-shell (4d105S0) electronic structure with coordinative saturation that have no tendency to interact with water. The results show that surface Ag2O benefited for hydrophobicity comes from the solute Ag atoms rather than precipitate metal Ag, in which the more Ag atoms incorporated into Nb-sublattice are able to further improve the hydrophobicity, whereas the precipitation of Ag nanoclusters would worsen it. The present work opens a window for fabricating robust hydrophobic surface through tailoring surface chemical bond states by doping Ag into transition metal nitrides.

Nitrogen Fixation by Photochemistry in the Atmosphere of Titan and Implications for Prebiotic Chemistry

NASA Astrophysics Data System (ADS)

Balucani, Nadia

The observation of N-containing organic molecules and the composition of the haze aerosols, as determined by the Aerosol Collector and Pyrolyser (ACP) on-board Huygens, are clear indications that some chemistry involving nitrogen active forms and hydrocarbons is operative in the upper atmosphere of Titan. Neutral-neutral reactions involving the first electronically excited state of atomic nitrogen, N(2D), and small hydrocarbons have the right prerequisites to be among the most significant pathways to formation of nitriles, imines and other simple N-containing organic molecules. The closed-shell products methanimine, ethanimine, ketenimine, 2H-azirine and the radical products CH3N, HCCN and CH2NCH can be the intermediate molecular species that, via addition reactions, polymerization and copolymerization form the N-rich organic aerosols of Titan as well as tholins in bulk reactors simulating Titan's atmosphere.

Analysis of the Structures and Properties of (GaSb)n (n = 4-9) Clusters through Density Functional Theory.

PubMed

Lu, Qi Liang; Luo, Qi Quan; Huang, Shou Guo; Li, Yi De; Wan, Jian Guo

2016-07-07

An optimization strategy combining global semiempirical quantum mechanical search with all-electron density functional theory was adopted to determine the lowest energy structure of (GaSb)n clusters up to n = 9. The growth pattern of the clusters differed from those of previously reported group III-V binary clusters. A cagelike configuration was found for cluster sizes n ≤ 7. The structure of (GaSb)6 deviated from that of other III-V clusters. Competition existed between core-shell and hollow cage structures of (GaSb)7. Novel noncagelike structures were energetically preferred over the cages for the (GaSb)8 and (GaSb)9 clusters. Electronic properties, such as vertical ionization potential, adiabatic electron affinities, HOMO-LUMO gaps, and average on-site charges on Ga or Sb atoms, as well as binding energies, were computed.

Insight into π-hole interactions containing the inorganic heterocyclic compounds S2N2/SN2P2.

PubMed

Lu, Bo; Zhang, Xueying; Meng, Lingpeng; Zeng, Yanli

2017-08-01

Similar to σ-hole interactions, the π-hole interaction has attracted much attention in recent years. According to the positive electrostatic potentials above and below the surface of inorganic heterocyclic compounds S 2 N 2 and three SN 2 P 2 isomers (heterocyclic compounds 1-4), and the negative electrostatic potential outside the X atom of XH 3 (X = N, P, As), S 2 N 2 /SN 2 P 2 ⋯XH 3 (X = N, P, As) complexes were constructed and optimized at the MP2/aug-cc-pVTZ level. The X atom of XH 3 (X = N, P, As) is almost perpendicular to the ring of the heterocyclic compounds. The π-hole interaction energy becomes greater as the trend goes from 1⋯XH 3 to 4⋯XH 3 . These π-hole interactions are weak and belong to "closed-shell" noncovalent interactions. According to the energy decomposition analysis, of the three attractive terms, the dispersion energy contributes more than the electrostatic energy. The polarization effect also plays an important role in the formation of π-hole complexes, with the contrasting phenomena of decreasing electronic density in the π-hole region and increasing electric density outside the X atom of XH 3 (X = N, P, As). Graphical abstract Computed density difference plots for the complexes 3⋯NH 3 (a 1 ), 3⋯PH 3 (b 1 ), 3⋯AsH 3 (c 1 ) and electron density shifts for the complexes 3⋯NH 3 (a 2 ), 3⋯PH 3 (b 2 ),3⋯AsH 3 (c 2 ) on the 0.001 a.u. contour.

Low-temperature nanosolders

DOEpatents

Boyle, Timothy J.; Lu, Ping; Vianco, Paul T.; Chandross, Michael E.

2016-10-11

A nanosolder comprises a first metal nanoparticle core coated with a second metal shell, wherein the first metal has a higher surface energy and smaller atomic size than the second metal. For example, a bimetallic nanosolder can comprise a protective Ag shell "glued" around a reactive Cu nanoparticle. As an example, a 3-D epitaxial Cu-core and Ag-shell structure was generated from a mixture of copper and silver nanoparticles in toluene at temperatures as low as 150.degree. C.

Dielectronic recombination of the 4p and 4d open sub-shell tungsten ions

NASA Astrophysics Data System (ADS)

Li, M. J.; Fu, Y. B.; Zhang, G. D.; Zhang, Y. Z.; Dong, C. Z.; Koike, F.

2014-04-01

Dielectronic recombination rate coefficients are given theoretically for several highly charged tungsten ions. As 4p open sub-shell ions, Ga-, Ge-, As-, Br-, Kr-like ions are considered. Rb-like ion is further considered as a 4d open sub-shell ion. Theoretical calculations are carried out using a relativistic atomic code FAC. The effect of configuration interaction is taking into account. Inner-shell electron excitations play a significant role for the dielectronic recombination process. Simple analytical formulae are given for the total rate coefficients by fitting to the presently obtained numerical results.

Direct evidence for radiative charge transfer after inner-shell excitation and ionization of large clusters

NASA Astrophysics Data System (ADS)

Hans, Andreas; Stumpf, Vasili; Holzapfel, Xaver; Wiegandt, Florian; Schmidt, Philipp; Ozga, Christian; Reiß, Philipp; Ben Ltaief, Ltaief; Küstner-Wetekam, Catmarna; Jahnke, Till; Ehresmann, Arno; Demekhin, Philipp V.; Gokhberg, Kirill; Knie, André

2018-01-01

We directly observe radiative charge transfer (RCT) in Ne clusters by dispersed vacuum-ultraviolet photon detection. The doubly ionized Ne2+-{{{N}}{{e}}}n-1 initial states of RCT are populated after resonant 1s-3p photoexcitation or 1s photoionization of Ne n clusters with < n> ≈ 2800. These states relax further producing Ne+-Ne+-{{{N}}{{e}}}n-2 final states, and the RCT photon is emitted. Ab initio calculations assign the observed RCT signal to the{}{{{N}}{{e}}}2+(2{{{p}}}-2{[}1{{D}}]){--}{{{N}}{{e}}}n-1 initial state, while transitions from other possible initial states are proposed to be quenched by competing relaxation processes. The present results are in agreement with the commonly discussed scenario, where the doubly ionized atom in a noble gas cluster forms a dimer which dissipates its vibrational energy on a picosecond timescale. Our study complements the picture of the RCT process in weakly bound clusters, providing information which is inaccessible by charged particle detection techniques.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scott, Aubrey D.; Pelmenschikov, Vladimir; Guo, Yisong

The properties of CO-inhibited Azotobacter vinelandii (Av) Mo-nitrogenase (N 2ase) have been examined by the combined application of nuclear resonance vibrational spectroscopy (NRVS), extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT). Dramatic changes in the NRVS are seen under high-CO conditions, especially in a 188 cm –1 mode associated with symmetric breathing of the central cage of the FeMo-cofactor. Similar changes are reproduced with the α-H195Q N 2ase variant. In the frequency region above 450 cm –1, additional features are seen that are assigned to Fe-CO bending and stretching modes (confirmed by 13CO isotope shifts). The EXAFSmore » for wild-type N 2ase shows evidence for a significant cluster distortion under high-CO conditions, most dramatically in the splitting of the interaction between Mo and the shell of Fe atoms originally at 5.08 Å in the resting enzyme. A DFT model with both a terminal ₋CO and a partially reduced ₋CHO ligand bound to adjacent Fe sites is consistent with both earlier FT-IR experiments, and the present EXAFS and NRVS observations for the wild-type enzyme. Another DFT model with two terminal CO ligands on the adjacent Fe atoms yields Fe-CO bands consistent with the α-H195Q variant NRVS. The calculations also shed light on the vibrational “shake” modes of the interstitial atom inside the central cage, and their interaction with the Fe-CO modes. We discuss implications for the CO and N 2 reactivity of N 2ase.« less

Nuclear Structure of 186Re

DTIC Science & Technology

2016-12-24

D population-depopulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 AME Atomic Mass Evaluation...this mass region are important for validating models of nuclear structure and reactions. The ENSDF feeds a specific data library relevant to nuclear...spherically asymmetric. Spherical asymmetry is common for nuclei between shell closures, such as those in the mid-shell 150  A  190 mass range of interest

Acetabular shell deformation as a function of shell stiffness and bone strength.

PubMed

Dold, Philipp; Pandorf, Thomas; Flohr, Markus; Preuss, Roman; Bone, Martin C; Joyce, Tom J; Holland, James; Deehan, David

2016-04-01

Press-fit acetabular shells used for hip replacement rely upon an interference fit with the bone to provide initial stability. This process may result in deformation of the shell. This study aimed to model shell deformation as a process of shell stiffness and bone strength. A cohort of 32 shells with two different wall thicknesses (3 and 4 mm) and 10 different shell sizes (44- to 62-mm outer diameter) were implanted into eight cadavers. Shell deformation was then measured in the cadavers using a previously validated ATOS Triple Scan III optical system. The shell-bone interface was then considered as a spring system according to Hooke's law and from this the force exerted on the shell by the bone was calculated using a combined stiffness consisting of the measured shell stiffness and a calculated bone stiffness. The median radial stiffness for the 3-mm wall thickness was 4192 N/mm (range, 2920-6257 N/mm), while for the 4-mm wall thickness the median was 9633 N/mm (range, 6875-14,341 N/mm). The median deformation was 48 µm (range, 3-187 µm), while the median force was 256 N (range, 26-916 N). No statistically significant correlation was found between shell stiffness and deformation. Deformation was also found to be not fully symmetric (centres 180° apart), with a median angle discrepancy of 11.5° between the two maximum positive points of deformation. Further work is still required to understand how the bone influences acetabular shell deformation. © IMechE 2016.

Site-resolved imaging of a bosonic Mott insulator using ytterbium atoms

NASA Astrophysics Data System (ADS)

Miranda, Martin; Inoue, Ryotaro; Tambo, Naoki; Kozuma, Mikio

2017-10-01

We demonstrate site-resolved imaging of a strongly correlated quantum system without relying on laser cooling techniques during fluorescence imaging. We observe the formation of Mott shells in the insulating regime and realize thermometry in an atomic cloud. This work proves the feasibility of the noncooled approach and opens the door to extending the detection technology to new atomic species.

Nanomechanical properties of phospholipid microbubbles.

PubMed

Buchner Santos, Evelyn; Morris, Julia K; Glynos, Emmanouil; Sboros, Vassilis; Koutsos, Vasileios

2012-04-03

This study uses atomic force microscopy (AFM) force-deformation (F-Δ) curves to investigate for the first time the Young's modulus of a phospholipid microbubble (MB) ultrasound contrast agent. The stiffness of the MBs was calculated from the gradient of the F-Δ curves, and the Young's modulus of the MB shell was calculated by employing two different mechanical models based on the Reissner and elastic membrane theories. We found that the relatively soft phospholipid-based MBs behave inherently differently to stiffer, polymer-based MBs [Glynos, E.; Koutsos, V.; McDicken, W. N.; Moran, C. M.; Pye, S. D.; Ross, J. A.; Sboros, V. Langmuir2009, 25 (13), 7514-7522] and that elastic membrane theory is the most appropriate of the models tested for evaluating the Young's modulus of the phospholipid shell, agreeing with values available for living cell membranes, supported lipid bilayers, and synthetic phospholipid vesicles. Furthermore, we show that AFM F-Δ curves in combination with a suitable mechanical model can assess the shell properties of phospholipid MBs. The "effective" Young's modulus of the whole bubble was also calculated by analysis using Hertz theory. This analysis yielded values which are in agreement with results from studies which used Hertz theory to analyze similar systems such as cells.

Shell structures of assemblies of equicharged particles subject to radial power-law confining potentials.

PubMed

Cioslowski, Jerzy

2010-12-21

Constituting the simplest generalization of spherical Coulomb crystals, assemblies of N equicharged particles confined by radial potentials proportional to the λth power of distance are amenable to rigorous analysis within the recently introduced shell model. Thanks to the power scaling of the confining potential and the resulting pruning property of the shell configurations (i.e., the lists of shell occupancies), the shell-model estimates of the energies and the mean radii of such assemblies at equilibrium geometries follow simple recursive formulas. The formulas greatly facilitate derivations of the first two leading terms in the large-N asymptotics of these estimates, which are given by power series in ξ(4/3) N(-2/3), where -(ξ/2) n(3/2) is the leading angular-correlation correction to the minimum energy of n electrons on the surface of a sphere with a unit radius (the solution of the Thomson problem). Although the scaled occupancies of the outermost shells conform to a universal scaling law, the actual filling of the shells tends to follow rather irregular patterns that vary strongly with λ. However, the number of shells K(N) for a given N decreases in general upon an increase in the power-law exponent, which is due to the (λ + 1)(2) ξ(2) dependence of shell capacities that roughly measure the maximum numbers of particles sustainable within individual shells. Several types of configuration transitions (i.e., the changes in the number of shells upon addition of one particle) are observed in the crystals with up to 10,000 particles and integer values of λ between 1 and 10, but the rule |K(N + 1)-K(N)| ≤ 1 is found to be strictly obeyed.

High-resolution nitrogen stable isotope sclerochronology of bivalve shell carbonate-bound organics

NASA Astrophysics Data System (ADS)

Gillikin, David P.; Lorrain, Anne; Jolivet, Aurélie; Kelemen, Zita; Chauvaud, Laurent; Bouillon, Steven

2017-03-01

Nitrogen stable isotope ratios (δ15N) of organic material have successfully been used to track food-web dynamics, nitrogen baselines, pollution, and nitrogen cycling. Extending the δ15N record back in time has not been straightforward due to a lack of suitable substrates in which δ15N records are faithfully preserved, thus sparking interest in utilizing skeletal carbonate-bound organic matter (CBOM) in mollusks, corals, and foraminifera. Here we test if calcite Pecten maximus shells from the Bay of Brest and the French continental shelf can be used as an archive of δ15N values over a large environmental gradient and at a high temporal resolution (approximately weekly). Bulk CBOM δ15N values from the growing tip of shells collected over a large nitrogen isotope gradient were strongly correlated with adductor muscle tissue δ15N values (R2 = 0.99, n = 6, p < 0.0001). We were able to achieve weekly resolution (on average) over the growing season from sclerochronological profiles of three shells, which showed large seasonal variations up to 3.4‰. However, there were also large inter-specimen differences (up to 2.5‰) between shells growing at the same time and location. Generally, high-resolution shell δ15N values follow soft-tissue δ15N values, but soft-tissues integrate more time, hence soft-tissue data are more time-averaged and smoothed. Museum-archived shells from the 1950s, 1965, and 1970s do not show a large difference in δ15N values through time despite expected increasing N loading to the Bay over this time, which could be due to anthropogenic N sources with contrasting values. Compiling shell CBOM δ15N data from several studies suggests that the offset between soft-tissue and shell δ15N values (Δtissue-shell) differs between calcite and aragonite shells. We hypothesize that this difference is caused by differences in amino acids used in constructing the different minerals, which should be specific to the CaCO3 polymorph being constructed. Future work should use compound specific isotope analyses (CSIA) to test this hypothesis, and to determine whether certain amino acids could specifically track N sources or possibly identify amino acids that are more resistant to diagenesis in fossil shells. In conclusion, bivalve shell CBOM δ15N values can be used in a similar manner to soft-tissue δ15N values, and can track various biogeochemical events at a very high-resolution.

Laser ablation of Au-CuO core-shell nanocomposite in water for optoelectronic devices

NASA Astrophysics Data System (ADS)

Ismail, Raid A.; Abdul-Hamed, Ryam S.

2017-12-01

Core-shell gold-copper oxide Au-CuO nanocomposites were synthesized using laser ablation of CuO target in colloidal solution of Au nanoparticles (NPs). The effect of laser fluence on the structural, morphological, electrical, and optical properties of Au-CuO nanocomposites was investigated using x-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL), Fourier transformed infrared spectroscopy (FTIR), Hall measurement, and UV-vis spectroscopy. X-ray diffraction results confirm the formation of polycrystalline Au-CuO NPs with monoclinic structure. The optical energy gap for CuO was 4 eV and for the Au-CuO core-shell nanocomposites was found to be in the range of 3.4-3.7 eV. SEM and TEM investigations revealed that the structure and morphology of Au-CuO core-shell nanocomposites were strongly depending on the laser fluence. A formation of Au-CuO nanospheres and platelets structures was observed. The photoluminescence data showed an emission of broad visible peaks between 407 and 420 nm. The effect of laser fluence on the dark and illuminated I-V characteristics of Au-CuO/n-Si heterojunction photodetectors was investigated and analyzed. The experimental data demonstrated that the photodetector prepared at optimum laser fluence exhibited photosensitivity of 0.6 AW-1 at 800 nm.

M shell X-ray production cross sections and fluorescence yields for the elements with 71 <= Z <= 92 using 5.96 keV photons

NASA Astrophysics Data System (ADS)

Puri, S.; Mehta, D.; Chand, B.; Singh, Nirmal; Mangal, P. C.; Trehan, P. N.

1993-03-01

Total M X-ray production (XRP) cross sections for ten elements in the atomic number region 71 ≤ Z ≤ 92 were measured at 5.96 keV incident photon energy. The average M shell fluorescence yields < overlineωM> have also been computed using the present measured cross section values and the theoretical M shell photoionisation cross sections. The results are compared with theoretical values.

The phase diagrams of a spin 1/2 core and a spin 1 shell nanoparticle with a disordered interface

NASA Astrophysics Data System (ADS)

Zaim, N.; Zaim, A.; Kerouad, M.

2016-12-01

The critical and compensation behaviors, of a spherical ferrimagnetic nanoparticle, consisting of a ferromagnetic core of spin-1/2 A atoms, a ferromagnetic shell of spin-1 B atoms and a disordered interface in between that is characterized by a random arrangement of A and B atoms of ApB1-p type and a negative A - B coupling, are studied. The ground state phase diagrams of the system have been determined in the (JAB, D/jA) and (JB, D/jA) planes. Monte Carlo simulation based on Metropolis algorithm has been used to study the effects of the concentration parameter p, the crystal field, the coupling between B - B atoms jB and the antiferromagnetic interface coupling jAB on the phase diagrams and the magnetic properties of the system. It has been found that one, two or even three compensation point(s) can appear for appropriate values of the system parameters.

Molecular dynamics investigation of water-exchange reactions on lanthanide ions in water/1-ethyl-3-methylimidazolium trifluoromethylsufate ([EMIm][OTf])

NASA Astrophysics Data System (ADS)

Tu, Yi-Jung; Lin, Zhijin; Allen, Matthew J.; Cisneros, G. Andrés

2018-01-01

We report a kinetic study of the water exchange on lanthanide ions in water/[1-ethyl-3-methylimidazolium][trifluoromethylsufate] (water/[EMIm][OTf]). The results from 17O-NMR measurements show that the water-exchange rates in water/[EMIm][OTf] increase with decreasing size of the lanthanide ions. This trend for water-exchange is similar to the previously reported trend in water/1-ethyl-3-methylimidazolium ethyl sulfate (water/[EMIm][EtSO4]) but opposite to that in water. To gain atomic-level insight into these water-exchange reactions, molecular dynamics simulations for lanthanide ions in water/[EMIm][OTf] have been performed using the atomic-multipole-optimized-energetics-for-biomolecular-application polarizable force field. Our molecular dynamics simulations reproduce the experimental water-exchange rates in terms of the trend and provide possible explanations for the observed experimental behavior. The smaller lanthanide ions in water/[EMIm][OTf] undergo faster water exchange because the smaller lanthanide ions coordinate to the first shell [OTf]- anions more tightly, resulting in a stronger screening effect for the second-shell water. The screening effect weakens the interaction of the lanthanide ions with the second-shell water molecules, facilitating the dissociation of water from the second-shell and subsequent association of water molecules from the outer solvation shells.

Molecular dynamics investigation of water-exchange reactions on lanthanide ions in water/1-ethyl-3-methylimidazolium trifluoromethylsufate ([EMIm][OTf]).

PubMed

Tu, Yi-Jung; Lin, Zhijin; Allen, Matthew J; Cisneros, G Andrés

2018-01-14

We report a kinetic study of the water exchange on lanthanide ions in water/[1-ethyl-3-methylimidazolium][trifluoromethylsufate] (water/[EMIm][OTf]). The results from 17 O-NMR measurements show that the water-exchange rates in water/[EMIm][OTf] increase with decreasing size of the lanthanide ions. This trend for water-exchange is similar to the previously reported trend in water/1-ethyl-3-methylimidazolium ethyl sulfate (water/[EMIm][EtSO 4 ]) but opposite to that in water. To gain atomic-level insight into these water-exchange reactions, molecular dynamics simulations for lanthanide ions in water/[EMIm][OTf] have been performed using the atomic-multipole-optimized-energetics-for-biomolecular-application polarizable force field. Our molecular dynamics simulations reproduce the experimental water-exchange rates in terms of the trend and provide possible explanations for the observed experimental behavior. The smaller lanthanide ions in water/[EMIm][OTf] undergo faster water exchange because the smaller lanthanide ions coordinate to the first shell [OTf] - anions more tightly, resulting in a stronger screening effect for the second-shell water. The screening effect weakens the interaction of the lanthanide ions with the second-shell water molecules, facilitating the dissociation of water from the second-shell and subsequent association of water molecules from the outer solvation shells.

Core-shell-structured nanothermites synthesized by atomic layer deposition

NASA Astrophysics Data System (ADS)

Qin, Lijun; Gong, Ting; Hao, Haixia; Wang, Keyong; Feng, Hao

2013-12-01

Thermite materials feature very exothermic solid-state redox reactions. However, the energy release rates of traditional thermite mixtures are limited by the reactant diffusion velocities. In this work, atomic layer deposition (ALD) is utilized to synthesize thermite materials with greatly enhanced reaction rates. By depositing certain types of metal oxides (oxidizers) onto a commercial Al nanopowder, core-shell-structured nanothermites can be produced. The average film deposition rate on the Al nanopowder is 0.17 nm/cycle for ZnO and 0.031 nm/cycle for SnO2. The thickness of the oxidizer layer can be precisely controlled by adjusting the ALD cycle number. The compositions, morphologies, and structures of the ALD nanothermites are characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The characterization results reveal nearly perfect coverage of the Al nanoparticles by uniform ALD oxidizer layers and confirm the formation of core-shell nanoparticles. Combustion properties of the nanothermites are probed by laser ignition technique. Reactions of the core-shell-structured nanothermites are several times faster than the mixture of nanopowders. The promoted reaction rate is mostly attributed to the uniform distribution of reactants on the nanometer scale. These core-shell-structured nanothermites provide a potential pathway to control and enhance thermite reactions.

Cargo-shell and cargo-cargo couplings govern the mechanics of artificially loaded virus-derived cages

NASA Astrophysics Data System (ADS)

Llauró, Aida; Luque, Daniel; Edwards, Ethan; Trus, Benes L.; Avera, John; Reguera, David; Douglas, Trevor; Pablo, Pedro J. De; Castón, José R.

2016-04-01

Nucleic acids are the natural cargo of viruses and key determinants that affect viral shell stability. In some cases the genome structurally reinforces the shell, whereas in others genome packaging causes internal pressure that can induce destabilization. Although it is possible to pack heterologous cargoes inside virus-derived shells, little is known about the physical determinants of these artificial nanocontainers' stability. Atomic force and three-dimensional cryo-electron microscopy provided mechanical and structural information about the physical mechanisms of viral cage stabilization beyond the mere presence/absence of cargos. We analyzed the effects of cargo-shell and cargo-cargo interactions on shell stability after encapsulating two types of proteinaceous payloads. While bound cargo to the inner capsid surface mechanically reinforced the capsid in a structural manner, unbound cargo diffusing freely within the shell cavity pressurized the cages up to ~30 atm due to steric effects. Strong cargo-cargo coupling reduces the resilience of these nanocompartments in ~20% when bound to the shell. Understanding the stability of artificially loaded nanocages will help to design more robust and durable molecular nanocontainers.Nucleic acids are the natural cargo of viruses and key determinants that affect viral shell stability. In some cases the genome structurally reinforces the shell, whereas in others genome packaging causes internal pressure that can induce destabilization. Although it is possible to pack heterologous cargoes inside virus-derived shells, little is known about the physical determinants of these artificial nanocontainers' stability. Atomic force and three-dimensional cryo-electron microscopy provided mechanical and structural information about the physical mechanisms of viral cage stabilization beyond the mere presence/absence of cargos. We analyzed the effects of cargo-shell and cargo-cargo interactions on shell stability after encapsulating two types of proteinaceous payloads. While bound cargo to the inner capsid surface mechanically reinforced the capsid in a structural manner, unbound cargo diffusing freely within the shell cavity pressurized the cages up to ~30 atm due to steric effects. Strong cargo-cargo coupling reduces the resilience of these nanocompartments in ~20% when bound to the shell. Understanding the stability of artificially loaded nanocages will help to design more robust and durable molecular nanocontainers. Electronic supplementary information (ESI) available: 6 figures, 3 tables and theory. See DOI: 10.1039/c6nr01007e

Time-resolved atomic inner-shell spectroscopy

NASA Astrophysics Data System (ADS)

Drescher, M.; Hentschel, M.; Kienberger, R.; Uiberacker, M.; Yakovlev, V.; Scrinzi, A.; Westerwalbesloh, Th.; Kleineberg, U.; Heinzmann, U.; Krausz, F.

2002-10-01

The characteristic time constants of the relaxation dynamics of core-excited atoms have hitherto been inferred from the linewidths of electronic transitions measured by continuous-wave extreme ultraviolet or X-ray spectroscopy. Here we demonstrate that a laser-based sampling system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows us to trace these dynamics directly in the time domain with attosecond resolution. We have measured a lifetime of 7.9-0.9^{+1.0fs of M-shell vacancies of krypton in such a pump-probe experiment.}

Observation of Interspecies Ion Separation in Inertial-Confinement-Fusion Implosions via Imaging X-ray spectroscopy

NASA Astrophysics Data System (ADS)

Joshi, Tirtha Raj

2016-10-01

Interspecies ion separation has been proposed as a yield-degradation mechanism in inertial-confinement-fusion (ICF) experiments. We present direct experimental evidence of interspecies ion separation in direct-drive ICF experiments performed at the OMEGA laser facility. These experiments were designed based on the fact that interspecies ion thermo-diffusion would be strongest for species with large mass and charge difference. The targets were spherical plastic shells filled with D2 and Ar (1% by atom). Ar K-shell spectral features were observed primarily between the time of first-shock convergence and slightly before neutron bang time, using a time- and space-integrated spectrometer, streaked crystal spectrometer, and two gated multi-monochromatic X-ray imagers fielded along quasi-orthogonal lines-of-sight. Detailed spectroscopic analyses of spatially resolved Ar K-shell lines reveal deviation from the initial 1%-Ar gas fill and show both Ar-concentration enhancement and depletion at different times and radial positions of the implosion. The experimental results are interpreted with radiation-hydrodynamic simulations that include recently implemented, first-principles models of interspecies ion diffusion. The experimentally inferred Ar-atom-fraction profiles agree gently with calculated profiles associated with the incoming and rebounding first shock. This work was done in collaboration with P. Hakel, S. C. Hsu, E. L. Vold, M. J. Schmitt, N. M. Hoffman, R. M. Rauenzahn, G. Kagan, X.-Z. Tang, Y. Kim, and H. W. Herrmann of LANL, and R. C. Mancini of UNR. LA-UR-16-24804. Supported by the LANL ICF and ASC Programs under US-DoE contract no. DE-AC52-06NA25396.

Comparative study of the double-K -shell-vacancy production in single- and double-electron-capture decay

NASA Astrophysics Data System (ADS)

Ratkevich, S. S.; Gangapshev, A. M.; Gavrilyuk, Yu. M.; Karpeshin, F. F.; Kazalov, V. V.; Kuzminov, V. V.; Panasenko, S. I.; Trzhaskovskaya, M. B.; Yakimenko, S. P.

2017-12-01

Background: A double-K -electron capture is a rare nuclear-atomic process in which two K electrons are captured simultaneously from the atomic shell. A "hollow atom" is created as a result of this process. In single-K -shell electron-capture decays, there is a small probability that the second electron in the K shell is excited to an unoccupied level or can (mostly) be ejected to the continuum. In either case, a double vacancy is created in the K shell. The relaxation of the double-K -shell vacancy, accompanied by the emission of two K -fluorescence photons, makes it possible to perform experimental studies of such rare processes with the large-volume proportional gas chamber. Purpose: The purpose of the present analysis is to estimate a double-K -shell vacancy creation probability per K -shell electron capture PK K of 81Kr, as well as to measure the half-life of 78Kr relative to 2 ν 2 K capture. Method: Time-resolving current pulse from the large low-background proportional counter (LPC), filled with the krypton sample, was applied to detect triple coincidences of "shaked" electrons and two fluorescence photons. Results: The number of K -shell vacancies per the K -electron capture, produced as a result of the shake-off process, has been measured for the decay of 81Kr. The probability for this decay was found to be PK K=(5.7 ±0.8 ) ×10-5 with a systematic error of (ΔPKK) syst=±0.4 ×10-5 . For the 78Kr(2 ν 2 K ) decay, the comparative study of single- and double-capture decays allowed us to obtain the signal-to-background ratio up to 15/1. The half-life T1/2 2 ν 2 K(g .s .→g .s .) =[1 .9-0.7+1.3(stat) ±0.3 (syst) ] ×1022 y is determined from the analysis of data that have been accumulated over 782 days of live measurements in the experiment that used samples consisted of 170.6 g of 78Kr. Conclusions: The data collected during low background measurements using the LPC were analyzed to search the rare atomic and nuclear processes. We have determined PKK exp for the E C decay of 81Kr, which are in satisfactory agreement with Z-2 dependence of PK K predicted by Primakoff and Porter. This made possible to more accurately determine the background contribution in the energy region of our interest for the search for the 2 K capture in 78Kr. The general procedure of data analysis allowed us to determine the half-life of 78Kr relative to 2 ν 2 K transition with a greater statistical accuracy than in our previous works.

Atomic structure considerations for the low-temperature opacity of Sn

DOE PAGES

Colgan, J.; Kilcrease, D. P.; Abdallah, J.; ...

2017-03-31

Here, we have begun a preliminary investigation into the opacity of Sn at low temperatures (< 50 eV). The emissivity and opacity of Sn is a crucial factor in determining the utility of Sn in EUV lithography, with numerous industrial implications. To this end, we have been exploring the accuracy of some approximations used in opacity models for the relevant ion stages of Sn (neutral through ~ 18 times ionized). We also find that the use of intermediate-coupling, as compared to full configuration-interaction, is not adequate to obtain accurate line positions of the important bound-bound transitions in Sn. One requiresmore » full configuration-interaction to properly describe the strong mixing between the various n=4 sub-shells that give rise to the Δn= 0 transitions that dominate the opacity spectrum at low temperatures. Furthermore, since calculations that include full configuration-interaction for large numbers of configurations quickly become computationally prohibitive, we have explored hybrid calculations, in which full configuration-interaction is retained for the most important transitions, while intermediate-coupling is employed for all other transitions. After extensive exploration of the atomic structure properties, local-thermodynamic-equilibrium (LTE) opacities are generated using the ATOMIC code at selected temperatures and densities and compared to experiment.« less

Atomic structure considerations for the low-temperature opacity of Sn

DOE Office of Scientific and Technical Information (OSTI.GOV)

Colgan, J.; Kilcrease, D. P.; Abdallah, J.

Here, we have begun a preliminary investigation into the opacity of Sn at low temperatures (< 50 eV). The emissivity and opacity of Sn is a crucial factor in determining the utility of Sn in EUV lithography, with numerous industrial implications. To this end, we have been exploring the accuracy of some approximations used in opacity models for the relevant ion stages of Sn (neutral through ~ 18 times ionized). We also find that the use of intermediate-coupling, as compared to full configuration-interaction, is not adequate to obtain accurate line positions of the important bound-bound transitions in Sn. One requiresmore » full configuration-interaction to properly describe the strong mixing between the various n=4 sub-shells that give rise to the Δn= 0 transitions that dominate the opacity spectrum at low temperatures. Furthermore, since calculations that include full configuration-interaction for large numbers of configurations quickly become computationally prohibitive, we have explored hybrid calculations, in which full configuration-interaction is retained for the most important transitions, while intermediate-coupling is employed for all other transitions. After extensive exploration of the atomic structure properties, local-thermodynamic-equilibrium (LTE) opacities are generated using the ATOMIC code at selected temperatures and densities and compared to experiment.« less

DFT Modeling of Cross-Linked Polyethylene: Role of Gold Atoms and Dispersion Interactions.

PubMed

Blaško, Martin; Mach, Pavel; Antušek, Andrej; Urban, Miroslav

2018-02-08

Using DFT modeling, we analyze the concerted action of gold atoms and dispersion interactions in cross-linked polyethylene. Our model consists of two oligomer chains (PEn) with 7, 11, 15, 19, or 23 carbon atoms in each oligomer cross-linked with one to three Au atoms through C-Au-C bonds. In structures with a single gold atom the C-Au-C bond is located in the central position of the oligomer. Binding energies (BEs) with respect to two oligomer radical fragments and Au are as high as 362-489 kJ/mol depending on the length of the oligomer chain. When the dispersion contribution in PEn-Au-PEn oligomers is omitted, BE is almost independent of the number of carbon atoms, lying between 293 and 296 kJ/mol. The dispersion energy contributions to BEs in PEn-Au-PEn rise nearly linearly with the number of carbon atoms in the PEn chain. The carbon-carbon distance in the C-Au-C moiety is around 4.1 Å, similar to the bond distance between saturated closed shell chains in the polyethylene crystal. BEs of pure saturated closed shell PEn-PEn oligomers are 51-187 kJ/mol. Both Au atoms and dispersion interactions contribute considerably to the creation of nearly parallel chains of oligomers with reasonably high binding energies.

Geometric Electron Models.

ERIC Educational Resources Information Center

Nika, G. Gerald; Parameswaran, R.

1997-01-01

Describes a visual approach for explaining the filling of electrons in the shells, subshells, and orbitals of the chemical elements. Enables students to apply the principles of atomic electron configuration while using manipulatives to model the building up of electron configurations as the atomic numbers of elements increase on the periodic…

Metal shell technology based upon hollow jet instability. [for inertial confinement fusion

NASA Technical Reports Server (NTRS)

Kendall, J. M.; Lee, M. C.; Wang, T. G.

1982-01-01

Spherical shells of submillimeter size are sought as ICF targets. Such shells must be dimensionally precise, smooth, of high strength, and composed of a high atomic number material. A technology for the production of shells based upon the hydrodynamic instability of an annular jet of molten metal is described. Shells in the 0.7-2.0 mm size range have been produced using tin as a test material. Specimens exhibit good sphericity, fair concentricity, and excellent finish over most of the surface. Work involving a gold-lead-antimony alloy is in progress. Droplets of this are amorphous and possess superior surface finish. The flow of tin models that of the alloy well; experiments on both metals show that the technique holds considerable promise.

In Situ Generation of Two-Dimensional Au–Pt Core–Shell Nanoparticle Assemblies

PubMed Central

2010-01-01

Two-dimensional assemblies of Au–Pt bimetallic nanoparticles are generated in situ on polyethyleneimmine (PEI) silane functionalized silicon and indium tin oxide (ITO) coated glass surfaces. Atomic force microscopy (AFM), UV–Visible spectroscopy, and electrochemical measurements reveal the formation of core–shell structure with Au as core and Pt as shell. The core–shell structure is further supported by comparing with the corresponding data of Au nanoparticle assemblies. Static contact angle measurements with water show an increase in hydrophilic character due to bimetallic nanoparticle generation on different surfaces. It is further observed that these Au–Pt core–shell bimetallic nanoparticle assemblies are catalytically active towards methanol electro-oxidation, which is the key reaction for direct methanol fuel cells (DMFCs). PMID:20651923

δ15N Values in Crassostrea virginica Shells Provides Early Direct Evidence for Nitrogen Loading to Chesapeake Bay

NASA Astrophysics Data System (ADS)

Black, H. D.; Andrus, C. F. T.; Lambert, W. J.; Rick, T. C.; Gillikin, D. P.

2017-03-01

Crassostrea virginica is one of the most common estuarine bivalves in the United States’ east coast and is frequently found in archaeological sites and sub-fossil deposits. Although there have been several sclerochronological studies on stable carbon and oxygen isotopes in the shells of this species, less is known about δ15N values within their shells, which could be a useful paleoenvironmental proxy to assess estuarine nitrogen dynamics. Modern C. virginica samples were collected in Chesapeake Bay for comparison with archaeological shells from nearby sites ranging in age from ~100 to 3,200 years old. Left valves were sampled by milling the hinge area and the resulting powder was analyzed for %N and δ15N values. Comparison of δ15N values between C. virginica shells shows relatively constant values from ~1250 BC to ~1800 AD. After ~1800 AD, there are rapid increases in 15N enrichment in the shells, which continue to increase in value up to the modern shell values. The increase in δ15N values is evidence of early anthropogenic impact in Chesapeake Bay. These results corroborate the observation that coastal nitrogen pollution occurred earlier than the 19th century and support the use of oyster shell δ15N values as a useful environmental proxy.

A hybrid neutron diffraction and computer simulation study on the solvation of N-methylformamide in dimethylsulfoxide

NASA Astrophysics Data System (ADS)

Cordeiro, João M. M.; Soper, Alan K.

2013-01-01

The solvation of N-methylformamide (NMF) by dimethylsulfoxide (DMSO) in a 20% NMF/DMSO liquid mixture is investigated using a combination of neutron diffraction augmented with isotopic substitution and Monte Carlo simulations. The aim is to investigate the solute-solvent interactions and the structure of the solution. The results point to the formation of a hydrogen bond (H-bond) between the H bonded to the N of the amine group of NMF and the O of DMSO particularly strong when compared with other H-bonded liquids. Moreover, a second cooperative H-bond is identified with the S atom of DMSO. As a consequence of these H-bonds, molecules of NMF and DMSO are rather rigidly connected, establishing very stable dimmers in the mixture and very well organized first and second solvation shells.

Direct mapping between exchange potentials of Hartree-Fock and Kohn-Sham schemes as origin of orbital proximity

NASA Astrophysics Data System (ADS)

Cinal, M.

2010-01-01

It is found that for closed-l-shell atoms, the exact local exchange potential vx(r) calculated in the exchange-only Kohn-Sham (KS) scheme of the density functional theory (DFT) is very well represented within the region of every atomic shell by each of the suitably shifted potentials obtained with the nonlocal Fock exchange operator for the individual Hartree-Fock (HF) orbitals belonging to this shell. This newly revealed property is not related to the well-known steplike shell structure in the response part of vx(r), but it results from specific relations satisfied by the HF orbital exchange potentials. These relations explain the outstanding proximity of the occupied HF and exchange-only KS orbitals as well as the high quality of the Krieger-Li-Iafrate and localized HF (or, equivalently, common-energy-denominator) approximations to the DFT exchange potential vx(r). Another highly accurate representation of vx(r) is given by the continuous piecewise function built of shell-specific exchange potentials, each defined as the weighted average of the shifted orbital exchange potentials corresponding to a given shell. The constant shifts added to the HF orbital exchange potentials, to map them onto vx(r), are nearly equal to the differences between the energies of the corresponding KS and HF orbitals. It is discussed why these differences are positive and grow when the respective orbital energies become lower for inner orbitals.

Charge-equilibrium and radiation of low-energy cosmic rays passing through interstellar medium

NASA Technical Reports Server (NTRS)

Rule, D. W.; Omidvar, K.

1977-01-01

The charge equilibrium and radiation of an oxygen and an iron beam in the MeV per nucleon energy range, representing a typical beam of low-energy cosmic rays passing through the interstellar medium, is considered. Electron loss of the beam has been taken into account by means of the First Born approximation allowing for the target atom to remain unexcited, or to be excited to all possible states. Electron capture cross sections have been calculated by means of the scaled Oppenheimer-Brinkman-Kramers approximation, taking into account all atomic shells of the target atoms. Radiation of the beam due to electron capture into the excited states of the ion, collisional excitation and collisional inner-shell ionization of the ions has been considered. Effective X-ray production cross sections and multiplicities for the most energetic X-ray lines emitted by the Fe and O beams have been calculated.

An experimental and theoretical study of the valence shell photoelectron spectra of 2-chloropyridine and 3-chloropyridine

NASA Astrophysics Data System (ADS)

Holland, D. M. P.; Powis, I.; Trofimov, A. B.; Menzies, R. C.; Potts, A. W.; Karlsson, L.; Badsyuk, I. L.; Moskovskaya, T. E.; Gromov, E. V.; Schirmer, J.

2017-10-01

The valence shell photoelectron spectra of 2-chloropyridine and 3-chloropyridine have been studied both experimentally and theoretically. Synchrotron radiation has been employed to record angle resolved photoelectron spectra in the photon energy range 20-100 eV, and these have enabled anisotropy parameters and branching ratios to be derived. The experimental results have been compared with theoretical predictions obtained using the continuum multiple scattering Xα approach. This comparison shows that the anisotropy parameter associated with the nominally chlorine lone-pair orbital lying in the molecular plane is strongly affected by the atomic Cooper minimum. In contrast, the photoionization dynamics of the second lone-pair orbital, orientated perpendicular to the molecular plane, seem relatively unaffected by this atomic phenomenon. The outer valence ionization has been studied theoretically using the third-order algebraic-diagrammatic construction (ADC(3)) approximation scheme for the one-particle Green's function, the outer valence Green's function method, and the equation-of-motion (EOM) coupled cluster (CC) theory at the level of the EOM-IP-CCSD and EOM-EE-CC3 models. The convergence of the results to the complete basis set limit has been investigated. The ADC(3) method has been employed to compute the complete valence shell ionization spectra of 2-chloropyridine and 3-chloropyridine. The relaxation mechanism for ionization of the nitrogen σ-type lone-pair orbital (σN LP) has been found to be different to that for the corresponding chlorine lone-pair (σCl LP). For the σN LP orbital, π-π* excitations play the main role in the screening of the lone-pair hole. In contrast, excitations localized at the chlorine site involving the chlorine πCl LP lone-pair and the Cl 4p Rydberg orbital are the most important for the σCl LP orbital. The calculated photoelectron spectra have allowed assignments to be proposed for most of the structure observed in the experimental spectra. The theoretical work also highlights the formation of satellite states, due to the breakdown of the single particle model of ionization, in the inner valence region.

An experimental and theoretical study of the valence shell photoelectron spectra of 2-chloropyridine and 3-chloropyridine.

PubMed

Holland, D M P; Powis, I; Trofimov, A B; Menzies, R C; Potts, A W; Karlsson, L; Badsyuk, I L; Moskovskaya, T E; Gromov, E V; Schirmer, J

2017-10-28

The valence shell photoelectron spectra of 2-chloropyridine and 3-chloropyridine have been studied both experimentally and theoretically. Synchrotron radiation has been employed to record angle resolved photoelectron spectra in the photon energy range 20-100 eV, and these have enabled anisotropy parameters and branching ratios to be derived. The experimental results have been compared with theoretical predictions obtained using the continuum multiple scattering Xα approach. This comparison shows that the anisotropy parameter associated with the nominally chlorine lone-pair orbital lying in the molecular plane is strongly affected by the atomic Cooper minimum. In contrast, the photoionization dynamics of the second lone-pair orbital, orientated perpendicular to the molecular plane, seem relatively unaffected by this atomic phenomenon. The outer valence ionization has been studied theoretically using the third-order algebraic-diagrammatic construction (ADC(3)) approximation scheme for the one-particle Green's function, the outer valence Green's function method, and the equation-of-motion (EOM) coupled cluster (CC) theory at the level of the EOM-IP-CCSD and EOM-EE-CC3 models. The convergence of the results to the complete basis set limit has been investigated. The ADC(3) method has been employed to compute the complete valence shell ionization spectra of 2-chloropyridine and 3-chloropyridine. The relaxation mechanism for ionization of the nitrogen σ-type lone-pair orbital (σ N LP ) has been found to be different to that for the corresponding chlorine lone-pair (σ Cl LP ). For the σ N LP orbital, π-π* excitations play the main role in the screening of the lone-pair hole. In contrast, excitations localized at the chlorine site involving the chlorine π Cl LP lone-pair and the Cl 4p Rydberg orbital are the most important for the σ Cl LP orbital. The calculated photoelectron spectra have allowed assignments to be proposed for most of the structure observed in the experimental spectra. The theoretical work also highlights the formation of satellite states, due to the breakdown of the single particle model of ionization, in the inner valence region.

Molecularly Tuning the Radicaloid N-H···O═C Hydrogen Bond.

PubMed

Lu, Norman; Chung, Wei-Cheng; Ley, Rebecca M; Lin, Kwan-Yu; Francisco, Joseph S; Negishi, Ei-Ichi

2016-03-03

Substituent effects on the open shell N-H···O═C hydrogen-bond has never been reported. This study examines how 12 functional groups composed of electron donating groups (EDG), halogen atoms and electron withdrawing groups (EWG) affect the N-H···O═C hydrogen-bond properties in a six-membered cyclic model system of O═C(Y)-CH═C(X)N-H. It is found that group effects on this open shell H-bonding system are significant and have predictive trends when X = H and Y is varied. When Y is an EDG, the N-H···O═C hydrogen-bond is strengthened; and when Y is an EWG, the bond is weakened; whereas the variation in electronic properties of X group do not exhibit a significant impact upon the hydrogen bond strength. The structural impact of the stronger N-H···O═C hydrogen-bond are (1) shorter H and O distance, r(H···O) and (2) a longer N-H bond length, r(NH). The stronger N-H···O═C hydrogen-bond also acts to pull the H and O in toward one another which has an effect on the bond angles. Our findings show that there is a linear relationship between hydrogen-bond angle and N-H···O═C hydrogen-bond energy in this unusual H-bonding system. In addition, there is a linear correlation of the r(H···O) and the hydrogen bond energy. A short r(H···O) distance corresponds to a large hydrogen bond energy when Y is varied. The observed trends and findings have been validated using three different methods (UB3LYP, M06-2X, and UMP2) with two different basis sets.

Shape-Controlled Synthesis of Colloidal Metal Nanocrystals by Replicating the Surface Atomic Structure on the Seed.

PubMed

Gilroy, Kyle D; Yang, Xuan; Xie, Shuifen; Zhao, Ming; Qin, Dong; Xia, Younan

2018-06-01

Controlling the surface structure of metal nanocrystals while maximizing the utilization efficiency of the atoms is a subject of great importance. An emerging strategy that has captured the attention of many research groups involves the conformal deposition of one metal as an ultrathin shell (typically 1-6 atomic layers) onto the surface of a seed made of another metal and covered by a set of well-defined facets. This approach forces the deposited metal to faithfully replicate the surface atomic structure of the seed while at the same time serving to minimize the usage of the deposited metal. Here, the recent progress in this area is discussed and analyzed by focusing on the synthetic and mechanistic requisites necessary for achieving surface atomic replication of precious metals. Other related methods are discussed, including the one-pot synthesis, electrochemical deposition, and skin-layer formation through thermal annealing. To close, some of the synergies that arise when the thickness of the deposited shell is decreased controllably down to a few atomic layers are highlighted, along with how the control of thickness can be used to uncover the optimal physicochemical properties necessary for boosting the performance toward a range of catalytic reactions. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly efficient one-step synthesis of carbon encapsulated nanocrystals by the oxidation of metal π-complexes

NASA Astrophysics Data System (ADS)

Liu, Boyang; Shao, Yingfeng; Xiang, Xin; Zhang, Fuhua; Yan, Shengchang; Li, Wenge

2017-08-01

Various carbon encapsulated nanocrystals, including MnS and MnO, Cr2O3, MoO2, Fe7S8 and Fe3O4, and ZrO2, are prepared in one step and in situ by a simple and highly efficient synthesis approach. The nanocrystals have an equiaxed morphology and a median size smaller than 30 nm. Tens and hundreds of these nanocrystals are entirely encapsulated by a wormlike amorphous carbon shell. The formation of a core-shell structure depends on the strongly exothermic reaction of metal π-complexes with ammonium persulfate in an autoclave at below 200 °C. During the oxidation process, the generated significant amounts of heat will destroy the molecular structure of the metal π-complex and cleave the ligands into small carbon fragments, which further transform into an amorphous carbon shell. The central metal atoms are oxidized to metal oxide/sulfide nanocrystals. The formation of a core-shell structure is independent of the numbers of ligands and carbon atoms as well as the metal types, implying that any metal π-complex can serve as a precursor and that various carbon encapsulated nanocrystals can be synthesized by this method.

TMAO and urea in the hydration shell of the protein SNase.

PubMed

Smolin, Nikolai; Voloshin, Vladimir P; Anikeenko, Alexey V; Geiger, Alfons; Winter, Roland; Medvedev, Nikolai N

2017-03-01

We performed all-atom MD simulations of the protein SNase in aqueous solution and in the presence of two major osmolytes, trimethylamine-N-oxide (TMAO) and urea, as cosolvents at various concentrations and compositions and at different pressures and temperatures. The distributions of the cosolvent molecules and their orientation in the surroundings of the protein were analyzed in great detail. The distribution of urea is largely conserved near the protein. It varies little with pressure and temperature, and does practically not depend on the addition of TMAO. The slight decrease with temperature of the number of urea molecules that are in contact with the SNase molecule is consistent with the view that the interaction of the protein with urea is mainly of enthalpic nature. Most of the TMAO molecules tend to be oriented to the protein by its methyl groups, a small amount of these molecules contact the protein by its oxygen, forming hydrogen bonds with the protein, only. Unlike urea, the fraction of TMAO in the hydration shell of SNase slightly increases with temperature (a signature of a prevailing hydrophobic interaction between TMAO and SNase), and decreases significantly upon the addition of urea. This behavior reflects the diverse nature of the interaction of the two osmolytes with the protein. Using the Voronoi volume of the atoms of the solvent molecules (water, urea, TMAO), we compared the fraction of the volume occupied by a given type of solvent molecule in the hydration shell and in the bulk solvent. The volume fraction of urea in the hydration shell is more than two times larger than in the bulk, whereas the volume fraction of TMAO in the hydration shell is only slightly larger in the binary solvent (TMAO + water) and becomes even less than in the bulk in the ternary solvent (TMAO + water + urea). Thus, TMAO tends to be excluded from the hydration shell of the protein. The behavior of the two cosolvents in the vicinity of the protein does not change much with pressure (from 1 to 5000 bar) and temperature (from 280 to 330 K). This is also in line with the conception of the "osmophobic effect" of TMAO to protect proteins from denaturation also at harsh environmental conditions. We also calculated the volumetric parameters of SNase and found that the cosolvents have a small but significant effect on the apparent volume and its contributions, i.e. the intrinsic, molecular and thermal volumes.

Physical parameters for proton induced K-, L-, and M-shell ionization processes

NASA Astrophysics Data System (ADS)

Shehla; Puri, Sanjiv

2016-10-01

The proton induced atomic inner-shell ionization processes comprising radiative and non-radiative transitions are characterized by physical parameters, namely, the proton ionization cross sections, X-ray emission rates, fluorescence yields and Coster-Kronig (CK) transition probabilities. These parameters are required to calculate the K/L/M shell X-ray production (XRP) cross sections and relative X-ray intensity ratios, which in turn are required for different analytical applications. The current status of different physical parameters is presented in this report for use in various applications.

Patched bimetallic surfaces are active catalysts for ammonia decomposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Wei; Vlachos, Dionisios G.

In this study, ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material’s structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-Hmore » bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.« less

Patched bimetallic surfaces are active catalysts for ammonia decomposition

DOE PAGES

Guo, Wei; Vlachos, Dionisios G.

2015-10-07

In this study, ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material’s structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-Hmore » bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.« less

First determination of ground state electromagnetic moments of 53Fe

NASA Astrophysics Data System (ADS)

Miller, A. J.; Minamisono, K.; Rossi, D. M.; Beerwerth, R.; Brown, B. A.; Fritzsche, S.; Garand, D.; Klose, A.; Liu, Y.; Maaß, B.; Mantica, P. F.; Müller, P.; Nörtershäuser, W.; Pearson, M. R.; Sumithrarachchi, C.

2017-11-01

The hyperfine coupling constants of neutron deficient 53Fe were deduced from the atomic hyperfine spectrum of the 3 d64 s25D4↔3 d64 s 4 p 5F5 transition, measured using the bunched-beam collinear laser spectroscopy technique. The low-energy 53Fe beam was produced by projectile-fragmentation reactions followed by gas stopping, and used for the first time for laser spectroscopy. Ground state magnetic-dipole and electric-quadrupole moments were determined as μ =-0.65 (1 ) μN and Q =+35 (15 ) e2fm2 , respectively. The multiconfiguration Dirac-Fock method was used to calculate the electric field gradient to deduce Q from the quadrupole hyperfine coupling constant, since the quadrupole coupling constant has not been determined for any Fe isotopes. Both experimental values agree well with nuclear shell model calculations using the GXPF1A effective interaction performed in a full f p shell model space, which support the soft nature of the 56Ni nucleus.

Theoretical L-shell Coster-Kronig energies 11 or equal to z or equal to 103

NASA Technical Reports Server (NTRS)

Chen, M. H.; Crasemann, B.; Huang, K. N.; Aoyagi, M.; Mark, H.

1976-01-01

Relativistic relaxed-orbital calculations of L-shell Coster-Kronig transition energies have been performed for all possible transitions in atoms with atomic numbers. Hartree-Fock-Slater wave functions served as zeroth-order eigenfunctions to compute the expectation of the total Hamiltonian. A first-order approximation to the local approximation was thus included. Quantum-electrodynamic corrections were made. Each transition energy was computed as the difference between results of separate self-consistent-field calculations for the initial, singly ionized state and the final two-hole state. The following quantities are listed: total transition energy, 'electric' (Dirac-Hartree-Fock-Slater) contribution, magnetic and retardation contributions, and contributions due to vacuum polarization and self energy.

Small size yet big action: a simple sulfate anion templated a discrete 78-nuclearity silver sulfur nanocluster with a multishell structure.

PubMed

Cheng, Li-Ping; Wang, Zhi; Wu, Qiao-Yu; Su, Hai-Feng; Peng, Tao; Luo, Geng-Geng; Li, Yan-An; Sun, Di; Zheng, Lan-Sun

2018-03-07

A discrete 78-nucleus silver-sulfur nanocluster with a sulfate-centered multishell structure was isolated and characterized. Its crystal structure revealed 18 and 60 Ag atoms in the inner and outer shell, respectively. The inner shell of 18-nuclearity Ag atoms is a very rare convex polyhedron featuring an elongated triangular orthobicupola. The incorporation of a sulfate anion and multishell arrangement in the nanocluster led to a dramatic decrease in the band gap (E g = 1.40 eV). Our study showed that simple anions can also induce the formation of high-nuclearity silver clusters with excellent optical properties.

Time-resolved x-ray spectra from laser-generated high-density plasmas

NASA Astrophysics Data System (ADS)

Andiel, U.; Eidmann, Klaus; Witte, Klaus-Juergen

2001-04-01

We focused frequency doubled ultra short laser pulses on solid C, F, Na and Al targets, K-shell emission was systematically investigated by time resolved spectroscopy using a sub-ps streak camera. A large number of laser shots can be accumulated when triggering the camera with an Auston switch system at very high temporal precision. The system provides an outstanding time resolution of 1.7ps accumulating thousands of laser shots. The time duration of the He-(alpha) K-shell resonance lines was observed in the range of (2-4)ps and shows a decrease with the atomic number. The experimental results are well reproduced by hydro code simulations post processed with an atomic kinetics code.

Structure determination in 55-atom Li-Na and Na-K nanoalloys.

PubMed

Aguado, Andrés; López, José M

2010-09-07

The structure of 55-atom Li-Na and Na-K nanoalloys is determined through combined empirical potential (EP) and density functional theory (DFT) calculations. The potential energy surface generated by the EP model is extensively sampled by using the basin hopping technique, and a wide diversity of structural motifs is reoptimized at the DFT level. A composition comparison technique is applied at the DFT level in order to make a final refinement of the global minimum structures. For dilute concentrations of one of the alkali atoms, the structure of the pure metal cluster, namely, a perfect Mackay icosahedron, remains stable, with the minority component atoms entering the host cluster as substitutional impurities. At intermediate concentrations, the nanoalloys adopt instead a core-shell polyicosahedral (p-Ih) packing, where the element with smaller atomic size and larger cohesive energy segregates to the cluster core. The p-Ih structures show a marked prolate deformation, in agreement with the predictions of jelliumlike models. The electronic preference for a prolate cluster shape, which is frustrated in the 55-atom pure clusters due to the icosahedral geometrical shell closing, is therefore realized only in the 55-atom nanoalloys. An analysis of the electronic densities of states suggests that photoelectron spectroscopy would be a sufficiently sensitive technique to assess the structures of nanoalloys with fixed size and varying compositions.

Equation-of-motion coupled-cluster method for ionised states with spin-orbit coupling using open-shell reference wavefunction

NASA Astrophysics Data System (ADS)

Wang, Zhifan; Wang, Fan

2018-04-01

The equation-of-motion coupled-cluster method for ionised states at the singles and doubles level (EOM-IP-CCSD) with spin-orbit coupling (SOC) included in post-Hartree-Fock (HF) steps is extended to spatially non-degenerate open-shell systems such as high spin states of s1, p3, σ1 or π2 configuration in this work. Pseudopotentials are employed to treat relativistic effects and spin-unrestricted scalar relativistic HF determinant is adopted as reference in calculations. Symmetry is not exploited in the implementation since both time-reversal and spatial symmetry is broken due to SOC. IPs with the EOM-IP-CCSD approach are those from the 3Σ1- states for high spin state of π2 configuration, while the ground state is the 3Σ0- state. When removing an electron from the high spin state of p3 configuration, only the 3P2 state can be reached. The open-shell EOM-IP-CCSD approach with SOC was employed in calculating IPs of some open-shell atoms with s1 configuration, diatomic molecules with π2 configuration and SOC splitting of the ionised π1 state, as well as IPs of VA atoms with p3 configuration. Our results demonstrate that this approach can be applied to ionised states of spatially non-degenerate open-shell states containing heavy elements with reasonable accuracy.

SU-E-I-43: Photoelectric Cross Section Revisited

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haga, A; Nakagawa, K; Kotoku, J

2015-06-15

Purpose: The importance of the precision in photoelectric cross-section value increases for recent developed technology such as dual energy computed tomography, in which some reconstruction algorithms require the energy dependence of the photo-absorption in each material composition of human being. In this study, we revisited the photoelectric cross-section calculation by self-consistent relativistic Hartree-Fock (HF) atomic model and compared with that widely distributed as “XCOM database” in National Institute of Standards and Technology, which was evaluated with localdensity approximation for electron-exchange (Fock)z potential. Methods: The photoelectric cross section can be calculated with the electron wave functions in initial atomic state (boundmore » electron) and final continuum state (photoelectron). These electron states were constructed based on the selfconsistent HF calculation, where the repulsive Coulomb potential from the electron charge distribution (Hartree term) and the electron exchange potential with full electromagnetic interaction (Fock term) were included for the electron-electron interaction. The photoelectric cross sections were evaluated for He (Z=2), Be (Z=4), C (Z=6), O (Z=8), and Ne (Z=10) in energy range of 10keV to 1MeV. The Result was compared with XCOM database. Results: The difference of the photoelectric cross section between the present calculation and XCOM database was 8% at a maximum (in 10keV for Be). The agreement tends to be better as the atomic number increases. The contribution from each atomic shell has a considerable discrepancy with XCOM database except for K-shell. However, because the photoelectric cross section arising from K-shell is dominant, the net photoelectric cross section was almost insensitive to the different handling in Fock potential. Conclusion: The photoelectric cross-section program has been developed based on the fully self-consistent relativistic HF atomic model. Due to small effect on the Fock potential for K-shell electrons, the difference from XCOM database was limited: 1% to 8% for low-Z elements in 10keV-1MeV energy ranges. This work was partly supported by the JSPS Core-to-Core Program (No. 23003)« less

Inner-shell chemistry under high pressure

NASA Astrophysics Data System (ADS)

Miao, Maosheng; Botana, Jorge; Pravica, Michael; Sneed, Daniel; Park, Changyong

2017-05-01

Chemistry at ambient conditions has implicit boundaries rooted in the atomic shell structure: the inner-shell electrons and the unoccupied outer-shell orbitals do not contribute as the major component to chemical reactions and in chemical bonds. These general rules govern our understanding of chemical structures and reactions. We review the recent progresses in high-pressure chemistry demonstrating that the above rules can be violated under extreme conditions. Using a first principles computation method and crystal structure search algorithm, we demonstrate that stable compounds involving inner shell electrons such as CsF3, CsF5, HgF3, and HgF4 can form under high external pressure and may present exotic properties. We also discuss experimental studies that have sought to confirm these predictions. Employing our recently developed hard X-ray photochemistry methods in a diamond anvil cell, we show promising early results toward realizing inner shell chemistry experimentally.

Effect of 0.25 and 2.0 MeV He-Ion Irradiation on Short-Range Ordering in Model (EFDA) Fe-Cr Alloys

NASA Astrophysics Data System (ADS)

Dubiel, Stanisław M.; Żukrowski, Jan; Serruys, Yves

2018-05-01

The effects of He+ irradiation on a distribution of Cr atoms in Fe100-x Cr x (x = 5.8, 10.75, 15.15) alloys were studied by 57Fe Conversion Electron Mössbauer Spectroscopy (CEMS). The alloys were irradiated with doses up to 12 × 1016 ions/cm2 with 0.25 and 2.0 MeV He+ ions. The distribution of Cr atoms within the first two coordination shells around Fe atoms was expressed with short-range order parameters α 1 (first-neighbor shell, 1NN), α 2 (second-neighbor shell, 2NN), and α 12 (1NN + 2NN). In non-irradiated alloys, α 1 >0 and α 2 <0 was revealed for all three samples. The value of α 12 ≈0, i.e., the distribution of Cr atoms averaged over 1NN and 2NN, was random. The effect of the irradiation of the Fe94.2Cr5.8 alloy was similar for the two energies of He+, viz., increase of number of Cr atoms in 1NN and decrease in 2NN. Consequently, the degree of ordering increased. For the other two samples, the effect of the irradiation depends on the composition, and is stronger for the less energetic ions where, for Fe89.25Cr10.75 alloy, the disordering disappeared and some traces of Cr clustering appeared. In Fe84.85Cr15.15 alloy, the clustering was clear. In the samples irradiated with 2. 0 MeV He+ ions, the ordering also survived in the samples with x = 10.75 and 15.15, yet its degree became smaller than in the Fe94.2Cr5.8 alloy.

Average M shell fluorescence yields for elements with 70≤Z≤92

NASA Astrophysics Data System (ADS)

Kahoul, A.; Deghfel, B.; Aylikci, V.; Aylikci, N. K.; Nekkab, M.

2015-03-01

The theoretical, experimental and analytical methods for the calculation of average M-shell fluorescence yield (ω¯M ) of different elements are very important because of the large number of their applications in various areas of physical chemistry and medical research. In this paper, the bulk of the average M-shell fluorescence yield measurements reported in the literature, covering the period 1955 to 2005 are interpolated by using an analytical function to deduce the empirical average M-shell fluorescence yield in the atomic range of 70≤Z≤92. The results were compared with the theoretical and fitted values reported by other authors. Reasonable agreement was typically obtained between our result and other works.

Synthesis and characterization of core-shell gold nanoparticles with poly(vinyl pyrrolidone) from a new precursor salt

NASA Astrophysics Data System (ADS)

Behera, M.; Ram, S.

2013-02-01

In this article, we report a facile one-step chemical synthesis of gold (Au) nanoparticles (GNPs) from a new precursor salt i.e., gold hydroxide in the presence of poly(vinyl pyrrolidone) (PVP) polymer. The non-aqueous dispersion of GNPs was comprehensively characterized by UV-Visible, FTIR, zeta potential, and transmission electron microscope (TEM). A strong surface plasmon resonance band at 529 nm in the UV-Visible spectrum confirms the formation of GNPs in the Au colloid. The FTIR spectroscopic results showed that PVP molecules get chemisorbed onto the surface of GNP via O-atom of carbonyl group. A negative zeta potential of (-)16 mV reveals accumulation of nonbonding electrons of O-atom of carbonyl group of PVP molecules on the nanosurface of GNP. TEM images demonstrate a core-shell nanostructure with an Au-crystalline core covered by a thin amorphous PVP-shell. PVP-capped GNPs could be a potential candidate for bio-sensing, catalysis, and other applications.

On the Highest Oxidation States of Metal Elements in MO4 Molecules (M = Fe, Ru, Os, Hs, Sm, and Pu).

PubMed

Huang, Wei; Xu, Wen-Hua; Schwarz, W H E; Li, Jun

2016-05-02

Metal tetraoxygen molecules (MO4, M = Fe, Ru, Os, Hs, Sm, Pu) of all metal atoms M with eight valence electrons are theoretically studied using density functional and correlated wave function approaches. The heavier d-block elements Ru, Os, Hs are confirmed to form stable tetraoxides of Td symmetry in (1)A1 electronic states with empty metal d(0) valence shell and closed-shell O(2-) ligands, while the 3d-, 4f-, and 5f-elements Fe, Sm, and Pu prefer partial occupation of their valence shells and peroxide or superoxide ligands at lower symmetry structures with various spin couplings. The different geometric and electronic structures and chemical bonding types of the six iso-stoichiometric species are explained in terms of atomic orbital energies and orbital radii. The variations found here contribute to our general understanding of the periodic trends of oxidation states across the periodic table.

Unit cell parameters of wurtzite InP nanowires determined by x-ray diffraction.

PubMed

Kriegner, D; Wintersberger, E; Kawaguchi, K; Wallentin, J; Borgström, M T; Stangl, J

2011-10-21

High resolution x-ray diffraction is used to study the structural properties of the wurtzite polytype of InP nanowires. Wurtzite InP nanowires are grown by metal-organic vapor phase epitaxy using S-doping. From the evaluation of the Bragg peak position we determine the lattice parameters of the wurtzite InP nanowires. The unit cell dimensions are found to differ from the ones expected from geometric conversion of the cubic bulk InP lattice constant. The atomic distances along the c direction are increased whereas the atomic spacing in the a direction is reduced in comparison to the corresponding distances in the zinc-blende phase. Using core/shell nanowires with a thin core and thick nominally intrinsic shells we are able to determine the lattice parameters of wurtzite InP with a negligible influence of the S-doping due to the much larger volume in the shell. The determined material properties will enable the ab initio calculation of electronic and optical properties of wurtzite InP nanowires.

Analysis of time-resolved argon line spectra from OMEGA direct-drive implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Florido, R.; Nagayama, T.; Mancini, R. C.

2008-10-15

We discuss the observation and data analysis of argon K-shell line spectra from argon-doped deuterium-filled OMEGA direct-drive implosion cores based on data recorded with two streaked crystal spectrometers. The targets were 870 {mu}m in diameter, 27 {mu}m wall thickness plastic shells filled with 20 atm of deuterium gas, and a tracer amount of argon for diagnostic purposes. The argon K-shell line spectrum is primarily emitted at the collapse of the implosion and its analysis provides a spectroscopic diagnostic of the core implosion conditions. The observed spectra includes the He{alpha}, Ly{alpha}, He{beta}, He{gamma}, Ly{beta}, and Ly{gamma} line emissions and their associatedmore » He- and Li-like satellites thus covering a broad photon energy range from 3100 to 4200 eV with a spectral resolution power of approximately 500. The data analysis relies on detailed atomic and spectral models that take into account nonequilibrium collisional-radiative atomic kinetics, Stark-broadened line shapes, and radiation transport calculations.« less

Anisotropic solvent model of the lipid bilayer. 1. Parameterization of long-range electrostatics and first solvation shell effects.

PubMed

Lomize, Andrei L; Pogozheva, Irina D; Mosberg, Henry I

2011-04-25

A new implicit solvation model was developed for calculating free energies of transfer of molecules from water to any solvent with defined bulk properties. The transfer energy was calculated as a sum of the first solvation shell energy and the long-range electrostatic contribution. The first term was proportional to solvent accessible surface area and solvation parameters (σ(i)) for different atom types. The electrostatic term was computed as a product of group dipole moments and dipolar solvation parameter (η) for neutral molecules or using a modified Born equation for ions. The regression coefficients in linear dependencies of solvation parameters σ(i) and η on dielectric constant, solvatochromic polarizability parameter π*, and hydrogen-bonding donor and acceptor capacities of solvents were optimized using 1269 experimental transfer energies from 19 organic solvents to water. The root-mean-square errors for neutral compounds and ions were 0.82 and 1.61 kcal/mol, respectively. Quantification of energy components demonstrates the dominant roles of hydrophobic effect for nonpolar atoms and of hydrogen-bonding for polar atoms. The estimated first solvation shell energy outweighs the long-range electrostatics for most compounds including ions. The simplicity and computational efficiency of the model allows its application for modeling of macromolecules in anisotropic environments, such as biological membranes.

Discovery of Molecular and Atomic Clouds Associated with the Magellanic Superbubble 30 Doradus C

NASA Astrophysics Data System (ADS)

Sano, H.; Yamane, Y.; Voisin, F.; Fujii, K.; Yoshiike, S.; Inaba, T.; Tsuge, K.; Babazaki, Y.; Mitsuishi, I.; Yang, R.; Aharonian, F.; Rowell, G.; Filipović, M. D.; Mizuno, N.; Tachihara, K.; Kawamura, A.; Onishi, T.; Fukui, Y.

2017-07-01

We analyzed the 2.6 mm CO and 21 cm H I lines toward the Magellanic superbubble 30 Doradus C, in order to reveal the associated molecular and atomic gas. We uncovered five molecular clouds in a velocity range from 251 to 276 km s-1 toward the western shell. The non-thermal X-rays are clearly enhanced around the molecular clouds on a parsec scale, suggesting possible evidence for magnetic field amplification via shock-cloud interaction. The thermal X-rays are brighter in the eastern shell, where there are no dense molecular or atomic clouds, opposite to the western shell. The TeV γ-ray distribution may spatially match the total interstellar proton column density as well as the non-thermal X-rays. If the hadronic γ-ray is dominant, the total energy of the cosmic-ray protons is at least ˜ 1.2× {10}50 erg with the estimated mean interstellar proton density ˜60 cm-3. In addition, the γ-ray flux associated with the molecular cloud (e.g., MC3) could be detected and resolved by the Cherenkov Telescope Array (CTA). This should permit CTA to probe the diffusion of cosmic-rays into the associated dense ISM.

Investigations of the Interactions of Radiation with Matter.

DTIC Science & Technology

1986-07-31

Process in Atoms, Molecules and Solids, eds. A. Mei-el and J. Finster , (Karl-Marx Universitat, Leipzig, 1984), p. 58. 10. S.T. Manson in High Enery Ion...H. Toburen, and S. T. Manson in X-Ra and Inner-Shell Process in Atoms, Molecules and Solids, eds. A. Meisel and J. Finster , (Karl-Marx- Universitat

Empirically constructed dynamic electric dipole polarizability function of magnesium and its applications

NASA Astrophysics Data System (ADS)

Babb, James F.

2015-08-01

The dynamic electric dipole polarizability function for the magnesium atom is formed by assembling the atomic electric dipole oscillator strength distribution from combinations of theoretical and experimental data for resonance oscillator strengths and for photoionization cross sections of valence and inner shell electrons. Consistency with the oscillator strength (Thomas-Reiche-Kuhn) sum rule requires the adopted principal resonance line oscillator strength to be several percent lower than the values given in two critical tabulations, though the value adopted is consistent with a number of theoretical determinations. The static polarizability is evaluated. Comparing the resulting dynamic polarizability as a function of the photon energy with more elaborate calculations reveals the contributions of inner shell electron excitations. The present results are applied to calculate the long-range interactions between two and three magnesium atoms and the interaction between a magnesium atom and a perfectly conducting metallic plate. Extensive comparisons of prior results for the principal resonance line oscillator strength, for the static polarizability, and for the van der Waals coefficient are given in the Appendix.

Emission Characteristics of InGaN/GaN Core-Shell Nanorods Embedded in a 3D Light-Emitting Diode.

PubMed

Jung, Byung Oh; Bae, Si-Young; Lee, Seunga; Kim, Sang Yun; Lee, Jeong Yong; Honda, Yoshio; Amano, Hiroshi

2016-12-01

We report the selective-area growth of a gallium nitride (GaN)-nanorod-based InGaN/GaN multiple-quantum-well (MQW) core-shell structure embedded in a three-dimensional (3D) light-emitting diode (LED) grown by metalorganic chemical vapor deposition (MOCVD) and its optical analysis. High-resolution transmission electron microscopy (HR-TEM) observation revealed the high quality of the GaN nanorods and the position dependence of the structural properties of the InGaN/GaN MQWs on multiple facets. The excitation and temperature dependences of photoluminescence (PL) revealed the m-plane emission behaviors of the InGaN/GaN core-shell nanorods. The electroluminescence (EL) of the InGaN/GaN core-shell-nanorod-embedded 3D LED changed color from green to blue with increasing injection current. This phenomenon was mainly due to the energy gradient and deep localization of the indium in the selectively grown InGaN/GaN core-shell MQWs on the 3D architecture.

Electrons on a spherical surface: Physical properties and hollow spherical clusters

NASA Astrophysics Data System (ADS)

Cricchio, Dario; Fiordilino, Emilio; Persico, Franco

2012-07-01

We discuss the physical properties of a noninteracting electron gas constrained to a spherical surface. In particular we consider its chemical potentials, its ionization potential, and its electric static polarizability. All these properties are discussed analytically as functions of the number N of electrons. The trends obtained with increasing N are compared with those of the corresponding properties experimentally measured or theoretically evaluated for quasispherical hollow atomic and molecular clusters. Most of the properties investigated display similar trends, characterized by a prominence of shell effects. This leads to the definition of a scale-invariant distribution of magic numbers which follows a power law with critical exponent -0.5. We conclude that our completely mechanistic and analytically tractable model can be useful for the analysis of self-assembling complex systems.

Improved Simulations of Astrophysical Plasmas: Computation of New Atomic Data

NASA Technical Reports Server (NTRS)

Gorczyca, Thomas W.; Korista, Kirk T.

2005-01-01

Our research program is designed to carry out state-of-the-art atomic physics calculations crucial to advancing our understanding of fundamental astrophysical problems. We redress the present inadequacies in the atomic data base along two important areas: dielectronic recombination and inner-shell photoionization and multiple electron ejection/Auger fluorescence therefrom. All of these data are disseminated to the astrophysical community in the proper format for implementation in spectral simulation code.

Spectrum lines of highly ionized zinc, germanium, selenium, zirconium, molybdenum, and silver injected into Princeton Large Torus and Tokamak Fusion Test Reactor tokamak discharges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hinnov, E.; Boody, F.; Cohen, S.

1986-10-01

Measured wavelengths of a number of highly ionized atoms are reported. These include the 3s/sup 2/3p--3s3p/sup 2/ and 3s/sup 2/3p--3s/sup 2/3d transitions in the aluminum isoelectronic sequence of Zn XVIII, Ge XX, Se XXII, Zr XXVIII, Mo XXX, and Ag XXXV; several transitions in the n = 2 shell of Zn XXII, Zn XXIII, and Zn XXIV; and the resonance and intercombination lines of Ag XXXVI--Ag XXXVII and of Ge XXIX--Ge XXX.

Cargo–shell and cargo–cargo couplings govern the mechanics of artificially loaded virus-derived cages†

PubMed Central

Llauró, Aida; Luque, Daniel; Edwards, Ethan; Trus, Benes L.; Avera, John; Reguera, David; Douglas, Trevor

2016-01-01

Nucleic acids are the natural cargo of viruses and key determinants that affect viral shell stability. In some cases the genome structurally reinforces the shell, whereas in others genome packaging causes internal pressure that can induce destabilization. Although it is possible to pack heterologous cargoes inside virus-derived shells, little is known about the physical determinants of these artificial nanocontainers’ stability. Atomic force and three-dimensional cryo-electron microscopy provided mechanical and structural information about the physical mechanisms of viral cage stabilization beyond the mere presence/absence of cargos. We analyzed the effects of cargo–shell and cargo–cargo interactions on shell stability after encapsulating two types of proteinaceous payloads. While bound cargo to the inner capsid surface mechanically reinforced the capsid in a structural manner, unbound cargo diffusing freely within the shell cavity pressurized the cages up to ~30 atm due to steric effects. Strong cargo–cargo coupling reduces the resilience of these nanocompartments in ~20% when bound to the shell. Understanding the stability of artificially loaded nanocages will help to design more robust and durable molecular nanocontainers. PMID:27091107

Understanding the interface of six-shell cuboctahedral and icosahedral palladium clusters on reduced graphene oxide: experimental and theoretical study.

PubMed

Gracia-Espino, Eduardo; Hu, Guangzhi; Shchukarev, Andrey; Wågberg, Thomas

2014-05-07

Studies on noble-metal-decorated carbon nanostructures are reported almost on a daily basis, but detailed studies on the nanoscale interactions for well-defined systems are very rare. Here we report a study of reduced graphene oxide (rGOx) homogeneously decorated with palladium (Pd) nanoclusters with well-defined shape and size (2.3 ± 0.3 nm). The rGOx was modified with benzyl mercaptan (BnSH) to improve the interaction with Pd clusters, and N,N-dimethylformamide was used as solvent and capping agent during the decoration process. The resulting Pd nanoparticles anchored to the rGOx-surface exhibit high crystallinity and are fully consistent with six-shell cuboctahedral and icosahedral clusters containing ~600 Pd atoms, where 45% of these are located at the surface. According to X-ray photoelectron spectroscopy analysis, the Pd clusters exhibit an oxidized surface forming a PdO(x) shell. Given the well-defined experimental system, as verified by electron microscopy data and theoretical simulations, we performed ab initio simulations using 10 functionalized graphenes (with vacancies or pyridine, amine, hydroxyl, carboxyl, or epoxy groups) to understand the adsorption process of BnSH, their further role in the Pd cluster formation, and the electronic properties of the graphene-nanoparticle hybrid system. Both the experimental and theoretical results suggest that Pd clusters interact with functionalized graphene by a sulfur bridge while the remaining Pd surface is oxidized. Our study is of significant importance for all work related to anchoring of nanoparticles on nanocarbon-based supports, which are used in a variety of applications.

Larger sized wire arrays on 1.5 MA Z-pinch generator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Safronova, A. S., E-mail: alla@unr.edu; Kantsyrev, V. L., E-mail: alla@unr.edu; Weller, M. E., E-mail: alla@unr.edu

Experiments on the UNR Zebra generator with Load Current Multiplier (LCM) allow for implosions of larger sized wire array loads than at standard current of 1 MA. Advantages of larger sized planar wire array implosions include enhanced energy coupling to plasmas, better diagnostic access to observable plasma regions, and more complex geometries of the wire loads. The experiments with larger sized wire arrays were performed on 1.5 MA Zebra with LCM (the anode-cathode gap was 1 cm, which is half the gap used in the standard mode). In particular, larger sized multi-planar wire arrays had two outer wire planes frommore » mid-atomic-number wires to create a global magnetic field (gmf) and plasma flow between them. A modified central plane with a few Al wires at the edges was put in the middle between outer planes to influence gmf and to create Al plasma flow in the perpendicular direction (to the outer arrays plasma flow). Such modified plane has different number of empty slots: it was increased from 6 up to 10, hence increasing the gap inside the middle plane from 4.9 to 7.7 mm, respectively. Such load configuration allows for more independent study of the flows of L-shell mid-atomic-number plasma (between the outer planes) and K-shell Al plasma (which first fills the gap between the edge wires along the middle plane) and their radiation in space and time. We demonstrate that such configuration produces higher linear radiation yield and electron temperatures as well as advantages of better diagnostics access to observable plasma regions and how the load geometry (size of the gap in the middle plane) influences K-shell Al radiation. In particular, K-shell Al radiation was delayed compared to L-shell mid-atomic-number radiation when the gap in the middle plane was large enough (when the number of empty slots was increased up to ten)« less

Inner-shell photodetachment of transition metal negative ions

NASA Astrophysics Data System (ADS)

Dumitriu, Ileana

This thesis focuses on the study of inner-shell photodetachment of transition metal negative ions, specifically Fe- and Ru- . Experimental investigations have been performed with the aim of gaining new insights into the physics of negative atomic ions and providing valuable absolute cross section data for astrophysics. The experiments were performed using the X-ray radiation from the Advanced Light Source, Lawrence Berkeley National Laboratory, and the merged-beam technique for photoion spectroscopy. Negative ions are a special class of atomic systems very different from neutral atoms and positive ions. The fundamental physics of the interaction of transition metal negative ions with photons is interesting but difficult to analyze in detail because the angular momentum coupling generates a large number of possible terms resulting from the open d shell. Our work reports on the first inner-shell photodetachment studies and absolute cross section measurements for Fe- and Ru -. In the case of Fe-, an important astrophysical abundant element, the inner-shell photodetachment cross section was obtained by measuring the Fe+ and Fe2+ ion production over the photon energy range of 48--72 eV. The absolute cross sections for the production of Fe+ and Fe2+ were measured at four photon energies. Strong shape resonances due to the 3p→3d photoexcitation were measured above the 3p detachment threshold. The production of Ru+, Ru2+, and Ru3+ from Ru- was measured over 30--90 eV photon energy range The absolute photodetachment cross sections of Ru - ([Kr] 4d75s 2) leading to Ru+, Ru2+, and Ru 3+ ion production were measured at three photon energies. Resonance effects were observed due to interference between transitions of the 4 p-electrons to the quasi-bound 4p54d85s 2 states and the 4d→epsilonf continuum. The role of many-particle effects, intershell interaction, and polarization seems much more significant in Ru- than in Fe- photodetachment.

Determination of K shell absorption jump factors and jump ratios of 3d transition metals by measuring K shell fluorescence parameters.

PubMed

Kaçal, Mustafa Recep; Han, İbrahim; Akman, Ferdi

2015-01-01

Energy dispersive X-ray fluorescence technique (EDXRF) has been employed for measuring K-shell absorption jump factors and jump ratios for Ti, Cr, Fe, Co, Ni and Cu elements. The jump factors and jump ratios for these elements were determined by measuring K shell fluorescence parameters such as the Kα X-ray production cross-sections, K shell fluorescence yields, Kβ-to-Kα X-rays intensity ratios, total atomic absorption cross sections and mass attenuation coefficients. The measurements were performed using a Cd-109 radioactive point source and an Si(Li) detector in direct excitation and transmission experimental geometry. The measured values for jump factors and jump ratios were compared with theoretically calculated and the ones available in the literature. Copyright © 2014 Elsevier Ltd. All rights reserved.

Time-resolved inner-shell photoelectron spectroscopy: From a bound molecule to an isolated atom

NASA Astrophysics Data System (ADS)

Brauße, Felix; Goldsztejn, Gildas; Amini, Kasra; Boll, Rebecca; Bari, Sadia; Bomme, Cédric; Brouard, Mark; Burt, Michael; de Miranda, Barbara Cunha; Düsterer, Stefan; Erk, Benjamin; Géléoc, Marie; Geneaux, Romain; Gentleman, Alexander S.; Guillemin, Renaud; Ismail, Iyas; Johnsson, Per; Journel, Loïc; Kierspel, Thomas; Köckert, Hansjochen; Küpper, Jochen; Lablanquie, Pascal; Lahl, Jan; Lee, Jason W. L.; Mackenzie, Stuart R.; Maclot, Sylvain; Manschwetus, Bastian; Mereshchenko, Andrey S.; Mullins, Terence; Olshin, Pavel K.; Palaudoux, Jérôme; Patchkovskii, Serguei; Penent, Francis; Piancastelli, Maria Novella; Rompotis, Dimitrios; Ruchon, Thierry; Rudenko, Artem; Savelyev, Evgeny; Schirmel, Nora; Techert, Simone; Travnikova, Oksana; Trippel, Sebastian; Underwood, Jonathan G.; Vallance, Claire; Wiese, Joss; Simon, Marc; Holland, David M. P.; Marchenko, Tatiana; Rouzée, Arnaud; Rolles, Daniel

2018-04-01

Due to its element and site specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here, we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH3I ) is investigated by ionization above the iodine 4 d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal-field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules.

Graphitic carbon nitride nanosheet@metal-organic framework core-shell nanoparticles for photo-chemo combination therapy

NASA Astrophysics Data System (ADS)

Chen, Rui; Zhang, Jinfeng; Wang, Yu; Chen, Xianfeng; Zapien, J. Antonio; Lee, Chun-Sing

2015-10-01

Recently, nanoscale metal-organic frameworks (NMOFs) have started to be developed as a promising platform for bioimaging and drug delivery. On the other hand, combination therapies using multiple approaches are demonstrated to achieve much enhanced efficacy. Herein, we report, for the first time, core-shell nanoparticles consisting of a photodynamic therapeutic (PDT) agent and a MOF shell while simultaneously carrying a chemotherapeutic drug for effective combination therapy. In this work, core-shell nanoparticles of zeolitic-imadazolate framework-8 (ZIF-8) as shell embedded with graphitic carbon nitride (g-C3N4) nanosheets as core are fabricated by growing ZIF-8 in the presence of g-C3N4 nanosheets. Doxorubicin hydrochloride (DOX) is then loaded into the ZIF-8 shell of the core-shell nanoparticles. The combination of the chemotherapeutic effects of DOX and the PDT effect of g-C3N4 nanosheets can lead to considerably enhanced efficacy. Furthermore, the red fluorescence of DOX and the blue fluorescence of g-C3N4 nanosheets provide the additional function of dual-color imaging for monitoring the drug release process.Recently, nanoscale metal-organic frameworks (NMOFs) have started to be developed as a promising platform for bioimaging and drug delivery. On the other hand, combination therapies using multiple approaches are demonstrated to achieve much enhanced efficacy. Herein, we report, for the first time, core-shell nanoparticles consisting of a photodynamic therapeutic (PDT) agent and a MOF shell while simultaneously carrying a chemotherapeutic drug for effective combination therapy. In this work, core-shell nanoparticles of zeolitic-imadazolate framework-8 (ZIF-8) as shell embedded with graphitic carbon nitride (g-C3N4) nanosheets as core are fabricated by growing ZIF-8 in the presence of g-C3N4 nanosheets. Doxorubicin hydrochloride (DOX) is then loaded into the ZIF-8 shell of the core-shell nanoparticles. The combination of the chemotherapeutic effects of DOX and the PDT effect of g-C3N4 nanosheets can lead to considerably enhanced efficacy. Furthermore, the red fluorescence of DOX and the blue fluorescence of g-C3N4 nanosheets provide the additional function of dual-color imaging for monitoring the drug release process. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04436g

Nonpolar InGaN/GaN Core-Shell Single Nanowire Lasers.

PubMed

Li, Changyi; Wright, Jeremy B; Liu, Sheng; Lu, Ping; Figiel, Jeffrey J; Leung, Benjamin; Chow, Weng W; Brener, Igal; Koleske, Daniel D; Luk, Ting-Shan; Feezell, Daniel F; Brueck, S R J; Wang, George T

2017-02-08

We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV-visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.

Nonpolar InGaN/GaN core–shell single nanowire lasers

DOE PAGES

Li, Changyi; Wright, Jeremy Benjamin; Liu, Sheng; ...

2017-01-24

We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core–shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core–shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core–shell nanowires, despite significantly shorter cavity lengths and reducedmore » active region volume. Mode simulations show that due to the core–shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. Furthermore, the results show the viability of this p-i-n nonpolar core–shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV–visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.« less

Micro-Raman investigations of InN-GaN core-shell nanowires on Si (111) substrate

NASA Astrophysics Data System (ADS)

Sangeetha, P.; Jeganathan, K.; Ramakrishnan, V.

2013-06-01

The electron-phonon interactions in InN-GaN core-shell nanowires grown by plasma assisted- molecular beam epitaxy (MBE) on Si (111) substrate have been analysed using micro-Raman spectroscopic technique with the excitation wavelength of 633, 488 and 325 nm. The Raman scattering at 633 nm reveals the characteristic E2 (high) and A1 (LO) phonon mode of InN core at 490 and 590 cm-1 respectively and E2 (high) phonon mode of GaN shell at 573 cm-1. The free carrier concentration of InN core is found to be low in the order ˜ 1016 cm-3 due to the screening of charge carriers by thin GaN shell. Diameter of InN core evaluated using the spatial correlation model is consistent with the transmission electron microscopic measurement of ˜15 nm. The phonon-life time of core-shell nanowire structure is estimated to be ˜0.4 ps. The micro-Raman mapping and its corresponding localised spectra for 325 nm excitation exhibit intense E2 (high) phonon mode of GaN shell at 573 cm-1 as the decrease of laser interaction length and the signal intensity is quenched at the voids due to high spacing of NWs.

Low temperature X-ray structure analyses combined with NBO studies of a new heteroleptic octa-coordinated Holmium(III) complex with N,N,N-tridentate hydrazono-phthalazine-type ligand

NASA Astrophysics Data System (ADS)

Soliman, Saied M.; El-Faham, Ayman

2018-04-01

The new heteroleptic [HoL(H2O)5]Br3 complex, L is hydrazono-phthalazine ligand, is synthesized and its molecular structure aspects were analyzed using single crystal X-ray structure (SCXRD), Hirshfeld (HF) analysis, quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) method. The SCXRD showed that the Ho is octa-coordinated with one N,N,N-tridentate ligand L and five water molecules. The HF analysis is used to analyze the molecular packing in the [HoL(H2O)5]Br3crystal structure. The complex cations are connected via strong Osbnd H⋯Br and Nsbnd H⋯Br H-bonding interactions which have greater importance than the Csbnd H⋯Br contacts. Also, all the Hosbnd N and Hosbnd O bonds have the characteristics of closed shell interactions using QTAIM. The natural orbitals included in these interactions were analyzed using NBO method. The alpha LP*(8)Ho and beta LP*(4)Ho which have mainly s-orbital characters are the most important anti-bonding natural orbitals included in all Ho-N and Hosbnd O bonds. The rest of the Ho anti-bonding orbitals which have either p or d-orbital characters shared partially in the Ho-ligands interactions. Natural charges analysis revealed the presence of significant amount of electron density (0.9225-0.9300 e) transferred from the ligands to Ho (2.0700-2.0775 e). Spherical spin density with ∼4.0 e is predicted over the Ho atom.

Formation of Core-Shell Ethane-Silver Clusters in He Droplets.

PubMed

Loginov, Evgeny; Gomez, Luis F; Sartakov, Boris G; Vilesov, Andrey F

2017-08-17

Ethane core-silver shell clusters consisting of several thousand particles have been assembled in helium droplets upon capture of ethane molecules followed by Ag atoms. The composite clusters were studied via infrared laser spectroscopy in the range of the C-H stretching vibrations of ethane. The spectra reveal a splitting of the vibrational bands, which is ascribed to interaction with Ag. A rigorous analysis of band intensities for a varying number of trapped ethane molecules and Ag atoms indicates that the composite clusters consist of a core of ethane that is covered by relatively small Ag clusters. This metastable structure is stabilized due to fast dissipation in superfluid helium droplets of the cohesion energy of the clusters.

Injection and trapping of tunnel-ionized electrons into laser-produced wakes.

PubMed

Pak, A; Marsh, K A; Martins, S F; Lu, W; Mori, W B; Joshi, C

2010-01-15

A method, which utilizes the large difference in ionization potentials between successive ionization states of trace atoms, for injecting electrons into a laser-driven wakefield is presented. Here a mixture of helium and trace amounts of nitrogen gas was used. Electrons from the K shell of nitrogen were tunnel ionized near the peak of the laser pulse and were injected into and trapped by the wake created by electrons from majority helium atoms and the L shell of nitrogen. The spectrum of the accelerated electrons, the threshold intensity at which trapping occurs, the forward transmitted laser spectrum, and the beam divergence are all consistent with this injection process. The experimental measurements are supported by theory and 3D OSIRIS simulations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Finzel, Kati, E-mail: kati.finzel@liu.se

The local conditions for the Pauli potential that are necessary in order to yield self-consistent electron densities from orbital-free calculations are investigated for approximations that are expressed with the help of a local position variable. It is shown that those local conditions also apply when the Pauli potential is given in terms of the electron density. An explicit formula for the Ne atom is given, preserving the local conditions during the iterative procedure. The resulting orbital-free electron density exhibits proper shell structure behavior and is in close agreement with the Kohn-Sham electron density. This study demonstrates that it is possiblemore » to obtain self-consistent orbital-free electron densities with proper atomic shell structure from simple one-point approximations for the Pauli potential at local density level.« less

Polaronic effects on the off-center donor impurity in AlAs/GaAs/SiO2 spherical core/shell quantum dots

NASA Astrophysics Data System (ADS)

El Haouari, M.; Feddi, E.; Dujardin, F.; Restrepo, R. L.; Mora-Ramos, M. E.; Duque, C. A.

2017-11-01

The ground state of a conduction electron coupled to an off-center impurity donor in a AlAS/GaAs spherical core/shell quantum dot is investigated theoretically. The image-charge effect and the influence of the electron-polar-LO-phonon interaction are considered. The electron-impurity binding energy is calculated via a variational procedure and is reported both as a function of the shell width and of the radial position of the donor atom. The polaronic effects on this quantity are particularly discussed.

Minima in generalized oscillator strengths for initially excited hydrogen-like atoms

NASA Technical Reports Server (NTRS)

Matsuzawa, M.; Omidvar, K.; Inokuti, M.

1976-01-01

Generalized oscillator strengths for transitions from an initially excited state of a hydrogenic atom to final states (either discrete or continuum) have complicated structures, including minima and shoulders, as functions of the momentum transfer. Extensive calculations carried out in the present work have revealed certain systematics of these structures. Some implications of the minima to the energy dependence of the inner-shell ionization cross section of heavy atoms by proton impact are discussed.

Neutron Nucleic Acid Crystallography.

PubMed

Chatake, Toshiyuki

2016-01-01

The hydration shells surrounding nucleic acids and hydrogen-bonding networks involving water molecules and nucleic acids are essential interactions for the structural stability and function of nucleic acids. Water molecules in the hydration shells influence various conformations of DNA and RNA by specific hydrogen-bonding networks, which often contribute to the chemical reactivity and molecular recognition of nucleic acids. However, X-ray crystallography could not provide a complete description of structural information with respect to hydrogen bonds. Indeed, X-ray crystallography is a powerful tool for determining the locations of water molecules, i.e., the location of the oxygen atom of H2O; however, it is very difficult to determine the orientation of the water molecules, i.e., the orientation of the two hydrogen atoms of H2O, because X-ray scattering from the hydrogen atom is very small.Neutron crystallography is a specialized tool for determining the positions of hydrogen atoms. Neutrons are not diffracted by electrons, but are diffracted by atomic nuclei; accordingly, neutron scattering lengths of hydrogen and its isotopes are comparable to those of non-hydrogen atoms. Therefore, neutron crystallography can determine both of the locations and orientations of water molecules. This chapter describes the current status of neutron nucleic acid crystallographic research as well as the basic principles of neutron diffraction experiments performed on nucleic acid crystals: materials, crystallization, diffraction experiments, and structure determination.

Average M shell fluorescence yields for elements with 70≤Z≤92

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kahoul, A., E-mail: ka-abdelhalim@yahoo.fr; LPMRN laboratory, Department of Materials Science, Faculty of Sciences and Technology, Mohamed El Bachir El Ibrahimi University, Bordj-Bou-Arreridj 34030; Deghfel, B.

2015-03-30

The theoretical, experimental and analytical methods for the calculation of average M-shell fluorescence yield (ω{sup ¯}{sub M}) of different elements are very important because of the large number of their applications in various areas of physical chemistry and medical research. In this paper, the bulk of the average M-shell fluorescence yield measurements reported in the literature, covering the period 1955 to 2005 are interpolated by using an analytical function to deduce the empirical average M-shell fluorescence yield in the atomic range of 70≤Z≤92. The results were compared with the theoretical and fitted values reported by other authors. Reasonable agreement wasmore » typically obtained between our result and other works.« less

Tuning the synthesis of platinum-copper nanoparticles with a hollow core and porous shell for the selective hydrogenation of furfural to furfuryl alcohol.

PubMed

Huang, Shuangshuang; Yang, Nating; Wang, Shibin; Sun, Yuhan; Zhu, Yan

2016-08-07

Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol.

Nuclear mass formula with the shell energies obtained by a new method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koura, H.; Tachibana, T.; Yamada, M.

1998-12-21

Nuclear shapes and masses are estimated by a new method. The main feature of this method lies in estimating shell energies of deformed nuclei from spherical shell energies by mixing them with appropriate weights. The spherical shell energies are calculated from single-particle potentials, and, till now, two mass formulas have been constructed from two different sets of potential parameters. The standard deviation of the calculated masses from all the experimental masses of the 1995 Mass Evaluation is about 760 keV. Contrary to the mass formula by Tachibana, Uno, Yamada and Yamada in the 1987-1988 Atomic Mass Predictions, the present formulasmore » can give nuclear shapes and predict on super-heavy elements.« less

Shell Model Far From Stability: Island of Inversion Mergers

NASA Astrophysics Data System (ADS)

Nowacki, F.; Poves, A.

2018-02-01

In this study we propose a common mechanism for the disappearance of shell closures far from stabilty. With the use of Large Scale Shell Model calculations (SM-CI), we predict that the region of deformation which comprises the heaviest Chromium and Iron isotopes at and beyond N=40 will merge with a new one at N=50 in an astonishing parallel to the N=20 and N=28 case in the Neon and Magnesium isotopes. We propose a valence space including the full pf-shell for the protons and the full sdg shell for the neutrons, which represents a come-back of the the harmonic oscillator shells in the very neutron rich regime. Our calculations preserve the doubly magic nature of the ground state of 78Ni, which, however, exhibits a well deformed prolate band at low excitation energy, providing a striking example of shape coexistence far from stability. This new Island of Inversion (IoI) adds to the four well documented ones at N=8, 20, 28 and 40.

Continuous-Flow MOVPE of Ga-Polar GaN Column Arrays and Core-Shell LED Structures

NASA Astrophysics Data System (ADS)

Wang, Xue; Li, Shunfeng; Mohajerani, Matin Sadat; Ledig, Johannes; Wehmann, Hergo-Heinrich; Mandl, Martin; Strassburg, Martin; Steegmüller, Ulrich; Jahn, Uwe; Lähnemann, Jonas; Riechert, Henning; Griffiths, Ian; Cherns, David; Waag, Andreas

2013-06-01

Arrays of dislocation free uniform Ga-polar GaN columns have been realized on patterned SiOx/GaN/sapphire templates by metal organic vapor phase epitaxy using a continuous growth mode. The key parameters and the physical principles of growth of Ga-polar GaN three-dimensional columns are identified, and their potential for manipulating the growth process is discussed. High aspect ratio columns have been achieved using silane during the growth, leading to n-type columns. The vertical growth rate increases with increasing silane flow. In a core-shell columnar LED structure, the shells of InGaN/GaN multi quantum wells and p-GaN have been realized on a core of n-doped GaN column. Cathodoluminescence gives insight into the inner structure of these core-shell LED structures.

ISICS2011, an updated version of ISICS: A program for calculation K-, L-, and M-shell cross sections from PWBA and ECPSSR theories using a personal computer

NASA Astrophysics Data System (ADS)

Cipolla, Sam J.

2011-11-01

In this new version of ISICS, called ISICS2011, a few omissions and incorrect entries in the built-in file of electron binding energies have been corrected; operational situations leading to un-physical behavior have been identified and flagged. New version program summaryProgram title: ISICS2011 Catalogue identifier: ADDS_v5_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADDS_v5_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 6011 No. of bytes in distributed program, including test data, etc.: 130 587 Distribution format: tar.gz Programming language: C Computer: 80486 or higher-level PCs Operating system: WINDOWS XP and all earlier operating systems Classification: 16.7 Catalogue identifier of previous version: ADDS_v4_0 Journal reference of previous version: Comput. Phys. Commun. 180 (2009) 1716. Does the new version supersede the previous version?: Yes Nature of problem: Ionization and X-ray production cross section calculations for ion-atom collisions. Solution method: Numerical integration of form factor using a logarithmic transform and Gaussian quadrature, plus exact integration limits. Reasons for new version: General need for higher precision in output format for projectile energies; some built-in binding energies needed correcting; some anomalous results occur due to faulty read-in data or calculated parameters becoming un-physical; erroneous calculations could result for the L and M shells when restricted K-shell options are inadvertently chosen; to achieve general compatibility with ISICSoo, a companion C++ version that is portable to Linux and MacOS platforms, has been submitted for publication in the CPC Program Library approximately at the same time as this present new standalone version of ISICS [1]. Summary of revisions: The format field for projectile energies in the output has been expanded from two to four decimal places in order to distinguish between closely spaced energy values. There were a few entries in the executable binding energy file that needed correcting; K shell of Eu, M shells of Zn, M1 shell of Kr. The corrected values were also entered in the ENERGY.DAT file. In addition, an alternate data file of binding energies is included, called ENERGY_GW.DAT, which is more up-to-date [2]. Likewise, an alternate atomic parameters data file is now included, called FLOURE_JC.DAT, which is more up-to-date [3] fluorescence yields for the K and L shells and Coster-Kronig parameters for the L shell. Both data files can be read in using the -f usage option. To do this, the original energy file should be renamed and saved (e.g., ENERGY_BB.DAT) and the new file (ENERGY_GW.DAT ) should be duplicated as ENERGY.DAT to be read in using the -f option. Similarly for reading in an alternate FLOURE.DAT file. As with previous versions, the user can also simply input different values of any input quantity by invoking the "specify your own parameters" option from the main menu. You can also use this option to simply check the values of the built-in values of the parameters. If it still happens that a zero binding energy for a particular sub-shell is read in, the program will not completely abort, but will calculate results for the other sub-shells while setting the affected sub-shell output to zero. In calculating the Coulomb deflection factor, if the quantity inside the radical sign of the parameter z z=√{(1} becomes zero or negative, to prevent the program from aborting, the PWBA cross sections are still calculated while the ECPSSR cross sections are set to zero. This situation can happen for very low energy collisions, such as were noticed for helium ions on copper at energies of E⩽11.2 keV. It was observed during the engineering of ISICSoo [1] that erroneous calculations could result for the L- and M-shell cases when restricted K-shell R or HSR scaling options were inappropriately chosen. The program has now been fixed so that these inappropriate options are ignored for the L and M shells. In the previous versions, the usage for inputting a batch data file was incorrectly stated in the Users Manual as -Bxxx; the correct designation is -Fxxx, or alternatively, -Ixxx, as indicated on the usage screen in running the program. A revised Users Manual is also available. Restrictions: The consumed CPU time increases with the atomic shell (K, L, M), but execution is still very fast. Running time: This depends on which shell and the number of different energies to be used in the calculation. The running time is not significantly changed from the previous version.

From GaN to ZnGa(2)O(4) through a low-temperature process: nanotube and heterostructure arrays.

PubMed

Lu, Ming-Yen; Zhou, Xiang; Chiu, Cheng-Yao; Crawford, Samuel; Gradečak, Silvija

2014-01-22

We demonstrate a method to synthesize GaN-ZnGa2O4 core-shell nanowire and ZnGa2O4 nanotube arrays by a low-temperature hydrothermal process using GaN nanowires as templates. Transmission electron microscopy and X-ray photoelectron spectroscopy results show that a ZnGa2O4 shell forms on the surface of GaN nanowires and that the shell thickness is controlled by the time of the hydrothermal process and thus the concentration of Zn ions in the solution. Furthermore, ZnGa2O4 nanotube arrays were obtained by depleting the GaN core from GaN-ZnGa2O4 core-shell nanowire arrays during the reaction and subsequent etching with HCl. The GaN-ZnGa2O4 core-shell nanowires exhibit photoluminescence peaks centered at 2.60 and 2.90 eV attributed to the ZnGa2O4 shell, as well as peaks centered at 3.35 and 3.50 eV corresponding to the GaN core. We also demonstrate the synthesis of GaN-ZnGa2O4 heterojunction nanowires by a selective formation process as a simple route toward development of heterojunction nanodevices for optoelectronic applications.

Nanoclusters as a new family of high temperature superconductors (Conference Presentation)

NASA Astrophysics Data System (ADS)

Halder, Avik; Kresin, Vitaly V.

2017-03-01

Electrons in metal clusters organize into quantum shells, akin to atomic shells in the periodic table. Such nanoparticles are referred to as "superatoms". The electronic shell levels are highly degenerate giving rise to sharp peaks in the density of states, which can enable exceptionally strong electron pairing in certain clusters containing tens to hundreds of atoms. A spectroscopic investigation of size - resolved aluminum nanoclusters has revealed a sharp rise in the density of states near the Fermi level as the temperature decreases towards 100 K. The effect is especially prominent in the closed-shell "magic" cluster Al66 [1, 2]. The characteristics of this behavior are fully consistent with a pairing transition, implying a high temperature superconducting state with Tc < 100K. This value exceeds that of bulk aluminum by two orders of magnitude. As a new class of high-temperature superconductors, such metal nanocluster particles are promising building blocks for high-Tc materials, devices, and networks. ---------- 1. Halder, A., Liang, A., Kresin, V. V. A novel feature in aluminum cluster photoionization spectra and possibility of electron pairing at T 100K. Nano Lett 15, 1410 - 1413 (2015) 2. Halder, A., Kresin, V. V. A transition in the density of states of metal "superatom" nanoclusters and evidence for superconducting pairing at T 100K. Phys. Rev. B 92, 214506 (2015).

Atomic Layer Deposition of Nickel on ZnO Nanowire Arrays for High-Performance Supercapacitors.

PubMed

Ren, Qing-Hua; Zhang, Yan; Lu, Hong-Liang; Wang, Yong-Ping; Liu, Wen-Jun; Ji, Xin-Ming; Devi, Anjana; Jiang, An-Quan; Zhang, David Wei

2018-01-10

A novel hybrid core-shell structure of ZnO nanowires (NWs)/Ni as a pseudocapacitor electrode was successfully fabricated by atomic layer deposition of a nickel shell, and its capacitive performance was systemically investigated. Transmission electron microscopy and X-ray photoelectron spectroscopy results indicated that the NiO was formed at the interface between ZnO and Ni where the Ni was oxidized by ZnO during the ALD of the Ni layer. Electrochemical measurement results revealed that the Ti/ZnO NWs/Ni (1500 cycles) electrode with a 30 nm thick Ni-NiO shell layer had the best supercapacitor properties including ultrahigh specific capacitance (∼2440 F g -1 ), good rate capability (80.5%) under high current charge-discharge conditions, and a relatively better cycling stability (86.7% of the initial value remained after 750 cycles at 10 A g -1 ). These attractive capacitive behaviors are mainly attributed to the unique core-shell structure and the combined effect of ZnO NW arrays as short charge transfer pathways for ion diffusion and electron transfer as well as conductive Ni serving as channel for the fast electron transport to Ti substrate. This high-performance Ti/ZnO NWs/Ni hybrid structure is expected to be one of a promising electrodes for high-performance supercapacitor applications.

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

NASA Astrophysics Data System (ADS)

Cancio, Antonio C.; Redd, Jeremy J.

2017-03-01

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

Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires.

PubMed

Song, Erdong; Li, Qiming; Swartzentruber, Brian; Pan, Wei; Wang, George T; Martinez, Julio A

2016-01-08

The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN core of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. Selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.

Masses from an inhomogeneous partial difference equation with higher-order isospin contributions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masson, P.J.; Jaenecke, J.

In the present work, a mass equation obtained as the solution of an inhomogeneous partial difference equation is used to predict masses of unknown neutron-rich and proton-rich nuclei. The inhomogeneous source terms contain shell-dependent symmetry energy expressions (quadratic in isospin), and include, as well, an independently derived shell-model Coulomb energy equation which describes all known Coulomb displacement energies with a standarad deviation of sigma/sub c/ = 41 keV. Perturbations of higher order in isospin, previously recognized as a cause of systematic effects in long-range mass extrapolations, are also incorporated. The most general solutions of the inhomogeneous difference equation have beenmore » deduced from a chi/sup 2/-minimization procedure based on the recent atomic mass adjustment of Wapstra, Audi, and Hoekstra. Subjecting the solutions further to the condition of charge symmetry preserves the accuracy of Coulomb energies and allows mass predictions for nuclei with both Ngreater than or equal toZ and Z>N. The solutions correspond to a mass equation with 470 parameters. Using this equation, 4385 mass values have been calculated for nuclei with Agreater than or equal to16 (except N = Z = odd for A<40), with a standard deviation of sigma/sub m/ = 194 keV from the experimental masses. copyright 1988 Academic Press, Inc.« less

Atomic Processes in X-ray Photoioinzed Gas

NASA Technical Reports Server (NTRS)

Kallman, Timothy

2005-01-01

It has long been known that photoionization and photoabsorption play a dominant role in determining the state of gas in nebulae surrounding hot stars and in active galaxies. Recent observations of X-ray spectra demonstrate that these processes are also dominant in highly ionized gas near compact objects, and also affect the transmission of X-rays from the majority of astronomical sources. This has led to new insights into the understanding of what is going on in these sources. It has also pointed out the need for accurate atomic cross sections for photoionization and absorption, notably for processes involving inner shells. The xstar code can be used for calculating the heating, ionization and reprocessing of X-rays by gas in a range of ionization states and temperatures. It has recently been updated to include an improved treatment of inner shell transitions in iron. I will review the capabilities of xstar, the atomic data, and illustrate some applications to recent X-ray spectral observations.

Study the Polyol Process of Preparing the ru Doped FePt Nanoparticles

NASA Astrophysics Data System (ADS)

Lee, Chih-Hao; Hsu, Jen-Ho; Su, Hui-Chia; Huang, Tzu Wen

The structure of Ru doped FePt nanoparticles using polyol process was studied. The particle size grown is around 5 nm, and a shell structure might be formed. By selecting the time and temperature of adding the Ru precursors into solution, three different processes to synthesize the FePtRu particles were studied resulting in different growing mechanics. The possible models during the reaction process are also discussed. The phase transition temperature for the as-grown FCC FePt nanoparticle to transform into L10 FePt nanoparticle is about 823 K which is about the same as the one without doping Ru atoms. From the XAS study of each element, the possible scenario is that: although Ru atoms with the size close to the Pt, they do not totally replace the Pt sites in the FePt alloy. Instead, most of Ru formed a shell outside the FePt nanoparticles and Fe atoms are replaced.

Estimations of Mo X-pinch plasma parameters on QiangGuang-1 facility by L-shell spectral analyses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Jian; Qiu, Aici; State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024

2013-08-15

Plasma parameters of molybdenum (Mo) X-pinches on the 1-MA QiangGuang-1 facility were estimated by L-shell spectral analysis. X-ray radiation from X-pinches had a pulsed width of 1 ns, and its spectra in 2–3 keV were measured with a time-integrated X-ray spectrometer. Relative intensities of spectral features were derived by correcting for the spectral sensitivity of the spectrometer. With an open source, atomic code FAC (flexible atomic code), ion structures, and various atomic radiative-collisional rates for O-, F-, Ne-, Na-, Mg-, and Al-like ionization stages were calculated, and synthetic spectra were constructed at given plasma parameters. By fitting the measured spectramore » with the modeled, Mo X-pinch plasmas on the QiangGuang-1 facility had an electron density of about 10{sup 21} cm{sup −3} and the electron temperature of about 1.2 keV.« less

Supercubes, Supersquares, and Superrods of Face-Centered Cubes (FCC): Atomic and Electronic Requirements of [Mm(SR)l(PR'3)8]q Nanoclusters (M = Coinage Metals) and Their Implications with Respect to Nucleation and Growth of FCC Metals.

PubMed

Teo, Boon K; Yang, Huayan; Yan, Juanzhu; Zheng, Nanfeng

2017-10-02

Understanding the nucleation and growth pathways of nanocrystallites allows precise control of the size and shape of functional crystalline nanomaterials of importance in nanoscience and nanotechnology. This paper provides a detailed analysis of the stereochemical and electronic requirements of three series of nanoclusters based on face-centered cubes (fcc) as the basic building blocks, namely, 1-, 2-, and 3-D assemblages of fcc to form superrods (n), supersquares (n 2 ), and supercubes (n 3 ). The generating functions for calculating the numbers (and arrangements) of surface and interior metal atoms, as well as the number and dispositions of the ligands, for these particular sequences of fcc metal clusters of the general formula [M m (SR) l (PR' 3 ) 8 ] q (where M = coinage metals; SR = thiolates (or group XI ligands), and PR' 3 = phosphines) are presented. An electron-counting scheme based on the jelliumatic shell nodel, a variant of the jellium model, predicts the electron requirements and hence the chemical compositions that are critical in the design and synthesis of the next generation of giant nanoclusters in the nanorealm. The ligand binding specificities, which are keys to effective surface ligand control of the size and shape of these nanoclusters, are defined. Finally, a connection is made with regard to the growth of fcc metals, n 3 , from fcc supercubes (n < 10) to fcc nanocrystallites/particles (10 < n < 10 2 ) and to fcc bulk phase (n > 10 2 ).

Nanoindentation studies of full and empty viral capsids and the effects of capsid protein mutations on elasticity and strength

NASA Astrophysics Data System (ADS)

Michel, J. P.; Ivanovska, I. L.; Gibbons, M. M.; Klug, W. S.; Knobler, C. M.; Wuite, G. J. L.; Schmidt, C. F.

2006-04-01

The elastic properties of capsids of the cowpea chlorotic mottle virus have been examined at pH 4.8 by nanoindentation measurements with an atomic force microscope. Studies have been carried out on WT capsids, both empty and containing the RNA genome, and on full capsids of a salt-stable mutant and empty capsids of the subE mutant. Full capsids resisted indentation more than empty capsids, but all of the capsids were highly elastic. There was an initial reversible linear regime that persisted up to indentations varying between 20% and 30% of the diameter and applied forces of 0.6-1.0 nN; it was followed by a steep drop in force that is associated with irreversible deformation. A single point mutation in the capsid protein increased the capsid stiffness. The experiments are compared with calculations by finite element analysis of the deformation of a homogeneous elastic thick shell. These calculations capture the features of the reversible indentation region and allow Young's moduli and relative strengths to be estimated for the empty capsids. atomic force microscopy | cowpea chlorotic mottle virus | finite element analysis | biomechanics

Nano-engineering of three-dimensional core/shell nanotube arrays for high performance supercapacitors

NASA Astrophysics Data System (ADS)

Grote, Fabian; Wen, Liaoyong; Lei, Yong

2014-06-01

Large-scale arrays of core/shell nanostructures are highly desirable to enhance the performance of supercapacitors. Here we demonstrate an innovative template-based fabrication technique with high structural controllability, which is capable of synthesizing well-ordered three-dimensional arrays of SnO2/MnO2 core/shell nanotubes for electrochemical energy storage in supercapacitor applications. The SnO2 core is fabricated by atomic layer deposition and provides a highly electrical conductive matrix. Subsequently a thin MnO2 shell is coated by electrochemical deposition onto the SnO2 core, which guarantees a short ion diffusion length within the shell. The core/shell structure shows an excellent electrochemical performance with a high specific capacitance of 910 F g-1 at 1 A g-1 and a good rate capability of remaining 217 F g-1 at 50 A g-1. These results shall pave the way to realize aqueous based asymmetric supercapacitors with high specific power and high specific energy.

Reconstruction of TiO2/MnO2-C nanotube/nanoflake core/shell arrays as high-performance supercapacitor electrodes

NASA Astrophysics Data System (ADS)

Xiong, Qinqin; Zheng, Cun; Chi, Hongzhong; Zhang, Jun; Ji, Zhenguo

2017-02-01

Construction of electrodes with fast reaction kinetics is of great importance for achieving advanced supercapacitors. Herein we report a facile combined synthetic strategy with atomic layer deposition (ALD) and electrodeposition to rationally fabricate nanotube/nanoflake core/shell arrays. ALD-TiO2 nanotubes are used as the skeleton core for assembly of electrodeposited MnO2-C nanoflake shells forming a core/shell structure. Highly porous architecture and good electrical conductivity are combined in this unique core/shell structure, resulting in fast ion/electron transfer. In tests of electrochemical performance, the TiO2/MnO2-C core/shell arrays are characterized as cathode for asymmetric supecapacitors and exhibit high specific capacitance (880 F g-1 at 2.5 A g-1), excellent rate properties (735 F g-1 at 30 A g-1) and good long-term cycling stability (94.3% capacitance retention after 20 000 cycles). The proposed electrode construction strategy is favorable for fabrication of other advanced supercapacitor electrodes.

Reconstruction of TiO2/MnO2-C nanotube/nanoflake core/shell arrays as high-performance supercapacitor electrodes.

PubMed

Xiong, Qinqin; Zheng, Cun; Chi, Hongzhong; Zhang, Jun; Ji, Zhenguo

2017-02-03

Construction of electrodes with fast reaction kinetics is of great importance for achieving advanced supercapacitors. Herein we report a facile combined synthetic strategy with atomic layer deposition (ALD) and electrodeposition to rationally fabricate nanotube/nanoflake core/shell arrays. ALD-TiO 2 nanotubes are used as the skeleton core for assembly of electrodeposited MnO 2 -C nanoflake shells forming a core/shell structure. Highly porous architecture and good electrical conductivity are combined in this unique core/shell structure, resulting in fast ion/electron transfer. In tests of electrochemical performance, the TiO 2 /MnO 2 -C core/shell arrays are characterized as cathode for asymmetric supecapacitors and exhibit high specific capacitance (880 F g -1 at 2.5 A g -1 ), excellent rate properties (735 F g -1 at 30 A g -1 ) and good long-term cycling stability (94.3% capacitance retention after 20 000 cycles). The proposed electrode construction strategy is favorable for fabrication of other advanced supercapacitor electrodes.

Shell-Isolated Tip-Enhanced Raman and Fluorescence Spectroscopy.

PubMed

Huang, Ya-Ping; Huang, Sheng-Chao; Wang, Xiang-Jie; Bodappa, Nataraju; Li, Chao-Yu; Yin, Hao; Su, Hai-Sheng; Meng, Meng; Zhang, Hua; Ren, Bin; Yang, Zhi-Lin; Zenobi, Renato; Tian, Zhong-Qun; Li, Jian-Feng

2018-06-18

Tip-enhanced Raman spectroscopy can provide molecular fingerprint information with ultrahigh spatial resolution, but the tip will be easily contaminated, thus leading to artifacts. It also remains a great challenge to establish tip-enhanced fluorescence because of the quenching resulting from the proximity of the metal tip. Herein, we report shell-isolated tip-enhanced Raman and fluorescence spectroscopies by employing ultrathin shell-isolated tips fabricated by atomic layer deposition. Such shell-isolated tips not only show outstanding electromagnetic field enhancement in TERS but also exclude interference by contaminants, thus greatly promoting applications in solution. Tip-enhanced fluorescence has also been achieved using these shell-isolated tips, with enhancement factors of up to 1.7×10 3 , consistent with theoretical simulations. Furthermore, tip-enhanced Raman and fluorescence signals are acquired simultaneously, and their relative intensities can be manipulated by changing the shell thickness. This work opens a new avenue for ultrahigh resolution surface analysis using plasmon-enhanced spectroscopies. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interpenetrating Triphase Cobalt-Based Nanocomposites as Efficient Bifunctional Oxygen Electrocatalysts for Long-Lasting Rechargeable Zn–Air Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Yi; Deng, Ya-Ping; Fu, Jing

Rational construction of atomic-scale interfaces in multiphase nanocomposites is an intriguing and challenging approach to developing advanced catalysts for both oxygen reduction (ORR) and evolution reactions (OER). In this paper, a hybrid of interpenetrating metallic Co and spinel Co 3O 4 “Janus” nanoparticles stitched in porous graphitized shells (Co/Co 3O 4@PGS) is synthesized via ionic exchange and redox between Co 2+ and 2D metal–organic-framework nanosheets. This strategy is proven to effectively establish highways for the transfer of electrons and reactants within the hybrid through interfacial engineering. Specifically, the phase interpenetration of mixed Co species and encapsulating porous graphitized shells providesmore » an optimal charge/mass transport environment. Furthermore, the defect-rich interfaces act as atomic-traps to achieve exceptional adsorption capability for oxygen reactants. Finally, robust coupling between Co and N through intimate covalent bonds prohibits the detachment of nanoparticles. As a result, Co/Co 3O 4@PGS outperforms state-of-the-art noble-metal catalysts with a positive half-wave potential of 0.89 V for ORR and a low potential of 1.58 V at 10 mA cm -2 for OER. Finally, in a practical demonstration, ultrastable cyclability with a record lifetime of over 800 h at 10 mA cm -2 is achieved by Zn–air batteries with Co/Co 3O 4@PGS within the rechargeable air electrode.« less

Interpenetrating Triphase Cobalt-Based Nanocomposites as Efficient Bifunctional Oxygen Electrocatalysts for Long-Lasting Rechargeable Zn–Air Batteries

DOE PAGES

Jiang, Yi; Deng, Ya-Ping; Fu, Jing; ...

2018-01-31

Rational construction of atomic-scale interfaces in multiphase nanocomposites is an intriguing and challenging approach to developing advanced catalysts for both oxygen reduction (ORR) and evolution reactions (OER). In this paper, a hybrid of interpenetrating metallic Co and spinel Co 3O 4 “Janus” nanoparticles stitched in porous graphitized shells (Co/Co 3O 4@PGS) is synthesized via ionic exchange and redox between Co 2+ and 2D metal–organic-framework nanosheets. This strategy is proven to effectively establish highways for the transfer of electrons and reactants within the hybrid through interfacial engineering. Specifically, the phase interpenetration of mixed Co species and encapsulating porous graphitized shells providesmore » an optimal charge/mass transport environment. Furthermore, the defect-rich interfaces act as atomic-traps to achieve exceptional adsorption capability for oxygen reactants. Finally, robust coupling between Co and N through intimate covalent bonds prohibits the detachment of nanoparticles. As a result, Co/Co 3O 4@PGS outperforms state-of-the-art noble-metal catalysts with a positive half-wave potential of 0.89 V for ORR and a low potential of 1.58 V at 10 mA cm -2 for OER. Finally, in a practical demonstration, ultrastable cyclability with a record lifetime of over 800 h at 10 mA cm -2 is achieved by Zn–air batteries with Co/Co 3O 4@PGS within the rechargeable air electrode.« less

Effects of gold diffusion on n-type doping of GaAs nanowires.

PubMed

Tambe, Michael J; Ren, Shenqiang; Gradecak, Silvija

2010-11-10

The deposition of n-GaAs shells is explored as a method of n-type doping in GaAs nanowires grown by the Au-mediated metal-organic chemical vapor deposition. Core-shell GaAs/n-GaAs nanowires exhibit an unintended rectifying behavior that is attributed to the Au diffusion during the shell deposition based on studies using energy dispersive X-ray spectroscopy, current-voltage, capacitance-voltage, and Kelvin probe force measurements. Removing the gold prior to n-type shell deposition results in the realization of n-type GaAs nanowires without rectification. We directly correlate the presence of gold impurities to nanowire electrical properties and provide an insight into the role of seed particles on the properties of nanowires and nanowire heterostructures.

Field-assisted organization, substrate effects and magnetic behavior of Ag 30Co 70 core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Crisan, A. D.; Angelakeris, M.; Simeonidis, K.; Tsiaoussis, I.; Crisan, O.

2010-11-01

In core-shell systems with non-magnetic core and magnetic shell, the electron transport and magnetic properties are expected to show enhanced behavior due to the particular morpho-structural features of the conductive and magnetic regions. This may lead to novel advanced GMR materials and spin valves. This is the case of core-shell Ag-Co colloidal nanoscale particles that organize into regular arrays. An insight on the structure and morphology of the newly synthesized Ag-Co nanoparticles deposited on different substrates will be presented. The influence of the substrate on different morphologies and organization dynamics is discussed. It is shown that the magnetic behavior of the Ag-Co nanoparticles is highly influenced by the corona-like morphology of Co shell, chemical environment of the magnetic atoms and by the fact that they exhibit strongly reduced coordination due to the surface states.

Wide-range tuning of the surface plasmon resonance of silver/gold core shell and alloyed nanoparticles

NASA Astrophysics Data System (ADS)

Hubenthal, Frank; Ziegler, Torsten; Hendrich, Christian; Träger, Frank

2004-03-01

For many applications like surface enhanced Raman scattering in which the optical field enhancement associated with surface plasmon excitation is exploited, tunability of this collective resonance over a wide range is required. For this purpose we have prepared Ag/Au core shell and Ag/Au alloyed nanoparticles with different shell thicknesses and different percentages of the two metals. The nanoparticles were made by subsequent deposition of Ag and Au atoms on dielectric substrates followed by diffusion and nucleation or heat treatment. Depending on the Au shell thickness the plasmon frequency can be tuned, e.g. from 2.8 eV (442 nm) to 2.1 eV (590 nm). Annealing of the core-shell nanoparticles causes a shift of the resonance frequency to 2.6 eV. Theoretical modelling allows us to attribute this observation to the production of alloyed nanoparticles. Possible application of the Ag/Au nanoparticles will be discussed.

Symmetric Resonance Charge Exchange Cross Section Based on Impact Parameter Treatment

NASA Technical Reports Server (NTRS)

Omidvar, Kazem; Murphy, Kendrah; Atlas, Robert (Technical Monitor)

2002-01-01

Using a two-state impact parameter approximation, a calculation has been carried out to obtain symmetric resonance charge transfer cross sections between nine ions and their parent atoms or molecules. Calculation is based on a two-dimensional numerical integration. The method is mostly suited for hydrogenic and some closed shell atoms. Good agreement has been obtained with the results of laboratory measurements for the ion-atom pairs H+-H, He+-He, and Ar+-Ar. Several approximations in a similar published calculation have been eliminated.

δ15N as a Potential Paleoenvironmental Proxy for Nitrogen Loading in Chesapeake Bay

NASA Astrophysics Data System (ADS)

Black, H. D.; Andrus, C. F.; Rick, T.; Hines, A.

2013-12-01

Stable isotope analysis of Eastern Oyster (Crassostrea virginica) and other mollusk shells from archaeological sites is a useful means of acquiring paleoenvironmental data. Recently, nitrogen isotopes have been identified as a potential new proxy in these shells. δ15N content in mollusk shells is affected by numerous anthropogenic and natural influences and may be used as an environmental proxy for nitrogen loading conditions. Chesapeake Bay is well known for both historic and modern pollution problems from numerous anthropogenic sources, such as fertilizer runoff, sewage discharge, and densely populated land use and serves as an ideal study location for long-term nitrogen loading processes. Longer records of these processes may be recorded in abundant archaeological remains around the bay, however, little is known about the stability of δ15N and %N in shell material over recent geologic time. In this study, 90 archaeological C. virginica shells were collected by the Smithsonian Institution from the Rhode River Estuary within Chesapeake Bay and range in age from ~150 to 3200 years old. Twenty-two modern C. virginica shells were also collected from nearby beds in the bay. All shell samples were subsampled from the resilifer region of the calcitic shell using a hand-held micro drill and were analyzed using EA-IRMS analysis to determine the potential temporal variability of δ15N and %N as well as creating a baseline for ancient nitrogen conditions in the bay area. Modern POM water samples and C. virginica soft tissues were also analyzed in this study to determine the degree of seasonal variation of δ15N and %N in Chesapeake Bay.

Neutron-antineutron oscillations in nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dover, C.B.; Gal, A.; Richard, J.M.

1983-03-01

We present calculations of the neutron-antineutron (n-n-bar) annihilation lifetime T in deuterium, /sup 16/O, and /sup 56/Fe in terms of the free-space oscillation time tau/sub n/n-bar. The coupled Schroedinger equations for the n and n-bar wave functions in a nucleus are solved numerically, using a realistic shell-model potential which fits the empirical binding energies of the neu- p tron orbits, and a complex n-bar-nucleus optical potential obtained from fits to p-bar-atom level shifts. Most previous estimates of T in nuclei, which exhibit large variations, are found to be quite inaccurate. When the nuclear-physics aspects of the problem are handled properlymore » (in particular, the finite neutron binding, the nuclear radius, and the surface diffuseness), the results are found to be rather stable with respect to allowable changes in the parameters of the nuclear model. We conclude that experimental limits on T in nuclei can be used to give reasonably precise constraints on tau/sub n/n-bar: T>10/sup 30/ or 10/sup 31/ yr leads to tau/sub n/n-bar>(1.5--2) x 10/sup 7/ or (5--6) x 10/sup 7/ sec, respectively.« less

Atomic structure calculations and identification of EUV and SXR spectral lines in Sr XXX

NASA Astrophysics Data System (ADS)

Goyal, Arun; Khatri, Indu; Aggarwal, Sunny; Singh, A. K.; Mohan, Man

2015-08-01

We report an extensive theoretical study of atomic data for Sr XXX in a wide range with L-shell electron excitations to the M-shell. We have calculated energy levels, wave-function compositions and lifetimes for lowest 113 fine structure levels and wavelengths of an extreme Ultraviolet (EUV) and soft X-ray (SXR) transitions. We have employed multi-configuration Dirac Fock method (MCDF) approach within the framework of Dirac-Coulomb Hamiltonian including quantum electrodynamics (QED) and Breit corrections. We have also presented the radiative data for electric and magnetic dipole (E1, M1) and quadrupole (E2, M2) transitions from the ground state. We have made comparisons with available energy levels compiled by NIST and achieve good agreement. But due to inadequate data in the literature, analogous relativistic distorted wave calculations have also been performed using flexible atomic code (FAC) to assess the reliability and accuracy of our results. Additionally, we have provided new atomic data for Sr XXX which is not published elsewhere in the literature and we believe that our results may be beneficial in fusion plasma research and astrophysical investigations and applications.

Density functional study of the structural, electronic, and magnetic properties of Mo n and Mo n S ( n = 1 - 10) clusters

NASA Astrophysics Data System (ADS)

Ziane, M.; Amitouche, F.; Bouarab, S.; Vega, A.

2017-12-01

Structural and electronic properties of pure molybdenum Mo n and molybdenum-sulfide Mo n S ( n = 1 - 10) clusters were investigated in the framework of the density functional theory within the generalized gradient approximation to exchange and correlation with the aim of addressing how doping with a single S atom affects the geometries, magnetic properties, and reactivity of pure molybdenum clusters. These clusters exhibit a less marked tendency to dimerization than their isoelectronic Cr counterparts despite sharing their half-filled valence shell configuration. Doping with a single S impurity is enough to change the structure of the host molybdenum cluster to a large extent, as well as to modify the bonding pattern, the magnetic state and the magnetic moment distribution in the Mo host. Vertical ionization potentials and electron affinities are calculated to determine global reactivity indicators like the electronegativity and the chemical hardness. The results are discussed in terms of the thermodynamical and relative stabilities, charge transfer effects, and spin-polarized densities of electronic states.

Statistical modeling of the reactions Fe(+) + N2O → FeO(+) + N2 and FeO(+) + CO → Fe(+) + CO2.

PubMed

Ushakov, Vladimir G; Troe, Jürgen; Johnson, Ryan S; Guo, Hua; Ard, Shaun G; Melko, Joshua J; Shuman, Nicholas S; Viggiano, Albert A

2015-08-14

The rates of the reactions Fe(+) + N2O → FeO(+) + N2 and FeO(+) + CO → Fe(+) + CO2 are modeled by statistical rate theory accounting for energy- and angular momentum-specific rate constants for formation of the primary and secondary cationic adducts and their backward and forward reactions. The reactions are both suggested to proceed on sextet and quartet potential energy surfaces with efficient, but probably not complete, equilibration by spin-inversion of the populations of the sextet and quartet adducts. The influence of spin-inversion on the overall reaction rate is investigated. The differences of the two reaction rates mostly are due to different numbers of entrance states (atom + linear rotor or linear rotor + linear rotor, respectively). The reaction Fe(+) + N2O was studied either with (6)Fe(+) or with (4)Fe(+) reactants. Differences in the rate constants of (6)Fe(+) and (4)Fe(+) reacting with N2O are attributed to different contributions from electronically excited potential energy surfaces, such as they originate from the open-electronic shell reactants.

Aluminum/hydrocarbon gel propellants: An experimental and theoretical investigation of secondary atomization and predicted rocket engine performance

NASA Astrophysics Data System (ADS)

Mueller, Donn Christopher

1997-12-01

Experimental and theoretical investigations of aluminum/hydrocarbon gel propellant secondary atomization and its potential effects on rocket engine performance were conducted. In the experimental efforts, a dilute, polydisperse, gel droplet spray was injected into the postflame region of a burner and droplet size distributions was measured as a function of position above the burner using a laser-based sizing/velocimetry technique. The sizing/velocimetry technique was developed to measure droplets in the 10-125 mum size range and avoids size-biased detection through the use of a uniformly illuminated probe volume. The technique was used to determine particle size distributions and velocities at various axial locations above the burner for JP-10, and 50 and 60 wt% aluminum gels. Droplet shell formation models were applied to aluminum/hydrocarbon gels to examine particle size and mass loading effects on the minimum droplet diameter that will permit secondary atomization. This diameter was predicted to be 38.1 and 34.7 mum for the 50 and 60 wt% gels, which is somewhat greater than the experimentally measured 30 and 25 mum diameters. In the theoretical efforts, three models were developed and an existing rocket code was exercised to gain insights into secondary atomization. The first model was designed to predict gel droplet properties and shell stresses after rigid shell formation, while the second, a one-dimensional gel spray combustion model was created to quantify the secondary atomization process. Experimental and numerical comparisons verify that secondary atomization occurs in 10-125 mum diameter particles although an exact model could not be derived. The third model, a one-dimensional gel-fueled rocket combustion chamber, was developed to evaluate secondary atomization effects on various engine performance parameters. Results show that only modest secondary atomization may be required to reduce propellant burnout distance and radiation losses. A solid propellant engine code was employed to estimate nozzle two-phase flow losses and engine performance for upper-stage and booster missions (3-6% and 2-3%, respectively). Given these losses and other difficulties, metallized gel propellants may be impractical in high-expansion ratio engines. Although uncertainties remain, it appears that performance gains will be minimal in gross-weight limited missions, but that significant gains may arise in volume-limited missions.

X-ray STM: Nanoscale elemental analysis & Observation of atomic track.

PubMed

Saito, Akira; Furudate, Y; Kusui, Y; Saito, T; Akai-Kasaya, M; Tanaka, Y; Tamasaku, K; Kohmura, Y; Ishikawa, T; Kuwahara, Y; Aono, M

2014-11-01

Scanning tunneling microscopy (STM) combined with brilliant X-rays from synchrotron radiation (SR) can provide various possibilities of original and important applications, such as the elemental analysis on solid surfaces at an atomic scale. The principle of the elemental analysis is based on the inner-shell excitation of an element-specific energy level "under STM observation". A key to obtain an atomic locality is to extract the element-specific modulation of the local tunneling current (not emission that can damage the spatial resolution), which is derived from the inner-shell excitation [1]. On this purpose, we developed a special SR-STM system and smart tip. To surmount a tiny core-excitation efficiency by hard X-rays, we focused two-dimensionally an incident beam having the highest photon density at the SPring-8.After successes in the elemental analyses by SR-STM [1,2] on a semiconductor hetero-interface (Ge on Si) and metal-semiconductor interface (Cu on Ge), we succeeded in obtaining the elemental contrast between Co nano-islands and Au substrate. The results on the metallic substrate suggest the generality of the method and give some important implications on the principle of contrast. For all cases of three samples, the spatial resolution of the analysis was estimated to be ∼1 nm or less, and it is worth noting that the measured surface domains had a deposition thickness of less than one atomic layer (Fig. 1, left and center).jmicro;63/suppl_1/i14-a/DFU045F1F1DFU045F1Fig. 1.(left) Topographic image and (center) beam-induced tip current image of Ge(111)-Cu (-2V, 0.2 nA). (right) X-ray- induced atomic motion tracks on Ge(111) that were newly imaged by the Xray-STM. On the other hand, we found that the "X-ray induced atomic motion" can be observed directly with atomic scale using the SR-STM system effectively under the incident photon density of ∼2 x10(15) photon/sec/mm(2) [3]. SR-STM visualized successfully the track of the atomic motion (Fig. 1, right), which enabled the further analysis on the mechanism of the atomic motion. It is worth comparing our results with past conventional thermal STM observations on the same surface [4], where the atomic motion was found to occur in the 2-dimensional domain. However, our results show the atomic track having a local chain distribution [3].The above mentioned results will allow us to investigate the chemical analysis and control of the local reaction with the spatial resolution of STM, giving hope of wide applications. © The Author 2014. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

TiO2/ZnO and ZnO/TiO2 core/shell nanofibers prepared by electrospinning and atomic layer deposition for photocatalysis and gas sensing

NASA Astrophysics Data System (ADS)

Boyadjiev, Stefan I.; Kéri, Orsolya; Bárdos, Péter; Firkala, Tamás; Gáber, Fanni; Nagy, Zsombor K.; Baji, Zsófia; Takács, Máté; Szilágyi, Imre M.

2017-12-01

In the present work, core TiO2 and ZnO oxide nanofibers were prepared by electrospinning, then shell oxide (ZnO, TiO2) layers were deposited on them by atomic layer deposition (ALD). The aim of preparing ZnO and TiO2 nanofibers, as well as ZnO/TiO2 and TiO2/ZnO nanocomposites is to study the interaction between the oxide materials when a pure oxide fiber is covered with thin film of the other oxide, and explore the influence of exchanging the core and shell materials on their photocatalytic and gas sensing properties. The composition, structure and morphology of the pure and composite nanofibers were studied by SEM-EDX, TEM, XRD, FTIR, UV-vis and Raman. The photocatalytic activity of the as-prepared materials was analyzed by UV-vis spectroscopy through decomposing aqueous methyl orange under UV irradiation. The gas sensing of the nanofibers was investigated by detecting 100 ppm NH3 at 150 and 220 °C using interdigital electrode based sensors.

xLIPA: Promotion of Electrons from the K-shell to 2 GeV using 10 PW Laser Pulses

DTIC Science & Technology

2015-08-19

field [34]. Since then numerous analytical and numerical approaches have been employed with special emphasis on laser photoionization . Besides interest in... photoionization as a fundamental physical process there are many applications for photoelectrons. Knowledge of the electron properties, e.g., energy...Schwinger field. Photoionization of inner-shell electrons in high-Z atoms is another example where relativistic effects are important. Two analytical

Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Xiaogang; Hamid, Ilyar; Duan, Haiming, E-mail: dhm@xju.edu.cn

2016-06-15

The dynamic stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 metal elements. The clusters originate from five different initial structures (icosahedron, truncated decahedron, octahedron, closed-shell fragment of an HCP structure, and non-closed-shell fragment of an HCP structure). The obtained order of the dynamic stabilities of the icosahedral-like clusters can be assigned to three groups, from stronger to weaker, according to the size ranges involved: (Zr, Al, Ti) > (Cu, Fe, Co, Ni, Mg, Ag) > (Pb, Au, Pd, Pt, Rh, Ir), which correspond to the predicted formation ability of the quasicrystals. The differences ofmore » the sequences can be explained by analyzing the parameters of the Gupta-type many-body inter-atomic potentials.« less

Ni3Si(Al)/a-SiOx core shell nanoparticles: characterization, shell formation, and stability

NASA Astrophysics Data System (ADS)

Pigozzi, G.; Mukherji, D.; Gilles, R.; Barbier, B.; Kostorz, G.

2006-08-01

We have used an electrochemical selective phase dissolution method to extract nanoprecipitates of the Ni3Si-type intermetallic phase from two-phase Ni-Si and Ni-Si-Al alloys by dissolving the matrix phase. The extracted nanoparticles are characterized by transmission electron microscopy, energy-dispersive x-ray spectrometry, x-ray powder diffraction, and electron powder diffraction. It is found that the Ni3Si-type nanoparticles have a core-shell structure. The core maintains the size, the shape, and the crystal structure of the precipitates that existed in the bulk alloys, while the shell is an amorphous phase, containing only Si and O (SiOx). The shell forms around the precipitates during the extraction process. After annealing the nanoparticles in nitrogen at 700 °C, the tridymite phase recrystallizes within the shell, which remains partially amorphous. In contrast, on annealing in air at 1000 °C, no changes in the composition or the structure of the nanoparticles occur. It is suggested that the shell forms after dealloying of the matrix phase, where Si atoms, the main constituents of the shell, migrate to the surface of the precipitates.

Ni(3)Si(Al)/a-SiO(x) core-shell nanoparticles: characterization, shell formation, and stability.

PubMed

Pigozzi, G; Mukherji, D; Gilles, R; Barbier, B; Kostorz, G

2006-08-28

We have used an electrochemical selective phase dissolution method to extract nanoprecipitates of the Ni(3)Si-type intermetallic phase from two-phase Ni-Si and Ni-Si-Al alloys by dissolving the matrix phase. The extracted nanoparticles are characterized by transmission electron microscopy, energy-dispersive x-ray spectrometry, x-ray powder diffraction, and electron powder diffraction. It is found that the Ni(3)Si-type nanoparticles have a core-shell structure. The core maintains the size, the shape, and the crystal structure of the precipitates that existed in the bulk alloys, while the shell is an amorphous phase, containing only Si and O (SiO(x)). The shell forms around the precipitates during the extraction process. After annealing the nanoparticles in nitrogen at 700 °C, the tridymite phase recrystallizes within the shell, which remains partially amorphous. In contrast, on annealing in air at 1000 °C, no changes in the composition or the structure of the nanoparticles occur. It is suggested that the shell forms after dealloying of the matrix phase, where Si atoms, the main constituents of the shell, migrate to the surface of the precipitates.

Microfluidic Synthesis of Hybrid Nanoparticles with Controlled Lipid Layers: Understanding Flexibility-Regulated Cell-Nanoparticle Interaction.

PubMed

Zhang, Lu; Feng, Qiang; Wang, Jiuling; Zhang, Shuai; Ding, Baoquan; Wei, Yujie; Dong, Mingdong; Ryu, Ji-Young; Yoon, Tae-Young; Shi, Xinghua; Sun, Jiashu; Jiang, Xingyu

2015-10-27

The functionalized lipid shell of hybrid nanoparticles plays an important role for improving their biocompatibility and in vivo stability. Yet few efforts have been made to critically examine the shell structure of nanoparticles and its effect on cell-particle interaction. Here we develop a microfluidic chip allowing for the synthesis of structurally well-defined lipid-polymer nanoparticles of the same sizes, but covered with either lipid-monolayer-shell (MPs, monolayer nanoparticles) or lipid-bilayer-shell (BPs, bilayer nanoparticles). Atomic force microscope and atomistic simulations reveal that MPs have a lower flexibility than BPs, resulting in a more efficient cellular uptake and thus anticancer effect than BPs do. This flexibility-regulated cell-particle interaction may have important implications for designing drug nanocarriers.

Measurements of K shell absorption jump factors and jump ratios using EDXRF technique

NASA Astrophysics Data System (ADS)

Kacal, Mustafa Recep; Han, İbrahim; Akman, Ferdi

2015-04-01

In the present work, the K-shell absorption jump factors and jump ratios for 30 elements between Ti ( Z = 22) and Er ( Z = 68) were measured by energy dispersive X-ray fluorescence (EDXRF) technique. The jump factors and jump ratios for these elements were determined by measuring the K shell fluorescence parameters such as the Kα X-ray production cross-sections, K shell fluorescence yields, Kβ-to- Kα X-rays intensity ratios, total atomic absorption cross sections and mass attenuation coefficients. The measurements were performed using an Am-241 radioactive point source and a Si (Li) detector in direct excitation and transmission experimental geometry. The results for jump factors and jump ratios were compared with theoretically calculated and the ones available in the literature.

Observations of emission lines in M supergiants

NASA Technical Reports Server (NTRS)

Lambert, D. L.

1979-01-01

Copernicus observations of Mg 2 h and k emission lines from M giants and supergiants are described. Supergiants with extensive circumstellar gas shells show an asymmetric k line. The asymmetry is ascribed to superimposed lines of Fe 1 and Mn 1. The Mg 2 line width fit the Wilson-Bappu relation derived from observations of G and K Stars. Results of correlated ground-based observations include (1) the discovery of K 1 fluorescent emission from the Betelgeuse shell; (2) extimates of the mass-loss rates; and (3) the proposal that silicate dust grains must account for the major fraction of the Si atoms in the Betelgeuse shell.

Benchmarking transition energies and emission strengths for X-ray astrophysics with measurements at the Livermore EBITs

NASA Astrophysics Data System (ADS)

Hell, Natalie

2017-03-01

K-shell transitions in astrophysically abundant metals and L-shell transitions in Fe group elements show characteristic signatures in the soft X-ray spectrum in the energy range 0.1-10 keV. These signatures have great diagnostic value for plasma parameters such as electron and ion temperatures and densities, and can thus help understand the physics controlling the energetic processes in astrophysical sources. This diagnostic power increases with advances in spectral resolution and effective area of the employed X-ray observatories. However, to make optimal use of the diagnostic potential - whether through global spectral modeling or through diagnostics from local modeling of individual lines - the underlying atomic physics has to be complete and well known. With the next generation of soft X-ray observatories featuring micro-calorimeters such as the SXS on Astro-H /Hitomi and the X-IFU on Athena, broadband high-resolution spectroscopy with large effective area will become more commonly available in the next decade. With these spectrometers, the accuracy of the plasma parameters derived from spectral modeling will be limited by the uncertainty of the reference atomic data rather than by instrumental factors, as is sometimes already the case for the high-resolution grating observations with Chandra-HETG and XMM-Newton-RGS. To take full advantage of the measured spectra, assessment of the accuracy of and improvements to the available atomic reference data are therefore important. Dedicated measurements in the laboratory are essential to benchmark the theoretical calculations providing the bulk of the reference data used in astrophysics. Experiments at the Lawrence Livermore National Laboratory electron beam ion traps (EBIT-I and SuperEBIT) have a long history of providing this service. In this work, I present new measurements of transition energies and absolute electron impact excitation cross sections geared towards currently open atomic physics data needs. First, I measured the energies of K α transitions in L-shell ions of Si and S at EBIT using the EBIT calorimeter spectrometer (ECS) with 4.5-5.0 eV resolution, i.e., a similar resolution to the Astro-H /Hitomi SXS soft X-ray spectrometer. While these lines will become interesting also for L-shell ions of other astrophysically abundant elements, they have been observed most prominently from L-shell ions of Si and S in the X-ray spectra of a variety of astrophysical sources. The measured line centers have an accuracy of 0.5 eV for the strong transitions and 1 eV for the weaker ones. This accuracy translates to Doppler shifts of less than 90 km s -1 , i.e., less than the calibration uncertainty of the Chandra high-energy transmission gratings. The measured line centers are identified with my own calculations with the Flexible Atomic Code (FAC) and compared to these and calculations by Palmeri et al. (2008). I demonstrate the impact of these measurements by re-evaluating Doppler shifts for the high-mass X-ray binaries Vela X-1 and Cyg X-1 with the new reference data. Using the high-resolution, imaging focusing spherical crystal spectrometer EBHiX with a quartz 101 crystal, I verified the results from the ECS measurements on K α transitions in N- through Li-like S. The measurement has a spectral resolution of better than 0.52 eV. The derived transition energies have an accuracy of 0.2 eV, corresponding to Doppler shifts of < 30 km s -1 , i.e., within the requirements set by the planned Athena X-ray observatory. Secondly, I used the EBHiX crystal spectrometer with a quartz 110 crystal in second order to measure the strongly blended K α spectra of M-shell Fe ions around 6.4 keV. Contributions to the 6.4 keV line complex from these ions are important for transient plasmas such as those in supernova remnants. While a simple FAC model of Cl- through F-like Fe suggested it should be possible to resolve major contributions from different charge states to this complex at a 2 eV resolution, the data did not allow us to identify any new lines, although the spectral resolution of this measurement was higher than in previous experiments. Thirdly, I measured absolute electron impact excitation (EIE) cross sections for He-like Fe line w and H-like Fe Ly α 1 and Ly α 2 at different electron energies and charge balances. The cross sections of the direct excitation lines are brought to an absolute scale by normalizing to the radiative recombination (RR) spectrum of the same ion. The direct excitation spectrum was measured with the low-energy pixels of the ECS with a spectral resolution of about 6 eV, while the RR spectrum was recorded with the ECS's thicker high-energy pixels with instrumental resolution of about 30 eV. The high-energy pixels thus allowed us, for the first time, to resolve the RR into the n = 2 shell of L-shell Fe ions at electron impact energies high enough to excite a K-shell electron in Fe ions. These measurements of absolute EIE cross sections using the ECS microcalorimeter at EBIT have accuracies on the 10% level, and therefore fulfill the requirements on atomic reference data identified by the astrophysics community. Benchmarking theoretical cross sections on this level tightens the constraints on important diagnostics for, e.g., elemental abundance measurements and resonance scattering in the high-resolution X-ray spectra of the Perseus galaxy cluster observed with Hitomi -SXS. Finally, the performance of the EBHiX crystal spectrometer at EBIT was evaluated for various quartz crystals and the ion temperatures of the ions trapped in EBIT were derived from thermal line broadening measured with EBHiX. The EBHiX's apability to measure the degree of linear polarization for X-ray transitions excited in EBIT was demonstrated for the H-like Mn Ly α line.

Calcium hydroxide coating on highly reactive nanoscale zero-valent iron for in situ remediation application.

PubMed

Wei, Cai-Jie; Xie, Yue-Feng; Wang, Xiao-Mao; Li, Xiao-Yan

2018-05-23

Nano scale zero-valent iron (nZVI), a promising engineering technology for in situ remediation, has been greatly limited by quick self-corrosion and low mobility in porous media. Highly reactive nZVI particles produced from the borohydride reduction method were enclosed in a releasable Ca(OH) 2 layer by the chemical deposition method. The amount of Ca(OH) 2 coated on nZVI surface were well controlled by the precursor dosage. At moderate Ca(OH) 2 dosage (R Ca/TFe  = 0.25) condition, the increment of Fe 0 content for the obtained nZVI/Ca-0.25 sample was observed. The interfacial reactions between the iron oxide shell and the Ca(OH) 2 saturated environment were delicately elucidated by the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) spectrum. And the coverage of Ca(OH) 2 shell on spherical nZVI surface was found more complete and uniform for the nZVI/Ca sample obtained from the moderate precursor dosage condition (R Ca/TFe  = 0.25). The Ca(OH) 2 shell before dissolution was demonstrated owning the anti-corrosion capability to slow down the oxidation of Fe 0 core in air, during ethanol storage and in aqueous environment. The mechanism of anti-corrosion capability for nZVI/Ca-0.25 particle was interestingly found to be attributed to the Ca(OH) 2 shell isolation and also be potentially due to the iron oxide shell phase transformation mediated by the outer Ca(OH) 2 shell. An improved trichloroethylene reduction performance was observed for nZVI/Ca-0.25 than bare nZVI. The mobility of nZVI/Ca particles in water-saturated porous media was moderately improved before shell dissolution. Copyright © 2018 Elsevier Ltd. All rights reserved.

Energetics and solvation structure of a dihalogen dopant (I2) in (4)He clusters.

PubMed

Pérez de Tudela, Ricardo; Barragán, Patricia; Valdés, Álvaro; Prosmiti, Rita

2014-08-21

The energetics and structure of small HeNI2 clusters are analyzed as the size of the system changes, with N up to 38. The full interaction between the I2 molecule and the He atoms is based on analytical ab initio He-I2 potentials plus the He-He interaction, obtained from first-principle calculations. The most stable structures, as a function of the number of solvent He atoms, are obtained by employing an evolutionary algorithm and compared with CCSD(T) and MP2 ab initio computations. Further, the classical description is completed by explicitly including thermal corrections and quantum features, such as zero-point-energy values and spatial delocalization. From quantum PIMC calculations, the binding energies and radial/angular probability density distributions of the thermal equilibrium state for selected-size clusters are computed at a low temperature. The sequential formation of regular shell structures is analyzed and discussed for both classical and quantum treatments.

Local structure of Iridium organometallic catalysts covalently bonded to carbon nanotubes.

NASA Astrophysics Data System (ADS)

Blasco, J.; Cuartero, V.; Subías, G.; Jiménez, M. V.; Pérez-Torrente, J. J.; Oro, L. A.; Blanco, M.; Álvarez, P.; Blanco, C.; Menéndez, R.

2016-05-01

Hybrid catalysts based on Iridium N-heterocyclic carbenes anchored to carbon nanotubes (CNT) have been studied by XAFS spectroscopy. Oxidation of CNT yields a large amount of functional groups, mainly hydroxyl groups at the walls and carboxylic groups at the tips, defects and edges. Different kinds of esterification reactions were performed to functionalize oxidized CNT with imidazolium salts. Then, the resulting products were reacted with an Ir organometallic compound to form hybrid catalysts efficient in hydrogen transfer processes. XANES spectroscopy agree with the presence of Ir(I) in these catalysts and the EXAFS spectra detected differences in the local structure of Ir atoms between the initial Ir organometallic compound and the Ir complexes anchored to the CNT. Our results confirm that the halide atom, present in the Ir precursor, was replaced by oxygen from -OH groups at the CNT wall in the first coordination shell of Ir. The lability of this group accounts for the good recyclability and the good efficiency shown by these hybrid catalysts.

Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Erdong; Li, Qiming; Swartzentruber, Brian

2015-11-25

The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN coremore » of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. As a result, selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.« less

Electron diffraction and microscopy study of nanotubes and nanowires

NASA Astrophysics Data System (ADS)

Deniz, Hakan

Carbon nanotubes have many excellent properties that are strongly influenced by their atomic structure. The realization of the ultimate potential of carbon nanotubes in technological applications necessitates a precise control of the structure of as-grown nanotubes as well as the identification of their atomic structures. Transmission electron microscopy (TEM) is a technique that can deliver this by combining the high resolution imaging and electron diffraction simultaneously. In this study, a new catalyst system (the Co/Si) was investigated in the production of single-walled carbon nanotubes (SWNTs) by laser ablation. It was discovered that the Co/Si mixture as a catalyst was as successful as the Ni/Co in the synthesis of SWNTs. The isolated individual SWNTs were examined by using nanobeam electron diffraction for the structure identification and it was found that carbon nanotubes grown by this catalyst mixture tend to be slightly more metallic. The electron diffraction technique has been refined to establish a new methodology to determine the chirality of each shell in a carbon nanotube and it has been applied to determine the atomic structure of double-walled carbon nanotubes (DWNT), few-walled carbon nanotubes (FWNT) and multi-walled carbon nanotubes (MWNT). We observed that there is no strong correlation in the structure of two adjacent shells in DWNTs. Several FWNTs and MWNTs have been examined by our new electron diffraction method to determine their atomic structures and to test the efficiency and the reliability of this method for structure identification. We now suggest that a carbon nanotube of up to 25 shells can be studied and the chirality of each shell can be identified by this new technique. The guidelines for the automation of such procedure have been laid down and explained in this work. The atomic structure of tungsten disulfide (WS2) nanotubes was studied by using the methods developed for the structure determination of carbon nanotubes. The WS2 nanotubes are another example of the tube forming ability of the layered structures and a member of the family of inorganic fullerene-like structures. These nanotubes are much larger in diameter than carbon nanotubes. The tubes studied here have helicities less than 18° and usually have near zigzag structure. The short-range order (SRO) in the atomic structure of carbon soot produced by laser ablation was investigated using electron diffraction and radial distribution function (RDF) analysis. The effects of the furnace temperature and the metal catalyst on the SRO in the carbon soot were also studied. It was discovered that the SRO structure is the same for all carbon soot samples studied and is very similar to that of amorphous carbon. These techniques were also applied to determine the atomic structure of amorphous boron nanowires. We found out that the atomic structure of these boron nanowires agree well with the previously reported structure of bulk amorphous boron.

Deciphering ligands' interaction with Cu and Cu2O nanocrystal surfaces by NMR solution tools.

PubMed

Glaria, Arnaud; Cure, Jérémy; Piettre, Kilian; Coppel, Yannick; Turrin, Cédric-Olivier; Chaudret, Bruno; Fau, Pierre

2015-01-12

The hydrogenolysis of [Cu2{(iPrN)2(CCH3)}2] in the presence of hexadecylamine (HDA) or tetradecylphosphonic acid (TDPA) in toluene leads to 6-9 nm copper nanocrystals. Solution NMR spectroscopy has been used to describe the nanoparticle surface chemistry during the dynamic phenomenon of air oxidation. The ligands are organized as multilayered shells around the nanoparticles. The shell of ligands is controlled by both their intermolecular interactions and their bonding strength on the nanocrystals. Under ambient atmosphere, the oxidation rate of colloidal copper nanocrystals closely relies on the chemical nature of the employed ligands (base or acid). Primary amine molecules behave as soft ligands for Cu atoms, but are even more strongly coordinated on surface Cu(I) sites, thus allowing a very efficient corrosion protection of the copper core. On the contrary, the TDPA ligands lead to a rapid oxidation rate of Cu nanoparticles and eventually to the re-dissolution of Cu(II) species at the expense of the nanocrystals. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Comprehensive analyses of core-shell InGaN/GaN single nanowire photodiodes

NASA Astrophysics Data System (ADS)

Zhang, H.; Guan, N.; Piazza, V.; Kapoor, A.; Bougerol, C.; Julien, F. H.; Babichev, A. V.; Cavassilas, N.; Bescond, M.; Michelini, F.; Foldyna, M.; Gautier, E.; Durand, C.; Eymery, J.; Tchernycheva, M.

2017-12-01

Single nitride nanowire core/shell n-p photodetectors are fabricated and analyzed. Nanowires consisting of an n-doped GaN stem, a radial InGaN/GaN multiple quantum well system and a p-doped GaN external shell were grown by catalyst-free metal-organic vapour phase epitaxy on sapphire substrates. Single nanowires were dispersed and the core and the shell regions were contacted with a metal and an ITO deposition, respectively, defined using electron beam lithography. The single wire photodiodes present a response in the visible to UV spectral range under zero external bias. The detector operation speed has been analyzed under different bias conditions. Under zero bias, the  -3 dB cut-off frequency is ~200 Hz for small light modulations. The current generation was modeled using non-equilibrium Green function formalism, which evidenced the importance of phonon scattering for carrier extraction from the quantum wells.

Neutral and charged gallium clusters: structures, physical properties and implications for the melting features

NASA Astrophysics Data System (ADS)

Núñez, Sara; López, José M.; Aguado, Andrés

2012-09-01

We report the putative Global Minimum (GM) structures and electronic properties of GaN+, GaN and GaN- clusters with N = 13-37 atoms, obtained from first-principles density functional theory structural optimizations. The calculations include spin polarization and employ an exchange-correlation functional which accounts for van der Waals dispersion interactions (vdW-DFT). We find a wide diversity of structural motifs within the located GM, including decahedral, polyicosahedral, polytetrahedral and layered structures. The GM structures are also extremely sensitive to the number of electrons in the cluster, so that the structures of neutral and charged clusters differ for most sizes. The main magic numbers (clusters with an enhanced stability) are identified and interpreted in terms of electronic and geometric shell closings. The theoretical results are consistent with experimental abundance mass spectra of GaN+ and with photoelectron spectra of GaN-. The size dependence of the latent heats of melting, the shape of the heat capacity peaks, and the temperature dependence of the collision cross-sections, all measured for GaN+ clusters, are properly interpreted in terms of the calculated cohesive energies, spectra of configurational excitations, and cluster shapes, respectively. The transition from ``non-melter'' to ``magic-melter'' behaviour, experimentally observed between Ga30+ and Ga31+, is traced back to a strong geometry change. Finally, the higher-than-bulk melting temperatures of gallium clusters are correlated with a more typically metallic behaviour of the clusters as compared to the bulk, contrary to previous theoretical claims.We report the putative Global Minimum (GM) structures and electronic properties of GaN+, GaN and GaN- clusters with N = 13-37 atoms, obtained from first-principles density functional theory structural optimizations. The calculations include spin polarization and employ an exchange-correlation functional which accounts for van der Waals dispersion interactions (vdW-DFT). We find a wide diversity of structural motifs within the located GM, including decahedral, polyicosahedral, polytetrahedral and layered structures. The GM structures are also extremely sensitive to the number of electrons in the cluster, so that the structures of neutral and charged clusters differ for most sizes. The main magic numbers (clusters with an enhanced stability) are identified and interpreted in terms of electronic and geometric shell closings. The theoretical results are consistent with experimental abundance mass spectra of GaN+ and with photoelectron spectra of GaN-. The size dependence of the latent heats of melting, the shape of the heat capacity peaks, and the temperature dependence of the collision cross-sections, all measured for GaN+ clusters, are properly interpreted in terms of the calculated cohesive energies, spectra of configurational excitations, and cluster shapes, respectively. The transition from ``non-melter'' to ``magic-melter'' behaviour, experimentally observed between Ga30+ and Ga31+, is traced back to a strong geometry change. Finally, the higher-than-bulk melting temperatures of gallium clusters are correlated with a more typically metallic behaviour of the clusters as compared to the bulk, contrary to previous theoretical claims. Electronic supplementary information (ESI) available: Atomic coordinates (in xyz format and Å units) and point group symmetries for the global minimum structures reported in this paper. See DOI: 10.1039/c2nr31222k

The influence of HCl concentration and demineralization temperature of Atrina pectinata shells on quality of chitin

NASA Astrophysics Data System (ADS)

Nugroho, Intan Lazuardi; Pursetyo, Kustiawan Tri; Masithah, Endang Dewi

2017-02-01

Atrina pectinata is one of shells species widely consumed by people, which means the high consumption will generate the availability of shells in the environment as waste. Chitin can be produced from the shells. Shells contain quite high minerals that it should be demineralized to reduce the mineral content from the shells. This study aimed to determine the effect of HCl concentration and temperature affect chitin characteristics as the result of demineralization process from pen shells. The method based on two steps, there were demineralization and deproteination. This study used Completely Randomized Design (CRD) with two factors, including HCl concentration (2N, 4N, and 6N) and temperature (33°C and 60°C) which consists six combination treatments and three replications. Data was analyzed by using Analysis of Variance (ANOVA) and followed by Duncan's Multiple Range Test. The results showed that interaction of HCl concentration and temperature has significant effect (p<0.05) to ash content of chitin. The use concentration of 6N and 33°C produced the lowest ash content. Characteristics chitin resulted from the treatment of 6N and 33°C produced ash content 25.33% ± 6.82, moisture content 3.67% ± 1.10, yield 0.72% ± 0.12 and protein content 5.86%.

ISICS2008: An expanded version of ISICS for calculating K-, L-, and M-shell cross sections from PWBA and ECPSSR theory

NASA Astrophysics Data System (ADS)

Cipolla, Sam J.

2009-09-01

New version program summaryProgram title: ISICS2008 Catalogue identifier: ADDS_v4_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADDS_v4_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 5420 No. of bytes in distributed program, including test data, etc.: 107 669 Distribution format: tar.gz Programming language: C Computer: 80 486 or higher level PCs Operating system: Windows XP and all earlier operating systems Classification: 16.7 Catalogue identifier of previous version: ADDS_v3_0 Journal reference of previous version: Comput. Phys. Comm. 179 (2008) 616 Does the new version supersede the previous version?: Yes Nature of problem: Ionization and X-ray production cross section calculations for ion-atom collisions. Solution method: Numerical integration of form factor using a logarithmic transform and Gaussian quadrature, plus exact integration limits. Reasons for new version: Addition of relativistic treatment of both projectile and K-shell electrons. Summary of revisions: A new addition to ISICS is the option (R) to calculate ECPSSR cross sections that account for the relativistic treatment of both projectile and K-shell electron, as proposed recently by Lapicki [1], accordingly as σKRECPSSR=Cṡ(1+0.07(()ṡσ(√{(mKRυ1R)}/Z,ςθ), where υ1R is the relativistic projectile velocity. The option can also be invoked in calculating ECPSShsR, where hsR stands for the Hartree-Slater description of the K-shell electron, which was already incorporated into ISICS2006 [2,3], and is now expressed in this option as, σKRECPSShsR=CṡhsR((2υ1R)/(Zςθ),Z/137)ṡ(1+0.07(()ṡσ(υ1R/Z,ςθ) using the function hsR that is already incorporated into ISICS2006. It should be noted that these expressions are corrected versions [4] from the ones published in Ref. [1]. In this new version, ISICS2008, the option line in the main menu that read "Use Relativistic Proj. velocity" has been replaced by "R option for K-shell … Uses Rel. Proj. vel.". As before, various combinations of options can be utilized and each is denoted in the output. Restrictions: The consumed CPU time increases with the atomic shell (K,L,M), but execution is still very fast. Additional comments: A revised User Manual is included in the distribution file. Running time: This depends on which shell and the number of different energies to be used in the calculation. The running time is not significantly changed from the previous version. As before, to calculate K-shell cross sections for protons striking carbon for 19 different proton energies it took less than 10 s; to calculate M-shell cross sections for protons on gold for 21 proton energies it took 4.2 min. References:G. Lapicki, J. Phys. B: At. Mol. Op. Phys. 41 (2008) 115201. S. Cipolla, Comput. Phys. Comm. 176 (2007) 157. S. Cipolla, Nucl. Instrum. Methods Phys. Res. B 261 (2007) 142. G. Lapicki, private communication.

Core–shell interaction and its impact on the optical absorption of pure and doped core-shell CdSe/ZnSe nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xinqin; Cui, Yingqi; Zeng, Qun

The structural, electronic, and optical properties of core-shell nanoclusters, (CdSe){sub x}@(CdSe){sub y} and their Zn-substituted complexes of x = 2–4 and y = 16–28, were studied with density functional theory calculations. The substitution was applied in the cores, the shells, and/or the whole clusters. All these clusters are characterized by their core-shell structures in which the core-shell interaction was found different from those in core or in shell, as reflected by their bondlengths, volumes, and binding energies. Moreover, the core and shell combine together to compose a new cluster with electronic and optical properties different from those of separated individuals,more » as reflected by their HOMO-LUMO gaps and optical absorptions. With the substitution of Cd by Zn, the structural, electronic, and optical properties of clusters change regularly. The binding energy increases with Zn content, attributed to the strong Zn–Se bonding. For the same core/shell, the structure with a CdSe shell/core has a narrower gap than that with a ZnSe shell/core. The optical absorption spectra also change accordingly with Zn substitution. The peaks blueshift with increasing Zn concentration, accompanying with shape variations in case large number of Cd atoms are substituted. Our calculations reveal the core-shell interaction and its influence on the electronic and optical properties of the core-shell clusters, suggesting a composition–structure–property relationship for the design of core-shell CdSe and ZnSe nanoclusters.« less

Properties of Kilonovae from Dynamical and Post-merger Ejecta of Neutron Star Mergers

NASA Astrophysics Data System (ADS)

Tanaka, Masaomi; Kato, Daiji; Gaigalas, Gediminas; Rynkun, Pavel; Radžiūtė, Laima; Wanajo, Shinya; Sekiguchi, Yuichiro; Nakamura, Nobuyuki; Tanuma, Hajime; Murakami, Izumi; Sakaue, Hiroyuki A.

2018-01-01

Ejected material from neutron star mergers gives rise to electromagnetic emission powered by radioactive decays of r-process nuclei, the so-called kilonova or macronova. While properties of the emission are largely affected by opacities in the ejected material, available atomic data for r-process elements are still limited. We perform atomic structure calculations for r-process elements: Se (Z = 34), Ru (Z = 44), Te (Z = 52), Ba (Z = 56), Nd (Z = 60), and Er (Z = 68). We confirm that the opacities from bound–bound transitions of open f-shell, lanthanide elements (Nd and Er) are higher than those of the other elements over a wide wavelength range. The opacities of open s-shell (Ba), p-shell (Se and Te), and d-shell (Ru) elements are lower than those of open f-shell elements, and their transitions are concentrated in the ultraviolet and optical wavelengths. We show that the optical brightness can be different by > 2 mag depending on the element abundances in the ejecta such that post-merger, lanthanide-free ejecta produce brighter and bluer optical emission. Such blue emission from post-merger ejecta can be observed from the polar directions if the mass of the preceding dynamical ejecta in these regions is small. For the ejecta mass of 0.01 {M}ȯ , observed magnitudes of the blue emission will reach 21.0 mag (100 Mpc) and 22.5 mag (200 Mpc) in the g and r bands within a few days after the merger, which are detectable with 1 m or 2 m class telescopes.

Selective isolation of the electron or hole in photocatalysis: ZnO-TiO2 and TiO2-ZnO core-shell structured heterojunction nanofibers via electrospinning and atomic layer deposition.

PubMed

Kayaci, Fatma; Vempati, Sesha; Ozgit-Akgun, Cagla; Donmez, Inci; Biyikli, Necmi; Uyar, Tamer

2014-06-07

Heterojunctions are a well-studied material combination in photocatalysis studies, the majority of which aim to improve the efficacy of the catalysts. Developing novel catalysts begs the question of which photo-generated charge carrier is more efficient in the process of catalysis and the associated mechanism. To address this issue we have fabricated core-shell heterojunction (CSHJ) nanofibers from ZnO and TiO2 in two combinations where only the 'shell' part of the heterojunction is exposed to the environment to participate in the photocatalysis. Core and shell structures were fabricated via electrospinning and atomic layer deposition, respectively which were then subjected to calcination. These CSHJs were characterized and studied for photocatalytic activity (PCA). These two combinations expose electrons or holes selectively to the environment. Under suitable illumination of the ZnO-TiO2 CSHJ, e/h pairs are created mainly in TiO2 and the electrons take part in catalysis (i.e. reduce the organic dye) at the conduction band or oxygen vacancy sites of the 'shell', while holes migrate to the core of the structure. Conversely, holes take part in catalysis and electrons diffuse to the core in the case of a TiO2-ZnO CSHJ. The results further revealed that the TiO2-ZnO CSHJ shows ∼1.6 times faster PCA when compared to the ZnO-TiO2 CSHJ because of efficient hole capture by oxygen vacancies, and the lower mobility of holes.

A non-LTE analysis of high energy density Kr plasmas on Z and NIF

NASA Astrophysics Data System (ADS)

Dasgupta, A.; Clark, R. W.; Ouart, N.; Giuliani, J.; Velikovich, A.; Ampleford, D. J.; Hansen, S. B.; Jennings, C.; Harvey-Thompson, A. J.; Jones, B.; Flanagan, T. M.; Bell, K. S.; Apruzese, J. P.; Fournier, K. B.; Scott, H. A.; May, M. J.; Barrios, M. A.; Colvin, J. D.; Kemp, G. E.

2016-10-01

Multi-keV X-ray radiation sources have a wide range of applications, from biomedical studies and research on thermonuclear fusion to materials science and astrophysics. The refurbished Z pulsed power machine at the Sandia National Laboratories produces intense multi-keV X-rays from argon Z-pinches, but for a krypton Z-pinch, the yield decreases much faster with atomic number ZA than similar sources on the National Ignition Facility (NIF) laser at the Lawrence Livermore National Laboratory. To investigate whether fundamental energy deposition differences between pulsed power and lasers could account for the yield differences, we consider the Kr plasma on the two machines. The analysis assumes the plasma not in local thermodynamic equilibrium, with a detailed coupling between the hydrodynamics, the radiation field, and the ionization physics. While for the plasma parameters of interest the details of krypton's M-shell are not crucial, both the L-shell and the K-shell must be modeled in reasonable detail, including the state-specific dielectronic recombination processes that significantly affect Kr's ionization balance and the resulting X-ray spectrum. We present a detailed description of the atomic model, provide synthetic K- and L-shell spectra, and compare these with the available experimental data from the Z-machine and from NIF to show that the K-shell yield behavior versus ZA is indeed related to the energy input characteristics. This work aims at understanding the probable causes that might explain the differences in the X-ray conversion efficiencies of several radiation sources on Z and NIF.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCurdy, C. W.; Rescigno, T. N.; Trevisan, C. S.

A dramatic symmetry breaking in K-shell photoionization of the CF 4 molecule in which a core-hole vacancy is created in one of four equivalent fluorine atoms is displayed in the molecular frame angular distribution of the photoelectrons. In observing the photoejected electron in coincidence with an F + atomic ion after Auger decay we see how selecting the dissociation path where the core hole was localized was almost exclusively on that atom. A combination of measurements and ab initio calculations of the photoelectron angular distribution in the frame of the recoiling CF 3 + and F + atoms elucidates themore » underlying physics that derives from the Ne-like valence structure of the F(1s -1) core-excited atom.« less

Central depression in nuclear density and its consequences for the shell structure of superheavy nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afanasjev, A.V.; Laboratory of Radiation Physics, Institute of Solid State Physics, University of Latvia, LV 2169 Salaspils, Miera str. 31; Frauendorf, S.

The influence of the central depression in the density distribution of spherical superheavy nuclei on the shell structure is studied within the relativistic mean-field theory. A large depression leads to the shell gaps at the proton Z=120 and neutron N=172 numbers, whereas a flatter density distribution favors N=184 and leads to the appearance of a Z=126 shell gap and to the decrease of the size of the Z=120 shell gap. The correlations between the magic shell gaps and the magnitude of the central depression are discussed for relativistic and nonrelativistic mean field theories.

Mechanistic profiling of the siRNA delivery dynamics of lipid-polymer hybrid nanoparticles.

PubMed

Colombo, Stefano; Cun, Dongmei; Remaut, Katrien; Bunker, Matt; Zhang, Jianxin; Martin-Bertelsen, Birte; Yaghmur, Anan; Braeckmans, Kevin; Nielsen, Hanne M; Foged, Camilla

2015-03-10

Understanding the delivery dynamics of nucleic acid nanocarriers is fundamental to improve their design for therapeutic applications. We investigated the carrier structure-function relationship of lipid-polymer hybrid nanoparticles (LPNs) consisting of poly(DL-lactic-co-glycolic acid) (PLGA) nanocarriers modified with the cationic lipid dioleoyltrimethyl-ammoniumpropane (DOTAP). A library of siRNA-loaded LPNs was prepared by systematically varying the nitrogen-to-phosphate (N/P) ratio. Atomic force microscopy (AFM) and cryo-transmission electron microscopy (cryo-TEM) combined with small angle X-ray scattering (SAXS) and confocal laser scanning microscopy (CLSM) studies suggested that the siRNA-loaded LPNs are characterized by a core-shell structure consisting of a PLGA matrix core coated with lamellar DOTAP structures with siRNA localized both in the core and in the shell. Release studies in buffer and serum-containing medium combined with in vitro gene silencing and quantification of intracellular siRNA suggested that this self-assembling core-shell structure influences the siRNA release kinetics and the delivery dynamics. A main delivery mechanism appears to be mediated via the release of transfection-competent siRNA-DOTAP lipoplexes from the LPNs. Based on these results, we suggest a model for the nanostructural characteristics of the LPNs, in which the siRNA is organized in lamellar superficial assemblies and/or as complexes entrapped in the polymeric matrix. Copyright © 2015 Elsevier B.V. All rights reserved.

Fluorescent Fe K Emission from High Density Accretion Disks

NASA Astrophysics Data System (ADS)

Bautista, Manuel; Mendoza, Claudio; Garcia, Javier; Kallman, Timothy R.; Palmeri, Patrick; Deprince, Jerome; Quinet, Pascal

2018-06-01

Iron K-shell lines emitted by gas closely orbiting black holes are observed to be grossly broadened and skewed by Doppler effects and gravitational redshift. Accordingly, models for line profiles are widely used to measure the spin (i.e., the angular momentum) of astrophysical black holes. The accuracy of these spin estimates is called into question because fitting the data requires very high iron abundances, several times the solar value. Meanwhile, no plausible physical explanation has been proffered for why these black hole systems should be so iron rich. The most likely explanation for the super-solar iron abundances is a deficiency in the models, and the leading candidate cause is that current models are inapplicable at densities above 1018 cm-3. We study the effects of high densities on the atomic parameters and on the spectral models for iron ions. At high densities, Debye plasma can affect the effective atomic potential of the ions, leading to observable changes in energy levels and atomic rates with respect to the low density case. High densities also have the effec of lowering energy the atomic continuum and reducing the recombination rate coefficients. On the spectral modeling side, high densities drive level populations toward a Boltzman distribution and very large numbers of excited atomic levels, typically accounted for in theoretical spectral models, may contribute to the K-shell spectrum.

Processes of energy deposition by heavy-particle and electron impact. Final progress report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salop, A.; Smith, F.T.

1978-04-18

Progress is reported in three areas of reasearch during the present period: K-shell ionization in high energy collisions of heavy ions with light target atoms using the sudden (Magnus) approximation, K-L level matching phenomena associated with K-shell vacancy production in heavy-ion collisions, and studies of low energy collisions of electrons with molecules using semi-classical perturbation theory. A brief discussion of each of these activities is given.

B(E2)↑ Measurements for Radioactive Neutron-Rich Ge Isotopes: Reaching the N=50 Closed Shell

NASA Astrophysics Data System (ADS)

Padilla-Rodal, E.; Galindo-Uribarri, A.; Baktash, C.; Batchelder, J. C.; Beene, J. R.; Bijker, R.; Brown, B. A.; Castaños, O.; Fuentes, B.; del Campo, J. Gomez; Hausladen, P. A.; Larochelle, Y.; Lisetskiy, A. F.; Mueller, P. E.; Radford, D. C.; Stracener, D. W.; Urrego, J. P.; Varner, R. L.; Yu, C.-H.

2005-03-01

The B(E2;0+1→2+1) values for the radioactive neutron-rich germanium isotopes 78,80Ge and the closed neutron shell nucleus 82Ge were measured at the HRIBF using Coulomb excitation in inverse kinematics. These data allow a study of the systematic trend between the subshell closures at N=40 and 50. The B(E2) behavior approaching N=50 is similar to the trend observed for heavier isotopic chains. A comparison of the experimental results with a shell model calculation demonstrates persistence of the N=50 shell gap and a strong sensitivity of the B(E2) values to the effective interaction.

Eco-friendly synthesis of core-shell structured (TiO2/Li2CO3) nanomaterials for low cost dye-sensitized solar cells.

PubMed

Karuppuchamy, S; Brundha, C

2016-12-01

Core-shell structured TiO 2 /Li 2 CO 3 electrode was successfully synthesized by eco-friendly solution growth technique. TiO 2 /Li 2 CO 3 electrodes were characterized using X-ray Diffractometer (XRD), Scanning electron microscopy (SEM) and photocurrent-voltage measurements. The synthesized core-shell electrode material was sensitized with tetrabutylammonium cis-di(thiocyanato)-N,N'-bis(4-carboxylato-4'-carboxylic acid-2,2'-bipyridine)ruthenate(II) (N-719). The performance of dye-sensitized solar cells (DSCs) based on N719 dye modified TiO 2 /Li 2 CO 3 electrodes was investigated. The effect of various shell thickness on the photovoltaic performance of the core-shell structured electrode is also investigated. We found that Li 2 CO 3 shells of all thicknesses perform as inert barriers which improve open-circuit voltage (V oc ) of the DSCs. The energy conversion efficiency was greatly dependent on the thickness of Li 2 CO 3 on TiO 2 film, and the highest efficiency of 3.7% was achieved at the optimum Li 2 CO 3 shell layer. Copyright © 2015 Elsevier Inc. All rights reserved.

Direct Measurements of Surface Energy, Elastic Modulus and Interparticle Forces of Titan Aerosol Analog (`Tholin') Using Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Yu, X.; Horst, S. M.; He, C.; McGuiggan, P.; Bridges, N. T.

2017-12-01

To understand the origin of the dunes on Titan, it is important to investigate the material properties of the sand particles on Titan, which are mainly made of organics deposited from the atmosphere [1]. The organic sand may behave differently compared to the quartz/basaltic sand on terrestrial planets (Earth, Venus, Mars) in terms of interparticle forces. We measured the surface energy (through contact angle measurements) and elastic modulus (through Atomic Force Microscopy, AFM) of Titan aerosol analog (tholins) produced in our lab. Tholins may be compositionally similar to sand on Titan. We directly measured the interparticle forces between a tholin particle adhered to an AFM cantilver and tholin particles on a substrate. We also measured the properties of walnut shells, a typical material used in the Titan Wind Tunnel (TWT, [2, 3]). We find the surface energy of a tholin thin film is about 70.9 mN/m and its elastic modulus is about 3.5 GPa (similar to hard polymers like PMMA and polystyrene). We used the two measured material properties of tholin to calculate its interparticle cohesion assuming simple sphere-sphere geometry [4]. For two 20 µm particles, the theoretical cohesion force is about 6682 nN. Under dry nitrogen (RH<1%), the directly measured interparticle forces using AFM was approximately 4000 nN, which is smaller than theoretical predictions but still relatively strong under dry conditions. The interparticle cohesion between walnut shell particles is only 200 nN, which is much lower than between tholin particles. The key finding of this study is that the interparticle cohesion forces are much larger for tholins and presumably Titan sand particles than for terrestrial sand and materials used in the wind tunnel. This suggests we should increase the interparticle force in both analog experiments (TWT) and threshold models (e.g. [5]) to correctly translate the results to real Titan conditions. The strong cohesion of tholins may also inform us how the small aerosol particles ( 1 µm) in Titan's atmosphere are transformed into large sand particles ( 200 µm). References: [1] J. W. Barnes et al. Icarus, 195, 400, 2008. [2] D. M. Burr, et al. Nat., 517, 60, 2015. [3] X. Yu et al., Icarus, 297, 97, 2017. [4] K. L. Johnson et al., Proc. R. Soc. Lond., A 324, 301, 1971. [5] Y. Shao & H. Lu, J. Geophys. Res., 105, 22437, 2000.

Ab-initio study of the segregation and electronic properties of neutral and charged B and P dopants in Si and Si/SiO{sub 2} nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schoeters, Bob, E-mail: bob.schoeters@uantwerpen.be; IMEC, Kapeldreef 75, B-3001 Leuven; Leenaerts, Ortwin, E-mail: ortwin.leenaerts@uantwerpen.be

We perform first-principles calculations to investigate the preferred positions of B and P dopants, both neutral and in their preferred charge state, in Si and Si/SiO{sub 2} core-shell nanowires (NWs). In order to understand the observed trends in the formation energy, we isolate the different effects that determine these formation energies. By making the distinction between the unrelaxed and the relaxed formation energy, we separate the impact of the relaxation from that of the chemical environment. The unrelaxed formation energies are determined by three effects: (i) the effect of strain caused by size mismatch between the dopant and the hostmore » atoms, (ii) the local position of the band edges, and (iii) a screening effect. In the case of the SiNW (Si/SiO{sub 2} NW), these effects result in an increase of the formation energy away from the center (interface). The effect of relaxation depends on the relative size mismatch between the dopant and host atoms. A large size mismatch causes substantial relaxation that reduces the formation energy considerably, with the relaxation being more pronounced towards the edge of the wires. These effects explain the surface segregation of the B dopants in a SiNW, since the atomic relaxation induces a continuous drop of the formation energy towards the edge. However, for the P dopants, the formation energy starts to rise when moving from the center but drops to a minimum just next to the surface, indicating a different type of behavior. It also explains that the preferential location for B dopants in Si/SiO{sub 2} core-shell NWs is inside the oxide shell just next to the interface, whereas the P dopants prefer the positions next to the interface inside the Si core, which is in agreement with recent experiments. These preferred locations have an important impact on the electronic properties of these core-shell NWs. Our simulations indicate the possibility of hole gas formation when B segregates into the oxide shell.« less

HF in clusters of molecular hydrogen. I. Size evolution of quantum solvation by parahydrogen molecules.

PubMed

Jiang, Hao; Bacić, Zlatko

2005-06-22

We present a theoretical study of the quantum solvation of the HF molecule by a small number of parahydrogen molecules, having n = 1-13 solvent particles. The minimum-energy cluster structures determined for n = 1-12 have all of the H(2) molecules in the first solvent shell. The first solvent shell closes at n = 12 and its geometry is icosahedral, with the HF molecule at the center. The quantum-mechanical ground-state properties of the clusters are calculated exactly using the diffusion Monte Carlo method. The zero-point energy of (p-H(2))(n)HF clusters is unusually large, amounting to 86% of the potential well depth for n > 7. The radial probability distribution functions (PDFs) confirm that the first solvent shell is complete for n = 12, and that the 13th p-H(2) molecule begins to fill the second solvent shell. The p-H(2) molecules execute large-amplitude motions and are highly mobile, making the solvent cage exceptionally fluxional. The anisotropy of the solvent, very pronounced for small clusters, decreases rapidly with increasing n, so that for n approximately 8-9 the solvent environment is practically isotropic. The analysis of the pair angular PDF reveals that for a given n, the parahydrogen solvent density around the HF is modulated in a pattern which clearly reflects the lowest-energy cluster configuration. The rigidity of the solvent clusters displays an interesting size dependence, increasing from n = 6 to 9, becoming floppier for n = 10, and increasing again up to n = 12, as the solvent shell is filled. The rigidity of the solvent cage appears to reach its maximum for n = 12, the point at which the first solvent shell is closed.

Study of Charge Transport in Vertically Aligned Nitride Nanowire Based Core Shell P-I-N Junctions

DTIC Science & Technology

2016-07-01

Vertically- Aligned Nitride Nanowire Based Core Shell P-I-N Junctions Distribution Statement A. Approved for public release; distribution is...Study of Charge Transport in Vertically- Aligned Nitride Nanowire Based Core Shell P-I-N Junctions Grant Number: HDTRA1-14-1-0003 Principal...Investigator: Abhishek Motayed University of Maryland DISTRIBUTION A: Public Release Study of Charge Transport in Vertically-Aligned Nitride Nanowire

N-doped yolk-shell hollow carbon sphere wrapped with graphene as sulfur host for high-performance lithium-sulfur batteries

NASA Astrophysics Data System (ADS)

Zhang, Yongzheng; Sun, Kai; Liang, Zhan; Wang, Yanli; Ling, Licheng

2018-01-01

N-doped yolk-shell hollow carbon sphere wrapped with reduced graphene oxide (rGO/N-YSHCS) is designed and fabricated as sulfur host for lithium-sulfur batteries. The shuttle effect of polysulfides can be suppressed effectively by the porous yolk-shell structure, graphene layer and N-doping. A good conductivity network is provided for electron transportation through the graphene layer coupled with the unique yolk-shell carbon matrix. Such unique structure offers the synthesized rGO/N-YSHCS/S electrode with a high reversible capacity (800 mAh g-1 at 0.2 C after 100 cycles) and good high-rate capability (636 mAh g-1 at 1 C and 540 mAh g-1 at 2 C).

Electrocatalysts having platium monolayers on palladium, palladium alloy, and gold alloy core-shell nanoparticles, and uses thereof

DOEpatents

Adzic, Radoslav; Mo, Yibo; Vukmirovic, Miomir; Zhang, Junliang

2010-12-21

The invention relates to platinum-coated particles useful as fuel cell electrocatalysts. The particles are composed of a noble metal or metal alloy core at least partially encapsulated by an atomically thin surface layer of platinum atoms. The invention particularly relates to such particles having a palladium, palladium alloy, gold alloy, or rhenium alloy core encapsulated by an atomic monolayer of platinum. In other embodiments, the invention relates to fuel cells containing these electrocatalysts and methods for generating electrical energy therefrom.

Double-shell target fabrication workshop-2016 report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Y. Morris; Oertel, John; Farrell, Michael

On June 30, 2016, over 40 representatives from Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), General Atomics (GA), Laboratory for Laser Energetics (LLE), Schafer Corporation, and NNSA headquarter attended a double-shell (DS) target fabrication workshop at Livermore, California. Pushered-single-shell (PSS) and DS metalgas platforms potentially have a large impact on programmatic applications. The goal of this focused workshop is to bring together target fabrication scientists, physicists, and designers to brainstorm future PSS and DS target fabrication needs and strategies. This one-day workshop intends to give an overall view of historical information, recent approaches, and future research activitiesmore » at each participating organization. Five topical areas have been discussed that are vital to the success of future DS target fabrications, including inner metal shells, foam spheres, outer ablators, fill tube assembly, and metrology.« less

Random crystal field effect on the magnetic and hysteresis behaviors of a spin-1 cylindrical nanowire

NASA Astrophysics Data System (ADS)

Zaim, N.; Zaim, A.; Kerouad, M.

2017-02-01

In this work, the magnetic behavior of the cylindrical nanowire, consisting of a ferromagnetic core of spin-1 atoms surrounded by a ferromagnetic shell of spin-1 atoms is studied in the presence of a random crystal field interaction. Based on Metropolis algorithm, the Monte Carlo simulation has been used to investigate the effects of the concentration of the random crystal field p, the crystal field D and the shell exchange interaction Js on the phase diagrams and the hysteresis behavior of the system. Some characteristic behaviors have been found, such as the first and second-order phase transitions joined by tricritical point for appropriate values of the system parameters, triple and isolated critical points can be also found. Depending on the Hamiltonian parameters, single, double and para hysteresis regions are explicitly determined.

The single-ion anisotropy effects in the mixed-spin ternary-alloy

NASA Astrophysics Data System (ADS)

Albayrak, Erhan

2018-04-01

The effect of single-ion anisotropy on the thermal properties of the ternary-alloy in the form of ABpC1-p is investigated on the Bethe lattice (BL) in terms of exact recursion relations. The simulation on the BL consists of placing A atoms (spin-1/2) on the odd shells and randomly placing B (spin-3/2) or C (spin-5/2) atoms with concentrations p and 1 - p, respectively, on the even shells. The phase diagrams are calculated in possible planes spanned by the system parameters: temperature, single-ion anisotropy, concentration and ratio of the bilinear interaction parameters for z = 3 corresponding to the honeycomb lattice. It is found that the crystal field drives the system to the lowest possible state therefore reducing the temperatures of the critical lines in agreement with the literature.

Interplay of spherical closed shells and N /Z asymmetry in quasifission dynamics

NASA Astrophysics Data System (ADS)

Mohanto, G.; Hinde, D. J.; Banerjee, K.; Dasgupta, M.; Jeung, D. Y.; Simenel, C.; Simpson, E. C.; Wakhle, A.; Williams, E.; Carter, I. P.; Cook, K. J.; Luong, D. H.; Palshetkar, C. S.; Rafferty, D. C.

2018-05-01

Background: Quasifission (QF) has gained tremendous importance in heavy-ion nuclear physics research because of its strong influence on superheavy-element synthesis. Collisions involving closed-shell nuclei in the entrance channel are found to affect the QF reaction mechanism. Hence, it is important to improve the understanding of their effect on QF. Apart from that, some recent studies show that the difference in N /Z of reaction partners influences the reaction dynamics. Since heavier doubly magic nuclei have different N /Z than lighter doubly magic nuclei, it is important to understand the effect of N /Z mismatch as well as the effect of shell closures. Purpose: To investigate the effect of entrance-channel shell closures and N /Z asymmetry on QF. The reactions were chosen to decouple these effects from the contributions of other entrance-channel parameters. Method: Fission fragment mass-angle distributions were measured using the CUBE fission spectrometer, consisting of two large area position-sensitive multi-wire proportional counters (MWPCs), for five reactions, namely, 50Cr+208Pb , 52Cr+Pb,208206 , 54Cr+Pb,208204 . Result: Two components were observed in the measured fragment mass angle distribution, a fast mass-asymmetric quasifission and a slow mass-symmetric component having a less significant mass-angle correlation. The ratio of these components was found to depend on spherical closed shells in the entrance channel nuclei and the magnitude of the N /Z mismatch between the two reaction partners, as well as the beam energy. Conclusions: Entrance-channel spherical closed shells can enhance compound nucleus formation provided the N /Z asymmetry is small. Increase in the N /Z asymmetry is expected to destroy the effect of entrance-channel spherical closed shells, through nucleon transfer reactions.

Waltzing route toward double-helix formation in cholesteric shells

NASA Astrophysics Data System (ADS)

Darmon, Alexandre; Benzaquen, Michael; Seč, David; Čopar, Simon; Dauchot, Olivier; Lopez-Leon, Teresa

2016-08-01

Liquid crystals, when confined to a spherical shell, offer fascinating possibilities for producing artificial mesoscopic atoms, which could then self-assemble into materials structured at a nanoscale, such as photonic crystals or metamaterials. The spherical curvature of the shell imposes topological constraints in the molecular ordering of the liquid crystal, resulting in the formation of defects. Controlling the number of defects, that is, the shell valency, and their positions, is a key success factor for the realization of those materials. Liquid crystals with helical cholesteric order offer a promising, yet unexplored way of controlling the shell defect configuration. In this paper, we study cholesteric shells with monovalent and bivalent defect configurations. By bringing together experiments and numerical simulations, we show that the defects appearing in these two configurations have a complex inner structure, as recently reported for simulated droplets. Bivalent shells possess two highly structured defects, which are composed of a number of smaller defect rings that pile up through the shell. Monovalent shells have a single radial defect, which is composed of two nonsingular defect lines that wind around each other in a double-helix structure. The stability of the bivalent configuration against the monovalent one is controlled by c = h/p, where h is the shell thickness and p the cholesteric helical pitch. By playing with the shell geometry, we can trigger the transition between the two configurations. This transition involves a fascinating waltz dynamics, where the two defects come closer while turning around each other.

An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods

PubMed Central

Bengtson, Stefan; Reguero, Marcelo A.; Mörs, Thomas

2017-01-01

Background The Subclass Coleoidea (Class Cephalopoda) accommodates the diverse present-day internally shelled cephalopod mollusks (Spirula, Sepia and octopuses, squids, Vampyroteuthis) and also extinct internally shelled cephalopods. Recent Spirula represents a unique coleoid retaining shell structures, a narrow marginal siphuncle and globular protoconch that signify the ancestry of the subclass Coleoidea from the Paleozoic subclass Bactritoidea. This hypothesis has been recently supported by newly recorded diverse bactritoid-like coleoids from the Carboniferous of the USA, but prior to this study no fossil cephalopod indicative of an endochochleate branch with an origin independent from subclass Bactritoidea has been reported. Methodology/Principal findings Two orthoconic conchs were recovered from the Early Eocene of Seymour Island at the tip of the Antarctic Peninsula, Antarctica. They have loosely mineralized organic-rich chitin-compatible microlaminated shell walls and broadly expanded central siphuncles. The morphological, ultrustructural and chemical data were determined and characterized through comparisons with extant and extinct taxa using Scanning Electron Microscopy/Energy Dispersive Spectrometry (SEM/EDS). Conclusions/Significance Our study presents the first evidence for an evolutionary lineage of internally shelled cephalopods with independent origin from Bactritoidea/Coleoidea, indicating convergent evolution with the subclass Coleoidea. A new subclass Paracoleoidea Doguzhaeva n. subcl. is established for accommodation of orthoconic cephalopods with the internal shell associated with a broadly expanded central siphuncle. Antarcticerida Doguzhaeva n. ord., Antarcticeratidae Doguzhaeva n. fam., Antarcticeras nordenskjoeldi Doguzhaeva n. gen., n. sp. are described within the subclass Paracoleoidea. The analysis of organic-rich shell preservation of A. nordenskjoeldi by use of SEM/EDS techniques revealed fossilization of hyposeptal cameral soft tissues. This suggests that a depositional environment favoring soft-tissue preservation was the factor enabling conservation of the weakly mineralized shell of A. nordenskjoeldi. PMID:28248970

Oxygen reduction kinetics on Pt monolayer shell highly affected by the structure of bimetallic AuNi cores

DOE PAGES

Chen, Guangyu; Kuttiyiel, Kurian A.; Su, Dong; ...

2016-07-12

Here, we describe pronounced effects of structural changes of the AuNi cores on the oxygen reduction reaction (ORR) activity of a Pt monolayer shell. The study of alloyed AuNi nanoparticles compared with AuNi core–shell structured nanoparticles revealed configurations having different electronic and electrochemical properties. Controlled alloying of Au with Ni was essential to tune the electronic properties of Au interacting with the Pt monolayer shell to achieve suitable adsorption of O 2 on Pt for expediting the ORR. The alloyed AuNi nanoparticles made the Pt shell more catalytically active for the ORR than the core–shell structured AuNi nanoparticles. The Ptmore » monolayer supported on the alloyed AuNi nanoparticles showed the Pt mass and specific activities as high as 1.52 A mg –1 and 1.18 mA cm –2, respectively, with almost no loss over 5 000 cycles of stability test. This high ORR activity is ascribed to the role of nonspecific steric configuration of Ni atoms changing the electronic properties of the alloy that affect the oxygen and water interaction with the Pt shell and facilitate increased ORR kinetics.« less

Role of N-methyl-2-pyrrolidone for preparation of Fe3O4@SiO2 controlled the shell thickness

NASA Astrophysics Data System (ADS)

Wee, Sung-Bok; Oh, Hyeon-Cheol; Kim, Tae-Gyun; An, Gye-Seok; Choi, Sung-Churl

2017-04-01

We developed a simple and novel approach for the synthesis of Fe3O4@SiO2 nanoparticles with controlled shell thickness, and studied the mechanism. The introduction of N-methyl-2-pyrrolidone (NMP) led to trapping of monomer nuclei in single shell and controlled the shell thickness. Fe3O4@SiO2 controlled the shell thickness, showing a high magnetization value (64.47 emu/g). Our results reveal the role and change in the chemical structure of NMP during the core-shell synthesis process. NMP decomposed to 4-aminobutanoic acid in alkaline condition and decreased the hydrolysis rate of the silica coating process.

Kβ/ Kα intensity ratios for X-ray production in 3d metals by gamma-rays and protons

NASA Astrophysics Data System (ADS)

Bhuinya, C. R.; Padhi, H. C.

1994-04-01

Systematic measurements of Kβ/ Kα intensity ratios for X-ray production in 3d metals have been carried out using γ-ray and fast proton ionization methods. The measured ratios from proton ionization experiments indicate production of multivacancies in the L shell giving rise to higher Kβ/ Kα ratios compared to the present γRF results and 2 MeV proton ionization results of Perujo et al. [Perujo A., Maxwell J. A., Teesdale W. J. and Cambell J. L. (1987) J. Phys. B: Atom. Molec. Phys.20, 4973]. This is consistent with the SCA model calculation which gives increased simultaneous K- and L-shell ionization at 4 MeV. The present results from γRF experiments are in close agreement with the 2 MeV proton ionization results of Perujo et al. (1987) and also with the theoretical calculation of jankowski and Polasik [Jankowski K. and Polasik M. (1989) J. Phys. B: Atom. Molec. Optic. Phys. 22, 2369] but the theoretical results of Scofield [Scofield J. H. (1974a) Atom. Data Nucl. Data Tables14, 12] are somewhat higher.

Synthesis reactions and radioactive properties of transactinoid elements

NASA Astrophysics Data System (ADS)

Oganessian, Yu. Ts.

1994-10-01

It is well known that the heaviest elements of the periodic table have been synthesized in the cold fusion of magic nuclei of Pb with Z less than 26 ions. Because of dynamic limitations for fusion under strong Coulomb interaction of nuclei, the cross-sections of cold fusion reactions diminish exponentially with growing compound nucleus atomic number. For element Z = 110 produced in the reaction Pb-208(Ni-62,n)(sub 271)110, the expected cross-section is 10(exp -36) sq cm. In still more asymmetric reactions, when isotopes of actinoid elements irradiated with relatively light ions (Z less than or equal 12) are used as the target material, the compound nuclei possess an excitation energy of approx. 50 MeV. At this energy the nuclear shell effects are strongly suppressed and, as a result, in the case of hot compound nuclei of transactinoid elements the fission barrier is practically absent. The transition of these nuclei into the ground state depends strongly on the dynamic properties of the system with respect to the fission degree of freedom. Experimental studies were going on in two directions: (1) determination of the fission time by measuring the prefission neutrons (of Cf-Fm nuclei) in a wide interval of excitation energies; (2) direct synthesis of known nuclides with Z = 102-105 in reactions with ions of Ne-22, Mg-26, Al-27 and P-31 when final nuclei are produced in the ground state after the evaporation of five or six neutrons from the excited compound nuclei (E(sub x) = 50-60 MeV). The dependence of the reaction cross-section (HI, 5-6n) on the atomic number of the compound nucleus in different target-ion combinations points to the possibility of synthesizing new elements in hot fusion reactions. The advantage of these reactions arises from the use of neutron-rich nuclei like Cm-248 and Cf-249 which allows us to synthesize nuclei close to the deformed shell N = 162, for which a considerable growth of stability against spontaneous fission is predicted. Experimental set-ups and methods of detecting rare events of formation and decay of transactinide nuclei are described.

Ion chemistry in germane/fluorocompounds gaseous mixtures: a mass spectrometric and theoretical study.

PubMed

Antoniotti, Paola; Rabezzana, Roberto; Turco, Francesca; Borocci, Stefano; Giordani, Maria; Grandinetti, Felice

2008-10-01

The ion-molecule reactions occurring in GeH(4)/NF(3), GeH(4)/SF(6), and GeH(4)/SiF(4) gaseous mixtures have been investigated by ion trap mass spectrometry and ab initio calculations. While the NF(x)(+) (x=1-3) react with GeH(4) mainly by the exothermic charge transfer, the open-shell Ge(+) and GeH(2)(+) undergo the efficient F-atom abstraction from NF(3) and form GeF(+) and F-GeH(2)(+) as the only ionic products. The mechanisms of these two processes are quite similar and involve the formation of the fluorine-coordinated complexes Ge-F-NF(2)(+) and H(2)Ge-F-NF(2)(+), their subsequent crossing to the significantly more stable isomers FGe-NF(2)(+) and F-GeH(2)-NF(2)(+), and the eventual dissociation of these ions into GeF(+) (or F-GeH(2)(+)) and NF(2). The closed-shell GeH(+) and GeH(3)(+) are instead much less reactive towards NF(3), and the only observed process is the less efficient formation of GeF(+) from GeH(+). The theoretical investigation of this unusual H/F exchange reaction suggests the involvement of vibrationally-hot GeH(+). Passing from NF(3) to SF(6) and SiF(4), the average strength of the M-F bond increases from 70 to 79 and 142 kcal mol(-1), and in fact the only process observed by reacting GeH(n)(+) (n=0-3) with SF(6) and SiF(4) is the little efficient F-atom abstraction from SF(6) by Ge(+). Irrespective of the experimental conditions, we did not observe any ionic product of Ge-N, Ge-S, or Ge-Si connectivity. This is in line with the previously observed exclusive formation of GeF(+) from the reaction between Ge(+) and C-F compounds such as CH(3)F. Additionally observed processes include in particular the conceivable formation of the elusive thiohypofluorous acid FSH from the reaction between SF(+) and GeH(4).

Nanocarbon synthesis by high-temperature oxidation of nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nomura, Ken-ichi; Kalia, Rajiv K.; Li, Ying

High-temperature oxidation of silicon-carbide nanoparticles (nSiC) underlies a wide range of technologies from high-power electronic switches for efficient electrical grid and thermal protection of space vehicles to self-healing ceramic nanocomposites. Here, multimillion-atom reactive molecular dynamics simulations validated by ab initio quantum molecular dynamics simulations predict unexpected condensation of large graphene flakes during high-temperature oxidation of nSiC. Initial oxidation produces a molten silica shell that acts as an autocatalytic ‘nanoreactor’ by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment. Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp 2 carbons with pentagonalmore » and heptagonal defects. Furthermore, this work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.« less

Nanocarbon synthesis by high-temperature oxidation of nanoparticles

DOE PAGES

Nomura, Ken-ichi; Kalia, Rajiv K.; Li, Ying; ...

2016-04-20

High-temperature oxidation of silicon-carbide nanoparticles (nSiC) underlies a wide range of technologies from high-power electronic switches for efficient electrical grid and thermal protection of space vehicles to self-healing ceramic nanocomposites. Here, multimillion-atom reactive molecular dynamics simulations validated by ab initio quantum molecular dynamics simulations predict unexpected condensation of large graphene flakes during high-temperature oxidation of nSiC. Initial oxidation produces a molten silica shell that acts as an autocatalytic ‘nanoreactor’ by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment. Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp 2 carbons with pentagonalmore » and heptagonal defects. Furthermore, this work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites.« less

Nanocarbon synthesis by high-temperature oxidation of nanoparticles

PubMed Central

Nomura, Ken-ichi; Kalia, Rajiv K.; Li, Ying; Nakano, Aiichiro; Rajak, Pankaj; Sheng, Chunyang; Shimamura, Kohei; Shimojo, Fuyuki; Vashishta, Priya

2016-01-01

High-temperature oxidation of silicon-carbide nanoparticles (nSiC) underlies a wide range of technologies from high-power electronic switches for efficient electrical grid and thermal protection of space vehicles to self-healing ceramic nanocomposites. Here, multimillion-atom reactive molecular dynamics simulations validated by ab initio quantum molecular dynamics simulations predict unexpected condensation of large graphene flakes during high-temperature oxidation of nSiC. Initial oxidation produces a molten silica shell that acts as an autocatalytic ‘nanoreactor’ by actively transporting oxygen reactants while protecting the nanocarbon product from harsh oxidizing environment. Percolation transition produces porous nanocarbon with fractal geometry, which consists of mostly sp2 carbons with pentagonal and heptagonal defects. This work suggests a simple synthetic pathway to high surface-area, low-density nanocarbon with numerous energy, biomedical and mechanical-metamaterial applications, including the reinforcement of self-healing composites. PMID:27095061

An efficient parallel algorithm for the calculation of unrestricted canonical MP2 energies.

PubMed

Baker, Jon; Wolinski, Krzysztof

2011-11-30

We present details of our efficient implementation of full accuracy unrestricted open-shell second-order canonical Møller-Plesset (MP2) energies, both serial and parallel. The algorithm is based on our previous restricted closed-shell MP2 code using the Saebo-Almlöf direct integral transformation. Depending on system details, UMP2 energies take from less than 1.5 to about 3.0 times as long as a closed-shell RMP2 energy on a similar system using the same algorithm. Several examples are given including timings for some large stable radicals with 90+ atoms and over 3600 basis functions. Copyright © 2011 Wiley Periodicals, Inc.

Absolute cross-section measurements of inner-shell ionization

NASA Astrophysics Data System (ADS)

Schneider, Hans; Tobehn, Ingo; Ebel, Frank; Hippler, Rainer

1994-12-01

Cross section ratios for K- and L-shell ionization of thin silver and gold targets by positron and electron impact have been determined at projectile energies of 30 70 keV. The experimental results are confirmed by calculations in plane wave Born approximation (PWBA) which include an electron exchange term and account for the deceleration or acceleration of the incident projectile in the nuclear field of the target atom. We report first absolute cross sections for K- and L-shell ionization of silver and gold targets by lepton impact in the threshold region. We have measured the corresponding cross sections for electron (e-) impact with an electron gun and the same experimental set-up.

A new bimetallic plasmonic photocatalyst consisting of gold(core)-copper(shell) nanoparticle and titanium(IV) oxide support

NASA Astrophysics Data System (ADS)

Sato, Yuichi; Naya, Shin-ichi; Tada, Hiroaki

2015-10-01

Ultrathin Cu layers (˜2 atomic layers) have been selectively formed on the Au surfaces of Au nanoparticle-loaded rutile TiO2 (Au@Cu/TiO2) by a deposition precipitation-photodeposition technique. Cyclic voltammetry and photochronopotentiometry measurements indicate that the reaction proceeds via the underpotential deposition. The ultrathin Cu shell drastically increases the activity of Au/TiO2 for the selective oxidation of amines to the corresponding aldehydes under visible-light irradiation (λ > 430 nm). Photochronoamperometry measurements strongly suggest that the striking Cu shell effect stems from the enhancement of the charge separation in the localized surface plasmon resonance-excited Au/TiO2.

Unambiguous observation of F-atom core-hole localization in CF 4 through body-frame photoelectron angular distributions

DOE PAGES

McCurdy, C. W.; Rescigno, T. N.; Trevisan, C. S.; ...

2017-01-17

A dramatic symmetry breaking in K-shell photoionization of the CF 4 molecule in which a core-hole vacancy is created in one of four equivalent fluorine atoms is displayed in the molecular frame angular distribution of the photoelectrons. In observing the photoejected electron in coincidence with an F + atomic ion after Auger decay we see how selecting the dissociation path where the core hole was localized was almost exclusively on that atom. A combination of measurements and ab initio calculations of the photoelectron angular distribution in the frame of the recoiling CF 3 + and F + atoms elucidates themore » underlying physics that derives from the Ne-like valence structure of the F(1s -1) core-excited atom.« less

Modified ferrite core-shell nanoparticles magneto-structural characterization

NASA Astrophysics Data System (ADS)

Klekotka, Urszula; Piotrowska, Beata; Satuła, Dariusz; Kalska-Szostko, Beata

2018-06-01

In this study, ferrite nanoparticles with core-shell structures and different chemical compositions of both the core and shell were prepared with success. Proposed nanoparticles have in the first and second series magnetite core, and the shell is composed of a mixture of ferrites with Fe3+, Fe2+ and M ions (where M = Co2+, Mn2+ or Ni2+) with a general composition of M0.5Fe2.5O4. In the third series, the composition is inverted, the core is composed of a mixture of ferrites and as a shell magnetite is placed. Morphology and structural characterization of nanoparticles were done using Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), and Infrared spectroscopy (IR). While room temperature magnetic properties were measured using Mössbauer spectroscopy (MS). It is seen from Mössbauer measurements that Co always increases hyperfine magnetic field on Fe atoms at RT, while Ni and Mn have opposite influences in comparison to pure Fe ferrite, regardless of the nanoparticles structure.

Toward “Green” Hybrid Materials: Core–Shell Particles with Enhanced Impact Energy Absorbing Ability

PubMed Central

2016-01-01

Restrained properties of “green” degradable products drive the creation of materials with innovative structures and retained eco-attributes. Herein, we introduce the creation of impact modifiers in the form of core–shell (CS) particles toward the creation of “green” composite materials. Particles with CS structure constituted of PLA stereocomplex (PLASC) and a rubbery phase of poly(ε-caprolactone-co-d,l-lactide) (P[CL-co-LA]) were successfully achieved by spray droplet atomization. A synergistic association of the soft P[CL-co-LA] and hard PLASC domains in the core–shell structure induced unique thermo-mechanical effects on the PLA-based composites. The core–shell particles enhanced the crystallization of PLA matrices by acting as nucleating agents. The core–shell particles functioned efficiently as impact modifiers with minimal effect on the composites stiffness and strength. These findings provide a new platform for scalable design of polymeric-based structures to be used in the creation of advanced degradable materials. PMID:29503773

Quantum transport through single and multilayer icosahedral fullerenes

NASA Astrophysics Data System (ADS)

Lovey, Daniel A.; Romero, Rodolfo H.

2013-10-01

We use a tight-binding Hamiltonian and Green functions methods to calculate the quantum transmission through single-wall fullerenes and bilayered and trilayered onions of icosahedral symmetry attached to metallic leads. The electronic structure of the onion-like fullerenes takes into account the curvature and finite size of the fullerenes layers as well as the strength of the intershell interactions depending on to the number of interacting atom pairs belonging to adjacent shells. Misalignment of the symmetry axes of the concentric iscosahedral shells produces breaking of the level degeneracies of the individual shells, giving rise some narrow quasi-continuum bands instead of the localized discrete peaks of the individual fullerenes. As a result, the transmission function for non symmetrical onions is rapidly varying functions of the Fermi energy. Furthermore, we found that most of the features of the transmission through the onions are due to the electronic structure of the outer shell with additional Fano-like antiresonances arising from coupling with or between the inner shells.

Nitrogen-polar core-shell GaN light-emitting diodes grown by selective area metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Li, Shunfeng; Wang, Xue; Fündling, Sönke; Erenburg, Milena; Ledig, Johannes; Wei, Jiandong; Wehmann, Hergo H.; Waag, Andreas; Bergbauer, Werner; Mandl, Martin; Strassburg, Martin; Trampert, Achim; Jahn, Uwe; Riechert, Henning; Jönen, Holger; Hangleiter, Andreas

2012-07-01

Homogeneous nitrogen-polar GaN core-shell light emitting diode (LED) arrays were fabricated by selective area growth on patterned substrates. Transmission electron microscopy measurements prove the core-shell structure of the rod LEDs. Depending on the growth facets, the InGaN/GaN multi-quantum wells (MQWs) show different dimensions and morphology. Cathodoluminescence (CL) measurements reveal a MQWs emission centered at about 415 nm on sidewalls and another emission at 460 nm from top surfaces. CL line scans on cleaved rod also indicate the core-shell morphology. Finally, an internal quantum efficiency of about 28% at room temperature was determined by an all-optical method on a LED array.

Empirical p-n interactions, the synchronized filling of Nilsson orbitals, and emergent collectivity

NASA Astrophysics Data System (ADS)

Cakirli, R. B.

2014-09-01

The onset of collectivity and deformation, changes to the single particle energies and magic numbers and so on are strongly influenced by, for example, proton (p) and neutron (n) interactions inside atomic nuclei. Experimentally, using binding energies (or masses), one can extract an average p-n interaction between the last two protons and the last two neutrons, called δVpn. We have studied δVpn values using calculations of spatial overlaps between p and n Nilsson orbitals, considering different deformations, for the Z= 50-82, N= 82-126 shells, and comparison of these theoretical results with experimental δVpn values. Our results show that enhanced valence p-n interactions are closely correlated with the development of collectivity, shape changes, and the saturation of deformation in nuclei. We note that the difference of the Nilsson quantum numbers of the last filled Nilsson p and n orbitals, has a special relation, 0[110], in which they differ by only a single quantum in the z-direction, for those nuclei where δVpn is largest for each Z in medium mass and heavy nuclei. The synchronised filling of such orbital pairs correlates with the emergence of collectivity.

Lego Bricks and the Octet Rule: Molecular Models for Biochemical Pathways with Plastic, Interlocking Toy Bricks

ERIC Educational Resources Information Center

Lin, Henry J.; Lehoang, Jennifer; Kwan, Isabel; Baghaee, Anita; Prasad, Priya; Ha-Chen, Stephanie J.; Moss, Tanesha; Woods, Jeremy D.

2018-01-01

The 8 studs on a 2 × 4 Lego brick conveniently represent the outer shell of electrons for carbon, nitrogen, and oxygen atoms. We used Lego bricks to model these atoms, which are then joined together to form molecules by following the Lewis octet rule. A variety of small biological molecules can be modeled in this way, such as most amino acids,…

Simulation of Ge Dopant Emission in Indirect-Drive ICF Implosion Experiments

NASA Astrophysics Data System (ADS)

Macfarlane, J. J.; Golovkin, I.; Kulkarni, S.; Regan, S.; Epstein, R.; Mancini, R.; Peterson, K.; Suter, L. J.

2013-10-01

We present results from simulations performed to study the radiative properties of dopants used in inertial confinement fusion indirect-drive capsule implosion experiments on NIF. In Rev5 NIF ignition capsules, a Ge dopant is added to an inner region of the CH ablator to absorb hohlraum x-ray preheat. Spectrally resolved emission from ablator dopants can be used to study the degree of mixing of ablator material into the ignition hot spot. Here, we study the atomic processes that affect the radiative characteristics of these elements using a set of simulation tools to first estimate the evolution of plasma conditions in the compressed target, and then to compute the atomic kinetics of the dopant and the resultant radiative emission. Using estimates of temperature and density profiles predicted by radiation-hydrodynamics simulations, we set up simple 2-D plasma grids where we allow dopant material to be embedded in the fuel, and perform multi-dimensional collisional-radiative simulations using SPECT3D to compute non-LTE atomic level populations and spectral signatures from the dopant. Recently improved Stark-broadened line shape modeling for Ge K-shell lines has been included. The goal is to study the radiative and atomic processes that affect the emergent spectra, including the effects of inner-shell photoabsorption and K α reemission from the dopant.

X-ray two-photon absorption with high fluence XFEL pulses

DOE PAGES

Hoszowska, Joanna; Szlachetko, J.; Dousse, J. -Cl.; ...

2015-09-07

Here, we report on nonlinear interaction of solid Fe with intense femtosecond hard x-ray free-electron laser (XFEL) pulses. The experiment was performed at the CXI end-station of the Linac Coherent Light Source (LCLS) by means of high- resolution x-ray emission spectroscopy. The focused x-ray beam provided extreme fluence of ~10 5 photons/Å 2. Two-photon absorption leading to K-shell hollow atom formation and to single K-shell ionization of solid Fe was investigated.

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

NASA Astrophysics Data System (ADS)

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

2015-05-01

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

Two-component dark-bright solitons in three-dimensional atomic Bose-Einstein condensates.

PubMed

Wang, Wenlong; Kevrekidis, P G

2017-03-01

In the present work, we revisit two-component Bose-Einstein condensates in their fully three-dimensional (3D) form. Motivated by earlier studies of dark-bright solitons in the 1D case, we explore the stability of these structures in their fully 3D form in two variants. In one the dark soliton is planar and trapping a planar bright (disk) soliton. In the other case, a dark spherical shell soliton creates an effective potential in which a bright spherical shell of atoms is trapped in the second component. We identify these solutions as numerically exact states (up to a prescribed accuracy) and perform a Bogolyubov-de Gennes linearization analysis that illustrates that both structures can be dynamically stable in suitable intervals of sufficiently low chemical potentials. We corroborate this finding theoretically by analyzing the stability via degenerate perturbation theory near the linear limit of the system. When the solitary waves are found to be unstable, we explore their dynamical evolution via direct numerical simulations which, in turn, reveal wave forms that are more robust. Finally, using the SO(2) symmetry of the model, we produce multi-dark-bright planar or shell solitons involved in pairwise oscillatory motion.

Luminescence emission from Al0.3Ga0.7N/GaN multi quantum disc core/shell nanowire: Numerical approach

NASA Astrophysics Data System (ADS)

Namvari, E.; Shojaei, S.; Asgari, A.

2017-09-01

In this work, a numerical approach to investigate the room temperature luminescence emission from core/shell nanowire is presented where GaN quantum discs (QDiscs), periodically distributed in AlxGa1-xN nanowire, is considered as core and AlxGa1-xN as shell. Thin disc shaped (Ring shaped) n-doped region has been placed at the GaN/ AlxGa1-xN (AlxGa1-xN /air) interface in AlxGa1-xN region in axial (radial) directions. To obtain energy levels and related wavefunctions, self-consistent procedure has been employed to solve Schrodinger-Poisson equations with considering the spontaneous and piezoelectric polarization. Then luminescence spectrum is studied in details to recognize the parameters influent in luminescence. The results show that the amount of doping, size of QDiscs and theirs numbers have remarkable effects on the band to band luminescence emission. Our numerical calculations gives some insights into the luminescence emission of core/shell nanowire and exhibits a useful tool to analyze findings in experiments.

He-Ion Microscopy as a High-Resolution Probe for Complex Quantum Heterostructures in Core-Shell Nanowires.

PubMed

Pöpsel, Christian; Becker, Jonathan; Jeon, Nari; Döblinger, Markus; Stettner, Thomas; Gottschalk, Yeanitza Trujillo; Loitsch, Bernhard; Matich, Sonja; Altzschner, Marcus; Holleitner, Alexander W; Finley, Jonathan J; Lauhon, Lincoln J; Koblmüller, Gregor

2018-06-13

Core-shell semiconductor nanowires (NW) with internal quantum heterostructures are amongst the most complex nanostructured materials to be explored for assessing the ultimate capabilities of diverse ultrahigh-resolution imaging techniques. To probe the structure and composition of these materials in their native environment with minimal damage and sample preparation calls for high-resolution electron or ion microscopy methods, which have not yet been tested on such classes of ultrasmall quantum nanostructures. Here, we demonstrate that scanning helium ion microscopy (SHeIM) provides a powerful and straightforward method to map quantum heterostructures embedded in complex III-V semiconductor NWs with unique material contrast at ∼1 nm resolution. By probing the cross sections of GaAs-Al(Ga)As core-shell NWs with coaxial GaAs quantum wells as well as short-period GaAs/AlAs superlattice (SL) structures in the shell, the Al-rich and Ga-rich layers are accurately discriminated by their image contrast in excellent agreement with correlated, yet destructive, scanning transmission electron microscopy and atom probe tomography analysis. Most interestingly, quantitative He-ion dose-dependent SHeIM analysis of the ternary AlGaAs shell layers and of compositionally nonuniform GaAs/AlAs SLs reveals distinct alloy composition fluctuations in the form of Al-rich clusters with size distributions between ∼1-10 nm. In the GaAs/AlAs SLs the alloy clustering vanishes with increasing SL-period (>5 nm-GaAs/4 nm-AlAs), providing insights into critical size dimensions for atomic intermixing effects in short-period SLs within a NW geometry. The straightforward SHeIM technique therefore provides unique benefits in imaging the tiniest nanoscale features in topography, structure and composition of a multitude of diverse complex semiconductor nanostructures.

A non-LTE analysis of high energy density Kr plasmas on Z and NIF

DOE PAGES

Dasgupta, A.; Clark, R. W.; Ouart, N.; ...

2016-10-20

We report that multi-keV X-ray radiation sources have a wide range of applications, from biomedical studies and research on thermonuclear fusion to materials science and astrophysics. The refurbished Z pulsed power machine at the Sandia National Laboratories produces intense multi-keV X-rays from argon Z-pinches, but for a krypton Z-pinch, the yield decreases much faster with atomic number Z A than similar sources on the National Ignition Facility (NIF) laser at the Lawrence Livermore National Laboratory. To investigate whether fundamental energy deposition differences between pulsed power and lasers could account for the yield differences, we consider the Kr plasma on themore » two machines. The analysis assumes the plasma not in local thermodynamic equilibrium, with a detailed coupling between the hydrodynamics, the radiation field, and the ionization physics. While for the plasma parameters of interest the details of krypton’s M-shell are not crucial, both the L-shell and the K-shell must be modeled in reasonable detail, including the state-specific dielectronic recombination processes that significantly affect Kr’s ionization balance and the resulting X-ray spectrum. We present a detailed description of the atomic model, provide synthetic K- and L-shell spectra, and compare these with the available experimental data from the Z-machine and from NIF to show that the K-shell yield behavior versus Z A is indeed related to the energy input characteristics. In conclusion, this work aims at understanding the probable causes that might explain the differences in the X-ray conversion efficiencies of several radiation sources on Z and« less

A non-LTE analysis of high energy density Kr plasmas on Z and NIF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dasgupta, A.; Clark, R. W.; Ouart, N.

We report that multi-keV X-ray radiation sources have a wide range of applications, from biomedical studies and research on thermonuclear fusion to materials science and astrophysics. The refurbished Z pulsed power machine at the Sandia National Laboratories produces intense multi-keV X-rays from argon Z-pinches, but for a krypton Z-pinch, the yield decreases much faster with atomic number Z A than similar sources on the National Ignition Facility (NIF) laser at the Lawrence Livermore National Laboratory. To investigate whether fundamental energy deposition differences between pulsed power and lasers could account for the yield differences, we consider the Kr plasma on themore » two machines. The analysis assumes the plasma not in local thermodynamic equilibrium, with a detailed coupling between the hydrodynamics, the radiation field, and the ionization physics. While for the plasma parameters of interest the details of krypton’s M-shell are not crucial, both the L-shell and the K-shell must be modeled in reasonable detail, including the state-specific dielectronic recombination processes that significantly affect Kr’s ionization balance and the resulting X-ray spectrum. We present a detailed description of the atomic model, provide synthetic K- and L-shell spectra, and compare these with the available experimental data from the Z-machine and from NIF to show that the K-shell yield behavior versus Z A is indeed related to the energy input characteristics. In conclusion, this work aims at understanding the probable causes that might explain the differences in the X-ray conversion efficiencies of several radiation sources on Z and« less

Growth and characterization of dilute nitride GaN{sub x}P{sub 1−x} nanowires and GaN{sub x}P{sub 1−x}/GaN{sub y}P{sub 1−y} core/shell nanowires on Si (111) by gas source molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sukrittanon, S.; Kuang, Y. J.; Dobrovolsky, A.

2014-08-18

We have demonstrated self-catalyzed GaN{sub x}P{sub 1−x} and GaN{sub x}P{sub 1−x}/GaN{sub y}P{sub 1−y} core/shell nanowire growth by gas-source molecular beam epitaxy. The growth window for GaN{sub x}P{sub 1−x} nanowires was observed to be comparable to that of GaP nanowires (∼585 °C to ∼615 °C). Transmission electron microscopy showed a mixture of cubic zincblende phase and hexagonal wurtzite phase along the [111] growth direction in GaN{sub x}P{sub 1−x} nanowires. A temperature-dependent photoluminescence (PL) study performed on GaN{sub x}P{sub 1−x}/GaN{sub y}P{sub 1−y} core/shell nanowires exhibited an S-shape dependence of the PL peaks. This suggests that at low temperature, the emission stems from N-related localizedmore » states below the conduction band edge in the shell, while at high temperature, the emission stems from band-to-band transition in the shell as well as recombination in the GaN{sub x}P{sub 1−x} core.« less

Structural and electronic properties of CdSe/ZnS and ZnS/CdSe core/shell nanowires via first principles study

NASA Astrophysics Data System (ADS)

Rehman, Shafiq Ur; Li, H. M.; Ding, Z. J.

2018-05-01

First principles calculations have been performed to predict the structural stability and electronic structures of hydrogen passivated wurtzite CdSe/ZnS and ZnS/CdSe core/shell nanowires (CSNWs) in the [0001] direction. The calculated binding energy shows that ZnS/CdSe CSNWs are more stable than CdSe/ZnS CSNWs and the stability of ZnS/CdSe CSNWs increases with increasing the thickness of ZnS shell. The modulated electronic band gap demonstrates an increase when the size of both CSNWs is reduced, as a result of the quantum confinement effect. The core-to-shell chemical composition of atoms shows that a strong composition effect also exists in these CSNWs, which in turn affects their electronic properties. Our simulated results show that the photoemission spectra of the CSNWs can be significantly improved by tuning the energy gap of CSNWs.

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

PubMed

Kaupp, Martin

2007-01-15

The role of radial nodes, or of their absence, in valence orbitals for chemical bonding and periodic trends is discussed from a unified viewpoint. In particular, we emphasize the special role of the absence of a radial node whenever a shell with angular quantum number l is occupied for the first time (lack of "primogenic repulsion"), as with the 1s, 2p, 3d, and 4f shells. Although the consequences of the very compact 2p shell (e.g. good isovalent hybridization, multiple bonding, high electronegativity, lone-pair repulsion, octet rule) are relatively well known, it seems that some of the aspects of the very compact 3d shell in transition-metal chemistry are less well appreciated, e.g., the often weakened and stretched bonds at equilibrium structure, the frequently colored complexes, and the importance of nondynamical electron-correlation effects in bonding. Copyright (c) 2006 Wiley Periodicals, Inc.

Coordination radii in diamond, zinc blende, and CaF2 structures

NASA Astrophysics Data System (ADS)

Hall, George L.

1982-07-01

The radii of all ''shells'' of atoms about any lattice point are given for these three structures, and for the zinc blende (AB) and CaF2 (AB2) structures it is shown that all shells about an A origin and all shells about a B origin are of pure type, i.e., contain only A's or only B's. The initial sequence (small radii) of shell types does not continue indefinitely and is broken according to rules completely specified. These results are analogous to those reported by Hall and Christy earlier for the NaCl and CsCl structures in which the ABABABṡṡṡ sequence for NaCl and the ABAABAABAAṡṡṡ for CsCl, both taken about an A origin, do not continue indefinitely. It is shown that Ferris-Prabhu's results for diamond violate theorem 1 of Hall and Christy.

Crossover from disordered to core-shell structures of nano-oxide Y{sub 2}O{sub 3} dispersed particles in Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higgins, M. P.; Wang, L. M.; Gao, F., E-mail: gaofeium@umich.edu

Molecular dynamic simulations of Y{sub 2}O{sub 3} in bcc Fe and transmission electron microscopy (TEM) observations were used to understand the structure of Y{sub 2}O{sub 3} nano-clusters in an oxide dispersion strengthened steel matrix. The study showed that Y{sub 2}O{sub 3} nano-clusters below 2 nm were completely disordered. Y{sub 2}O{sub 3} nano-clusters above 2 nm, however, form a core-shell structure, with a shell thickness of 0.5–0.7 nm that is independent of nano-cluster size. Y{sub 2}O{sub 3} nano-clusters were surrounded by off-lattice Fe atoms, further increasing the stability of these nano-clusters. TEM was used to corroborate our simulation results and showed a crossover frommore » a disordered nano-cluster to a core-shell structure.« less

Nanoscale zero-valent iron (nZVI): aspects of the core-shell structure and reactions with inorganic species in water.

PubMed

Yan, Weile; Herzing, Andrew A; Kiely, Christopher J; Zhang, Wei-Xian

2010-11-25

Aspects of the core-shell model of nanoscale zero-valent iron (nZVI) and their environmental implications were examined in this work. The structure and elemental distribution of nZVI were characterized by X-ray energy-dispersive spectroscopy (XEDS) with nanometer-scale spatial resolution in an aberration-corrected scanning transmission electron microscope (STEM). The analysis provides unequivocal evidence of a layered structure of nZVI consisting of a metallic iron core encapsulated by a thin amorphous oxide shell. Three aqueous environmental contaminants, namely Hg(II), Zn(II) and hydrogen sulfide, were studied to probe the reactive properties and the surface chemistry of nZVI. High-resolution X-ray photoelectron spectroscopy (HR-XPS) analysis of the reacted particles indicated that Hg(II) was sequestrated via chemical reduction to elemental mercury. On the other hand, Zn(II) removal was achieved via sorption to the iron oxide shell followed by zinc hydroxide precipitation. Hydrogen sulfide was immobilized on the nZVI surface as disulfide (S(2)(2-)) and monosulfide (S(2-)) species. Their relative abundance in the final products suggests that the retention of hydrogen sulfide occurs via reactions with the oxide shell to form iron sulfide (FeS) and subsequent conversion to iron disulfide (FeS(2)). The results presented herein highlight the multiple reactive pathways permissible with nZVI owing to its two functional constituents. The core-shell structure imparts nZVI with manifold functional properties previously unexamined and grants the material with potentially new applications. Copyright © 2010 Elsevier B.V. All rights reserved.

Squeezed between shells? The origin of the Lupus I molecular cloud. II. APEX CO and GASS H I observations

NASA Astrophysics Data System (ADS)

Gaczkowski, B.; Roccatagliata, V.; Flaischlen, S.; Kröll, D.; Krause, M. G. H.; Burkert, A.; Diehl, R.; Fierlinger, K.; Ngoumou, J.; Preibisch, T.

2017-12-01

Context. Lupus I cloud is found between the Upper Scorpius (USco) and Upper Centaurus-Lupus (UCL) subgroups of the Scorpius-Centaurus OB association, where the expanding USco H I shell appears to interact with a bubble currently driven by the winds of the remaining B stars of UCL. Aims: We investigate whether the Lupus I molecular could have formed in a colliding flow, and in particular, how the kinematics of the cloud might have been influenced by the larger scale gas dynamics. Methods: We performed APEX 13CO(2-1)and C18O(2-1) line observations of three distinct parts of Lupus I that provide kinematic information on the cloud at high angular and spectral resolution. We compare those results to the atomic hydrogen data from the GASS H I survey and our dust emission results presented in the previous paper. Based on the velocity information, we present a geometric model for the interaction zone between the USco shell and the UCL wind bubble. Results: We present evidence that the molecular gas of Lupus Iis tightly linked to the atomic material of the USco shell. The CO emission in Lupus Iis found mainly at velocities between vLSR = 3-6 km s-1, which is in the same range as the H I velocities. Thus, the molecular cloud is co-moving with the expanding USco atomic H I shell. The gas in the cloud shows a complex kinematic structure with several line-of-sight components that overlay each other. The nonthermal velocity dispersion is in the transonic regime in all parts of the cloud and could be injected by external compression. Our observations and the derived geometric model agree with a scenario in which Lupus Iis located in the interaction zone between the USco shell and the UCL wind bubble. Conclusions: The kinematics observations are consistent with a scenario in which the Lupus Icloud formed via shell instabilities. The particular location of Lupus I between USco and UCL suggests that counterpressure from the UCL wind bubble and pre-existing density enhancements, perhaps left over from the gas stream that formed the stellar subgroups, may have played a role in its formation. This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX), which is a collaboration between the Max-Planck-Institut fur Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.The 13CO(2-1) and C18O(2-1) spectral cubes are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/608/A102

Low- and high-spin iron (II) complexes studied by effective crystal field method combined with molecular mechanics.

PubMed

Darkhovskii, M B; Pletnev, I V; Tchougréeff, A L

2003-11-15

A computational method targeted to Werner-type complexes is developed on the basis of quantum mechanical effective Hamiltonian crystal field (EHCF) methodology (previously proposed for describing electronic structure of transition metal complexes) combined with the Gillespie-Kepert version of molecular mechanics (MM). It is a special version of the hybrid quantum/MM approach. The MM part is responsible for representing the whole molecule, including ligand atoms and metal ion coordination sphere, but leaving out the effects of the d-shell. The quantum mechanical EHCF part is limited to the metal ion d-shell. The method reproduces with reasonable accuracy geometry and spin states of the Fe(II) complexes with monodentate and polydentate aromatic ligands with nitrogen donor atoms. In this setting a single set of MM parameters set is shown to be sufficient for handling all spin states of the complexes under consideration. Copyright 2003 Wiley Periodicals, Inc.

Core-shell structured ceramic nonwoven separators by atomic layer deposition for safe lithium-ion batteries

NASA Astrophysics Data System (ADS)

Shen, Xiu; Li, Chao; Shi, Chuan; Yang, Chaochao; Deng, Lei; Zhang, Wei; Peng, Longqing; Dai, Jianhui; Wu, Dezhi; Zhang, Peng; Zhao, Jinbao

2018-05-01

Safety is one of the most factors for lithium-ion batteries (LIBs). In this work, a novel kind of ceramic separator with high safety insurance is proposed. We fabricated the core-shell nanofiber separators for LIBs by atomic layer deposition (ALD) of 30 nm Al2O3 on the electrospinning nonwoven fiber of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). The separators show a pretty high heat resistance up to 200 °C without any shrinkage, an excellent fire-resistant property and a wide electrochemical window. Besides, with higher uptake and ionic conductivity, cells assembled with the novel separator shows better electrochemical performance. The ALD produced separators exhibit great potential in elaborate products like 3C communications and in energy field with harsh requirements for safety such as electric vehicles. The application of ALD on polymer fiber membranes brings a new strategy and opportunity for improving the safety of the advanced LIBs.

Reverse-Engineering Laboratory Astrophysics: Oxygen Inner-shell Absorption in the ISM

NASA Technical Reports Server (NTRS)

Garcia, J.; Gatuzz, E.; Kallman, T. R.; Mendoza, C.; Gorczyca, T. W.

2017-01-01

The modeling of X-ray spectra from photoionized astrophysical plasmas has been significantly improved due to recent advancements in the theoretical and numerical frameworks, as well as a consolidated and reliable atomic database of inner-shell transitions for all the relevant ions. We discuss these developments and the current state of X-ray spectral modeling in the context of oxygen cold absorption in the interstellar medium (ISM). Unconventionally, we use high-resolution astrophysical observations to accurately determine line positions, and adjust the theoretical models for a comprehensive interpretation of the observed X-ray spectra. This approach has brought to light standing discrepancies in the neutral oxygen absorption-line positions determined from observations and laboratory measurements. We give an overview of our current efforts to devise a definitive model of oxygen photoabsorption that can help to resolve the existing controversy regarding ISM atomic and molecular fractions.

Anomalous photo-ionization of 4d shell in medium-Z ionized atoms

NASA Astrophysics Data System (ADS)

Klapisch, M.; Busquet, M.

2013-09-01

Photoionization (PI) cross sections (PICS) are necessary for the simulation of astrophysical and ICF plasmas. In order to be used in plasma modeling, the PICS are usually fit to simple analytical formulas. We observed an unusual spectral shape of the PICS of the 4d shell of ionized Xe and other elements, computed with different codes: a local minimum occurs around twice the threshold energy. We explain this phenomenon as interference between the bound 4d wavefunction and the free electron wavefunction, which is similar to the Cooper minima for neutral atoms. Consequently, the usual fitting formulas, which consist of a combination of inverse powers of the frequency beyond threshold, may yield rates for PI and radiative recombination (RR) that are incorrect by orders of magnitude. A new fitting algorithm is proposed and is included in the latest version of HULLAC.v9.5.

Reverse-engineering laboratory astrophysics: Oxygen inner-shell absorption in the ISM

NASA Astrophysics Data System (ADS)

García, J.; Gatuzz, E.; Kallman, T. R.; Mendoza, C.; Gorczyca, T. W.

2017-03-01

The modeling of X-ray spectra from photoionized astrophysical plasmas has been significantly improved due to recent advancements in the theoretical and numerical frameworks, as well as a consolidated and reliable atomic database of inner-shell transitions for all the relevant ions. We discuss these developments and the current state of X-ray spectral modeling in the context of oxygen cold absorption in the interstellar medium (ISM). Unconventionally, we use high-resolution astrophysical observations to accurately determine line positions, and adjust the theoretical models for a comprehensive interpretation of the observed X-ray spectra. This approach has brought to light standing discrepancies in the neutral oxygen absorption-line positions determined from observations and laboratory measurements. We give an overview of our current efforts to devise a definitive model of oxygen photoabsorption that can help to resolve the existing controversy regarding ISM atomic and molecular fractions.

Adhesion of Silicone Elastomer Seals for NASA's Crew Exploration Vehicle

NASA Technical Reports Server (NTRS)

deGroh, Henry C., III; Miller, Sharon K. R.; Smith, Ian M.; Daniels, Christopher C.; Steinetz, Bruce M

2008-01-01

Silicone rubber seals are being considered for a number of interfaces on NASA's Crew Exploration Vehicle (CEV). Some of these joints include the docking system, hatches, and heat shield-to-back shell interface. A large diameter molded silicone seal is being developed for the Low Impact Docking System (LIDS) that forms an effective seal between the CEV and International Space Station (ISS) and other future Constellation Program spacecraft. Seals between the heat shield and back shell prevent high temperature reentry gases from leaking into the interface. Silicone rubber seals being considered for these locations have inherent adhesive tendencies that would result in excessive forces required to separate the joints if left unchecked. This paper summarizes adhesion assessments for both as-received and adhesion-mitigated seals for the docking system and the heat shield interface location. Three silicone elastomers were examined: Parker Hannifin S0899-50 and S0383-70 compounds, and Esterline ELA-SA-401 compound. For the docking system application various levels of exposure to atomic oxygen (AO) were evaluated. Moderate AO treatments did not lower the adhesive properties of S0899-50 sufficiently. However, AO pretreatments of approximately 10(exp 20) atoms/sq cm did lower the adhesion of S0383-70 and ELA-SA-401 to acceptable levels. For the heat shield-to-back shell interface application, a fabric covering was also considered. Molding Nomex fabric into the heat shield pressure seal appreciably reduced seal adhesion for the heat shield-to-back shell interface application.

Noncontact atomic force microscopy in liquid environment with quartz tuning fork and carbon nanotube probe

NASA Astrophysics Data System (ADS)

Kageshima, Masami; Jensenius, Henriette; Dienwiebel, Martin; Nakayama, Yoshikazu; Tokumoto, Hiroshi; Jarvis, Suzanne P.; Oosterkamp, Tjerk H.

2002-03-01

A force sensor for noncontact atomic force microscopy in liquid environment was developed by combining a multiwalled carbon nanotube (MWNT) probe with a quartz tuning fork. Solvation shells of octamethylcyclotetrasiloxane on a graphite surface were detected both in the frequency shift and dissipation. Due to the high aspect ratio of the CNT probe, the long-range background force was barely detectable in the solvation region.

Relativistic Calculations and Measurements of Energies, Auger Rates, and Lifetimes.

DTIC Science & Technology

1982-12-01

Research and Industry, Denton, Texas, 8-10 November 1982. 7. B. Crasemann: "Efectos Relativ’sticos y de QED Sobre las Transiciones Rayos - X y Auger Entre...INNER-SHELL IONIZATION BY PROTONS X -RAY EMISSION BREIT INTERACTION AUGER TRANSITIONS DIRAC-HARTREE-SLATER COMPUTATIONS SYNCHROTRON RADIATION RESONANT...computations, including relativistic and quantum- electrodynamic effects, of atomic energy levels and of x -ray and Auger transitions in atoms with one or

Controlling interactions between highly magnetic atoms with Feshbach resonances.

PubMed

Kotochigova, Svetlana

2014-09-01

This paper reviews current experimental and theoretical progress in the study of dipolar quantum gases of ground and meta-stable atoms with a large magnetic moment. We emphasize the anisotropic nature of Feshbach resonances due to coupling to fast-rotating resonant molecular states in ultracold s-wave collisions between magnetic atoms in external magnetic fields. The dramatic differences in the distribution of resonances of magnetic (7)S3 chromium and magnetic lanthanide atoms with a submerged 4f shell and non-zero electron angular momentum is analyzed. We focus on dysprosium and erbium as important experimental advances have been recently made to cool and create quantum-degenerate gases for these atoms. Finally, we describe progress in locating resonances in collisions of meta-stable magnetic atoms in electronic P-states with ground-state atoms, where an interplay between collisional anisotropies and spin-orbit coupling exists.

Coherent quantum depletion of an interacting atom condensate

PubMed Central

Kira, M.

2015-01-01

Sufficiently strong interactions promote coherent quantum transitions in spite of thermalization and losses, which are the adversaries of delicate effects such as reversibility and correlations. In atomic Bose–Einstein condensates (BECs), strong atom–atom interactions can eject atoms from the BEC to the normal component, yielding quantum depletion instead of temperature depletion. A recent experiment has already been verified to overcome losses. Here I show that it also achieves coherent quantum-depletion dynamics in a BEC swept fast enough from weak to strong atom–atom interactions. The elementary coherent process first excites the normal component into a liquid state that evolves into a spherical shell state, where the atom occupation peaks at a finite momentum to shield 50% of the BEC atoms from annihilation. The identified coherent processes resemble ultrafast semiconductor excitations expanding the scope of BEC explorations to many-body non-equilibrium studies. PMID:25767044

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, X. M.; Wang, X. D., E-mail: wangxd@zju.edu.cn, E-mail: jiangjz@zju.edu.cn; Yu, Q.

The atomic structures of Al{sub 89}Y{sub 11}, Al{sub 90}Y{sub 6.5}La{sub 3.5}, and Al{sub 82.8}Y{sub 6.07}Ni{sub 8}La{sub 3.13} metallic glasses have been studied by using high energy X-ray diffraction, X-ray absorption fine structure combined with the ab initio molecular dynamics and reverse Monte Carlo simulations. It is demonstrated that the partial replacement of Y atoms by La has limited improvement of the glass forming ability (GFA), although La atoms reduce the ordering around Y atoms and also the fractions of icosahedron-like polyhedra centered by Al atoms. In contrast, Ni atoms can significantly improve the GFA, which are inclined to locate inmore » the shell of polyhedra centered by Al, Y, and La atoms, mainly forming Ni-centered icosahedron-like polyhedra to enhance the spatial connectivity between clusters and suppress the crystallization.« less

Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta₂O₅)

DOE PAGES

Bassiri, Riccardo; Liou, Franklin; Abernathy, Matthew R.; ...

2015-03-01

Amorphous tantala (a-Ta₂O₅) is a technologically important material often used in high-performance coatings. Understanding this material at the atomic level provides a way to further improve performance. This work details extended X-ray absorption fine structure measurements of a-Ta₂O₅ coatings, where high-quality experimental data and theoretical fits have allowed a detailed interpretation of the nearest-neighbor distributions. It was found that the tantalum atom is surrounded by four shells of atoms in sequence; oxygen, tantalum, oxygen, and tantalum. A discussion is also included on how these models can be interpreted within the context of published crystalline Ta₂O₅ and other a-T₂O₅ studies.

Fullerenes formation in flames

NASA Technical Reports Server (NTRS)

Howard, Jack B.

1993-01-01

Fullerenes are composed of carbon atoms arranged in approximately spherical or ellipsoidal cages resembling the geodesic domes designed by Buckminster Fuller, after whom the molecules were named. The approximately spherical fullerene, which resembles a soccer ball and contains sixty atoms (C60), is called buckminsterfullerene. The fullerene containing seventy carbon atoms (C70) is approximately ellipsoidal, similar to a rugby ball. Fullerenes were first detected in 1985, in carbon vapor produced by laser evaporation of graphite. The closed shell structure, which has no edge atoms vulnerable to reaction, was proposed to explain the observed high stability of certain carbon clusters relative to that of others at high temperatures and in the presence of an oxidizing gas.

Luminescence emission from nonpolar Al0.3Ga0.7N/GaN core-shell and core-multi-shell nanowires

NASA Astrophysics Data System (ADS)

Namvari, E.; Shojaei, S.; Asgari, A.

2017-12-01

In the present work, we theoretically study the possibility of luminescence emission from two systems of nonpolar Al0.3Ga0.7N/GaN Core-shell and core-multi-shell c-axis oriented nanowires with hexagonal cross section. To obtain energy levels and wave functions through the solution of Schrodinger-Poisson equations, numerical Self-consistent procedure has been employed. N-type doping has been considered to investigate the two-dimensional electron gas formation and its effect on luminescence. The detailed analysis of the results as a function of the various structural parameters has been carried out. The results presents an examination of the band to band luminescence feature and its changes with involved parameters. We found that the size of the system determines the feature of luminescence emission. As main finding, our calculations show that the intensity of luminescence spectrum in facet to facet route of NW cross section is significant than that of corner to corner route. In addition, no shift of the peak position is observed with changing the amount of doping. Our numerical calculations give more insights into the luminescence emission of nonpolar GaN/AlGaN core/shell nanowire and have many implications in experiment.

Minute co-variations of Sr/Ca ratios and microstructures in the aragonitic shell of Cerastoderma edule (Bivalvia) - Are geochemical variations at the ultra-scale masking potential environmental signals?

NASA Astrophysics Data System (ADS)

Füllenbach, Christoph S.; Schöne, Bernd R.; Shirai, Kotaro; Takahata, Naoto; Ishida, Akizumi; Sano, Yuji

2017-05-01

It remains a challenging task to reconstruct water temperatures from Sr/Ca ratios of bivalve shells. Although in many aragonitic species, Sr/Ca is negatively correlated to temperature - which is expected based on abiogenic precipitation experiments, the incorporation of Sr into the shell of bivalves is strongly controlled by physiological processes and occurs away from the predicted thermodynamic equilibrium. Strontium-to-calcium ratios of aragonitic shells remain far below that of the ambient water. Moreover, Sr concentrations vary considerably among shell portions consisting of different microstructures and/or organic content. Values observed at annual growth lines and within the intervening shell portions (= annual growth increments) deviate much stronger from each other than expected from a change in temperature or Sr/Cawater. As demonstrated here by ultra-high-resolution chemical analysis (EPMA, NanoSIMS) of a Cerastoderma edule shell, Sr concentrations are also heterogeneously distributed at approximately micrometer resolution. For example, in the outer portion of the outer shell layer, Sr/Ca ratios were statistically significantly (t-, u-tests) higher at circatidal growth lines (irregular simple prismatic structure; arithmetic mean ± 1 standard deviation = 2.86 ± 0.38 mmol/mol; n = 53) than within circatidal increments (nondenticular prismatic structure; 2.42 ± 0.25 mmol/mol; n = 51). S/Cashell, a representative of the concentration of organics, showed the opposite pattern, i.e., significantly higher values in circatidal increments (2.37 ± 0.29 mmol/mol; n = 51) than at circatidal growth lines (2.13 ± 0.47 mmol/mol; n = 53). Overall highest values of Sr/Cashell (3.47 ± 0.65 mmol/mol; n = 3) and S/Cashell (3.98 ± 0.65 mmol/mol; n = 3), however, were typically associated with annual growth lines and larger biomineral units. The intimate link between Sr/Cashell, S/Cashell and shell architecture may indicate that microstructures or the processes controlling their formation exert a strong control over the incorporation of strontium into shells of C. edule. Analytical techniques with lower sampling resolution, e.g., LA-ICP-MS, cannot resolve such fine-scale Sr variations. As a result, the signal-to-noise ratio decreases and the data generated by such techniques may therefore not seem to provide useful paleotemperature data. Future studies should therefore employ a combined analysis of Sr/Cashell and shell microstructures, and interpret Sr/Ca values of shell portions with different microstructures separately.

Atomic-level simulation of ferroelectricity in perovskite solid solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sepliarsky, M.; Instituto de Fisica Rosario, CONICET-UNR, Rosario,; Phillpot, S. R.

2000-06-26

Building on the insights gained from electronic-structure calculations and from experience obtained with an earlier atomic-level method, we developed an atomic-level simulation approach based on the traditional Buckingham potential with shell model which correctly reproduces the ferroelectric phase behavior and dielectric and piezoelectric properties of KNbO{sub 3}. This approach now enables the simulation of solid solutions and defected systems; we illustrate this capability by elucidating the ferroelectric properties of a KTa{sub 0.5}Nb{sub 0.5}O{sub 3} random solid solution. (c) 2000 American Institute of Physics.

Magnetic interaction reversal in watermelon nanostructured Cr-doped Fe nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaur, Maninder; Qiang, You, E-mail: youqiang@uidaho.edu; Dai, Qilin

2013-11-11

Cr-doped core-shell Fe/Fe-oxide nanoclusters (NCs) were synthesized at varied atomic percentages of Cr from 0 at. % to 8 at. %. The low concentrations of Cr (<10 at. %) were selected in order to inhibit the complete conversion of the Fe-oxide shell to Cr{sub 2}O{sub 3} and the Fe core to FeCr alloy. The magnetic interaction in Fe/Fe-oxide NCs (∼25 nm) can be controlled by antiferromagnetic Cr-dopant. We report the origin of σ-FeCr phase at very low Cr concentration (2 at. %) unlike in previous studies, and the interaction reversal from dipolar to exchange interaction in watermelon-like Cr-doped core-shell NCs.

Self-consistent calculations for the electronic structure of a vacancy in copper. A solution of the embedding problem

NASA Astrophysics Data System (ADS)

Zeller, R.; Braspenning, P. J.

1982-06-01

The charge density and the local density of states for a vacancy in Cu and for the first shell of Cu neighbours are calculated by the KKR-Green's function technique. The muffin-tin potentials for the vacancy and the neighbour shell atoms are determined self-consistently in the local density approximation of density functional theory. By the use of the proper host Green's function the embedding of this cluster of 13 perturbed muffin-tins into the infinite array of bulk Cu muffin-tin potentials is described rigorously, thus representing a solution of the embedding problem. The calculations demonstrate a rather large charge transfer of 1.1 electrons from the first neighbour shell to the vacancy.

Shell Corrections Stabilizing Superheavy Nuclei and Semi-spheroidal Atomic Clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poenaru, Dorin N.

2008-01-24

The macroscopic-microscopic method is used to illustrate the shell effect stabilizing superheavy nuclei and to study the stability of semi-spheroidal clusters deposited on planar surfaces. The alpha decay of superheavy nuclei is calculated using three models: the analytical superasymmetric fission model; the universal curve, and the semiempirical formula taking into account the shell effects. Analytical relationships are obtained for the energy levels of the new semi-spheroidal harmonic oscillator (SSHO) single-particle model and for the surface and curvature energies of the semi-spheroidal clusters. The maximum degeneracy of the SSHO is reached at a super-deformed prolate shape for which the minimum ofmore » the liquid drop model energy is also attained.« less

Core/multishell nanowire heterostructures as multicolor, high-efficiency light-emitting diodes.

PubMed

Qian, Fang; Gradecak, Silvija; Li, Yat; Wen, Cheng-Yen; Lieber, Charles M

2005-11-01

We report the growth and characterization of core/multishell nanowire radial heterostructures, and their implementation as efficient and synthetically tunable multicolor nanophotonic sources. Core/multishell nanowires were prepared by metal-organic chemical vapor deposition with an n-GaN core and InxGa1-xN/GaN/p-AlGaN/p-GaN shells, where variation of indium mole fraction is used to tune emission wavelength. Cross-sectional transmission electron microscopy studies reveal that the core/multishell nanowires are dislocation-free single crystals with a triangular morphology. Energy-dispersive X-ray spectroscopy clearly shows shells with distinct chemical compositions, and quantitatively confirms that the thickness and composition of individual shells can be well controlled during synthesis. Electrical measurements show that the p-AlGaN/p-GaN shell structure yields reproducible hole conduction, and electroluminescence measurements demonstrate that in forward bias the core/multishell nanowires function as light-emitting diodes, with tunable emission from 365 to 600 nm and high quantum efficiencies. The ability to synthesize rationally III-nitride core/multishell nanowire heterostructures opens up significant potential for integrated nanoscale photonic systems, including multicolor lasers.

Direct correlations of structural and optical properties of three-dimensional GaN/InGaN core/shell micro-light emitting diodes

NASA Astrophysics Data System (ADS)

Sadat Mohajerani, Matin; Müller, Marcus; Hartmann, Jana; Zhou, Hao; Wehmann, Hergo-H.; Veit, Peter; Bertram, Frank; Christen, Jürgen; Waag, Andreas

2016-05-01

Three-dimensional (3D) InGaN/GaN quantum-well (QW) core-shell light emitting diodes (LEDs) are a promising candidate for the future solid state lighting. In this contribution, we study direct correlations of structural and optical properties of the core-shell LEDs using highly spatially-resolved cathodoluminescence spectroscopy (CL) in combination with scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). Temperature-dependent resonant photoluminescence (PL) spectroscopy has been performed to understand recombination mechanisms and to estimate the internal quantum efficiency (IQE).

Preparation of monodispersed macroporous core-shell molecularly imprinted particles and their application in the determination of 2,4-dichlorophenoxyacetic acid.

PubMed

Liu, Yongliang; He, Yonghuan; Jin, Yulong; Huang, Yanyan; Liu, Guoquan; Zhao, Rui

2014-01-03

Porous polymers have aroused extensive attention due to their controllable porous structure in favor of mass transfer and binding capacity. In this work, the novel macroporous core-shell molecularly imprinted polymers (MIP) for selective recognition of 2,4-dichlorophenoxyacetic acid (2,4-D) were prepared by surface initiated atom transfer radical polymerization (si-ATRP). By using one-step swelling and polymerization method, the monodispersed macroporous poly(glycidyl methacrylate) (PGMA) particles were synthesized and used as supporting matrix for preparing surface MIP particles (PGMA@MIP). Thanks to the inner and outer surface-located binding cavities and the macroporous structure, the PGMA@MIPs revealed desirable efficiency for template removal and mass transfer, and thus excellent accessibility and affinity toward template 2,4-D. Moreover, PGMA@MIPs exhibited much higher selectivity toward 2,4-D than PGMA@NIPs. PGMA@MIP particles were directly used to selectively enrich 2,4-D from tap water and the recoveries of 2,4-D were obtained as 90.0-93.4% with relative standard division of 3.1-3.4% (n=3). The macroporous PGMA@MIPs also possessed steady and excellent reusable performance for 2,4-D in four extraction/stripping cycles. This novel macroporous core-shell imprinted material may become a powerful tool for rapid and efficient enrichment and separation of target compounds from the complicated samples. Copyright © 2013 Elsevier B.V. All rights reserved.

On the interplay of shell structure with low- and high-frequency mechanics of multifunctional magnetic microbubbles.

PubMed

Poehlmann, Melanie; Grishenkov, Dmitry; Kothapalli, Satya V V N; Härmark, Johan; Hebert, Hans; Philipp, Alexandra; Hoeller, Roland; Seuss, Maximilian; Kuttner, Christian; Margheritelli, Silvia; Paradossi, Gaio; Fery, Andreas

2014-01-07

Polymer-shelled magnetic microbubbles have great potential as hybrid contrast agents for ultrasound and magnetic resonance imaging. In this work, we studied US/MRI contrast agents based on air-filled poly(vinyl alcohol)-shelled microbubbles combined with superparamagnetic iron oxide nanoparticles (SPIONs). The SPIONs are integrated either physically or chemically into the polymeric shell of the microbubbles (MBs). As a result, two different designs of a hybrid contrast agent are obtained. With the physical approach, SPIONs are embedded inside the polymeric shell and with the chemical approach SPIONs are covalently linked to the shell surface. The structural design of hybrid probes is important, because it strongly determines the contrast agent's response in the considered imaging methods. In particular, we were interested how structural differences affect the shell's mechanical properties, which play a key role for the MBs' US imaging performance. Therefore, we thoroughly characterized the MBs' geometric features and investigated low-frequency mechanics by using atomic force microscopy (AFM) and high-frequency mechanics by using acoustic tests. Thus, we were able to quantify the impact of the used SPIONs integration method on the shell's elastic modulus, shear modulus and shear viscosity. In summary, the suggested approach contributes to an improved understanding of structure-property relations in US-active hybrid contrast agents and thus provides the basis for their sustainable development and optimization.

Experimental validation of L-shell x-ray fluorescence computed tomography imaging: phantom study

PubMed Central

Bazalova-Carter, Magdalena; Ahmad, Moiz; Xing, Lei; Fahrig, Rebecca

2015-01-01

Abstract. Thanks to the current advances in nanoscience, molecular biochemistry, and x-ray detector technology, x-ray fluorescence computed tomography (XFCT) has been considered for molecular imaging of probes containing high atomic number elements, such as gold nanoparticles. The commonly used XFCT imaging performed with K-shell x rays appears to have insufficient imaging sensitivity to detect the low gold concentrations observed in small animal studies. Low energy fluorescence L-shell x rays have exhibited higher signal-to-background ratio and appeared as a promising XFCT mode with greatly enhanced sensitivity. The aim of this work was to experimentally demonstrate the feasibility of L-shell XFCT imaging and to assess its achievable sensitivity. We built an experimental L-shell XFCT imaging system consisting of a miniature x-ray tube and two spectrometers, a silicon drift detector (SDD), and a CdTe detector placed at ±120  deg with respect to the excitation beam. We imaged a 28-mm-diameter water phantom with 4-mm-diameter Eppendorf tubes containing gold solutions with concentrations of 0.06 to 0.1% Au. While all Au vials were detectable in the SDD L-shell XFCT image, none of the vials were visible in the CdTe L-shell XFCT image. The detectability limit of the presented L-shell XFCT SDD imaging setup was 0.007% Au, a concentration observed in small animal studies. PMID:26839910

Chemical Structure, Ensemble and Single-Particle Spectroscopy of Thick-Shell InP-ZnSe Quantum Dots.

PubMed

Reid, Kemar R; McBride, James R; Freymeyer, Nathaniel J; Thal, Lucas B; Rosenthal, Sandra J

2018-02-14

Thick-shell (>5 nm) InP-ZnSe colloidal quantum dots (QDs) grown by a continuous-injection shell growth process are reported. The growth of a thick crystalline shell is attributed to the high temperature of the growth process and the relatively low lattice mismatch between the InP core and ZnSe shell. In addition to a narrow ensemble photoluminescence (PL) line-width (∼40 nm), ensemble and single-particle emission dynamics measurements indicate that blinking and Auger recombination are reduced in these heterostructures. More specifically, high single-dot ON-times (>95%) were obtained for the core-shell QDs, and measured ensemble biexciton lifetimes, τ 2x ∼ 540 ps, represent a 7-fold increase compared to InP-ZnS QDs. Further, high-resolution energy dispersive X-ray (EDX) chemical maps directly show for the first time significant incorporation of indium into the shell of the InP-ZnSe QDs. Examination of the atomic structure of the thick-shell QDs by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals structural defects in subpopulations of particles that may mitigate PL efficiencies (∼40% in ensemble), providing insight toward further synthetic refinement. These InP-ZnSe heterostructures represent progress toward fully cadmium-free QDs with superior photophysical properties important in biological labeling and other emission-based technologies.

Rationalization of Au concentration and distribution in AuNi@Pt core-shell nanoparticles for oxygen reduction reaction

DOE PAGES

An, Wei; Liu, Ping

2015-09-18

Improving the activity and stability of Pt-based core–shell nanocatalysts for proton exchange membrane fuel cells while lowering Pt loading has been one of the big challenges in electrocatalysis. Here, using density functional theory, we report the effect of adding Au as the third element to enhance the durability and activity of Ni@Pt core–shell nanoparticles (NPs) during the oxygen reduction reaction (ORR). Our results show that the durability and activity of a Ni@Pt NP can be finely tuned by controlling Au concentration and distribution. For a NiAu@Pt NP, the durability can be greatly promoted by thermodynamically favorable segregation of Au tomore » replace the Pt atoms at vertex, edge, and (100) facets on the shell, while still keeping the ORR activity on the active Pt(111) shell as high as that of Ni@Pt nanoparticles. Such behavior strongly depends on a direct interaction with the Ni interlayer. The results not only highlight the importance of interplay between surface strain on the shell and the interlayer–shell interaction in determining the durability and activity but also provide guidance on how to maximize the usage of Au to optimize the performance of core–shell (Pt) nanoparticles. As a result, such understanding has allowed us to discover a novel NiAu@Pt nanocatalyst for the ORR.« less

A Novel Acidic Matrix Protein, PfN44, Stabilizes Magnesium Calcite to Inhibit the Crystallization of Aragonite*

PubMed Central

Pan, Cong; Fang, Dong; Xu, Guangrui; Liang, Jian; Zhang, Guiyou; Wang, Hongzhong; Xie, Liping; Zhang, Rongqing

2014-01-01

Magnesium is widely used to control calcium carbonate deposition in the shell of pearl oysters. Matrix proteins in the shell are responsible for nucleation and growth of calcium carbonate crystals. However, there is no direct evidence supporting a connection between matrix proteins and magnesium. Here, we identified a novel acidic matrix protein named PfN44 that affected aragonite formation in the shell of the pearl oyster Pinctada fucata. Using immunogold labeling assays, we found PfN44 in both the nacreous and prismatic layers. In shell repair, PfN44 was repressed, whereas other matrix proteins were up-regulated. Disturbing the function of PfN44 by RNAi led to the deposition of porous nacreous tablets with overgrowth of crystals in the nacreous layer. By in vitro circular dichroism spectra and fluorescence quenching, we found that PfN44 bound to both calcium and magnesium with a stronger affinity for magnesium. During in vitro calcium carbonate crystallization and calcification of amorphous calcium carbonate, PfN44 regulated the magnesium content of crystalline carbonate polymorphs and stabilized magnesium calcite to inhibit aragonite deposition. Taken together, our results suggested that by stabilizing magnesium calcite to inhibit aragonite deposition, PfN44 participated in P. fucata shell formation. These observations extend our understanding of the connections between matrix proteins and magnesium. PMID:24302723

Dynamics of Hollow Atom Formation in Intense X-Ray Pulses Probed by Partial Covariance Mapping

NASA Astrophysics Data System (ADS)

Frasinski, L. J.; Zhaunerchyk, V.; Mucke, M.; Squibb, R. J.; Siano, M.; Eland, J. H. D.; Linusson, P.; v. d. Meulen, P.; Salén, P.; Thomas, R. D.; Larsson, M.; Foucar, L.; Ullrich, J.; Motomura, K.; Mondal, S.; Ueda, K.; Osipov, T.; Fang, L.; Murphy, B. F.; Berrah, N.; Bostedt, C.; Bozek, J. D.; Schorb, S.; Messerschmidt, M.; Glownia, J. M.; Cryan, J. P.; Coffee, R. N.; Takahashi, O.; Wada, S.; Piancastelli, M. N.; Richter, R.; Prince, K. C.; Feifel, R.

2013-08-01

When exposed to ultraintense x-radiation sources such as free electron lasers (FELs) the innermost electronic shell can efficiently be emptied, creating a transient hollow atom or molecule. Understanding the femtosecond dynamics of such systems is fundamental to achieving atomic resolution in flash diffraction imaging of noncrystallized complex biological samples. We demonstrate the capacity of a correlation method called “partial covariance mapping” to probe the electron dynamics of neon atoms exposed to intense 8 fs pulses of 1062 eV photons. A complete picture of ionization processes competing in hollow atom formation and decay is visualized with unprecedented ease and the map reveals hitherto unobserved nonlinear sequences of photoionization and Auger events. The technique is particularly well suited to the high counting rate inherent in FEL experiments.

Palladium-platinum core-shell electrocatalysts for oxygen reduction reaction prepared with the assistance of citric acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Lulu; Su, Dong; Zhu, Shangqian

Core–shell structure is a promising alternative to solid platinum (Pt) nanoparticles as electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). A simple method of preparing palladium (Pd)–platinum (Pt) core–shell catalysts (Pd@Pt/C) in a gram-batch was developed with the assistance of citric acid. The Pt shell deposition involves three different pathways: galvanic displacement reaction between Pd atoms and Pt cations, chemical reduction by citric acid, and reduction by negative charges on Pd surfaces. The uniform ultrathin (~0.4 nm) Pt shell was characterized by in situ X-ray diffraction (XRD) and high-angle annular dark-field scanning transmission electron microscopymore » (HAADF-STEM) images combined with electron energy loss spectroscopy (EELS). Compared with state-of-the-art Pt/C, the Pd@Pt/C core–shell catalyst showed 4 times higher Pt mass activity and much better durability upon potential cycling. As a result, both the mass activity and durability were comparable to that of Pd@Pt/C synthesized by a Cu-mediated-Pt-displacement method, which is more complicated and difficult for mass production.« less

Palladium-platinum core-shell electrocatalysts for oxygen reduction reaction prepared with the assistance of citric acid

DOE PAGES

Zhang, Lulu; Su, Dong; Zhu, Shangqian; ...

2016-04-26

Core–shell structure is a promising alternative to solid platinum (Pt) nanoparticles as electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). A simple method of preparing palladium (Pd)–platinum (Pt) core–shell catalysts (Pd@Pt/C) in a gram-batch was developed with the assistance of citric acid. The Pt shell deposition involves three different pathways: galvanic displacement reaction between Pd atoms and Pt cations, chemical reduction by citric acid, and reduction by negative charges on Pd surfaces. The uniform ultrathin (~0.4 nm) Pt shell was characterized by in situ X-ray diffraction (XRD) and high-angle annular dark-field scanning transmission electron microscopymore » (HAADF-STEM) images combined with electron energy loss spectroscopy (EELS). Compared with state-of-the-art Pt/C, the Pd@Pt/C core–shell catalyst showed 4 times higher Pt mass activity and much better durability upon potential cycling. As a result, both the mass activity and durability were comparable to that of Pd@Pt/C synthesized by a Cu-mediated-Pt-displacement method, which is more complicated and difficult for mass production.« less

Rotational excitations of N2O in small helium clusters and the role of Bose permutation symmetry

NASA Astrophysics Data System (ADS)

Paesani, F.; Whaley, K. B.

2004-09-01

We present a detailed study of the energetics, structures, and Bose properties of small clusters of 4He containing a single nitrous oxide (N2O) molecule, from N=1 4He up to sizes corresponding to completion of the first solvation shell around N2O (N=16 4He). Ground state properties are calculated using the importance-sampled rigid-body diffusion Monte Carlo method, rotational excited state calculations are made with the projection operator imaginary time spectral evolution method, and Bose permutation exchange and associated superfluid properties are calculated with the finite temperature path integral method. For N⩽5 the helium atoms are seen to form an equatorial ring around the molecular axis, at N=6 helium density starts to occupy the second (local) minimum of the N2O-He interaction at the oxygen side of the molecule, and N=9 is the critical size at which there is onset of helium solvation all along the molecular axis. For N⩾8 six 4He atoms are distributed in a symmetric, quasirigid ring around N2O. Path integral calculations show essentially complete superfluid response to rotation about the molecular axis for N⩾5, and a rise of the perpendicular superfluid response from zero to appreciable values for N⩾8. Rotational excited states are computed for three values of the total angular momentum, J=1-3, and the energy levels fitted to obtain effective spectroscopic constants that show excellent agreement with the experimentally observed N dependence of the effective rotational constant Beff. The non-monotonic behavior of the rotational constant is seen to be due to the onset of long 4He permutation exchanges and associated perpendicular superfluid response of the clusters for N⩾8. We provide a detailed analysis of the role of the helium solvation structure and superfluid properties in determining the effective rotational constants.

The linearly scaling 3D fragment method for large scale electronic structure calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Zhengji; Meza, Juan; Lee, Byounghak

2009-07-28

The Linearly Scaling three-dimensional fragment (LS3DF) method is an O(N) ab initio electronic structure method for large-scale nano material simulations. It is a divide-and-conquer approach with a novel patching scheme that effectively cancels out the artificial boundary effects, which exist in all divide-and-conquer schemes. This method has made ab initio simulations of thousand-atom nanosystems feasible in a couple of hours, while retaining essentially the same accuracy as the direct calculation methods. The LS3DF method won the 2008 ACM Gordon Bell Prize for algorithm innovation. Our code has reached 442 Tflop/s running on 147,456 processors on the Cray XT5 (Jaguar) atmore » OLCF, and has been run on 163,840 processors on the Blue Gene/P (Intrepid) at ALCF, and has been applied to a system containing 36,000 atoms. In this paper, we will present the recent parallel performance results of this code, and will apply the method to asymmetric CdSe/CdS core/shell nanorods, which have potential applications in electronic devices and solar cells.« less

The Linearly Scaling 3D Fragment Method for Large Scale Electronic Structure Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Zhengji; Meza, Juan; Lee, Byounghak

2009-06-26

The Linearly Scaling three-dimensional fragment (LS3DF) method is an O(N) ab initio electronic structure method for large-scale nano material simulations. It is a divide-and-conquer approach with a novel patching scheme that effectively cancels out the artificial boundary effects, which exist in all divide-and-conquer schemes. This method has made ab initio simulations of thousand-atom nanosystems feasible in a couple of hours, while retaining essentially the same accuracy as the direct calculation methods. The LS3DF method won the 2008 ACM Gordon Bell Prize for algorithm innovation. Our code has reached 442 Tflop/s running on 147,456 processors on the Cray XT5 (Jaguar) atmore » OLCF, and has been run on 163,840 processors on the Blue Gene/P (Intrepid) at ALCF, and has been applied to a system containing 36,000 atoms. In this paper, we will present the recent parallel performance results of this code, and will apply the method to asymmetric CdSe/CdS core/shell nanorods, which have potential applications in electronic devices and solar cells.« less

Energy levels, wavelengths, and transition rates of multipole transitions (E1, E2, M1, M2) in Au{sup 67+} and Au{sup 66+} ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamasha, Safeia, E-mail: safeia@hu.edu.jo

2013-11-15

The fully relativistic configuration interaction method of the FAC code is used to calculate atomic data for multipole transitions in Mg-like Au (Au{sup 67+}) and Al-like Au (Au{sup 66+}) ions. Generated atomic data are important in the modeling of M-shell spectra for heavy Au ions and Au plasma diagnostics. Energy levels, oscillator strengths and transition rates are calculated for electric-dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2) for transitions between excited and ground states 3l−nl{sup ′}, such that n=4,5,6,7. The local central potential is derived using the Dirac–Fock–Slater method. Correlation effects to all orders are consideredmore » by the configuration interaction expansion. All relativistic effects are included in the calculations. Calculated energy levels are compared against published values that were calculated using the multi-reference many body perturbation theory, which includes higher order QED effects. Favorable agreement was observed, with less than 0.15% difference.« less

The contribution of oyster microbiomes to denitrification and nitrous oxide emissions in estuarine and coastal ecosystems

NASA Astrophysics Data System (ADS)

Arfken, A. M.; Song, B.; Smyth, A.

2016-02-01

Oysters are important nitrogen transformers in estuaries. Studies have shown that benthic-pelagic coupling by oysters stimulates sedimentary denitrification. The microbiomes living in and on oysters may also have high denitrification activity, generating N2O and N2 as end products. In order to evaluate the importance of oyster microbiome denitrification and its contribution to N2O emission in estuaries, continuous flow experiments with 15NO3- addition were conducted with oyster reef adjacent sediments, live oysters, live oysters with biofilm removed, and oyster shells. Denitrification rates were highest in live oysters, followed by scrubbed oysters, oyster shells, and finally by sediments, with the lowest activity. N2O production followed a similar trend, but with scrubbed oysters and shells being similar. We also found a significant linear correlation between N2 and N2O production, which indicates that denitrification is the source of N2O from oyster and oyster shells. Molecular analysis of microbiomes in oyster shells, guts and gills will be conducted using next generation sequencing of 16S rRNA gene and quantitative PCR assays targeting the functional genes in denitrification. We expect that within live oysters, the anaerobic gut microbiome will have higher abundances of denitrifiers than the shell biofilms or sediments, corresponding to higher denitrification activities in live oysters. This study will demonstrate that enhanced denitrification activity in oysters, in conjunction with sedimentary denitrification stimulated by oyster biodeposits, leads to oyster reefs being nitrogen removal hotspots and potential emission sources of N2O in estuarine and coastal ecosystems. In addition, the importance of microbiome structures in relation to oyster denitrification will be revealed.

Hydration water and bulk water in proteins have distinct properties in radial distributions calculated from 105 atomic resolution crystal structures.

PubMed

Chen, Xianfeng; Weber, Irene; Harrison, Robert W

2008-09-25

Water plays a critical role in the structure and function of proteins, although the experimental properties of water around protein structures are not well understood. The water can be classified by the separation from the protein surface into bulk water and hydration water. Hydration water interacts closely with the protein and contributes to protein folding, stability, and dynamics, as well as interacting with the bulk water. Water potential functions are often parametrized to fit bulk water properties because of the limited experimental data for hydration water. Therefore, the structural and energetic properties of the hydration water were assessed for 105 atomic resolution (

TiO(2) doping by hydroxyurea at the nucleation stage: towards a new photocatalyst in the visible spectral range.

PubMed

Azouani, R; Tieng, S; Chhor, K; Bocquet, J-F; Eloy, P; Gaigneaux, E M; Klementiev, K; Kanaev, A V

2010-10-07

We report an original method of preparation of OCN-doped TiO(2) for photocatalysis in the visible spectral range. The preparation is achieved by a sol-gel route using titanium tetraisopropoxide precursor. Special attention was paid to fluid micromixing, which enables homogeneous reaction conditions in the reactor bulk and monodispersity of the produced clusters/nanoparticles. The dopant hydroxyurea (HyU, CH(4)N(2)O(2)) is injected into the reactive fluid at the nucleation stage, which lasts tens of milliseconds. The doping results in a strong yellow coloration of the nanocolloids due to the absorption band in the spectral range 380-550 nm and accelerates the aggregation kinetics of both nuclei at the induction stage and sub-nuclei units (clusters) at the nucleation stage. FTIR, Raman and UV-visible absorption analyses show the formation of a stable HyU-TiO(2) complex. EXAFS spectra indicate no appreciable changes of the first-shell Ti atom environment. The doping agent takes available surface sites of TiO(2) clusters/nanoparticles attaining ∼10% molar loading. The reaction kinetics then accelerates due to a longer collisional lifetime between nanoparticles induced by the formation of a weak [double bond, length as m-dash]OTi bond. The OCN-group bonding to titanium atoms produces a weakening of the C[double bond, length as m-dash]O double bond and a strengthening of the C-N and N-O bonds.

Superplastic Forming of Duplex Stainless Steel for Aerospace Part

NASA Astrophysics Data System (ADS)

Lee, Ho-Sung; Yoon, Jong-Hoon; Yoo, Joon-Tae; Yi, Young-Moo

2011-08-01

In this study, the high temperature forming behavior of duplex stainless steel has been characterized and the outer shell of a combustion chamber was fabricated with pressure difference of hot gas. It consists of two parts which are the outer skin made of stainless steel to sustain the internal pressure and the inner shell made of copper alloy for regenerative cooling channels. Two outer skins partitioned to half with respect to the symmetric axis was prepared by hot gas forming process with a maximum pressure of 7 MPa following to FEM analysis. For inner layer, copper alloy was machined for cooling channels and then placed in the gas pressure welding fixture. It is shown that the optimum condition of gas pressure welding is 7 MPa at 890 °C, for one hour. EDX analysis and scanning electron microscope micrograph confirm the atomic diffusion process is observed at the interface and copper atoms diffuse into steel, while iron and chrome atoms diffuse into copper. The result shows that the manufacturing method with superplastic forming and gas pressure welding of steel and copper alloy has been successful for near net shape manufacturing of scaled combustion chamber of launch vehicle.

Controlled formation of intense hot spots in Pd@Ag core-shell nanooctapods for efficient photothermal conversion

NASA Astrophysics Data System (ADS)

Liu, Maochang; Yang, Yang; Li, Naixu; Du, Yuanchang; Song, Dongxing; Ma, Lijing; Wang, Yi; Zheng, Yiqun; Jing, Dengwei

2017-08-01

Plasmonic Ag nanostructures have been of great interest for such applications in cancer therapy and catalysis, etc. However, the relatively week Ag-Ag interaction and spontaneous atom diffusion make it very difficult to generate concaved or branched structures in Ag nanocrystals with sizes less than 100 nm, which has been considered very favorable for plasmonic effects. Herein, by employing a cubic Pd seed and a specific reducing agent to restrict the surface diffusion of Ag atoms, Pd@Ag core-shell nanooctapod structures where Ag atoms can be selectively deposited onto the corner sites of the Pd cubes were obtained. Such selective decoration enables us to precisely control the locations for the hot spot formation during light irradiation. We find that the branched nanooctapod structure shows strong absorption in the visible-light region and generates intense hot spots around the octapod arms of Ag. As such, the photothermal conversion efficiency could be significantly improved by more than 50% with a colloid solution containing only ppm-level nanooctapods compared with pure water. The reported nanostructure is expected to find extensive applications due to its controlled formation of light-induced hot spots at certain points on the crystal surface.

The realization of the dipole (γ, γ) method and its application to determine the absolute optical oscillator strengths of helium.

PubMed

Xu, Long-Quan; Liu, Ya-Wei; Kang, Xu; Ni, Dong-Dong; Yang, Ke; Hiraoka, Nozomu; Tsuei, Ku-Ding; Zhu, Lin-Fan

2015-12-17

The dipole (γ, γ) method, which is the inelastic x-ray scattering operated at a negligibly small momentum transfer, is proposed and realized to determine the absolute optical oscillator strengths of the vanlence-shell excitations of atoms and molecules. Compared with the conventionally used photoabsorption method, this new method is free from the line saturation effect, which can seriously limit the accuracies of the measured photoabsorption cross sections for discrete transitions with narrow natural linewidths. Furthermore, the Bethe-Born conversion factor of the dipole (γ, γ) method varies much more slowly with the excitation energy than does that of the dipole (e, e) method. Absolute optical oscillator strengths for the excitations of 1s(2) → 1 snp(n = 3-7) of atomic helium have been determined using the high-resolution dipole (γ, γ) method, and the excellent agreement of the present measurements with both those measured by the dipole (e, e) method and the previous theoretical calculations indicates that the dipole (γ, γ) method is a powerful tool to measure the absolute optical oscillator strengths of the valence-shell excitations of atoms and molecules.

Charge equilibrium and radiation of low-energy cosmic rays passing through interstellar medium

NASA Technical Reports Server (NTRS)

Rule, D. W.; Omidvar, K.

1979-01-01

The charge equilibrium and radiation of an oxygen and an iron beam in the MeV per nucleon energy range, representing a typical beam of low-energy cosmic rays passing through the interstellar medium, are considered. Electron loss of the beam has been taken into account by means of the first Born approximation, allowing for the target atom to remain unexcited or to be excited to all possible states. Electron-capture cross sections have been calculated by means of the scaled Oppenheimer-Brinkman-Kramers approximation, taking into account all atomic shells of the target atoms and capture into all excited states of the projectile. The capture and loss cross sections are found to be within 20%-30% of the existing experimental values for most of the cases considered. Radiation of the beam due to electron capture into the excited states of the ion, collisional excitation, and collisional inner-shell ionization, taking into account the fluorescence yield of the ions, has been considered. Effective X-ray production cross sections and multiplicities for the most energetic X-ray lines emitted by the Fe and O beams have been calculated, and error estimates made for the results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vissers, Daniel R.; Isheim, Dieter; Zhan, Chun

Lithium-ion batteries utilizing 5 V spinel material, LixMn1.5Ni0.5O4 have received considerable interest in recent years for their ability to deliver high energy and power densities. In this paper, we report an atomic scale analysis of the surface layer of a core–shell 5 V spinel structure where a small amount of the manganese lattice sites have been substituted with cobalt in the shell to reach a stoichiometry of LixMn1.18Ni0.55Co0.27O4. Our analyses include electrochemical analysis, atom probe tomography (APT) analysis, kinetic analysis of the interfacial reactions, and high resolution scanning transmission electron microscopy (HR-TEM) analysis. The APT analysis is performed on themore » material before and after long-term cycling at room temperature to provide insights into the atomic scale phenomena within the surface layer of the electrode material. Our APT data reveals a 25–30 nano-meter (nm) region which forms after cycling. From our analyses, we believe that the outer few nanometers of this region stabilizes the 5 V spinel within the chemical environment of the lithium-ion cell such that its structure is not compromised and thereby enables this material to cycle without significant capacity fading.« less

Simulation of Ge Dopant Emission in Indirect-Drive ICF Implosion Experiments

NASA Astrophysics Data System (ADS)

Macfarlane, Joseph; Golovkin, I.; Regan, S.; Epstein, R.; Mancini, R.; Peterson, K.; Suter, L.

2012-10-01

We present results from simulations performed to study the radiative properties of dopants used in inertial confinement fusion indirect-drive capsule implosion experiments on NIF. In Rev5 NIF ignition capsules, a Ge dopant is added to an inner region of the CH ablator to absorb hohlraum x-ray preheat. Spectrally resolved emission from ablator dopants can be used to study the degree of mixing of ablator material into the ignition hot spot. Here, we study the atomic processes that affect the radiative characteristics of these elements using a set of simulation tools to first estimate the evolution of plasma conditions in the compressed target, and then to compute the atomic kinetics of the dopant and the resultant radiative emission. Using estimates of temperature and density profiles predicted by radiation-hydrodynamics simulations, we set up simple plasma grids where we allow dopant material to be embedded in the fuel, and perform multi-dimensional collisional-radiative simulations using SPECT3D to compute non-LTE atomic level populations and spectral signatures from the dopant. Recently improved Stark-broadened line shape modeling for Ge K-shell lines has been included. The goal is to study the radiative and atomic processes that affect the emergent spectra, including the effects of inner-shell photoabsorption and Kα reemission from the dopant, and to study the sensitivity of the emergent spectra to the dopant and the hot spot and ablator conditions.

The isotopic biosignatures of photo- vs. thiotrophic bivalves: are they preserved in fossil shells?

PubMed

Dreier, A; Loh, W; Blumenberg, M; Thiel, V; Hause-Reitner, D; Hoppert, M

2014-09-01

Symbiont-bearing and non-symbiotic marine bivalves were used as model organisms to establish biosignatures for the detection of distinctive symbioses in ancient bivalves. For this purpose, the isotopic composition of lipids (δ13C) and bulk organic shell matrix (δ13C, δ34S, δ15N) from shells of several thiotrophic, phototrophic, or non-symbiotic bivalves were compared (phototrophic: Fragum fragum, Fragum unedo, Tridacna maxima; thiotrophic: Codakia tigerina, Fimbria fimbriata, Anodontia sp.; non-symbiotic: Tapes dorsatus, Vasticardium vertebratum, Scutarcopagia sp.). ∆13C values of bulk organic shell matrices, most likely representing mainly original shell protein/chitin biomass, were depleted in thio- and phototrophic bivalves compared to non-symbiotic bivalves. As the bulk organic shell matrix also showed a major depletion of δ15N (down to -2.2 ‰) for thiotrophic bivalves, combined δ13C and δ15N values are useful to differentiate between thio-, phototrophic, and non-symbiotic lifestyles. However, the use of these isotopic signatures for the study of ancient bivalves is limited by the preservation of the bulk organic shell matrix in fossils. Substantial alteration was clearly shown by detailed microscopic analyses of fossil (late Pleistocene) T. maxima and Trachycardium lacunosum shell, demonstrating a severe loss of quantity and quality of bulk organic shell matrix with time. Likewise, the composition and δ13C-values of lipids from empty shells indicated that a large part of these compounds derived from prokaryotic decomposers. The use of lipids from ancient shells for the reconstruction of the bivalve's life style therefore appears to be restricted. © 2014 John Wiley & Sons Ltd.

Target electron ionization in Li2+-Li collisions: A multi-electron perspective

NASA Astrophysics Data System (ADS)

Śpiewanowski, M. D.; Gulyás, L.; Horbatsch, M.; Kirchner, T.

2015-05-01

The recent development of the magneto-optical trap reaction-microscope has opened a new chapter for detailed investigations of charged-particle collisions from alkali atoms. It was shown that energy-differential cross sections for ionization from the outer-shell in O8+-Li collisions at 1500 keV/amu can be readily explained with the single-active-electron approximation. Understanding of K-shell ionization, however, requires incorporating many-electron effects. An ionization-excitation process was found to play an important role. We present a theoretical study of target electron removal in Li2+-Li collisions at 2290 keV/amu. The results indicate that in outer-shell ionization a single-electron process plays the dominant part. However, the K-shell ionization results are more difficult to interpret. On one hand, we find only weak contributions from multi-electron processes. On the other hand, a large discrepancy between experimental and single-particle theoretical results indicate that multi-electron processes involving ionization from the outer shell may be important for a complete understanding of the process. Work supported by NSERC, Canada and the Hungarian Scientific Research Fund.

Solvation of carbonaceous molecules by para-H2 and ortho-D2 clusters. II. Fullerenes.

PubMed

Calvo, F; Yurtsever, E

2016-08-28

The coating of various fullerenes by para-hydrogen and ortho-deuterium molecules has been computationally studied as a function of the solvent amount. Rotationally averaged interaction potentials for structureless hydrogen molecules are employed to model their interaction with neutral or charged carbonaceous dopants containing between 20 and 240 atoms, occasionally comparing different fullerenes having the same size but different shapes. The solvation energy and the size of the first solvation shell obtained from path-integral molecular dynamics simulations at 2 K show only minor influence on the dopant charge and on the possible deuteration of the solvent, although the shell size is largest for ortho-D2 coating cationic fullerenes. Nontrivial finite size effects have been found with the shell size varying non-monotonically close to its completion limit. For fullerenes embedded in large hydrogen clusters, the shell size and solvation energy both follow linear scaling with the fullerene size. The shell sizes obtained for C60 (+) and C70 (+) are close to 49 and 51, respectively, and agree with mass spectrometry experiments.

Solvation of carbonaceous molecules by para-H2 and ortho-D2 clusters. II. Fullerenes

NASA Astrophysics Data System (ADS)

Calvo, F.; Yurtsever, E.

2016-08-01

The coating of various fullerenes by para-hydrogen and ortho-deuterium molecules has been computationally studied as a function of the solvent amount. Rotationally averaged interaction potentials for structureless hydrogen molecules are employed to model their interaction with neutral or charged carbonaceous dopants containing between 20 and 240 atoms, occasionally comparing different fullerenes having the same size but different shapes. The solvation energy and the size of the first solvation shell obtained from path-integral molecular dynamics simulations at 2 K show only minor influence on the dopant charge and on the possible deuteration of the solvent, although the shell size is largest for ortho-D2 coating cationic fullerenes. Nontrivial finite size effects have been found with the shell size varying non-monotonically close to its completion limit. For fullerenes embedded in large hydrogen clusters, the shell size and solvation energy both follow linear scaling with the fullerene size. The shell sizes obtained for C 60+ and C 70+ are close to 49 and 51, respectively, and agree with mass spectrometry experiments.

Surface coating with Ca(OH)2 for improvement of the transport of nanoscale zero-valent iron (nZVI) in porous media.

PubMed

Wei, Cai-jie; Li, Xiao-yan

2013-01-01

A novel thermal deposition method was developed to coat Ca(OH)2 on the surface of nanoscale zero-valent iron (nZVI). The nZVI particles with the Ca(OH)2 coating layer, nZVI/Ca(OH)2, had a clear core-shell structure based on the transmission electron microscopy observations, and the Ca(OH)2 shell was identified as an amorphous phase. The Ca(OH)2 coating shell would not only function as an effective protection layer for nZVI but also improve the mobility of nZVI in porous media for its use in environmental decontamination. A 10% Ca/Fe mass ratio was found to result in a proper thickness of the Ca(OH)2 shell on the nZVI surface. Based on the filtration tests in sand columns, the Ca(OH)2-based surface coating could greatly improve the mobility and transport of nZVI particles in porous media. In addition, batch experiments were conducted to evaluate the reactivity of Ca(OH)2-coated nZVI particles for the reduction of Cr(VI) and its removal from water.

Gamow-Teller response in the configuration space of a density-functional-theory-rooted no-core configuration-interaction model

NASA Astrophysics Data System (ADS)

Konieczka, M.; Kortelainen, M.; Satuła, W.

2018-03-01

Background: The atomic nucleus is a unique laboratory in which to study fundamental aspects of the electroweak interaction. This includes a question concerning in medium renormalization of the axial-vector current, which still lacks satisfactory explanation. Study of spin-isospin or Gamow-Teller (GT) response may provide valuable information on both the quenching of the axial-vector coupling constant as well as on nuclear structure and nuclear astrophysics. Purpose: We have performed a seminal calculation of the GT response by using the no-core configuration-interaction approach rooted in multireference density functional theory (DFT-NCCI). The model treats properly isospin and rotational symmetries and can be applied to calculate both the nuclear spectra and transition rates in atomic nuclei, irrespectively of their mass and particle-number parity. Methods: The DFT-NCCI calculation proceeds as follows: First, one builds a configuration space by computing relevant, for a given physical problem, (multi)particle-(multi)hole Slater determinants. Next, one applies the isospin and angular-momentum projections and performs the isospin and K mixing in order to construct a model space composed of linearly dependent states of good angular momentum. Eventually, one mixes the projected states by solving the Hill-Wheeler-Griffin equation. Results: The method is applied to compute the GT strength distribution in selected N ≈Z nuclei including the p -shell 8Li and 8Be nuclei and the s d -shell well-deformed nucleus 24Mg. In order to demonstrate a flexibility of the approach we present also a calculation of the superallowed GT β decay in doubly-magic spherical 100Sn and the low-spin spectrum in 100In. Conclusions: It is demonstrated that the DFT-NCCI model is capable of capturing the GT response satisfactorily well by using a relatively small configuration space, exhausting simultaneously the GT sum rule. The model, due to its flexibility and broad range of applicability, may either serve as a complement or even as an alternative to other theoretical approaches, including the conventional nuclear shell model.

δ15N as a proxy for historic anthropogenic nitrogen loading in Charleston Harbor, SC, USA

NASA Astrophysics Data System (ADS)

Payne, T. N.; Andrus, C. F. T.

2015-12-01

Bivalve shell geochemistry can serve as a useful indicator of changes in coastal environments. There is increasing interest in developing paleoenvironmental proxies from mollusk shell organic components. Numerous studies have focused on how the δ15N obtained from bivalve tissues can be used to trace present-day wastewater input into estuaries. However, comparatively little attention has been paid to tracing the impact of anthropogenic nitrogen loading into estuaries over time. By measuring historic levels of δ15N in the organic fraction of oyster shells (Crassostrea virginica) from archaeological sites around Charleston Harbor and comparing those levels to the δ15N content of modern shells, it is possible to assess how nitrogen has fluctuated historically in the area. Whole-shell samples from the Late Archaic Period (~3000-4000 BP, Late Woodland Period (~1400-800 BP), 18th and 19th centuries, and modern controls were measured for %N and d15N. Evidence of increased anthropogenic input of N is expected to begin in the early historic period based on similar analysis in Chesapeake Bay. More ancient samples may give insight into baseline conditions prior to recent population growth and industrialization. This information could help understand how large-scale anthropogenic nitrogen loading has affected coastal ecosystems over time and guide future remediation. Furthermore, this project will help refine and improve this novel proxy of past environmental conditions.

Characterization of Substituted Phenol-Formaldehyde Resins Using Solid-State Carbon-13 NMR

DTIC Science & Technology

1989-05-22

synthesized from cashew nut shell liquid, 3-n-pentadecylphenol and phenol with formaldehyde. The resulting resins were crosslinked and then investigated using...should be sent SYNOPSIS Crosslinked substituted phenol-formaldehyde resins were synthesized from cashew nut shell liquid, 3-n-pentadecylphenol and... nut shell liquid (CNSL) and are the basis for binder resins and friction particles in composite friction materials. CNSL is isolated from cashew nut

Effect Of N = 40 Shell Closure On Barrier Distributions In 18O+58,60Ni Reactions

NASA Astrophysics Data System (ADS)

Danu, L. S.; Nayak, B. K.; Saxena, A.; Biswas, D. C.; John, B. V.; Thomas, R. G.; Gupta, Y. K.; Choudhury, R. K.

2009-03-01

The quasi-elastic scattering measurements for 18O+58,62Ni systems have been carried out at Θlab = 150° around Coulomb barrier energies to investigate the effect of nuclear shell closure on the barrier distributions. The 18O+58Ni system leads to N = 40 neutron shell closure and 18O+62Ni system is having N = 44 in the compound system. It is observed that target 2+ and 3-, projectile 2+ inelastic and 2n-transfer couplings are required in coupled-channels fusion model (CCFULL) calculations to get good comparison with the experimental barrier distribution of 18O+62Ni system, whereas projectile 2+ inelastic state coupling is not required for 18O+58Ni system. However, the low energy structure observed in the barrier distribution of 18O+58Ni system is not reproduced by coupled-channels calculations. This suggests, a possible additional effect due to N = 40 shell closure in the compound system not accounted for in coupled-channels calculations.

On ballooning instability in current sheets

NASA Astrophysics Data System (ADS)

Leonovich, Anatoliy; Kozlov, Daniil

2015-06-01

The problem of instability of the magnetotail current sheet to azimuthally small-scale Alfvén and slow magnetosonic (SMS) waves is solved. The solutions describe unstable oscillations in the presence of a current sheet and correspond to the region of stretched closed field lines of the magnetotail. The spectra of eigen-frequencies of several basic harmonics of standing Alfvén and SMS waves are found in the local and WKB approximation, which are compared. It is shown that the oscillation properties obtained in these approximations differ radically. In the local approximation, the Alfvén waves are stable in the entire range of magnetic shells. SMS waves go into the aperiodic instability regime (the regime of the "ballooning" instability), on magnetic shells crossing the current sheet. In the WKB approximation, both the Alfvén and SMS oscillations go into an unstable regime with a non-zero real part of their eigen-frequency, on magnetic shells crossing the current sheet. The structure of azimuthally small-scale Alfvén waves across magnetic shells is determined.

Coulomb Excitation of n-rich nuclei along the N = 50 shell closure

NASA Astrophysics Data System (ADS)

Padilla-Rodal, E.; Galindo-Uribarri, A.; Batchelder, J. C.; Beene, J. R.; Bingham, C.; Brown, B. A.; Lagergren, K. B.; Mueller, P. E.; Radford, D. C.; Stracener, D. W.; Urrego-Blanco, J. P.; Varner, R. L.; Yu, C.-H.

2008-04-01

Recently, we have been investigating characteristics of nuclear states around the neutron-rich mass A=80 region [1]. Using the Radioactive Ion Beams (RIBs) produced at HRIBF, we have successfully measured the B(E2) values for ^78,80,82Ge , using Coulomb excitation in inverse kinematics. For the germanium isotopes, these data allow a study of the systematic trend between the subshell N= 40 and the N=50 shell. Using the same technique, we have measured the B(E2) value of various nuclei along the N=50 shell including the radioactive nucleus ^84Se. This value together with our previously measured ^82Ge, and the recent result on ^80Zn from ISOLDE [2] are providing basic experimental information needed for a better understanding of the neutron-rich nuclei around A˜80. We report the new results and compare with shell model calculations. [1] E. Padilla-Rodal et al., Phys. Rev. Lett. 94 (2005) 122501. [2] J. Van de Walle et al., Phys. Rev. Lett. 99 (2007) 142501.

Structural and electronic properties for atomic clusters

NASA Astrophysics Data System (ADS)

Sun, Yan

We have studied the structural and electronic properties for different groups of atomic clusters by doing a global search on the potential energy surface using the Taboo Search in Descriptors Space (TSDS) method and calculating the energies with Kohn-Sham Density Functional Theory (KS-DFT). Our goal was to find the structural and electronic principles for predicting the structure and stability of clusters. For Ben (n = 3--20), we have found that the evolution of geometric and electronic properties with size reflects a change in the nature of the bonding from van der Waals to metallic and then bulk-like. The cluster sizes with extra stability agree well with the predictions of the jellium model. In the 4d series of transition metal (TM) clusters, as the d-type bonding becomes more important, the preferred geometric structure changes from icosahedral (Y, Zr), to distorted compact structures (Nb, Mo), and FCC or simple cubic crystal fragments (Tc, Ru, Rh) due to the localized nature of the d-type orbital. Analysis of relative isomer energies and their electronic density of states suggest that these clusters tend to follow a maximum hardness principle (MHP). For A4B12 clusters (A is divalent, B is monovalent), we found unusually large (on average 1.95 eV) HOMO-LUMO gap values. This shows the extra stability at an electronic closed shell (20 electrons) predicted by the jellium model. The importance of symmetry, closed electronic and ionic shells in stability is shown by the relative stability of homotops of Mg4Ag12 which also provides support for the hypothesis that clusters that satisfy more than one stability criterion ("double magic") should be particularly stable.

Room-temperature fabrication of core-shell nano-ZnO/pollen grain biocomposite for adsorptive removal of organic dye from water

NASA Astrophysics Data System (ADS)

Tzvetkov, George; Kaneva, Nina; Spassov, Tony

2017-04-01

A new core-shell nano-ZnO/pollen grain (n-ZnO/PG) biocomposite has been successfully synthesized via simple and low-temperature two-step liquid precipitation method. The synthetic strategy consists of grafting the surface of pine pollen grains (PG) with Zn2+-organic complexes followed by a treatment in Zn(CH3COO)2/NaOH solution, thus producing a closed n-ZnO shell around the organic core, with a thickness of ∼450 nm. Scanning electron microscopy, X-ray diffraction, FTIR, XPS and UV-vis spectroscopy measurements along with N2 adsorption/desorption were used to characterize the resulting n-ZnO/PG biocomposite. The as-prepared core-shell microparticles are meso-/macro-porous with BET surface area of 25 m2 g-1 and total pore volume of 0.26 cm3 g-1. The adsorption properties of n-ZnO/PG were evaluated through adsorption of Malachite Green (MG) from aqueous medium at room temperature (25 °C). For the sake of comparison, the physico-chemical and adsorptive properties of the raw PG and pure n-ZnO were also examined. Results indicate that n-ZnO/PG is the most favorable for the adsorption of MG under the conditions used in this study. The adsorption kinetic data for PG, n-ZnO and n-ZnO/PG follow the pseudo-second order equation and the maximum adsorption capacity follows an order of n-ZnO/PG > n-ZnO > PG. For n-ZnO/PG an adsorption uptake up to 145.9 mg g-1 is observed. The as-prepared core-shell biocomposite material is a promising cost-effective and environmentally friendly adsorbent due to its textural properties, surface chemistry, adsorption capacity and recyclability.

Theoretical investigation of the relative stability of Na{sup +}He{sub n} (n = 2–24) clusters: Many-body versus delocalization effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Issaoui, Noureddine, E-mail: issaoui-noureddine@yahoo.fr; Abdessalem, Kawther; Ghalla, Houcine

2014-11-07

The solvation of the Na{sup +} ion in helium clusters has been studied theoretically using optimization methods. A many-body empirical potential was developed to account for Na{sup +}–He and polarization interactions, and the most stable structures of Na{sup +}He{sub n} clusters were determined using the basin-hopping method. Vibrational delocalization was accounted for using zero-point energy corrections at the harmonic or anharmonic levels, the latter being evaluated from quantum Monte Carlo simulations for spinless particles. From the static perspective, many-body effects are found to play a minor role, and the structures obtained reflect homogeneous covering up to n = 10, followedmore » by polyicosahedral packing above this size, the cluster obtained at n = 12 appearing particularly stable. The cationic impurity binds the closest helium atoms sufficiently to negate vibrational delocalization at small sizes. However, this snowball effect is obliterated earlier than shell completion, the nuclear wavefunctions of {sup 4}He{sub n}Na{sup +} with n = 5–7, and n > 10 already exhibiting multiple inherent structures. The decrease in the snowball size due to many-body effects is consistent with recent mass spectrometry measurements.« less

Characterizing inner-shell with spectral phase interferometry for direct electric-field reconstruction

PubMed Central

Mashiko, Hiroki; Yamaguchi, Tomohiko; Oguri, Katsuya; Suda, Akira; Gotoh, Hideki

2014-01-01

In many atomic, molecular and solid systems, Lorentzian and Fano profiles are commonly observed in a broad research fields throughout a variety of spectroscopies. As the profile structure is related to the phase of the time-dependent dipole moment, it plays an important role in the study of quantum properties. Here we determine the dipole phase in the inner-shell transition using spectral phase interferometry for direct electric-field reconstruction (SPIDER) with isolated attosecond pulses (IAPs). In addition, we propose a scheme for pulse generation and compression by manipulating the inner-shell transition. The electromagnetic radiation generated by the transition is temporally compressed to a few femtoseconds in the extreme ultraviolet (XUV) region. The proposed pulse-compression scheme may provide an alternative route to producing attosecond pulses of light. PMID:25510971

Spontaneous formation of GaN/AlN core-shell nanowires on sapphire by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Trassoudaine, Agnès; Roche, Elissa; Bougerol, Catherine; André, Yamina; Avit, Geoffrey; Monier, Guillaume; Ramdani, Mohammed Réda; Gil, Evelyne; Castelluci, Dominique; Dubrovskii, Vladimir G.

2016-11-01

Spontaneous GaN/AlN core-shell nanowires with high crystal quality were synthesized on sapphire substrates by vapor-liquid-solid hydride vapor phase epitaxy (VLS-HVPE) without any voluntary aluminum source. Deposition of aluminum is difficult to achieve in this growth technique which uses metal-chloride gaseous precursors: the strong interaction between the AlCl gaseous molecules and the quartz reactor yields a huge parasitic nucleation on the walls of the reactor upstream the substrate. We open up an innovative method to produce GaN/AlN structures by HVPE, thanks to aluminum etching from the sapphire substrate followed by redeposition onto the sidewalls of the GaN core. The paper presents the structural characterization of GaN/AlN core-shell nanowires, speculates on the growth mechanism and discusses a model which describes this unexpected behavior.