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Sample records for au cluster properties

  1. Ligand effects on the optical and chiroptical properties of the thiolated Au18 cluster.

    PubMed

    Tlahuice-Flores, Alfredo

    2016-10-12

    The effect of chiral and achiral ligands protecting the inner Au9 core of the Au18(SR)14 cluster is studied based on density functional theory (DFT) and its corrected long-range interaction (DFT-D) approach. It was found that the electronic properties (energy levels) depend on the specific ligands, which induce distinct distortions on the Au-S framework. However, the substitution of S-c-C6H11 as SCH3 ligands may be considered to be correct given the obtained resemblance to the displayed bonding, optical and chiroptical properties. A further comparison of the CD and UV spectra displayed by the Au18 cluster protected by chiral and achiral ligands attests that more intense profiles are featured by ligands including phenyl rings and/or oxygen atoms such that the Au18 cluster protected by either achiral meta-mercaptobenzoic acid (m-MBA) or achiral SPh ligands displays more intense UV and CD signals. These results provide new insight into the effect of ligands on thiolated gold clusters.

  2. Quantum-size effect on the electronic and optical properties of hybrid TiO{sub 2}/Au clusters

    SciTech Connect

    Liu, Chun-Sheng E-mail: yexiaojuan1980@gmail.com; Wang, Xiangfu; Yan, Xiaohong; Ye, Xiaojuan E-mail: yexiaojuan1980@gmail.com; Zeng, Zhi

    2014-08-07

    Although TiO{sub 2}/Au nanosystems exhibit high photocatalytic activities under solar radiation in the experiment, the quantum-size effect of TiO{sub 2} on the growth, electronic properties, and reactivity of Au clusters remains elusive. Using (time dependent) density functional theory, it is found that Au atoms attach to low-coordinated Ti and O atoms and serve as seeds for the growth of Au clusters, and the electronic (optical) properties of hybrid Au-TiO{sub 2} nano-clusters depend strongly upon the type of supported Au clusters. Interestingly, decorating TiO{sub 2} nano-particles with even-numbered Au clusters (Au{sub 8} or Au{sub 10}) can enhance the photocatalytic activity by: (i) spatially separating electron and hole states and (ii) balancing redox strength and visible light absorption. Furthermore, the interactions between the Au-TiO{sub 2} clusters and a single water molecule have been studied. It will open up new avenues for exploring controlled photocatalysts in semiconductor-based quantum-confined systems.

  3. Quantum-size effect on the electronic and optical properties of hybrid TiO2/Au clusters

    NASA Astrophysics Data System (ADS)

    Liu, Chun-Sheng; Ye, Xiaojuan; Wang, Xiangfu; Yan, Xiaohong; Zeng, Zhi

    2014-08-01

    Although TiO2/Au nanosystems exhibit high photocatalytic activities under solar radiation in the experiment, the quantum-size effect of TiO2 on the growth, electronic properties, and reactivity of Au clusters remains elusive. Using (time dependent) density functional theory, it is found that Au atoms attach to low-coordinated Ti and O atoms and serve as seeds for the growth of Au clusters, and the electronic (optical) properties of hybrid Au-TiO2 nano-clusters depend strongly upon the type of supported Au clusters. Interestingly, decorating TiO2 nano-particles with even-numbered Au clusters (Au8 or Au10) can enhance the photocatalytic activity by: (i) spatially separating electron and hole states and (ii) balancing redox strength and visible light absorption. Furthermore, the interactions between the Au-TiO2 clusters and a single water molecule have been studied. It will open up new avenues for exploring controlled photocatalysts in semiconductor-based quantum-confined systems.

  4. Quantum-size effect on the electronic and optical properties of hybrid TiO₂/Au clusters.

    PubMed

    Liu, Chun-Sheng; Ye, Xiaojuan; Wang, Xiangfu; Yan, Xiaohong; Zeng, Zhi

    2014-08-07

    Although TiO2/Au nanosystems exhibit high photocatalytic activities under solar radiation in the experiment, the quantum-size effect of TiO2 on the growth, electronic properties, and reactivity of Au clusters remains elusive. Using (time dependent) density functional theory, it is found that Au atoms attach to low-coordinated Ti and O atoms and serve as seeds for the growth of Au clusters, and the electronic (optical) properties of hybrid Au-TiO2 nano-clusters depend strongly upon the type of supported Au clusters. Interestingly, decorating TiO2 nano-particles with even-numbered Au clusters (Au8 or Au10) can enhance the photocatalytic activity by: (i) spatially separating electron and hole states and (ii) balancing redox strength and visible light absorption. Furthermore, the interactions between the Au-TiO2 clusters and a single water molecule have been studied. It will open up new avenues for exploring controlled photocatalysts in semiconductor-based quantum-confined systems.

  5. Ligand and solvation effects on the electronic properties of Au55 clusters: a density functional theory study.

    PubMed

    Periyasamy, Ganga; Remacle, F

    2009-08-01

    The electronic properties of the neutral, positively and negatively charged bare Au(55), passivated Au(55)(PH(3))(12), Au(55)(PH(3))(12)Cl(6), and solvated Au(55)(PH(3))(12)Cl(6) 54 H(2)O clusters are studied using density functional theory. The presence of Cl atoms in the ligand shell favors a nonmetallic behavior while a more metallic behavior is induced by explicit solvation of Au(55)(PH(3))(12)Cl(6) with water molecules. The trends observed in the electronic properties upon ligation and solvation are in agreement with experimental studies.

  6. Geometric, stability, and electronic properties of gold-doped Pd clusters (Pd n Au, n = 3 20)

    NASA Astrophysics Data System (ADS)

    Huan, Hao; Chen, Yan; Wang, Tao; Ye, Xiang; Gu, Xiao

    2016-11-01

    The structure, stability, and electronic properties of Pd n Au ( n = 3 20) clusters are studied by density functional theory. The results show that the clusters studied here prefer three-dimensional structures even with very small atom number. It is found that the binding energies of Pd n Au clusters are higher than the corresponding pure Pd n clusters with the same atom number. Most Pd n Au clusters studied here are magnetic with magnetic moments ranging from 1.0 to 7.0 μ B. The dissociation energies of Pd atoms are lower than the doped gold atom, that is the doped Au atom will increase the mother clusters stability and activity.

  7. Electronic structure and optical properties of the thiolate-protected Au28(SMe)20 cluster.

    PubMed

    Knoppe, Stefan; Malola, Sami; Lehtovaara, Lauri; Bürgi, Thomas; Häkkinen, Hannu

    2013-10-10

    The recently reported crystal structure of the Au28(TBBT)20 cluster (TBBT: p-tert-butylbenzenethiolate) is analyzed with (time-dependent) density functional theory (TD-DFT). Bader charge analysis reveals a novel trimeric Au3(SR)4 binding motif. The cluster can be formulated as Au14(Au2(SR)3)4(Au3(SR)4)2. The electronic structure of the Au14(6+) core and the ligand-protected cluster were analyzed, and their stability can be explained by formation of distorted eight-electron superatoms. Optical absorption and circular dichroism (CD) spectra were calculated and compared to the experiment. Assignment of handedness of the intrinsically chiral cluster is possible.

  8. Equilibrium geometries, stabilities, and electronic properties of the bimetallic M2-doped Au(n) (M = Ag, Cu; n = 1-10) clusters: comparison with pure gold clusters.

    PubMed

    Zhao, Ya-Ru; Kuang, Xiao-Yu; Zheng, Bao-Bing; Li, Yan-Fang; Wang, Su-Juan

    2011-02-10

    The density functional method with relativistic effective core potential has been employed to investigate systematically the geometrical structures, relative stabilities, growth-pattern behaviors, and electronic properties of small bimetallic M(2)Au(n) (M = Ag, Cu; n = 1-10) and pure gold Au(n) (n ≤ 12) clusters. The optimized geometries reveal that M(2) substituted Au(n+2) clusters and one Au atom capped M(2)Au(n-1) structures are dominant growth patterns of the stable alloyed M(2)Au(n) clusters. The calculated averaged atomic binding energies, fragmentation energies, and the second-order difference of energies as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. The analytic results exhibit that the planar structure Ag(2)Au(4) and Cu(2)Au(2) isomers are the most stable geometries of Ag(2)Au(n) and Cu(2)Au(n) clusters, respectively. In addition, the HOMO-LUMO gaps, charge transfers, chemical hardnesses and polarizabilities have been analyzed and compared further.

  9. The effect of CNTs on structures and catalytic properties of AuPd clusters for H2O2 synthesis.

    PubMed

    Yang, Hua-feng; Xie, Peng-yang; Yu, Hui-you; Li, Xiao-nian; Wang, Jian-guo

    2012-12-28

    The structures and catalytic properties of AuPd clusters supported on carbon nanotubes (CNTs) for H(2)O(2) synthesis have been investigated by means of density functional theory calculations. Firstly, the structures of AuPd clusters are strongly influenced by CNTs, in which the bottom layers are mainly composed of Pd and the top layers are a mix of Au and Pd due to the stronger binding of Pd than Au on CNTs. Especially, it is found that O(2) adsorption on the Pd/CNTs interfacial sites is much weaker than that on the only Pd sites, which is in contrast to transition metal oxide (for example TiO(2), Al(2)O(3), CeO(2)) supported metal clusters. Furthermore, Pd ensembles on the interfacial sites have far superior catalytic properties for H(2)O(2) formation than those away from CNT supports due to the changes in electronic structures caused by the CNTs. Therefore, our study provides a physical insight into the enhanced role of carbon supports in H(2)O(2) synthesis over supported AuPd catalysts.

  10. Structural and electronic properties of Au{sub n−x}Pt{sub x} (n = 2–14; x ⩽ n) clusters: The density functional theory investigation

    SciTech Connect

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

    2014-03-15

    The structural evolutions and electronic properties of bimetallic Au{sub n–x}Pt{sub x} (n = 2–14; x ⩽ n) clusters are investigated by using the density functional theory (DFT) with the generalized gradient approximation (GGA). The monatomic doping Au{sub n–1}Pt clusters are emphasized and compared with the corresponding pristine Au{sub n} clusters. The results reveal that the planar configurations are favored for both Au{sub n–1}Pt and Au{sub n} 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 Au{sub 6} and Au{sub 6}Pt, which adopt regular planar triangle (D{sub 3h}) and hexagon-ring (D{sub 6h}) 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 Pt{sub n} 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, Au{sub n}Pt 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.

  11. Equilibrium geometries, stabilities, and electronic properties of the cationic Au n Be + (n = 1-8) clusters: comparison with pure gold clusters.

    PubMed

    Shao, Peng; Kuang, Xiao-Yu; Zhao, Ya-Ru; Li, Yan-Fang; Wang, Su-Juan

    2012-08-01

    Ab initio method based on density functional theory at PW91PW91 level has been applied in studying the geometrical structures, relative stabilities, and electronic properties of small bimetallic Au(n)Be(+) (n = 1-8) cluster cations. The geometrical optimizations indicate that a transition point from preferentially planar (two-dimensional) to three-dimensional (3D) structures occurs at n = 6. The relative stabilities of Au(n)Be(+) clusters for the ground-state structures are analyzed based on the averaged binding energies, fragmentation energies, and second-order difference of energies. The calculated results reveal that the AuBe(+) and Au(5)Be(+) clusters possess higher relative stability for small size Au(n)Be(+) (n = 1-8) clusters. The HOMO-LUMO energy gaps as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. Sequently, the natural population analysis and polarizability for our systems have been analyzed and compared further.

  12. Opto-electronic Properties of Monolayer-Protected Clusters of Au functionalized with a New Fluorescent Ligand

    NASA Astrophysics Data System (ADS)

    Kountz, Thomas; Thanthirige, Viraj; Reber, Keith; Devadas, Mary Sajini

    Metal nanoclusters are the focus of intense study due to their interesting optical, electronic, and catalytic properties; specifically gold clusters. The applications of gold monolayer-protected clusters (MPCs) are being researched by a series of optical spectroscopic and voltammetric analyses to determine core size, atom-level composition, charge states, and optical/electrical properties. Understanding these fundamental properties is critical for both expansion of applications and creation of new MPCs. The purpose of this study is to expand the applications of gold MPCs, with the attachment of a new coumarin surface ligand - synthesized specifically for this experiment. Our focus in this research is on quantum clusters - specifically Au25(C6S)18. This MPC is researched particularly because of its inherent stability being a magic number cluster. It is created by means of a modified Burst-Schiffrin method. The applications that are influenced include but are not limited to: catalytic activity, solar energy conversion, size-tunable florescence, sensors, and optical electronics.

  13. Low-energy isomer identification, structural evolution, and magnetic properties in manganese-doped gold clusters MnAu(n) (n = 1-16).

    PubMed

    Zhang, Meng; Zhang, Hongyu; Zhao, Lina; Li, Yan; Luo, Youhua

    2012-02-16

    The size-dependent electronic, structural, and magnetic properties of Mn-doped gold clusters have been systematically investigated by using relativistic all-electron density functional theory with generalized gradient approximation. A number of new isomers are obtained for neutral MnAu(n) (n = 1-16) clusters to probe the structural evolution. The two-dimensional (2D) to three-dimensional (3D) transition occurs in the size range n = 7-10 with manifest structure competitions. From size n = 13 to n = 16, the MnAu(n) prefers a gold cage structure with Mn atom locating at the center. The relative stabilities of the ground-state MnAu(n) clusters show a pronounced odd-even oscillation with the number of Au atoms. The magnetic moments of MnAu(n) clusters vary from 3 μ(B) to 6 μ(B) with the different cluster size, suggesting that nonmagnetic Au(n) clusters can serve as a flexible host to tailor the dopant's magnetism, which has potential applications in new nanomaterials with tunable magnetic properties.

  14. Geometric structure, electronic structure and optical absorption properties of one-dimensional thiolate-protected gold clusters containing a quasi-face-centered-cubic (quasi-fcc) Au-core: a density-functional theoretical study.

    PubMed

    Ma, Zhongyun; Wang, Pu; Pei, Yong

    2016-09-29

    Based on the recently reported atomic structures of thiolate-protected Au28(SR)20, Au36(SR)24, Au44(SR)28, and Au52(SR)32 clusters, a family of homogeneous, linear, thiolate-protected gold superstructures containing novel quasi-face-centered-cubic (quasi-fcc) Au-cores is theoretically envisioned, denoted as the Au20+8N(SR)16+4N cluster. By means of density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, a unified view of the geometric structure, electronic structure, magic stable size and size-dependent NIR absorption properties of Au20+8N(SR)16+4N clusters is provided. We find that the Au20+8N(SR)16+4N clusters demonstrate oscillating transformation energies dependent on N. The odd-N clusters show more favorable (negative) reaction energies than the even-N clusters. The magic stability of recently reported Au28(SR)20, Au36(SR)24, Au44(SR)28, Au52(SR)32 and Au76(SR)44 clusters can be addressed from the relative reaction energies and geometric distortion of Au-cores. A novel 4N + 4 magic electron-number is suggested for the Au20+8N(SR)16+4N cluster. Using the polyhedral skeletal electron pair theory (PSEPT) and the extended Hückel molecular orbital (EHMO) calculations, we suggest that the magic 4N + 4 electron number is correlated with the quasi-fcc Au-cores, which can be viewed as double helical tetrahedron-Au4 chains. The size-dependent optical absorption properties of Au20+8N(SR)16+4N clusters are revealed based on TD-DFT calculations. We propose that these clusters are potential candidates for the experimental synthesis of atomically precise one-dimensional ligand protected gold superstructures with tunable NIR absorption properties.

  15. Density functional studies of small Au clusters adsorbed on α-FeOOH: Structural and electronic properties

    NASA Astrophysics Data System (ADS)

    Fortunato, Leandro F.; Zubieta, Carolina E.; Fuente, Silvia A.; Belelli, Patricia G.; Ferullo, Ricardo M.

    2016-11-01

    We report a density functional theory (DFT) investigation on the interaction of tiny Aun (n = 1-5) clusters with the bare and hydroxylated (110) surfaces of goethite (α-FeOOH). Both adsorption and atom-by-atom nucleation processes were modeled. The adsorption is shown to be strong on the bare surface and takes place preferentially through the interaction of Au atoms with unsaturated surface oxygen anions, accompanied with an electronic charge transfer from the metal to the support. Au3, Au4 and Au5 planar structures resulted to be particularly stable due to polarization effects; indeed, Coulombic repulsion between basal Au atoms and surface oxygen anions promotes the displacement of the electronic density toward terminal Au atoms producing a Au+δ(basal)/Au-δ(terminal) polarization. On the hydroxylated surface, Au clusters adsorb more weakly with respect to the bare surface, mainly through monocoordinated surface hydroxyl groups and tricoordinated oxygen ions. Concerning the nucleation mechanism, while on the hydroxylated surface the nucleation energy is governed by the spin of the interacting systems, on the bare surface polarization effects seems to play a predominant role.

  16. Effect of Au clustering on ferromagnetism in Au doped TiO2 films: theory and experiments investigation

    NASA Astrophysics Data System (ADS)

    Zou, Zhaorui; Zhou, Zhongpo; Wang, Haiying; Yang, Zongxian

    2017-01-01

    In this paper, we investigated the physical properties especially the magnetic properties of the TiO2 films and Au cluster doped TiO2 films fabricated by sol-gel and sputtering methods combined experiments and first-principles calculations. All the samples annealed under air and N2 atmosphere respectively exhibit room temperature ferromagnetism with the crystal phase of anatase. The values of the saturation magnetizations are in the order of Au δ-doped TiO2 (annealed in N2)>undoped TiO2 (annealed in air)>Au δ-doped TiO2 (annealed in air). The first principles calculation results show that the formation energy of Au cluster doped TiO2 films is lower than that of the oxygen vacancy and Au cluster codoped TiO2 films. The effects of the Au cluster dopant are the retard of the formation of surface oxygen vacancy and the electrons transfer from 3d states of Ti atoms to Au 5d states in Au cluster doped TiO2 films. The codoping of surface oxygen vacancies, bulk oxygen vacancies and Au clusters led to the spin-split of Ti 3d and O 2p in Au cluster doped TiO2 films (annealed in N2) which yield the highest saturation magnetization.

  17. Au40: A Large Tetrahedral Magic Cluster

    SciTech Connect

    Jiang, Deen; Walter, Michael

    2011-01-01

    40 is a magic number for tetrahedral symmetry predicted in both nuclear physics and the electronic jellium model. We show that Au{sub 40} could be such a magic cluster from density functional theory-based basin hopping for global minimization. The putative global minimum found for Au{sub 40} has a twisted pyramid structure, reminiscent of the famous tetrahedral Au{sub 20}, and a sizable HOMO-LUMO gap of 0.69 eV, indicating its molecular nature. Analysis of the electronic states reveals that the gap is related to shell closings of the metallic electrons in a tetrahedrally distorted effective potential.

  18. Fully Cationized Gold Clusters: Synthesis of Au25(SR(+))18.

    PubMed

    Ishida, Yohei; Narita, Kunihiro; Yonezawa, Tetsu; Whetten, Robert L

    2016-10-06

    Although many thiolate-protected Au clusters with different numbers of Au atoms and a variety of thiolate ligands have been synthesized, to date there has been no report of a fully cationized Au cluster protected with cationic thiolates. Herein, we report the synthesis of the first member of a new series of thiolate-protected Au cluster molecules: a fully cationized Au25(SR(+))18 cluster.

  19. Characterization of Pt-Au and Ni-Au Clusters on TiO2(110)

    SciTech Connect

    S Tenney; W He; J Ratliff; D Mullins; D Chen

    2011-12-31

    The surface composition and properties of Pt-Au and Ni-Au clusters on TiO{sub 2}(110) have been studied by scanning tunneling microscopy (STM), low energy ion scattering (LEIS) and soft X-ray photoelectron spectroscopy (sXPS). STM studies show that bimetallic clusters are formed during sequential deposition of the two metals, regardless of the order of deposition. At the 2 ML of Au/2 ML of Pt or Ni coverages studied here, the second metal contributes to the growth of existing clusters rather than forming new pure metal clusters. LEIS experiments demonstrate that the surfaces of the bimetallic clusters are almost 100% Au when 2 ML of Au is deposited on top of 2 ML of Pt or Ni. However, a much larger fraction of Pt or Ni (50 and 20%, respectively) remains at the surface when 2 ML of Pt or Ni is deposited on 2 ML of Au, most likely due to limited diffusion of atoms within the clusters at room temperature. According to sXPS investigations, the binding energies of the metals in the bimetallic clusters are shifted from those observed for pure metal clusters; the Pt(4f{sub 7/2}) and Ni(3p{sub 3/2}) peaks are shifted to lower binding energies while the position of the Au(4f{sub 7/2}) peak is dominated by surface core level shifts. Pure Pt clusters as well as 0.4 ML of Au on 2 ML of Pt clusters reduce the titania support upon encapsulation after annealing to 800 K, whereas 2 ML of Au on 2 ML of Pt clusters do not reduce titania, presumably because there is no Pt at the surface of the clusters. Pure Ni clusters are also known to become encapsulated upon heating, but the reduction of titania is much less extensive compared to that of pure Pt clusters.

  20. System size dependence of cluster properties from two-particle angular correlations in Cu+Cu and Au+Au collisions at sq root(s{sub NN})=200 GeV

    SciTech Connect

    Alver, B.; Ballintijn, M.; Busza, W.; Gulbrandsen, K.; Henderson, C.; Kane, J. L.; Kulinich, P.; Li, W.; Loizides, C.; Reed, C.; Roland, C.; Roland, G.; Stephans, G. S. F.; Nieuwenhuizen, G. J. van; Vaurynovich, S. S.; Verdier, R.; Veres, G. I.; Wenger, E.; Wyslouch, B.; Back, B. B.

    2010-02-15

    We present results on two-particle angular correlations in Cu+Cu and Au+Au collisions at a center-of-mass energy per nucleon pair of 200 GeV over a broad range of pseudorapidity (eta) and azimuthal angle (phi) values as a function of collision centrality. The PHOBOS detector at the Relativistic Heavy Ion Collider has a uniquely large angular coverage for inclusive charged particles, which allows for the study of correlations on both long- and short-range scales. A complex two-dimensional correlation structure in {Delta}{eta} and {Delta}{phi} emerges, which is interpreted in the context of a cluster model. The effective cluster size and decay width are extracted from the two-particle pseudorapidity correlation functions. The effective cluster size found in semicentral Cu+Cu and Au+Au collisions is comparable to that found in proton-proton collisions but a nontrivial decrease in size with increasing centrality is observed. Moreover, a comparison of results from Cu+Cu versus Au+Au collisions shows an interesting scaling of the effective cluster size with the measured fraction of total cross section (which is related to the ratio of the impact parameter to the nuclear radius, b/2R), suggesting a geometric origin. Further analysis for pairs from restricted azimuthal regions shows that the effective cluster size at {Delta}{phi}{approx}180 deg. drops more rapidly toward central collisions than the size at {Delta}{phi}{approx}0 deg. The effect of limited {eta} acceptance on the cluster parameters is also addressed, and a correction is applied to present cluster parameters for full {eta} coverage, leading to much larger effective cluster sizes and widths than previously noted in the literature. These results should provide insight into the hot and dense medium created in heavy ion collisions.

  1. Polymorphism in magic-sized Au144(SR)60 clusters

    PubMed Central

    Jensen, Kirsten M.Ø.; Juhas, Pavol; Tofanelli, Marcus A.; Heinecke, Christine L.; Vaughan, Gavin; Ackerson, Christopher J.; Billinge, Simon J. L.

    2016-01-01

    Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles. However, their small size challenges the conventional methods for structure characterization. Here we present the structure of ultra-stable Au144(SR)60 magic-sized nanoclusters obtained from atomic pair distribution function analysis of X-ray powder diffraction data. The study reveals structural polymorphism in these archetypal nanoclusters. In addition to confirming the theoretically predicted icosahedral-cored cluster, we also find samples with a truncated decahedral core structure, with some samples exhibiting a coexistence of both cluster structures. Although the clusters are monodisperse in size, structural diversity is apparent. The discovery of polymorphism may open up a new dimension in nanoscale engineering. PMID:27297400

  2. Polymorphism in magic-sized Au144(SR)60 clusters

    NASA Astrophysics Data System (ADS)

    Jensen, Kirsten M. Ø.; Juhas, Pavol; Tofanelli, Marcus A.; Heinecke, Christine L.; Vaughan, Gavin; Ackerson, Christopher J.; Billinge, Simon J. L.

    2016-06-01

    Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles. However, their small size challenges the conventional methods for structure characterization. Here we present the structure of ultra-stable Au144(SR)60 magic-sized nanoclusters obtained from atomic pair distribution function analysis of X-ray powder diffraction data. The study reveals structural polymorphism in these archetypal nanoclusters. In addition to confirming the theoretically predicted icosahedral-cored cluster, we also find samples with a truncated decahedral core structure, with some samples exhibiting a coexistence of both cluster structures. Although the clusters are monodisperse in size, structural diversity is apparent. The discovery of polymorphism may open up a new dimension in nanoscale engineering.

  3. Polymorphism in magic-sized Au144(SR)60 clusters

    SciTech Connect

    Jensen, Kirsten M. O.; Juhas, Pavol; Tofanelli, Marcus A.; Heinecke, Christine L.; Vaughan, Gavin; Ackerson, Christopher J.; Billinge, Simon J. L.

    2016-06-14

    Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles. However, their small size challenges the conventional methods for structure characterization. We present the structure of ultra-stable Au144(SR)60 magic-sized nanoclusters obtained from atomic pair distribution function analysis of X-ray powder diffraction data. Our study reveals structural polymorphism in these archetypal nanoclusters. Additionally, in order to confirm the theoretically predicted icosahedral-cored cluster, we also find samples with a truncated decahedral core structure, with some samples exhibiting a coexistence of both cluster structures. Although the clusters are monodisperse in size, structural diversity is apparent. Finally, the discovery of polymorphism may open up a new dimension in nanoscale engineering.

  4. Polymorphism in magic-sized Au144(SR)60 clusters

    DOE PAGES

    Jensen, Kirsten M. O.; Juhas, Pavol; Tofanelli, Marcus A.; ...

    2016-06-14

    Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles. However, their small size challenges the conventional methods for structure characterization. We present the structure of ultra-stable Au144(SR)60 magic-sized nanoclusters obtained from atomic pair distribution function analysis of X-ray powder diffraction data. Our study reveals structural polymorphism in these archetypal nanoclusters. Additionally, in order to confirm the theoretically predicted icosahedral-cored cluster, we also find samples with a truncated decahedral core structure, with some samples exhibiting a coexistence of both cluster structures. Although the clusters are monodisperse in size, structural diversity is apparent. Finally,more » the discovery of polymorphism may open up a new dimension in nanoscale engineering.« less

  5. First-principles insights into interaction of Au with small Co clusters

    NASA Astrophysics Data System (ADS)

    Aghajani, Mahdieh; Javad Hashemifar, S.; Akbarzadeh, Hadi

    2014-08-01

    The effects of Au doping on structural, electronic, magnetic, and dynamical properties of the Con nano-clusters are investigated by using density functional computations and numeric atom-centered orbitals method. The Au doping that enhances stability of the planar structures of the Con clusters over their 3-dimensional structures is discussed. Doping with the nonmagnetic Au atom is found to decrease the spin moments of the Con clusters. The calculated binding energies and their various derivatives are used to investigate the structural stability of the doped clusters. The electronic energy levels of the clusters are accurately determined and discussed after applying the many body based GW correction. The vibrational and infrared spectra of the doped clusters are calculated to provide spectroscopic finger print of these clusters.

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

    SciTech Connect

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

    2014-03-12

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

  7. Thiophenol and thiophenol radical and their complexes with gold clusters Au 5 and Au 6

    NASA Astrophysics Data System (ADS)

    Remacle, F.; Kryachko, E. S.

    2004-12-01

    The longstanding controversy between experiment and theory regarding which conformer of thiophenol, planar or perpendicular, is the most stable and what is the magnitude of the corresponding rotational barrier of the S-H group is discussed. We propose a variety of rather modest high-level computational methods within the density theory, which corroborate the experimental data. These methods demonstrate that the planar structure of thiophenol is the most stable and the magnitude of the rotational barrier falls within the experimental range of 3.35±0.84 kJ mol -1. However, the barrier is of the order of RT at room temperature, which might prevent to clearly identify the most stable conformer of thiophenol in experiments and leads to a large-amplitude motion of the thiolic hydrogen. On the other hand, such low value of the barrier may lead to some error in evaluating the thermodynamic properties of thiophenol within the rigid-rotor-harmonic oscillator model, in particular for the bond dissociation enthalpy. We also show the existence of a large entropy contribution to the Gibbs free energy difference between the planar and perpendicular conformers which is the order of the rotational barrier (≈4 kJ mol -1). This might be of interest for experimental study. The most stable complexes of thiophenol with the gold clusters Au 5 and Au 6 are also investigated. It is shown that the sulfur atom prefers to anchor to two- and three-coordinated atoms of gold in these clusters to form a strongly directional gold-sulfur bond. The hydrogen abstraction from the S-H group of thiophenol bonded to the two-coordinated gold atom in Au 5 yields the bridging Au-S dibond and results in a spectacular reduction of the bond dissociation energy of thiophenol by nearly a factor of three.

  8. FT-ICR/MS and ab initio study of polynuclear Au and Au-Cu clusters in aqueous fluids

    NASA Astrophysics Data System (ADS)

    Lemke, K.; Tse, K.; Sadjadi, A.

    2011-12-01

    3.5 kJ/mol higher in energy. Theoretical [Au2Cl5]+ ion cluster geometries are then used to compute higher temperature heat capacity data that may be used to predict fundamental thermodynamic properties of transition metal-charged aqueous systems at elevated temperatures. Results from such mass spectrometric and ab initio studies would allow modeling of gold and copper speciation in crustal fluids and assist in understanding prenucleation processes in metal halides in nature.

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

    PubMed

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

    2015-09-14

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

  10. Structure and mobility of metal clusters in MOFs: Au, Pd, and AuPd clusters in MOF-74.

    PubMed

    Vilhelmsen, Lasse B; Walton, Krista S; Sholl, David S

    2012-08-01

    Understanding the adsorption and mobility of metal-organic framework (MOF)-supported metal nanoclusters is critical to the development of these catalytic materials. We present the first theoretical investigation of Au-, Pd-, and AuPd-supported clusters in a MOF, namely MOF-74. We combine density functional theory (DFT) calculations with a genetic algorithm (GA) to reliably predict the structure of the adsorbed clusters. This approach allows comparison of hundreds of adsorbed configurations for each cluster. From the investigation of Au(8), Pd(8), and Au(4)Pd(4) we find that the organic part of the MOF is just as important for nanocluster adsorption as open Zn or Mg metal sites. Using the large number of clusters generated by the GA, we developed a systematic method for predicting the mobility of adsorbed clusters. Through the investigation of diffusion paths a relationship between the cluster's adsorption energy and diffusion barrier is established, confirming that Au clusters are highly mobile in the MOF-74 framework and Pd clusters are less mobile.

  11. Luminescent, bimetallic AuAg alloy quantum clusters in protein templates

    NASA Astrophysics Data System (ADS)

    Mohanty, Jyoti Sarita; Xavier, P. Lourdu; Chaudhari, Kamalesh; Bootharaju, M. S.; Goswami, N.; Pal, S. K.; Pradeep, T.

    2012-06-01

    We report the synthesis of luminescent AuAg alloy quantum clusters (QCs) in bovine serum albumin (BSA), for the first time, with experimentally determined atomic composition. Mixing of the as-synthesized protein-protected Au and Ag clusters resulted in the formation of alloy AuAg clusters within the BSA. Mass spectrometric analysis of the product of a 1 : 1 molar ratio reaction mixture of AuQC@BSA and AgQC@BSA suggested that the alloy clusters could be Au38-xAgx@BSA. Further analyses by standard techniques revealed that the alloy cluster core of ~1.2 nm diameter is composed of nearly zero valent Au and Ag atoms that exhibit distinctly different steady state and time resolved excited state luminescence profiles compared to the parent clusters. Tuning of the alloy composition was achieved by varying the molar ratio of the parent species in the reaction mixture and compositional changes were observed by mass spectrometry. In another approach, mixing of Au3+ ions with the as-synthesized AgQC@BSA also resulted in the formation of alloy clusters through galvanic exchange reactions. We believe that alloy clusters with the combined properties of the constituents in versatile protein templates would have potential applications in the future. The work presents interesting aspects of the reactivity of the protein-protected clusters.We report the synthesis of luminescent AuAg alloy quantum clusters (QCs) in bovine serum albumin (BSA), for the first time, with experimentally determined atomic composition. Mixing of the as-synthesized protein-protected Au and Ag clusters resulted in the formation of alloy AuAg clusters within the BSA. Mass spectrometric analysis of the product of a 1 : 1 molar ratio reaction mixture of AuQC@BSA and AgQC@BSA suggested that the alloy clusters could be Au38-xAgx@BSA. Further analyses by standard techniques revealed that the alloy cluster core of ~1.2 nm diameter is composed of nearly zero valent Au and Ag atoms that exhibit distinctly different

  12. Spin resonance transport properties of a single Au atom in S-Au-S junction and Au-Au-Au junction

    NASA Astrophysics Data System (ADS)

    Fangyuan, Wang; Guiqin, Li

    2016-07-01

    The spin transport properties of S-Au-S junction and Au-Au-Au junction between Au nanowires are investigated with density functional theory and the non-equilibrium Green's function. We mainly focus on the spin resonance transport properties of the center Au atom. The breaking of chemical bonds between anchor atoms and center Au atom significantly influences their spin transmission characteristics. We find the 0.8 eV orbital energy shift between anchor S atoms and the center Au atom can well protect the spin state stored in the S-Au-S junction and efficiently extract its spin state to the current by spin resonance mechanism, while the spin interaction of itinerant electrons and the valence electron of the center Au atom in the Au-Au-Au junction can extract the current spin information into the center Au atom. Fermi energy drift and bias-dependent spin filtering properties of the Au-Au-Au junction may transform information between distance, bias, and electron spin. Those unique properties make them potential candidates for a logical nanocircuit. Project supported by the National Basic Research Program of China (Grants No. 2011CB921602) and the National Natural Science Foundation of China (Grants No. 20121318158).

  13. [Au7](3+): a missing link in the four-electron gold cluster family.

    PubMed

    Shichibu, Yukatsu; Zhang, Mingzhe; Kamei, Yutaro; Konishi, Katsuaki

    2014-09-17

    Ligand-stabilized ultrasmall gold clusters offer a library of diverse geometrical and electronic structures. Among them, clusters with four valence electrons form an exceptional but interesting family because of their unique geometrical structures and optical properties. Here, we report a novel diphosphine-ligated four-electron Au7 cluster (2). In good agreement with previous theoretical predictions, 2 has a "core+one" structure to exhibit a prolate shape. The absorption spectrum showed an isolated band, similar to the spectra of Au6 and Au8 clusters with "core+two" structures. TD-DFT studies demonstrated that the attachment of only one gold atom to a polyhedral core is sufficient to generate unique electronic structures and characteristic absorptions. The present result fills the missing link between Au6 and Au8 in the four-electron cluster family, showing that the HOMO-LUMO gap increases with increasing nuclearity in the case of the tetrahedron-based "core+exo" clusters.

  14. A family of Au-Tl loosely bound butterfly clusters.

    PubMed

    Fernández, Eduardo J; López-de-Luzuriaga, José M; Olmos, M Elena; Pérez, Javier; Laguna, Antonio; Lagunas, M Cristina

    2005-08-22

    By treatment of the polymeric species [AuTl(C6Cl5)2]n with ketones or with acetylacetone and 4,4'-bipyridine, the new tetranuclear complexes [Au2Tl2(C6Cl5)4] x L (L = PhMeC=O, acacH) or [Au2Tl2(C6Cl5)4(bipy)] x (acacH) have been prepared. Their crystal structures have been determined by X-ray diffraction methods and they all present a central Au2Tl2 core formed via one Tl...Tl and four Au...Tl unsupported interactions resulting in a loosely bound butterfly cluster. These complexes are strongly luminescent in both the solid state and solution showing an optical behavior in agreement with the maintenance of the Tl...Tl contact even in solution.

  15. Electron transfer catalysis with monolayer protected Au25 clusters

    NASA Astrophysics Data System (ADS)

    Antonello, Sabrina; Hesari, Mahdi; Polo, Federico; Maran, Flavio

    2012-08-01

    Au25L18 (L = S(CH2)2Ph) clusters were prepared and characterized. The resulting monodisperse clusters were reacted with bis(pentafluorobenzoyl) peroxide in dichloromethane to form Au25L18+ quantitatively. The kinetics and thermodynamics of the corresponding electron transfer (ET) reactions were characterized via electrochemistry and thermochemical calculations. Au25L18+ was used in homogeneous redox catalysis experiments with a series of sym-substituted benzoyl peroxides, including the above peroxide, bis(para-cyanobenzoyl) peroxide, dibenzoyl peroxide, and bis(para-methoxybenzoyl) peroxide. Peroxide dissociative ET was catalyzed using both the Au25L18/Au25L18- and the Au25L18+/Au25L18 redox couples as redox mediators. Simulation of the CV curves led to determination of the ET rate constant (kET) values for concerted dissociative ET to the peroxides. The ET free energy ΔG° could be estimated for all donor-acceptor combinations, leading to observation of a nice activation-driving force (log kETvs. ΔG°) relationship. Comparison with the kET obtained using a ferrocene-type donor with a formal potential similar to that of Au25L18/Au25L18- showed that the presence of the capping monolayer affects the ET rate rather significantly, which is attributed to the intrinsic nonadiabaticity of peroxide acceptors.Au25L18 (L = S(CH2)2Ph) clusters were prepared and characterized. The resulting monodisperse clusters were reacted with bis(pentafluorobenzoyl) peroxide in dichloromethane to form Au25L18+ quantitatively. The kinetics and thermodynamics of the corresponding electron transfer (ET) reactions were characterized via electrochemistry and thermochemical calculations. Au25L18+ was used in homogeneous redox catalysis experiments with a series of sym-substituted benzoyl peroxides, including the above peroxide, bis(para-cyanobenzoyl) peroxide, dibenzoyl peroxide, and bis(para-methoxybenzoyl) peroxide. Peroxide dissociative ET was catalyzed using both the Au25L18/Au25L18- and

  16. Hydrogen-bonded clusters of ferrocenecarboxylic acid on Au(111).

    PubMed

    Quardokus, Rebecca C; Wasio, Natalie A; Christie, John A; Henderson, Kenneth W; Forrest, Ryan P; Lent, Craig S; Corcelli, Steven A; Kandel, S Alex

    2014-09-14

    Self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH) contain two fundamental units, both stabilized by intermolecular hydrogen bonding: dimers and cyclic five-membered catemers. At surface coverages below a full monolayer, however, there is a significantly more varied structure that includes double-row clusters containing two to twelve FcCOOH molecules. Statistical analysis shows a distribution of cluster sizes that is sharply peaked compared to a binomial distribution. This rules out simple nucleation-and-growth mechanisms of cluster formation, and strongly suggests that clusters are formed in solution and collapse into rows when deposited on the Au(111) surface.

  17. Ab Initio Studies of Anatase TiO2 (101) Surface-supported Au8 Clusters.

    PubMed

    Mikolajczyk, A; Pinto, H P; Gajewicz, A; Puzyn, T; Leszczynski, J

    2015-01-01

    Supported transition metals on TiO2 surfaces have shown exceptional catalytic properties in many important process such as CO oxidation, selective propane oxidation, hydrogenation, water adsorption and other catalytic and photocatalytic oxidation reaction at low-temperature. Among the three polymorphs of TiO2, the anatase crystal is the more photoactive. The anatase (101) surface attracts more attention since it has lower surface energy relative to (001) and (100) surfaces and it is observed to adsorb small molecules on its surface. Using density-functional theory (DFT) with on-site Coulomb interactions corrections, we have computed the structural and electronic properties of selected Au8 clusters interacting with clean and reduced anatase TiO2(101) surfaces. The computed adsorption energies are suggesting that the considered Au8 clusters are only physisorbed onto pristine TiO2(101) surface. Oxygen vacancies are found to enhance the absorption of Au8 on the Ti2(101) surface. Accurate simulations required spin polarized DFT since the ground state of Au8 interacting with defective TiO2(101) shows magnetic solutions. The results show that Au8 clusters are chemically bonded to the surface around the locality of the oxygen vacancy. The surface oxygen vacancy is found to be energetically more favourable than sub-surface oxygen vacancy configuration. These vacancy sites may act as nucleation sites for small Au clusters or Au atoms. Finally, the computed electronic structure of all the Au8/TiO2(101) configurations considered in this work are analysed in the light of available experimental data.

  18. Density Functional Investigation of the Inclusion of Gold Clusters on a CH 3 S Self-Assembled Lattice on Au(111)

    DOE PAGES

    Allen, Darnel J.; Archibald, Wayne E.; Harper, John A.; ...

    2016-01-01

    We employ first-principles density functional theoretical calculations to address the inclusion of gold (Au) clusters in a well-packed CH 3 S self-assembled lattice. We compute CH 3 S adsorption energies to quantify the energetic stability of the self-assembly and gold adsorption and dissolution energies to characterize the structural stability of a series of Au clusters adsorbed at the SAM-Au interface. Our results indicate that the inclusion of Au clusters with less than four Au atoms in the SAM-Au interface enhances the binding of CH 3 S species. In contrast, larger Au clusters destabilize the self-assembly. We attribute this effectmore » to the low-coordinated gold atoms in the cluster. For small clusters, these low-coordinated sites have significantly different electronic properties compared to larger islands, which makes the binding with the self-assembly energetically more favorable. Our results further indicate that Au clusters in the SAM-Au interface are thermodynamically unstable and they will tend to dissolve, producing Au adatoms incorporated in the self-assembly in the form of CH 3 S-Au-SCH 3 species. This is due to the strong S-Au bond which stabilizes single Au adatoms in the self-assembly. Our results provide solid insight into the impact of adatom islands at the CH 3 S-Au interface.« less

  19. Derivatives of the thiolate-protected gold cluster Au25(SR)18 -1

    NASA Astrophysics Data System (ADS)

    Lopez-Acevedo, O.; Häkkinen, H.

    2011-07-01

    Loss of small fragments (like AuL, Au2L3, Au4L4) have been found systematically in several MALDI and FAB experiments on thiolate-protected gold clusters of different sizes. When using the cluster Au25L18 -1 as parent cluster, the fragmented cluster Au21L14 -1 has been reported to be obtained in high proportion (L = SCH2CH2Ph). Here we analyse a few possible fragmentation patterns of the well-known parent cluster Au25L18 -1 (L = SCH3). Using DFT calculations we study the different atomic configurations obtained after a AuL fragment is lost from Au25L18 -1. We found energetically favourable configurations that can be written as Au13 [Au2L3]6- z [AuL2] z -1, where the modification can be described as a replacement of the long protecting unit by a short one (Au2L3 → AuL2). A full replacement ( z = 6) gives rise to a protected Au19L12 -1 cluster. This mechanism does not modify the super-atomic electronic structure of the gold core, i.e., all these fragments remain an 8 electron super-atom clusters exactly like the parent Au25L18 -1. We suggest that the Au19L12 -1 cluster could be realized by using a bulky thiolate, such as the tert-butyl thiolate SC(CH3)3.

  20. Gold Cluster Formation on C60 Surfaces: Au-Cluster Beads and Self-Organized Structures

    NASA Astrophysics Data System (ADS)

    Reinke, Petra; Liu, Hui

    2007-03-01

    Petra Reinke, Hui Liu, Department of Materials Science and Engineering, University of Virginia The investigation of C60-Au interaction is central to the advancement of solar cell and nanotechnology applications of C60. C60 grows in a quasi-layer-by-layer mode on a pristine graphite surface and form a special surface structure (coexistence of round and fractal islands). The deposition of Au leads to the formation of a complex array of different surface structures, while the basic island structure of the C60 is preserved. The Au-clusters nucleate preferentially at the graphite-first fullerene layer islands edge forming beadlike structures. A roughness analysis of the fullerene surface indicates the presence of Au atoms embedded in the fullerene surface, situated in the troughs in between the large molecules. The analysis of the spatial and size distributions of Au clusters provides the basis for the development of a qualitative model which describes the relevant surface processes in the Au-fullerene system. The simultaneous deposition of Au and C60 leads to the formation of organized structures, in which Au clusters are embedded in a ring of fullerene molecules with a constant width.

  1. Electronic structure transformation in small bare Au clusters as seen by x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Andersson, T.; Zhang, C.; Björneholm, O.; Mikkelä, M.-H.; Jänkälä, K.; Anin, D.; Urpelainen, S.; Huttula, M.; Tchaplyguine, M.

    2017-01-01

    Free bare gold clusters in the size range from few tens to few hundred atoms (≤1 nm dimensions) have been produced in a beam, and the size-dependent development of their full valence band including the 5d and 6s parts has been mapped ‘on the fly’ by synchrotron-based photoelectron spectroscopy. The Au 4f core level has been also probed, and the cluster-specific Au 4f ionization energies have been used to estimate the cluster size. The recorded in the present work valence spectra of the small clusters are compared with the spectra of the large clusters ( N ∼ 103) created by us using a magnetron-based gas aggregation source. The comparison shows a substantially narrower 5d valence band and the decrease in its splitting for gold clusters in the size range of few hundred atoms and below. Our DFT calculations involving the pseudopotential method show that the 5d band width of the ground state increases with the cluster size and by the size N = 20 becomes comparable with the experimental width of the valence photoelectron spectrum. Similar to the earlier observations on supported clusters we interpret our experimental and theoretical results as due to the undercoordination of a large fraction of atoms in the clusters with N ∼ 102 and below. The consequences of such electronic structure of small gold clusters are discussed in connection with their specific physical and chemical properties related to nanoplasmonics and nanocatalysis.

  2. Polarization properties of fluorescent BSA protected Au25 nanoclusters

    NASA Astrophysics Data System (ADS)

    Raut, Sangram; Chib, Rahul; Rich, Ryan; Shumilov, Dmytro; Gryczynski, Zygmunt; Gryczynski, Ignacy

    2013-03-01

    BSA protected gold nanoclusters (Au25) are attracting a great deal of attention due to their unique spectroscopic properties and possible use in biophysical applications. Although there are reports on synthetic strategies, spectroscopy and applications, little is known about their polarization behavior. In this study, we synthesized the BSA protected Au25 nanoclusters and studied their steady state and time resolved fluorescence properties including polarization behavior in different solvents: glycerol, propylene glycol and water. We demonstrated that the nanocluster absorption spectrum can be separated from the extinction spectrum by subtraction of Rayleigh scattering. The nanocluster absorption spectrum is well approximated by three Gaussian components. By a comparison of the emissions from BSA Au25 clusters and rhodamine B in water, we estimated the quantum yield of nanoclusters to be higher than 0.06. The fluorescence lifetime of BSA Au25 clusters is long and heterogeneous with an average value of 1.84 μs. In glycerol at -20 °C the anisotropy is high, reaching a value of 0.35. However, the excitation anisotropy strongly depends on the excitation wavelengths indicating a significant overlap of the different transition moments. The anisotropy decay in water reveals a correlation time below 0.2 μs. In propylene glycol the measured correlation time is longer and the initial anisotropy depends on the excitation wavelength. BSA Au25 clusters, due to long lifetime and high polarization, can potentially be used in studying large macromolecules such as protein complexes with large molecular weight.BSA protected gold nanoclusters (Au25) are attracting a great deal of attention due to their unique spectroscopic properties and possible use in biophysical applications. Although there are reports on synthetic strategies, spectroscopy and applications, little is known about their polarization behavior. In this study, we synthesized the BSA protected Au25 nanoclusters and

  3. Magnetism of CoPd self-organized alloy clusters on Au(111)

    NASA Astrophysics Data System (ADS)

    Ohresser, P.; Otero, E.; Wilhelm, F.; Rogalev, A.; Goyhenex, C.; Joly, L.; Bulou, H.; Romeo, M.; Speisser, V.; Arabski, J.; Schull, G.; Scheurer, F.

    2013-12-01

    Magnetic properties of gold-encapsulated CoxPd1-x self-organized nano-clusters on Au(111) are analyzed by x-ray magnetic circular dichroism for x = 0.5, 0.7, and 1.0. The clusters are superparamagnetic with a blocking temperature decreasing with increasing Pd concentration, due to a reduction of the out-of-plane anisotropy strength. No magnetic moment is detected on Pd in these clusters, within the detection limit, contrary to thick CoPd films. Both reduction of anisotropy and vanishing Pd moment are attributed to strain.

  4. Tailoring the local structure and electronic property of AuPd nanoparticles by selecting capping molecules

    NASA Astrophysics Data System (ADS)

    Liu, Feng; Zhang, Peng

    2010-01-01

    Nine AuPd nanoparticle samples selectively capped with tetraoctylphosphonium bromide, primary amine and tertiary amine molecules were studied with the Au L3-edge x-ray absorption spectroscopy (XAS). The AuPd mixing patterns were analyzed by comparing the XAS results with the theoretical coordination numbers of 24 AuPd model clusters of varied size, Au concentration, and bimetal mixing pattern. It was found that the use of amines, particularly tertiary amine, produced a more homogeneous AuPd mixing pattern and the Au d-electron density was fine-tunable by tailoring the density of Au-Pd bonds. Mechanisms for the tailored structural and electronic properties of these nanoparticles were proposed.

  5. Nonresonant chemical mechanism in surface-enhanced Raman scattering of pyridine on M@Au12 clusters.

    PubMed

    Chen, Lei; Gao, Yang; Cheng, Yingkun; Li, Haichao; Wang, Zhigang; Li, Zhengqiang; Zhang, Rui-Qin

    2016-02-21

    By employing density functional theory (DFT), this study presents a detailed analysis of nonresonant surface-enhanced Raman scattering (SERS) of pyridine on M@Au12 (M = V(-), Nb(-), Ta(-), Cr, Mo, W, Mn(+), Tc(+), and Re(+))-the stable 13-atom neutral and charged gold buckyball clusters. Changing the core atom in M@Au12 enabled us to modulate the direct chemical interactions between pyridine and the metal cluster. The results of our calculations indicate that the ground-state chemical enhancement does not increase as the binding interaction strengthens or the transfer charge increases between pyridine and the cluster. Instead, the magnitude of the chemical enhancement is governed, to a large extent, by the charged properties of the metal clusters. Pyridine on M@Au12 anion clusters exhibits strong chemical enhancement of a factor of about 10(2), but the equivalent increase for pyridine adsorbed on M@Au12 neutral and cation clusters is no more than 10. Polarizability and deformation density analyses clearly show that compared with the neutral and cation clusters, the anion clusters have more delocalized electrons and occupy higher energy levels in the pyridine-metal complex. Accordingly, they produce larger polarizability, leading to a stronger nonresonant enhancement effect.

  6. Catalytic reduction of N2O by CO over PtlAu-m clusters: A first-principles study

    NASA Astrophysics Data System (ADS)

    Mi, Hong; Wei, Shi-Hao; Duan, Xiang-Mei; Pan, Xiao-Yin

    2015-09-01

    Based on the density functional theory, we investigate negatively charged clusters , which show significant catalytic properties in the simultaneous removal of N2O and CO. We find that in these clusters, the platinum atom acts as the adsorption center for N2O, the gold and Pt atoms act as electron donors during the reaction, and the charge transfers from the bimetallic cluster to the N2O molecule. As the proportion of Au in the cluster increases, the d band center shifts down further away from the Fermi level, meanwhile more charge is transferred to the N2O molecule, resulting in weaker N-O bond strength. Therefore bimetallic cluster shows better catalytic properties than the other clusters, especially pure Pt4- and Au4- clusters. This means that there is a synergetic effect between the Pt and Au atoms in the negatively charged bimetallic clusters. Our results help to reveal the mechanism of bimetallic clusters as excellent catalysts. Project supported by the National Natural Science Foundation of China (Grants Nos. 10804058, 11174164, and 11275100), the Science Foundation of Zhejiang Province, China (Grant No. Y607546), and the K. C. Wong Magna Foundation in Ningbo University, China.

  7. Size evolution relativistic DFT-QTAIM study on the gold cluster complexes Au4-S-CnH2n-S‧-Au4‧ (n = 2-5)

    NASA Astrophysics Data System (ADS)

    Rodríguez, Juan I.; Uribe, Emilbus A.; Baltazar-Méndez, María I.; Autschbach, Jochen; Castillo-Alvarado, F. L.; Gutiérrez-González, Israel

    2016-09-01

    We introduce relativistic density functional theory (DFT) calculations on the gold cluster complexes (cluster-molecule-cluster) Au4-S-CnH2n-S‧-Au4‧ (n = 2-5). The structural, electronic and relativistic (ZORA) Bader's quantum theory of atoms in molecules (QTAIM) properties of the two lowest-energy complex isomers were computed as a function of the alkanedithiol size (n). The lowest-energy isomer is a triplet spin state independently of the complex size. According to QTAIM, the Au-Au and S-Au bonds are classified as closed shell (non-covalent) type. The HOMO-LUMO gap of the cluster complexes shows a zigzag behavior typical of gold nanoclusters with respect to the size of the alkanedithiol chain (n).

  8. Core-shell-like Au sub-nanometer clusters in Er-implanted silica.

    PubMed

    Maurizio, Chiara; Cesca, Tiziana; Perotto, Giovanni; Kalinic, Boris; Michieli, Niccolò; Scian, Carlo; Joly, Yves; Battaglin, Giancarlo; Mazzoldi, Paolo; Mattei, Giovanni

    2015-05-21

    The very early steps of Au metal cluster formation in Er-doped silica have been investigated by high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS). A combined analysis of the near-edge and extended part of the experimental spectra shows that Au cluster nucleation starts from a few Au and O atoms covalently interconnected, likely in the presence of embryonic Au-Au correlation. The first Au clusters, characterized by a well defined Au-Au coordination distance, form upon 400 °C inert annealing. The estimated upper limit of the Gibbs free energy for the associated heterogeneous nucleation is 0.06 eV per atom, suggesting that the Au nucleation is assisted by matrix defects, most likely non-bridging oxygen atoms. The experimental results indicate that the formed subnanometer Au clusters can be applied as effective core-shell systems in which the Au atoms of the 'core' develop a metallic character, whereas the Au atoms in the 'shell' can retain a partially covalent bond with O atoms of the silica matrix. High structural disorder at the Au site is found upon neutral annealing at a moderate temperature (600 °C), likely driven by the configurational disorder of the defective silica matrix. A suitable choice of the Au concentration and annealing temperature allows tailoring of the Au cluster size in the sub-nanometer range. The interaction of the Au cluster surface with the surrounding silica matrix is likely responsible for the infrared luminescence previously reported on the same systems.

  9. Activation and Transformation of Ethane by Au2 VO3(+) Clusters with Closed-Shell Electronic Structures.

    PubMed

    Li, Ya-Ke; Li, Zi-Yu; Zhao, Yan-Xia; Liu, Qing-Yu; Meng, Jing-Heng; He, Sheng-Gui

    2016-01-26

    The study of chemical reactions between gold-containing heteronuclear oxide clusters and small molecules can provide molecular level mechanisms to understand the excellent activity of gold supported by metal oxides. While the promotion role of gold in alkane transformation was identified in the clusters with atomic oxygen radicals (O(-.)), the role of gold in the systems without O(-.) is not clear. By employing mass spectrometry and quantum chemistry calculations, the reactivity of Au2 VO3(+) clusters with closed-shell electronic structures toward ethane was explored. Both the dehydrogenation and ethene elimination channels were identified. It is gold rather than oxygen species initiating the C-H activation. The Au-Au dimer formed during the reactions plays important roles in ethane transformation. The reactivity comparison between Au2 VO3(+) and bare Au2(+) demonstrates that Au2 VO3(+) not only retains the property of bare Au2(+) that transforming ethane to dihydrogen, but also exhibits new functions in converting ethane to ethene, which reveals the importance of the composite system. This study provides a further understanding of the reactivity of metal oxide supported gold in alkane activation and transformation.

  10. Molecular-receptor-specific, non-toxic, near-infrared-emitting Au cluster-protein nanoconjugates for targeted cancer imaging

    NASA Astrophysics Data System (ADS)

    Retnakumari, Archana; Setua, Sonali; Menon, Deepthy; Ravindran, Prasanth; Muhammed, Habeeb; Pradeep, Thalappil; Nair, Shantikumar; Koyakutty, Manzoor

    2010-02-01

    Molecular-receptor-targeted imaging of folate receptor positive oral carcinoma cells using folic-acid-conjugated fluorescent Au25 nanoclusters (Au NCs) is reported. Highly fluorescent Au25 clusters were synthesized by controlled reduction of Au+ ions, stabilized in bovine serum albumin (BSA), using a green-chemical reducing agent, ascorbic acid (vitamin-C). For targeted-imaging-based detection of cancer cells, the clusters were conjugated with folic acid (FA) through amide linkage with the BSA shell. The bioconjugated clusters show excellent stability over a wide range of pH from 4 to 14 and fluorescence efficiency of ~5.7% at pH 7.4 in phosphate buffer saline (PBS), indicating effective protection of nanoclusters by serum albumin during the bioconjugation reaction and cell-cluster interaction. The nanoclusters were characterized for their physico-chemical properties, toxicity and cancer targeting efficacy in vitro. X-ray photoelectron spectroscopy (XPS) suggests binding energies correlating to metal Au 4f7/2~83.97 eV and Au 4f5/2~87.768 eV. Transmission electron microscopy and atomic force microscopy revealed the formation of individual nanoclusters of size ~1 nm and protein cluster aggregates of size ~8 nm. Photoluminescence studies show bright fluorescence with peak maximum at ~674 nm with the spectral profile covering the near-infrared (NIR) region, making it possible to image clusters at the 700-800 nm emission window where the tissue absorption of light is minimum. The cell viability and reactive oxygen toxicity studies indicate the non-toxic nature of the Au clusters up to relatively higher concentrations of 500 µg ml-1. Receptor-targeted cancer detection using Au clusters is demonstrated on FR+ve oral squamous cell carcinoma (KB) and breast adenocarcinoma cell MCF-7, where the FA-conjugated Au25 clusters were found internalized in significantly higher concentrations compared to the negative control cell lines. This study demonstrates the potential of using

  11. Gold Apes Hydrogen. The Structure and Bonding in the Planar B7Au2- and B7Au2 Clusters

    SciTech Connect

    Zhai, Hua JIN.; Wang, Lai S.; Zubarev, Dmitry Y.; Boldyrev, Alexander I.

    2006-02-09

    We produced the B7Au2- mixed cluster and studied its electronic structure and chemical bonding using photoelectron spectroscopy and ab initio calculations. The photoelectron spectra of B7Au2- were observed to be relatively simple with vibrational resolution, in contrast to the complicated spectra observed for pure B7-, which had contributions from three isomers (Alexandrova et al., J. Phys. Chem. A, 2004, 108, 3509). Theoretical calculations show that B7Au2- possesses an extremely stable planar structure, identical to that of B7H2-, demonstrating that Au mimics H in its bonding to boron, analogous to the Au-Si bonding. The ground state structure of B7Au2- (B7H2-) can be viewed as adding two Au (H) atoms to the terminal B atoms of a higher-lying planar isomer of B7-. The bonding and stability in the planar B7Au2- (B7H2-) clusters are elucidated on the basis of the strong covalent B-Au (H) bonding and the concepts of aromaticity/antiaromaticity in these systems.

  12. Crystal structure of Au25(SePh)18 nanoclusters and insights into their electronic, optical and catalytic properties

    NASA Astrophysics Data System (ADS)

    Song, Yongbo; Zhong, Juan; Yang, Sha; Wang, Shuxin; Cao, Tiantian; Zhang, Jun; Li, Peng; Hu, Daqiao; Pei, Yong; Zhu, Manzhou

    2014-10-01

    The crystal structure of selenolate-capped Au25(SePh)18- nanoclusters has been unambiguously determined for the first time, and provides a solid basis for a deeper understanding of the structure-property relationships. The selenolate-capped Au25 cluster shows noticeable differences from the previously reported Au25(SCH2CH2Ph)18- counterpart, albeit both share the icosahedral Au13 core and semi-ring Au2(SeR)3 or Au2(SR)3 motifs. Distinct differences in the electronic structure and optical, catalytic and electrochemical properties are revealed by the coupling experiments with density functional theory (TD-DFT) calculations. Overall, the successful determination of the Au25(SePh)18- structure removes any ambiguity about its structure, and comparison with the thiolated Au25 counterpart helps us to further understand how the ligands affect the properties of the nanocluster.The crystal structure of selenolate-capped Au25(SePh)18- nanoclusters has been unambiguously determined for the first time, and provides a solid basis for a deeper understanding of the structure-property relationships. The selenolate-capped Au25 cluster shows noticeable differences from the previously reported Au25(SCH2CH2Ph)18- counterpart, albeit both share the icosahedral Au13 core and semi-ring Au2(SeR)3 or Au2(SR)3 motifs. Distinct differences in the electronic structure and optical, catalytic and electrochemical properties are revealed by the coupling experiments with density functional theory (TD-DFT) calculations. Overall, the successful determination of the Au25(SePh)18- structure removes any ambiguity about its structure, and comparison with the thiolated Au25 counterpart helps us to further understand how the ligands affect the properties of the nanocluster. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr04631e

  13. The Golden Crown: A Single Au Atom that Boosts the CO Oxidation Catalyzed by a Palladium Cluster on Titania Surfaces

    SciTech Connect

    Zhang, Jin; Alexandrova, Anastassia N.

    2013-07-18

    We show that at the subnano scale, the catalytic properties of surface-supported clusters can be majorly impacted by strategic doping and the choice for the supporting surface. This is a first-principles investigation of CO oxidation catalyzed by two subnanoclusters, Pd4Au and Pd5, deposited on rutile TiO2(110) surfaces. The titania surface was found to participate in the reaction directly via providing additional reaction pathways. The bimetallic cluster Pd4Au shows enhanced catalytic activity, whereas the monometallic Pd5 is poisoned and deactivated in the presence of CO and oxygen, and this trend is reversed from that in the gas phase.

  14. On the structure of the thiolated Au6Ag7 cluster.

    PubMed

    Tlahuice-Flores, Alfredo

    2014-09-14

    The structure of the recently synthesized mercaptosuccinic acid-protected Au6Ag7(SR)10 cluster has been elucidated by a DFT approach, following an isoelectronic substitution of seven Au atoms by Ag atoms on the [Au13(SR)10](+) cluster. After a systematic search for the lowest-energy isomers, it is demonstrated that its structure comprises one octahedral-like Ag6 core covered by two monoatomic dimer motifs and one Au2Ag1(SR)4 staple-like motif. This result confirms that Ag atoms prefer the inner (core) positions while Au atoms are located on surface staple-like motifs.

  15. Au13-nAgn clusters: a remarkably simple trend.

    PubMed

    Munoz, Francisco; Varas, Alejandro; Rogan, José; Valdivia, Juan Alejandro; Kiwi, Miguel

    2015-11-11

    The planar to three dimensional transition of Au13-nAgn clusters is investigated. To do so the low lying energy configurations for all possible concentrations (n values) are evaluated. Many thousands of possible conformations are examined. They are generated using the procedure developed by Rogan et al. in combination with the semi-empirical Gupta potential. A large fraction of these (the low lying energy ones) are minimized by means of Density Functional Theory (DFT) calculations. We employ the Tao, Perdew, Staroverov, and Scuseria (TPSS) meta-GGA functional and the Perdew, Burke and Ernzerhof (PBE) GGA functional, and compare their results. The effect of spin-orbit coupling is studied as well as the s-d hybridization. As usual in this context the results are functional-dependent. However, both functionals lead to agreement as far as trends are concerned, yielding just two relevant motifs, but their results differ quantitatively.

  16. Meteoroids at 1 AU: Dynamic and Properties

    NASA Astrophysics Data System (ADS)

    McDonnell, J. A. M.; McBride, N.

    1996-12-01

    Lines of evidence from both retrieved spacecraft and meteoroid studies have been examined to define the properties and understanding of the particulate impact environment at 1 AU. Key studies include: From LDEF and Eureca experiments comprising both thin foils and thick targets, exposed under identical exposures, have permitted physical properties of the meteoroids to be deduced such as shape factor and density. Comparison of such detectors pointing in different directions on the same spacecraft permits the velocity of meteoroids to be assessed and compared with that of radar meteoroids. Results are compared with velocity distributions currently used for ESABASE. Comparison of science experiments exposed on LDEF and Eureca, where different altitude stabilisation configurations apply, leads to a measure for the upper limit of space debris without recourse to chemical analyses. Radar meteoroids provide the only effective measure of the velocity distribution at 1 AU; but the meteor phenomenon differs (in sensitivity to velocity) from the impact cratering. Modelling has been performed, therefore, to derive Apex to Anti-Apex flux distributions appropriate to spacecraft environment modelling as in e.g. ESABASE. High sensitivity in-situ detectors in deep space, in particular HEOS II and Pioneers 8 and 9, provide evidence of the changing distributions and directivity of meteoroids and a swing to beta meteoroids which are being expelled from the solar system. Advances in the characterisation of these populations are presented.

  • The Electronic Properties and L3 XANES of Au and Nano-Au

    SciTech Connect

    Yiu, Y.M.; Zhang, P.; Sham, T.K.

    2004-04-20

    The electronic properties of Au crystal and nano Au have been investigated by theory and experiment. Molecularly capped nano-Au was synthesized using the two-phase method. Au nano-particles have been characterized by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). They retain the fcc crystal structure. Their sizes have been determined to be in a range from 5.5 nm to 1.7 nm. The L3 X-ray Absorption Near Edge Structure (XANES) of nano-Au and Au foil have been recorded using synchrotron radiation, and examined by theoretical calculation based on the first principles. Both theory and experiment show that the nano-Au particles have essentially all the Au L3 XANES features of bulk Au in the near edge region with less pronounced resonance peaks. It is also shown that nano Au exhibits lower 4f binding energy than bulk Au in good agreement with quantum confined Au systems reported previously.

  • Ce@Au14: A Bimetallic Superatom Cluster with 18-Electron Rule

    NASA Astrophysics Data System (ADS)

    Gao, Yang; Liu, Xizhe; Wang, Zhigang

    2016-09-01

    Doping of gold clusters and nanoparticles has received substantial attention due to their ability to encapsulate atoms and molecules. Here, the geometric and electronic properties of the cerium-encapsulated nanocage Ce@Au14 are reported using density functional theory. Calculated results show that its ground electronic state is a singlet state and conforms to the superatomic 18-electron configuration of 1S 21P 61D 10 jellium state, both primarily involving the bonding interaction between s- and d-shell atomic orbitals of the Ce atom and superatomic orbitals of the hollow polyhedral Au14 cage. In addition, it should be noted that f electrons in rare earth atoms trend to retain their localized state, and their doping in gold clusters could easily lead to clusters with large magnetic moments. However, in the case of superatom clusters, the f-shell electrons will be the preferential arrangement at the unfilled d-shell to satisfy the superatomic electron structure. Further analysis of the electronic structure also proves that the unoccupied 1F superatomic orbitals mainly originate from the contribution of the 4f-shell. As a consequence, this work provides a theoretical basis for the future design and synthesis of f-elements-encapsulated gold nanoclusters.

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

    SciTech Connect

    Chen, Wanghua; Roca i Cabarrocas, Pere; Pareige, Philippe; Castro, Celia; Xu, Tao; Grandidier, Bruno; Stiévenard, Didier

    2015-09-14

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

  • Formation of bimetallic nanoalloys by Au coating of size-selected Cu clusters

    NASA Astrophysics Data System (ADS)

    Yin, Feng; Wang, Zhi Wei; Palmer, Richard E.

    2012-10-01

    Bimetallic clusters display new characteristics that could not be obtained by varying either the size of pure metallic systems or the composition of bulk bimetals alone. Coating of pre-deposited clusters by vapour deposition is a typical synthesis process of bimetallic clusters. Here, we have demonstrated that hierarchical, gold cluster-decorated copper clusters as well as both heterogeneous and homogeneous Cu-Au bimetallic clusters (4.6 to 10.7 nm) can be prepared by coating pre-deposited, size-selected Cu5000 (4.6 ± 0.2 nm) with Au evaporation at various temperatures. These bimetallic clusters were analyzed by aberration-corrected scanning transmission electron microscopy and associated electron energy loss spectroscopy. The results indicate that the growth of bimetallic clusters is controlled by a competition between nucleation and diffusion of the coating Au atoms.

    1. Probing the structural and electronic properties of bimetallic chromium-gold clusters CrmAun(m+n≤6): comparison with pure chromium and gold clusters.

      PubMed

      Lu, Peng; Liu, Guang-Hua; Kuang, Xiao-Yu

      2014-08-01

      Bimetallic chromium-gold CrmAun(m+n≤6) clusters are systematically investigated using the density functional theory at PW91P86 level with LanL2TZ basis set to understand the evolution of various structural, electronic, magnetic, and energetic properties as a function of size (m+n) and composition (m/n) of the system. Theoretical results show a logical evolution of the properties depending on the size and the composition of the system. Cr m clusters clearly prefer 3D structures while Au n clusters favor planar configurations. The geometry of the bimetallic Cr m Au n clusters mainly depends on their composition, i.e., clusters enriched in Cr atoms prefer 3D structures while increasing Au contents promotes planar configurations. The stability is maximized when the composition of binary Cr m Au n clusters is nearly balanced. Meanwhile, the number of hetero Cr-Au bonds and charge transfer from Cr to Au are maximized for clusters with m≈n. The most probable dissociation channels of the Cr m Au n clusters are calculated and analyzed. Natural population analysis reveals that Au atoms tend to be negatively charged while Cr atoms tend to be positively charged. Combined with the trend that Au atoms favor the surface/edges/vertices and Cr atoms tend to be inside, the outer part of the cluster tends to be negatively charged, and the inner part tends to be positively charged.

    2. Evolution Properties of Clusters and AXAF Contributions to understanding Clusters

      NASA Technical Reports Server (NTRS)

      Jones, Christine

      1998-01-01

      Our ROSAT survey for distant clusters of galaxies contains the largest solid angle of all ROSAT pointed surveying and thus has sufficient area to test the previously reported cluster evolution. We find significant negative cluster evolution, i.e,, at high redshifts there are fewer luminous clusters than at present. We compare optical cluster properties for the most distant clusters in the ROSAT survey with those measured for nearby clusters. We also present AXAF capabilities and show how AXAF will significantly extend our understanding of cluster properties and their cosmological evolution.

    3. New insight into the structure of thiolated gold clusters: a structural prediction of the Au187(SR)68 cluster.

      PubMed

      Tlahuice-Flores, A

      2015-02-28

      The structure of the thiolated Au187 cluster has been elucidated by density functional theory calculations. The structural model comprises a Marks-decahedral Au153 core protected with 34 monomer motifs. The predicted structure accomplished in this study is in good agreement with the experimental X-ray diffraction pattern. It is noteworthy that the used methodology represents an advance in the prediction of the molecular structure of thiolated gold clusters constituted by hundreds of gold atoms.

    4. Core-level photoemission from nanocluster-matrix composites: Au clusters in amorphous carbon

      NASA Astrophysics Data System (ADS)

      Calliari, L.; Minati, L.; Speranza, G.; Paris, A.; Baranov, A.; Fanchenko, S.

      2014-09-01

      We investigate a system consisting of Au nano-clusters and amorphous carbon (a-C) via core-level photoemission. While the ability of photoemission to characterize nano-sized metal clusters is well-known, still some issues deserve investigation. For example, the well-established dominance of final-state relaxation effects in core-level spectra from nano-clusters necessarily involves a crucial role of the cluster dielectric-environment. To the best of our knowledge however, a thorough discussion on this point is lacking. We thus intend to investigate dielectric-environment effects by considering several configurations for Au clusters, i.e. supported and embedded, with the latter obtained either by depositing a-C on top of supported clusters or by co-depositing a-C and Au. We analyze the Au4 f spectrum from clusters accounting for both cluster size and cluster location with respect to the a-C matrix. We show that spectral changes caused by a-C deposition are entirely explained in terms of changes in the cluster dielectric environment. Moreover, we prove that supported clusters are in a well-characterized dielectric environment, while embedded clusters are not. This is because embedded clusters, whatever the method of production, are spatially distributed over the matrix surface-region which is characterized by rapid fluctuations in the dielectric constant.

    5. Surface morphology and optical properties of porphyrin/Au and Au/porphyrin/Au systems

      PubMed Central

      2013-01-01

      Porphyrin/Au and Au/porphyrin/Au systems were prepared by vacuum evaporation and vacuum sputtering onto glass substrate. The surface morphology of as-prepared systems and those subjected to annealing at 160°C was studied by optical microscopy, atomic force microscopy, and scanning electron microscopy techniques. Absorption and luminescence spectra of as-prepared and annealed samples were measured. Annealing leads to disintegration of the initially continuous gold layer and formation of gold nanoclusters. An amplification of Soret band magnitude was observed on the Au/meso-tetraphenyl porphyrin (TPP) system in comparison with mere TPP. Additional enhancement of luminescence was observed after the sample annealing. In the case of sandwich Au/porphyrin/Au structure, suppression of one of the two porphyrins’ luminescence maxima and sufficient enhancement of the second one were observed. PMID:24373347

    6. Mechanical properties and grindability of experimental Ti-Au alloys.

      PubMed

      Takahashi, Masatoshi; Kikuchi, Masafumi; Okuno, Osamu

      2004-06-01

      Experimental Ti-Au alloys (5, 10, 20 and 40 mass% Au) were made. Mechanical properties and grindability of the castings of the Ti-Au alloys were examined. As the concentration of gold increased to 20%, the yield strength and the tensile strength of the Ti-Au alloys became higher without markedly deteriorating their ductility. This higher strength can be explained by the solid-solution strengthening of the a titanium. The Ti-40%Au alloy became brittle because the intermetallic compound Ti3Au precipitated intensively near the grain boundaries. There was no significant difference in the grinding rate and grinding ratio among all the Ti-Au alloys and the pure titanium at any speed.

    7. Electronic structure and optical properties of the intrinsically chiral 16-electron superatom complex [Au20(PP3)4](4+).

      PubMed

      Knoppe, Stefan; Lehtovaara, Lauri; Häkkinen, Hannu

      2014-06-12

      The recently solved crystal structure of the [Au20(PP3)4]Cl4 cluster (PP3: tris(2-(diphenylphophino)ethyl)phosphine) is examined using density functional theory (DFT). The Au20 core of the cluster is intrinsically chiral by the arrangement of the Au atoms. This is in contrast to the chirality of thiolate-protected gold clusters, in which the protecting Au-thiolate units are arranged in chiral patterns on achiral cores. We interpret the electronic structure of the [Au20(PP3)4]Cl4 cluster in terms of the superatom complex model. The 16-electron cluster cannot be interpreted as a dimer of 8-electron clusters (which are magic). Instead, a superatomic electron configuration of 1S(2) 1P(6) 1D(6) 2S(2) is found. The 2S band is strongly stabilized, and the 1D states are nondegenerate with a large gap. Ligand protection of the (Au20)(4+) core leads to a significant increase of the HL-gap and thus stabilization. We also tested a charge of +II, which would give rise to an 18-electron superatom complex. Our results indicate that the 16-electron cluster is indeed more stable. We also investigate the optical properties of the cluster. The experimental absorption spectrum is well-reproduced by time-dependent DFT. Prominent transitions are analyzed by time-dependent density-functional perturbation theory. The intrinsic chirality of the cluster is compared to that of Au38(SR)24. We observe that the chiral arrangement of the protecting Au-SR units in Au38(SR)24 has very strong influence on the strength of the CD spectra, whereas phosphine protection in the title compound does not.

    8. O(2) adsorption and dissociation on neutral, positively and negatively charged Au(n) (n = 5-79) clusters.

      PubMed

      Roldán, Alberto; Ricart, Josep Manel; Illas, Francesc; Pacchioni, Gianfranco

      2010-09-28

      The adsorption and dissociation of an O(2) molecule on gas-phase gold clusters of size varying from 5 to 79 atoms have been investigated by means of first principles density functional theory calculations. The adsorption energies and dissociation barriers have been determined for neutral, positively and negatively charged gold clusters in order to analyze in a systematic way the role of the charge on the cluster reactivity. While there is beneficial effect on O(2) activation of an extra electron on the small gold clusters (Au(5) and Au(13)), the effect is absent for positively charged clusters. The effect of the charge vanishes rapidly by increasing the cluster size and is not visible for clusters containing about 40 atoms or more. Au(38) appears to be the most reactive among the clusters considered and strong oscillations in adsorption energies and dissociation barriers are found even for clusters containing several tens of atoms like Au(38), Au(55), and Au(79).

    9. Nanopore integrated with Au clusters formed under electron beam irradiation for single molecule analysis

      NASA Astrophysics Data System (ADS)

      Choi, Seong Soo; Park, Myoung Jin; Han, Chul Hee; Kim, Sung In; Yoo, Jung Ho; Park, Kyung Jin; Park, Nam Kyou; Kim, Yong-Sang

      2016-02-01

      Recently the single molecules such as protein and deoxyribonucleic acid (DNA) have been successfully characterized using a solidstate nanopore with an electrical detection technique. However, the optical plasmonic nanopore has yet to be fabricated. The optical detection technique can be better utilized as next generation ultrafast geneome sequencing devices due to the possible utilization of the current optical technique for genome sequencing. In this report, we have investigated the Au nanopore formation under the electron beam irradiation on an Au aperture. The circular-type nanoopening with ~ 5 nm diameter on the diffused membrane is fabricated by using 2 keV electron beam irradiation by using field emission scanning electron microscopy (FESEM). We found the Au cluster on the periphery of the drilled aperture under a 2 keV electron beam irradiation. Immediately right after electron beam irradiation, no Au cluster and no Au crystal lattice structure on the diffused plane are observed. However, after the sample was kept for ~ 6 months under a room environment, the Au clusters are found on the diffused membrane and the Au crystal lattice structures on the diffused membrane are also found using high resolution transmission electron microscopy. These phenomena can be attributed to Ostwald ripening. In addition, the Au nano-hole on the 40 nm thick Au membrane was also drilled by using 200 keV scanning transmission electron microscopy.

    10. A study of the electronic properties of Au nanowires and Au nanoislands on Au(111) surfaces.

      PubMed

      Schouteden, K; Lijnen, E; Muzychenko, D A; Ceulemans, A; Chibotaru, Liviu F; Lievens, P; Van Haesendonck, C

      2009-09-30

      By means of ion bombardment of clean Au(111) films, atomically flat nanoparticles of various shapes and sizes were created, ranging from several tens of nm(2) down to only a few nm(2). Both two-dimensional Au islands as well as one-dimensional Au nanowire-like structures have been investigated by means of low-temperature scanning tunneling microscopy and spectroscopy. We were able to probe their local electronic structure in a broad energy range, which was found to be dominated by pronounced size-dependent confinement effects. Mapping of the local density of states revealed complex standing wave patterns that arise due to interference of scattered Au surface state electrons at the edges of the Au nanoparticles. The observed phenomena could be modeled with high accuracy by theoretical particle-in-a-box calculations based on a variational method that can be applied to '2D boxes' of arbitrary polygonal shape and that we have previously successfully applied to explain the electronic wave patterns on Co islands on Au(111). Our findings support the general validity of this particle-in-a-box model.

    11. Comparison of laser ablation and sputter desorption of clusters from Au7Cu5Al4

      NASA Astrophysics Data System (ADS)

      King, B. V.; Moore, J. F.; Cui, Y.; Veryovkin, I. V.; Tripa, C. E.

      2014-12-01

      Ionized and neutral clusters were desorbed from spangold, a polycrystalline ternary alloy with composition Au7Cu5Al4, using both a femtosecond laser beam and an energetic ion beam and the resulting time of flight mass spectra compared. Neutral clusters containing up to 7 atoms were ejected by the 15 keV Ar+ beam whereas only smaller positively and negatively charged clusters were observed from the laser ablated spangold surface. Laser ionization mass spectrometry (LIMS) positive ion spectra were dominated by Al containing cluster ions whereas Au containing ions dominated the negative LIMS spectrum. An odd-even variation in LIMS cluster yield was observed, consistent with previous results and due to fragmentation of photoionized clusters. The laser sputtered neutral mass spectrometry (laser SNMS) spectrum showed that larger desorbed clusters were gold rich. The cluster signals also followed a power law dependence with cluster size with the exponent value of 6-7.6 for sputtered mixed clusters being greater than that found from sputtering of pure elements, similar to the result found previously in the Cu-Au system.

    12. Gold-rich R3Au7Sn3: Establishing the interdependence between electronic features and physical properties

      DOE PAGES

      Provino, Alessia; Steinberg, Simon; Smetana, Volodymyr; ...

      2015-05-18

      Two new polar intermetallic compounds Y3Au7Sn3 (I) and Gd3Au7Sn3 (II) have been synthesized and their structures have been determined by single crystal X-ray diffraction (P63/m; Z = 2, a = 8.148(1)/8.185(3), and c = 9.394(2)/9.415(3) for I/II, respectively). They can formally be assigned to the Cu10Sn3 type and consist of parallel slabs of Sn centered, edge-sharing trigonal Au6 antiprisms connected through R3 (R = Y, Gd) triangles. Additional Au atoms reside in the centres of trigonal Au6 prisms forming Au@Au6 clusters with Au–Au distances of 2.906–2.960 Å, while the R–R contacts in the R3 groups are considerably larger than themore » sums of their metallic radii. These exclusive structural arrangements provide alluring systems to study the synergism between strongly correlated systems, particularly, those in the structure of (II), and extensive polar intermetallic contacts, which has been inspected by measurements of the magnetic properties, heat capacities and electrical conductivities of both compounds. Gd3Au7Sn3 shows an antiferromagnetic ordering at 13 K, while Y3Au7Sn3 is a Pauli paramagnet and a downward curvature in its electrical resistivity at about 1.9 K points to a superconducting transition. DFT-based band structure calculations on R3Au7Sn3 (R = Y, Gd) account for the results of the conductivity measurements and different spin ordering models of (II) provide conclusive hints about its magnetic structure. As a result, chemical bonding analyses of both compounds indicate that the vast majority of bonding originates from the heteroatomic Au–Gd and Au–Sn interactions, while homoatomic Au–Au bonding is evident within the Au@Au6 clusters.« less

    13. Increase of the mean inner Coulomb potential in Au clusters induced by surface tension and its implication for electron scattering

      SciTech Connect

      Popescu, Radian; Mueller, Erich; Wanner, Matthias; Gerthsen, Dagmar; Schowalter, Marco; Rosenauer, Andreas; Boettcher, Artur; Loeffler, Daniel; Weis, Patrick

      2007-12-15

      Electron holography in a transmission electron microscope was applied to measure the phase shift {delta}{phi} induced by Au clusters as a function of the cluster size. Large {delta}{phi} observed for small Au clusters cannot be described by the well-known equation {delta}{phi}=C{sub E}V{sub 0}t (C{sub E}, interaction constant; V{sub 0}, mean inner Coulomb potential (MIP) of bulk gold; and t, cluster thickness). The rapid increase of the Au MIP with decreasing cluster size derived from {delta}{phi} can be explained by the compressive strain of surface atoms in the cluster.

    14. Fabrication of Au nanotube arrays and their plasmonic properties

      NASA Astrophysics Data System (ADS)

      Zhu, Haojun; Chen, Huanjun; Wang, Jianfang; Li, Quan

      2013-04-01

      Large-scale Au nanotube arrays on ITO/glass with tunable inner diameters and wall thicknesses were fabricated via a CdSe nanotube array templating method. The initial tubular morphology of the CdSe-nanotube template was maintained during the synthesis, while the composition was converted from CdSe to Au. The obtained Au nanotube arrays showed two surface plasmon resonances in the extinction spectrum, mainly contributed by electron oscillation along the transverse and the longitudinal directions. When used as the substrate for surface-enhanced Raman spectroscopy (SERS), the Raman scattering of the probe molecules (4-mercaptobenzoic acid) was amplified by approximately 4 orders of magnitude, mainly due to the plasmonic enhancement effect of the Au nanotube arrays.Large-scale Au nanotube arrays on ITO/glass with tunable inner diameters and wall thicknesses were fabricated via a CdSe nanotube array templating method. The initial tubular morphology of the CdSe-nanotube template was maintained during the synthesis, while the composition was converted from CdSe to Au. The obtained Au nanotube arrays showed two surface plasmon resonances in the extinction spectrum, mainly contributed by electron oscillation along the transverse and the longitudinal directions. When used as the substrate for surface-enhanced Raman spectroscopy (SERS), the Raman scattering of the probe molecules (4-mercaptobenzoic acid) was amplified by approximately 4 orders of magnitude, mainly due to the plasmonic enhancement effect of the Au nanotube arrays. Electronic supplementary information (ESI) available: Basic characterizations, optical and SERS properties of Au nanotube arrays obtained from CdSe nanowire arrays; SERS spectra of Au-sputtered ITO/glass and bare ITO/glass; the calculation details of the enhancement factor. See DOI: 10.1039/c3nr33658a

    15. Structural properties of Au and Ag nanoclusters embedded in MgO

      NASA Astrophysics Data System (ADS)

      van Huis, M. A.; Fedorov, A. V.; van Veen, A.; Falub, C. V.; Eijt, S. W. H.; Kooi, B. J.; De Hosson, J. Th. M.; Hibma, T.; Zimmerman, R. L.

      2002-05-01

      Gold and silver nanoclusters embedded in MgO were created by means of ion implantation of 1.0 MeV Au or 600 keV Ag ions to a dose of 10 16 cm -2 into single crystals of MgO(1 0 0) and subsequent annealing at 1473 K for a period of 22 h. The structural properties of the nanoclusters were characterised by optical absorption spectroscopy (OAS), high-resolution X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Nanocluster sizes are estimated using three different methods: using the Doyle formula for the broadening of the optical absorption peak associated with Mie plasmon resonance; using the Scherrer formula for the broadening of the Au and Ag XRD peaks, and from direct observation of TEM images. For the Au clusters, the methods are in excellent agreement with mean cluster sizes of 4-5 nm. For the Ag clusters, the optical Doyle method yields a mean nanocluster size of 5 nm while the XRD and XTEM methods yield 10-11 nm. The XRD and XTEM results reveal a cube-on-cube orientation relationship of the Au and Ag nanoclusters with respect to the MgO matrix.

    16. Direct atomic imaging and density functional theory study of the Au24Pd1 cluster catalyst.

      PubMed

      Bruma, A; Negreiros, F R; Xie, S; Tsukuda, T; Johnston, R L; Fortunelli, A; Li, Z Y

      2013-10-21

      In this study we report a direct, atomic-resolution imaging of calcined Au24Pd1 clusters supported on multiwall carbon nanotubes by employing aberration-corrected scanning transmission electron microscopy. Using gold atoms as mass standards, we confirm the cluster size to be 25 ± 2, in agreement with the Au24Pd1(SR)18 precursor used in the synthesis. Concurrently, a Density-Functional/Basin-Hopping computational algorithm is employed to locate the low-energy configurations of free Au24Pd1 cluster. Cage structures surrounding a single core atom are found to be favored, with a slight preference for Pd to occupy the core site. The cluster shows a tendency toward elongated arrangements, consistent with experimental data. The degree of electron transfer from the Pd dopant to Au is quantified through a Löwdin charge analysis, suggesting that Pd may act as an electron promoter to the surrounding Au atoms when they are involved in catalytic reactions.

    17. Magnetic properties of nanosize iron clusters

      SciTech Connect

      Venturini, E.L.; Wilcoxon, J.P.; Newcomer, P.P.

      1993-12-31

      Isolated, monodisperse {alpha}-Fe clusters between 1.4 and 15 nm in diameter were prepared inside inverse micelles using an oil-continuous, nonaqueous system. The magnetic properties of these clusters were studied in a SQUID magnetometer as a function of cluster size, temperature and applied magnetic field. The blocking temperature, coercive field and remanent moment of 12.5 nm Fe clusters in inverse micelles are significantly lower than those reported for clusters of similar {alpha}-Fe core size but with a surface oxide. The novel synthesis technique may yield metallic clusters with essentially intrinsic magnetic properties.

    18. Tunable optical properties of nano-Au on vanadium dioxide

      NASA Astrophysics Data System (ADS)

      Xu, Gang; Huang, Chun-Ming; Tazawa, Masato; Jin, Ping; Chen, Li-Hua

      2009-03-01

      The optical properties of Au nanoparticles deposited on thermochromic thin films of VO2 are investigated using spectroscopy. A localized modification on the transmittance spectrum of VO2 film is formed due to the presence of Au nanoparticles which exhibit localized surface plasmon resonance (LSPR) in the visible-near IR region. The position of the modification wavelength region shows a strong dependence on the Au mass thickness and shifts toward the red as it increases. On the other hand, it was found that the LSPR of Au nanoparticles can be thermally tunable because of the thermochromism of the supporting material of VO2. The LSPR wavelength, λSPR, shifts to the blue with increasing temperature, and shifts back to the red as temperature decreases. A fine tuning is achieved when the temperature is increased in a stepwise manner.

    19. Energetic, electronic, and thermal effects on structural properties of Ag-Au nanoalloys.

      PubMed

      Chen, Fuyi; Johnston, Roy L

      2008-01-01

      Using a genetic algorithm global optimization approach combined with density functional theory calculations, a search has been made for the lowest energies of (AgAu)(m) nanoalloys with 20-150 atoms (diameters of 1.0-2.0 nm). A total of 31 decahedra, 35 icosahedra, and 2 close-packed motifs are identified in two icosahedral windows and one Marks-decahedral window. These structural motifs have twinned, capped, defective, and distorted atomic packing compared to classical clusters, such as the icosahedron. The magic numbers, atomic ordering, electronic structure, and melting behavior are further studied, and a new poly-nanocrystalline decahedral motif, Ag(44)Au(44), is found to have high structural, electronic, and thermal stability. Our results show that alloying can lead to a remarkable stabilization of local order and provide a comprehensive model for the structures and properties of Ag-Au nanoalloys.

    20. A critical size for emergence of nonbulk electronic and geometric structures in dodecanethiolate-protected Au clusters.

      PubMed

      Negishi, Yuichi; Nakazaki, Tafu; Malola, Sami; Takano, Shinjiro; Niihori, Yoshiki; Kurashige, Wataru; Yamazoe, Seiji; Tsukuda, Tatsuya; Häkkinen, Hannu

      2015-01-28

      We report on how the transition from the bulk structure to the cluster-specific structure occurs in n-dodecanethiolate-protected gold clusters, Au(n)(SC12)m. To elucidate this transition, we isolated a series of Au(n)(SC12)m in the n range from 38 to ∼520, containing five newly identified or newly isolated clusters, Au104(SC12)45, Au(∼226)(SC12)(∼76), Au(∼253)(SC12)(∼90), Au(∼356)(SC12)(∼112), and Au(∼520)(SC12)(∼130), using reverse-phase high-performance liquid chromatography. Low-temperature optical absorption spectroscopy, powder X-ray diffractometry, and density functional theory (DFT) calculations revealed that the Au cores of Au144(SC12)60 and smaller clusters have molecular-like electronic structures and non-fcc geometric structures, whereas the structures of the Au cores of larger clusters resemble those of the bulk gold. A new structure model is proposed for Au104(SC12)45 based on combined approach between experiments and DFT calculations.

    1. M atom (M = Cu, Ag and Au) interaction with Ag and Au substrates: a first-principles study using cluster and slab models.

      PubMed

      Nigam, Sandeep; Majumder, Chiranjib

      2010-11-03

      Using state-of-the-art first-principles calculations we report the interaction of M atoms (M = Cu, Ag and Au) with small Ag(n), Au(n) clusters (n = 3 and 6) and periodic Ag(111) and Au(111) surfaces. All calculations were performed using the plane wave pseudo-potential approach under the spin polarized version of the generalized gradient approximation scheme. The result shows that the equilibrium geometry of all MAg(3) and MAu(3) clusters favor a planar rhombus structure. From the charge distribution analysis of MAg(n)/MAu(n) clusters it is found that, while Cu and Ag donates electronic charge towards the host clusters, the Au atom acts as an acceptor, thus creating charge polarization in the system. The difference in orbital decomposed charges before and after the M interaction reveals that enhanced s-d hybridization is responsible for keeping the MAu(6) cluster planar, and increased p-orbital participation induces three-dimensional configurations in MAg(6) clusters. The optimization of M atom deposition on the Ag(111) and Au(111) surfaces shows that M atoms prefer to adsorb on the threefold fcc site over other well-defined sites. From the orbital decomposed charge analysis it is inferred that, although there is significant difference in the absolute magnitude of the interaction energy between M atoms and the Ag or Au substrates, the nature of chemical bonding is similar for the finite size clusters as well as in slab models.

    2. Thermal Dihydrogen Activation by a Closed-Shell AuCeO2(+) Cluster.

      PubMed

      Meng, Jing-Heng; He, Sheng-Gui

      2014-11-06

      Laser-ablation-generated AuCeO2(+) and CeO2(+) oxide clusters were mass-selected using a quadrupole mass filter and reacted with H2 in an ion trap reactor at ambient conditions. The reactions were characterized by mass spectrometry and density functional theory calculations. The gold-cerium bimetallic oxide cluster AuCeO2(+) is more reactive in H2 activation than the pure cerium oxide cluster CeO2(+). The gold atom is the active adsorption site and facilitates the heterolytic cleavage of H2 in collaboration with the separated O(2-) ion of the CeO2 support. To the best of our knowledge, this is the first example of thermal H2 activation by a closed-shell atomic cluster, which provides molecular-level insights into the single gold atom catalysis over metal oxide supports.

    3. Gd@Au15: A magic magnetic gold cluster for cancer therapy and bioimaging

      NASA Astrophysics Data System (ADS)

      Yadav, Brahm Deo; Kumar, Vijay

      2010-09-01

      We report from ab initio calculations a magic magnetic cage cluster of gold, Gd@Au15, obtained by doping of a Gd atom in gold clusters. It has a highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.31 eV within the generalized gradient approximation that makes it a potential candidate for cancer therapy with an additional attractive feature that its large magnetic moment of 7 μB could be beneficial for magnetic resonance imaging.

    4. Structural and dynamical properties of liquid Al-Au alloys

      NASA Astrophysics Data System (ADS)

      Peng, H. L.; Voigtmann, Th.; Kolland, G.; Kobatake, H.; Brillo, J.

      2015-11-01

      We investigate temperature- and composition-dependent structural and dynamical properties of Al-Au melts. Experiments are performed to obtain accurate density and viscosity data. The system shows a strong negative excess volume, similar to other Al-based binary alloys. We develop a molecular-dynamics (MD) model of the melt based on the embedded-atom method (EAM), gauged against the available experimental liquid-state data. A rescaling of previous EAM potentials for solid-state Au and Al improves the quantitative agreement with experimental data in the melt. In the MD simulation, the admixture of Au to Al can be interpreted as causing a local compression of the less dense Al system, driven by less soft Au-Au interactions. This local compression provides a microscopic mechanism explaining the strong negative excess volume of the melt. We further discuss the concentration dependence of self- and interdiffusion and viscosity in the MD model. Al atoms are more mobile than Au, and their increased mobility is linked to a lower viscosity of the melt.

    5. Superconductivity of Au-Ge-Yb Approximants with Tsai-Type Clusters

      NASA Astrophysics Data System (ADS)

      Deguchi, Kazuhiko; Nakayama, Mika; Matsukawa, Shuya; Imura, Keiichiro; Tanaka, Katsumasa; Ishimasa, Tsutomu; Sato, Noriaki K.

      2015-02-01

      We report the emergence of bulk superconductivity in Au64.0Ge22.0Yb14.0 and Au63.5Ge20.5Yb16.0 below 0.68 and 0.36 K, respectively. This is the first observation of superconductivity in Tsai-type crystalline approximants of quasicrystals. The Tsai-type cluster center is occupied by Au and Ge ions in the former approximant, and by an Yb ion in the latter. For magnetism, the latter system shows a larger magnetization than the former. To explain this observation, we propose a model that the cluster-center Yb ion is magnetic. The relationship between the magnetism and the superconductivity is also discussed.

    6. Theoretical investigation of the hetero-junction effect in PVP-stabilized Au 13 clusters. The role of PVP in their catalytic activities

      NASA Astrophysics Data System (ADS)

      Okumura, Mitsutaka; Kitagawa, Yasutaka; Kawakami, Takashi; Haruta, Masatake

      2008-06-01

      Hybrid density functional calculations have been carried out for Au 13-poly( N-vinyl-2-pyrrolidone), abbreviated as Au 13-PVP, and related model clusters, Au 13-PVP 4, Au 13-PVP-O 2 and Au 13-PVP 4-O 2, to discuss the variation in the electronic structure of Au 13 clusters by PVP adsorption. The calculations have shown that the charge transfer from the adsorbed PVP to Au 13 produces negatively charged O 2 on Au 13-PVP 4. These findings suggest that PVP acts not only as a stabilizer to prevent the aggregation of Au clusters but also as an electron donor to Au clusters. Thus we conclude that the catalytic activities of Au clusters are affected by the adsorbed PVPs.

    7. Study of the nucleation and growth of antibiotic labeled Au NPs and blue luminescent Au8 quantum clusters for Hg2+ ion sensing, cellular imaging and antibacterial applications

      NASA Astrophysics Data System (ADS)

      Khandelwal, Puneet; Singh, Dheeraj K.; Sadhu, Subha; Poddar, Pankaj

      2015-11-01

      Herein, we report a detailed experimental study supported by DFT calculations to understand the mechanism behind the synthesis of cefradine (CFD - an antibiotic) labeled gold nanoparticles (Au NPs) by employing CFD as both a mild reducing and capping agent. The analysis of the effect of growth conditions reveals that a higher concentration of HAuCl4 results in the formation of an increasing fraction of anisotropic structures, higher temperature leads to the formation of quasi-spherical particles instead of anisotropic ones, and larger pH leads to the formation of much smaller particles. The cyclic voltammetry (CV) results show that when the pH of the reaction medium increases from 4 to 6, the reduction potential of CFD increases which leads to the synthesis of nanoparticles (in a pH 4 reaction) to quantum clusters (in a pH 6 reaction). The MALDI-TOF mass spectrometry results of supernatant of the pH 6 reaction indicate the formation of [Au8(CFD)2S6] QCs which show fluorescence at ca. 432 nm with a Stokes shift of ca. 95 nm. The blue luminescence from Au8 QCs was applied for sensing of Hg2+ ions on the basis of an aggregation-induced fluorescence quenching mechanism and offers good selectivity and a high sensitivity with a limit of detection ca. 2 nM which is lower than the detection requirement of 10 nM by the U.S. EPA and 30 nM by WHO for drinking water. We have also applied the sensing probe to detect Hg2+ ions in bacterial samples. Further, we have investigated the antibacterial property of as-synthesized Au NPs using MIC, growth curve and cell survival assay. The results show that Au NPs could reduce the cell survival very efficiently rather than the cell growth in comparison to the antibiotic itself. The scanning electron microscopy study shows the degradation and blebbing of the bacterial cell wall upon exposure with Au NPs which was further supported by fluorescence microscopy results. These Au NPs did not show reactive oxygen species generation. We believe

    8. Morphological effects of Au13 clusters on the adsorption of CO2 over anatase TiO2(101)

      NASA Astrophysics Data System (ADS)

      Liu, Li; Liu, Zhongbo; Sun, Honggang; Zhao, Xian

      2017-03-01

      Density functional theory was employed to investigate the interaction between CO2 and anatase TiO2(101) surface in the presence of Au13 clusters. Two Au13 clusters (icosahedral and cuboctahedral) were used to identify correlations among activity, structural stability, and morphology of supported Au13 clusters on the TiO2(101) surface. The effects of oxygen vacancy were also studied. A strong morphological effect of Au13 clusters on the adsorption and activation of CO2 over anatase TiO2 (101) has been identified. The structural dynamic fluxionality of Au13 clusters, i.e., its adaptability toward the adsorbed CO2, plays an important role in the bonding and activation of CO2. The flexibility of the icosahedral Au13 cluster allows it to readjust so as to enable the maximum orbital overlap between the Au13 clusters and CO2, making the stabilization of CO2 feasible. In contrast, the cuboctahedral Au13 cluster tends to maintain its own structure even after CO2 adsorption, resulting in weaker CO2 binding strength. The presence of oxygen vacancy was found to introduce additional adsorption sites, and CO2 adsorption on defective TiO2(101) surface can be substantially modified by the presence of the cuboctahedral Au13 cluster. In addition, we find that the interfacial site is the preferred adsorption site for CO2 adsorption and activation on the Au13/TiO2(101) surface. These findings shed light on the importance of cluster dynamics during catalytic reaction and provide key guidelines for engineering more efficient metal-oxide interfaces in catalysis.

    9. Synthesis and Catalytic Properties of Au Pd Nanoflowers

      SciTech Connect

      Xu, Jianguang; Wilson, Adria; Howe, Jane Y; Chi, Miaofang; Wiley, Benjamin J

      2011-01-01

      Reduction of Pd ions by hydroquinone in the presence of gold nanoparticles and polyvinylpyrrolidone resulted in the formation of nanoflowers with a Au core and Pd petals. Addition of HCl to the synthesis halted the reduction by hydroquinone and enabled the acquisition of snapshots of the nanoflowers at different stages of growth. TEM images of the reaction after 10 s show that the nanoflower morphology resulted from the homogeneous nucleation of Pd clusters in solution and their subsequent attachment to gold seeds coated with a thin (0.8 0.1 nm) shell of Pd. UV visible spectra also indicate Pd clusters formed in the early stages of the reaction and disappeared as the nanoflowers grew. The speed at which this reaction can be halted is useful not only for producing a variety of bimetallic nanostructures with precisely controlled dimensions and morphologies but also for understanding the growth mechanism of these structures. The ability of the AuPd core shell structure to catalyze the Suzuki coupling reaction of iodobenzene to phenylboronic acid was probed and compared against the activity of Pd nanocubes and thin-shelled AuPd core shell nanoparticles. The results of this study suggest that Suzuki coupling was not affected by the surface structure or subsurface composition of the nanoparticles, but instead was primarily catalyzed by molecular Pd species that leached from the nanostructures.

    10. Synthesis and catalytic properties of Au-Pd nanoflowers.

      PubMed

      Xu, Jianguang; Wilson, Adria R; Rathmell, Aaron R; Howe, Jane; Chi, Miaofang; Wiley, Benjamin J

      2011-08-23

      Reduction of Pd ions by hydroquinone in the presence of gold nanoparticles and polyvinylpyrrolidone resulted in the formation of nanoflowers with a Au core and Pd petals. Addition of HCl to the synthesis halted the reduction by hydroquinone and enabled the acquisition of snapshots of the nanoflowers at different stages of growth. TEM images of the reaction after 10 s show that the nanoflower morphology resulted from the homogeneous nucleation of Pd clusters in solution and their subsequent attachment to gold seeds coated with a thin (0.8 ± 0.1 nm) shell of Pd. UV-visible spectra also indicate Pd clusters formed in the early stages of the reaction and disappeared as the nanoflowers grew. The speed at which this reaction can be halted is useful not only for producing a variety of bimetallic nanostructures with precisely controlled dimensions and morphologies but also for understanding the growth mechanism of these structures. The ability of the AuPd core-shell structure to catalyze the Suzuki coupling reaction of iodobenzene to phenylboronic acid was probed and compared against the activity of Pd nanocubes and thin-shelled AuPd core-shell nanoparticles. The results of this study suggest that Suzuki coupling was not affected by the surface structure or subsurface composition of the nanoparticles, but instead was primarily catalyzed by molecular Pd species that leached from the nanostructures.

    11. Thermodynamic Properties of Liquid Ag-Au-Sn Alloys

      NASA Astrophysics Data System (ADS)

      Hindler, M.; Knott, S.; Mikula, A.

      2010-10-01

      The thermodynamic properties of liquid Ag-Au-Sn alloys were studied with an electromotive force (EMF) method using the eutectic mixture of KCl/LiCl as a liquid electrolyte. Activities of Sn in the liquid alloys were measured at three cross-sections with constant molar ratios of Ag:Au = 2:1, 1:1, and 1:2 with tin in the concentration range between 20 at.% and 90 at.% from the liquidus of the samples up to 1030 K. The integral Gibbs energies at 973 K and the integral enthalpies were calculated by Gibbs-Duhem integration.

    12. Intercalation of bovine serum albumin coated gold clusters between phospholipid bilayers: temperature-dependent behavior of lipid-AuQC@BSA assemblies with red emission and superlattice structure.

      PubMed

      Söptei, Balázs; Mihály, Judith; Visy, Júlia; Wacha, András; Bóta, Attila

      2014-04-10

      A method has been developed to encapsulate bovine serum albumin (BSA)-coated gold quantum clusters (AuQC@BSA) in a multilamellar system of dipalmitoylphosphatidylcholine (DPPC). Results have shown that intercalation of AuQC@BSA particles into lipid bilayers occurs in the presence of CaCl2. Intense red photoluminescence emission was observed after encapsulation of the clusters. A well-defined structure was found with periodic distances drastically larger than that in the pure DPPC/water system. Although Ca(2+) ions can change the dipole characteristics of the lipid bilayer surface, leading to unbinding between the bilayers of multilamellar DPPC/water system, the repulsion is shielded in the presence of AuQC@BSA particles. A coherent superlattice structure evolves due to mixed Ca(2+)-DPPC and Ca(2+)-AuQC@BSA interactions. Studies at different temperatures have suggested a correlation between the luminescence properties of the clusters and phase transition of the lipid layers. The temperature-dependent behavior assumes the connection between the coating and the lipid bilayer surface. Temperature-dependent features of lipid intercalated Au clusters provide new opportunities in their application.

    13. Stable and solubilized active Au atom clusters for selective epoxidation of cis-cyclooctene with molecular oxygen

      PubMed Central

      Qian, Linping; Wang, Zhen; Beletskiy, Evgeny V.; Liu, Jingyue; dos Santos, Haroldo J.; Li, Tiehu; Rangel, Maria do C.; Kung, Mayfair C.; Kung, Harold H.

      2017-01-01

      The ability of Au catalysts to effect the challenging task of utilizing molecular oxygen for the selective epoxidation of cyclooctene is fascinating. Although supported nanometre-size Au particles are poorly active, here we show that solubilized atomic Au clusters, present in ng ml−1 concentrations and stabilized by ligands derived from the oxidized hydrocarbon products, are active. They can be formed from various Au sources. They generate initiators and propagators to trigger the onset of the auto-oxidation reaction with an apparent turnover frequency of 440 s−1, and continue to generate additional initiators throughout the auto-oxidation cycle without direct participation in the cycle. Spectroscopic characterization suggests that 7–8 atom clusters are effective catalytically. Extension of work based on these understandings leads to the demonstration that these Au clusters are also effective in selective oxidation of cyclohexene, and that solubilized Pt clusters are also capable of generating initiators for cyclooctene epoxidation. PMID:28348389

    14. Properties of Solar Flare Clustering

      NASA Astrophysics Data System (ADS)

      Title, Alan; DeRosa, Marc

      The continuous full disk observations provided by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) give an observer the impression that flare and filament eruptions are related. However, both detailed analysis of a number of events as well as a number of statistical studies have provided only rare examples of clear causal behavior. But the mechanisms of flare triggering are not well understood, so the lack of hard evidence is not surprising. Here we have examined the waiting-time statistics of GOES X-ray flares of magnitude C5 or greater during the last sunspot cycle with the aim of assessing the degree to which flares are clustered in time. Clusters are groups of flares in which all successive flares occur within a fixed separation time - the linking window. While many of the flares in a cluster may come from the same active region, the clusters that last more than a disk passage must result from flares in multiple active regions. The longest cluster of the last cycle lasted more than 42 days. None of the flares were separated by more than 36 hours. Since that cluster lasted more than three disk passages, it could not have been caused by a single region. We find that during the last maximum, eight clusters contributed 44% of all flares. All of these clusters spanned multiple disk passages, but occupied only 16.5% of the cycle duration. Two of the clusters provided 34% of the flares. We suggest that this behavior implies that a component of the observed coordinated behavior has its origin in the solar dynamo.

    15. Geometrical structure, stability and electronic properties of AunHg(1 ≤ n ≤ 12) clusters

      NASA Astrophysics Data System (ADS)

      Wan, Wei; Kuang, Xiangjun

      2016-08-01

      The geometrical structures, relative stabilities, electronic properties and chemical hardness of AunHg( n=1-12) clusters are systematically investigated using the density functional theory with relativistic all-electron methods. The optimized low-lying energy geometries exhibit two-dimensional and three-dimensional structures. Furthermore, all the lowest-energy structures of AunHg( n=1-12) clusters favor planar geometries with slight distortion, in which the dopant Hg atom prefers to occupy a peripheral site with a lower coordination. The geometrical, electronic and chemical stabilities of the AunHg cluster with even number of valence electrons are higher than those of the neighboring AunHg cluster with odd number of valence electrons. Besides, 5 d valence electrons of impurity Hg atom in the AunHg cluster hardly join in the orbital interactions compared with 5 d valence electrons of corresponding Au atom in Aun+1 cluster. Au-Hg bonds in AunHg clusters are weaker and have more obviously ionic-like characteristics than the corresponding Au-Au bonds in Aun+1 clusters.

    16. EARLY STAGES OF CLUSTER FORMATION: FRAGMENTATION OF MASSIVE DENSE CORES DOWN TO {approx}< 1000 AU

      SciTech Connect

      Palau, Aina; Girart, Josep M.; Fuente, Asuncion; Estalella, Robert; Ho, Paul T. P.; Zhang, Qizhou; Sanchez-Monge, Alvaro; Fontani, Francesco; Cesaroni, Riccardo; Busquet, Gemma; Commercon, Benoit; Hennebelle, Patrick; Boissier, Jeremie; Zapata, Luis A.

      2013-01-10

      In order to study the fragmentation of massive dense cores, which constitute the cluster cradles, we observed the continuum at 1.3 mm and the CO (2-1) emission of four massive cores with the Plateau de Bure Interferometer in the most extended configuration. We detected dust condensations down to {approx}0.3 M {sub Sun} and separate millimeter sources down to 0.''4 or {approx}< 1000 AU, comparable to the sensitivities and separations reached in optical/infrared studies of clusters. The CO (2-1) high angular resolution images reveal high-velocity knots usually aligned with previously known outflow directions. This, in combination with additional cores from the literature observed at similar mass sensitivity and spatial resolution, allowed us to build a sample of 18 protoclusters with luminosities spanning three orders of magnitude. Among the 18 regions, {approx}30% show no signs of fragmentation, while 50% split up into {approx}> 4 millimeter sources. We compiled a list of properties for the 18 massive dense cores, such as bolometric luminosity, total mass, and mean density, and found no correlation of any of these parameters with the fragmentation level. In order to investigate the combined effects of the magnetic field, radiative feedback, and turbulence in the fragmentation process, we compared our observations to radiation magnetohydrodynamic simulations and found that the low-fragmented regions are reproduced well in the magnetized core case, while the highly fragmented regions are consistent with cores where turbulence dominates over the magnetic field. Overall, our study suggests that the fragmentation in massive dense cores could be determined by the initial magnetic field/turbulence balance in each particular core.

    17. Self-assembly of methanethiol on cluster arrays of Co/Au(111)

      NASA Astrophysics Data System (ADS)

      Nenchev, Georgi; Diaconescu, Bogdan; Pohl, Karsten

      2007-03-01

      Self-assembly on strained metallic interfaces is an attractive option for growing highly ordered multi-functional nanopatterns. We present a Variable Temperature STM and Auger Electron Spectroscopy study of selective adsorption of sulfur-terminated CH3SH molecules on the lattice of Co clusters on Au(111). We investigate the growth of a uniform network of Co on the reconstructed Au(111) surface, the temperature evolution of the island height and the termination, and the onset of surface alloying. Further we will show the evolution of morphology of the CH3SH film on Au (111) as a function of coverage and temperature, and the importance of the herringbone reconstruction for the SAM formation and orientation. Successful combination and control of these two processes leads to the creation of an ordered, stable patterned Co/CH3SH heterostructure with nanometer-sized unit cell.

    18. A density functional investigation of thiolate-protected bimetal PdAu(24)(SR)(18)(z) clusters: doping the superatom complex.

      PubMed

      Kacprzak, Katarzyna A; Lehtovaara, Lauri; Akola, Jaakko; Lopez-Acevedo, Olga; Häkkinen, Hannu

      2009-09-07

      Structure, electronic properties, optical absorption and charging properties of methylthiolate-protected bimetal PdAu(24)(SR)(18)(z) (R = Me) clusters with various charge states (-3 properties of the well-understood singly anionic pure gold complex Au(25)(SR)(18)((-1)) [J. Akola, M. Walter, H. Häkkinen and H. Grönbeck, J. Am. Chem. Soc., 2008, 130, 3756]. The atomic structure of this all-gold complex can be written in a "divide-and-protect" way [H. Häkkinen, M. Walter and H. Grönbeck, J. Phys. Chem. B, 2006, 110, 9927] as Au(13)[Au(2)(SR)(3)](6)((-1)) where 6 v-shaped Au(2)(SR)(3) ligands protect the close-to-icosahedral Au(13) core and where eight delocalized metal electrons, derived from Au(6s) electrons, comprise a stable closed-shell 1S(2)1P(6)"superatom" configuration in the core. We show that the di-anion PdAu(24)(SR)(18)((-2)) is a corresponding eight-electron closed-shell species whereas the clusters PdAu(24)(SR)(18)(z), -1 Au by Pd at the center of the core, at the surface of the core or in one of the protecting Au(2)(SR)(3) ligands. However, optical absorption and the HOMO-LUMO and electrochemical gaps depend sensitively on the site of the doping Pd atom, which may turn out be useful for assigning the structure of PdAu(24)(SR)(18) from experimental data.

    19. Structure and Electrical Properties of an Assembly of Au Nanoclusters

      DTIC Science & Technology

      2001-01-01

      Nanoclusters DISTRIBUTION: Approved for public release, distribution unlimited This paper is part of the following report: TITLE: Materials Research...Materials Research Society Structure and Electrical Properties of an Assembly of Au Nanoclusters G. Muralidharan, L. Maya and T. Thundat Oak Ridge National...interest both for understanding the fundamental physics involved and for potential applications. In this study, we describe a technique for preparing

    20. Approximate treatment of semicore states in GW calculations with application to Au clusters

      NASA Astrophysics Data System (ADS)

      Xian, Jiawei; Baroni, Stefano; Umari, P.

      2014-03-01

      We address the treatment of transition metal atoms in GW electronic-structure calculations within the plane-wave pseudo-potential formalism. The contributions of s and p semi-core electrons to the self-energy, which are essential to grant an acceptable accuracy, are dealt with using a recently proposed scheme whereby the exchange components are treated exactly at the G0W0 level, whereas a suitable approximation to the correlation components is devised. This scheme is benchmarked for small gold nano-clusters, resulting in ionization potentials, electron affinities, and density of states in very good agreement with those obtained from calculations where s and p semicore states are treated as valence orbitals, and allowing us to apply this same scheme to clusters of intermediate size, Au20 and Au32, that would be otherwise very difficult to deal with.

    1. Approximate treatment of semicore states in GW calculations with application to Au clusters.

      PubMed

      Xian, Jiawei; Baroni, Stefano; Umari, P

      2014-03-28

      We address the treatment of transition metal atoms in GW electronic-structure calculations within the plane-wave pseudo-potential formalism. The contributions of s and p semi-core electrons to the self-energy, which are essential to grant an acceptable accuracy, are dealt with using a recently proposed scheme whereby the exchange components are treated exactly at the G0W0 level, whereas a suitable approximation to the correlation components is devised. This scheme is benchmarked for small gold nano-clusters, resulting in ionization potentials, electron affinities, and density of states in very good agreement with those obtained from calculations where s and p semicore states are treated as valence orbitals, and allowing us to apply this same scheme to clusters of intermediate size, Au20 and Au32, that would be otherwise very difficult to deal with.

    2. Approximate treatment of semicore states in GW calculations with application to Au clusters

      SciTech Connect

      Xian, Jiawei; Baroni, Stefano; Umari, P.

      2014-03-28

      We address the treatment of transition metal atoms in GW electronic-structure calculations within the plane-wave pseudo-potential formalism. The contributions of s and p semi-core electrons to the self-energy, which are essential to grant an acceptable accuracy, are dealt with using a recently proposed scheme whereby the exchange components are treated exactly at the G{sub 0}W{sub 0} level, whereas a suitable approximation to the correlation components is devised. This scheme is benchmarked for small gold nano-clusters, resulting in ionization potentials, electron affinities, and density of states in very good agreement with those obtained from calculations where s and p semicore states are treated as valence orbitals, and allowing us to apply this same scheme to clusters of intermediate size, Au{sub 20} and Au{sub 32}, that would be otherwise very difficult to deal with.

    3. Structural, electronic and magnetic properties of Au-based monolayer derivatives in honeycomb structure

      NASA Astrophysics Data System (ADS)

      Kapoor, Pooja; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.

      2016-05-01

      We present electronic properties of atomic layer of Au, Au2-N, Au2-O and Au2-F in graphene-like structure within the framework of density functional theory (DFT). The lattice constant of derived monolayers are found to be higher than the pristine Au monolayer. Au monolayer is metallic in nature with quantum ballistic conductance calculated as 4G0. Similarly, Au2-N and Au2-F monolayers show 4G0 and 2G0 quantum conductance respectively while semiconducting nature with calculated band gap of 0.28 eV has been observed for Au2-O monolayer. Most interestingly, half metalicity has been predicted for Au2-N and Au2-F monolayers. Our findings may have importance for the application of these monolayers in nanoelectronic and spintronics.

    4. The electronic structure of Au25 clusters: between discrete and continuous

      NASA Astrophysics Data System (ADS)

      Katsiev, Khabiboulakh; Lozova, Nataliya; Wang, Lu; Sai Krishna, Katla; Li, Ruipeng; Mei, Wai-Ning; Skrabalak, Sara E.; Kumar, Challa S. S. R.; Losovyj, Yaroslav

      2016-08-01

      Here, an approach based on synchrotron resonant photoemission is employed to explore the transition between quantization and hybridization of the electronic structure in atomically precise ligand-stabilized nanoparticles. While the presence of ligands maintains quantization in Au25 clusters, their removal renders increased hybridization of the electronic states in the vicinity of the Fermi level. These observations are supported by DFT studies.Here, an approach based on synchrotron resonant photoemission is employed to explore the transition between quantization and hybridization of the electronic structure in atomically precise ligand-stabilized nanoparticles. While the presence of ligands maintains quantization in Au25 clusters, their removal renders increased hybridization of the electronic states in the vicinity of the Fermi level. These observations are supported by DFT studies. Electronic supplementary information (ESI) available: Experimental details including chemicals, sample preparation, and characterization methods. Computation techniques, SV-AUC, GIWAXS, XPS, UPS, MALDI-TOF, ESI data of Au25 clusters. See DOI: 10.1039/c6nr02374f

    5. Prediction of unusual stable ordered structures of Au-Pd alloys via a first-principles cluster expansion

      NASA Astrophysics Data System (ADS)

      Barabash, Sergey V.; Blum, Volker; Müller, Stefan; Zunger, Alex

      2006-07-01

      We describe an iterative procedure which yields an accurate cluster expansion for Au-Pd using only a limited number of ab initio formation enthalpies. Our procedure addresses two problems: (a) given the local-density-approximation (LDA) formation energies for a fixed set of structures, it finds the pair and many-body cluster interactions best able to predict the formation energies of new structures, and (b) given such pair and many-body interactions, it augments the LDA set of “input structures” by identifying additional structures that carry most information not yet included in the “input.” Neither step can be done by intuitive selection. Using methods including genetic algorithm and statistical analysis to iteratively solve these problems, we build a cluster expansion able to predict the formation enthalpy of an arbitrary fcc lattice configuration with precision comparable to that of ab initio calculations themselves. We also study possible competing non-fcc structures of Au-Pd, using the results of a “data mining” study. We then address the unresolved problem of bulk ordering in Au-Pd. Experimentally, the phase diagram of Au-Pd shows only a disordered solid solution. Even though the mixing enthalpy is negative, implying ordering, no ordered bulk phases have been detected. Thin film growth shows L12 -ordered structures with composition Au3Pd and AuPd3 and L10 structure with composition AuPd. We find that (i) all the ground states of Au-Pd are fcc structures; (ii) the low- T ordered states of bulk Au-Pd are different from those observed experimentally in thin films; specifically, the ordered bulk Au3Pd is stable in D023 structure and and AuPd in chalcopyritelike Au2Pd2 (201) superlattice structure, whereas thin films are seen in the L12 and L10 structures; (iii) AuPd3 L12 is stable and does not phase separate, contrary to the suggestions of an earlier investigation; (iv) at compositions around Au3Pd , we find several long-period superstructures (LPS

    6. Ultraviolet Photodissociation of Selected Gold Clusters: Ultraefficient Unstapling and Ligand Stripping of Au25(pMBA)18 and Au36(pMBA)24.

      PubMed

      Black, David M; Crittenden, Christopher M; Brodbelt, Jennifer S; Whetten, Robert L

      2017-03-16

      We report the first results of ultraviolet photodissociation (UVPD) mass spectrometry of trapped monolayer-protected cluster (MPC) ions generated by electrospray ionization. Gold clusters Au25(pMBA)18 and Au36(pMBA)24 (pMBA = para-mercaptobenzoic acid) were analyzed in both the positive and negative modes. Whereas activation methods including collisional- and electron-based methods produced relatively few fragment ions, even a single ultraviolet pulse (at λ = 193 nm) caused extensive fragmentation of the positively charged clusters. Upon photoactivation using a low number of laser pulses, the staple motifs of both clusters were cleaved and stripped of the protecting ligand portions without removal of any contained gold atoms. This striking process involved Au-S and C-S bond cleavages via a pathway made possible by 6.4 eV photon absorption. Monomer evaporation (neutral gold atom loss) occurred upon exposure to multiple pulses, resulting in a size series of bare gold-cluster ions. All tandem mass spectrometric methods produced the singly charged ring tetramer ion, [Au4(pMBA)4 + Na](+), for each cluster.

    7. Structures and Stabilities of the Metal Doped Gold Nano-Clusters: M@Au10 (M = W, Mo, Ru, Co).

      PubMed

      Hossain, Delwar; Pittman, Charles U; Gwaltney, Steven R

      2014-01-01

      The structures and stabilities of a series of endohedral gold clusters containing ten gold atoms M@Au10 (M = W, Mo, Ru, Co) have been determined using density functional theory. The gradient-corrected functional BP86, the Tao-Perdew-Staroverov-Scuseria TPSS meta-GGA functional, and the hybrid density functionals B3LYP and PBE1PBE were employed to calculate the structures, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for these clusters. The LanL2DZ effective core potentials and the corresponding valence basis sets were employed. The M@Au10 (M = W, Mo, Ru, Co) clusters have higher binding energies than an empty Au10 cluster. In addition, the large HOMO-LUMO gaps suggest that the M@Au10 (M = W, Mo, Ru, Co) clusters are all likely to be stable chemically. The ionization potentials and electron affinities for these clusters are very high, and the W@Au10 and Mo@Au10 clusters have electron affinities similar to the super-halogen Al13.

    8. Structures and Stabilities of the Metal Doped Gold Nano-Clusters: M@Au10 (M = W, Mo, Ru, Co)

      PubMed Central

      Hossain, Delwar; Pittman, Charles U.; Gwaltney, Steven R.

      2014-01-01

      The structures and stabilities of a series of endohedral gold clusters containing ten gold atoms M@Au10 (M = W, Mo, Ru, Co) have been determined using density functional theory. The gradient-corrected functional BP86, the Tao-Perdew-Staroverov-Scuseria TPSS meta-GGA functional, and the hybrid density functionals B3LYP and PBE1PBE were employed to calculate the structures, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for these clusters. The LanL2DZ effective core potentials and the corresponding valence basis sets were employed. The M@Au10 (M = W, Mo, Ru, Co) clusters have higher binding energies than an empty Au10 cluster. In addition, the large HOMO–LUMO gaps suggest that the M@Au10 (M = W, Mo, Ru, Co) clusters are all likely to be stable chemically. The ionization potentials and electron affinities for these clusters are very high, and the W@Au10 and Mo@Au10 clusters have electron affinities similar to the super-halogen Al13. PMID:24611036

    9. Single crystal XRD structure and theoretical analysis of the chiral Au30S(S-t-Bu)18 cluster.

      PubMed

      Crasto, David; Malola, Sami; Brosofsky, Grace; Dass, Amala; Häkkinen, Hannu

      2014-04-02

      Au30S(S-t-Bu)18 cluster, related closely to the recently isolated "green gold" compound Au30(S-t-Bu)18, has been structurally solved via single-crystal XRD and analyzed by density functional theory calculations. The molecular protecting layer shows a combination of monomeric (RS-Au-SR) and trimeric (RS-Au-SR-Au-SR-Au-SR) gold-thiolate units, bridging thiolates, and a single sulfur (sulfide) in a novel μ3-coordinating position. The chiral gold core has a geometrical component that is identical to the core of the recently reported Au28(SPh-t-Bu)20. Both enantiomers of Au30S(S-t-Bu)18 are found in the crystal unit cell. The calculated CD spectrum bears a close resemblance to that of Au28(SPh-t-Bu)20. This is the first time when two structurally characterized thiol-stabilized gold clusters are found to have such closely related metal core structures and the results may increase understanding of the formation of gold clusters when stabilized by bulky thiolates.

    10. Revealing the properties of Mn2Au for antiferromagnetic spintronics.

      PubMed

      Barthem, V M T S; Colin, C V; Mayaffre, H; Julien, M-H; Givord, D

      2013-01-01

      The continuous reduction in size of spintronic devices requires the development of structures, which are insensitive to parasitic external magnetic fields, while preserving the magnetoresistive signals of existing systems based on giant or tunnel magnetoresistance. This could be obtained in tunnel anisotropic magnetoresistance structures incorporating an antiferromagnetic, instead of a ferromagnetic, material. To turn this promising concept into real devices, new magnetic materials with large spin-orbit effects must be identified. Here we demonstrate that Mn2Au is not a Pauli paramagnet as hitherto believed but an antiferromagnet with Mn moments of ~4 μB. The particularly large strength of the exchange interactions leads to an extrapolated Néel temperature well above 1,000 K, so that ground-state magnetic properties are essentially preserved up to room temperature and above. Combined with the existence of a significant in-plane anisotropy, this makes Mn2Au the most promising material for antiferromagnetic spintronics identified so far.

    11. Structure and Stability of GeAu{sub n}, n = 1-10 clusters: A Density Functional Study

      SciTech Connect

      Priyanka,; Dharamvir, Keya; Sharma, Hitesh

      2011-12-12

      The structures of Germanium doped gold clusters GeAu{sub n} (n = 1-10) have been investigated using ab initio calculations based on density functional theory (DFT). We have obtained ground state geometries of GeAu{sub n} clusters and have it compared with Silicon doped gold clusters and pure gold clusters. The ground state geometries of the GeAu{sub n} clusters show patterns similar to silicon doped gold clusters except for n = 5, 6 and 9. The introduction of germanium atom increases the binding energy of gold clusters. The binding energy per atom of germanium doped cluster is smaller than the corresponding silicon doped gold cluster. The HUMO-LOMO gap for Au{sub n}Ge clusters have been found to vary between 0.46 eV-2.09 eV. The mullikan charge analysis indicates that charge of order of 0.1e always transfers from germanium atom to gold atom.

    12. Non-lithographic SERS substrates: tailoring surface chemistry for Au nanoparticle cluster assembly.

      PubMed

      Adams, Sarah M; Campione, Salvatore; Caldwell, Joshua D; Bezares, Francisco J; Culbertson, James C; Capolino, Filippo; Ragan, Regina

      2012-07-23

      Near-field plasmonic coupling and local field enhancement in metal nanoarchitectures, such as arrangements of nanoparticle clusters, have application in many technologies from medical diagnostics, solar cells, to sensors. Although nanoparticle-based cluster assemblies have exhibited signal enhancements in surface-enhanced Raman scattering (SERS) sensors, it is challenging to achieve high reproducibility in SERS response using low-cost fabrication methods. Here an innovative method is developed for fabricating self-organized clusters of metal nanoparticles on diblock copolymer thin films as SERS-active structures. Monodisperse, colloidal gold nanoparticles are attached via a crosslinking reaction on self-organized chemically functionalized poly(methyl methacrylate) domains on polystyrene-block-poly(methyl methacrylate) templates. Thereby nanoparticle clusters with sub-10-nanometer interparticle spacing are achieved. Varying the molar concentration of functional chemical groups and crosslinking agent during the assembly process is found to affect the agglomeration of Au nanoparticles into clusters. Samples with a high surface coverage of nanoparticle cluster assemblies yield relative enhancement factors on the order of 10⁹ while simultaneously producing uniform signal enhancements in point-to-point measurements across each sample. High enhancement factors are associated with the narrow gap between nanoparticles assembled in clusters in full-wave electromagnetic simulations. Reusability for small-molecule detection is also demonstrated. Thus it is shown that the combination of high signal enhancement and reproducibility is achievable using a completely non-lithographic fabrication process, thereby producing SERS substrates having high performance at low cost.

    13. Isolation of atomically precise mixed ligand shell PdAu24 clusters

      NASA Astrophysics Data System (ADS)

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

      2016-05-01

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

    14. Structures, Stabilities, and Electronic Properties for Rare-Earth Lanthanum Doped Gold Clusters

      NASA Astrophysics Data System (ADS)

      Zhao, Ya-Ru

      2015-02-01

      The structures, stabilities, and electronic properties of rare-earth lanthanum doped gold La2Aun (n = 1-9) and pure gold Aun (n ≤ 11) clusters have been investigated by using density functional theory. The optimized geometries show that the lowest energy structures of La2Aun clusters favour the 3D structure at n ≥ 3. The lanthanum atoms can strongly enhance the stabilities of gold clusters and tend to occupy the most highly coordinated position. By analysing the gap, vertical ionization potential, and chemical hardness, it is found that the La2Au6 isomer possesses higher stability for small-sized La2Aun clusters (n = 1-9). The charges in the La2Aun clusters transfer from La atoms to the Aun host. In addition, Wiberg bond indices analysis reveals that the intensity of different bonds of La2Aun clusters exhibits a sequence of La-La bond > La-Au bond > Au-Au bond.

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

      SciTech Connect

      Owen, R.K.

      1990-12-01

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

    16. Effects of Au layer thickness and number of bilayers on the properties of Au/ZnO multilayers

      SciTech Connect

      Cespedes, Eva; Prieto, Carlos; Babonneau, David; Sousa Meneses, Domingos de; Fonda, Emiliano; Lyon, Olivier; Briand, Emrick; Traverse, Agnes

      2011-05-01

      Multilayered films of Au/ZnO were prepared by physical vapor deposition. Varying the Au thickness, t{sub Au}, and the number of bilayers, n, allowed us to investigate the role of these parameters on the sample structural and electronic properties. X-ray diffraction, X-ray absorption spectroscopy, grazing incidence small angle X-ray scattering and transmission electron microscopy experiments, have been combined to UV-visible and infrared spectroscopy to characterize the multilayers in the as-prepared state and after annealing. In the as-prepared state, the strong Au and ZnO lattice interaction leads to ZnO epitaxy on Au. Gold appears either as continuous layers or in form of nanoparticles. ZnO experiences a structural transformation from wurztite to rock salt monitored by the Au morphology. Annealing at 500 deg. C destroys the lattice matching. The electronic and optical properties of the systems are understood in line with the Au morphology and ZnO structural state.

    17. Effect of Au Content on Thermal Stability and Mechanical Properties of Au-Cu-Ag-Si Bulk Metallic Glasses

      NASA Astrophysics Data System (ADS)

      Guo, H.; Zhang, W.; Chen, M. W.; Saotome, Y.; Fukuhara, M.; Inoue, A.

      2011-06-01

      The thermal stability, glass-forming ability (GFA), and mechanical and electrical properties of Au-based Au x Si17Cu75.5- x Ag7.5 ( x = 40 to 75.5 at. pct) metallic glasses were investigated. The glass transition temperature ( T g ) and crystallization temperature ( T x ) decreased with increasing Au content. The ultralow T g values below 373 K (100 °C) were obtained for alloys with x = 55 to 75.5. The alloys with x = 45 to 70 exhibited a high stabilization of supercooled liquid and a high GFA, and the supercooled liquid region and critical sample diameter for glass formation were in the range of 31 K to 50 K and 2 to 5 mm, respectively. The compressive fracture strength ( σ c,f ), Young's modulus ( E), and Vicker's hardness ( H v ) of the bulk metallic glasses (BMGs) decreased with increasing Au content. A linear correlation between Au concentration and the characteristic temperature, i.e., T g and T x , and mechanical properties, i.e., σ c,f , E, and H v , as well as electrical resistivity can be found in the BMGs, which will be helpful for the composition design of the desirable Au-based BMGs with tunable physical properties.

    18. Quantum chemical study of the interaction of elemental Hg with small neutral, anionic and cationic Au{sub n} (n = 1–6) clusters

      SciTech Connect

      Siddiqui, Shamoon Ahmad; Bouarissa, Nadir; Rasheed, Tabish; Al-Assiri, M.S.

      2013-03-15

      Graphical abstract: Binding energies as a function of cluster size for Au{sub n}Hg, Au{sub n}Hg{sup +} and Au{sub n}Hg{sup −} complexes. Highlights: ► Hg adsorption of neutral and charged Au{sub n} (n = 1–6) clusters has been discussed. ► Size and charged state of cluster significantly affect the Hg adsorption. ► Transfer of electron mainly found from s orbital of Hg to s orbital of Au. - Abstract: Adsorption of elemental mercury (Hg) on small neutral, cationic and anionic gold clusters (Au{sub n}, n = 1–6) has been studied by using the density functional theory (DFT). Results of this investigation show that frontier molecular orbital theory is a useful tool to predict the selectivity of Hg adsorption. It is found that adsorption of Hg on neutral, cationic and anionic Au{sub n} (n = 1–6) clusters are thermodynamically favorable. The binding energies of Hg on the cationic Au{sub n} clusters are greater than those on the neutral and anionic clusters. Natural bond orbital (NBO) analysis indicates that the flow of electrons in the neutral and charged clusters is mainly due to the s orbitals of Hg and Au. Results of NBO analysis also indicate that the binding energy of Hg with Au{sub n} clusters is directly proportional to the charge transfer, i.e. greater is the charge transfer, higher is the binding energy.

    19. Preparation of multi-coloured different sized fluorescent gold clusters from blue to NIR, structural analysis of the blue emitting Au7 cluster, and cell-imaging by the NIR gold cluster.

      PubMed

      Roy, Subhasish; Baral, Abhishek; Bhattacharjee, Rameswar; Jana, Batakrishna; Datta, Ayan; Ghosh, Surajit; Banerjee, Arindam

      2015-02-07

      Blue, green, orange-red, red and NIR emitting gold quantum clusters have been prepared in aqueous media by using a bioactive peptide glutathione (reduced) at physiological pH. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) analyses show that the core structure sizes of the five different gold clusters are Au7 (blue), Au16 (green), Au19 (orange-red), Au21 (red) and Au22 (NIR). The photo-stability and pH-stability of these quantum clusters have been measured, and these are photo-stable against continuous UV irradiation for a few hours. They also exhibit moderate to good pH-stability within the pH range of 5-12.5. A computational study reveals the organisation of gold atoms in the thiolate-protected blue quantum cluster and its several structural parameters, including the mode of interaction of ligand molecules with Au atoms in the Au7 cluster. Interestingly, it has been found that NIR emitting gold quantum cluster can easily be internalized into the adenocarcinomic human alveolar basal epithelial cell line (A549 cell line). Moreover, a MTT assay indicates that our NIR emitting gold quantum cluster show very low cytotoxicy to A549 cancer cells.

    20. Stability, structural and electronic properties of benzene molecule adsorbed on free standing Au layer

      NASA Astrophysics Data System (ADS)

      Katoch, Neha; Kapoor, Pooja; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.

      2016-05-01

      We report stability and electronic properties of benzene molecule adsorbed on the Au atomic layer within the framework of density function theory (DFT). Horizontal configuration of benzene on the top site of Au monolayer prefers energetically over other studied configurations. On the adsorption of benzene, the ballistic conductance of Au monolayer is found to decrease from 4G0 to 2G0 suggesting its applications for the fabrications of organic sensor devices based on the Au atomic layers.

    1. Systematic Study on the Self-Assembled Hexagonal Au Voids, Nano-Clusters and Nanoparticles on GaN (0001).

      PubMed

      Pandey, Puran; Sui, Mao; Li, Ming-Yu; Zhang, Quanzhen; Kim, Eun-Soo; Lee, Jihoon

      2015-01-01

      Au nano-clusters and nanoparticles (NPs) have been widely utilized in various electronic, optoelectronic, and bio-medical applications due to their great potentials. The size, density and configuration of Au NPs play a vital role in the performance of these devices. In this paper, we present a systematic study on the self-assembled hexagonal Au voids, nano-clusters and NPs fabricated on GaN (0001) by the variation of annealing temperature and deposition amount. At relatively low annealing temperatures between 400 and 600°C, the fabrication of hexagonal shaped Au voids and Au nano-clusters are observed and discussed based on the diffusion limited aggregation model. The size and density of voids and nano-clusters can systematically be controlled. The self-assembled Au NPs are fabricated at comparatively high temperatures from 650 to 800°C based on the Volmer-Weber growth model and also the size and density can be tuned accordingly. The results are symmetrically analyzed and discussed in conjunction with the diffusion theory and thermodynamics by utilizing AFM and SEM images, EDS maps and spectra, FFT power spectra, cross-sectional line-profiles and size and density plots.

    2. Systematic Study on the Self-Assembled Hexagonal Au Voids, Nano-Clusters and Nanoparticles on GaN (0001)

      PubMed Central

      Pandey, Puran; Sui, Mao; Li, Ming-Yu; Zhang, Quanzhen; Kim, Eun-Soo; Lee, Jihoon

      2015-01-01

      Au nano-clusters and nanoparticles (NPs) have been widely utilized in various electronic, optoelectronic, and bio-medical applications due to their great potentials. The size, density and configuration of Au NPs play a vital role in the performance of these devices. In this paper, we present a systematic study on the self-assembled hexagonal Au voids, nano-clusters and NPs fabricated on GaN (0001) by the variation of annealing temperature and deposition amount. At relatively low annealing temperatures between 400 and 600°C, the fabrication of hexagonal shaped Au voids and Au nano-clusters are observed and discussed based on the diffusion limited aggregation model. The size and density of voids and nano-clusters can systematically be controlled. The self-assembled Au NPs are fabricated at comparatively high temperatures from 650 to 800°C based on the Volmer-Weber growth model and also the size and density can be tuned accordingly. The results are symmetrically analyzed and discussed in conjunction with the diffusion theory and thermodynamics by utilizing AFM and SEM images, EDS maps and spectra, FFT power spectra, cross-sectional line-profiles and size and density plots. PMID:26285135

    3. Visible photoluminescence from nearly monodispersed Au 12 clusters protected by meso-2,3-dimercaptosuccinic acid

      NASA Astrophysics Data System (ADS)

      Negishi, Yuichi; Tsukuda, Tatsuya

      2004-01-01

      Nearly monodispersed Au 12 clusters protected by monolayers of meso-2,3-dimercaptosuccinic acid (DMSA) exhibited luminescence at 630 nm with a quantum yield of 1 × 10 -6 upon the photoexcitation at 395 nm to the lowest electronic excited state. The visible PL is assigned to phosphorescence originating from a triplet-like excited state based on the large Stokes shift (1.2 eV). The PL quantum yield was enhanced up to ≈0.9%, greater by eight orders of magnitude than that of bulk gold, by thickening the protecting layer and freezing a solvent at 77 K. The emission peak energy is discussed within the context of core-size dependent electronic structures by comparison with those of thiolate-protected gold clusters reported in the literature.

    4. Cluster Formation during Expansion of Hot and Compressed Nuclear Matter Produced in Central Collisions of Au on Au at 250 A MeV

      NASA Astrophysics Data System (ADS)

      Petrovici, M.; Herrmann, N.; Legrand, I.; Gobbi, A.; Hildenbrand, K. D.; Reisdorf, W.; Buta, A.; Freifelder, R.; Jeong, S. C.; Krämer, M.; Moisa, D.; Schüll, D.; Simion, V.; Sodan, U.; Teh, K.; Wessels, J. P.; Wienold, T.; Alard, J. P.; Amouroux, V.; Basrak, Z.; Bastid, N.; Belyaev, I. M.; Berger, L.; Blaich, Th.; Boussange, S.; Čaplar, R.; Cerruti, C.; Cindro, N.; Coffin, J. P.; Donà, R.; Dupieux, P.; Erö, J.; Fintz, P.; Fodor, Z.; Fraysse, L.; Guillaume, G.; Hölbling, S.; Houari, A.; Jundt, F.; Kecskemeti, J.; Koncz, P.; Korchagin, Y.; Kotte, R.; Kuhn, C.; Ibnouzahir, M.; Lebedev, A.; Maguire, C.; Manko, V.; Mösner, J.; Montarou, G.; Montbel, I.; Morel, P.; Neubert, W.; Pelte, D.; Rami, F.; Ramillien, V.; Sadchikov, A.; Seres, Z.; Sikora, B.; Smolyankin, S.; Tezkratt, R.; Trzaska, M.; Vasiliev, M. A.; Wagner, P.; Wilhelmi, Z.; Wohlfarth, D.; Zhilin, A. V.

      1995-06-01

      Complete distributions of the light and intermediate mass fragments ( Z = 1-6) produced within the polar angular range 1∘<=Θlab<=30∘ in highly central collisions of 250 A MeV Au + Au are presented. The results of this measurement and a model analysis are used to study the expansion and clustering of the hot and compressed transient state formed in central collisions of such a heavy system. The influence of the initial conditions on the final observables is discussed.

    5. 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.

    6. Brightest cluster galaxies in the extended GMRT radio halo cluster sample. Radio properties and cluster dynamics

      NASA Astrophysics Data System (ADS)

      Kale, R.; Venturi, T.; Cassano, R.; Giacintucci, S.; Bardelli, S.; Dallacasa, D.; Zucca, E.

      2015-09-01

      Aims: First-ranked galaxies in clusters, usually referred to as brightest cluster galaxies (BCGs), show exceptional properties over the whole electromagnetic spectrum. They are the most massive elliptical galaxies and show the highest probability to be radio loud. Moreover, their special location at the centres of galaxy clusters raises the question of the role of the environment in shaping their radio properties. In the attempt to separate the effect of the galaxy mass and of the environment on their statistical radio properties, we investigate the possible dependence of the occurrence of radio loudness and of the fractional radio luminosity function on the dynamical state of the hosting cluster. Methods: We studied the radio properties of the BCGs in the Extended GMRT Radio Halo Survey (EGRHS), which consists of 65 clusters in the redshift range 0.2-0.4, with X-ray luminosity LX ≥ 5 × 1044 erg s-1, and quantitative information on their dynamical state from high-quality Chandra imaging. We obtained a statistical sample of 59 BCGs, which we divided into two classes, depending on whether the dynamical state of the host cluster was merging (M) or relaxed (R). Results: Of the 59 BCGs, 28 are radio loud and 31 are radio quiet. The radio-loud sources are favourably located in relaxed clusters (71%), while the reverse is true for the radio-quiet BCGs, which are mostly located in merging systems (81%). The fractional radio luminosity function for the BCGs in merging and relaxed clusters is different, and it is considerably higher for BCGs in relaxed clusters, where the total fraction of radio loudness reaches almost 90%, to be compared to the ~30% in merging clusters. For relaxed clusters, we found a positive correlation between the radio power of the BCGs and the strength of the cool core, consistent with previous studies on local samples. Conclusions: Our study suggests that the radio loudness of the BCGs strongly depends on the cluster dynamics; their fraction is

    7. The Radio Properties of Brightest Cluster Galaxies

      NASA Astrophysics Data System (ADS)

      Hogan, M. T.

      2014-09-01

      Energetic feedback from the Active Galactic Nucleus (AGN) of the Brightest Cluster Galaxy (BCG) is required to prevent catastrophic cooling of the intra-cluster medium (ICM) in galaxy clusters. Evidence for this is seen through the inflation of cavities in the ICM by AGN-launched, radio-emitting jets, and understanding this process is an active area of research. Radio observations play an integral role in this, as they trace the active stages of the feedback cycle. Understanding the radio properties of BCGs is therefore paramount for understanding both galaxy clusters and AGN feedback processes globally. Within this thesis, the BCGs in a large (>700) sample of X-ray selected clusters are studied. We observe these BCGs with a wide variety of facilities, building a census of their radio properties across a range of frequencies, timescales and angular resolutions. Radio spectral energy distributions (SEDs) are built for over 200 BCGs, and then decomposed into two components; a core, attributable to ongoing nuclear activity, and a non-core, attributable to historical accretion. Both components are not only more common, but also significantly more powerful in cool-core (CC) clusters than non-cool core (NCC) clusters. However, it is the presence of an active core that shows BCGs in CC clusters are constantly `on' - explaining how they regulate their environments over gigayear timescales. We observe 35 currently active BCGs at high (15-353 GHz) radio frequencies, and monitor their variability. Self-absorbed, active components are found to be common at high frequency. Little variability is seen on < year timescales, although longer term variation of ~10% annually over few-decade timescales is observed. Evidence is presented for a hitherto unseen component in BCG spectra that may be attributable to a naked Advection Dominated Accretion Flow (ADAF). The milli-arcsecond scale radio properties of 59 sources are studied, with a large range of morphologies recovered although no

    8. Unique Bonding Properties of the Au36(SR)24 Nanocluster with FCC-Like Core.

      PubMed

      Chevrier, Daniel M; Chatt, Amares; Zhang, Peng; Zeng, Chenjie; Jin, Rongchao

      2013-10-03

      The recent discovery on the total structure of Au36(SR)24, which was converted from biicosahedral Au38(SR)24, represents a surprising finding of a face-centered cubic (FCC)-like core structure in small gold-thiolate nanoclusters. Prior to this finding, the FCC feature was only expected for larger (nano)crystalline gold. Herein, we report results on the unique bonding properties of Au36(SR)24 that are associated with its FCC-like core structure. Temperature-dependent X-ray absorption spectroscopy (XAS) measurements at the Au L3-edge, in association with ab initio calculations, show that the local structure and electronic behavior of Au36(SR)24 are of more molecule-like nature, whereas its icosahedral counterparts such as Au38(SR)24 and Au25(SR)18 are more metal-like. Moreover, site-specific S K-edge XAS studies indicate that the bridging motif for Au36(SR)24 has different bonding behavior from the staple motif from Au38(SR)24. Our findings highlight the important role of "pseudo"-Au4 units within the FCC-like Au28 core in interpreting the bonding properties of Au36(SR)24 and suggest that FCC-like structure in gold thiolate nanoclusters should be treated differently from its bulk counterpart.

    9. 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.

    10. Atmospheric Ion Clusters: Properties and Size Distributions

      NASA Astrophysics Data System (ADS)

      D'Auria, R.; Turco, R. P.

      2002-12-01

      Ions are continuously generated in the atmosphere by the action of galactic cosmic radiation. Measured charge concentrations are of the order of 103 ~ {cm-3} throughout the troposphere, increasing to about 5 x 103 ~ {cm-3} in the lower stratosphere [Cole and Pierce, 1965; Paltridge, 1965, 1966]. The lifetimes of these ions are sufficient to allow substantial clustering with common trace constituents in air, including water, nitric and sulfuric acids, ammonia, and a variety of organic compounds [e.g., D'Auria and Turco, 2001 and references cited therein]. The populations of the resulting charged molecular clusters represent a pre-nucleation phase of particle formation, and in this regard comprise a key segment of the over-all nucleation size spectrum [e.g., Castleman and Tang, 1972]. It has been suggested that these clusters may catalyze certain heterogeneous reactions, and given their characteristic crystal-like structures may act as freezing nuclei for supercooled droplets. To investigate these possibilities, basic information on cluster thermodynamic properties and chemical kinetics is needed. Here, we present new results for several relevant atmospheric ion cluster families. In particular, predictions based on quantum mechanical simulations of cluster structure, and related thermodynamic parameters, are compared against laboratory data. We also describe a hybrid approach for modeling cluster sequences that combines laboratory measurements and quantum predictions with the classical liquid droplet (Thomson) model to treat a wider range of cluster sizes. Calculations of cluster mass distributions based on this hybrid model are illustrated, and the advantages and limitations of such an analysis are summarized. References: Castelman, A. W., Jr., and I. N. Tang, Role of small clusters in nucleation about ions, J. Chem. Phys., 57, 3629-3638, 1972. Cole, R. K., and E. T. Pierce, Electrification in the Earth's atmosphere for altitudes between 0 and 100 kilometers, J

    11. Phosphane-stabilized gold clusters: investigation of the stability of [Au(13)(PMe (2)Ph) (10)Cl (2)] (3+).

      PubMed

      Li, Jia; Wang, Shu-Guang

      2010-03-01

      The phosphane-stabilized gold cluster [Au(13)(PMe(2)Ph)(10)Cl(2)](3+) was studied using density functional theory. The extraordinary stability of the cluster has been attributed to the stability of the gold core and the protection conferred by ligands. Here, five stability factors of the gold core were explained and verified by investigating the Au (13) (5+) core in detail. Interactions between the gold core and several PR(3) ligands (R = Me, H, I, Br, Cl, F) were investigated according to the different electron donor abilities of each ligand; bonding energy between the ligand and the gold core was found to increase with the electronegativity of the R substituent. Furthermore, two other aspects of the ligands were clarified: how the ligand stabilizes the Au (13) (5+) core, and which kind of ligand provides the best stabilization for the cluster.

    12. Cluster Properties via Sunyaev-Zel Effect

      NASA Astrophysics Data System (ADS)

      Cooray, Asantha

      We will discuss the role played by the Sunyaev-Zel'dovich (SZ) effect in uderstanding the physical properties of the intracluster medium. While the SZ effect has been considered widely for its cosmological purposes when combined with multiwavelength observations the SZ effect data can also be used to understand the nature and evolution of the ICM including its thermal structure and the presence of nonthermal plasma. We also discuss future opportunities on this aspect involving observations from the planned South Pole Telescope Planck mission and various other attempts to image the SZ effect in galaxy clusters using wide-field bolometer arrays and other techniques. We will also explore the connection between gas in clusters and the general intergalactic medium and how one can use detailed wide-field SZ maps beyond those towards individual clusters to study such possibilities.

    13. Monodisperse semiconductors nano-clusters and their optoelectronic properties

      SciTech Connect

      Wang, Y.; Herron, N.

      1993-12-31

      This paper will discuss recent progress towards fabricating monodisperse CdS clusters (quantum dots) using controlled cluster fusion technique. The case of a single-size, {approximately}15-{angstrom} CdS cluster will be highlighted. Its spectroscopic, photophysical, and photoconductive properties will be discussed. The interesting effect of cluster size on the photoconductive properties will also be presented.

    14. Formation of H2O2 on Au20 and Au19Pd clusters: understanding the structure effect on the atomic level.

      PubMed

      Beletskaya, Anna V; Pichugina, Daria A; Shestakov, Alexander F; Kuz'menko, Nikolay E

      2013-08-08

      Supported gold nanoparticles are promising catalysts for production of H2O2 from O2 and H2. Size, structure, and palladium doping effects play the key role in activity and selectivity of a gold catalyst. We performed a study of the influence of Au20 and Au19Pd structure features on the main steps of H2O2 formation on the atomic level, using the DFT/PBE approach with relativistic all electron basis set. The top, edge, and facet atoms of the tetrahedral Au20 cluster as well as a palladium atom of Au19Pd located on the top, edge, and facet of a tetrahedron have been considered as active sites of steps involved in H2O2 synthesis. The thermodynamic and kinetic data including Gibbs free energies and the activation Gibbs free energies were calculated for the steps determining the formation of H2O2 (H(s) + OOH(s) = H2O(2(s)), H2O(2(s)) = H2O(2(g))) and for one step decreasing the selectivity (H2O(2(s)) = OH(s) + OH(s)). Gold tends to have low activity and high selectivity in H2O2 synthesis regardless of the structure of active site. Low coordinated palladium atoms promote H2O2 formation as well as its dissociation. Pd on a facet of a cluster facilitates H2O2 production with high activity and selectivity.

    15. Prediction of unusual stable ordered structures of Au-Pd alloys via a first-principles cluster expansion

      SciTech Connect

      Barabash, Sergey V.; Blum, Volker; Zunger, Alex; Mueller, Stefan

      2006-07-15

      We describe an iterative procedure which yields an accurate cluster expansion for Au-Pd using only a limited number of ab initio formation enthalpies. Our procedure addresses two problems: (a) given the local-density-approximation (LDA) formation energies for a fixed set of structures, it finds the pair and many-body cluster interactions best able to predict the formation energies of new structures, and (b) given such pair and many-body interactions, it augments the LDA set of 'input structures' by identifying additional structures that carry most information not yet included in the 'input'. Neither step can be done by intuitive selection. Using methods including genetic algorithm and statistical analysis to iteratively solve these problems, we build a cluster expansion able to predict the formation enthalpy of an arbitrary fcc lattice configuration with precision comparable to that of ab initio calculations themselves. We also study possible competing non-fcc structures of Au-Pd, using the results of a 'data mining' study. We then address the unresolved problem of bulk ordering in Au-Pd. Experimentally, the phase diagram of Au-Pd shows only a disordered solid solution. Even though the mixing enthalpy is negative, implying ordering, no ordered bulk phases have been detected. Thin film growth shows L1{sub 2}-ordered structures with composition Au{sub 3}Pd and AuPd{sub 3} and L1{sub 0} structure with composition AuPd. We find that (i) all the ground states of Au-Pd are fcc structures; (ii) the low-T ordered states of bulk Au-Pd are different from those observed experimentally in thin films; specifically, the ordered bulk Au{sub 3}Pd is stable in D0{sub 23} structure and and AuPd in chalcopyritelike Au{sub 2}Pd{sub 2} (201) superlattice structure, whereas thin films are seen in the L1{sub 2} and L1{sub 0} structures; (iii) AuPd{sub 3} L1{sub 2} is stable and does not phase separate, contrary to the suggestions of an earlier investigation; (iv) at compositions around

    16. Monodisperse Au11 Clusters Prepared by Soft Landing of Mass Selected Ions

      SciTech Connect

      Johnson, Grant E.; Wang, Chong M.; Priest, Thomas A.; Laskin, Julia

      2011-11-01

      Preparation of clean monodisperse samples of clusters and nanoparticles for characterization using cutting-edge analytical techniques is essential to understanding their size-dependent properties. Herein, we report a general method for the preparation of high surface coverage samples of monodisperse clusters containing an exact number of atoms. Polydisperse solutions of diphosphine-capped gold clusters were produced by reduction synthesis. Electrospray ionization was used to introduce the clusters into the gas phase where they were filtered by mass-tocharge ratio allowing clusters of a selected size to be deposited onto carbon coated copper grids at well controlled kinetic energies. Scanning transmission electron microscopy (STEM) analysis of the soft landed clusters confirms their monodispersity and high coverage on the substrate. The soft landing approach may be extended to other materials compatible with an array of available ionization techniques and, therefore, has widespread utility as a means for controlled preparation of monodisperse samples of nanoparticles and clusters for analysis by transmission electron microscopy (TEM)

    17. Monodisperse Au11 clusters prepared by soft landing of mass selected ions.

      PubMed

      Johnson, Grant E; Wang, Chongmin; Priest, Thomas; Laskin, Julia

      2011-11-01

      Preparation of clean monodisperse samples of clusters and nanoparticles for characterization using cutting-edge analytical techniques is essential to understanding their size-dependent properties. Herein, we report a general method for the preparation of high surface coverage samples of monodisperse clusters containing an exact number of atoms. Polydisperse solutions of diphosphine-capped gold clusters were produced by reduction synthesis. Electrospray ionization was used to introduce the clusters into the gas phase where they were filtered by mass-to-charge ratio allowing clusters of a selected size to be deposited onto carbon coated copper grids at well controlled kinetic energies. Scanning transmission electron microscopy (STEM) analysis of the soft landed clusters confirms their monodispersity and high coverage on the substrate. The soft landing approach may be extended to other materials compatible with an array of available ionization techniques and, therefore, has widespread utility as a means for controlled preparation of monodisperse samples of nanoparticles and clusters for analysis by transmission electron microscopy (TEM).

    18. Charge-Transfer Effects in Ligand Exchange Reactions of Au25 Monolayer-Protected Clusters.

      PubMed

      Carducci, Tessa M; Blackwell, Raymond E; Murray, Royce W

      2015-04-16

      Reported here are second-order rate constants of associative ligand exchanges of Au25L18 nanoparticles (L = phenylethanethiolate) of various charge states, measured by proton nuclear magnetic resonance at room temperature and below. Differences in second-order rate constants (M(-1) s(-1)) of ligand exchange (positive clusters ∼1.9 × 10(-5) versus negative ones ∼1.2 × 10(-4)) show that electron depletion retards ligand exchange. The ordering of rate constants between the ligands benzeneselenol > 4-bromobenzene thiol > benzenethiol reveals that exchange is accelerated by higher acidity and/or electron donation capability of the incoming ligand. Together, these observations indicate that partial charge transfer occurs between the nanoparticle and ligand during the exchange and that this is a rate-determining effect in the process.

    19. The wet synthesis and quantification of ligand-free sub-nanometric Au clusters in solid matrices.

      PubMed

      Oliver-Meseguer, Judit; Dominguez, Irene; Gavara, Rafael; Doménech-Carbó, Antonio; González-Calbet, J M; Leyva-Pérez, Antonio; Corma, Avelino

      2017-01-17

      The synthesis of ligand-free sub-nanometric metal clusters on a large scale suffers typically from very low yields (<5% yield) and needs very high dilutions. Here we show that Au clusters can be prepared with ethylene-vinyl alcohol copolymers (EVOH), charcoal, and different metal oxides (CeO2, Al2O3, TiO2 and ZnO) in >15% yields, as unambiguously determined using a very simple and extremely sensitive analytical reaction test.

    20. Semiconducting Properties of Swift Au Ion-Irradiated ZnO Thin Films at Room Temperature

      NASA Astrophysics Data System (ADS)

      Kwon, Sera; Park, Hyun-Woo; Chung, Kwun-Bum

      2017-02-01

      The semiconducting properties of Au ion-irradiated ZnO thin films were investigated as a function of ion irradiation dose at room temperature. The Au ion irradiation was conducted with acceleration energy of 130 MeV in the ion dose range from 1 × 1011 to 5 × 1012 ions/cm2. The physical properties showed no change regardless of the Au ion irradiation dose; however, the electrical properties of Au ion-irradiated ZnO thin films changed, depending on the Au ion irradiation dose. The electronic structure drastically changed with the evolution of hybridized molecular orbital structure for the conduction band and band edge states below the conduction band. These remarkable changes in electronic structure correlate with changes in electrical properties, such as carrier concentration and mobility.

    1. Structural properties of small rhodium clusters

      SciTech Connect

      Soon, Yee Yeen; Yoon, Tiem Leong; Lim, Thong Leng

      2015-04-24

      We report a systematic study of the structural properties of rhodium clusters at the atomistic level. A novel global-minimum search algorithm, known as parallel tempering multicanonical basin hopping plus genetic algorithm (PTMBHGA), is used to obtain the geometrical structures with lowest minima at the semi-empirical level where Gupta potential is used to describe the atomic interaction among the rhodium atoms. These structures are then re-optimized at the density functional theory (DFT) level with exchange-correlation energy approximated by Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA). The structures are optimized for different spin multiplicities. The ones with lowest energies will be taken as ground-state structures. In most cases, we observe only minor changes in the geometry and bond length of the clusters as a result of DFT-level re-optimization. Only in some limited cases, the initial geometries obtained from the PTMBHGA are modified by the re-optimization. The variation of structural properties, such as ground-state geometry, symmetry and binding energy, with respect to the cluster size is studied and agreed well with other results available in the literature.

    2. Electrochemical anion sensing using electrodes chemically modified with Au(I)-Cu(I) heterotrimetallic alkynyl cluster complexes containing ferrocenyl groups.

      PubMed

      Doménech, Antonio; Koshevoy, Igor O; Montoya, Noemí; Pakkanen, Tapani A

      2010-07-01

      A novel family of electrochemical anion sensors operating in aqueous media, based on the heterometallic Au(I)-Cu(I) [{Au(3)Cu(2)(C(2)R)(6)}Au(3)(PPh(2)C(6)H(4)PPh(2))(3)](PF(6))(2) (L1, R = Fc; L2, R = C(6)H(4)Fc) alkynyl cluster complexes, is presented. Upon attachment to graphite and gold electrodes, these compounds exhibit a well-defined, essentially reversible, solid-state electrochemistry in contact with aqueous media, based on ferrocenyl-centered oxidation processes involving anion insertion, leading to distinctive pH-independent electrochemical responses for fluoride, chloride, bromide, perchlorate, bicarbonate, carbonate, phosphate, hydrogen phosphate, dihydrogen phosphate, and nitrate anions. Cluster-modified electrodes can be used as potentiometric sensors as a result of the reversible, diffusion-controlled electrochemistry obtained for the anion-assisted electrochemical oxidation of L1 and L2.

    3. Comparison of photoluminescence properties of HSA-protected and BSA-protected Au25 nanoclusters

      NASA Astrophysics Data System (ADS)

      Tsukamoto, Masato; Kawasaki, Hideya; Saitoh, Tadashi; Inada, Mitsuru; Kansai Univ. Collaboration

      Gold nanoclusters (NCs) have attracted great interest for a wide range of applications. In particular, red light-emitting Au25 NCs have been prepared with various biological ligands. It has been shown that Au25 NCs have Au13-core/6Au2(SR)3-semiring structure. The red luminescence thought to be originated from both core (670 nm) and semiring (625 nm). It is important to reveal a structure of Au25 NCs to facilitate the progress of applications. However, the precise structure of Au25 NCs has not been clarified. There is a possibility of obtaining structural information about Au25 NCs to compare optical properties of the NCs that protected by slightly different molecules. Bovine and human serum albumin (BSA, HSA) are suitable one for this purpose. It has been suggested that rich tyrosine and cysteine residues in these molecules are important to produce the thiolate-protected Au NCs. If Au25 NCs have core/shell structure, only the luminescence of the semiring will be affected by the difference of the albumin molecules. We carefully compared PL characteristics of BSA- and HSA- protected Au25 NCs. As a result, there was no difference in the PL at 670 nm (core), while differences were observed in the PL at 625 nm (semiring). The results support that Au25 NCs have core/semiring structure.

    4. Microstructural Evolution and Mechanical Properties in (AuSn)eut-Cu Interconnections

      NASA Astrophysics Data System (ADS)

      Dong, Hongqun; Vuorinen, Vesa; Laurila, Tomi; Paulasto-Kröckel, Mervi

      2016-10-01

      The interfacial reactions between the widely employed solder Au-20wt.%Sn and the common contact metallizations (e.g. Ni, Cu and Pt) are normally complex and not well determined. In order to identify the proper contactor for Au-20wt.%Sn solder, the present study focuses on (1) rationalizing the interfacial reaction mechanisms of Au-20wt.%Sn|Cu as well as (2) measuring the mechanical properties of individual intermetallics formed at the interface. The evolution of interfacial reaction products were rationalized by using the experimental results in combination with the calculated Au-Cu-Sn phase diagram information. It was found that the growth of the AuCu interfacial intermetallic layer was diffusion-controlled. The diffusion path of Au-20wt.%Sn|Cu at 150°C was proposed. The hardness and indentation modulus of the interfacial reaction products were measured using nanoindentation tests. The results revealed a significant influence of the Cu solubility on the mechanical properties of (Au,Cu)Sn and (Au,Cu)5Sn, i.e. their hardness and contact modulus increased with the increase in the amount of Cu. Furthermore, results obtained here for the Au-20wt.%Sn|Cu joints were compared to those from Au-20wt.%Sn|Ni in order to assess the similarities and differences between these widely used interconnection metallization systems.

    5. Self-assembled monolayer of organic iodine on a Au surface for attachment of redox-active metal clusters.

      PubMed

      Yu, Ying; Dubey, Manish; Bernasek, Steven L; Dismukes, G Charles

      2007-07-17

      The attachment of a bifunctional iodo-organo-phosphinate compound to gold (Au) surfaces via chemisorption of the iodine atom is described and used to chelate a redox-active metal cluster via the phosphinate group. XPS, AFM, and electrochemical measurements show that (4-iodo-phenyl)phenyl phosphinic acid (IPPA) forms a tightly bound self-assembled monolayer (SAM) on Au surfaces. The surface coverage of an IPPA monolayer on Au was quantified by an electrochemical method and found to be 0.40 +/- 0.03 nmol/cm2, roughly corresponding to 0.4 monolayers. We show that the Au/IPPA SAM, but not the underivatized Au, adsorbs Mn4O4(Ph2PO2)6 from solution by a phosphinate exchange reaction to yield Au/IPPA/Mn4O4(Ph2PO2)5 SAM. The resulting SAM is firmly bound and not removed by sonication, as confirmed by manganese XPS (Mn 2p1/2) and by AFM. Electrochemistry confirms that Mn4O4(Ph2PO2)6 is anchored on the Au/IPPA surface and that redox chemistry can be mediated between the electrode and the surface-attached complex. Mn4O4(Ph2PO2)6 contains the reactive Mn4O46+ cubane core, a redox-active bioinspired catalyst.

    6. Surface enhanced vibrational spectroscopy and first-principles study of L-cysteine adsorption on noble trimetallic Au/Pt@Rh clusters.

      PubMed

      Loganathan, B; Chandraboss, V L; Senthilvelan, S; Karthikeyan, B

      2015-09-07

      The Rh shell of the Au/Pt/Rh trimetallic nanoparticles induces a wide variety of interesting surface reactions by allowing the adsorption of amino acids like L-cysteine (L-Cys). We present a snapshot of theoretical and experimental investigation of L-Cys adsorption on the surface of noble trimetallic Au/Pt@Rh colloidal nanocomposites. Density functional theoretical (DFT) investigations of L-Cys interaction with the Rhodium (Rh) shell of a trimetallic Au/Pt@Rh cluster in terms of geometry, binding energy (E(B)), binding site, energy gap (E(g)), electronic and spectral properties have been performed. L-Cys establishes a strong interaction with the Rh shell. It binds to Rh by the S1-site, which makes a stable L-Cys-Rh surface complex. DFT can be taken as a valuable tool to assign the vibrational spectra of the adsorption of L-Cys on trimetallic Au/Pt@Rh colloidal nanocomposites and mono-metallic Rh nanoparticles. Surface-enhanced infrared spectroscopy (SEIRS) with L-Cys on a Rh6 cluster surface has been simulated for the first time. Experimental information on the L-Cys-Rh surface complex is included to examine the interaction. The experimental spectral observations are in good agreement with the simulated DFT results. Characterization of the synthesized trimetallic Au/Pt@Rh colloidal nanocomposites has been done by high-resolution transmission electron microscopy (HR-TEM) with selected area electron diffraction (SAED) pattern, energy dispersive X-ray (EDX) spectroscopy, dynamic light scattering (DLS) measurements, zeta potential, zeta deviation analysis and UV-visible (UV-Vis) spectroscopic studies.

    7. Electronic coupling between ligand and core energy states in dithiolate-monothiolate stabilized Au clusters.

      PubMed

      Ahuja, Tarushee; Wang, Dengchao; Tang, Zhenghua; Robinson, Donald A; Padelford, Jonathan W; Wang, Gangli

      2015-07-15

      Electron transfer activities of metal clusters are fundamentally significant and have promising potential in catalysis, charge or energy storage, sensing, biomedicine and other applications. Strong resonance coupling between the metal core energy states and the ligand molecular orbitals has not been established experimentally, albeit exciting progress has been achieved in the composition and structure determination of these types of nanomaterials recently. In this report, the coupling between core and ligand energy states is demonstrated by the rich electron transfer activities of Au130 clusters. Quantized electron transfers to the core and multi-electron transfers involving the durene-dithiolate ligands were observed at lower and higher potentials, respectively, in voltammetric studies. After a facile multi-electron oxidation from +1.34 to +1.40 V, several reversal reduction processes at more negative potentials, i.e. +0.91 V, +0.18 V and -0.34 V, were observed in an electrochemically irreversible fashion or with sluggish kinetics. The number of electrons and the shifts of the respective reduction potentials in the reversal process were attributed to the electronic coupling or energy relaxation processes. The electron transfer activities and subsequent relaxation processes are drastically reduced at lower temperatures. The time- and temperature-dependent relaxation, involving multiple energy states in the reversal reduction processes upon the oxidation of ligands, reveals the coupling between core and ligand energy states.

    8. Elevated Temperature Creep Properties of Conventional 50Au-50Cu and 47Au 50Cu-3Ni Braze Alloys

      SciTech Connect

      STEPHENS JR.,JOHN J.; SCHMALE,DAVID T.

      2000-12-18

      The elevated temperature creep properties of the 50Au-50Cu wt% and 47Au-50Cu-3Ni braze alloys have been evaluated over the temperature range 250-850 C. At elevated temperatures, i.e., 450-850 C, both alloys were tested in the annealed condition (2 hrs. 750 C/water quenched). The minimum strain rate properties over this temperature range are well fit by the Garofalo sinh equation. At lower temperatures (250 and 350 C), power law equations were found to characterize the data for both alloys. For samples held long periods of time at 375 C (96 hrs.) and slowly cooled to room temperature, an ordering reaction was observed. For the case of the 50Au-50Cu braze alloy, the stress necessary to reach the same, strain rate increased by about 15% above the baseline data. The limited data for ordered 47Au-50Cu-3Ni alloy reflected a,smaller strength increase. However, the sluggishness of this ordering reaction in both alloys does not appear to pose a problem for braze joints cooled at reasonable rates following brazing.

    9. Electrochemical Synthesis and Catalytic Properties of Encapsulated Metal Clusters within Zeolitic Imidazolate Frameworks.

      PubMed

      Wang, Pengyuan; Liu, Jia; Liu, Chuanfang; Zheng, Bin; Zou, Xiaoqin; Jia, Mingjun; Zhu, Guangshan

      2016-11-07

      It is very interesting and also a big challenge to encapsulate metal clusters within microporous solids to expand their application diversity. For this target, herein, we present an electrochemical synthesis strategy for the encapsulation of noble metals (Au, Pd, Pt) within ZIF-8 cavities. In this method, metal precursors of AuCl4(2-) , PtCl6(2-) , and PdCl4(2-) are introduced into ZIF-8 crystals during the concurrent crystallization of ZIF-8 at the anode. As a consequence, very small metal clusters with sizes around 1.2 nm are obtained within ZIF-8 crystals after hydrogen reduction; these clusters exhibit high thermal stability, as evident from the good maintenance of their original sizes after a high-temperature test. The catalytic properties of the encapsulated metal clusters within ZIF-8 are evaluated for CO oxidations. Because of the small pore window of ZIF-8 (0.34 nm) and the confinement effect of small pores, about 80 % of the metal clusters (fractions of 0.74, 0.77, and 0.75 for Au, Pt, and Pd in ZIF-8, respectively) retain their catalytic activity after exposure to the organosulfur poison thiophene (0.46 nm), which is in contrast to their counterparts (fractions of 0.22, 0.25, and 0.20 for Au, Pt, and Pd on the SiO2 support). The excellent performances of metal clusters encapsulated within ZIF-8 crystals give new opportunities for catalytic reactions.

    10. An isothermal-isobaric Langevin thermostat for simulating nanoparticles under pressure: application to Au clusters.

      PubMed

      Kohanoff, Jorge; Caro, Alfredo; Finnis, Michael W

      2005-09-05

      We present a method for simulating clusters or molecules subjected to an external pressure, which is exerted by a pressure-transmitting medium. It is based on the canonical Langevin thermostat, but extended in such a way that the Brownian forces are allowed to operate only from the region exterior to the cluster. We show that the frictional force of the Langevin thermostat is linked to the pressure of the reservoir in a unique way, and that this property manifests itself when the particle it acts upon is not pointlike but has finite dimensions. By choosing appropriately the strength of the random forces and the friction coefficient, both temperature and pressure can be controlled independently. We illustrate the capabilities of this new method by calculating the compressibility of small gold clusters under pressure.

    11. A Controlled Route to a Luminescent 3 d(10) -5 d(10) Sulfido Cluster Containing Unique AuCu2 (μ3 -S) Motifs.

      PubMed

      Polgar, Alexander M; Khadka, Chhatra B; Azizpoor Fard, Mahmood; Nikkel, Brian; O'Donnell, Terrence; Neumann, Tobias; Lahring, Kiana; Thompson, Kyle; Cadogan, Carolyn; Weigend, Florian; Corrigan, John F

      2016-12-19

      The first examples of gold(I) trimethylsilylchalcogenolate complexes were synthesized and their reactivity showcased in the preparation of a novel gold-copper-sulfur cluster [Au4 Cu4 S4 (dppm)2 ] (dppm=bis(diphenylphosphino)methane). The unprecedented structural chemistry of this compound gives rise to interesting optoelectronic properties, including long-lived orange luminescence in the solid state. Through time-dependent density functional theory calculations, this emission is shown to originate from ligand-to-metal charge transfer facilitated by Au⋅⋅⋅Cu metallophilic bonding.

    12. Influence of hydrofluoric acid treatment on electroless deposition of Au clusters.

      PubMed

      Milazzo, Rachela G; Mio, Antonio M; D'Arrigo, Giuseppe; Smecca, Emanuele; Alberti, Alessandra; Fisichella, Gabriele; Giannazzo, Filippo; Spinella, Corrado; Rimini, Emanuele

      2017-01-01

      The morphology of gold nanoparticles (AuNPs) deposited on a (100) silicon wafer by simple immersion in a solution containing a metal salt and hydrofluoric acid (HF) is altered by HF treatment both before and after deposition. The gold clusters are characterized by the presence of flat regions and quasispherical particles consistent with the layer-by-layer or island growth modes, respectively. The cleaning procedure, including HF immersion prior to deposition, affects the predominantly occurring gold structures. Flat regions, which are of a few tens of nanometers long, are present after immersion for 10 s. The three-dimensional (3D) clusters are formed after a cleaning procedure of 4 min, which results in a large amount of spherical particles with a diameter of ≈15 nm and in a small percentage of residual square layers of a few nanometers in length. The samples were also treated with HF after the deposition and we found out a general thickening of flat regions, as revealed by TEM and AFM analysis. This result is in contrast to the coalescence observed in similar experiments performed with Ag. It is suggested that the HF dissolves the silicon oxide layer formed on top of the thin flat clusters and promotes the partial atomic rearrangement of the layered gold atoms, driven by a reduction of the surface energy. The X-ray diffraction investigation indicated changes in the crystalline orientation of the flat regions, which partially lose their initially heteroepitaxial relationship with the substrate. A postdeposition HF treatment for almost 70 s has nearly the same effect of long duration, high temperature annealing. The process presented herein could be beneficial to change the spectral response of nanoparticle arrays and to improve the conversion efficiency of hybrid photovoltaic devices.

    13. Influence of hydrofluoric acid treatment on electroless deposition of Au clusters

      PubMed Central

      Mio, Antonio M; D’Arrigo, Giuseppe; Smecca, Emanuele; Alberti, Alessandra; Fisichella, Gabriele; Giannazzo, Filippo; Spinella, Corrado; Rimini, Emanuele

      2017-01-01

      The morphology of gold nanoparticles (AuNPs) deposited on a (100) silicon wafer by simple immersion in a solution containing a metal salt and hydrofluoric acid (HF) is altered by HF treatment both before and after deposition. The gold clusters are characterized by the presence of flat regions and quasispherical particles consistent with the layer-by-layer or island growth modes, respectively. The cleaning procedure, including HF immersion prior to deposition, affects the predominantly occurring gold structures. Flat regions, which are of a few tens of nanometers long, are present after immersion for 10 s. The three-dimensional (3D) clusters are formed after a cleaning procedure of 4 min, which results in a large amount of spherical particles with a diameter of ≈15 nm and in a small percentage of residual square layers of a few nanometers in length. The samples were also treated with HF after the deposition and we found out a general thickening of flat regions, as revealed by TEM and AFM analysis. This result is in contrast to the coalescence observed in similar experiments performed with Ag. It is suggested that the HF dissolves the silicon oxide layer formed on top of the thin flat clusters and promotes the partial atomic rearrangement of the layered gold atoms, driven by a reduction of the surface energy. The X-ray diffraction investigation indicated changes in the crystalline orientation of the flat regions, which partially lose their initially heteroepitaxial relationship with the substrate. A postdeposition HF treatment for almost 70 s has nearly the same effect of long duration, high temperature annealing. The process presented herein could be beneficial to change the spectral response of nanoparticle arrays and to improve the conversion efficiency of hybrid photovoltaic devices. PMID:28243555

    14. Water-soluble Au25(Capt)18 nanoclusters: synthesis, thermal stability, and optical properties

      NASA Astrophysics Data System (ADS)

      Kumar, Santosh; Jin, Rongchao

      2012-06-01

      This work was motivated by the unsatisfactory stability of Au25(SG)18 in solution under thermal conditions (e.g. 70-90 °C for DNA melting). Thus, we searched for a better, water-soluble thiol ligand. Herein, we report a one-pot synthesis and investigation of the stability and optical properties of captopril (abbreviated Capt)-protected Au25(Capt)18 nanoclusters. The Au25(Capt)18 (anionic, counterion: Na+) nanoclusters were formed via size focusing under ambient conditions. Significantly, Au25(Capt)18 nanoclusters exhibit largely improved thermal stability compared to the glutathione (HSG) capped Au25(SG)18. Both Au25(Capt)18 and Au25(SG)18 nanoclusters show fluorescence centered at ~700 nm. The chiral ligands (Capt, SG, as well as chirally modified phenylethanethiol (PET*)) give rise to distinct chiroptical features. The high thermal stability and distinct optical properties of Au25(Capt)18 nanoclusters render this material quite promising for biological applications.This work was motivated by the unsatisfactory stability of Au25(SG)18 in solution under thermal conditions (e.g. 70-90 °C for DNA melting). Thus, we searched for a better, water-soluble thiol ligand. Herein, we report a one-pot synthesis and investigation of the stability and optical properties of captopril (abbreviated Capt)-protected Au25(Capt)18 nanoclusters. The Au25(Capt)18 (anionic, counterion: Na+) nanoclusters were formed via size focusing under ambient conditions. Significantly, Au25(Capt)18 nanoclusters exhibit largely improved thermal stability compared to the glutathione (HSG) capped Au25(SG)18. Both Au25(Capt)18 and Au25(SG)18 nanoclusters show fluorescence centered at ~700 nm. The chiral ligands (Capt, SG, as well as chirally modified phenylethanethiol (PET*)) give rise to distinct chiroptical features. The high thermal stability and distinct optical properties of Au25(Capt)18 nanoclusters render this material quite promising for biological applications. Electronic supplementary

    15. Metal clusters and nanoparticles in dielectric matrices: Formation and optical properties

      NASA Astrophysics Data System (ADS)

      Gladskikh, I. A.; Vartanyan, T. A.

      2016-12-01

      The optical properties of thin dielectric films with metal inclusions and their dependence on thermal and laser annealing are studied experimentally. Metal clusters (Ag, Au, and Cu) in dielectric materials (Al2O3 and SiO2) are obtained by simultaneous vacuum deposition of metal and dielectric on the surface of a corresponding dielectric substrate (sapphire and quartz). It is shown that, depending on the deposited dielectric material, on the weight ratio of deposited metal and dielectric, and on the subsequent thermal treatment, one can obtain different metal structures, from clusters with a small number of atoms to complex dendritic plasmonic structures.

    16. Structural and electronic properties of uranium-encapsulated Au14 cage

      PubMed Central

      Gao, Yang; Dai, Xing; Kang, Seung-gu; Jimenez-Cruz, Camilo Andres; Xin, Minsi; Meng, Yan; Han, Jie; Wang, Zhigang; Zhou, Ruhong

      2014-01-01

      The structural properties of the uranium-encapsulated nano-cage U@Au14 are predicted using density functional theory. The presence of the uranium atom makes the Au14 structure more stable than the empty Au14-cage, with a triplet ground electronic state for U@Au14. Analysis of the electronic structure shows that the two frontier single-occupied molecular orbital electrons of U@Au14 mainly originate from the 5f shell of the U atom after charge transfer. Meanwhile, the bonding orbitals and charge population indicate that the designed U@Au14 nano-cage structure is stabilized by ionocovalent interactions. The current findings provide theoretical basis for future syntheses and further study of actinide doped gold nanoclusters, which might subsequently facilitate applications of such structure in radio-labeling, nanodrug carrier and other biomedical applications. PMID:25069968

    17. Three-Dimensional Assignment of the Structures of Atomic Clusters: an Example of Au8M (M=Si, Ge, Sn) Anion Clusters

      PubMed Central

      Liu, Yi-Rong; Huang, Teng; Gai, Yan-Bo; Zhang, Yang; Feng, Ya-Juan; Huang, Wei

      2015-01-01

      Identification of different isomer structures of atomic and molecular clusters has long been a challenging task in the field of cluster science. Here we present a three-dimensional (3D) assignment method, combining the energy (1D) and simulated (2D) spectra to assure the assignment of the global minimum structure. This method is more accurate and convenient than traditional methods, which only consider the total energy and first vertical detachment energies (VDEs) of anion clusters. There are two prerequisites when the 3D assignment method is ultilized. First, a reliable global minimum search algorithm is necessary to explore enough valleys on the potential energy surface. Second, trustworthy simulated spectra are necessary, that is to say, spectra that are in quantitative agreement. In this paper, we demonstrate the validity of the 3D assignment method using Au8M− (M = Si, Ge, Sn) systems. Results from this study indicate that the global minimum structures of Au8Ge− and Au8Sn− clusters are different from those described in previous studies. PMID:26631620

    18. Coupling between magnetic and optical properties of stable Au-Fe solid solution nanoparticles

      NASA Astrophysics Data System (ADS)

      de Julián Fernández, C.; Mattei, G.; Paz, E.; Novak, R. L.; Cavigli, L.; Bogani, L.; Palomares, F. J.; Mazzoldi, P.; Caneschi, A.

      2010-04-01

      Au-Fe nanoparticles constitute one of the simplest prototypes of a multifunctional nanomaterial that can exhibit both magnetic and optical (plasmonic) properties. This solid solution, not feasible in the bulk phase diagram in thermal equilibrium, can be formed as a nanostructure by out-of-equilibrium processes. Here, the novel magnetic, optical and magneto-optical properties of ion-implanted Au-Fe solid solution nanoparticles dispersed in a SiO2 matrix are investigated and correlated. The surface plasmon resonance of the Au-Fe nanoparticles with almost equicomposition is strongly damped when compared to pure Au and to Au-rich Au-Fe nanoparticles. In all cases, the Au atoms are magnetically polarized, as measured by x-ray magnetic circular dichroism, and ferromagnetically coupled with Fe atoms. Although the chemical stability of Au-Fe nanoparticles is larger than that of Fe nanoparticles, both the magnetic moment per Fe atom and the order temperature are smaller. These results suggest that electronic and magnetic properties are more influenced by the hybridization of the electronic bands in the Au-Fe solid solution than by size effects. On the other hand, the magneto-optical transitions allowed in the vis-nIR spectral regions are very similar. In addition, we also observe, after studying the properties of thermally treated samples, that the Au-Fe alloy is stabilized, not by surface effects, but by the combination of the out-of-equilibrium nature of the ion implantation technique and by changes in the properties due to size effects.

    19. Au on MgAl2O4 spinels: The effect of support surface properties in glycerol oxidation

      SciTech Connect

      Villa, Alberto; Gaiassi, Aureliano; Rossetti, Ilenia; Bianchi, Claudia; van Benthem, Klaus; Veith, Gabriel M; Prati, Laura

      2010-01-01

      Here we investigated the properties of Au nanoparticles, prepared via three different techniques and supported on three different MgAl2O4 spinels. The surface composition and area of the spinel plays an important role in determining the selectivity of the catalyst in the selective oxidation of glycerol. it was found that aluminum rich surfaces enhance the C-C bond cleavage reaction for large gold particles which is opposite of what is normally observed for large clusters which typically show no C-C cleavage. We also report that similarly sized AuNPs on the different MgAl2O4 spinels with the same surface Al/Mg ratio, show a similar selectivity; however activity depends on surface area.

    20. Enhanced electron field emission properties of conducting ultrananocrystalline diamond films after Cu and Au ion implantation.

      PubMed

      Sankaran, Kamatchi Jothiramalingam; Chen, Huang-Chin; Panda, Kalpataru; Sundaravel, Balakrishnan; Lee, Chi-Young; Tai, Nyan-Hwa; Lin, I-Nan

      2014-04-09

      The effects of Cu and Au ion implantation on the structural and electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films were investigated. High electrical conductivity of 186 (Ω•cm)(-1) and enhanced EFE properties with low turn-on field of 4.5 V/μm and high EFE current density of 6.70 mA/cm(2) have been detected for Au-ion implanted UNCD (Au-UNCD) films that are superior to those of Cu-ion implanted UNCD (Cu-UNCD) ones. Transmission electron microscopic investigations revealed that Au-ion implantation induced a larger proportion of nanographitic phases at the grain boundaries for the Au-UNCD films in addition to the formation of uniformly distributed spherically shaped Au nanoparticles. In contrast, for Cu-UNCD films, plate-like Cu nanoparticles arranged in the row-like pattern were formed, and only a smaller proportion of nanographite phases along the grain boundaries was induced. From current imaging tunneling spectroscopy and local current-voltage curves of scanning tunneling spectroscopic measurements, it is observed that the electrons are dominantly emitted from the grain boundaries. Consequently, the presence of nanosized Au particles and the induction of abundant nanographitic phases in the grain boundaries of Au-UNCD films are believed to be the authentic factors, ensuing in high electrical conductivity and outstanding EFE properties of the films.

    1. Site Preference in Multimetallic Nanoclusters: Incorporation of Alkali Metal Ions or Copper Atoms into the Alkynyl-Protected Body-Centered Cubic Cluster [Au7 Ag8 (C≡C(t) Bu)12 ]().

      PubMed

      Wang, Yu; Su, Haifeng; Ren, Liting; Malola, Sami; Lin, Shuichao; Teo, Boon K; Häkkinen, Hannu; Zheng, Nanfeng

      2016-11-21

      The synthesis, structure, substitution chemistry, and optical properties of the gold-centered cubic monocationic cluster [Au@Ag8 @Au6 (C≡C(t) Bu)12 ](+) are reported. The metal framework of this cluster can be described as a fragment of a body-centered cubic (bcc) lattice with the silver and gold atoms occupying the vertices and the body center of the cube, respectively. The incorporation of alkali metal atoms gave rise to [Mn Ag8-n Au7 (C≡C(t) Bu)12 ](+) clusters (n=1 for M=Na, K, Rb, Cs and n=2 for M=K, Rb), with the alkali metal ion(s) presumably occupying the vertex site(s), whereas the incorporation of copper atoms produced [Cun Ag8 Au7-n (C≡C(t) Bu)12 ](+) clusters (n=1-6), with the Cu atom(s) presumably occupying the capping site(s). The parent cluster exhibited strong emission in the near-IR region (λmax =818 nm) with a quantum yield of 2 % upon excitation at λ=482 nm. Its photoluminescence was quenched upon substitution with a Na(+) ion. DFT calculations confirmed the superatom characteristics of the title compound and the sodium-substituted derivatives.

    2. Role of Au in the growth and nanoscale optical properties of ZnO nanowires

      SciTech Connect

      Brewster, M.; Zhou, Xiang; Lim, S. K.; Gradecak, S.

      2011-03-17

      Metallic nanoparticles play a crucial role in nanowire growth and have profound consequences on nanowire morphology and their physical properties. Here, we investigate the evolving role of the Au nanoparticle during ZnO nanowire growth and its effects on nanoscale photoemission of the nanowires. We observe the transition from Au-assisted to non-assisted growth mechanisms during a single nanowire growth, with significant changes in growth rates during these two regimes. This transition occurs through the reduction of oxygen partial pressure, which modifies the ZnO facet stability and increases Au diffusion. Nanoscale quenching of ZnO cathodoluminescence occurs near the Au nanoparticle due to excited electron diffusion to the nanoparticle. Thus, the Au nanoparticle is critically linked to the nanowire growth mechanism and corresponding growth rate through the energy of its interface with the ZnO nanowire, and its presence modifies nanowire optical properties on the nanoscale.

    3. Anomalous electrical properties of Au/SrTiO3 interface

      NASA Astrophysics Data System (ADS)

      Xu, Lun; Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

      2016-08-01

      Metal/dielectric interface properties of Au/SrTiO3 (STO) and SrRuO3/SrTiO3 (SRO/STO) interfaces were investigated using metal/STO/heavily Nb-doped STO (0.5 wt % Nb:STO) capacitors. The observed interfacial capacitance at SRO/STO accords with results predicted theoretically, whereas that at the Au/STO interface is strongly suppressed, suggesting an intrinsic low-k (dielectric constant) interfacial layer formation at the Au/STO interface owing to in situ evaporated Au after STO film deposition. Furthermore, metal/0.01 wt % Nb:STO junctions were also analyzed. It was found that the SRO/Nb:STO junction forms an ideal Schottky dipole, whereas the Au/Nb:STO junction exhibits anomalous electrical properties.

    4. Gold-rich R3Au7Sn3: Establishing the interdependence between electronic features and physical properties

      SciTech Connect

      Provino, Alessia; Steinberg, Simon; Smetana, Volodymyr; Kulkarni, Ruta; Dhar, Sudesh K.; Manfrinetti, Pietro; Mudring, Anja -Verena

      2015-05-18

      Two new polar intermetallic compounds Y3Au7Sn3 (I) and Gd3Au7Sn3 (II) have been synthesized and their structures have been determined by single crystal X-ray diffraction (P63/m; Z = 2, a = 8.148(1)/8.185(3), and c = 9.394(2)/9.415(3) for I/II, respectively). They can formally be assigned to the Cu10Sn3 type and consist of parallel slabs of Sn centered, edge-sharing trigonal Au6 antiprisms connected through R3 (R = Y, Gd) triangles. Additional Au atoms reside in the centres of trigonal Au6 prisms forming Au@Au6 clusters with Au–Au distances of 2.906–2.960 Å, while the R–R contacts in the R3 groups are considerably larger than the sums of their metallic radii. These exclusive structural arrangements provide alluring systems to study the synergism between strongly correlated systems, particularly, those in the structure of (II), and extensive polar intermetallic contacts, which has been inspected by measurements of the magnetic properties, heat capacities and electrical conductivities of both compounds. Gd3Au7Sn3 shows an antiferromagnetic ordering at 13 K, while Y3Au7Sn3 is a Pauli paramagnet and a downward curvature in its electrical resistivity at about 1.9 K points to a superconducting transition. DFT-based band structure calculations on R3Au7Sn3 (R = Y, Gd) account for the results of the conductivity measurements and different spin ordering models of (II) provide conclusive hints about its magnetic structure. As a result, chemical bonding analyses of both compounds indicate that the vast majority of bonding originates from the heteroatomic Au–Gd and Au–Sn interactions, while homoatomic Au–Au bonding is evident within the Au@Au6 clusters.

    5. Gold-rich R3Au7Sn3: Establishing the interdependence between electronic features and physical properties

      SciTech Connect

      Provino, Alessia; Steinberg, Simon; Smetana, Volodymyr; Kulkarni, Ruta; Dhar, Sudesh K.; Manfrinetti, Pietro; Mudring, Anja -Verena

      2015-05-18

      Two new polar intermetallic compounds Y3Au7Sn3 (I) and Gd3Au7Sn3 (II) have been synthesized and their structures have been determined by single crystal X-ray diffraction (P63/m; Z = 2, a = 8.148(1)/8.185(3), and c = 9.394(2)/9.415(3) for I/II, respectively). They can formally be assigned to the Cu10Sn3 type and consist of parallel slabs of Sn centered, edge-sharing trigonal Au6 antiprisms connected through R3 (R = Y, Gd) triangles. Additional Au atoms reside in the centres of trigonal Au6 prisms forming Au@Au6 clusters with Au–Au distances of 2.906–2.960 Å, while the R–R contacts in the R3 groups are considerably larger than the sums of their metallic radii. These exclusive structural arrangements provide alluring systems to study the synergism between strongly correlated systems, particularly, those in the structure of (II), and extensive polar intermetallic contacts, which has been inspected by measurements of the magnetic properties, heat capacities and electrical conductivities of both compounds. Gd3Au7Sn3 shows an antiferromagnetic ordering at 13 K, while Y3Au7Sn3 is a Pauli paramagnet and a downward curvature in its electrical resistivity at about 1.9 K points to a superconducting transition. DFT-based band structure calculations on R3Au7Sn3 (R = Y, Gd) account for the results of the conductivity measurements and different spin ordering models of (II) provide conclusive hints about its magnetic structure. As a result, chemical bonding analyses of both compounds indicate that the vast majority of bonding originates from the heteroatomic Au–Gd and Au–Sn interactions, while homoatomic Au–Au bonding is evident within the Au@Au6 clusters.

    6. CD33 monoclonal antibody conjugated Au cluster nano-bioprobe for targeted flow-cytometric detection of acute myeloid leukaemia

      NASA Astrophysics Data System (ADS)

      Retnakumari, Archana; Jayasimhan, Jasusri; Chandran, Parwathy; Menon, Deepthy; Nair, Shantikumar; Mony, Ullas; Koyakutty, Manzoor

      2011-07-01

      Protein stabilized gold nanoclusters (Au-NCs) are biocompatible, near-infrared (NIR) emitting nanosystems having a wide range of biomedical applications. Here, we report the development of a Au-NC based targeted fluorescent nano-bioprobe for the flow-cytometric detection of acute myeloid leukaemia (AML) cells. Au-NCs with ~ 25-28 atoms showing bright red-NIR fluorescence (600-750 nm) and average size of ~ 0.8 nm were prepared by bovine serum albumin assisted reduction-cum-stabilization in aqueous phase. The protein protected clusters were conjugated with monoclonal antibody against CD33 myeloid antigen, which is overexpressed in ~ 99.2% of the primitive population of AML cells, as confirmed by immunophenotyping using flow cytometry. Au-NC-CD33 conjugates having average size of ~ 12 nm retained bright fluorescence over an extended duration of ~ a year, as the albumin protein protects Au-NCs against degradation. Nanotoxicity studies revealed excellent biocompatibility of Au-NC conjugates, as they showed no adverse effect on the cell viability and inflammatory response. Target specificity of the conjugates for detecting CD33 expressing AML cells (KG1a) in flow cytometry showed specific staining of ~ 95.4% of leukaemia cells within 1-2 h compared to a non-specific uptake of ~ 8.2% in human peripheral blood cells (PBMCs) which are CD33low. The confocal imaging also demonstrated the targeted uptake of CD33 conjugated Au-NCs by leukaemia cells, thus confirming the flow cytometry results. This study demonstrates that novel nano-bioprobes can be developed using protein protected fluorescent nanoclusters of Au for the molecular receptor targeted flow cytometry based detection and imaging of cancer cells.

    7. Dealloying-based facile synthesis and highly catalytic properties of Au core/porous shell nanoparticles

      NASA Astrophysics Data System (ADS)

      Kim, Minho; Ko, Sung Min; Nam, Jwa-Min

      2016-06-01

      Porous nanostructures exhibit excellent catalytic properties due to high surface-to-volume ratio, good surface reactivity and various structural features, but controlling the distribution, size, shape and density of pores and structural features of these particles is highly challenging. Herein, we report a tunable dealloying-based facile synthetic strategy to form highly porous Au core/porous shell nanoparticles (CPS NPs) in high yield by selectively dissolving Ag atoms from Au/Au-Ag core/alloy shell NPs. The CPS NPs exhibit a very short induction time, high conversion rate constant, low activation energy and high turnover frequency due to their catalytically active porous shells containing networked thin ligaments, surface defects, ultra-high porosity and photothermal properties. The CPS NPs are more catalytic Au NPs than other reported Au nanostructures, and the strategy and results open avenues in porous nanostructures and nanocatalysts.Porous nanostructures exhibit excellent catalytic properties due to high surface-to-volume ratio, good surface reactivity and various structural features, but controlling the distribution, size, shape and density of pores and structural features of these particles is highly challenging. Herein, we report a tunable dealloying-based facile synthetic strategy to form highly porous Au core/porous shell nanoparticles (CPS NPs) in high yield by selectively dissolving Ag atoms from Au/Au-Ag core/alloy shell NPs. The CPS NPs exhibit a very short induction time, high conversion rate constant, low activation energy and high turnover frequency due to their catalytically active porous shells containing networked thin ligaments, surface defects, ultra-high porosity and photothermal properties. The CPS NPs are more catalytic Au NPs than other reported Au nanostructures, and the strategy and results open avenues in porous nanostructures and nanocatalysts. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01321j

    8. Sub-nanometre sized metal clusters: from synthetic challenges to the unique property discoveries.

      PubMed

      Lu, Yizhong; Chen, Wei

      2012-05-07

      Sub-nanometre sized metal clusters, with dimensions between metal atoms and nanoparticles, have attracted more and more attention due to their unique electronic structures and the subsequent unusual physical and chemical properties. However, the tiny size of the metal clusters brings the difficulty of their synthesis compared to the easier preparation of large nanoparticles. Up to now various synthetic techniques and routes have been successfully applied to the preparation of sub-nanometre clusters. Among the metals, gold clusters, especially the alkanethiolate monolayer protected clusters (MPCs), have been extensively investigated during the past decades. In recent years, silver and copper nanoclusters have also attracted enormous interest mainly due to their excellent photoluminescent properties. Meanwhile, more structural characteristics, particular optical, catalytic, electronic and magnetic properties and the related technical applications of the metal nanoclusters have been discovered in recent years. In this critical review, recent advances in sub-nanometre sized metal clusters (Au, Ag, Cu, etc.) including the synthetic techniques, structural characterizations, novel physical, chemical and optical properties and their potential applications are discussed in detail. We finally give a brief outlook on the future development of metal nanoclusters from the viewpoint of controlled synthesis and their potential applications.

    9. Role of hydroxyl groups on the stability and catalytic activity of Au clusters on rutile surface

      SciTech Connect

      Kent, Paul R

      2011-01-01

      Hydroxyls are present as surface terminations of transition metal oxides under ambient conditions and may modify the properties of supported catalysts. We perform first-principles density functional theory calculations to investigate the role of hydroxyls on the catalytic activity of supported gold clusters on TiO{sub 2} (rutile). We find that they have a long-range effect increasing the adhesion of gold clusters on rutile. While hydroxyls make one gold atom more electronegative, a more complex charge-transfer scenario is observed on larger clusters which are important for catalytic applications. This enhances the molecular adsorption and coadsorption energies of CO and O{sub 2}, thereby increasing the catalytic activity of gold clusters for CO oxidation, consistent with reported experiments. Hydroxyls at the interface between gold and rutile surface are most important to this process, even when not directly bound to gold. As such, accurate models of catalytic processes on gold and other catalysts should include the effect of surface hydroxyls.

    10. Optical properties of ion-beam-synthesized Au nanoparticles in SiO2 matrix

      NASA Astrophysics Data System (ADS)

      Hsieh, Chang-Lin; Oyoshi, Keiji; Chao, Der-Sheng; Tsai, Hsu-Sheng; Hong, Wei-Lun; Takeda, Yoshihiko; Liang, Jenq-Horng

      2016-05-01

      In recent years, gold (Au) nanoparticles have been synthesized via various methods and used in optical and biomedical detection. Au nanoparticles contain some remarkable dimension-dependent optical properties due to surface plasmon resonance (SPR) in Au nanoparticles which causes high absorption in visible light regions. Since SPR in well-crystallized Au nanoparticles can enhance the local electromagnetic field, it is thus expected that greater efficiency in the photoluminescence (PL) originating from oxygen deficiency centers (ODC) can be achieved in Au-implanted SiO2 matrix. In order to demonstrate the enhancement of PL, Au nanoparticles were formed in SiO2 film using ion beam synthesis and their optical and microstructural properties were also investigated in this study. The results revealed that a clear absorption peak at approximately 530 nm was identified in the UV-Vis spectra and was attributed to SPR induced by Au nanoparticles in SiO2. The SPR of Au nanoparticles is also dependent on thermal treatment conditions, such as post-annealing temperature and ambient. The Au nanoparticle-containing SiO2 film also displayed several distinctive peaks at approximately 320, 360, 460, and 600 nm in the PL spectra and were found to be associated with ODC-related defects and non-bridging oxygen hole centers (NBOHC) in SiO2. In addition, the PL peak intensities increased as post-annealing temperature increased, a finding contradictory to the defect recovery but highly consistent with the SPR tendency. A maximum PL emission was achieved when the Au-implanted SiO2 film was annealed at 1100 °C for 1 h under N2. Therefore, the existence of Au nanoparticles in SiO2 film can induce SPR effects as well as enhance PL emission resulting from defect-related luminescence centers.

    11. The Massive Protostellar Cluster NGC 6334I at 220 au Resolution: Discovery of Further Multiplicity, Diversity, and a Hot Multi-core

      NASA Astrophysics Data System (ADS)

      Brogan, C. L.; Hunter, T. R.; Cyganowski, C. J.; Chandler, C. J.; Friesen, R.; Indebetouw, R.

      2016-12-01

      We present Very Large Array and Atacama Large Millimeter/submillimeter Array imaging of the deeply embedded protostellar cluster NGC 6334I from 5 cm to 1.3 mm at angular resolutions as fine as 0.″17 (220 au). The dominant hot core MM1 is resolved into seven components at 1.3 mm, clustered within a radius of 1000 au. Four of the components have brightness temperatures >200 K, radii ˜300 au, minimum luminosities ˜104 L ⊙, and must be centrally heated. We term this new phenomenon a “hot multi-core.” Two of these objects also exhibit compact free-free emission at longer wavelengths, consistent with a hypercompact H ii region (MM1B) and a jet (MM1D). The spatial kinematics of the water maser emission centered on MM1D are consistent with it being the origin of the high-velocity bipolar molecular outflow seen in CO. The close proximity of MM1B and MM1D (440 au) suggests a proto-binary or a transient bound system. Several components of MM1 exhibit steep millimeter spectral energy distributions indicative of either unusual dust spectral properties or time variability. In addition to resolving MM1 and the other hot core (MM2) into multiple components, we detect five new millimeter and two new centimeter sources. Water masers are detected for the first time toward MM4A, confirming its membership in the protocluster. With a 1.3 mm brightness temperature of 97 K coupled with a lack of thermal molecular line emission, MM4A appears to be a highly optically thick 240 L ⊙ dust core, possibly tracing a transient stage of massive protostellar evolution. The nature of the strongest water maser source CM2 remains unclear due to its combination of non-thermal radio continuum and lack of dust emission.

    12. Au-Ag hollow nanostructures with tunable SERS properties

      NASA Astrophysics Data System (ADS)

      Jiji, S. G.; Gopchandran, K. G.

      2017-01-01

      Fabrication of hollow Au-Ag nanoparticles is done by the sequential action of galvanic replacement and Kirkendall effect. Polyol synthesized silver nanoparticles were used as templates and the size of cavities is controlled by the systematic addition of the HAuCl4. Au-Ag nanoparticles carved in different depths were tested for application as substrates for surface enhanced Raman scattering. Two medically important Raman active analytes-Nile blue chloride and Crystal violet were used in the surface enhanced Raman scattering (SERS) performance analysis. A systematic study has been made on the Raman enhancement of hollow nanoparticles fabricated with different cavity dimensions and compared with that of the silver templates used. The enhancement observed for these hollow substrates with cavities is of interest since Au protected hollow nanostructures are vital and an active area of interest in drug delivery systems.

    13. Level densities and thermodynamical properties of Pt and Au isotopes

      NASA Astrophysics Data System (ADS)

      Giacoppo, F.; Bello Garrote, F. L.; Bernstein, L. A.; Bleuel, D. L.; Eriksen, T. K.; Firestone, R. B.; Görgen, A.; Guttormsen, M.; Hagen, T. W.; Kheswa, B. V.; Klintefjord, M.; Koehler, P. E.; Larsen, A. C.; Nyhus, H. T.; Renstrøm, T.; Sahin, E.; Siem, S.; Tornyi, T.

      2014-11-01

      The nuclear level densities of Pt-196194 and Au,198197 below the neutron separation energy have been measured using transfer and scattering reactions. All the level density distributions follow the constant-temperature description. Each group of isotopes is characterized by the same temperature above the energy threshold corresponding to the breaking of the first Cooper pair. A constant entropy excess Δ S =1.9 kB and 1.1 kB is observed in 195Pt and 198Au with respect to 196Pt and 197Au, respectively, giving information on the available single-particle level space for the last unpaired valence neutron. The breaking of nucleon Cooper pairs is revealed by sequential peaks in the microcanonical caloric curve.

    14. Role of vacancies in tuning the electronic properties of Au-MoS{sub 2} contact

      SciTech Connect

      Su, Jie E-mail: lpfeng@nwpu.edu.cn; Li, Ning; Zhang, Yingying; Feng, Liping E-mail: lpfeng@nwpu.edu.cn; Liu, Zhengtang

      2015-07-15

      Understanding the electronic properties between molybdenum disulfide (MoS{sub 2}) and metal electrodes is vital for the designing and realization of nanoelectronic devices. In this work, influence of intrinsic vacancies in monolayer MoS{sub 2} on the electronic structure and electron properties of Au-MoS{sub 2} contacts is investigated using first-principles calculations. Upon formation of vacancies in monolayer MoS{sub 2}, both tunnel barriers and Schottky Barriers between metal Au and monolayer MoS{sub 2} are decreased. Perfect Au-MoS{sub 2} top contact exhibits physisorption interface with rectifying character, whereas Au-MoS{sub 2} contact with Mo-vacancy shows chemisorption interface with Ohmic character. Partial density of states and electron density of defective Au-MoS{sub 2} top contacts are much higher than those of perfect one, indicating the lower contact resistance and higher electron injection efficiency of defective Au-MoS{sub 2} top contacts. Notably, Mo-vacancy in monolayer MoS{sub 2} is beneficial to get high quality p-type Au-MoS{sub 2} top contact, whereas S-vacancy in monolayer MoS{sub 2} is favorable to achieve high quality n-type Au-MoS{sub 2} top contact. Our results provide guidelines for designing and fabrication of novel 2D nanoelectronic devices.

    15. Scaling Properties of Hyperon Production in Au + Au Collisions at sqrt sNN = 200 GeV

      SciTech Connect

      Adams, J.

      2006-06-08

      We present the scaling properties of Lambda, Xi, and their anti-particles produced at mid-rapidity in Au+Au collisions at RHIC at psNN = 200 GeV. The yield of multi-strange baryons per participant nucleon increases from peripheral to central collisions more rapidly than the Lambda yield, which appears to correspond to an increasing strange quark density of matter produced. The value of the strange phase space occupancy factor gamma s, obtained from a thermal model fit to the data, approaches unity for the most central collisions. We also show that the nuclear modification factors, RCP, of Lambda and Xi are consistent with each other and with that of protons in the transverse momentum range2.0< pT< 5.0 GeV/c. This scaling behaviour is consistent with a scenario of hadron formation from constituent quark degrees of freedom through quark recombination or coalescence.

    16. Magnetic properties of magnetoactive spin clusters

      SciTech Connect

      Khamzin, A. M.; Nigmatullin, R. R.

      2010-01-15

      A simple model is proposed for describing magnetic properties of magnetoactive nanoclusters, which permits exact analytic solution. Exact expressions are obtained for thermodynamic characteristics of the model, which hold in the entire range of temperatures, magnetic fields, and interaction parameters. It is found that in the case of easy-axis anisotropy, the field dependence of magnetization of a nanocluster consisting of N particles with a spin of 1/2 has [N/2] fractional plateaus ([ Horizontal-Ellipsis ] is the integer part) corresponding to polarized phases with ruptures singlet pairs. A nonmonotonic behavior observed for the magnetic susceptibility of an easy-plane cluster is typical of gap magnets. The spin gap between the ground state and excited states is proportional to the anisotropy parameter.

    17. The mechanism of N-Ag bonding determined tunability of surface-enhanced Raman scattering of pyridine on MAg (M = Cu, Ag, Au) diatomic clusters.

      PubMed

      Chen, Lei; Gao, Yang; Xu, Haoran; Wang, Zhigang; Li, Zhengqiang; Zhang, Rui-Qin

      2014-10-14

      Binary coinage metal clusters can show a significantly different enhancement in surface-enhanced Raman scattering (SERS) from that of pure element clusters, owing to their tunable surface plasmon resonance energies affected by the composition and atomic ordering. Yet, the tunability by composition requires a deep understanding in order to further optimize the SERS-based detection technique. Here, to fill this deficiency, we conducted detailed analyses of the SERS of pyridine adsorbed through N-Ag bonding on the homonuclear diatomic metal cluster Ag2 and heteronuclear diatomic metal clusters of AuAg and CuAg, as well as the involved charge transfer under an intracluster excitation, based on calculations using time-dependent density functional theory with a short-time approximation for the Raman cross-section. We find that although the SERS enhancements for all complexes can reach the order of 10(3)-10(4), the corresponding wavelengths used for SERS excitation are significantly different. Our molecular orbital analysis reveals that the complexes based on heteronuclear metal clusters can produce varied electronic transitions owing to the polarization between different metal atoms, which tune the SERS enhancements with altered optical properties. Our analyses are expected to provide a theoretical basis for exploring the multi-composition SERS substrates applicable for single molecular detection, nanostructure characterization, and biological molecular identification.

    18. Gold clusters on Nb-doped SrTiO3: effects of metal-insulator transition on heterogeneous Au nanocatalysis.

      PubMed

      Zhou, Miao; Feng, Yuan Ping; Zhang, Chun

      2012-07-21

      Doping induced metal-insulator transition (MIT) in transition-metal (TM) oxides has been the topic of continued interest outside the field of catalysis chemistry. In this paper, via ab initio (GGA+U) calculations, we show that Nb-doping induced MIT in SrTiO(3) causes a dimensionality crossover of supported Au clusters, and at the same time, greatly enhances the stability and catalytic activity of these clusters. Underlying the predicted high catalytic activity of Au clusters towards the CO oxidation is the MIT induced interaction between the O(2) antibonding 2π* orbital and Au conduction bands, leading to a shift in the population of electrons from Au to the antibonding orbital and the activation of the O(2) molecule. We expect these results to provide a new methodology for the control of catalytic performance of TM-oxide supported Au nanoclusters.

    19. Structural and mechanical properties of magnetron-sputtered Al-Au thin films

      NASA Astrophysics Data System (ADS)

      Azadmanjiri, Jalal; Wang, James; Berndt, Christopher C.; Wen, Cuie; Srivastava, Vijay K.; Kapoor, Ajay

      2017-01-01

      There is global interest in improving the mechanical properties of light metals such as aluminum (Al)-based alloys by tailoring their microstructures at the nanometer scale. On the other hand, gold (Au) has been widely applied as a wire bonding material due to its prominent ductility and conductivity. In this study, the microstructure, hardness and elastic modulus of DC magnetron-sputtered aluminum/gold (Al/Au) composite thin films of different thicknesses were investigated. It is shown that in addition to the formation of AlAu2 phase, additional Al and Au nanosegregated phases also formed. The Al/Au thin films of 600 and 800 nm thickness exhibit the maximum hardness ( 5.40 GPa) and elastic modulus ( 97.00 GPa). However, film thicknesses of 1000 and 1200 nm demonstrate a reduction in hardness and elastic modulus due to different growth mechanisms and the formation of voids that can be attributed to the Kirkendall phenomenon.

    20. Synthesis of gold nano-wire and nano-dumbbell shaped colloids and AuC60 nano-clusters

      NASA Astrophysics Data System (ADS)

      Landon, Preston B.; Jarvis, Brandon C.; Gilleland, Cody L.; Renfro, Tim; Gutierrez, Jose; Synowczynski, Jennifer; Hirsch, Samuel G.; Glosser, Robert

      2005-08-01

      A technique for the fabrication of colloidal gold nano-wire and nano-dumbbell shaped particles using carbon nanotubes and rod shaped viruses as templates is described. The gold (Au) encapsulation process was accomplished by the precipitation of gold chloride from aqueous solutions. When this process was conducted in the presence of hydroxylated C60, small pieces of phase-separated composites of AuC60 appeared to have formed. These nano-clusters may turn out to be large noble metal analogs of the alkali metal fullerides with the smallest geometrically possible Au aggregate consisting of 55 gold atoms. The existence of noble metal fullerene composites has been previously theorized. The alkali metal fullerides are examples of phase separated solids and have exhibited superconductivity with temperatures as high 33K. The mechanism required for the binding energy between C60 and gold has been observed to exist between C60 and many of the mirror metals (Al, Ag, Au, Cu, Ni). This binding energy is a charge transfer from the metal Fermi level into the C60 LUMO. If this bonding energy, is greater than the metals coagulation energy an Au/C60 size terminated mechanism during the formation of the gold aggregates by the adhesion of C60 to the surface is energetically favorable.

    1. Structure, bonding, and linear optical properties of a series of silver and gold nanorod clusters: DFT/TDDFT studies.

      PubMed

      Liao, Meng-Sheng; Bonifassi, Pierre; Leszczynski, Jerzy; Ray, Paresh C; Huang, Ming-Ju; Watts, John D

      2010-12-09

      DFT/TDDFT calculations have been carried out for a series of silver and gold nanorod clusters (Ag(n), Au(n), n = 12-120) whose structures are of cigar-type. Pentagonal Ag(n) clusters with n = 49-121 and hexagonal Au(n) clusters with n = 14-74 were also calculated for comparison. Metal-metal distances, binding energies per atom, ionization potentials, and electron affinities were determined, and their trends with cluster size were examined. The TDDFT calculated excitation energies and oscillator strengths were fit by a Lorentz line shape modification, which gives rise to the simulated absorption spectra. The significant features of the experimental spectra for actual silver and gold nanorod particles are well reproduced by the calculations on the clusters. The calculated spectral patterns are also in agreement with previous theoretical results on different-type Ag(n) clusters. Many differences in the calculated properties are found between the Ag(n) and Au(n) clusters, which can be explained by relativistic effects.

    2. Crystal structure and electronic properties of a thiolate-protected Au24 nanocluster

      NASA Astrophysics Data System (ADS)

      Das, Anindita; Li, Tao; Li, Gao; Nobusada, Katsuyuki; Zeng, Chenjie; Rosi, Nathaniel L.; Jin, Rongchao

      2014-05-01

      Solving the total structures of gold nanoclusters is of critical importance for understanding their electronic, optical and catalytic properties. Herein, we report the X-ray structure of a charge-neutral Au24(SCH2Ph-tBu)20 nanocluster. This structure features a bi-tetrahedral Au8 kernel protected by four tetrameric staple-like motifs. Electronic structure analysis is further carried out and the optical absorption spectrum is interpreted. The Au24(SCH2Ph-tBu)20, Au23(S-c-C6H11)16 and Au25(SCH2CH2Ph)18 nanoclusters constitute the first crystallographically characterized ``trio''.Solving the total structures of gold nanoclusters is of critical importance for understanding their electronic, optical and catalytic properties. Herein, we report the X-ray structure of a charge-neutral Au24(SCH2Ph-tBu)20 nanocluster. This structure features a bi-tetrahedral Au8 kernel protected by four tetrameric staple-like motifs. Electronic structure analysis is further carried out and the optical absorption spectrum is interpreted. The Au24(SCH2Ph-tBu)20, Au23(S-c-C6H11)16 and Au25(SCH2CH2Ph)18 nanoclusters constitute the first crystallographically characterized ``trio''. Electronic supplementary information (ESI) available: Experimental and supporting Fig. S1-S3. CCDC NUMBER(1000102). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4nr01350f

    3. Modification of the catalytic properties of the Au4 nanocluster for the conversion of methane-to-methanol: synergistic effects of metallic adatoms and a defective graphene support.

      PubMed

      Sirijaraensre, J; Limtrakul, J

      2015-04-21

      Decorating graphene with nano-clusters offers potential for a wide range of industrial applications. For catalysis, embedding precisely controlled mono- and bimetallic nanoclusters into graphene can greatly increase their catalytic activities, especially for oxidation reactions. The catalytic performance of a gold nanocluster can be modified dramatically by changing its electronic properties. The results of this work demonstrate by means of DFT calculations that by strategic doping and promotion from the support material the catalytic activity improvement of a gold-based catalyst for the partial oxidation reaction of methane can be drastically enhanced. The transition metal-mediated catalysis is significantly affected by the two spin-state reactivities over them. The investigated catalytic processes consist of N2O decomposition and methane hydroxylation over three subnanoclusters (Au5, Au4Pd, and Au4Pt) deposited on a single vacancy graphene support. It was found that graphene acts not only as a support but also supports the catalysis through charge transfer between the subnanocluster and graphene. Graphene-supported Au4Pd exhibits enhanced catalytic activity for both steps of methane-to-methanol conversion, whereas the supported Au5 is good for N2O decomposition but ineffective for methane hydroxylation, mainly due to the involvement of a very stable intermediate (methyl-hydroxo-grafted nanocluster). The activation energies for N2O decomposition, C-H bond activation and methanol formation over the supported Au4Pd cluster are 13.8, 15.7, and 24.9 kcal mol(-1), respectively. Without the graphene support, the catalytic trend is reversed and Au4Pd becomes an inert cluster for these reactions.

    4. Electrical transport properties of Co-based skutterudites filled with Ag and Au

      NASA Astrophysics Data System (ADS)

      Stoica, Maria; Lo, Cynthia S.

      2012-09-01

      This work presents theoretical calculations of the electrical transport properties of the Ag, Au, and La fractionally filled bulk skutterudites: CoSb3, CoAs3, and CoP3. Density functional theory, along with projector augmented wave potentials, was used to calculate bulk band structures and partial density of states. The Seebeck coefficient (S), electrical conductivity (σ), and power factor (S2σ) were calculated as a function of temperature and filling fraction using the momentum matrix method along the entire first Brillouin zone. Calculated trends in the electrical transport properties agree with previously published experimental measurements for p-type unfilled and La-filled CoSb3. The calculated S and σ values for the Ag- and Au-filled compounds indicate that the most promising electronic properties are exhibited by p-type Au0.125(CoSb3)4, Au0.25(CoSb3)4, and Au(CoSb3)4. Au is therefore recommended as a promising filler for improved thermoelectric properties in cobalt antimonides. Ag is also a good filler for cobalt phosphides; the creation of a negative indirect band gap is observed in Ag(CoP3)4, which indicates semimetallic behavior, so this compound may possibly exhibit lower thermal conductivity than metallic CoP3. Finally, we recommend future directions for improving the thermoelectric figure of merit of these materials.

    5. Photophysical properties of Au-CdTe hybrid nanostructures of varying sizes and shapes.

      PubMed

      Haldar, Krishna Kanta; Sen, Tapasi; Mandal, Sadananda; Patra, Amitava

      2012-12-07

      We design well-defined metal-semiconductor nanostructures using thiol-functionalized CdTe quantum dots (QDs)/quantum rods (QRs) with bovine serum albumin (BSA) protein-conjugated Au nanoparticles (NPs)/nanorods (NRs) in aqueous solution. The main focus of this article is to address the impacts of size and shape on the photophysical properties, including radiative and nonradiative decay processes and energy transfers, of Au-CdTe hybrid nanostructures. The red shifting of the plasmonic band and the strong photoluminescence (PL) quenching reveal a strong interaction between plasmons and excitons in these Au-CdTe hybrid nanostructures. The PL quenching of CdTe QDs varies from 40 to 86 % by changing the size and shape of the Au NPs. The radiative as well as the nonradiative decay rates of the CdTe QDs/QRs are found to be affected in the presence of both Au NPs and NRs. A significant change in the nonradiative decay rate from 4.72×10(6) to 3.92×10(10) s(-1) is obtained for Au NR-conjugated CdTe QDs. It is seen that the sizes and shapes of the Au NPs have a pronounced effect on the distance-dependent energy transfer. Such metal-semiconductor hybrid nanostructures should have great potentials for nonlinear optical properties, photovoltaic devices, and chemical sensors.

    6. Microstructural Evolution and Mechanical Properties of Au-20wt.%Sn|Ni Interconnection

      NASA Astrophysics Data System (ADS)

      Dong, H. Q.; Vuorinen, V.; Liu, X. W.; Laurila, T.; Li, J.; Paulasto-Kröckel, M.

      2016-01-01

      In this paper, the microstructural evolution and properties of Au-20wt.%Sn|Ni reaction couples were investigated from two perspectives: (1) by analyzing the microstructure of the as-soldered and aged samples, as well as (2) by measuring the mechanical properties of the intermetallic compounds formed within the reaction zone. The evolution of interfacial reaction products for both the as-soldered and aged interconnections was rationalized by using the experimental results in combination with assessed thermodynamic data from the Au-Ni-Sn system. Moreover, nanoindentation tests were implemented to measure the indentation modulus and hardness of the compounds formed at the interface. It was found that aging had a negligible influence on the elastic modulus and hardness of AuSn and Au5Sn, while the solubility of the third element significantly changed the indentation modulus and hardness of the intermetallic compounds.

    7. Galaxy Clusters and Properties in the CFHTLS/VIPERS Survey

      NASA Astrophysics Data System (ADS)

      Gallego Gallego, Sofia Carolina; Murphy, David; Hyazinth Puzia, Thomas

      2015-08-01

      We present our analysis of clusters in the CFHTLS Wide fields using a red-sequence based cluster finding code. The deep five-band photometry and panoramic coverage permits detection of galaxy clusters between z=0 and z~1 over 132 square degrees. We present a cluster catalogue and optical richness estimates as mass proxies, derived cluster properties from a novel template-fitting analysis and cluster redshift measurements utilizing data from the VLT/VIPERS spectroscopic survey.We complement our analysis with studies of mock cluster catalogues generated from N-body simulation lightcones featuring semi-analytic prescriptions of galaxy formation. These provide us with an insight into the performance of the cluster-finding technique, uncertainties in the derived properties of the detected cluster populations and an important comparison of the popular “lambda” optical richness estimator to known dark matter halo properties.This study serves as the perfect precursor to LSST-depth cluster science, providing an important input into how models describe the evolution of clusters and their members as a function of redshift and mass, and the role high-density environments play in galaxy evolution over half the Hubble time.

    8. Scattering properties of dense clusters of colloidal nanoparticles.

      PubMed

      Lattuada, Marco; Ehrl, Lyonel

      2009-04-30

      In this work, we present a new methodology to accurately calculate scattering properties of fractal clusters with arbitrary large fractal dimension, d(f) (up to 3), and arbitrary primary particle size and material optical properties. Our approach is based on a combination of Monte Carlo simulations to generate cluster structures and mean-field T-matrix theory for the calculation of scattering properties. We have used a conventional cluster-cluster aggregation algorithm to generate clusters with d(f) up to 2.1, a tunable cluster-cluster aggregation algorithm for clusters with d(f) up to 2.5 and a newly developed Voronoi tessellation-based densification algorithm for clusters with d(f) up to 3. The scattering properties of clusters have been computed by means of mean-field T-matrix code (proposed by Botet; et al. Appl. Opt. 1997, 36 , 8791 - 8797 ), which can account for intracluster multiple scattering at a very low computational cost, thus overcoming the major limitations of commonly used Rayleigh-Debye-Gans (RDG) theory. The results of the calculations show significant deviations of the scattering cross sections and zero-angle intensities as compared to RDG theory for large primary particle sizes and high d(f). Good accuracies of the method have been confirmed by comparisons with full T-matrix calculations. The proposed approach is an ideal compromise between accuracy and high computational efficiency, and is suitable for inversion of experimental scattering data.

    9. Preparation of hyperstar polymers with encapsulated Au25(SR)18 clusters as recyclable catalysts for nitrophenol reduction.

      PubMed

      Hu, Daqiao; Jin, Shan; Shi, Yi; Wang, Xiaofeng; Graff, Robert W; Liu, Wenqi; Zhu, Manzhou; Gao, Haifeng

      2017-03-09

      A robust approach is developed to prepare hyperstar polymer-Au25(SR)18 nanocomposites for catalysis. The synthesis started with atom transfer radical copolymerization of an inimer with a cyclic disulfide-containing methacrylate monomer in a microemulsion to produce hyperbranched copolymers with high molar mass, low polydispersity, and a vital fraction of dangling disulfide groups. The core-shell structured hyperstar polymers were then prepared using hyperbranched copolymers as macroinitiators to polymerize oligo(ethylene glycol) methyl ether methacrylate (Mn = 500) and grow the radiating arms. The hyperstar polymers with disulfide groups were proved to efficiently encapsulate Au25(SR)18 nanoclusters through ligand exchange without destroying the fine structure of the Au25(SR)18 clusters. The obtained hyperstar-Au25(SR)18 nanocomposites showed great stability with no size change after a three-month shelf storage. They were used as efficient catalysts for the catalytic reduction of 4-nitrophenol by NaBH4, showing convenient recovery and reuse without losing catalytic efficiency.

    10. Antibacterial properties of Au doped polycarbonate synthesized by gamma radiation assisted diffusion method

      NASA Astrophysics Data System (ADS)

      Hareesh, K.; Deore, Avinash V.; Dahiwale, S. S.; Sanjeev, Ganesh; Kanjilal, D.; Ojha, Sunil; Dhole, N. A.; Kodam, K. M.; Bhoraskar, V. N.; Dhole, S. D.

      2015-07-01

      Gold (Au)-Polycarbonate (PC) matrix was prepared by gamma radiation assisted diffusion of Au nanoparticles in PC matrix. UV-Visible spectroscopy showed the surface plasmon resonance around 550 nm which corresponds to Au and this peak shift towards lower wavelength i.e. blue shift indicating the decrease in particle size of Au. Rutherford Backscattering (RBS) experiment confirmed the diffusion of Au in PC and depth of diffusion is found to be around 0.85 μm. X-ray Diffractogram (XRD) results also revealed the diffusion of Au in PC where the peak observed at 2θ∼38.29° which correspond to the FCC structure. Scanning Electron Microscope (SEM) images showed the hexagonal shaped Au nanoparticles and average particle size is found to be around 110 nm. These samples also showed anti-bacterial properties with both gram positive and gram negative bacteria's and revealed the inhibition of the overall growth of the bacteria with gamma dose.

    11. From the Au nano-clusters to the nanoparticles on 4H-SiC (0001).

      PubMed

      Li, Ming-Yu; Zhang, Quanzhen; Pandey, Puran; Sui, Mao; Kim, Eun-Soo; Lee, Jihoon

      2015-09-10

      The control over the configuration, size, and density of Au nanoparticles (NPs) has offered a promising route to control the spatial confinement of electrons and photons, as a result, Au NPs with a various configuration, size and density are witnessed in numerous applications. In this work, we investigate the evolution of self-assembled Au nanostructures on 4H-SiC (0001) by the systematic variation of annealing temperature (AT) with several deposition amount (DA). With the relatively high DAs (8 and 15 nm), depending on the AT variation, the surface morphology drastically evolve in two distinctive phases, i.e. (I) irregular nano-mounds and (II) hexagonal nano-crystals. The thermal energy activates adatoms to aggregate resulting in the formation of self-assembled irregular Au nano-mounds based on diffusion limited agglomeration at comparatively low annealing temperature, which is also accompanied with the formations of hillocks and granules due to the dewetting of Au films and surface reordering. At high temperature, hexagonal Au nano-crystals form with facets along {111} and {100} likely due to anisotropic distribution of surface energy induced by the increased volume of NPs. With the small DA (3 nm), only dome shaped Au NPs are fabricated along with the variation of AT from low to elevated temperature.

    12. From the Au nano-clusters to the nanoparticles on 4H-SiC (0001)

      PubMed Central

      Li, Ming-Yu; Zhang, Quanzhen; Pandey, Puran; Sui, Mao; Kim, Eun-Soo; Lee, Jihoon

      2015-01-01

      The control over the configuration, size, and density of Au nanoparticles (NPs) has offered a promising route to control the spatial confinement of electrons and photons, as a result, Au NPs with a various configuration, size and density are witnessed in numerous applications. In this work, we investigate the evolution of self-assembled Au nanostructures on 4H-SiC (0001) by the systematic variation of annealing temperature (AT) with several deposition amount (DA). With the relatively high DAs (8 and 15 nm), depending on the AT variation, the surface morphology drastically evolve in two distinctive phases, i.e. (I) irregular nano-mounds and (II) hexagonal nano-crystals. The thermal energy activates adatoms to aggregate resulting in the formation of self-assembled irregular Au nano-mounds based on diffusion limited agglomeration at comparatively low annealing temperature, which is also accompanied with the formations of hillocks and granules due to the dewetting of Au films and surface reordering. At high temperature, hexagonal Au nano-crystals form with facets along {111} and {100} likely due to anisotropic distribution of surface energy induced by the increased volume of NPs. With the small DA (3 nm), only dome shaped Au NPs are fabricated along with the variation of AT from low to elevated temperature. PMID:26354098

    13. From the Au nano-clusters to the nanoparticles on 4H-SiC (0001)

      NASA Astrophysics Data System (ADS)

      Li, Ming-Yu; Zhang, Quanzhen; Pandey, Puran; Sui, Mao; Kim, Eun-Soo; Lee, Jihoon

      2015-09-01

      The control over the configuration, size, and density of Au nanoparticles (NPs) has offered a promising route to control the spatial confinement of electrons and photons, as a result, Au NPs with a various configuration, size and density are witnessed in numerous applications. In this work, we investigate the evolution of self-assembled Au nanostructures on 4H-SiC (0001) by the systematic variation of annealing temperature (AT) with several deposition amount (DA). With the relatively high DAs (8 and 15 nm), depending on the AT variation, the surface morphology drastically evolve in two distinctive phases, i.e. (I) irregular nano-mounds and (II) hexagonal nano-crystals. The thermal energy activates adatoms to aggregate resulting in the formation of self-assembled irregular Au nano-mounds based on diffusion limited agglomeration at comparatively low annealing temperature, which is also accompanied with the formations of hillocks and granules due to the dewetting of Au films and surface reordering. At high temperature, hexagonal Au nano-crystals form with facets along {111} and {100} likely due to anisotropic distribution of surface energy induced by the increased volume of NPs. With the small DA (3 nm), only dome shaped Au NPs are fabricated along with the variation of AT from low to elevated temperature.

    14. On the Electronic and Atomic Structures of Small Au-N(-) (N=4-14) Clusters: A Photoelectron Spectroscopy and Density-Functional Study

      SciTech Connect

      Hakkinen, Hannu; Yoon, Bokwon; Landman, Uzi; Li, Xi; Zhai, Hua-Jin; Wang, Lai S.

      2003-10-17

      We report a joint experimental and theoretical study of the electronic and atomic structures of small gold clusters with up to 14 atoms. Well-resolved photoelectron spectra were obtained for Au-N(-) (N= 1-14) at several photon energies. Even-odd alternations were observed, where the even-sized clusters (except Au-10(-)) exhibit an energy gap between the lowest binding energy peak and the rest of the spectrum, indicating that all the neutral even-sized clusters have closed shells. The Au-10(-) spectrum reveals the existence of isomers, with the ground-state cluster exhibiting an extremely high electron binding energy. Evidence of multiple isomers was also observed in the spectra of N= 4, 8, 12, and 13. The structures of the gold cluster anions in the range N= 4-14 were investigated using first-principles simulations. A striking feature of the anionic clusters in this range is the occurrence of planar ground-state structures, which were predicted in earlier theoretical studies (Hakkinen, H.; et al. Phys. Rev. Lett. 2002, 89, 033401) and observed in ion-mobility experiments (Furche, F.; et al. J. Chem. Phys. 2002, 117, 6982) and the existence of close-lying isomers. The calculated electron detachment energies and density of states were compared with the measured data, which confirmed the ground-state structures of the anions. It is found that the main isomers observed experimentally indeed consist of planar clusters up to Au-12(-), Whereas for Au-13(-) and Au-14(-) the theoretical results from three-dimensional isomers agree better with the experiment, providing further support for the 2D to 3D structural transition at Au-12(-), as concluded from previous ion mobility experiments. We also find that small neutral clusters exhibit a tendency to form two-dimensional structures up to a size of 13 atoms.

    15. Nanostructured, mesoporous Au/TiO(2) model catalysts - structure, stability and catalytic properties.

      PubMed

      Roos, Matthias; Böcking, Dominique; Gyimah, Kwabena Offeh; Kucerova, Gabriela; Bansmann, Joachim; Biskupek, Johannes; Kaiser, Ute; Hüsing, Nicola; Behm, R Jürgen

      2011-01-01

      Aiming at model systems with close-to-realistic transport properties, we have prepared and studied planar Au/TiO(2) thin-film model catalysts consisting of a thin mesoporous TiO(2) film of 200-400 nm thickness with Au nanoparticles, with a mean particle size of ~2 nm diameter, homogeneously distributed therein. The systems were prepared by spin-coating of a mesoporous TiO(2) film from solutions of ethanolic titanium tetraisopropoxide and Pluronic P123 on planar Si(100) substrates, calcination at 350 °C and subsequent Au loading by a deposition-precipitation procedure, followed by a final calcination step for catalyst activation. The structural and chemical properties of these model systems were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N(2) adsorption, inductively coupled plasma ionization spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The catalytic properties were evaluated through the oxidation of CO as a test reaction, and reactivities were measured directly above the film with a scanning mass spectrometer. We can demonstrate that the thin-film model catalysts closely resemble dispersed Au/TiO(2) supported catalysts in their characteristic structural and catalytic properties, and hence can be considered as suitable for catalytic model studies. The linear increase of the catalytic activity with film thickness indicates that transport limitations inside the Au/TiO(2) film catalyst are negligible, i.e., below the detection limit.

    16. Temperature influence on microstructure and optical properties of TiO2-Au thin films

      NASA Astrophysics Data System (ADS)

      Lahmar, A.; Benchaabane, A.; Aderdour, M.; Zeinert, A.; Es-Souni, M.

      2016-02-01

      TiO2-Au thin films were deposited on quartz substrate using sol-gel technique. The influence of the annealing temperature on microstructure and optical properties was examined. SEM micrographs showed a homogeneous distribution of Au nanoparticles when the annealing temperature is increased. X-ray diffraction and Raman spectroscopy allowed the identification of the anatase phase at 500 °C that persisted up to 800 °C. Optical spectra showed the presence of localized plasmon resonance as a result of the presence of Au nanoparticles; the loci of the absorption peaks were found to depend on the annealing temperature. The effective medium model was used to describe the spectrophotometric measurements. Numerical calculations permitted the determination of optical constants. The band gap E g of TiO2-Au thin films was found to decrease from 3.21 to 2.71 eV with increasing annealing temperature.

    17. Effect of ambient on electrical transport properties of ultra-thin Au nanowires

      NASA Astrophysics Data System (ADS)

      Amin, Kazi Rafsanjani; Kundu, Subhajit; Biswas, Sangram; Roy, Ahin; Singh, Abhishek Kumar; Ravishankar, N.; Bid, Aveek

      2016-12-01

      In this letter we present systematic studies of the dynamics of surface adsorption of various chemicals on ultra-thin single crystalline gold nanowires (AuNW) through sensitive resistance fluctuation spectroscopy measurements coupled with ab initio simulations. We show that, contrary to expectations, the adsorption of common chemicals like methanol and acetone has a profound impact on the electrical transport properties of the AuNW. Our measurements and subsequent calculations establish conclusively that in AuNW, semiconductor-like sensitivity to the ambient arises because of changes induced in its local density of states by the surface adsorbed molecules. The extreme sensitivity of the resistance fluctuations of the AuNW to ambient suggests their possible use as solid-state sensors.

    18. First-principles study of structural, elastic and thermodynamic properties of AuIn2

      NASA Astrophysics Data System (ADS)

      Wu, Hai Ying; Chen, Ya Hong; Deng, Chen Rong; Yin, Peng Fei; Cao, Hong

      2015-12-01

      The structural, elastic and thermodynamic properties of AuIn2 in the CaF2 structure under pressure have been investigated using ab initio plane wave pseudopotential method within the generalized gradient approximation. The calculated structural parameters and equation of state are in excellent agreement with the available experimental and theoretical results. The elastic constants of AuIn2 at ambient condition are calculated, and the bulk modulus obtained from these calculated elastic constants agrees well with the experimental data. The pressure dependence of the elastic constants, bulk modulus, shear modulus and Young’s modulus has also been investigated. The Debye temperature presents a slight increase with pressure. AuIn2 exhibits ductibility and low hardness characteristics, the ductibility increases while the hardness decreases with the increasing of pressure. The pressure effect on the heat capacity and thermal expansion coefficient for AuIn2 is much larger.

    19. Global optimization of bimetallic cluster structures. I. Size-mismatched Ag-Cu, Ag-Ni, and Au-Cu systems.

      PubMed

      Rapallo, Arnaldo; Rossi, Giulia; Ferrando, Riccardo; Fortunelli, Alessandro; Curley, Benjamin C; Lloyd, Lesley D; Tarbuck, Gary M; Johnston, Roy L

      2005-05-15

      A genetic algorithm approach is applied to the optimization of the potential energy of a wide range of binary metallic nanoclusters, Ag-Cu, Ag-Ni, Au-Cu, Ag-Pd, Ag-Au, and Pd-Pt, modeled by a semiempirical potential. The aim of this work is to single out the driving forces that make different structural motifs the most favorable at different sizes and chemical compositions. Paper I is devoted to the analysis of size-mismatched systems, namely, Ag-Cu, Ag-Ni, and Au-Cu clusters. In Ag-Cu and Ag-Ni clusters, the large size mismatch and the tendency of Ag to segregate at the surface of Cu and Ni lead to the location of core-shell polyicosahedral minimum structures. Particularly stable polyicosahedral clusters are located at size N = 34 (at the composition with 27 Ag atoms) and N = 38 (at the composition with 32 and 30 Ag atoms). In Ag-Ni clusters, Ag32Ni13 is also shown to be a good energetic configuration. For Au-Cu clusters, these core-shell polyicosahedra are less common, because size mismatch is not reinforced by a strong tendency to segregation of Au at the surface of Cu, and Au atoms are not well accommodated upon the strained polyicosahedral surface.

    20. K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light

      NASA Astrophysics Data System (ADS)

      Lin, Yen-Ting; Mohr, Joseph J.

      2004-12-01

      We investigate the near-infrared K-band properties of the brightest cluster galaxies (BCGs) in a sample of 93 X-ray galaxy clusters and groups, using data from the Two Micron All Sky Survey. Our cluster sample spans a factor of 70 in mass, making it sensitive to any cluster mass-related trends. We derive the cumulative radial distribution for the BCGs in the ensemble and find that 70% of the BCGs are centered in the cluster to within 5% of the virial radius r200; this quantifies earlier findings that BCG position coincides with the cluster center as defined by the X-ray emission peak. We study the correlations between the luminosity of the BCGs (Lb) and the mass and the luminosity of the host clusters, finding that BCGs in more massive clusters are more luminous than their counterparts in less massive systems and that the BCGs become less important in the overall cluster light (L200) as cluster mass increases. By examining a large sample of optically selected groups, we find that these correlations hold for galactic systems less massive than our clusters (<3×1013 Msolar). From the differences between luminosity functions in high- and low-mass clusters, we argue that BCGs grow in luminosity mainly by merging with other luminous galaxies as the host clusters grow hierarchically; the decreasing BCG luminosity fraction (Lb/L200) with cluster mass indicates that the rate of luminosity growth in BCGs is slow compared to the rate at which clusters acquire galaxy light from the field or other merging clusters. Utilizing the observed correlation between the cluster luminosity and mass and a merger tree model for cluster formation, we estimate that the amount of intracluster light (ICL) increases with cluster mass; our calculations suggest that in 1015 Msolar clusters more than 50% of total stellar mass is in ICL, making the role of ICL very important in the evolution and thermodynamic history of clusters. The cluster baryon fraction accounting for the ICL is in good

    1. Improvement on electrical conductivity and electron field emission properties of Au-ion implanted ultrananocrystalline diamond films by using Au-Si eutectic substrates

      SciTech Connect

      Sankaran, K. J.; Sundaravel, B.; Tai, N. H. E-mail: inanlin@mail.tku.edu.tw; Lin, I. N. E-mail: inanlin@mail.tku.edu.tw

      2015-08-28

      In the present work, Au-Si eutectic layer was used to enhance the electrical conductivity/electron field emission (EFE) properties of Au-ion implanted ultrananocrystalline diamond (Au-UNCD) films grown on Si substrates. The electrical conductivity was improved to a value of 230 (Ω cm){sup −1}, and the EFE properties was enhanced reporting a low turn-on field of 2.1 V/μm with high EFE current density of 5.3 mA/cm{sup 2} (at an applied field of 4.9 V/μm) for the Au-UNCD films. The formation of SiC phase circumvents the formation of amorphous carbon prior to the nucleation of diamond on Si substrates. Consequently, the electron transport efficiency of the UNCD-to-Si interface increases, thereby improving the conductivity as well as the EFE properties. Moreover, the salient feature of these processes is that the sputtering deposition of Au-coating for preparing the Au-Si interlayer, the microwave plasma enhanced chemical vapor deposition process for growing the UNCD films, and the Au-ion implantation process for inducing the nanographitic phases are standard thin film preparation techniques, which are simple, robust, and easily scalable. The availability of these highly conducting UNCD films with superior EFE characteristics may open up a pathway for the development of high-definition flat panel displays and plasma devices.

    2. The IC1396N proto-cluster at a scale of ~250 AU

      NASA Astrophysics Data System (ADS)

      Neri, R.; Fuente, A.; Ceccarelli, C.; Caselli, P.; Johnstone, D.; van Dishoeck, E. F.; Wyrowski, F.; Tafalla, M.; Lefloch, B.; Plume, R.

      2007-06-01

      Aims:We investigate the mm-morphology of IC 1396 N with unprecedented spatial resolution to analyze its dust and molecular gas properties, and draw comparisons with objects of similar mass. Methods: We have carried out sensitive observations in the most extended configurations of the IRAM Plateau de Bure interferometer, to map the thermal dust emission at 3.3 and 1.3 mm, and the emission from the J=13_k→ 12k hyperfine transitions of methyl cyanide (CH3CN). Results: We unveil the existence of a sub-cluster of hot cores in IC 1396 N, distributed in a direction perpendicular to the emanating outflow. The cores are embedded in a common envelope of extended and diffuse dust emission. We find striking differences in the dust properties of the cores (β≃ 0) and the surrounding envelope (β≃ 1), very likely testifying to differences in the formation and processing of dust material. The CH3CN emission peaks towards the most massive hot core and is marginally extended in the outflow direction. Based on observations obtained at the IRAM Plateau de Bure Interferometer (PdBI). IRAM is funded by the Centre Nationale de la Recherche Scientifique (France), the Max-Planck Gesellschaft (Germany), and the Instituto Geográfico Nacional (Spain).

    3. Relaxed structural property of Al nano-cluster: Theory

      NASA Astrophysics Data System (ADS)

      Diwan, Bhoopendra Dhar; Khaskalam, Amit

      2013-06-01

      In this paper we have studied the thermodynamic property of metallic Aluminium (Al) nano-clusters with relaxed structure by model approach. The relaxed cohesive energy is higher than that of the un-relaxed one due to relaxation process decreasing the total energy. It is found that cohesive energy of nano-clauster depends on the size of the clusters and increase with increasing the cluster size.

    4. Probing the Structures and Electronic Properties of Dual-Phosphorus-Doped Gold Cluster Anions (AunP-2, n = 1–8): A Density functional Theory Investigation

      SciTech Connect

      Xu, Kang-Ming; Huang, Teng; Liu, Yi-Rong; Jiang, Shuai; Zhang, Yang; Lv, Yu-Zhou; Gai, Yan-Bo; Huang, Wei

      2015-07-29

      The geometries of gold clusters doped with two phosphorus atoms, (AunP-2, n = 1–8) were investigated using density functional theory (DFT) methods. Various two-dimensional (2D) and three-dimensional (3D) structures of the doped clusters were studied. The results indicate that the structures of dual-phosphorus-doped gold clusters exhibit large differences from those of pure gold clusters with small cluster sizes. In our study, as for Au6P-2, two cis–trans isomers were found. The global minimum of Au8P-2 presents a similar configuration to that of Au-20, a pyramid-shaped unit, and the potential novel optical and catalytic properties of this structure warrant further attention. The higher stability of AunP-2 clusters relative to Au-n+2 (n = 1–8) clusters was verified based on various energy parameters, and the results indicate that the phosphorus atom can improve the stabilities of the gold clusters. We then explored the evolutionary path of (n = 1–8) clusters. We found that AunP-2 clusters exhibit the 2D–3D structural transition at n = 6, which is much clearer and faster than that of pure gold clusters and single-phosphorus-doped clusters. The electronic properties of AunP-2 (n = 1–8) were then investigated. The photoelectron spectra provide additional fundamental information on the structures and molecular orbitals shed light on the evolution of AunP-2 (n = 1–8). Natural bond orbital (NBO) described the charge distribution in stabilizing structures and revealed the strong relativistic effects of the gold atoms.

    5. Necklace-shaped Au-Ag nanoalloys: laser-assisted synthesis and nonlinear optical properties

      NASA Astrophysics Data System (ADS)

      Jafarkhani, P.; Torkamany, M. J.; Dadras, S.; Chehrghani, A.; Sabbaghzadeh, J.

      2011-06-01

      Here in this paper, necklace-shaped Au-Ag nanoalloys (NAs) have been synthesized by a laser-based approach. A chain of Ag nanoparticles (NPs), which were joined together with Au junctions, was formed upon copper vapor laser (CVL) irradiation of a colloidal mixture of Ag and Au NPs; while the corresponding NPs were separately provided by laser ablation of gold and silver targets in deionized water by a 1064 nm Q-switched Nd:YAG laser. Dependence of the NAs development process on the CVL irradiation time in three distinct stages of as-mixed, nucleation and complete formation has been systematically studied by UV-vis optical absorption spectroscopy analysis as well as by transmission electron microscopy (TEM), which was exploited to visually confirm the NAs evolution through the process. Furthermore, the x-ray photoelectron spectroscopy (XPS) technique was accurately employed to determine the synthesized alloy content. On the other hand, using the open-and closed-aperture Z-scan technique, the nonlinear absorption (NLA) as well as nonlinear refraction (NLR) changes in Au-Ag NAs were investigated through their formation. The deduced results from the nonlinear optical properties of the colloidal NAs in the mentioned stages were interpreted considering the spectroscopic and microscopic observations. The total change of individual Au and Ag NPs saturable absorption (SA) into the reverse saturable absorption (RSA) behavior was concluded through the evolution into Au-Ag NAs.

    6. Vibrational properties at the ordered metallic surface alloy system Au(110)-1×2-Pd

      NASA Astrophysics Data System (ADS)

      Kheffache, Sedik; Chadli, Rabah; Khater, Antoine

      2016-06-01

      We present a calculation for the vibrational properties of the ordered surface alloy Au(110)-1×2-Pd on a crystalline substrate of Au. The surface phonon dispersion curves and the local vibrations densities of states (LDOS) are calculated in the harmonic approximation for the system, using the phase field matching theory (PFMT) method and associated real space Green’s functions. In particular, it is shown that the surface alloy presents optic vibrational modes above the Au bulk bands, along the directions of high-symmetry ΓX¯, XS¯, SY¯ and Y Γ¯ of the corresponding two-dimensional Brillouin zone. Measurements of the surface phonon dispersion branches can hence be made by different techniques such as helium atom scattering (HAS) to compare with. The calculated LDOS for Au and Pd atomic sites in the four top surface atomic layers span a wider range of frequencies than those for the individual Au(110) or Pd(110) metallic surfaces. These LDOS provide a spectral signature for the progressive transition from the surface dynamics to that of the Au crystal bulk. Knowledge of these LDOS for the surface alloy can also serve as an input for modeling the diffusion and reaction rates of chemical species at its surface.

    7. Differences in intermediate structures and electronic states associated with oxygen adsorption onto Pt, Cu, and Au clusters as oxygen reduction catalysts

      NASA Astrophysics Data System (ADS)

      Morishita, Tetsunori; Ueno, Tomonaga; Panomsuwan, Gasidit; Hieda, Junko; Bratescu, Maria Antoaneta; Saito, Nagahiro

      2016-10-01

      We used ab initio molecular orbital (MO) calculations to study the differences in the intermediate structures and the electronic states involved in the adsorption of O2 onto 13-atom metal clusters of Pt, Cu, and Au. Additionally, the conditions required for the electrocatalytic oxygen reduction reaction (ORR) on the Pt, Cu, and Au clusters were investigated and discussed. The intermediates involved in O2 adsorption onto Pt, Cu, and Au were found to be (Pt-O)-(Pt-O), Cu-O, and Au-O2, respectively. The differences in the O2 adsorption intermediates is explained on the basis of our analysis of the projected density of state (PDOS) area of the new MOs produced from a mixture of the 2pπ * orbitals of O2 and the d orbitals of the metal clusters. The formation of the (Pt-O)-(Pt-O) intermediate after the adsorption of O2 onto the Pt cluster is attributed to the emergence of an antibonding orbital above the Fermi level. Thus, this electronic state can lead to the decomposition and desorption of O2 molecules, thereby promoting the high-activity level of ORR. For the Cu cluster, a new antibonding orbital was observed below the Fermi level. Moreover, the Cu cluster surface can only promote O2 decomposition and not O2 desorption due to the formation of copper oxides. For the Au cluster, no new MOs related to 2pπ * orbitals of O2 appeared because O2 was molecularly adsorbed, implying that the Au cluster is an inefficient ORR catalyst.

    8. Gold-bismuth clusters.

      PubMed

      Martínez, Ana

      2014-08-07

      Metal clusters have interesting characteristics, such as the relationship between properties and size of the cluster. This is not always apparent, so theoretical studies can provide relevant information. In this report, optimized structures and electron donor-acceptor properties of AunBim clusters are reported (n + m = 2-7, 20). Density functional theory calculations were performed to obtain optimized structures. The ground states of gold clusters formed with up to seven atoms are planar. The presence of Bi modifies the structure, and the clusters become 3-D. Several optimized geometries have at least one Bi atom bonded to gold or bismuth atoms and form structures similar to NH3. This fragment is also present in clusters with 20 atoms, where the formation of Au3Bi stabilizes the structures. Bismuth clusters are better electron donors and worse electron acceptors than gold clusters. Mixed clusters fall in between these two extremes. The presence of Bi atoms in gold clusters modifies the electron donor-acceptor properties of the clusters, but there is no correlation between the number of Bi atoms present in the cluster and the capacity for donating electrons. The effect of planarity in Au19Bi clusters is the same as that in Au20 clusters. The properties of pure gold clusters are certainly interesting, but clusters formed by Bi and Au are more important because the introduction of different atoms modifies the geometry, the stability, and consequently the physical and chemical properties. Apparently, the presence of Bi may increase the reactivity of gold clusters, but further studies are necessary to corroborate this hypothesis.

    9. Magnetic properties of one-dimensional Au-Co chains on the copper(110) surface

      NASA Astrophysics Data System (ADS)

      Kolesnikov, S. V.; Tsysar, K. M.; Saletsky, A. M.

      2015-08-01

      Magnetic properties of cobalt atoms in Au-Co chains on the Cu(110) surface (such as the magnetic moment, magnetic anisotropy energy, and exchange energy) have been calculated in the framework of the density functional theory. It has been found, at zero temperature, an infinitely long Au-Co chain is in the ferromagnetic state. The magnetostatic and magnetodynamic properties of finite-length Au-Co chains at a nonzero temperature have been investigated within the Heisenberg model using the kinetic Monte Carlo method. The dependences of the Curie temperature and magnetization reversal time on the chain length have been obtained, as well as the dependences of the coercivity of the chain on the temperature, chain length, and magnetization reversal rate.

    10. The Dependence of Cluster Galaxy Properties on the Central Entropy of their Host Cluster

      NASA Astrophysics Data System (ADS)

      Kim, Jae-Woo; Ko, Jongwan; Hwang, Ho Seong; Edge, Alastair C.; Lee, Joon Hyeop; Lee, Jong Chul; Jeong, Hyunjin

      2017-02-01

      We present a study of the connection between brightest cluster galaxies (BCGs) and their host galaxy clusters. Using galaxy clusters at 0.1< z< 0.3 from the Hectospec Cluster Survey (HeCS) with X-ray information from the Archive of Chandra Cluster Entropy Profile Tables (ACCEPT), we confirm that BCGs in low central entropy clusters are well aligned with the X-ray center. Additionally, the magnitude difference between BCG and the second brightest galaxy also correlates with the central entropy of the intracluster medium. From the red-sequence (RS) galaxies, we cannot find significant dependence of RS color scatter and stellar population on the central entropy of the intracluster medium of their host cluster. However, BCGs in low-entropy clusters are systematically less massive than those in high-entropy clusters, although this is dependent on the method used to derive the stellar mass of BCGs. In contrast, the stellar velocity dispersion of BCGs shows no dependence on BCG activity and cluster central entropy. This implies that the potential of the BCG is established earlier and the activity leading to optical emission lines is dictated by the properties of the intracluster medium in the cluster core.

    11. Interlocked catenane-like structure predicted in Au24(SR)20: implication to structural evolution of thiolated gold clusters from homoleptic gold(I) thiolates to core-stacked nanoparticles.

      PubMed

      Pei, Yong; Pal, Rhitankar; Liu, Chunyan; Gao, Yi; Zhang, Zhuhua; Zeng, Xiao Cheng

      2012-02-15

      Atomic structure of a recently synthesized ligand-covered cluster Au(24)(SR)(20) [J. Phys. Chem. Lett., 2010, 1, 1003] is resolved based on the developed classical force-field based divide-and-protect approach. The computed UV-vis absorption spectrum and powder X-ray diffraction (XRD) curve for the lowest-energy isomer are in good agreement with experimental measurements. Unique catenane-like staple motifs are predicted for the first time in core-stacked thiolate-group (RS-) covered gold nanoparticles (RS-AuNPs), suggesting the onset of structural transformation in RS-AuNPs at relatively low Au/SR ratio. Since the lowest-energy structure of Au(24)(SR)(20) entails interlocked Au(5)(SR)(4) and Au(7)(SR)(6) oligomers, it supports a recently proposed growth model of RS-AuNPs [J. Phys. Chem. Lett., 2011, 2, 990], that is, Au(n)(SR)(n-1) oligomers are formed during the initial growth of RS-AuNPs. By comparing the Au-core structure of Au(24)(SR)(20) with other structurally resolved RS-AuNPs, we conclude that the tetrahedral Au(4) motif is a prevalent structural unit for small-sized RS-AuNPs with relatively low Au/SR ratio. The structural prediction of Au(24)(SR)(20) offers additional insights into the structural evolution of thiolated gold clusters from homoleptic gold(I) thiolate to core-stacked RS-AuNPs. Specifically, with the increase of interfacial bond length of Au(core)-S in RS-AuNPs, increasingly larger "metallic" Au-core is formed, which results in smaller HOMO-LUMO (or optical) gap. Calculations of electronic structures and UV-vis absorption spectra of Au(24)(SR)(20) and larger RS-AuNPs (up to ~2 nm in size) show that the ligand layer can strongly affect optical absorption behavior of RS-AuNPs.

    12. Hydrogen-bonded clusters of 1, 1'-ferrocenedicarboxylic acid on Au(111) are initially formed in solution.

      PubMed

      Quardokus, Rebecca C; Wasio, Natalie A; Brown, Ryan D; Christie, John A; Henderson, Kenneth W; Forrest, Ryan P; Lent, Craig S; Corcelli, Steven A; Kandel, S Alex

      2015-03-14

      Low-temperature scanning tunneling microscopy is used to observe self-assembled structures of ferrocenedicarboxylic acid (Fc(COOH)2) on the Au(111) surface. The surface is prepared by pulse-deposition of Fc(COOH)2 dissolved in methanol, and the solvent is evaporated before imaging. While the rows of hydrogen-bonded dimers that are common for carboxylic acid species are observed, the majority of adsorbed Fc(COOH)2 is instead found in six-molecule clusters with a well-defined and chiral geometry. The coverage and distribution of these clusters are consistent with a random sequential adsorption model, showing that solution-phase species are determinative of adsorbate distribution for this system under these reaction conditions.

    13. Integrated spectral properties of 7 galactic open clusters

      NASA Astrophysics Data System (ADS)

      Ahumada, A. V.; Clariá, J. J.; Bica, E.; Piatti, A. E.

      2000-01-01

      This paper presents flux-calibrated integrated spectra in the range 3600-9000 Ä for 7 concentrated, relatively populous Galactic open clusters. We perform simultaneous estimates of age and foreground interstellar reddening by comparing the continuum distribution and line strengths of the cluster spectra with those of template cluster spectra with known parameters. For five clusters these two parameters have been determined for the first time (Ruprecht 144, BH 132, Pismis 21, Lyng\\aa 11 and BH 217), while the results here derived for the remaining two clusters (Hogg 15 and Melotte 105) show very good agreement with previous studies based mainly on colour-magnitude diagrams. We also provide metallicity estimates for six clusters from the equivalent widths of CaII triplet and TiO features. The present cluster sample improves the age resolution around solar metal content in the cluster spectral library for population synthesis. We compare the properties of the present sample with those of clusters in similar directions. Hogg 15 and Pismis 21 are among the most reddened clusters in sectors centered at l = 270o and l = 0o, respectively. Besides, the present results would favour an important dissolution rate of star clusters in these zones. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

    14. Prediction of Solvent Physical Properties using the Hierarchical Clustering Method

      EPA Science Inventory

      Recently a QSAR (Quantitative Structure Activity Relationship) method, the hierarchical clustering method, was developed to estimate acute toxicity values for large, diverse datasets. This methodology has now been applied to the estimate solvent physical properties including sur...

    15. Evaluation of gas-sensing properties of ZnO nanostructures electrochemically doped with Au nanophases.

      PubMed

      Dilonardo, Elena; Penza, Michele; Alvisi, Marco; Di Franco, Cinzia; Palmisano, Francesco; Torsi, Luisa; Cioffi, Nicola

      2016-01-01

      A one-step electrochemical method based on sacrificial anode electrolysis (SAE) was used to deposit stabilized gold nanoparticles (Au NPs) directly on the surface of nanostructured ZnO powders, previously synthesized through a sol-gel process. The effect of thermal annealing temperatures (300 and 550 °C) on chemical, morphological, and structural properties of pristine and Au-doped ZnO nancomposites (Au@ZnO) was investigated. Transmission and scanning electron microscopy (TEM and SEM), as well as X-ray photoelectron spectroscopy (XPS), revealed the successful deposition of nanoscale gold on the surface of spherical and rod-like ZnO nanostructures, obtained after annealing at 300 and 550 °C, respectively. The pristine ZnO and Au@ZnO nanocomposites are proposed as active layer in chemiresistive gas sensors for low-cost processing. Gas-sensing measurements towards NO2 were collected at 300 °C, evaluating not only the Au-doping effect, but also the influence of the different ZnO nanostructures on the gas-sensing properties.

    16. 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.

    17. The effect of alkali metal on the surface properties of potassium doped Au-Beta zeolites

      SciTech Connect

      Sobczak, Izabela; Rydz, Michal; Ziolek, Maria

      2013-02-15

      Graphical abstract: Display Omitted Highlights: ► Interaction of gold with K leads to the change of electronic state and redox properties of gold. ► The amount of potassium incorporated into Au-zeolites determines the size of gold particles. ► K(0.2 wt.%)/Au-Beta exhibits the best performance in decomposition of N{sub 2}O and removal of Bu{sub 2}S. -- Abstract: Beta zeolite was applied as support for gold introduced by gold-precipitation method and potassium added by impregnation or adsorption. The effect of zeolite composition and the amount of potassium introduced on the surface properties of the final materials was considered. Moreover, the interaction of gold and potassium species was found to be related to the adsorptive and catalytic behaviour of zeolites in NO reduction with propene and deodorization. K/Au-Beta(Impregnated) exhibits the best performance in the above mentioned processes because of the small gold particles (between 2 and 5 nm) and interaction of gold with potassium species leading to the change of electronic properties of the surface (the appearance of cationic gold species). Potassium added as a promoter improves the catalytic properties of Au-zeolite in N{sub 2}O decomposition and also in deodorization (increase of the ability to dibutyl sulphide oxidation). The catalysts prepared were characterized by XRD, XPS, UV–vis, TEM, pyridine adsorption combined with FTIR and test reaction (2-propanol transformation).

    18. Chemically induced magnetism in atomically precise gold clusters.

      PubMed

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

      2014-03-12

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

    19. Electrostatic assembles and optical properties of Au CdTe QDs and Ag/Au CdTe QDs

      NASA Astrophysics Data System (ADS)

      Yang, Dongzhi; Wang, Wenxing; Chen, Qifan; Huang, Yuping; Xu, Shukun

      2008-09-01

      Au-CdTe and Ag/Au-CdTe assembles were firstly investigated through the static interaction between positively charged cysteamine-stabilized CdTe quantum dots (QDs) and negatively charged Au or core/shell Ag/Au nano-particles (NCs). The CdTe QDs synthesized in aqueous solution were capped with cysteamine which endowed them positive charges on the surface. Both Au and Ag/Au NCs were prepared through reducing precursors with gallic acid obtained from the hydrolysis of natural plant poly-phenols and favored negative charges on the surface of NCs. The fluorescence spectra of CdTe QDs exhibited strong quenching with the increase of added Au or Ag/Au NCs. Railey resonance scattering spectra of Au or Ag/Au NCs increased firstly and decreased latter with the concentration of CdTe QDs, accompanied with the solution color changing from red to purple and colorless at last. Experimental results on the effects of gallic acid, chloroauric acid tetrahydrate and other reagents demonstrated the static interaction occurred between QDs and NCs. This finding reveals the possibilities to design and control optical process and electromagnetic coupling in hybrid structures.

    20. OPEN CLUSTERS AS PROBES OF THE GALACTIC MAGNETIC FIELD. I. CLUSTER PROPERTIES

      SciTech Connect

      Hoq, Sadia; Clemens, D. P. E-mail: clemens@bu.edu

      2015-10-15

      Stars in open clusters are powerful probes of the intervening Galactic magnetic field via background starlight polarimetry because they provide constraints on the magnetic field distances. We use 2MASS photometric data for a sample of 31 clusters in the outer Galaxy for which near-IR polarimetric data were obtained to determine the cluster distances, ages, and reddenings via fitting theoretical isochrones to cluster color–magnitude diagrams. The fitting approach uses an objective χ{sup 2} minimization technique to derive the cluster properties and their uncertainties. We found the ages, distances, and reddenings for 24 of the clusters, and the distances and reddenings for 6 additional clusters that were either sparse or faint in the near-IR. The derived ranges of log(age), distance, and E(B−V) were 7.25–9.63, ∼670–6160 pc, and 0.02–1.46 mag, respectively. The distance uncertainties ranged from ∼8% to 20%. The derived parameters were compared to previous studies, and most cluster parameters agree within our uncertainties. To test the accuracy of the fitting technique, synthetic clusters with 50, 100, or 200 cluster members and a wide range of ages were fit. These tests recovered the input parameters within their uncertainties for more than 90% of the individual synthetic cluster parameters. These results indicate that the fitting technique likely provides reliable estimates of cluster properties. The distances derived will be used in an upcoming study of the Galactic magnetic field in the outer Galaxy.

    1. Cluster observations on linear magnetic decreases in the solar wind at 1 AU

      NASA Astrophysics Data System (ADS)

      Xiao, T.; Shi, Q.; Tian, A.; Fu, S.; Pu, Z.; Zong, Q.; Sun, W.; Lucek, E. A.; Reme, H.

      2013-12-01

      Magnetic decreases (MDs) are structures observed in interplanetary space with significant decreases in the magnetic field magnitude, of which the events with no or little change in the field direction are linear magnetic decreases (LMDs). Xiao et al., (2010) have reported that the geometrical shape of LMDs observed in the solar wind at 1 AU was consistent with rotational ellipsoid, and the occurrence rate was about 3.7 LMDs/d. It was found that not only the occurrence rate but also the geometrical shape of LMDs had no significant change from 0.72 AU to 1 AU in comparison with Zhang et al., (2008)'s results, which may infer that most of LMDs observed at 1 AU were formed and fully developed before 0.72 AU. Recently, we have focused on the magnetic field and plasma (e.g. ion density and velocity) characteristics of those LMD structures observed during the period of 2001 to 2009. Compared with the average solar wind condition, it is shown that the LMDs prefer to be observed in the region with relatively lower magnetic field magnitude, higher ion density, larger plasma β (ratio of the thermal pressure to the magnetic pressure) and slower solar wind velocity. We also investigated the LMDs which located in the interplanetary coronal mass ejections (ICME) or the sheath of the ICME. It is found that the events related to ICMEs could account for more than 20% of LMDs during solar maximum. Therefore, the ICME should be an important source of the LMDs during the solar maximum. However, other mechanisms during the solar minimum may be more important, because the occurrence rate of LMDs during the solar minimum is higher than that of the solar maximum. We also calculate the propagation speed of the structures in the solar wind frame to infer the generation mechanism of these structures.

    2. A Grand Avenue to Au Nanocluster Electrochemiluminescence.

      PubMed

      Hesari, Mahdi; Ding, Zhifeng

      2017-02-21

      In most cases of semiconductor quantum dot nanocrystals, the inherent optical and electrochemical properties of these interesting nanomaterials do not translate into expected efficient electrochemiluminescence or electrogenerated chemiluminescence (ECL) because of the surface-state induction effect. Thus, their low ECL efficiencies, while very interesting to explore, limit their applications. As their electrochemistry is not well-defined, insight into their ECL mechanistic details is also limited. Alternatively, gold nanoclusters possess monodispersed sizes with atomic precision, low and well defined HOMO-LUMO energy gaps, and stable optical and electrochemical properties that make them suitable for potential ECL applications. In this Account, we demonstrate strong and sustainable ECL of gold nanoclusters Au25(z) (i.e., Au25(SR)18(z), z = 1-, 0, 1+), Au38(SR)24, and Au144(SR)60, where the ligand SR is 2-phenylethanethiol. By correlation of the optical and electrochemical features of Au25 nanoclusters, a Latimer-type diagram can be constructed to reveal thermodynamic relationships of five oxidation states (Au25(2+), Au25(+), Au25(0), Au25(-), and Au25(2-)) and three excited states (Au25(-)*, Au25(0)*, and Au25(+)*). We describe ECL mechanisms and reaction kinetics by means of conventional ECL-voltage curves and novel spooling ECL spectroscopy. Notably, their ECL in the presence of tri-n-propylamine (TPrA), as a coreactant, is attributed to emissions from Au25(-)* (950 nm, strong), Au25(0)* (890 nm, very strong), and Au25(+)* (890 nm, very strong), as confirmed by the photoluminescence (PL) spectra of the three Au25 clusters electrogenerated in situ. The ECL emissions are controllable by adjustment of the concentrations of TPrA· and Au25(-), Au25(0), and Au25(+) species in the vicinity of the working electrode and ultimately the applied potential. It was determined that the Au25(-)/TPrA coreactant system should have an ECL efficiency of >50% relative to the Ru(bpy)3

    3. First principles calculation of the structural, electronic, and magnetic properties of Au-Pd atomic chains

      SciTech Connect

      Dave, Mudra R.; Sharma, A. C.

      2015-06-24

      The structural, electronic and magnetic properties of free standing Au-Pd bimetallic atomic chain is studied using ab-initio method. It is found that electronic and magnetic properties of chains depend on position of atoms and number of atoms. Spin polarization factor for different atomic configuration of atomic chain is calculated predicting a half metallic behavior. It suggests a total spin polarised transport in these chains.

    4. Two Point Measurements of statistical properties of solar wind turbulence using Cluster data

      NASA Astrophysics Data System (ADS)

      Matthaeus, W. H.; Weygand, J. M.; Dasso, S.; Smith, C. W.; Kivelson, M. G.

      2006-12-01

      Multipoint measurements with widely ranging spatial separations and well controlled time calibration are required to unravel the space-time structure of MHD scale turbulence, which presents complexity in both domains. We have been addressing these problems using recently developed methods for statistical and correlation analyses of multiple streams of spacecraft data. [see 1,2,3] In particular, to determine the two-point spatial correlation properties of solar wind turbulence near 1 AU, we have been employing datastreams from pairs of spacecraft including ACE, Wind and Cluster. The Wind-AcE datasets have been most useful in establishing the long wavelength values of the direction averaged spatial correlation function, and the correlation (outer) scale. The Cluster data have been essential to evaluate the finer scale correlation function, and to extract the value of the Taylor microscale. The correlation scale is determined to be 1.2 × 106 km, the Taylor scale is 2500 km. [1,2,3]. Here we review the method leading to the above results, and focus in particular on the use of Cluster data at available separations to obtain a stable value for the estimate of the Taylor scale. We plan also to compare these results with single spacecraft determinations of the same quantities using the traditional "frozen in flow" approximation. This research supported by the Cluster project and the Cluster GI program. [1] W H Matthaeus et al, Phys Rev Lett., 95, 231101 (2005) \

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

      PubMed

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

      2014-06-01

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

    6. Influence of structural defects on the optical properties of strongly coupled Au nanoshell arrays

      NASA Astrophysics Data System (ADS)

      Zhou, Xin; Fang, JianShu; Liao, XiangPing; Zhu, QianQuan; Liu, ZhiMin; Tang, Bin

      2013-09-01

      The effects of different defects on optical properties and plasmon resonances properties of Au nanoshell arrays were investigated by using the finite-difference time-domain (FDTD) theory. It is found that the optical properties of the nanoshell arrays are strongly influenced by different defects. We show that when the hollow Au nanoshell arrays are placed in air, there is a wide photonic band gap (PBG) in the infrared region, but the band gap becomes narrower as we introduced different defects. Based on the distributions of electric field component E z and the total energy distribution of the electric and the magnetic field, we show that there exhibit dipoles field distributions for the plasmon mode at the long-wavelength edge of the band gap, but composite higher order modes are excited at the short-wavelength edge of the band gap. The plasmon resonant modes also can be controlled by introducing defects.

    7. Correlation effects on the properties of small cobalt clusters

      NASA Astrophysics Data System (ADS)

      Hancock, Yvette; Iäs, Mari

      2009-03-01

      Demands for higher-density magnetic storage media and smaller memory devices require atomic-scale magnetic components with stable magnetic properties. One such candidate for this application is a small transition metal cluster. The magnetic properties of transition metal clusters are very sensitive to the geometry of the cluster, the local atomic and structural environments, and to the system size. In this work, the GGA + U DFT approach is used for the first time to study the system properties of small cobalt clusters consisting of 2 to 5 atoms. Previous studies using DFT and tight-binding approaches have been found to overestimate the binding energies, dissociation energies and vibrational frequencies of the clusters against their known experimental values. By including a Hubbard U correction between 2 -- 3 eV, the DFT method can then be fitted to reproduce the experimental results, thereby improving upon previous theoretical descriptions of these systems. The effect of U on the calculated magnetic and structural properties of the clusters is also discussed.

    8. Nanometer scale mechanical properties of Au(111) thin films

      SciTech Connect

      Salmeron, M.; Folch, A.; Neubauer, G.

      1992-11-01

      The mechanical properties of gold films of (111) orientation were studied as a function of load when contacted by a single asperity Pt-Rh alloy tip. The interaction forces were measured in the direction perpendicular to the surface. The contribution of various types of forces (van der Waals, capillarity from contaminants, and metallic adhesion) in the process of contact was determined. We investigated the elastic and plastic response of the gold film as a function of applied load by examination of the contact area in subsequent imaging with STM and AFM.

    9. The effect of low Au concentrations on the properties of eutectic Sn/Pb

      SciTech Connect

      Kramer, P.A.

      1992-05-01

      This study was of the effects moderately low Au concentrations ({le} 10 wt%) have on the mechanical properties and microstructure of an eutectic Sn/Pb alloy. Vibration (60--90 Hz swept sine wave for 30 hours) and thermal cycling (0--110C for 1450 cycles) reliability tests were performed on fine pitch leaded chip carriers using eutectic Sn/Pb solder on PCBs (printed circuit boards) with 0, 5, 10, 20, and 50{mu}in nominal Au thicknesses. Testing was also performed on double shear creep specimens consisting of arrays of regular pitch joints. There was a dramatic increase in the number of joints containing voids with increasing Au concentration, an effect more pronounced in the creep joints than in the reliability joints. These voids tended to coalesce and grow during rework simulation of the reliability joints. AuSn{sub 4} intermetallics present in toe of 4.8 wt% (50 {mu}in) Au vibration joints rotated from initial vertical perpendicular to surface of PCB metallization, solidification positions to roughly horizontal (parallel to plating surface) orientations during rework simulation and during aging of the parts. The AuSn{sub 4} intermetallics in the toe of the 4.8 wt% (50{mu}in) Au reflowed joints also rotated after vibration testing. No joint failures were observed in either vibration tested or thermally cycled specimens. Cracks formed in some of the vibration tested specimen joints under the heel of the gull-wing lead at Pb-rich phases. Thermally cycled specimens showed eutectic microstructure and intermetallic coarsening without crack formation. Creep tests showed loss of the superplasticity in eutectic Sn/Pb alloys with even the lowest Au concentration tested of 0.2 wt% Au. Intermetallic rotation was not a factor in crack propagation, but void presence was. Cracks tended to form in joints containing voids before forming in void-free joints. Crack propagation followed Sn/Sn grain boundaries and Sn/Pb phase boundaries from Pb-rich phase to Pb-rich phase.

    10. Star Cluster Formation in Cosmological Simulations. I. Properties of Young Clusters

      NASA Astrophysics Data System (ADS)

      Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.; Meng, Xi; Semenov, Vadim A.; Kravtsov, Andrey V.

      2017-01-01

      We present a new implementation of star formation in cosmological simulations by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope is α ≈ 1.8{--}2, while the cutoff at high mass scales with the star formation rate (SFR). A related trend is a positive correlation between the surface density of the SFR and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clusters is preferred during bursts of star formation. These bursts are often associated with major-merger events. We also find that the median timescale for cluster formation ranges from 0.5 to 4 Myr and decreases systematically with increasing star formation efficiency. Local variations in the gas density and cluster accretion rate naturally lead to the scatter of the overall formation efficiency by an order of magnitude, even when the instantaneous efficiency is kept constant. Comparison of the formation timescale with the observed age spread of young star clusters provides an additional important constraint on the modeling of star formation and feedback schemes.

    11. Laser desorption and matrix-assisted laser desorption/ionization mass spectrometry of 29-kDa Au:SR cluster compounds.

      PubMed

      Schaaff, T Gregory

      2004-11-01

      Positive and negative ions generated by laser-based ionization methods from three gold:thiolate cluster compounds are mass analyzed by time-of-flight mass spectrometry. The three compounds have similar inorganic core masses ( approximately 29 kDa, approximately 145 Au atoms) but different n-alkanethiolate ligands associated with each cluster compound (Au:SR, R = butane, hexane, dodecane). Irradiation of neat films (laser desorption/ionization) and films generated by dilution of the cluster compounds in an organic acid matrix (matrix-assisted laser desorption/ionization) with a nitrogen laser (337 nm) produced distinct ion abundances that are relevant to different structural aspects of the cluster compound. Laser desorption/ionization of neat Au:SR compound films produces ions consistent with the inorganic core mass (i.e., devoid of original hydrocarbon content). Matrix-assisted laser desorption/ionization produces either ions with m/z values consistent with the core mass of the cluster compounds or ions with m/z values consistent with the approximate molecular weight of the cluster compounds, depending on ionization conditions. The ion abundances, and ionization conditions under which they are detected, provide insight into desorption/ionization processes for these unique cluster compounds as well as other analytes typically studied by matrix-assisted laser desorption/ionization.

    12. Effect of the charge state (z = -1, 0, +1) on the nuclear magnetic resonance of monodisperse Au25[S(CH2)2Ph]18(z) clusters.

      PubMed

      Venzo, Alfonso; Antonello, Sabrina; Gascón, José A; Guryanov, Ivan; Leapman, Richard D; Perera, Neranjan V; Sousa, Alioscka; Zamuner, Martina; Zanella, Alessandro; Maran, Flavio

      2011-08-15

      Monodisperse Au(25)L(18)(0) (L = S(CH(2))(2)Ph) and [n-Oct(4)N(+)][Au(25)L(18)(-)] clusters were synthesized in tetrahydrofuran. An original strategy was then devised to oxidize them: in the presence of bis(pentafluorobenzoyl) peroxide, the neutral or the negatively charged clusters react as efficient electron donors in a dissociative electron-transfer (ET) process, in the former case yielding [Au(25)L(18)(+)][C(6)F(5)CO(2)(-)]. As opposed to other reported redox methods, this dissociative ET approach is irreversible, easily controllable, and clean, particularly for NMR purposes, as no hydrogen atoms are introduced. By using this approach, the -1, 0, and +1 charge states of Au(25)L(18) could be fully characterized by (1)H and (13)C NMR spectroscopy, using one- and two-dimensional techniques, in various solvents, and as a function of temperature. For all charge states, the NMR results and analysis nicely match recent structural findings about the presence of two different ligand populations in the capping monolayer, each resonance of the two ligand families displaying distinct NMR patterns. The radical nature of Au(25)L(18)(0) is particularly evident in the (1)H and (13)C NMR patterns of the inner ligands. The NMR behavior of radical Au(25)L(18)(0) was also simulated by DFT calculations, and the interplay between theory and experiments revealed a fundamental paramagnetic contribution coming from Fermi contact shifts. Interestingly, the NMR patterns of Au(25)L(18)(-) and Au(25)L(18)(+) were found to be quite similar, pointing to the latter cluster form as a diamagnetic species.

    13. The structural and electronic properties of Ag-adsorbed (SiO2)n (n=1-7) clusters.

      PubMed

      Zhao, Gao-feng; Zhi, Li-li; Guo, Ling-ju; Zeng, Zhi

      2007-12-21

      Equilibrium geometries, charge distributions, stabilities, and electronic properties of the Ag-adsorbed (SiO(2))(n) (n=1-7) clusters have been investigated using density functional theory with generalized gradient approximation for exchange-correlation functional. The results show that the Ag atom preferably binds to silicon atom with dangling bond in nearly a fixed direction, and the incoming Ag atoms tend to cluster on the existing Ag cluster leading to the formation of Ag islands. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of the silica clusters is minor, attributing to the tendency of stability order of Ag(SiO(2))(n) (n=1-7) clusters in consistent with silica clusters. In addition, the energy gaps between the highest occupied and lowest unoccupied molecular orbitals remarkably decrease compared with the pure (SiO(2))(n) (n=1-7) clusters, eventually approaching the near infrared radiation region. This suggests that these small clusters may be an alternative material which has a similar functionality in treating cancer to the large gold-coated silica nanoshells and the small Au(3)(SiO(2))(3) cluster.

    14. Electrical properties of Au/CdZnTe/Au detectors grown by the boron oxide encapsulated Vertical Bridgman technique

      NASA Astrophysics Data System (ADS)

      Turturici, A. A.; Abbene, L.; Gerardi, G.; Benassi, G.; Bettelli, M.; Calestani, D.; Zambelli, N.; Raso, G.; Zappettini, A.; Principato, F.

      2016-09-01

      In this work we report on the results of electrical characterization of new CdZnTe detectors grown by the Boron oxide encapsulated Vertical Bridgman technique (B-VB), currently produced at IMEM-CNR (Parma, Italy). The detectors, with gold electroless contacts, have different thicknesses (1 and 2.5 mm) and the same electrode layout, characterized by a central anode surrounded by a guard-ring electrode. Investigations on the charge transport mechanisms and the electrical contact properties, through the modeling of the measured current-voltage (I-V) curves, were performed. Generally, the detectors are characterized by low leakage currents at high bias voltages even at room temperature: 34 nA/cm2 (T=25 °C) at 10,000 V/cm, making them very attractive for high flux X-ray measurements, where high bias voltage operation is required. The Au/CdZnTe barrier heights of the devices were estimated by using the interfacial layer-thermionic-diffusion (ITD) model in the reverse bias voltage range. Comparisons with CdZnTe detectors, grown by Traveling Heater Method (THM) and characterized by the same electrode layout, deposition technique and resistivity, were also performed.

    15. Roles of clustering properties for degree-mixing pattern networks

      NASA Astrophysics Data System (ADS)

      Yu, Pei; Guo, Qiang; Li, Ren-De; Han, Jing-Ti; Liu, Jian-Guo

      The clustering coefficients have been extensively investigated for analyzing the local structural properties of complex networks. In this paper, the clustering coefficients for triangle and square structures, namely C3 and C4, are introduced to measure the local structure properties for different degree-mixing pattern networks. Firstly, a network model with tunable assortative coefficients is introduced. Secondly, the comparison results between the local clustering coefficients C3(k) and C4(k) are reported, one can find that the square structures would increase as the degree k of nodes increasing in disassortative networks. At the same time, the Pearson coefficient p between the clustering coefficients C3(k) and C4(k) is calculated for networks with different assortative coefficients. The Pearson coefficient p changes from ‑0.5 to 0.98 as the assortative coefficient r increasing from ‑0.5 to 0.45, which suggests that the triangle and square structures have the same growth trend in assortative networks whereas the opposite one in disassortative networks. Finally, we analyze the clustering coefficients and for networks with tunable assortative coefficients and find that the clustering coefficient increases from 0.0038 to 0.5952 while the clustering coefficient increases from 0.00039 to 0.005, indicating that the number of cliquishness of the disassortative networks is larger than that of assortative networks.

    16. Au@Ag core/shell cuboids and dumbbells: Optical properties and SERS response

      NASA Astrophysics Data System (ADS)

      Khlebtsov, Boris N.; Liu, Zhonghui; Ye, Jian; Khlebtsov, Nikolai G.

      2015-12-01

      Recent studies have conclusively shown that the plasmonic properties of Au nanorods can be finely controlled by Ag coating. Here, we investigate the effect of asymmetric silver overgrowth of Au nanorods on their extinction and surface-enhanced Raman scattering (SERS) properties for colloids and self-assembled monolayers. Au@Ag core/shell cuboids and dumbbells were fabricated through a seed-mediated anisotropic growth process, in which AgCl was reduced by use of Au nanorods with narrow size and shape distribution as seeds. Upon tailoring the reaction rate, monodisperse cuboids and dumbbells were synthesized and further transformed into water-soluble powders of PEGylated nanoparticles. The extinction spectra of AuNRs were in excellent agreement with T-matrix simulations based on size and shape distributions of randomly oriented particles. The multimodal plasmonic properties of the Au@Ag cuboids and dumbbells were investigated by comparing the experimental extinction spectra with finite-difference time-domain (FDTD) simulations. The SERS efficiencies of the Au@Ag cuboids and dumbbells were compared in two options: (1) individual SERS enhancers in colloids and (2) self-assembled monolayers formed on a silicon wafer by drop casting of nanopowder solutions mixed with a drop of Raman reporters. By using 1,4-aminothiophenol Raman reporter molecules, the analytical SERS enhancement factor (AEF) of the colloidal dumbbells was determined to be 5.1×106, which is an order of magnitude higher than the AEF=4.0×105 for the cuboids. This difference can be explained by better fitting of the dumbbell plasmon resonance to the excitation laser wavelength. In contrast to the colloidal measurements, the AEF=5×107 of self-assembled cuboid monolayers was almost twofold higher than that for dumbbell monolayers, as determined with rhodamine 6G Raman reporters. According to TEM data and electromagnetic simulations, the better SERS response of the self-assembled cuboids is due to uniform

    17. Crystal structures and magnetic properties of CeAu 4Si 2 and CeAu 2Si 2

      NASA Astrophysics Data System (ADS)

      Sefat, Athena S.; Palasyuk, Andriy M.; Bud'ko, Sergey L.; Corbett, John D.; Canfield, Paul C.

      2008-02-01

      Single crystals of CeAu 4Si 2 and CeAu 2Si 2 have been grown out of ternary fluxes rich in Au, and the former, also by sintering the stoichiometric composition at 750 °C. The single-crystal X-ray refinement result for CeAu 4Si 2 is orthorhombic, Cmmm (No. 65, Z=2), different from a tetragonal result found from an X-ray powder diffraction refinement [H. Nakashima, et al., J. Alloys Compds. 424 (2006) 7]. For CeAu 2Si 2, this is the first report of the stoichiometric crystalline phase, in the known tetragonal I4/ mmm structure. The anisotropic field- and temperature-dependent magnetizations, as well as specific heat and resistivity data are compared. Although both compounds have related structural packing, they present unique magnetic features. CeAu 2Si 2 is a typical antiferromagnet with TN=8.8(1) K and CeAu 4Si 2 features a ferromagnetic component below Tc=3.3(1) K. Both phases have effective moments close in value to that of free Ce 3+.

    18. Crystal structures and magnetic properties of CsAu4Si2 and CeAu2Si2

      SciTech Connect

      Sefat, A.; Palasyuk, A.; Bud'ko, S.; Corbett, J.; Canfield, P.

      2007-12-03

      Single crystals of CeAu{sub 4}Si{sub 2} and CeAu{sub 2}Si{sub 2} have been grown out of ternary fluxes rich in Au, and the former, also by sintering the stoichiometric composition at 750 C. The single-crystal X-ray refinement result for CeAu{sub 4}Si{sub 2} is orthorhombic, Cmmm (No. 65, Z=2), different from a tetragonal result found from an X-ray powder diffraction refinement [H. Nakashima, et al., J. Alloys Compds. 424 (2006) 7]. For CeAu{sub 2}Si{sub 2}, this is the first report of the stoichiometric crystalline phase, in the known tetragonal I4/mmm structure. The anisotropic field- and temperature-dependent magnetizations, as well as specific heat and resistivity data are compared. Although both compounds have related structural packing, they present unique magnetic features. CeAu{sub 2}Si{sub 2} is a typical antiferromagnet with T{sub N} = 8.8(1) K and CeAu{sub 4}Si{sub 2} features a ferromagnetic component below T{sub c}=3.3(1) K. Both phases have effective moments close in value to that of free Ce{sup 3+}.

    19. Structural and Dynamical Properties of 29 Galactic Globular Clusters

      NASA Astrophysics Data System (ADS)

      Sohn, Young-Jong; Chun, Mun-Suk; Yim, Hong-Suh; Byun, Yong-Ik

      1997-12-01

      We use B band CCD images to investigate the surface brightness distributions and dynamical properties of 29 Galactic globular clusters. Model fits suggest that 22 clusters show King type surface brightness profiles, while 7 clusters are characterized by power law cusp profiles. For the King type clusters, concentration parameters (c = log(rt =rc)) range from 1.20 to 2.10, and core radii are 0.4 to 1.9 pc. The mean value of power law slopes of 7 cuspy clusters was estimated as ¥á = 1.011 +/- 0.065. Total masses of King type globular clusters are in the range of 1.7 x 104M to 1.0 x 106M with a mean of 1.7 x 105M . A significant positive correlation between mass and mass-to-light ratio of King type globular clusters has been confirmed with a Pearson's correlation coefficient r = 0.52 and a confidence level of 99%. Our data also confirm a linear relation between total mass and absolute magnitude of King type globular clusters.

    20. Lead-free solder alloys: Thermodynamic properties of the (Au + Sb + Sn) and the (Au + Sb) system.

      PubMed

      Hindler, Michael; Guo, Zhongnan; Mikula, Adolf

      2012-12-01

      The thermodynamic properties of liquid (Au-Sb-Sn) alloys were studied with an electromotive force (EMF) method using the eutectic mixture of KCl/LiCl with addition of SnCl2 as a liquid electrolyte. Activities of Sn in the liquid alloys were measured at three cross-sections with constant molar ratios of Au:Sb = 2:1, 1:1, and 1:2 with tin in the concentration range between 5 at.% and 90 at.% from the liquidus of the samples up to 1073 K. The integral Gibbs excess energies and the integral enthalpies at 873 K were calculated by Gibbs-Duhem integration. Additionally liquid Au-Sb alloys have been measured at 913 K with the EMF method as no reliable data for the Gibbs excess energies have been found in literature. The eutectic mixture of KCl/LiCl with addition of SbCl3 has been used as an electrolyte for the measurements. The Gibbs excess energies from the (Au + Sb) system were necessary for the integration of the thermodynamic properties of the ternary (Au + Sb + Sn) system.

    1. Thermoelectric properties of Au-based metallic glass at low temperatures

      NASA Astrophysics Data System (ADS)

      Pryadun, V. V.; Louzguine-Luzgin, D. V.; Shvanskaya, L. V.; Vasiliev, A. N.

      2015-04-01

      The thermoelectric properties of Au49Cu26.9Ag5.5Pd2.3Si16.3 glassy alloy have been studied using electrical resistivity, thermal conductivity and Seebeck coefficient measurements over temperature range 2-390 K. At heating, resistivity ρ decreases in a power-law manner from residual value ρ0 ˜ 150 μΩ cm. The temperature coefficient of resistivity, α = ρ-1(∂ρ/∂ T), is rather small and varies non-monotonously. Thermal conductivity κ rises linearly at low temperatures; it exhibits a plateau-like feature and sharply increases at elevated temperatures. Seebeck coefficient S increases with temperature and exhibits a characteristic "knee" feature. At elevated temperatures, S increases linearly with temperature but with a different slope. It total, thermoelectric properties of Au-based glassy alloy demonstrate behavior of a highly disordered system in a most pronounced manner.

    2. Zinc Oxide nanorod/Au composite arrays and their enhanced photocatalytic properties.

      PubMed

      Liu, Xueqin; Li, Zhen; Zhao, Wen; Zhao, Caixin; Yang, Jianbo; Wang, Yang

      2014-10-15

      In this paper, a high-performance photocatalyst of ZnO nanorod/Au composite arrays (ZAs) was synthesized via a facile low-temperature wet chemical method. The samples were characterized using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) emission spectroscopy and ultraviolet-visible (UV-Vis) absorption. The unique nanostructured composite showed great adsorptivity of dyes, extended light absorption range, and efficient charge separation properties simultaneously. Hence, a significant enhancement in the photocatalytic properties in comparison with pure ZnO as demonstrated in photodegradation of methyl orange due to the incorporation of Au nanoparticles in ZnO nanorods.

    3. Ab initio molecular electrostatic potential of hexanuclear Cu, Ag, and Au clusters

      NASA Astrophysics Data System (ADS)

      Posada-Amarillas, Alvaro

      DFT calculations of electrostatic potential (ESP) are carried out under the PBE/SDD theory level. Planar initial structures are given as input to perform DFT optimization with the aim of obtaining ground state structures. ESP is thus calculated and results show the existence of both, nucleophilic and electrophilic sites. In each case, the latter are located over the cluster planes while the former are observed in cluster vertices. Binding energy is provided, as well as structural parameters of ground state structures. CONACyT-México is acknowledged for funding Project No. 180424.

    4. DFT study of the structures and energetics of 98-atom AuPd clusters

      NASA Astrophysics Data System (ADS)

      Bruma, Alina; Ismail, Ramli; Oliver Paz-Borbón, L.; Arslan, Haydar; Barcaro, Giovanni; Fortunelli, Alessandro; Li, Z. Y.; Johnston, Roy L.

      2012-12-01

      The energetics, structures and segregation of 98-atom AuPd nanoclusters are investigated using a genetic algorithm global optimization technique with the Gupta empirical potential (comparing three different potential parameterisations) followed by local minimizations using Density Functional Theory (DFT) calculations. A shell optimization program algorithm is employed in order to study the energetics of the highly symmetric Leary Tetrahedron (LT) structure and optimization of the chemical ordering of a number of structural motifs is carried out using the Basin Hopping Monte Carlo approach. Although one of the empirical potentials is found to favour the LT structure, it is shown that Marks Decahedral and mixed FCC-HCP motifs are lowest in energy at the DFT level.The energetics, structures and segregation of 98-atom AuPd nanoclusters are investigated using a genetic algorithm global optimization technique with the Gupta empirical potential (comparing three different potential parameterisations) followed by local minimizations using Density Functional Theory (DFT) calculations. A shell optimization program algorithm is employed in order to study the energetics of the highly symmetric Leary Tetrahedron (LT) structure and optimization of the chemical ordering of a number of structural motifs is carried out using the Basin Hopping Monte Carlo approach. Although one of the empirical potentials is found to favour the LT structure, it is shown that Marks Decahedral and mixed FCC-HCP motifs are lowest in energy at the DFT level. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr32517a

    5. A Density Functional Investigation of the Structural, Elastic and Thermodynamic Properties of the Au-Sn Intermetallics

      NASA Astrophysics Data System (ADS)

      Tian, Yali; Zhou, Wei; Wu, Ping

      2016-01-01

      The structural, elastic and thermodynamic properties of AuSn, AuSn2, AuSn4 and Au5Sn are investigated by first-principles calculations. Through calculation, the four intermetallic compounds are all thermodynamically stable and AuSn has the largest negative formation energy. They are all ductile, anisotropic and have low stiffness. In addition, Au5Sn is different from the others, since it is elastically unstable and possesses the highest anisotropy and hardness, mainly due to the strong Au-Au covalent bonds. Based on the quasi-harmonic Debye model, the thermodynamic properties of AuSn, such as the volume, thermal expansion coefficient, bulk modulus, Debye temperature and heat capacity with temperature variation in the range of 0-20 GPa, are obtained. The results indicate the increments of both the volume and thermal expansion coefficient with temperature become slow when the pressure is more than 10 GPa, and the bulk modulus and Debye temperature are almost constant below 100 K and then become linear decreasing as temperature increases. It is found that the influence of temperature on heat capacity is much more obvious than that of pressure.

    6. Bulk Properties of Ni3Al(gamma') With Cu and Au Additions

      NASA Technical Reports Server (NTRS)

      Bozzolo, Guillermo; Ferrante, John

      1995-01-01

      The BFS method for alloys is applied to the study of 200 alloys obtained from adding Cu and Au impurities to a Ni3Al matrix. We analyze the trends in the bulk properties of these alloys (heat of formation, lattice parameter, and bulk modulus) and detect specific alloy compositions for which these quantities have particular values. A detailed analysis of the atomic interactions that lead to the preferred ordering patterns is presented.

    7. Luminescent properties of fluorophosphate glasses with molecular cadmium selenide clusters

      NASA Astrophysics Data System (ADS)

      Kolobkova, E. V.; Kukushkin, D. S.; Nikonorov, N. V.; Sidorov, A. I.; Shakhverdov, T. A.

      2015-02-01

      It is experimentally shown that, prior to the formation of CdSe quantum dots in fluorophosphate glasses with cadmium and selenium ions in the process of synthesis, subnanosized molecular clusters (CdSe) n are formed, which exhibit luminescence in the visible spectral region upon UV excitation. Heat treatment of the glasses increases the size of molecular clusters and makes their optical properties closer to the optical properties of CdSe semiconductor quantum dots. An increase in the sample temperature from 20 to 250°C leads to reversible thermal quenching of the luminescence.

    8. Scaling properties of proton and antiproton production in sqrt[s(NN)]=200 GeV Au+Au collisions.

      PubMed

      Adler, S S; Afanasiev, S; Aidala, C; Ajitanand, N N; Akiba, Y; Alexander, J; Amirikas, R; Aphecetche, L; Aronson, S H; Averbeck, R; Awes, T C; Azmoun, R; Babintsev, V; Baldisseri, A; Barish, K N; Barnes, P D; Bassalleck, B; Bathe, S; Batsouli, S; Baublis, V; Bazilevsky, A; Belikov, S; Berdnikov, Y; Bhagavatula, S; Boissevain, J G; Borel, H; Borenstein, S; Brooks, M L; Brown, D S; Bruner, N; Bucher, D; Buesching, H; Bumazhnov, V; Bunce, G; Burward-Hoy, J M; Butsyk, S; Camard, X; Chai, J-S; Chand, P; Chang, W C; Chernichenko, S; Chi, C Y; Chiba, J; Chiu, M; Choi, I J; Choi, J; Choudhury, R K; Chujo, T; Cianciolo, V; Cobigo, Y; Cole, B A; Constantin, P; d'Enterria, D G; David, G; Delagrange, H; Denisov, A; Deshpande, A; Desmond, E J; Dietzsch, O; Drapier, O; Drees, A; du Rietz, R; Durum, A; Dutta, D; Efremenko, Y V; El Chenawi, K; Enokizono, A; En'yo, H; Esumi, S; Ewell, L; Fields, D E; Fleuret, F; Fokin, S L; Fox, B D; Fraenkel, Z; Frantz, J E; Franz, A; Frawley, A D; Fung, S-Y; Garpman, S; Ghosh, T K; Glenn, A; Gogiberidze, G; Gonin, M; Gosset, J; Goto, Y; Granier de Cassagnac, R; Grau, N; Greene, S V; Grosse Perdekamp, G; Guryn, W; Gustafsson, H-A; Hachiya, T; Haggerty, J S; Hamagaki, H; Hansen, A G; Hartouni, E P; Harvey, M; Hayano, R; He, X; Heffner, M; Hemmick, T K; Heuser, J M; Hibino, M; Hill, J C; Holzmann, W; Homma, K; Hong, B; Hoover, A; Ichihara, T; Ikonnikov, V V; Imai, K; Isenhower, L D; Ishihara, M; Issah, M; Isupov, A; Jacak, B V; Jang, W Y; Jeong, Y; Jia, J; Jinnouchi, O; Johnson, B M; Johnson, S C; Joo, K S; Jouan, D; Kametani, S; Kamihara, N; Kang, J H; Kapoor, S S; Katou, K; Kelly, S; Khachaturov, B; Khanzadeev, A; Kikuchi, J; Kim, D H; Kim, D J; Kim, D W; Kim, E; Kim, G-B; Kim, H J; Kistenev, E; Kiyomichi, A; Kiyoyama, K; Klein-Boesing, C; Kobayashi, H; Kochenda, L; Kochetkov, V; Koehler, D; Kohama, T; Kopytine, M; Kotchetkov, D; Kozlov, A; Kroon, P J; Kuberg, C H; Kurita, K; Kuroki, Y; Kweon, M J; Kwon, Y; Kyle, G S; Lacey, R; Ladygin, V; Lajoie, J G; Lebedev, A; Leckey, S; Lee, D M; Lee, S; Leitch, M J; Li, X H; Lim, H; Litvinenko, A; Liu, M X; Liu, Y; Maguire, C F; Makdisi, Y I; Malakhov, A; Manko, V I; Mao, Y; Martinez, G; Marx, M D; Masui, H; Matathias, F; Matsumoto, T; McGaughey, P L; Melnikov, E; Messer, F; Miake, Y; Milan, J; Miller, T E; Milov, A; Mioduszewski, S; Mischke, R E; Mishra, G C; Mitchell, J T; Mohanty, A K; Morrison, D P; Moss, J M; Mühlbacher, F; Mukhopadhyay, D; Muniruzzaman, M; Murata, J; Nagamiya, S; Nagle, J L; Nakamura, T; Nandi, B K; Nara, M; Newby, J; Nilsson, P; Nyanin, A S; Nystrand, J; O'Brien, E; Ogilvie, C A; Ohnishi, H; Ojha, I D; Okada, K; Ono, M; Onuchin, V; Oskarsson, A; Otterlund, I; Oyama, K; Ozawa, K; Pal, D; Palounek, A P T; Pantuev, V S; Papavassiliou, V; Park, J; Parmar, A; Pate, S F; Peitzmann, T; Peng, J-C; Peresedov, V; Pinkenburg, C; Pisani, R P; Plasil, F; Purschke, M L; Purwar, A; Rak, J; Ravinovich, I; Read, K F; Reuter, M; Reygers, K; Riabov, V; Riabov, Y; Roche, G; Romana, A; Rosati, M; Rosnet, P; Ryu, S S; Sadler, M E; Saito, N; Sakaguchi, T; Sakai, M; Sakai, S; Samsonov, V; Sanfratello, L; Santo, R; Sato, H D; Sato, S; Sawada, S; Schutz, Y; Semenov, V; Seto, R; Shaw, M R; Shea, T K; Shibata, T-A; Shigaki, K; Shiina, T; Silva, C L; Silvermyr, D; Sim, K S; Singh, C P; Singh, V; Sivertz, M; Soldatov, A; Soltz, R A; Sondheim, W E; Sorensen, S P; Sourikova, I V; Staley, F; Stankus, P W; Stenlund, E; Stepanov, M; Ster, A; Stoll, S P; Sugitate, T; Sullivan, J P; Takagui, E M; Taketani, A; Tamai, M; Tanaka, K H; Tanaka, Y; Tanida, K; Tannenbaum, M J; Tarján, P; Tepe, J D; Thomas, T L; Tojo, J; Torii, H; Towell, R S; Tserruya, I; Tsuruoka, H; Tuli, S K; Tydesjö, H; Tyurin, N; Van Hecke, H W; Velkovska, J; Velkovsky, M; Villatte, L; Vinogradov, A A; Volkov, M A; Vznuzdaev, E; Wang, X R; Watanabe, Y; White, S N; Wohn, F K; Woody, C L; Xie, W; Yang, Y; Yanovich, A; Yokkaichi, S; Young, G R; Yushmanov, I E; Zajc, W A; Zhang, C; Zhou, S; Zolin, L

      2003-10-24

      We report on the yield of protons and antiprotons, as a function of centrality and transverse momentum, in Au+Au collisions at sqrt[s(NN)]=200 GeV measured at midrapidity by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider. In central collisions at intermediate transverse momenta (1.5Au+Au, p+p, and e(+)e(-) collisions. This enhancement is limited to p(T)<5 GeV/c as deduced from the ratio of charged hadrons to pi(0) measured in the range 1.5

    9. Physicochemical and catalytic properties of Au nanorods micro-assembled in solvents of varying dipole moment and refractive index

      SciTech Connect

      Kaur, Rupinder; Pal, Bonamali

      2015-02-15

      Highlights: • Physicochemical activities of Au nanorods in water largely differ from organic solvents. • Au nanorods agglomeration increased with dipole moments of different polar solvents. • Refractive indexes of Au nanorods dispersion in various polar solvents are enhanced. • Electrokinetics significantly altered depending on agglomerated size of Au nanorods. • Catalysis or co-catalysis activity is varied as per the extent of Au nanorods coagulation. - Abstract: This paper deals with the impact of dipole moment (1.66–3.96 D) and refractive index (1.333–1.422) of the dispersion solvent on the plasmon absorption, surface charge, zeta potential, and adsorption properties of Au nanorods (AuNRs). AuNRs (length ≈ 53 nm and width ≈ 20 nm) undergo agglomeration (size 50–180 nm) with increase in the dipole moment of solvent (iPrOH < MeOH < DMF < DMSO). Whereas, no such coagulation occurs in H{sub 2}O and CCl{sub 4} suspension as confirmed by DLS and TEM size distribution. The electrostatic interaction of AuNRs with its surface adsorbed solvent dipoles leads to alteration of the their ionic state, absolute electronic charge and zeta potential (+49.79 mV in H{sub 2}O, +8.99 mV in DMF and −4.65 mV in MeOH dispersion) to a greater extent. This interaction distinctly modifies the adsorption behavior of polar molecules like p-nitrophenol and salicylic acid on AuNRs surface, as evidenced by the measured changes in their electro-kinetic parameters. As a result, we observe a substantial difference in catalytic and co-catalytic activities of AuNRs dispersed in various solvents as mentioned above because the catalytic properties of AuNRs are strongly dependent on the type of solvent in which they are dispersed.

    10. Electronic states of linear Au clusters supported on metal surfaces: why are they like those of a particle in a box?

      PubMed

      Mills, Greg; Wang, Bing; Ho, Wilson; Metiu, Horia

      2004-04-22

      Scanning tunneling spectroscopy and microscopy show that the empty states of linear Au clusters supported on a metal surface behave as if they are the states of an electron in an empty one-dimensional box. We show here that certain difficulties of this description are removed by a particle-in-a-cylinder model. This interpretation is supported by density functional calculations.

    11. A comparative DFT study of interactions of Au and small gold clusters Aun (n = 2-4) with CH3S and CH2 radicals

      NASA Astrophysics Data System (ADS)

      Blaško, Martin; Rajský, Tomáš; Urban, Miroslav

      2017-03-01

      We compare DFT binding energies (BEs) of Au and small gold clusters interacting with CH3S and CH2 ligands (Aun-L complexes, n = 1-4). The spin state and the binding mechanism in Aun-L varies with the participation of singly occupied non-bonding orbitals or doubly occupied lone-pair orbitals of a ligand and on the number of atoms (even or odd) of Aun. The highest BE, 354 kJ/mol, exhibits the Au3-CH2 complex with the covalent bond in which participate two singly occupied orbitals of the triplet state of CH2. With CH3S the highest BE (277 kJ/mol) is calculated for Au3-SCH3 with the single Au-S bond.

    12. Uncommon and Emissive {[Au2(C3H6NS2)2][Au(C3H6NS2)2]2(PF6)2} Mixed Au(+) and Au(3+) Pseudotetranuclear Crystalline Compound: Synthesis, Structural Characterization, and Optical Properties.

      PubMed

      Langaro, Ana P; Souza, Ana K R; Morassuti, Claudio Y; Lima, Sandro M; Casagrande, Gleison A; Deflon, Victor M; Nunes, Luiz A O; Da Cunha Andrade, Luis H

      2016-11-23

      An uncommon emissive pseudotetranuclear compound, {[Au2(C3H6NS2)2][Au(C3H6NS2)2]2(PF6)2}, was synthesized and characterized in terms of its structure and optical properties. The synthesis produced a crystalline compound composed of four gold atoms with two different oxidation states (Au(+) and Au(3+)) in the same crystalline structure. The title complex belonged to a triclinic crystalline system involving the centrosymmetric P1̅ space group. X-ray diffractometry and vibrational spectroscopy (infrared, Raman, and SERS) were used for structural characterization of the new crystal. The vibrational spectroscopy techniques supported the X-ray diffraction results and confirmed the presence of bonds including Au-Au and Au-S. Optical characterization performed using UV-vis spectroscopy showed that under ultraviolet excitation, the emissive crystalline complex presented characteristic broad luminescent bands centered at 420 and 670 nm.

    13. DFT study of the structures and energetics of 98-atom AuPd clusters.

      PubMed

      Bruma, Alina; Ismail, Ramli; Paz-Borbón, L Oliver; Arslan, Haydar; Barcaro, Giovanni; Fortunelli, Alessandro; Li, Z Y; Johnston, Roy L

      2013-01-21

      The energetics, structures and segregation of 98-atom AuPd nanoclusters are investigated using a genetic algorithm global optimization technique with the Gupta empirical potential (comparing three different potential parameterisations) followed by local minimizations using Density Functional Theory (DFT) calculations. A shell optimization program algorithm is employed in order to study the energetics of the highly symmetric Leary Tetrahedron (LT) structure and optimization of the chemical ordering of a number of structural motifs is carried out using the Basin Hopping Monte Carlo approach. Although one of the empirical potentials is found to favour the LT structure, it is shown that Marks Decahedral and mixed FCC-HCP motifs are lowest in energy at the DFT level.

    14. PHOTOMETRIC PROPERTIES OF THE M33 STAR CLUSTER SYSTEM

      SciTech Connect

      San Roman, Izaskun; Sarajedini, Ata; Aparicio, Antonio E-mail: ata@astro.ufl.ed

      2010-09-10

      We present a catalog of 2990 extended sources in a 1{sup 0} x 1{sup 0} area centered on M33 using the MegaCam camera on the 3.6 m Canada-France-Hawaii Telescope. The catalog includes 599 new candidate stellar clusters, 204 previously confirmed clusters, 1969 likely background galaxies, and 218 unknown extended objects. We present ugriz integrated magnitudes of the candidates and confirmed star clusters (SCs) as well as the full width at half maximum, ellipticity, and stellarity. Based on the properties of the confirmed SCs, we select a sub-sample of highly probable clusters composed of 246 objects. The integrated photometry of the complete cluster catalog reveals a wide range of colors of -0.4 < (g - r) < 1.5 and -1.0 < (r - i) < 1.0 with no obvious cluster subpopulations. Comparisons with models of simple stellar populations suggest a large range of ages some as old as {approx}10 Gyr. In addition, we find a sequence in the color-color diagrams that deviates from the expected direction of evolution. This feature could be associated with very young clusters (<10{sup 7} yr) possessing significant nebular emission. Analysis of the radial density distribution suggests that the cluster system of M33 has suffered from significant depletion possibly due to interactions with M31. We also detect a gap in the cluster distribution in the color-color diagram at (g - r) {approx_equal} 0.3 and (u - g) {approx_equal} 0.8. This gap could be interpreted as an evolutionary effect. This complete catalog provides promising targets for deep photometry and high-resolution spectroscopy to study the structure and star formation history of M33.

    15. Structural and Optical Properties of Discrete Dendritic Pt Nanoparticles on Colloidal Au Nanoprisms

      PubMed Central

      2016-01-01

      Catalytic and optical properties can be coupled by combining different metals into nanoscale architectures in which both the shape and the composition provide fine-tuning of functionality. Here, discrete, small Pt nanoparticles (diameter = 3–6 nm) were grown in linear arrays on Au nanoprisms, and the resulting structures are shown to retain strong localized surface plasmon resonances. Multidimensional electron microscopy and spectroscopy techniques (energy-dispersive X-ray spectroscopy, electron tomography, and electron energy-loss spectroscopy) were used to unravel their local composition, three-dimensional morphology, growth patterns, and optical properties. The composition and tomographic analyses disclose otherwise ambiguous details of the Pt-decorated Au nanoprisms, revealing that both pseudospherical protrusions and dendritic Pt nanoparticles grow on all faces of the nanoprisms (the faceted or occasionally twisted morphologies of which are also revealed), and shed light on the alignment of the Pt nanoparticles. The electron energy-loss spectroscopy investigations show that the Au nanoprisms support multiple localized surface plasmon resonances despite the presence of pendant Pt nanoparticles. The plasmonic fields at the surface of the nanoprisms indeed extend into the Pt nanoparticles, opening possibilities for combined optical and catalytic applications. These insights pave the way toward comprehensive nanoengineering of multifunctional bimetallic nanostructures, with potential applications in plasmon-enhanced catalysis and in situ monitoring of chemical processes via surface-enhanced spectroscopy. PMID:27688821

    16. Transport properties of droplet clusters in gravity-free fields

      NASA Technical Reports Server (NTRS)

      Brenner, Howard

      1986-01-01

      Clusters of liquid droplets are suspended in an atmosphere of saturated vapor and are subjected to an external force field. This system can be modeled as a continuum whose macroscopic properties may be determined by applying the generalized theory of Taylor dispersion.

    17. Composition dependent adsorption of multiple CO molecules on binary silver-gold clusters Ag(n)Au(m)+ (n + m = 5): theory and experiment.

      PubMed

      Popolan, Denisia M; Nössler, Melanie; Mitrić, Roland; Bernhardt, Thorsten M; Bonacić-Koutecký, Vlasta

      2010-07-28

      The binding energies of multiple CO molecules to five-atom silver-gold cluster cations have been obtained employing temperature dependent gas phase ion trap measurements and ab initio calculations. The CO binding energies to Ag(n)Au(m)(+) (n + m = 5) decrease with increasing number of silver atoms. Most strikingly, after the adsorption of the fourth CO to Au(5)(+) and of the third CO to Ag(5)(+), respectively, a pronounced decrease in the binding energies of further CO molecules was observed. This is related to a CO-induced structural transformation yielding more compact metal cluster geometries. First principles calculations revealed that the exact structure of the carbonyl complexes with multiple CO and the nature of the CO-induced structural transformation strongly depend on the composition of the metal cluster as well as on the number of adsorbed CO molecules.

    18. Effects of cross-section on mechanical properties of Au nanowire

      SciTech Connect

      Vazinishayan, Ali; Yang, Shuming Duongthipthewa, Anchalee; Wang, Yiming

      2016-02-15

      The aim of this paper is study of the effects of multiple cross-section of Au nanowire on mechanical properties. Different cross-section models of Au nanowires including circular, hexagonal, pentagonal and rectangular were simulated by finite element modeling using ABAQUS. In this study, the bending technique was applied so that both ends of the model were clamped with mid-span under loading condition. The cross-sections had the length of 400 nm and the diameter of 40 nm, except the circular cross-section while the rest of the cross-sections had an equivalent diameter. Von Misses stresses distribution were used to define the stress distribution in the cross-section under loading condition, and elastic deformation was analyzed by the beam theory. The results disclosed that the circular and the rectangular models had highest and lowest strengths against plastic deformation, respectively.

    19. Structural and Magnetic Properties of Fe and Au Ion-Implanted Al2O3 Single Crystals

      NASA Astrophysics Data System (ADS)

      Kinoshita, Ryosuke; Sakamoto, Isao; Hayashi, Nobuyuki; Nomura, Kiyoshi; Honda, Shigeo; Ishida, Tomoya; Iio, Satoshi; Tashiro, Hiroyuki; Toriyama, Tamotsu

      2011-01-01

      Au ion implantation in Fe ion-implanted Al2O3 (Fe/Al2O3) has been performed in order to tailor the structural, magnetic and optical properties of Fe granules in Al2O3 matrix. After Au ion implantation, Rutherford backscattering (RBS) measurements indicate the decrease and the redistribution of retained Fe atoms with the inclusion of Au atoms, and the patterns of X-ray diffraction (XRD) show the formation of Au granules in the Fe/Al2O3. Besides, the magnetization curves of the Fe/Al2O3 after Au ion implantation show still the superparamagnetic characteristics and the decrease of saturation magnetization, and the optical absorption measurements indicate the formation of Au granules in the Fe/Al2O3 in accordance with the XRD result. In addition, we investigated a behavior of Fe granules in Al2O3 matrix by conversion electron Mössbauer spectroscopy (CEMS), which indicates the decrease of superparamagnetic state as a function of Au ion dose. As a result, it is suggested that Au ion implantation has potentialities to tailor the physical properties of Fe granules in Al2O3 matrix.

    20. Fluorescence analysis of 6-mercaptopurine with the use of a nano-composite consisting of BSA-capped Au nano-clusters and core-shell Fe3O4-SiO2 nanoparticles.

      PubMed

      Li, Zhuo; Wang, Yong; Ni, Yongnian; Kokot, Serge

      2015-08-15

      A magnetic and fluorescent nano-composite was prepared. It comprised of a core of Fe3O4 nanoparticles (NPs), a silica shell and satellitic Au nano-clusters (AuNCs) capped with bovine serum albumin (BSA). This nano-composite has many desirable properties, e.g. magnetism, red emission, high water solubility, and high resistance to photo-bleaching. On addition of the analyte, 6-mercaptopurine (6-MP) or indeed other similar thiols, AuNCs formed aggregates because the existing cross-links within the Fe3O4 NPs@SiO2 and AuNC structure were broken in favor of the gold-thiol bonds. On suitable irradiation of such aggregates, red fluorescence was emitted at 613 nm. It decreased significantly as a function of the added 6-MP concentration, and the quenching ratio (F0 - F) / F0 was related linearly to the concentration of 6-MP in the range of 0.01 to 0.5 μmol L(-1). The detection limit was 0.004 μmol L(-1) (S/N=3). The method was strongly selective for 6-MP in the presence of oxidants, phenols, heavy-metal ions, and especially bio-thiols.

    1. Electronic and magnetic properties of small rhodium clusters

      SciTech Connect

      Soon, Yee Yeen; Yoon, Tiem Leong; Lim, Thong Leng

      2015-04-24

      We report a theoretical study of the electronic and magnetic properties of rhodium-atomic clusters. The lowest energy structures at the semi-empirical level of rhodium clusters are first obtained from a novel global-minimum search algorithm, known as PTMBHGA, where Gupta potential is used to describe the atomic interaction among the rhodium atoms. The structures are then re-optimized at the density functional theory (DFT) level with exchange-correlation energy approximated by Perdew-Burke-Ernzerhof generalized gradient approximation. For the purpose of calculating the magnetic moment of a given cluster, we calculate the optimized structure as a function of the spin multiplicity within the DFT framework. The resultant magnetic moments with the lowest energies so obtained allow us to work out the magnetic moment as a function of cluster size. Rhodium atomic clusters are found to display a unique variation in the magnetic moment as the cluster size varies. However, Rh{sub 4} and Rh{sub 6} are found to be nonmagnetic. Electronic structures of the magnetic ground-state structures are also investigated within the DFT framework. The results are compared against those based on different theoretical approaches available in the literature.

    2. Evidence for rapid epithermal mineralization and coeval bimodal volcanism, Bruner Au-Ag property, NV USA

      NASA Astrophysics Data System (ADS)

      Baldwin, Dylan

      The character of Au-Ag mineralization and volcanic/hydrothermal relationships at the underexplored Miocene-age Bruner low-sulfidation epithermal Au-Ag deposit are elucidated using field and laboratory studies. Bruner is located in central Nevada within the Great Basin extensional province, near several major volcanic trends (Western Andesite, Northern Nevada Rift) associated with world-class Miocene-age epithermal Au-Ag provinces. Despite its proximity to several >1 Moz Au deposits, and newly discovered high-grade drill intercepts (to 117 ppm Au/1.5m), there is no published research on the deposit, the style of mineralization has not been systematically characterized, and vectors to mineralization remain elusive. By investigating the nature of mineralization and time-space relationships between volcanic/hydrothermal activity, the deposit has been integrated into a regional framework, and exploration targeting improved. Mineralization occurs within narrow quartz + adularia +/- pyrite veins that manifest as sheeted/stockwork zones, vein swarms, and rare 0.3-2 m wide veins hosted by two generations of Miocene high-K, high-silica rhyolite flow dome complexes overlying an andesite flow unit. The most prominent structural controls on veining are N­striking faults and syn-mineral basalt/rhyolite dikes. Productive veins have robust boiling indicators (high adularia content, bladed quartz after calcite, recrystallized colloform quartz bands), lack rhythmic banding, and contain only 1-2 stages; these veins overprint, or occur separately from another population of barren to weakly mineralized rhythmically banded quartz-only veins. Ore minerals consist of coarse Au0.5Ag 0.5 electrum, fine Au0.7Ag0.3 electrum, acanthite, uytenbogaardtite (Ag3AuS2) and minor embolite Ag(Br,Cl). Now deeply oxidized, veins typically contain <1% pyrite/goethite + Au-Ag minerals, with trace marcasite and microscopic Fe-poor sphalerite. Property-scale K-feldspar alteration related to a pre

    3. Phosphine-stabilised Au{sub 9} clusters interacting with titania and silica surfaces: The first evidence for the density of states signature of the support-immobilised cluster

      SciTech Connect

      Andersson, Gunther G. E-mail: vladimir.golovko@canterbury.ac.nz Al Qahtani, Hassan S.; Golovko, Vladimir B. E-mail: vladimir.golovko@canterbury.ac.nz; Alvino, Jason F.; Bennett, Trystan; Wrede, Oliver; Mejia, Sol M.; Metha, Gregory F. E-mail: vladimir.golovko@canterbury.ac.nz; Adnan, Rohul; Gunby, Nathaniel; Anderson, David P.

      2014-07-07

      Chemically made, atomically precise phosphine-stabilized clusters Au{sub 9}(PPh{sub 3}){sub 8}(NO{sub 3}){sub 3} were deposited on titania and silica from solutions at various concentrations and the samples heated under vacuum to remove the ligands. Metastable induced electron spectroscopy was used to determine the density of states at the surface, and X-ray photoelectron spectroscopy for analysing the composition of the surface. It was found for the Au{sub 9} cluster deposited on titania that the ligands react with the titania substrate. Based on analysis using the singular value decomposition algorithm, the series of MIE spectra can be described as a linear combination of 3 base spectra that are assigned to the spectra of the substrate, the phosphine ligands on the substrate, and the Au clusters anchored to titania after removal of the ligands. On silica, the Au clusters show significant agglomeration after heat treatment and no interaction of the ligands with the substrate can be identified.

    4. PROPERTIES OF THE OLD OPEN CLUSTER CZERNIK 30

      SciTech Connect

      Hayes, Christian R.; Friel, Eileen D.; Slack, Taleah J.; Boberg, Owen M. E-mail: efriel@indiana.edu

      2015-12-15

      We present new photometric and spectroscopic data of the old open cluster Czernik 30. Wide field BVI photometry allows us to correct for the high field contamination by statistical subtraction to produce a color–magnitude diagram (CMD) that clearly reveals the cluster sequence. From spectra of stars in the cluster field obtained with the Hydra spectrograph on the Wisconsin-Indiana-Yale-NOAO 3.5 m telescope we determine a mean cluster velocity of +79.9 ± 1.5 km s{sup −1} and provide membership information that helps further define the cluster giant branch and red clump. Stellar abundances for the brighter giants in the cluster indicate a mean metallicity of [Fe/H] = −0.2 ± 0.15. Fitting theoretical isochrones to the CMD we determine the following properties of Czernik 30: age = 2.8 ± 0.3 Gyr, (m − M){sub v} = 14.8 ± 0.1, E(B − V) = 0.24 ± 0.06, and E(V − I) = 0.36 ± 0.04. Czernik 30 is an old, sub-solar metallicity cluster located at a Galactocentric radius of R{sub gc}  ∼ 13.3 kpc. Given its age and position just beyond the transition to a flat abundance gradient seen in the open cluster population, Czernik 30 provides an interesting target for future observations.

    5. Geochemical properties of soils surrounding the Deliklitaş Au deposit, Turkey

      NASA Astrophysics Data System (ADS)

      Kirat, Güllü; Aydin, Nasuh

      2016-08-01

      The Deliklitaş gold deposit is in northwest Turkey, where a renowned gold province containing many major hydrothermal deposits related to Tertiary volcanic rocks. Because of the limited outcrops in the region, one of the most effective ways to prospect for new deposits is soil sampling. In this study, 183 soil samples were systematically collected from the area around the Deliklitaş Au deposit. Metal content of the samples, and their relationships and distribution according to distance away from the ore body were statistically investigated. The analysis of metals and metalloids in soil samples yielded the following metal ranges: Au from 0.005 to 0.54 mg/kg (average 0.04); Ag from 0.03 to 2.66 (average 0.22); As from 3.4 to 315 (average 30.3); Sb from 0.15 to 19.25 (average 1.62); Cu from 2.5 to 35 (average 11.73); Pb from 17.4 to 545 (average 73.76) and from Zn 14-1240 mg/kg of soil (average 106.71). For the areal distribution of metals 50%, 70%, 90% and 95% of the cumulative data were used for contouring element contents in the soils, using 50% as the baseline value and 95% as the anomalous value. Eigen values, Varimax Rotation method with Kaiser Normalization tested and determined the suitability of the number of data sets. Factor numbers were determined as 3, according to Eigen values determined for the soil samples. Factor 1 refers to ore minerals of epithermal system, Factor 2 refers to main rock sources of Pb and Zn and Factor 3 refers to environmental effects. Agsbnd Au, Pbsbnd Zn and Sbsbnd As pairs show high correlation in the cluster analysis indicating element relations. Please add an overarching sentence here, on implications etc.

    6. Structural and electronic properties of graphene nanoflakes on Au(111) and Ag(111)

      NASA Astrophysics Data System (ADS)

      Tesch, Julia; Leicht, Philipp; Blumenschein, Felix; Gragnaniello, Luca; Fonin, Mikhail; Marsoner Steinkasserer, Lukas Eugen; Paulus, Beate; Voloshina, Elena; Dedkov, Yuriy

      2016-03-01

      We investigate the electronic properties of graphene nanoflakes on Ag(111) and Au(111) surfaces by means of scanning tunneling microscopy and spectroscopy as well as density functional theory calculations. Quasiparticle interference mapping allows for the clear distinction of substrate-derived contributions in scattering and those originating from graphene nanoflakes. Our analysis shows that the parabolic dispersion of Au(111) and Ag(111) surface states remains unchanged with the band minimum shifted to higher energies for the regions of the metal surface covered by graphene, reflecting a rather weak interaction between graphene and the metal surface. The analysis of graphene-related scattering on single nanoflakes yields a linear dispersion relation E(k), with a slight p-doping for graphene/Au(111) and a larger n-doping for graphene/Ag(111). The obtained experimental data (doping level, band dispersions around EF, and Fermi velocity) are very well reproduced within DFT-D2/D3 approaches, which provide a detailed insight into the site-specific interaction between graphene and the underlying substrate.

    7. Gas sensing properties of MWCNT layers electrochemically decorated with Au and Pd nanoparticles

      PubMed Central

      Alvisi, Marco; Rossi, Riccardo; Cassano, Gennaro; Di Franco, Cinzia; Palmisano, Francesco; Torsi, Luisa

      2017-01-01

      Multiwalled carbon nanotube (MWCNT)-based chemiresistors were electrochemically decorated with Au and Pd nanoparticles (NPs), resulting in an improvement in the detection of gaseous pollutants as compared to sensors based on pristine MWCNTs. Electrophoresis was used to decorate MWCNTs with preformed Au or Pd NPs, thus preserving their nanometer-sized dimensions and allowing the metal content to be tuned by simply varying the deposition time. The sensing response of unmodified and metal-decorated MWCNTs was evaluated towards different gaseous pollutants (e.g., NO2, H2S, NH3 and C4H10) at a wide range of concentrations in the operating temperature range of 45–200 °C. The gas sensing results were related to the presence, type and loading of metal NPs used in the MWCNT functionalization. Compared to pristine MWCNTs, metal-decorated MWCNTs revealed a higher gas sensitivity, a faster response, a better stability, reversibility and repeatability, and a low detection limit, where all of these sensing properties were controlled by the type and loading of the deposited metal catalytic NPs. Specifically, in the NO2 gas sensing experiments, MWCNTs decorated with the lowest Au content revealed the highest sensitivity at 150 °C, while MWCNTs with the highest Pd loading showed the highest sensitivity when operated at 100 °C. Finally, considering the reported gas sensing results, sensing mechanisms have been proposed, correlating the chemical composition and gas sensing responses. PMID:28382249

    8. Resonance energy transfer between fluorescent BSA protected Au nanoclusters and organic fluorophores

      NASA Astrophysics Data System (ADS)

      Raut, Sangram; Rich, Ryan; Fudala, Rafal; Butler, Susan; Kokate, Rutika; Gryczynski, Zygmunt; Luchowski, Rafal; Gryczynski, Ignacy

      2013-12-01

      Bovine serum albumin (BSA) protected nanoclusters (Au and Ag) represent a group of nanomaterials that holds great promise in biophysical applications due to their unique fluorescence properties and lack of toxicity. These metal nanoclusters have utility in a variety of disciplines including catalysis, biosensing, photonics, imaging and molecular electronics. However, they suffer from several disadvantages such as low fluorescence quantum efficiency (typically near 6%) and broad emission spectrum (540 nm to 800 nm). We describe an approach to enhance the apparent brightness of BSA Au clusters by linking them with a high extinction donor organic dye pacific blue (PB). In this conjugate PB acts as a donor to BSA Au clusters and enhances its brightness by resonance energy transfer (RET). We found that the emission of BSA Au clusters can be enhanced by a magnitude of two-fold by resonance energy transfer (RET) from the high extinction donor PB, and BSA Au clusters can act as an acceptor to nanosecond lifetime organic dyes. By pumping the BSA Au clusters using a high extinction donor, one can increase the effective brightness of less bright fluorophores like BSA Au clusters. Moreover, we prepared another conjugate of BSA Au clusters with the near infrared (NIR) dye Dylight 750 (Dy750), where BSA Au clusters act as a donor to Dy750. We observed that BSA Au clusters can function as a donor, showing 46% transfer efficiency to the NIR dye Dy750 with a long lifetime component in the acceptor decay through RET. Such RET-based probes can be used to prevent the problems of a broad emission spectrum associated with the BSA Au clusters. Moreover, transferring energy from BSA Au clusters to Dy750 will result in a RET probe with a narrow emission spectrum and long lifetime component which can be utilized in imaging applications.Bovine serum albumin (BSA) protected nanoclusters (Au and Ag) represent a group of nanomaterials that holds great promise in biophysical applications due to

    9. Cluster properties via Sunyaev-Zel'dovich effect

      NASA Astrophysics Data System (ADS)

      Cooray, Asantha

      2005-01-01

      We will discuss the role played by the Sunyaev-Zel'dovich (SZ) effect in uderstanding the physical properties of the intracluster medium. While the SZ effect has been considered widely for its cosmological purposes when combined with multiwavelength observations the SZ effect data can also be used to understand the nature and evolution of the ICM including its thermal structure and the presence of nonthermal plasma. We also discuss future opportunities on this aspect involving observations from the planned South Pole Telescope Planck mission and various other attempts to image the SZ effect in galaxy clusters using wide-field bolometer arrays and other techniques. We will also explore the connection between gas in clusters and the general intergalactic medium and how one can use detailed wide-field SZ maps beyond those towards individual clusters to study such possibilities.

    10. Magnetic properties of nearly stoichiometric CeAuBi{sub 2} heavy fermion compound

      SciTech Connect

      Adriano, C.; Jesus, C. B. R.; Pagliuso, P. G.; Rosa, P. F. S.; Grant, T.; Fisk, Z.; Garcia, D. J.

      2015-05-07

      Motivated by the interesting magnetic anisotropy found in the heavy fermion family CeTX{sub 2} (T = transition metal and X = pnictogen), here, we study the novel parent compound CeAu{sub 1−x}Bi{sub 2−y} by combining magnetization, pressure dependent electrical resistivity, and heat-capacity measurements. The magnetic properties of our nearly stoichiometric single crystal sample of CeAu{sub 1−x}Bi{sub 2−y} (x = 0.92 and y = 1.6) revealed an antiferromagnetic ordering at T{sub N} = 12 K with an easy axis along the c-direction. The field dependent magnetization data at low temperatures reveal the existence of a spin-flop transition when the field is applied along the c-axis (H{sub c} ∼ 7.5 T and T = 5 K). The heat capacity and pressure dependent resistivity data suggest that CeAu{sub 0.92}Bi{sub 1.6} exhibits a weak heavy fermion behavior with strongly localized Ce{sup 3+} 4f electrons. Furthermore, the systematic analysis using a mean field model including anisotropic nearest-neighbors interactions and the tetragonal crystalline electric field (CEF) Hamiltonian allows us to extract a CEF scheme and two different values for the anisotropic J{sub RKKY} exchange parameters between the Ce{sup 3+} ions in this compound. Thus, we discuss a scenario, considering both the anisotropic magnetic interactions and the tetragonal CEF effects, in the CeAu{sub 1−x}Bi{sub 2−y} compounds, and we compare our results with the isostructural compound CeCuBi{sub 2}.

    11. Tuning the Luminescent Properties of a Ag/Au Tetranuclear Complex Featuring Metallophilic Interactions via Solvent-Dependent Structural Isomerization.

      PubMed

      Donamaría, Rocío; Gimeno, M Concepción; Lippolis, Vito; López-de-Luzuriaga, José M; Monge, Miguel; Olmos, M Elena

      2016-11-07

      In this paper the reaction products of the basic gold(I) species [Au(C6Cl5)2](-) against the acid salt Ag(OClO3) in the presence of the S-donor macrocyclic ligand 1,4,7-trithiacyclononane ([9]aneS3) are studied in different solvents. Two different isomers of stoichiometry [{Au(C6Cl5)2}Ag([9]aneS3)]2 were isolated depending on the solvent used, dichloromethane or tetrahydrofuran, which show different luminescence in the solid state. X-ray diffraction studies of these compounds reveals that both show the same heteropolynuclear Ag···Au···Au···Ag system but with different Au···Au interaction distances and different relative positions of the cationic fragment [Ag([9]aneS3)](+) in the structure with respect the bimetallic Au···Au core. This work includes a study of the optical properties of both isomers, as well as time-dependent density functional theory calculations that were performed to determine the origin of their different luminescence.

    12. Growth mode, magnetic and magneto-optical properties of pulsed-laser-deposited Au/Co/Au(1 1 1) trilayers

      NASA Astrophysics Data System (ADS)

      Clavero, C.; Cebollada, A.; Armelles, G.; Fruchart, O.

      2010-03-01

      The growth mode, magnetic and magneto-optical properties of epitaxial Au/Co/Au(1 1 1) ultrathin trilayers grown by pulsed-laser deposition (PLD) under ultra-high vacuum are presented. Sapphire wafers buffered with a single-crystalline Mo(1 1 0) buffer layer were used as substrates. Owing to PLD-induced interfacial intermixing at the lower Co/Au(1 1 1) interface, a close-to layer-by-layer growth mode is promoted. Surprisingly, despite this intermixing, ferromagnetic behavior is found at room temperature for coverings starting at 1 atomic layer (AL). The films display perpendicular magnetization with anisotropy constants reduced by 50% compared to TD-grown or electrodeposited films, and with a coercivity more than one order of magnitude lower (≲5 mT). The magneto-optical (MO) response in the low Co thickness range is dominated by Au/Co interface contributions. For thicknesses starting at 3 AL Co, the MO response has a linear dependence with the Co thickness, indicative of a continuous-film-like MO behavior.

    13. Reduced oxide sites and surface corrugation affecting the reactivity, thermal stability, and selectivity of supported Au-Pd bimetallic clusters on SiO2/Si(100).

      PubMed

      Gross, Elad; Sorek, Elishama; Murugadoss, Arumugam; Asscher, Micha

      2013-05-21

      The morphology and surface elemental composition of Au-Pd bimetallic nanoclusters are reported to be sensitive to and affected by reduced silicon defect sites and structural corrugation on SiO2/Si(100), generated by argon ion sputtering under ultrahigh vacuum (UHV) conditions. Metastable structures of the bimetallic clusters, where Au atoms are depleted from the top surface upon annealing, are stabilized by the interaction with the reduced silica sites, as indicated from CO temperature programmed desorption (TPD) titration measurements. Acetylene conversion to ethylene and benzene has been studied as a probe reaction, revealing the modification of selectivity and reactivity enhancement in addition to improved thermal stability on substrates rich in reduced-silica sites. These observations suggest that these unique sites play an important role in anchoring thermodynamically metastable conformations of supported Au-Pd bimetallic catalysts and dictate their high-temperature activity.

    14. AuCd4: a Hume-Rothery Phase with VEC of 1.8 and icosahedral and trigonal-prismatic clusters as building blocks.

      PubMed

      Jana, Partha P; Lidin, Sven

      2015-02-02

      The η phase in the Au-Cd binary system has been synthesized, and the structure has been analyzed by single-crystal X-ray diffraction. The compound η-AuCd(4) crystallizes in the hexagonal space group P6(3)/m (No. 176). The unit cell contains ∼273 atoms. The compound AuCd(4) represents a √3a × √3a × c superstructure of the AgMg(4) type. The structure can be well described by icosahedral and trigonal-prismatic clusters. A phase transition to the high-temperature ε phase occurs exothermically at around 578 K. The compound is formed at a sharp valence electron concentration of 1.8 e/a. The compound can be understood within the framework of the Hume-Rothery stabilization mechanism.

    15. Wade's rules and the stability of AunGem clusters

      NASA Astrophysics Data System (ADS)

      McDermott, Danielle; Newman, Kathie E.

      2015-03-01

      The properties of clusters formed from two connected Gem cage-like clusters, such as experimentally synthesized Au3Ge{18/5-}, are examined using first-principles DFT methods. We focus particularly on AunGe{12/q-} formed from a Wade-rules stable Ge6 cluster, where n = 0-3 and q = 0,2. The geometries, electronic structure, and thermal excitations of these clusters are examined using the SIESTA code. Cluster stability is tested using short molecular dynamics simulations. We find that intercluster bridges between Ge m cages, formed of either Ge-Ge or Au-Ge bonds, can either bind a cluster together or tear it apart depending on the orientation of the bridging atoms with respect to the cages. The properties of neutrally charged AuGe12 and Au2Ge12 are characterized, and we observe that radially directed molecular orbitals stabilize AuGe12 while a geometric asymmetry stabilizes Au2Ge12 and Au3Ge18. A two-dimensional {2/∞}[Au2Ge6] structure is examined and found to be more stable than other periodic [AunGe6] subunits. While no stable neutral isomers of Au3Ge12 are observed in our calculations, our work suggests additional charge stabilizes isomers of both Au2Ge12 and Au3Ge12.

    16. Efficient electrocatalytic conversion of CO.sub.2 to CO using ligand-protected Au.sub.25 clusters

      DOEpatents

      Kauffman, Douglas; Matranga, Christopher; Qian, Huifeng; Jin, Rongchao; Alfonso, Dominic R.

      2015-09-22

      An apparatus and method for CO.sub.2 reduction using an Au.sub.25 electrode. The Au.sub.25 electrode is comprised of ligand-protected Au.sub.25 having a structure comprising an icosahedral core of 13 atoms surrounded by a shell of six semi-ring structures bonded to the core of 13 atoms, where each semi-ring structure is typically --SR--Au--SR--Au--SR or --SeR--Au--SeR--Au--SeR. The 12 semi-ring gold atoms within the six semi-ring structures are stellated on 12 of the 20 faces of the icosahedron of the Au.sub.13 core, and organic ligand --SR or --SeR groups are bonded to the Au.sub.13 core with sulfur or selenium atoms. The Au.sub.25 electrode and a counter-electrode are in contact with an electrolyte comprising CO.sub.2 and H+, and a potential of at least -0.1 volts is applied from the Au.sub.25 electrode to the counter-electrode.

    17. Internal-Modified Dithiol DNA-Directed Au Nanoassemblies: Geometrically Controlled Self-Assembly and Quantitative Surface-Enhanced Raman Scattering Properties

      NASA Astrophysics Data System (ADS)

      Yan, Yuan; Shan, Hangyong; Li, Min; Chen, Shu; Liu, Jianyu; Cheng, Yanfang; Ye, Cui; Yang, Zhilin; Lai, Xuandi; Hu, Jianqiang

      2015-11-01

      In this work, a hierarchical DNA-directed self-assembly strategy to construct structure-controlled Au nanoassemblies (NAs) has been demonstrated by conjugating Au nanoparticles (NPs) with internal-modified dithiol single-strand DNA (ssDNA) (Au-B-A or A-B-Au-B-A). It is found that the dithiol-ssDNA-modified Au NPs and molecule quantity of thiol-modified ssDNA grafted to Au NPs play critical roles in the assembly of geometrically controlled Au NAs. Through matching Au-DNA self-assembly units, geometrical structures of the Au NAs can be tailored from one-dimensional (1D) to quasi-2D and 2D. Au-B-A conjugates readily give 1D and quasi-2D Au NAs while 2D Au NAs can be formed by A-B-Au-B-A building blocks. Surface-enhanced Raman scattering (SERS) measurements and 3D finite-difference time domain (3D-FDTD) calculation results indicate that the geometrically controllable Au NAs have regular and linearly “hot spots”-number-depended SERS properties. For a certain number of NPs, the number of “hot spots” and accordingly enhancement factor of Au NAs can be quantitatively evaluated, which open a new avenue for quantitative analysis based on SERS technique.

    18. Internal-Modified Dithiol DNA-Directed Au Nanoassemblies: Geometrically Controlled Self-Assembly and Quantitative Surface-Enhanced Raman Scattering Properties.

      PubMed

      Yan, Yuan; Shan, Hangyong; Li, Min; Chen, Shu; Liu, Jianyu; Cheng, Yanfang; Ye, Cui; Yang, Zhilin; Lai, Xuandi; Hu, Jianqiang

      2015-11-19

      In this work, a hierarchical DNA-directed self-assembly strategy to construct structure-controlled Au nanoassemblies (NAs) has been demonstrated by conjugating Au nanoparticles (NPs) with internal-modified dithiol single-strand DNA (ssDNA) (Au-B-A or A-B-Au-B-A). It is found that the dithiol-ssDNA-modified Au NPs and molecule quantity of thiol-modified ssDNA grafted to Au NPs play critical roles in the assembly of geometrically controlled Au NAs. Through matching Au-DNA self-assembly units, geometrical structures of the Au NAs can be tailored from one-dimensional (1D) to quasi-2D and 2D. Au-B-A conjugates readily give 1D and quasi-2D Au NAs while 2D Au NAs can be formed by A-B-Au-B-A building blocks. Surface-enhanced Raman scattering (SERS) measurements and 3D finite-difference time domain (3D-FDTD) calculation results indicate that the geometrically controllable Au NAs have regular and linearly "hot spots"-number-depended SERS properties. For a certain number of NPs, the number of "hot spots" and accordingly enhancement factor of Au NAs can be quantitatively evaluated, which open a new avenue for quantitative analysis based on SERS technique.

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

      SciTech Connect

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

      2008-12-05

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

    20. Crystal structure and thermodynamic properties of NdCu4Au compound

      NASA Astrophysics Data System (ADS)

      Tchoula Tchokonté, Moise Bertin; Bashir, Aiman Kamal; Strydom, A. M.

      2016-03-01

      We report the synthesis of the antiferromagnet cubic-type structure NdCu4Au derived by substituting Au for Cu in the parent binary NdCu5 compound. The room temperature X-ray diffraction analysis indicates a cubic MgCu4Sn-type structure with space group F 4 bar 3 m (No. 216) for the NdCu4Au compound. The thermodynamic properties of NdCu4Au have been probed by magnetic susceptibility, χ(T), magnetization, M(μ0 H), and specific heat, Cp(T), measured down to 1.8 K. The low temperature χ(T) data shows probably an antiferromagnetic (AFM)-like anomaly associated with a Néel temperature TN=3.9 K. In the paramagnetic region, χ(T) data follows the modified Curie-Weiss law with an effective magnetic moment μeff = 3.547(5) μB and Weiss temperature θp = - 10.19(8) K. The value for μeff is close to the value of 3.62 μB expected for the Nd3+-ion. No evidence of metamagnetic transition was observed from the isothermal M(μ0 H) results. Cp(T) data confirm the AFM phase transition at TN=3.5 K close to the value of 3.9 K observed in χ(T). The 4f-electron specific heat shows a Schottky-type anomaly around 20 K associated with crystalline-electric-field (CEF), with energy splitting Δ1=62(5) K and Δ2=109(9) K of the Nd3+ (J=9/2) multiplet, that are associated with the first and second excited state of Nd3+-ion. From the results of the 4f-electron magnetic entropy, it is speculated that the CEF ground state of Nd3+ (J=9/2) ions is the Γ6 doublet for NdCu4Au.

    1. Fe(3)O(4)@Au/polyaniline multifunctional nanocomposites: their preparation and optical, electrical and magnetic properties.

      PubMed

      Yu, Qiaozhen; Shi, Minmin; Cheng, Yunan; Wang, Mang; Chen, Hong-Zheng

      2008-07-02

      Fe(3)O(4)@Au/polyaniline (PANI) nanocomposites were fabricated by in situ polymerization in the presence of mercaptocarboxylic acid. The mercaptocarboxylic acid was used to introduce hydrogen bonding and/or electrostatic interaction; it acts as a template in the formation of Fe(3)O(4)@Au/PANI nanorods. The morphology and structure of the resulting nanocomposites were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, x-ray diffraction and x-ray energy dispersion spectroscopy (EDS). It was found that the nanocomposites were rod-like with an average diameter of 153 nm, and they exhibited a core-shell structure. A UV-visible spectrometer, semiconductor parameter analyzer and vibrating sample magnetometer (VSM) were used to characterize the optical, electrical and magnetic properties of the Fe(3)O(4)@Au/PANI nanocomposites. It was interesting to find that these properties are dependent on the molar ratio of Au to Fe(3)O(4) when the molar ratio of Fe(3)O(4)@Au to PANI is fixed. The magnetic property of the Fe(3)O(4)@Au/PANI nanocomposite is very close to superparamagnetic behavior.

    2. Experimental correlation between nonlinear optical and magnetotransport properties observed in Au-Co thin films

      SciTech Connect

      Yang, Kaida; Kryutyanskiy, Victor; Kolmychek, Irina; Murzina, Tatiana V.; Lukaszew, R. Alejandra

      2016-01-01

      Magnetic materials where at least one dimension is in the nanometer scale typically exhibit different magnetic, magnetotransport, and magnetooptical properties compared to bulk materials. Composite magnetic thin films where the matrix composition, magnetic cluster size, and overall composite film thickness can be experimentally tailored via adequate processing or growth parameters offer a viable nanoscale platform to investigate possible correlations between nonlinear magnetooptical and magnetotransport properties, since both types of properties are sensitive to the local magnetization landscape. As a result, it has been shown that the local magnetization contrast affects the nonlinear magnetooptical properties as well as the magnetotransport properties in magnetic-metal/nonmagnetic metal multilayers; thus, nanocomposite films showcase another path to investigate possible correlations between these distinct properties which may prove useful for sensing applications.

    3. Quantum Monte Carlo methods and lithium cluster properties

      SciTech Connect

      Owen, R.K.

      1990-12-01

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

    4. Intracluster medium cooling, AGN feedback, and brightest cluster galaxy properties of galaxy groups. Five properties where groups differ from clusters

      NASA Astrophysics Data System (ADS)

      Bharadwaj, V.; Reiprich, T. H.; Schellenberger, G.; Eckmiller, H. J.; Mittal, R.; Israel, H.

      2014-12-01

      Aims: We aim to investigate cool-core and non-cool-core properties of galaxy groups through X-ray data and compare them to the AGN radio output to understand the network of intracluster medium (ICM) cooling and feedback by supermassive black holes. We also aim to investigate the brightest cluster galaxies (BCGs) to see how they are affected by cooling and heating processes, and compare the properties of groups to those of clusters. Methods: Using Chandra data for a sample of 26 galaxy groups, we constrained the central cooling times (CCTs) of the ICM and classified the groups as strong cool-core (SCC), weak cool-core (WCC), and non-cool-core (NCC) based on their CCTs. The total radio luminosity of the BCG was obtained using radio catalogue data and/or literature, which in turn was compared to the cooling time of the ICM to understand the link between gas cooling and radio output. We determined K-band luminosities of the BCG with 2MASS data, and used a scaling relation to constrain the masses of the supermassive black holes, which were then compared to the radio output. We also tested for correlations between the BCG luminosity and the overall X-ray luminosity and mass of the group. The results obtained for the group sample were also compared to previous results for clusters. Results: The observed cool-core/non-cool-core fractions for groups are comparable to those of clusters. However, notable differences are seen: 1) for clusters, all SCCs have a central temperature drop, but for groups this is not the case as some have centrally rising temperature profiles despite very short cooling times; 2) while for the cluster sample, all SCC clusters have a central radio source as opposed to only 45% of the NCCs, for the group sample, all NCC groups have a central radio source as opposed to 77% of the SCC groups; 3) for clusters, there are indications of an anticorrelation trend between radio luminosity and CCT. However, for groups this trend is absent; 4) the indication of

    5. Stabilization of Au at edges of bimetallic PdAu nanocrystallites.

      PubMed

      Yudanov, Ilya V; Neyman, Konstantin M

      2010-05-21

      Density functional calculations were performed to study the distribution of Au atoms in bimetallic PdAu nanoparticles. A series of Pd(79-n)Au(n) clusters of truncated octahedral shape with different content of Au ranging from n = 1 to 60 was used to model such bimetallic nanosystems. Segregation of Au to the particle surface is found to be thermodynamically favorable. The most stable sites for Au substitution are located at the edges of the PdAu nanoclusters. The stabilization at the edges is rationalized by their higher flexibility for surface relaxation which minimizes the strain induced by larger atomic radius of Au as compared to Pd. This stabilization of Au at the edges indicates the possibility to synthesize PdAu particles with Pd atoms located mainly on the facets, and edges "decorated" by Au atoms. Such nanocrystallites are expected to exhibit peculiar catalytic properties and, being thermodynamically stable, should be prone to retaining their initial shape under catalytic conditions.

    6. ISO Lensing Studies: background galaxies and foreground cluster properties

      NASA Astrophysics Data System (ADS)

      Perez-Martinez, Ricardo

      2003-02-01

      A number of ISO programmes, totaling over 100 hours of observation time, made use of the gravitational lensing phenomenon to extend the sensitivity of ISO observations. Substantial results derived from those programmes have been published, or are in the peer review process, addressing the MIR properties of the background lensed galaxy population. These results, which have important implications for galaxy evolution, and which resolve a large fraction of the 15 and 7 μm infrared-background light, will be briefly summarised. But the data has much further potential. Little has been published to date concerning the implications of the ISO lensing data for the foreground clusters themselves, nor addressing the overlap between the observed ISO sources and lensed populations seen at X-Ray and Sub-mm wavelengths. We report briefly on an ongoing programme to systematically reassess the set of ISO observations of lensing galaxy clusters and to describe and compare the IR properties of the clusters themselves. The overlap between ISO source lists and recently published lists of X-Ray and Sub-mm sources in the same fields is under study.

    7. Au25 cluster functionalized metal-organic nanostructures for magnetically targeted photodynamic/photothermal therapy triggered by single wavelength 808 nm near-infrared light

      NASA Astrophysics Data System (ADS)

      Yang, Dan; Yang, Guixin; Gai, Shili; He, Fei; An, Guanghui; Dai, Yunlu; Lv, Ruichan; Yang, Piaoping

      2015-11-01

      Near-infrared (NIR) light-induced cancer therapy has gained considerable interest, but pure inorganic anti-cancer platforms usually suffer from degradation issues. Here, we designed metal-organic frameworks (MOFs) of Fe3O4/ZIF-8-Au25 (IZA) nanospheres through a green and economic procedure. The encapsulated Fe3O4 nanocrystals not only produce hyperthemal effects upon NIR light irradiation to effectively kill tumor cells, but also present targeting and MRI imaging capability. More importantly, the attached ultrasmall Au25(SR)18- clusters (about 2.5 nm) produce highly reactive singlet oxygen (1O2) to cause photodynamic effects through direct sensitization under NIR light irradiation. Furthermore, the Au25(SR)18- clusters also give a hand to the hyperthemal effect as photothermal fortifiers. This nanoplatform exhibits high biocompatibility and an enhanced synergistic therapeutic effect superior to any single therapy, as verified by in vitro and in vivo assay. This image-guided therapy based on a metal-organic framework may stimulate interest in developing other kinds of metal-organic materials with multifunctionality for tumor diagnosis and therapy.Near-infrared (NIR) light-induced cancer therapy has gained considerable interest, but pure inorganic anti-cancer platforms usually suffer from degradation issues. Here, we designed metal-organic frameworks (MOFs) of Fe3O4/ZIF-8-Au25 (IZA) nanospheres through a green and economic procedure. The encapsulated Fe3O4 nanocrystals not only produce hyperthemal effects upon NIR light irradiation to effectively kill tumor cells, but also present targeting and MRI imaging capability. More importantly, the attached ultrasmall Au25(SR)18- clusters (about 2.5 nm) produce highly reactive singlet oxygen (1O2) to cause photodynamic effects through direct sensitization under NIR light irradiation. Furthermore, the Au25(SR)18- clusters also give a hand to the hyperthemal effect as photothermal fortifiers. This nanoplatform exhibits high

    8. Experimental correlation between nonlinear optical and magnetotransport properties observed in Au-Co thin films

      DOE PAGES

      Yang, Kaida; Kryutyanskiy, Victor; Kolmychek, Irina; ...

      2016-01-01

      Magnetic materials where at least one dimension is in the nanometer scale typically exhibit different magnetic, magnetotransport, and magnetooptical properties compared to bulk materials. Composite magnetic thin films where the matrix composition, magnetic cluster size, and overall composite film thickness can be experimentally tailored via adequate processing or growth parameters offer a viable nanoscale platform to investigate possible correlations between nonlinear magnetooptical and magnetotransport properties, since both types of properties are sensitive to the local magnetization landscape. As a result, it has been shown that the local magnetization contrast affects the nonlinear magnetooptical properties as well as the magnetotransport propertiesmore » in magnetic-metal/nonmagnetic metal multilayers; thus, nanocomposite films showcase another path to investigate possible correlations between these distinct properties which may prove useful for sensing applications.« less

    9. DFT global optimisation of gas-phase and MgO-supported sub-nanometre AuPd clusters.

      PubMed

      Hussein, Heider A; Davis, Jack B A; Johnston, Roy L

      2016-09-21

      The Birmingham Parallel Genetic Algorithm (BPGA) has been adopted for the global optimization of free and MgO(100)-supported Pd, Au and AuPd nanocluster structures, over the size range N = 4-10. Structures were evaluated directly using density functional theory, which has allowed the identification of Pd, Au and AuPd global minima. The energetics, structures, and tendency of segregation have been evaluated by different stability criteria such as binding energy, excess energy, second difference in energy, and adsorption energy. The ability of the approach in searching for putative global minimum has been assessed against a systematic homotop search method, which shows a high degree of success.

    10. Superatom-atom super-bonding in metallic clusters: a new look to the mystery of an Au20 pyramid.

      PubMed

      Cheng, Longjiu; Zhang, Xiuzhen; Jin, Baokang; Yang, Jinlong

      2014-11-07

      Using the super valence bond model, a generalized chemical picture for the electronic shells of an Au20 pyramid is given. It is found that Au20 can be viewed to be a superatomic molecule, of which its superatomic 16c-16e core (T) is in D(3)S hybridization bonded with four vertical Au atoms for the molecule-like (TAu4) electronic shell-closure. Based on such a superatom-atom bonding model, TX4 (X = F, Cl, or Br) are predicted to be very stable. Such a superatom-atom T-Au/T-X bonding enriches the scope of chemistry.

    11. Electron-Induced Secondary Electron Emission Properties of MgO/Au Composite Thin Film Prepared by Magnetron Sputtering

      NASA Astrophysics Data System (ADS)

      Li, Jie; Hu, Wenbo; Wei, Qiang; Wu, Shengli; Hua, Xing; Zhang, Jintao

      2016-12-01

      As a type of electron-induced secondary electron emitter, MgO/Au composite thin film was prepared by reactive magnetron sputtering of individual Mg target and Au target, and the effects of key process parameters on its surface morphology and secondary electron emission (SEE) properties were investigated. It is found that to deposit a NiO buffer layer on the substrate is conducive to the subsequent growth of MgO grains owing to the lattice matching. The gold addition can raise the electrical conductivity of MgO film and further suppress the surface charging. However, the gold deposition would interfere with the MgO crystallization and increase the surface roughness of MgO/Au film. Therefore, MgO/Au composite thin film with a NiO buffer layer and proper deposition times of MgO and Au can achieve superior SEE properties due to good MgO crystallization, low surface roughness and reasonable electrical conductivity. The optimized MgO/Au composite thin film has a higher SEE coefficient and a lower 1-h SEE degradation rate under electron beam bombardment in comparison with MgO film.

    12. Electron-Induced Secondary Electron Emission Properties of MgO/Au Composite Thin Film Prepared by Magnetron Sputtering

      NASA Astrophysics Data System (ADS)

      Li, Jie; Hu, Wenbo; Wei, Qiang; Wu, Shengli; Hua, Xing; Zhang, Jintao

      2017-03-01

      As a type of electron-induced secondary electron emitter, MgO/Au composite thin film was prepared by reactive magnetron sputtering of individual Mg target and Au target, and the effects of key process parameters on its surface morphology and secondary electron emission (SEE) properties were investigated. It is found that to deposit a NiO buffer layer on the substrate is conducive to the subsequent growth of MgO grains owing to the lattice matching. The gold addition can raise the electrical conductivity of MgO film and further suppress the surface charging. However, the gold deposition would interfere with the MgO crystallization and increase the surface roughness of MgO/Au film. Therefore, MgO/Au composite thin film with a NiO buffer layer and proper deposition times of MgO and Au can achieve superior SEE properties due to good MgO crystallization, low surface roughness and reasonable electrical conductivity. The optimized MgO/Au composite thin film has a higher SEE coefficient and a lower 1-h SEE degradation rate under electron beam bombardment in comparison with MgO film.

    13. Tensile Creep Properties of the 50Au-50Cu Braze Alloy

      SciTech Connect

      Stephens, J.J.

      1999-05-28

      The 50Au-50CU (wt.%) alloy is a solid-solution strengthened braze alloy used extensively in conventional, hermetic metal/ceramic brazing applications where low vapor pressure is a requirement. Typical metal/ceramic base materials would be KovarTM alloy and metallized and Ni-plated 94% alumina ceramic. The elevated temperature mechanical properties are important for permitting FEA evaluation of residual stresses in metal/ceramic brazes given specific geometries and braze cooldown profiles. For material with an atomic composition of 76.084 at.% CL 23.916 Au (i.e., on the Cu-rich side of Cu3Au) that was annealed for 2 hr. at 750°C and water quenched a Garofalo sinh equation was found to adequately characterize the minimum strain rate data over the temperature mnge 450-850°C. At lower temperatures (250 arid 350°C), a conventional power law equation was found to characterize the data. For samples held long periods of time at 375°C (96 hrs.) and slowly cooled to room temperature, a slight strengthening reaction was observed: with the stress necessary to reach the same strain rate increasing by about 15% above the baseline annealed and quenched data. X-ray diffiction indicates that the 96 hr at 375°C + slow cool condition does indeed order. The microhardness of the ordered samples indicates a value of 94.5 VHN, compared to 93.7 VHN for the baseline annealed and quenched (disordered FCC) samples. From a brazing perspective, the relative sluggishness of this ordering reaction does not appear to pose a problem for braze joints cooled at reasonable rates following brazing.

    14. Tensile creep properties of the 50Au-50Cu braze alloys

      SciTech Connect

      Stephens, J.J.

      1999-07-01

      The 50Au-50Cu (wt.%) alloy is a solid-solution strengthened braze alloy used extensively in conventional, hermetic metal/ceramic brazing applications where low vapor pressure is a requirement. Typical metal/ceramic base materials would be Kovar{trademark} alloy and metallized and Ni-plated 94% alumina ceramic. The elevated temperature mechanical properties are important for permitting FEA evaluation of residual stresses in metal/ceramic brazes given specific geometries and braze cooldown profiles. For material with an atomic composition of 76.084 at.%Cu, 23.916 Au (i.e., on the Cu-rich side of Cu{sub 3}Au) that was annealed for 2 hr. at 750 C and water quenched, a Garofalo sinh equation was found to adequately characterize the minimum strain rate data over the temperature range 450--850 C. At lower temperatures (250 and 350 C), a conventional power law equation was found to characterize the data. For samples held long periods of time at 375 C (96 hrs.) and slowly cooled to room temperature, a slight strengthening reaction was observed: with the stress necessary to reach the same strain rate increasing by about 15% above the baseline annealed and quenched data. X-ray diffraction indicates that the 96 hr at 375 C + slow cool condition does indeed order. The microhardness of the ordered samples indicates a value of 94.5 VHN, compared to 93.7 VHN for the baseline annealed and quenched (disordered FCC) samples. From a brazing perspective, the relative sluggishness of this ordering reaction does not appear to pose a problem for braze joints cooled at reasonable rates following brazing.

    15. Probing of the pseudogap via thermoelectric properties in the Au-Al-Gd quasicrystal approximant

      NASA Astrophysics Data System (ADS)

      Ishikawa, Asuka; Takagiwa, Yoshiki; Kimura, Kaoru; Tamura, Ryuji

      2017-03-01

      The pseudogap of the recently discovered Au-Al-Gd quasicrystal approximant crystal (AC) is investigated over a wide electron-per-atom (e /a ) ratio of ˜0.5 using thermoelectric properties as an experimental probe. This Au-Al-Gd AC provides an ideal platform for fine probing of the pseudogap among a number of known ACs because the Au-Al-Gd AC possesses an extraordinarily wide single-phase region with respect to the variation in the electron concentration [A. Ishikawa, T. Hiroto, K. Tokiwa, T. Fujii, and R. Tamura, Phys. Rev. B 93, 024416 (2016), 10.1103/PhysRevB.93.024416], in striking contrast to, for instance, binary stoichiometric C d6R ACs. As a result, a salient peak structure is observed in the Seebeck coefficient, S , with the composition as well as that of the power factor S2σ , in addition to a gradual variation in the conductivity, σ , and S . These two features are directly associated with rapid and slow variations, respectively, of spectral conductivity σ (E ) , and hence the fine structure inside the pseudogap, in the vicinity of the Fermi level EF. Based on the observed continuous variation of the Fermi wave vector reported in the previous experimental work, fine tuning of EF toward an optimal position was attempted, which led to the successful observation of a sharp peak in S2σ with a value of ˜270 μ W /m .K2 at 873 K. This is the highest value ever reported among both Tsai-type and Bergman-type compounds. The dimensionless figure of merit was determined as 0.026 at 873 K, which is also the highest reported among both Tsai-type and Bergman-type compounds.

    16. Transport properties of zigzag graphene nanoribbon decorated with copper clusters

      SciTech Connect

      Berahman, M.; Sheikhi, M. H.

      2014-09-07

      Using non-equilibrium green function with density functional theory, the present study investigates the transport properties of decorated zigzag graphene nanoribbon with a copper cluster. We have represented the decoration of zigzag graphene nanoribbon with single copper atom and cluster containing two and three copper atoms. In all the cases, copper atoms tend to occupy the edge state. In addition, we have shown that copper can alter the current-voltage characteristic of zigzag graphene nanoribbon and create new fluctuations and negative differential resistance. These alternations are made due to discontinuity in the combination of orbitals along the graphene nanoribbon. Decoration alters these discontinuities and creates more visible fluctuations. However, in low bias voltages, the changes are similar in all the cases. The study demonstrates that in the decorated zigzag graphene nanoribbon, the edge states are the main states for transporting electron from one electrode to another.

    17. Properties of ordered titanium templates covered with Au thin films for SERS applications

      NASA Astrophysics Data System (ADS)

      Grochowska, Katarzyna; Siuzdak, Katarzyna; Sokołowski, Michał; Karczewski, Jakub; Szkoda, Mariusz; Śliwiński, Gerard

      2016-12-01

      Currently, roughened metal nanostructures are widely studied as highly sensitive Raman scattering substrates that show application potential in biochemistry, food safety or medical diagnostic. In this work the structural properties and the enhancement effect due to surface enhanced Raman scattering (SERS) of highly ordered nano-patterned titanium templates covered with thin (5-20 nm) gold films are reported. The templates are formed by preparation of a dense structure of TiO2 nanotubes on a flat Ti surface (2 × 2 cm2) and their subsequent etching down to the substrate. SEM images reveal the formation of honeycomb nanostructures with the cavity diameter of 80 nm. Due to the strongly inhomogeneous distribution of the electromagnetic field in the vicinity of the Au film discontinuities the measured average enhancement factor (107-108) is markedly higher than observed for bare Ti templates. The enhancement factor and Raman signal intensity can be optimized by adjusting the process conditions and thickness of the deposited Au layer. Results confirm that the obtained structures can be used in surface enhanced sensing.

    18. Kinetics-controlled growth of bimetallic RhAg on Au nanorods and their catalytic properties.

      PubMed

      Ye, Wei; Guo, Xia; Xie, Fang; Zhu, Rui; Zhao, Qing; Yang, Jian

      2014-04-21

      Controlled growth of hybrid metallic nanocomposites for a desirable structure in a combination of selected components is highly important for their applications. Herein, the controllable growth of RhAg on the gold nanorods is achieved from the dumbbell-like RhAg-tipped nanorods to the brushy RhAg-coated nanorods, or the rod-like Au@Ag-Rh nanorattles. These different growth modes of RhAg on the gold nanorods are correlated with the reducing kinetics of RhCl₃ and AgNO₃. In view of the promising catalytic properties of Rh, the gold nanorods modified by RhAg in different structures are examined as catalysts for the oxidation of o-phenylenediamine. It is found that brushy RhAg-coated nanorods present a higher catalytic efficiency than dumbbell-like RhAg-tipped nanorods and rod-like Au@Ag-Rh nanorattles. These results would benefit the overgrowth control on the one-dimensional metallic nanorods and the rational design of new generation heterogeneous catalysts and optical devices.

    19. Asymmetric photoelectric property of transparent TiO2 nanotube films loaded with Au nanoparticles

      NASA Astrophysics Data System (ADS)

      Wang, Hui; Liang, Wei; Liu, Yiming; Zhang, Wanggang; Zhou, Diaoyu; Wen, Jing

      2016-11-01

      Semitransparent composite films of Au loaded TiO2 nanotubes (TNT-Au) were prepared by sputtering Au nanoparticles on highly transparent TiO2 nanotubes films, which were fabricated directly on FTO glasses by anodizing the Ti film sputtered on the FTO glasses. Compared with pure TNT films, the prepared TNT-Au films possessed excellent absorption ability and high photocurrent response and improved photocatalytic activity under visible-light irradiation. It could be concluded that Au nanoparticles played important roles in improving the photoelectrochemical performance of TNT-Au films. Moreover, in this work, both sides of TNT-Au films were researched and compared owing to theirs semitransparency. It was firstly found that the photoelectric activity of TNT-Au composite films with back-side illumination was obviously superior to front-side illumination.

    20. Facet-dependent and au nanocrystal-enhanced electrical and photocatalytic properties of Au-Cu2O core-shell heterostructures.

      PubMed

      Kuo, Chun-Hong; Yang, Yu-Chen; Gwo, Shangjr; Huang, Michael H

      2011-02-02

      We report highly facet-dependent electrical properties of Cu(2)O nanocubes and octahedra and significant enhancement of gold nanocrystal cores to the electrical conductivity of Au-Cu(2)O core-shell octahedra. Cu(2)O nanocubes and octahedra and Au-Cu(2)O core-shell cubes and octahedra were synthesized by following our reported facile procedures at room temperature. Two oxide-free tungsten probes attached to a nanomanipulator installed inside a scanning electron microscope made contacts to a single Cu(2)O nanocrystal for the I-V measurements. Pristine Cu(2)O octahedra bounded by {111} facets are 1100 times more conductive than pristine Cu(2)O cubes enclosed by {100} faces, which are barely conductive. Core-shell cubes are only slightly more conductive than pristine cubes. A 10,000-fold increase in conductivity over a cube has been recorded for an octahedron. Remarkably, core-shell octahedra are far more conductive than pristine octahedra. The same facet-dependent electrical behavior can still be observed on a single nanocrystal exposing both {111} and {100} facets. This new fundamental property may be observable in other semiconductor nanocrystals. We also have shown that both core-shell cubes and octahedra outperform pristine cubes and octahedra in the photodegradation of methyl orange. Efficient photoinduced charge separation is attributed to this enhanced photocatalytic activity. Interestingly, facet-selective etching occurred over the {100} corners of some octahedra and core-shell octahedra during photocatalysis. The successful preparation of Au-Cu(2)O core-shell heterostructures with precise shape control has offered opportunities to discover new and exciting physical and chemical properties of nanocrystals.

    1. High-accuracy coupled cluster calculations of atomic properties

      NASA Astrophysics Data System (ADS)

      Borschevsky, A.; Yakobi, H.; Eliav, E.; Kaldor, U.

      2015-01-01

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

    2. High-accuracy coupled cluster calculations of atomic properties

      SciTech Connect

      Borschevsky, A.; Yakobi, H.; Eliav, E.; Kaldor, U.

      2015-01-22

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

    3. Homogeneous nucleation rate measurements and the properties of critical clusters

      SciTech Connect

      Wyslouzil, Barbara E.; Strey, Reinhard; Wölk, Judith; Wilemski, Gerald; Kim, Yoojeong

      2009-10-06

      By combining a range of experimental techniques, quantitative nucleation rate measurements can now be made over {approx} 20 orders of magnitude. These rates can be used to directly test the predictions of nucleation theories or scaling laws. They can also provide direct information regarding the properties of the critical clusters - the first fragments of the new phase that are in unstable equilibrium with the supersaturated mother phase. This paper reviews recent progress in the field of vapor phase nucleation with a special focus on integrating the results from supersonic nozzle and nucleation pulse chamber studies.

    4. The Herschel Virgo Cluster Survey - XII. FIR properties of optically selected Virgo cluster galaxies

      NASA Astrophysics Data System (ADS)

      Auld, R.; Bianchi, S.; Smith, M. W. L.; Davies, J. I.; Bendo, G. J.; di Serego, S. Alighieri; Cortese, L.; Baes, M.; Bomans, D. J.; Boquien, M.; Boselli, A.; Ciesla, L.; Clemens, M.; Corbelli, E.; De Looze, I.; Fritz, J.; Gavazzi, G.; Pappalardo, C.; Grossi, M.; Hunt, L. K.; Madden, S.; Magrini, L.; Pohlen, M.; Verstappen, J.; Vlahakis, C.; Xilouris, E. M.; Zibetti, S.

      2013-01-01

      The Herschel Virgo Cluster Survey (HeViCS) is the deepest, confusion-limited survey of the Virgo Cluster at far-infrared (FIR) wavelengths. The entire survey at full depth covers ˜55 deg2 in five bands (100-500 μm), encompassing the areas around the central dominant elliptical galaxies (M87, M86 and M49) and extends as far as the NW cloud, the W cloud and the Southern extension. The survey extends beyond this region with lower sensitivity so that the total area covered is 84 deg2. In this paper we describe the data, the data acquisition techniques and present the detection rates of the optically selected Virgo Cluster Catalogue (VCC). We detect 254 (34 per cent) of 750 VCC galaxies found within the survey boundary in at least one band and 171 galaxies are detected in all five bands. For the remainder of the galaxies we have measured strict upper limits for their FIR emission. The population of detected galaxies contains early as well as late types although the latter dominate the detection statistics. We have modelled 168 galaxies, showing no evidence of a strong synchrotron component in their FIR spectra, using a single-temperature modified blackbody spectrum with a fixed emissivity index (β = 2). A study of the χ2 distribution indicates that this model is not appropriate in all cases, and this is supported by the FIR colours which indicate a spread in β = 1-2. Statistical comparison of the dust mass and temperature distributions from 140 galaxies with χ2d.o.f. = 3 < 7.8 (95 per cent confidence level) shows that late types have typically colder, more massive dust reservoirs; the early-type dust masses have a mean of log[/M⊙] = 6.3 ± 0.3, while for late types log[/M⊙] = 7.1 ± 0.1. The late-type dust temperatures have a mean of = 19.4 ± 0.2 K, while for the early types, = 21.1 ± 0.8 K. Late-type galaxies in the cluster exhibit slightly lower dust masses than those in the field, but the cluster environment seems to have little effect on

    5. Global optimization of bimetallic cluster structures. II. Size-matched Ag-Pd, Ag-Au, and Pd-Pt systems.

      PubMed

      Rossi, Giulia; Ferrando, Riccardo; Rapallo, Arnaldo; Fortunelli, Alessandro; Curley, Benjamin C; Lloyd, Lesley D; Johnston, Roy L

      2005-05-15

      Genetic algorithm global optimization of Ag-Pd, Ag-Au, and Pd-Pt clusters is performed. The 34- and 38-atom clusters are optimized for all compositions. The atom-atom interactions are modeled by a semiempirical potential. All three systems are characterized by a small size mismatch and a weak tendency of the larger atoms to segregate at the surface of the smaller ones. As a result, the global minimum structures exhibit a larger mixing than in Ag-Cu and Ag-Ni clusters. Polyicosahedral structures present generally favorable energetic configurations, even though they are less favorable than in the case of the size-mismatched systems. A comparison between all the systems studied here and in the previous paper (on size-mismatched systems) is presented.

    6. Connectivity properties of the random-cluster model

      NASA Astrophysics Data System (ADS)

      Weigel, Martin; Metin Elci, Eren; Fytas, Nikolaos G.

      2016-02-01

      We investigate the connectivity properties of the random-cluster model mediated by bridge bonds that, if removed, lead to the generation of new connected components. We study numerically the density of bridges and the fragmentation kernel, i.e., the relative sizes of the generated fragments, and find that these quantities follow a scaling description. The corresponding scaling exponents are related to well known equilibrium critical exponents of the model. Using the Russo-Margulis formalism, we derive an exact relation between the expected density of bridges and the number of active edges. The same approach allows us to study the fluctuations in the numbers of bridges, thereby uncovering a new singularity in the random- cluster model as q < 4 cos2 (π/√3) in two dimensions. For numerical simulations of the model directly in the language of individual bonds, known as Sweeny's algorithm, the prevalence of bridges and the scaling of the sizes of clusters connected by bridges and candidate-bridges play a pivotal role. We discuss several different implementations of the necessary connectivity algorithms and assess their relative performance.

    7. Microstructural evolution and micromechanical properties of gamma-irradiated Au ball bonds

      SciTech Connect

      Yusoff, Wan Yusmawati Wan; Ismail, Roslina; Jalar, Azman; Othman, Norinsan Kamil; Abdul Rahman, Irman

      2014-07-01

      The effect of gamma radiation on the mechanical and structural properties of gold ball bonds was investigated. Gold wires from thermosonic wire bonding were exposed to gamma rays from a Cobalt-60 source at a low dose (5 Gy). The load–depth curve of nanoindentation for the irradiated gold wire bond has an apparent staircase shape during loading compared to the as-received sample. The hardness of the specimens calculated from the nanoindentation shows an increase in value from 0.91 to 1.09 GPa for specimens after exposure. The reduced elastic modulus for irradiated specimens significantly increased as well, with values from 75.18 to 98.55 GPa. The change in intrinsic properties due to gamma radiation was investigated using dual-focused ion beam and high-resolution transmission electron microscope analysis. The dual-focused ion beam and high-resolution transmission electron microscope images confirmed the changes in grain structure and the presence of dislocations. The scanning electron microscope micrographs of focused ion beam cross sections showed that the grain structure of the gold became elongated and smaller after exposure to gamma rays. Meanwhile, high-resolution transmission electron microscopy provided evidence that gamma radiation induced dislocation of the atomic arrangement. - Highlights: • Nanoindentation technique provides a detailed characterisation of Au ball bond. • P–h curve of irradiated Au ball bond shows an apparent pop-in event. • Hardness and reduced modulus increased after exposure. • Elongated and smaller grain structure in irradiated specimens • Prevalent presence of dislocations in the atomic arrangement.

    8. Atomic structure and electronic properties of the two-dimensional (Au ,Al )/Si (111 )2 ×2 compound

      NASA Astrophysics Data System (ADS)

      Gruznev, D. V.; Bondarenko, L. V.; Matetskiy, A. V.; Tupchaya, A. Y.; Chukurov, E. N.; Hsing, C. R.; Wei, C. M.; Eremeev, S. V.; Zotov, A. V.; Saranin, A. A.

      2015-12-01

      A combination of scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, ab initio random structure searching, and density functional theory electronic structure calculations was applied to elucidate the atomic arrangement and electron band structure of the (Au ,Al )/Si (111 )2 ×2 two-dimensional compound formed upon Al deposition onto the mixed 5 ×2 /√{3 }×√{3 } Au/Si(111) surface. It was found that the most stable 2 ×2 -(Au, Al) compound incorporates four Au atoms, three Al atoms, and two Si atoms per 2 ×2 unit cell. Its atomic arrangement can be visualized as an array of meandering Au atomic chains with two-thirds of the Al atoms incorporated into the chains and one-third of the Al atoms interconnecting the chains. The compound is metallic and its electronic properties can be controlled by appropriate Al dosing since energetic location of the bands varies by ˜0.5 eV during increasing of Al contents. The 2 ×2 -(Au, Al) structure appears to be lacking the C3 v symmetry typical for the hexagonal lattices. The consequence of the peculiar atomic structure of the two-dimensional alloy is spin splitting of the metallic states, which should lead to anisotropy of the current-induced in-plane spin polarization.

    9. Fabrication and temperature-dependent magnetic properties of one-dimensional multilayer Au–Ni–Au–Ni–Au nanowires

      SciTech Connect

      Ishrat, S.; Maaz, K.; Lee, Kyu-Joon; Jung, Myung-Hwa; Kim, Gil-Ho

      2014-02-15

      Multilayer Au–Ni–Au–Ni–Au nanowires with a controlled diameter of ∼100 nm were synthesized by electrochemical deposition in porous alumina templates. The length of each Ni-segment was controlled up to ∼230 nm, while the length of the Au segment sandwiched between two Ni segments was ∼180 nm. X-ray diffraction patterns and energy-dispersive X-ray spectra confirmed the formation of purely crystalline nanowires. The magnetic properties of the multilayer Au–Ni–Au–Ni–Au nanowires were investigated in the temperature range 2–300 K. Room-temperature magnetic hysteresis confirmed the ferromagnetic nature of the nanowires. The plot of coercivity as a function of temperature (from 2 to 300 K) followed law applicable for ferromagnetic nanostructures. The magnetization tended to increase as the temperature decreased, following the modified Bloch's law similar to ferromagnetic nanoparticles. - Graphical abstract: (a) SEM image of Au–Ni–Au–Ni–Au nanowire with 230 nm Ni segment length and 180 nm Au sandwiched between Ni segments (b) Kneller's law (c) Bloch's law Display Omitted - Highlights: • Electrochemical fabrication of Au–Ni–Au–Ni–Au nanowires in alumina templates. • Formation of beadlike structure of Ni segments. • Coercivity versus T follows Kneller's law for ferromagnetic materials. • Magnetization as a function of temperature follows the modified Bloch's law.

    10. Recent Impacts on Mars: Cluster Properties and Seismic Signal Predictions

      NASA Astrophysics Data System (ADS)

      Justine Daubar, Ingrid; Schmerr, Nicholas; Banks, Maria; Marusiak, Angela; Golombek, Matthew P.

      2016-10-01

      Impacts are a key source of seismic waves that are a primary constraint on the formation, evolution, and dynamics of planetary objects. Geophysical missions such as InSight (Banerdt et al., 2013) will monitor seismic signals from internal and external sources. New martian craters have been identified in orbital images (Malin et al., 2006; Daubar et al., 2013). Seismically detecting such impacts and subsequently imaging the resulting craters will provide extremely accurate epicenters and source crater sizes, enabling calibration of seismic velocities, the efficiency of impact-seismic coupling, and retrieval of detailed regional and local internal structure.To investigate recent impact-induced seismicity on Mars, we have assessed ~100 new, dated impact sites. In approximately half of new impacts, the bolide partially disintegrates in the atmosphere, forming multiple craters in a cluster. We incorporate the resulting, more complex, seismic effects in our model. To characterize the variation between sites, we focus on clustered impacts. We report statistics of craters within clusters: diameters, morphometry indicating subsurface layering, strewn-field azimuths indicating impact direction, and dispersion within clusters indicating combined effects of bolide strength and elevation of breakup.Measured parameters are converted to seismic predictions for impact sources using a scaling law relating crater diameter to the momentum and source duration, calibrated for impacts recorded by Apollo (Lognonne et al., 2009). We use plausible ranges for target properties, bolide densities, and impact velocities to bound the seismic moment. The expected seismic sources are modeled in the near field using a 3-D wave propagation code (Petersson et al., 2010) and in the far field using a 1-D wave propagation code (Friederich et al., 1995), for a martian seismic model. Thus we calculate the amplitudes of seismic phases at varying distances, which can be used to evaluate the detectability

    11. Electrochemical behavior of polypyrrol/AuNP composites deposited by different electrochemical methods: sensing properties towards catechol

      PubMed Central

      García-Hernández, Celia; Medina-Plaza, Cristina; Martín-Pedrosa, Fernando; Blanco, Yolanda; de Saja, José Antonio

      2015-01-01

      Summary Two different methods were used to obtain polypyrrole/AuNP (Ppy/AuNP) composites. One through the electrooxidation of the pyrrole monomer in the presence of colloidal gold nanoparticles, referred to as trapping method (T), and the second one by electrodeposition of both components from one solution containing the monomer and a gold salt, referred to as cogeneration method (C). In both cases, electrodeposition was carried out through galvanostatic and potentiostatic methods and using platinum (Pt) or stainless steel (SS) as substrates. Scanning electron microscopy (SEM) demonstrated that in all cases gold nanoparticles of similar size were uniformly dispersed in the Ppy matrix. The amount of AuNPs incorporated in the Ppy films was higher when electropolymerization was carried out by chronopotentiometry (CP). Besides, cogeneration method allowed for the incorporation of a higher number of AuNPs than trapping. Impedance experiments demonstrated that the insertion of AuNPs increased the conductivity. As an electrochemical sensor, the Ppy/AuNp deposited on platinum exhibited a strong electrocatalytic activity towards the oxidation of catechol. The effect was higher in films obtained by CP than in films obtained by chronoamperometry (CA). The influence of the method used to introduce the AuNPs (trapping or cogeneration) was not so important. The limits of detection (LOD) were in the range from 10−5 to 10−6 mol/L. LODs attained using films deposited on platinum were lower due to a synergy between AuNPs and platinum that facilitates the electron transfer, improving the electrocatalytic properties. Such synergistic effects are not so pronounced on stainless steel, but acceptable LOD are attained with lower price sensors. PMID:26665076

    12. Seed-mediated growth of Au nanorings with size control on Pd ultrathin nanosheets and their tunable surface plasmonic properties

      NASA Astrophysics Data System (ADS)

      Wang, Wenxing; Yan, Yucong; Zhou, Ning; Zhang, Hui; Li, Dongsheng; Yang, Deren

      2016-02-01

      Nanorings made of noble metals such as Au and Ag have attracted particular interest in plasmonic properties since they allow remarkable tunability of plasmon resonance wavelengths associated with their unique structural features. Unfortunately, most of the syntheses for Au nanorings involve complex procedures and/or require highly specialized and expensive facilities. Here, we report a seed-mediated approach for selective deposition of Au nanorings on the periphery of Pd seeds with the structure of an ultrathin nanosheet through the island growth mode. In combination with selective etching of Pd nanosheets, Au nanorings are eventually produced. We can control the outer diameter and wall thickness of the nanorings by simply varying the size of the Pd nanosheets and reaction time. By taking the advantage of this size controllability, the nanorings show tunable surface plasmonic properties in the near infrared (NIR) region arising from both the in-plane dipole and face resonance modes. Owing to their good surface plasmonic properties, the nanorings show substantially enhanced surface-enhanced Raman spectroscopy (SERS) performance for rhodamine 6G, and are therefore confirmed as good SERS substrates to detect trace amounts of molecules.Nanorings made of noble metals such as Au and Ag have attracted particular interest in plasmonic properties since they allow remarkable tunability of plasmon resonance wavelengths associated with their unique structural features. Unfortunately, most of the syntheses for Au nanorings involve complex procedures and/or require highly specialized and expensive facilities. Here, we report a seed-mediated approach for selective deposition of Au nanorings on the periphery of Pd seeds with the structure of an ultrathin nanosheet through the island growth mode. In combination with selective etching of Pd nanosheets, Au nanorings are eventually produced. We can control the outer diameter and wall thickness of the nanorings by simply varying the

    13. Structural and optical properties of solid-state synthesized Au dendritic structures

      NASA Astrophysics Data System (ADS)

      Gentile, A.; Ruffino, F.; Romano, L.; Boninelli, S.; Reitano, R.; Piccitto, G.; Grimaldi, M. G.

      2014-03-01

      Au dendrites (Au Ds) are synthesized, on various substrates, by a simple physical methodology involving the deposition of a thin Au film on a Si surface followed by thermal processes at high temperatures (>1273 K) in an inert ambient (N2), using fast heating and cooling rates (1273 K/min). Microscopic analyses reveal the evolution, thanks to the thermal processes, of the Au film from a continuous coating to dendritic structures covering the entire sample surface. In particular, transmission electron microscopy analyses indicate that, below the Au surface, the dendritic structures consist of Si atoms originating from the substrate. Furthermore, optical characterizations reveal the ability of the Au Ds to serve as scattering centers in the infrared region. Finally, on the basis of the experimental observations, a phenomenological model for the growth of the Au Ds is proposed.

    14. Structural and electronic properties of cadmium sulfide clusters

      SciTech Connect

      Joswig, J.O.; Springborg, M.; Seifert, G.

      2000-03-30

      Crystalline cadmium sulfide is a semiconductor for which the wurtzite and zinc blend structures are energetically almost degenerate. Due to quantum-confinement effects, it is possible to tune the optical properties of finite cadmium sulfide clusters by varying their size. The authors report results of a theoretical study devoted to the properties of stoichiometric Cd{sub n}S{sub n} clusters as a function of their size n. The authors have optimized the structure, whereby the initial structures are spherical parts of either of the two crystal structures, and have studied systems with up to almost 200 atoms. The calculations were performed by using a simplified LCAO-DFT-LDA scheme. The results include the structure, electronic energy levels (in particular the frontier orbitals HOMO and LUMO), and stability as a function of size. The results allow for a unique definition of a surface region. The Mulliken populations indicate that the bonds within this region are more ionic than in the bulk. Furthermore, whereas the HOMO is delocalized over major parts of the nanoparticle, the LUMO is a surface state, which confirms recent experimental findings. Finally, the relative stability of the zinc blend and wurtzite structures is strongly dependent on the size of the system, and there is a close connection between the HOMO-LUMO energy gap and stability.

    15. The effect of stress on the nanomechanical properties of Au surfaces

      SciTech Connect

      Houston, J.E.

      1996-12-31

      Stress in thin films plays a critical role in many technologically important areas. The role is a beneficial one in strained layer superlattices where semiconductor electrical and optical properties can be tailored with film stress. On the negative side, residual stress in thin-film interconnects in microelectronics can lead to cracking and delamination. In spite of their importance, however, surface and thin-film stresses are difficult to measure and control, especially on a local level. In recent studies, we used the Interfacial Force Microscope (IFM) in a nanoindenter mode to survey the nanomechanical properties of Au films grown on various substrates. Quantitative tabulations of the indentation modulus and the maximum shear stress at the plastic threshold showed consistent values over individual samples but a wide variation from substrate to substrate. These values were compared with film properties such as surface roughness, average grain size and interfacial adhesion and no correlation was found. However, in a subsequent analysis of the results, we found consistencies which support the integrity of the data and point to the fact that the results are sensitive to some property of the various film/substrate combinations. In recent measurements on two of the original substrate materials we found a direct correlation between the nanomechanical values and the residual stress in the films, as measured globally by a wafer warping technique. In the present paper, we review these earlier results and show recent measurements dealing with stresses externally applied to the films which supports our earlier conclusion concerning the role of stress on our measurements. In addition, we present very recent results concerning morphological effects on nanomechanical properties which add additional support to the suggestion that near-threshold indentation holds promise of being able to measure stress on a very local level.

    16. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Enhanced nonlinear optical absorption of Au/SiO2 nano-composite thin films

      NASA Astrophysics Data System (ADS)

      Zhao, Cui-Hua; Zhang, Bo-Ping; Shang, Peng-Peng

      2009-12-01

      Nano metal-particle dispersed glasses are the attractive candidates for nonlinear optical material applications. Au/SiO2 nano-composite thin films with 3 vol% to 65 vol% Au are prepared by inductively coupled plasma sputtering. Au particles as perfect spheres with diameters between 10 nm and 30 nm are uniformly dispersed in the SiO2 matrix. Optical absorption peaks due to the surface plasmon resonance of Au particles are observed. The absorption property is enhanced with the increase of Au content, showing a maximum value in the films with 37 vol% Au. The absorption curves of the Au/SiO2 thin films with 3 vol% to 37 vol% Au accord well with the theoretical optical absorption spectra obtained from Mie resonance theory. Increasing Au content over 37 vol% results in the partial connection of Au particles, whereby the intensity of the absorption peak is weakened and ultimately replaced by the optical absorption of the bulk. The band gap decreases with Au content increasing from 3 vol% to 37 vol% but increases as Au content further increases.

    17. Properties of liquid clusters in large-scale molecular dynamics nucleation simulations

      SciTech Connect

      Angélil, Raymond; Diemand, Jürg; Tanaka, Kyoko K.; Tanaka, Hidekazu

      2014-02-21

      We have performed large-scale Lennard-Jones molecular dynamics simulations of homogeneous vapor-to-liquid nucleation, with 10{sup 9} atoms. This large number allows us to resolve extremely low nucleation rates, and also provides excellent statistics for cluster properties over a wide range of cluster sizes. The nucleation rates, cluster growth rates, and size distributions are presented in Diemand et al. [J. Chem. Phys. 139, 74309 (2013)], while this paper analyses the properties of the clusters. We explore the cluster temperatures, density profiles, potential energies, and shapes. A thorough understanding of the properties of the clusters is crucial to the formulation of nucleation models. Significant latent heat is retained by stable clusters, by as much as ΔkT = 0.1ε for clusters with size i = 100. We find that the clusters deviate remarkably from spherical—with ellipsoidal axis ratios for critical cluster sizes typically within b/c = 0.7 ± 0.05 and a/c = 0.5 ± 0.05. We examine cluster spin angular momentum, and find that it plays a negligible role in the cluster dynamics. The interfaces of large, stable clusters are thinner than planar equilibrium interfaces by 10%−30%. At the critical cluster size, the cluster central densities are between 5% and 30% lower than the bulk liquid expectations. These lower densities imply larger-than-expected surface areas, which increase the energy cost to form a surface, which lowers nucleation rates.

    18. Statistics of physical properties of dark matter clusters

      SciTech Connect

      Shaw, Laurie; Weller, Jochen; Ostriker, Jeremiah P.; Bode, Paul; /Princeton U. Observ.

      2005-09-01

      We have identified over 2000 well resolved cluster halos, and also their associated bound subhalos, from the output of 1024{sup 3} particle cosmological N-body simulation (of box size 320h{sup -1}Mpc and softening length 3.2h{sup -1}kpc). We present an algorithm to identify those halos still in the process of relaxing into dynamical equilibrium, and a detailed analysis of the integral and internal physical properties for all the halos in our sample. The majority are prolate, and tend to rotate around their minor principle axis. We find there to be no correlation between the spin and virial mass of the clusters halos and that the higher mass halos are less dynamically relaxed and have a lower concentration. Additionally, the orbital angular momentum of the substructure is typically well aligned with the rotational angular momentum of the ''host'' halo. There is also evidence of the transfer of angular momentum from subhalos to their host. Overall, we find that measured halo properties are often significantly influenced by the fraction of mass contained within substructure. Dimensionless properties do depend weakly on the ratio of halo mass (M{sub h}) to our characteristic mass scale (M{sub *} = 8 x 10{sup 14}h{sup -1}M{sub {circle_dot}}). This lack of self-similarity is in the expected sense in that, for example, ''old halos'' with M{sub h}/M{sub *} << 1 have less substructure than ''young halos'' with M{sub h}/M{sub *} >> 1.

    19. Temperature-dependent electrical transport properties of (Au/Ni)/n-GaN Schottky barrier diodes

      NASA Astrophysics Data System (ADS)

      Dogan, Hulya; Elagoz, Sezai

      2014-09-01

      The temperature-dependent electrical properties of (Au/Ni)/n-GaN Schottky barrier diodes (SBDs)have been investigated in the wide temperature range of 40-400 K. The analysis of the main electrical characteristics such as zero-bias barrier height (ΦB0), ideality factor (n) and series resistance (Rs) were found strongly temperature dependent. Such behavior is attributed to barrier inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at the interface. It is evident that the diode parameters such as zero-bias barrier height increases and the ideality factor decreases with increasing temperature. The values of series resistance that are obtained from Cheung's method are decreasing with increasing temperature. The temperature dependence of Schottky barrier height (SBD) and ideality factor (n) are explained by invoking three sets of Gaussian distribution of (SBH) in the temperature ranges of 280-400 K, 120-260 K and 40-100 K, respectively. (Au/Ni)/n-GaN Schottky barrier diode have been shown a Gaussian distribution giving mean BHs (ΦbarB0) of 1.167, 0.652 and 0.356 eV and standard deviation σs of 0.178, 0.087 and 0.133 V for the three temperature regions. A modified ln(I0/T2)-q2σ2/2k2T2 vs. 1/kT plot have given ΦbarB0 and A* as 1.173 eV and 34.750 A/cm2 K2, 0.671 eV and 26.293 A/cm2 K2, 0.354 eV and 10.199 A/cm2 K2, respectively.

    20. Influence of decavanadate clusters on the rheological properties of gelatin.

      PubMed

      Carn, Florent; Djabourov, Madeleine; Coradin, Thibaud; Livage, Jacques; Steunou, Nathalie

      2008-10-09

      The influence of polyoxovanadate clusters ([H(2)V(10)O(28)](4-)) on the thermo-reversible gelation of porcine skin gelatin solution (type A, M w approximately 40 000 g.mol (-1), pH = 3.4 < isoelectric point (IEP) approximately 8) has been investigated as a function of temperature and vanadate concentration by combining rheology and microcalorimetry. This work shows that the rheological properties of the system depend on electrostatic interactions between [H(2)V(10)O(28)](4-) and positively charged gelatin chains. In a first stage, we describe the renaturation of the gelatin triple helices in the presence of decavanadate clusters. We reveal that, when gelatin chains are in coil conformation (30 degrees C < T < 50 degrees C), the inorganic clusters act as physical cross-linkers that govern the visco-elastic properties of the mixture with an exponential dependence of the (G', G'') modulus with the vanadate concentration. Below 30 degrees C, we show that gelatin triple helix nucleation is slightly favored by the presence of vanadate, but above a helix concentration of 0.012 g.cm (-3), G' is fully governed by the helix concentration. During the melting process, we reveal the non-fully reversible behavior of the vanadate/gelatin rheological properties and the stabilization of gelatin triple helices due to vanadate species until 50 degrees C. This non-reversible character has also been observed in the same experimental conditions with collagen/vanadate solutions. This is the first time that such a stabilization of triple helices has been reported in the case of gelatin hydrogels chemically cross-linked or not. We propose to analyze these results by considering that triple helix aggregates should persist because of decavanadate bridging, that the nucleation of an extended triple helix network may induce a strong modification of the vanadate cross-linker distribution in the system, or both, thus promoting the formation of thermally stable vanadate/gelatin micro-gels in the

    1. A facile strategy to fabricate Au/TiO2 nanotubes photoelectrode with excellent photoelectrocatalytic properties

      NASA Astrophysics Data System (ADS)

      Zhang, Guowei; Miao, Hui; Hu, Xiaoyun; Mu, Jianglong; Liu, Xixi; Han, Tongxin; Fan, Jun; Liu, Enzhou; Yin, Yunchao; Wan, Jun

      2017-01-01

      Highly ordered titanium dioxide nanotubes (TiO2 NTs) were prepared by a low-temperature hydrothermal process with Ti sheet as precursor in NaOH solutions. Gold nanoparticles (Au NPs) were then deposited on the surface of TiO2 NTs by a microwave-assisted chemical reduction route. The investigation reveal that the Au NPs are well dispersed on the surface of TiO2 NTs in metallic state, and Au NPs can effectively promote the separation of photogenerated electron-hole pairs. Besides, Au NPs also can enhance the visible light absorption of TiO2 NTs due to their localized surface plasmon resonance (LSPR) effect. The experimental results indicate that 0.5 Au/TiO2 NTs film with an photocurrent of 19.0 μA/cm2 exhibits the highest photoelectrocatalytic (PEC) activity, when under a low bias of 0.5 V, in the degradation of methylene blue (MB). Additionally, the mechanism for the enhanced PEC performance of Au/TiO2 NTs is preliminarily discussed. The Au NPs decorated TiO2 NTs displayed a more effective separation of photogenerated electron-hole pairs. The enhanced visible light absorption was owning to the Au NPs localized surface plasmon resonance (LSPR) effect. Finally, the mechanism for the enhanced PEC performance of Au/TiO2 NTs was also proposed.

    2. A quantum Monte Carlo study on electron correlation in all-metal aromatic clusters MAl4(-) (M = Li, Na, K, Rb, Cu, Ag and Au).

      PubMed

      Brito, Bráulio Gabriel A; Hai, G-Q; Teixeira Rabelo, J N; Cândido, Ladir

      2014-05-14

      Using fixed-node diffusion quantum Monte Carlo (FN-DMC) simulation we investigate the electron correlation in all-metal aromatic clusters MAl4(-) (with M = Li, Na, K, Rb, Cu, Ag and Au). The electron detachment energies and electron affinities of the clusters are obtained. The vertical electron detachment energies obtained from the FN-DMC calculations are in very good agreement with the available experimental results. Calculations are also performed within the Hartree-Fock approximation, density-functional theory (DFT), and the couple-cluster (CCSD(T)) method. From the obtained results, we analyse the impact of the electron correlation effects in these bimetallic clusters and find that the correlation of the valence electrons contributes significantly to the detachment energies and electron affinities, varying between 20% and 50% of their total values. Furthermore, we discuss the electron correlation effects on the stability of the clusters as well as the accuracy of the DFT and CCSD(T) calculations in the present systems.

    3. Molecular dynamics simulation of joining process of Ag-Au nanowires and mechanical properties of the hybrid nanojoint

      SciTech Connect

      Ding, Su; Tian, Yanhong Jiang, Zhi; He, Xiaobin

      2015-05-15

      The nanojoining process of Ag-Au hybrid nanowires at 800K was comprehensively studied by virtue of molecular dynamics (MD) simulation. Three kinds of configurations including end-to-end, T-like and X-like were built in the simulation aiming to understand the nanojoining mechanism. The detailed dynamic evolution of atoms, crystal structure transformation and defects development during the nanojoining processes were performed. The results indicate that there are two stages in the nanojoining process of Ag-Au nanowires which are atom diffusion and new bonds formation. Temperature is a key parameter affecting both stages ascribed to the energy supply and the optimum temperature for Ag-Au nanojoint with diameter of 4.08 nm has been discussed. The mechanical properties of the nanojoint were examined with simulation of tensile test on the end-to-end joint. It was revealed that the nanojoint was strong enough to resist fracture at the joining area.

    4. Correlation of the plasmon-enhanced photoconductance and photovoltaic properties of core-shell Au@TiO2 network

      NASA Astrophysics Data System (ADS)

      Yang, Yiqun; Wu, Judy; Li, Jun

      2016-08-01

      This study reveals the contribution of hot electrons from the excited plasmonic nanoparticles in dye sensitized solar cells (DSSCs) by correlating the photoconductance of a core-shell Au@TiO2 network on a micro-gap electrode and the photovolatic properties of this material as photoanodes in DSSCs. The distinct wavelength dependence of these two devices reveals that the plasmon-excited hot electrons can easily overcome the Schottky barrier at Au/TiO2 interface in the whole visible wavelength range and transfer from Au nanoparticles into the TiO2 network. The enhanced charge carrier density leads to higher photoconductance and facilitates more efficient charge separation and photoelectron collection in the DSSCs.

    5. UV-visible absorption of small gold clusters in neon: Au(n) (n = 1-5 and 7-9).

      PubMed

      Lecoultre, S; Rydlo, A; Félix, C; Buttet, J; Gilb, S; Harbich, W

      2011-02-21

      We present optical absorption spectra in the UV-visible range (1.5 eV < E < 6 eV) for mass selected neutral gold clusters Au(n) (n = 1-5 and 7-9) embedded in solid Ne at 7 K. The experimental spectra are compared with time-dependent density functional calculations. Electronic transitions are distributed over the whole energy range without any concentration of the oscillator strength in a small energy window, characteristic for the more s-like metals such as the alkalis or silver. Contrary to the case of silver and partly copper clusters, transitions issued from mainly d-type states are significantly involved in low energy transitions. The measured integrated cross section is smaller (<20%) than expected from a free-electron system, manifesting the strong screening of the s electrons due to the proximity of the s and d levels in gold.

    6. A coupled-cluster study on the noble gas binding ability of metal cyanides versus metal halides (metal = Cu, Ag, Au).

      PubMed

      Pan, Sudip; Gupta, Ashutosh; Saha, Ranajit; Merino, Gabriel; Chattaraj, Pratim K

      2015-11-05

      A coupled-cluster study is carried out to investigate the efficacy of metal(I) cyanide (MCN; M = Cu, Ag, Au) compounds to bind with noble gas (Ng) atoms. The M-Ng bond dissociation energy, enthalpy change, and Gibbs free energy change for the dissociation processes producing Ng and MCN are computed to assess the stability of NgMCN compounds. The Ng binding ability of MCN is then compared with the experimentally detected NgMX (X = F, Cl, Br) compounds. While CuCN and AgCN have larger Ng binding ability than those of MCl and MBr (M = Cu, Ag), AuCN shows larger efficacy toward bond formation with Ng than that of AuBr. Natural bond orbital analysis, energy decomposition analysis in conjunction with the natural orbital for chemical valence theory, and the topological analysis of the electron density are performed to understand the nature of interaction occurring in between Ng and MCN. The Ng-M bonds in NgMCN are found comprise an almost equal contribution from covalent and electrostatic types of interactions. The different electron density descriptors also reveal the partial covalent character in the concerned bonds.

    7. Evaluation of Hollow Golden Icosahedrons: Bonding and Spherical Aromatic Properties of [Au11 E](3-) Superatoms (E=Se and Te) from Relativistic DFT calculations, Persistent Structures?

      PubMed

      Muñoz-Castro, Alvaro

      2017-01-04

      Two novel clusters were proposed according to the superatom model involving a favorable inclusion of Se and Te into a Au12 cage leading to [Au11 E](3-) clusters. Such structures retain a hollow gold-based icosahedron with spherical aromatic character, according to the 18-valence electron rule. Interestingly, it is shown that despite the favorable electronic structure and aromatic behavior, the titled structure is further found to be a local minimum in the potential surface, which exhibits a planar isomer as a plausible candidate for the lowest-energy structure. The proposed strategy employed to vary the electron count of the cage is useful for the further design of novel spherical aromatic superatoms and ligand-protected clusters, for which the main variation is generated directly in the surface of the cluster, in addition to the extensive formation of endohedral clusters with different heteroatoms.

    8. Tuning electronic properties of novel metal oxide nanocrystals using interface interactions: MoO3 monolayers on Au(111)

      SciTech Connect

      Quek, S; Biener, M M; Biener, J; Friend, C M; Kaxiras, E

      2004-04-20

      Metal oxide nanocrystals deposited on metal surfaces have novel electronic properties due to interface and nanoscale effects. Crystals and nanoscale ribbons of MoO{sub 3} are highly effective catalysts and field emitters. This renders MoO{sub 3} an interesting prototype. Whilst MoO{sub 3} exists as bilayers in the bulk crystal5, in this work, monolayer MoO{sub 3} nanocrystals were grown epitaxially on Au(111). Ab initio calculations reveal that Au stabilizes the MoO{sub 3} monolayer through electronic charge redistribution at the interface. The Mo-O bonds are able to rotate about one another, allowing the MoO{sub 3} monolayer to adjust to the Au lattice. As a result, the monolayer is semimetallic, unlike bulk MoO{sub 3} which is semiconducting. This remarkable flexibility of the oxide lattice suggests the possibility of tuning electronic properties of transition metal oxides via interface interactions. The overall surface pattern obtained is affected by an interplay between the Au(111) surface reconstruction and the edges of the deposited MoO{sub 3} islands.

    9. Galaxy clusters in visible light (I): catalogues, large-scale distribution, and general properties.

      NASA Astrophysics Data System (ADS)

      Bian, Yulin

      1995-12-01

      While the nature, behaviour, and evolution of galaxy clusters is a such wide research field, only some of their optical properties are underlined in the present review. The whole article is divided into two parts, of which this is the first one, contributed to cluster catalogues, large-scale distribution, and some general characteristics of galaxy clusters.

    10. Magnetic properties of bimetallic Au/Co nanoparticles prepared by thermal laser treatment

      NASA Astrophysics Data System (ADS)

      Sosunov, A. V.; Spivak, L. V.

      2016-07-01

      The irradiation of metallic films by a nanosecond pulsed laser leads to a self-assembly of nanoparticle arrays. This method has been used to prepare bimetallic Au/Co nanoparticles on a SiO2 substrate. The microstructure and morphology of the bimetallic nanoparticles have been investigated using scanning electron microscopy and transmission electron microscopy. It has been shown that the bimetallic nanoparticles have a hemispherical shape with a single-crystal structure and an average size of ~50 nm. The magnetic properties of these nanoparticles have been examined using a vibrating-sample magnetometer in the transverse and longitudinal directions. It has been found that the direction of the magnetization of the bimetallic nanoparticles lies in the plane of the substrate, and the coercive forces in the transverse and longitudinal directions differ by 25%. The use of the vibrating-sample magnetometer method makes it possible to investigate the differences in the magnetic saturations and the coercive forces of an array of bimetallic nanoparticles on a large surface area. The performed investigations have demonstrated that the anisotropic nanomagnetic materials with the desired magnetic orientation can be easily and quickly prepared by means of thermal laser treatment.

    11. Effect of Metallic Au Seed Layer Annealing on the Properties of Electrodeposited ZnO Nanorods.

      PubMed

      Park, Youngbin; Nam, Giwoong; Kim, Byunggu; Leem, Jae-Young

      2015-11-01

      This study focuses on the effect of annealing the Au seed layer (ASL) on the structural and optical properties of electrodeposited ZnO nanorods. ZnO nanorods were fabricated in a three-step approach. In the first step, ASLs were deposited using an ion sputter technique. In the second step, layers were annealed in air at various temperatures ranging from 400 degrees C to 600 degrees C. Finally, ZnO nanorods were grown using an electrodeposition method. The field-emission scanning electron microscopy analysis showed that better aligned ZnO nanorods are fabricated on the annealed ASL compared with non-annealed ASL The X-ray diffraction analysis showed a notable improvement in directional growth along the (002) crystallographic plane when ZnO nanorods were grown on the annealed ASL. The photoluminescence analysis showed that the UV emission peak of ZnO nanorods on the annealed ASL at 400 degrees C was blue-shifted and increased.

    12. VizieR Online Data Catalog: Hi-GAL cluster candidates physical properties (Beuret+, 2017)

      NASA Astrophysics Data System (ADS)

      Beuret, M.; Billot, N.; Cambresy, L.; Eden, D. J.; Elia, D.; Molinari, S.; Pezzuto, S.; Schisano, E.

      2016-11-01

      Physical properties for 1633 Hi-GAL cluster candidates in the inner part of the Galactic Plane are presented. The 1633 cluster candidates are splitted into two tables : 496 reliable cluster candidates and 1137 potential cluster candidates. For each of the 1633 cluster candidates central positions, angular minor and major axis, position angles of the ellipses, the total number of clumps and the ratio of number of pre-stellar clumps over proto-stellar clumps are given. Besides these properties, for each reliable cluster candidates heliocentric distances, galactocentric distances, scale heights, linear minor and major axis, surface densities and closest HII regions are given. For each potential cluster candidates angular surface density and a flag that determines their classifications as potential cluster candidates are given. (2 data files).

    13. TSCA Work Plan Chemical Technical Supplement – Physicochemical Properties and Environmental Fate of the Brominated Phthalates Cluster (BPC) Chemicals

      EPA Pesticide Factsheets

      TSCA Work Plan Chemical Technical Supplement – Physicochemical Properties and Environmental Fate of the Brominated Phthalates Cluster (BPC) Chemicals -- Brominated Phthalates Cluster Flame Retardants.

    14. Crystal Structure of Superconducting 1/1 Cubic Au-Ge-Yb Approximant with Tsai-Type Cluster

      NASA Astrophysics Data System (ADS)

      Deguchi, Kazuhiko; Nakayama, Mika; Matsukawa, Shuya; Imura, Keiichiro; Tanaka, Katsumasa; Ishimasa, Tsutomu; Sato, Noriaki K.

      2015-01-01

      We report the synthesis of a single-phase sample of the superconducting crystalline approximant Au64.0Ge22.0Yb14.0 and present a structure model refined by Rietveld analysis for X-ray diffraction data.

    15. Gas sensing properties of conducting polymer/Au-loaded ZnO nanoparticle composite materials at room temperature

      NASA Astrophysics Data System (ADS)

      Kruefu, Viruntachar; Wisitsoraat, Anurat; Tuantranont, Adisorn; Phanichphant, Sukon

      2014-09-01

      In this work, a new poly (3-hexylthiophene):1.00 mol% Au-loaded zinc oxide nanoparticles (P3HT:Au/ZnO NPs) hybrid sensor is developed and systematically studied for ammonia sensing applications. The 1.00 mol% Au/ZnO NPs were synthesized by a one-step flame spray pyrolysis (FSP) process and mixed with P3HT at different mixing ratios (1:1, 2:1, 3:1, 4:1, and 1:2) before drop casting on an Al2O3 substrate with interdigitated gold electrodes to form thick film sensors. Particle characterizations by X-ray diffraction (XRD), nitrogen adsorption analysis, and high-resolution transmission electron microscopy (HR-TEM) showed highly crystalline ZnO nanoparticles (5 to 15 nm) loaded with ultrafine Au nanoparticles (1 to 2 nm). Film characterizations by XRD, field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, and atomic force microscopy (AFM) revealed the presence of P3HT/ZnO mixed phases and porous nanoparticle structures in the composite thick film. The gas sensing properties of P3HT:1.00 mol% Au/ZnO NPs composite sensors were studied for reducing and oxidizing gases (NH3, C2H5OH, CO, H2S, NO2, and H2O) at room temperature. It was found that the composite film with 4:1 of P3HT:1.00 mol% Au/ZnO NPs exhibited the best NH3 sensing performances with high response (approximately 32 to 1,000 ppm of NH3), fast response time (4.2 s), and high selectivity at room temperature. Plausible mechanisms explaining the enhanced NH3 response by composite films were discussed.

    16. Gas sensing properties of conducting polymer/Au-loaded ZnO nanoparticle composite materials at room temperature

      PubMed Central

      2014-01-01

      In this work, a new poly (3-hexylthiophene):1.00 mol% Au-loaded zinc oxide nanoparticles (P3HT:Au/ZnO NPs) hybrid sensor is developed and systematically studied for ammonia sensing applications. The 1.00 mol% Au/ZnO NPs were synthesized by a one-step flame spray pyrolysis (FSP) process and mixed with P3HT at different mixing ratios (1:1, 2:1, 3:1, 4:1, and 1:2) before drop casting on an Al2O3 substrate with interdigitated gold electrodes to form thick film sensors. Particle characterizations by X-ray diffraction (XRD), nitrogen adsorption analysis, and high-resolution transmission electron microscopy (HR-TEM) showed highly crystalline ZnO nanoparticles (5 to 15 nm) loaded with ultrafine Au nanoparticles (1 to 2 nm). Film characterizations by XRD, field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, and atomic force microscopy (AFM) revealed the presence of P3HT/ZnO mixed phases and porous nanoparticle structures in the composite thick film. The gas sensing properties of P3HT:1.00 mol% Au/ZnO NPs composite sensors were studied for reducing and oxidizing gases (NH3, C2H5OH, CO, H2S, NO2, and H2O) at room temperature. It was found that the composite film with 4:1 of P3HT:1.00 mol% Au/ZnO NPs exhibited the best NH3 sensing performances with high response (approximately 32 to 1,000 ppm of NH3), fast response time (4.2 s), and high selectivity at room temperature. Plausible mechanisms explaining the enhanced NH3 response by composite films were discussed. PMID:25246871

    17. Synthesis and properties of Au/ZnO nanorods as a plasmonic photocatalyst

      NASA Astrophysics Data System (ADS)

      Lu, Jia; Wang, Huihu; Peng, Daluo; Chen, Tao; Dong, Shijie; Chang, Ying

      2016-04-01

      It is of great interest to develop plasmonic photocatalysts with high activity and stability recently. In this paper, Au/ZnO nanorods were synthesized via a facile hydrothermal method and used as photocatalysts for methyl orange dye degradation. The results revealed an interesting phenomenon that photocorrosion cracks were produced specially along the c-axis of pure ZnO nanorods for five cycles photodegradation experiments under UV-vis. light irradiation, while Au nanoparticles surface modification can effectively inhibit the occurrence of photocorrosion and improve its photocatalytic activity. The formation of photocorrossion cracks along the c-axis of pure ZnO nanorods verifies the photogenerated charges may follow the route that electrons migrate to Zn-terminated (0001) plane and holes to O-terminated (000 1 -) plane. SPR effect of Au nanoparticles enhances the light absorption ability and the electrons capture ability of Au/ZnO nanorods. Moreover, the surface adsorbed hydroxyl groups content is also increased due to Au nanoparticles modification. As Au nanoparticles can capture photogenerated electrons and hydroxyl groups are the favorable holes scavenger, the charges generation and separation in photocatalysis are strengthened. Especially, the charges separation path in Au/ZnO nanorods have changed, thus inhibiting the occurrence of photocorrosion along the c-axis of ZnO nanorods and improving the photocatalytic activity.

    18. Fabrication and properties of poly(vinylidenefluoride)/PbS/Au heterogeneous nanostructures.

      PubMed

      Lee, Kwang-Pill; Gopalan, Anantha Iyengar; Park, Jong Wook; Ragupathy, Dhanusuraman; Manesh, Kalayil Manian

      2009-01-01

      We report on the fabrication of polyvinylidenefluoride (PVdF) PVdF/PbS and PVdF/PbS/Au heterogeneous nanostructures by the processes, electrospinning and chemical treatment. Initially electrospinning a solution consisting of PVdF and lead acetate was used to form PVdF nanofibers loaded with Pb ions. Exposure of Pb ions loaded PVdF fibers to H2S resulted in PVdF/PbS nanostructures. The deposition of gold nanoparticles onto PVdF/PbS nanostructures results in PVdF/PbS/Au heterogeneous structure. The existence of PbS particles with an average diameter of 11 nm is evident from field emission transmission electron microscopy (FETEM) image of PVdF/PbS. The results from X-ray diffraction of PVdF/PbS also predict the size of PbS particles as in accordance with FETEM. A blue shift in the optical transition of PbS is noticed in the UV-visible spectrum of PVdF/PbS as a result of quantum confinement effect. The band gap of PbS is influenced by the presence of Au nanoparticles over the PbS particles. An equal atomic weight % of Au and PbS is found in the PVdF/PbS/Au nanostructure as inferred from energy dispersive X-ray spectroscopy (EDX). Photoluminescence (PL) spectra of PVdF/PbS and PVdF/PbS/Au are compared. Emission peaks are noticed at 400 nm and 480 nm for PVdF/PbS and PVdF/PbS/Au nanostructures respectively for an excitation wavelength of 254 nm. The presence of Au nanoclusters in PVdF/PbS/Au diminishes the intensity of photo emission of PbS.

    19. Insights into the structural, electronic and magnetic properties of V-doped copper clusters: comparison with pure copper clusters

      NASA Astrophysics Data System (ADS)

      Die, Dong; Zheng, Ben-Xia; Zhao, Lan-Qiong; Zhu, Qi-Wen; Zhao, Zheng-Quan

      2016-08-01

      The structural, electronic and magnetic properties of Cun+1 and CunV (n = 1–12) clusters have been investigated by using density functional theory. The growth behaviors reveal that V atom in low-energy CunV isomer favors the most highly coordinated position and changes the geometry of the three-dimensional host clusters. The vibrational spectra are predicted and can be used to identify the ground state. The relative stability and chemical activity of the ground states are analyzed through the binding energy per atom, energy second-order difference and energy gap. It is found that that the stability of CunV (n ≥ 8) is higher than that of Cun+1. The substitution of a V atom for a Cu atom in copper clusters alters the odd-even oscillations of stability and activity of the host clusters. The vertical ionization potential, electron affinity and photoelectron spectrum are calculated and simulated for all of the most stable clusters. Compare with the experimental data, we determine the ground states of pure copper clusters. The magnetism analyses show that the magnetic moments of CunV clusters are mainly localized on the V atom and decease with the increase of cluster size. The magnetic change is closely related to the charge transfer between V and Cu atoms.

    20. Insights into the structural, electronic and magnetic properties of V-doped copper clusters: comparison with pure copper clusters

      PubMed Central

      Die, Dong; Zheng, Ben-Xia; Zhao, Lan-Qiong; Zhu, Qi-Wen; Zhao, Zheng-Quan

      2016-01-01

      The structural, electronic and magnetic properties of Cun+1 and CunV (n = 1–12) clusters have been investigated by using density functional theory. The growth behaviors reveal that V atom in low-energy CunV isomer favors the most highly coordinated position and changes the geometry of the three-dimensional host clusters. The vibrational spectra are predicted and can be used to identify the ground state. The relative stability and chemical activity of the ground states are analyzed through the binding energy per atom, energy second-order difference and energy gap. It is found that that the stability of CunV (n ≥ 8) is higher than that of Cun+1. The substitution of a V atom for a Cu atom in copper clusters alters the odd-even oscillations of stability and activity of the host clusters. The vertical ionization potential, electron affinity and photoelectron spectrum are calculated and simulated for all of the most stable clusters. Compare with the experimental data, we determine the ground states of pure copper clusters. The magnetism analyses show that the magnetic moments of CunV clusters are mainly localized on the V atom and decease with the increase of cluster size. The magnetic change is closely related to the charge transfer between V and Cu atoms. PMID:27534599

    1. Solid phase metallurgy strategy to sub-5 nm Au-Pd and Ni-Pd bimetallic nanoparticles with controlled redox properties.

      PubMed

      Tang, Yu; Xu, Shaodan; Dai, Yihu; Yan, Xiaoqing; Li, Renhong; Xiao, Liping; Fan, Jie

      2014-01-07

      A solid phase metallurgy strategy is applied to synthesize Au-Pd and Ni-Pd bimetallic nanoparticles (BMNPs) with a tight sub-5 nm particle size distribution. The near-surface elemental composition and redox properties of Au-Pd BMNPs can be well tailored, which leads to an optimized catalytic performance in n-hexane combustion.

    2. The properties, origin and evolution of stellar clusters in galaxy simulations and observations

      NASA Astrophysics Data System (ADS)

      Dobbs, C. L.; Adamo, A.; Few, C. G.; Calzetti, D.; Dale, D. A.; Elmegreen, B. G.; Evans, A. S.; Gouliermis, D. A.; Grasha, K.; Grebel, E. K.; Johnson, K. E.; Kim, H.; Lee, J. C.; Messa, M.; Ryon, J. E.; Smith, L. J.; Thilker, D.; Ubeda, L.; Whitmore, B.

      2017-01-01

      We investigate the properties and evolution of star particles in two simulations of isolated spiral galaxies, and two galaxies from cosmological simulations. Unlike previous numerical work, where typically each star particle represents one `cluster', for the isolated galaxies we are able to model features we term `clusters' with groups of particles. We compute the spatial distribution of stars with different ages, and cluster mass distributions, comparing our findings with observations including the recent LEGUS survey. We find that spiral structure tends to be present in older (100s Myr) stars and clusters in the simulations compared to the observations. This likely reflects differences in the numbers of stars or clusters, the strength of spiral arms, and whether the clusters are allowed to evolve. Where we model clusters with multiple particles, we are able to study their evolution. The evolution of simulated clusters tends to follow that of their natal gas clouds. Massive, dense, long-lived clouds host massive clusters, whilst short-lived clouds host smaller clusters which readily disperse. Most clusters appear to disperse fairly quickly, in basic agreement with observational findings. We note that embedded clusters may be less inclined to disperse in simulations in a galactic environment with continuous accretion of gas on to the clouds than isolated clouds and correspondingly, massive young clusters which are no longer associated with gas tend not to occur in the simulations. Caveats of our models include that the cluster densities are lower than realistic clusters, and the simplistic implementation of stellar feedback.

    3. Internal-Modified Dithiol DNA–Directed Au Nanoassemblies: Geometrically Controlled Self–Assembly and Quantitative Surface–Enhanced Raman Scattering Properties

      PubMed Central

      Yan, Yuan; Shan, Hangyong; Li, Min; Chen, Shu; Liu, Jianyu; Cheng, Yanfang; Ye, Cui; Yang, Zhilin; Lai, Xuandi; Hu, Jianqiang

      2015-01-01

      In this work, a hierarchical DNA–directed self–assembly strategy to construct structure–controlled Au nanoassemblies (NAs) has been demonstrated by conjugating Au nanoparticles (NPs) with internal–modified dithiol single-strand DNA (ssDNA) (Au–B–A or A–B–Au–B–A). It is found that the dithiol–ssDNA–modified Au NPs and molecule quantity of thiol–modified ssDNA grafted to Au NPs play critical roles in the assembly of geometrically controlled Au NAs. Through matching Au–DNA self–assembly units, geometrical structures of the Au NAs can be tailored from one–dimensional (1D) to quasi–2D and 2D. Au–B–A conjugates readily give 1D and quasi–2D Au NAs while 2D Au NAs can be formed by A–B–Au–B–A building blocks. Surface-enhanced Raman scattering (SERS) measurements and 3D finite–difference time domain (3D-FDTD) calculation results indicate that the geometrically controllable Au NAs have regular and linearly “hot spots”–number–depended SERS properties. For a certain number of NPs, the number of “hot spots” and accordingly enhancement factor of Au NAs can be quantitatively evaluated, which open a new avenue for quantitative analysis based on SERS technique. PMID:26581251

    4. PHOTOVOLTAIC PROPERTIES OF AU-MEROCYANINE-TiO2 SANDWICH CELLS. I. DARK ELECTRICAL PROPERTIES AND TRANSIENT EFFECT

      SciTech Connect

      Skotheim, T.; Yang, J.-M.; Otvos, J.; Klein, M.P.

      1980-07-01

      The electrical properties of thin films (200-3000 {angstrom}) of merocyanine photosensitizing dye sandwiched between a TiO{sub 2} single crystal doped n type and a thin (200 {angstrom}) Au metal layer has been studied. Dark current voltage measurements revealed that the current is space-charge limited at high current densities with an electron trapping density of -10{sup 17} cm{sup -3}. This was determined by using TiO{sub 2} as an electron injecting contact. Interpretation of the kinetics of rise and decay of the photocurrent suggests that the mobility of holes, the majority carriers in merocyanine, is dependent on traps, the dominant trapping level having a depth of 0.11 eV. The decay of the photocurrent is monomolecular at short times and dominated by bimolecular recombination kinetics for long times of the order of seconds. The high series resistance in the merocyanine prevents any band bending in the TiO{sub 2}, as the entire built-in voltage in the junction falls across the merocyanine film. This is supported by capacitance voltage data showing a complete absence of mobile charge carriers in the junction region.

    5. Photo-induced transformation process at gold clusters-semiconductor interface: Implications for the complexity of gold clusters-based photocatalysis

      PubMed Central

      Liu, Siqi; Xu, Yi-Jun

      2016-01-01

      The recent thrust in utilizing atomically precise organic ligands protected gold clusters (Au clusters) as photosensitizer coupled with semiconductors for nano-catalysts has led to the claims of improved efficiency in photocatalysis. Nonetheless, the influence of photo-stability of organic ligands protected-Au clusters at the Au/semiconductor interface on the photocatalytic properties remains rather elusive. Taking Au clusters–TiO2 composites as a prototype, we for the first time demonstrate the photo-induced transformation of small molecular-like Au clusters to larger metallic Au nanoparticles under different illumination conditions, which leads to the diverse photocatalytic reaction mechanism. This transformation process undergoes a diffusion/aggregation mechanism accompanied with the onslaught of Au clusters by active oxygen species and holes resulting from photo-excited TiO2 and Au clusters. However, such Au clusters aggregation can be efficiently inhibited by tuning reaction conditions. This work would trigger rational structural design and fine condition control of organic ligands protected-metal clusters-semiconductor composites for diverse photocatalytic applications with long-term photo-stability. PMID:26947754

    6. Modeling Mechanical Properties of Carbon Molecular Clusters and Carbon Nanostructural Materials

      DTIC Science & Technology

      2003-01-01

      UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP014264 TITLE: Modeling Mechanical Properties of Carbon Molecular...Clusters and Carbon Nanostructural Materials DISTRIBUTION: Approved for public release, distribution unlimited This paper is part of the following report...Res. Soc. Symp. Proc. Vol. 740 © 2003 Materials Research Society 17.2 Modeling mechanical properties of carbon molecular clusters and carbon

    7. Synthesis of Au@Pt bimetallic nanoparticles with concave Au nanocuboids as seeds and their enhanced electrocatalytic properties in the ethanol oxidation reaction

      NASA Astrophysics Data System (ADS)

      Tan, Lingyu; Li, Lidong; Peng, Yi; Guo, Lin

      2015-12-01

      Herein, a new type of uniform and well-structured Au@Pt bimetallic nanoparticles (BNPs) with highly active concave Au nanocuboids (NCs) as seeds was successfully synthesized by using the classic seed-mediated method. Electrochemical measurements were conducted to demonstrate their greatly enhanced catalytic performance in the ethanol oxidation reaction (EOR). It was found that the electrochemical performance for Au@Pt BNPs with the concave Au NCs as seeds, which were enclosed by {611} high-index facets, could be seven times higher than that of the Au@Pt bimetallic nanoparticles with regular spherical Au NPs as seeds. Furthermore, our findings show that the morphology and electrocatalytic activity of the Au@Pt BNPs can be tuned simply by changing the compositional ratios of the growth solution. The lower the amount of H2PtCl6 used in the growth solution, the thinner the Pt shell grew, and the more high-index facets of concave Au NCs seeds were exposed in Au@Pt BNPs, leading to higher electrochemical activity. These as-prepared concave Au@Pt BNPs will open up new strategies for improving catalytic efficiency and reducing the use of the expensive and scarce resource of platinum in the ethanol oxidation reaction, and are potentially applicable as electrochemical catalysts for direct ethanol fuel cells.

    8. Synthesis of Au@Pt bimetallic nanoparticles with concave Au nanocuboids as seeds and their enhanced electrocatalytic properties in the ethanol oxidation reaction.

      PubMed

      Tan, Lingyu; Li, Lidong; Peng, Yi; Guo, Lin

      2015-12-18

      Herein, a new type of uniform and well-structured Au@Pt bimetallic nanoparticles (BNPs) with highly active concave Au nanocuboids (NCs) as seeds was successfully synthesized by using the classic seed-mediated method. Electrochemical measurements were conducted to demonstrate their greatly enhanced catalytic performance in the ethanol oxidation reaction (EOR). It was found that the electrochemical performance for Au@Pt BNPs with the concave Au NCs as seeds, which were enclosed by {611} high-index facets, could be seven times higher than that of the Au@Pt bimetallic nanoparticles with regular spherical Au NPs as seeds. Furthermore, our findings show that the morphology and electrocatalytic activity of the Au@Pt BNPs can be tuned simply by changing the compositional ratios of the growth solution. The lower the amount of H2PtCl6 used in the growth solution, the thinner the Pt shell grew, and the more high-index facets of concave Au NCs seeds were exposed in Au@Pt BNPs, leading to higher electrochemical activity. These as-prepared concave Au@Pt BNPs will open up new strategies for improving catalytic efficiency and reducing the use of the expensive and scarce resource of platinum in the ethanol oxidation reaction, and are potentially applicable as electrochemical catalysts for direct ethanol fuel cells.

    9. Study of the effects of MeV Ag, Cu, Au, and Sn implantation on the optical properties of LiNbO3

      NASA Technical Reports Server (NTRS)

      Williams, E. K.; Ila, D.; Sarkisov, S.; Curley, M.; Poker, D. B.; Hensley, D. K.; Borel, C.

      1998-01-01

      The authors present the results of characterization of linear absorption and nonlinear refractive index of Au, Ag, Cu and Sn ion implantation into LiNbO3. Ag was implanted at 1.5 MeV to fluences of 2 to 17 x 17(exp 16)/sq cm at room temperature. Au and Cu were implanted to fluences of 5 to 20 x 10(exp 16)/sq cm at an energy of 2.0 MeV. Sn was implanted to a fluence of 1.6 x 10(exp 17)/sq cm at 160 kV. Optical absorption spectrometry indicated an absorption peak for the Au implanted samples after heat treatment at 1,000 C at approx. 620 nm. The Ag implanted samples absorption peaks shifted from approx. 450 nm before heat treatment to 550 nm after 500 C for 1h. Heat treatment at 800 C returned the Ag implanted crystals to a clear state. Cu nanocluster absorption peaks disappears at 500 C. No Sn clusters were observed by optical absorption or XRD. The size of the Ag and Au clusters as a function of heat treatment were determined from the absorption peaks. The Ag clusters did not change appreciably in size with heat treatment. The Au clusters increased from 3 to 9 nm diameter upon heat treatment at 1000 C. TEM analysis performed on a Au implanted crystal indicated the formation of Au nanocrystals with facets normal to the c-axis. Measurements of the nonlinear refractive indices were carried out using the Z-scan method with a tunable dye laser pumped by a frequency doubled mode-locked Nd:YAG laser. The dye laser had a 4.5 ps pulse duration time and 76 MHz pulse repetition rate (575 nm).

    10. Syntheses optimization, structural and thermoelectric properties of 1/1 Tsai-type quasicrystal approximants in RE-Au-SM systems (RE=Yb, Gd and SM=Si, Ge)

      NASA Astrophysics Data System (ADS)

      Hailu Gebresenbut, Girma; Tamura, Ryuji; Eklöf, Daniel; Pay Gómez, Cesar

      2013-04-01

      Yb-Cd (Tsai-type) quasicrystals constitute the largest icosahedral quasicrystal family where Yb can be replaced by other rare earth elements (RE) and Cd by pairs of p- and d-block elements. YbCd6 is a prototype 1/1 Tsai-type approximant phase which has a similar local structure to the Yb-Cd quasicrystal. In this study, the syntheses of Yb15.78Au65.22Ge19.00, Gd14.34Au67.16Ge18.5 and Gd14.19Au69.87Si15.94 Tsai-type 1/1 quasicrystal approximants are optimized using the self-flux technique. The crystal structures of the compounds are refined by collecting single crystal x-ray diffraction data. The structural refinements indicated that the compounds are essentially isostructural with some differences at their cluster centers. The basic polyhedral cluster unit in all the three compounds can be described by concentric shells of icosahedra symmetry and of disordered tetrahedra and/or a rare earth atom at the cluster center. Furthermore, the thermoelectric properties of the compounds are probed and their dimensionless figures of merit are calculated at different temperatures. A significant difference is observed in their thermoelectric properties, which could arise due to the slight difference in their crystal structure and chemical composition, as we move from Ge to Si and/or Gd to Yb. Therefore, this study shows the systematic effect of the chemical substitution of structurally similar materials on their thermoelectric properties.

    11. Syntheses optimization, structural and thermoelectric properties of 1/1 Tsai-type quasicrystal approximants in RE-Au-SM systems (RE=Yb, Gd and SM=Si, Ge).

      PubMed

      Gebresenbut, Girma Hailu; Tamura, Ryuji; Eklöf, Daniel; Gómez, Cesar Pay

      2013-04-03

      Yb-Cd (Tsai-type) quasicrystals constitute the largest icosahedral quasicrystal family where Yb can be replaced by other rare earth elements (RE) and Cd by pairs of p- and d-block elements. YbCd6 is a prototype 1/1 Tsai-type approximant phase which has a similar local structure to the Yb-Cd quasicrystal. In this study, the syntheses of Yb15.78Au65.22Ge19.00, Gd14.34Au67.16Ge18.5 and Gd14.19Au69.87Si15.94 Tsai-type 1/1 quasicrystal approximants are optimized using the self-flux technique. The crystal structures of the compounds are refined by collecting single crystal x-ray diffraction data. The structural refinements indicated that the compounds are essentially isostructural with some differences at their cluster centers. The basic polyhedral cluster unit in all the three compounds can be described by concentric shells of icosahedra symmetry and of disordered tetrahedra and/or a rare earth atom at the cluster center. Furthermore, the thermoelectric properties of the compounds are probed and their dimensionless figures of merit are calculated at different temperatures. A significant difference is observed in their thermoelectric properties, which could arise due to the slight difference in their crystal structure and chemical composition, as we move from Ge to Si and/or Gd to Yb. Therefore, this study shows the systematic effect of the chemical substitution of structurally similar materials on their thermoelectric properties.

    12. Organogold oligomers: Exploiting iClick and aurophilic cluster formation to prepare solution stable Au4 repeating units

      DOE PAGES

      Yang, Xi; Wang, Shanshan; Ghiviriga, Ion; ...

      2015-05-19

      A novel synthetic method to create gold based metallo–oligomers/polymers via the combination of inorganic click (iClick) with intermolecular aurophilic interactions is demonstrated. Complexes [PEt3Au]4(μ-N3C2C6H5) (1) and [PPhMe2Au]43C2C6H5) (2) and {[PEt3Au]4[(μ-N3C2)2-9,9-dihexyl-9H-fluorene]}n (8) have been synthesized via iClick. The tetranuclear structures of 1 and 2, induced by aurophilic bonding, are confirmed in the solid state through single crystal X-ray diffraction experiments and in solution via variable temperature NMR spectroscopy. The extended 1D structure of 8 is constructed by aurophilic induced self-assembly. 1H DOSY NMR analysis reveals that the aurophilic bonds in 1, 2, and 8 are retained in the solution phase. Themore » degree of polymerization within complex 8 is temperature and concentration dependent, as determined by 1H DOSY NMR. The complex 8 is a rare example of a solution stable higher ordered structure linked by aurophilic interactions.« less

    13. Scaling properties of azimuthal anisotropy in Au+Au and Cu+Cu Collisions at sqrt[s NN]=200 GeV.

      PubMed

      Adare, A; Afanasiev, S; Aidala, C; Ajitanand, N N; Akiba, Y; Al-Bataineh, H; Alexander, J; Al-Jamel, A; Aoki, K; Aphecetche, L; Armendariz, R; Aronson, S H; Asai, J; Atomssa, E T; Averbeck, R; Awes, T C; Azmoun, B; Babintsev, V; Baksay, G; Baksay, L; Baldisseri, A; Barish, K N; Barnes, P D; Bassalleck, B; Bathe, S; Batsouli, S; Baublis, V; Bauer, F; Bazilevsky, A; Belikov, S; Bennett, R; Berdnikov, Y; Bickley, A A; Bjorndal, M T; Boissevain, J G; Borel, H; Boyle, K; Brooks, M L; Brown, D S; Bucher, D; Buesching, H; Bumazhnov, V; Bunce, G; Burward-Hoy, J M; Butsyk, S; Campbell, S; Chai, J-S; Chang, B S; Charvet, J-L; Chernichenko, S; Chiba, J; Chi, C Y; Chiu, M; Choi, I J; Chujo, T; Chung, P; Churyn, A; Cianciolo, V; Cleven, C R; Cobigo, Y; Cole, B A; Comets, M P; Constantin, P; Csanád, M; Csörgo, T; Dahms, T; Das, K; David, G; Deaton, M B; Dehmelt, K; Delagrange, H; Denisov, A; d'Enterria, D; Deshpande, A; Desmond, E J; Dietzsch, O; Dion, A; Donadelli, M; Drachenberg, J L; Drapier, O; Drees, A; Dubey, A K; Durum, A; Dzhordzhadze, V; Efremenko, Y V; Egdemir, J; Ellinghaus, F; Emam, W S; Enokizono, A; En'yo, H; Espagnon, B; Esumi, S; Eyser, K O; Fields, D E; Finger, M; Finger, M; Fleuret, F; Fokin, S L; Forestier, B; Fraenkel, Z; Frantz, J E; Franz, A; Frawley, A D; Fujiwara, K; Fukao, Y; Fung, S-Y; Fusayasu, T; Gadrat, S; Garishvili, I; Gastineau, F; Germain, M; Glenn, A; Gong, H; Gonin, M; Gosset, J; Goto, Y; Granier de Cassagnac, R; Grau, N; Greene, S V; Grosse Perdekamp, M; Gunji, T; Gustafsson, H-A; Hachiya, T; Hadj Henni, A; Haegemann, C; Haggerty, J S; Hagiwara, M N; Hamagaki, H; Han, R; Harada, H; Hartouni, E P; Haruna, K; Harvey, M; Haslum, E; Hasuko, K; Hayano, R; Heffner, M; Hemmick, T K; Hester, T; Heuser, J M; He, X; Hiejima, H; Hill, J C; Hobbs, R; Hohlmann, M; Holmes, M; Holzmann, W; Homma, K; Hong, B; Horaguchi, T; Hornback, D; Hur, M G; Ichihara, T; Imai, K; Inaba, M; Inoue, Y; Isenhower, D; Isenhower, L; Ishihara, M; Isobe, T; Issah, M; Isupov, A; Jacak, B V; Jia, J; Jin, J; Jinnouchi, O; Johnson, B M; Joo, K S; Jouan, D; Kajihara, F; Kametani, S; Kamihara, N; Kamin, J; Kaneta, M; Kang, J H; Kano, H; Kanou, H; Kawagishi, T; Kawall, D; Kazantsev, A V; Kelly, S; Khanzadeev, A; Kikuchi, J; Kim, D H; Kim, D J; Kim, E; Kim, Y-S; Kinney, E; Kiss, A; Kistenev, E; Kiyomichi, A; Klay, J; Klein-Boesing, C; Kochenda, L; Kochetkov, V; Komkov, B; Konno, M; Kotchetkov, D; Kozlov, A; Král, A; Kravitz, A; Kroon, P J; Kubart, J; Kunde, G J; Kurihara, N; Kurita, K; Kweon, M J; Kwon, Y; Kyle, G S; Lacey, R; Lai, Y-S; Lajoie, J G; Lebedev, A; Le Bornec, Y; Leckey, S; Lee, D M; Lee, M K; Lee, T; Leitch, M J; Leite, M A L; Lenzi, B; Lim, H; Liska, T; Litvinenko, A; Liu, M X; Li, X; Li, X H; Love, B; Lynch, D; Maguire, C F; Makdisi, Y I; Malakhov, A; Malik, M D; Manko, V I; Mao, Y; Masek, L; Masui, H; Matathias, F; McCain, M C; McCumber, M; McGaughey, P L; Miake, Y; Mikes, P; Miki, K; Miller, T E; Milov, A; Mioduszewski, S; Mishra, G C; Mishra, M; Mitchell, J T; Mitrovski, M; Morreale, A; Morrison, D P; Moss, J M; Moukhanova, T V; Mukhopadhyay, D; Murata, J; Nagamiya, S; Nagata, Y; Nagle, J L; Naglis, M; Nakagawa, I; Nakamiya, Y; Nakamura, T; Nakano, K; Newby, J; Nguyen, M; Norman, B E; Nyanin, A S; Nystrand, J; O'Brien, E; Oda, S X; Ogilvie, C A; Ohnishi, H; Ojha, I D; Okada, H; Okada, K; Oka, M; Omiwade, O O; Oskarsson, A; Otterlund, I; Ouchida, M; Ozawa, K; Pak, R; Pal, D; Palounek, A P T; Pantuev, V; Papavassiliou, V; Park, J; Park, W J; Pate, S F; Pei, H; Peng, J-C; Pereira, H; Peresedov, V; Peressounko, D Yu; Pinkenburg, C; Pisani, R P; Purschke, M L; Purwar, A K; Qu, H; Rak, J; Rakotozafindrabe, A; Ravinovich, I; Read, K F; Rembeczki, S; Reuter, M; Reygers, K; Riabov, V; Riabov, Y; Roche, G; Romana, A; Rosati, M; Rosendahl, S S E; Rosnet, P; Rukoyatkin, P; Rykov, V L; Ryu, S S; Sahlmueller, B; Saito, N; Sakaguchi, T; Sakai, S; Sakata, H; Samsonov, V; Sato, H D; Sato, S; Sawada, S; Seele, J; Seidl, R; Semenov, V; Seto, R; Sharma, D; Shea, T K; Shein, I; Shevel, A; Shibata, T-A; Shigaki, K; Shimomura, M; Shohjoh, T; Shoji, K; Sickles, A; Silva, C L; Silvermyr, D; Silvestre, C; Sim, K S; Singh, C P; Singh, V; Skutnik, S; Slunecka, M; Smith, W C; Soldatov, A; Soltz, R A; Sondheim, W E; Sorensen, S P; Sourikova, I V; Staley, F; Stankus, P W; Stenlund, E; Stepanov, M; Ster, A; Stoll, S P; Sugitate, T; Suire, C; Sullivan, J P; Sziklai, J; Tabaru, T; Takagi, S; Takagui, E M; Taketani, A; Tanaka, K H; Tanaka, Y; Tanida, K; Tannenbaum, M J; Taranenko, A; Tarján, P; Thomas, T L; Togawa, M; Toia, A; Tojo, J; Tomásek, L; Torii, H; Towell, R S; Tram, V-N; Tserruya, I; Tsuchimoto, Y; Tuli, S K; Tydesjö, H; Tyurin, N; Vale, C; Valle, H; van Hecke, H W; Velkovska, J; Vertesi, R; Vinogradov, A A; Virius, M; Vrba, V; Vznuzdaev, E; Wagner, M; Walker, D; Wang, X R; Watanabe, Y; Wessels, J; White, S N; Willis, N; Winter, D; Woody, C L; Wysocki, M; Xie, W; Yamaguchi, Y L; Yanovich, A; Yasin, Z; Ying, J; Yokkaichi, S; Young, G R; Younus, I; Yushmanov, I E; Zajc, W A; Zaudtke, O; Zhang, C; Zhou, S; Zimányi, J; Zolin, L

      2007-04-20

      Differential measurements of elliptic flow (v2) for Au+Au and Cu+Cu collisions at sqrt[sNN]=200 GeV are used to test and validate predictions from perfect fluid hydrodynamics for scaling of v2 with eccentricity, system size, and transverse kinetic energy (KE T). For KE T identical with mT-m up to approximately 1 GeV the scaling is compatible with hydrodynamic expansion of a thermalized fluid. For large values of KE T mesons and baryons scale separately. Quark number scaling reveals a universal scaling of v2 for both mesons and baryons over the full KE T range for Au+Au. For Au+Au and Cu+Cu the scaling is more pronounced in terms of KE T, rather than transverse momentum.

    14. Magnetic properties of iron cluster/chromium matrix nanocomposites

      PubMed Central

      Kruk, Robert; Wang, Di; Hahn, Horst

      2015-01-01

      Summary A custom-designed apparatus was used for the fine-tuned co-deposition of preformed Fe clusters into antiferromagnetic Cr matrices. Three series of samples with precisely defined cluster sizes, with accuracy to a few atoms, and controlled concentrations were fabricated, followed by a complete characterization of structure and magnetic performance. Relevant magnetic characteristics, reflecting the ferromagnetic/antiferromagnetic coupling between Fe clusters and the Cr matrix, i.e., blocking temperature, coercivity field, and exchange bias were measured and their dependence on cluster size and cluster concentration in the matrix was analyzed. It is evident that the blocking temperatures are clearly affected by both the cluster size and their concentration in the Cr matrix. In contrast the coercivity shows hardly any dependence on size or inter-cluster distance. The exchange bias was found to be strongly sensitive to the cluster size but not to the inter-cluster distances. Therefore, it was concluded to be an effect that is purely localized at the interfaces. PMID:26171292

    15. Investigating energetics of Au8 on graphene/Ru(0001) using a genetic algorithm and density functional theory

      NASA Astrophysics Data System (ADS)

      Teng, Dieh; Vilhelmsen, Lasse B.; Sholl, David S.

      2014-10-01

      Gold nanoparticles have been extensively studied for their catalytic activity both theoretically and experimentally. The moiré pattern formed by graphene supported on single crystal substrates creates a useful environment where the properties of Au nanoclusters can be studied, provided the structure and evolution of these clusters can be controlled. We used a genetic algorithm combined with DFT calculations to predict the lowest energy structures of a Au8 cluster on graphene/Ru(0001). The most stable cluster forms a double-layer Au wall structure for Au8 in the fcc region of the moiré pattern, where the Au8 cluster is most strongly adsorbed. Further calculations give estimates for the net diffusion barrier of Au8 as an intact cluster on the surface. Our results are consistent with the Au island structure experimentally observed on graphene/Ru(0001), and support the hypothesis that Au clusters aggregate through Oswald ripening with Au dimers being the most important diffusing species.

    16. Structure and properties of Ti-Ni-Au shape memory alloys

      NASA Astrophysics Data System (ADS)

      Butler, Todd

      Ternary Ti-Ni-X based alloys, where X = Pt, Pd, Hf, Au or Zr, show promise as high temperature shape memory alloys (HTSMAs). In comparison to binary Ni-Ti alloys, some hypo-stoichiometric versions of these ternary compositions exhibit higher transformation temperatures and better mechanical stability due to the formation of nano-scale precipitates. In this study, a Ti 49Ni26Au25 (at.%) alloy was solution annealed at 1050°C for 3 hours and isothermally aged at 400°C and 550°C. A specimen was also annealed at 1050°C for 3 hours and furnace cooled. Ageing resulted in a very high peak micro-hardness for both temperatures. The structures and chemistries of the phases formed during ageing were characterized by wavelength dispersive x-ray spectroscopy (WDS), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), transmission electron microscopy (TEM), three-dimensional atom probe tomography (3DAP), x-ray diffraction (XRD), and differential scanning calorimetry (DSC). It was found that ageing at both 400°C and 550°C resulted in the formation of two different precipitates. First, two variants of a (Au,Ni)4Ti3 type phase form with SADPs similar to tetragonal D1a. The proposed orientation relationships with the matrix are the following: [001]D1a || [100] B2 with (011)B2 // (310)D1a and [001¯ ]D1a || [100]B2 with {011}B2 || (310) D1a. It is then postulated that the (Au,Ni)-rich phase creates local Ti-rich regions that promote the precipitation of two Ti2(Ni,Au) variants with tetragonal (I4/mmm) type symmetry. Their proposed orientation relationships with the matrix are the following: [100]Ti2(Ni,Au) || [100]B2 with (001)B2 || (001)Ti2(Ni.Au) and (001)B2 || (100)Ti2(Ni,Au). The combination of both phases appears to inhibit martensitic transformation by stabilizing the high temperature austenite phase, as evident by no transformation peaks in the aged specimens via DSC. However, it is interesting to note that the as-cast and 1050°C furnace cooled

    17. The imprint of feedback on the properties of the intra-cluster medium

      NASA Astrophysics Data System (ADS)

      Borgani, Stefano

      I will describe the role played by cosmological hydrodynamical simulations to understand the role that feedback processes have on the observable properties of the hot intra-cluster medium (ICM). After reviewing the current status of numerical simulations of galaxy clusters, I will focus my presentation on the different imprints that supernova feedback and AGN feedback have on the thermodynamical and chemical properties of the ICM. I will also highlight how different feedback mechanisms also affect the properties of the galaxy population in clusters, thus calling for a unified multi-wavelength view of clusters. Finally, I will discuss to what degree current uncertainties in the numerical description of feedback processes impact on the calibration through simulations of cluster mass proxies, a necessary step to use clusters as precision tools for cosmology.

    18. Structural Transitions from Pyramidal to Fused Planar to Tubular to Core/Shell Compact in Gold Clusters: Au-n (n=21-25)

      SciTech Connect

      Bulusu, Satya; Li, Xi; Wang, Lai S.; Zeng, Xiao Cheng

      2007-03-22

      We report a joint theoretical and experimental study of low-lying structures and structural transitions of gold cluster anions Aun- in the size range of n ) 21-25. Well-resolved photoelectron spectra are used to compare with density functional theory calculations and to identify the low-lying structures of the gold cluster anions. Due to the high stability of the tetrahedral Au20, the pyramid-based structures are found to be competitive for n ) 21-23. In addition to the pyramid-based structures, global-minimum searches also reveal two other generic structural types of low-lying clusters in the size range of n ) 21-24, namely, the fused-planar and the hollow-tubular structures. At n ) 24, the pyramid-based structures are no longer competitive and the hollow-tubular structures dominate the low-lying population. At n ) 25, a structural transition from hollowtubular to core/shell compact structure is observed.

    19. Observation of enhanced field emission properties of Au/TiO2 nanocomposite

      NASA Astrophysics Data System (ADS)

      Patil, Girish P.; Bagal, Vivekanand S.; Suryawanshi, Sachin R.; Late, Dattatray J.; More, Mahendra A.; Chavan, Padmakar G.

      2016-05-01

      Simple and low-cost method of thermal annealing was used to decorate Gold (Au) nanoparticles on aligned TiO2 nanotubes. The aligned TiO2 nanotubes were decorated by Au nanoparticles with an average diameter of 9, 18 and 28 nm (aligned TiO2 nanotubes referred as specimen A and TiO2 nanotubes decorated by Au nanoparticles with average diameter of 9, 18 and 28 nm are referred as specimen B, C and D, respectively). The detailed characterization such as structural, morphological and elemental analysis of TiO2 and Au/TiO2 nanocomposite have been carried out using X-ray diffraction, field emission scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and Raman spectroscopy. Furthermore, the meticulous comparative field emission characteristics of the aligned TiO2 nanotubes and Au/TiO2 nanocomposite have been performed. The turn-on field defined for the current density of 10 μA/cm2 has been found to be 3.9, 2.8, 3.2 and 3.7 V/μm for specimen A, B, C and D, respectively. The observed low turn-on field of specimen B has been found to be superior than the other semiconducting nanocomposites reported in the literature. The emission current stability over a period of 3 h is found to be better for all the specimens. To the best of our knowledge, a systematic field emission study of Au/TiO2 nanocomposite has not been explored. The observed superior field emission study of Au/TiO2 nanocomposite indicates their possible use in micro/nanoelectronic devices.

    20. Synthesis and photocatalytic properties of multi-morphological AuCu3-ZnO hybrid nanocrystals

      NASA Astrophysics Data System (ADS)

      Zeng, Deqian; Chen, Yuanzhi; Peng, Jian; Xie, Qingshui; Peng, Dong-Liang

      2015-10-01

      Noble metal-semiconductor hybrid nanocrystals represent an important class of materials for many potential applications, especially for photocatalysis. The utilization of transition metals to form alloys with noble metals can not only reduce the preparation costs, but may also offer tunable optical and catalytic properties for a broader range of applications. In this study, we report on the solution synthesis of AuCu3-ZnO hybrid nanocrystals with three interesting morphologies, including urchin-like, flower-like and multipod-like nanocrystals. In the synthetic strategy, Au-Cu bimetallic alloy seeds formed in situ are used to induce the heteroepitaxial growth of ZnO nanocrystals on the surface of bimetallic alloy cores; thus different types of morphologies can be achieved by controlling the reaction conditions. Through high-resolution transmission electron microscopy observations, well-defined interfaces between ZnO and AuCu3 are observed, which indicate that ZnO has a (0001) orientation and prefers to grow on AuCu3 {111} facets. The as-prepared hybrid nanocrystals demonstrate morphology- and composition-dependent surface plasmon resonance (SPR) absorption bands. In addition, much higher photocatalytic efficiency than pure ZnO nanocrystals is observed for the hybrid nanocrystals in the degradation of methylene blue. In particular, the multipod-like AuCu3-ZnO hybrid nanocrystals show the highest catalytic performance, as well as more than three times higher photocurrent density than the pure ZnO sample. The reported synthetic strategy provides a facile route to the effective combination of a plasmonic alloy with semiconductor components at the nanoscale in a controlled manner.

    1. THERMODYNAMIC PROPERTIES OF THE METALLIC SYSTEM Au(111)-(3×3)R30∘-Pd

      NASA Astrophysics Data System (ADS)

      Chadli, R.; Kheffache, S.; Khater, A.

      2016-02-01

      This work constitutes an analysis of the thermodynamic properties in the ordered metallic surface alloy system Au(111)-(3×3)R30∘-Pd. The equilibrium structural characteristics as well as the thermodynamic functions are examined by the matching method, associated with real space Green’s function formalism, evaluated in the harmonic approximation. Our numerical results, for this metallic system of surface alloy, show in particular a significant dependence between the thermodynamic properties and the coordination number and the values of the force constants.

    2. On scaling properties of cluster distributions in Ising models

      NASA Astrophysics Data System (ADS)

      Ruge, C.; Wagner, F.

      1992-01-01

      Scaling relations of cluster distributions for the Wolff algorithm are derived. We found them to be well satisfied for the Ising model in d=3 dimensions. Using scaling and a parametrization of the cluster distribution, we determine the critical exponent β/ν=0.516(6) with moderate effort in computing time.

    3. Small Al clusters on the Cu(111) surface: Atomic relaxation and vibrational properties

      NASA Astrophysics Data System (ADS)

      Rusina, G. G.; Borisova, S. D.; Chulkov, E. V.

      2010-11-01

      The relaxation and vibrational properties of both Al clusters and the (111) surface of a copper sub-strate were studied using the interatomic interaction potentials obtained in a tight-binding approximation. The presence of small aluminum clusters led to modification of the vibrational states of the substrate, a shift of the Rayleigh mode, and excitation of new Z-polarized modes. Hybridized modes localized on the cluster adatoms and the neighboring atoms of the substrate were found in the phonon spectrum. The localized dipole-active modes of the cluster and their strong hybridization with vibrations of the substrate points to desorption stability of the tri- and heptaatomic clusters.

    4. Electronic and crystallographic properties of reconstructed and nonreconstructed Au[l brace]001[r brace

      SciTech Connect

      Wu, S.C. Physics Department, Peking University, Beijing 100871 ); Li, H.; Quinn, J.; Tian, D.; Li, Y.S.; Begley, A.M.; Kim, S.K.; Jona, F.; Marcus, P.M. )

      1994-03-15

      Low-energy-electron-diffraction analyses of Fe-, Mn-, and Rh-stabilized Au[l brace]001[r brace]1[times]1 surfaces find the atomic structure to be a relaxed bulk termination. The first and the second interlayer spacings are contracted by about (2[plus minus]2.8)% and (2.8[plus minus]2.8)%, respectively, of the bulk spacing along [l angle]001[r angle]. Photoemission experiments with synchrotron radiation on reconstructed Au[l brace]001[r brace]5[times]20 find a surface-resonance band above the bulk [ital d] bands which exhibits dispersion with photon energies between 14 and 24 eV, in accordance with the buckled character of the hexagonal overlayer responsible for the surface reconstruction. All remaining features in the photoemission spectra from Au[l brace]001[r brace]5[times]20 can be explained on the basis of the self-consistent relativistic calculation of Eckardt, Fritsche, and Noffke to within 0.4 eV. Photoemission from Rh-stabilized Au[l brace]001[r brace]1[times]1 is similar to that from the reconstructed surface except for the surface resonance, which is markedly reduced on the 1[times]1 surface, and a shift of one band which points toward a transfer of [ital s]-like charge from the Rh to the Au atoms in the surface region.

    5. Frictional and morphological properties of Au-MoS2 films sputtered from a compact target

      NASA Technical Reports Server (NTRS)

      Spalvins, T.

      1984-01-01

      AuMoS2 films 0.02 to 1.2 microns thick were sputtered from target compacted from 5 wt % Au + 95 wt % MoS2, to investigate the frictional and morphological film growth characteristics. The gold dispersion effects in MoS2 films are of interest to increase the densitification and strengthening of the film structure. Three microstructural growth stages were identified on the nano-micro-macrostructural level. During sliding both sputtered Au-MoS2 and MoS2 films have a tendency to break within the columner region. The remaining or effective film, about 0.2 microns thick, performs the lubrication. The Au-MoS2 films displayed a lower friction coefficient with a high degree of frictional stability and less wear debris generation as compared to pure MoS2 films. The more favorable frictional characteristics of the Au-MoS2 films are attributed to the effective film thickness and the high density packed columner zone which has a reduced effect on the fragmentation of the tapered crystallites during fracture.

    6. Structural and magnetic properties of core-shell Au/Fe3O4 nanoparticles

      NASA Astrophysics Data System (ADS)

      León Félix, L.; Coaquira, J. A. H.; Martínez, M. A. R.; Goya, G. F.; Mantilla, J.; Sousa, M. H.; Valladares, L. De Los Santos; Barnes, C. H. W.; Morais, P. C.

      2017-02-01

      We present a systematic study of core-shell Au/Fe3O4 nanoparticles produced by thermal decomposition under mild conditions. The morphology and crystal structure of the nanoparticles revealed the presence of Au core of d = (6.9 ± 1.0) nm surrounded by Fe3O4 shell with a thickness of ~3.5 nm, epitaxially grown onto the Au core surface. The Au/Fe3O4 core-shell structure was demonstrated by high angle annular dark field scanning transmission electron microscopy analysis. The magnetite shell grown on top of the Au nanoparticle displayed a thermal blocking state at temperatures below TB = 59 K and a relaxed state well above TB. Remarkably, an exchange bias effect was observed when cooling down the samples below room temperature under an external magnetic field. Moreover, the exchange bias field (HEX) started to appear at T~40 K and its value increased by decreasing the temperature. This effect has been assigned to the interaction of spins located in the magnetically disordered regions (in the inner and outer surface of the Fe3O4 shell) and spins located in the ordered region of the Fe3O4 shell.

    7. Structural and magnetic properties of core-shell Au/Fe3O4 nanoparticles

      PubMed Central

      León Félix, L.; Coaquira, J. A. H.; Martínez, M. A. R.; Goya, G. F.; Mantilla, J.; Sousa, M. H.; Valladares, L. de los Santos; Barnes, C. H. W.; Morais, P. C.

      2017-01-01

      We present a systematic study of core-shell Au/Fe3O4 nanoparticles produced by thermal decomposition under mild conditions. The morphology and crystal structure of the nanoparticles revealed the presence of Au core of d = (6.9 ± 1.0) nm surrounded by Fe3O4 shell with a thickness of ~3.5 nm, epitaxially grown onto the Au core surface. The Au/Fe3O4 core-shell structure was demonstrated by high angle annular dark field scanning transmission electron microscopy analysis. The magnetite shell grown on top of the Au nanoparticle displayed a thermal blocking state at temperatures below TB = 59 K and a relaxed state well above TB. Remarkably, an exchange bias effect was observed when cooling down the samples below room temperature under an external magnetic field. Moreover, the exchange bias field (HEX) started to appear at T~40 K and its value increased by decreasing the temperature. This effect has been assigned to the interaction of spins located in the magnetically disordered regions (in the inner and outer surface of the Fe3O4 shell) and spins located in the ordered region of the Fe3O4 shell. PMID:28165012

    8. Effects of coating molecules on the magnetic heating properties of Au-Fe3O4 heterodimer nanoparticles

      NASA Astrophysics Data System (ADS)

      Yamamoto, Y.; Ogasawara, J.; Himukai, H.; Itoh, T.

      2016-10-01

      In this paper, we report the heating properties of gold-magnetite (Au-Fe3O4) heterodimer nanoparticles (NPs) subjected to an alternating magnetic field. The Au-Fe3O4 NPs coated with oleic acid and oleylamine (OA) were synthesized through a method that combines seed mediation and high-temperature decomposition. The coating was replaced with dimercaptosuccinic acid (DMSA) by the ligand-exchange method. The specific absorption rates (SARs) for the OA- and DMSA-coated Au-Fe3O4 NPs coated with OA and DMSA at room temperature were determined through the calorimetric and magnetometric methods. SAR depended on the square of the magnetic field H up to an H value of 4 kA/m. The absolute value of the SAR for DMSA-coated NPs is about fivefold higher than that of the OA-coated NPs. The AC magnetic hysteresis measurements showed the recovery of the magnetic volume and the decrease in the magnetic anisotropy of the DMSA-coated NPs relative to those of the OA-coated NPs. These results suggest that the protective agent influences the magnetic properties of magnetite NPs via gold NPs.

    9. Tuning the energetics and tailoring the optical properties of silver clusters confined in zeolites

      NASA Astrophysics Data System (ADS)

      Fenwick, Oliver; Coutiño-Gonzalez, Eduardo; Grandjean, Didier; Baekelant, Wouter; Richard, Fanny; Bonacchi, Sara; de Vos, Dirk; Lievens, Peter; Roeffaers, Maarten; Hofkens, Johan; Samorì, Paolo

      2016-09-01

      The integration of metal atoms and clusters in well-defined dielectric cavities is a powerful strategy to impart new properties to them that depend on the size and geometry of the confined space as well as on metal-host electrostatic interactions. Here, we unravel the dependence of the electronic properties of metal clusters on space confinement by studying the ionization potential of silver clusters embedded in four different zeolite environments over a range of silver concentrations. Extensive characterization reveals a strong influence of silver loading and host environment on the cluster ionization potential, which is also correlated to the cluster’s optical and structural properties. Through fine-tuning of the zeolite host environment, we demonstrate photoluminescence quantum yields approaching unity. This work extends our understanding of structure-property relationships of small metal clusters and applies this understanding to develop highly photoluminescent materials with potential applications in optoelectronics and bioimaging.

    10. Investigation of the structures and chemical ordering of small Pd-Au clusters as a function of composition and potential parameterisation.

      PubMed

      Ismail, Ramli; Johnston, Roy L

      2010-08-14

      The energetics, structures and segregation of Pd-Au nanoalloys (all compositions for 34- and 38-atoms) have been studied using a genetic algorithm global optimization technique with the Gupta empirical potential. Three modifications of the Pd-Au parameters have been studied: parameter set I in which all parameters (A, xi, p, q and r(0)) in the Gupta potential are weighted in a symmetrical fashion; parameter set II (symmetric weighting of only the pair and many-body energy scaling parameters A and xi); and parameter set III (antisymmetric weighting of A and xi). Structural analysis reveals competition between a range of structural families; decahedra, polyicosahedra and truncated octahedra (for 34 atoms) and incomplete-icosahedra-Mackay, decahedra, polyicosahedra (low-symmetry), six-fold-polyicosahedra and a mixed octahedron-icosahedron (Oh-Ih) structure (for 38 atoms). It is shown that, by finely tuning the Gupta potential, it is possible to qualitatively reproduce the results observed at higher levels of theory (e.g. Density Functional Theory). There are four main types of chemical ordering which are observed: core-shell; spherical cap; ball-and-cup; and mixed. It is shown that the chemical ordering and the proportion of Pd-Au heteronuclear bonds in these clusters are strongly dependent on the potential parameters. Comparison of the results from parameter set III and two previously fitted potentials shows that the DFT-fit potential gives rise to similar results for energies, and lowest energy structures and homotops to those for parameter set III with w(a) = 0.8, but the exp-fit potential gives rise to qualitatively different results.

    11. Mechanical and charge transport properties of alkanethiol self-assembled monolayers on Au (111) surface: The Role of Molecular Tilt

      SciTech Connect

      Mulleregan, Alice; Qi, Yabing; Ratera, Imma; Park, Jeong Y.; Ashby, Paul D.; Quek, Su Ying; Neaton, J. B.; Salmeron, Miquel

      2007-11-12

      The relationship between charge transport and mechanical properties of alkanethiol self-assembled monolayers (SAM) on Au(111) films has been investigated using an atomic force microscope with a conductive tip. Molecular tilts induced by the pressure applied by the tip cause stepwise increases in film conductivity. A decay constant {beta} = 0.57 {+-} 0.03 {angstrom}{sup -1} was found for the current passing through the film as a function of tip-substrate separation due to this molecular tilt. This is significantly smaller than the value of {approx} 1 {angstrom}{sup -1} found when the separation is changed by changing the length of the alkanethiol molecules. Calculations indicate that for isolated dithiol molecules S-bonded to hollow sites, the junction conductance does not vary significantly as a function of molecular tilt. The impact of S-Au bonding on SAM conductance is discussed.

    12. STEM Electron Diffraction and High Resolution Images Used in the Determination of the Crystal Structure of Au144(SR)60 Cluster

      PubMed Central

      Bahena, Daniel; Bhattarai, Nabraj; Santiago, Ulises; Tlahuice, Alfredo; Ponce, Arturo; Bach, Stephan B. H.; Yoon, Bokwon; Whetten, Robert L.; Landman, Uzi; Jose-Yacaman, Miguel

      2013-01-01

      Determination of the total structure of molecular nanocrystals is an outstanding experimental challenge that has been met, in only a few cases, by single-crystal X-ray diffraction. Described here is an alternative approach that is of most general applicability and does not require the fabrication of a single crystal. The method is based on rapid, time-resolved nanobeam electron diffraction (NBD) combined with high-angle annular dark field scanning/transmission electron microscopy (HAADF-STEM) images in a probe corrected STEM microscope, operated at reduced voltages. The results are compared with theoretical simulations of images and diffraction patterns obtained from atomistic structural models derived through first-principles density functional theory (DFT) calculations. The method is demonstrated by application to determination of the structure of the Au144(SCH2CH2Ph)60 cluster. PMID:23687562

    13. A statistical study of EMIC waves observed by Cluster. 1. Wave properties. EMIC Wave Properties

      SciTech Connect

      Allen, R. C.; Zhang, J. -C.; Kistler, L. M.; Spence, H. E.; Lin, R. -L.; Klecker, B.; Dunlop, M. W.; André, M.; Jordanova, V. K.

      2015-07-23

      Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In our study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of data from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. Thus, the statistical analysis is presented in two papers. OUr paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.

    14. A statistical study of EMIC waves observed by Cluster. 1. Wave properties. EMIC Wave Properties

      DOE PAGES

      Allen, R. C.; Zhang, J. -C.; Kistler, L. M.; ...

      2015-07-23

      Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L-shell (MLT-L) frame within a limited magnetic latitude (MLAT) range. In our study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of datamore » from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. Thus, the statistical analysis is presented in two papers. OUr paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.« less

    15. How Accurate Can a Local Coupled Cluster Approach Be in Computing the Activation Energies of Late-Transition-Metal-Catalyzed Reactions with Au, Pt, and Ir?

      PubMed

      Kang, Runhua; Lai, Wenzhen; Yao, Jiannian; Shaik, Sason; Chen, Hui

      2012-09-11

      To improve the accuracy of local coupled cluster (LCC) methods in computing activation energies, we propose herein a new computational scheme. Its applications to various types of late-transition-metal-catalyzed reactions involving Au, Pt, and Ir indicate that the new corrective approach for LCC methods can downsize the mean unsigned deviation and maximum deviation, from the CCSD(T)/CBS reference, to about 0.3 and 0.9 kcal/mol. Using this method, we also calibrated the performance of popular density functionals, with respect to the same test set of reactions. It is concluded that the best functional is the general-purpose double hybrid functional B2GP-PLYP. Other well-performing functionals include the "kinetic" functionals M06-2X and BMK, which have a large percentage of HF exchange, and general-purpose functionals like PBE0 and wB97X. Comparatively, general-purpose functionals like PBE0 and TPSSh perform much better than the tested "kinetic" functionals for Pt-/Ir-catalyzed reactions, while the opposite is true for Au-catalyzed reactions. In contrast, wB97X performs more uniformly in these two classes of reactions. These findings hint that even within the scope of late transition metals, different types of reactions may require different types of optimal DFT methods. Empirical dispersion correction of DFT was found to have a small or no effect on the studied reactions barriers.

    16. Facile synthesis and optical properties of polymer-laced ZnO-Au hybrid nanoparticles

      PubMed Central

      2014-01-01

      Bi-phase dispersible ZnO-Au hybrid nanoparticles were synthesized via one-pot non-aqueous nanoemulsion using the triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) as the surfactant. The characterization shows that the polymer-laced ZnO-Au nanoparticles are monosized and of high crystallinity and demonstrate excellent dispersibility and optical performance in both organic and aqueous medium, revealing the effects of quantum confinement and medium. The findings show two well-behaved absorption bands locating at approximately 360 nm from ZnO and between 520 and 550 nm from the surface plasmon resonance of the nanosized Au and multiple visible fingerprint photoluminescent emissions. Consequently, the wide optical absorbance and fluorescent activity in different solvents could be promising for biosensing, photocatalysis, photodegradation, and optoelectronic devices. PMID:24606946

    17. Electrical conductivity, optical property and ammonia sensing studies on HCl Doped Au@polyaniline nanocomposites

      NASA Astrophysics Data System (ADS)

      Hasan, Mudassir; Ansari, Mohd Omaish; Cho, Moo Hwan; Lee, Moonyong

      2015-01-01

      This paper reports the synthesis of HCl-doped Au@polyaniline (Pani) nanocomposite fibers by the in situ oxidative polymerization of aniline in the presence of gold nanoparticles. Thus prepared nanocomposite fibers were characterized by SEM, TEM, XRD, Raman spectroscopy, XPS, UV-visible diffused reflectance spectroscopy, TGA, and DSC. The Au@Pani nanocomposite fibers showed superior DC electrical conductivity to HCl-doped Pani, which might be due to the increased mobility of the charge carriers after the incorporation of gold nanoparticle in Pani. Au@Pani also exhibited a better ammonia sensing and recovery response than Pani, which might be due to the increase in the surface area of Pani after the incorporation of gold nanoparticles.

    18. Facile synthesis and optical properties of polymer-laced ZnO-Au hybrid nanoparticles

      NASA Astrophysics Data System (ADS)

      Wang, XianHong; Zhang, XiaoYan; Cheng, WenZheng; Shao, HongQin; Liu, Xiao; Li, XueMei; Liu, HongLing; Wu, JunHua

      2014-03-01

      Bi-phase dispersible ZnO-Au hybrid nanoparticles were synthesized via one-pot non-aqueous nanoemulsion using the triblock copolymer poly(ethylene glycol)- block-poly(propylene glycol)- block-poly(ethylene glycol) as the surfactant. The characterization shows that the polymer-laced ZnO-Au nanoparticles are monosized and of high crystallinity and demonstrate excellent dispersibility and optical performance in both organic and aqueous medium, revealing the effects of quantum confinement and medium. The findings show two well-behaved absorption bands locating at approximately 360 nm from ZnO and between 520 and 550 nm from the surface plasmon resonance of the nanosized Au and multiple visible fingerprint photoluminescent emissions. Consequently, the wide optical absorbance and fluorescent activity in different solvents could be promising for biosensing, photocatalysis, photodegradation, and optoelectronic devices.

    19. Correlations of the stability, static dipole polarizabilities, and electronic properties of yttrium clusters.

      PubMed

      Li, Xi-Bo; Wang, Hong-Yan; Lv, Ran; Wu, Wei-Dong; Luo, Jiang-Shan; Tang, Yong-Jian

      2009-09-24

      Static dipole polarizabilities for the ground-state geometries of yttrium clusters (Yn, n < or = 15) are investigated by using the numerically finite field method in the framework of density functional theory. The structural size dependence of electronic properties, such as the highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) gap, ionization energy, electron affinity, chemical hardness and softness, etc., has been determined for yttrium clusters. The energetic analysis, minimum polarizability principle, and principle of maximum hardness are used to characterize the stability of yttrium clusters. The correlations of stability, static dipole polarizabilities, and electronic properties are analyzed especially. The results show that static polarizability and electronic structure can reflect obviously the stability of yttrium clusters. The static polarizability per atom decreases slowly with an increase in the cluster size and exhibits a local minimum at the magic number cluster. The ratio of the mean static polarizability to the HOMO-LUMO gap has a much lower value for the most stable clusters. The static dipole polarizabilities of yttrium clusters are highly dependent on their electronic properties and are also partly related to their geometrical characteristics. A large HOMO-LUMO gap of an yttrium cluster usually corresponds to a large dipole moment. Strong correlative relationships of the ionization potential, softness, and static dipole polarizability are observed for yttrium clusters.

    20. Crystal structures and magnetic properties of CeAu{sub 4}Si{sub 2} and CeAu{sub 2}Si{sub 2}

      SciTech Connect

      Sefat, Athena S. Palasyuk, Andriy M.; Bud'ko, Sergey L.; Corbett, John D.; Canfield, Paul C.

      2008-02-15

      Single crystals of CeAu{sub 4}Si{sub 2} and CeAu{sub 2}Si{sub 2} have been grown out of ternary fluxes rich in Au, and the former, also by sintering the stoichiometric composition at 750 deg. C. The single-crystal X-ray refinement result for CeAu{sub 4}Si{sub 2} is orthorhombic, Cmmm (No. 65, Z=2), different from a tetragonal result found from an X-ray powder diffraction refinement [H. Nakashima, et al., J. Alloys Compds. 424 (2006) 7]. For CeAu{sub 2}Si{sub 2}, this is the first report of the stoichiometric crystalline phase, in the known tetragonal I4/mmm structure. The anisotropic field- and temperature-dependent magnetizations, as well as specific heat and resistivity data are compared. Although both compounds have related structural packing, they present unique magnetic features. CeAu{sub 2}Si{sub 2} is a typical antiferromagnet with T{sub N}=8.8(1) K and CeAu{sub 4}Si{sub 2} features a ferromagnetic component below T{sub c}=3.3(1) K. Both phases have effective moments close in value to that of free Ce{sup 3+}. - Graphical abstract: The magnetization versus applied field for CeAu{sub 2}Si{sub 2} along two crystallographic directions.

    1. The investigation of thermal properties on multilayer Sb2Te3/Au thermoelectric material system with ultra-thin Au interlayers

      NASA Astrophysics Data System (ADS)

      Zhang, Haiming; Ye, Fengjie; Hu, Yangsen; Liu, Jun; Zhang, Yan; Wu, Yigui; Hu, Zhiyu

      2016-01-01

      The manipulation of heat transport across multilayer thin films with metal-semicounductor interfaces is of great interest for thermoelectric material optimization. Here we fabricated Sb2Te3/Au multilayer films with different Au thickness by magnetron sputtering. We demonstrated that the thermal conductivity of the system can be facilely manipulated by simply changing the Au layer thickness, where an optimal thickness (5 nm) value exists with the lowest thermal conductivity (˜0.44 Wm-1K-1, 44% of the pure Sb2Te3 thin film thermal conductivity). It has been proved that the decreased thermal conductivity was mainly attributed to the strong electron-phonon coupling in a metal-nonmetal multilayered system with Au layer thickness larger than 5 nm, where the Two Temperature Model (TTM) predicts the experimental data perfectly. It was also proposed that the grain boundary effect may dominiate the phonon scattering when the Au layer is in a discountinuous form (<5 nm).

    2. Stellar population properties of the most massive globular clusters and ultra-compact dwarf galaxies of the Fornax cluster

      NASA Astrophysics Data System (ADS)

      Hilker, Michael

      2017-03-01

      Most ultra-compact dwarf galaxies (UCDs) and very massive globular clusters reside in nearby galaxy clusters or around nearby giant galaxies. Due to their distance (> 4 Mpc) and compactness (r eff < 100 pc) they are barely resolved, and thus it is difficult to obtain their internal properties. Here I present our most recent attempts to constrain the mass function, stellar content and dynamical state of UCDs in the Fornax cluster. Thanks to radial velocity membership assignment of ~ 950 globular clusters (GCs) and UCDs in the core of Fornax, the shape of their mass function is well constrained. It is consistent with the `standard' Gaussian mass function of GCs. Our recent simulations on the disruption process of nucleated dwarf galaxies in cluster environments showed that ~ 40% of the most massive UCDs should originate from nuclear star clusters. Some Fornax UCDs actually show evidence for this scenario, as revealed by extended low surface brightness disks around them and onsets of tidal tails. Multi-band UV to optical imaging as well as low to medium resolution spectroscopy revealed that there exist UCDs with youngish ages, (sub-)solar [α/Fe] abundances, and probably He-enriched populations.

    3. Stellar and circumstellar properties of visual binaries in the Orion Nebula Cluster

      NASA Astrophysics Data System (ADS)

      Correia, S.; Duchêne, G.; Reipurth, B.; Zinnecker, H.; Daemgen, S.; Petr-Gotzens, M. G.; Köhler, R.; Ratzka, Th.; Aspin, C.; Konopacky, Q. M.; Ghez, A. M.

      2013-09-01

      Context. Our general understanding of multiple star and planet formation is primarily based on observations of young multiple systems in low density regions like Tau-Aur and Oph. Since many, if not most, of the stars are born in clusters, observational constraints from young binaries in those environments are fundamental for understanding both the formation of multiple systems and planets in multiple systems throughout the Galaxy. Aims: We build upon the largest survey for young binaries in the Orion Nebula Cluster (ONC), which is based on Hubble Space Telescope observations to derive both stellar and circumstellar properties of newborn binary systems in this cluster environment. Methods: We present adaptive optics spatially-resolved JHKL'-band photometry and K-band R ~ 5000 spectra for a sample of eight ONC binary systems from this database. We characterize the stellar properties of binary components and obtain a census of protoplanetary disks through K - L' color excess. For a combined sample of ONC binaries including 7 additional systems with NIR spectroscopy from the literature, we derive mass ratio and relative age distributions. We compare the stellar and circumstellar properties of binaries in ONC with those in Tau-Aur and Oph from samples of binaries with stellar properties derived for each component from spectra and/or visual photometry and with a disk census obtained through K - L color excess. Results: The mass ratio distribution of ONC binaries is found to be indistinguishable from that of Tau-Aur and, to some extent, to that of Oph in the separation range 85-560 AU and for primary mass in the range 0.15 to 0.8 M⊙. A trend toward a lower mass ratio with larger separation is suggested in ONC binaries, which is not seen in Tau-Aur binaries. The components of ONC binaries are found to be significantly more coeval than the overall ONC population and as coeval as components of binaries in Tau-Aur and Oph. There is a hint of a larger fraction of mixed pairs

    4. The cluster distribution as a test of dark matter models - I. Clustering properties

      NASA Astrophysics Data System (ADS)

      Borgani, Stefano; Plionis, Manolis; Coles, Peter; Moscardini, Lauro

      1995-12-01

      We present extended simulations of the large-scale distribution of galaxy clusters in several dark matter models, using an optimized version of the truncated Zel'dovich approximation (TZA). In order to test the reliability of our simulations, we compare them with N-body-based cluster simulations. We find that the TZA provides a very accurate description of the cluster distribution as long as fluctuations on the cluster mass-scale are in the mildly non-linear regime (sigma_8<~1). The low computational cost of this simulation technique allows us to run a large ensemble of 50 realizations for each model, so we are able to quantify accurately the effects of cosmic variance. Six different dark matter models are studied in this work: standard CDM (SCDM), tilted CDM (TCDM) with primordial spectral index n=0.7, cold+hot DM (CHDM) with Omega_hot=0.3, low Hubble constant (h=0.3) CDM (LOWH), and two spatially flat low-density CDM models with Omega_0=0.2 and Omega_Lambda=0.8, having two different normalizations, sigma_8=0.8 (LambdaCDM_1) and sigma_8=1.3 (LambdaCDM_2). We compare the cluster simulations with an extended redshift sample of Abell/ACO clusters, using various statistical measures, such as the integral of the two-point correlation function, J_3, and the probability density function (pdf). We find that the models that best reproduce the clustering of the Abell/ACO cluster sample are the CHDM and the LambdaCDM_1 models. The LambdaCDM_2 model is too strongly clustered, and this clustering is probably overestimated in our simulations as a result of the large sigma_8-value of this model. All of the other models are ruled out at a high confidence level. The pdfs of all models are well approximated by a lognormal distribution, consistent with similar findings for Abell/ACO clusters. The low-order moments of all the pdfs are found to obey a variance-skewness relation of the form gamma~=S_3sigma^4, with S_3~=1.9, independent of the primordial spectral shape and consistent

    5. Effect of Ni and Pd Addition on Mechanical, Thermodynamic, and Electronic Properties of AuSn4-Based Intermetallics: A Density Functional Investigation

      NASA Astrophysics Data System (ADS)

      Tian, Yali; Zhou, Wei; Wu, Ping

      2016-08-01

      The effects of Ni and Pd addition on the mechanical, thermodynamic, and electronic properties of AuSn4-based intermetallic compounds (IMCs) have been investigated by first-principles calculations to reveal the essence of Au embrittlement. Three kinds of doped (namely Ni-doped, Pd-doped, and Ni/Pd-codoped) IMCs are considered in this work. The polycrystalline elastic properties are deduced from single-crystal elastic constants. It is found that the doped systems together with nondoped AuSn4 are all ductile phases. For Ni-doped AuSn4, the modulus, hardness, brittleness, Debye temperature, and minimum thermal conductivity increase with the Ni fraction, but this is not the case for the Pd-doped material, since Au0.75Pd0.25Sn4 is the more brittle phase. For Au0.5Pd0.25Ni0.25Sn4, the mechanical, thermodynamic, and electronic properties are similar to those of Au0.5Pd0.5Sn4.

    6. Cluster variation study of the underpotential deposition of Cu on Au(111) in the presence of bisulfate

      NASA Astrophysics Data System (ADS)

      Huckaby, Dale A.; Legault, Marc D.; Blum, L.

      1998-09-01

      A cluster variation method is developed to study the phase transitions and the structures of phases which occur at the fluid-crystal interface during the underpotential deposition of a metal on an electrode in the presence of an anion, such as bisulfate. In addition to the possibility of first-order condensation phase transitions occurring during the deposition of a metal, the steric repulsion of adsorbed anions can also cause an order-disorder transition. Using clusters containing six adsorption sites, the method is applied to the underpotential deposition of copper on (111) gold in the presence of bisulfate. In order to fix a constant in the expression for the entropy, the effect of the hard-core exclusion of a pair of first-neighbor bisulfates, in addition to the effect of finite interactions, is calculated exactly in the limit of high temperature. The cluster method yields two coupled adsorption isotherms for copper and bisulfate in terms of their activities and coverages. The resulting isotherms show an order-disorder transition due to the hard-core exclusion of neighboring bisulfate ions, as well as two first-order phase transitions in the copper and bisulfate coverages which correspond to the two spikes in the experimental voltammogram. The cluster method also gives the local structure of the phases which occur as the voltage is changed.

    7. Structural and electronic properties of small silver-sulfur clusters: A density functional study

      NASA Astrophysics Data System (ADS)

      Li, Yan-Fang; Li, Yang; Li, Ying; Tan, Jia-Jin; Li, Hui-Li

      2016-10-01

      Density functional theory calculations have been performed to systematically investigate the structural and electronic properties of neutral and anionic AgnSm (2≤n+m≤6) clusters. The results show that the ground-state structures of neutral clusters are different from those of anionic clusters. Theoretical electron detachment energies (both vertical and adiabatic) are compared with the experimental measurements to verify the ground states of silver-sulfur clusters obtained in the present study. For both neutral and anionic systems, the highest occupied-lowest unoccupied molecular orbital energy gaps exhibit an odd-even oscillation as a function of the cluster size. In addition, the natural population analysis reveals that the charges transfer from Ag atoms to S atoms in AgnSm clusters, and the extra electron of AgnSm- clusters is mainly localized on the 3p subshells of S atoms.

    8. Corrosion properties of Ag-Au-Cu-Pd system alloys containing indium.

      PubMed

      Hattori, Masayuki; Tokizaki, Teruhiko; Matsumoto, Michihiko; Oda, Yutaka

      2010-01-01

      In this study, the corrosion resistance of Ag-Au-Cu-Pd system alloys consisting of 5 or 10 mass% indium was evaluated. Levels of element release and tarnish were determined and electrochemical measurements performed. Results were compared with those for commercial silver-palladium-gold alloy. In terms of electrochemical behavior, the transpassive potential of these experimental alloys was 168-248mV. Experimental alloys with 25 mass% Au showed similar corrosion resistance to control gold-silver-palladium alloy. Amount of released elements was 14-130microg/cm(2) at 7 days, which is in the allowable range for dental alloys. Addition of indium to Ag-Au-Cu-10mass%Pd system alloys was effective in increasing resistance to tarnish and alloys containing 10 mass% of indium showed a minimal decrease in L(*) values after immersion. These findings indicate that 25Au-37.5Ag-15Cu-10Pd-2Zn-10In-0.5Ir alloy is applicable in dental practice.

    9. Electrical and magnetic properties of CuCo and AuCo solid solutions

      NASA Astrophysics Data System (ADS)

      Zibold, G.; Korn, D.

      1981-08-01

      CuCo and AuCo films are quench condensed at cryogenic temperature (4 K). The electrical resistivity and the AC susceptibility are measured at different annealing stages (80 K ≤ T a ≤ 900 K) as a function of temperature and Co concentration, Cu 1-xCo x with x ≤ 0,06 and Au 1-yCo y with y ≤ 0.23. The residual resistivity increases linearly with Co concentration in alloys containing x < 0,03 and y < 0.08. Concerning random solid solutions, the negative slope of the resistivity measured near 5 K is proportional to the square of the Co concentration in the range x < 0,03 and y < 0.02. AC susceptibility measurements of films containing x,y ≤ 0,04 yield small values with respect to magnetic moment p and freezing temperature T f. In CuCo ferromagnetism occurs near x =0,08 whereas in AuCo near y = 0.2. This difference can be ascribed to the smaller lattice constant in Cu as compared to that in Au.

    10. Preparation and multiple antitumor properties of AuNRs/spinach extract/PEGDA composite hydrogel.

      PubMed

      Wang, Yunlong; Zhang, Buchang; Zhu, Lin; Li, Yanjie; Huang, Fangzhi; Li, Shikuo; Shen, Yuhua; Xie, Anjian

      2014-09-10

      In this study, a novel composite hydrogel that contains spinach extract (SE), gold nanorods (AuNRs), and poly(ethylene glycol) double acrylates (PEGDA) is prepared through a one-step in situ photopolymerization under noninvasive 660 nm laser irradiation for localized antitumor activity. SE plays a role as a photoinitiator for initiating the formation of the PEGDA hydrogel and as an excellent photosensitizer for generating cytotoxic singlet oxygen ((1)O2) with oxygen to kill tumor cells. AuNRs can be used as a photoabsorbing agent to generate heat from optical energy. Moreover, the introduction of AuNRs is conducive to the formation of the hydrogel and accelerates the rate of (1)O2 generation. The composite hydrogel shell, which has good biocompatibility on tumor cells, can prevent the photosensitizer from migrating to normal tissue and maintains a high concentration on lesions, thereby enhancing the curative effect. The combination of NIR light-triggered mild photothermal heating of AuNRs, the photodynamic treatment using SE, and localized gelation by photopolymerization exhibits a synergistic effect for the destruction of cancer cells.

    11. Exploiting intrinsic triangular geometry in relativistic (3)He+Au collisions to disentangle medium properties.

      PubMed

      Nagle, J L; Adare, A; Beckman, S; Koblesky, T; Koop, J Orjuela; McGlinchey, D; Romatschke, P; Carlson, J; Lynn, J E; McCumber, M

      2014-09-12

      Recent results in d+Au and p+Pb collisions at RHIC and the LHC provide evidence for collective expansion and flow of the created medium. We propose a control set of experiments to directly compare particle emission patterns from p+Pb, d+Au, and ^{3}He+Au or t+Au collisions at the same sqrt[s_{NN}] . Using a Monte Carlo Glauber simulation we find that a ^{3}He or triton projectile, with a realistic wave function description, induces a significant intrinsic triangular shape to the initial medium. If the system lives long enough, this survives into a significant third-order flow moment v_{3} even with viscous damping. By comparing systems with one, two, and three initial hot spots, one could disentangle the effects from the initial spatial distribution of the deposited energy and viscous damping. These are key tools for answering the question of how small a droplet of matter is necessary to form a quark-gluon plasma described by nearly inviscid hydrodynamics.

    12. Exploiting Intrinsic Triangular Geometry in Relativistic He3+Au Collisions to Disentangle Medium Properties

      NASA Astrophysics Data System (ADS)

      Nagle, J. L.; Adare, A.; Beckman, S.; Koblesky, T.; Koop, J. Orjuela; McGlinchey, D.; Romatschke, P.; Carlson, J.; Lynn, J. E.; McCumber, M.

      2014-09-01

      Recent results in d +Au and p +Pb collisions at RHIC and the LHC provide evidence for collective expansion and flow of the created medium. We propose a control set of experiments to directly compare particle emission patterns from p +Pb, d +Au, and He3+Au or t +Au collisions at the same √sNN . Using a Monte Carlo Glauber simulation we find that a He3 or triton projectile, with a realistic wave function description, induces a significant intrinsic triangular shape to the initial medium. If the system lives long enough, this survives into a significant third-order flow moment v3 even with viscous damping. By comparing systems with one, two, and three initial hot spots, one could disentangle the effects from the initial spatial distribution of the deposited energy and viscous damping. These are key tools for answering the question of how small a droplet of matter is necessary to form a quark-gluon plasma described by nearly inviscid hydrodynamics.

    13. Quantum-chemical study of the effect of ligands on the structure and properties of gold clusters

      NASA Astrophysics Data System (ADS)

      Golosnaya, M. N.; Pichugina, D. A.; Oleinichenko, A. V.; Kuz'menko, N. E.

      2017-02-01

      The structures of [Au4(dpmp)2X2]2+clusters, where X =-C≡CH,-CH3,-SCH3,-F,-Cl,-Br,-I, dpmp is bis((diphenylphosphino)methyl)(phenyl)phosphine, are calculated at the level of density functional theory with the PBE functional and a modified Dirac-Coulomb-Breit Hamiltonian in an all-electron basis set (Λ). Using the example of [Au4(dpmp)2(C≡CC6H5)2]2+, the interatomic distances and bond angles calculated by means of PBE0/LANL2DZ, TPSS/LANL2DZ, TPSSh/LANL2DZ, and PBE/Λ are compared to X-ray crystallography data. It is shown that PBE/Λ yields the most accurate calculation of the geometrical parameters of this cluster. The ligand effect on the electronic stability of a cluster and the stability in reactions of decomposition into different fragments is studied, along with the capability of ligand exchange. Stability is predicted for [Au4(dpmp)2F2]2+ and [Au4(dpmp)2(SCH3)2]2+, while [Au4(dpmp)2I2]2+ cluster is unstable and its decomposes into two identical fragments is supposed.

    14. Nanoporous Gold Nanoparticles and Au/Al2O3 Hybrid Nanoparticles with Large Tunability of Plasmonic Properties.

      PubMed

      Rao, Wenye; Wang, Dong; Kups, Thomas; Baradács, Eszter; Parditka, Bence; Erdélyi, Zoltán; Schaaf, Peter

      2017-02-22

      Nanoporous gold nanoparticles (NPG-NPs) with controlled particle size and pore size are fabricated via a combination of solid-state dewetting and a subsequent dealloying process. Because of the combined effects of size and porosity, the NPG-NPs exhibit greater plasmonic tunability and significantly higher local field enhancement as compared to solid NPs. The effects of the nanoscale porosity and pore size on the optical extinction are investigated for the NPG-NPs with different particle sizes experimentally and theoretically. The influences of both porosity and pore size on the plasmonic properties are very complicated and clearly different for small particles with dominated dipole mode and large particles with dominated quadrupole mode. Au/Al2O3 hybrid porous NPs with controlled porosity and composition ratio are fabricated through plasma-enhanced atomic layer deposition of Al2O3 into the porous structure. In the Au/Al2O3 hybrid porous NPs, both Au and Al2O3 components are bicontinuously percolated over the entire structure. A further red shift of the plasmon peak is observed in the hybrid NPs due to the change of the environmental refractive index. The high tunability of the plasmonic resonances in the NPG-NPs and the hybrid porous NPs can be very useful for many applications in sensing biological and organic molecules.

    15. Clusters of Word Properties as Predictors of Elementary School Children's Performance on Two Word Tasks

      ERIC Educational Resources Information Center

      Tellings, Agnes; Coppens, Karien; Gelissen, John; Schreuder, Rob

      2013-01-01

      Often, the classification of words does not go beyond "difficult" (i.e., infrequent, late-learned, nonimageable, etc.) or "easy" (i.e., frequent, early-learned, imageable, etc.) words. In the present study, we used a latent cluster analysis to divide 703 Dutch words with scores for eight word properties into seven clusters of words. Each cluster…

    16. Determination of relative sensitivity factors during secondary ion sputtering of silicate glasses by Au+, Au2+ and Au3+ ions.

      PubMed

      King, Ashley; Henkel, Torsten; Rost, Detlef; Lyon, Ian C

      2010-01-01

      In recent years, Au-cluster ions have been successfully used for organic analysis in secondary ion mass spectrometry. Cluster ions, such as Au(2)(+) and Au(3)(+), can produce secondary ion yield enhancements of up to a factor of 300 for high mass organic molecules with minimal sample damage. In this study, the potential for using Au(+), Au(2)(+) and Au(3)(+) primary ions for the analysis of inorganic samples is investigated by analyzing a range of silicate glass standards. Practical secondary ion yields for both Au(2)(+) and Au(3)(+) ions are enhanced relative to those for Au(+), consistent with their increased sputter rates. No elevation in ionization efficiency was found for the cluster primary ions. Relative sensitivity factors for major and trace elements in the standards showed no improvement in quantification with Au(2)(+) and Au(3)(+) ions over the use of Au(+) ions. Higher achievable primary ion currents for Au(+) ions than for Au(2)(+) and Au(3)(+) allow for more precise analyses of elemental abundances within inorganic samples, making them the preferred choice, in contrast to the choice of Au(2)(+) and Au(3)(+) for the analysis of organic samples. The use of delayed secondary ion extraction can also boost secondary ion signals, although there is a loss of overall sensitivity.

    17. Templated Atom-Precise Galvanic Synthesis and Structure Elucidation of a [Ag24Au(SR)18](-) Nanocluster.

      PubMed

      Bootharaju, Megalamane S; Joshi, Chakra P; Parida, Manas R; Mohammed, Omar F; Bakr, Osman M

      2016-01-18

      Synthesis of atom-precise alloy nanoclusters with uniform composition is challenging when the alloying atoms are similar in size (for example, Ag and Au). A galvanic exchange strategy has been devised to produce a compositionally uniform [Ag24Au(SR)18](-) cluster (SR: thiolate) using a pure [Ag25(SR)18](-) cluster as a template. Conversely, the direct synthesis of Ag24Au cluster leads to a mixture of [Ag(25-x)Au(x)(SR)18](-), x=1-8. Mass spectrometry and crystallography of [Ag24Au(SR)18](-) reveal the presence of the Au heteroatom at the Ag25 center, forming Ag24Au. The successful exchange of the central Ag of Ag25 with Au causes perturbations in the Ag25 crystal structure, which are reflected in the absorption, luminescence, and ambient stability of the particle. These properties are compared with those of Ag25 and Ag24Pd clusters with same ligand and structural framework, providing new insights into the modulation of cluster properties with dopants at the single-atom level.

    18. Thermoelectric Properties of Au- Containing Type-I Clathrates Ba8AuxGa16-3xGe30+2x

      SciTech Connect

      Ye, Zuxin; Cho, Jung Young; Tessema, Misle M.; Salvador, James R.; Waldo, Richard A.; Yang, Jihui; Wang, Hsin; Cai, Wei; Kirkham, Melanie J; Yang, Jiong; Zhang, Wenqing

      2014-01-01

      Type I clathrates, with compositions based on Ba8Ga16Ge30, are a class of promising thermoelectric materials due to their intrinsically low thermal conductivity. It has been demonstrated previously that the thermoelectric performance can be improved by transition metal substitution of the framework atoms. In this study, the effects of Au substitution for Ga/Ge on thermal and electrical transport properties of type I clathrate compounds have been investigated. Polycrystalline samples with a large range of Au content have been synthesized using conventional solid state techniques with the actual compositions of resulting materials approximately following Zintl-Klemm rules. The charge carrier type changes from electrons (n) to holes (p) as the Au content increases. The Seebeck coefficient (S) and power factor (S2/ where is the electrical resistivity) were improved by Au substitution and the resulting overall thermoelectric properties were enhanced by Au substitution with a thermoelectric figure of merit ZT ~ 0.63 at temperature T = 740 K for the composition Ba8Au5.47Ge39.96. The results presented herein show that Au-containing type I clathrates are promising p-type thermoelectric materials for high temperature applications.

    19. Dimerization of argon and the properties of its small clusters

      NASA Astrophysics Data System (ADS)

      Titov, S. V.; Serov, S. A.; Ostrovskii, G. M.

      2016-12-01

      Statistical thermodynamic means are used to study the bound state of a small cluster AN (2 ≤ N ≤ 5) of Lennard-Jones particles in a spherical cavity. The statistical sum is calculated by the Monte Carlo method. For the dimer, integration is reduced to quadratures. The integration region contains only phase space points corresponding to the bound cluster state. Dimerization constant 2A = A2 is calculated via the probability of finding a molecule in the bound state using the example of argon.

    20. Highly tapered pentagonal bipyramidal Au microcrystals with high index faceted corrugation: Synthesis and optical properties

      PubMed Central

      Mettela, Gangaiah; Boya, Radha; Singh, Danveer; Kumar, G. V. Pavan; Kulkarni, G. U.

      2013-01-01

      Focusing light at sub-wavelength region opens up interesting applications in optical sensing and imaging beyond the diffraction limit. In the past, tapered Au wires with carved gratings have been employed to achieve nanofocusing. The fabrication process however, is expensive and the obtained wires are polycrystalline with high surface roughness. A chemical synthetic method overcoming these hurdles should be an attractive alternative. Here, we report a method to chemically synthesize Au microcrystals (~10 μm) bearing pentagonal bipyramidal morphology with surface corrugations assignable to high index planes. The method is a single step solid state synthesis at a temperature amenable to common substrates. The microcrystals are tapered at both ends forming sharp tips (~55 nm). Individual microcrystals have been used as pick and probe SERS substrates for a dye embedded in a polymer matrix. The unique geometry of the microcrystal also enables light propagation across its length.

    1. Electronic and structural properties of oligophenylene ethynylenes on Au(111) surfaces

      NASA Astrophysics Data System (ADS)

      Miao, Ling; Seminario, Jorge M.

      2007-05-01

      The interaction of oligophenylene ethynylene (OPE) on the (111) surface of a gold slab resembling a self-assembled monolayer (SAM) is investigated using ab initio density functional theory calculations. The authors performed a full optimization including all atoms in the OPE and in the slab to better understand OPE adsorption on the surface. It is found that OPE has two energetically favorable adsorption sites on the Au surface with relatively different molecular geometries: the nontop site adsorption greatly modifies the (111) surface structure; however, the extensive electron interactions enable a delocalized electron density distribution, implying an improved conductivity between OPE and Au, and the top site which is 0.9eV higher in energy than the nontop and features weaker Au-S bonds. Interestingly the on top configuration shows a strong spin imbalance along the molecule and the nontop shows a small spin imbalance on the surface. This feature is of strong interest for the development of resonators for the detection of chemical and biological agents. They have also calculated the frequency spectrum of these SAMs, which yield deformations in the gold surface yielding peak frequency shifts specific to each absorption site.

    2. New Structure Model of Au22(SR)18: Bitetrahederon Golden Kernel Enclosed by [Au6(SR)6] Au(I) Complex.

      PubMed

      Pei, Yong; Tang, Jian; Tang, Xianqiong; Huang, Yunqing; Zeng, Xiao Cheng

      2015-04-16

      The study of atomic structure of thiolate-protected gold with decreased core size is important to explore the structural evolution from Au(I) complex to Au nanoclusters. In this work, we theoretically predicted the structure of recently synthesized four valence electron (4e) Au22(SR)18 cluster. The Au22(SR)18 cluster is proposed to possess a bitetrahedron Au7 kernel that is surrounded by a unique [Au6(SR)6] Au(I) complex and three Au3(SR)4 staple motifs. More interestingly, the Au22(SR)18 exhibits structural connections with Au24(SR)20 and Au20(SR)16. The stability of Au22(SR)18 can be understood from the superatom electronic configuration of the Au kernel as well as the formation of superatomic network. The present study can offer new insight into the structural evolution as well as electronic structure of thiolate-protected Au nanoclusters.

    3. [Electronic and structural properties of individual nanometer-size supported metallic clusters]. Final performance report

      SciTech Connect

      Reifenberger, R.

      1993-09-01

      This report summarizes the work performed under contract DOE-FCO2-84ER45162. During the past ten years, our study of electron emission from laser-illuminated field emission tips has taken on a broader scope by addressing problems of direct interest to those concerned with the unique physical and chemical properties of nanometer-size clusters. The work performed has demonstrated that much needed data can be obtained on individual nanometer-size clusters supported on a wide-variety of different substrates. The work was performed in collaboration with R.P. Andres in the School of Chemical Engineering at Purdue University. The Multiple Expansion Cluster Source developed by Andres and his students was essential for producing the nanometer-size clusters studied. The following report features a discussion of these results. This report provides a motivation for studying the properties of nanometer-size clusters and summarizes the results obtained.

    4. Structural and electronic properties of small neutral (MgO)n clusters

      NASA Astrophysics Data System (ADS)

      de La Puente, E.; Aguado, A.; Ayuela, A.; López, J. M.

      1997-09-01

      Ab initio perturbed ion calculations are reported for neutral stoichiometric (MgO)n (n<=13) clusters. A great number of isomer structures are identified and studied. For the isomers of (MgO)n (n<=7) clusters, a full geometrical relaxation is considered. Correlation corrections are included for all cluster sizes using the Coulomb-Hartree-Fock model proposed by Clementi [IBM J. Res. Dev. 9, 2 (1965)]. The results obtained compare favorably with the experimental data and other previous theoretical studies. The inclusion of correlation is crucial in order to achieve a good description of these systems. We find a number of important isomers that allow us to interpret the experimental magic numbers without the assumption of structures based on (MgO)3 subunits. Finally, as an electronic property, the variations in the cluster ionization potential with the cluster size are studied and related to the structural isomer properties.

    5. Vibrational properties of small cobalt clusters on the Cu(111) surface

      NASA Astrophysics Data System (ADS)

      Borisova, S. D.; Rusina, G. G.; Eremeev, S. V.; Chulkov, E. V.

      2009-06-01

      Vibrational properties of small cobalt clusters (dimer and trimer) adsorbed on the Cu(111) surface are studied using interatomic interaction potentials obtained in a tight-binding approximation. The complete (lateral and vertical) relaxation of the surface, the local phonon density of states, and the polarization of vibration modes of clusters and atoms of the substrate are discussed. It is shown that the adsorption of small cobalt clusters leads to a local modification of the vibrational properties of the substrate surface and to excitation of new vibration modes localized on both the cluster adatoms and substrate surface atoms. An increase in the cluster size causes a decrease in the intensity of peaks of the local density of states and their broadening and also a shift in the frequencies of the peaks.

    6. Towards Nano-Materials with Precise Control over Properties via Cluster-Assemblies

      NASA Astrophysics Data System (ADS)

      Qian, Meichun; Reber, Arthur; Khanna, Shiv; Ugrinov, Angel; Chaki, Nirmalya; Mandal, Sukhendu; Saavedra, Héctor; Sen, Ayusman; Weiss, Paul

      2010-03-01

      One pathway towards nanomaterials with controllable band gaps is to assemble solids where atomic clusters serve as building blocks, because clusters' electronic structures vary with size, composition, and the charged state. To study the role of architecture in cluster assemblies, we synthesized multiple architectures of As7^3- clusters through controlling the counter-cations. Optical measurements revealed that the band gaps vary from 1.1-2.1 eV, even though the assemblies are constructed from identical cluster building blocks. First principles theoretical studies reveal that the variation is a result of altering the LUMO levels by changing the counter-cations. Additional variation in the gap is found by covalently linking the clusters with species of varying electronegativity to alter the degree of charge transfer. The findings offer a novel protocol for synthesis of nanoassemblies with tunable electronic properties.

    7. The MUSIC of galaxy clusters - II. X-ray global properties and scaling relations

      NASA Astrophysics Data System (ADS)

      Biffi, V.; Sembolini, F.; De Petris, M.; Valdarnini, R.; Yepes, G.; Gottlöber, S.

      2014-03-01

      We present the X-ray properties and scaling relations of a large sample of clusters extracted from the Marenostrum MUltidark SImulations of galaxy Clusters (MUSIC) data set. We focus on a sub-sample of 179 clusters at redshift z ˜ 0.11, with 3.2 × 1014 h-1 M⊙ < Mvir < 2 × 1015 h-1 M⊙, complete in mass. We employed the X-ray photon simulator PHOX to obtain synthetic Chandra observations and derive observable-like global properties of the intracluster medium (ICM), as X-ray temperature (TX) and luminosity (LX). TX is found to slightly underestimate the true mass-weighted temperature, although tracing fairly well the cluster total mass. We also study the effects of TX on scaling relations with cluster intrinsic properties: total (M500 and gas Mg,500 mass; integrated Compton parameter (YSZ) of the Sunyaev-Zel'dovich (SZ) thermal effect; YX = Mg,500 TX. We confirm that YX is a very good mass proxy, with a scatter on M500-YX and YSZ-YX lower than 5 per cent. The study of scaling relations among X-ray, intrinsic and SZ properties indicates that simulated MUSIC clusters reasonably resemble the self-similar prediction, especially for correlations involving TX. The observational approach also allows for a more direct comparison with real clusters, from which we find deviations mainly due to the physical description of the ICM, affecting TX and, particularly, LX.

    8. Rayleigh light scattering properties of atmospheric molecular clusters consisting of sulfuric acid and bases.

      PubMed

      Elm, Jonas; Norman, Patrick; Mikkelsen, Kurt V

      2015-06-28

      The Rayleigh light scattering properties of (H2SO4)a(NH3)b and (H2SO4)a((CH3)2NH)b atmospheric molecular clusters have been investigated using a response theory approach. Using density functional theory the molecular structures and stepwise formation free energies of clusters with a and b up to 4 have been re-investigated. The Rayleigh scattering intensities are calculated from the dipole polarizability tensor α using the CAM-B3LYP functional by applying linear response methods. The intrinsic scattering properties of (H2SO4)a(NH3)b and (H2SO4)a((CH3)2NH)b indicate that amine containing clusters scatter light significantly more efficiently then their ammonia containing counterparts. Using the Atmospheric Cluster Dynamics Code (ACDC) the steady state cluster concentrations are estimated and the effective scattering is calculated. The effective scattering is shown to be highly dependent on the estimated concentrations and indicates that there exist competitive pathways, such as nucleation and coagulation, which influence the cluster distributions. The frequency dependence of the scattering is found to depend on the cluster composition and show increased responses when clusters contain more bases than acid molecules. Based on structures obtained using semi-empirical molecular dynamics simulations the Rayleigh scattering properties of clusters with up to 20 acid-base pairs are evaluated. This study represents the first step towards gaining a fundamental understanding of the scattering properties of small atmospheric clusters in the ambient atmosphere.

    9. Structure and electronic behavior of 26-atom Cu-Ag and Cu-Au nanoalloys

      NASA Astrophysics Data System (ADS)

      Guzmán-Ramírez, Gregorio; Robles, Juvencio; Aguilera-Granja, Faustino

      2016-09-01

      We hereby present a density functional theory (DFT) study of the structural, energetic, and electronic properties of the binary clusters Cu n X26- n (with X = Ag and Au). Our electronic calculations were performed with the DFT package GAUSSIAN 09, and we chose the BPW91 exchange correlation functional in combination with an effective core potential LANL2DZ basis set as our level of theory. We find that in the case of these clusters and in a completely different way - as compared to the bulk chemical order observed in both alloys CuAg (segregation) and CuAu (ordering) -, for small n both Ag and Au clusters exhibit a similar chemical order, finding the Cu atoms in the center of the cluster with the tendency to form core shell structures. On the other hand, for large n values the Ag and Au atoms tend to occupy surface positions forming separated surface islands that keep the two metal atoms separated as long as the concentration allows it. Concerning the structural properties, a clear increase in the interatomic distance of the Ag-Ag and Au-Au surface pairs is observed, particularly in the equiatomic region. In conclusion, both nanoalloys CuAg and CuAu behave quite similarly in contrast to their respective bulk cases.

    10. Effects of Ga addition on the mechanical properties of 35Ag-30Pd-20Au-15Cu alloy.

      PubMed

      Yamanaka, Masahiko; Goto, Shin-ichi; Churnjitapirom, Pornkiat; Ogura, Hideo

      2002-12-01

      Ten 35Ag-30Pd-20Au-15Cu alloys containing 0.00, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 2.00, 4.00, or 6.00% Ga were experimentally prepared to investigate the effect of Ga on their mechanical properties in addition to their use for denture frameworks, connectors and clasps. The effect of Ga addition on the mechanical properties was marked with a significant increase in the tensile strength, 0.2% off-set proof stress (proof stress) and Vickers hardness observed at low Ga contents (0.25-2.00%). On the other hand, the elongation significantly decreased with the addition of Ga at all contents used in this study. The tensile strength, proof stress and Vickers hardness of the 35Ag-30Pd-20Au-15Cu alloys containing 0.25-2.00% Ga were in the range of 809-957 MPa, 669-857 MPa and 260-301 MPa, respectively. These values are similar to those of Co-Cr alloys, suggesting that 0.25-2.00% Ga alloys can be used for denture frameworks, clasps and connectors.

    11. Cu2O and Au/Cu2O particles: surface properties and applications in glucose sensing.

      PubMed

      Won, Yu-Ho; Stanciu, Lia A

      2012-09-26

      In this work we investigated the surface and facet-dependent catalytic properties of metal oxide particles as well as noble metal/metal oxide heterogeneous structures, with cuprous oxide (Cu(2)O) and Au/Cu(2)O being selected as model systems. As an example of application, we explored the potential of these materials in developing electrocatalytic devices. Cu(2)O particles were synthesized in various shapes, then used for testing their morphology-dependent electrochemical properties applied to the detection of glucose. While we did not attempt to obtain the best detection limit reported to date, the octahedral and hexapod Cu(2)O particles showed reasonable detection limits of 0.51 and 0.60 mM, respectively, which are physiologically relevant concentrations. However, detection limit seems to be less affected by particle shapes than sensitivity. Heterogeneous systems where Au NPs were deposited on the surface of Cu(2)O particles were also tested with similar results in terms of the effect of surface orientation.

    12. Density functional theory based studies on the nature of Raman and resonance Raman scattering of nerve agent bound to gold and oxide-supported gold clusters: a plausible way of detection.

      PubMed

      Majumdar, D; Roszak, Szczepan; Leszczynski, Jerzy

      2010-04-01

      A detailed theoretical investigation has been carried out at the density functional level of theories to investigate the nature of Raman intensities of the -P=O stretching mode of a model nerve agent DFP (diisopropylfluorophosphate) when bound to different gold (Au(8), Au(20)) and oxide-supported gold (MgO...Au(4), CaO...Au(4), TiO(2)...Au(4), Al(2)O(3)...Au(4), M(16)O(16)...Au(8), and [M(16)O(15)...Au(8)](2+), M = Ca, Mg) clusters. All of these clusters and the DFP-bound clusters are fully optimized, and the computed energetics shows that DFP attaches itself weakly to these clusters. The normal Raman spectra calculations on these clusters show that there is substantial enhancement of the -P=O stretching mode of DFP compared to the isolated species. This enhancement has been found to be due to the polarization of the -P=O bond of DFP when bound to the clusters. Significant enhancement in intensity has been observed in the case of Au(n)...DFP (n = 8, 20), M(16)O(16)...Au(8)...DFP, and [M(16)O(15)...Au(8)](2+)...DFP (M = Ca, Mg) clusters. The resonance Raman calculations on the Au(n)...DFP (n = 8, 20) reveals that this enhancement could be made quite large and selective, which is a feature that is unique to the nerve agents and could be used as a property for detecting them.

    13. Properties and Chemisorptive Reactivity of Transition Metal Clusters

      DTIC Science & Technology

      1991-12-14

      structure of metal complexes that go beyond ligand field theory ideas, and of practical importance, in that it is crucial to understand how magnetic...aggregates or clusters of these metals with quntum mechanics, we will be able to develop a detailed understanding of metallic bonding. So far, we have...interactions between early and late TM’s in these so-called Engel-Brewer intermetallic compounds. The only theory that has attempted to explain the high

    14. Clustering Properties of Radio Sources in the FIRST Survey

      NASA Astrophysics Data System (ADS)

      Magliocchetti, M.; Maddox, S. J.; Lahav, O.; Wall, J. V.

      We investigate the large-scale clustering of radio sources in the FIRST 1.4 GHz survey by analysing the distribution function (Counts in Cells) of this sample. We select a reliable galaxy sample from the the FIRST catalogue, paying particular attention to the problem of how to define single radio sources from the multiple components listed in the FIRST catalogue. We also consider the incompleteness of the catalogue. We estimate angular two-point correlation function w(theta), the variance, Psi_2, and skewness, Psi_3, of the distribution for the galaxy subsample. Both w(theta) and Psi_2 show power-law behaviour with an amplitude corresponding a spatial correlation length of r_0 ~10 h^{-1} Mpc. We detect significant skewness in the distribution, and find that it is related to the variance through the relation Psi_3 = S_3(Psi_2)alpha with alpha = 1.9 +- 0.1 consistent with the non-linear growth of perturbations from primordial Gaussian initial conditions. We show that the amplitude of clustering (corresponding to a spatial correlation length of r_0 ~10 h^{-1} Mpc) and skewness are consistent with realistic models of galaxy clustering.

    15. A comprehensive study of the radio properties of brightest cluster galaxies

      NASA Astrophysics Data System (ADS)

      Hogan, M. T.; Edge, A. C.; Hlavacek-Larrondo, J.; Grainge, K. J. B.; Hamer, S. L.; Mahony, E. K.; Russell, H. R.; Fabian, A. C.; McNamara, B. R.; Wilman, R. J.

      2015-10-01

      We examine the radio properties of the brightest cluster galaxies (BCGs) in a large sample of X-ray selected galaxy clusters comprising the Brightest Cluster Sample (BCS), the extended BCS and ROSAT-ESO Flux Limited X-ray cluster catalogues. We have multifrequency radio observations of the BCG using a variety of data from the Australia Telescope Compact Array, Jansky Very Large Array and Very Long Baseline Array telescopes. The radio spectral energy distributions of these objects are decomposed into a component attributed to on-going accretion by the active galactic nuclei (AGN) that we refer to as `the core', and a more diffuse, ageing component we refer to as the `non-core'. These BCGs are matched to previous studies to determine whether they exhibit emission lines (principally Hα), indicative of the presence of a strong cooling cluster core. We consider how the radio properties of the BCGs vary with cluster environmental factors. Line emitting BCGs are shown to generally host more powerful radio sources, exhibiting the presence of a strong, distinguishable core component in about 60 per cent of cases. This core component more strongly correlates with the BCG's [O III] 5007 Å line emission. For BCGs in line emitting clusters, the X-ray cavity power correlates with both the extended and core radio emission, suggestive of steady fuelling of the AGN over bubble-rise time-scales in these clusters.

    16. Facile assembly of tetragonal Pt clusters on graphene oxide for enhanced nonlinear optical properties

      NASA Astrophysics Data System (ADS)

      Zheng, Chan; Li, Yubing; Huang, Li; Li, Wei; Chen, Wenzhe

      2015-11-01

      A facile method to assemble tetragonal Pt clusters on the surface of graphene oxide (Pt-cluster/GO) using anatase TiO2 as a template is proposed. The morphology and structure of Pt-cluster/GO were investigated, revealing that tetragonal Pt clusters with a diameter of 20-50 nm composed of 2-3 nm Pt nanoparticles (NPs) were homogenously decorated on the surface of GO. The nonlinear optical properties were characterized by the open-aperture Z-scan technique in the nanosecond regime using a laser with wavelength of 532 nm. The as-prepared Pt-cluster/GO hybrid was found to show strong optical limiting (OL) effects for nanosecond laser pulses at 532 nm, and the OL performance is superior to that of carbon nanotubes, a benchmark optical limiter. Furthermore, the Z-scan results showed that the OL performance of the Pt-cluster/GO hybrid is superior to that of GO and the Pt-NP/GO hybrid. The OL behavior of the metal/GO composite nanostructure can be effectively tailored by altering the aggregation means of metal NPs. Scattering measurements suggested that nonlinear scattering (NLS) played an important role in the observed OL behavior in the Pt-cluster/GO hybrid. The OL properties of the Pt-cluster/GO hybrid are attributed to the reverse saturable absorption in the GO sheet and NLS in the metal NPs.

    17. 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.

    18. Optical properties of Au-dispersed ZrO2 thin films

      NASA Astrophysics Data System (ADS)

      Huang, Weimin; Arizpe-Chávez, Humberto; Ramírez-Bon, Rafael; Espinoza-Beltrán, Francisco

      2002-03-01

      The optical absorption of gold nanoparticles dispersed within mesoporous zirconia thin films has been investigated. The samples of this material were prepared by the sol-gel technique. TEM studies showed Au nanoparticles with sizes in the range from 5 to 20 nm, embedded into the zirconia matrix. Also, XR diffraction spectra showed Au diffraction peaks corresponding to metallic nanoparticles with sizes in the range 7-9 nm. The accepted surface plasma resonance value for gold is 556 nm. The absorption spectra showed a red shift on the SPR position for samples thermally annealed. Also, a red shift is observed for samples treated with monoethanolamine (MEA) vapor. A lowering in the intensities of the absorption peaks for the treated samples is observed. On the other hand, larger gold dopping produces a blue shift in the absorption spectra, with an increment in the intensity of the absorption peaks. The Tauc-Lorentz fitting model allowed us to measure changes in the dielectric function of the material. Therefore, we conclude that not only the particle size drives the optical absorption spectra in gold-doped films. The observed opposite results can be explained if we introduce changes in the dielectric constant of the films.

    19. Physico-chemical and antimicrobial properties of co-sputtered Ag Au/PTFE nanocomposite coatings

      NASA Astrophysics Data System (ADS)

      Zaporojtchenko, V.; Podschun, R.; Schürmann, U.; Kulkarni, A.; Faupel, F.

      2006-10-01

      In this work, we used co-sputtering of noble metals together with polytetrafluorethylene (PTFE) as a method for producing antibacterial metal/polymer nanocomposite coatings, where the precious metals are only incorporated in a thin surface layer. Moreover, they are finely dispersed as nanoparticles, thus saving additional material and providing a very large effective surface for metal ion release. Nanocomposite films with thickness between 100 and 300 nm were prepared with a wide range of metal filling between 10 and 40%. The antimicrobial effect of the nanocomposite coatings was evaluated by means of two different assays. The bactericidal activity due to silver release from the surface was determined by a modification of conventional disc diffusion methods. Inhibition of bacterial growth on the coated surface was investigated through a modified proliferation assay. Staphylococcus aureus and S. epidermidis were used as test bacteria, as these species commonly cause infections associated with medical polymer devices. The antibacterial efficiency of the coatings against different bacteria was demonstrated at extremely small noble metal consumption: Au: ~1 mg m-2 and Ag: ~0.1 g m-2. The maximum ability for having an antibacterial effect was shown by the Ag-Au/PTFE nanocomposite, followed by the Ag/PTFE nanocomposite.

    20. Facet-dependent optical properties of polyhedral Au-Cu₂O core-shell nanocrystals.

      PubMed

      Yang, Yu-Chen; Wang, Hsiang-Ju; Whang, Jennifer; Huang, Jer-Shing; Lyu, Lian-Ming; Lin, Po-Heng; Gwo, Shangjr; Huang, Michael H

      2014-04-21

      We fabricated Au-Cu₂O core-shell octahedra, cuboctahedra, and nanocubes having sizes of 90-220 nm using 50 nm octahedral cores. The smaller particle sizes minimize the strong light scattering features from the Cu₂O shells and enable the surface plasmon resonance (SPR) absorption band of the gold cores to be clearly identified. Beyond a lower shell thickness limit, the SPR band positions of the gold cores are independent of the shell thickness, but are strongly dependent on the exposed particle surfaces. The plasmonic band red-shifts from Au-Cu₂O octahedra to cuboctahedra and nanocubes, and differs by as much as 26 nm between the octahedra and the nanocubes. The same facet-dependent optical effects were observed using larger octahedral gold cores and cubic gold cores. In contrast, simulation spectra show progressively red-shifted SPR band positions with increasing shell thickness. The Cu₂O shells are also found to exhibit facet-dependent optical behavior. These nanocrystals can respond to changes in the solvent environment such as solvents with different refractive indices, indicating that the plasmonic field of the gold cores can extend beyond the particle surfaces despite the presence of thick shells. Plane-selective spectral responses to low concentrations of surfactants were also recorded.

    1. Study of Optical Properties on Fractal Aggregation Using the GMM Method by Different Cluster Parameters

      NASA Astrophysics Data System (ADS)

      Chang, Kuo-En; Lin, Tang-Huang; Lien, Wei-Hung

      2015-04-01

      Anthropogenic pollutants or smoke from biomass burning contribute significantly to global particle aggregation emissions, yet their aggregate formation and resulting ensemble optical properties are poorly understood and parameterized in climate models. Particle aggregation refers to formation of clusters in a colloidal suspension. In clustering algorithms, many parameters, such as fractal dimension, number of monomers, radius of monomer, and refractive index real part and image part, will alter the geometries and characteristics of the fractal aggregation and change ensemble optical properties further. The cluster-cluster aggregation algorithm (CCA) is used to specify the geometries of soot and haze particles. In addition, the Generalized Multi-particle Mie (GMM) method is utilized to compute the Mie solution from a single particle to the multi particle case. This computer code for the calculation of the scattering by an aggregate of spheres in a fixed orientation and the experimental data have been made publicly available. This study for the model inputs of optical determination of the monomer radius, the number of monomers per cluster, and the fractal dimension is presented. The main aim in this study is to analyze and contrast several parameters of cluster aggregation aforementioned which demonstrate significant differences of optical properties using the GMM method finally. Keywords: optical properties, fractal aggregation, GMM, CCA

    2. Characterizing the properties of cluster precursors in the MALT90 survey

      NASA Astrophysics Data System (ADS)

      Contreras, Yanett; Rathborne, Jill M.; Guzman, Andres; Jackson, James; Whitaker, Scott; Sanhueza, Patricio; Foster, Jonathan

      2017-04-01

      In the Milky Way there are thousands of stellar clusters each harbouring from a hundred to a million stars. Although clusters are common, the initial conditions of cluster formation are still not well understood. To determine the processes involved in the formation and evolution of clusters it is key to determine the global properties of cluster-forming clumps in their earliest stages of evolution. Here, we present the physical properties of 1244 clumps identified from the MALT90 survey. Using the dust temperature of the clumps as a proxy for evolution we determined how the clump properties change at different evolutionary stages. We find that less-evolved clumps exhibiting dust temperatures lower than 20 K have higher densities and are more gravitationally bound than more-evolved clumps with higher dust temperatures. We also identified a sample of clumps in a very early stage of evolution, thus potential candidates for high-mass star-forming clumps. Only one clump in our sample has physical properties consistent with a young massive cluster progenitor, reinforcing the fact that massive protoclusters are very rare in the Galaxy.

    3. Chirality in thiolate-protected gold clusters.

      PubMed

      Knoppe, Stefan; Bürgi, Thomas

      2014-04-15

      Over recent years, research on thiolate-protected gold clusters Au(m)(SR)n has gained significant interest. Milestones were the successful determination of a series of crystal structures (Au102(SR)44, Au25(SR)18, Au38(SR)24, Au36(SR)24, and Au28(SR)20). For Au102(SR)44, Au38(SR)24, and Au28(SR)20, intrinsic chirality was found. Strong Cotton effects (circular dichroism, CD) of gold clusters protected by chiral ligands have been reported a long time ago, indicating the transfer of chiral information from the ligand into the cluster core. Our lab has done extensive studies on chiral thiolate-protected gold clusters, including those protected with chiral ligands. We demonstrated that vibrational circular dichroism can serve as a useful tool for the determination of conformation of the ligand on the surface of the cluster. The first reports on crystal structures of Au102(SR)44 and Au38(SR)24 revealed the intrinsic chirality of these clusters. Their chirality mainly arises from the arrangement of the ligands on the surface of the cluster cores. As achiral ligands are used to stabilize the clusters, racemic mixtures are obtained. However, the separation of the enantiomers by HPLC was demonstrated which enabled the measurement of their CD spectra. Thermally induced inversion allows determination of the activation parameters for their racemization. The inversion demonstrates that the gold-thiolate interface is anything but fixed; in contrast, it is rather flexible. This result is of fundamental interest and needs to be considered in future applications. A second line of our research is the selective introduction of chiral, bidentate ligands into the ligand layer of intrinsically chiral gold clusters. The ligand exchange reaction is highly diastereoselective. The bidentate ligand connects two of the protecting units on the cluster surface and thus effectively stabilizes the cluster against thermally induced inversion. A minor (but significant) influence of chiral ligands to

    4. Structure and properties of bimetallic titanium and vanadium oxide clusters.

      PubMed

      Helmich, Benjamin; Sierka, Marek; Döbler, Jens; Sauer, Joachim

      2014-05-14

      By employing a genetic algorithm together with density functional theory (B3LYP), we investigate the most stable minimum structures of several bimetallic titanium and vanadium oxide clusters that contain four metal atoms. The following compositions are studied: VnTin-4O10(-) (n = 1-4), (TiO2)VOn(-) (n = 1-4), and (TiO2)VOn(+) (n = 1-3). Apart from (TiO2)3VO(-), vanadium oxo groups are always part of the most stable minimum structures when vanadium is present. Anti-ferromagnetic coupling lowers the energy substantially if spin centers are located at neighbored metal atoms rather than at distant oxygen radical sites. Vanadium-rich or oxygen-poor compositions prefer symmetric adamantane-like cage structures, some of which have already been proposed in a previous study. In contrast, vanadium-poor and oxygen-rich compositions show versatile structural motifs that cannot be intuitively derived from the symmetric cage motif. Particularly, for Ti4O10(-) there are several non-symmetric and distorted cages that have an up to 68 kJ mol(-1) lower energy than the symmetric adamantane-like cage structure. Nevertheless, for the adamantane-like cage the simulated infra-red spectrum (within the harmonic approximation) agrees best with the experimental vibrational spectrum. The oxidative power of the (TiO2)3VO3(-) and (TiO2)3VO2(+) clusters as measured by the energy of removing 1/2 O2 (297 and 227 kJ mol(-1), respectively) is less than that of the pure vanadium oxide clusters (V2O5)VO3(-) and (V2O5)VO2(+) (283 and 165 kJ mol(-1), respectively).

    5. Wave Properties of Equatorial Magnetosonic Waves as Observed by Cluster

      NASA Astrophysics Data System (ADS)

      Balikhin, M. A.; Walker, S. N.; Shprits, Y.

      2014-12-01

      A survey of the Cluster STAFF data set shows a number of periods in which Equatorial Magnetosonic Waves display a discrete spectrum. In some of these instances, the frequency of emissions varies in the same fashion as the background magnetic field, indicating that the wars are observed within their source region. This paper analyses the propagation characteristics of these emissions and investigates the appropriateness of the quasi-linear assumption of a gaussian spectrum used in the numerical modelling of their role in the electron dynamics within the radiation belts based in the Chirikov resonance overlap criterion.

    6. Synthesis, structural characterization, and antiinflammatory activity of triethylphosphinegold(I) sulfanylpropenoates of the type [(AuPEt3)2xspa] [H2xspa = 3-(aryl)-2-sulfanylpropenoic acid]: an (H2O)6 cluster in the lattice of the complexes [(AuPEt3)2xspa] x 3 H2O.

      PubMed

      Barreiro, Elena; Casas, José S; Couce, María D; Gato, Angeles; Sánchez, Agustín; Sordo, José; Varela, José M; Vázquez López, Ezequiel M

      2008-07-21

      Gold complexes of the type [(AuPEt3)2xspa] were prepared by reacting AuPEt3Cl in basic media with the 3-(aryl)-2-sulfanylpropenoic acids H2xspa [x = p, Clp, -o-mp, -p-mp, -o-hp, -p-hp, diBr-o-hp, f, t, -o-py; p = 3-phenyl, Clp = 3-(2-chlorophenyl)-, -o-mp = 3-(2-methoxyphenyl)-, -p-mp = 3-(4-methoxyphenyl)-, -o-hp = 3-(2-hydroxyphenyl)-, -p-hp = 3-(4-hydroxyphenyl)-, diBr-o-hp = 3-(3,5- dibromo-2-hydroxyphenyl)-, f = 3-(2-furyl)-, t = 3-(2-thienyl)-, -o-py = 3-(2-pyridyl); spa = 2-sulfanylpropenoato], and 2-cyclopentylidene-2-sulfanylacetic acid (H2cpa). The complexes were characterized by spectroscopic methods (IR, (1)H, (13)C and (31)P NMR) and mass spectrometry, and the complexes [(AuPEt3)2pspa] x 3 H2O, [(AuPEt3)2-p-hpspa] x 3 H2O, [(AuPEt3)2tspa)] x 3 H2O, and [(AuPEt3)2-o-hpspa] by X-ray diffractometry. The crystals of the first three complexes contain (H2O)6 clusters hydrogen bonded to [(AuPEt3)2xspa]2 dimer units, whereas in the -o-hpspa derivative the hydrogen bonds are between the monomer [(AuPEt3)2-o-hpspa] units. The antiinflammatory activity of the complexes against plantar edema induced by carrageenan in rats is generally significant, with the values for the o-hpspa and tspa derivatives being particularly high.

    7. The evolution of dielectric properties of sodium, silicon and argon clusters

      NASA Astrophysics Data System (ADS)

      Jackson, Koblar; Yang, Mingli; Ma, Li; Jellinek, Julius

      2012-02-01

      We used a computational scheme based on site-specific polarizabilities to study the evolution of the dielectric properties of sodium, silicon and argon clusters. In this approach, the total cluster polarizability is decomposed into local dipole (LD) and charge-transfer (CT) parts. The local dipole part measures the redistribution of charge within an atomic volume, while the CT part describes the movement of charge between volumes. We find distinct differences in the relative contributions of the LD and CT components to the total polarizability as a function of cluster size for the different cluster types and relate this to the development of metallic behavior. The method also directly probes the extent of electrostatic screening of the cluster interior to an applied electric field.

    8. Optical and electronic properties of graphene nanoribbons upon adsorption of ligand-protected aluminum clusters.

      PubMed

      Gomes da Rocha, Claudia; Clayborne, P Andre; Koskinen, Pekka; Häkkinen, Hannu

      2014-02-28

      We have carried out first-principles calculations to investigate how the electronic and optical features of graphene nanoribbons are affected by the presence of atomic clusters. Aluminum clusters of different sizes and stabilized by organic ligands were deposited on graphene nanoribbons from which the energetic features of the adsorption plus electronic structure were treated within density-functional theory. Our results point out that, depending on their size and structure shape, the clusters perturb distinctively the electronic properties of the ribbons. We suggest that such selective response can be measured through optical means revealing that graphene nanoribbons can work as an efficient characterization medium of atomic clusters. In addition, we demonstrate that atomic clusters can fine-tune the electronic and spin-polarized states of graphene ribbons from which novel spin-filter devices could be designed.

    9. Nanomanufacturing of titania interfaces with controlled structural and functional properties by supersonic cluster beam deposition

      SciTech Connect

      Podestà, Alessandro E-mail: pmilani@mi.infn.it; Borghi, Francesca; Indrieri, Marco; Bovio, Simone; Piazzoni, Claudio; Milani, Paolo E-mail: pmilani@mi.infn.it

      2015-12-21

      Great emphasis is placed on the development of integrated approaches for the synthesis and the characterization of ad hoc nanostructured platforms, to be used as templates with controlled morphology and chemical properties for the investigation of specific phenomena of great relevance in interdisciplinary fields such as biotechnology, medicine, and advanced materials. Here, we discuss the crucial role and the advantages of thin film deposition strategies based on cluster-assembling from supersonic cluster beams. We select cluster-assembled nanostructured titania (ns-TiO{sub 2}) as a case study to demonstrate that accurate control over morphological parameters can be routinely achieved, and consequently, over several relevant interfacial properties and phenomena, like surface charging in a liquid electrolyte, and proteins and nanoparticles adsorption. In particular, we show that the very good control of nanoscale morphology is obtained by taking advantage of simple scaling laws governing the ballistic deposition regime of low-energy, mass-dispersed clusters with reduced surface mobility.

    10. The geometry structures and electronic properties of LimBn (m + n = 12) clusters

      NASA Astrophysics Data System (ADS)

      Ruan, Wen; Xie, An-Dong; Wu, Dong-Lan; Luo, Wen-Lang; Yu, Xiao-Guang

      2014-03-01

      The geometric structures, electronic properties, total and binding energies, harmonic frequencies, the highest occupied molecular orbital to the lowest unoccupied molecular orbital energy gaps, and the vertical ionization potential energies of small LimBn (m+n = 12) clusters were investigated by the density functional theory B3LYP with a 6-311+G (2d, 2p) basis set. All the calculations were performed using the Gaussian09 program. For the study of the LimBn clusters, the global minimum of the B12 cluster was chosen as the starting point and the boron atoms were gradually replaced by Li atoms. The results showed that as the number of Li atoms increased, the stability of the LimBn cluster decreased and the physical and chemical properties became more active. In addition, on average there was a large charge transfer from the Li atoms to the B atoms.

    11. Nanomanufacturing of titania interfaces with controlled structural and functional properties by supersonic cluster beam deposition

      NASA Astrophysics Data System (ADS)

      Podestà, Alessandro; Borghi, Francesca; Indrieri, Marco; Bovio, Simone; Piazzoni, Claudio; Milani, Paolo

      2015-12-01

      Great emphasis is placed on the development of integrated approaches for the synthesis and the characterization of ad hoc nanostructured platforms, to be used as templates with controlled morphology and chemical properties for the investigation of specific phenomena of great relevance in interdisciplinary fields such as biotechnology, medicine, and advanced materials. Here, we discuss the crucial role and the advantages of thin film deposition strategies based on cluster-assembling from supersonic cluster beams. We select cluster-assembled nanostructured titania (ns-TiO2) as a case study to demonstrate that accurate control over morphological parameters can be routinely achieved, and consequently, over several relevant interfacial properties and phenomena, like surface charging in a liquid electrolyte, and proteins and nanoparticles adsorption. In particular, we show that the very good control of nanoscale morphology is obtained by taking advantage of simple scaling laws governing the ballistic deposition regime of low-energy, mass-dispersed clusters with reduced surface mobility.

    12. Electronic properties and topological phases of ThXY (X = Pb, Au, Pt and Y = Sb, Bi, Sn) compounds

      NASA Astrophysics Data System (ADS)

      Zahra, Nourbakhsh; Aminollah, Vaez

      2016-03-01

      The electronic properties and topological phases of ThXY (X = Pb, Au, Pt, Pd and Y = Sb, Bi, Sn) compounds in the presence of spin-orbit coupling, using density functional theory are investigated. The ThPtSn compound is stable in the ferromagnetic phase and the other ThXY compounds are stable in nonmagnetic phases. Band structures of these compounds in topological phases (insulator or metal) and normal phases within generalized gradient approximation (GGA) and Engel-Vosko generalized gradient approximation (GGA_EV) are compared. The ThPtSn, ThPtBi, ThPtSb, ThPdBi, and ThAuBi compounds have topological phases and the other ThXY compounds have normal phases. Band inversion strengths and topological phases of these compounds at different pressure are studied. It is seen that the band inversion strengths of these compounds are sensitive to pressure and for each compound a second-order polynomial fitted on the band inversion strengths-pressure curves.

    13. Thermodynamic properties and phase transitions in CO2 molecular clusters

      NASA Technical Reports Server (NTRS)

      Etters, R. D.; Flurchick, K.; Pan, R. P.; Chandrasekharan, V.

      1981-01-01

      The thermodynamic properties of (CO2)N molecular aggregates of size N between 2 and 13 have been investigated. These crystallites exhibit well defined orientational order-disorder rotational transitions accompanied by a structural transition into a plastic crystallite phase. In addition, they exhibit melting and disassociation transitions. It is shown that the interpretation of experimental data, based upon dimer properties, depends crucially on these results. Equilibrium structures and orientations are also given.

    14. Vibrational properties of vacancy in Au using modified embedded atom method potentials

      NASA Astrophysics Data System (ADS)

      Ram, P. N.; Gairola, Vandana; Semalty, P. D.

      2016-07-01

      Much improved result for lattice dynamics of Au is obtained with the use of modified embedded atom method (MEAM) potentials compared to the earlier embedded atom method (EAM) potentials. The MEAM potentials along with experimental phonons are utilised to calculate local spectra of neighbours of vacancy using Green's function method. The local spectrum of first neighbour of vacancy shows general loss of modes at lower frequencies with a resonance like sharp peak near the top end of the spectrum. The spectrum of second neighbour shows small changes from the host spectra except a pronounced dip in the middle. In accordance with the obtained features of local spectra of neighbours the calculated mean-square displacements are lower for both first and second neighbours as compared to that of host atoms. The calculated formation entropy is in reasonable agreement with other calculations and available experimental values.

    15. Geometries, stabilities and electronic properties of copper and selenium doped copper clusters: Density functional theory study

      NASA Astrophysics Data System (ADS)

      Li, Cheng-Gang; Zhang, Jie; Yuan, Yu-Quan; Tang, Ya-Nan; Ren, Bao-Zeng; Chen, Wei-Guang

      2017-02-01

      The structures properties of Cun+1 and CunSe clusters have been investigated using an unbiased CALYPSO structure searching method. Firstly, an unbiased search relying on several structurally different initial clusters have been undertaken. Subsequently, geometry optimization by means of density functional theory is carried out to determine the relative stability of various candidates for low lying clusters obtained from the unconstrained search. The results shown that the ground state Cu9 cluster is found to prefer a unique and previously unrecognized structure, with the total energies much lower than all structures proposed in the literature so far. The Cu2Se cluster is the most stable geometries for CunSe clusters. Additionally, the calculated HOMO-LUMO gaps ranges from 1.27 to 2.85 eV, which make CunSe clusters suitable candidates in photocatalyst materials. Lastly, the molecular orbital energy and density of states; the adaptive natural density partitioning; the electron localization function, localized orbital locator and Mayer Bond order are also studied for the ground state to develop a deeper understanding on the electronic properties.

    16. Tensile properties of thin Au-Ni brazes between strong base materials

      SciTech Connect

      Tolle, M.C.; Kassner, M.E.

      1991-12-01

      It has long been known that when relatively strong base materials are joined by thin, soft, interlayer metals such as with brazing or various solid state joining processes, the ultimate tensile strength (UTS) of the bond may be several factors higher than the UTS of the bulk, or unconstrained, interlayer metals. However, earlier work reported by the authors confirmed that delayed or ``creep`` failure of the bond may occur at stresses much less than the UTS. It was found that for thin silver interlayers, prepared by brazing and physical vapor deposition (PVD), joining elastically deforming base materials (i.e. no measurable plastic deformation occurs in the base metal at the applied stresses), the ambient (and near-ambient) temperature time to failure is controlled by the creep rate of the silver interlayer which is determined by the effective stress within the interlayer. The plastic deformation within the interlayer causes cavity nucleation which continues until the concentration of nuclei is sufficiently high to lead to instability and eventual failure. The delayed failure may be accelerated by base material creep resulting from the effective stress in the base material. Plastic deformation in the base metal causes corresponding deformation in the interlayer, and cavities nucleate as with elastic base metal case. The delayed failure phenomenon was confirmed by the authors only for silver interlayers; other compositions were not tested. In this study, maraging steel was joined with an Au-Ni braze alloy with 57.5 at. % Au and 42.5 at. % Ni. The microstructure is expected to be a refined two-phase (spinodal) alloy with higher strength than the PVD silver of our previous investigation.

    17. Tensile properties of thin Au-Ni brazes between strong base materials

      SciTech Connect

      Tolle, M.C.; Kassner, M.E. )

      1991-12-01

      It has long been known that when relatively strong base materials are joined by thin, soft, interlayer metals such as with brazing or various solid state joining processes, the ultimate tensile strength (UTS) of the bond may be several factors higher than the UTS of the bulk, or unconstrained, interlayer metals. However, earlier work reported by the authors confirmed that delayed or creep'' failure of the bond may occur at stresses much less than the UTS. It was found that for thin silver interlayers, prepared by brazing and physical vapor deposition (PVD), joining elastically deforming base materials (i.e. no measurable plastic deformation occurs in the base metal at the applied stresses), the ambient (and near-ambient) temperature time to failure is controlled by the creep rate of the silver interlayer which is determined by the effective stress within the interlayer. The plastic deformation within the interlayer causes cavity nucleation which continues until the concentration of nuclei is sufficiently high to lead to instability and eventual failure. The delayed failure may be accelerated by base material creep resulting from the effective stress in the base material. Plastic deformation in the base metal causes corresponding deformation in the interlayer, and cavities nucleate as with elastic base metal case. The delayed failure phenomenon was confirmed by the authors only for silver interlayers; other compositions were not tested. In this study, maraging steel was joined with an Au-Ni braze alloy with 57.5 at. % Au and 42.5 at. % Ni. The microstructure is expected to be a refined two-phase (spinodal) alloy with higher strength than the PVD silver of our previous investigation.

    18. 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.

    19. Star Cluster Properties in Two LEGUS Galaxies Computed with Stochastic Stellar Population Synthesis Models

      NASA Astrophysics Data System (ADS)

      Krumholz, Mark R.; Adamo, Angela; Fumagalli, Michele; Wofford, Aida; Calzetti, Daniela; Lee, Janice C.; Whitmore, Bradley C.; Bright, Stacey N.; Grasha, Kathryn; Gouliermis, Dimitrios A.; Kim, Hwihyun; Nair, Preethi; Ryon, Jenna E.; Smith, Linda J.; Thilker, David; Ubeda, Leonardo; Zackrisson, Erik

      2015-10-01

      We investigate a novel Bayesian analysis method, based on the Stochastically Lighting Up Galaxies (slug) code, to derive the masses, ages, and extinctions of star clusters from integrated light photometry. Unlike many analysis methods, slug correctly accounts for incomplete initial mass function (IMF) sampling, and returns full posterior probability distributions rather than simply probability maxima. We apply our technique to 621 visually confirmed clusters in two nearby galaxies, NGC 628 and NGC 7793, that are part of the Legacy Extragalactic UV Survey (LEGUS). LEGUS provides Hubble Space Telescope photometry in the NUV, U, B, V, and I bands. We analyze the sensitivity of the derived cluster properties to choices of prior probability distribution, evolutionary tracks, IMF, metallicity, treatment of nebular emission, and extinction curve. We find that slug's results for individual clusters are insensitive to most of these choices, but that the posterior probability distributions we derive are often quite broad, and sometimes multi-peaked and quite sensitive to the choice of priors. In contrast, the properties of the cluster population as a whole are relatively robust against all of these choices. We also compare our results from slug to those derived with a conventional non-stochastic fitting code, Yggdrasil. We show that slug's stochastic models are generally a better fit to the observations than the deterministic ones used by Yggdrasil. However, the overall properties of the cluster populations recovered by both codes are qualitatively similar.

    20. THE SPATIAL STRUCTURE OF YOUNG STELLAR CLUSTERS. III. PHYSICAL PROPERTIES AND EVOLUTIONARY STATES

      SciTech Connect

      Kuhn, Michael A.; Feigelson, Eric D.; Getman, Konstantin V.; Sills, Alison; Bate, Matthew R.; Borissova, Jordanka

      2015-10-20

      We analyze the physical properties of stellar clusters that are detected in massive star-forming regions in the MYStIX project—a comparative, multiwavelength study of young stellar clusters within 3.6 kpc that contain at least one O-type star. Tabulated properties of subclusters in these regions include physical sizes and shapes, intrinsic numbers of stars, absorptions by the molecular clouds, and median subcluster ages. Physical signs of dynamical evolution are present in the relations of these properties, including statistically significant correlations between subcluster size, central density, and age, which are likely the result of cluster expansion after gas removal. We argue that many of the subclusters identified in Paper I are gravitationally bound because their radii are significantly less than what would be expected from freely expanding clumps of stars with a typical initial stellar velocity dispersion of ∼3 km s{sup −1} for star-forming regions. We explore a model for cluster formation in which structurally simpler clusters are built up hierarchically through the mergers of subclusters—subcluster mergers are indicated by an inverse relation between the numbers of stars in a subcluster and their central densities (also seen as a density versus radius relation that is less steep than would be expected from pure expansion). We discuss implications of these effects for the dynamical relaxation of young stellar clusters.

    1. STAR CLUSTER PROPERTIES IN TWO LEGUS GALAXIES COMPUTED WITH STOCHASTIC STELLAR POPULATION SYNTHESIS MODELS

      SciTech Connect

      Krumholz, Mark R.; Adamo, Angela; Fumagalli, Michele; Wofford, Aida; Calzetti, Daniela; Grasha, Kathryn; Lee, Janice C.; Whitmore, Bradley C.; Bright, Stacey N.; Ubeda, Leonardo; Gouliermis, Dimitrios A.; Kim, Hwihyun; Nair, Preethi; Ryon, Jenna E.; Smith, Linda J.; Zackrisson, Erik E-mail: adamo@astro.su.se

      2015-10-20

      We investigate a novel Bayesian analysis method, based on the Stochastically Lighting Up Galaxies (slug) code, to derive the masses, ages, and extinctions of star clusters from integrated light photometry. Unlike many analysis methods, slug correctly accounts for incomplete initial mass function (IMF) sampling, and returns full posterior probability distributions rather than simply probability maxima. We apply our technique to 621 visually confirmed clusters in two nearby galaxies, NGC 628 and NGC 7793, that are part of the Legacy Extragalactic UV Survey (LEGUS). LEGUS provides Hubble Space Telescope photometry in the NUV, U, B, V, and I bands. We analyze the sensitivity of the derived cluster properties to choices of prior probability distribution, evolutionary tracks, IMF, metallicity, treatment of nebular emission, and extinction curve. We find that slug's results for individual clusters are insensitive to most of these choices, but that the posterior probability distributions we derive are often quite broad, and sometimes multi-peaked and quite sensitive to the choice of priors. In contrast, the properties of the cluster population as a whole are relatively robust against all of these choices. We also compare our results from slug to those derived with a conventional non-stochastic fitting code, Yggdrasil. We show that slug's stochastic models are generally a better fit to the observations than the deterministic ones used by Yggdrasil. However, the overall properties of the cluster populations recovered by both codes are qualitatively similar.

    2. Structural and electronic properties of small silicon clusters

      NASA Astrophysics Data System (ADS)

      Baturin, V. S.; Lepeshkin, S. V.; Magnitskaya, M. V.; Matsko, N. L.; Uspenskii, Yu A.

      2014-05-01

      The atomic structure and electronic spectrum of silicon nanoclusters (Si-ncs) Si7, Si10,Si10H16 and Si10H20 are calculated using the evolutionary algorithm with total energy computed within density functional theory and generalized gradient approximation (DFT-GGA). When analysing the low-energy structures, we pay significant attention to their symmetry and interatomic bond geometry. The candidate structures arising in the process of evolutionary algorithm convergence are also considered and classified by their topology and grouping near local energy minima. Possible ways to improve the convergence of evolutionary computation are discussed. Addressing qualitative criteria for the ground-state atomic structure of Si-ncs, we consider correlations between the density of electronic states and the total energetics of clusters in the ground state and low-energy-isomer configurations.

    3. Decoding the pair correlations and properties of equilibrium microscopic cluster phases

      NASA Astrophysics Data System (ADS)

      Bollinger, Jonathan; Jadrich, Ryan; Truskett, Thomas

      Due to competing interactions acting between particles, dispersed colloidal suspensions can reversibly transition to phases comprising aggregate clusters. Cluster phases have been reported for both 'model' colloidal particles and complex monomers (e.g., proteins); however, many questions remain regarding how to detect and characterize cluster phases given only pair structural correlations (the information most accessible across diverse systems) and how to relate clustering susceptibility and behavior to underlying monomer-monomer interactions. Using molecular simulations and liquid-state theory across a wide survey of conditions, we decode the widely-observed intermediate range order pre-peak in the structure factor by: (1) validating a physically-intuitive rule for detecting clustering based on the pre-peak thermal correlation length; and (2) relating pre-peak position to cluster size and bulk monomer density. We further demonstrate how clustering transitions and resultant properties relate to monomer interactions along coordinates tunable in experiments. These trends are suitable for comparing against clustering systems that can be directly visualized (via, e.g., confocal microscopy), which should aid in assessing the realism of commonly-adopted monomer interaction potentials.

    4. NanoClusters Surface Area Allows Nanoparticle Dissolution with Microparticle Properties

      PubMed Central

      Kuehl, Christopher; El-Gendy, Nashwa; Berkland, Cory

      2016-01-01

      Poorly water soluble drugs comprise the majority of new drug molecules. Nanoparticle agglomerates, called NanoClusters, can increase the dissolution rate of poorly soluble compounds by increasing particle surface area. Budesonide and danazol, two poorly soluble steroids, were studied as model compounds. NanoCluster suspensions were made using a Netzsch MiniCer media mill with samples collected between 5 and 15 hours and lyophilized. DSC and PXRD were used to evaluate the physicochemical properties of the powders and BET was used to determine surface area. SEM confirmed NanoClusters were between 1 and 5 μm. NanoCluster samples showed an increase in dissolution rate compared to the micronized stock and similar to a dried nanoparticle suspension. BET analysis determined an increase in surface area of 8 times for budesonide NanoClusters and 10 to 15 times for danazol NanoClusters compared to micronized stock. Melting temperatures decreased with increased mill time of NanoClusters by DSC. The increased surface area of NanoClusters provides a potential micron-sized alternative to nanoparticles to increase dissolution rate of poorly water soluble drugs. PMID:24788354

    5. Localized Surface Plasmon Resonance properties of copper nano-clusters: A theoretical study of size dependence

      NASA Astrophysics Data System (ADS)

      Ziashahabi, A.; Ghodselahi, T.; Heidari saani, M.

      2013-07-01

      Density functional theory (DFT) calculations are carried out to study the electronic, structural stability and Localized Surface Plasmon Resonance (LSPR) properties of copper nano-clusters. These nano-clusters consisted of 14, 38, 62 and 116 atoms. We studied surface charge density and interband-transitions effects on damping and broadening of the surface plasmon resonance absorption spectra. An enhancement in interband-transition energy and a reduction in surface charge density with decrease in the size of clusters are observed. These features result in the damping and broadening of the LSPR absorption spectra. We also study the structural stability and HOMO-LUMO energy gap of copper clusters. The structural stability of nano-clusters reduces by decreasing the size of the clusters. The HOMO-LUMO energy gap is not zero for the clusters with size less than 2 nm which indicates the lack of conduction electrons which are necessary for LSPR absorption. The calculated interband transition energies are in agreement with LSPR absorption data. We also discuss the difference between size dependent LSPR in copper and gold nano-clusters in the experiment based on calculated surface charge density.

    6. Development of Ag-Pd-Au-Cu alloys for multiple dental applications. Part 2. Mechanical properties of experimental Ag-Pd-Au-Cu alloys containing Sn or Ga for ceramic-metal restorations.

      PubMed

      Goto, S; Nakai, A; Miyagawa, Y; Ogura, H

      2001-06-01

      Eighteen Ag-Pd-Au-Cu alloys, consisting of nine Ag-Pd-Au-Cu mother compositions (Pd: 20, 30 or 40%, Au: 20%, Cu: 10, 15 or 20%, Ag: balance) containing either 5% Sn or 5% Ga as an additive metal, were experimentally prepared. Tensile strength, proof stress, elongation, elastic modulus, and Vickers hardness of these alloys were evaluated to clarify the potential of these alloys for use as ceramic-metal restorations as well as the effects of the Pd and Cu contents on their mechanical properties. The tensile strength, proof stress, elongation, elastic modulus and Vickers hardness of the 18 experimental alloys were in the range of 410.0-984.0 MPa, 289.7-774.3 MPa, 2.2-23.7%, 81.3-123.0 GPa and 135.7-332.3 HV1, respectively. Ten of the 18 experimental alloys can be used for ultra-low fusing ceramics based on their proof stress, elastic modulus, elongation and hardness. Between the Ga- and Sn-added alloys, differences in tensile strength, proof stress, elongation and hardness were found at several Ag-Pd-Au-Cu compositions.

    7. Ab-initio study of the magneto-optical properties of the ultrathin films of Fen/Au(001)

      NASA Astrophysics Data System (ADS)

      Boukelkoul, Mebarek; Haroun, Mohamed Fahim; Haroun, Abdelhalim

      2016-12-01

      With the aim of understand the microscopic origin of the magneto-optical response in the Fe ultrathin films, we used the first principle full-relativistic Spin-Polarized Relativistic Linear Muffin-Tin Orbitals with Atomic Sphere Approximation. We performed an ab-initio study of the structural, magnetic and magneto-optical properties of Fe deposited on semi-infinite Au(001). The structure and growth of the film leads to a pseudomorphic body centered tetragonal structure with tetragonality ratio c/a=1.62, and the pseudomorphic growth is found to be larger than 3 monolayers. The magnetic study revealed a ferromagnetic phase with a large magnetic moment compared to the bulk one. The magneto-optical response is calculated via the polar magneto-optical Kerr effect over a photon energy range up to 10 eV. The most important features of the Kerr rotation spectra are interpreted trough the interband transitions between localized states.

    8. Multishell Au/Ag/SiO2 nanorods with tunable optical properties as single particle orientation and rotational tracking probes.

      PubMed

      Chen, Kuangcai; Lin, Chia-Cheng; Vela, Javier; Fang, Ning

      2015-04-21

      Three-layer core-shell plasmonic nanorods (Au/Ag/SiO2-NRs), consisting of a gold nanorod core, a thin silver shell, and a thin silica layer, were synthesized and used as optical imaging probes under a differential interference contrast microscope for single particle orientation and rotational tracking. The localized surface plasmon resonance modes were enhanced upon the addition of the silver shell, and the anisotropic optical properties of gold nanorods were maintained. The silica coating enables surface functionalization with silane coupling agents and provides enhanced stability and biocompatibility. Taking advantage of the longitudinal LSPR enhancement, the orientation and rotational information of the hybrid nanorods on synthetic lipid bilayers and on live cell membranes were obtained with millisecond temporal resolution using a scientific complementary metal-oxide-semiconductor camera. The results demonstrate that the as-synthesized hybrid nanorods are promising imaging probes with improved sensitivity and good biocompatibility for single plasmonic particle tracking experiments in biological systems.

    9. Galaxy properties in low X-ray luminosity clusters at z=0.25

      NASA Astrophysics Data System (ADS)

      Balogh, Michael; Bower, R. G.; Smail, Ian; Ziegler, B. L.; Davies, Roger L.; Gaztelu, A.; Fritz, Alexander

      2002-11-01

      We present the first spectroscopic survey of intrinsically low X-ray luminosity clusters at z>> 0, with Hubble Space Telescope (HST) WFPC2 imaging and spectroscopy from Calar Alto and WHT-LDSS2. We study 172 confirmed cluster members in a sample of ten clusters at 0.23 < z < 0.3, with LX<~ 4 × 1043h-2 erg s-1[0.1-2.4 keV] (Ωm= 0.3, Λ= 0.7). The core of each cluster is imaged with WFPC2 in the F702W filter, and the spectroscopic sample is statistically complete to Mr~-19.0 + 5 log h, within an 11 arcmin (~1.8 h-1 Mpc) field. The clusters are dynamically well-separated from the surrounding field and most have velocity distributions consistent with Gaussians. The velocity dispersions range from ~350-850 km s-1, consistent with the local LX-σ correlation. All 10 clusters host a bright, giant elliptical galaxy without emission lines, near the centre of the X-ray emission. We measure the equivalent width of two nebular emission lines, [OII] and Hα, and the Hδ absorption line to classify the cluster members spectrally. Galaxy morphologies are measured from the HST images, using the two-dimensional surface-brightness fitting software GIM2D. Emission-line galaxies in these clusters are relatively rare, comprising only 22 +/- 4 per cent of the sample. There is no evidence that these emission-line galaxies are dynamically distinct from the majority of the cluster population, though our sample is too small to rule out the ~30 per cent difference that has been observed in more massive clusters. We find 11 galaxies, comprising 6 per cent of the cluster members, that are disc-dominated but show no sign of emission in their spectrum. Most of these are relatively isolated, spiral galaxies with smooth discs. We find no cluster members with a starburst or post-starburst spectrum. The striking similarity between the spectral and morphological properties of galaxies in these clusters and those of galaxies in more massive systems at similar redshifts implies that the physical

    10. Conventional and stuffed Bergman-type phases in the Na-Au-T (T = Ga, Ge, Sn) systems: syntheses, structures, coloring of cluster centers, and Fermi sphere-brillouin zone interactions.

      PubMed

      Lin, Qisheng; Smetana, Volodymyr; Miller, Gordon J; Corbett, John D

      2012-08-20

      Bergman-type phases in the Na-Au-T (T = Ga, Ge, and Sn) systems were synthesized by solid-state means and structurally characterized by single-crystal X-ray diffraction studies. Two structurally related (1/1) Bergman phases were found in the Na-Au-Ga system: (a) a conventional Bergman-type (CB) structure, Na(26)Au(x)Ga(54-x), which features empty innermost icosahedra, as refined with x = 18.1 (3), Im3, a = 14.512(2) Å, and Z = 2; (b) a stuffed Bergman-type (SB) structure, Na(26)Au(y)Ga(55-y), which contains Ga-centered innermost icosahedra, as refined with y = 36.0 (1), Im3, a = 14.597(2) Å, and Z = 2. Although these two subtypes have considerable phase widths along with respective tie lines at Na ≈ 32.5 and 32.1 atom %, they do not merge into a continuous solid solution. Rather, a quasicrystalline phase close to the Au-poor CB phase and an orthorhombic derivative near the Au-rich SB phase lie between them. In contrast, only Au-rich SB phases exist in the Ge and Sn systems, in which the innermost icosahedra are centered by Au rather than Ge or Sn. These were refined for Na(26)Au(40.93(5))Ge(14.07(5)) (Im3, a = 14.581(2) Å, and Z = 2) and Na(26)Au(39.83(6))Sn(15.17(6)) (Im3, a = 15.009(2) Å, and Z = 2), respectively. Occupations of the centers of Bergman clusters are rare. Such centering and coloring correlate with the sizes of the neighboring icosahedra, the size ratios between electropositive and electronegative components, and the values of the average valence electron count per atom (e/a). Theoretical calculations revealed that all of these phases are Hume-Rothery phases, with evident pseudogaps in the density of states curves that arise from the interactions between Fermi surface and Brillouin zone boundaries corresponding to a strong diffraction intensity.

    11. A combined experimental and computational study of AuPd nanoparticles

      NASA Astrophysics Data System (ADS)

      Bruma, Alina

      The thesis is focused on the investigation of structural properties of AuPd nanoparticles via theoretical and experimental studies. For the first system, the 98-atom AuPd nanoclusters, a theoretical analysis has been employed to study the energetics and segregation effects and to assess how typical is the Leary Tetrahedron (LT). Although this motif is the most stable at the empirical level, it loses stability at the DFT level against FCC or Marks Decahedron. The second system is the Au24Pd1 nanoclusters. Theoretically, by performing a search at the DFT level using Basin Hopping Monte Carlo, we identified pyramidal cage structures as putative global minima, where Pd sits in the core and Au occupies surface positions. The Lowdin analysis emphasized charge transfer between Pd and Au, explaining the enhanced catalytic activity with respect to Au25 clusters. Experimentally, STEM has been employed for the structural characterization of Au24Pd1 clusters supported on Multiwall Carbon Nanotubes. Whenever possible, we have tried to link the experimental analysis to the theoretical findings. The third system has been the evaporated AuPd nanoparticles. We observed that the annealing process led to the formation of L12 ordered phases as well as layered and core-shell structures. This study aimed to bring an insight on the segregation and energetics effects of AuPd nanoparticles with potential applications in nanocatalysis.

    12. Fe-DOPED Ga12N12 CLUSTERS: ELECTRONIC AND MAGNETIC PROPERTIES

      NASA Astrophysics Data System (ADS)

      Lu, Pengfei; Wu, Chengjie; Cong, Zixiang; Li, Yiluan; Zhang, Xianlong; Yu, Zhongyuan; Cao, Huawei

      2013-12-01

      In this paper, we have investigated the structural, electronic and magnetic properties of Ga12N12 cluster doped with monodoped and bidoped Fe atoms within the density functional theory (DFT). Substitutional, exohedral and endohedral doping are considered. It is observed that both monodoped and bidoped clusters tend to be in exohedral doping. Mulliken population analysis is performed to obtain the charge transfer and magnetic moment. The magnetic moment is mainly derived from 3d orbitals of Fe atom for all isomers, while the magnetic properties would rely on the Fe-Fe distance.

    13. Dynamic and static properties of the invaded cluster algorithm

      NASA Astrophysics Data System (ADS)

      Moriarty, K.; Machta, J.; Chayes, L. Y.

      1999-02-01

      Simulations of the two-dimensional Ising and three-state Potts models at their critical points are performed using the invaded cluster (IC) algorithm. It is argued that observables measured on a sublattice of size l should exhibit a crossover to Swendsen-Wang (SW) behavior for l sufficiently less than the lattice size L, and a scaling form is proposed to describe the crossover phenomenon. It is found that the energy autocorrelation time τɛ(l,L) for an l×l sublattice attains a maximum in the crossover region, and a dynamic exponent zIC for the IC algorithm is defined according to τɛ,max~LzIC. Simulation results for the three-state model yield zIC=0.346+/-0.002, which is smaller than values of the dynamic exponent found for the SW and Wolff algorithms and also less than the Li-Sokal bound. The results are less conclusive for the Ising model, but it appears that zIC<0.21 and possibly that τɛ,max~ln L so that zIC=0-similar to previous results for the SW and Wolff algorithms.

    14. Anisotropic physical properties and pressure dependent magnetic ordering of CrAuTe4

      DOE PAGES

      Jo, Na Hyun; Kaluarachchi, Udhara S.; Wu, Yun; ...

      2016-11-11

      Systematic measurements of temperature-dependent magnetization, resistivity, and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as well as resistivity under pressures up to 5.25 GPa were conducted on single crystals of CrAuTe4. Magnetization data suggest that magnetic moments are aligned antiferromagnetically along the crystallographic c axis below TN = 255 K. ARPES measurements show band reconstruction due to the magnetic ordering. Magnetoresistance data show clear anisotropy, and, at high fields, quantum oscillations. The Néel temperature decreases monotonically under pressure, decreasing to TN = 236 K at 5.22 GPa. The pressure dependencies of (i) TN, (ii) the residual resistivity ratio, and (iii)more » the size and power-law behavior of the low-temperature magnetoresistance all show anomalies near 2 GPa suggesting that there may be a phase transition (structural, magnetic, and/or electronic) induced by pressure. Lastly, for pressures higher than 2 GPa a significantly different quantum oscillation frequency emerges, consistent with a pressure induced change in the electronic states.« less

    15. Electronic properties and STM images of vacancy clusters and chains in functionalized silicene and germanene

      NASA Astrophysics Data System (ADS)

      Jamdagni, Pooja; Kumar, Ashok; Sharma, Munish; Thakur, Anil; Ahluwalia, P. K.

      2017-01-01

      Electronic properties and STM topographical images of X (=F, H, O) functionalized silicene and germanene have been investigated by introducing various kind of vacancy clusters and chain patterns in monolayers within density functional theory (DFT) framework. The relative ease of formation of vacancy clusters and chain patterns is found to be energetically most favorable in hydrogenated silicene and germanene. F- and H-functionalized silicene and germanene are direct bandgap semiconducting with bandgap ranging between 0.1-1.9 eV, while O-functionalized monolayers are metallic in nature. By introducing various vacancy clusters and chain patterns in both silicene and germanene, the electronic and magnetic properties get modified in significant manner e.g. F- and H-functionalized silicene and germanene with hexagonal and rectangle vacancy clusters are non-magnetic semiconductors with modified bandgap values while pentagonal and triangle vacancy clusters induce metallicity and magnetic character in monolayers; hexagonal vacancy chain patterns induce direct-to-indirect gap transition while zigzag vacancy chain patterns retain direct bandgap nature of monolayers. Calculated STM topographical images show distinctly different characteristics for various type of vacancy clusters and chain patterns which may be used as electronic fingerprints to identify various vacancy patterns in silicene and germanene created during the process of functionalization.

    16. Theoretical study of physical and thermodynamic properties of AlnNm clusters*

      NASA Astrophysics Data System (ADS)

      Loukhovitski, Boris I.; Sharipov, Alexander S.; Starik, Alexander M.

      2016-11-01

      Geometrical structures and physical properties, such as collision diameter, rotational constants, characteristic vibrational temperatures, dipole moment, static isotropic polarizability, enthalpy of formation of various forms of AlnNm clusters with n = 0,...,5, m = 0,...,5, are analyzed with the usage of density functional theory. Different isomeric forms of these clusters with the isomerization energy up to 5 eV have been identified by using the original multistep heuristic algorithm that was based on semiempirical calculations, ab initio and density functional theory approaches and comprises the elements of genetic algorithms. Temperature dependencies of enthalpy, entropy and specific heat capacity have been calculated both for the individual isomers and for the Boltzmann ensemble of each class of clusters taking into account the anharmonicity of cluster vibrations and the contribution of excited electronic states of clusters. Novel criterion of the stability of isomeric forms, based on the maximal vibrational energy of the modes of cluster, has been proposed. The potentialities of the application of small AlnNm clusters as the components of energetic materials are also considered. Supplementary material in the form of one zip file available from the Journal web page at http://dx.doi.org/10.1140/epjd/e2016-70429-5

    17. Probing dynamic fluorescence properties of single and clustered quantum dots toward quantitative biomedical imaging of cells.

      PubMed

      Kang, Hyeong-Gon; Tokumasu, Fuyuki; Clarke, Matthew; Zhou, Zhenping; Tang, Jianyong; Nguyen, Tinh; Hwang, Jeeseong

      2010-01-01

      We present results on the dynamic fluorescence properties of bioconjugated nanocrystals or quantum dots (QDs) in different chemical and physical environments. A variety of QD samples was prepared and compared: isolated individual QDs, QD aggregates, and QDs conjugated to other nanoscale materials, such as single-wall carbon nanotubes (SWCNTs) and human erythrocyte plasma membrane proteins. We discuss plausible scenarios to explain the results obtained for the fluorescence characteristics of QDs in these samples, especially for the excitation time-dependent fluorescence emission from clustered QDs. We also qualitatively demonstrate enhanced fluorescence emission signals from clustered QDs and deduce that the band 3 membrane proteins in erythrocytes are clustered. This approach is promising for the development of QD-based quantitative molecular imaging techniques for biomedical studies involving biomolecule clustering.

    18. Nucleation-mediated synthesis and enhanced catalytic properties of Au-Pd bimetallic tripods and bipyramids with twinned structures and high-energy facets

      NASA Astrophysics Data System (ADS)

      Zhang, Lei; Chen, Qiaoli; Wang, Xue; Jiang, Zhiyuan

      2016-01-01

      The Au-Pd alloy has been proved to be an excellent catalyst in many applications, such as the electro-oxidation of formic acid, CO oxidation and oxidation of alcohols to aldehydes. However, most of the research has been focused on the shape-controlled Au-Pd alloy NCs with a single-crystal structure. Due to the existence of high-energy atoms on the twin defects, twinned structures usually will further increase their catalytic activities. It is necessary to develop a method to prepare the Au-Pd alloy with twinned structures and investigate their catalytic properties. Herein, we successfully synthesized Au-Pd alloy tripods and bipyramids with twinned structures by the cooperation of cetyltrimethyl ammonium chloride (CTAC) and cetyltrimethyl ammonium bromide (CTAB). The tripods contain one twin plane, while the bipyramids consist of a fivefold-twinned structure. In addition, the tripods and bipyramids are both exposed by high-energy facets. We proposed that the tripods and bipyramids are evolved from bipyramid seeds and fivefold twinned seeds, respectively. The as-prepared Au-Pd tripods and bipyramids performed better activity for electrocatalytic oxidation of formic acid compared to the cubic Au-Pd nanoparticles.The Au-Pd alloy has been proved to be an excellent catalyst in many applications, such as the electro-oxidation of formic acid, CO oxidation and oxidation of alcohols to aldehydes. However, most of the research has been focused on the shape-controlled Au-Pd alloy NCs with a single-crystal structure. Due to the existence of high-energy atoms on the twin defects, twinned structures usually will further increase their catalytic activities. It is necessary to develop a method to prepare the Au-Pd alloy with twinned structures and investigate their catalytic properties. Herein, we successfully synthesized Au-Pd alloy tripods and bipyramids with twinned structures by the cooperation of cetyltrimethyl ammonium chloride (CTAC) and cetyltrimethyl ammonium bromide (CTAB

    19. Pulsed laser deposition of two-dimensional ZnO nanocrystals on Au(111): growth, surface structure and electronic properties

      NASA Astrophysics Data System (ADS)

      Tumino, F.; Casari, C. S.; Passoni, M.; Bottani, C. E.; Li Bassi, A.

      2016-11-01

      Two-dimensional (2D) ZnO structures have been deposited on the Au(111) surface by means of the pulsed laser deposition technique. In situ scanning tunneling microscopy and scanning tunneling spectroscopy measurements have been performed to characterize morphological, structural and electronic properties of 2D ZnO at the nanoscale. Starting from a sub-monolayer coverage, we investigated the growth of ZnO, identifying different atomic layers (up to the fifth). At low coverage, we observed single- and bi-layer nanocrystals, characterized by a surface moiré pattern that is associated to a graphene-like ZnO structure. By increasing the coverage, we revealed a morphological change starting from the fourth layer, which was attributed to a transition toward a bulk-like structure. Investigation of the electronic properties revealed the semiconducting character of 2D ZnO. We observed a dependence of the density of states (DOS) and, in particular, of the conduction band (CB) on the ZnO thickness, with a decreasing of the CB onset energy for increasing thickness. The CB DOS of 2D ZnO shows a step-like behaviour which may be interpreted as due to a 2D quantum confinement effect in ZnO atomic layers.

    20. Photocatalytic and antibacterial properties of Au-TiO{sub 2} nanocomposite on monolayer graphene: From experiment to theory

      SciTech Connect

      He, Wangxiao; Huang, Hongen; Yan, Jin; Zhu, Jian

      2013-11-28

      The formation of the Au-TiO{sub 2} nanocomposite on monolayer Graphene (GTA) by sequentially depositing titanium dioxide particles and gold nanoparticles on graphene sheet was synthesized and analyzed in our work. The structural, morphological, and physicochemical properties of samples were thoroughly investigated by UV-Vis spectrophotometer, Raman spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscope, and transmission electron microscope. Photocatalytic performance of GTA, graphene (GR), TiO{sub 2,} and TiO{sub 2} -graphene nanocomposite (GT) were comparatively studied for degradation of methyl orange, and it was found that GTA had highest performance among all samples. More importantly, antibacterial performance of this novel composite against Gram-positive bacteria, Gram-negative bacteria, and fungus was predominant compared to GR, TiO{sub 2}, and GT. And the result of biomolecules oxidation tests suggested that antimicrobial actions were contributed by oxidation stress on both membrane and antioxidant systems. Besides, the rate of two decisive processes during photocatalytic reaction, the rate of the charge transfer (k{sub CT}) and the rate of the electron-hole recombination (k{sub R}) have been studied by Perturbation theory, Radiation theory, and Schottky barrier theory. Calculation and derivation results show that GTA possesses superior charge separation and transfer rate, which gives an explanation for the excellent oxidation properties of GTA.

    1. Photocatalytic and antibacterial properties of Au-TiO2 nanocomposite on monolayer graphene: From experiment to theory

      NASA Astrophysics Data System (ADS)

      He, Wangxiao; Huang, Hongen; Yan, Jin; Zhu, Jian

      2013-11-01

      The formation of the Au-TiO2 nanocomposite on monolayer Graphene (GTA) by sequentially depositing titanium dioxide particles and gold nanoparticles on graphene sheet was synthesized and analyzed in our work. The structural, morphological, and physicochemical properties of samples were thoroughly investigated by UV-Vis spectrophotometer, Raman spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscope, and transmission electron microscope. Photocatalytic performance of GTA, graphene (GR), TiO2, and TiO2 -graphene nanocomposite (GT) were comparatively studied for degradation of methyl orange, and it was found that GTA had highest performance among all samples. More importantly, antibacterial performance of this novel composite against Gram-positive bacteria, Gram-negative bacteria, and fungus was predominant compared to GR, TiO2, and GT. And the result of biomolecules oxidation tests suggested that antimicrobial actions were contributed by oxidation stress on both membrane and antioxidant systems. Besides, the rate of two decisive processes during photocatalytic reaction, the rate of the charge transfer (kCT) and the rate of the electron-hole recombination (kR) have been studied by Perturbation theory, Radiation theory, and Schottky barrier theory. Calculation and derivation results show that GTA possesses superior charge separation and transfer rate, which gives an explanation for the excellent oxidation properties of GTA.

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

      NASA Astrophysics Data System (ADS)

      Mahtout, Sofiane; Tariket, Yacine

      2016-06-01

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

    3. Insight of dipole surface plasmon mediated optoelectronic property tuning of ZnO thin films using Au

      NASA Astrophysics Data System (ADS)

      Dixit, Tejendra; Shukla, Mayoorika; Palani, I. A.; Singh, Vipul

      2016-12-01

      Surface plasmon mediated photoluminescence (PL) studies of ZnO, ZnO/Au, ZnO/Au/ZnO and Au/ZnO films have been investigated. An enhancement of UV and visible light emission has been observed in ZnO/Au and ZnO/Au/ZnO films, compared to that of ZnO thin films, while for Au/ZnO films quenching of PL intensity was observed. Excitation intensity (EI) dependent PL spectra have shown dominance of horizontal dipole surface plasmon mode for ZnO/Au/ZnO, ZnO/Au samples, which led enhanced greenish-yellow and orange emissions respectively. Moreover, confocal laser scanning microscope measurements and diffuse reflectance spectroscopy were conducted to investigate the mechanism behind the variations and involvement of Urbach tail. UV and visible region absorption were selectively enhanced by varying the Au and ZnO configuration and can be assigned to the interaction of the dipole surface plasmon resonance with localized trapping levels and phonon subsystem. The excellent photoluminescence performance has immense potential for ZnO thin film based optoelectronic devices.

    4. Blue Stragglers in Clusters and Integrated Spectral Properties of Stellar Populations

      NASA Astrophysics Data System (ADS)

      Xin, Yu; Deng, Licai

      Blue straggler stars are the most prominent bright objects in the colour-magnitude diagram of a star cluster that challenges the theory of stellar evolution. Star clusters are the closest counterparts of the theoretical concept of simple stellar populations (SSPs) in the Universe. SSPs are widely used as the basic building blocks to interpret stellar contents in galaxies. The concept of an SSP is a group of coeval stars which follows a given distribution in mass, and has the same chemical property and age. In practice, SSPs are more conveniently made by the latest stellar evolutionary models of single stars. In reality, however, stars can be more complicated than just single either at birth time or during the course of evolution in a typical environment. Observations of star clusters show that there are always exotic objects which do not follow the predictions of standard theory of stellar evolution. Blue straggler stars (BSSs), as discussed intensively in this book both observationally and theoretically, are very important in our context when considering the integrated spectral properties of a cluster, or a simple stellar population. In this chapter, we are going to describe how important the contribution of BSSs is to the total light of a cluster.

    5. Laser Desorption Ionization Quadrupole Ion Trap Time-of-Flight Mass Spectrometry of Au m Fe n +/- Clusters Generated from Gold-Iron Nanoparticles and their Giant Nanoflowers. Electrochemical and/or Plasma Assisted Synthesis

      NASA Astrophysics Data System (ADS)

      Mawale, Ravi Madhukar; Ausekar, Mayuri Vilas; Pavliňák, David; Galmiz, Oleksandr; Kubáček, Pavel; Havel, Josef

      2017-02-01

      Gold nanoparticles (NP) with average diameter 100 nm synthesized from tetrachloroauric acid solution using stainless steel as a reducing agent were found to contain iron. Applying simultaneously high frequency (HF) plasma discharge in solution during the electrochemical reduction, giant gold-iron nanoflowers with average size 1000-5000 nm were formed. Scanning electron microscopy (SEM) shows the morphology of the nanopowders produced as polygonal yet nearly spherical, whereas iron content in both products determined by energy dispersive X-ray analysis (EDX) was found to be at 2.5 at. %. Laser desorption ionization (LDI) of both nanomaterials and mass spectrometric analysis show the formation of Au m Fe n +/- ( m = 1-35; n = 1-3) clusters. Structure of few selected clusters in neutral or monocharged forms were computed by density functional theory (DFT) calculations and it was found that typical distances of an iron nucleus from adjacent gold nuclei lie in the interval 2.5 to 2.7 Å. Synthetized Au-Fe nanoparticles were found stable for at least 2 mo at room temperature (even in aqueous solution) without any stabilizing agent. Produced Au-Fe nanoparticles in combination with standard MALDI matrices enhance ionization of peptides and might find use in nanomedicine.

    6. NMR properties of hydrogen-bonded glycine cluster in gas phase

      NASA Astrophysics Data System (ADS)

      Carvalho, Jorge R.; da Silva, Arnaldo Machado; Ghosh, Angsula; Chaudhuri, Puspitapallab

      2016-11-01

      Density Functional Theory (DFT) calculations have been performed to study the effect of the hydrogen bond formation on the Nuclear Magnetic Resonance (NMR) parameters of hydrogen-bonded clusters of glycine molecules in gas-phase. DFT predicted isotropic chemical shifts of H, C, N and O of the isolated glycine with respect to standard reference materials are in reasonable agreement with available experimental data. The variations of isotropic and anisotropic chemical shifts for all atoms constituting these clusters containing up to four glycine molecules have been investigated systematically employing gradient corrected hybrid B3LYP functional with three different types of extended basis sets. The clusters are mainly stabilized by a network of strong hydrogen bonds among the carboxylic (COOH) groups of glycine monomers. The formation of hydrogen bond influences the molecular structure of the clusters significantly which, on the other hand, gets reflected in the variations of NMR properties. The carbon (C) atom of the sbnd COOH group, the bridging hydrogen (H) and the proton-donor oxygen (O) atom of the Osbnd H bond suffer downfield shift due to the formation of hydrogen bond. The hydrogen bond lengths and the structural complexity of the clusters are found to vary with the number of participating monomers. A direct correlation between the hydrogen bond length and isotropic chemical shift of the bridging hydrogen is observed in all cases. The individual variations of the principal axis elements in chemical shift tensor provide additional insight about the different nature of the monomers within the cluster.

    7. Structural and magnetic properties of Ti12M clusters (M=Sc to Zn)

      NASA Astrophysics Data System (ADS)

      Sun, Houqian; Xu, Ning

      2016-12-01

      The geometries, electronic, and magnetic properties of the 3d atom doped icosahedron (ICO) Ti12M (M=Sc to Zn), where a dopant atom replaces either the centra l(Ti12Mc) or surface (Ti12Ms) Ti atom in ICO Ti13 cluster, have been systematically investigated by using the density functional theory. The structures of all the optimized Ti12Mc and Ti12Ms clusters are distorted ICO. Sc, Ni, Cu, and Zn atoms prefer to displace surface Ti atom, V, Cr, Mn, and Fe atoms prefer to displace central Ti atom. The position of impurity atom depends on the strength of the interaction between the central atom and the surface atoms. As compared to the pure Ti13 cluster, Ti12Mc and Ti12Ms (M=V, Fe, Co, and Ni) clusters are more stable, Ti12Mc and Ti12Ms (M=Sc, Cr, Mn, Cu, and Zn) are less stable. Both Ti12Nis and Ti12Nic are magic clusters, which originate from their electronic as well as geometric closed shells. Because the exchange interaction prevails over the crystal field in Ti12M clusters, the valence electrons fill molecular orbitals in terms of Hund's rule of maximum spin.

    8. Synthesis and optical power limiting properties of heteroleptic Mo3S7 clusters.

      PubMed

      Recatalá, David; Llusar, Rosa; Barlow, Adam; Wang, Genmiao; Samoc, Marek; Humphrey, Mark G; Guschin, Artem L

      2015-08-07

      Substitution of the halide ligands in (Bu4N)2[Mo3S7X6] (X = Cl, Br) by diimine ligands, such as 4,4'-dimethyl-2,2'-bipyridine (dmbpy), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen), affords the neutral heteroleptic clusters Mo3S7Cl4(dmbpy) (), Mo3S7Br4(dmbpy) (), Mo3S7Br4(bpy) (), and Mo3S7Br4(phen) (). Further substitution of the halide ligands in Mo3S7Br4(diimine) clusters by dmit (1,3-dithiole-2-thione-4,5-dithiolate) allows the preparation of the mixed diimine-dithiolene neutral cluster complexes Mo3S7(dnbpy)(dmit)2 (, dnbpy = 4,4'-dinonyl-2,2'-bipyridine), Mo3S7(dcmbpy)(dmit)2 (, dcmbpy = 4,4'-dimethoxycarbonyl-2,2'-bipyridine), and Mo3S7(dcbpy)(dmit)2 (, dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid). The optical limiting properties of complexes have been assessed by the open-aperture Z-scan technique at 570 nm, employing a nanosecond optical parametric oscillator. In order to investigate the effect of increasing the π-system, complexes , with the general formula Mo3S7X4(diimine), (X = Cl, Br), were compared to clusters , containing the dmit ligand. The influence of the metal content on the optical power limiting properties was also investigated by comparing the trinuclear series of complexes prepared herein with the bis(dithiolene) dinuclear cluster (Et4N)2[Mo2O2S2(BPyDTS2)2], which has been recently prepared by our group. All trinuclear clusters are efficient optical limiters (σeff > σ0) with the threshold limiting fluence F15% decreasing on proceeding from dinuclear to trinuclear clusters and, generally, on extending the π-system.

    9. New Insights into the Au(I)···Pb(II) Closed-Shell Interaction: Tuning of the Emissive Properties with the Intermetallic Distance.

      PubMed

      Echeverría, Raquel; López-de-Luzuriaga, José M; Monge, Miguel; Moreno, Sonia; Olmos, M Elena

      2016-10-05

      Reaction of [Au2Ag2R4(Et2O)2] (R = C6Cl2F3(-) or C6F5(-)) with [Pb{HB(pz)3}]Cl in a 1:2 molar ratio led to complexes [AuPb{HB(pz)3}R2] (R = C6Cl2F3(-) (2) or C6F5(-) (3)) through transmetalation reactions. The crystal structures of these complexes display unsupported Au(I)···Pb(II) interactions of 3.0954(4) (2) and 3.2778(4) (3) Å, together with one (2) or two (3) F···Pb weak contacts. These intermetallic distances are compared to the shortest one found for the previously reported complex [Pb{HB(pz)3}Au(C6Cl5)2] (1) of 3.0494(4) (1) Å, showing a clear dependence with the donating properties of the different aurate units. The complexes are emissive in the solid state due to charge transfer transitions associated with the presence of Au(I)···Pb(II) interactions, in which the intermetallic distance plays a crucial role. Density functional theory and time-dependent density functional theory calculations support the assignment of the luminescent properties of the complexes. Ab initio Hartree-Fock and MP2 calculations on model systems of complexes 2 and 3 show the presence of strong Au(I)···Pb(II) closed-shell interactions of an ionic plus dispersive nature together with weak F···Pb contacts of a dispersive origin in the case of complexes 2 and 3.

    10. Nonlinear Optical Properties of Au-Nanoparticles Conjugated with Lipoic Acid in Water

      NASA Astrophysics Data System (ADS)

      Trejo-Durán, M.; Cornejo-Monroy, D.; Alvarado-Méndez, E.; Olivares-Vargas, A.; Castano, V. M.

      2014-08-01

      Gold nanoparticles were chemically conjugated with lipoic acid to control their optical properties. Z-scan and other optical techniques were used to characterize the non-linear behavior of the resulting nanostructured materials. T