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Sample records for au cluster properties

  1. Structures, stabilities, and magnetic properties of the Fe n Au (n = 1-12) clusters

    NASA Astrophysics Data System (ADS)

    Jin, Lv; Jiang-Yan, Zhang; Rui-Rui, Liang; Hai-Shun, Wu

    2016-06-01

    The configurations, stabilities, electronic, and magnetic properties of Fe n Au (n = 1-12) clusters are investigated systematically by using the relativistic all-electron density functional theory with the generalized gradient approximation. The substitutional effects of Au in Fe n+1 (n = 1, 2, 4, 5, 10-12) clusters are found in optimized structures which keep the similar frameworks with the most stable Fe n+1 clusters. And the growth way for Fe n Au (n = 6-9) clusters is that the Au atom occupies a peripheral position of Fe n cluster. The peaks appear respectively at n = 6 and 9 for Fe n Au clusters and at n = 5 and 10 for Fe n+1 clusters based on the size dependence of second-order difference of energy, implying that these clusters possess relatively high stabilities. The analysis of atomic net charge Q indicates that the charge always transfers from Fe to Au atom which causes the Au atom to be nearly non-magnetic, and the doped Au atom has little effect on the average magnetic moment of Fe atoms in Fe n Au cluster. Finally, the total magnetic moment is reduced by 3 μB for each of Fe n Au clusters except n = 3, 11, and 12 compared with for corresponding pure Fe n +1 clusters. Project supported by the National Natural Science Foundation of China (Grant No. 21301112) and the Ph. D. Program Foundation of the Education Ministry of China (Grant No. 20131404120001).

  2. Optical properties of Au and Ag clusters, alloys, and cluster arrays

    NASA Astrophysics Data System (ADS)

    Wilcoxon, Jess; Martin, James

    2001-03-01

    The size-dependence of the optical absorbance of individual clusters of noble metals is one of the oldest problems in colloid science yet many issues still remain unresolved. Recent improvements in both chemical synthesis methods and novel separation approaches allow us to investigate issues such as the size dependence of the optical plasmon absorbance resonance and its damping (width) with great precision. In particular, the ability to size select, chemically purify, and identify sizes with 1-2 Å resolution over the size range from 1.2 to 10 nm using size exclusion chromatography has demonstrated a true intrinsic blue shift of the plasmon peak in Au but a red shift over a comparable size range in Ag. Extreme broadening of the plasmon peak was observed with decreasing size-molecular like features being observed in the smallest clusters. Using heterogeneous growth from monodisperse seed nanocrystals we have also synthesized core/shell particles of Au/Ag and Ag/Au. Alloys were also grown by co-reduction. The optical properties of these two classes of materials are strikingly different for identical composition and size. By spray drying purified nanocrystal solutions onto glass slides and other substrates we have formed 2-D hexagonally packed arrays and investigated the absorbance changes as these arrays are heated until sintering and formation of metallic films occurs. Metallic film formation accompanied by high conductivity and high reflectivity occurs at vastly reduced temperatures compared to bulk values.

  3. 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.

  4. Tuning magneto-transport properties of Fe-Au granular thin films by cluster organization

    NASA Astrophysics Data System (ADS)

    Stanciu, A. E.; Kuncser, A.; Schinteie, G.; Palade, P.; Leca, A.; Greculeasa, S. G.; Catrina, A.; Kuncser, V.

    2017-07-01

    A comparative study of morpho-structural, magnetic and magneto-transport properties of two Fe-Au granular films with different concentrations of Fe nanoclusters of almost similar size is reported. Different organizations of the Fe clusters, i.e. in lamellar-like or random-like configuration, were obtained by varying the amount of Fe in the Fe-Au films. The specific magnetic behaviour was investigated with respect to local structure and morpho-structural aspects by combining magneto-optic Kerr effect and superconducting quantum interference device magnetometry, 57Fe conversion electron Mössbauer spectroscopy and a wide range of electron microscopy techniques. A strong in-plane magnetic texture with uniaxial anisotropy was observed in the case of the lamellar-like organization of the clusters (specific to the Fe-Au film with higher Fe concentration) whereas a superparamagnetic behaviour was evidenced in the case of random distribution of the clusters (specific to the Fe-Au film with lower Fe concentration), despite the similar average size of the clusters in the two samples. Specific magnetoresistance effects were investigated with respect to both the involved magnetic configurations and magnetic interactions of the Fe clusters.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Geometric, electronic, and bonding properties of AuNM (N = 1-7, M = Ni, Pd, Pt) clusters.

    PubMed

    Yuan, D W; Wang, Yang; Zeng, Zhi

    2005-03-15

    Employing first-principles methods, based on density functional theory, we report the ground state geometric and electronic structures of gold clusters doped with platinum group atoms, Au(N)M (N = 1-7, M = Ni, Pd, Pt). The stability and electronic properties of Ni-doped gold clusters are similar to that of pure gold clusters with an enhancement of bond strength. Due to the strong d-d or s-d interplay between impurities and gold atoms originating in the relativistic effects and unique properties of dopant delocalized s-electrons in Pd- and Pt-doped gold clusters, the dopant atoms markedly change the geometric and electronic properties of gold clusters, and stronger bond energies are found in Pt-doped clusters. The Mulliken populations analysis of impurities and detailed decompositions of bond energies as well as a variety of density of states of the most stable dopant gold clusters are given to understand the different effects of individual dopant atom on bonding and electronic properties of dopant gold clusters. From the electronic properties of dopant gold clusters, the different chemical reactivity toward O(2), CO, or NO molecule is predicted in transition metal-doped gold clusters compared to pure gold clusters.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Geometries and electronic properties of Au nPd m ( n=1-4, m=-1, 0, 1) clusters

    NASA Astrophysics Data System (ADS)

    Wu, Z. J.; Zhou, S. H.; Shi, J. S.; Zhang, S. Y.

    2003-01-01

    Possible conformers for Au nPd m ( n=1-4, m=-1, 0, 1) clusters have been presented and studied by use of density functional theory. The results indicate that for n=2, linear conformer with C ∞v symmetry is the most stable for anion species, while for cation and neutral species, conformer with C 2v symmetry is the most stable. For n=3, 4, conformers with C 2v symmetry (kite-shape) are energetically favored. The calculated electron affinities (EAs) and vertical detachment energies (VDEs) are in good agreement with experiments for n=1-4. It is also interesting to note that for even n ( n=2, 4), the most stable conformers do not give the best agreement between calculated and experimental EA and VDE values, while for odd n ( n=3), the lowest energy conformer also gives the best agreement. The ionization potentials (IPs) of Au nPd clusters are calculated as well.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Characterization of Pt-Au and Ni-Au Clusters on TiO(2)(110)

    SciTech Connect

    Chen, D. A.; Mullins, David R; Ratliff, J. S.; He, Wei; Tenney, Samuel

    2011-01-01

    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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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).

  17. 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.

  18. 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

  19. A redox-switchable Au8-cluster sensor.

    PubMed

    Wu, Te-Haw; Hsu, Yu-Yen; Lin, Shu-Yi

    2012-07-09

    The proof of concept of a simple sensing platform based on the fluorescence of a gold cluster consisting of eight atoms, which is easily manipulated by reduction and oxidation of a specific molecule in the absence of chemical linkers, is demonstrated. Without using any coupling reagents to arrange the distance of the donor-acceptor pair, the fluorescence of the Au(8) -cluster is immediately switched off in the presence of 2-pyridinethiol (2-PyT) quencher. Through an upward-curving Stern-Volmer plot, the system shows complex fluorescence quenching with a combination of static and dynamic quenching processes. To analyze the static quenching constant (V) by a "sphere of action" model, the collisional encounter between the Au(8) -cluster and 2-PyT presents a quenching radius (r) ≈5.8 nm, which is larger than the sum of the radii of the Au(8) -cluster and 2-PyT. This implies that fluorescence quenching can occur even though the Au(8) -cluster and 2-PyT are not very close to each other. The quenching pathway may be derived from a photoinduced electron-transfer process of the encounter pair between the Au(8) -cluster (as an electron donor) and 2-PyT (as an electron acceptor) to allow efficient fluorescence quenching in the absence of coupling reagents. Interestingly, the fluorescence is restored by oxidation of 2-PyT to form the corresponding disulfide compound and then quenched again after the reduction of the disulfide. This redox-switchable fluorescent Au(8) -cluster platform is a novel discovery, and its utility as a promising sensor for detecting H(2) O(2) -generating enzymatic transformations is demonstrated. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. [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.

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. Atomistic simulation of finite-temperature magnetism of nanoparticles: Application to cobalt clusters on Au(111)

    NASA Astrophysics Data System (ADS)

    Lászlóffy, A.; Udvardi, L.; Szunyogh, L.

    2017-05-01

    We developed a technique to determine suitable spin models for small embedded clusters of arbitrary geometry by combining the spin-cluster expansion with the relativistic disordered local moment scheme. We present results for uncovered and covered hexagonal Co clusters on Au(111) surface, and use classical Monte Carlo simulations to study the temperature dependent properties of the systems. To test the new method we compare the calculated spin-model parameters of the uncovered clusters with those of a Co monolayer deposited on Au(111). In general, the isotropic and Dzyaloshinsky-Moriya interactions are larger between atoms at the perimeter than at the center of the clusters. For Co clusters covered by Au, both the contribution to the magnetic anisotropy and the easy axis direction of the perimeter atoms differ from those of the inner atoms due to reduced symmetry. We investigate the spin reversals of the covered clusters with perpendicular magnetic anisotropy and based on the variance of the magnetization component parallel to the easy direction we suggest a technique to determine the blocking temperature of superparamagnetic particles. We also determine the Néel relaxation time from the Monte Carlo simulations and find that it satisfies the Néel-Arrhenius law with an energy barrier close to the magnetic anisotropy energy of the clusters.

  7. 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.

  8. Binding of Trivalent Arsenic onto the Tetrahedral Au20 and Au19Pt Clusters: Implications in Adsorption and Sensing.

    PubMed

    Cortés-Arriagada, Diego; Oyarzún, María Paz; Sanhueza, Luis; Toro-Labbé, Alejandro

    2015-07-02

    The interaction of arsenic(III) onto the tetrahedral Au20 cluster was studied computationally to get insights into the interaction of arsenic traces (presented in polluted waters) onto embedded electrodes with gold nanostructures. Pollutant interactions onto the vertex, edge, or inner gold atoms of Au20 were observed to have a covalent character by forming metal-arsenic or metal-oxygen bonding, with adsorption energies ranging from 0.5 to 0.8 eV, even with a stable physisorption; however, in aqueous media, the Au-vertex-pollutant interaction was found to be disadvantageous. The substituent effect of a platinum atom onto the Au20 cluster was evaluated to get insights into the changes in the adsorption and electronic properties of the adsorbent-adsorbate systems due to chemical doping. It was found that the dopant atom increases both the metal-pollutant adsorption energy and stability onto the support in a water media for all interaction modes; adsorption energies were found to be in a range of 0.6 to 1.8 eV. All interactions were determined to be accompanied by electron transfer as well as changes in the local reactivity that determine the amount of transferred charge and a decrease in the HOMO-LUMO energy gap with respect to the isolated substrate.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Computational study of AuSi{sub n} (n=1-9) nanoalloy clusters invoking DFT based descriptors

    SciTech Connect

    Ranjan, Prabhat; Kumar, Ajay; Chakraborty, Tanmoy E-mail: tanmoychem@gmail.com

    2016-04-13

    Nanoalloy clusters formed between Au and Si are topics of great interest today from both scientific and technological point of view. Due to its remarkable catalytic, electronic, mechanical and magnetic properties Au-Si nanoalloy clusters have extensive applications in the field of microelectronics, catalysis, biomedicine, and jewelry industry. Density Functional Theory (DFT) is a new paradigm of quantum mechanics, which is very much popular to study the electronic properties of materials. Conceptual DFT based descriptors have been invoked to correlate the experimental properties of nanoalloy clusters. In this venture, we have systematically investigated AuSi{sub n} (n=1-9) nanoalloy clusters in the theoretical frame of the B3LYP exchange correlation. The experimental properties of AuSi{sub n} (n=1-9) nanoalloy clusters are correlated in terms of DFT based descriptors viz. HOMO-LUMO gap, Electronegativity (χ), Global Hardness (η), Global Softness (S) and Electrophilicity Index (ω). The calculated HOMO-LUMO gap exhibits interesting odd-even alteration behaviour, indicating that even numbered clusters possess higher stability as compare to their neighbour odd numbered clusters. This study also reflects a very well agreement between experimental bond length and computed data.

  15. BSA-stabilized Au clusters as peroxidase mimetics for use in xanthine detection.

    PubMed

    Wang, Xian-Xiang; Wu, Qi; Shan, Zhi; Huang, Qian-Ming

    2011-04-15

    In this paper, we demonstrated that bovine serum albumin (BSA) stabilized Au clusters exhibited highly intrinsic peroxidase-like activity. Unlike nature enzymes, the BSA-Au clusters have strong robustness and can be used over a wide range of pH and temperature. Because of ultra-small size, good stability and high biocompatibility in water solution compare with other kinds of nanoparticles as peroxidase mimetics, such as Fe(3)O(4), FeS or graphene oxide, it is more competent for bioanalysis. Furthermore, we make use of the novel properties of BSA-Au clusters as peroxidase mimetics to detect H(2)O(2). The as-prepared BSA-Au clusters were used to catalyze the oxidation of a peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) by H(2)O(2) to the oxidized colored product, and which provides a colorimetric detection of H(2)O(2). As low as 2.0 × 10(-8)M H(2)O(2) could be detected with a linear range from 5.0 × 10(-7) to 2.0 × 10(-5)M via this method. More importantly, a sensitive and selective method for xanthine detection was developed using xanthine oxidase (XOD) and the as-prepared BSA-Au clusters. The detection limit of this assay for xanthine was 5 × 10(-7)M and the proposed method was successfully applied for the determination of xanthine in urine and human serum sample. Copyright © 2011 Elsevier B.V. All rights reserved.

  16. Stable structures and potential energy surface of the metallic clusters: Ni, Cu, Ag, Au, Pd, and Pt

    NASA Astrophysics Data System (ADS)

    Wu, Xia; Sun, Yan

    2017-06-01

    Metallic clusters have been widely studied due to their special electrical, optical, and catalytic properties. The many-body Gupta potential is applied to describe the interatomic interaction of Ni, Cu, Ag, Au, Pd, and Pt clusters, and their global minimal structures within 100 atoms are optimized using dynamic lattice searching (DLS) method. The configurational distribution of global minima is analyzed, and the geometrical difference among these clusters is demonstrated. Results show that the dominant motif of Ni and Cu clusters is the icosahedron, and in Ag and Au clusters the number of decahedra is slightly larger than that of the icosahedra. However, more face-centered cubic (fcc), stacking fault fcc, and amorphous structures are formed in Au clusters than in Ag clusters. Furthermore, the main motif of Pd and Pt clusters is the decahedron. In particular, Ni98 adopts a Leary tetrahedral motif, and Pt54 is a central vacant icosahedron. The difference related to the potential parameters of these metallic clusters is further investigated by energy analysis. Moreover, the potential energy surfaces (PES) of 38-atom metallic clusters is characterized in terms of conformational analysis. It was found that the sequence of the number of local minima on the PES from large to low is Ni, Cu, Ag, Pt, Pd, and Au.

  17. Effect of reducible oxide-metal cluster charge transfer on the structure and reactivity of adsorbed Au and Pt atoms and clusters on anatase TiO2

    NASA Astrophysics Data System (ADS)

    Wang, Honghong; An, Taicheng; Selloni, Annabella

    2017-05-01

    We carried out density functional theory calculations to study the influence of oxide-metal charge transfers on the structure, energetics, and reactivity of Au and Pt atoms, dimers, and trimers adsorbed on the (101) surface of reduced anatase TiO2. Pt clusters interact much more strongly with the TiO2 support than Au clusters, and, with the exception of single Pt adatoms, generally behave as electron acceptors on reduced TiO2, whereas Au clusters can both accept and donate charge on the reduced surface. The reactivity of the supported clusters was probed by considering their interaction with CO and co-adsorbed O2. The effect of surface reduction on the interaction with CO is particularly significant when the CO adsorption site is an interfacial metal atom directly in contact with the TiO2 surface and/or in the presence of co-adsorbed O2. Pt clusters interact strongly with co-adsorbed O2 and form Pt-O2 complexes that can easily accept electrons from reduced surfaces. In contrast, Au clusters donate charge to co-adsorbed O2 even in the presence of excess electrons from a reduced support. The computed differences in the properties of the supported Pt and Au clusters are consistent with several experimental observations and highlight the important role of excess surface electrons in the behavior of supported metal catalysts on reducible oxides.

  18. 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.

  19. 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.

  20. 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).

  1. 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

  2. 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.

  3. 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.

  4. 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.

  • 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

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • Photoelectron imaging and theoretical calculations of gold-silver hydrides: comparing the characteristics of Au, Ag and H in small clusters.

    PubMed

    Xie, Hua; Xing, Xiaopeng; Liu, Zhiling; Cong, Ran; Qin, Zhengbo; Wu, Xia; Tang, Zichao; Fan, Hongjun

    2012-09-07

    Structures and electronic properties of the mixed metal hydride anions AuAgH(-), Au(2)AgH(-), AuAg(2)H(-) and their neutrals are studied using anionic photoelectron imaging and theoretical calculations. The three isomers of AuAgH(-) are determined to be linear and those of AuAgH are determined to have C(s) symmetry. The structures of Au(2)AgH(-), AuAg(2)H(-) and their corresponding neutrals are determined to be planar with C(s) or C(2v) symmetries. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) of these anions are reported. Similar to the homonuclear Au(m)(-) and Ag(n)(-) clusters, the metal hydride anions with an even number of valence electrons have higher VDEs than those with an odd number. Variation of the VDEs of these metal hydride anions with interchange of Au, Ag and H (for example Au(m)Ag(n)(-)→ Au(m-1)Ag(n+ 1)(-), or Au(m-1)Ag(n)H(-)) will be shown to be characterized by the electronegativities of Au, Ag and H. The results presented in this study provide important insights into the similar and different characteristics of these three elements in small clusters.

  • Mixed protein-templated luminescent metal clusters (Au and Pt) for H2O2 sensing

    NASA Astrophysics Data System (ADS)

    Li, Min; Yang, Da-Peng; Wang, Xiansong; Lu, Jianxin; Cui, Daxiang

    2013-04-01

    A simple and cost-effective method to synthesize the luminescent noble metal clusters (Au and Pt) in chicken egg white aqueous solution at room temperature is reported. The red-emitting Au cluster is used as fluorescent probe for sensitive detection of H2O2.

  • 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.

  • Preparation and characterization of keratin and chicken egg white-templated luminescent Au cluster composite film

    NASA Astrophysics Data System (ADS)

    Xing, Yao; Liu, Hongling; Yu, Weidong

    2016-02-01

    The characterization of keratin-chicken egg white-templated luminescent Au cluster composite films were studied using fourier-transform infrared spectroscopy (FTIR) to demonstrate and quantify the secondary transformation of composite films. The results showed that the secondary structure of treated films was transformed from disordered structure to ordered conformation including α-helix conformation and β-pleated-sheet conformation due to the increase of protein-templated luminescent Au cluster. The absorption features of treated films were exhibited by the UV-vis spectra. The bule-shift and decreased intensity indicated the change of microenvironment due to the concentration of protein-templated luminescent Au cluster. The transmission electron microscopy images of composite films supported the aggregation resulting from microenvironment. The effect of protein-templated luminescent Au cluster was characterized by the laser scanning confocal microscope (LSCM) images which showed the gradually intensive luminescence with increasing Au cluster and the transformation from the whiskers to nanoparticle.

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

    NASA Astrophysics Data System (ADS)

    Gao, Yang; Liu, Xizhe; Wang, Zhigang

    2017-07-01

    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 1 S 21 P 61 D 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 1 F superatomic orbitals mainly originate from the contribution of the 4 f-shell. As a consequence, this work provides a theoretical basis for the future design and synthesis of f-elements-encapsulated gold nanoclusters.

  • 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.

  • Role of metal contacts in the mechanical properties of molecular nanojunctions: Comparative ab initio study of Au/1,8-octanedithiol and Au/4,4-bipyridine

    NASA Astrophysics Data System (ADS)

    Vélez, P.; Dassie, S. A.; Leiva, E. P. M.

    2010-06-01

    A comparative study of the mechanical properties of Au/4,4' -bipyridine ( 4,4' BPD) and Au/1,8-octanedithiol (1,8 ODT) molecular nanojunctions is developed using different metal wires and small clusters to represent the metal contact. Rupture of the junction at different bonds is analyzed. While in the case of 1,8 ODT, rupture at Au-Au bonds is always found; in the case of 4,4' BPD, rupture of a N-Au bond also appears as possible. Comparison of rupture forces, maximum elongations and force constants with the experimental values lead to the conclusion that the most common geometrical arrangement in scanning tunneling microscopy break junctions should be that where the number of Au atoms is of the order of 4. Activation energies for the rupture of these structures are calculated at sample elongations.

  • 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

  • From superatomic Au25(SR)18(-) to superatomic M@Au24(SR)18(q) core-shell clusters.

    PubMed

    Jiang, De-en; Dai, Sheng

    2009-04-06

    Au(25)(SR)(18)(-) belongs to a new type of superatom that features an icosahedral Au(13) core-shell structure and a protective layer of six RS(Au-SR)(2) motifs. This superatom has a magic number of 8 free electrons that fully fill the 1s and 1p levels of the electron-shell model. By applying this superatom concept to the core-substitution chemistry of Au(25)(SR)(18)(-), we first scanned the periodic table for the potential core atom M by applying a simple rule derived from the 8-electron count and then optimized the selected candidates by density functional theory calculations to create many series of M@Au(24)(SR)(18)(q) core-shell nanoclusters. We found that 16 elements from groups 1, 2, and 10-14 of the periodic table can maintain both electronic and geometric structures of the original Au(25)(SR)(18)(-) magic cluster, indicating that the electron-counting rule based on the superatom concept is powerful in predicting viable M@Au(24)(SR)(18)(q) clusters. Our work opens up a promising area for experimental exploration.

  • From Superatomic Au25(SR)18- to Superatomic M@Au24(SR)18q Core-shell Clusters.

    SciTech Connect

    Jiang, Deen; Dai, Sheng

    2009-01-01

    Au{sub 25}(SR){sub 18}{sup -} belongs to a new type of superatom that features an icosahedral Au{sub 13} core-shell structure and a protective layer of six RS(Au-SR){sub 2} motifs. This superatom has a magic number of 8 free electrons that fully fill the 1s and 1p levels of the electron-shell model. By applying this superatom concept to the core-substitution chemistry of Au{sub 25}(SR){sub 18}{sup -}, we first scanned the periodic table for the potential core atom M by applying a simple rule derived from the 8-electron count and then optimized the selected candidates by density functional theory calculations to create many series of M{at}Au{sub 24}(SR){sub 18}{sup q} core-shell nanoclusters. We found that 16 elements from groups 1, 2, and 10-14 of the periodic table can maintain both electronic and geometric structures of the original Au{sub 25}(SR){sub 18}{sup -} magic cluster, indicating that the electron-counting rule based on the superatom concept is powerful in predicting viable M{at}Au{sub 24}(SR){sub 18}{sup q} clusters. Our work opens up a promising area for experimental exploration.

    1. 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.

    2. 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.

    3. Efficient red luminescence from organic-soluble Au25 clusters by ligand structure modification

      NASA Astrophysics Data System (ADS)

      Mathew, Ammu; Varghese, Elizabeth; Choudhury, Susobhan; Pal, Samir Kumar; Pradeep, T.

      2015-08-01

      An efficient method to enhance visible luminescence in a visibly non-luminescent organic-soluble 4-(tert butyl)benzyl mercaptan (SBB)-stabilized Au25 cluster has been developed. This method relies mainly on enhancing the surface charge density on the cluster by creating an additional shell of thiolate on the cluster surface, which enhances visible luminescence. The viability of this method has been demonstrated by imparting red luminescence to various ligand-protected quantum clusters (QCs), observable to the naked eye. The bright red luminescent material derived from Au25SBB18 clusters was characterized using UV-vis and luminescence spectroscopy, TEM, SEM/EDS, XPS, TG, ESI and MALDI mass spectrometry, which collectively proposed an uncommon molecular formula of Au29SBB24S, suggested to be due to different stapler motifs protecting the Au25 core. The critical role of temperature on the emergence of luminescence in QCs has been studied. The restoration of the surface ligand shell on the Au25 cluster and subsequent physicochemical modification to the cluster were probed by various mass spectral and spectroscopic techniques. Our results provide fundamental insights into the ligand characteristics determining luminescence in QCs.An efficient method to enhance visible luminescence in a visibly non-luminescent organic-soluble 4-(tert butyl)benzyl mercaptan (SBB)-stabilized Au25 cluster has been developed. This method relies mainly on enhancing the surface charge density on the cluster by creating an additional shell of thiolate on the cluster surface, which enhances visible luminescence. The viability of this method has been demonstrated by imparting red luminescence to various ligand-protected quantum clusters (QCs), observable to the naked eye. The bright red luminescent material derived from Au25SBB18 clusters was characterized using UV-vis and luminescence spectroscopy, TEM, SEM/EDS, XPS, TG, ESI and MALDI mass spectrometry, which collectively proposed an uncommon

    4. 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.

    5. 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.

    6. 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.

    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. 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.

    9. Interaction of energetic clusters (Au 3, Au 400 and C 60) with organic material and adsorbed gold nanoparticles

      NASA Astrophysics Data System (ADS)

      Restrepo, Oscar A.; Prabhakaran, Aneesh; Delcorte, Arnaud

      2011-07-01

      Using molecular dynamics simulations (MD), this contribution compares the interaction of three energetic clusters (Au3, Au400 and C60) with a hybrid surface of crystalline polyethylene (PE) covered by a layer of gold nanoparticles. This model system mimics the situation encountered in metal-assisted secondary ion mass spectrometry. The chosen impact points are representative of the PE surface, the metal particles and the frontier between the metal and the polymer. The simulations show the differences between the impact over the Au nanoparticle and the polymer surface, in terms of projectile penetration, crater formation and sputtering yield of PE and gold species. For C60 and Au3 projectiles, a simple correlation is found between the quantity of energy deposited in the top polymeric layers and the quantity of sputtered polymer material, including all the impact points. The results obtained with Au400 do not fit on this line, indicating that other physical parameters are prevalent. The mechanistic view of the interaction provided by the MD helps explain the differences. In short, while C60 and Au3 quickly break apart, creating energetic recoils and severing many bonds in the surface, Au400, with the largest total momentum by far (∼10 times larger than the others) and the lowest energy per atom (25 eV), tends to act and implant in the solid as a single entity, pushing the polymeric material downwards and breaking few bonds in the surface.

    10. 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).

    11. 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.

    12. 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.

    13. Effective Dielectric Properties of Au-ZnS and Au-ZnO Plasmonics Nanocomposites in the Terahertz Regime

      NASA Astrophysics Data System (ADS)

      Zolanvar, A.; Sadeghi, H.; Ranjgar, A.

      2014-10-01

      Composite materials based on plasmonic nanoparticles allow building metamaterials with very large effective permittivity (positive or negative). Moreover, if clustered or combined with other nanoparticles, it is also possible to generate effective magnetic permeability (positive or negative), and an ad-hoc design would result in the generation of double negative materials, and therefore backward wave propagation. In this work, the optical properties such as the effective permittivity, permeability and refractive index of Au-ZnS and Au-ZnO nanocomposites in a broad frequency range are studied. The enhancement is attributed to energy transfer from ZnS or ZnO to Au followed by a large local electromagnetic field on or near the surface of the Au nanoparticles. Local surface plasmon resonance could be the key reason for this enhancement. The surface plasmon, in response to changes in the refractive index of the local environment, also depends on the type of metal through the bulk plasma wavelength and the nano-particle compositions and geometry.

    14. Thermodynamic and structural properties of liquid Al-Au alloys

      NASA Astrophysics Data System (ADS)

      Olajire, B. A.; Musari, A. A.

      2017-08-01

      The mixing properties of liquid Al-Au alloys with respect to the concentration of each constituent is determined using a method based on hard sphere system and pseudo-potential perturbation. These models were used to get relevant information on mixing properties of the Al-Au alloys like the Gibbs energy and the entropy of mixing. The concentration fluctuations, chemical short range order for the hard sphere mixture (quasi-lattice theory) and the activity are calculated to know the extent of order in the liquid alloys. The results revealed that there is a degree of ordering in liquid Al-Au alloy (hetero-coordinated).

    15. Structural and optical properties of the naked and passivated Al5Au5 bimetallic nanoclusters

      NASA Astrophysics Data System (ADS)

      Grande-Aztatzi, Rafael; Formoso, Elena; Mercero, Jose M.; Matxain, Jon M.; Grabowski, Slawomir J.; Ugalde, Jesus M.

      2016-03-01

      The structural and optical properties of both the naked and passivated bimetallic Al5Au5 nanoclusters have been analyzed based on data obtained from ab initio density functional theory and quantum molecular dynamics simulations. It has been found that the Al5Au5 nanocluster possesses a hollow shaped minimum energy structure with segregated Al and Au layered domains, the former representing the electrophilic domain and the latter the nucleophilic domain. In particular, it has been shown that alkali metal cations attach in the nucleophilic domain and hop from one Au site to the next one in the picoseconds time scale, while anions are bound tightly to the Al atoms of the electrophilic domain. Simulating annealing studies are very suggestive of the proneness of the nanocluster towards coalescence into large cluster units, when the cluster is left unprotected by appropriate ligands. Further passivation studies with NaF salt suggest, nonetheless, the possibility of the isolation of the Al5Au5 cluster in molten salts or ionic liquids.

    16. Synthesis and Characterization of a Series of Triethylphosphine-Ligated Pt-Au Cluster Compounds. X-ray Crystal and Molecular Structure of [Pt(AuPEt(3))(9)](NO(3))(3).

      PubMed

      Krogstad, Don A.; Konze, Wayde V.; Pignolet, Louis H.

      1996-11-06

      explained by consideration of the steric and electronic properties of the PEt(3) ligand. These new compounds will be useful as models for hydrogen activation by Pt-Au clusters and as precursors for supported Pt-Au catalysts.

    17. 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

    18. Large scale structural optimization of trimetallic Cu-Au-Pt clusters up to 147 atoms

      NASA Astrophysics Data System (ADS)

      Wu, Genhua; Sun, Yan; Wu, Xia; Chen, Run; Wang, Yan

      2017-10-01

      The stable structures of Cu-Au-Pt clusters up to 147 atoms are optimized by using an improved adaptive immune optimization algorithm (AIOA-IC method), in which several motifs, such as decahedron, icosahedron, face centered cubic, sixfold pancake, and Leary tetrahedron, are randomly selected as the inner cores of the starting structures. The structures of Cu8AunPt30-n (n = 1-29), Cu8AunPt47-n (n = 1-46), and partial 75-, 79-, 100-, and 147-atom clusters are analyzed. Cu12Au93Pt42 cluster has onion-like Mackay icosahedral motif. The segregation phenomena of Cu, Au and Pt in clusters are explained by the atomic radius, surface energy, and cohesive energy.

    19. 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.

    20. 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

    1. 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.

    2. 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.

    3. Study of the nucleation and growth of antibiotic labeled Au NPs and blue luminescent Au8 quantum clusters for Hg(2+) ion sensing, cellular imaging and antibacterial applications.

      PubMed

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

      2015-12-21

      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 Hg(2+) 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 Hg(2+) 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

    4. 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.

    5. 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.

    6. Electronic properties of [core+exo]-type gold clusters: factors affecting the unique optical transitions.

      PubMed

      Shichibu, Yukatsu; Konishi, Katsuaki

      2013-06-03

      Unusual visible absorption properties of [core+exo]-type Au6 (1), Au8 (2), and Au11 (3) clusters were studied from experimental and theoretical aspects, based on previously determined crystal structures. Unlike conventional core-only clusters having no exo gold atoms, these nonspherical clusters all showed an isolated visible absorption band in solution. Density functional theory (DFT) studies on corresponding nonphenyl models (1'-3') revealed that they had similar electronic structures with discrete highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) bands. The theoretical spectra generated by time-dependent DFT (TD-DFT) calculations agreed well with the experimentally measured properties of 1-3, allowing assignment of the characteristic visible bands to HOMO-LUMO transitions. The calculated HOMO-LUMO transition energies increased in the order Au11 < Au6 < Au8, as was found experimentally. Frontier orbital analyses indicated that the HOMO and LUMO were both found in proximity to the terminal Au3 triangles containing the exo gold atom, with the HOMO → LUMO transition occurring in the core → exo direction. The HOMO/LUMO distribution patterns of 1' and 3' were similar to each other but were markedly different from that of 2', which has longer core-to-exo distances. These findings showed that not only nuclearity (size) but also geometric structures have profound effects on electronic properties and optical transitions of the [core+exo]-type clusters.

    7. 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.

    8. Au13(8e): A secondary block for describing a special group of liganded gold clusters containing icosahedral Au13 motifs

      NASA Astrophysics Data System (ADS)

      Xu, Wen Wu; Zeng, Xiao Cheng; Gao, Yi

      2017-05-01

      A grand unified model (GUM) has been proposed recently to understand structure anatomy and evolution of liganded gold clusters. In this work, besides the two types of elementary blocks (triangular Au3(2e) and tetrahedral Au4(2e)), we introduce a secondary block, namely, the icosahedral Au13 with 8e valence electrons, noted as Au13(8e). Using this secondary block, structural anatomy and evolution of a special group of liganded gold nanoclusters containing icosahedral Au13 motifs can be conveniently analyzed. In addition, a new ligand-protected cluster Au49(PR3)10(SR)15Cl2 is predicted to exhibit high chemical and thermal stability, suggesting likelihood of its synthesis in the laboratory.

    9. Water-soluble phosphine-protected Au9 clusters: Electronic structures and nuclearity conversion via phase transfer

      NASA Astrophysics Data System (ADS)

      Yao, Hiroshi; Tsubota, Shuhei

      2017-08-01

      In this article, isolation, exploration of electronic structures, and nuclearity conversion of water-soluble triphenylphosphine monosulfonate (TPPS)-protected nonagold (Au9) clusters are outlined. The Au9 clusters are obtained by the reduction of solutions containing TPPS and HAuCl4 and subsequent electrophoretic fractionation. Mass spectrometry and elemental analysis reveal the formation of [Au9(TPPS)8]5- nonagold cluster. UV-vis absorption and magnetic circular dichroism (MCD) spectra of aqueous [Au9(TPPS)8]5- are quite similar to those of [Au9(PPh3)8]3+ in organic solvent, so the solution-phase structures are likely similar for both systems. Simultaneous deconvolution analysis of absorption and MCD spectra demonstrates the presence of some weak electronic transitions that are essentially unresolved in the UV-vis absorption. Quantum chemical calculations for a model compound [Au9(pH3)8]3+ show that the possible (solution-phase) skeletal structure of the nonagold cluster has D2h core symmetry rather than C4-symmetrical centered crown conformation, which is known as the crystal form of the Au9 compound. Moreover, we find a new nuclearity conversion route from Au9 to Au8; that is, phase transfer of aqueous [Au9(TPPS)8]5- into chloroform using tetraoctylammonium bromide yields [Au8(TPPS)8]6- clusters in the absence of excess phosphine.

    10. 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.

    11. 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.

    12. 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.

    13. 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.

    14. Excited state interactions between the chiral Au38L24 cluster and covalently attached porphyrin.

      PubMed

      Varnholt, Birte; Letrun, Romain; Bergkamp, Jesse J; Fu, Yongchun; Yushchenko, Oleksandr; Decurtins, Silvio; Vauthey, Eric; Liu, Shi-Xia; Bürgi, Thomas

      2015-06-14

      A protected S-acetylthio porphyrin was synthesized and attached to the Au38(2-phenylethanethiolate)24 cluster in a ligand exchange reaction. Chiral high performance liquid chromatography of the functionalized cluster yielded enantiomeric pairs of clusters probably differing in the binding site of the porphyrin. As proven by circular dichroism, the chirality was maintained. Exciton coupling between the cluster and the chromophore is observed. Zinc can be incorporated into the porphyrin attached to the cluster, as evidenced by absorption and fluorescence spectroscopy, however, the reaction is slow. Quenching of the chromophore fluorescence is observed, which can be explained by energy transfer from the porphyrin to the cluster. Transient absorption spectra of Au38(2-phenylethanethiolate)24 and the functionalized cluster probe the bleach of the gold cluster due to ground state absorption and the characteristic excited state absorption signals. Zinc incorporation does not have a pronounced effect on the photophysical behaviour. Decay times are typical for the molecular behaviour of small monolayer protected gold clusters.

    15. 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.

    16. 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.

    17. 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

    18. 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.

    19. 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.

    20. 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.

    1. 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.

    2. 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.

    3. K(23)Au(12)Sn(9)--an intermetallic compound containing a large gold-tin cluster: synthesis, structure, and bonding.

      PubMed

      Li, Bin; Kim, Sung-Jin; Miller, Gordon J; Corbett, John D

      2010-02-15

      A polyanionic unit {Au(12)Sn(9)} with a novel "corrugated sheet" shape occurs in K(23)Au(12)Sn(9). The compound was obtained by fusion of the pure elements in tantalum ampules at high temperatures followed by programmed cooling, and the structure was determined by X-ray diffraction: I42m (No. 121), a = 20.834(3), c = 6.818(1) A, Z = 2. The large heteroatomic cluster has D(2d) point symmetry and features a central four bonded (4b-) Sn, eight 3b- or 2b-Sn on the perimeter, and 24 linking nearly linear Sn-Au bonds at 12 Au atoms. Formula splitting according to the Zintl concept suggests that the compound is one electron deficient, and linear muffin-tin-orbital (LMTO) electronic structure calculations show that the Fermi level (E(F)) lies near a band gap at around 0.5 eV, that is, an incompletely filled valence band in concert with favorable atom packing. Large relative -ICOHP values for Au-Sn are consistent with the observed maximization of the number of heteroatomic bonds, whereas the numerous K-Sn and K-Au contacts contribute approximately 40 % of the total -ICOHP. Extended-Huckel population and molecular orbital analyses indicate that the open band feature originates from 5p states that are associated with the 2b-corner Sn atoms. In accord with the electronic structure calculations, magnetic susceptibility measurements show a nearly temperature-independent paramagnetic property.

    4. 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.

    5. 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

    6. 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

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

      SciTech Connect

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

      2016-05-23

      We present electronic properties of atomic layer of Au, Au{sub 2}-N, Au{sub 2}-O and Au{sub 2}-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 4G{sub 0}. Similarly, Au{sub 2}-N and Au{sub 2}-F monolayers show 4G{sub 0} and 2G{sub 0} quantum conductance respectively while semiconducting nature with calculated band gap of 0.28 eV has been observed for Au{sub 2}-O monolayer. Most interestingly, half metalicity has been predicted for Au{sub 2}-N and Au{sub 2}-F monolayers. Our findings may have importance for the application of these monolayers in nanoelectronic and spintronics.

    8. 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.

    9. Molecular dynamics study of bimetallic nanoparticles: the case of Au xCu y alloy clusters

      NASA Astrophysics Data System (ADS)

      Rodríguez-López, J. L.; Montejano-Carrizales, J. M.; José-Yacamán, M.

      2003-10-01

      Gold and copper nanoparticles present atomic structures which are either icosahedral (I h), decahedral (D h) or octahedral (O h), depending of the particle size. Some experimental results had previously reported the stabilization of the I h phase in AuCu and AuFe clusters, being this phase predominant at 25% copper concentration in both systems. Another result reports an fcc-like and core/shell structure under similar experimental conditions and/or similar systems. In the present work, we study the possible phase conformations and thermal behavior of AuCu binary clusters using classical molecular dynamics simulations with a Sutton and Chen inter-atomic potential, addressing under which conditions the different phases mentioned above take place. To discern between the structures of bimetallic systems, the following main factors are determinant: the cluster size N, the concentration and nature of the elements in the alloy, and the annealing temperature. We choose the particles in our study closed to the sizes reported experimentally, with the cubo-octahedral symmetry as starting point. We have changed the concentration of copper from 50 to 10%, simulating an annealing process around the temperature of 750 K. We have found optimum stability of the icosahedral phase at concentrations of copper around 75 and 25% in fair agreement with experimental reports, and a trend to adopt a quasi-spherical shape with a core/shell structure at high temperatures in the cluster, just before the melting temperature.

    10. Energetics of small clusters of group IB metals (Cu, Ag, and Au) adsorbed on graphene

      NASA Astrophysics Data System (ADS)

      Kaur, Gagandeep; Gupta, Shuchi; Dharamvir, Keya

      2013-06-01

      The 2D structure of graphene maximizes the interaction of adsorbate on the layer. Many experiments have been devised to form stable metallic clusters of different sizes. We study the structure and binding energies of group IB clusters Mn (M=Au, Ag, Cu n=1, 3) adsorbed on graphene using Gupta potential [1] (for M-M interaction) and Lennard-Jones potential [2] (for metal-carbon interaction). The total energy of the system has been obtained by placing each of Mn cluster a certain distance above the graphene sheet at various positions and in various orientations. The minimized energy configurations, for all Mn clusters, lie above the center of a hexagon and parallel to the graphene sheet. Binding energy per atom for Ag and Cu metal clusters are less than those of respective Au indicating the lower stability of Ag/Cu metal-graphene system. Using various energy barriers, we can calculate the energy required to move small cluster from one position of minimum energy to another on graphene.

    11. 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.

    12. 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.

    13. 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.

    14. 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.

    15. 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.

    16. The synthesis and electrical transport of ligand-protected Au13 clusters

      NASA Astrophysics Data System (ADS)

      Wei, Zhongxia; Jiang, Wanrun; Bai, Zhanbin; Lian, Zhen; Wang, Zhigang; Song, Fengqi

      2017-09-01

      The ligand-protected Au13 clusters have been synthesized by using meso-2,3-dimercaptosuccinic acid as the reducing and stabilizing agent. Transmission electron microscopic analysis shows a size distribution of 1.4 ± 0.6 nm. Optical spectrum shows an absorbance peak at 390 nm. The electrical transport measurement devices are fabricated using the electro-migration method. Coulomb blockade is observed at the temperature of 1.6 K, revealing the formation of the tunneling junction. The Coulomb oscillation's on/off ratio is nearly 5. Three peaks are extracted in the dI/ dV data and attributed to the energy levels of Au13 clusters, gapped by about 60 meV. First principle calculations are carried out to interpret the energy diagram.

    17. 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.

    18. 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.

    19. 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.

    20. Crystal chemistry and spectroscopic properties of ScAuSn, YAuSn, and LuAuSn

      NASA Astrophysics Data System (ADS)

      Sebastian, C. Peter; Eckert, Hellmut; Rayaprol, Sudhindra; Hoffmann, Rolf-Dieter; Pöttgen, Rainer

      2006-05-01

      The stannides ScAuSn, YAuSn, and LuAuSn were synthesized as single phase materials from the elements via arc-melting. All samples were characterized by X-ray diffraction on powders and single crystals: MgAgAs type, F4¯3m, a=641.94(12) pm, wR2=0.035, 85 F values, 5 variables for ScAuSn, a=656.52(8) pm, wR2=0.029, 89 F values, 5 variables for LuAuSn, and NdPtSb type, P6mc, a=463.55(16), c=737.26(15) pm, wR2=0.057, 233 F values, 11 variables for YAuSn. The gold and tin atoms in ScAuSn and LuAuSn build up three-dimensional [AuSn] networks of corner-sharing AuSn 4/4 tetrahedra (278 and 284 pm Au sbnd Sn in ScAuSn and LuAuSn, respectively) similar to the blende type structure. The scandium atoms fill octahedral voids formed by the tin substructure. In contrast, the [AuSn] network of YAuSn is two-dimensional. The gold and tin atoms build up layers of puckered [Au 3Sn 3] hexagons with intralayer Au sbnd Sn distances of 277 pm, while the interlayer Au sbnd Sn distances of 297 pm are much longer. In every other layer the [Au 3Sn 3] hexagons are rotated by 60°. The layers are separated by the yttrium atoms. Spectroscopic measurements indicate significant differences in the chemical bonding properties: As revealed by both 119Sn Mössbauer spectroscopy and 119Sn solid-state NMR data, the local electronic environment at the tin site is more anisotropic in YAuSn as compared to the other materials, which feature tin on a site with cubic point symmetry. In ScAuSn, the cubic site symmetry of the scandium position is reflected by a single sharp line in the 45Sc solid-state NMR spectrum.

    1. 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.

    2. Hollow Au-Ag Alloy Nanorices and Their Optical Properties.

      PubMed

      Yu, Keke; Sun, Xiaonan; Pan, Liang; Liu, Ting; Liu, Anping; Chen, Guo; Huang, Yingzhou

      2017-09-04

      Hollow noble metal nanoparticles have excellent performance not only in surface catalysis but also in optics. In this work, the hollow Au-Ag alloy nanorices are fabricated by the galvanic replacement reaction. The dark-field spectrum points out that there is a big difference in the optical properties between the pure Ag nanorices and the hollow alloy nanorices that exhibit highly tunable localized surface plasmon resonances (LSPR) and that possess larger radiative damping, which is also indicated by the finite element method. Furthermore, the surface enhanced Raman scattering (SERS) and oxidation test indicate that hollow Au-Ag alloy nanorices show good anti-oxidation and have broad application prospects in surface-plasmon-related fields.

    3. Dependence of cluster ranges on target cohesive energy: Molecular-dynamics study of energetic Au 402 cluster impacts

      NASA Astrophysics Data System (ADS)

      Anders, Christian; Urbassek, Herbert M.

      2008-01-01

      It has long been known that the stopping and ranges of atoms and clusters depends on the projectile-target atom mass ratio. Recently, Carroll et al. [S.J. Carroll, P.D. Nellist, R.E. Palmer, S. Hobday, R. Smith, Phys. Rev. Lett. 84 (2000) 2654] proposed that the stopping of clusters also depends on the cohesive energy of the target. We investigate this dependence using a series of molecular-dynamics simulations, in which we systematically change the target cohesive energy, while keeping all other parameters fixed. We focus on the specific case of Au 402 cluster impact on van-der-Waals bonded targets. As target, we employ Lennard-Jones materials based on the parameters of Ar, but for which we vary the cohesive energy artificially up to a factor of 20. We show that for small impact energies, E0 ≲ 100 eV/atom, the range D depends on the target cohesive energy U, D ∝ U- β. The exponent β increases with decreasing projectile energy and assumes values up to β = 0.25 for E0 = 10 eV/atom. For higher impact energies, the cluster range becomes independent of the target cohesive energy. These results have their origin in the so-called 'clearing-the way' effect of the heavy Au 402 cluster; this effect is strongly reduced for E0 ≳ 100 eV/atom when projectile fragmentation sets in, and the fragments are stopped independently of each other. These results are relevant for studies of cluster stopping and ranges in soft matter.

    4. 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

    5. 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.

    6. Kinetic Investigation of Homogeneous H(2)-D(2) Equilibration Catalyzed by Pt-Au Cluster Compounds. Characterization of the Cluster [(H)Pt(AuPPh(3))(9)](NO(3))(2).

      PubMed

      Rubinstein, Leon I.; Pignolet, Louis H.

      1996-11-06

      The new Pt-Au hydrido cluster compound [(H)Pt(AuPPh(3))(9)](NO(3))(2) (3) has been synthesized and characterized by NMR, FABMS, and single-crystal X-ray diffraction [triclinic, P&onemacr;, a = 17.0452(1) Å, b = 17.4045(2) Å, c = 55.2353(1) Å, alpha = 89.891(1) degrees, beta = 85.287(1) degrees, gamma = 75.173(1) degrees, V = 15784.0(2) Å(3), Z = 4 (two molecules in asymmetric unit), residual R = 0.089 for 45 929 observed reflections and 3367 variables, Mo Kalpha radiation]. The Pt(AuP)(9) core geometry is a distorted icosahedron with three vertices vacant. The Pt-Au, Au-Au, and Au-P distances are within the normal ranges observed in other Pt-Au clusters. This cluster is a catalyst for H(2)-D(2) equilibration in homogeneous solution phase and has been used in a general mechanistic study of this reaction catalyzed by Pt-Au clusters. We previously proposed that a key step in the mechanism for catalytic H(2)-D(2) equilibration is the dissociation of a PPh(3) ligand to give a cluster with an open Au site for bonding of H(2) or D(2). This was based on qualitative observations that PPh(3) inhibited the rate of HD production with [Pt(AuPPh(3))(8)](NO(3))(2) (1) as catalyst. In order to test this hypothesis, phosphine inhibition (on the rate of HD production) and phosphine ligand exchange kinetic experiments were carried out with [(H)(PPh(3))Pt(AuPPh(3))(7)](NO(3))(2) (2) and 3. In this paper we show that the rate constant for phosphine dissociation determined from the PPh(3) inhibition rate study of H(2)-D(2) equilibration with cluster 2 is nearly identical to the rate constant for dissociative phosphine ligand exchange. The slower rate for H(2)-D(2) equilibration observed with 3 compared with 2 (5.5 x 10(-3) vs 7.7 x 10(-2) turnover s(-1)) is explained by its smaller rate constant for phosphine dissociation (2.8 x 10(-5) vs 2.9 x 10(-4) s(-1)). The fact that clusters 2 and 3 show similar kinetic behaviors suggests that the PPh(3) dissociation step in the catalytic H(2

    7. 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

    8. 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.

    9. 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

    10. 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.

    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. 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.

    14. 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

    15. The chemical bond between Au(I) and the noble gases. Comparative study of NgAuF and NgAu+ (Ng = Ar, Kr, Xe) by density functional and coupled cluster methods.

      PubMed

      Belpassi, Leonardo; Infante, Ivan; Tarantelli, Francesco; Visscher, Lucas

      2008-01-23

      The nature of the chemical bond between gold and the noble gases in the simplest prototype of Au(I) complexes (NgAuF and NgAu+, where Ng = Ar, Kr, Xe), has been theoretically investigated by state of art all-electron fully relativistic DC-CCSD(T) and DFT calculations with extended basis sets. The main properties of the molecules, including dipole moments and polarizabilities, have been computed and a detailed study of the electron density changes upon formation of the Ng-Au bond has been made. The Ar-Au dissociation energy is found to be nearly the same in both Argon compounds. It almost doubles along the NgAuF series and nearly triples in the corresponding NgAu+ series. The formation of the Ng-Au(I) bonds is accompanied by a large and very complex charge redistribution pattern which not only affects the outer valence region but reaches deep into the core-electron region. The charge transfer from the noble gas to Au taking place in the NgAu+ systems is largely reduced in the fluorides but the Ng-Au chemical bond in the latter systems is found to be tighter near the equilibrium distance. The density difference analysis shows, for all three noble gases, a qualitatively identical nature of the Ng-Au bond, characterized by the pronounced charge accumulation in the middle of the Ng-Au internuclear region which is typical of a covalent bond. This bonding density accumulation is more pronounced in the fluorides, where the Au-F bond is found to become more ionic, while the overall density deformation is more evident and less localized in the NgAu+ systems. Accurate density difference maps and charge-transfer curves help explain very subtle features of the chemistry of Au(I), including its peculiar preference for tight linear bicordination.

    16. Au microstructure and the functional properties of Ni/Au finishes on ceramic IC packages

      SciTech Connect

      Winters, E.D.; Baxter, W.K.; Braski, D.N.; Watkins, T.R.

      1995-12-31

      Ni/Au plated finishes used on thick-film metallized multilayer ceramic packages for integrated circuits must meet functional requirements such as bondability, sealability, and solderability. Their ability to do so is dependent, among other things, on the ability of the Au deposit to inhibit the grain boundary diffusion and subsequent surface oxidation of Ni. In this study, the relation between functional performance, Ni diffusionr ate, and Au microstructure was examined. Extent of Ni diffusion during heating was determined by Auger electron spectroscopy for several electrolytic and electroless Ni/Au finishing processes. Results were correlated with differences in Au microstructures determined by SEM, atomic force microscopy, and XRD.

    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. 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.

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

      SciTech Connect

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

      2016-05-23

      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 4G{sub 0} to 2G{sub 0} suggesting its applications for the fabrications of organic sensor devices based on the Au atomic layers.

    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. Electronic and vibrational signatures of the Au102(p-MBA)44 cluster.

      PubMed

      Hulkko, Eero; Lopez-Acevedo, Olga; Koivisto, Jaakko; Levi-Kalisman, Yael; Kornberg, Roger D; Pettersson, Mika; Häkkinen, Hannu

      2011-03-23

      Optical absorption of a gold nanocluster of 102 Au atoms protected by 44 para-mercaptobenzoic acid (p-MBA) ligands is measured in the range of 0.05-6.2 eV (mid-IR to UV) by a combination of several techniques for purified samples in solid and solution phases. The results are compared to calculations for a model cluster Au(102)(SMe)(44) based on the time-dependent density functional theory in the linear-response regime and using the known structure of Au(102)(p-MBA)(44). The measured and calculated molar absorption coefficients in the NIR-vis region are comparable, within a factor of 2, in the absolute scale. Several characteristic features are observed in the absorption in the range of 1.5-3.5 eV. The onset of the electronic transitions in the mid-IR region is experimentally observed at 0.45 ± 0.05 eV which compares well with the lowest calculated transition at 0.55 eV. Vibrations in the ligand layer give rise to fingerprint IR features below the onset of low-energy metal-to-metal electronic transitions. Partial exchange of the p-MBA ligand to glutathione does not affect the onset of the electronic transitions, which indicates that the metal core of the cluster is not affected by the ligand exchange. The full spectroscopic characterization of the Au(102)(p-MBA)(44) reported here for the first time gives benchmarks for further studies of manipulation and functionalization of this nanocluster to various applications.

    2. A tray-shaped, Pd(II)-clipped Au₃ complex as a scaffold for the modular assembly of [3×n] Au ion clusters.

      PubMed

      Osuga, Takafumi; Murase, Takashi; Hoshino, Manabu; Fujita, Makoto

      2014-10-13

      A tray-shaped Pd(II)3Au(I)3 complex (1) is prepared from 3,5-bis(3-pyridyl)pyrazole by means of tricyclization with Au(I) followed by Pd(II) clipping. Tray 1 is an efficient scaffold for the modular assembly of [3×n] Au(I) clusters. Treatment of 1 with the Au(I)3 tricyclic guest 2 in H2O/CH3CN (7:3) or H2O results in the selective formation of a [3×2] cluster (1⋅2) or a [3×3] cluster (1⋅2⋅1), respectively. Upon subsequent addition of Ag(I) ions, these complexes are converted to an unprecedented Au3-Au3-Ag-Au3-Au3 metal ion cluster. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    3. Stability of the DMF-protected Au nanoclusters: photochemical, dispersion, and thermal properties.

      PubMed

      Kawasaki, Hideya; Yamamoto, Hiroko; Fujimori, Hiroaki; Arakawa, Ryuichi; Iwasaki, Yasuhiko; Inada, Mitsuru

      2010-04-20

      We have reported the synthesis of dimethylformamide (DMF)-protected gold nanoclusters using a surfactant-free DMF reduction method. DMF-protected gold nanoclusters (Au NCs) are obtained without the formation of gold nanoparticles and bulk metals as byproducts using a hot injection process for the homogeneous reduction. The as-prepared DMF-protected Au NCs were a mixture of various-sized Au NCs with a cluster number of less than 20 including at least Au(8) and Au(13). The photoluminescence emission from Au(8) and Au(13) was confirmed in the photoluminescence spectra. The Au NCs are stabilized with DMF molecules through the interaction of amide groups of DMF with Au NCs. DMF-protected Au NCs in solution were found to have high thermal stability, high dispersion stability in various solvents, and high photochemical stability. The DMF-protected Au NCs dispersed well for at least a month in various solvents such as water, acid (pH 2), alkali (pH 12) and 0.5 M NaCl aqueous solution, and methanol without further surface modification. The thermal stability of DMF-protected Au NCs was approximately 150 degrees C, which was comparable to that of thiolate-protected Au NCs. The photobleaching of Au NCs in water gradually occurred under UV light irradiation (356 nm, 1.3 mW/cm(2)) because of the photoinduced oxidation of Au NCs. After 8 h irradiation, the fluorescence intensity slowly decreased to approximately 50% of the maximum and to approximately 20% after 96 h under the present condition, compared to the photobleaching of CdSe semiconductor quantum dots. We also found that the fluorescence intensity remained to be about 30% of the maximum even in the presence of concentrated 30% H(2)O(2). These findings demonstrate that the photobleaching process under the UV irradiation is effectively suppressed for DMF-protected Au NCs.

    4. 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.

    5. 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.

    6. 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

    7. 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.

    8. Intense fluorescence of Au20

      NASA Astrophysics Data System (ADS)

      Yu, Chongqi; Harbich, Wolfgang; Sementa, Luca; Ghiringhelli, Luca; Aprá, Edoardo; Stener, Mauro; Fortunelli, Alessandro; Brune, Harald

      2017-08-01

      Ligand-protected Au clusters are non-bleaching fluorescence markers in bio- and medical applications. Here we show that their fluorescence can be an intrinsic property of the Au cluster itself. We find a very intense and sharp fluorescence peak located at λ =739.2 nm (1.68 eV) for Au20 clusters in a Ne matrix held at 6 K. The fluorescence reflects the Highest Occupied Molecular Orbital-Lowest Unoccupied Molecular Orbital (HOMO-LUMO) diabatic bandgap of the cluster. Au20 shows a very rich absorption fine structure reminiscent of well defined molecule-like quantum levels. These levels are resolved since Au20 has only one stable isomer (tetrahedral); therefore our sample is mono-disperse in cluster size and conformation. Density-functional theory (DFT) and time-dependent DFT calculations clarify the nature of optical absorption and predict both main absorption peaks and intrinsic fluorescence in fair agreement with experiment.

    9. 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.

    10. 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.

    11. Effect of Spin Multiplicity in O2 Adsorption and Dissociation on Small Bimetallic AuAg Clusters.

      PubMed

      García-Cruz, Raúl; Poulain, Enrique; Hernández-Pérez, Isaías; Reyes-Nava, Juan A; González-Torres, Julio C; Rubio-Ponce, A; Olvera-Neria, Oscar

      2017-08-17

      To dispose of atomic oxygen, it is necessary the O2 activation; however, an energy barrier must be overcome to break the O-O bond. This work presents theoretical calculations of the O2 adsorption and dissociation on small pure Aun and Agm and bimetallic AunAgm (n + m ≤ 6) clusters using the density functional theory (DFT) and the zeroth-order regular approximation (ZORA) to explicitly include scalar relativistic effects. The most stable AunAgm clusters contain a higher concentration of Au with Ag atoms located in the center of the cluster. The O2 adsorption energy on pure and bimetallic clusters and the ensuing geometries depend on the spin multiplicity of the system. For a doublet multiplicity, O2 is adsorbed in a bridge configuration, whereas for a triplet only one O-metal bond is formed. The charge transfer from metal toward O2 occupies the σ*O-O antibonding natural bond orbital, which weakens the oxygen bond. The Au3 ((2)A) cluster presents the lowest activation energy to dissociate O2, whereas the opposite applies to the AuAg ((3)A) system. In the O2 activation, bimetallic clusters are not as active as pure Aun clusters due to the charge donated by Ag atoms being shared between O2 and Au atoms.

    12. 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.

    13. Properties of Open Clusters Containing Blue Stragglers

      NASA Astrophysics Data System (ADS)

      Lee, Hyun-Uk; Chang, Heon-Young

      2017-06-01

      The presence of blue stragglers pose challenges to standard stellar evolution theory, in the sense that explaining their presence demands a complex interplay between stellar evolution and cluster dynamics. In the meantime, mass transfer in binary systems and stellar collisions are widely studied as a blue straggler formation channel. We explore properties of the Galactic open clusters where blue stragglers are found, in attempting to estimate the relative importance of these two favored processes, by comparing them with those resulting from open clusters in which blue stragglers are absent as of now. Unlike previous studies which require a sophisticated process in understanding the implication of the results, this approach is straightforward and has resulted in a supplementary supporting evidence for the current view on the blue straggler formation mechanism. Our main findings are as follows: (1) Open clusters in which blue stragglers are present have a broader distribution with respect to the Z-axis pointing towards the North Galactic Pole than those in which blue stragglers are absent. The probability that two distributions with respect to the Z-axis are drawn from the same distribution is 0.2%. (2) Average values of log_{10}(t) of the clusters with blue stragglers and those without blue stragglers are 8.58 ± 0.232 and 7.52 ± 0.285, respectively. (3) The clusters with blue stragglers tend to be relatively redder than the others, and are distributed broader in colors. (4) The clusters with blue stragglers are likely brighter than those without blue stragglers. (5) Finally, blue stragglers seem to form in condensed clusters rather than simply dense clusters. Hence, we conclude that mass transfer in binaries seems to be a relatively important physical mechanism of the generation of blue stragglers in open clusters, provided they are sufficiently old.

    14. Structural, electronic and mechanical properties of alloyed Au-Cu monolayer

      NASA Astrophysics Data System (ADS)

      Kapoor, Pooja; Sharma, Munish; Kumar, A.; Chandel, S. K.; Ahluwalia, P. K.

      2017-05-01

      We present a DFT based comparative study of structural, electronic and mechanical properties of Au-Cu alloyed monolayer with its pristine counterparts (Au, Cu monolayer). The value of lattice constant, binding energy and bond length of Au-Cu alloyed monolayer lies in between the values for pristine Au and Cu monolayer. An indirect band gap of 0.46 eV has been found for Au-Cu alloyed monolayer while its pristine counterparts are metallic. The band gap in alloyed Au-Cu monolayer can be further tuned with biaxial compression strain. These tunable properties of Au-Cu alloyed monolayer could have applications in nanoelectronics, sensors and nano-electromechanical systems (NEMS).

    15. 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.

    16. Magnetic properties of free metal clusters

      NASA Astrophysics Data System (ADS)

      Jiang, Wei

      In this dissertation, results of Stern-Gerlach type magnetic deflection experiments on Chromium, Iron, and Aluminum clusters consisting of ˜20-200 atoms are reported. These metal clusters were produced using a laser vaporization technique in helium, and their beams were formed using supersonic expansion into vacuum. Measurements of their magnetic deflections were conducted at temperature ranging from 50K to 250K and at various magnetic field strengths. Both Chromium and Iron clusters are found to behave in accordance with a superparamagnetic model and to have enhanced magnetism compared to their bulks. For Chromium clusters with N≥34, each cluster has at least two isomers with distinguishable magnetic moments at low temperatures. For Iron clusters with Tvib=55 K, some deviations from the superparamagnetic model were observed. Aluminum clusters with odd numbers of atoms exhibit paramagnetic properties at low temperatures, which are believed to be related to superconductivity. At temperatures as low as 55K, the predicted large diamagnetism of Al56 due to superconductivity was not observed, within our system's resolution.

    17. Electron emission from nanometer-size metallic clusters: Electronic states and structural stability of supported Au clusters

      SciTech Connect

      Lin, M.E.; Ramachandra, A.; Andres, R.P.; Reifenberger, R.

      1992-12-31

      Techniques developed to measure the thermodynamic and electronic properties of a single metallic cluster with nanometer-size dimensions are described. Using these techniques, experiments that resolve the quantized energy spectrum of electrons in a nanometer-size cluster of metallic atoms at room temperature have been performed. Studies on the stability of the electron emission current from an individual nanometer-size cluster supported on a tungsten tip have been performed to learn more about the intrinsic stability of these nanometer-size objects. The data show abrupt jumps between different emission states that are revisited as time progresses. This phenomenon is attributed to a rearrangement of the duster structure and/or orientation on the substrate and provides new evidence of multiple `isomeric` structures for small clusters of metallic atoms.

    18. A homoleptic, all-alkynyl-stabilized highly luminescent Au8Ag8 cluster with a single crystal X-ray structure.

      PubMed

      Zhang, Rui; Zhao, Chongyang; Li, Xiumin; Zhang, Zongyao; Ai, Xicheng; Chen, Hui; Cao, Rui

      2016-08-09

      A homoleptic, all-alkynyl-stabilized [Au8Ag8(ArC[triple bond, length as m-dash]C)16] (1, Ar = 3,5-di-tert-butylphenyl) cluster was synthesized and characterized with a single crystal X-ray structure. Reactions of 3,5-di-tert-butyl-phenylacetylene with Ag(i) and Au(i) gave [Ag(ArC[triple bond, length as m-dash]C)]n and Au(PPh3)(ArC[triple bond, length as m-dash]C), respectively, where both have unusually high solubility in nonpolar organic solvents. In addition to drastically increased solubility, the two bulky tert-butyl substituents on the phenyl ring can confine the metal core to a certain size by preventing infinite aggregation of d(10) metals. This feature makes the isolation of an all-alkynyl-stabilized Au-Ag cluster possible. Complex 1 is intensely luminescent with a very high quantum yield of 0.67 in solution at room temperature. Theoretical studies offered valuable insights into the intriguing photophysical properties, and revealed the significant role of metal-alkynyl bond interactions and enhanced molecular rigidity provided by tert-butyl groups.

    19. 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.

    20. 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.

    1. 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.

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

      DOE PAGES

      Qian, Linping; Wang, Zhen; Beletskiy, Evgeny V.; ...

      2017-03-28

      Here, 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 themore » 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.« less

    3. 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

    4. 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.

    5. 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

    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. 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

    8. 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.

    9. 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.

    10. 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.

    11. 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.

    12. 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.

    13. 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)

    14. 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).

    15. 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.

    16. 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.

    17. Spin-orbit effect into isomerization barrier of small gold Clusters. Oh ↔ D2h Fluxionality of the Au62+ cluster Investigated by relativistic methods

      NASA Astrophysics Data System (ADS)

      Muñoz-Castro, Alvaro; Paez-Hernandez, Dayan; Arratia-Perez, Ramiro

      2017-09-01

      The Oh-[Au6]2+ cluster exhibits an open-shell 1s21p2 which trend to a more stable D2h isomer in 31.5 kcal/mol, as observed in the experimental [Au6{P(C6H4Me-o)pH2}6] cluster. By taking into account the spin-orbit coupling (SOC) in Oh-[Au6]2+, a resulting 1s1/221p1/22 closed-shell superatomic configuration is obtained stabilizing such structure by about 14.7 kcal/mol, decreasing the isomerization barrier. Thus, the spin-orbit term favors the Oh ↔ D2h conformation rearrangement depicting a decrease in the calculated energy difference between both conformations, an interesting consequence which is not obtained in the hypothetical lighter counterparts.

    18. 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.

    19. 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.

    20. Study of the interaction between cisplatin and the Au18(SR)14 cluster: in search of an appropriate cisplatin carrier.

      PubMed

      Palacios-Álvarez, O; Tlahuice-Flores, A

      2017-10-11

      Cisplatin is a well known anti-cancer drug and considered as essential by the World Health Organization. However, cisplatin features side effects during medical treatments due to its lack of selectivity resulting in the indiscriminate death of cells including healthy cells. To solve this issue, it is mandatory to improve its delivery towards affected organs or tissues. The well known bio-compatibility of gold clusters encouraged us to study the interaction between cisplatin molecules and the Au18(SR)14 cluster (named Au18) and our DFT calculations have provided insight into this aspect. Calculated adsorption energy values of the cisplatinn/Au18 complexes are within the 0.5-3.6 eV range, which attests to their unique interaction. In addition, their calculated optical absorption (UV-vis) and circular dichroism (CD) spectra display distinct peaks in such a manner that UV/CD spectra can be used as fingerprints by experimentalists.

    1. A Multivariate Analysis of Galaxy Cluster Properties

      NASA Astrophysics Data System (ADS)

      Ogle, P. M.; Djorgovski, S.

      1993-05-01

      We have assembled from the literature a data base on on 394 clusters of galaxies, with up to 16 parameters per cluster. They include optical and x-ray luminosities, x-ray temperatures, galaxy velocity dispersions, central galaxy and particle densities, optical and x-ray core radii and ellipticities, etc. In addition, derived quantities, such as the mass-to-light ratios and x-ray gas masses are included. Doubtful measurements have been identified, and deleted from the data base. Our goal is to explore the correlations between these parameters, and interpret them in the framework of our understanding of evolution of clusters and large-scale structure, such as the Gott-Rees scaling hierarchy. Among the simple, monovariate correlations we found, the most significant include those between the optical and x-ray luminosities, x-ray temperatures, cluster velocity dispersions, and central galaxy densities, in various mutual combinations. While some of these correlations have been discussed previously in the literature, generally smaller samples of objects have been used. We will also present the results of a multivariate statistical analysis of the data, including a principal component analysis (PCA). Such an approach has not been used previously for studies of cluster properties, even though it is much more powerful and complete than the simple monovariate techniques which are commonly employed. The observed correlations may lead to powerful constraints for theoretical models of formation and evolution of galaxy clusters. P.M.O. was supported by a Caltech graduate fellowship. S.D. acknowledges a partial support from the NASA contract NAS5-31348 and the NSF PYI award AST-9157412.

    2. Geometric and electronic properties of porphyrin molecules on Au(111) and NaCl surfaces

      NASA Astrophysics Data System (ADS)

      Kim, Seong Heon; Jeong, H. G.; Lim, S. J.; Ham, U. D.; Song, Y. J.; Yu, J.; Kuk, Y.

      2013-07-01

      Geometric and electronic properties of platinum octaethyl porphyrin (PtOEP) molecules on thin insulating sodium chloride (NaCl) and bare Au(111) surfaces are studied using scanning tunneling microscopy and scanning tunneling spectroscopy (STS). In the STS study, a slight downward shift of a highest occupied molecular orbital peak is observed for a PtOEP molecule on NaCl(100)/Au(111). Density functional theory calculations for PtOEP molecules on the NaCl(100)/Au(111) and the bare Au(111) confirm the experimental findings.

    3. 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

    4. 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.

    5. 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.

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

      NASA Astrophysics Data System (ADS)

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

      2014-07-01

      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.

    7. 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

    8. THE CLUSTERING PROPERTIES OF THE FIRST GALAXIES

      SciTech Connect

      Stiavelli, Massimo; Trenti, Michele

      2010-06-20

      We study the clustering properties of the first galaxies formed in the universe. We find that, due to chemical enrichment of the interstellar medium by isolated Population III stars formed in mini-halos at redshift z {approx_gt} 30, the (chronologically) first galaxies are composed of metal-poor Population II stars and are highly clustered on small scales. In contrast, chemically pristine galaxies in halos with mass M {approx} 10{sup 8} M{sub sun} may form at z < 20 in relatively underdense regions of the universe. This occurs once self-enrichment by Population III in mini-halos is quenched by the buildup of an H{sub 2} photodissociating radiative background in the Lyman-Werner bands. We find that these chemically pristine galaxies are spatially uncorrelated. Thus, we expect that deep fields with the James Webb Space Telescope (JWST) may detect clusters of chemically enriched galaxies but individual chemically pristine objects. We predict that metal-free galaxies at 10 {approx}< z {approx}< 15 have surface densities of about 80 arcmin{sup -2} and per unit redshift but most of them will be too faint even for JWST. However, the predicted density makes these objects interesting targets for searches behind lensing clusters.

    9. 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.

    10. 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.

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

      PubMed

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

      2010-04-23

      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 SiO(2) 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.

    12. 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.

    13. 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.

    14. 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.

    15. 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.

    16. 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.

    17. 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.

    18. 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.

    19. 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.

    20. 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

    1. 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.

    2. 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.

    3. 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

    4. Reaction mechanisms of CO oxidation on cationic, neutral, and anionic X-O-Cu (X = Au, Ag) clusters

      NASA Astrophysics Data System (ADS)

      Zhang, Yan; He, Xiao

      2017-10-01

      We performed extensive DFT calculations for the microscopic mechanism of CO oxidation on cationic, neutral and anionic X-O-Cu (X = Au, Ag) clusters. We obtained following findings. First, the reaction mechanism of neutral X-O-Cu (X = Au, Ag) to the CO follows the Eley-Rideal-like (ER) mechanism and Langmuir-Hinshelwood-like (LH) mechanism. Second, as compared to the pure Au clusters, new reaction pathways have been found via a Langmuir-Hinshelwood-like (LH) mechanism. The oxidation of CO on cationic Au-O-Cu in nature follows an Eley-Rideal-like (ER) mechanism. Third, comparing with their reaction profiles between cationic, neutral and anionic Au-O-Cu and CO, all the reactions on Ag-O-Cu can occur more easily. Furthermore, the selectivity of the oxidation of CO on Ag-O-Cu will be improved. On the basis of our calculations, we suggest that AgCu may also be a good catalyst due to its high oxidation performance.

    5. 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.

    6. 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.

    7. 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.

    8. 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.

    9. 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.

    10. Scaling properties of hyperon production in Au+Au collisions at square root [sNN]=200 GeV.

      PubMed

      Adams, J; Aggarwal, M M; Ahammed, Z; Amonett, J; Anderson, B D; Anderson, M; Arkhipkin, D; Averichev, G S; Bai, Y; Balewski, J; Barannikova, O; Barnby, L S; Baudot, J; Bekele, S; Belaga, V V; Bellingeri-Laurikainen, A; Bellwied, R; Bezverkhny, B I; Bhardwaj, S; Bhasin, A; Bhati, A K; Bichsel, H; Bielcik, J; Bielcikova, J; Bland, L C; Blyth, C O; Blyth, S-L; Bonner, B E; Botje, M; Bouchet, J; Brandin, A V; Bravar, A; Bystersky, M; Cadman, R V; Cai, X Z; Caines, H; Calderón de la Barca Sánchez, M; Castillo, J; Catu, O; Cebra, D; Chajecki, Z; Chaloupka, P; Chattopadhyay, S; Chen, H F; Chen, J H; Chen, Y; Cheng, J; Cherney, M; Chikanian, A; Choi, H A; Christie, W; Coffin, J P; Cormier, T M; Cosentino, M R; Cramer, J G; Crawford, H J; Das, D; Das, S; Daugherity, M; de Moura, M M; Dedovich, T G; DePhillips, M; Derevschikov, A A; Didenko, L; Dietel, T; Djawotho, P; Dogra, S M; Dong, W J; Dong, X; Draper, J E; Du, F; Dunin, V B; Dunlop, J C; Dutta Mazumdar, M R; Eckardt, V; Edwards, W R; Efimov, L G; Emelianov, V; Engelage, J; Eppley, G; Erazmus, B; Estienne, M; Fachini, P; Fatemi, R; Fedorisin, J; Filimonov, K; Filip, P; Finch, E; Fine, V; Fisyak, Y; Fu, J; Gagliardi, C A; Gaillard, L; Gans, J; Ganti, M S; Ghazikhanian, V; Ghosh, P; Gonzalez, J E; Gorbunov, Y G; Gos, H; Grebenyuk, O; Grosnick, D; Guertin, S M; Guimaraes, K S F F; Guo, Y; Gupta, N; Gutierrez, T D; Haag, B; Hallman, T J; Hamed, A; Harris, J W; He, W; Heinz, M; Henry, T W; Hepplemann, S; Hippolyte, B; Hirsch, A; Hjort, E; Hoffmann, G W; Horner, M J; Huang, H Z; Huang, S L; Hughes, E W; Humanic, T J; Igo, G; Jacobs, P; Jacobs, W W; Jakl, P; Jia, F; Jiang, H; Jones, P G; Judd, E G; Kabana, S; Kang, K; Kapitan, J; Kaplan, M; Keane, D; Kechechyan, A; Khodyrev, V Yu; Kim, B C; Kiryluk, J; Kisiel, A; Kislov, E M; Klein, S R; Koetke, D D; Kollegger, T; Kopytine, M; Kotchenda, L; Kouchpil, V; Kowalik, K L; Kramer, M; Kravtsov, P; Kravtsov, V I; Krueger, K; Kuhn, C; Kulikov, A I; Kumar, A; Kuznetsov, A A; Lamont, M A C; Landgraf, J M; Lange, S; Lapointe, S; Laue, F; Lauret, J; Lebedev, A; Lednicky, R; Lee, C-H; Lehocka, S; Levine, M J; Li, C; Li, Q; Li, Y; Lin, G; Lindenbaum, S J; Lisa, M A; Liu, F; Liu, H; Liu, J; Liu, L; Liu, Z; Ljubicic, T; Llope, W J; Long, H; Longacre, R S; Lopez-Noriega, M; Love, W A; Lu, Y; Ludlam, T; Lynn, D; Ma, G L; Ma, J G; Ma, Y G; Magestro, D; Mahapatra, D P; Majka, R; Mangotra, L K; Manweiler, R; Margetis, S; Markert, C; Martin, L; Matis, H S; Matulenko, Yu A; McClain, C J; McShane, T S; Melnick, Yu; Meschanin, A; Miller, M L; Minaev, N G; Mioduszewski, S; Mironov, C; Mischke, A; Mishra, D K; Mitchell, J; Mohanty, B; Molnar, L; Moore, C F; Morozov, D A; Munhoz, M G; Nandi, B K; Nattrass, C; Nayak, T K; Nelson, J M; Netrakanti, P K; Nikitin, V A; Nogach, L V; Nurushev, S B; Odyniec, G; Ogawa, A; Okorokov, V; Oldenburg, M; Olson, D; Pachr, M; Pal, S K; Panebratsev, Y; Panitkin, S Y; Pavlinov, A I; Pawlak, T; Peitzmann, T; Perevoztchikov, V; Perkins, C; Peryt, W; Petrov, V A; Phatak, S C; Picha, R; Planinic, M; Pluta, J; Poljak, N; Porile, N; Porter, J; Poskanzer, A M; Potekhin, M; Potrebenikova, E; Potukuchi, B V K S; Prindle, D; Pruneau, C; Putschke, J; Rakness, G; Raniwala, R; Raniwala, S; Ray, R L; Razin, S V; Reinnarth, J; Relyea, D; Retiere, F; Ridiger, A; Ritter, H G; Roberts, J B; Rogachevskiy, O V; Romero, J L; Rose, A; Roy, C; Ruan, L; Russcher, M J; Sahoo, R; Sakrejda, I; Salur, S; Sandweiss, J; Sarsour, M; Sazhin, P S; Schambach, J; Scharenberg, R P; Schmitz, N; Schweda, K; Seger, J; Selyuzhenkov, I; Seyboth, P; Shabetai, A; Shahaliev, E; Shao, M; Sharma, M; Shen, W Q; Shimanskiy, S S; Sichtermann, E; Simon, F; Singaraju, R N; Smirnov, N; Snellings, R; Sood, G; Sorensen, P; Sowinski, J; Speltz, J; Spinka, H M; Srivastava, B; Stadnik, A; Stanislaus, T D S; Stock, R; Stolpovsky, A; Strikhanov, M; Stringfellow, B; Suaide, A A P; Sugarbaker, E; Sumbera, M; Sun, Z; Surrow, B; Swanger, M; Symons, T J M; Szanto de Toledo, A; Tai, A; Takahashi, J; Tang, A H; Tarnowsky, T; Thein, D; Thomas, J H; Timmins, A R; Timoshenko, S; Tokarev, M; Trainor, T A; Trentalange, S; Tribble, R E; Tsai, O D; Ulery, J; Ullrich, T; Underwood, D G; Van Buren, G; van der Kolk, N; van Leeuwen, M; Vander Molen, A M; Varma, R; Vasilevski, I M; Vasiliev, A N; Vernet, R; Vigdor, S E; Viyogi, Y P; Vokal, S; Voloshin, S A; Waggoner, W T; Wang, F; Wang, G; Wang, J S; Wang, X L; Wang, Y; Watson, J W; Webb, J C; Westfall, G D; Wetzler, A; Whitten, C; Wieman, H; Wissink, S W; Witt, R; Wood, J; Wu, J; Xu, N; Xu, Q H; Xu, Z; Yepes, P; Yoo, I-K; Yurevich, V I; Zhan, W; Zhang, H; Zhang, W M; Zhang, Y; Zhang, Z P; Zhao, Y; Zhong, C; Zoulkarneev, R; Zoulkarneeva, Y; Zubarev, A N; Zuo, J X

      2007-02-09

      We present the scaling properties of Lambda, Xi, and Omega in midrapidity Au+Au collisions at the Brookhaven National Laboratory Relativistic Heavy Ion Collider at sqrt[s_{NN}]=200 GeV. The yield of multistrange baryons per participant nucleon increases from peripheral to central collisions more rapidly than that of Lambda, indicating an increase of the strange-quark density of the matter produced. The strange phase-space occupancy factor gamma_{s} approaches unity for the most central collisions. Moreover, the nuclear modification factors of p, Lambda, and Xi are consistent with each other for 2

    11. 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.

    12. 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.

    13. 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

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

      NASA Astrophysics Data System (ADS)

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

      2015-12-01

      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.

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

      PubMed

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

      2015-12-03

      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.

    16. 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.

    17. 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.

    18. 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.

    19. 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

    20. 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.

    1. 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.

    2. 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.

    3. Effect of Alkali Metal Atoms Doping on Structural and Nonlinear Optical Properties of the Gold-Germanium Bimetallic Clusters.

      PubMed

      Li, Xiaojun; Li, Shuna; Ren, Hongjiang; Yang, Juxiang; Tang, Yongqiang

      2017-07-17

      A new series of alkali-based complexes, AM@GenAu (AM = Li, Na, and K), have been theoretically designed and investigated by means of the density functional theory calculations. The geometric structures and electronic properties of the species are systematically analyzed. The adsorption of alkali metals maintains the structural framework of the gold-germanium bimetallic clusters, and the alkali metals prefer energetically to be attached on clusters' surfaces or edges. The high chemical stability of Li@Ge12Au is revealed by the spherical aromaticity, the hybridization between the Ge atoms and Au-4d states, and delocalized multi-center bonds, as well as large binding energies. The static first hyperpolarizability (βtot) is related to the cluster size and geometric structure, and the AM@GenAu (AM = Na and K) clusters exhibit the much larger βtot values up to 13050 a.u., which are considerable to establish their strong nonlinear optical (NLO) behaviors. We hope that this study will promote further application of alkali metals-adsorbed germanium-based semiconductor materials, serving for the design of remarkable and tunable NLO materials.

    4. Au10(SG)10: A Chiral Gold Catenane Nanocluster with Zero Confined Electrons. Optical Properties and First-Principles Theoretical Analysis.

      PubMed

      Bertorelle, Franck; Russier-Antoine, Isabelle; Calin, Nathalie; Comby-Zerbino, Clothilde; Bensalah-Ledoux, Amina; Guy, Stephan; Dugourd, Philippe; Brevet, Pierre-François; Sanader, Željka; Krstić, Marjan; Bonačić-Koutecký, Vlasta; Antoine, Rodolphe

      2017-05-04

      We report facile synthesis of the Au10(SG)10 nanoclusters, where SG stands for glutathione, found to be promising as a new class of radiosensitizers for cancer radiotherapy. The homoleptic catenane structure with two Au5SG5 interconnected rings, among different isomer structures, gives the best agreement between theoretical and experimental optical spectra and XRD patterns. This catenane structure exhibits a centrosymmetry-broken structure, resulting in enhanced second harmonic response and new characteristic circular dichroism signals in the spectral region of 250-400 nm. This is the first determination of the nonlinear optical properties of a ligated cluster with an equal Au-to-ligand ratio, thus without a metallic core and therefore zero confined electrons. Insight into the nonlinear and chiroptical efficiencies arising from interplay between structural and electronic properties is provided by the TD-DFT approach.

    5. 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.

    6. 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.

    7. 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.

    8. 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.

    9. Magnetic properties of cobalt and chromium clusters

      NASA Astrophysics Data System (ADS)

      Payne, Forrest William

      We have used the Stern-Gerlach deflection technique to study magnetism in cobalt clusters of 13-187 atoms and chromium clusters with between 20-133 atoms. These clusters were observed at temperatures ranging from 60K to 250K and at magnetic field gradients up to 360 T/m. Using superparamagnetic theory we have determined the moment per atom for each cluster size and find enhanced magnetism due to reduced dimensionality of the clusters. Remarkably, we find that we are capable of making chromium clusters in two magnetically distinguishable forms for each cluster size with ≥34 atoms. We attribute this observation to the presence of structural isomers.

    10. 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.

    11. 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.

    12. 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.

    13. Cytocompatibility and electrochemical properties of Ti-Au alloys for biomedical applications.

      PubMed

      Oh, Keun-Taek; Kang, Dong-Kuk; Choi, Good-Sun; Kim, Kyoung-Nam

      2007-11-01

      The purpose of this study was to develop Ti-Au alloys with a higher resistant to corrosion, better biocompatibility, and better mechanical properties than the commercially pure titanium and its alloys. Ti-Au alloys were designed with a gold content that ranged from 0 to 5.0 at % in steps of 1.0 at %. Properties of the alloys including chemical composition, microstructure, phase, hardness, electrochemical properties, and the cytotoxicity were investigated. Only the alpha phase existed in the Ti-Au alloys. The addition of gold to the titanium decreased the alpha to beta transformation temperature. The acicular alpha phase became thinner and the hardness value increased with increasing gold content. In the electrochemical tests, Ti-Au alloys had a higher resistant to corrosion than had pure titanium and did not exhibit pitting corrosion in artificial saliva. The cytotoxicities of the Ti-Au alloys were similar to that of pure titanium. Therefore, Ti-Au alloys could be used as biomaterials in the medical and dental fields.

    14. 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.

    15. Electronic Absorption and MCD Spectra for Pd(AuPPh(3))(8)(2+), Pt(AuPPh(3))(8)(2+), and Related Platinum-Centered Gold Cluster Complexes.

      PubMed

      Adrowski, Michael J.; Mason, W. Roy

      1997-03-26

      Electronic absorption and 7.0 T magnetic circular dichroism (MCD) spectra in the UV-vis region, 1.6 to approximately 4.0 &mgr;m(-)(1) (1 &mgr;m(-)(1) = 10(4) cm(-)(1)) are reported for [Pd(AuPPh(3))(8)](NO(3))(2) and [Pt(AuPPh(3))(8)](NO(3))(2) in acetonitrile solutions at room temperature. The MCD spectra are better resolved than the absorption spectra and consist of both A and B terms. The spectra are interpreted in terms of D(4)(d)() skeletal geometry and MO's that are approximated by 5s and 6s orbitals for Pd and Pt/Au atoms, respectively. The lowest energy excited configurations and states are attributed to intraframework (IF) Au(8)(2+) transitions. Evidence is also presented for Pt 5d --> Au 6s transitions in the MCD spectra for Pt(AuPPh(3))(8)(2+). Acetonitrile solution absorption and MCD spectra for the related Pt-centered cluster complexes [Pt(CO)(AuPPh(3))(8)](NO(3))(2), [Pt(AuP(p-tolyl)(3))(8)](NO(3))(2), [Pt(CuCl)(AuPPh(3))(8)](NO(3))(2), [Pt(AgNO(3))(AuPPh(3))(8)](NO(3))(2), [Pt(Hg)(2)(AuPPh(3))(8)](NO(3))(2), [Pt(HgCl)(2)(AuPPh(3))(8)](BF(4))(2), and [Pt(HgNO(3))(2)(AuPPh(3))(8)](BF(4))(2) are also reported and interpreted within the context of the model developed for the M(AuPPh(3))(8)(2+) complexes.

    16. Preparation, Spectroscopic Characterization, and Frontier MO Study of the Heteronuclear Luminescent [Pt(2)Au(2)(dmb)(2)(PPh(3))(4)](PF(6))(2) Cluster (dmb = 1,8-Diisocyano-p-menthane). A Cluster with a Formal Au(0)-Au(0) Bond Encapsulated inside a "Pt(2)(dmb)(2)(2+) " Fragment.

      PubMed

      Zhang, Tianle; Drouin, Marc; Harvey, Pierre D.

      1999-11-01

      The title compound is prepared from the direct reaction of Pt(2)(dba)(3) (dba = dibenzylideneacetone) and [Au(PPh(3))(2)](PF(6)) in the presence of 1,8-diisocyano-p-methane (dmb), with Pt(2)(dmb)(2)Cl(2), [Pt(4)(dmb)(4)(PPh(3))(2)](PF(6))(2), and (PPh(3))AuCl being formed as parallel products. X-ray crystallography reveals the presence of a quasi-linear PPh(3)Au-AuPPh(3) fragment encapsulated inside a "Pt(2)(dmb)(2)(2+)" ring which is axially coordinated with two PPh(3) ligands. The d(AuAu) is 2.5977(6) Å and is indicative of a strong Au-Au single bond. The IR nu(CN) data reveal that the Pt oxidation state is I, which places the Au oxidation state at 0. The PtAu distances are 2.8422(5) and 2.8082(5) Å. The Raman-active nu(Au(2)), nu(PtAu) (b(2g) + a(g)), nu(PtP), nu(AuP), and nu(PtC) are found at 121.2, approximately 100, 85.5, 162.1, 183.1, and 457.2, and 440.9 cm(-)(1), respectively. The PtAu (0.67 mdyn Å(-)(1)) and Au(2) (1.21 mdyn Å(-)(1)) force constants (F) confirm the presence of medium PtAu and strong Au(2) bonding interactions. The absorption spectra are characterized by strong bands at lambda(max) (epsilon, M(-1) cm(-1)) at 316 (32 300), 366 (37 800), and 418 nm (21 500) and lower intensity features at 516 (2860) and 655 nm (834). The cluster is luminescent at low temperatures (solid and frozen glasses), and in the solid state at room temperature, and exhibits an emission band at approximately 875 nm, and an emission lifetime, tau(e), of 4.4 +/- 0.4 ns (solvent = butyronitrile, T = 77 K).

    17. Au3+ ion implantation on FTO coated glasses: Effect on structural, electrical, optical and phonon properties

      NASA Astrophysics Data System (ADS)

      Sahu, Bindu; Dey, Ranajit; Bajpai, P. K.

      2017-06-01

      Effects of 11.00 MeV Au3+ ions implanted in FTO coated (thickness ≈300 nm) silicate glasses on structural, electrical optical and phonon behavior have been explored. It has been observed that metal clustering near the surface and sub-surface region below glass-FTO interface changes electrical and optical properties significantly. Ion implantation does not affect the crystalline structure of the coated films; however, the unit cell volume decreases with increase in fluence and the tetragonal distortion (c/a ratio) also decreases systematically in the implanted samples. The sheet resistivity of the films increases from 11 × 10-5 ohm-cm (in pristine) to 7.5 × 10-4 ohm-cm for highest ion beam fluence ≈1015 ions/cm2. The optical absorption decreases with increasing fluence whereas, the optical transmittance as well as reflectance increases with increasing fluence. The Raman spectra are observed at ∼530 cm-1 and ∼1103 cm-1 in pristine sample. The broad band at 530 cm-1 shifts towards higher wave number in the irradiated samples. This may be correlated with increased disorder and strain relaxation in the samples as a result of ion beam irradiation.

    18. Core-size-dependent catalytic properties of bimetallic Au/Ag core-shell nanoparticles.

      PubMed

      Haldar, Krishna Kanta; Kundu, Simanta; Patra, Amitava

      2014-12-24

      Bimetallic core-shell nanoparticles have recently emerged as a new class of functional materials because of their potential applications in catalysis, surface enhanced Raman scattering (SERS) substrate and photonics etc. Here, we have synthesized Au/Ag bimetallic core-shell nanoparticles with varying the core diameter. The red-shifting of the both plasmonic peaks of Ag and Au confirms the core-shell structure of the nanoparticles. Transmission electron microscopy (TEM) analysis, line scan EDS measurement and UV-vis study confirm the formation of core-shell nanoparticles. We have examined the catalytic activity of these core-shell nanostructures in the reaction between 4-nitrophenol (4-NP) and NaBH4 to form 4-aminophenol (4-AP) and the efficiency of the catalytic reaction is found to be increased with increasing the core size of Au/Ag core-shell nanocrystals. The catalytic efficiency varies from 41.8 to 96.5% with varying core size from 10 to 100 nm of Au/Ag core-shell nanoparticles, and the Au100/Ag bimetallic core-shell nanoparticle is found to be 12-fold more active than that of the pure Au nanoparticles with 100 nm diameter. Thus, the catalytic properties of the metal nanoparticles are significantly enhanced because of the Au/Ag core-shell structure, and the rate is dependent on the size of the core of the nanoparticles.

    19. 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.

    20. Electron transfer processes on Ag and Au clusters supported on TiO{sub 2}(110) and cluster size effects

      SciTech Connect

      Canario, Ana Rita; Esaulov, Vladimir A.

      2006-06-14

      The results of a detailed study of Li{sup +} neutralization in scattering on Ag and Au clusters and thin films supported on TiO{sub 2} are presented. A very efficient neutralization is observed on small clusters with a decrease for the smallest clusters. These results closely follow the size-effects observed in the reactivity of these systems. The energy dependence of the neutralization was studied for the larger clusters (>4 nm) and observed to be similar in trend to the one observed on films and bulk (111) crystals. A general discussion of possible reasons of the enhancement in neutralization is presented and these changes are then tentatively discussed in terms of progressive modifications in the electronic structure of clusters as a function of reduction in size and as it evolves from metallic-like to discretised states. The highest neutralization efficiency would appear to correspond to clusters sizes for which a metal to nonmetal transition occurs. The relative position of the Li level and the highest occupied molecular orbital in the molecular cluster can be expected to strongly affect the electron transfer processes, which in this case should be described in a molecular framework.

    1. Quantum chemical assessment of the ligand effect on the properties and structure of protected gold clusters

      NASA Astrophysics Data System (ADS)

      Nikitina, N. A.; Pichugina, D. A.; Kuz'menko, N. E.

      2017-08-01

      A procedure based on density functional theory is proposed for calculation of Au20(XCH3)16 (X = S, Se, Te) isomers. It is established that the most stable isomer for all X has a core‒shell structure: Au7@(AuXCH3)8(XCH3(AuXCH3)3)(XCH3AuXCH3)2. Optical and IR spectra, ionization potential, and electron affinity are calculated for the first time for all clusters. It is shown that a cluster protected by thiolate ligands has the greatest electronic and thermodynamic stability.

    2. Magnetic properties of supported metal atoms and clusters

      NASA Astrophysics Data System (ADS)

      Martins, Michael; Wurth, Wilfried

      2016-12-01

      Clusters are small systems ranging from a few atoms up to several thousand atoms. They are of high interest in basic research, but also for applications due to their specific electronic, magnetic or chemical properties depending on size and composition. For small clusters, quantum size effects play an important role and specific material properties might be tailored by choosing a special size or composition of the cluster. Here, we review the magnetic properties of adatoms and supported small mass-selected transition-metal clusters in the few-atom limit investigated by x-ray magnetic circular dichroism spectroscopy in the soft x-ray regime. The influence of cluster size, composition, the cluster-surface and intra-cluster interaction on the spin and orbital magnetic moments will be discussed.

    3. Development of open-boundary cluster model approach for electrochemical systems and its application to Ag+ adsorption on Au(111) and Ag(111) electrodes.

      PubMed

      Iida, Kenji; Yasuike, Tomokazu; Nobusada, Katsuyuki

      2013-09-14

      We present a theoretical method to investigate electrochemical processes on the basis of a finite-temperature density functional theory (FT-DFT) approach combined with our recently developed open-boundary cluster model (OCM). A semi-infinite electrode is well mimicked by a finite-sized simple cluster with an open quantum boundary condition rationalized by OCM. An equilibrium state between adsorbates and an electrode is described by the grand canonical formulation of FT-DFT. These implements allow us to calculate electronic properties of an adsorbate and electrode system at a constant chemical potential μ, i.e., electrode potential. A solvation effect is approximated by a conductor-like polarized continuum model. The method is applied to the electrochemical processes of Ag(+) adsorption on Au(111) and Ag(111). The present constant μ approach has proved essential to electrochemical systems, demonstrating that the method qualitatively reproduces the experimental evidence that Ag(+) adsorbs more on the Au electrode than the Ag one, while the conventional quantum chemistry approach with a constant number of electrons incorrectly gives exactly the opposite result.

    4. 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.

    5. 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.

    6. 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.

    7. 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.

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

      NASA Astrophysics Data System (ADS)

      Sankaran, K. J.; Sundaravel, B.; Tai, N. H.; Lin, I. N.

      2015-08-01

      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)-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/cm2 (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.

    9. 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.

    10. How do Water Solvent and Glutathione Ligands Affect the Structure and Electronic Properties of Au25(SR)18(-)?

      PubMed

      Rojas-Cervellera, Víctor; Rovira, Carme; Akola, Jaakko

      2015-10-01

      The effects of aqueous solvent and biological ligands on the structural and electronic properties of thiolate-protected Au25(SR)18(-) clusters have been studied by performing quantum mechanics/molecular mechanics (QM/MM) simulations. Analysis of bond distances and angles show that the solvated nanocluster experiences modest structural changes, which are reflected as flexibility of the Au core. The hydrophilic glutathione ligands shield the metallic core effectively and distort its symmetry via sterical hindrance effects. We show that the previously reported agreement between the calculated HOMO-LUMO gap of the cluster and the optical measurement is due to cancellation of errors, where the typical underestimation of the theoretical band gap compensates the effect of the missing solvent. The use of a hybrid functional results in a HOMO-LUMO gap value of 1.5 eV for the solvated nanocluster with glutathione ligands, in good agreement with optical measurements. Our results demonstrate that ligand/solvent effects should be considered for a proper comparison between theory and experiment.

    11. Effect of Alkali Metal Atoms Doping on Structural and Nonlinear Optical Properties of the Gold-Germanium Bimetallic Clusters

      PubMed Central

      Li, Xiaojun; Li, Shuna; Ren, Hongjiang; Yang, Juxiang; Tang, Yongqiang

      2017-01-01

      A new series of alkali-based complexes, AM@GenAu (AM = Li, Na, and K), have been theoretically designed and investigated by means of the density functional theory calculations. The geometric structures and electronic properties of the species are systematically analyzed. The adsorption of alkali metals maintains the structural framework of the gold-germanium bimetallic clusters, and the alkali metals prefer energetically to be attached on clusters’ surfaces or edges. The high chemical stability of Li@Ge12Au is revealed by the spherical aromaticity, the hybridization between the Ge atoms and Au-4d states, and delocalized multi-center bonds, as well as large binding energies. The static first hyperpolarizability (βtot) is related to the cluster size and geometric structure, and the AM@GenAu (AM = Na and K) clusters exhibit the much larger βtot values up to 13050 a.u., which are considerable to establish their strong nonlinear optical (NLO) behaviors. We hope that this study will promote further application of alkali metals-adsorbed germanium-based semiconductor materials, serving for the design of remarkable and tunable NLO materials. PMID:28714906

    12. 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.

    13. 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

    14. 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.

    15. 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.

    16. 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.

    17. Properties of the gold-sulphur interface: from self-assembled monolayers to clusters

      NASA Astrophysics Data System (ADS)

      Bürgi, Thomas

      2015-09-01

      The gold-sulphur interface of self-assembled monolayers (SAMs) was extensively studied some time ago. More recently tremendous progress has been made in the preparation and characterization of thiolate-protected gold clusters. In this feature article we address different properties of the two systems such as their structure, the mobility of the thiolates on the surface and other dynamical aspects, the chirality of the structures and characteristics related to it and their vibrational properties. SAMs and clusters are in the focus of different communities that typically use different experimental approaches to study the respective systems. However, it seems that the nature of the Au-S interfaces in the two cases is quite similar. Recent single crystal X-ray structures of thiolate-protected gold clusters reveal staple motifs characterized by gold ad-atoms sandwiched between two sulphur atoms. This finding contradicts older work on SAMs. However, newer studies on SAMs also reveal ad-atoms. Whether this finding can be generalized remains to be shown. In any case, more and more studies highlight the dynamic nature of the Au-S interface, both on flat surfaces and in clusters. At temperatures slightly above ambient thiolates migrate on the gold surface and on clusters. Evidence for desorption of thiolates at room temperature, at least under certain conditions, has been demonstrated for both systems. The adsorbed thiolate can lead to chirality at different lengths scales, which has been shown both on surfaces and for clusters. Chirality emerges from the organization of the thiolates as well as locally at the molecular level. Chirality can also be transferred from a chiral surface to an adsorbate, as evidenced by vibrational spectroscopy.

    18. Properties of the gold-sulphur interface: from self-assembled monolayers to clusters.

      PubMed

      Bürgi, Thomas

      2015-10-14

      The gold-sulphur interface of self-assembled monolayers (SAMs) was extensively studied some time ago. More recently tremendous progress has been made in the preparation and characterization of thiolate-protected gold clusters. In this feature article we address different properties of the two systems such as their structure, the mobility of the thiolates on the surface and other dynamical aspects, the chirality of the structures and characteristics related to it and their vibrational properties. SAMs and clusters are in the focus of different communities that typically use different experimental approaches to study the respective systems. However, it seems that the nature of the Au-S interfaces in the two cases is quite similar. Recent single crystal X-ray structures of thiolate-protected gold clusters reveal staple motifs characterized by gold ad-atoms sandwiched between two sulphur atoms. This finding contradicts older work on SAMs. However, newer studies on SAMs also reveal ad-atoms. Whether this finding can be generalized remains to be shown. In any case, more and more studies highlight the dynamic nature of the Au-S interface, both on flat surfaces and in clusters. At temperatures slightly above ambient thiolates migrate on the gold surface and on clusters. Evidence for desorption of thiolates at room temperature, at least under certain conditions, has been demonstrated for both systems. The adsorbed thiolate can lead to chirality at different lengths scales, which has been shown both on surfaces and for clusters. Chirality emerges from the organization of the thiolates as well as locally at the molecular level. Chirality can also be transferred from a chiral surface to an adsorbate, as evidenced by vibrational spectroscopy.

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

      NASA Astrophysics Data System (ADS)

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

      2005-05-01

      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.

    1. 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.

    2. 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.

    3. 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.

    4. 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.

    5. 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.

    6. 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).

    7. Fundamental Properties of Galaxy Clusters: A Prelude to Large Scale SZE/Near-IR Cluster Surveys

      NASA Astrophysics Data System (ADS)

      Lin, Y.-T.

      2005-12-01

      Within the context of precision cosmology, the systematics of a cluster survey must be carefully controlled. These require knowledge of the cluster selection function, the sources of contamination, and the evolution of clusters. For surveys aiming to study the dark energy, probing the redshift range z = 1-2 is essential. This can be most efficiently carried out by a Sunyaev-Zel'dovich effect (SZE) survey supplemented with near-IR follow-up. The cluster sample with SZE+near-IR data will also provide an excellent opportunity for understanding the cluster galaxy population evolution. This dissertation is developed under the two themes central to such a survey, i.e. the control of systematics, and the nature and evolution of cluster galaxy populations. We first conduct an analysis of a deep SZE survey and offer considerations for determining the survey mass sensitivity and for extracting cosmological constraints. Because the radio-loud AGNs can potentially contaminate the cluster SZE signal, we also investigate the properties of cluster AGNs to facilitate modeling their effects on the survey yields. The second thrust of the dissertation is a systematic survey of the near-IR properties of cluster galaxies. With a large nearby cluster sample that spans a wide range in mass, we study scaling relations between the total galaxy luminosity or number and the cluster mass. The origins of such correlations are discussed in terms of the hierarchical structure formation, among other possibilities. We proceed to study the properties of various cluster components, including the brightest cluster galaxies (BCGs), and the stars and gas that exist within the intracluster space. Constraints on BCG formation and the thermodynamic history of the intracluster medium are presented. Finally, with deep near-IR imaging data, we examine the luminosity function for a smaller cluster sample that extends to z ˜ 1. We confirm the existence of the scaling relations and determine their evolution

    8. 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).

    9. Electronic and structural properties of alkali-halide cluster anions

      NASA Astrophysics Data System (ADS)

      Fatemi, Fredrik Kurosh

      We have used photoelectron spectroscopy to study alkali- halide clusters containing excess electrons. These measurements addressed five major aspects of the electronic and structural properties of the clusters. The underlying motivations for studying these clusters are to understand the transition from atomic to bulk behavior as a function of particle size and to identify those properties which are unique to clusters. We have observed excited states in many of the single excess electron clusters, and tested simple theoretical models against our experimental results. The two excess electron systems also contain excited states. However, the absorption of a photon in these systems often leads to the desorption of a negatively charged alkali ion. The abundance of various isomers of the cesium-halide systems depends strongly on the temperature of the source in which they are created, while those of the potassium and sodium halides do not. We have proven that this behavior indicates that the clusters undergo rapid structural interconversions on a subnanosecond time scale. The properties of alkali-halide clusters usually depend only on the type of alkali in the cluster. To understand the effect of different alkali ions on the electronic and structural properties of the clusters, we have examined mixed clusters which contain more than one alkali species. There properties are influenced most by the larger cations in single excess electron systems, and by the smaller cations in multiple excess electron particles. Finally, our measurements have shown that some of the potassium-rich potassium-iodide cluster anions (KI)m K- n( m=2- 7,n=1- 4) appear to separate into a purely metallic component K-n supported by an ionic component (KI)m. This behavior is clear for m = 2, 3, 4, and 6. For m = 5 and 7, the ions comprising the cluster show a high degree of mixing.

    10. 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

    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. 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.

    13. 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.

    14. 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.

    15. 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

    16. Properties of young clusters near reflection nebulae

      NASA Technical Reports Server (NTRS)

      Sellgren, K.

      1983-01-01

      Near infrared observations in the reflection nebulae NGC 7023, 2023, and 2068 are used to study clusters of young stars found associated with these nebulae. At least 30% to 60% of these stars are pre-main sequence objects, as indicated by their infrared excesses, hydrogen line emission, or irregular variability. The spatial distributions and observed luminosity functions of these young open clusters are derived, and the inferred mass function and star formation efficiencies are discussed.

    17. Theoretical study of oxygen adsorption on pure Au(n+1)+ and doped MAu(n)+ cationic gold clusters for M = Ti, Fe and n = 3-7.

      PubMed

      Torres, M Begoña; Fernández, Eva M; Balbás, Luis C

      2008-07-24

      A comparative study of the adsorption of an O2 molecule on pure Au(n+1)+ and doped MAu(n)+ cationic gold clusters for n = 3-7 and M = Ti, Fe is presented. The simultaneous adsorption of two oxygen atoms also was studied. This work was performed by means of first principles calculations based on norm-conserving pseudo-potentials and numerical basis sets. For pure Au4 +, Au6+, and Au7+ clusters, the O2 molecule is adsorbed preferably on top of low coordinated Au atoms, with an adsorption energy smaller than 0.5 eV. Instead, for Au5+ and Au8+, bridge adsorption sites are preferred with adsorption energies of 0.56 and 0.69 eV, respectively. The ground-state geometry of Au(n)+ is almost unperturbed after O2 adsorption. The electronic charge flows towards O2 when the molecule is adsorbed in bridge positions and towards the gold cluster when O2 is adsorbed on top of Au atoms, and both the adsorption energy and the O-O bond length of adsorbed oxygen increase when the amount of electronic charge on O2 increases. On the other hand, we studied the adsorption of an O2 molecule on doped MAu(n)+ clusters, leading to the formation of (MAu(n)O2+) ad complexes with different equilibrium configurations. The highest adsorption energy was obtained when both atoms of O2 bind on top of the M impurity, and it is larger for Ti doped clusters than for Fe doped clusters, showing an odd-even effect trend with size n, which is opposite for Ti as compared to Fe complexes. For those adsorption configurations of (MAu(n)O2+) ad involving only Au sites, the adsorption energy is similar to or smaller than that for similar configurations of Au(n)+1O2 + complexes. However, the highest adsorption energy of (MAu(n)O2+) ad is higher than that for (Au(n)+1O2+) ad by a factor of approximately 4.0 (1.2) for M = Ti (M = Fe). The trends with size n are rationalized in terms of O-O and O-M bond distances, as well as charge transfer between oxygen and cluster substrates. The spin multiplicity of those (MAu

    18. 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.

    19. Effects of TiO2 sol on the microstructure and properties of Au-Co coatings

      NASA Astrophysics Data System (ADS)

      Tay, See Leng; van Vliet, Jowin; Wang, Yuxin; Hou, Fengyan; Xiong, Chao; Gao, Wei

      2017-07-01

      Gold (Au) coatings are widely used for electrical contacts in devices, decoration and jewelry. However, the relatively low hardness and poor wear resistance of pure Au coatings lead to a short service life and limit their application. Ni is frequently used as an alloying element to enhance the hardness but it lowers the conductivity of Au coatings. In this research, Co was co-deposited as an alloying element with Au to improve its mechanical properties while maintaining conductivity. TiO2 sol in different concentrations was added to the Au-Co plating bath to further enhance the coating strength. Systematic studies including surface morphology, hardness, wear resistance and electrical conductivity have been carried out. Key results from nanoindentation tests demonstrated that the hardness of Au-Co-TiO2 composite coating was increased by 30% when compared to a pure Au-Co coating, while the electrical conductivity has been kept at the same level.

    20. 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.

    1. Multiple Stellar Populations in Galactic Globular Clusters: General Properties

      NASA Astrophysics Data System (ADS)

      Piotto, Giampaolo

      2015-08-01

      Globular clusters are the most ancient stellar systems for which we can have a reliable age estimate, and therefore bring information on star formation processes in the early Universe. The discovery that these objects host different, distinct populations of stars drastically changed our view on their origin and evolution. Some of the most plausible scenarios able to account for the photometric and chemical properties of multiple stellar populations in globular clusters necessarily imply that these objects must have been much more massive in the past. Whether globular clusters should be considered either as remnants of massive star clusters or nuclei of former dwarf galaxies (or both of them) is an open issue. Surely, we need to better know the chemical and kinematical properties of the different populations hosted by single clusters, and their relation with the cluster parameters, in order to shed light on this problem. Determination of the basic properties of stars hosted by (young ) massive clusters, nuclear clusters, and dwarf galaxies and a comparison with the parameters characterizing multiple stellar populations in globular cluster is a complementary approach that shall be pursued.For the first time, in my talk, I will discuss the results of a large, legacy multi-wavelength, astrometric and photometric survey based on ACS and WFC3/HST observations which include UV data. A census of the presence and frequency of multiple populations in almost half of the globular clusters of our Galaxy, their chemical tagging, radial distribution and kinematics will be presented. The relation between multiple population properties and cluster parameters will be illustrated. Consequences of these observational facts on different scenarios proposed for the formation and evolution of globular cluster stars will be critically discussed. Future perspectives towards our understanding if this complex phenomenon will be highlighted.

    2. 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.

    3. 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.

    4. The SAMI Galaxy Survey: the cluster redshift survey, target selection and cluster properties

      NASA Astrophysics Data System (ADS)

      Owers, M. S.; Allen, J. T.; Baldry, I.; Bryant, J. J.; Cecil, G. N.; Cortese, L.; Croom, S. M.; Driver, S. P.; Fogarty, L. M. R.; Green, A. W.; Helmich, E.; de Jong, J. T. A.; Kuijken, K.; Mahajan, S.; McFarland, J.; Pracy, M. B.; Robotham, A. G. S.; Sikkema, G.; Sweet, S.; Taylor, E. N.; Verdoes Kleijn, G.; Bauer, A. E.; Bland-Hawthorn, J.; Brough, S.; Colless, M.; Couch, W. J.; Davies, R. L.; Drinkwater, M. J.; Goodwin, M.; Hopkins, A. M.; Konstantopoulos, I. S.; Foster, C.; Lawrence, J. S.; Lorente, N. P. F.; Medling, A. M.; Metcalfe, N.; Richards, S. N.; van de Sande, J.; Scott, N.; Shanks, T.; Sharp, R.; Thomas, A. D.; Tonini, C.

      2017-06-01

      We describe the selection of galaxies targeted in eight low-redshift clusters (APMCC0917, A168, A4038, EDCC442, A3880, A2399, A119 and A85; 0.029 < z < 0.058) as part of the Sydney-AAO Multi-Object Integral field spectrograph Galaxy Survey (SAMI-GS). We have conducted a redshift survey of these clusters using the AAOmega multi-object spectrograph on the 3.9-m Anglo-Australian Telescope. The redshift survey is used to determine cluster membership and to characterize the dynamical properties of the clusters. In combination with existing data, the survey resulted in 21 257 reliable redshift measurements and 2899 confirmed cluster member galaxies. Our redshift catalogue has a high spectroscopic completeness (˜94 per cent) for rpetro ≤ 19.4 and cluster-centric distances R < 2R200. We use the confirmed cluster member positions and redshifts to determine cluster velocity dispersion, R200, virial and caustic masses, as well as cluster structure. The clusters have virial masses 14.25 ≤ log(M200/M⊙) ≤ 15.19. The cluster sample exhibits a range of dynamical states, from relatively relaxed-appearing systems, to clusters with strong indications of merger-related substructure. Aperture- and point spread function matched photometry are derived from Sloan Digital Sky Survey and VLT Survey Telescope/ATLAS imaging and used to estimate stellar masses. These estimates, in combination with the redshifts, are used to define the input target catalogue for the cluster portion of the SAMI-GS. The primary SAMI-GS cluster targets have R cluster regions.

    5. 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.

    6. 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...

    7. 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...

    8. 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.

    9. 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.

    10. Generation of Au(p)Ag(q)Te(r) clusters via laser ablation synthesis using Au-Ag-Te nano-composite as precursor: quadrupole ion-trap time-of-flight mass spectrometry.

      PubMed

      Mawale, Ravi Madhukar; Amato, Filippo; Alberti, Milan; Havel, Josef

      2014-07-30

      Metal tellurides have applications in various fields of science and technology but only a few gold-silver tellurides have been reported. The laser ablation synthesis (LAS) method allows the preparation of nano-materials from solid substrates. Therefore, this method was selected to synthesise some gold-silver tellurides. Laser desorption ionisation quadrupole ion trap time-of-flight mass spectrometry (LDI QIT TOF MS) was used for the generation of new Au(p)Ag(q)Te(r) clusters. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to characterise the materials. The stoichiometry of the clusters generated was determined via collision-induced dissociation (CID) and modeling of isotopic patterns. Chemisorption of gold and silver nano-particles on tellurium powder led to the formation of a new kind of Au-Ag-Te nano-composite. The LDI of this nano-composite yielded nine unary (Ag(q), Te(r)), 40 binary (Au(p)Te(r) and Ag(p)Te(r)) and 78 ternary clusters. The stoichiometry of these novel Au(p)Ag(q)Te(r) clusters is reported here for the first time. The new Au-Ag-Te nano-composite was found to be a more suitable precursor for the generation of clusters than the mixtures of the elements. TOF MS was shown to be a useful technique for following the generation of gold-silver tellurides. Knowledge of the cluster stoichiometry could accelerate the further development of novel high-tech materials such as chalcogenide glasses. Copyright © 2014 John Wiley & Sons, Ltd.

    11. 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.

    12. High-mass heterogeneous cluster formation by ion bombardment of the ternary alloy Au7Cu5Al4

      DOE PAGES

      Zinovev, Alexander V.; King, Bruce V.; Veryovkin, Igor V.; ...

      2016-02-04

      The ternary alloy Au7Cu5Al4 was irradiated with 0.1–10 keV Ar+ and the surface composition analyzed using laser sputter neutral mass spectrometry. Ejected clusters containing up to seven atoms, with masses up to 2000 amu, were observed. By monitoring the signals from sputtered clusters, the surface composition of the alloy was seen to change with 100 eV Ar+ dose, reaching equilibrium after 10 nm of the surface was eroded, in agreement with TRIDYN simulation and indicating that the changes were due to preferential sputtering of Al and Cu. Ejected gold containing clusters were found to increase markedly in intensity while aluminummore » containing clusters decreased in intensity as a result of Ar sputtering. Such an effect was most pronounced for low energy (<1 keV) Ar+ sputtering and was consistent with TRIDYN simulations of the depth profiling. As a result, the component sputter yields from the ternary alloy were consistent with previous binary alloy measurements but showed greater Cu surface concentrations than expected from TRIDYN simulations.« less

    13. 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.

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

      SciTech Connect

      Kramer, Pamela Ann

      1992-05-01

      This study was of the effects moderately low Au concentrations (≤ 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 50μin 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. AuSn4 intermetallics present in toe of 4.8 wt% (50 μin) 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 AuSn4 intermetallics in the toe of the 4.8 wt% (50μin) 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.

    15. 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.

    16. 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.

    17. Probing the Microscopic with the Macroscopic: from Properties of Star Cluster Systems to Properties of Cluster-Forming Regions

      NASA Astrophysics Data System (ADS)

      Parmentier, G.

      To understand how systems of star clusters have reached their presently observed properties constitutes a powerful probe into the physics of cluster formation, without needing to resort to high spatial resolution observations of individual cluster-forming regions (CFRg) in distant galaxies. In this contribution I focus on the mass-radius relation of CFRgs, how it can be uncovered by studying the gas expulsion phase of forming star clusters, and what the implications are. I demonstrate that, through the tidal field impact upon exposed star clusters, the CFRg mass-radius relation rules cluster infant weight-loss in dependence of cluster mass. The observational constraint of a time-invariant slope for the power-law young cluster mass function is robustly satisfied by CFRgs with a constant mean volume density. In contrast, a constant mean surface density would be conducive to the preferential destruction of high-mass clusters. A purely dynamical line-of-reasoning leads therefore to a conclusion consistent with star formation a process driven by a volume density threshold. Developing this concept further, properties of molecular clumps and CFRgs naturally get dissociated. This allows to understand: (i) why the star cluster mass function is steeper than the molecular cloud/clump mass function; (ii) the presence of a massive star formation limit in the mass-size space of molecular structures.

    18. 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.

    19. Molecular adsorption properties of CO and H2O on Au-, Cu-, and AuxCuy-doped MoS2 monolayer

      NASA Astrophysics Data System (ADS)

      Kadioglu, Yelda; Gökoğlu, Gökhan; Üzengi Aktürk, Olcay

      2017-12-01

      In this study, we investigate the adsorption properties of Au, Cu, and AuxCuy nanoclusters on MoS2 sheet and the interactions of the adsorbed systems with CO and H2O molecules by using first principles calculations. Results indicate that Au, Cu, or AuxCuy strongly binds to MoS2 monolayer resulting in enhanced chemical activity and sensitivity toward CO and H2O molecules compared to bare MoS2 monolayer. Although both CO and H2O molecules bind weakly to pristine MoS2 monolayer, CO strongly binds to MoS2 sheet in the presence of Au, Cu atoms or AuxCuy clusters. Semiconductor MoS2 monolayer turns into metal upon Au or Cu adsorption. AuxCuy nanocluster adsorption decreases the band gap of MoS2 monolayer acting as a n-type dopant. AuxCuy-doped MoS2 systems have improved adsorption properties for CO and H2O molecules, so the conclusions provided in this study can be useful as a guide for next generation device modeling.

    20. 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.

    1. 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.

    2. 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

    3. 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) \

    4. 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+.

    5. 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+}.

    6. 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.

    7. 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.

    8. 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.

    9. 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.

    10. 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.

    11. 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.

    12. The properties of energetically unbound stars in stellar clusters

      NASA Astrophysics Data System (ADS)

      Claydon, Ian; Gieles, Mark; Zocchi, Alice

      2017-04-01

      Several Milky Way star clusters show a roughly flat velocity dispersion profile at large radii, which is not expected from models with a tidal cut-off energy. Possible explanations for this excess velocity include the effects of a dark matter halo, modified gravity theories and energetically unbound stars inside of clusters. These stars are known as potential escapers (PEs) and can exist indefinitely within clusters that are on circular orbits. Through a series of N-body simulations of star cluster systems, where we vary the galactic potential, orbital eccentricity and stellar mass function, we investigate the properties of the PEs and their effects on the kinematics. We derive a prediction for the scaling of the velocity dispersion at the Jacobi surface due to PEs, as a function of cluster mass, angular velocity of the cluster orbit, and slope of the mass profile of the host galaxy. We see a tentative signal of the mass and orbital velocity dependence in kinematic data of globular clusters from the literature. We also find that the fraction of PEs depends sensitively on the galactic mass profile, reaching as high as 40 per cent in the cusp of a Navarro-Frenk-White profile and as the velocity anisotropy also depends on the slope of the galactic mass profile, we conclude that PEs provide an independent way of inferring the properties of the dark matter mass profile at the galactic radius of (globular) clusters in the Gaia era.

    13. 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.

    14. Photoelectric properties of ZnS/Au/ZnS transparent conductive tri-layer films

      NASA Astrophysics Data System (ADS)

      Wang, Caifeng; Hu, Bo

      2017-09-01

      ZnS/Au/ZnS tri-layer films are deposited on quartz glass by pulsed laser deposition (PLD) at room temperature, and have been annealed in air at different temperatures. The effect of annealing temperature on the optical and electrical properties of ZnS/Au/ZnS tri-layer films is investigated. X-ray diffraction (XRD) patterns show that the increase in annealing temperature improves the crystallinity of the structures. Scanning electron microscope (SEM) images of the samples show that the particle size becomes larger as the annealing temperature increases. Moreover, with the increase of annealing temperature, sheet resistance of the tri-layer films decreases initially, and increases further by increasing the annealing temperature to 300 °C. High quality ZnS/Au/ZnS tri-layer films with the sheet resistance of 27 Ω/sq and the maximum optical transmittance of 86.2% in the visible light region (400-800 nm) are obtained when the sample is annealed at 200 °C. The figure of merit is calculated to evaluate the performance of ZnS/Au/ZnS tri-layer films.

    15. 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

    16. 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.

    17. 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.

    18. 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.

    19. Theoretical study of Au(n)V-CO, n = 1-14: the dopant vanadium enhances CO adsorption on gold clusters.

      PubMed

      Nhat, Pham Vu; Tai, Truong Ba; Nguyen, Minh Tho

      2012-10-28

      The CO adsorption on vanadium-doped gold clusters Au(n)V with n = 1-14 is studied by density functional theory computations, using the BB95 and B3LYP functionals along with the cc-pVDZ-PP basis for metals and cc-pVTZ for non-metals. When both Au and V sites are exposed, CO adsorption on V is thermodynamically favorable because with partially filling d orbitals vanadium is more willing to interact with CO empty or filled orbitals. When vanadium is confined inside a gold cage, the low-coordinated Au atoms become the preferred sites for CO attachment. The presence of V tends to reinforce CO adsorption as compared with the bare gold clusters. The diatomic AuV is predicted to have the largest CO adsorption affinity as it has a typical π-back donation bond. Au(n)V-CO complexes typically have the larger CO binding energies and larger CO frequency shift than the isoatomic gold-carbonyl Au(n+1)-CO counterparts.

    20. Star cluster formation in cosmological simulations. I. Properties of young clusters

      DOE PAGES

      Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.; ...

      2017-01-03

      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 ismore » $$\\alpha \\approx 1.8\\mbox{–}2$$, 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. As a result, 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.« less

    1. 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.

    2. 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.

    3. The Cluster-EAGLE project: global properties of simulated clusters with resolved galaxies

      NASA Astrophysics Data System (ADS)

      Barnes, David J.; Kay, Scott T.; Bahé, Yannick M.; Dalla Vecchia, Claudio; McCarthy, Ian G.; Schaye, Joop; Bower, Richard G.; Jenkins, Adrian; Thomas, Peter A.; Schaller, Matthieu; Crain, Robert A.; Theuns, Tom; White, Simon D. M.

      2017-10-01

      We introduce the Cluster-EAGLE (c-eagle) simulation project, a set of cosmological hydrodynamical zoom simulations of the formation of 30 galaxy clusters in the mass range of 1014 < M200/M⊙ < 1015.4 that incorporates the Hydrangea sample of Bahé et al. (2017). The simulations adopt the state-of-the-art eagle galaxy formation model, with a gas particle mass of 1.8 × 106 M⊙ and physical softening length of 0.7 kpc. In this paper, we introduce the sample and present the low-redshift global properties of the clusters. We calculate the X-ray properties in a manner consistent with observational techniques, demonstrating the bias and scatter introduced by using estimated masses. We find the total stellar content and black hole masses of the clusters to be in good agreement with the observed relations. However, the clusters are too gas rich, suggesting that the active galactic nucleus (AGN) feedback model is not efficient enough at expelling gas from the high-redshift progenitors of the clusters. The X-ray properties, such as the spectroscopic temperature and the soft-band luminosity, and the Sunyaev-Zel'dovich properties are in reasonable agreement with the observed relations. However, the clusters have too high central temperatures and larger-than-observed entropy cores, which is likely driven by the AGN feedback after the cluster core has formed. The total metal content and its distribution throughout the intracluster medium are a good match to the observations.

    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. 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.

    6. 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.

    7. 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

    8. Engineered Au Core@Prussian Blue Analogous Shell Nanoheterostructures: Their Magnetic and Optical Properties.

      PubMed

      Maurin-Pasturel, Guillaume; Long, Jérôme; Palacios, Maria A; Guérin, Christian; Charnay, Clarence; Willinger, Marc-Georg; Trifonov, Alexander A; Larionova, Joulia; Guari, Yannick

      2017-06-01

      We report a new approach for the synthesis of multifunctional Au core@Prussian Blue analogous (PBA) shell nanoheterostructures that involves PBA shell growth on the surface of cyanide-stabilized gold nanoparticles. It permits the assembly of Au@KNi(II) [Fe(II) (CN)6 ] core@shell and Au@KNi(II) [Fe(II) (CN)6 ]@KNi(II) [Cr(III) (CN)6 ] core@shell@shell heterostructures with well-defined and size-controlled gold cores and PBA shells. These heterostructures exhibit tunable size- and shape-dependent magnetic and optical properties: (i) the surface plasmon resonance band position and intensity mainly depend on the PBA shell thickness, and (ii) the magnetic properties (the transition temperature, the coercivity, and magnetic regime) depend in a complex manner on the thickness as well as the particular morphology of the magnetic shell. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

    9. 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.

    10. 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.

    11. Formation and properties of metal clusters isolated in helium droplets.

      PubMed

      Tiggesbäumker, Josef; Stienkemeier, Frank

      2007-09-14

      The unique conditions forming atomic and molecular complexes and clusters using superfluid helium nanodroplets have opened up an innovative route for studying the physical and chemical properties of matter on the nanoscale. This review summarizes the specific characteristics of the formation of atomic clusters partly generated far from equilibrium in the helium environment. Special emphasis is on the optical response, electronic properties as well as dynamical processes which are mostly affected by the surrounding quantum matrix. Experiments include the optical induced response of isolated cluster systems in helium under quite different excitation conditions ranging from the linear regime up to the violent interaction with a strong laser field leading to Coulomb explosion and the generation of highly charged atomic fragments. The variety of results on the outstanding properties in the quantum size regime highlights the peculiar capabilities of helium nanodroplet isolation spectroscopy.

    12. 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.

    13. 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.

    14. The structural and electronic properties of tubular gold clusters with a spinal support.

      PubMed

      Priyanka; Dharamvir, Keya

      2013-08-07

      Scalar relativistic density functional theory (DFT) is used to investigate the structural and electronic properties of an endohedrally doped hollow tube of gold with a hexagonal cross-section, X(M)Au(N) (X = Si, Al and Au, M = 3, 6, 9 and N = 24, 42, 60). Only Si as a dopant can be encapsulated to provide a stable backbone to the parent tubular Au(N) whereas structures containing an Al or Au backbone are distorted into non-cage like structures as the size increases. The dopant atoms increase the electron density around the Fermi level and shift the d-energy levels to deeper energy levels, thus reducing the HOMO–LUMO gap of the AuN tube. The effect is more pronounced in the Si doped Au(N) than the Al or Au doped Au(N) tubes. The Si9Au60 structure, though stable, shows a slight bending which can be corrected by removing one Si atom from the backbone which provides it with the correct amount of space. It can be concluded that Si and Al atoms can form long chains within the Au nanotube if a gap is present after every 4–6 layers of Au atoms to accommodate the size mismatch between the Si–Si and Al–Al bonds and the Au layers. Si doping within the Au(N) tube is more compatible than Al doping, as confirmed by Mulliken charge analysis.

    15. 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.

    16. 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

    17. 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.

    18. 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.

    19. Quantitative properties of clustering within modern microscopic nuclear models

      SciTech Connect

      Volya, A.; Tchuvil’sky, Yu. M.

      2016-09-15

      A method for studying cluster spectroscopic properties of nuclear fragmentation, such as spectroscopic amplitudes, cluster form factors, and spectroscopic factors, is developed on the basis of modern precision nuclear models that take into account the mixing of large-scale shell-model configurations. Alpha-cluster channels are considered as an example. A mathematical proof of the need for taking into account the channel-wave-function renormalization generated by exchange terms of the antisymmetrization operator (Fliessbach effect) is given. Examples where this effect is confirmed by a high quality of the description of experimental data are presented. By and large, the method in question extends substantially the possibilities for studying clustering phenomena in nuclei and for improving the quality of their description.

    20. 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.

    1. Au doping effect on the electrical and magnetic properties of Fe3O4 nanoparticles

      NASA Astrophysics Data System (ADS)

      Mahmood, Asif; Ramay, Shahid Mahmood; Al-Zaghayer, Yousef S.; Alhazaa, A. N.; Al Masary, Waheed A.; Atiq, Shahid

      2015-12-01

      Impurities free ferromagnetic Fe3O4 was prepared via sol-gel auto-combustion method and then gold was doped with various concentrations 1, 3 and 5 wt.% using conventional deposition-precipitation method. All samples of Fe3O4 with/without Au doping were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The room temperature magnetic hysteresis loops of all the samples were measured using a physical property measuring system (PPMS), and the results showed a ferromagnetic behavior at room temperature. The results obtained confirmed the fabrication of magnetite-gold composite nanoparticles. The results showed that the resistance and the magnetic behavior of the samples decrease sharply with the increase of Au concentration indicating semiconducting behavior. The saturation magnetization (Ms) of the bare Fe3O4 sample (94.72 emu/g) is much higher than that (66.78 emu/g) of the 5 wt.% Au-doped Fe3O4 sample.

    2. 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

    3. Optical properties of truncated Au nanocages with different size and shape

      NASA Astrophysics Data System (ADS)

      Chen, Qin; Qi, Hong; Ren, Ya-Tao; Sun, Jian-Ping; Ruan, Li-Ming

      2017-06-01

      The hollow nanostructures are conducive to applications including drug delivery, energy storage and conversion, and catalysis. In the present work, a versatile type of Au nanoparticles, i.e. nanocage with hollow interior, was studied thoroughly. Simulation of the optical properties of nanocages with different sizes and shapes was presented, which is essential for tuning the localized surface plasmon resonance peak. The edge length, side length of triangle, and wall thickness were used as structural parameters of truncated Au nanocage. The dependence of absorption efficiency, resonant wavelength, and absorption quantum yield on the structural parameters were discussed. Meanwhile, the applications of absorption quantum yield in biomedical imaging and laser induced thermal therapy were investigated. It was found that the phenomenon of multipolar plasmon resonances exists on truncated Au nanocage. Furthermore, the electric field distribution at different resonant wavelengths was also investigated. It is found that the electromagnetic field corresponds to the dipolar mode in an individual nanocage is largely distributed at the corners. Whereas, the electromagnetic field corresponds to the multipolar region is mainly located in the internal corners and edges.

    4. 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.

    5. Chemically synthesized Au-Fe3O4 nanostructures with controlled optical and magnetic properties

      NASA Astrophysics Data System (ADS)

      Velasco, Victor; Muñoz, Laura; Mazarío, Eva; Menéndez, Nieves; Herrasti, Pilar; Hernando, Antonio; Crespo, Patricia

      2015-01-01

      Au-Fe3O4 dumbbell-like, flower-like and core-shell nanostructures with different sizes ranging between 4-15 nm have been synthesized via the thermal decomposition of iron pentacarbonyl and reduction of gold salts. By means of the variation of the precursors’ molar ratio, the injection temperature and the reaction time, the optical and magnetic properties have been tailored. A strong dependence on the dielectric function of the present Fe3O4 nanoparticles (NPs) was detected. The gold characteristic plasmon peak shifts from 525 nm (pure gold NPs) to close to 600 nm showing an electron damping in the Au NPs surrounded by Fe3O4. These NPs are ferromagnetic at low temperature, exhibiting a coercive field ranging between 85-500 Oe, whereas they behave as a superparamagnetic system above the blocking temperature, which is found to be between 18-110 K. A high magnetic anisotropy is generated in the interface of Au-Fe3O4 NPs.

    6. 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.

    7. Imaging with mass spectrometry: a secondary ion and VUV-photoionization study of ion-sputtered atoms and clusters from GaAs and Au.

      PubMed

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

      2009-04-23

      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 As(2), Au, and Au(2), are more efficiently detected through the neutral channel. Continuously tuning the photon wavelength allows photoionization efficiency (PIE) curves to be obtained for sputtered As(m) (m = 1,2) and Au(n) (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 approximately 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.

    8. 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.

    9. 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}.

    10. Ohmic Pd/Zn/Au/LaB6/Au contacts on p-type In0.53Ga0.47As: Electrical and metallurgical properties

      NASA Astrophysics Data System (ADS)

      Ressel, P.; Leech, P. W.; Veit, P.; Nebauer, E.; Klein, A.; Kuphal, E.; Reeves, G. K.; Hartnagel, H. L.

      1998-07-01

      The development of a shallow and low-resistive contact on moderately doped (p≈5×1018cm-3) In0.53Ga0.47As is demonstrated. By reducing the layer thicknesses of a conventional Pd/Zn/Pd/Au scheme to a minimum and coupling this system to an outer Au layer via an amorphous LaB6 diffusion barrier, contact resistivities ⩽1×10-6 Ω cm2 were achieved only slightly exceeding that of the conventional scheme (2-4×10-7 Ω cm2). The contact reaction depth, however, could be reduced from several hundred to well below 100 nm, since the LaB6 barrier effectively prevents the outer Au layer from reaction with the semiconductor during contact formation. The influence of Zn content on electrical and metallurgical properties has been studied by varying it over orders of magnitude using both implantation and evaporation as a means of introducing Zn into the metallization. Implanted contacts with low Zn content annealed at 375 °C exhibit a reaction depth as low as 55 nm with the Zn diffusion depth practically coinciding with the reaction depth. If Zn is evaporated, the reaction depth is enhanced and the Zn diffusion depth exceeds the reaction depth noticeably. Secondary ion mass spectrometry demonstrated the onset of ohmic behavior to be correlated with the buildup of high interfacial Zn concentrations suggesting that these contacts conform to the standard model of interfacial doping. Simultaneously a solution phase emerges, reported here first, namely (Pd,Au)12(Ga,In)5As2 based on hexagonal Pd12Ga5As2 as revealed by cross-sectional transmission electron microscopy and x-ray diffraction analysis. Contacts with evaporated Zn exhibit stable resistivity during thermal stressing at 400 °C for 24 h. The stability loss for longer times is correlated with the appearance of (Au,Pd)9In4, a solution phase based on cubic Au9In4, evolving from indiffused Au and replacing increasingly the low-resistive (Pd,Au)12(Ga,In)5As2/p+-In0.53Ga0.47As junction areas.

    11. 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.

    12. 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.

    13. The Correlation of Stress-State and Nano-Mechanical Properties in Au

      SciTech Connect

      HOUSTON,JACK E.; JARAUSCH,K.F.; KIELY,J.D.; RUSSELL,P.E.

      1999-10-07

      A dependence of elastic response on the stress-state of a thin film has been demonstrated using the interfacial force microscope (IFM). Indentation response was measured as a function of the applied biaxial stress-state for 100 nm thick Au films. An increase in measured elastic modulus with applied compressive stress, and a decrease with applied tensile stress was observed. Measurements of elastic modulus before and after applying stress were identical indicating that the observed change in response is not due to a permanent change in film properties.

    14. 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.

    15. Synthesis and properties of plasma-polymerized polypyrrole/Au composite nanofibers.

      PubMed

      Zhou, Jie; Fisher, Ellen R

      2004-05-01

      Nanostructured composites have a wide variety of potential applications in microelectronics, chemical sensors, and electrochemical energy production. Here, we report the chemical, structural, and electrochemical characteristics of a nanostructured composite material formed from plasma-polymerized polypyrrole-coated Au fibers. The properties of the plasma-polymerized polypyrrole (PPPy) films were characterized by FTIR, X-ray photoelectron spectroscopy (XPS), and UV-Vis spectroscopy, as well as cyclic voltammetry (CV), and scanning electron microscopy (SEM). These spectroscopy analyses suggest that thermal treatment of the materials results in elimination of loosely-bound, low mass oligomers in the films. Mass spectral analysis of the plasma phase suggests that plasma polymerization of the pyrrole takes place on the substrate surface as a result of diffusion of radicals produced in the plasma. In addition, thermal treatment enhances the electrochemical properties of the PPPy films because of changes in the surface morphology and bulk structure of the films. However, as-deposited PPPy films coated on Au nanotubes demonstrate better electrochemical properties than as-deposited PPPy films coated on flat ITO electrodes as a result of the increase in surface area and decrease in film thickness.

    16. Interaction forces and conduction properties between multi wall carbon nanotube tips and Au(111).

      PubMed

      Luna, M; de Pablo, P J; Colchero, J; Gomez-Herrero, J; Baro, A M; Tokumoto, H; Jarvis, S P

      2003-07-01

      We have studied the interaction forces and electrical conduction properties arising between multiwall carbon nanotube tips and the Au(111) surface in air, by means of amplitude modulation scanning force microscopy, also called intermittent contact. We have centered our work on tips with metallic electronic structure and for the specific parameters used we have found a preliminary interaction range where there is no contact between tip and surface. Stable imaging in this non-contact range is possible with multiwall carbon nanotube tips. These tips have also been used to obtain simultaneous topographic and current maps of the surface. They show excellent properties as tips due to their high aspect ratio and durability, as a result of their elastic and non-reactive properties. Correspondingly, multiwall carbon nanotube tips allow high resolution local analysis of electrical conductivity on a nanometer scale.

    17. 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.

    18. 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

    19. 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.

    20. 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.

    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. Antibacterial activity of Ag-Au alloy NPs and chemical sensor property of Au NPs synthesized by dextran.

      PubMed

      Bankura, Kalipada; Maity, Dipanwita; Mollick, Md Masud Rahaman; Mondal, Dibyendu; Bhowmick, Biplab; Roy, Indranil; Midya, Tarapada; Sarkar, Joy; Rana, Dipak; Acharya, Krishnendu; Chattopadhyay, Dipankar

      2014-07-17

      Gold and silver-gold alloy nanoparticles with mean diameter of 10nm and narrow size distribution were prepared by reduction of the correspondent metal precursors using aqueous dextran solution which acts as both a reducing and capping agent. The formation of nanoparticles was characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS). The silver and gold nanoparticles exhibited absorption maxima at 425 and 551 nm respectively; while for the bimetallic Ag-Au alloy appeared 520 nm in between them. TEM images showed monodispersed particles in the range of 8-10nm. The crystallinity of the nanoparticles was assured by XRD analysis. DLS data gave particle size distribution. The dextran stabilized Au nanoparticles used as a colorimetric sensor for detection and estimation of pesticide present in water. The dextran stabilized Ag-Au alloy nanoparticles exhibited interesting antimicrobial activity against bacteria at micromolar concentrations. Copyright © 2014 Elsevier Ltd. All rights reserved.

    3. 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.

    4. Electronic Structure and Properties of Metal Cluster Isomers

      NASA Astrophysics Data System (ADS)

      Jena, Puru

      1997-03-01

      One of the most interesting features of clusters is that they exhibit many isomeric forms. The geometries, binding energies, and electronic structure of isomers of alkali and transition metal clusters have been studied using first principles calculations based on molecular orbital theory. The existence of energetically degenerate isomers manifests in many novel features in photoelectron spectroscopy, reactivity, and magnetic properties. The theoretical results will be used not only to explain recent anomalous experimental data but also to predict phenomena that could be verified by future experiments.

    5. 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.

    6. 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.

    7. Geometrical and electronic structures of Au(m)Ag(n) (2 < or = m + n < or = 8).

      PubMed

      Zhao, G F; Zeng, Z

      2006-07-07

      The structural and electronic properties of Au(m)Ag(n) binary clusters (2 < or = m + n < or = 8) have been investigated by density functional theory with relativistic effective core potentials. The results indicate that Au atoms tend to occupy the surface of Au(m)Ag(n) clusters (n > or = 2 and m > or = 2). As a result, segregation of small or big bimetallic clusters can be explained according to the atomic mass. The binding energies of the most stable Au(m)Ag(n) clusters increase with increasing m+n. The vertical ionization potentials of the most stable Au(m)Ag(n) clusters show odd-even oscillations with changing m+n. The possible dissociation channels of the clusters considered are also discussed.

    8. Ultraviolet properties of hot stars in globular clusters

      SciTech Connect

      Altner, B.M.

      1988-01-01

      Most of the interesting and important stages of stellar evolution beyond the horizontal branch (HB) occur in the temperature realms best investigated by ultraviolet (UV) astronomy. In this dissertation the author studies the UV properties of hot HB and post-HB stars found in a sample of galactic globular clusters, based on spectra obtained with the International Ultraviolet Explorer (IUE). Using techniques developed specifically for the purpose, he separates the overlapping spectra of individual hot stars in the crowded central regions of the clusters. He determines the physical properties of the separated core sources by comparing them to model stellar atmospheres, Population I standards, faint blue halo stars and previously known UV-bright cluster stars, from which he attempts to better understand their evolutionary status. The majority of the more than one hundred spatially separated components turn out to be individual blue HB stars, but a few have properties similar to those of the more evolved supra-HB stars or post-asymptotic-giant-branch (post-AGB) stars, substantially increasing the number of UV-bright stars found in galactic globular clusters. Derived properties of the post-AGB stars imply, through the use of the Paczynski mass-luminosity relation, that these stars span a very narrow range in total core mass, with a mean value near 0.55 Mass of sun - somewhat smaller than that derived for central stars of planetary nebulae in the galactic disk. Several of the clusters observed to have luminous ultraviolet sources in their cores have also shown the presence of a central cusp in the visual.

    9. Thickness Dependence of the Morphology and Electronic Properties of Ultrathin Quench Condensed Pb and Au Films

      NASA Astrophysics Data System (ADS)

      Ekinci, K. L.; Valles, J. M., Jr.

      1998-03-01

      Films formed by quench condensing (QC) metals onto substrates held at cryogenic temperatures (T<= 77K) have been used in numerous studies of the effects of disorder and dimensionality on the elec tronic properties of metals. Despite this, little direct information has been obtained regarding the interplay between QC film structure and electronic transport. For instance, it is not known wha t controls the thickness at which these films first become electrically continuous. In situ STM measurements reveal that the morphology of QC Pb and Au films depend strongly on thickness. Below a critical thickness (d_c), the films form a structureless morphology. This observation is consistent with the proposed amorphous state that is believed to precede the conducting, metallic phase. Above d_c, the films form a granular polycrystalline phase. We will present our latest in situ STM and STS measurements on the morphology and local electronic properties of quench condensed P b and Au films with different thicknesses. We will discuss the implications of these results for possible mechanisms for the onset of electrical conductivity in QC films.

    10. Anomalous random correlations of force constants on the lattice dynamical properties of disordered Au-Fe alloys

      NASA Astrophysics Data System (ADS)

      Kangsabanik, Jiban; Chouhan, Rajiv K.; Johnson, D. D.; Alam, Aftab

      2017-09-01

      Gold iron (Au-Fe) alloys are of immense interest due to their biocompatibility, anomalous Hall conductivity, and applications in various medical treatments. However, irrespective of the method of preparation, they often exhibit a high level of disorder with properties sensitive to the thermal or magnetic annealing temperatures. We calculate the lattice dynamical properties of Au1 -xFex alloys using density functional theory methods where, being multisite properties, reliable interatomic force constant (IFC) calculations in disordered alloys remain a challenge. We follow a twofold approach: (1) an accurate IFC calculation in an environment with nominally zero chemical pair correlations to mimic the homogeneously disordered alloy and (2) a configurational averaging for the desired phonon properties (e.g., dispersion, density of states, and entropy). We find an anomalous change in the IFC's and phonon dispersion (split bands) near x =0.19 , which is attributed to the local stiffening of the Au-Au bonds when Au is in the vicinity of Fe. Other results based on mechanical and thermophysical properties reflect a similar anomaly: Phonon entropy, e.g., becomes negative below x =0.19 , suggesting a tendency for chemical unmixing, reflecting the onset of a miscibility gap in the phase diagram. Our results match fairly well with reported data wherever available.

    11. 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.

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

      SciTech Connect

      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.

    13. 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.

    14. 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.

    15. 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.

    16. A reexamination of the I.S. results for the cluster compound Au55(PPh3)12Cl6

      NASA Astrophysics Data System (ADS)

      Thiel, R. C.; Dirken, M. W.; Zanoni, R.

      1990-07-01

      The observed low I.S. values [1] for the four distinct gold sites in the cluster compound Au55(PPh3)12Cl6 have been explained in terms of a decrease of the 6s electron density at the nucleus, due either to a lattice expansion or to a delocalization of 6s electrons over the ligand shell surrounding the gold core. Recent EXAFS measurements [2] indicate a single average distance between the gold atoms, about 3.5% less than for bulk gold. This not only excludes the lattice expansion hypothesis, it effectively increases the density of 6s electrons, making an explanation for the observed I.S. even more difficult. For an understanding of the I.S. values it is necessary to reconsider the probable occupation of the 5d orbitals within the framework provided by the XPS surface atom core level shifts developed by Citrin and Wertheim [3]. Partial confirmation has been found in preliminary XPS results [5]. The consequences for the f-factor and specific heat results [1] will also be examined.

    17. Infrared properties of the SDSS-maxBCG galaxy clusters

      NASA Astrophysics Data System (ADS)

      Roncarelli, M.; Pointecouteau, E.; Giard, M.; Montier, L.; Pello, R.

      2010-03-01

      Context. The physics of galaxy clusters has proven to be influenced by several processes connected with their galactic component which pollutes the intracluster medium (ICM) with metals, stars and dust. However, it is not clear whether the presence of diffuse dust can play a role in clusters physics since a characterisation of the infrared (IR) properties of galaxy clusters is very challenging and yet to be completely achieved. Aims: In our study we focus on the recent work of Giard et al. (2008, A&A, 490, 547) who performed a stacking analysis of the IRAS data in the direction of several thousands of galaxy clusters, providing a statistical characterisation of their IR luminosity and redshift evolution. We model the IR properties of the galactic population of the SDSS-maxBCG clusters (0.1properties of the galaxies of the SDSS-maxBCG clusters, we estimate their emission in the 60 and 100 μm IRAS bands making use of modeled spectral energy distributions of different spectral types (E/S0, Sa, Sb, Sc and starburst). We also consider the evolution of the galactic population/luminosity with redshift. Results: The total galactic emission, which is dominated by the contribution of star-forming late-type galaxies, is consistent with the observed signal. In fact, our galactic emission model slightly overestimates the observed fluxes, with the excess being concentrated in low-redshift clusters (z ⪉ 0.17). Conclusions: Our results indicate that, if present, the IR emission from intracluster dust must be very small compared to the one associated to the galaxy members. This translates into an upper limit on the dust-to-gas mass ratio in the ICM of Zd ⪉ 5 × 10-5. The excess in luminosity obtained at low redshift constitutes an indication that the cluster environment is driving a process

    18. 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.

    19. Intrinsic Magnetic Properties of fct FePt Nanocubes and Rods by Cluster Beam Deposition

      NASA Astrophysics Data System (ADS)

      Akdogan, Ozan; Li, Wanfeng; Hadjipanayis, George; Skomski, Ralph; Sellmyer, David

      2012-02-01

      In this work, single crystal fct FePt nanocubes have been successfully produced by a cluster beam deposition technique without the need of post annealing. Particles have been deposited by DC magnetron sputtering using high Ar pressures (0.5 to 2 Torr) on both single crystal Si substrates and Au grids for the measurement of magnetic and structural properties, respectively. The nanocubes have a uniform size distribution with an average size of 6.5 nm. At 1 Torr, the particles have the fct structure with an order parameter of 0.5 and a RT coercivity of 2 kOe with high switching fields seen in the hysteresis loop. Particle size was controlled by changing the pressure and power and also by ex-situ annealing. In addition to these nanocubes, micron size rods (which consist of 20 nm nanoparticles) with the fct structure have been observed near the cluster gun. These particles show a room temperature coercivity of 8 kOe with an order parameter of 0.85. Intrinsic magnetic properties (Curie temperature, HA, MS and magnetic viscosity) of the nanocubes and the nanoparticles (separated from the rods) have been extensively studied and the results will be reported.

    20. 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.

    1. Structure and Electronic Properties of Ionized PAH Clusters

      NASA Astrophysics Data System (ADS)

      Joblin, Christine; Kokkin, Damian L.; Sabbah, Hassan; Bonnamy, Anthony; Dontot, Leo; Rapacioli, Mathias; Simon, Aude; Spiegelman, Fernand; Parneix, Pascal; Pino, Thomas; Pirali, Olivier; Falvo, Cyril; Gamboa, Antonio; Brechignac, Philippe; Garcia, Gustavo A.; Nahon, Laurent

      2014-06-01

      Polycyclic aromatic hydrocarbon (PAH) clusters have been proposed as candidates for evaporating very small grains that are revealed by their mid-IR emission at the surface of UV-irradiated clouds in interstellar space. This suggestion is a motivation for further characterization of the properties of these clusters in particular when they are ionized. We have used a molecular beam coupled to the photoelectron-photoion coincidence spectrometer DELICIOUS II/ III at the VUV beamline DESIRS of the synchrotron SOLEIL to characterize the electronic properties of cationic coronene (C24H12) and pyrene (C16H10) clusters up to the pentamer and heptamer, respectively. These experimental results are analysed in the light of electronic structure calculations. Simulations of the properties of ionized PAH clusters are faced with the difficulty of describing charge delocalization in these large systems. We will show that recent developments combining a Density Functional Tight Binding method with Configuration Interaction scheme is successful in simulating the ionization potential, which gives strong confidence into the predicted structures for these PAH clusters. We will also present current effort to study charge transfer states by performing complementary measurements with the PIRENEA ion trap set-up. Joint ANR project GASPARIM, ANR-10-BLAN-501 M. Rapacioli, C. Joblin and P. Boissel Astron. & Astrophys., 429 (2005), 193-204. G. Garcia, H. Soldi-Lose and L. Nahon Rev. Sci. Instrum., 80 (2009), 023102; G. Garcia, B. Cunha de Miranda, M. Tia, S. Daly, L. Nahon, Rev. Sci. Instrum., 84 (2013), 053112 M. Rapacioli, A. Simon, L. Dontot and F. Spiegelman Phys. Status Solidi B, 249 (2) (2012), 245-258; L. Dontot, M. Rapacioli and F. Spiegelman (2014) submitted

    2. Kinematical evolution of tidally limited star clusters: rotational properties

      NASA Astrophysics Data System (ADS)

      Tiongco, Maria A.; Vesperini, Enrico; Varri, Anna Lisa

      2017-07-01

      We present the results of a set of N-body simulations following the long-term evolution of the rotational properties of star cluster models evolving in the external tidal field of their host galaxy, after an initial phase of violent relaxation. The effects of two-body relaxation and escape of stars lead to a redistribution of the ordered kinetic energy from the inner to the outer regions, ultimately determining a progressive general loss of angular momentum; these effects are reflected in the overall decline of the rotation curve as the cluster evolves and loses stars. We show that all of our models share the same dependence of the remaining fraction of the initial rotation on the fraction of the initial mass lost. As the cluster evolves and loses part of its initial angular momentum, it becomes increasingly dominated by random motions, but even after several tens of relaxation times, and losing a significant fraction of its initial mass, a cluster can still be characterized by a non-negligible ratio of the rotational velocity to the velocity dispersion. This result is in qualitative agreement with the recently observed kinematical complexity that characterizes several Galactic globular clusters.

    3. 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.

    4. 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.

    5. 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.

    6. 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.

    7. 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.

    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. Properties of the galaxy population in hydrodynamical simulations of clusters

      NASA Astrophysics Data System (ADS)

      Saro, A.; Borgani, S.; Tornatore, L.; Dolag, K.; Murante, G.; Biviano, A.; Calura, F.; Charlot, S.

      2006-11-01

      We present a study of the galaxy population predicted by hydrodynamical simulations of galaxy clusters. These simulations, which are based on the GADGET-2 TREE + SPH code, include gas cooling, star formation, a detailed treatment of stellar evolution and chemical enrichment, as well as supernova energy feedback in the form of galactic winds. As such, they can be used to extract the spectrophotometric properties of the simulated galaxies, which are identified as clumps in the distribution of star particles. Simulations have been carried out for a representative set of 19 cluster-sized haloes, having mass M200 in the range 5 × 1013-1.8 × 1015h-1Msolar. All simulations have been performed for two choices of the stellar initial mass function (IMF), namely using a standard Salpeter IMF with power-law index x = 1.35, and a top-heavy IMF with x = 0.95. In general, we find that several of the observational properties of the galaxy population in nearby clusters are reproduced fairly well by simulations. A Salpeter IMF is successful in accounting for the slope and the normalization of the colour-magnitude relation for the bulk of the galaxy population. In contrast, the top-heavy IMF produces too red galaxies, as a consequence of their exceedingly large metallicity. Simulated clusters have a relation between mass and optical luminosity, which generally agrees with observations, both in normalization and in slope. Also in keeping with observational results, galaxies are generally bluer, younger and more star forming in the cluster outskirts. However, we find that our simulated clusters have a total number of galaxies which is significantly smaller than the observed one, falling short by about a factor of 2-3. We have verified that this problem does not have an obvious numerical origin, such as lack of mass and force resolution. Finally, the brightest cluster galaxies are always predicted to be too massive and too blue, when compared to observations. This is due to gas

    10. 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.

    11. 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.

    12. Derivatization of Phosphine Ligands with Bulky Deltahedral Zintl Clusters-Synthesis of Charge Neutral Zwitterionic Tetrel Cluster Compounds [(Ge9{Si(TMS)3}2)(t)Bu2P]M(NHC(Dipp)) (M: Cu, Ag, Au).

      PubMed

      Geitner, Felix S; Dums, Jasmin V; Fässler, Thomas F

      2017-08-30

      Reactions of silylated clusters [Ge9{Si(TMS)3}3](-) or [Ge9{Si(TMS)3}2](2-) with dialkylhalophosphines R2PCl (Cy, (i)Pr, (t)Bu) at ambient temperature yield the first tetrel Zintl cluster compounds bearing phosphine moieties. Varying reactivity of the dialkylhalophosphines toward the silylated clusters is observed depending on the bulkiness of the phosphine's alkyl substituents and on the number of hypersilyl groups at the tetrel cluster. Reactions between phosphines with small cyclohexyl- (Cy) or isopropyl- ((i)Pr) groups and the tris-silylated cluster [Ge9{Si(TMS)3}3](-) yield the novel neutral cluster compounds [Ge9{Si(TMS)3}3PR2] (R: Cy (1), (i)Pr (2)) with discrete Ge-P exo bonds. By contrast, the bulkier phosphine (t)Bu2PCl does not react with [Ge9{Si(TMS)3}3](-) due to steric crowding. However, the reaction with the bis-silylated cluster [Ge9{Si(TMS)3}2](2)(-) yields the novel cluster compound [Ge9{Si(TMS)3}2P(t)Bu2](-) (3). Subsequent reactions of compound 3 with NHC(Dipp)MCl (M: Cu, Ag, Au) yield the charge neutral zwitterionic compounds [(Ge9{Si(TMS)3}2)(t)Bu2P]M(NHC(Dipp)) (M: Cu, Ag, Au) (4-6), in which compound 3 acts as a phosphine ligand bearing a bulky tetrel Zintl cluster moiety. Compounds 4-6 also represent the first uncharged examples for 3-fold substituted tetrel Zintl clusters.

    13. 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.

    14. X-ray absorbing and mechanical properties of Au-C film for x-ray mask absorber

      NASA Astrophysics Data System (ADS)

      Fukushima, Hiroshi; Yamada, Hitomi; Matsui, Teruyuki; Tagawa, Takashi; Morita, Shinzo; Hattori, Shuzo

      1990-05-01

      The X-ray absorption and mechanical properties of gold containing (Au-C) absorber formed on polyimide membrane for X-ray lithography mask have been investigated. The Au-C films were deposited by the same method as the previous investigators(Itoh et al.)1. (1) The compositional dependence of film stress before and after the exposure to SOR radiation has been observed. As a result, the stress in film changed monotonically ranging from compression (-3xlO8N/m2) to tension (l.2xlO8N/m2) with increasing Au content. Zero film stress was observed at Au atomic composition of 30%. Films originally being compressive (-l.5xlO7N/m2) were found to become tensile (l.OxlO8N/m2) after absorbing l500J/cm3 X-ray. This tendency differs from that of the BN film observed by King et al (2) X-ray absorption ratio in Au-C films were determined by measuring the amount of reduced thickness of resist on development after the exposure of X-ray through Au-C films with various composition ratios. It was found that it tended to fall from 92% to 68% with a decrease of Au atomic composition ratio from 0.85 to 0.11 at the constant absorber thickness of 0.5 pm. (3) Au-C films of various atomic composition ratio were patterned with EB lithography using the PMMA(Polyrnethylmethacrylate) resist and Reactive Ion Etching (RIE) with 02 gas. It was found that the etching rate of the film decreases with increasing Au content. The typical obtained value was approximately 100A/min at around 50% to 60% of Au composition and this was about 4 times higher than etching rate of pure Au. It is concluded that the Au-C absorber on polyimide membrane X-ray mask is practical for VLSI use for submicron pattern fabrication.

    15. Quantum Monte Carlo methods and lithium cluster properties

      SciTech Connect

      Owen, Richard Kent

      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. 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.

    17. 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.

    18. 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

    19. 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.

    20. 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

    1. Effect of dynamical interactions on integrated properties of globular clusters

      NASA Astrophysics Data System (ADS)

      Zhuang, Yulong; Zhang, Fenghui; Anders, Peter; Ruan, Zhifeng; Cheng, Liantao; Kang, Xiaoyu

      2015-02-01

      Globular clusters (GCs) are generally treated as natural validators of simple stellar population (SSP) models. However, there are still some differences between real GCs and SSPs. In this work, we use a direct N-body simulation code NBODY6 to study the influences of dynamical interactions, metallicity and primordial binaries on Milky Way GCs' integrated properties. Our models start with N = 100 000 stars, covering a metallicity range Z = 0.0001 ˜ 0.02, a subset of our models contain primordial binaries, resulting in a binary fraction as currently observed at a model age of GCs. Stellar evolution and external tidal field representative for an average Milky Way GC are taken into consideration. The integrated colours and Lick indices are calculated using BaSeL and Bluered stellar spectral libraries separately. By including dynamical interactions, our model clusters show integrated features (i.e. colours up to 0.01 mag bluer, Hβ up to 0.1 Å greater and [MgFe]' 0.05 Å smaller) making the clusters appear slightly younger than the model clusters without dynamical interactions. This effect is caused mainly by the preferential loss of low-mass stars which have a stronger contribution to redder passbands as well as different spectral features compared to higher mass stars. In addition, this effect is larger at lower metallicities. On the contrary, the incorporation of primordial binaries reduces this effect.

    2. 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.

    3. Effect of Au coating on optical properties of CdS nanoparticles and their optical limiting studies

      NASA Astrophysics Data System (ADS)

      Mathew, S.; Samuel, Boni; Mujeeb, A.; Kailasnath, M.; Nampoori, V. P. N.; Girijavallabhan, C. P.

      2017-10-01

      We synthesized Au coated CdS nanoparticles by a novel synthesis route in which CdS is acting as a core. Transmission electron microscopy of the prepared CdS and Au coated nanoparticles shows that the size of the nanoparticles are in the range of 5 nm. TEM elemental maps of the Au coated CdS nanoparticles confirms the presence of Au nanoparticles on the surface of CdS nanoparticles. Nonlinear optical characteristics of these nanoparticles embedded in PVA thin films were studied by the Z-scan technique using Q-switched nanosecond Nd:YAG laser (532 nm). An enhancement in nonlinear optical property was observed for the prepared Au coated CdS embedded PVA nanocomposite films compared to that of bare CdS embedded PVA nanocomposite films. Nonlinear optical absorption coefficient and positive nonlinear refractive index of these films were measured to be 6.28 × 10-6cm/W and 4.86 × 10-11 cm2/W respectively. Au coated CdS nanoparticles embedded PVA film possesses a low limiting threshold of 34 MW/cm2 and also possess good positive nonlinear refractive index making suitable for optical limiting and optical switching applications.

    4. 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.

    5. 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.

    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. 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

    8. 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

    9. 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.

    10. 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.

    11. Electronic Structure and Magnetic Properties of Mixed Clusters.

      NASA Astrophysics Data System (ADS)

      Reddy, Budda V.

      We have investigated the geometry, electronic structure and magnetic properties of low dimensional structures like the clusters and multi-layers. The first part of this work is devoted to studies on the effect of geometry, size, symmetry and dimensionality on the magnetic properties of transition metal elements. The effect of geometry is studied by performing Monte Carlo Simulations in order to investigate the behavior of magnetic moment as a function of field and temperature in antiferromagnetic Cuboctahedral and Icosahedral clusters. Size and symmetry are exploited to reveal giant magnetic moments in 13-atom 4d-clusters of Rh, Ru and Pd. Further, it is shown that dimensionality and size play a very important role in determining the nature of magnetic coupling in Fe layers separated by the spacer layers of Sc, Ti, V, Cr, Co, Ni and Cu. The later part of the thesis is devoted to the study of Met-Car; an unusually stable cage like structure containing 8 Ti and 12 C atoms. The energetics of Ti_8C _{12} are compared with that of the bulk fcc fragments Ti_{14 }C_{13} and the processes that govern the formation of each are illustrated through studies on small clusters of TiC, TiC_2, Ti_2C_2 and Ti_2C_3. The fragmentation patterns of Ti_8C_{12 } are investigated and a special fragment Ti _4C_{12} is shown to possess a huge electron affinity of 4.8 eV. Towards the end, we point the differences in the formation patterns of metal-carbides and metal-nitrides.

    12. 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.

    13. 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.

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

      NASA Astrophysics Data System (ADS)

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

      2005-05-01

      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.

    15. 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.

    16. 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.

    17. 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.

    18. 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.

    19. 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.

    20. Benchmark study of structural and vibrational properties of scandium clusters

      NASA Astrophysics Data System (ADS)

      Sajjad, Saira; Maria; Mahmood, Tariq; Ayub, Khurshid

      2017-08-01

      Geometries and most stable spin states of Sc2 and Sc3 are studied through coupled cluster CCSD(T) calculations. The CCSD(T) calculations at dunning series basis sets (aug-cc-pVDZ, aug-cc-pVTZ and aug-cc-pVQZ) have been performed in order to analyze the stable structure and spin state of the Sc2 and Sc3. Then, a series of diverse DFT methods at different basis sets (6-31G (d), LANL2DZ and LANL2MB) are assessed for structural and vibrational properties in order to propose low cost accurate alternative to CCSD(T). Among all the employed DFT methods, BPV86/LANL2MB delivered better results for structural and frequency analysis. On the basis of better agreement, BPV86/LANL2MB is taken for the structural and vibrational analysis of the higher cluster n = 4-14. The vibrational analysis for higher clusters of scandium is reported for the first time.

    1. 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.

    2. Automatic detection of false annotations via binary property clustering

      PubMed Central

      Kaplan, Noam; Linial, Michal

      2005-01-01

      Background Computational protein annotation methods occasionally introduce errors. False-positive (FP) errors are annotations that are mistakenly associated with a protein. Such false annotations introduce errors that may spread into databases through similarity with other proteins. Generally, methods used to minimize the chance for FPs result in decreased sensitivity or low throughput. We present a novel protein-clustering method that enables automatic separation of FP from true hits. The method quantifies the biological similarity between pairs of proteins by examining each protein's annotations, and then proceeds by clustering sets of proteins that received similar annotation into biological groups. Results Using a test set of all PROSITE signatures that are marked as FPs, we show that the method successfully separates FPs in 69% of the 327 test cases supplied by PROSITE. Furthermore, we constructed an extensive random FP simulation test and show a high degree of success in detecting FP, indicating that the method is not specifically tuned for PROSITE and performs well on larger scales. We also suggest some means of predicting in which cases this approach would be successful. Conclusion Automatic detection of FPs may greatly facilitate the manual validation process and increase annotation sensitivity. With the increasing number of automatic annotations, the tendency of biological properties to be clustered, once a biological similarity measure is introduced, may become exceedingly helpful in the development of such automatic methods. PMID:15755318

    3. 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

    4. 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.

    5. Surface properties of clean and Au or Pd covered hematite (α-Fe(2)O(3)) (0001).

      PubMed

      Kiejna, Adam; Pabisiak, Tomasz

      2012-03-07

      The structure and electronic properties of different terminations of the α-Fe(2)O(3)(0001) surface were studied with spin-polarized density functional theory (DFT) and the DFT + U method accounting for the effect of strong on-site Coulomb correlations. The results for lattice relaxation, electronic and magnetic properties are presented and discussed. Though the DFT and DFT + U methods provide qualitatively very similar surface geometries they differ very much in the prediction of the electronic and magnetic properties, and the surface energetics of the clean α-Fe(2)O(3)(0001). The most stable single iron terminated (0001) surface and the oxygen-rich termination were chosen to study Au and Pd atom adsorption. The results show that both Au and Pd bind strongly to hematite surfaces and induce large changes in their geometry. The DFT + U bonding is weaker by 0.3-0.6 eV than DFT on the iron terminated surface and about 2 eV stronger on the oxygen terminated one. The binding is stronger for Pd than Au and for both adsorbates is distinctly stronger at the oxygen than at the iron terminated surface. On the iron terminated surface the adsorption binding energy per adatom increases both with Au and Pd coverage, whereas for the oxygen terminated one the opposite trend is observed.

    6. Ab initio study of the electronic and optical properties of Ag3AuS2 polymorphs

      NASA Astrophysics Data System (ADS)

      Shah, Syed Sarmad Ali; Khan, Afzal; Haidar Khan, Shah; Muhammad, Nisar; Ayaz Khan, Saleem; Gulbahar Ashiq, M.; Murtaza, G.

      2017-08-01

      Natural and synthetic uytenbogaardtite (Ag3AuS2) polymorphs have been studied for their structural, compositional and thermodynamic properties. We investigated their electronic and optical properties for the first time using density functional theory. These calculations are based on the full potential linearized augmented plane wave method using the modified Becke-Johnson potential. Our calculations reveal that Ag3AuS2 is a direct band gap semiconductor exhibiting three crystal phases, cubic, trigonal and triclinic. The calculated band gaps for cubic, trigonal and triclinic phases are 1.15, 2.15 and 1.73 eV, respectively. The band gaps of the Ag3AuS2 polymorphs in the near infrared and visible region highlight the importance of these polymorphs for optoelectronic applications such as resistive switches, low-loss optical fibers, thin-film solar cells and thin-film photovoltaic devices. Furthermore, our calculations show that the electronic and optical properties of Ag3AuS2 are crystal phase dependent.

    7. 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.

    8. 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.

    9. 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

    10. 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.

    11. σ-Aromatic cyclic M3(+) (M = Cu, Ag, Au) clusters and their complexation with dimethyl imidazol-2-ylidene, pyridine, isoxazole, furan, noble gases and carbon monoxide.

      PubMed

      Pan, Sudip; Saha, Ranajit; Mandal, Subhajit; Chattaraj, Pratim K

      2016-04-28

      The σ-aromaticity of M3(+) (M = Cu, Ag, Au) is analyzed and compared with that of Li3(+) and a prototype σ-aromatic system, H3(+). Ligands (L) like dimethyl imidazol-2-ylidene, pyridine, isoxazole and furan are employed to stabilize these monocationic M3(+) clusters. They all bind M3(+) with favorable interaction energy. Dimethyl imidazol-2-ylidene forms the strongest bond with M3(+) followed by pyridine, isoxazole and furan. Electrostatic contribution is considerably more than that of orbital contribution in these M-L bonds. The orbital interaction arises from both L → M σ donation and L ← M back donation. M3(+) clusters also bind noble gas atoms and carbon monoxide effectively. In general, among the studied systems Au3(+) binds a given L most strongly followed by Cu3(+) and Ag3(+). Computation of the nucleus-independent chemical shift (NICS) and its different extensions like the NICS-rate and NICS in-plane component vs. NICS out-of-plane component shows that the σ-aromaticity in L bound M3(+) increases compared to that of bare clusters. The aromaticity in pyridine, isoxazole and furan bound Au3(+) complexes is quite comparable with that in the recently synthesized Zn3(C5(CH3)5)3(+). The energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital also increases upon binding with L. The blue-shift and red-shift in the C-O stretching frequency of M3(CO)3(+) and M3(OC)3(+), respectively, are analyzed through reverse polarization of the σ- and π-orbitals of CO as well as the relative amount of OC → M σ donation and M → CO π back donation. The electron density analysis is also performed to gain further insight into the nature of interaction.

    12. Manipulating the optical properties of symmetrically branched Au/Pd nanocrystals through interior design.

      PubMed

      DeSantis, Christopher J; Skrabalak, Sara E

      2014-05-25

      Au/Pd octopods with hollow, cubic interiors and Oh symmetry were synthesized for the first time by etching core@shell Pd@Au/Pd octopods to selectively remove their Pd interiors. Integration of multiple architectural features - in this case branching symmetry, composition, and interior design - into one nanostructure provides design strategies to new plasmonic colloids.

    13. Evolution of the multiscale statistical properties of corotating streams from 1 to 95 AU

      NASA Astrophysics Data System (ADS)

      Burlaga, L. F.; Wang, C.; Richardson, J. D.; Ness, N. F.

      2003-07-01

      This paper discusses the multiscale structure of the large-scale speed fluctuations between 1 and 95 AU during the declining phase of the solar cycle, when corotating streams are dominant structures close to the Sun. A deterministic, multifluid, one-dimensional MHD model with the WIND data at 1 AU during 1995 as input was used to compute the time series of daily averages of speed, V(ti), with a length on the order of 1 year at R = 5, 10, … 95 AU, from which we calculated various statistical functions describing the solar wind speed. The probability distribution functions (PDFs) of the running speed differences dVn(ti) were calculated at scales τ from 1 to 64 days. The theoretical PDFs at 50 AU have the same qualitative forms as those observed by Voyager 2 (V2) between 46 and 49 AU. The theoretical PDF at a scale of 1 day at 15 AU agrees with the corresponding PDF observed by V2 between 13 and 16 AU. With increasing distance from the Sun, the width of the predicted PDF with τ = 1 decreases and the tail becomes more prominent. The standard deviation of dVn(ti) at various R computed from the model, SD(τ, R), decreases nearly exponentially with increasing R, and it is consistent with the observations of SD(τ, R) made by V2 near 15 and 50 AU. The skewness at a scale of 1 day increases almost linearly with R beyond ≈35 AU, but it shows structure between 5 and 35 AU; it is consistent with the observations of V2 near 15 and 50 AU. The theoretical power spectral density of the speed fluctuations, PSD(f, R), agrees with the observations of V2 near 15 and 50 AU. For frequencies f > 8.5 × 10-7 Hz, PSD(f, R) ∝ f-s(R). The observed and predicted s are ≤-2 beyond 40 AU, consistent with the jump-ramp structure of V(t) in the distant heliosphere. We predict that the PDF for τ = 1 which will be observed by V2 at 70 AU in 2003 will have a core whose width is only ≈5 km/s and a tail extending up to 60 km/s that represents the major jumps in the speed profile. The

    14. 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.

    15. 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.

    16. 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.

    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. 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.

    19. 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.

    20. Ultrasoft magnetic properties in nanocrystalline alloy Finemet with Au substituted for Cu

      NASA Astrophysics Data System (ADS)

      Chau, N.; Hoa, N. Q.; The, N. D.; Niem, P. Q.

      2006-09-01

      The amorphous ribbon Fe 73.5Si 13.5B 9Nb 3Au 1 has been prepared by rapid cooling on a copper wheel. The ribbon is 16.8 μm thick and 7 mm wide. The DSC curves show the first peak at 547-579 °C (corresponds to the crystallization of α-Fe(Si) phase) depending on heating rate from 10 to 50 °C/min which is a little higher than that of pure Finemet (542-570 °C, respectively). From the Kissinger plot, the crystallization activation energy is determined and shown to be 2.8 eV for α-Fe(Si) phase, less than that of Finemet ( E=3.25 eV). By annealing at 530 °C for 30, 60 and 90 min, the crystallization volume fraction of α-Fe(Si) phase increased from 73% to 78% and 84%, respectively. After appropriate annealing, the ultrasoft magnetic properties are achieved. The maximum magnetic entropy change, ∣Δ Sm∣ max, showed a giant value of 7.8 J/kg K which occurred at around Curie temperature of amorphous phase of the ribbon.

    1. 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

    2. 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

    3. 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.

    4. 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.

    5. Fundamental properties of galaxy clusters: A prelude to large scale Sunyaev- Zel'dovich effect/near-IR cluster surveys

      NASA Astrophysics Data System (ADS)

      Lin, Yen-Ting

      Within the context of precision cosmology, the systematics of a cluster survey must be carefully controlled and understood. These require knowledge of the selection function of the clusters, the sample variance, the sources of contamination, and evolution of clusters. For surveys aiming to study the nature of the dark energy that drives the accelerating expansion of the Universe, probing the redshift range z = 1--2 is essential. This can be most efficiently carried out by a Sunyaev-Zel'dovich effect (SZE) survey supplemented with near-IR follow-up observations. The cluster sample with SZE+near-IR data will also provide an excellent opportunity for understanding the galaxy population evolution in clusters. This dissertation is developed under the two themes central to such a survey, i.e. the control of systematics, and the nature and evolution of cluster galaxy populations. For the first part, we conduct an analysis of a deep SZE survey and offer careful considerations for determining the survey mass sensitivity and for extracting cosmological constraints. In addition, because the radio- loud AGNs can potentially contaminate the cluster SZE signal, we investigate the radio properties of cluster AGNs to facilitate modeling their effects on the survey yields. The second thrust of the dissertation is a systematic survey of the near-IR properties of cluster galaxies. With a large nearby cluster sample that spans a wide range in mass, we study scaling relations between the total galaxy luminosity or number and the cluster binding mass. The origins of such correlations are discussed in terms of a variation of star formation efficiency with cluster mass, various dynamical processes that affect galaxy evolution, and the hierarchical formation of structure. We proceed to study the properties of various cluster components, including the brightest cluster galaxies (BCGs) and the stars and gas that exist within the intracluster space. Constraints on BCG formation and the

    6. Coope