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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. Supramolecular functionalization and concomitant enhancement in properties of Au(25) clusters.

    PubMed

    Mathew, Ammu; Natarajan, Ganapati; Lehtovaara, Lauri; Häkkinen, Hannu; Kumar, Ravva Mahesh; Subramanian, Venkatesan; Jaleel, Abdul; Pradeep, Thalappil

    2014-01-28

    We present a versatile approach for tuning the surface functionality of an atomically precise 25 atom gold cluster using specific host-guest interactions between β-cyclodextrin (CD) and the ligand anchored on the cluster. The supramolecular interaction between the Au25 cluster protected by 4-(t-butyl)benzyl mercaptan, labeled Au25SBB18, and CD yielding Au25SBB18∩CDn (n = 1, 2, 3, and 4) has been probed experimentally using various spectroscopic techniques and was further analyzed by density functional theory calculations and molecular modeling. The viability of our method in modifying the properties of differently functionalized Au25 clusters is demonstrated. Besides modifying their optoelectronic properties, the CD moieties present on the cluster surface provide enhanced stability and optical responses which are crucial in view of the potential applications of these systems. Here, the CD molecules act as an umbrella which protects the fragile cluster core from the direct interaction with many destabilizing agents such as metal ions, ligands, and so on. Apart from the inherent biocompatibility of the CD-protected Au clusters, additional capabilities acquired by the supramolecular functionalization make such modified clusters preferred materials for applications, including those in biology. PMID:24313537

  3. Structures and chiroptical properties of the BINAS-monosubstituted Au38(SCH3)24 cluster

    NASA Astrophysics Data System (ADS)

    Molina, Bertha; Sánchez-Castillo, Ariadna; Knoppe, Stefan; Garzón, Ignacio L.; Bürgi, Thomas; Tlahuice-Flores, Alfredo

    2013-10-01

    The structure and optical properties of a set of R-1,1'-binaphthyl-2,2'-dithiol (R-BINAS) monosubstituted A-Au38(SCH3)24 clusters are studied by means of time dependent density functional theory (TD-DFT). While it was proposed earlier that BINAS selectively binds to monomer motifs (SR-Au-SR) covering the Au23 core, our calculations suggest a binding mode that bridges two dimer (SR-Au-SR-Au-RS) motifs. The more stable isomers show a negligible distortion induced by BINAS adsorption on the Au38(SCH3)24 cluster which is reflected by similar optical and Circular Dichroism (CD) spectra to those found for the parent cluster. The results furthermore show that BINAS adsorption does not enhance the CD signals of the Au38(SCH3)24 cluster.The structure and optical properties of a set of R-1,1'-binaphthyl-2,2'-dithiol (R-BINAS) monosubstituted A-Au38(SCH3)24 clusters are studied by means of time dependent density functional theory (TD-DFT). While it was proposed earlier that BINAS selectively binds to monomer motifs (SR-Au-SR) covering the Au23 core, our calculations suggest a binding mode that bridges two dimer (SR-Au-SR-Au-RS) motifs. The more stable isomers show a negligible distortion induced by BINAS adsorption on the Au38(SCH3)24 cluster which is reflected by similar optical and Circular Dichroism (CD) spectra to those found for the parent cluster. The results furthermore show that BINAS adsorption does not enhance the CD signals of the Au38(SCH3)24 cluster. Electronic supplementary information (ESI) available: Comparison of calculated and experimental optical absorption and CD spectra of the A-38 enantiomer; bond distribution of the A-38 enantiomer, and four studied regioisomers; tables with the excitation energies, oscillator strengths and weights of the electronic transitions; xyz relaxed coordinates of studied regioisomers, frontier orbitals of the relaxed structures. See DOI: 10.1039/c3nr03403h

  4. Strong non-linear effects in the chiroptical properties of the ligand-exchanged Au38 and Au40 clusters

    NASA Astrophysics Data System (ADS)

    Knoppe, Stefan; Dass, Amala; Bürgi, Thomas

    2012-06-01

    Ligand exchange reactions on size-selected Au38(2-PET)24 and Au40(2-PET)24 clusters (2-PET: 2-phenylethylthiol) with mono- and bi-dentate chiral thiols were performed. The reactions were monitored with MALDI mass spectrometry and the arising chiroptical properties were compared to the number of incorporated chiral ligands. Only a small fraction of chiral ligands is needed to induce significant optical activity to the clusters. The use of bidentate 1,1'-binaphthyl-2,2'-dithiol (BINAS) leads to slow exchange, but the optical activity measured is strong. Moreover, a non-linear behaviour between optical activity and the number of chiral ligands is found in the BINAS case for both Au38 and Au40, which may indicate different exchange rates of enantiopure BINAS with the enantiomers of inherently chiral (but racemic) clusters. This is ascribed to effects arising from the bidentate nature of BINAS. In contrast, the use of monodentate camphor-10-thiol (CamSH) leads to comparably fast exchange on both clusters. The arising optical activity is weak. This is the first study where chiroptical effects are directly correlated with the composition of the ligand shell.Ligand exchange reactions on size-selected Au38(2-PET)24 and Au40(2-PET)24 clusters (2-PET: 2-phenylethylthiol) with mono- and bi-dentate chiral thiols were performed. The reactions were monitored with MALDI mass spectrometry and the arising chiroptical properties were compared to the number of incorporated chiral ligands. Only a small fraction of chiral ligands is needed to induce significant optical activity to the clusters. The use of bidentate 1,1'-binaphthyl-2,2'-dithiol (BINAS) leads to slow exchange, but the optical activity measured is strong. Moreover, a non-linear behaviour between optical activity and the number of chiral ligands is found in the BINAS case for both Au38 and Au40, which may indicate different exchange rates of enantiopure BINAS with the enantiomers of inherently chiral (but racemic) clusters

  5. Probing the Unique Size-Dependent Properties of Small Au Clusters, Au Alloy Clusters, and CO Chemisorbed Au Clusters in the Gas Phase

    SciTech Connect

    Zhai, Hua-jin; Li, Xi; Wang, Lai S.

    2007-04-01

    When materials are reduced in size to the nanometer scale, their physical and chemical properties undergo major changes and become size-dependent, forming the foundation for nanoscience and nanotechnology. Gold nanoparticles and small gold clusters have been the focus of intensive research activities lately. The modern “goldrush” is largely motivated by the recent discoveries that (i) nanogold shows unexpected catalytic properties for a wide spectrum of chemical reactions [1], (ii) nanogold enables selective binding to biomolecules such as DNA and thus can serve as biosensors [2], (iii) gold has important potential applications in nanoelectronics [3,4], and (iv) gold clusters and gold-containing compounds possess unique chemical properties [5]. All these golden discoveries have made gold a surprising and rewarding subject of investigation in nanoscience and cluster science. Indeed, some of our oldest notions regarding gold, such as its inertness, are being changed dramatically by the recent findings in nanogold.

  6. 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.

  7. Au20: A Tetrahedral Cluster

    SciTech Connect

    Li, Jun; Li, Xi; Zhai, Hua Jin; Wang, Lai S.

    2003-02-07

    Photoelectron spectroscopy revealed that a 20 atom gold cluster has an extremely large energy gap, which is even greater than that of C60, and an electron affinity comparable with that of C60. This observation suggests that the Au20 cluster must be extremely stable and chemically inert. Using relativistic density functional calculations, we found that Au20 possesses a remarkable tetrahedral structure, which is a fragment of the bulk face-centered cubic lattice of gold with a small structural relaxation. Au20 is thus a true cluster molecule, while at the same time it is exactly part of the bulk, but with very different properties. The tetrahedral Au20 may possess interesting catalytic properties and may be synthesized in bulk quantity or assembled on non-interacting surfaces.

  8. 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. PMID:23032860

  9. 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.

  10. Structure, stability, and electronic property of carbon-doped gold clusters Au{sub n}C{sup −} (n = 1–10): A density functional theory study

    SciTech Connect

    Yan, Li-Li; Liu, Yi-Rong; Huang, Teng; Jiang, Shuai; Wen, Hui; Gai, Yan-Bo; Zhang, Wei-Jun E-mail: wjzhang@aiofm.ac.cn; Huang, Wei E-mail: wjzhang@aiofm.ac.cn

    2013-12-28

    The equilibrium geometric structures, relative stabilities, and electronic properties of Au{sub n}C{sup −} and Au{sub n+1}{sup −} (n = 1–10) clusters are systematically investigated using density functional theory with hyper-generalized gradient approximation. The optimized geometries show that one Au atom capped on Au{sub n−1}C{sup −} clusters is a dominant growth pattern for Au{sub n}C{sup −} clusters. In contrast to Au{sub n+1}{sup −} clusters, Au{sub n}C{sup −} clusters are most stable in a quasi-planar or three-dimensional structure because C doping induces the local non-planarity while the rest of the structure continues to grow in a planar mode, resulting in an overall non-2D configuration. The relative stability calculations show that the impurity C atom can significantly enhance the thermodynamic stability of pure gold clusters. Moreover, the effect of C atom on the Au{sub n}{sup −} host decreases with the increase of cluster size. The HOMO-LUMO gap curves show that the interaction of the C atom with Au{sub n}{sup −} clusters improves the chemical stability of pure gold clusters, except for Au{sub 3}{sup −} and Au{sub 4}{sup −} clusters. In addition, a natural population analysis shows that the charges in corresponding Au{sub n}C{sup −} clusters transfer from the Au{sub n}{sup −} host to the C atom. Meanwhile, a natural electronic configuration analysis also shows that the charges mainly transfer between the 2s and 2p orbitals within the C atom.

  11. Gold nanowired: a linear (Au25)(n) polymer from Au25 molecular clusters.

    PubMed

    De Nardi, Marco; Antonello, Sabrina; Jiang, De-en; Pan, Fangfang; Rissanen, Kari; Ruzzi, Marco; Venzo, Alfonso; Zoleo, Alfonso; Maran, Flavio

    2014-08-26

    Au25(SR)18 has provided fundamental insights into the properties of clusters protected by monolayers of thiolated ligands (SR). Because of its ultrasmall core, 1 nm, Au25(SR)18 displays molecular behavior. We prepared a Au25 cluster capped by n-butanethiolates (SBu), obtained its structure by single-crystal X-ray crystallography, and studied its properties both experimentally and theoretically. Whereas in solution Au25(SBu)18(0) is a paramagnetic molecule, in the crystal it becomes a linear polymer of Au25 clusters connected via single Au-Au bonds and stabilized by proper orientation of clusters and interdigitation of ligands. At low temperature, [Au25(SBu)18(0)]n has a nonmagnetic ground state and can be described as a one-dimensional antiferromagnetic system. These findings provide a breakthrough into the properties and possible solid-state applications of molecular gold nanowires. PMID:25088331

  12. 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. PMID:22225504

  13. 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.

  14. DNA-stabilized Ag-Au bimetallic clusters: the effects of alloying and embedding on optical properties.

    PubMed

    Palagin, Dennis; Doye, Jonathan P K

    2016-08-10

    Global geometry optimization and time-dependent density functional theory calculations have been used to study the structural evolution and optical properties of AgnAun (n = 2-6) nanoalloys both as individual clusters and as clusters stabilized with the fragments of DNA of different size. We show that alloying can be used to control and tune the level of interaction between the metal atoms of the cluster and the organic fragments of the DNA ligands. For instance, gold and silver atoms are shown to exhibit synergistic effects in the process of charge transfer from the nucleobase to the cluster, with the silver atoms directly connected to the nitrogen atoms of cytosine increasing their positive partial charge, while their more electronegative neighbouring gold atoms host the excess negative charge. This allows the geometrical structures and optical absorption spectra of small bimetallic clusters to retain many of their main features upon aggregation with relatively large DNA fragments, such as a cytosine-based 9-nucleotide hairpin loop, which suggests a potential synthetic route to such hybrid metal-organic compounds, and opens up the possibility of bringing the unique tunable properties of bimetallic nanoalloys to biological applications. PMID:27459508

  15. Structural, electronic, and magnetic properties of gold cluster anions doped with zinc: Au(n)Zn- (2 < or = n < or = 10).

    PubMed

    Wang, Huai-Qian; Kuang, Xiao-Yu; Li, Hui-Fang

    2009-12-24

    The geometrical structures, relative stabilities, electronic, and magnetic properties of zinc-doped gold cluster anions Au(n)Zn(-) (2 < or = n < or = 10) have been systematically investigated by means of first-principles density functional calculations at the B3LYP level. The results show that the most stable isomers have a planar structure and resemble pure gold cluster anions in shape, and no 3D isomers were obtained. Calculated dissociation energy, the second difference energy, and the highest occupied-lowest unoccupied molecular orbital gaps as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. The first vertical detachment energy of the anion clusters were calculated and compared with available experimental results. A good agreement between experimental and theoretical results suggests good prediction of the lowest-energy structures for all clusters calculated in the present study. Furthermore, both the local and total magnetic moments display a pronounced odd-even oscillation with the number of gold atoms. PMID:19874045

  16. 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.

  17. Au40: A large tetrahedral magic cluster

    NASA Astrophysics Data System (ADS)

    Jiang, De-En; Walter, Michael

    2011-11-01

    40 is a magic number for tetrahedral symmetry predicted in both nuclear physics and the electronic jellium model. We show that Au40 could be such a a magic cluster from density functional theory-based basin hopping for global minimization. The putative global minimum found for Au40 has a twisted pyramid structure, reminiscent of the famous tetrahedral Au20, and a sizable HOMO-LUMO gap of 0.69 eV, indicating its molecular nature. Analysis of the electronic states reveals that the gap is related to shell closings of the metallic electrons in a tetrahedrally distorted effective potential.

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

    PubMed

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

    2012-07-21

    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 Au(QC)@BSA and Ag(QC)@BSA suggested that the alloy clusters could be Au(38-x)Ag(x)@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 Au(3+) ions with the as-synthesized Ag(QC)@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. PMID:22684267

  19. Orbit and spin resolved magnetic properties of size selected [ConRh]⁺ and [ConAu]⁺ nanoalloy clusters.

    PubMed

    Dieleman, Dennis; Tombers, Matthias; Peters, Lars; Meyer, Jennifer; Peredkov, Sergey; Jalink, Jeroen; Neeb, Matthias; Eberhardt, Wolfgang; Rasing, Theo; Niedner-Schatteburg, Gereon; Kirilyuk, Andrei

    2015-11-14

    Bi-metallic nanoalloys of mixed 3d-4d or 3d-5d elements are promising candidates for technological applications. The large magnetic moment of the 3d materials in combination with a high spin-orbit coupling of the 4d or 5d materials give rise to a material with a large magnetic moment and a strong magnetic anisotropy, making them ideally suitable in for example magnetic storage devices. Especially for clusters, which already have a higher magnetic moment compared to the bulk, these alloys can profit from the cooperative role of alloying and size reduction in order to obtain magnetically stable materials with a large magnetic moment. Here, the influence of doping of small cobalt clusters on the spin and orbital magnetic moment has been studied for the cations [Co(8-14)Au](+) and [Co(10-14)Rh](+). Compared to the undoped pure cobalt [Co(N)](+) clusters we find a significant increase in the spin moment for specific Co(N-1)Au(+) clusters and a very strong increase in the orbital moment for some Co(N-1)Rh(+) clusters, with more than doubling for Co12Rh(+). This result shows that substitutional doping of a 3d metal with even just one atom of a 4d or 5d metal can lead to dramatic changes in both spin and orbital moment, opening up the route to novel applications. PMID:26104269

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

    PubMed

    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

  1. 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.

  2. 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

  3. 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.

  4. Tuning Properties in Silver Clusters.

    PubMed

    Joshi, Chakra P; Bootharaju, Megalamane S; Bakr, Osman M

    2015-08-01

    The properties of Ag nanoclusters are not as well understood as those of their more precious Au cousins. However, a recent surge in the exploration of strategies to tune the physicochemical characteristics of Ag clusters addresses this imbalance, leading to new insights into their optical, luminescence, crystal habit, metal-core, ligand-shell, and environmental properties. In this Perspective, we provide an overview of the latest strategies along with a brief introduction of the theoretical framework necessary to understand the properties of silver nanoclusters and the basis for their tuning. The advances in cluster research and the future prospects presented in this Perspective will eventually guide the next large systematic study of nanoclusters, resulting in a single collection of data similar to the periodic table of elements. PMID:26267198

  5. Doping golden clusters: MAu-19 and M2Au-18 (M = Cu and Na)

    NASA Astrophysics Data System (ADS)

    Zhang, Feng; Fa, Wei

    2012-04-01

    The structural and electronic properties of MAu-19 and M2Au-18 (M = Cu and Na) have been studied by the relativistic density-functional calculations. It is found that the most stable configurations of CuAu-19 and Cu2Au-18 are the face-centered and two-face-centered doped structures based upon the tetrahedral structure Au-20. In contrast, the ground states of Na-doped gold clusters (NaAu-19 and Na2Au-18) exhibit flat-cage configurations. The PES of these ground states are depicted that may be helpful to identify their configurations in the future experiments. The face-centered and two-face-centered doped tetrahedral structures of CuAu-19 and Cu2Au-18 have a large HOMO-LUMO gap, indicating that they are chemically stable.

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

    SciTech Connect

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

    2014-03-12

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

  7. 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. PMID:26248205

  8. Pt{sub 3}Au and PtAu clusters: Electronic states and potential energy surfaces

    SciTech Connect

    Dai, D.; Balasubramanian, K.

    1994-03-15

    We carried out complete active space multiconfiguration self-consistent-field calculations followed by multireference singles+doubles configuration interaction with the Davidson correction which included up to 3.55 million configurations employing relativistic effective core potentials on Pt{sub 3}+Au and PtAu clusters. Four low-lying electronic states were identified for Pt{sub 3}+Au. The {sup 2}{ital A}{sub 2} electronic state ({ital C}{sub 3{ital v}}) was found to be the ground state of Pt{sub 3}Au. Spin--orbit effects were found to be significant. We also computed six low-lying electronic states of PtAu and four low-lying electronic states of PtAu{sup +}. The 5/2 ({sup 2}{Delta}) and 0{sup +}({sup 1}{Sigma}{sup +}) states were found to be the ground states of PtAu and PtAu{sup +}, respectively.

  9. Enantiospecific adsorption of cysteine on a chiral Au34 cluster

    NASA Astrophysics Data System (ADS)

    Pelayo, José de Jesús; Valencia, Israel; Díaz, Gabriela; López-Lozano, Xóchitl; Garzón, Ignacio L.

    2015-12-01

    The interaction of biological molecules like chiral amino acids with chiral metal clusters is becoming an interesting and active field of research because of its potential impact in, for example, chiral molecular recognition phenomena. In particular, the enantiospecific adsorption (EA) of cysteine (Cys) on a chiral Au55 cluster was theoretically predicted a few years ago. In this work, we present theoretical results, based on density functional theory, of the EA of non-zwitterionic cysteine interacting with the C3-Au34 chiral cluster, which has been experimentally detected in gas phase, using trapped ion electron diffraction. Our results show that, indeed, the adsorption energy of the amino acid depends on which enantiomers participate in the formation Cys-Au34 chiral complex. EA was obtained in the adsorption modes where both the thiol, and the thiol-amino functional groups of Cys are adsorbed on low-coordinated sites of the metal cluster surface. Similarly to what was obtained for the Cys-Au55 chiral complex, in the present work, it is found that the EA is originated from the different strength and location of the bond between the COOH functional group and surface Au atoms of the Au34 chiral cluster. Calculations of the vibrational spectrum for the different Cys-Au34 diastereomeric complexes predict the existence of a vibro-enantiospecific effect, indicating that the vibrational frequencies of the adsorbed amino acid depend on its handedness.

  10. Computational study of AuSin (n=1-9) nanoalloy clusters invoking DFT based descriptors

    NASA Astrophysics Data System (ADS)

    Ranjan, Prabhat; Kumar, Ajay; Chakraborty, Tanmoy

    2016-04-01

    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 AuSin (n=1-9) nanoalloy clusters in the theoretical frame of the B3LYP exchange correlation. The experimental properties of AuSin (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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  12. Gold chloride clusters with Au(III) and Au(I) probed by FT-ICR mass spectrometry and MP2 theory.

    PubMed

    Lemke, Kono H

    2014-05-01

    Microsolvated clusters of gold chloride are probed by electrospray ionization mass spectrometry (ESI-MS) and scalar relativistic electronic structure calculations. Electrospray ionization of aqueous AuCl3 leads to mononuclear clusters of types [AuCl2](+)(H2O)n (n = 0-4), [AuOHCl](+)(H2O)n (n = 0-1) and [AuCl2](+)(HCl)2(H2O)n (n = 0-4). In addition, strong ion signals due to dinuclear [Au2Cl5-xOHx](+)(H2O)n (x = 0-1) are present in ESI mass spectra of aqueous AuCl3, with the abundance of individual dinuclear species controlled by the concentration-dependent variation of the precursor complexes [AuCl2-xOHx](+)(H2O)n and AuCl3. Equilibrium structures, energies and thermodynamic properties of mono- and dinuclear gold clusters have been predicted using MP2 and CCSD(T) theory, and these data have been applied to examine the influence of microsolvation on cluster stability. Specifically, results from CCSD(T) calculations indicate that non-covalently bound ion-neutral complexes Au(+)(Cl2)(H2O)n, with formal Au(I), are the dominant forms of mononuclear gold with n = 0-2, while higher hydrates (n > 2) are covalently bound [AuCl2](+)(H2O)n complexes in which gold exists as Au(III). MP2 calculations show that the lowest energy structure of dinuclear gold is an ion-molecule cluster [Au2Cl(Cl2)2](+) consisting of a single-bridged digold-chloronium ion bound end-on to two dichlorine ligands, with two higher energy isomers, single-bridged [Au2Cl3(Cl2)](+) and double-bridged [Au2Cl5](+) clusters. Finally, AuAu interactions in the singly-bridged clusters [Au2Cl(Cl2)2](+)(H2O)n and [Au2Cl3(Cl2)](+)(H2O)n are examined employing a wide range of computational tools, including natural bond order (NBO) analysis and localized orbital locator (LOL) profiles. PMID:24643288

  13. Magnetic doping of the golden cage cluster M@Au16 - (M=Fe,Co,Ni)

    SciTech Connect

    Wang, Leiming; Bai, Jaeil; Lechtken, Anne; Huang, Wei; Schooss, Detlef; Kappes, Manfred M; Zeng, Xiao Cheng; Wang, Lai S

    2009-01-01

    Structural, electronic, and magnetic properties of the golden cage doped with a transition-metal atom, MAu16(M=Fe,Co,Ni),are investigated using trapped ion electron diffraction, photoelectron spectroscopy, and density-functional theory. The best agreement to experiment is obtained for endohedral M@Au16 structures but with considerable distortions to the parent Au16 cage. Fe@Au16 and Co@Au16 are found to have similar structures with C2 symmetry while a C1 structure is obtained for Ni@Au16. The 4s electrons are observed to transfer to the Au16 cage, whereas atomiclike magnetism due to the unpaired 3d electrons is retained for all the doped clusters.

  14. Enantiospecific adsorption of cysteine on a chiral Au34 cluster

    NASA Astrophysics Data System (ADS)

    de Jesús Pelayo, José; Valencia, Israel; Díaz, Gabriela; López-Lozano, Xóchitl; Garzón, Ignacio L.

    2015-12-01

    The interaction of biological molecules like chiral amino acids with chiral metal clusters is becoming an interesting and active field of research because of its potential impact in, for example, chiral molecular recognition phenomena. In particular, the enantiospecific adsorption (EA) of cysteine (Cys) on a chiral Au55 cluster was theoretically predicted a few years ago. In this work, we present theoretical results, based on density functional theory, of the EA of non-zwitterionic cysteine interacting with the C3-Au34 chiral cluster, which has been experimentally detected in gas phase, using trapped ion electron diffraction. Our results show that, indeed, the adsorption energy of the amino acid depends on which enantiomers participate in the formation Cys-Au34 chiral complex. EA was obtained in the adsorption modes where both the thiol, and the thiol-amino functional groups of Cys are adsorbed on low-coordinated sites of the metal cluster surface. Similarly to what was obtained for the Cys-Au55 chiral complex, in the present work, it is found that the EA is originated from the different strength and location of the bond between the COOH functional group and surface Au atoms of the Au34 chiral cluster. Calculations of the vibrational spectrum for the different Cys-Au34 diastereomeric complexes predict the existence of a vibro-enantiospecific effect, indicating that the vibrational frequencies of the adsorbed amino acid depend on its handedness. Contribution to the Topical Issue "Atomic Cluster Collisions (7th International Symposium)", edited by G. Delgado Barrio, A. Solov'Yov, P. Villarreal, R. Prosmiti.

  15. 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. PMID:25961526

  16. Statistical properties of convex clustering

    PubMed Central

    Tan, Kean Ming; Witten, Daniela

    2016-01-01

    In this manuscript, we study the statistical properties of convex clustering. We establish that convex clustering is closely related to single linkage hierarchical clustering and k-means clustering. In addition, we derive the range of the tuning parameter for convex clustering that yields a non-trivial solution. We also provide an unbiased estimator of the degrees of freedom, and provide a finite sample bound for the prediction error for convex clustering. We compare convex clustering to some traditional clustering methods in simulation studies.

  17. 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

    2015-07-01

    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. PMID:26061641

  18. 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

  19. 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.

  20. Magnetic doping of the golden cage cluster M@Au16¯ (M=Fe,Co,Ni)

    SciTech Connect

    Lei-Ming, Wang; Jaeil, Bai; Anne, Lechtken; Wei, Huang; Detlef, Schooss; Manfred, Kappes; Xiao, Zeng; Lai-Sheng, Wang

    2009-01-01

    Structural, electronic, and magnetic properties of the golden cage doped with a transition-metal atom, M@Au16¯ (M=Fe,Co,Ni), are investigated using trapped ion electron diffraction, photoelectron spectroscopy, and density-functional theory. The best agreement to experiment is obtained for endohedral M@Au16¯structures but with considerable distortions to the parent Au16¯ cage. Fe@Au16¯ and Co@Au16¯ are found to have similar structures with C2 symmetry while a C1 structure is obtained for Ni@Au16¯. The 4s electrons are observed to transfer to the Au16 cage, whereas atomiclike magnetism due to the unpaired 3d electrons is retained for all the doped clusters.

  1. First enantioseparation and circular dichroism spectra of Au38 clusters protected by achiral ligands

    PubMed Central

    Dolamic, Igor; Knoppe, Stefan; Dass, Amala; Bürgi, Thomas

    2012-01-01

    Bestowing chirality to metals is central in fields such as heterogeneous catalysis and modern optics. Although the bulk phase of metals is symmetric, their surfaces can become chiral through adsorption of molecules. Interestingly, even achiral molecules can lead to locally chiral, though globally racemic, surfaces. A similar situation can be obtained for metal particles or clusters. Here we report the first separation of the enantiomers of a gold cluster protected by achiral thiolates, Au38(SCH2CH2Ph)24, achieved by chiral high-performance liquid chromatography. The chirality of the nanocluster arises from the chiral arrangement of the thiolates on its surface, forming 'staple motifs'. The enantiomers show mirror-image circular dichroism responses and large anisotropy factors of up to 4×10−3. Comparison with reported circular dichroism spectra of other Au38 clusters reveals that the influence of the ligand on the chiroptical properties is minor. PMID:22531183

  2. Structural and electronic properties of AuIr nanoalloys

    NASA Astrophysics Data System (ADS)

    Jiménez-Díaz, Laura M.; Pérez, Luis A.

    2013-01-01

    The lowest-energy structures of binary (AuIr) n , (AuIr3) s , and (Au3Ir) s clusters, with n = 2-20, and s = 5, modeled by the many-body Gupta potential, were obtained by using a genetic-symbiotic algorithm. These structures were further relaxed within the density functional theory to obtain the most stable structures for each composition. Segregation is observed in all the AuIr clusters, where the Ir atoms occupy the cluster core and the Au atoms are situated on the cluster surface. On the other hand, there is experimental evidence that the (AuIr) n nanoalloys could have an enhanced catalytic activity for CO oxidation. In order to study this phenomenon, we also performed first-principles density functional calculations of the CO and O2 adsorption on these bimetallic nanoclusters, considering three different compositions and a fixed cluster size of 20 atoms.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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 102, 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.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

  4. Influence of Sn interaction on the structural evolution of Au clusters: A first principles study

    NASA Astrophysics Data System (ADS)

    Sahoo, Suman Kalyan; Nigam, Sandeep; Sarkar, Pranab; Majumder, Chiranjib

    2012-08-01

    Here we report the structural and electronic properties of AunSn (n = 2-13) clusters by using pseudo-potential and LCAO-MO method. A comparison between the structures of Aun and AunSn clusters reveals that while Aun clusters favor planar isomers up to n = 13, AunSn clusters follow a different trend; 3D structure for n = 3 and 4, quasi planar in the size range n = 5-11, and again 3D isomers from n = 12 onwards. Enhanced contribution of Au p-orbital and significant charge transfer from Sn to the gold atoms is attributed for such interesting growth pattern of AunSn clusters.

  5. Coarsening of mass-selected Au clusters on amorphous carbon at room temperature

    NASA Astrophysics Data System (ADS)

    Popescu, R.; Schneider, R.; Gerthsen, D.; Böttcher, A.; Löffler, D.; Weis, P.; Kappes, M. M.

    2009-10-01

    Low-energy cluster beam deposition was used to deposit mass-selected Au n clusters ( n = 4, 6, 13 and 20) on amorphous carbon (a-C) substrates. The resulting samples were stored at room temperature under ambient conditions for time periods up to 32 months to analyze the coarsening behaviour of the clusters. Cluster-size distributions were measured in regular time intervals by transmission electron microscopy (TEM). The TEM experiments show a significant increase of the average cluster size with time analogous to classical surface Ostwald ripening (OR). The coarsening of Au clusters can be well described by steady-state diffusion-limited kinetics. The derived surface mass-transport diffusion coefficients at room temperature range between 1.1 and 3.8·10 -25 m 2 s -1 for our samples. A detailed analysis of Ds' values suggests that, the rate of the surface OR for mass-selected Au n clusters increases with the cluster size in the sequence: Au 4 ≈ Au 6 < Au 13 < Au 20 for the investigated range of Au clusters. Given that the initial, on-surface cluster-size distributions are nominally monodisperse, classical OR with cluster coarsening based only on the Gibbs-Thomson effect cannot explain the observed coarsening. The activation of the coarsening process is rationalized by initial variations of the cluster sizes due to the deposition process itself and/or the interaction of the clusters with the substrate. Moreover, the presence of initial deposited Au clusters as different isomers with slightly different chemical potential on the substrate, may also initiate the coarsening by surface OR. Furthermore, we find that the coarsening is most pronounced for the paucidispersed sample with Au m (10 ⩽ m ⩽ 20) clusters. A possible explanation of this behaviour is the presence of an initial distribution of different cluster sizes directly after deposition.

  6. Au(n)Hg(m) clusters: mercury aurides, gold amalgams, or van der Waals aggregates?

    PubMed

    Zaleski-Ejgierd, Patryk; Pyykkö, Pekka

    2009-11-12

    The class of bimetallic clusters, Au(n)M(m) (M = Zn, Cd, Hg), is calculated at the ab initio level using the DFT, RI-MP2, and CCSD(T) methods. For the triatomic Au2M (M = Zn, Cd), the auride-type linear Au-M-Au structures are preferred; for Au2Hg, the linear Au-Au-Hg "amalgam" is preferred. The mixed cation [HgAuHg]+, an analog of the known solid-state species Hg32+, is predicted. For larger Au(n)Hg(m) clusters, the results are similar to the isoelectronic Au(n)M- anions. Several local minima and transition states are identified. All are found to be planar. PMID:19228004

  7. 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.

  8. 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

    2016-02-11

    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. PMID:26822548

  9. 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. PMID:25921415

  10. 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. PMID:26679978

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

    PubMed

    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 Au(25) nanoclusters (Au NCs) is reported. Highly fluorescent Au(25) 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 approximately 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 4f(7/2) approximately 83.97 eV and Au 4f(5/2) approximately 87.768 eV. Transmission electron microscopy and atomic force microscopy revealed the formation of individual nanoclusters of size approximately 1 nm and protein cluster aggregates of size approximately 8 nm. Photoluminescence studies show bright fluorescence with peak maximum at approximately 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 microg 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 Au(25) clusters were found internalized in significantly higher

  12. 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

  13. 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

  14. 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.

  15. Density functional study of Au nRh ( n=1-8) clusters

    NASA Astrophysics Data System (ADS)

    Yang, Ji-Xian; Wei, Cheng-Fu; Guo, Jian-Jun

    2010-12-01

    The density functional method PW91P86 with relativistic effective core potentials (RECPs) and LANL2DZ basis set has been used to investigate the possible stable geometrical configurations and relative stabilities of the lowest-lying isomers of rhodium-doped gold clusters, Au nRh ( n=1-8). Several low-lying isomers were determined. The results indicate that the ground-state Au nRh, n=1-8, clusters have planar structures except for n=5 and 8. The stability trend of the Au nRh clusters shows that the clusters with even numbers of atoms are more stable than the clusters with odd numbers of atoms, indicating that the Au 5Rh cluster is a magic cluster with high chemical stability.

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

    PubMed Central

    2013-01-01

    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. PMID:23601828

  17. 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.

  18. 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.

  19. Decomposition of dimethyl methylphosphonate on Pt, Au, and Au-Pt clusters supported on TiO2(110).

    PubMed

    Ratliff, Jay S; Tenney, Samuel A; Hu, Xiaofeng; Conner, Sean F; Ma, Shuguo; Chen, Donna A

    2009-01-01

    The decomposition of dimethyl methylphosphonate (DMMP) was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) on TiO(2)-supported Pt, Au, and Au-Pt clusters as well as on TiO(2)(110) itself. In agreement with previous work, TPD experiments for DMMP on TiO(2)(110) showed that methyl and methane were the main gaseous products. Multiple DMMP adsorption-reaction cycles on TiO(2)(110) demonstrated that active sites for DMMP decomposition were blocked after a single cycle, but some activity for methyl production was sustained even after five cycles. Furthermore, the activity of the TiO(2) surface could be regenerated by heating in O(2) at 800 K or heating in vacuum to 965 K to remove surface carbon and phosphorus, which are byproducts of DMMP decomposition. On 0.5 ML Pt clusters deposited on TiO(2)(110), TPD studies of DMMP reaction showed that CO and H(2) were the main gas products, with methyl and methane as minor products. The Pt clusters were more active than TiO(2) both in terms of the total amount of DMMP reaction and the ability to break C-H, P-O, and P-OCH(3) bonds in DMMP. However, the Pt clusters had no sustained activity for DMMP decomposition, since the product yields dropped to zero after a single adsorption-reaction cycle. This loss of activity is attributed to a combination of poisoning of active sites by surface phosphorus species and encapsulation of the Pt clusters by reduced titania after heating above 600 K due to strong metal support interactions (SMSI). On 0.5 ML Au clusters, CO and H(2) were also the main products detected in TPD experiments, in addition to methane and methyl produced from reaction on the support. The Au clusters were less active for DMMP decomposition to CO and H(2) as well as P-O bond scission, but surface phosphorus was removed from the Au clusters by desorption at approximately 900 K. Au-Pt bimetallic clusters on TiO(2)(110) were prepared by

  20. 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.

  1. Chair like NiAu6: Clusters assemblies and CO oxidation study by ab initio methods

    NASA Astrophysics Data System (ADS)

    Nigam, Sandeep; Sahoo, Suman Kalyan; Sarkar, Pranab; Majumder, Chiranjib

    2013-10-01

    Based on the first-principles approach, this Letter reports that the ground state geometry of the Ni@Au6 cluster forms chair-like conformation, which is distinctly different than the Pd@Au6 and Pt@Au6 clusters, where hexagonal planar structure is favored over non-planar isomers. The higher stability of the chair-like conformation has been verified through various complementary basis sets and methodologies. Further investigations were carried out to show the stability of a cluster assembled material (CAM) based on these small clusters and the CO oxidation reaction was carried out to establish their uses as an industrial catalyst.

  2. Reactions and properties of clusters

    NASA Astrophysics Data System (ADS)

    Castleman, A. W., Jr.

    1992-09-01

    The elucidation from a molecular point of view of the differences and similarities in the properties and reactivity of matter in the gaseous compared to the condensed state is a subject of considerable current interest. One of the promising approaches to this problem is to utilize mass spectrometry in conjunction with laser spectroscopy and fast-flow reaction devices to investigate the changing properties, structure and reactivity of clusters as a function of the degree of solvation under well-controlled conditions. In this regard, an investigation of molecular cluster ions has provided considerable new insight into the basic mechanisms of ion reactions within a cluster, and this paper reviews some of the recent advances in cluster production, the origin of magic numbers and relationship to cluster ion stabilities, and solvation effects on reactions. There have been some notable advances in the production of large cluster ions under thermal reaction conditions, enabling a systematic study of the influence of solvation on reactions to be carried out. These and other new studies of magic numbers have traced their origin to the thermochemical stability of cluster ions. There are several classes of reaction where solvation has a notable influence on reactivity. A particularly interesting example comes from recent studies of the reactions of the hydroxyl anion with CO2 and SO2, studied as a function of the degree of hydration of OH-. Both reactions are highly exothermic, yet the differences in reactivity are dramatic. In the case of SO2, the reaction occurs at near the collision rate. By contrast, CO2 reactivity plummets dramatically for clusters having more than four water molecules. The slow rate is in accord with observations in the liquid phase.

  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. Cluster-π electronic interaction in a superatomic Au13 cluster bearing σ-bonded acetylide ligands.

    PubMed

    Sugiuchi, Mizuho; Shichibu, Yukatsu; Nakanishi, Takayuki; Hasegawa, Yasuchika; Konishi, Katsuaki

    2015-09-11

    An organometallic Au13 cluster having two σ-bonded acetylide ligands was synthesized and its structure was determined by X-ray crystallography. Absorption spectral studies indicated the presence of electronic coupling between the superatomic Au13 core and the acetylide π-orbitals, which was supported by theoretical considerations. PMID:26215256

  5. 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.

  6. Mixed-Monolayer-Protected Au25 Clusters with Bulky Calix[4]arene Functionalities.

    PubMed

    Hassinen, Jukka; Pulkkinen, Petri; Kalenius, Elina; Pradeep, Thalappil; Tenhu, Heikki; Häkkinen, Hannu; Ras, Robin H A

    2014-02-01

    Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here, we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix[4]arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix[4]arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix[4]arenes to the Au25 cluster surface with two or four thiolates per moiety. PMID:26276613

  7. Patterning of gold-polydimethylsiloxane (Au-PDMS) nanocomposites by supersonic cluster beam implantation

    NASA Astrophysics Data System (ADS)

    Ghisleri, C.; Borghi, F.; Ravagnan, L.; Podestà, A.; Melis, C.; Colombo, L.; Milani, P.

    2014-01-01

    Patterned gold-polydimethylsiloxane (Au-PDMS) nanocomposites were fabricated by supersonic cluster beam implantation (SCBI) of neutral gold nanoparticles in PDMS through stencil masks. The influence of nanoparticle dose on the surface roughness and morphology of the micropatterned regions of the nanocomposite was characterized. Nanoparticle implantation causes the swelling of PDMS without affecting substantially the lateral resolution of the patterns. In order to have an insight on the mechanism and the influence of nanoparticle implantation on the polymeric matrix, large-scale molecular dynamics simulations of the implantation process have been performed. The simulations show that even a single cluster impact on PDMS substrate strongly affects the polymer local temperature and density. Our results show that SCBI is a promising methodology for the efficient fabrication of nanocomposite microstructures on polymers with interesting morphological, structural and functional properties.

  8. Electronic and geometric structures of Au30 clusters: a network of 2e-superatom Au cores protected by tridentate protecting motifs with u3-S

    NASA Astrophysics Data System (ADS)

    Tian, Zhimei; Cheng, Longjiu

    2015-12-01

    Density functional theory calculations have been performed to study the experimentally synthesized Au30S(SR)18 and two related Au30(SR)18 and Au30S2(SR)18 clusters. The patterns of thiolate ligands on the gold cores for the three thiolate-protected Au30 nanoclusters are on the basis of the ``divide and protect'' concept. A novel extended protecting motif with u3-S, S(Au2(SR)2)2AuSR, is discovered, which is termed the tridentate protecting motif. The Au cores of Au30S(SR)18, Au30(SR)18 and Au30S2(SR)18 clusters are Au17, Au20 and Au14, respectively. The superatom-network (SAN) model and the superatom complex (SAC) model are used to explain the chemical bonding patterns, which are verified by chemical bonding analysis based on the adaptive natural density partitioning (AdNDP) method and aromatic analysis on the basis of the nucleus-independent chemical shift (NICS) method. The Au17 core of the Au30S(SR)18 cluster can be viewed as a SAN of one Au6 superatom and four Au4 superatoms. The shape of the Au6 core is identical to that revealed in the recently synthesized Au18(SR)14 cluster. The Au20 core of the Au30(SR)18 cluster can be viewed as a SAN of two Au6 superatoms and four Au4 superatoms. The Au14 core of Au30S2(SR)18 can be regarded as a SAN of two pairs of two vertex-sharing Au4 superatoms. Meanwhile, the Au14 core is an 8e-superatom with 1S21P6 configuration. Our work may aid understanding and give new insights into the chemical synthesis of thiolate-protected Au clusters.Density functional theory calculations have been performed to study the experimentally synthesized Au30S(SR)18 and two related Au30(SR)18 and Au30S2(SR)18 clusters. The patterns of thiolate ligands on the gold cores for the three thiolate-protected Au30 nanoclusters are on the basis of the ``divide and protect'' concept. A novel extended protecting motif with u3-S, S(Au2(SR)2)2AuSR, is discovered, which is termed the tridentate protecting motif. The Au cores of Au30S(SR)18, Au30(SR)18 and Au30S

  9. Non-linear optical properties of gold quantum clusters. The smaller the better.

    PubMed

    Russier-Antoine, Isabelle; Bertorelle, Franck; Vojkovic, Marin; Rayane, Driss; Salmon, Estelle; Jonin, Christian; Dugourd, Philippe; Antoine, Rodolphe; Brevet, Pierre-François

    2014-11-21

    By developing a new method for synthesizing atomically monodisperse Au15 nanoclusters stabilized with glutathione molecules and using the current state-of-the-art methods for synthesizing monodisperse protected Au25 nanoclusters, we investigated their nonlinear optical (NLO) properties after two-photon absorption. The two-photon emission spectra and the first hyperpolarizabilities of these particles were obtained using, in particular, a hyper-Rayleigh scattering technique. The influence on NLO of the excitation wavelength, the size as well as the nature of the ligands is also explored and discussed. Au15, the smallest stable thiolated gold nanocluster, presents remarkable nonlinear properties with respect to two-photon processes. The two-photon absorption cross-section at 780 nm for Au15 is ∼65,700 GM. This experimental cross-section value points to a quantum yield for two-photon emission of about 3 × 10(-7) at 475 nm for Au15. The first hyperpolarizability β for Au15 clusters (509 × 10(-30) esu), as compared to Au25 clusters (128 × 10(-30) esu), is larger considering the difference in the number of gold atoms. Also, 10(30) β per atom values reported for Au15 and Au25 clusters are more than two orders of magnitude larger than the values reported for Au NPs in the size range 10-50 nm, outlining the quantum cluster regime. PMID:25268982

  10. Bridging gold in electron-deficient Al2Au(n)(0/-) and BAlAu(n)(0/-) (n = 1-3) clusters.

    PubMed

    Yao, Wen-Zhi; Liu, Bing-Tao; Lu, Zhang-Hui; Li, Si-Dian

    2013-06-20

    The geometrical and electronic structures of the electron-deficient dialuminum aurides Al2Aun(0/-) and hybrid boron-aluminum aurides BAlAun(0/-) (n = 1-3) are systematically investigated based on the density and wave function theories. Ab initio theoretical evidence strongly suggests that bridging gold atoms exist in the ground states of C2v Al2Au(-) ((3)B1), C2v Al2Au ((2)B1), C2v Al2Au2(-) ((2)A1), C2v Al2Au2 ((1)A1), Cs Al2Au3(-) ((1)A'), and D3h Al2Au3 ((2)A1), which prove to possess an Al-Au-Al τ bond. For BAlAun(0/-) (n = 1-3) mixed clusters, bridging B-Au-Al units only exist in Cs BAlAu3(-) ((1)A') and Cs BAlAu3 ((2)A'), whereas Cs BAlAu(-) ((3)A''), Cs BAlAu ((2)A''), Cs BAlAu2(-) ((2)A'), and Cs BAlAu2 ((1)A') do not possess a bridging gold, as demonstrated by the fact that B-Al and B-Au exhibit significantly stronger electronic interaction than Al-Au in the same clusters. Orbital analyses indicate that Au 6s contributes approximately 98%-99% to the Au-based orbital in these Al-Au-Al/B-Au-Al interactions, whereas Au 5d contributes 1%-2%. The adiabatic and vertical detachment energies of Al2Aun(-) (n = 1-3) are calculated to facilitate future experimental characterizations. The results obtained in this work establish an interesting τ bonding model (Al-Au-Al/B-Au-Al) for electron-deficient systems in which Au 6s plays a major factor. PMID:23718624

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

    NASA Astrophysics Data System (ADS)

    Kalachyova, Yevgeniya; Lyutakov, Oleksiy; Solovyev, Andrey; Slepička, Petr; Švorčík, Vaclav

    2013-12-01

    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.

  12. Ab initio study of small Au nY 2 ( n=1-4) clusters

    NASA Astrophysics Data System (ADS)

    Jian-Jun, Guo; Ji-Xian, Yang; Dong, Die

    2008-11-01

    The geometries of the lowest-lying isomers of Au nY 2 ( n=1-4) clusters are determined systematically via the density functional method B3LYP with relativistic effective core potentials (RECP) and LANL2DZ basis set. Several low-lying isomers were determined, and many of them in electronic configurations with a high-spin multiplicity. The gold-yttrium interaction is strong enough to modify the known growth pattern of bare gold clusters. The stability trend of Y-doped Au n clusters is compared to that of pure Au n clusters. The results show that the inclusion of two Y atoms in the clusters improves the cluster stability, and indicate higher stability as the structures grow in size. The present calculations are useful to understand the enhanced catalytic activity and selectivity gained by using yttrium-doped gold catalyst.

  13. Effect of trimetallization in thiolate-protected Au24-nCunPd clusters

    NASA Astrophysics Data System (ADS)

    Sharma, Sachil; Kurashige, Wataru; Nobusada, Katsuyuki; Negishi, Yuichi

    2015-06-01

    We synthesized a mixture of Au24-nCunPd(SC12H25)18 (n = 0-3) and Au25-nCun(SC12H25)18 (n = 0-7) and compared their stability. The results showed that, in a cluster containing one Cu atom, the presence of Pd is effective in improving the cluster stability. Conversely, the presence of Pd has different effects depending on the number of Cu atoms in the cluster: cluster formation was inhibited for clusters containing four or more Cu atoms.We synthesized a mixture of Au24-nCunPd(SC12H25)18 (n = 0-3) and Au25-nCun(SC12H25)18 (n = 0-7) and compared their stability. The results showed that, in a cluster containing one Cu atom, the presence of Pd is effective in improving the cluster stability. Conversely, the presence of Pd has different effects depending on the number of Cu atoms in the cluster: cluster formation was inhibited for clusters containing four or more Cu atoms. Electronic supplementary information (ESI) available: Details of product characterization data. See DOI: 10.1039/c5nr01491c

  14. 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.

  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. Tuning the electronic properties of the golden buckyball by endohedral doping: M@Au16(-) (M=Ag,Zn, In)

    SciTech Connect

    Wang, Leiming; Pal, R.; Huang, Wei; Zeng, Xiao Cheng; Wang, Lai S.

    2009-02-07

    The golden Au16 cage is doped systematically with an external atom of different valence electrons:Ag, Zn, and In. The electronic and structural properties of the doped clusters, MAu16 (M=Ag,Zn, In), are investigated by photoelectron spectroscopy and theoretical calculations. It is observed that the characteristic spectral features of Au16, reflecting its near tetrahedral (Td) symmetry, are retained in the photoelectron spectra of MAu16, suggesting endohedral structures with little distortion from the parent Au16 cage for the doped clusters. Density functional calculations show that the endohedral structures of M@Au16 with Td symmetry are low-lying structures, which give simulated photoelectron spectra in good agreement with the experiment. It is found that the dopant atom does not significantly perturb the electronic and atomic structures of Au16, but simply donate its valence electrons to the parent Au16 cage, resulting in a closed-shell 18-electron system for Ag@Au16, a 19-electron system for Zn@Au16 with a large energy gap,and a 20-electron system for In@Au16. The current work shows that the electronic properties of the golden buckyball can be systematically tuned through doping.

  17. 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.

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

    DOE PAGESBeta

    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 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

  19. Multiple CO Oxidation Promoted by Au2 Dimers in Au2 TiO4 (-) Cluster Anions.

    PubMed

    Li, Xiao-Na; Li, Zi-Yu; Li, Hai-Fang; He, Sheng-Gui

    2016-06-20

    Time-of-flight mass spectrometry experiments demonstrated that laser ablation generated and mass selected Au2 TiO4 (-) cluster anions can unexpectedly oxidize three CO molecules in an ion trap reactor. This is an improvement on the more commonly observed oxidation of at most two CO molecules by a doped cluster. Quantum chemistry calculations were performed to rationalize the reactions. The lowest energy isomer of Au2 TiO4 (-) contains a superoxide unit, the participation of which in CO oxidation can be promoted by the Au2 dimer. The Au2 dimer functions as a rather flexible electron reservoir in each CO oxidation step in terms of the release and storage of electrons to drive the dissociation of superoxide to peroxide and then to lattice oxygen atoms, which can be removed by reaction with CO molecules. This gas-phase study enriches our understanding toward the nature of reactive oxygen species involved in gold-catalyzed oxidation reactions. PMID:27172816

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

    SciTech Connect

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

    2007-12-15

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

  1. Communication: Coupled-cluster interpretation of the photoelectron spectrum of Au{sub 3}{sup −}

    SciTech Connect

    Bauman, Nicholas P.; Piecuch, Piotr; Hansen, Jared A.; Ehara, Masahiro

    2014-09-14

    We use the scalar relativistic ionized equation-of-motion coupled-cluster approaches, correlating valence and semi-core electrons and including up to 3-hole-2-particle terms in the ionizing operator, to investigate the photoelectron spectrum of Au{sub 3}{sup −}. We provide an accurate assignment of peaks and shoulders in the experimental photoelectron spectrum of Au{sub 3}{sup −} for the first time.

  2. Structural stability and electronic properties of small gold clusters induced by 3p electron atoms

    NASA Astrophysics Data System (ADS)

    Zhang, Meng; Yang, Su-Bin; Feng, Xiao-Juan; Zhao, Li-Xia; Zhang, Hong-Yu; Luo, You-Hua

    2013-01-01

    The geometries and electronic properties of gold clusters doped with atoms containing 3 p valence electrons (MAu n ; M = Al, Si, P, S, Cl; n = 2-8) have been systematically investigated using density functional theory (DFT) at the PBE/LANL2DZ level. A number of low-energy isomers are identified for neutral MAu n clusters. It is found that doping with different 3 p impurity atoms can drastically influence the geometrical structures, relative stabilities, electronic properties, and growth-pattern behaviors of gold clusters, which is very different from the case of 3 d transition-metal impurity doped Au n clusters. Partially filled 3 p electron impurities can stabilize Au clusters. In particular, SiAu4 cluster with T d symmetry have been found to have highly stable geometries and electronic structures with binding energies of 2.43 eV per atom (0.96 eV higher than pristine Au5 clusters), large HOMO-LUMO gaps (2.17 eV), and vertical ionization potentials of 8.68 eV. Using scalar relativistic molecular dynamics at T = 300 K, we show that the T d symmetry structure of SiAu4 is stable. The frontier molecular orbitals (HOMO and LUMO) and the partial densities of states (PDOS) show that strong hybridization occurs between the atomic orbitals of Si and Au atoms, resulting in strong Si-Au bonding. In addition, the vertical ionization potential, the vertical electron affinity, and charge transfers of MAu n clusters have also been analyzed. Our results are in good agreement with available experimental data.

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

    PubMed

    Meng, Jing-Heng; He, Sheng-Gui

    2014-11-01

    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. PMID:26278765

  4. 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.

  5. Properties of The Brightest Cluster Galaxy and Its Host Cluster

    NASA Astrophysics Data System (ADS)

    Katayama, H.; Hayashida, K.; Takahara, F.

    2001-09-01

    We investigate the relation between the brightest cluster galaxy (BCG) and its host cluster. A BCG is a bright and massive elliptical galaxy in a cluster of galaxies. The luminosity of a BCG is 10 times larger than that of normal field galaxy and the mass of a BCG is about 1013Msolar which corresponds to that of galaxy group. In order to explain the origin of BCGs, the following three models are proposed: (1) star formation from cooling flow. In this model, intracluster gas gradually condenses at the center of the cluster and forms the BCG. (2) ``Galactic cannibalism'' or the accretion of smaller galaxies. In this model, dynamical friction accounts for the formation of the BCG. These two models predict the BCG evolves with the evolution of cluster. (3) Galaxy merging in the early history of the formation of the cluster. In this model, the property of BCGs is determined no later than cluster collapse. In any model, the formation of BCGs is related to the collapse and formation of its host cluster. The relation between the BCG and its host cluster was studied by Edge (1991). Edge (1991) found that the optical luminosity of the BCG is positively correlated with the X-ray luminosity and temperature of its host cluster. Edge (1991) concludes that these correlations indicate that the BCG responds to the overall cluster properties. In order to investigate the other relation between the BCG and its host cluster, we analyzed ROSAT archival data and compared the displacement between the X-ray peak and the BCG with the Z parameter of the fundamental relation found by Fujita and Takahara (1999). It is found that the displacement is larger with decreasing Z. Furthermore, the large Z clusters tend to have a regular X-ray profile, which implies a relaxed system. The fundamental parameter Z depends mainly on the virial density ρvir, and is considered to be related to the formation epoch of the cluster, i.e., large Z clusters are old clusters and small Z clusters are young

  6. Gold(III) Mediated Activation and Transformation of Methane on Au1-Doped Vanadium Oxide Cluster Cations AuV2O6(.).

    PubMed

    Li, Zi-Yu; Li, Hai-Fang; Zhao, Yan-Xia; He, Sheng-Gui

    2016-08-01

    Gold in the +III oxidation state (Au(III)) has been proposed as a promising species to mediate challenging chemical reactions. However, it is difficult to characterize the chemistry of individual Au(III) species in condensed-phase systems mainly due to the interference from the Au(I) counterpart. Herein, by doping Au atoms into gas-phase vanadium oxide clusters, we demonstrate that the Au(III) cation in the AuV2O6(+) cluster is active for activation and transformation of methane, the most stable alkane molecule, into formaldehyde under mild conditions. In contrast, the AuV2O6(+) cluster isomers with the Au(I) cation can only absorb CH4. The clusters were generated by laser ablation and mass selected to react with CH4, CD4, or CH2D2 in an ion trap reactor. The reactivity was characterized by mass spectrometry and quantum chemistry calculations. The structures of the reactant and product ions were identified by using collision-induced and 425 nm photo-induced dissociation techniques. PMID:27385079

  7. Choline-induced selective fluorescence quenching of acetylcholinesterase conjugated Au@BSA clusters.

    PubMed

    Mathew, Meegle S; Baksi, Ananya; Pradeep, T; Joseph, Kuruvilla

    2016-07-15

    We have developed a highly selective sensitive fluorescent detection of acetylcholine (ACh) using bovine serum albumin (BSA) protected atomically precise clusters of gold. The gold quantum clusters (AuQC@BSA) synthesized using bovine serum albumin and conjugated with acetylcholinesterase (AChE), an enzyme specific for acetylcholine, resulting in AuQC@BSA-AChE. The enzyme, AChE hydrolyzes acetylcholine (ACh) to choline (Ch) which in turn interacts with AuQC@BSA-AChE and quenches its fluorescence, enabling sensing. We have carried out the real time monitoring of the hydrolysis of ACh using electrospray ionization mass spectrometry (ESI MS) to find out the mechanism of fluorescent quenching. The validity of present method for determination of concentration of acetylcholine in real system such as blood was demonstrated. Further, the sensor, AuQC@BSA-AChE can be easily coated on paper and an efficient and cheap sensor can be developed and detection limit for ACh is found to be 10nM. The fluorescent intensity of AuQC@BSA-AChE is sensitive towards acetylcholine in range of 10nM to 6.4µM. This suggests that AuQC@BSA-AChE has an excellent potential to be used for diagnosis of various neuropsychological and neuropsychiatric disorders. PMID:26921554

  8. Do cluster properties affect the quenching rate?

    NASA Astrophysics Data System (ADS)

    Raichoor, A.; Andreon, S.

    2014-10-01

    The quenching rate is known to depend on galaxy stellar mass and environment, however, possible dependences on the hosting halo properties, such as mass, richness, and dynamical status, are still debated. The determination of these dependences is hampered by systematics, induced by noisy estimates of cluster mass or by the lack of control on galaxy stellar mass, which may mask existing trends or introduce fake trends. We studied a sample of local clusters (20 with 0.02 < z < 0.1 and log (M200/M⊙) ≳ 14), selected independent of the galaxy properties under study, having homogeneous optical photometry and X-ray estimated properties. Using those top quality measurements of cluster mass, hence of cluster scale, richness, iron abundance, and cooling time/presence of a cool-core, we study the simultaneous dependence of quenching on these cluster properties on galaxy stellar mass M and normalised cluster-centric distance r/r200. We found that the quenching rate can be completely described by two variables only, galaxy stellar mass and normalised cluster-centric distance, and is independent of halo properties (mass, richness, iron abundance, and central cooling time/presence of a cool-core). These halo properties change, in most cases, by less than 3% the probability that a galaxy is quenched, once the mass-size (M200 - r200) scaling relation is accounted for through cluster-centric distance normalisation. Appendix A is available in electronic form at http://www.aanda.org

  9. 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.

  10. Electrical properties of AuN thin films

    NASA Astrophysics Data System (ADS)

    Quintero, J. H.; Ospina, R.; Cárdenas, O. O.; Alzate, G. I.; Devia, A.

    2008-10-01

    Gold nitride (AuN) is a recently synthesized component and is being studied for properties like optical, electrical and mechanical. Plasma-assisted physical vapor deposition (PAPVD) in pulsed arc system is used for deposition of AuN thin film. The system is formed of a reactor in which there are two faced electrodes, and a power-controlled system that performs the discharge systematically. Chemical analyses were realized by x-ray photoelectron spectroscopy (XPS) technique, and narrow N 1s and Au 4f spectra are shown using film stoichiometry, and I-V curves were obtained in two ways (substrate-film and film-substrate), to observe the electrical properties.

  11. Long-timescale dynamics of thiol capped Au nanoparticle clusters at the air-water interface

    NASA Astrophysics Data System (ADS)

    Choudhuri, Madhumita; Datta, Alokmay

    2014-04-01

    A two-dimensional network of thiol-capped Au nanoparticle (AuNP) clusters is self-organized on a Stearic Acid (amphiphilic fatty acid) Langmuir monolayer on water surface. The AuNP clusters are found to form a pattern of connected and enclosed microspaces in the stearic acid template. The network features can be controlled by changing the surface pressure of the monolayer during compression. The two-dimensional dynamics of this network has been studied over a long timescale using Brewster Angle Microscopy (BAM). The dynamics is very slow, indicating the stability of the network system, and is essentially driven by the tendency to lower the number of nodes or joints in the network.

  12. Mechanical Properties and Fracture Behavior of Nanoporous Au

    SciTech Connect

    Biener, J; Hodge, A M; Wang, Y M; Hayes, J R; Hamza, A V

    2005-06-16

    Nanoporous metals have recently attracted considerable interest fueled by potential sensor and actuator applications. From a material science point of view, one of the key issues in this context is the synthesis of nanoporous metals with both high tensile and compressive strength. Nanoporous gold (np-Au) has been suggested as a candidate material for this application due to its monolithic character. The material can be synthesized by electrochemically-driven dealloying of Ag-Au alloys, and exhibits an open sponge-like structure of interconnecting ligaments with a typical pore size distribution on the nanometer length scale. However, besides the observation of a ductile-brittle transition very little is known about the mechanical behavior of this material. Here, we present our results regarding the mechanical properties and the fracture behavior of np-Au. Depth-sensing nanoindentation reveals that the yield strength of np-Au is almost one order of magnitude higher than the value predicted by scaling laws developed for macroscopic open-cell foams. The unexpectedly high value of the yield strength indicates the presence of a distinct size effect of the mechanical properties due to the sub-micron dimensions of the ligaments, thus potentially opening a door to a new class of high yield strength--low density materials. The failure mechanism of np-Au under tensile stress was evaluated by microscopic examination of fracture surfaces using scanning electron microscopy. On a macroscopic level, np-Au is a very brittle material. However, microscopically np-Au is very ductile as ligaments strained by as much as 200% can be observed in the vicinity of crack tips. Cell-size effects on the microscopic failure mechanism were studied by annealing experiments whereby increasing the typical pore size/ligament diameter from {approx}100 nm to {approx}1{micro}m.

  13. 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

  14. 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.

  15. Electrodynamic properties of fractal clusters

    NASA Astrophysics Data System (ADS)

    Maksimenko, V. V.; Zagaynov, V. A.; Agranovski, I. E.

    2014-07-01

    An influence of interference on a character of light interaction both with individual fractal cluster (FC) consisting of nanoparticles and with agglomerates of such clusters is investigated. Using methods of the multiple scattering theory, effective dielectric permeability of a micron-size FC composed of non-absorbing nanoparticles is calculated. The cluster could be characterized by a set of effective dielectric permeabilities. Their number coincides with the number of particles, where space arrangement in the cluster is correlated. If the fractal dimension is less than some critical value and frequency corresponds to the frequency of the visible spectrum, then the absolute value of effective dielectric permeability becomes very large. This results in strong renormalization (decrease) of the incident radiation wavelength inside the cluster. The renormalized photons are cycled or trapped inside the system of multi-scaled cavities inside the cluster. A lifetime of a photon localized inside an agglomerate of FCs is a macroscopic value allowing to observe the stimulated emission of the localized light. The latter opens up a possibility for creation of lasers without inverse population of energy levels. Moreover, this allows to reconsider problems of optical cloaking of macroscopic objects. One more feature of fractal structures is a possibility of unimpeded propagation of light when any resistance associated with scattering disappears.

  16. Photometric Properties of Galaxies in Poor Clusters

    NASA Astrophysics Data System (ADS)

    Sharma, M.; Prabhu, T.

    We study several statistical properties of galaxies in four poor clusters of galaxies using optical photometry. We select these poor clusters as luminous, extended X-ray sources identified with poor galaxy systems in the EMSS catalogue of clusters of galaxies. The clusters are at moderate redshifts (0.08Cluster. The fraction of blue galaxies is similar to those of low-redshift richness 0 clusters and higher than those of richer clusters at similar redshifts. The luminosity functions (LFs) of the individual clusters are not significantly different from each other. Using these, we construct composite LFs in B, V , and R bands (to MV=-18). The faint-end of these LFs are flat, like the V-band LF of other (e.g., MKW/AWM) poor clusters, but steeper than the field LF in the R-band. In terms of the statistical properties of their member galaxies, poor clusters appear to be lower-mass extensions of their rich counterparts.

  17. Isolation of atomically precise mixed ligand shell PdAu24 clusters.

    PubMed

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

    2016-06-01

    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. PMID:27180647

  18. Photometric Properties of Poor Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Sharma, M.; Prabhu, T. P.

    2002-12-01

    We study several statistical properties of galaxies in four poor clusters of galaxies using multi-color optical photometry obtained at the Vainu Bappu Telescope, India. The clusters, selected from the EMSS Catalog, are at moderate redshifts (0.08 < z < 0.25), of equivalent Abell richness R=0, and appear to be dynamically young. The early-type galaxy populations are clearly evolved, as traced by the tightness of the color-magnitude relations and the accordance of the latter with those of the Virgo cluster. The blue galaxy fractions are similar to those of R=0 clusters and higher than those of richer clusters at similar redshifts. The composite luminosity functions (LFs) in B, V, and R bands are flat at the faint end, similar to the V-band LF derived by Yamagata & Maehara for other (MKW/AWM) poor clusters but steeper than the R-band field LF derived by Lin et al. In terms of the statistical properties of their member galaxies, poor clusters appear to be lower-mass extensions of their rich counterparts. The brightest galaxies of three of these poor clusters appear to be luminous ellipticals with no incontrovertible signatures of a halo. It is likely that they were formed from multiple mergers early in the history of the clusters.

  19. 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.

  20. 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.

  1. An insight into the optical properties of a sub nanosize glutathione stabilized gold cluster.

    PubMed

    Nair, Lakshmi V; Nair, Resmi V; Jayasree, Ramapurath S

    2016-07-28

    In this study, gold quantum clusters with distinct fluorescence properties were developed and their structural and physical behaviour was evaluated. The clusters were prepared by etching gold nanoparticles with glutathione. Three different Au33 clusters with emission profiles in the NIR region and one blue emitting cluster, Au8 were developed by varying the geometrical arrangement of atoms within the cluster. These clusters having sizes in the range of 0.7 to 2 nm were synthesized by choosing different reaction temperatures from 0 °C to 70 °C and pH between 1.5 and 10. In the three cases, formation of self assembled atoms within the cluster and the corresponding changes in optical properties were observed. A detailed evaluation of the number of atoms and the core-ligand ratio using MALDI-MS and a change in the binding energy as seen in the XPS study confirmed this finding. The study demonstrates that the self assembly of atoms and their arrangement is an important factor in determining the characteristics of the cluster. In this communication, we put forward a new concept where the number of atoms and their arrangement within the clusters play a crucial role in tuning their optical properties. PMID:27356966

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

    SciTech Connect

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

    2014-03-28

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

  3. Disorder and cluster formation during ion irradiation of Au nanoparticles in SiO2

    NASA Astrophysics Data System (ADS)

    Kluth, P.; Johannessen, B.; Foran, G. J.; Cookson, D. J.; Kluth, S. M.; Ridgway, M. C.

    2006-07-01

    Au nanoparticles (NPs) have been formed by ion beam synthesis in 600nm thin SiO2 . Subsequently the NPs were irradiated with 2.3MeV Sn ions at liquid nitrogen temperature. Samples were analyzed using extended x-ray absorption fine structure (EXAFS) spectroscopy and small angle x-ray scattering (SAXS) as a function of Sn irradiation dose. Transmission electron microscopy shows that the NPs largely retain their spherical shape upon irradiation. However, we observe a reduction in average NP size and a concomitant significant narrowing of the size distribution with increasing irradiation dose as consistent with inverse Ostwald ripening. At lower irradiation doses, significant structural disorder is apparent with an effective bond length expansion as consistent with amorphous material. At higher irradiation doses, EXAFS measurements indicate dissolution of a significant fraction of Au from the NPs into the SiO2 matrix (as monomers) and the formation of small Au clusters (dimers, trimers, etc.). We estimate the volume fraction of such monomers/clusters. Ion irradiation thus yields disordering then dissolution of Au NPs.

  4. Spin-orbit coupling effects in gold clusters: The case of Au13

    NASA Astrophysics Data System (ADS)

    Flores, Mauricio A.; Menéndez-Proupin, Eduardo

    2016-05-01

    Non relativistic description of the chemical bonding for heavy atom systems is unrealistic. However, only few relativistic DFT calculations have been reported for gold clusters. In this work, we investigate the effect of the spin-orbit coupling in the structure, relative stability and HOMO-LUMO gap of the lowest-lying isomers of neutral Au13 clusters. Our results show that spin-orbit coupling increases the energy gap between 2D and 3D isomers and a relativistic bond contraction appears. Moreover, the relative energy of some isomers change when the spin-orbit coupling is included.

  5. Spin and structural features of oxygen dissociation on tetrahedral Ag20 and Ag19Au clusters.

    PubMed

    Pichugina, D A; Polynskaya, Y G; Kuz'menko, N E

    2016-07-21

    The spin-crossing mechanism of oxygen dissociation on Ag20 and monodoped Ag19Au clusters was investigated via spin-polarized scalar-relativistic DFT calculations using the PBE, TPSSh, M06L, mPBE, BLYP, OLYP, and B3LYP functionals. In particular, the singlet and triplet O-O bond rupture pathways at vertex-edge and facet-edge sites on the tetrahedral clusters were studied. The calculations reveal that for the Ag20O2 and Ag19AuO2 complexes, the spin inversion from the triplet to singlet state occurs during the last step, which involves O-O bond rupture through a singlet transition state (TS). When spin crossing during oxygen dissociation on the clusters is considered, the activation energies decrease by 10-29 kJ mol(-1); however, they are still high due to the magic nature of the clusters and high vertical spin excitation energies. For these silver clusters, size effects based on the relationship between the TS structure and oxidation activation energy were predicted. PMID:27327106

  6. 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. PMID:24611036

  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. 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. 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.

  10. 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.

  11. 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

  12. 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

  13. Properties and Formation of Star Clusters

    NASA Astrophysics Data System (ADS)

    Sharina, M. E.

    2016-03-01

    Many key problems in astrophysics involve research on the properties of star clusters, for example: stellar evolution and nucleosynthesis, the history of star formation in galaxies, formation dynamics of galaxies and their subsystems, the calibration of the fundamental distance scale in the universe, and the luminosity functions of stars and star clusters. This review is intended to familiarize the reader with modern observational and theoretical data on the formation and evolution of star clusters in our galaxy and others. Unsolved problems in this area are formulated and research on ways to solve them is discussed. In particular, some of the most important current observational and theoretical problems include: (1) a more complete explanation of the physical processes in molecular clouds leading to the formation and evolution of massive star clusters; (2) observation of these objects in different stages of evolution, including protoclusters, at wavelengths where interstellar absorption is minimal; and, (3) comparison of the properties of massive star clusters in different galaxies and of galaxies during the most active star formation phase at different red shifts. The main goal in solving these problems is to explain the variations in the abundance of chemical elements and in the multiple populations of stars in clusters discovered at the end of the twentieth century.

  14. Photoelectron spectroscopy of boron-gold alloy clusters and boron boronyl clusters: B3Au(n)(-) and B3(BO)n(-) (n = 1, 2).

    PubMed

    Chen, Qiang; Bai, Hui; Zhai, Hua-Jin; Li, Si-Dian; Wang, Lai-Sheng

    2013-07-28

    Photoelectron spectroscopy and density-functional theory are combined to study the structures and chemical bonding in boron-gold alloy clusters and boron boronyl clusters: B3Au(n)(-) and B3(BO)n(-) (n = 1, 2). Vibrationally resolved photoelectron spectra are obtained for all four species and the B-Au and B-BO clusters exhibit similar spectral patterns, with the latter species having higher electron binding energies. The electron affinities of B3Au, B3Au2, B3(BO), and B3(BO)2 are determined to be 2.29 ± 0.02, 3.17 ± 0.03, 2.71 ± 0.02, and 4.44 ± 0.02 eV, respectively. The anion and neutral clusters turn out to be isostructural and isovalent to the B3H(n)(-)∕B3H(n) (n = 1, 2) species, which are similar in bonding owing to the fact that Au, BO, and H are monovalent σ ligands. All B3Au(n)(-) and B3(BO)n(-) (n = 1, 2) clusters are aromatic with 2π electrons. The current results provide new examples for the Au∕H and BO∕H isolobal analogy and enrich the chemistry of boronyl and gold. PMID:23901981

  15. Synthesis and optical property characterization of elongated AuPt and Pt@Au metal nanoframes

    NASA Astrophysics Data System (ADS)

    Lee, Sangji; Jang, Hee-Jeong; Jang, Ho Young; Hong, Soonchang; Moh, Sang Hyun; Park, Sungho

    2016-02-01

    We report a facile method to synthesize elongated nanoframes consisting of Pt and Au in solution. Pentagonal Au nanorods served as templates and successfully led to an elongated AuPt nanoframe after etching the core Au. Subsequently, the coating of Au around Pt ridges resulted in Pt@Au metal nanoframes. The resulting elongated nanostructure exhibited 5 well-defined ridges continuously connected along the long axis. During the shape evolution from pure Au nanorods to elongated Pt@Au metal nanoframes, their corresponding localized surface plasmon resonance bands were monitored. Especially, unique surface plasmon features were observed for elongated Pt@Au nanoframes where the short-axis oscillation of surface free electrons is strongly coupled but the long-axis oscillation is not coupled among the ridges.We report a facile method to synthesize elongated nanoframes consisting of Pt and Au in solution. Pentagonal Au nanorods served as templates and successfully led to an elongated AuPt nanoframe after etching the core Au. Subsequently, the coating of Au around Pt ridges resulted in Pt@Au metal nanoframes. The resulting elongated nanostructure exhibited 5 well-defined ridges continuously connected along the long axis. During the shape evolution from pure Au nanorods to elongated Pt@Au metal nanoframes, their corresponding localized surface plasmon resonance bands were monitored. Especially, unique surface plasmon features were observed for elongated Pt@Au nanoframes where the short-axis oscillation of surface free electrons is strongly coupled but the long-axis oscillation is not coupled among the ridges. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08200e

  16. Effect of ligand on the geometric and electronic structure of Au13 cluster

    NASA Astrophysics Data System (ADS)

    Shafai, Ghazal; Hong, Sampyo; Rahman, Talat; Bertino, Massimo

    2008-03-01

    We have carried out calculations based on the density functional theory in the projector augmented wave scheme (PAW) and the pseudopotential approach, to examine the effect of the ligand on the geometric and electronic structure of Au13 cluster. We find bare Au13 to form a flat flake, in agreement with previous theoretical calculations. This structure is lower in energy by 2.60 eV in comparison with the well ordered icosahedron geometry. Our results show, however, that the Au13 cluster covered with ligands of phosphine (PH3) forms a stable spherical structure (icosahedron) in agreement with the experiment [1] which is by 0.08 eV lower in energy when compared to the flat-flake complex. If the phosphine is replaced by H, the spherical structure is no longer stable, but it still maintains a 3 dimensional form, signifying the effect of the ligand in stabilization of the structure. We observe a narrow d-band for flat-flake gold atoms in the complex, while in the icosahedron structure the d-band is wider. We also find a stronger overlap between the p orbitals of the P atom with d orbitals of gold atoms in the icosahedron complex. [1] M. F. Bertino et. al. Phys. Chem. B Lett. 110, 21416 (2006)

  17. Experimental and computational investigation of Au25 clusters and CO2: a unique interaction and enhanced electrocatalytic activity.

    PubMed

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

    2012-06-20

    Atomically precise, inherently charged Au(25) clusters are an exciting prospect for promoting catalytically challenging reactions, and we have studied the interaction between CO(2) and Au(25). Experimental results indicate a reversible Au(25)-CO(2) interaction that produced spectroscopic and electrochemical changes similar to those seen with cluster oxidation. Density functional theory (DFT) modeling indicates these changes stem from a CO(2)-induced redistribution of charge within the cluster. Identification of this spontaneous coupling led to the application of Au(25) as a catalyst for the electrochemical reduction of CO(2) in aqueous media. Au(25) promoted the CO(2) → CO reaction within 90 mV of the formal potential (thermodynamic limit), representing an approximate 200-300 mV improvement over larger Au nanoparticles and bulk Au. Peak CO(2) conversion occurred at -1 V (vs RHE) with approximately 100% efficiency and a rate 7-700 times higher than that for larger Au catalysts and 10-100 times higher than those for current state-of-the-art processes. PMID:22616945

  18. 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. PMID:21348523

  19. 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

  20. Effects of stretching and compression on conducting properties of an Au-alkanedithiol-Au molecular junction

    NASA Astrophysics Data System (ADS)

    Xie, Fang; Zhang, Xiao-Jiao; Yu, Ji-Hai; Xu, Hua; Chu, Yu-Fang; Fan, Zhi-Qiang

    2016-03-01

    We have studied the effects of stretching and compression on the electronic properties of 7-alkanedithiol covalently linked to two Au electrodes. Results show a progressive increase in conductivity upon molecule compression and decrease with molecule stretching. The notable conductance increase at high compression is attributed to a significant modification of HOMO and LUMO orbitals of the junction, which enhances electron delocalization and promotes tunneling across the junction. More important, the current switching ratios between the various stages of compressed/extended geometries almost maintain the constant values on the bias region from 0 V to 2 V. In other word, the mechanically-induced conductance enhancement and weakening are stable within a large bias voltage range.

  1. 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.

  2. Electronic transport properties of silicon clusters

    NASA Astrophysics Data System (ADS)

    Matsuura, Yukihito

    2016-02-01

    The electronic transport properties of silicon clusters were examined via theoretical calculations using the first-principles method. Additionally, p-type doping and n-type doping were analyzed by calculating conductance and current of boron- and phosphorus-doped silicon clusters. The p-type doping and n-type doping provided a new transmission peak at an energy level around the Fermi level to increase conductance. Furthermore, simultaneous boron and phosphorus doping resulted in noticeable rectifying characteristics, with the current drive in forward bias being three times higher than that in the reverse bias. A p-n junction was achieved even on a molecular scale.

  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. Structure & Bonding of the Gold-Subhalide Cluster I-Au144Cl60[z

    PubMed Central

    Black, David M.; Bach, Stephan B. H.; Jose-Yacamán, Miguel

    2013-01-01

    The structure and bonding of the gold-subhalide compounds Au144Cl60[z] are related to those of the ubiquitous thiolated gold clusters, or Faradaurates, by iso-electronic substitution of thiolate by chloride. Exact I-symmetry holds for the [z] = [2+,4+] charge-states, in accordance with new ESI-MS measurements and the predicted electron shell filling. The High symmetry facilitates analysis of the global structure as well as the bonding network, with some striking results. PMID:24105400

  5. 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. PMID:26285135

  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. 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.

  8. 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.

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

    PubMed

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

    2009-04-30

    By bonding gold atoms to the magic number cluster (SiO(2))(4)O(2)H(4), two groups of Au-adsorbed shell-like clusters Au(n)(SiO(2))(4)O(2)H(4-n) (n = 1-4) and Au(n)(SiO(2))(4)O(2) (n = 5-8) were obtained, and their spectral properties were studied. The ground-state structures of these clusters were optimized by density functional theory, and the results show that in despite of the different numbers and types of the adsorbed Au atoms, the cluster core (SiO(2))(4)O(2) of T(d) point-group symmetry keeps almost unchanged. The absorption spectra were obtained by time-dependent density functional theory. From one group to the other, an extension of absorption wavelength from the UV-visible to the NIR region was observed, and in each group the absorption strengths vary linearly with the number of Au atoms. These features indicate their advantages for exploring novel materials with easily controlled tunable optical properties. Furthermore, due to the weak electronic charge transfer between the Au atoms, the clusters containing Au(2) dimers, especially Au(8)(SiO(2))(4)O(2), absorb strongly NIR light at 900 approximately 1200 nm. Such strong absorption suggests potential applications of these shell-like clusters in tumor cells thermal therapy, like the gold-coated silica nanoshells with larger sizes. PMID:19354211

  10. Adsorption of small Au clusters on MgO and MgO/Mo: the role of oxygen vacancies and the Mo-support

    NASA Astrophysics Data System (ADS)

    Frondelius, P.; Häkkinen, H.; Honkala, K.

    2007-09-01

    We report a systematic density functional theory investigation of adsorption of small Aun (n =1-6) clusters on ideal and defected MgO(100) single crystal surfaces and Mo(100) supported thin MgO(100) films. As a model defect, we consider a neutral surface oxygen vacancy (Fs). Optimal adsorption geometries and energies, cluster formation energies and cluster charges are discussed and compared in detail over four different substrates. For a given cluster size, the adsorption energy among these substrates increases in the order MgO, Fs/MgO, MgO/Mo and Fs/MgO/Mo. While cluster growth by association of atoms from gas phase is exothermic on all the substrates, cluster growth by diffusion and aggregation of pre-adsorbed Au atoms is an endothermic process for Au1→Au2, Au3→Au4 and Au5→Au6 on MgO/Mo and Au2→Au3 and Au5→Au6 on Fs/MgO/Mo. The adsorbed clusters are close to neutral on MgO, but adopt a significant anionic charge on other supports with the increasing order: MgO/Mo, Fs/MgO and Fs/MgO/Mo. The adsorption strength thus correlates with the amount of negative charge transferred from the substrate to gold.

  11. 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.

  12. Thermochemical property estimation of hydrogenated silicon clusters.

    PubMed

    Adamczyk, Andrew J; Broadbelt, Linda J

    2011-08-18

    The thermochemical properties for selected hydrogenated silicon clusters (Si(x)H(y), x = 3-13, y = 0-18) were calculated using quantum chemical calculations and statistical thermodynamics. Standard enthalpy of formation at 298 K and standard entropy and constant pressure heat capacity at various temperatures, i.e., 298-6000 K, were calculated for 162 hydrogenated silicon clusters using G3//B3LYP. The hydrogenated silicon clusters contained ten to twenty fused Si-Si bonds, i.e., bonds participating in more than one three- to six-membered ring. The hydrogenated silicon clusters in this study involved different degrees of hydrogenation, i.e., the ratio of hydrogen to silicon atoms varied widely depending on the size of the cluster and/or degree of multifunctionality. A group additivity database composed of atom-centered groups and ring corrections, as well as bond-centered groups, was created to predict thermochemical properties most accurately. For the training set molecules, the average absolute deviation (AAD) comparing the G3//B3LYP values to the values obtained from the revised group additivity database for standard enthalpy of formation and entropy at 298 K and constant pressure heat capacity at 500, 1000, and 1500 K were 3.2%, 1.9%, 0.40%, 0.43%, and 0.53%, respectively. Sensitivity analysis of the revised group additivity parameter database revealed that the group parameters were able to predict the thermochemical properties of molecules that were not used in the training set within an AAD of 3.8% for standard enthalpy of formation at 298 K. PMID:21728331

  13. A comparative theoretical study for the methanol dehydrogenation to CO over Pt3 and PtAu2 clusters.

    PubMed

    Zhong, Wenhui; Liu, Yuxia; Zhang, Dongju

    2012-07-01

    The density functional theory (DFT) calculations are carried out to study the mechanism details and the ensemble effect of methanol dehydrogenation over Pt(3) and PtAu(2) clusters, which present the smallest models of pure Pt clusters and bimetallic PtAu clusters. The energy diagrams are drawn out along both the initial O-H and C-H bond scission pathways via the four sequential dehydrogenation processes, respectively, i.e., CH(3)OH → CH(2)OH → CH(2)O → CHO → CO and CH(3)OH → CH(3)O → CH(2)O → CHO → CO, respectively. It is revealed that the reaction kinetics over PtAu(2) is significantly different from that over Pt(3). For the Pt(3)-mediated reaction, the C-H bond scission pathway, where an ensemble composed of two Pt atoms is required to complete methanol dehydrogenation, is energetically more favorable than the O-H bond scission pathway, and the maximum barrier along this pathway is calculated to be 12.99 kcal mol(-1). In contrast, PtAu(2) cluster facilitates the reaction starting from the O-H bond scission, where the Pt atom acts as the active center throughout each elementary step of methanol dehydrogenation, and the initial O-H bond scission with a barrier of 21.42 kcal mol(-1) is the bottom-neck step of methanol decomposition. Importantly, it is shown that the complete dehydrogenation product of methanol, CO, can more easily dissociate from PtAu(2) cluster than from Pt(3) cluster. The calculated results over the model clusters provide assistance to some extent for understanding the improved catalytic activity of bimetal PtAu catalysts toward methanol oxidation in comparison with pure Pt catalysts. PMID:22160734

  14. Properties of Stream Interactions at One AU During 1995 2004

    NASA Astrophysics Data System (ADS)

    Jian, L.; Russell, C. T.; Luhmann, J. G.; Skoug, R. M.

    2006-12-01

    A stream interaction region (SIR) forms when a fast solar stream overtakes a slow stream, leading to structure that evolves as an SIR moves away from the Sun. Based on Wind (1995 2004) and ACE (1998 2004) in situ observations, we have conducted a comprehensive survey of SIRs at one AU, including a separate assessment of the longer-lasting corotating interaction regions (CIRs) that recur on more than one solar rotation. In all there are 196 CIRs, accounting for about 54% of the 365 SIRs. The largest proportion of CIRs to SIRs (64%) appears in 1999, and the smallest proportion (49%) is in 2002. Over the ten years, the annual number of SIR events varies little, from 32 up to 45. On average, the occurrence rate of shocks at SIRs at one AU is about 24%. Seventy percent of the SIRs with shocks have only forward shocks, more than twice the percentage of SIRs with only reverse shocks. This preponderance of forward shocks is consistent with the deflections of forward and reverse shocks relative to the ecliptic plane. In order to help address the effect of SIRs and CIRs on geomagnetic activity, we determine the solar-cycle variation of the event duration, scale size, the change in velocity from slow stream to fast stream, and the solar-cycle variation of the maximum magnetic field, peak total perpendicular pressure, and other properties. These statistics also provide a baseline for future studies at other heliocentric distances and for validating heliospheric models.

  15. Revealing the properties of Mn2Au for antiferromagnetic spintronics

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  16. 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. PMID:24327004

  17. 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.

  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

    2016-08-01

    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. PMID:27461071

  19. Manipulating the charge state of Au clusters on rutile TiO2(110) single crystal surfaces through molecular reactions probed by infrared spectroscopy.

    PubMed

    Cao, Yunjun; Hu, Shujun; Yu, Min; Wang, Tingting; Huang, Shiming; Yan, Shishen; Xu, Mingchun

    2016-07-14

    The charge state of Au clusters deposited on rutile TiO2(110) single crystal surfaces was studied by UHV-FTIRS using CO as a probe. The as-deposited Au clusters on oxidized TiO2(110) surfaces are electrically neutral and are identified by the 2105-2112 cm(-1) vibrational frequency of adsorbed CO depending on Au coverage. Annealing Au/TiO2(110) in a moderate O2 atmosphere at 400 K blue shifts the CO vibrational frequency by only 2-3 cm(-1) both on bare TiO2(110) surfaces and on Au clusters. However, NO exposure blue shifts the CO vibrational frequency by 16-26 cm(-1) for CO adsorbed on Au atoms near the interface and by 3-4 cm(-1) for CO adsorbed on top of Au clusters. As the acceptors of the intense charge transfer from Au, the Oa atoms generated through (NO)2→ N2O + Oa reactions on the small fraction of the bare TiO2(110) surface reside around the Au/TiO2(110) interface perimeter, causing the neutral Au(0) to be cationic Au(δ+) states. This is a new approach to manipulate the charge state of Au clusters on oxide surfaces, which may be helpful in regulating the catalytic redox reactions on oxide supported metal systems. PMID:27306113

  20. 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.

  1. Structural properties of small rhodium clusters

    SciTech Connect

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

    2015-04-24

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

  2. 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)

  3. cluster-lensing: Tools for calculating properties and weak lensing profiles of galaxy clusters

    NASA Astrophysics Data System (ADS)

    Ford, Jes

    2016-05-01

    The cluster-lensing package calculates properties and weak lensing profiles of galaxy clusters. Implemented in Python, it includes cluster mass-richness and mass-concentration scaling relations, and NFW halo profiles for weak lensing shear, the differential surface mass density ΔΣ(r), and for magnification, Σ(r). Optionally the calculation will include the effects of cluster miscentering offsets.

  4. Carbon dot cluster as an efficient "off-on" fluorescent probe to detect Au(III) and glutathione.

    PubMed

    Gu, Jiangjiang; Hu, Donghua; Wang, Weina; Zhang, Qiuhong; Meng, Zhen; Jia, Xudong; Xi, Kai

    2015-06-15

    In this paper, we reported for the first time that Au(III) decorated carbon dot cluster (Au(III)/CDC) was synthesized to detect glutathione through fluorescence "off-on" approach. The "off" process was realized by the introduction of Au(III) on luminescent carbon dots (CDs), which formed the complex of Au(III)/CDC and quenched the fluorescence of CDs efficiently. This "off" process was used to detect Au(III) with the selectivity among 21 metal ions and the limitation was 0.48 μM (S/N=3). Au(III) could be removed from the complex by biothiol in the solution, which restored the fluorescence of CDC to achieve the "on" process. This process was selective for biothiols (especially for glutathione) among saccharides, dopamine and amino acids and the limit of detection was 2.02 μM (S/N=3). Due to the dependence of the fluorescence restoration on the concentration of glutathione, Au(III)/CDC was applied as the fluorescence sensor for detection of glutathione in the solution and cellular cytosol. By referring to the fluorescence change in the solution, the intracellular glutathione with/without oxygen stress was evaluated. As compared with the commercial assay, our Au(III)/CDC based assay was simple, facile and low cost, which would be useful to measure intracellular glutathione at different cellular states. PMID:25558871

  5. Clustering properties of dynamical dark energy models

    SciTech Connect

    Avelino, P. P.; Beca, L. M. G.; Martins, C. J. A. P.

    2008-05-15

    We provide a generic but physically clear discussion of the clustering properties of dark energy models. We explicitly show that in quintessence-type models the dark energy fluctuations, on scales smaller than the Hubble radius, are of the order of the perturbations to the Newtonian gravitational potential, hence necessarily small on cosmological scales. Moreover, comparable fluctuations are associated with different gauge choices. We also demonstrate that the often used homogeneous approximation is unrealistic, and that the so-called dark energy mutation is a trivial artifact of an effective, single fluid description. Finally, we discuss the particular case where the dark energy fluid is nonminimally coupled to dark matter.

  6. 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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.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

  7. A density functional theory study on structures, stabilities, and electronic and magnetic properties of AunC (n = 1-9) clusters

    NASA Astrophysics Data System (ADS)

    Hou, Xiao-Fei; Yan, Li-Li; Huang, Teng; Hong, Yu; Miao, Shou-Kui; Peng, Xiu-Qiu; Liu, Yi-Rong; Huang, Wei

    2016-06-01

    The equilibrium geometric structures, relative stabilities, electronic stabilities, and electronic and magnetic properties of the AunC and Aun+1 (n = 1-9) clusters are systematically investigated using density functional theory (DFT) with hyper-generalized gradient approximation (GGA). The optimized geometries show that one Au atom added to the Aun-1C cluster is the dominant growth pattern for the AunC clusters. In contrast to the pure gold clusters, the AunC clusters are most stable in a quasi-planar or three-dimensional (3D) structure because the C dopant induces the local non-planarity, with exceptions of the Au6,8C clusters who have 2D structures. The analysis of the relative and electronic stabilities reveals that the Au4C and Au6 clusters are the most stable in the series of studied clusters, respectively. In addition, a natural bond orbital (NBO) analysis shows that the charges in the AunC clusters transfer from the Aun host to the C atom. Moreover, the Au and C atoms interact with each other mostly via covalent bond rather than ionic bond, which can be confirmed through the average ionic character of the Au-C bond. Meanwhile, the charges mainly transfer between 2s and 2p orbitals within the C atom, and among 5d, 6s, and 6p orbitals within the Au atom for the AunC clusters. As for the magnetic properties of the AunC clusters, the total magnetic moments are 1 μB for n = odd clusters, with the total magnetic moments mainly locating on the C atoms for Au1,3,9C and on the Aun host for Au5,7C clusters. However, the total magnetic moments of the AunC clusters are zero for n = even clusters. Simultaneously, the magnetic moments mainly locate on the 2p orbital within the C atom and on the 5d, 6s orbitals within the Au atom.

  8. Some Provable Properties of VERI Clustering

    SciTech Connect

    OSBOURN,GORDON C.

    2000-07-01

    We present mathematical proofs for two useful properties of the clusters generated by the visual empirical region of influence (VERI) shape. The first proof shows that, for any d-dimensional vector set with more than one distinct vector, that there exists a bounded spherical volume about each vector v which contains all of the vectors that can VERI cluster with v, and that the radius of this d-dimensional volume scales linearly with the nearest neighbor distance to v. We then prove, using only each vector's nearest neighbor as an inhibitor, that there is a single upper bound on the number of VERI clusterings for each vector in any d-dimensional vector set, provided that there are no duplicate vectors. These proofs guarantee significant improvement in VERI algorithm runtimes over the brute force O(N{sup 3}) implementation required for general d-dimensional region of influence implementations and indicate a method for improving approximate O(NlogN) VERI implementations. We also present a related region of influence shape called the VERI bow tie that has been recently used in certain swam intelligence algorithms. We prove that the VERI bow tie produces connected graphs for arbitrary d-dimensional data sets (if the bow tie boundary line is not included in the region of influence). We then prove that the VERI bow tie also produces a bounded number of clusterings for each vector in any d-dimensional vector set, provided that there are no duplicate vectors (and the bow tie boundary line is included in the region of influence).

  9. Facile modulation of optical properties of octagold clusters through the control of ligand-mediated interactions.

    PubMed

    Iwasaki, Mitsuhiro; Kobayashi, Naoki; Shichibu, Yukatsu; Konishi, Katsuaki

    2016-07-28

    In the recent development of structurally defined ligand-stabilized gold clusters, it has been revealed that not only the inorganic units but also the surrounding organic ligands substantially affect their electronic/optical properties. In this work, a series of core + exo type Au8 clusters decorated by dppp (Ph2P(CH2)3PPh2) and arylthiolate ligands ([Au8(dppp)4(SR)2](2+), 1-5) were synthesized, and their optical properties were studied in order to gain insights into the perturbation effects of the organic ligands. 1-5 showed visible absorption and photoluminescence emission bands at longer wavelengths compared to their chloro- and acetylide-modified analogues, suggesting the contribution of weak non-bonding interactions of the Au framework with the ligand heteroatoms. Upon acid treatment, 2- and 4-pyridinethiolate clusters (R = Py, 2 and 4) showed larger red shifts of the absorption and emission bands than the 3-pyridyl isomer (3), implying the involvement of the resonance structures of the SPy units. On the other hand, all regioisomers (2-4) showed large photoluminescence enhancements upon pyridine protonation. X-ray crystallographic and NMR analyses of 4 and its protonated form (4') showed that the electron-deficient pyridinium rings of 4' form π-stacks with neighbouring phenyl groups of dppp, suggesting that the orientation of the surface aromatics is a plausible factor governing the emission efficiency. These observations provide examples of successful modulation of optical properties of small gold clusters through the electronic and/or steric perturbation by the proximal organic ligands, highlighting the importance of the ligand design in the fine tuning of cluster properties directed for optical chemosensors and luminescent materials. PMID:27378218

  10. 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

    2015-09-01

    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. PMID:25650352

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  13. Density functional study of structural and electronic properties of maximum-spin n+1Aun-1Ag clusters

    NASA Astrophysics Data System (ADS)

    Jiang, Zhen-Yi; Hou, Yu-Qin; Lee, Kuo-Hsing; Chu, San-Yan

    The structures and relative stabilities of high-spin n+1Aun-1Ag and nAun-1Ag+ (n = 2-8) clusters have been studied with density functional calculation. We predicted the existence of a number of previously unknown isomers. Our results revealed that all structures of high-spin neutral or cationic Aun-1Ag clusters can be understood as a substitution of an Au atom by an Ag atom in the high-spin neutral or cationic Aun clusters. The properties of mixed gold-silver clusters are strongly sized and structural dependence. The high-spin bimetallic clusters tend to be holding three-dimensional geometry rather than planar form represented in their low-spin situations. Silver atom prefers to occupy those peripheral positions until to n = 8 for high-spin clusters, which is different from its position occupied by light atom in the low-spin situations. Our theoretical calculations indicated that in various high-spin Aun-1Ag neutral and cationic species, 5Au3Ag, 3AuAg and 5Au4Ag+ hold high stability, which can be explained by valence bond theory.

  14. Electronic and chemical properties of supported Au nanoparticles

    NASA Astrophysics Data System (ADS)

    Lim, Dong Chan; Lopez-Salido, Ignacio; Dietsche, Rainer; Bubek, Moritz; Kim, Young Dok

    2006-11-01

    Oxidation and reduction behaviors of Au nanoparticles with different sizes on highly ordered pyrolytic graphite (HOPG) and silica were studied using X-ray photoelectron spectroscopy (XPS). For Au nanoparticles smaller than ˜6 nm in diameter, we found a novel oxygen species formed in Au nanoparticles, which is absent in larger particles and Au bulk crystals. This new oxygen species is attributed to the subsurface oxygen: for a complete understanding of the structures of catalytically active Au, the new oxygen species should be taken into account. In this context, it is worth mentioning that the subsurface oxygen species has been suggested to play an important role in heterogeneous catalysis. With decreasing Au particle size, a positive core level shift can be observed, which can be mostly attributed to the final state effects. Increase of the number of undercoordinated atoms with decreasing particle size is evidenced by a reduced splitting between 5d 3/2 and 5d 5/2 states and a band narrowing. Our results on electronic structures of Au nanoparticles on silica are compared to those on other substrates such as zirconia and titania to shed light onto the metal-support interactions.

  15. Properties of star clusters - II. Scaleheight evolution of clusters

    NASA Astrophysics Data System (ADS)

    Buckner, Anne S. M.; Froebrich, Dirk

    2014-10-01

    Until now, it has been impossible to observationally measure how star cluster scaleheight evolves beyond 1 Gyr as only small samples have been available. Here, we establish a novel method to determine the scaleheight of a cluster sample using modelled distributions and Kolmogorov-Smirnov tests. This allows us to determine the scaleheight with a 25 per cent accuracy for samples of 38 clusters or more. We apply our method to investigate the temporal evolution of cluster scaleheight, using homogeneously selected sub-samples of Kharchenko et al. (MWSC), Dias et al. (DAML02), WEBDA, and Froebrich et al. (FSR). We identify a linear relationship between scaleheight and log(age/yr) of clusters, considerably different from field stars. The scaleheight increases from about 40 pc at 1 Myr to 75 pc at 1 Gyr, most likely due to internal evolution and external scattering events. After 1 Gyr, there is a marked change of the behaviour, with the scaleheight linearly increasing with log(age/yr) to about 550 pc at 3.5 Gyr. The most likely interpretation is that the surviving clusters are only observable because they have been scattered away from the mid-plane in their past. A detailed understanding of this observational evidence can only be achieved with numerical simulations of the evolution of cluster samples in the Galactic disc. Furthermore, we find a weak trend of an age-independent increase in scaleheight with Galactocentric distance. There are no significant temporal or spatial variations of the cluster distribution zero-point. We determine the Sun's vertical displacement from the Galactic plane as Z⊙ = 18.5 ± 1.2 pc.

  16. Photoelectron spectroscopy of aromatic compound clusters of the B12 all-boron benzene: B12Au- and B12(BO)-.

    PubMed

    Bai, Hui; Zhai, Hua-Jin; Li, Si-Dian; Wang, Lai-Sheng

    2013-06-28

    We report a photoelectron spectroscopy and density-functional theory study of the B12Au(-) and B13O(-) clusters and their neutrals, which are shown to be six π electron aromatic compounds between the quasi-planar all-boron B12 benzene-analogue and a monovalent Au or BO ligand. Electron affinities of B12Au and B13O are measured to be 3.48 ± 0.04 and 3.90 ± 0.04 eV, respectively. Structural searches are performed for B12Au(-) and B13O(-), which are compared with the isovalent B12H(-) cluster. The global minima of B12Au(-) and B13O(-) both feature an almost intact B12 cluster with the Au and BO ligands bonded to its periphery, respectively. For B12Au(-), a low-lying isomer is also identified, which is only 0.4 kcal mol(-1) above the global minimum, in agreement with the experimental observation of a weakly populated isomer in the cluster beam of B12Au(-). These aromatic compound clusters provide new examples for the Au/H isolobal analogy and the boronyl (BO) chemistry. PMID:23666408

  17. Transition from exohedral to endohedral structures of AuGen(-) (n = 2-12) clusters: photoelectron spectroscopy and ab initio calculations.

    PubMed

    Lu, Sheng-Jie; Hu, Lian-Rui; Xu, Xi-Ling; Xu, Hong-Guang; Chen, Hui; Zheng, Wei-Jun

    2016-07-27

    Gold-doped germanium clusters, AuGen(-) (n = 2-12), were investigated by using anion photoelectron spectroscopy in combination with ab initio calculations. Their geometric structures were determined by comparison of the theoretical calculations with the experimental results. The results show that the most stable isomers of AuGen(-) with n = 2-10 are all exohedral structures with the Au atom capping the vertex, edge or face of Gen clusters, while AuGe11(-) is found to be the critical size of the endohedral structure. Interestingly, AuGe12(-) has an Ih symmetric icosahedral structure with the Au atom located at the center. The molecular orbital analysis of the AuGe12(-) cluster suggests that the interactions between the 5d orbitals of the Au atom and the 4s4p hybridized orbitals of the Ge atoms may stabilize the Ih symmetric icosahedral cage and promote the Au atom to be encapsulated in the cage of Ge12. The NICS(0) and NICS(1) values are calculated to be -143.7 ppm and -36.3 ppm, respectively, indicating that the icosahedral AuGe12(-) cluster is significantly aromatic. PMID:27066757

  18. Electrical properties of nanofibers and structural characterization of DNA-Au(III) complexes.

    PubMed

    Kwon, Young-Wan; Lee, Chang Hoon; Jin, Jung-Il; Hwang, Jong Seung; Hwang, Sung Woo

    2014-05-23

    In order to realize deoxyribonucleic acid (DNA)-based molecular electronics, chemical modifications of DNA are needed to improve electrical conductivity. We developed a novel method utilizing the incorporation of Au(III) ions into DNA bases to alter their electronic properties. When Au(III) ions were incorporated proportionally into DNA bases, conductance increased up to an Au(III) content of 0.42 Au(III) ion/nucleotide. Surprisingly, electron paramagnetic resonance signals of Au(II) ions were detected at g ∼1.98, and the calculated spin number of Au(II) ions ranged from ∼10(13) to ∼10(15). The structural deformation of the DNA helix occurred when complexed with Au(III); simultaneously, the conductance of DNA-Au(III) complexes decreased when the content of Au(III) was higher than 0.42 atom/nucleotide. This observation implies that the maintenance of helical structure in the Au(III) doped state of DNA molecules is very important to the enhancement of the carrier mobility of DNA. PMID:24786616

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

    SciTech Connect

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

    2010-01-01

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

  20. Intramolecular d10-d10 interactions in a Ni6C(CO)9(AuPPh3)4 bimetallic nickel-gold carbide carbonyl cluster.

    PubMed

    Ciabatti, Iacopo; Femoni, Cristina; Iapalucci, Maria Carmela; Ienco, Andrea; Longoni, Giuliano; Manca, Gabriele; Zacchini, Stefano

    2013-09-16

    The Ni6C(CO)9(AuPPh3)4 bimetallic carbide carbonyl cluster was obtained from the reaction of [Ni9C(CO)17](2-) with Au(PPh3)Cl. It contains a rare carbon-centered (distorted) Ni6C octahedral core decorated by four Au(PPh3) fragments. These are μ3-bonded to four contiguous Ni3-triangular faces and display weak intramolecular Au···Au d(10)-d(10) interactions. The cluster has been characterized in the solid state on two different solvato crystals, i.e., Ni6C(CO)9(AuPPh3)4·THF and Ni6C(CO)9(AuPPh3)4·THF·0.5C6H14. The two solvates show some interesting differences concerning the weak Au···Au contacts. Density functional theory calculations have demonstrated that the presence of the two isomers is related to solid-state packing effects and not to the existence of two double minima in the potential energy surface. This, in turn, confirms that Au···Au d(10)-d(10) interactions are rather soft and thus influenced also by weak van der Waals forces because of the interaction of the cluster with the cocrystallized solvent molecules. PMID:24004143

  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. Synthesis of Cu2SnSe3-Au heteronanostructures with optoelectronic and photocatalytic properties

    NASA Astrophysics Data System (ADS)

    Wang, Wenliang; Ding, Tao; Chen, Guihuan; Zhang, Li; Yu, Yongqiang; Yang, Qing

    2015-09-01

    Cu2SnSe3-Au heteronanostructures have been successfully synthesized for the first time using a seed-mediated growth method. Such new Cu2SnSe3-Au heteronanostructures demonstrate enhanced and broadened optical absorption in the Vis-NIR region. We have also investigated the optoelectronic and photocatalytic properties of the Cu2SnSe3-Au heteronanostructures and proposed a mechanism to illustrate the improved photocurrent and photocatalytic performance as compared to bare Cu2SnSe3.Cu2SnSe3-Au heteronanostructures have been successfully synthesized for the first time using a seed-mediated growth method. Such new Cu2SnSe3-Au heteronanostructures demonstrate enhanced and broadened optical absorption in the Vis-NIR region. We have also investigated the optoelectronic and photocatalytic properties of the Cu2SnSe3-Au heteronanostructures and proposed a mechanism to illustrate the improved photocurrent and photocatalytic performance as compared to bare Cu2SnSe3. Electronic supplementary information (ESI) available: Experimental details including materials, sample preparation, characterization, size-distribution histogram, XRD, TEM, EDX, ATR-FTIR, ICP-AES, the influence of different Au loading values on the optical and optoelectronic properties of CTSe-Au heteronanostructures, estimation of the Cu2SnSe3 band edges and photocatalytic measurements. See DOI: 10.1039/c5nr04468e

  4. 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.

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

    PubMed

    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. PMID:27221241

  6. 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.

  7. 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.

  8. Intensification of electrochemiluminescence of luminol on TiO2 supported Au atomic cluster nano-hybrid modified electrode.

    PubMed

    Yu, Zhimin; Wei, Xiuhua; Yan, Jilin; Tu, Yifeng

    2012-04-21

    With TiO(2) nanoparticles as carrier, a supported nano-material of Au atomic cluster/TiO(2) nano-hybrid was synthesized. It was then modified onto the surface of indium tin oxide (ITO) by Nafion to act as a working electrode for exciting the electrochemiluminescence (ECL) of luminol. The properties of the nano-hybrid and the modified electrode were characterized by XRD, XPS, electronic microscopy, electrochemistry and spectroscopy. The experimental results demonstrated that the modification of this nano-hybrid onto the ITO electrode efficiently intensified the ECL of luminol. It was also revealed that the ECL intensity of luminol on this modified electrode showed very sensitive responses to oxygen and hydrogen peroxide. The detection limits for dissolved oxygen and hydrogen peroxide were 2 μg L(-1) and 5.5 × 10(-12) M, respectively. Besides the discussion of the intensifying mechanism of this nano-hybrid for ECL of luminol, the developed method was also applied for monitoring dissolved oxygen and evaluating the scavenging efficiency of reactive oxygen species of the Ganoderma lucidum spore. PMID:22382937

  9. 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.

  10. 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

  11. Plasmonic photocatalysis properties of Au nanoparticles precipitated anatase/rutile mixed TiO2 nanotubes

    NASA Astrophysics Data System (ADS)

    Wen, Yan; Liu, Bitao; Zeng, Wei; Wang, Yuhua

    2013-09-01

    Anatase/rutile mixed titania nanotubes (TiO2 NTs) precipitated with gold nanoparticles (Au NPs), i.e. Au/TiO2, have been synthesized and investigated on visible photocatalysis properties. A deposition-precipitation (DP) method was adopted to reduce the gold precursor to Au NPs within the preformed TiO2 NTs by the emulsion electrospinning technique. The optimal visible photocatalytic activity was found in the sample Au3(DP350)/TiO2 with a loading of 3 wt% Au NPs and calcining at 350 °C. Through transmission electron microscopy, Au NPs of 4.16 nm diameter were observed at the interface between the anatase and rutile phases in the optimal Au3(DP350)/TiO2 sample, and these joint active sites at the interface were beneficial for charge separation. The obtained optimal photocatalytic efficiency of Au3(DP350)/TiO2 was ascribed to the synergistic effect of the enhanced visible absorption and the anatase/rutile mixed-phase composition, and the possible mechanism for this was discussed in detail.Anatase/rutile mixed titania nanotubes (TiO2 NTs) precipitated with gold nanoparticles (Au NPs), i.e. Au/TiO2, have been synthesized and investigated on visible photocatalysis properties. A deposition-precipitation (DP) method was adopted to reduce the gold precursor to Au NPs within the preformed TiO2 NTs by the emulsion electrospinning technique. The optimal visible photocatalytic activity was found in the sample Au3(DP350)/TiO2 with a loading of 3 wt% Au NPs and calcining at 350 °C. Through transmission electron microscopy, Au NPs of 4.16 nm diameter were observed at the interface between the anatase and rutile phases in the optimal Au3(DP350)/TiO2 sample, and these joint active sites at the interface were beneficial for charge separation. The obtained optimal photocatalytic efficiency of Au3(DP350)/TiO2 was ascribed to the synergistic effect of the enhanced visible absorption and the anatase/rutile mixed-phase composition, and the possible mechanism for this was discussed in

  12. 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. PMID:25157565

  13. Determining the properties of gas-phase clusters

    NASA Astrophysics Data System (ADS)

    Hopkins, W. Scott

    2015-11-01

    As our understanding of clusters has improved, we have found that rather than being models for surface and condensed phase phenomena, clusters often display chemical and physical properties that are quite distinct from those of their atomic constituents or associated bulk materials. Indeed, identifying and utilising the unique properties of dimensionally confined species is a major theme in nanotechnology. Consequently, numerous experimental and computational methods have been employed to investigate the structures and properties of cluster systems. In this article, the techniques of infrared multiple photon dissociation and differential mobility spectrometry are discussed using the examples of [Ag.B12F12]- and tetraalkylammonium/solvent ionic clusters, respectively.

  14. Effects of the proximity of Au nanoparticles on magnetic and transport properties of LSMO ultrathin layers

    SciTech Connect

    Brivio, S.; Magen Dominguez, Cesar; Sidorenko, A; Petti, D.; Cantoni, M.; Finazzi, M; Ciccacci, F; Renzi, R; Varela del Arco, Maria; Picozzi, S.; Bertacco, R.

    2010-01-01

    The effect of the proximity of Au nanoparticles on the transport and magnetic properties of ultrathin La2/3Sr1/3MnO3 (LSMO) films has been investigated. We find a huge increase of the resistivity of the manganite (by four orders of magnitude for a Au nominal thickness of 2 nm), which is accompanied by a strong decrease of the Curie temperature. A combined scanning transmission electron microscopy and electron energy loss spectroscopy (STEM-EELS) analysis shows that interfaces are coherent and atomically sharp, and that the structural quality is very high. On the other end, a strong reduction of the Mn oxidation state is seen upon Au capping. NMR data show a strong attenuation of the double exchange signal upon formation of Au nanoparticles. Ab-initio calculations indicate a negligible influence of Au on LSMO at an ideal interface, with the LSMO surface magnetic and electronic properties essentially unchanged upon creation of the Au/LSMO interface. In view of these calculations, the experimental results cannot be explained in terms of purely electrostatic effects induced by the proximity of a noble metal. Here we propose that the main driving force underlying the observed change in physical properties is the high reactivity of Au nanoparticles which can locally pump oxygen from the manganite, thus favouring a phase separation ensuing from O inhomogeneity which deteriorates the transport and electrical properties.

  15. 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).

  16. 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.

  17. 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.

  18. Growth and electronic properties of Ti nanoislands on Au(111)

    NASA Astrophysics Data System (ADS)

    Carrozzo, P.; Tumino, F.; Passoni, M.; Bottani, C. E.; Casari, C. S.; Li Bassi, A.

    2014-01-01

    The initial growth of titanium nanoislands on the reconstructed Au(111) surface was investigated by Scanning Tunneling Microscopy and Scanning Tunneling Spectroscopy (STM/STS). Ti atoms evaporated onto room temperature substrate start to nucleate preferentially at the elbows of the Au(111) herringbone reconstruction; however ordered nucleation is accompanied by an early occurrence of out-of-elbow islands. Titanium islands are irregularly shaped, composed of smaller sub-units as grains of about 1-2 nm2 and their growth leads to a distortion of the underlying gold surface. We observe a retarded coalescence of titanium first layer islands with respect to other similar systems. Comparing the experimental data with a diffusive model, quantitative information about the interlayer diffusion of the first two layers is obtained. STS spectra and differential conductivity maps show peculiar electronic features outlining an important interaction between Ti atoms and the Au(111) surface.

  19. PtCo/Au nanocomposite: Synthesis, characterization, and magnetic properties

    NASA Astrophysics Data System (ADS)

    Dai, Jingtao; Du, Yukou; Wang, Fangwei; Yang, Ping

    2007-09-01

    Magnetic PtCo/Au nanocomposites with narrow size distribution were synthesized in a reverse micelle, followed by a post-synthesis handling of the stabilizer-exchange technique. The PtCo/Au nanocomposites were characterized by ultraviolet visible spectroscopy, X-ray diffraction and transmission electron microscopy, respectively. Superconducting quantum interference device studies revealed that the nanocomposites were superparamagnetic above the blocking temperature ( TB=69 K), while the samples were ferromagnetic with Hc (628 Oe) and Ms (2.97 emu /g) at 5 K.

  20. 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.

  1. HRTEM and STEM-HAADF characterisation of Au-TiO2 and Au-Al2O3 catalysts for a better understanding of the parameters influencing their properties in CO oxidation.

    PubMed

    Delannoy, Laurent; Chantry, Ruth L; Casale, Sandra; Li, Z Y; Borensztein, Yves; Louis, Catherine

    2013-03-14

    Gold catalysts supported on titania (Au-TiO(2)) and alumina (Au-Al(2)O(3)) were prepared by deposition-precipitation with urea and then activated before characterisation and reaction in CO oxidation, either by calcination in air at 500 °C or reduction under H(2) at 300 °C. Gold nanoparticles with average size in the range 2-4 nm were obtained, with calcination leading to larger gold nanoparticles than reduction. For Au-TiO(2), high activity was observed in CO oxidation at room temperature, independent of the activation treatment. This high activity could not be correlated to the presence of sub-nanometer gold clusters as reported in the literature, since they could not be detected by atomic-resolution high-angle annular dark-field scanning-transmission electron microscopy (HAADF-STEM). In the case of Au-Al(2)O(3), the performance in CO oxidation was found to strongly depend on the water content in the reaction gas feed and on the activation conditions, with calcination resulting in a poorly active catalyst whereas reduction gave activity of the same order as Au-TiO(2). A comparative study of Au-TiO(2) and Au-Al(2)O(3) by electron microscopy did not reveal distinct differences in the shapes of the Au nanoparticles, which are mostly flattened through interaction with the substrate in both samples, with side profile shapes varying from rounded hemispherical to well faceted truncated cubo-octahedra. More faceting is found for the samples calcined at 500 °C than reduced at 300 °C. Various possible parameters affecting the catalytic properties of gold in CO oxidation are discussed in the context of the relevant literature. PMID:23361459

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

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

    PubMed

    Sirijaraensre, J; Limtrakul, J

    2015-04-21

    Decorating graphene with nano-clusters offers potential for a wide range of industrial applications. For catalysis, embedding precisely controlled mono- and bimetallic nanoclusters into graphene can greatly increase their catalytic activities, especially for oxidation reactions. The catalytic performance of a gold nanocluster can be modified dramatically by changing its electronic properties. The results of this work demonstrate by means of DFT calculations that by strategic doping and promotion from the support material the catalytic activity improvement of a gold-based catalyst for the partial oxidation reaction of methane can be drastically enhanced. The transition metal-mediated catalysis is significantly affected by the two spin-state reactivities over them. The investigated catalytic processes consist of N2O decomposition and methane hydroxylation over three subnanoclusters (Au5, Au4Pd, and Au4Pt) deposited on a single vacancy graphene support. It was found that graphene acts not only as a support but also supports the catalysis through charge transfer between the subnanocluster and graphene. Graphene-supported Au4Pd exhibits enhanced catalytic activity for both steps of methane-to-methanol conversion, whereas the supported Au5 is good for N2O decomposition but ineffective for methane hydroxylation, mainly due to the involvement of a very stable intermediate (methyl-hydroxo-grafted nanocluster). The activation energies for N2O decomposition, C-H bond activation and methanol formation over the supported Au4Pd cluster are 13.8, 15.7, and 24.9 kcal mol(-1), respectively. Without the graphene support, the catalytic trend is reversed and Au4Pd becomes an inert cluster for these reactions. PMID:25772613

  4. 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.

  5. Some properties of ion and cluster plasma

    SciTech Connect

    Gudzenko, L.I.; Derzhiev, V.I.; Yakovlenko, S.I.

    1982-11-01

    The aggregate of problems connected with the physics of ion and cluster plasma is qualitatively considered. Such a plasma can exist when a dense gas is ionized by a hard ionizer. The conditions for the formation of an ion plasma and the difference between its characteristics and those of an ordinary electron plasma are discussed; a solvated-ion model and the distribution of the clusters with respect to the number of solvated molecules are considered. The recombination rate of the positively and negatively charged clusters is roughly estimated. The parameters of a ball-lightning plasma are estimated on the basis of the cluster model.

  6. Phospholipid Encapsulated AuNR@Ag/Au Nanosphere SERS Tags with Environmental Stimulus Responsive Signal Property.

    PubMed

    Su, Xueming; Wang, Yunqing; Wang, Wenhai; Sun, Kaoxiang; Chen, Lingxin

    2016-04-27

    Surface-enhanced Raman scattering (SERS) tags draw much attention due to the ultrasensitivity and multiplex labeling capability. Recently, a new kind of SERS tags was rationally designed by encapsulating metal nanoparticles with phospholipid bilayers, showing great potential in theranostics. The lipid bilayer coating confers biocompatibility and versatility to changing surface chemistry of the tag; however, its "soft" feature may influence SERS signal stability, which is rarely investigated. Herein, we prepared phospholipid-coated AuNR@Ag/Au nanosphere SERS tags by using three different kinds of Raman reporters, i.e., thio-containing 4-nitrothiophenol (NT), nitrogen-containing hydrophobic chromophore cyanine 7 monoacid (Cy7), and alkyl chain-chromophore conjugate 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine (DiD). It was found that signal responses were different upon additional stimulation which the tags may encounter in theranostic applications including the presence of detergent Triton X-100, lipid membrane, and photothermal treatment. Living-cell imaging also showed signal changing distinction. The different SERS signal performances were attributed to the different Raman reporter releasing behaviors from the tags. This work revealed that Raman reporter structure determined signal stability of lipid-coated SERS tags, providing guidance for the design of stimulus responsive tags. Moreover, it also implied the potential of SERS technique for real time drug release study of lipid based nanomedicine. PMID:27052206

  7. A theoretical study of O2 activation by the Au7-cluster on Mg(OH)2: roles of surface hydroxyls and hydroxyl defects.

    PubMed

    Jia, Chuanyi; Fan, Weiliu

    2015-11-11

    Using density functional theory (DFT) calculations, we investigated O2 activation by the Au7-cluster supported on the perfect and hydroxyl defective Mg(OH)2(0001) surface. It is revealed that hydroxyl groups on the perfect Mg(OH)2(0001) surface can not only enhance the stability of the Au7-cluster, but also help the adsorption of the O2 molecule through hydrogen-bonding interactions with the 2nd-layered interfacial Au sites. Density of states (DOS) analysis shows that the d-band centers of the 2nd-layered interfacial Au atoms are very close to the Fermi level, which thereby reduce the Pauli repulsion and promote the O2 adsorption. These two responses make the 2nd-layered interfacial Au atoms favor O2 activation. Interestingly, the surface hydrogen atoms activated by the 1st-layered Au atoms can facilitate the O2 dissociation process as well. Such a process is dynamically favorable and more inclined to occur at low temperatures compared to the direct dissociation process. Meanwhile, the hydroxyl defects of Mg(OH)2(0001) located right under the Au7-cluster can also up-shift the d-band centers of the surrounding Au atoms toward the Fermi level, enhancing its catalytic activity for O2 dissociation. In contrast, the d-band center of Au atoms surrounding the hydroxyl defect near the Au7-cluster exhibits an effective down-shift to lower energies, and therefore holds low activity. These results unveiled the roles of surface hydroxyls and hydroxyl defects on the Au/Mg(OH)2 catalyst in O2 activation and could provide a theoretical guidance for chemists to efficiently synthesize Au/hydroxide catalysts. PMID:26529519

  8. 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

  9. Plasmonic photocatalysis properties of Au nanoparticles precipitated anatase/rutile mixed TiO2 nanotubes.

    PubMed

    Wen, Yan; Liu, Bitao; Zeng, Wei; Wang, Yuhua

    2013-10-21

    Anatase/rutile mixed titania nanotubes (TiO2 NTs) precipitated with gold nanoparticles (Au NPs), i.e. Au/TiO2, have been synthesized and investigated on visible photocatalysis properties. A deposition-precipitation (DP) method was adopted to reduce the gold precursor to Au NPs within the preformed TiO2 NTs by the emulsion electrospinning technique. The optimal visible photocatalytic activity was found in the sample Au3(DP350)/TiO2 with a loading of 3 wt% Au NPs and calcining at 350 °C. Through transmission electron microscopy, Au NPs of 4.16 nm diameter were observed at the interface between the anatase and rutile phases in the optimal Au3(DP350)/TiO2 sample, and these joint active sites at the interface were beneficial for charge separation. The obtained optimal photocatalytic efficiency of Au3(DP350)/TiO2 was ascribed to the synergistic effect of the enhanced visible absorption and the anatase/rutile mixed-phase composition, and the possible mechanism for this was discussed in detail. PMID:23963545

  10. Au@TiO2 double-shelled octahedral nanocages with improved catalytic properties.

    PubMed

    Lv, Xiaoming; Zhu, Yihua; Jiang, Hongliang; Zhong, Hua; Yang, Xiaoling; Li, Chunzhong

    2014-10-28

    A novel and facile strategy has been successfully developed to synthesize uniform gold@titanium dioxide octahedral nanocages (Au@TiO2), which have a well-defined double-shelled structure with Au as the internal shell and TiO2 as the external shell. The unique Au@TiO2 double-shelled octahedral nanocages were elaborately fabricated by a Cu2O-templated strategy combining with spatially confined galvanic replacement. The formation process of these delicate hierarchical octahedral architectures is discussed in detail. The catalytic performance of the Au@TiO2 double-shelled octahedral nanocages was investigated using the reduction of 4-nitrophenol as a model reaction. The mesoporous structure of both the Au and TiO2 shells provides direct access for the reactant molecules to diffuse and subsequently interact with the Au shell. This novel catalyst shows excellent and stable activity for the catalytic reduction of 4-nitrophenol, which can be recycled for ten successive cycles of the reaction with a conversion efficiency of more than 90%. The superior catalytic activity attributes to mesoporous double shells, enhanced synergistic effects between the Au and TiO2 shells and the unique properties of the octahedral structure. More importantly, the as-obtained Au@TiO2 double-shelled octahedral nanocages also show potential applications in solar cells, organocatalysis and water splitting. PMID:25166883

  11. 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.

  12. Kinetic Properties of Magnetic Decreases Observed in the Solar Wind at ~ 1 au

    NASA Astrophysics Data System (ADS)

    Lee, Ensang; Parks, George K.

    2016-04-01

    In this study, we investigate the kinetic properties of magnetic decreases observed in the solar wind at ˜1 AU using the Cluster observations. We study two different magnetic decreases: one with a short observation duration of ˜2.5 minutes and stable structure and the other with a longer observation duration of ˜40 minutes and some fluctuations and substructures. Despite the contrast in durations and magnetic structures, the velocity space distributions of ions are similar in both events. The velocity space distribution becomes more anisotropic along the direction parallel to the magnetic field, which differs from observations obtained at high heliographic latitudes. On the other hand, electrons show different features from the ions. The core component of the electrons shows similar anisotropy to the ions, though the anisotropy is much weaker. However, while ions are heated in the magnetic decreases, the core electrons are slightly cooled, especially in the perpendicular direction. The halo component does not change much in the magnetic decreases from the ambient solar wind. The strahl component is observed only in one of the magnetic decreases. The results imply that the ions and electrons in the magnetic decreases can behave differently, which should be considered for the formation mechanism of the magnetic decreases.}

  13. 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.

  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. Magnetic and thermodynamic properties of GdCu4Au

    NASA Astrophysics Data System (ADS)

    Bashir, Aiman K.; Tchoula Tchokonté, Moise B.; Britz, Douglas; Sondezi, B. M.; Strydom, André M.

    2015-03-01

    The results of magnetic susceptibility, χ(T), magnetization, σ(μ0H), and specific heat, CP(T), for GdCu4Au are presented. The room temperature powder X-ray diffraction studies indicate a cubic MgCu4Sn - type crystal structure with space group Fbar 43m (No.216). The low field dc χ(T) data shows an antiferromagnetic - like (AFM) anomaly associated with a Néel temperature TN = 10.8 K for GdCu4Au. In the paramagnetic region above TN, χ(T) data follows the Curies - Weiss law with an effective magnetic moment μeff = 7.444(1) μB and paramagnetic Weiss temperature θP = -15.01(2) K. The experimental value of is close to the calculated value of 7.94 μB expected for the free Gd3+-ion. The field-cooled (FC) and zero-field-cooled (ZFC) χ(T) data provide evidence for the formation of spin-glass state with a freezing temperature Tf = 15 K. σ(μ0H) measured in the ordering region (below TN) shows that GdCu4Au undergoes metamagnetic transition above 0.7 T, characterized by a slight upward curvature above this field. Measurement of σ(μ0H) in the paramagnetic regions show a linear behaviour up to 0.7 T and a downward curvature at high fields. CP(T) data shows an AFM - like phase transition at TN = 10.4 K close to the phase transition observed in χ(T) results. The 4f-electron entropy reaches the value of Rln2 close to TN at 9.02 K and reaches the value of Rln(2J + 1) at T = 180 K.

  16. Adsorption Structures and Electronic Properties of 1,4-Phenylene Diisocyanide on the Au(111) Surface

    SciTech Connect

    White, M.G.; Zhou, J.; Acharya, D.; Camillone III, N.; Sutter, P.

    2011-01-10

    The adsorption structures and electronic properties of 1,4-phenylene diisocyanide (PDI) on a Au(111) surface have been studied using temperature programmed desorption (TPD), two-photon photoemission (2PPE), and scanning tunneling microscopy (STM). As deposited at 95 K, PDI molecules form disordered islands and short one-dimensional chains on Au(111) terraces. The work function decreases with increasing PDI coverage, and an occupied electronic state appears at 0.88 eV below the Fermi level. Annealing to 300 K causes the PDI molecules to reorganize on the surface and form ordered, one-dimensional molecular chains that extend for many tens of nanometers across the Au(111) terraces. The repeating structure of the molecular chains is consistent with a recently proposed [-Au-PDI-]{sub n} structure in which PDI molecules lie parallel to the surface and are interconnected by Au adatoms released from the Au(111) surface. The formation of the molecular chains is accompanied by a large drop in the work function which we attribute to an increase in the number and magnitude of interfacial dipoles. The electronic structure of the molecular chains is also characterized by occupied and unoccupied states at -0.88 eV below and +3.32 eV above the Fermi level, respectively. The latter are most prominent after annealing a PDI/Au(111) surface to 300 K, indicating that they are associated with interfacial states of the one-dimensional molecular chains.

  17. 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. PMID:25456348

  18. 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.

  19. 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...

  20. 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

    2015-01-01

    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

  1. 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.

  2. 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

  3. 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.

  4. Sensitivity of Structural and Electronic Properties of Gold-Thiolate Nanoclusters to the Atomic Composition: A Comparative X-ray Study of Au19(SR)13 and Au25(SR)18

    SciTech Connect

    Chevrier, Daniel M; MacDonald, Mark A; Chatt, Amares; Zhang, Peng; Wu, Zhikun; Jin, Rongchao

    2013-03-04

    With the recent successful synthesis of an increasing number of atomically precise thiolate–gold nanoclusters (NCs), there are growing demands for a better understanding of their atomic structures and structure–property relationships in response to composition change. Herein, we present X-ray experimental results on structural and electronic properties of a recently synthesized gold–thiolate nanocluster, Au19(SR)13, in comparison with the structurally well-known Au25(SR)18 reference. The atomic structure of Au19(SR)13 was first probed with extended X-ray absorption fine structure (EXAFS). A multishell EXAFS fitting method (consisting of one Au–S and three Au–Au shells) allowed for a detailed structural comparison of the two nanoclusters, which revealed a sizable increase of the bond distances between the surface–surface and surface–staple Au atoms upon the decrease of Au atoms in the nanocluster. X-ray photoemission experiments and ab initio calculations further demonstrated the sensitive change of electronic properties of the nanoclusters when the cluster composition was varied, that is, the Au19(SR)13 nanocluster has a differently shaped and positively shifted Au 5d band relative to Au25(SR)18. These experimental findings highlight the sensitivity of the local structure and electronic properties of thiolate-gold nanoclusters to even a small change of the metal core from Au13 to Au11.

  5. Computational design of peptide-Au cluster probe for sensitive detection of αIIbβ3 integrin.

    PubMed

    Zhao, Lina; Zhai, Jiao; Zhang, Xuejie; Gao, Xueyun; Fang, Xiaohong; Li, Jingyuan

    2016-02-11

    We have designed a novel peptide-Au cluster probe to specifically bind to αIIbβ3 integrin. As indicated by molecular dynamics (MD) simulations, the binding mode of the native ligand of αIIbβ3 integrin, γC peptide, can be realized by the designed probe. More importantly, the peptide-Au probe can provide multiple coating peptides to form additional salt bridges with protein, and the binding stability of the probe is comparable to the native ligand. The designed probe was then successfully synthesized. The specific binding in a cellular environment was validated by colocalization analysis of confocal microscopy. In addition, the binding affinity was confirmed by atomic force microscopy (AFM) based single molecule force spectroscopy. Our results suggest the combination of computational design and experimental verification can be a useful strategy for the development of nanoprobes. PMID:26831577

  6. Au25 Clusters as Electron-Transfer Catalysts Induced the Intramolecular Cascade Reaction of 2-nitrobenzonitrile

    PubMed Central

    Chong, Hanbao; Li, Peng; Wang, Shuxin; Fu, Fangyu; Xiang, Ji; Zhu, Manzhou; Li, Yadong

    2013-01-01

    Design of atomically precise metal nanocluster catalysts is of great importance in understanding the essence of the catalytic reactions at the atomic level. Here, for the first time, Au25z nanoslusters were employed as electron transfer catalysts to induce an intramolecular cascade reaction at ambient conditions and gave rise to high conversion (87%) and selectivity (96%). Electron spin-resonance spectra indeed confirmed the consecutive electron transfer process and the formation of N radical. UV-vis absorption spectra also verified Au25z was intact after the catalytic circle. Our research may open up wide opportunities for extensive organic reactions catalyzed by Au25z. PMID:24225495

  7. Nanostructured, mesoporous Au/TiO2 model catalysts – structure, stability and catalytic properties

    PubMed Central

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

    2011-01-01

    Summary Aiming at model systems with close-to-realistic transport properties, we have prepared and studied planar Au/TiO2 thin-film model catalysts consisting of a thin mesoporous TiO2 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 TiO2 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), N2 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/TiO2 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/TiO2 film catalyst are negligible, i.e., below the detection limit. PMID:22003465

  8. Factors affecting the optical properties of Pd-free Au-Pt-based dental alloys.

    PubMed

    Shiraishi, Takanobu; Takuma, Yasuko; Miura, Eri; Tanaka, Yasuhiro; Hisatsune, Kunihiro

    2003-12-01

    The optical properties of experimental Au-Pt-based alloys containing a small amount of In, Sn, and Zn were investigated by spectrophotometric colorimetry to extract factors affecting color of Au-Pt-based high-karat dental alloys. It was found that the optical properties of Au-Pt-based alloys are strongly affected by the number of valence electrons per atom in an alloy, namely, the electron:atom ratio, e/a. That is, by increasing the e/a-value, activities of reflection in the long-wavelength range and absorption in the short-wavelength range in the visible spectrum apparently increased. As a result, the maximum slope of the spectral reflectance curve at the absorption edge, which is located near 515 nm (approximately 2.4 eV), apparently increased with e/a-value. Due to this effect, the b*-coordinate (yellow-blue) in the CIELAB color space considerably increased and the a*-coordinate (red-green) slightly increased with e/a-value. The addition of a third element with a higher number of valence electrons to the binary Au-Pt alloy is, therefore, effective in giving a gold tinge to the parent Au-Pt alloy. This information may be useful in controlling the color of Au-Pt-based dental alloys. PMID:15348493

  9. 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.

  10. Properties of He clustering in α-Fe grain boundaries

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Fu, Chu-Chun; Hayward, Erin; Lu, Guang-Hong

    2015-04-01

    Classical molecular dynamics and density functional theory calculations are performed to study the impact of two distinct Fe grain boundaries (GBs) on the clustering properties of helium (He) and the possible He effect on GB decohesion. Several He concentrations are considered. Common properties of He clustering are found for the both GBs, which are visibly different from the bcc bulk. In particular, He clusters in the GBs are always elongated in the directions parallel to the interface and contracted in the direction normal to the GB plane, while they are isotropic in the bcc bulk. When the He number in the clusters is sufficiently large, the strong local pressure promotes the occurrence of loop punching, which is easier to trigger in the GBs than in the bulk, resulting in a lower He-to-vacancy ratio in the GB clusters. The emitted self-interstitial atoms (SIAs) can more easily dissociate from the clusters in the GBs than in the bulk, leading to relatively lower local pressures around the clusters in the GBs, and facilitating the clusters growth. He is found to decrease GB cohesion, and the embrittling effect of He increases with its concentration. But interestingly, this effect decreases with He clustering. The present findings are fully compatible with existing experimental evidence, for instance, for a stronger GB embrittlement due to He at rather low temperatures than at higher temperatures.

  11. Computational design of peptide-Au cluster probe for sensitive detection of αIIbβ3 integrin

    NASA Astrophysics Data System (ADS)

    Zhao, Lina; Zhai, Jiao; Zhang, Xuejie; Gao, Xueyun; Fang, Xiaohong; Li, Jingyuan

    2016-02-01

    We have designed a novel peptide-Au cluster probe to specifically bind to αIIbβ3 integrin. As indicated by molecular dynamics (MD) simulations, the binding mode of the native ligand of αIIbβ3 integrin, γC peptide, can be realized by the designed probe. More importantly, the peptide-Au probe can provide multiple coating peptides to form additional salt bridges with protein, and the binding stability of the probe is comparable to the native ligand. The designed probe was then successfully synthesized. The specific binding in a cellular environment was validated by colocalization analysis of confocal microscopy. In addition, the binding affinity was confirmed by atomic force microscopy (AFM) based single molecule force spectroscopy. Our results suggest the combination of computational design and experimental verification can be a useful strategy for the development of nanoprobes.We have designed a novel peptide-Au cluster probe to specifically bind to αIIbβ3 integrin. As indicated by molecular dynamics (MD) simulations, the binding mode of the native ligand of αIIbβ3 integrin, γC peptide, can be realized by the designed probe. More importantly, the peptide-Au probe can provide multiple coating peptides to form additional salt bridges with protein, and the binding stability of the probe is comparable to the native ligand. The designed probe was then successfully synthesized. The specific binding in a cellular environment was validated by colocalization analysis of confocal microscopy. In addition, the binding affinity was confirmed by atomic force microscopy (AFM) based single molecule force spectroscopy. Our results suggest the combination of computational design and experimental verification can be a useful strategy for the development of nanoprobes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr09175f

  12. DFT study on size-dependent geometries, stabilities, and electronic properties of AunM2 (M = Si, P; n = 1-8) clusters1

    NASA Astrophysics Data System (ADS)

    Li, Y.; Cao, Y. P.; Li, Y. F.; Shi, S. P.; Kuang, X. Y.

    2012-01-01

    The ab initio method based on density functional theory at the PW91PW91 level has been employed to systematically study the structures, stabilities, electronic, and magnetic properties of gold clusters with or without silicon/phosphorus doping. The optimized geometries show that the most stable isomers for Au n Si2 and Au n P2 ( n = 1-8) clusters prefer a three-dimensional structure when n = 2 and n = 3 upwards, respectively, and they can be viewed as grown from the already observed Au n-1M2 (M = Si, P). The relative stabilities of calculated Au n M2 (M = Si, P) clusters have been analyzed through the atomic average binding energy, fragmentation energy, second-order difference of energy, and HOMO-LUMO gap. A pronounced odd-even alternative phenomenon indicates that the clusters with even-numbered valence electrons possess a higher stability than their neighboring ones. For both systems, natural population analysis reveals that electronic properties of dopant atoms in the corresponding configuration are mainly related to s and p states. We also investigated magnetic effects of clusters as a function of cluster size, however, their oscillatory magnetic moments were found to vary inversely to the fragmentation energy, second-order difference of energy, and HOMO-LUMO gap.

  13. 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.

  14. 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.

  15. 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).

  16. Tailoring the Electronic and Catalytic Properties of Au25 Nanoclusters via Ligand Engineering.

    PubMed

    Li, Gao; Abroshan, Hadi; Liu, Chong; Zhuo, Shuo; Li, Zhimin; Xie, Yan; Kim, Hyung J; Rosi, Nathaniel L; Jin, Rongchao

    2016-08-23

    To explore the electronic and catalytic properties of nanoclusters, here we report an aromatic-thiolate-protected gold nanocluster, [Au25(SNap)18](-) [TOA](+), where SNap = 1-naphthalenethiolate and TOA = tetraoctylammonium. It exhibits distinct differences in electronic and catalytic properties in comparison with the previously reported [Au25(SCH2CH2Ph)18](-), albeit their skeletons (i.e., Au25S18 framework) are similar. A red shift by ∼10 nm in the HOMO-LUMO electronic absorption peak wavelength is observed for the aromatic-thiolate-protected nanocluster, which is attributed to its dilated Au13 kernel. The unsupported [Au25(SNap)18](-) nanoclusters show high thermal and antioxidation stabilities (e.g., at 80 °C in the present of O2, excess H2O2, or TBHP) due to the effects of aromatic ligands on stabilization of the nanocluster's frontier orbitals (HOMO and LUMO). Furthermore, the catalytic activity of the supported Au25(SR)18/CeO2 (R = Nap, Ph, CH2CH2Ph, and n-C6H13) is examined in the Ullmann heterocoupling reaction between 4-methyl-iodobenzene and 4-nitro-iodobenzene. Results show that the activity and selectivity of the catalysts are largely influenced by the chemical nature of the protecting thiolate ligands. This study highlights that the aromatic ligands not only lead to a higher conversion in catalytic reaction but also markedly increase the yield of the heterocoupling product (4-methyl-4'-nitro-1,1'-biphenyl). Through a combined approach of experiment and theory, this study sheds light on the structure-activity relationships of the Au25 nanoclusters and also offers guidelines for tailoring nanocluster properties by ligand engineering for specific applications. PMID:27442235

  17. Strain-dependent electronic and magnetic properties of Au-doped WS2 monolayer

    NASA Astrophysics Data System (ADS)

    Chen, Peng; Zhao, Xu; Wang, Tianxing; Dai, Xianqi; Xia, Congxin

    2016-03-01

    Using first-principles calculations, we investigated electronic and magnetic properties of Au-doped WS2 monolayer with strain from -10% to 10%. The results show that the band gap gradually decreases with increasing isotropic strain including compressive and tensile strain. Moreover, the tensile strain appears to be more effective in reducing the band gap of Au-doped WS2 monolayer than the compressive strain. The magnetic moment under tensile strain is enhanced from 0.813 to 1.167μB. But when the compressive strain is beyond -5%, the net magnetic moment is greatly enhanced, the maximum magnetic moment comes to 3.736 μB at -9% strain, nearly five times of the original moment 0.813 μB. The compressive strain is more effective on the magnetic moment in Au-doped WS2 monolayer than the tensile strain. Strain changes the redistribution of charges, and the hybridization of between the d orbital of Au atom, d orbital of W atom and p orbital of S atom, induces to magnetic moment. Moreover, the formation energy is lower under S-rich conditions, which indicates that it is energy favorable and relatively easier to incorporate Au atom into WS2 monolayer under S-rich experimental conditions. Our calculation show that the strain-induced Au-doped WS2 monolayer can be a two dimension Diluted magnetic semiconductor (DMS) at -9% strain.

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

    NASA Astrophysics Data System (ADS)

    Cui-Ju, FENG; Bin-Zhou, MI

    2016-05-01

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

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

    PubMed Central

    Penza, Michele; Alvisi, Marco; Di Franco, Cinzia; Palmisano, Francesco; Torsi, Luisa

    2016-01-01

    Summary 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. PMID:26925349

  20. 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).

  1. Polymorphic copper iodide clusters: insights into the mechanochromic luminescence properties.

    PubMed

    Benito, Quentin; Le Goff, Xavier F; Maron, Sébastien; Fargues, Alexandre; Garcia, Alain; Martineau, Charlotte; Taulelle, Francis; Kahlal, Samia; Gacoin, Thierry; Boilot, Jean-Pierre; Perruchas, Sandrine

    2014-08-13

    An in-depth study of mechanochromic and thermochromic luminescent copper iodide clusters exhibiting structural polymorphism is reported and gives new insights into the origin of the mechanochromic luminescence properties. The two different crystalline polymorphs exhibit distinct luminescence properties with one being green emissive and the other one being yellow emissive. Upon mechanical grinding, only one of the polymorphs exhibits great modification of its emission from green to yellow. Interestingly, the photophysical properties of the resulting partially amorphous crushed compound are closed to those of the other yellow polymorph. Comparative structural and optical analyses of the different phases including a solution of clusters permit us to establish a correlation between the Cu-Cu bond distances and the luminescence properties. In addition, the local structure of the [Cu4I4P4] cluster cores has been probed by (31)P and (65)Cu solid-state NMR analysis, which readily indicates that the grinding process modifies the phosphorus and copper atoms environments. The mechanochromic phenomenon is thus explained by the disruption of the crystal packing within intermolecular interactions inducing shortening of the Cu-Cu bond distances in the [Cu4I4] cluster core and eventually modification of the emissive state. These results definitely establish the role of cuprophilic interactions in the mechanochromism of copper iodide clusters. More generally, this study constitutes a step further into the understanding of the mechanism involved in the mechanochromic luminescent properties of metal-based compounds. PMID:25076411

  2. Properties of the Old Open Cluster Czernik 30

    NASA Astrophysics Data System (ADS)

    Hayes, Christian R.; Friel, Eileen D.; Slack, Taleah J.; Boberg, Owen M.

    2015-12-01

    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-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)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 Rgc ˜ 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.

  3. 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.

  4. Atomically resolved structure of ligand-protected Au9 clusters on TiO2 nanosheets using aberration-corrected STEM

    NASA Astrophysics Data System (ADS)

    Al Qahtani, Hassan S.; Kimoto, Koji; Bennett, Trystan; Alvino, Jason F.; Andersson, Gunther G.; Metha, Gregory F.; Golovko, Vladimir B.; Sasaki, Takayoshi; Nakayama, Tomonobu

    2016-03-01

    Triphenylphosphine ligand-protected Au9 clusters deposited onto titania nanosheets show three different atomic configurations as observed by scanning transmission electron microscopy. The configurations observed are a 3-dimensional structure, corresponding to the previously proposed Au9 core of the clusters, and two pseudo-2-dimensional (pseudo-2D) structures, newly found by this work. With the help of density functional theory (DFT) calculations, the observed pseudo-2D structures are attributed to the low energy, de-ligated structures formed through interaction with the substrate. The combination of scanning transmission electron microscopy with DFT calculations thus allows identifying whether or not the deposited Au9 clusters have been de-ligated in the deposition process.

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

    PubMed

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

    2014-06-01

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

  6. Tailoring the electrical properties of MoS2 field effect transistors by depositing Au nanoparticles and alkanethiol molecules

    NASA Astrophysics Data System (ADS)

    Cho, Kyungjune; Jeong, Hyunhak; Kim, Tae-Young; Pak, Jinsu; Kim, Jae-Keun; Choi, Barbara Yuri; Lee, Takhee

    2016-05-01

    We fabricated and characterized MoS2 field effect transistors. First, we measured the electrical properties of MoS2 field effect transistors (FETs) that were made with mechanically exfoliated MoS2 flakes. Then, we deposited Au nanoparticles on the MoS2 channel and measured the electrical properties. We observed whether the source-drain current increased or decreased after the Au particles were deposited. The deposited Au particles either formed an extra current path and increased the current or behaved as charge-withdrawing sites and decreased the current. Next, we deposited alkanethiol molecules on the Au particles to reduce the work function of the Au. Alkanethiol molecules are known to form a self-assembled monolayer on the Au surface, and the electric dipole moment of the molecules causes the work function of the Au to decrease. Au particles can capture electrons from the MoS2 channel due to their high work function. However, the decreased work function of the Au particles subjected to alkanethiol treatment could cause captured electrons to be released from the Au particles to MoS2. Therefore, the current increased after alkanethiol treatment. This study may provide useful methods to utilize surface treatments with particles and molecules to tailor the electrical properties of MoS2-based FETs.

  7. Tailoring the electrical properties of MoS2 field effect transistors by depositing Au nanoparticles and alkanethiol molecules.

    PubMed

    Cho, Kyungjune; Jeong, Hyunhak; Kim, Tae-Young; Pak, Jinsu; Kim, Jae-Keun; Choi, Barbara Yuri; Lee, Takhee

    2016-05-11

    We fabricated and characterized MoS2 field effect transistors. First, we measured the electrical properties of MoS2 field effect transistors (FETs) that were made with mechanically exfoliated MoS2 flakes. Then, we deposited Au nanoparticles on the MoS2 channel and measured the electrical properties. We observed whether the source-drain current increased or decreased after the Au particles were deposited. The deposited Au particles either formed an extra current path and increased the current or behaved as charge-withdrawing sites and decreased the current. Next, we deposited alkanethiol molecules on the Au particles to reduce the work function of the Au. Alkanethiol molecules are known to form a self-assembled monolayer on the Au surface, and the electric dipole moment of the molecules causes the work function of the Au to decrease. Au particles can capture electrons from the MoS2 channel due to their high work function. However, the decreased work function of the Au particles subjected to alkanethiol treatment could cause captured electrons to be released from the Au particles to MoS2. Therefore, the current increased after alkanethiol treatment. This study may provide useful methods to utilize surface treatments with particles and molecules to tailor the electrical properties of MoS2-based FETs. PMID:27057642

  8. 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.

  9. 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.

  10. Confinement, Ordering, and Optical Properties of Au Nanorods in Polymer Thin Films

    NASA Astrophysics Data System (ADS)

    Hore, Michael J. A.; Composto, Russell J.

    2010-03-01

    Gold nanorods (Au NRs) possess interesting optical properties in terms of absorbance and polarizaton of light that can be further manipulated by controlling their long range order in polymer thin films. We systematically investigate orientational correlations for low aspect ratio (L/D = 3.3) Au NRs functionalized with poly(ethylene glycol) (PEG) confined within a poly(methyl methacrylate) (PMMA) film as a function of nanorod volume fraction and PMMA molecular weight. The NR spacing decreases as φrod-0.5 whereas the local 2D orientational order parameter increases linearly with φrod, approaching a maximum value of 0.4 at high volume fractions of rods. We compare these results to Au NRs confined in a poly(ethylene oxide) (PEO) thin film as well as simulations of non-interacting rods.

  11. Developing an aqueous approach for synthesizing Au and M@Au (M = Pd, CuPt) hybrid nanostars with plasmonic properties.

    PubMed

    Du, Jingshan; Yu, Junjie; Xiong, Yalin; Lin, Zhuoqing; Zhang, Hui; Yang, Deren

    2015-01-14

    Anisotropic Au nanoparticles show unique localized surface plasmon resonance (LSPR) properties, which make them attractive in optical, sensing, and biomedical applications. In this contribution, we report a general and facile strategy towards aqueous synthesis of Au and M@Au (M = Pd, CuPt) hybrid nanostars by reducing HAuCl4 with ethanolamine in the presence of cetyltrimethylammonium bromide (CTAB). According to electron microscopic observations and spectral monitoring, we found that the layered epitaxial growth mode (i.e., the Frank-van der Merwe mechanism) contributes to the enlargement of the core, while the random attachment of Au nanoclusters onto the cores accounts for the formation of the branches. Both of them are indispensable to the formation of the nanostars. The LSPR properties of the Au nanoparticles have been well investigated with morphology control via the precursor amount and growth temperature. The Au nanostars showed improved surface-enhanced Raman spectroscopy (SERS) performance for rhodamine 6G due to their sharp edges and tips, which were therefore confirmed as good SERS substrates to detect trace amounts of molecules. PMID:25420730

  12. Optical properties of ZnSe doped with Ag and Au

    NASA Astrophysics Data System (ADS)

    Dean, P. J.; Fitzpatrick, B. J.; Bhargava, R. N.

    1982-08-01

    We present bound-exciton (BE) and donor-acceptor-pair (DAP) spectra of ZnSe grown by liquid-phase epitaxy and doped with the transition metals (TM) Ag and Au. Luminescence, luminescence excitation, and time decay spectra establish the assignments of the spectral features and show that Ag forms a medium deep acceptor, (EA)Ag=431+/-2 meV, consistent with the activation energy for thermal quenching of the DAP spectra. This thermal technique, together with the less precise spectral measurements available for the more-strongly-phonon-coupled Au acceptor indicate that (EA)Au~550 meV, appreciably less than the probable value for Cu, ~650 meV. Peculiarities in the BE properties within this TM sequence are discussed with reference to the influence of their d-state characteristics. Strong BE luminescence with no-phonon energy near 2.747 eV is attributed to a neutral AgZn-AgI associate, possibly a split interstitial. Reasons for its absence in ZnSe: Au are discussed. Isotope effects in this spectrum and that of the Li neutral acceptor BE are contrasted. The latter provides proof that LiZn is the persistent shallow Td site acceptor in ZnSe. Further associate BE luminescence is tentatively identified for ZnSe: Ag and ZnSe: Au.

  13. Ion-beam-assisted deposition of Au nanocluster/Nb 2O 5 thin films with nonlinear optical properties

    NASA Astrophysics Data System (ADS)

    Cotell, C. M.; Schiestel, S.; Carosella, C. A.; Flom, S.; Hubler, G. K.; Knies, D. L.

    1997-05-01

    Gold nanocluster thin films (˜ 200 nm thickness) consisting of metal clusters ˜ 5 nm in size embedded in a matrix of Nb 2O 5 were deposited by ion beam-assisted deposition (IBAD) by coevaporation of Au and Nb with O 2+ ion bombardment. The microstructure and optical characteristics of these films were examined as-deposited and after annealing at 600°C. Annealing crystallized the amorphous oxide matrix and ripened the nanoclusters. A strong linear absorption at the wavelength of the surface plasmon resonance for Au developed as a result of annealing. The linear optical behavior was modeled using Mie scattering theory. Good agreement was found between the nanocluster sizes predicted by the theory and the particle sizes observed experimentally using transmission electron microscopy (TEM). The nonlinear optical (NLO) properties of the nanocluster films were probed experimentally using degenerate four wave mixing and nonlinear transmission. The wavelength was near the peak of the surface plasmon resonance as measured by VIS/UV spectroscopy. Values of | χxxxx(3)| were 7.3 × 10 -8 and 3.0 × 10 -10 esu for annealed and unannealed samples, respe The dominant mechanism for the nonlinear response was change in dielectric constant due to the generation of a distribution of hot, photoexcited electrons.

  14. 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. PMID:15516109

  15. The comprehensive evaluation of the structural and functional properties of the gas- statically treated Au-CdZnTe-Au structures for X- and gamma-ray detectors

    NASA Astrophysics Data System (ADS)

    Nasieka, Iu.; Strelchuk, V.; Boyko, M.; Rybka, A.; Kutniy, V.; Nakonechnyj, D.

    2015-08-01

    The influence of the gas-static processing on the optical, structural and electrophysical properties of Au-CdZnTe-Au structures, used in X- and gamma-ray detectors, was investigated. The processing, which is described in detail in the experimental part, was done in a laboratory-scale setup "GAUS-4/2000-35" with the following process parameters: pressure=0.32±0.02 GPa, temperature ~170 °C, time=2 h. The influence of the mentioned processing on the photoluminescence, the Raman scattering, the electric resistance, the I-V characteristics and the spectrometric parameters of the Au-CdZnTe-Au structures was determined. The physical mechanisms, through which the gas-static processing induces changes in the structural and functional properties, were analyzed. It was observed that the gas-static processing (with the above-mentioned process parameters) of the Au-CdZnTe-Au structures leads to a significant increase of the electric resistance of the structures; it also leads to the increase of the intensity of the photoelectric absorption peak when the respective detector is registering X- and gamma-radiation with energy near 32.19 keV. The Raman and photoluminescence data indicates the formation of the surface oxides TeOx and the compensation of Cd vacancies by Au atoms. The assumption that, under the discussed processing, two different rival processes modify the Au-CdZnTe junction due to the influence of the increased temperature ~170 °C and pressure ~0.3 GPa, was suggested. The first process is the formation of TeO2 oxide (which increases the electric resistance) on the contact; the second process is the destruction of the surface films of the oxides and the absorbed gases. Most likely, the first process is dominant, which was evidenced by the Raman and photoluminescence measurements.

  16. The photometric properties of brightest cluster galaxies. I - Absolute magnitudes in 116 nearby Abell clusters

    NASA Technical Reports Server (NTRS)

    Hoessel, J. G.; Gunn, J. E.; Thuan, T. X.

    1980-01-01

    Two-color aperture photometry of the brightest galaxies in a complete sample of nearby Abell clusters is presented. The results are used to anchor the bright end of the Hubble diagram; essentially the entire formal error for this method is then due to the sample of distant clusters used. New determinations of the systematic trend of galaxy absolute magnitude with the cluster properties of richness and Bautz-Morgan type are derived. When these new results are combined with the Gunn and Oke (1975) data on high-redshift clusters, a formal value (without accounting for any evolution) of q sub 0 = -0.55 + or - 0.45 (1 standard deviations) is found.

  17. Au-Ag nanoalloy molecule-like clusters for enhanced quantum efficiency emission of Er³⁺ ions in silica.

    PubMed

    Cesca, Tiziana; Kalinic, Boris; Michieli, Niccolò; Maurizio, Chiara; Trapananti, Angela; Scian, Carlo; Battaglin, Giancarlo; Mazzoldi, Paolo; Mattei, Giovanni

    2015-11-14

    The occurrence of a very efficient non-resonant energy transfer process forming ultrasmall Au-Ag nanoalloy clusters and Er(3+) ions is investigated in silica. The enhancement of the room temperature Er(3+) emission efficiency by an order of magnitude is achieved by coupling rare-earth ions to molecule-like (Au(x)Ag(1-x))N alloy nanoclusters with N = 10-15 atoms and x = 0.6 obtained by optimized sequential ion implantation on Er-implanted silica. For comparison, AuN nanoclusters obtained by the same approach and with the same size and numerical density showed an enhancement by only a factor of 2 with respect to pure Er emission, demonstrating the beneficial effect of using nanoalloyed clusters. The temperature evolution of the energy transfer process is investigated by photoluminescence and exhibits a maximum efficiency at about 600 °C, where the clusters reach the optimal size and the silica matrix completely recovers the implantation damage. The nanoalloy cluster composition and size have been studied by EXAFS analysis, which indicated a stronger Ag-O interaction with respect to the Au-O one and a preferential location of the Ag atoms at the nanoalloy cluster surface. PMID:25921085

  18. 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.

  19. 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.

  20. Noble metals (Ag, Au) nanoparticles addition effects on superconducting properties of CuTl-1223 phase

    NASA Astrophysics Data System (ADS)

    Jabbar, Abdul; Mumtaz, Muhammad; Nadeem, Kashif

    2015-03-01

    Low anisotropic (Cu0.5Tl0.5) Ba2Ca2Cu3O10 - δ (CuTl-1223) high temperature superconducting phase was synthesized by solid-state reaction, silver (Ag) nanoparticles were prepared by sol-gel method and gold (Au) nanoparticles were extracted from colloidal solution. We added Ag and Au nanoparticles in CuTl-1223 matrix separately with same concentration during the final sintering process to get (M)x/CuTl-1223; M = Ag nanoparticles or Au nanoparticles (x = 0 and 1.0 wt.%) nano-superconductor composites. We investigated and compared the effects of these noble metals nanoparticles addition on structural, morphological and superconducting transport properties of CuTl-1223 phase. The crystal structure of the host CuTl-1223 superconducting phase was not affected significantly after the addition of these nanoparticles. The enhancement of superconducting properties was observed after the addition of both Ag and Au nanoparticles, which is most probably due to improved inter-grains weak-links and reduction of defects such as oxygen deficiencies, etc. The reduction of normal state room temperature resistivity is the finger prints of the reduction of barriers and facilitation to the carriers transport across the inter-crystallite sites due to improved inter-grains weak-links. The greater improvement of superconducting properties in Ag nanoparticles added samples is attributed to the higher conductivity of silver as compared to gold, which also suits for practical applications due to lower cost and easy synthesis of Ag nanoparticles as compared to Au nanoparticles.

  1. Scaling properties of light-cluster production

    NASA Astrophysics Data System (ADS)

    Chajecki, Zbigniew; Youngs, Michael; Coupland, Daniel D.; Lynch, William; Tsang, Betty; Chbihi, Abdelouahad; Danielewicz, Pawel; Desouza, Romualdo; Famiano, Michael; Ghosh, Tilak; Giacherio, B.; Henzl, Vlad; Henzlova, Daniela; Hudan, Sylvie; Kilburn, Micha; Lee, Jenny; Lu, Fei; Rogers, Andrew; Russotto, Paulo; Verde, Giuseppe; Sanetullaev, Alisher; Showalter, Rachel; Sobotka, Lee; Wallace, Mark; Winkelbauer, Jack

    2014-09-01

    We show, using the experimental data from Ca+Ca and Sn+Sn collisions, that ratios of light-particle energy spectra display scaling properties that can be accurately described by effective local chemical potentials. This demonstrates the equivalence of t/3He and n/p spectral ratios and provides an essential test of theoretical predictions of isotopically resolved light-particle spectra. In addition, this approach allows direct comparisons of many theoretical n/p spectral ratios to experiments where charged-particle spectra but not neutron spectra are accurately measured. Such experiments may provide much more quantitative constraints on the density and momentum dependence of the symmetry energy.

  2. EuAu3Al2: Crystal and Electronic Structures and Spectroscopic, Magnetic, and Magnetocaloric Properties.

    PubMed

    Schmiegel, Jan-Patrick; Block, Theresa; Gerke, Birgit; Fickenscher, Thomas; Touzani, Rachid St; Fokwa, Boniface P T; Janka, Oliver

    2016-09-01

    The intermetallic compound EuAu3Al2 has been prepared by reaction of the elements in tantalum ampules. The structure was refined from single-crystal data, indicating that the title compound crystallizes in the orthorhombic crystal system (a = 1310.36(4), b = 547.87(1), c = 681.26(2) pm) with space group Pnma (wR2 = 0.0266, 1038 F(2) values, 35 parameters) and is isostructural to SrAu3Al2 (LT-SrZn5 type). Full ordering of the gold and aluminum atoms was observed. Theoretical calculations confirm that the title compound can be described as a polar intermetallic phase containing a polyanionic [Au3Al2](δ-) network featuring interconnected strands of edge-sharing [AlAu4] tetrahedra. Magnetic measurements and (151)Eu Mössbauer spectroscopic investigations confirmed the divalent character of the europium atoms. Ferromagnetic ordering below TC = 16.5(1) K was observed. Heat capacity measurements showed a λ-type anomaly at T = 15.7(1) K, in line with the ordering temperature from the susceptibility measurements. The magnetocaloric properties of EuAu3Al2 were determined, and a magnetic entropy of ΔSM = -4.8 J kg(-1) K(-1) for a field change of 0 to 50 kOe was determined. Band structure calculations found that the f-bands of Eu present at the Fermi level of non-spin-polarized calculations are responsible for the ferromagnetic ordering in this phase, whereas COHP chemical bonding coupled with Bader charge analysis confirmed the description of the structure as covalently bonded polyanionic [Au3Al2](δ-) network interacting ionically with Eu(δ+). PMID:27532875

  3. 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

  4. 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.

  5. Optical properties of Ag nanoparticle-polymer composite film based on two-dimensional Au nanoparticle array film

    NASA Astrophysics Data System (ADS)

    Wang, Long-De; Zhang, Tong; Zhang, Xiao-Yang; Song, Yuan-Jun; Li, Ruo-Zhou; Zhu, Sheng-Qing

    2014-03-01

    The nanocomposite polyvinyl pyrrolidone (PVP) films containing Ag nanoparticles and Rhodamine 6G are prepared on the two-dimensional distinctive continuous ultrathin gold nanofilms. We investigate the optical properties and the fluorescence properties of silver nanoparticles-PVP polymer composite films influenced by Ag nanoparticles and Au nanoparticles. Absorption spectral analysis suggests that the prominently light absorption in Ag nanowire/PVP and Ag nanowire/PVP/Au film arises from the localized surface plasmon resonance of Ag nanowire and Au nanofilm. The enhanced fluorescence is observed in the presence of Ag nanowire and Au nanofilm, which is attributed to the excitation of surface plasmon polariton resonance of Ag nanowire and Au nanofilm. The gold nanofilm is proven to be very effective fluorescence resonance energy transfer donors. The fabricated novel structure, gold ultrathin continuous nanofilm, possesses high surface plasmon resonance properties and prominent fluorescence enhancement effect. Therefore, the ultrathin continuous gold nanofilm is an active substrate on nanoparticle-enhanced fluorescence.

  6. A New Database of Globular Clusters Parameters: Distributions of Cluster Properties and Correlations Between Them

    NASA Astrophysics Data System (ADS)

    Djorgovski, S.; Meylan, G.

    1993-05-01

    The forthcoming ASPCS volume, ``Structure and Dynamics of Globular Clusters'' (expected publication date: early summer of 1993) will contain a set of appendices with data resources on Galactic globular clusters; the authors of these papers include I.R. King, S. Peterson, C.T. Pryor, S.C. Trager, and ourselves. From these papers we have compiled a data base of various observed and derived parameters for globular clusters (143 of them at last count). Our main purpose is to use these data for correlative studies of globular cluster properties. Others may find it useful for similar purposes, for planning and support of observations, for testing of theoretical models, etc. We will describe the data base, and present some simple analysis of the cluster properties and correlations among them. The data will be made available to the community in a computer form, as ASCII files. Interested users should send an email message to the Internet address: george @ deimos.caltech.edu, and may also find the above mentioned ASPCS volume useful in their work. We thank our colleagues who contributed data for this compilation for their efforts. S.D. acknowledges a partial support from the NASA contract NAS5-31348, and the NSF PYI award AST-9157412.

  7. 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. PMID:23126715

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

    PubMed

    Priyanka; Dharamvir, Keya

    2013-08-01

    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. PMID:24003446

  9. 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+}.

  10. 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.