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Sample records for au ag pd

  1. Precipitation hardening of a Cu-free Au-Ag-Pd-In dental alloy

    International Nuclear Information System (INIS)

    The hardening mechanism and related microstructural changes of the Cu-free dental casting alloy composed of Au-Ag-Pd-In was examined by means of hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations and electron probe microanalysis (EPMA). The Au-Ag-Pd-In alloy showed apparent age-hardenability. In the SEM photograph, three phases were observed in the solution-treated specimen, that is, the Au-Ag based phase with small amounts of In and Pd as matrix, the InPd phase as particle-like structures, and the Pd-rich phase as lamellar precipitates. By aging the specimen, the very fine Pd-rich inter-granular precipitates grew toward the grain interior as lamellar structure, and finally the coarsened Pd-rich precipitates covered a large part of the Au-Ag based matrix. The hardness increase in the early stage of the age-hardening process was assumed to be caused by the diffusion and aggregation of Pd atoms from the Au-Ag based matrix. The hardness decrease in the later stage of age-hardening process was caused by coarsening of the lamellar precipitates composed of the Pd-rich phase

  2. Asymmetric AgPd-AuNR heterostructure with enhanced photothermal performance and SERS activity

    Science.gov (United States)

    Zhang, Han; Liu, Zeke; Kang, Xiaolin; Guo, Jun; Ma, Wanli; Cheng, Si

    2016-01-01

    Most as-reported nanostructures through galvanic replacement reactions are still symmetric hollow structures, until now. Asymmetric structures fabricated through a galvanic replacement reaction have been rarely reported. However, asymmetric heterostructures can generally lead to new intriguing properties through asymmetric synergistic coupling. Here, we report a simple synthesis of an asymmetric one-ended AgPd bimetal on Au nanorods (AuNR) by combining a galvanic replacement reaction with an Ostwald ripening process. The morphological evolution from a nanodumbbell to a dandelion structure is thoroughly investigated. The unique asymmetric AgPd-AuNR heterostructures possess the required plasmonic performance and avoid strong damping caused by the poor plasmonic metal Pd, resulting in a superior photothermal heating performance and enhanced SERS sensitivity for in situ monitoring of a catalytic reaction compared with the symmetric counterparts.Most as-reported nanostructures through galvanic replacement reactions are still symmetric hollow structures, until now. Asymmetric structures fabricated through a galvanic replacement reaction have been rarely reported. However, asymmetric heterostructures can generally lead to new intriguing properties through asymmetric synergistic coupling. Here, we report a simple synthesis of an asymmetric one-ended AgPd bimetal on Au nanorods (AuNR) by combining a galvanic replacement reaction with an Ostwald ripening process. The morphological evolution from a nanodumbbell to a dandelion structure is thoroughly investigated. The unique asymmetric AgPd-AuNR heterostructures possess the required plasmonic performance and avoid strong damping caused by the poor plasmonic metal Pd, resulting in a superior photothermal heating performance and enhanced SERS sensitivity for in situ monitoring of a catalytic reaction compared with the symmetric counterparts. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07333b

  3. Genetic Pd, Pt, Au, Ag, and Rh mineralogy in Noril'sk sulfide ores

    Science.gov (United States)

    Spiridonov, E. M.; Kulagov, E. A.; Serova, A. A.; Kulikova, I. M.; Korotaeva, N. N.; Sereda, E. V.; Tushentsova, I. N.; Belyakov, S. N.; Zhukov, N. N.

    2015-09-01

    The undeformed ore-bearing intrusions of the Noril'sk ore field (NOF) cut through volcanic rocks of the Late Permian-Early Triassic trap association folded in brachysynclines. Due to the nonuniform load on the roof of intrusive bodies, most sulfide melts were squeezed, up to the tops of ore-bearing intrusions; readily fusible Ni-Fe-Cu sulfide melts were almost completely squeezed. In our opinion, not only one but two stages of mineralization developed at the Noril'sk deposits: (i) syntrap magmatic and (ii) epigenetic post-trap metamorphic-hydrothermal. All platinum-group minerals (PGM) and minerals of gold are metasomatic in the Noril'sk ores. They replaced sulfide solid solutions and exsolution structures. All types of PGM and Au minerals occur in the ores, varying in composition from pyrrhotite to chalcopyrite, talnakhite, mooihoekite, and rich in galena; they are localized in the inner and outer contact zones and differ only in the quantitative proportions of ore minerals. The aureoles of PGM and Au-Ag minerals are wider than the contours of sulfide bodies and coincide with halos of fluid impact on orebodies and adjacent host rocks. The pneumatolytic PGM and Au-Ag minerals are correlated in abundance with the dimensions of sulfide bodies. Their amounts are maximal in veins of late fusible ore composed of eutectic PbS ss and iss intergrowths, as well as at their contacts. The Pd and Pt contents in eutectic sulfide ores of NOF are the world's highest. In the process of noble-metal mineral formation, the fluids supply Pd, Pt, Au, As, Sb, Sn, Bi, and a part of Te, whereas Fe, Ni, Cu, Pb, Ag, Rh, a part of Te and Pd are leached from the replaced sulfide minerals. The pneumatolytic PGM of the early stage comprises Pd and Pt intermetallic compounds enriched in Au along with Pd-Pt-Fe-Ni-Cu-Sn-Pb(As) and (Pd,Pt,Au)(Sn,Sb,Bi,Te,As) solid solutions. Pneumatolytic PGM and Au minerals of the middle stage are products of solid-phase transformation and recrystallization of

  4. Age-hardening and related phase transformation in an experimental Ag-Cu-Pd-Au alloy

    International Nuclear Information System (INIS)

    The age-hardening behaviour, phase transformation and related microstructural changes of an experimental Ag-Cu-Pd-Au alloy were examined by means of hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations and electron probe microanalysis (EPMA). The specimen alloy showed apparent age-hardenability at the aging temperatures of 350 deg. C and 400 deg. C. By aging the solution-treated specimen at 400 deg. C, two phases of the Ag-rich α1 phase and the Pd-containing Cu-rich α2 phase were transformed into four phases of the Ag-rich α1' phase, the Cu-rich α2' phase, the CsCl-type CuPd phase and the AuCu(I) ordered phase. Microstructure of the solution-treated specimen consisted of the Ag-rich α1 matrix, Cu-rich α2 particle-like structures of various sizes and the lamellar structure of the α1 and α2 phases. When the peak hardness was obtained, the very fine lamellar structure consisting of the Ag-rich α1' and Cu-rich α2' phases was newly formed in the matrix. By further aging, the very fine lamellar structure grew and coarsened apparently, and the matrix was covered with the coarsened lamellar structure. The hardness increase was considered to be caused mainly by the diffusion and precipitation of Cu from the Ag-rich α1 matrix, and the hardness decrease in the latter stage of age-hardening process was caused by the coarsening of the very fine lamellar structure. The CsCl-type CuPd phase and the AuCu(I) ordered phase did not contribute to the hardness increase

  5. Electron-spectroscopy study of YbXCu4 (X=Ag,Au,Pd)

    International Nuclear Information System (INIS)

    We have studied the electronic structure of the heavy-electron compounds YbXCu4, with X = Ag,Au,Pd, using x-ray photoemission and bremsstrahlung isochromat spectroscopies. Consistent with other evidence of small Kondo temperatures, we find that Yb in this system is nearly trivalent and that Kondo features in the Yb 4f BIS spectra are either absent or weak

  6. Thermodynamic Measurements on Alloys and Compounds in Ag-Au-Se and Ag-Pd systems by the Electromotive Force Method

    OpenAIRE

    Feng, Dawei

    2014-01-01

    Gold and silver chalcogenides are significant minerals and major carriers of precious metals, and silver palladium alloy is one of the most important silver alloys with various industrial applications. The Ag-Au-Se ternary system and the Ag-Pd binary system have been investigated by the electromotive force (EMF) method in this study. For the Ag-Au-Se ternary system, the numerical values of the standard thermodynamic functions of the compounds Ag2Se (naumannite), AuSe, and Ag3AuSe2 (fisches...

  7. Phase transformation and microstructural changes during ageing process of an Ag-Pd-Cu-Au alloy

    International Nuclear Information System (INIS)

    Age-hardening behaviour and the related phase transformation and microstructural changes during isothermal ageing process were studied to elucidate the age-hardening mechanism of an Ag-based dental casting alloy composed of Ag-Pd-Cu-Au-Zn, Ir and In by means of hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations and energy dispersive spectroscopic microanalysis (EDS). In the hardness test at 350 and 400 deg. C, the hardness of the solution-treated specimen began to increase and reached a maximum value with increasing ageing time, and subsequently the hardness decreased gradually. By considering XRD results and SEM observations together, the solution-treated specimen consisted of three phases, the Ag-rich α1 phase as a matrix, the Cu-Pd α2 phase and the CuPd β phase with a CsCl-type as particle-like structures. By ageing the solution-treated specimen, the Ag-rich α1 and Cu-Pd α2 phases were transformed into the Ag-rich α'1 and Cu3Pd α'2 phases, respectively. The CuPd β phase with a CsCl-type was not changed apparently during the ageing process. From the results of the hardness test, XRD study, SEM observations and EDS analysis, it could be derived that the hardness increased by the diffusion and precipitation of the Cu-rich phase from the Ag-rich matrix during the early stage of phase transformation of α1 into α'1 and that the progress of coarsening of the Cu-rich precipitates with an entanglement structure caused the hardness decrease during the later stage of phase transformation of α1 into α'1. The particle-like structures composed of the Cu-Pd α2 and the CuPd β phase with a CsCl-type contributed little to the hardness increase which occurred in the early stage of aging process

  8. Beet juice utilization: Expeditious green synthesis of nobel metal nanoparticles (Ag, Au, Pt, and Pd) using microwaves

    Science.gov (United States)

    Metal nanoparticles of Ag, Au, Pt, and Pd were prepared in aqueous solutions via a rapid microwave-assisted green method using beet juice, an abundant sugar-rich agricultural produce, served as both a reducing and a capping reagent. The Ag nanoparticles with capping prepared by b...

  9. Hardening mechanism of an Ag-Pd-Cu-Au dental casting alloy

    International Nuclear Information System (INIS)

    Age-hardening behaviour and the related microstructural changes were studied to elucidate the hardening mechanism of an Ag-Pd-Cu-Au dental casting alloy by means of hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations and electron probe microanalysis (EPMA). By considering hardness test and XRD results together, it was revealed that the hardness increased during the early stage of phase transformation of α into α1. In the SEM photographs, two phases of matrix and particle-like structures were observed, and the precipitation of element from the matrix progressed during isothermal aging. By SEM observations and EPMA analysis, it could be supposed that the increase in hardness was caused by the diffusion and aggregation of Cu atoms from the Ag-rich α matrix containing Au and Cu in the early stage of age-hardening process, and that the decrease in hardness was caused by the progress of coarsening of Cu-rich lamellar precipitates in the later stage of the age-hardening process. The changes in the Ag-rich matrix caused both the increase and decrease in hardness, and the CuPd phase containing small amounts of Zn and Sn did not contribute to the hardness changes

  10. PdAgAu alloy with high resistance to corrosion by H2S

    Energy Technology Data Exchange (ETDEWEB)

    Braun, Fernando [Inst. de Investigaciones en Catalisis y Petroquimica, Santa Fe (Argentina); Miller, James B. [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Chemical Engineering; National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Gellman, Andrew J. [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Chemical Engineering; National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Tarditi, Ana M. [Inst. de Investigaciones en Catalisis y Petroquimica, Santa Fe (Argentina); Fleutot, Benoit [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Chemical Engineering; Kondratyuk, Petro [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Chemical Engineering; National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Cornaglia, Laura M. [Inst. de Investigaciones en Catalisis y Petroquimica, Santa Fe (Argentina)

    2012-12-01

    PdAgAu alloy films were prepared on porous stainless steel supports by sequential electroless deposition. Two specific compositions, Pd83Ag2Au15 and Pd74Ag14Au12, were studied for their sulfur tolerance. The alloys and a reference Pd foil were exposed to 1000 H2S /H2 at 623 K for periods of 3 and 30 hours. The microstructure, morphology and bulk composition of both nonexposed and H2S-exposed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD and SEM analysis revealed time-dependent growth of a bulk Pd{sub 4}S phase on the Pd foil during H2S exposure. In contrast, the PdAgAu ternary alloys displayed the same FCC structure before and after H2S exposure. In agreement with the XRD and SEM results, sulfur was not detected in the bulk of either ternary alloy samples by EDS, even after 30 hours of H2S exposure. X-ray photoelectron spectroscopy (XPS) depth profiles were acquired for both PdAgAu alloys after 3 and 30 hours of exposure to characterize sulfur contamination near their surfaces. Very low S 2p and S 2s XPS signals were observed at the top-surfaces of the PdAgAu alloys, and those signals disappeared before the etch depth reached ~ 10 nm, even for samples exposed to H2S for 30 hours. The depth profile analyses also revealed silver and gold segregation to the surface of the alloys; preferential location of Au on the alloys surface may be related to their resistance to bulk sulfide formation. In preliminary tests, a PdAgAu alloy membrane displayed higher initial H{sub 2} permeability than a similarly prepared pure Pd sample and, consistent with resistance to bulk sulfide formation, lower permeability loss in H2S than pure Pd.

  11. Grain boundary sliding mechanisms in ZrN-Ag, ZrN-Au, and ZrN-Pd nanocomposite films

    International Nuclear Information System (INIS)

    Nanocomposite films of ZrN-Me (Me=Ag, Au, or Pd) were produced by reactive unbalanced magnetron sputtering and were found to form a dense and homogeneous microstructure whereby nanocrystals of Me are distributed evenly throughout the ZrN matrix. Interestingly, the Young's modulus was found to decrease much more dramatically with the increase in metal content for the ZrN-Ag system. A systematic ab initio study was undertaken to understand the mechanism of grain boundary sliding in these nanostructures. The maximum energy variation during the sliding was found to be the largest and the smallest for ZrN-Pd and ZrN-Ag, respectively

  12. Thermal cyclic test for Sn-4Ag-0.5Cu solders on high P Ni/Au and Ni/Pd/Au surface finishes

    Directory of Open Access Journals (Sweden)

    M.A. Azmah Hanim

    2015-12-01

    Full Text Available In electronic packaging, the reliability of the interconnection changes with the surface finish and the type of solders being used. Thermal cycling is one method of reliability assessment. In thermal cycling experiments, the strain state is simplified by soldering together regular shaped pieces of materials with different coefficients of thermal expansion and exposing the joint to repeated fluctuations of temperature within a certain range. Thus, this study focuses on the intermetallic evolution of Sn-4Ag-0.5Cu on Ni/Au and Ni/Pd/Au surface finishes with thermal cycling up to 1000 cycles with the range of temperature varying from 10 to 80 °C. Sandwich samples were prepared by placing solder balls of Sn-4Ag-0.5Cu between two substrates of two different surface finishes: Ni/Au and Ni/Pd/Au. Optical microscope and FESEM (Field emission scanning electron microscope were used to analyze the samples. From the study, it was observed that the intermetallic changes from (Cu, Ni6Sn5 to (Ni, Cu3Sn4 after 1000 thermal cycles for Ni/Au. These changes promote the formation of cracks at the solder joint because of the different mechanical properties between Ni-Sn based intermetallic and Cu-Sn intermetallics. However, for the Ni/Pd/Au surface finishes, no cracks formed after thermal cycling up to 1000 cycles. This shows that the reliability of the solder joint is higher for Ni/Pd/Au surface finishes in this experiment. Based on these results, it can be concluded that the reliability of the Ni/Pd/Au surface finishes with Sn-4Ag-0.5Cu solders is higher within the given condition of this research.

  13. Leaching of Au, Ag, and Pd from waste printed circuit boards of mobile phone by iodide lixiviant after supercritical water pre-treatment

    Energy Technology Data Exchange (ETDEWEB)

    Xiu, Fu-Rong, E-mail: xiu_chem@hotmail.com [College of Ecological Environment and Urban Construction, Fujian University of Technology, Fuzhou 350108 (China); Qi, Yingying [College of Ecological Environment and Urban Construction, Fujian University of Technology, Fuzhou 350108 (China); Zhang, Fu-Shen [Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085 (China)

    2015-07-15

    Highlights: • We report a novel process for recovering Au, Ag, and Pd from waste PCBs. • The effect of SCWO on the leaching of Au, Ag, and Pd in waste PCBs was studied. • SCWO was highly efficient for enhancing the leaching of Au, Ag, and Pd. • The optimum leaching parameters for Au, Ag, and Pd in iodine–iodide were studied. - Abstract: Precious metals are the most attractive resources in waste printed circuit boards (PCBs) of mobile phones. In this work, an alternative process for recovering Au, Ag, and Pd from waste PCBs of mobile phones by supercritical water oxidation (SCWO) pre-treatment combined with iodine–iodide leaching process was developed. In the process, the waste PCBs of mobile phones were pre-treated in supercritical water, then a diluted hydrochloric acid leaching (HL) process was used to recovery the Cu, whose leaching efficiency was approximately 100%, finally the resulting residue was subjected to the iodine–iodide leaching process for recovering the Au, Ag, and Pd. Experimental results indicated that SCWO pre-treatment temperature, time, and pressure had significant influence on the Au, Ag, and Pd leaching from (SCWO + HL)-treated waste PCBs. The optimal SCWO pre-treatment conditions were 420 °C and 60 min for Au and Pd, and 410 °C and 30 min for Ag. The optimum dissolution parameters for Au, Pd, and Ag in (SCWO + HL)-treated PCBs with iodine–iodide system were leaching time of 120 min (90 min for Ag), iodine/iodide mole ratio of 1:5 (1:6 for Ag), solid-to-liquid ratio (S/L) of 1:10 g/mL (1:8 g/mL for Ag), and pH of 9, respectively. It is believed that the process developed in this study is environment friendly for the recovery of Au, Ag, and Pd from waste PCBs of mobile phones by SCWO pre-treatment combined with iodine–iodide leaching process.

  14. Leaching of Au, Ag, and Pd from waste printed circuit boards of mobile phone by iodide lixiviant after supercritical water pre-treatment

    International Nuclear Information System (INIS)

    Highlights: • We report a novel process for recovering Au, Ag, and Pd from waste PCBs. • The effect of SCWO on the leaching of Au, Ag, and Pd in waste PCBs was studied. • SCWO was highly efficient for enhancing the leaching of Au, Ag, and Pd. • The optimum leaching parameters for Au, Ag, and Pd in iodine–iodide were studied. - Abstract: Precious metals are the most attractive resources in waste printed circuit boards (PCBs) of mobile phones. In this work, an alternative process for recovering Au, Ag, and Pd from waste PCBs of mobile phones by supercritical water oxidation (SCWO) pre-treatment combined with iodine–iodide leaching process was developed. In the process, the waste PCBs of mobile phones were pre-treated in supercritical water, then a diluted hydrochloric acid leaching (HL) process was used to recovery the Cu, whose leaching efficiency was approximately 100%, finally the resulting residue was subjected to the iodine–iodide leaching process for recovering the Au, Ag, and Pd. Experimental results indicated that SCWO pre-treatment temperature, time, and pressure had significant influence on the Au, Ag, and Pd leaching from (SCWO + HL)-treated waste PCBs. The optimal SCWO pre-treatment conditions were 420 °C and 60 min for Au and Pd, and 410 °C and 30 min for Ag. The optimum dissolution parameters for Au, Pd, and Ag in (SCWO + HL)-treated PCBs with iodine–iodide system were leaching time of 120 min (90 min for Ag), iodine/iodide mole ratio of 1:5 (1:6 for Ag), solid-to-liquid ratio (S/L) of 1:10 g/mL (1:8 g/mL for Ag), and pH of 9, respectively. It is believed that the process developed in this study is environment friendly for the recovery of Au, Ag, and Pd from waste PCBs of mobile phones by SCWO pre-treatment combined with iodine–iodide leaching process

  15. Determination of the compositions of the DIGM zone in nanocrystalline Ag/Au and Ag/Pd thin films by secondary neutral mass spectrometry

    Science.gov (United States)

    Molnár, Gábor Y; Shenouda, Shenouda S; Katona, Gábor L; Langer, Gábor A

    2016-01-01

    Summary Alloying by grain boundary diffusion-induced grain boundary migration is investigated by secondary neutral mass spectrometry depth profiling in Ag/Au and Ag/Pd nanocrystalline thin film systems. It is shown that the compositions in zones left behind the moving boundaries can be determined by this technique if the process takes place at low temperatures where solely the grain boundary transport is the contributing mechanism and the gain size is less than the half of the grain boundary migration distance. The results in Ag/Au system are in good accordance with the predictions given by the step mechanism of grain boundary migration, i.e., the saturation compositions are higher in the slower component (i.e., in Au or Pd). It is shown that the homogenization process stops after reaching the saturation values and further intermixing can take place only if fresh samples with initial compositions, according to the saturation values, are produced and heat treated at the same temperature. The reversal of the film sequence resulted in the reversal of the inequality of the compositions in the alloyed zones, which is in contrast to the above theoretical model, and explained by possible effects of the stress gradients developed by the diffusion processes itself.

  16. Phase formation study of noble metal (Au, Ag and Pd) doped lanthanum perovskites synthesized by hydrothermal method

    International Nuclear Information System (INIS)

    Noble metal (Au, Ag and Pd) doped Lanthanum perovskites (LaMnO3, LaCrO3 and LaFeO3) have been synthesized by hydrothermal method. The effect of dopant and their concentration on the phase purity, crystallite size, morphology and magnetic character of the synthesized perovskites were systematically studied by FTIR spectroscopy, XRD, TGA, SEM, ICP-AES and VSM. The results show that phase pure products were obtained only after calcining the hydrothermally synthesized products above 760 °C for a minimum of 6 h. Nature and concentration of the dopant plays an important role in determining the phase formation temperature, morphology and magnetic character. The dopant ion preferentially occupies A-site and homogeneous phase of product is obtained upto a dopant concentration of 4%, higher concentration results in phase separation. The products exhibit spherical morphology. Lanthanum ferrite shows ferromagnetic nature, while the doped samples show weak magnetic properties. - Highlights: • Hydrothermal synthesis of noble metal doped lanthanum perovskites. • Site preference of noble metal (Au, Ag and Pd) doping in LaBO3 (B = Mn, Cr and Fe). • Dopant ions affect the phase formation temperature and morphology the perovskites. • 4% appears to be the maximum limit of doping at A-site

  17. The Nature of the Binding of Au, Ag, and Pd to Benzene, Coronene, and Graphene: From Benchmark CCSD(T) Calculations to Plane-Wave DFT Calculations

    OpenAIRE

    Granatier, Jaroslav; Lazar, Petr; Otyepka, Michal; Hobza, Pavel

    2011-01-01

    The adsorption of Ag, Au, and Pd atoms on benzene, coronene, and graphene has been studied using post Hartree–Fock wave function theory (CCSD(T), MP2) and density functional theory (M06-2X, DFT-D3, PBE, vdW-DF) methods. The CCSD(T) benchmark binding energies for benzene–M (M = Pd, Au, Ag) complexes are 19.7, 4.2, and 2.3 kcal/mol, respectively. We found that the nature of binding of the three metals is different: While silver binds predominantly through dispersion interactions, the binding of...

  18. Structure and properties of EuTSb (T = Cu, Pd, Ag, Pt, Au) and YbIrSb

    Energy Technology Data Exchange (ETDEWEB)

    Mishra, Trinath; Schellenberg, Inga; Eul, Matthias; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie

    2011-07-01

    The equiatomic antimonides EuTSb (T = Cu, Pd, Ag, Pt, Au) and YbIrSb were synthesized from the elements in sealed tantalum tubes in an induction furnace. The samples were investigated by powder X-ray diffraction and the structures were refined on the basis of single crystal X-ray diffractometer data: ZrBeSi type, P6{sub 3}/mmc, a = 450.7(5), c = 853.2(7) pm, wR2 = 0.032, 273 F{sup 2} values, 8 variables for EuCuSb, a = 474.9(1), c = 829.4(3) pm, wR2 = 0.028, 166 F{sup 2} values, 8 variables for EuAgSb, a = 467.1(2), c = 848.8(3) pm, wR2 = 0.042, 162 F{sup 2} values, 8 variables for EuAuSb, and TiNiSi type, space group Pnma, a = 762.5(3), b = 469.1(1), c = 792.1(1) pm, wR2 = 0.046, 670 F{sup 2} values, 20 variables for EuPdSb, and a = 700.7(1), b = 444.68(8), c = 781.3(1) pm, wR2 = 0.075, 592 F{sup 2} values, 20 variables for YbIrSb. The structures are ordered superstructure variants of the aristotype AlB{sub 2}3 with planar T{sub 3}Sb{sub 3} hexagons in EuTSb (T = Cu, Ag, Au) and puckered T{sub 3}Sb{sub 3} hexagons in EuTSb (T = Pd, Pt) and YbIrSb. TiNiSi type EuPtSb was characterized via powder data: a = 759.8(3), b = 465.4(3), c = 791.4(3) pm. Temperature dependent magnetic susceptibility measurements indicate antiferromagnetic ordering for all compounds. The samples were additionally characterized by {sup 121}Sb and {sup 151}Eu Moessbauer spectra. (orig.)

  19. Tunable Catalysis of Water to Peroxide with Anionic, Cationic, and Neutral Atomic Au, Ag, Pd, Rh, and Os

    CERN Document Server

    Suggs, Kelvin; Tesfamichael, Aaron; Felfli, Zineb; Msezane, Alfred Z

    2014-01-01

    Fundamental anionic, cat-ionic, and neutral atomic metal predictions utilizing density functional theory calculations validate the recent discovery identifying the interplay between the resonances and the RT minimum obtained through complex angular momentum analysis as the fundamental atomic mechanism underlying nano-scale catalysis. Here we investigate the optimization of the catalytic behavior of Au, Ag, Pd, Rh, and Os atomic systems via polarization effects and conclude that anionic atomic systems are optimal and therefore ideal for catalyzing the oxidation of water to peroxide, with anionic Os being the best candidate. The discovery that cat-ionic systems increase the transition energy barrier in the synthesis of peroxide could be important as inhibitors in controlling and regulating catalysis. These findings usher in a fundamental and comprehensive atomic theoretical framework for the generation of tun-able catalytic systems.

  20. Interfacial reaction and elemental redistribution in Sn3.0Ag0.5Cu-xPd/immersion Au/electroless Ni solder joints after aging

    Energy Technology Data Exchange (ETDEWEB)

    Wang, I-Tai [Department of Material Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan (China); Duh, Jenq-Gong, E-mail: jgd@mx.nthu.edu.tw [Department of Material Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan (China); Cheng, Chih-Yuan; Wang, Jim [Shenmao Technology Inc. Micro Material Institute, Taoyuan, Taiwan (China)

    2012-02-15

    Highlights: Black-Right-Pointing-Pointer Pd doping has significant effect on the microstructural development of Sn3.0Ag0.5Cu solder. Black-Right-Pointing-Pointer The growth of intermetallics reduced by adding Pd. Black-Right-Pointing-Pointer Pd mainly dissolved in Cu{sub 6}Sn{sub 5}. Black-Right-Pointing-Pointer Adding Pd into the solder improves stability of the intermetallics. - Abstract: Sn3.0Ag0.5Cu solder doped with 0, 100, and 500 ppm Pd was reflowed with electroless Ni/immersion Au substrate. As Pd concentration increased in the solder, formation and growth of (Cu,Ni){sub 6}Sn{sub 5} were suppressed. After thermal aging, Cu{sub 4}Ni{sub 2}Sn{sub 5} and Cu{sub 5}NiSn{sub 5} were observed at interface of Sn3.0Ag0.5Cu-xPd/Au/Ni systems. As compared to Cu{sub 4}Ni{sub 2}Sn{sub 5}, more Pd dissolved in Cu{sub 5}NiSn{sub 5}. In addition, Pd doping enhanced the growth of Cu{sub 4}Ni{sub 2}Sn{sub 5} and slowed the formation of Cu{sub 5}NiSn{sub 5}, which would stabilize the intermetallic compound. Based on quantitative analysis by field emission electron probe microanalyzer, the correlation between Pd doping and elemental redistribution in solder joints was probed and discussed. This study described a possible mechanism of the formation of different intermetallic compounds in Pd-doped lead-free solder.

  1. Distribution of Precious Metals (Ag, Au, Pd, Pt, and Rh) Between Copper Matte and Iron Silicate Slag

    Science.gov (United States)

    Avarmaa, Katri; Johto, Hannu; Taskinen, Pekka

    2016-02-01

    The distributions of precious metals (Ag, Au, Pd, Pt, and Rh) between copper matte and silica-saturated iron silicate slag were determined at 1523 K to 1623 K (1250 °C to 1350 °C), in controlled CO-CO2-SO2-Ar gas mixtures. The experiments were done in silica crucibles and a fixed partial pressure of sulfur dioxide for matte grades of 55, 65, and 75 wt pct Cu. High-temperature equilibration/quenching/electron probe X-ray microanalysis technique was used to obtain compositions of the equilibrated matte and slag. The technique was applied for the first time to the distributions of precious metals in simulated flash smelting conditions. The resolution of electron probe microanalysis became critical as the detection limits were insufficient to measure reliably the precious metals concentrations (except silver) in the slag. The distribution coefficient of silver, L m/s[Ag] = [wt pctAg in matte]/(wt pctAg in slag), was found to be between 200 and 300, which agrees well with the latest studies in the literature. For other precious metals, the minimum values of distribution coefficients were determined according to the detection limits in the slag. The values obtained were for gold and platinum >250, for palladium >1000, and for rhodium >900. The distribution coefficients of palladium, although locating above distribution coefficient of the detection limit, formed a clear dependency with a good repeatability as a function of the matte grade. It increased along with matte grade and was approximately 1000 at 50 pct Cu and 2000 to 3000 at 70 pct Cu. The precious metals replace metal in the matte structure and they are present as sulfides in the copper matte.

  2. Copper-based alloys, crystallographic and crystallochemical parameters of alloys in binary systems Cu-Me (Me=Co, Rh, Ir, Cu, Ag, Au, Ni, Pd, Pt)

    International Nuclear Information System (INIS)

    The article presents the results of the analysis of phase equilibrium of ordered phases in binary systems based on copper Cu- Me (where Me - Co, Rh, Ir, Ag, Au, Ni, Pd, Pt) to find correlations of crystallochemical and crystallographic factors. It is established that the packing index in disordered solid solutions in binary systems based on copper is close to the value of 0.74 against the background of an insignificant deviation of atomic volumes from the Zen’s law

  3. Copper-based alloys, crystallographic and crystallochemical parameters of alloys in binary systems Cu-Me (Me=Co, Rh, Ir, Cu, Ag, Au, Ni, Pd, Pt)

    Science.gov (United States)

    Porobova, Svetlana; Markova, Tat'jana; Klopotov, Vladimir; Klopotov, Anatoliy; Loskutov, Oleg; Vlasov, Viktor

    2016-01-01

    The article presents the results of the analysis of phase equilibrium of ordered phases in binary systems based on copper Cu- Me (where Me - Co, Rh, Ir, Ag, Au, Ni, Pd, Pt) to find correlations of crystallochemical and crystallographic factors. It is established that the packing index in disordered solid solutions in binary systems based on copper is close to the value of 0.74 against the background of an insignificant deviation of atomic volumes from the Zen's law.

  4. Copper-based alloys, crystallographic and crystallochemical parameters of alloys in binary systems Cu-Me (Me=Co, Rh, Ir, Cu, Ag, Au, Ni, Pd, Pt)

    Energy Technology Data Exchange (ETDEWEB)

    Porobova, Svetlana, E-mail: porobova.sveta@yandex.ru; Loskutov, Oleg, E-mail: lom58@mail.ru [Tomsk State University of Architecture and Building, Russia, Tomsk, 2 Solyanaya sq, Tomsk, 634003 (Russian Federation); Markova, Tat’jana, E-mail: patriot-rf@mail.ru [Siberian State Industrial University. 42 Kirov St., Novokuznetsk, 654007 (Russian Federation); Klopotov, Vladimir, E-mail: vdklopotov@mail.ru [Research Tomsk Polytechnic University, 30 Lenin Ave., Tomsk, 634050 (Russian Federation); Klopotov, Anatoliy, E-mail: klopotovaa@tsuab.ru [Tomsk State University of Architecture and Building, Russia, Tomsk, 2 Solyanaya sq, Tomsk, 634003 (Russian Federation); National Research Tomsk State University, 36, Lenin Ave., Tomsk, 634050 (Russian Federation); Vlasov, Viktor, E-mail: vik@tsuab.ru [Tomsk State University of Architecture and Building, Russia, Tomsk, 2 Solyanaya sq, Tomsk, 634003 (Russian Federation); Research Tomsk Polytechnic University, 30 Lenin Ave., Tomsk, 634050 (Russian Federation)

    2016-01-15

    The article presents the results of the analysis of phase equilibrium of ordered phases in binary systems based on copper Cu- Me (where Me - Co, Rh, Ir, Ag, Au, Ni, Pd, Pt) to find correlations of crystallochemical and crystallographic factors. It is established that the packing index in disordered solid solutions in binary systems based on copper is close to the value of 0.74 against the background of an insignificant deviation of atomic volumes from the Zen’s law.

  5. DFT study of Hg adsorption on M-substituted Pd(1 1 1) and PdM/γ-Al2O3(1 1 0) (M = Au, Ag, Cu) surfaces

    Science.gov (United States)

    Wang, Jiancheng; Yu, Huafeng; Geng, Lu; Liu, Jianwen; Han, Lina; Chang, Liping; Feng, Gang; Ling, Lixia

    2015-11-01

    The adsorption of Hgn (n = 1-3) on the Au-, Ag-, Cu-substituted Pd(1 1 1) surfaces as well as the PdM/γ-Al2O3(1 1 0) (M = Au, Ag, Cu) surfaces has been investigated using spin-polarized density functional theory calculations. It is found that M-substituted Pd(1 1 1) surfaces show as good Hg adsorption capacity as the perfect Pd(1 1 1) at low Hg coverage, while the Hg adsorption capacity is only slightly weakened at high Hg coverage. On the basis of stepwise adsorption energies analysis, it is concluded that M-substituted Pd(1 1 1) surfaces can contribute to the binding of Hg atom on the surfaces at high Hg coverage. The electronic properties of the second metal atoms are the main factor contributes to the Hg adsorption capacity. Gas phase Pd2 shows better Hg adsorption capacity than Pd2/γ-Al2O3, while PdM/γ-Al2O3 can adsorb Hg more efficiently than bare PdM clusters. It suggests that the γ-Al2O3 support can enhance the activity of PdM for Hg adsorption and reduces the activity of Pd2. It is also found that Pd is the main active composition responsible for the interaction of mercury with the surface for PdM/γ-Al2O3 sorbent. Taking Hg adsorption capacity and economic costs into account, Cu addition is a comparatively good candidate for Hg capture.

  6. Elaboration and characterization of bimetallic nanoparticles obtained by laser ablation of Ni75Pd25 and Au75Ag25 targets in water

    International Nuclear Information System (INIS)

    A YAG laser operating at the second harmonic wavelength (532 nm, 10 Hz, 8 ns and 40 mJ) was used to elaborate bimetallic nanoparticles by laser ablation of Ni75Pd25 and Au75Ag25 targets in water. TEM-EDX, UV-Vis spectroscopy and PIXE measurements were performed to obtain information on their mean sizes, size distributions and chemical composition as a function of the time of laser ablation. The surface of the laser impacted regions of the targets were characterized by RBS in order to check their composition after the laser ablation. The so-obtained bimetallic nanoparticles always show a homogeneous composition. However, while the composition of Au-Ag nanoparticles was found to be very similar to the one of the alloy target, the composition of the Ni-Pd nanoparticles can be different from the nominal composition of the alloy target. Segregation phenomena can be invoked to explain the difference between the Ni-Pd nanoparticles and the Au-Ag nanoparticles compositions obtained in the same conditions. However, an influence of chemical reactions occurring in the high pressure plasma created locally at liquid-solid interface (called 'reactive quenching') cannot be completely ruled out.

  7. Self-consistent linear-muffin-tin-orbitals coherent-potential technique for bulk and surface calculations: Cu-Ni, Ag-Pd, and Au-Pt random alloys

    OpenAIRE

    Abrikosov, I. A.; Skriver, Hans Lomholt

    1993-01-01

    We present an efficient technique for calculating surface properties of random alloys based on the coherent-potential approximation within a tight-binding linear-muffin-tin-orbitals basis. The technique has been applied in the calculation of bulk thermodynamic properties as well as (001) surface energies and work functions for three fcc-based alloys (Cu-Ni, Ag-Pd, and Au-Pt) over the complete concentration range. The calculated mixing enthalpies for the Ag-Pd and Au-Pt systems agrees with exp...

  8. Self-consistent linear-muffin-tin-orbitals coherent-potential technique for bulk and surface calculations: Cu-Ni, Ag-Pd, and Au-Pt random alloys

    DEFF Research Database (Denmark)

    Abrikosov, I. A.; Skriver, Hans Lomholt

    1993-01-01

    We present an efficient technique for calculating surface properties of random alloys based on the coherent-potential approximation within a tight-binding linear-muffin-tin-orbitals basis. The technique has been applied in the calculation of bulk thermodynamic properties as well as (001) surface...... energies and work functions for three fcc-based alloys (Cu-Ni, Ag-Pd, and Au-Pt) over the complete concentration range. The calculated mixing enthalpies for the Ag-Pd and Au-Pt systems agrees with experimental values, and the calculated concentration dependence of the lattice parameters agrees with...

  9. Thin-films interdiffusion Ti/Pd/Au, Ti/Au/Pd

    International Nuclear Information System (INIS)

    Rutherford backscattering spectroscopy (RBS) is used to study the interdiffusion in Ti/Pd/Au and Ti/Au/Pd thin films system. The purpose of our study is to prepare an alloy of high resistance against corrosion, due to its important use in space industries, optical and visual receivers. In addition to another scientific results for future applications. Interdiffusion in the Ti/Pd/Au thin film system is measured using Rutherford backscattering. Interdiffusion rates of Pd/Au for temperatures between 200 and 490 centigrade degree have been correlated with the defect structure of the films. Air, as compared with vacuum, annealing enhances interdiffusion in the Ti/Au couple and inhibits interdiffusion in Ti/Pd, Ti/Pd and Ti/Au interdiffusion in the Ti/Pd/Au and Ti/Au/Pd ternary systems is strongly reduced in comparison with interdiffusion in the corresponding Ti/Pd or Ti/Au couples for vacuum annealing. (Author)

  10. Magnesium and cadmium in covalently bonded networks. Synthesis and structure of AETMg and AETCd (AE = Ca, Sr; T = Pd, Ag, Pt, Au) with TiNiSi type structure and the solid solution Yb2-xPtMgx

    International Nuclear Information System (INIS)

    The equiatomic intermetallic compounds AETMg and AETCd (AE = Ca, Sr; T = Pd, Ag, Pt, Au) and the whole solid solution Yb2-xPtMgx were synthesized from the elements in sealed niobium tubes in a high-frequency or a muffle furnace. All samples were characterized on the basis of their powder X-ray diffraction patterns. The structures of SrAuCd, CaPdCd, CaPtCd, CaPdMg, SrPtMg, CaAg1.017Mg0.983, SrAg1.032Mg0.968, and Yb1.792PtMg0.208 were refined on the basis of single-crystal X-ray diffractometer data. Some of the crystals showed small homogeneity ranges. All compounds crystallize with the orthorhombic TiNiSi type structure, space group Pnma. The crystal chemistry is briefly discussed and variations in chemical bonding as a result of the electronegativity of the transition metal are described. (orig.)

  11. Designer electrode interfaces simultaneously comprising three different metal nanoparticle (Au, Ag, Pd)/carbon microsphere/carbon nanotube composites: progress towards combinatorial electrochemistry.

    Science.gov (United States)

    Dai, Xuan; Wildgoose, Gregory G; Compton, Richard G

    2006-11-01

    In this report gold, silver and palladium metal nanoparticles are separately supported on glassy carbon microspheres (GCM) using bulk electroless deposition techniques to produce three different materials labelled as GCM-Au, GCM-Ag and GCM-Pd respectively. These three materials are then combined together into a composite film on a glassy carbon (GC) electrode surface using multiwalled carbon nanotubes (MWCNTs). The MWCNTs serve to not only mechanically support this composite film as a "binder" but they also help to "wire up" each modified GCM to the underlying substrate. The intelligently designed structure of this electrode interface allows this single modified electrode to simultaneously behave as if it were a macrodisc electrode constructed of gold, silver or palladium, whilst using only a fraction of the equivalent amount of these precious metals. Furthermore this unique structure allows the possibility of combinatorial electrochemistry to be realised using a relatively facile electrode construction which avoids the problems of alloy formation, co-deposition and the formation of bimetallic species. For instance a mixture of several different analytes, which can each only be detected on a different specific substrate, can simultaneously be determined using one electrode in a single voltammetric experiment! Alternatively a substrate could undergo electrocatalytic reactions on one substrate, whilst the products, and hence the progress of this reaction, can be studied at a different substrate simultaneously at the same electrode surface. Proof-of-concept examples are presented herein and the designer electrode interface is shown to produce analytical responses to model target analytes such as hydrazine, bromide and thallium(I) ions that are comparable, if not better, than those obtained at metal macrodisc electrodes and even at other state-of-the-art nanoparticle modified electrodes. PMID:17066193

  12. Influence of the noble metals (Pd, Au, Ag) in the thermoluminescent signal induced by radiation in the ZrO2

    International Nuclear Information System (INIS)

    When increasing the use of the ionizing and non ionizing radiations (for example, gamma and ultraviolet radiation) in different areas of the science and technology, there is necessary to apply more accurate safety measures and to avoid over-exposures that could put in risk the life of workers that manipulate radiation sources, patient that are exposed to this under some medical treatment, as well as materials that undergo intentionally to radiation. Also, the UV radiation that arrives to the earth can cause some damages, to the one to weaken the protector layer of ozone the UV radiation increases that arrives to the earth surface being able to affect the alive beings and the materials. By this so much the development of new materials able to take a census of in a more accurate way, fields of gamma and UV radiation is becoming necessary. In this sense, this work presents the obtained results when quantifying radiation fields, through the analysis in the thermoluminescent behavior (TL) induced by the gamma and UV radiation in the zirconium dioxide synthesized by the sol gel method and doped with nanoparticles of Pd, Au and Ag. It is necessary to mention that in reported works in this respect its mention that the zircon has good thermoluminescent sensitivity induced by these radiation types, however it has shown high thermoluminescent instability that is translated in an important lost of the information after the irradiation. For that through the incorporation of the metallic nanoparticles it was intended to stabilize the TL behavior of zircon. The results showed that the doped zircon has a high sensitivity to the gamma and UV radiation. These also show that the ionizing and non ionizing radiation induce a thermoluminescent curve consisting of two TL peaks with maxima located around 65 C and 145 C and that the intensity is increased with the dose, following a lineal behavior in certain interval of dose exposure that is influenced by the presence of the nanoparticles

  13. Propiedades de aleaciones Ag-Pd para usos odontológicos

    OpenAIRE

    Basualto, J.; Barceló, C.; Gaete, A.

    1996-01-01

    In this search for economically alternative alloys for odontological uses, three complex Ag-Pd alloys, Ag-Pd-Au-Cu type, are studied: two experimental alloys and one commercial product. Chemical and mechanical properties were obtained for these alloys and a comparative analysis of these results was made. The cost, important factor, is established in relation to the materials cost of the commercial product. Vickers hardness values obtained from Ag-Pd alloys with different heat treatments allow...

  14. Au@Pd core-shell nanobricks with concave structures and their catalysis of ethanol oxidation.

    Science.gov (United States)

    Wang, Wenjin; Zhang, Jie; Yang, Shengchun; Ding, Bingjun; Song, Xiaoping

    2013-10-01

    Au@Pd core-shell nanobricks (CNBs) with concave surfaces and Pd shells with a thickness of approximately 5 nm were synthesized by co-reduction of HAuCl4 and H2 PdCl4 in the presence of Au seeds and Ag ions. These as-synthesized concave CNBs exhibit significantly enhanced catalytic activity for the electrooxidation of ethanol in alkaline media compared to the commercially-used Pd black. The improved performance of the Au@Pd CNBs can be attributed to the exposed stepped surfaces, high-index facets, and the synergistic effects of the core and shell metals. PMID:23929810

  15. LaMgX and CeMgX (X = Ga, In, Tl, Pd, Ag, Pt, Au) with ZrNiAl type structure - A systematic view on electronic structure and chemical bonding

    Science.gov (United States)

    Matar, Samir F.; Etourneau, Jean; Pöttgen, Rainer

    2015-05-01

    The intermetallic magnesium compounds LaMgX and CeMgX (X = Ga, In, Tl, Pd, Ag, Pt, Au) crystallize with the hexagonal ZrNiAl type structure, space group P 6 bar 2 m , with full Mg-X ordering. From density functional theory calculations carried out exemplarily on four representative compounds: LaMgX and CeMgX with X = Ga, Pd, significant differences were traced out as to the magnetism arising only for the Ce series leading to identify CeMgGa as an antiferromagnet in its ground state, in agreement with experiment. The bulk module magnitudes show the trend of harder transition metal based ternaries and the cohesive energies favor the X = Pd compounds versus X = Ga ones. Such features were clarified by examining the properties of chemical bonding which exhibit more directional bonds thanks to the Pd d states. Rationalizing the trends of charge transfers, negatively charged triel and transition element atoms are observed. The resulting chemical pictures assign these compounds as gallides and palladides.

  16. Influence of the noble metals (Pd, Au, Ag) in the thermoluminescent signal induced by radiation in the ZrO{sub 2}; Influencia de los metales nobles (Pd, Au, Ag) en la senal termoluminiscente inducida por la radiacion en la ZrO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Villa S, G

    2006-07-01

    When increasing the use of the ionizing and non ionizing radiations (for example, gamma and ultraviolet radiation) in different areas of the science and technology, there is necessary to apply more accurate safety measures and to avoid over-exposures that could put in risk the life of workers that manipulate radiation sources, patient that are exposed to this under some medical treatment, as well as materials that undergo intentionally to radiation. Also, the UV radiation that arrives to the earth can cause some damages, to the one to weaken the protector layer of ozone the UV radiation increases that arrives to the earth surface being able to affect the alive beings and the materials. By this so much the development of new materials able to take a census of in a more accurate way, fields of gamma and UV radiation is becoming necessary. In this sense, this work presents the obtained results when quantifying radiation fields, through the analysis in the thermoluminescent behavior (TL) induced by the gamma and UV radiation in the zirconium dioxide synthesized by the sol gel method and doped with nanoparticles of Pd, Au and Ag. It is necessary to mention that in reported works in this respect its mention that the zircon has good thermoluminescent sensitivity induced by these radiation types, however it has shown high thermoluminescent instability that is translated in an important lost of the information after the irradiation. For that through the incorporation of the metallic nanoparticles it was intended to stabilize the TL behavior of zircon. The results showed that the doped zircon has a high sensitivity to the gamma and UV radiation. These also show that the ionizing and non ionizing radiation induce a thermoluminescent curve consisting of two TL peaks with maxima located around 65 C and 145 C and that the intensity is increased with the dose, following a lineal behavior in certain interval of dose exposure that is influenced by the presence of the nanoparticles

  17. Crystal and electronic structure study of AgPd3Se

    International Nuclear Information System (INIS)

    The AgPd3Se compound was synthesised from individual elements by solid-state chemical reactions and structurally characterized by powder X-ray diffraction data. AgPd3Se displays cubic symmetry, space group Pa3-bar , unit cell parameter a=8.6289(1) A and Z=8. Double-Friauf polyhedra (DFP), defined by Pd and Se atoms, form the basic structural building block of the AgPd3Se crystal structure. The Ag atoms occupy the centres of DFPs forming an Ag-Ag dimer (2.792(2) A). The packing of DFPs forms two kinds of interpenetrating networks that show similar features as three-dimensional Penrose tiles. AgPd3Se is isostructural with CaAu3Ga. The electric resistivity as well as the electronic structure calculation suggests metallic behaviour. - Graphical abstract: (a) Prolate rhombohedron formed by Pd and Se atoms, (b) oblate rhombohedron formed by Ag atoms and (c) their interpenetration at unit cell level. (d) 3D network of prolate and oblate rhombohedra. Highlights: → Crystal structure of AgPd3Se was determined from powder X-ray diffraction data. → Double-Friauf polyhedra form the basic structural block of the AgPd3Se structure. → Packing of double-Friauf polyhedra produces two kinds of interpenetrating networks. → Metallic behavior was observed.

  18. Strain distributions of confined Au/Ag and Ag/Au nanoparticles

    Institute of Scientific and Technical Information of China (English)

    黄红华; 章英; 刘晓山; 骆兴芳; 袁彩雷; 叶双莉

    2015-01-01

    The strain distributions of Au/Ag and Ag/Au nanoparticles confined in the Al2O3 matrix with different core sizes are investigated by using the finite element method, respectively. The simulation results clearly indicate that the compressive strains exerted on the Au/Ag and Ag/Au nanoparticles can be induced by the Al2O3 matrix. Moreover, it can be found that the strain gradient existing in a Au/Ag nanoparticle is much larger than that in a Ag/Au nanoparticle, which could be due to the larger Young’s modulus of Au than that of Ag. With the core size increasing, the strain gradient existing in the Au/Ag nanoparticle becomes larger, while the strain gradient existing in the Ag/Au nanoparticle keeps constant. These different strain distributions may have significant infl uences on the structures and morphologies of the Au/Ag and Ag/Au nanoparticles, leading to the different physical properties for potential applications.

  19. Au, Ag and Au:Ag colloidal nanoparticles synthesized by pulsed laser ablation as SERS substrates

    Institute of Scientific and Technical Information of China (English)

    M. Vinod; K.G.Gopchandran

    2014-01-01

    Chemically pure colloidal suspensions of gold and silver nanoparticles were synthesized using pulsed laser ablation. The dependence of laser fluence on the surface plasmon characteristics of the nanoparticles was investigated. Au:Ag colloidal suspensions were prepared by mixing highly monodisperse Au and Ag nanocolloids. The plasmon band of these mixtures was found to be highly sensitive to Au:Ag concentration ratio and wavelength of the laser beam used in the ablation process. The Au:Ag mixture consists of almost spherical shaped nanostructures with a tendency to join with adjacent ones. The surface enhanced Raman scattering activity of the Au, Ag and Au:Ag colloidal suspensions was tested using crystal violet as probe molecules. Enhancement in Raman signal obtained with Au:Ag substrates was found to be promising and strongly depends on its plasmon characteristics.

  20. Au, Ag and Au:Ag colloidal nanoparticles synthesized by pulsed laser ablation as SERS substrates

    Directory of Open Access Journals (Sweden)

    M. Vinod

    2014-12-01

    Full Text Available Chemically pure colloidal suspensions of gold and silver nanoparticles were synthesized using pulsed laser ablation. The dependence of laser fluence on the surface plasmon characteristics of the nanoparticles was investigated. Au:Ag colloidal suspensions were prepared by mixing highly monodisperse Au and Ag nanocolloids. The plasmon band of these mixtures was found to be highly sensitive to Au:Ag concentration ratio and wavelength of the laser beam used in the ablation process. The Au:Ag mixture consists of almost spherical shaped nanostructures with a tendency to join with adjacent ones. The surface enhanced Raman scattering activity of the Au, Ag and Au:Ag colloidal suspensions was tested using crystal violet as probe molecules. Enhancement in Raman signal obtained with Au:Ag substrates was found to be promising and strongly depends on its plasmon characteristics.

  1. Hollow Au@Pd and Au@Pt core-shell nanoparticles as electrocatalysts for ethanol oxidation reactions

    KAUST Repository

    Song, HyonMin

    2012-09-27

    Hybrid alloys among gold, palladium and platinum become a new category of catalysts primarily due to their enhanced catalytic effects. Enhancement means not only their effectiveness, but also their uniqueness as catalysts for the reactions that individual metals may not catalyze. Here, preparation of hollow Au@Pd and Au@Pt core-shell nanoparticles (NPs) and their use as electrocatalysts are reported. Galvanic displacement with Ag NPs is used to obtain hollow NPs, and higher reduction potential of Au compared to Ag, Pd, and Pt helps to produce hollow Au cores first, followed by Pd or Pt shell growth. Continuous and highly crystalline shell growth was observed in Au@Pd core-shell NPs, but the sporadic and porous-like structure was observed in Au@Pt core-shell NPs. Along with hollow core-shell NPs, hollow porous Pt and hollow Au NPs are also prepared from Ag seed NPs. Twin boundaries which are typically observed in large size (>20 nm) Au NPs were not observed in hollow Au NPs. This absence is believed to be due to the role of the hollows, which significantly reduce the strain energy of edges where the two lattice planes meet. In ethanol oxidation reactions in alkaline medium, hollow Au@Pd core-shell NPs show highest current density in forward scan. Hollow Au@Pt core-shell NPs maintain better catalytic activities than metallic Pt, which is thought to be due to the better crystallinity of Pt shells as well as the alloy effect of Au cores. © 2012 The Royal Society of Chemistry.

  2. Electrical properties of thin-film structures formed by pulsed laser deposition of Au, Ag, Cu, Pd, Pt, W, Zr metals on n-6H-SiC crystal

    International Nuclear Information System (INIS)

    Diode structures with ideality factors of 1.28-2.14 and potential barriers from 0.58 to 0.62 eV on the semiconductor side were formed by pulsed laser deposition of Au, Ag, Cu, Pd, Pt, W, and Zr metal films on n-6H-SiC crystal without epitaxial layer preparation. A high density of surface acceptor and donor states was formed at the metal-semiconductor interface during deposition of the laser-induced atomic flux, which violated the correlation between the potential barrier height and metal work function. The barrier heights determined from characteristic currents and capacitance measurements were in quite good agreement. For the used low-resistance semiconductor and contact elements, the sizes of majority carrier (electron) depletion regions were determined as 26-60 nm.

  3. Screening on binary Zr-1X (X = Ti, Nb, Mo, Cu, Au, Pd, Ag, Ru, Hf and Bi) alloys with good in vitro cytocompatibility and magnetic resonance imaging compatibility.

    Science.gov (United States)

    Zhou, F Y; Qiu, K J; Li, H F; Huang, T; Wang, B L; Li, L; Zheng, Y F

    2013-12-01

    In this study, the microstructures, mechanical properties, corrosion behaviors, in vitro cytocompatibility and magnetic susceptibility of Zr-1X alloys with various alloying elements, including Ti, Nb, Mo, Cu, Au, Pd, Ag, Ru, Hf and Bi, were systematically investigated to explore their potential use in biomedical applications. The experimental results indicated that annealed Zr-1X alloys consisted entirely or primarily of α phase. The alloying elements significantly increased the strength and hardness of pure Zr and had a relatively slight influence on elastic modulus. Ru was the most effective enhancing element and Zr-1Ru alloy had the largest elongation. The results of electrochemical corrosion indicated that adding various elements to Zr improved its corrosion resistance, as indicated by the reduced corrosion current density. The extracts of the studied Zr-1X alloys produced no significant deleterious effects on osteoblast-like cells (MG 63), indicating good in vitro cytocompatibility. All except for Zr-1Ag alloy showed decreased magnetic susceptibility compared to pure Zr, and Zr-1Ru alloy had the lowest magnetic susceptibility value, being comparable to that of α' phase Zr-Mo alloy and Zr-Nb alloy and far lower than that of Co-Cr alloy and Ti-6Al-4V alloy. Among the experimental Zr-1X alloys, Zr-1Ru alloy possessing high strength coupled with good ductility, good in vitro cytocompatibility and low magnetic susceptibility may be a good candidate alloy for medical devices within a magnetic resonance imaging environment. PMID:23928334

  4. Development of highly transparent Pd-coated Ag nanowire electrode for display and catalysis applications

    International Nuclear Information System (INIS)

    Highlights: • Highly uniform thin-layer coating of Pd onto Ag nanowire surface was accomplished. • A transparent electrode of Pd-coated Ag nanowire was uniformly deposited on flexible substrate. • 95% of optical transmittance and 175 Ω/sq sheet resistance were obtained. • Extremely low haze of 1.9% and high oxidation stability proved an efficient transparent electrode. • This electrode can be used as Pd-catalyst for synthesis reactions and fuel cell electrode applications. - Abstract: Ag nanowire transparent electrode has excellent transmittance (90%) and sheet resistance (20 Ω/sq), yet there are slight drawbacks such as optical haze and chemical instability against aerial oxidation. Chemical stability of Ag nanowires needs to be improved in order for it to be suitable for electrode applications. In our recent article, we demonstrated that coating Ag nanowires with a thin layer of Au through galvanic exchange reactions enhances the chemical stability of Ag nanowire films highly and also helps to obtain lower haze. In this study, coating of a thin Pd layer has been applied successfully onto the surface of Ag nanowires. A mild Pd complex oxidant [Pd(en)2](NO3)2 was prepared in order to oxidize Ag atoms partially on the surface via galvanic displacement. The mild galvanic exchange allowed for a thin layer (1–2 nm) of Pd coating on the Ag nanowires with minimal truncation of the nanowire, where the average length and the diameter were 12.5 μm and 59 nm, respectively. The Pd-coated Ag nanowires were suspended in methanol and then electrostatically sprayed on flexible polycarbonate substrates. It has been revealed that average total transmittance remain around 95% within visible spectrum region (400–800 nm) whereas sheet resistance rises up to 175 Ω/sq. To the best of our knowledge, for the first time in the literature, Pd coating was employed on Ag nanowires in order to design transparent electrodes for high transparency and strong chemical resistivity

  5. Development of highly transparent Pd-coated Ag nanowire electrode for display and catalysis applications

    Energy Technology Data Exchange (ETDEWEB)

    Canlier, Ali, E-mail: ali.canlier@agu.edu.tr [Department of Materials Science and Nanotechnology Engineering, Abdullah Gul University, P.O. Box 38080, Kayseri (Turkey); Ucak, Umit Volkan, E-mail: sirvolkan@gmail.com [Department of Materials Science and Nanotechnology Engineering, Abdullah Gul University, P.O. Box 38080, Kayseri (Turkey); Graduate School of Energy, Environment, Water, and Sustainability (EEWS), Korea Advanced Institute of Science and Technology (KAIST), P.O. Box 305-701, Daejeon (Korea, Republic of); Usta, Hakan, E-mail: husta38@gmail.com [Department of Materials Science and Nanotechnology Engineering, Abdullah Gul University, P.O. Box 38080, Kayseri (Turkey); Cho, Changsoon, E-mail: cscho@kaist.ac.kr [Graduate School of Energy, Environment, Water, and Sustainability (EEWS), Korea Advanced Institute of Science and Technology (KAIST), P.O. Box 305-701, Daejeon (Korea, Republic of); Lee, Jung-Yong, E-mail: jungyong.lee@kaist.ac.kr [Graduate School of Energy, Environment, Water, and Sustainability (EEWS), Korea Advanced Institute of Science and Technology (KAIST), P.O. Box 305-701, Daejeon (Korea, Republic of); Sen, Unal, E-mail: senunal@gmail.com [Department of Mechanical Engineering, Abdullah Gul University, P.O. Box 38080, Kayseri (Turkey); Citir, Murat, E-mail: muratcitir@gmail.com [Department of Chemical Engineering, Abdullah Gul University, P.O. Box 38080, Kayseri (Turkey)

    2015-09-30

    Highlights: • Highly uniform thin-layer coating of Pd onto Ag nanowire surface was accomplished. • A transparent electrode of Pd-coated Ag nanowire was uniformly deposited on flexible substrate. • 95% of optical transmittance and 175 Ω/sq sheet resistance were obtained. • Extremely low haze of 1.9% and high oxidation stability proved an efficient transparent electrode. • This electrode can be used as Pd-catalyst for synthesis reactions and fuel cell electrode applications. - Abstract: Ag nanowire transparent electrode has excellent transmittance (90%) and sheet resistance (20 Ω/sq), yet there are slight drawbacks such as optical haze and chemical instability against aerial oxidation. Chemical stability of Ag nanowires needs to be improved in order for it to be suitable for electrode applications. In our recent article, we demonstrated that coating Ag nanowires with a thin layer of Au through galvanic exchange reactions enhances the chemical stability of Ag nanowire films highly and also helps to obtain lower haze. In this study, coating of a thin Pd layer has been applied successfully onto the surface of Ag nanowires. A mild Pd complex oxidant [Pd(en){sub 2}](NO{sub 3}){sub 2} was prepared in order to oxidize Ag atoms partially on the surface via galvanic displacement. The mild galvanic exchange allowed for a thin layer (1–2 nm) of Pd coating on the Ag nanowires with minimal truncation of the nanowire, where the average length and the diameter were 12.5 μm and 59 nm, respectively. The Pd-coated Ag nanowires were suspended in methanol and then electrostatically sprayed on flexible polycarbonate substrates. It has been revealed that average total transmittance remain around 95% within visible spectrum region (400–800 nm) whereas sheet resistance rises up to 175 Ω/sq. To the best of our knowledge, for the first time in the literature, Pd coating was employed on Ag nanowires in order to design transparent electrodes for high transparency and strong

  6. Probing the rupture of a Ag atomic junction in a Ag-Au mixed electrode

    Science.gov (United States)

    Kim, Taekyeong

    2015-09-01

    We probed that the atomic junction in Ag part ruptures during stretching of atomic sized contacts of Ag-Au mixed electrodes, resulting in Ag-Ag electrodes through a scanning tunneling microscope breaking junction (STM-BJ) technique. We observed that the conductance and tunneling decay constant for a series of amine-terminated oligophenyl molecular junctions are essentially the same for the Ag-Au mixed and the Ag-Ag electrodes. We also found the molecular plateau length and the evolution patterns with the Ag-Au mixed electrodes are similar to those with Ag-Ag electrodes rather than the Au-Au electrodes in the molecular junction elongation. This result is attributed to the smaller binding energy of Ag atoms compared to that of Au atoms, so the Ag junction part is more easily broken than that of Au part in stretching of Ag-Au mixed electrodes. Furthermore, we successfully observed that the rupture force of the atomic junction for the Ag-Au mixed electrodes was identical to that for the Ag-Ag electrodes and smaller than that for the Au-Au electrodes. This study may advance the understanding of the electrical and the mechanical properties in molecular devices with Ag and Au electrodes in future.

  7. XPS and DFT studies of the electronic structures of AgAuS and Ag3AuS2

    International Nuclear Information System (INIS)

    Highlights: • Photoelectron spectra and DOS were obtained for AgAuS and Ag3AuS2 for the first time. • Essentially higher Au 4f binding energy was found in case of Ag3AuS2. • DFT calculations show a larger overlapping of S 3p and Au 5d valence states for Ag3AuS2. • Energy position of Au 4f levels is mainly influenced by Au–Ag interactions. - Abstract: X-ray photoelectron spectra of core levels and the valence bands were acquired, and the density-of-states (DOS) were calculated using periodic density functional theory (DFT) for synthetic ternary compounds AgAuS and Ag3AuS2, known as minerals petrovskaite uytenbogaardtite, respectively, for the first time. The chemical shift of the Au 4f binding energy as large as 0.65 eV relative to bulk elemental gold was found for Ag3AuS2, in contrast to only about 0.3 eV for AgAuS. The DFT analysis showed, in particular, that the S 3p states are largely pushed out from the Ag 4d and Au 5d bands affording two sub-bands in the valence region of both substances, but the overlapping of the S 3p and Au 5d states is larger for Ag3AuS2. It was demonstrated that the energy position of Au 4f levels is mainly influenced by Au–Ag interaction, and increasing the number of Ag atoms in the first coordination shell of S–Au–S units on going from AgAuS to Ag3AuS2 results in the positive shift of the Au 4f bands consistent with the experimental data

  8. Monodispersed bimetallic PdAg nanoparticles with twinned structures: Formation and enhancement for the methanol oxidation

    OpenAIRE

    Zhen Yin; Yining Zhang; Kai Chen; Jing Li; Wenjing Li; Pei Tang; Huabo Zhao; Qingjun Zhu; Xinhe Bao; Ding Ma

    2014-01-01

    Monodispersed bimetallic PdAg nanoparticles can be fabricated through the emulsion-assisted ethylene glycol (EG) ternary system. Different compositions of bimetallic PdAg nanoparticles, Pd80Ag20, Pd65Ag35 and Pd46Ag54 can be obtained via adjusting the reaction parameters. For the formation process of the bimetallic PdAg nanoparticles, there have two-stage growth processes: firstly, nucleation and growth of the primary nanoclusters; secondly, formation of the secondary nanoparticles with the s...

  9. Structure and Mobility of Metal Clusters in MOFs: Au, Pd, and AuPd Clusters in MOF-74

    DEFF Research Database (Denmark)

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

    2012-01-01

    Understanding the adsorption and mobility of metal–organic framework (MOF)-supported metal nanoclusters is critical to the development of these catalytic materials. We present the first theoretical investigation of Au-, Pd-, and AuPd-supported clusters in a MOF, namely MOF-74. We combine density...... functional theory (DFT) calculations with a genetic algorithm (GA) to reliably predict the structure of the adsorbed clusters. This approach allows comparison of hundreds of adsorbed configurations for each cluster. From the investigation of Au8, Pd8, and Au4Pd4 we find that the organic part of the MOF is......’s adsorption energy and diffusion barrier is established, confirming that Au clusters are highly mobile in the MOF-74 framework and Pd clusters are less mobile....

  10. Biosynthesis and stabilization of Au and Au-Ag alloy nanoparticles by fungus, Fusarium semitectum

    International Nuclear Information System (INIS)

    Crystallized and spherical-shaped Au and Au-Ag alloy nanoparticles have been synthesized and stabilized using a fungus, F . semitectum in an aqueous system. Aqueous solutions of chloroaurate ions for Au and chloroaurate and Ag+ ions (1 : 1 ratio) for Au-Ag alloy were treated with an extracellular filtrate of F . semitectum biomass for the formation of Au nanoparticles (AuNP) and Au-Ag alloy nanoparticles (Au-AgNP). Analysis of the feasibility of the biosynthesized nanoparticles and core-shell alloy nanoparticles from fungal strains is particularly significant. The resultant colloidal suspensions are highly stable for many weeks. The obtained Au and Au-Ag alloy nanoparticles were characterized by the surface plasmon resonance (SPR) peaks using a UV-vis spectrophotometer, and the structure, morphology and size were determined by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and transmission electron microscopy (TEM). Possible optoelectronics and medical applications of these nanoparticles are envisaged.

  11. Near-Field Plasmonic Behavior of Au/Pd Nanocrystals with Pd-Rich Tips

    CERN Document Server

    Ringe, Emilie; Collins, Sean M; Duchamp, Martial; Dunin-Borkowski, Rafal E; Skrabalak, Sara E; Midgley, Paul A

    2015-01-01

    Using nanometer spatial resolution electron-energy loss spectroscopy (EELS), energy dispersive X-ray spectroscopy (EDS), and cathodoluminescence (CL) mapping, we demonstrate that Au alloys containing a poor plasmonic metal (Pd) can nevertheless sustain multiple size-dependent localized surface plasmon resonances and observe strong field enhancement at Pd-rich tips, where the composition is in fact least favorable for plasmons. These Au/Pd stellated nanocrystals are also involved in substrate and interparticle coupling, as unraveled by EELS tilt series.

  12. Alumina supported model Pd Ag catalysts: A combined STM, XPS, TPD and IRAS study

    Science.gov (United States)

    Khan, N. A.; Uhl, A.; Shaikhutdinov, S.; Freund, H.-J.

    2006-05-01

    The bimetallic Pd-Ag model catalysts were prepared by physical vapor deposition on thin alumina films. The morphology and structure of the Pd-Ag particles were studied by STM, XPS, and by TPD and IRAS of CO. The results showed the formation of true alloy particles with Ag segregated at the surface. The addition of Ag first suppresses the most strongly bonded CO on threefold hollow sites of Pd. With further increasing Ag coverage, only isolated Pd atoms surrounded by Ag atoms are likely present on the surface. The results on CO adsorption suggest that the model Pd-Ag system mimics the structure of the real Pd-Ag catalysts.

  13. Fabricating a Homogeneously Alloyed AuAg Shell on Au Nanorods to Achieve Strong, Stable, and Tunable Surface Plasmon Resonances

    KAUST Repository

    Huang, Jianfeng

    2015-08-13

    Colloidal metal nanocrystals with strong, stable, and tunable localized surface plasmon resonances (SPRs) can be useful in a corrosive environment for many applications including field-enhanced spectroscopies, plasmon-mediated catalysis, etc. Here, a new synthetic strategy is reported that enables the epitaxial growth of a homogeneously alloyed AuAg shell on Au nanorod seeds, circumventing the phase segregation of Au and Ag encountered in conventional synthesis. The resulting core–shell structured bimetallic nanorods (AuNR@AuAg) have well-mixed Au and Ag atoms in their shell without discernible domains. This degree of mixing allows AuNR@AuAg to combine the high stability of Au with the superior plasmonic activity of Ag, thus outperforming seemingly similar nanostructures with monometallic shells (e.g., Ag-coated Au NRs (AuNR@Ag) and Au-coated Au NRs (AuNR@Au)). AuNR@AuAg is comparable to AuNR@Ag in plasmonic activity, but that it is markedly more stable toward oxidative treatment. Specifically, AuNR@AuAg and AuNR@Ag exhibit similarly strong signals in surface-enhanced Raman spectroscopy that are some 30-fold higher than that of AuNR@Au. When incubated with a H2O2 solution (0.5 m), the plasmonic activity of AuNR@Ag immediately and severely decayed, whereas AuNR@AuAg retained its activity intact. Moreover, the longitudinal SPR frequency of AuNR@AuAg can be tuned throughout the red wavelengths (≈620–690 nm) by controlling the thickness of the AuAg alloy shell. The synthetic strategy is versatile to fabricate AuAg alloyed shells on different shaped Au, with prospects for new possibilities in the synthesis and application of plasmonic nanocrystals.

  14. Optical absorption engineering in stacked plasmonic Au-SiO₂-Pd nanoantennas.

    Science.gov (United States)

    Wadell, Carl; Antosiewicz, Tomasz J; Langhammer, Christoph

    2012-09-12

    The nonradiative decay of a localized surface plasmon through absorption of a captured photon and excitation of an energetic electron-hole pair is a potentially very effective way to enhance chemical reactions on metal nanoparticle surfaces, so far limited to Ag (and Au). Here we explore the possibility of efficient and spectrally widely tunable optical absorption engineering based on heterometallic optical nanoantennas. They consist of an optimized antenna element made of Au (or Ag) and a catalytically active second metallic element separated by a thin SiO(2) layer. Specifically, we find that stacked Au-SiO(2)-Pd nanodisk antennas exhibit pronounced local absorption enhancement in the catalytic Pd particle. The effect is caused by efficient power transfer from the Au disk, exhibiting a narrow low-loss resonance and acting as an antenna collecting photons, to the Pd disk due to strong coupling between the two. The Pd element thus acts as receiver that efficiently dissipates energy into electron-hole pairs owing to efficient coupling to intra and interband transitions. In fact, the energy transfer is found to be so effective that the absorption efficiency at a given wavelength can be enhanced up to 6 to 9 times, and the total absorption integrated over a wide spectral range (400-900 nm) up to 2-fold, depending on the antenna dimensions. This finding suggests a novel route toward highly efficient plasmon-enhanced catalysis on widely selectable catalytic metal particle surfaces not limited to the "classic" plasmonic metals Au and Ag. PMID:22916998

  15. Component conversion from pure Au nanorods to multiblock Ag-Au-Ag nanorods assisted by Pt nanoframe templates

    Science.gov (United States)

    Lee, Sangji; Jang, Hee-Jeong; Jang, Ho Young; Kim, Seong Kyu; Park, Sungho

    2016-06-01

    We developed a new method for synthesizing multiblock Ag-Au-Ag nanorods using Pt nanoframes that had been deposited on the edges of Au nanorod seeds. As a function of Au etching time, the length of the Au nanorod decreased symmetrically starting from the two ends, leading to the formation of empty inner space at the ends. Subsequent reduction of Ag ions could be selectively performed in the inner space confined by Pt nanoframes and the resulting Ag-Au-Ag nanorods exhibited characteristic LSPR modes originating from each block component (in a transverse direction) and SPR coupling (in a longitudinal direction). The high quality of the resulting multiblock nanorods enabled observation of the longitudinal quadrupole mode that was induced by Ag-Au SPR coupling in a long axis. The mode exhibited high sensitivity in accordance with the change in the surrounding media, demonstrating great potential for sensor applications.We developed a new method for synthesizing multiblock Ag-Au-Ag nanorods using Pt nanoframes that had been deposited on the edges of Au nanorod seeds. As a function of Au etching time, the length of the Au nanorod decreased symmetrically starting from the two ends, leading to the formation of empty inner space at the ends. Subsequent reduction of Ag ions could be selectively performed in the inner space confined by Pt nanoframes and the resulting Ag-Au-Ag nanorods exhibited characteristic LSPR modes originating from each block component (in a transverse direction) and SPR coupling (in a longitudinal direction). The high quality of the resulting multiblock nanorods enabled observation of the longitudinal quadrupole mode that was induced by Ag-Au SPR coupling in a long axis. The mode exhibited high sensitivity in accordance with the change in the surrounding media, demonstrating great potential for sensor applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03484e

  16. Comparative study of electroless copper deposition based on the seed layers of Pd, PtPd and AuPd

    International Nuclear Information System (INIS)

    The article reports on electroless deposition of copper films onto p-silicon (1 0 0) using different seed (co-seed) layers of Pd, PtPd and AuPd. The dependence of the compositions and morphologies of different seed layers on resultant Cu films were comparatively studied in detail by atomic force microscopy (AFM), field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). The activities of electroless copper deposition on the p-silicon (1 0 0) with different seed (co-seed) layers were evaluated by polarization curve. It is concluded that the bimetallic AuPd seed displayed the highest catalytic activity for electroless copper deposition, and followed by the order of PtPd > Pd.

  17. Hollow Ag/Pd triangular nanoplate: a novel activator for electroless nickel deposition

    International Nuclear Information System (INIS)

    Hollow Ag/Pd triangular nanoplates have been successfully prepared by a galvanic displacement reaction, in which added Pd2+ ions react with Ag triangular nanoplates as templates. By altering the sizes of the Ag nanotemplates, Ag/Pd triangular nanoplates of different sizes can be prepared. Additionally, the large alloy nanoplates show maximum electrochemical activity when Ag/Pd triangular nanoplates of different sizes are applied as new activators for electroless nickel deposition

  18. Using supported Au nanoparticles as starting material for preparing uniform Au/Pd bimetallic catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Villa, Alberto [Universita di Milano, Italy; Prati, Laura [Universita di Milano, Italy; Su, Dangshen [Fritz Haber Institute of the Max Planck Society, Berlin, Germany; Wang, Di [Fritz Haber Institute of the Max Planck Society, Berlin, Germany; Veith, Gabriel M [ORNL

    2010-01-01

    One of the best methods for producing bulk homogeneous (composition) supported bimetallic AuPd clusters involves the immobilization of a protected Au seed followed by the addition of Pd. This paper investigates the importance of this gold seed in controlling the resulting bimetallic AuPd clusters structures, sizes and catalytic activities by investigating three different gold seeds. Uniform Au-Pd alloy were obtained when a steric/electrostatic protecting group, poly(vinyl alcohol) (PVA), was used to form the gold clusters on activated carbon (AC). In contrast Au/AC precursors prepared using Au nanoparticles with only electrostatic stabilization (tetrakis(hydroxypropyl)phosphonium chloride (THPC)), or no stabilization (magnetron sputtering) produced inhomogeneous alloys and segregation of the gold and palladium. The uniform alloyed catalyst (Pd{at}Au{sub PVA}/AC) is the most active and selective catalyst, while the inhomogenous catalysts are less active and selective. Further study of the PVA protected Au clusters revealed that the amount of PVA used is also critical for the preparation of uniform alloyed catalyst, their stability, and their catalytic activity.

  19. Thermal induced structural transformation of bimetallic AuPd nanoparticles

    International Nuclear Information System (INIS)

    High Angle Annular Dark Field Scanning Transmission Electron Microscope (HAADF-STEM) has been employed for the study of thermal effects of structural transformation of AuPd nanoparticles produced by physical vapour deposition. Depending on the duration of annealing at a temperature of 500 K, atomic resolved imaging analysis reveals the formation of various structure morphologies from the ordered L12 superlattice to the core-shell structure. The effects of Pd-oxides are also discussed

  20. The production of 103Pd and 109Cd from a proton irradiated tandem natAg/natAg targets

    International Nuclear Information System (INIS)

    This paper describes a new method for the production of 103Pd and 109Cd using the 66 MeV proton beam of iThemba LABS on a tandem natural silver target (Ag/Ag). The radiochemical separation of the Pd radionuclides (103Pd, 100Pd) from the bulk natAg was done using a Chelex-100 chelating resin column. The recovery of 103Pd from the irradiated natAg target was found to be >98 % without any Ag or Rh impurities detected. The radiochemical separation of 109Cd from the bulk natAg target was done by the precipitation of Ag ions by Cu followed by the separation of 109Cd, traces of Ag, Cu2+ and Rh using a AG1-X10 anion exchange resin column. The recovery yield of 109Cd was >99 % without any Ag or Rh impurities detected. (author)

  1. Controllable galvanic synthesis of triangular Ag-Pd alloy nanoframes for efficient electrocatalytic methanol oxidation.

    Science.gov (United States)

    Xu, Lin; Luo, Zhimin; Fan, Zhanxi; Yu, Sijia; Chen, Junze; Liao, Yusen; Xue, Can

    2015-06-01

    Triangular Ag-Pd alloy nanoframes were successfully synthesized through galvanic replacement by using Ag nanoprisms as sacrificial templates. The ridge thickness of the Ag-Pd alloy nanoframes could be readily tuned by adjusting the amount of the Pd source during the reaction. These obtained triangular Ag-Pd alloy nanoframes exhibit superior electrocatalytic activity for the methanol oxidation reaction as compared with the commercial Pd/C catalyst due to the alloyed Ag-Pd composition as well as the hollow-framed structures. This work would be highly impactful in the rational design of future bimetallic alloy nanostructures with high catalytic activity for fuel cell systems. PMID:25925988

  2. Synthesis of Pt, Pd, Pt/Ag and Pd/Ag nanoparticles by microwave-polyol method

    Indian Academy of Sciences (India)

    Kirti Patel; Sudhir Kapoor; Devilal Purshottam Dave; Tulsi Mukherjee

    2005-07-01

    Pt, Pd, Pt-Ag and Pd-Ag bimetallic nanoparticles were synthesized in ethylene glycol and glycerol using the microwave technique in the presence of a stabilizer poly(N-vinylpyrrolidone) (PVP). It has been observed that PVP is capable of complexing and stabilizing nanoparticles. Mixed clusters were formed by simultaneous reduction of the metal ions. The clusters were characterized using UV-Vis spectra, XRD and dynamic light scattering. To understand the mechanism of formation of mixed nanoparticles, several experimental parameters such as in situ irradiation of mixed metal salts and mixing of individual sols were attempted.

  3. Ordered phase formation and diffusion composition path in Cu3Au/Pd couple

    International Nuclear Information System (INIS)

    EDX-TEM technique, IKL-ALCHEMI and Monte Carlo simulation were employed to reveal the relation between diffusion composition path and the ordered structures in Cu3Au/Pd diffusion couple annealed at 573 K. A Cu3Au layer including Pd, a CuAu layer including Pd, a CuPd layer and a Pd layer including Cu existed in sequence between Cu3Au and Pd. The Au concentration increased by up-hill diffusion from the Cu3Au layer to the CuAu layer, whereas Au scarcely diffused from the CuAu into the CuPd layer. The diffusion composition path deviated from the Cu3Au-Pd line in the Cu-Au-Pd Gibbs triangle and exhibited an 'S-shaped' curve through the CuAu and CuPd existence regions. The atomic configurations in the L10-type phase were highly ordered and consistent with the equilibrium state. In the Monte Carlo simulation, diffusion couples were virtually produced. The diffusion composition paths, Fourier power spectra and Warren-Cowley parameters were estimated in this way. The strong ordering interactions of the Cu-Au pair and Cu-Pd pair in the first nearest neighbor and the high activation barrier for migration of Au reproduced experimental results

  4. Photoreduction of Ag{sup +} in Ag/Ag{sub 2}S/Au memristor

    Energy Technology Data Exchange (ETDEWEB)

    Mou, N.I.; Tabib-Azar, M., E-mail: azar.m@utah.edu

    2015-06-15

    Highlights: • The effect of illumination on the operating voltages and switching speed of Ag/Ag{sub 2}S/Au memristors is studied • Illumination decreased the average switching time from high to low resistance states by ∼19% and decreased the turn-off voltages dramatically from −0.8 V to −0.25 V. • Photo-induced reduction of silver in Ag{sub 2}S may be used in three dimensional optical memories that can be electronically read and reset. • Illumination changed sulfur's valency and modified its oxidation/reduction potential. - Abstract: Silver halides and chalcogenides are excellent memristor materials that have been extensively used in the past as photosensitive layers in photography. Here we examine the effect of illumination on the operating voltages and switching speed of Ag/Ag{sub 2}S/Au memristors using a green laser (473–523 nm). Our results indicate that illumination decreases the average switching time from high to low resistance states by ∼19% and decreases the turn-off voltages dramatically from −0.8 V to −0.25 V that we attribute to the change in sulfur valency and a photo-induced change in its oxidation/reduction potential. Photo-induced reduction of silver in Ag{sub 2}S may be used in three dimensional optical memories that can be electronically read and reset.

  5. Hydrogen evolution on Au(111) covered with submonolayers of Pd

    DEFF Research Database (Denmark)

    Björketun, Mårten; Karlberg, Gustav; Rossmeisl, Jan;

    2011-01-01

    . The energetics of adsorption and desorption of hydrogen on/from different types of sites on the Pd-Au(111) surface are assessed by means of density functional theory calculations combined with thermodynamic modeling. Based on the density functional and Monte Carlo data, the hydrogen evolution activity...

  6. Propiedades de aleaciones Ag-Pd para usos odontológicos

    Directory of Open Access Journals (Sweden)

    Basualto, J.

    1996-10-01

    Full Text Available In this search for economically alternative alloys for odontological uses, three complex Ag-Pd alloys, Ag-Pd-Au-Cu type, are studied: two experimental alloys and one commercial product. Chemical and mechanical properties were obtained for these alloys and a comparative analysis of these results was made. The cost, important factor, is established in relation to the materials cost of the commercial product. Vickers hardness values obtained from Ag-Pd alloys with different heat treatments allow to show their versatility in relation to restorative uses and to classify them according to standard practice. Electrochemical and tarnish behavior were obtained that allow to compare the trends. It is concluded that chemical properties are acceptable, when they are compared with odontological alloys of reference. Experimental alloys A1 y A2 were installed in mouth, over a year ago, with satisfactory results until now, which validate previous laboratory predictions.

    En la búsqueda de aleaciones para usos odontológicos, económicamente alternativas, se trabaja con tres aleaciones Ag-Pd complejas, del tipo Ag-Pd-Au-Cu-Otros, dos aleaciones experimentales y un producto comercial. Se determinan las propiedades mecánicas y químicas de estas aleaciones y se hace un análisis comparativo de los resultados. El costo, factor importante, se establece con relación a los materiales del producto comercial. Se determina la dureza Vickers de las aleaciones Ag-Pd con diversos tratamientos térmicos, lo que permite mostrar su versatilidad en cuanto a usos restauradores y clasificarlas según norma. Se determina su comportamiento electroquímico y la resistencia a la pigmentación, lo que permite comparar las tendencias exhibidas. Se concluye que las propiedades químicas son aceptables cuando se compara con aleaciones odontológicas de referencia. Se instalaron en boca aleaciones experimentales A1 y A2, hace más de un año, con resultados satisfactorios hasta

  7. Selective Hydrogenation of Acetylene over Pd, Au, and PdAu Supported Nanoparticles

    Science.gov (United States)

    Walker, Michael P.

    The removal of trace amounts of acetylene in ethylene streams is a high-volume industrial process that must possess high selectivity of alkyne hydrogenation over hydrogenation of alkenes. Current technology uses metallic nanoparticles, typically palladium or platinum, for acetylene removal. However, problems arise due to the deactivation of the catalysts at high temperatures as well as low selectivities at high conversions. Pore expanded MCM-41 is synthesized via a two-step strategy in which MCM-41 was prepared via cetyltrimethylammonium bromide (CTMABr) followed by the hydrothermal treatment with N,N-dimethyldecylamine (DMDA). This material was washed with ethanol to remove DMDA, or calcined to remove both surfactants. PE-MCM-41 based materials were impregnated with palladium, gold, and palladium-gold nanoparticles. The removal of DMDA had an effect on both the conversion and selectivity, in which they were found to drop significantly. However, by using the bimetallic PdAu catalysts, higher selectivity could be achieved due to increased electron density.

  8. Thermodynamic description of Au-Ag-Si ternary system

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Based on the available experimental information, the Ag-Si binary system was thermodynamically assessed using the CALPHAD method. The solution phases, including liquid, fcc-Al and diamond-A4, were modeled as substitutional solutions, of which the excess Gibbs energies were expressed by Redlich-Kister polynomial functions. Combined with previous assessment of the Ag-Au and Au-Si binary systems, thermodynamic description of the Au-Ag-Si ternary system was performed to reproduce the reported phase equilibria. Thermodynamic properties of liquid alloys, liquidus projection and several vertical and isothermal sections of this ternary system were calculated, which are in reasonable agreement with the reported experimental data.

  9. Highly Active Carbon Supported Pd-Ag Nanofacets Catalysts for Hydrogen Production from HCOOH.

    Science.gov (United States)

    Wang, Wenhui; He, Ting; Liu, Xuehua; He, Weina; Cong, Hengjiang; Shen, Yangbin; Yan, Liuming; Zhang, Xuetong; Zhang, Jinping; Zhou, Xiaochun

    2016-08-17

    Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag{hcp}). Then, the Pd-Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd-Ag alloy nanofacets, such as Pd-Ag{111}, Pd-Ag{100}, and Pd-Ag{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd-Ag{hcp} > Pd-Ag{111} > Pd-Ag{100}. Particularly, the activity of Pd-Ag{hcp} is up to an extremely high value, i.e., TOF{hcp} = 19 000 ± 1630 h(-1) at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd-Ag alloy nanocatalyst. The initial activity of Pd-Ag{hcp} even reaches (3.13 ± 0.19) × 10(6) h(-1) at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst. PMID:27454194

  10. Fermi Surfaces of Surface States on Si(111) + Ag, Au

    OpenAIRE

    Crain, J. N.; Altmann, K. N.; Bromberger, Ch.; Himpsel, F. J.

    2002-01-01

    Metallic surface states on semiconducting substrates provide an opportunity to study low-dimensional electrons decoupled from the bulk. Angle resolved photoemission is used to determine the Fermi surface, group velocity, and effective mass for surface states on Si(111)sqrt3xsqrt3-Ag, Si(111)sqrt3x sqrt3-Au, and Si(111)sqrt21xsqrt21-(Ag+Au). For Si(111)sqrt3xsqrt3-Ag the Fermi surface consists of small electron pockets populated by electrons from a few percent excess Ag. For Si(111)sqrt21xsqrt...

  11. Controlled Synthesis of Au@AgAu Yolk-Shell Cuboctahedra with Well-Defined Facets.

    Science.gov (United States)

    Londono-Calderon, Alejandra; Bahena, Daniel; Yacaman, Miguel J

    2016-08-01

    The synthesis of Au@AgAu yolk-shell cuboctahedra nanoparticles formed by galvanic replacement in a seed-mediated method is described. Initially, single-crystal Au seeds are used for the formation of Au@Ag core-shell nanocubes, which serve as the template material for the deposition of an external Au layer. The well-controlled synthesis yields the formation of cuboctahedra nanoparticles with smooth inner and outer Au/Ag surfaces. The deposition/oxidation process is described to understand the formation of cuboctahedra and octahedra nanoparticles. The Au core maintains the initial morphology of the seed and remains static at the center of the yolk-shell because of residual Ag. Structural analysis of the shell indicates intrinsic stacking faults (SFs) near the surface. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) compositional analysis show an Au-Ag nonordered alloy forming the shell. The three-dimensional structure of the nanoparticles presented open facets on the [111] as observed by electron tomography SIRT reconstruction over a stack of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images. The geometrical model was validated by analyzing the direction of streaks in coherent nanobeam diffraction (NBD). The catalytic activity was evaluated using a model reaction based on the reduction of 4-nitrophenol (4-NTP) by NaBH4 in the presence of Au@AgAu yolk-shell nanoparticles. PMID:27385583

  12. Triangular Ag-Pd alloy nanoprisms: rational synthesis with high-efficiency for electrocatalytic oxygen reduction

    Science.gov (United States)

    Xu, Lin; Luo, Zhimin; Fan, Zhanxi; Zhang, Xiao; Tan, Chaoliang; Li, Hai; Zhang, Hua; Xue, Can

    2014-09-01

    We report the generation of triangular Ag-Pd alloy nanoprisms through a rationally designed synthetic strategy based on silver nanoprisms as sacrificial templates. The galvanic replacement between Ag nanoprisms and H2PdCl4 along with co-reduction of Ag+/Pd2+ is responsible for the formation of final prismatic Ag-Pd alloy nanostructures. Significantly, these Ag-Pd alloy nanoprisms exhibited superior electrocatalytic activity for the oxygen reduction reaction (ORR) as compared with the commercial Pd/C catalyst. Such a high catalytic activity is attributed to not only the alloyed Ag-Pd composition but also the dominant {111} facets of the triangular Ag-Pd nanoprisms. This work demonstrates the rational design of bimetallic alloy nanostructures with control of selective crystal facets that are critical to achieve high catalytic activity for fuel cell systems.We report the generation of triangular Ag-Pd alloy nanoprisms through a rationally designed synthetic strategy based on silver nanoprisms as sacrificial templates. The galvanic replacement between Ag nanoprisms and H2PdCl4 along with co-reduction of Ag+/Pd2+ is responsible for the formation of final prismatic Ag-Pd alloy nanostructures. Significantly, these Ag-Pd alloy nanoprisms exhibited superior electrocatalytic activity for the oxygen reduction reaction (ORR) as compared with the commercial Pd/C catalyst. Such a high catalytic activity is attributed to not only the alloyed Ag-Pd composition but also the dominant {111} facets of the triangular Ag-Pd nanoprisms. This work demonstrates the rational design of bimetallic alloy nanostructures with control of selective crystal facets that are critical to achieve high catalytic activity for fuel cell systems. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr03600j

  13. Study on antibacterial activity of chemically synthesized PANI-Ag-Au nanocomposite

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • New method of synthesizing PANI-Ag-Au nanocomposite. • Surface Plasmon resonance and formation of composite at nano level were analyzed. • HR-TEM study revealed uniform distribution of nanoparticles. • PANI-Ag-Au nanocomposite exhibited good antibacterial activity. - Abstract: Pristine polyaniline (PANI), PANI-Ag, PANI-Au and PANI-Ag-Au nanocomposites have been successfully synthesized by chemical oxidative polymerization method using aniline as monomer, ammonium persulphate as oxidant and metal (Ag, Au and Ag-Au) colloids. UV-Vis analysis exhibited surface Plasmon resonances of Ag, Au, Ag-Au nanoparticles. FT-IR spectra revealed the shift in peak position of N-H stretching. X-ray diffraction (XRD) results confirm the presence of Ag, Au and Au-Ag nanoparticles. HR-TEM images show nanosizes of Ag, Au, Ag-Au and the incorporation of such nanoparticles into the PANI matrix. Pristine PANI, PANI-Ag, PANI-Au and PANI-Ag-Au nanocomposites were tested for antibacterial activity by agar well diffusion method. PANI-Ag-Au nanocomposite exhibited higher antibacterial activity against both gram-positive [Streptococcus sp. (MTCC 890), Staphylococcus sp. (MTCC 96)] and gram-negative bacteria [Escherichia coli (MTCC 1671) and Klebsiella sp. (MTCC 7407)] when compared with PANI-Ag nanocomposite, PANI-Au nanocomposite and pristine PANI. The novelty of this study is the polymer-bimetal synthesis and its antibacterial potential

  14. Study on antibacterial activity of chemically synthesized PANI-Ag-Au nanocomposite

    Energy Technology Data Exchange (ETDEWEB)

    Boomi, Pandi [Department of Industrial Chemistry, School of Chemical Sciences, Alagappa University, Karaikudi 630 003, Tamil Nadu (India); Prabu, Halliah Gurumallesh, E-mail: hgprabu2010@gmail.com [Department of Industrial Chemistry, School of Chemical Sciences, Alagappa University, Karaikudi 630 003, Tamil Nadu (India); Manisankar, Paramasivam [Department of Industrial Chemistry, School of Chemical Sciences, Alagappa University, Karaikudi 630 003, Tamil Nadu (India); Ravikumar, Sundaram [Department of Oceanography and Coastal Area Studies, School of Marine Sciences, Alagappa University, Thondi Campus 623 409, Tamil Nadu (India)

    2014-05-01

    Graphical abstract: - Highlights: • New method of synthesizing PANI-Ag-Au nanocomposite. • Surface Plasmon resonance and formation of composite at nano level were analyzed. • HR-TEM study revealed uniform distribution of nanoparticles. • PANI-Ag-Au nanocomposite exhibited good antibacterial activity. - Abstract: Pristine polyaniline (PANI), PANI-Ag, PANI-Au and PANI-Ag-Au nanocomposites have been successfully synthesized by chemical oxidative polymerization method using aniline as monomer, ammonium persulphate as oxidant and metal (Ag, Au and Ag-Au) colloids. UV-Vis analysis exhibited surface Plasmon resonances of Ag, Au, Ag-Au nanoparticles. FT-IR spectra revealed the shift in peak position of N-H stretching. X-ray diffraction (XRD) results confirm the presence of Ag, Au and Au-Ag nanoparticles. HR-TEM images show nanosizes of Ag, Au, Ag-Au and the incorporation of such nanoparticles into the PANI matrix. Pristine PANI, PANI-Ag, PANI-Au and PANI-Ag-Au nanocomposites were tested for antibacterial activity by agar well diffusion method. PANI-Ag-Au nanocomposite exhibited higher antibacterial activity against both gram-positive [Streptococcus sp. (MTCC 890), Staphylococcus sp. (MTCC 96)] and gram-negative bacteria [Escherichia coli (MTCC 1671) and Klebsiella sp. (MTCC 7407)] when compared with PANI-Ag nanocomposite, PANI-Au nanocomposite and pristine PANI. The novelty of this study is the polymer-bimetal synthesis and its antibacterial potential.

  15. Fermi surfaces of surface states on Si(111)-Ag, Au

    Science.gov (United States)

    Crain, J. N.; Altmann, K. N.; Bromberger, C.; Himpsel, F. J.

    2002-11-01

    Metallic surface states on semiconducting substrates provide an opportunity to study low-dimensional electrons decoupled from the bulk. Angle resolved photoemission is used to determine the Fermi surface, group velocity, and effective mass for surface states on Si(111)(3)×(3)-Ag, Si(111)(3)×(3)-Au, and Si(111)(21)×(21)-(Ag+Au). For Si(111)(3)×(3)-Ag the Fermi surface consists of small electron pockets populated by electrons from a few % excess Ag. For Si(111)(21)×(21)-(Ag+Au) the pockets increase their size corresponding to a filling by three electrons per unit cell. The (21)×(21) superlattice leads to an intricate surface umklapp pattern and to minigaps of 110 meV, giving an interaction potential of 55 meV for the (21)×(21) superlattice.

  16. PdAu/C catalysts prepared by plasma sputtering for the electro-oxidation of glycerol

    OpenAIRE

    Mougenot, Mathieu; Caillard, Amaël; Simoes, Mario; Baranton, Steve; Coutanceau, Christophe; Brault, Pascal

    2011-01-01

    Co-sputtered Pd0.7Au0.3 catalyst and alternate sputtered Pd0.35Au0.3Pd0.35 and Au0.15Pd0.7Au0.15 materials were prepared by plasma deposition of Au and Pd atoms on a carbon diffusion layer. Atomic composition and metal loadings were evaluated from EDX and RBS, respectively. The low amount of metal deposited and the resulting low metallic film thickness made TEM and XRD characterizations difficult to perform, therefore, catalyst microstructures and surface compositions were determined from ele...

  17. Ti-Ag-Pd alloy with good mechanical properties and high potential for biological applications.

    Science.gov (United States)

    Zadorozhnyy, V Yu; Shi, X; Gorshenkov, M V; Kozak, D S; Wada, T; Louzguine-Luzgin, D V; Inoue, A; Kato, H

    2016-01-01

    Ti-based alloys containing Ag were produced by tilt-casting method and their properties were studied. Even in its as-cast state, Ti94Ag3Pd3 showed relatively high tensile properties, good electrochemical behavior, and good biocompatibility. The relatively good mechanical properties of the as-cast α-Ti-type Ti94Ag3Pd3 alloy (tensile strength up to 850 MPa and elongation of ~10%) can be explained by its severely deformed, fine crystalline structure. The high biocompatibility of Ti94Ag3Pd3 can be explained by the Ag-Pd interaction, which inhibits the release of Ag ions from the surface. Ag, in combination with Pd has no toxic effects and demonstrates useful antimicrobial properties. The Ti94Ag3Pd3 alloy shows a good potential to be applied as a biomedical implant alloy. PMID:27122177

  18. Photoreduction of Ag+ in Ag/Ag2S/Au memristor

    Science.gov (United States)

    Mou, N. I.; Tabib-Azar, M.

    2015-06-01

    Silver halides and chalcogenides are excellent memristor materials that have been extensively used in the past as photosensitive layers in photography. Here we examine the effect of illumination on the operating voltages and switching speed of Ag/Ag2S/Au memristors using a green laser (473-523 nm). Our results indicate that illumination decreases the average switching time from high to low resistance states by ∼19% and decreases the turn-off voltages dramatically from -0.8 V to -0.25 V that we attribute to the change in sulfur valency and a photo-induced change in its oxidation/reduction potential. Photo-induced reduction of silver in Ag2S may be used in three dimensional optical memories that can be electronically read and reset.

  19. Au/Pd core-shell nanoparticles with varied hollow Au cores for enhanced formic acid oxidation

    Science.gov (United States)

    Hsu, Chiajen; Huang, Chienwen; Hao, Yaowu; Liu, Fuqiang

    2013-03-01

    A facile method has been developed to synthesize Au/Pd core-shell nanoparticles via galvanic replacement of Cu by Pd on hollow Au nanospheres. The unique nanoparticles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet-visible spectroscopy, and electrochemical measurements. When the concentration of the Au solution was decreased, grain size of the polycrystalline hollow Au nanospheres was reduced, and the structures became highly porous. After the Pd shell formed on these Au nanospheres, the morphology and structure of the Au/Pd nanoparticles varied and hence significantly affected the catalytic properties. The Au/Pd nanoparticles synthesized with reduced Au concentrations showed higher formic acid oxidation activity (0.93 mA cm-2 at 0.3 V) than the commercial Pd black (0.85 mA cm-2 at 0.3 V), suggesting a promising candidate as fuel cell catalysts. In addition, the Au/Pd nanoparticles displayed lower CO-stripping potential, improved stability, and higher durability compared to the Pd black due to their unique core-shell structures tuned by Au core morphologies.

  20. Compositional changes of Pd-Au bimetallic nanoclusters upon hydrogenation

    OpenAIRE

    Di Vece, M; Bals, S.; Verbeeck, J.; Lievens, P.; van Tendeloo, G.

    2009-01-01

    Changes in the size distribution and composition of bimetallic Pd-Au nanoclusters have been observed after hydrogen exposure. This effect is caused by hydrogen-induced Ostwald ripening whereby the hydrogen reduces the binding energy of the cluster atoms leading to their detachment from the cluster. The composition changes due to a difference in mobility of the detached palladium and gold atoms on the surface. Fast palladium atoms contribute to the formation of larger nanoclusters, while the s...

  1. Enhanced optical responses of Au@Pd core/shell nanobars.

    Science.gov (United States)

    Zhang, Ke; Xiang, Yanjuan; Wu, Xiaochun; Feng, Lili; He, Weiwei; Liu, Jianbo; Zhou, Weiya; Xie, Sishen

    2009-01-20

    A Pd nanoshell was epitaxially grown on a Au nanorod (NR) via simple seed-mediated growth. Compared with the cylindrical shape of the Au NR, the Au core/Pd shell (Au@Pd) nanorods change to a rectangular shape due to the disappearance of {110} facets. The Au NRs exhibit a strong longitudinal surface plasmon resonance (LSPR). As Pd is deposited, damping and broadening occur to the LSPR band. Interestingly, the LSPR band maximum first shows a small red-shift (ca. 40 nm) which then is followed by a blue-shift as the amount of Pd is increased. A thickness-dependent LSPR feature of the Pd shell is believed to contribute to the shift. At a thinner Pd thickness, the Au@Pd nanobars exhibit a well-defined LSPR band in the visible and near-infrared region, which demonstrates a higher dielectric sensitivity than that of the corresponding Au NRs. It thus opens up the potential of Pd nanostructures for SPR-based sensing. Investigations on the surface-enhanced Raman scattering (SERS) indicate that the SERS activities of the Au@Pd nanobars at thicknesses smaller than 2.5 nm mainly originate from the Au cores; thus, the SERS activities can be improved by tuning the aspect ratio of the Au core and/or the Pd shell thickness. PMID:19090666

  2. Au/Pd core-shell nanoparticles with varied hollow Au cores for enhanced formic acid oxidation

    OpenAIRE

    Hsu, Chiajen; Huang, Chienwen; Hao, Yaowu; Liu, Fuqiang

    2013-01-01

    A facile method has been developed to synthesize Au/Pd core-shell nanoparticles via galvanic replacement of Cu by Pd on hollow Au nanospheres. The unique nanoparticles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet–visible spectroscopy, and electrochemical measurements. When the concentration of the Au solution was decreased, grain size of the polycrystalline hollow Au nanospheres was reduced, and the structures became ...

  3. Carbon nanofiber supported bimetallic PdAu nanoparticles for formic acid electrooxidation

    Science.gov (United States)

    Qin, Yuan-Hang; Jiang, Yue; Niu, Dong-Fang; Zhang, Xin-Sheng; Zhou, Xing-Gui; Niu, Li; Yuan, Wei-Kang

    2012-10-01

    Carbon nanofiber (CNF) supported PdAu nanoparticles are synthesized with sodium citrate as the stabilizing agent and sodium borohydride as the reducing agent. High resolution transmission electron microscopy (HRTEM) characterization indicates that the synthesized PdAu particles are well dispersed on the CNF surface and X-ray diffraction (XRD) characterization indicates that the alloying degree of the synthesized PdAu nanoparticles can be improved by adding tetrahydrofuran to the synthesis solution. The results of electrochemical characterization indicate that the addition of Au can promote the electrocatalytic activity of Pd/C catalyst for formic acid oxidation and the CNF supported high-alloying PdAu catalyst possesses better electrocatalytic activity and stability for formic acid oxidation than either the CNF supported low-alloying PdAu catalyst or the CNF supported Pd catalyst.

  4. Pd-Au/C catalysts with different alloying degrees for ethanol oxidation in alkaline media

    International Nuclear Information System (INIS)

    High alloyed Pd-Au/C catalyst is prepared through a rate-limiting strategy in water/ethylene glycol solution. Pd/C and low alloyed Pd-Au/C catalysts are prepared with trisodium citrate and sodium borohydride as stabilizing and reducing agents, respectively. Transmission electron microscopy (TEM) shows that the synthesized Pd(Au) particles are well dispersed on the catalysts. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) show that the high alloyed Pd-Au/C catalyst presents a relatively homogenous structure while the low alloyed Pd-Au/C catalyst presents a Pd-rich shell/Au-rich core structure. Electrochemical characterization shows that the low alloyed Pd-Au/C catalyst exhibits the best catalytic activity for ethanol oxidation reaction (EOR) in alkaline media, which could be attributed to its relatively large exposed Pd surface area as compared with the high alloyed Pd-Au/C catalyst due to its Pd-rich shell structure and its enhanced adsorption of OHads as compared with Pd/C catalyst due to its core-shell structure

  5. Study on antibacterial activity of chemically synthesized PANI-Ag-Au nanocomposite

    Science.gov (United States)

    Boomi, Pandi; Prabu, Halliah Gurumallesh; Manisankar, Paramasivam; Ravikumar, Sundaram

    2014-05-01

    Pristine polyaniline (PANI), PANI-Ag, PANI-Au and PANI-Ag-Au nanocomposites have been successfully synthesized by chemical oxidative polymerization method using aniline as monomer, ammonium persulphate as oxidant and metal (Ag, Au and Ag-Au) colloids. UV-Vis analysis exhibited surface Plasmon resonances of Ag, Au, Ag-Au nanoparticles. FT-IR spectra revealed the shift in peak position of N-H stretching. X-ray diffraction (XRD) results confirm the presence of Ag, Au and Au-Ag nanoparticles. HR-TEM images show nanosizes of Ag, Au, Ag-Au and the incorporation of such nanoparticles into the PANI matrix. Pristine PANI, PANI-Ag, PANI-Au and PANI-Ag-Au nanocomposites were tested for antibacterial activity by agar well diffusion method. PANI-Ag-Au nanocomposite exhibited higher antibacterial activity against both gram-positive [Streptococcus sp. (MTCC 890), Staphylococcus sp. (MTCC 96)] and gram-negative bacteria [Escherichia coli (MTCC 1671) and Klebsiella sp. (MTCC 7407)] when compared with PANI-Ag nanocomposite, PANI-Au nanocomposite and pristine PANI. The novelty of this study is the polymer-bimetal synthesis and its antibacterial potential.

  6. A simple approach for facile synthesis of Ag, anisotropic Au and bimetallic (Ag/Au) nanoparticles using cruciferous vegetable extracts

    International Nuclear Information System (INIS)

    We present a simple and straightforward approach for the synthesis and stabilization of relatively monodisperse Ag, Au and bimetallic (Ag/Au) nanoparticles by using cruciferous vegetable (green/red) extracts by simply adjusting the pH environment in the aqueous medium. The vegetable extracts act both as reducing and capping agents. The monometallic and bimetallic nanoparticles of Ag and Au so obtained were characterized by UV–visible spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS) and transmission electron microscopy (TEM). It is shown that red cabbage extract can be used for the preparation of anisotropic Au nanoparticles. The formation of Au anisotropic nanoparticles was found to depend on a number of environmental factors, such as the pH of the reaction medium, reaction time, and initial reactant concentrations. Additionally, it is shown that these extract-stabilized Au and Ag nanoparticles can be used as a seed for preparation of bimetallic Au/Ag nanoparticles. For bimetallic alloy nanoparticles the absorption peak was observed between the two maxima of the corresponding metallic particles. The surface plasmon absorption maxima for bimetallic nanoparticles changed linearly with increasing Au mole ratio content in various alloy compositions. It has been shown that the formation of hollow Au spheres depends on the experimental conditions. - Graphical abstract: TEM image of gold nanoparticles at pH 3.27 formed by red cabbage extract. Highlights: ► First report on the reactivity of the extracts toward metal ions using a spectrophotometric technique. ► Red cabbage extract has better reducing properties than green cabbage extract. ► Red cabbage extract can reduce metal ions at any pH. ► Reduction of metal ions can have important consequences in the study of soil chemistry.

  7. A simple approach for facile synthesis of Ag, anisotropic Au and bimetallic (Ag/Au) nanoparticles using cruciferous vegetable extracts

    Energy Technology Data Exchange (ETDEWEB)

    Jacob, Jasmine; Mukherjee, Tulsi; Kapoor, Sudhir, E-mail: sudhirk@barc.gov.in

    2012-10-01

    We present a simple and straightforward approach for the synthesis and stabilization of relatively monodisperse Ag, Au and bimetallic (Ag/Au) nanoparticles by using cruciferous vegetable (green/red) extracts by simply adjusting the pH environment in the aqueous medium. The vegetable extracts act both as reducing and capping agents. The monometallic and bimetallic nanoparticles of Ag and Au so obtained were characterized by UV-visible spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS) and transmission electron microscopy (TEM). It is shown that red cabbage extract can be used for the preparation of anisotropic Au nanoparticles. The formation of Au anisotropic nanoparticles was found to depend on a number of environmental factors, such as the pH of the reaction medium, reaction time, and initial reactant concentrations. Additionally, it is shown that these extract-stabilized Au and Ag nanoparticles can be used as a seed for preparation of bimetallic Au/Ag nanoparticles. For bimetallic alloy nanoparticles the absorption peak was observed between the two maxima of the corresponding metallic particles. The surface plasmon absorption maxima for bimetallic nanoparticles changed linearly with increasing Au mole ratio content in various alloy compositions. It has been shown that the formation of hollow Au spheres depends on the experimental conditions. - Graphical abstract: TEM image of gold nanoparticles at pH 3.27 formed by red cabbage extract. Highlights: Black-Right-Pointing-Pointer First report on the reactivity of the extracts toward metal ions using a spectrophotometric technique. Black-Right-Pointing-Pointer Red cabbage extract has better reducing properties than green cabbage extract. Black-Right-Pointing-Pointer Red cabbage extract can reduce metal ions at any pH. Black-Right-Pointing-Pointer Reduction of metal ions can have important consequences in the study of soil chemistry.

  8. Ag/Pd core-shell nanoparticles by a successive method: Pulsed laser ablation of Ag in water and reduction reaction of PdCl2

    International Nuclear Information System (INIS)

    In this study Ag/Pd nanoparticles (NPs) have been fabricated by a successive method; first, colloids of Ag nanoparticles (NPs) have been prepared in water by pulsed laser ablation in liquid (PLAL) method. Then PdCl2 solution (up to 0.2 g/l) were added to the as-prepared or aged colloidal Ag NPs. Characterizations were done using UV–vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmissions electron microscopy (TEM) techniques. Spectroscopy data showed that surface plasmon resonance (SPR) peaks of as-prepared Ag NPs at about λ = 400 nm were completely extinguished after addition of PdCl2 solution while this effect was not observed when aged Ag NPs are used. XRD and XPS results revealed that by addition of the PdCl2 solution into the as-prepared Ag NPs, metallic palladium, and silver chloride composition products are generated. TEM images revealed that as a result of this reaction, single and core-shell nanoparticles are obtained and their average sizes are 2.4 nm (Ag) and 3.2 nm (Ag/Pd). The calculated d-spacing values form XRD data with observations on high magnification TEM images were able to explain the chemical nature of different parts of Ag/Pd NPs.

  9. Ethanol electro-oxidation in an alkaline medium using Pd/C, Au/C and PdAu/C electrocatalysts prepared by electron beam irradiation

    International Nuclear Information System (INIS)

    Carbon-supported Pd, Au and bimetallic PdAu (Pd:Au 90:10, 50:50 and 30:70 atomic ratios) electrocatalysts were prepared using electron beam irradiation. The obtained materials were characterized by energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and transmission electron microscopy (TEM), and their catalytic activities toward ethanol electro-oxidation were evaluated in an alkaline medium using electrochemical techniques, in situ attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR) analysis and a single alkaline direct ethanol fuel cell (ADEFC). EDX analyses showed that the actual Pd:Au atomic ratios were very similar to the nominal ones. X-ray diffractograms of PdAu/C electrocatalysts evidenced the presence of Pd-rich (fcc) and Au-rich (fcc) phases. TEM analysis showed a homogeneous dispersion of nanoparticles on the carbon support, with an average size in the range of 3–5 nm and broad size distributions. Cyclic voltammetry (CV) and chronoamperometry (CA) experiments revealed the superior ambient activity toward ethanol electro-oxidation of PdAu/C electrocatalysts with Pd:Au ratios of 90:10 and 50:50. In situ ATR-FTIR spectroscopy measurements have shown that the mechanism for ethanol electro-oxidation is dependent on catalyst composition, leading to different reaction products, such as acetaldehyde and acetate, depending on the number of electrons transferred. Experiments on a single ADEFC were conducted between 50 and 90 °C, and the best performance of 44 mW cm−2 in 2.0 mol L−1 ethanol was obtained at 85 °C for the Pd:Au 90:10 catalysts. This superior performance is most likely associated with enhancement of ethanol adsorption on Pd, oxidation of the intermediates, the presence of gold oxide-hydroxyl species, low mean particle diameters and better distribution of particles on the support

  10. Synthesis of ultrathin face-centered-cubic Au@Pt and Au@Pd core-shell nanoplates from hexagonal-close-packed Au square sheets

    KAUST Repository

    Fan, Zhanxi

    2015-03-17

    The synthesis of ultrathin face-centered-cubic (fcc) Au@Pt rhombic nanoplates is reported through the epitaxial growth of Pt on hexagonal-close-packed (hcp) Au square sheets (AuSSs). The Pt-layer growth results in a hcp-to-fcc phase transformation of the AuSSs under ambient conditions. Interestingly, the obtained fcc Au@Pt rhombic nanoplates demonstrate a unique (101)f orientation with the same atomic arrangement extending from the Au core to the Pt shell. Importantly, this method can be extended to the epitaxial growth of Pd on hcp AuSSs, resulting in the unprecedented formation of fcc Au@Pd rhombic nanoplates with (101)f orientation. Additionally, a small amount of fcc (100)f-oriented Au@Pt and Au@Pd square nanoplates are obtained with the Au@Pt and Au@Pd rhombic nanoplates, respectively. We believe that these findings will shed new light on the synthesis of novel noble bimetallic nanostructures. Phase change: Ultrathin Au@Pt and Au@Pd core-shell nanoplates were prepared from Au square sheets. A phase transformation from hexagonal close-packed (hcp) to face-centered cubic (fcc) is observed upon coating the hcp Au square sheets with Pt or Pd under ambient conditions. The prepared fcc Au@Pt and Au@Pd rhombic nanoplates demonstrate unique (101)f orientation (picture shows a typical fcc Au@Pt rhombic nanoplate). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. The synthesis of single PdAu bimetallic nanowire: feasibility study for hydrogen sensing

    International Nuclear Information System (INIS)

    Single PdAu bimetallic nanowires have been synthesized via the sequential processes of electrochemical deposition and dielectrophoresis (DEP). In the first step, Pd/Au grains on predefined Au electrodes were grown by electrochemical deposition and could assist effectively the formation of a single PdAu nanowire with a good directionality by the subsequent DEP process. The synthesized PdAu nanowires have an average of ∼10 at.% of Pd, a good resistance of a few hundred Ω, diameters of 300 nm on average and lengths of up to 15 μm. Based on the single PdAu nanowire, hydrogen detection was demonstrated in the range from 100 to 2500 ppm.

  12. The synthesis of single PdAu bimetallic nanowire: feasibility study for hydrogen sensing

    Energy Technology Data Exchange (ETDEWEB)

    Jo, S Y; Kang, B R; Kim, J T; Ra, H W; Im, Y H, E-mail: yeonhoim@chonbuk.ac.kr [School of Semiconductor and Chemical Engineering and Technology, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)

    2010-02-05

    Single PdAu bimetallic nanowires have been synthesized via the sequential processes of electrochemical deposition and dielectrophoresis (DEP). In the first step, Pd/Au grains on predefined Au electrodes were grown by electrochemical deposition and could assist effectively the formation of a single PdAu nanowire with a good directionality by the subsequent DEP process. The synthesized PdAu nanowires have an average of {approx}10 at.% of Pd, a good resistance of a few hundred {Omega}, diameters of 300 nm on average and lengths of up to 15 {mu}m. Based on the single PdAu nanowire, hydrogen detection was demonstrated in the range from 100 to 2500 ppm.

  13. Hysteresis-free nanoplasmonic pd-au alloy hydrogen sensors

    DEFF Research Database (Denmark)

    Wadell, Carl; Nugroho, Ferry Anggoro Ardy; Lidström, Emil;

    2015-01-01

    hydrogen sensors. By increasing the amount of Au in the alloy nanoparticles up to 25 atom %, we are able to suppress the hysteresis between hydrogen absorption and desorption, thereby increasing the sensor accuracy to below 5% throughout the investigated 1 mbar to 1 bar hydrogen pressure range. Furthermore......, we observe an 8-fold absolute sensitivity enhancement at low hydrogen pressures compared to sensors made of pure Pd, and an improved sensor response time to below one second within the 0-40 mbar pressure range, that is, below the flammability limit, by engineering the nanoparticle size....

  14. Ti/Pd/Ag Contacts to n-Type GaAs for High Current Density Devices

    Science.gov (United States)

    Huo, Pengyun; Rey-Stolle, Ignacio

    2016-06-01

    The metallization stack Ti/Pd/Ag on n-type Si has been readily used in solar cells due to its low metal/semiconductor specific contact resistance, very high sheet conductance, bondability, long-term durability, and cost-effectiveness. In this study, the use of Ti/Pd/Ag metallization on n-type GaAs is examined, targeting electronic devices that need to handle high current densities and with grid-like contacts with limited surface coverage (i.e., solar cells, lasers, or light emitting diodes). Ti/Pd/Ag (50 nm/50 nm/1000 nm) metal layers were deposited on n-type GaAs by electron beam evaporation and the contact quality was assessed for different doping levels (from 1.3 × 1018 cm-3 to 1.6 × 1019 cm-3) and annealing temperatures (from 300°C to 750°C). The metal/semiconductor specific contact resistance, metal resistivity, and the morphology of the contacts were studied. The results show that samples doped in the range of 1018 cm-3 had Schottky-like I- V characteristics and only samples doped 1.6 × 1019 cm-3 exhibited ohmic behavior even before annealing. For the ohmic contacts, increasing annealing temperature causes a decrease in the specific contact resistance ( ρ c,Ti/Pd/Ag ~ 5 × 10-4 Ω cm2). In regard to the metal resistivity, Ti/Pd/Ag metallization presents a very good metal conductivity for samples treated below 500°C ( ρ M,Ti/Pd/Ag ~ 2.3 × 10-6 Ω cm); however, for samples treated at 750°C, metal resistivity is strongly degraded due to morphological degradation and contamination in the silver overlayer. As compared to the classic AuGe/Ni/Au metal system, the Ti/Pd/Ag system shows higher metal/semiconductor specific contact resistance and one order of magnitude lower metal resistivity.

  15. First-principles theory of short-range order in size-mismatched metal alloys: Cu-Au, Cu-Ag, and Ni-Au

    International Nuclear Information System (INIS)

    We describe a first-principles technique for calculating the short-range order (SRO) in disordered alloys, even in the presence of large anharmonic atomic relaxations. The technique is applied to several alloys possessing large size mismatch: Cu-Au, Cu-Ag, Ni-Au, and Cu-Pd. We find the following: (i) The calculated SRO in Cu-Au alloys peaks at (or near) the left-angle 100 right-angle point for all compositions studied, in agreement with diffuse scattering measurements. (ii) A fourfold splitting of the X-point SRO exists in both Cu0.75Au0.25 and Cu0.70Pd0.30, although qualitative differences in the calculated energetics for these two alloys demonstrate that the splitting in Cu0.70Pd0.30 may be accounted for by T=0 K energetics while T≠0 K configurational entropy is necessary to account for the splitting in Cu0.75Au0.25. Cu0.75Au0.25 shows a significant temperature dependence of the splitting, in agreement with recent in situ measurements, while the splitting in Cu0.70Pd0.30 is predicted to have a much smaller temperature dependence. (iii) Although no measurements exist, the SRO of Cu-Ag alloys is predicted to be of clustering type with peaks at the left-angle 000 right-angle point. Streaking of the SRO peaks in the left-angle 100 right-angle and left-angle 1 (1) /(2) 0 right-angle directions for Ag- and Cu-rich compositions, respectively, is correlated with the elastically soft directions for these compositions. (iv) Even though Ni-Au phase separates at low temperatures, the calculated SRO pattern in Ni0.4Au0.6, like the measured data, shows a peak along the left-angle ζ00 right-angle direction, away from the typical clustering-type left-angle 000 right-angle point. (v) The explicit effect of atomic relaxation on SRO is investigated and it is found that atomic relaxation can produce significant qualitative changes in the SRO pattern, changing the pattern from ordering to clustering type, as in the case of Cu-Ag. copyright 1998 The American Physical Society

  16. Phytosynthesis of Au, Ag and Au-Ag bimetallic nanoparticles using aqueous extract and dried leaf of Anacardium occidentale

    Science.gov (United States)

    Sheny, D. S.; Mathew, Joseph; Philip, Daizy

    2011-06-01

    Present study reports a green chemistry approach for the biosynthesis of Au, Ag, Au-Ag alloy and Au core-Ag shell nanoparticles using the aqueous extract and dried powder of Anacardium occidentale leaf. The effects of quantity of extract/powder, temperature and pH on the formation of nanoparticles are studied. The nanoparticles are characterized using UV-vis and FTIR spectroscopies, XRD, HRTEM and SAED analyses. XRD studies show that the particles are crystalline in the cubic phase. The formation of Au core-Ag shell nanoparticles is evidenced by the dark core and light shell images in TEM and is supported by the appearance of two SPR bands in the UV-vis spectrum. FTIR spectra of the leaf powder before and after the bioreduction of nanoparticles are used to identify possible functional groups responsible for the reduction and capping of nanoparticles. Water soluble biomolecules like polyols and proteins are expected to bring about the bio-reduction.

  17. Monodispersed bimetallic PdAg nanoparticles with twinned structures: Formation and enhancement for the methanol oxidation

    Science.gov (United States)

    Yin, Zhen; Zhang, Yining; Chen, Kai; Li, Jing; Li, Wenjing; Tang, Pei; Zhao, Huabo; Zhu, Qingjun; Bao, Xinhe; Ma, Ding

    2014-03-01

    Monodispersed bimetallic PdAg nanoparticles can be fabricated through the emulsion-assisted ethylene glycol (EG) ternary system. Different compositions of bimetallic PdAg nanoparticles, Pd80Ag20, Pd65Ag35 and Pd46Ag54 can be obtained via adjusting the reaction parameters. For the formation process of the bimetallic PdAg nanoparticles, there have two-stage growth processes: firstly, nucleation and growth of the primary nanoclusters; secondly, formation of the secondary nanoparticles with the size-selection and relax process via the coalescence or aggregation of the primary nanoclusters. The as-prepared PdAg can be supported on the carbon black without any post-treatment, which exhibited high electro-oxidation activity towards methanol oxidation under alkaline media. More importantly, carbon-supported Pd80Ag20 nanoparticles reveal distinctly superior activities for the methanol oxidation, even if compared with commercial Pt/C electro-catalyst. It is concluded that the enhanced activity is dependant on the unique twinning structure with heterogeneous phase due to the dominating coalescence growth in EG ternary system.

  18. Hadron yields and spectra in Au+Au collisions at the AGS

    OpenAIRE

    Lacasse, Roger; Collaboration, the E877

    1996-01-01

    Inclusive double differential multiplicities and rapidity density distributions of hadrons are presented for 10.8 A GeV/c Au+Au collisions as measured at the AGS by the E877 collaboration. The results indicate that large amounts of stopping and collective transverse flow effects are present. The data are also compared to the results from the lighter Si+Al system.

  19. Results from experiment E917 for Au + Au collisions at the AGS

    International Nuclear Information System (INIS)

    The effects of baryon stopping and its resulting energy deposition on the dynamics of Au + Au collisions at 6, 8 and 10.8 GeV/nucleon are explored with recent results from the AGS experiment E917. Current analyses of stopping, collective flow signals and HBT parameters are presented. Strangeness and anti-baryon production is examined using the yields of anti-lambdas and anti-protons

  20. One step electrochemical synthesis of bimetallic PdAu supported on nafion–graphene ribbon film for ethanol electrooxidation

    Energy Technology Data Exchange (ETDEWEB)

    Shendage, Suresh S., E-mail: sureshsshendage@gmail.com; Singh, Abilash S.; Nagarkar, Jayashree M., E-mail: jm.nagarkar@ictmumbai.edu.in

    2015-10-15

    Highlights: • Electrochemical deposition of bimetallic PdAu NPs. • Highly loaded PdAu NPs are obtained. • Nafion–graphene supported PdAu NPs shows good activity for ethanol electrooxidation. - Abstract: A nafion–graphene ribbon (Nf–GR) supported bimetallic PdAu nanoparticles (PdAu/Nf–GR) catalyst was prepared by electrochemical codeposition of Pd and Au at constant potential. The prepared catalyst was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD). The average particle size of PdAu nanoparticles (NPs) determined from XRD was 3.5 nm. The electrocatalytic activity of the PdAu/Nf–GR catalyst was examined by cyclic voltametry. It was observed that the as prepared catalyst showed efficient activity and good stability for ethanol electrooxidation in alkaline medium.

  1. 70%Ag30%Pd Coated BaTiO3 Powder for Internal Electrode Applications

    OpenAIRE

    Juin-wei Peng; Stephenson, R. C.

    2002-01-01

    Recent trends in the electronic passive component manufacturing industry have been to eliminate or reduce reliance of pure Pd and high palladium contained Ag/Pd electrodes by substituting nickel or significantly lowers palladium content in Ag/Pd alloys. The conversion to base metal technology represents a substantial capital expense; the resistance to replace traditional air-fired kilns to nitrogen or reducing atmosphere kilns has created the need for new low cost air fired electrode technolo...

  2. Au/Ag nanoalloy shells as near-infrared SERS nanoprobe for the detection of protein

    International Nuclear Information System (INIS)

    We provide a highly sensitive, uniform and reproducible surface-enhanced Raman scattering (SERS) performance obtained from the randomly aggregated Au/Ag nanoalloy shells substrate. Au/Ag nanoalloy shells consist of SiO2 core and Au/Ag alloy shells layer. The obtained Au/Ag nanoalloy shells with a monodisperse size distribution exhibit different morphology by the analysis of TEM. By changing the ratio of Au and Ag, the plasmonic extinction of Au/Ag nanoshells varied in near-infrared window region. In this experiment, Au/Ag nanoshells with controllable ratio can obtain larger SERS signals, which can be used for ultrasensitive detection of biomolecules. These SERS-active spheres show interesting properties as a novel Raman tag for immunoassays. (paper)

  3. Strain Distribution of Au and Ag Nanoparticles Embedded in Al2O3 Thin Film

    Directory of Open Access Journals (Sweden)

    Honghua Huang

    2014-01-01

    Full Text Available Au and Ag nanoparticles embedded in amorphous Al2O3 matrix are fabricated by the pulsed laser deposition (PLD method and rapid thermal annealing (RTA technique, which are confirmed by the experimental high-resolution transmission electron microscope (HRTEM results, respectively. The strain distribution of Au and Ag nanoparticles embedded in the Al2O3 matrix is investigated by the finite-element (FE calculations. The simulation results clearly indicate that both the Au and Ag nanoparticles incur compressive strain by the Al2O3 matrix. However, the compressive strain existing on the Au nanoparticle is much weaker than that on the Ag nanoparticle. This phenomenon can be attributed to the reason that Young’s modulus of Au is larger than that of Ag. This different strain distribution of Au and Ag nanoparticles in the same host matrix may have a significant influence on the technological potential applications of the Au-Ag alloy nanoparticles.

  4. Volcano-like Behavior of Au-Pd Core-shell Nanoparticles in the Selective Oxidation of Alcohols

    OpenAIRE

    Silva, Tiago A. G.; Teixeira-Neto, Erico; López, Núria; Rossi, Liane M.

    2014-01-01

    Gold-palladium (AuPd) nanoparticles have shown significantly enhanced activity relative to monometallic Au and Pd catalysts. Knowledge of composition and metal domain distributions is crucial to understanding activity and selectivity, but these parameters are difficult to ascertain in catalytic experiments that have primarily been devoted to equimolar nanoparticles. Here, we report AuPd nanoparticles of varying Au:Pd molar ratios that were prepared by a seed growth method. The selective oxida...

  5. Permeability of hydrogen isotopes through Pd-Ag membrane

    International Nuclear Information System (INIS)

    This paper represents the permeabilities, diffusion coefficients and isotope effects for hydrogen and deuterium through Pd-25 wt.% Ag alloy tubes The feed gas H2 or D2 flowing into the permeation cell was preheated before it reached to the outer surface of the permeation tube made of palladium-silver alloy. Permeation time lag method could be successfully carried out with the present apparatus to measure both permeability and diffusion coefficient. The square-root pressure dependence for the permeation of hydrogen isotopes was observed. The observed systematic temperature dependence indicates that the approximation of the Arrhenius' relation was effective within this experimental conditions. Some tendency of permeation fluxes in relation to the reciprocal temperature, 1/T, was seen. The permeability ratio was larger than the square root of isotopic mass ratio, and it decreased with temperature rise. On the contrary, the diffusion coefficient ratio was much smaller than the square root of isotopic mass ratio. (Kato, T.)

  6. Characterization of PdAg/Al2O3 composite membrane by electroless co-deposition

    International Nuclear Information System (INIS)

    In this work, PdAg/Al2O3 composite membranes prepared by electroless co-deposition technique have been studied. Effects of plating time, Ag composition and total concentration of metal ions on surface morphologies, composition and microstructure of the resulting layers were investigated. Scanning electron microscope, energy dispersive spectrometer and nitrogen permeation technique were used to characterize the as-prepared composite membranes. From the experimental results, it shows that the surface morphology of the deposited PdAg layer is strongly affected by the Ag content of the plating bath. Since large differences of deposition rates and growth modes are observed between Pd and Ag grains, the PdAg layer exhibits the dendritic structure. As the Ag content is approximately 50%, the dendritic structured PdAg layer reveals the largest nitrogen permeability with the smallest size of residual pores. Furthermore, a comprehensive electrochemical analysis is proposed to interpret the composition and structure of the PdAg layer. Eventually, the experimental results are quite consistent with those predicted from the electrochemical analysis

  7. Au-Ag-Cu nano-alloys: tailoring of permittivity

    Science.gov (United States)

    Hashimoto, Yoshikazu; Seniutinas, Gediminas; Balčytis, Armandas; Juodkazis, Saulius; Nishijima, Yoshiaki

    2016-04-01

    Precious metal alloys enables new possibilities to tailor materials for specific optical functions. Here we present a systematic study of the effects of a nanoscale alloying on the permittivity of Au-Ag-Cu metals at 38 different atomic mixing ratios. The permittivity was measured and analyzed numerically by applying the Drude model. X-ray diffraction (XRD) revealed the face centered cubic lattice of the alloys. Both, optical spectra and XRD results point towards an equivalent composition-dependent electron scattering behavior. Correlation between the fundamental structural parameters of alloys and the resulting optical properties is elucidated. Plasmonic properties of the Au-Ag-Cu alloy nanoparticles were investigated by numerical simulations. Guidelines for designing plasmonic response of nano- structures and their patterns are presented from the material science perspective.

  8. Au-Ag-Cu nano-alloys: tailoring of permittivity

    Science.gov (United States)

    Hashimoto, Yoshikazu; Seniutinas, Gediminas; Balčytis, Armandas; Juodkazis, Saulius; Nishijima, Yoshiaki

    2016-01-01

    Precious metal alloys enables new possibilities to tailor materials for specific optical functions. Here we present a systematic study of the effects of a nanoscale alloying on the permittivity of Au-Ag-Cu metals at 38 different atomic mixing ratios. The permittivity was measured and analyzed numerically by applying the Drude model. X-ray diffraction (XRD) revealed the face centered cubic lattice of the alloys. Both, optical spectra and XRD results point towards an equivalent composition-dependent electron scattering behavior. Correlation between the fundamental structural parameters of alloys and the resulting optical properties is elucidated. Plasmonic properties of the Au-Ag-Cu alloy nanoparticles were investigated by numerical simulations. Guidelines for designing plasmonic response of nano- structures and their patterns are presented from the material science perspective. PMID:27118459

  9. Au-Ag-Cu nano-alloys: tailoring of permittivity.

    Science.gov (United States)

    Hashimoto, Yoshikazu; Seniutinas, Gediminas; Balčytis, Armandas; Juodkazis, Saulius; Nishijima, Yoshiaki

    2016-01-01

    Precious metal alloys enables new possibilities to tailor materials for specific optical functions. Here we present a systematic study of the effects of a nanoscale alloying on the permittivity of Au-Ag-Cu metals at 38 different atomic mixing ratios. The permittivity was measured and analyzed numerically by applying the Drude model. X-ray diffraction (XRD) revealed the face centered cubic lattice of the alloys. Both, optical spectra and XRD results point towards an equivalent composition-dependent electron scattering behavior. Correlation between the fundamental structural parameters of alloys and the resulting optical properties is elucidated. Plasmonic properties of the Au-Ag-Cu alloy nanoparticles were investigated by numerical simulations. Guidelines for designing plasmonic response of nano- structures and their patterns are presented from the material science perspective. PMID:27118459

  10. Synthesis, Annealing and Performance of Pd-Au Asymmetric Composite Membranes for Hydrogen Purification

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Yi Hua [Worcester Polytechnic Institute; Chen, Chao-Huang [Worcester Polytechnic Institute; Catalano, Jacopo [Worcester Polytechnic Institute; Guazzone, Federico [Worcester Polytechnic Institute; Payzant, E Andrew [ORNL

    2013-01-01

    Composite asymmetric Pd-Au membranes, based on porous Inconel and Hastelloy tubular supports, were prepared by means of electroless deposition and galvanic displacement techniques and tested, before and after Au deposition, in pure H2 atmosphere. The final membranes, with Au average bulk composition up to 16.7 wt%, were 9 15 m thick and showed, for the entire duration of characterization, H2/He ideal selectivity in excess of 900. The annealing of the as-prepared membranes was conducted through the coating and diffusion mechanism in He and H2 atmospheres at 500 C. The annealing conditions were chosen after non-isothermal and isothermal HT-XRD studies on coupons synthetized with similar preparation methods. After the formation of the Pd-Au layer, the membranes showed steady flux and a stable Au gradient on the membrane top layer. Comparisons between permeance for Pd/Au and pure Pd membranes indicated that the membranes with an Au average bulk composition of 4.5 and 5.4 wt% had an enhancement, up to 20%, of the H2 permeability in the temperature range 250 450 C with respect to pure Pd membranes. On the other hand, the membrane having the highest Au composition, 16.7 wt%, even though characterized by a lower H2 permeability (77% of pure Pd) had a rather high surface Au composition (approximately 46 wt%), which might provide good H2S poisoning tolerance.

  11. Ordering fluctuation dynamics in AuAgZn 2

    OpenAIRE

    Livet, Frédéric; Fèvre, Mathieu; Beutier, Guillaume; Sutton, Mark

    2015-01-01

    The second-order ordering transition of the AuAgZn2 alloy has been studied by coherent x-ray scattering. Within a few degrees above the critical temperature Tc, equilibrium critical fluctuations are observed together with some pre-transitional local ordering connected to sample defects. The speckles observed correspond to heterodyne interference between local ordering and fluctuations and show a mixed static and dynamical behaviour in a narrow domain of a few tenths of degree above Tc. The dy...

  12. Promotion of Phenol Photodecomposition over TiO2 Using Au, Pd, and AuPd Nanoparticles

    DEFF Research Database (Denmark)

    Su, Ren; Tiruvalam, Ramchandra; He, Qian;

    2012-01-01

    using phenol as a probe molecule. A different phenol degradation pathway was observed when using M/TiO2 catalysts as compared to pristine TiO2.We propose a mechanism to illustrate how the noble metal nanoparticles enhance the efficiency of phenol decomposition based on photoreduction of p......-benzoquinone under anaerobic conditions. Our results suggest that the metal nanoparticles not only play a role in capturing photogenerated electrons, but are strongly involved in the photocatalytic reaction mechanism. The analysis of the reaction intermediates allows us to conclude that on M/TiO2 undesired redox...... reactions that consume photogenerated radicals are effectively suppressed. The analysis of the final products shows that the reusability performance of the catalyst is largely dependent on the pretreatment of the catalyst and the identity of the metal nanoparticle. Interestingly, the as-prepared Pd and Au...

  13. The role of Pd in the transport of Ag in SiC

    Energy Technology Data Exchange (ETDEWEB)

    Olivier, E.J., E-mail: jolivier@nmmu.ac.za [Centre for High Resolution Transmission Electron Microscopy, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Neethling, J.H. [Centre for High Resolution Transmission Electron Microscopy, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa)

    2013-01-15

    This paper presents results in support of a newly proposed transport mechanism to account for the release of Ag from intact TRISO particles during HTR reactor operation. The study reveals that the migration of Ag in polycrystalline SiC can occur in association with Pd, a relatively high yield metallic fission product. The migration takes place primarily along grain boundary routes, seen in the form of distinct Pd, Ag and Si containing nodules. Pd is known to rapidly migrate to the SiC and iPyC interface within TRISO particles during operation. It has been shown to chemically corrode the SiC to form palladium silicides. These palladium silicides are found present along SiC grain boundaries in nodule like form. It is suggested that Ag penetrates these nodules together with the palladium silicide, to form a Pd, Ag and Si solution capable of migrating along SiC grain boundaries over time.

  14. The role of Pd in the transport of Ag in SiC

    International Nuclear Information System (INIS)

    This paper presents results in support of a newly proposed transport mechanism to account for the release of Ag from intact TRISO particles during HTR reactor operation. The study reveals that the migration of Ag in polycrystalline SiC can occur in association with Pd, a relatively high yield metallic fission product. The migration takes place primarily along grain boundary routes, seen in the form of distinct Pd, Ag and Si containing nodules. Pd is known to rapidly migrate to the SiC and iPyC interface within TRISO particles during operation. It has been shown to chemically corrode the SiC to form palladium silicides. These palladium silicides are found present along SiC grain boundaries in nodule like form. It is suggested that Ag penetrates these nodules together with the palladium silicide, to form a Pd, Ag and Si solution capable of migrating along SiC grain boundaries over time.

  15. One-step facile synthesis of carbon-supported PdAu nanoparticles and their electrochemical property and stability

    International Nuclear Information System (INIS)

    Graphical abstract: Well-crystallized PdAu alloy nanoparticles with the average size of 2–5 nm supported on Ketjen Black (KB) were successfully fabricated from the metal wire electrodes via a one-step solution plasma process in water at atmospheric pressure. Multi-scan cyclic voltammetry showed they have better electrochemical stability in alkaline than in acidic solution. - Highlights: • Carbon-supported PdAu nanoparticles were fabricated by a solution plasma technique. • As-obtained PdAu nanoparticles were confirmed to be alloy. • PdAu nanoparticles have good electrochemical activities and stabilities. • PdAu nanoparticles in alkaline have better stability than that in acidic solution. - Abstract: Well-crystallized PdAu nanoparticles supported on Ketjen Black (KB) were successfully fabricated when both Pd and Au wires were served as the electrode pair by a solution plasma technique at atmospheric pressure. The synthesis of PdAu nanoparticles was almost simultaneous with their dispersion on KB. As-obtained PdAu nanoparticles were confirmed to be alloy by ultraviolet–visible spectrophotometer, transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) of each particle. PdAu nanoparticles with the average diameter of 2–5 nm were equably distributed on KB. PdAu nanoparticles showed good electrocatalytic activity both in acidic and alkaline solution corresponding to their obvious oxidation and reduction features. PdAu nanoparticles have improved electrochemical stability compared with the electrochemical properties of Pd and Au nanoparticles mixture after long time multi-scan cyclic voltammetry. Multi-scan cyclic voltammetry also presented the PdAu nanoparticles in alkaline solution have better stability than that in acidic solution. Thus as-obtained PdAu alloy nanoparticles would become a promising electrocatalysts for fuel cells or Li-air batteries. This novel process showed its potential applications in designing optimization of

  16. One-step facile synthesis of carbon-supported PdAu nanoparticles and their electrochemical property and stability

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Xiulan, E-mail: whoxiulan@163.com [College of Materials Science and Engineering, Nanjing Tech University (China); Shi, Junjun; Zhang, Jianbo [College of Materials Science and Engineering, Nanjing Tech University (China); Tang, Weiping [Shanghai Institute of Space Power Sources, Shanghai (China); Zhu, Haikui; Shen, Xiaodong [College of Materials Science and Engineering, Nanjing Tech University (China); Saito, Nagahiro [Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University (Japan)

    2015-01-15

    Graphical abstract: Well-crystallized PdAu alloy nanoparticles with the average size of 2–5 nm supported on Ketjen Black (KB) were successfully fabricated from the metal wire electrodes via a one-step solution plasma process in water at atmospheric pressure. Multi-scan cyclic voltammetry showed they have better electrochemical stability in alkaline than in acidic solution. - Highlights: • Carbon-supported PdAu nanoparticles were fabricated by a solution plasma technique. • As-obtained PdAu nanoparticles were confirmed to be alloy. • PdAu nanoparticles have good electrochemical activities and stabilities. • PdAu nanoparticles in alkaline have better stability than that in acidic solution. - Abstract: Well-crystallized PdAu nanoparticles supported on Ketjen Black (KB) were successfully fabricated when both Pd and Au wires were served as the electrode pair by a solution plasma technique at atmospheric pressure. The synthesis of PdAu nanoparticles was almost simultaneous with their dispersion on KB. As-obtained PdAu nanoparticles were confirmed to be alloy by ultraviolet–visible spectrophotometer, transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) of each particle. PdAu nanoparticles with the average diameter of 2–5 nm were equably distributed on KB. PdAu nanoparticles showed good electrocatalytic activity both in acidic and alkaline solution corresponding to their obvious oxidation and reduction features. PdAu nanoparticles have improved electrochemical stability compared with the electrochemical properties of Pd and Au nanoparticles mixture after long time multi-scan cyclic voltammetry. Multi-scan cyclic voltammetry also presented the PdAu nanoparticles in alkaline solution have better stability than that in acidic solution. Thus as-obtained PdAu alloy nanoparticles would become a promising electrocatalysts for fuel cells or Li-air batteries. This novel process showed its potential applications in designing optimization of

  17. Critical assessment and optimization of the Ag-Au-Pb system

    Energy Technology Data Exchange (ETDEWEB)

    Hassam, S., E-mail: Shahrazade.hassam@univ-cezanne.fr [Institut Materiaux Microelectronique Nanosciences de Provence (IM2NP), UMR 6242 CNRS, Universites Paul Cezanne, Provence et Sud Toulon-Var, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20 (France); Boa, D. [Laboratoire de Thermodynamique et de Physico-Chimie du Milieu, Universite d' Abobo-Adjame, UFR-SFA, 02 BP 801 Abidjan 02 (Cote d' Ivoire); Benigni, P.; Rogez, J. [Institut Materiaux Microelectronique Nanosciences de Provence (IM2NP), UMR 6242 CNRS, Universites Paul Cezanne, Provence et Sud Toulon-Var, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20 (France)

    2010-10-20

    By means of an optimization procedure, the ternary Ag-Au-Pb system has been assessed. All available experimental data of the ternary system and the results derived from thermodynamic descriptions for the three limiting binary systems are used. For the Ag-Au and Au-Pb systems, optimized Gibbs energy expressions were taken from the literature. A new assessment of the binary Ag-Pb system based on our calorimetric investigations is presented in this paper. Calculated phase diagrams and some calculated thermochemical functions for the binary Ag-Pb and the ternary Ag-Au-Pb systems are compared with experimental data.

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

    International Nuclear Information System (INIS)

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

  19. Study of Ag and Au Nanoparticles Synthesized by Arc Discharge in Deionized Water

    Directory of Open Access Journals (Sweden)

    Der-Chi Tien

    2010-01-01

    Full Text Available The paper presents a study of Ag and Au nanofluids synthesized by the arc discharge method (ADM in deionized water. The metallic Ag nanoparticle (Ag0 and ionic Ag (Ag+ have played an important role in the battle against germs which are becoming more drug-resistant every year. Our study indicates that Ag nanoparticle suspension (SNPS fabricated by using ADM without added surfactants exclusively contains the metallic Ag nanoparticle and ionic Ag. Besides that, the ADM in deionized water has also been employed for the fabrication process of Au nanoparticles. The experimental results indicate that the prepared Ag nanoparticles can react with the dissolved H2CO3 in deionized water, leading to the formation of Ag2CO3. Significantly different to Ag, the prepared Au nanoparticles with their surfaces bonded by oxygen are suspended in deionized water by the formation of hydrogen bonded with the neighboring water molecules.

  20. Understanding the effect of ultrathin AuPd alloy shells of irregularly shaped Au@AuPd nanoparticles with high-index facets on enhanced performance of ethanol oxidation

    Science.gov (United States)

    Bi, Cuixia; Feng, Cong; Miao, Tingting; Song, Yahui; Wang, Dayang; Xia, Haibing

    2015-11-01

    In this study, irregularly shaped, concave cuboidal Au@AuPd nanoparticles (ISCC-Au@AuPd NPs) with high-index facets were synthesized via Pd overgrowth on pre-formed ISCC-Au NPs with a concentration of Pd precursors as low as 2%. The AuPd alloy nature of the resulting shells was confirmed by X-ray photoelectron spectroscopy, cyclic voltammogram analysis, and energy dispersive X-ray spectroscopy. Among the irregularly shaped NPs obtained, the ISCC-Au97.5@Au0.5Pd2.0 NPs display the largest electrochemically active surface area (up to 92.11 m2 g-1), as their closed-packed agglomeration was prevented, and the best long-term stability with respect to ethanol oxidation (0.50 M) in alkaline media (0.30 KOH) by efficiently removing intermediates. Their mass- and ECSA-normalized current densities (4.15 A mgPd-1 and 4.51 mA cm-2) are about 20.7 times and 6.9 times higher than those of commercial Pd/C catalysts (0.20 A mgPd-1 and 0.65 mA cm-2), respectively.In this study, irregularly shaped, concave cuboidal Au@AuPd nanoparticles (ISCC-Au@AuPd NPs) with high-index facets were synthesized via Pd overgrowth on pre-formed ISCC-Au NPs with a concentration of Pd precursors as low as 2%. The AuPd alloy nature of the resulting shells was confirmed by X-ray photoelectron spectroscopy, cyclic voltammogram analysis, and energy dispersive X-ray spectroscopy. Among the irregularly shaped NPs obtained, the ISCC-Au97.5@Au0.5Pd2.0 NPs display the largest electrochemically active surface area (up to 92.11 m2 g-1), as their closed-packed agglomeration was prevented, and the best long-term stability with respect to ethanol oxidation (0.50 M) in alkaline media (0.30 KOH) by efficiently removing intermediates. Their mass- and ECSA-normalized current densities (4.15 A mgPd-1 and 4.51 mA cm-2) are about 20.7 times and 6.9 times higher than those of commercial Pd/C catalysts (0.20 A mgPd-1 and 0.65 mA cm-2), respectively. Electronic supplementary information (ESI) available: High magnification TEM

  1. Interference removals on Pd, Ru and Au with ICP-QQQ-MS in PGE RM

    Science.gov (United States)

    Nadeem Hussain Bokhari, Syed; Meisel, Thomas; Walkner, Christoph

    2015-04-01

    Gold and platinum group elements (PGE) are essential industrial precious metals with high world demand due to their unique properties. Struggle for natural exploration of PGE is on great pace and recycling from industrial wastes, electronics and catalytic convertor is on the rise for PGE supply chain. Along with these developments it is becoming more challenging for analytical chemists to determine gold and PGE out of complex matrix which causes severe interferences. The current state of art is online analysis coupled with chromatographic separation of interferences. The ICP-QQQ-MS Agilent 8800 has the capability of using multi tunes and mass shifts. We aim to remove interferences on Pd+ (for direct and isotope dilution analysis) Au+ and Ru+ in lieu of chemical separations. YO+, SrOH+, ZnAr+, NiAr+, ZrO+, CuAr+, MoO+ , Ru+and Cd+ are expected interferences on Pd+ while Au+ is interfered by TaO+, HfOH+, GdAr+ and 102Ru+ ,104Ru+ by 102Pd+ ,104Pd+ etc. Initial test were performed on pure solutions of 1mg/l (interfering elements): 1 ng/l (Pd, Ru & Au) respectively. The outcomes of initial tests were applied on PGE reference material (RM) WMG-1 and SARM-7 (digested with Na2O2 sintering). The results obtained show that YO+, SrOH+ interfere (104Pd,105Pd), 104 Ru+ on (104Pd), ZnAr+ has slight interference on (104Pd and106Pd), ZrO+, NiAr+, CuAr+ interferences are negligible, MoO+ has severe interference on (108Pd, 110Pd) and that Cd+ has severe isobaric interference on (106Pd,108Pd, 110Pd). These interference have been removed by formation of Pd(NH3)3+complex. The TaO+, HfOH+ and GdAr+ interferences on Au+ are best removed by formation of Au(NH3)+ and Au(NH3)2+ complexes. 102Pd+,104Pd+interference on 102Ru+ ,104Ru+ can be removed by formation of Ru(NH3)4+ and RuO+ compounds. The results obtained comply with certified values of RM. The developed method is being tested on low concentration PGE reference materials. References: Sugiyama, N. " Removal of complex spectral

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

    International Nuclear Information System (INIS)

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

  3. Phase Equilibria in System Pd-Au-Sn and Pd-Cu-Sn at 800℃ and 500℃

    Institute of Scientific and Technical Information of China (English)

    KABANOVA E. G.; KAREVA M. A.; KUZNETSOV V. N.; VASEKIN V. V.

    2012-01-01

    Alloys of Pd-Au-Sn and Pd-Cu-Sn systems were investigated using metallography,electron microprobe,X-ray diff action and DTA.Partial isothermal sections were plots at 800℃ and 500℃.Ternary τ-phase having tetragonal structure has been established in each systems.The region of existence of phases in equilibrium with the solid solution based on palladium.

  4. Synthesis, Study, and Discrete Dipole Approximation Simulation of Ag-Au Bimetallic Nanostructures.

    Science.gov (United States)

    Hu, Yang; Zhang, An-Qi; Li, Hui-Jun; Qian, Dong-Jin; Chen, Meng

    2016-12-01

    Water-soluble Ag-Au bimetallic nanostructures were prepared via co-reduction and seed-mediated growth routes employing poly-(4-styrenesulfonic acid-co-maleic acid) (PSSMA) as both a reductant and a stabilizer. Ag-Au alloy nanoparticles were obtained by the co-reduction of AgNO3 and HAuCl4, while Ag-Au core-shell nanostructures were prepared through seed-mediated growth using PSSMA-Au nanoparticle seeds in a heated AgNO3 solution. The optical properties of the Ag-Au alloy and core-shell nanostructures were studied, and the growth mechanism of the bimetallic nanoparticles was investigated. Plasmon resonance bands in the range 422 to 517 nm were observed for Ag-Au alloy nanoparticles, while two plasmon resonances were found in the Ag-Au core-shell nanostructures. Furthermore, discrete dipole approximation theoretical simulation was used to assess the optical property differences between the Ag-Au alloy and core-shell nanostructures. Composition and morphology studies confirmed that the synthesized materials were Ag-Au bimetallic nanostructures. PMID:27094823

  5. SERS monitoring of Pd-catalysed reduction processes of nitroarenes adsorbed on Ag/Pd colloidal nanoparticles

    Science.gov (United States)

    Muniz-Miranda, Maurizio; Pergolese, Barbara; Bigotto, Adriano

    2006-05-01

    The catalytic activity of palladium has been verified in Ag/Pd colloids for two different nitroarenes, 2-amino,5-nitropyridine (ANP) and 4-nitrobenzoic acid (PNBA). Palladium, deposited as nanoclusters onto the silver core, can act as catalyst for the ligands, while silver ensures the SERS enhancement, which is necessary to detect the Raman spectra of the adsorbates. The SERS measurements show that the nitrogroup of ANP is reduced to aminogroup in Ag/Pd colloids, whereas, in the case of PNBA, the azo-derivative is obtained as stable product.

  6. Evaluation of Pd-Ag alloys as electrocatalysts for oxygen reduction reaction

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, M.C.; Rego, R. [Univ. de Tas-os-Montes e Alto Douro Apartado (Portugal). Dept. de Quimica, Centro de Quimica

    2010-07-01

    Alkaline fuel cells (AFCs) provide a less corrosive environment and can provide higher electrode reaction kinetics than proton exchange membrane fuel cells (PEMFCs). The alkaline media also allows for the replacement of platinum (Pt) based electrocatalysts with non-Pt electrocatalysts. Studies have shown that palladium (Pd) and silver (Ag) form a homogenous solid solution with a face-centred cubic structure within a large range of temperatures. This study described the results of an oxygen reduction reaction (ORR) on lead-silver (Pd-Ag) alloy electrodes in alkaline media. The reaction was compared with Pd and Ag electrodes. The alloys were synthesized as thin films using a sequential electroless deposition of Pd and Ag on stainless steel discs followed by an annealing procedure in an Ar stream. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize catalyst structure, morphology, and composition. 4 refs.

  7. Structured Pd-Au/Cu-fiber catalyst for gas-phase hydrogenolysis of dimethyl oxalate to ethylene glycol.

    Science.gov (United States)

    Zhang, Li; Han, Lupeng; Zhao, Guofeng; Chai, Ruijuan; Zhang, Qiaofei; Liu, Ye; Lu, Yong

    2015-07-01

    Galvanic co-deposition of 0.5 wt% Au and 0.1 wt% Pd on a microfibrous-structure using 8 μm Cu-fibers delivers a Pd-Au/Cu-fiber catalyst, which is highly active, selective and stable for the hydrogenolysis of dimethyl oxalate to ethylene glycol. Au and Pd synergistically promote the hydrogenolysis activity of Cu(+) sites, while Au also critically stabilizes Cu(+) sites to prevent deep reductive deactivation. PMID:26040855

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

    Science.gov (United States)

    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.

  9. Synthesis of biocompatible AuAgS/Ag2S nanoclusters and their applications in photocatalysis and mercury detection

    International Nuclear Information System (INIS)

    In this paper, a facile approach for preparation of AuAgS/Ag2S nanoclusters was developed. The unique AuAgS/Ag2S nanoclusters capped with biomolecules exhibit interesting excellent optical and catalytic properties. The fluorescent AuAgS/Ag2S nanoclusters show tunable luminescence depending on the nanocluster size. The apoptosis assay demonstrated that the AuAgS/Ag2S nanoclusters showed low cytotoxicity and good biocompatibility. Therefore, the nanoclusters can be used not only as a probe for labeling cells but also for their photocatalytic activity for photodegradation of organic dye. Moreover, a highly selective and sensitive assay for detection of mercury including Hg2+ and undissociated mercury complexes was developed based on the quenching fluorescent AuAgS/Ag2S nanoclusters, which provides a promising approach for determining various forms of Hg in the mercury-based compounds in environment. These unique nanoclusters may have potential applications in biological labeling, sensing mercury, and photodegradation of various organic pollutants in waste water.Graphical Abstract

  10. Synthesis of biocompatible AuAgS/Ag{sub 2}S nanoclusters and their applications in photocatalysis and mercury detection

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Qian; Chen, Shenna; Zhang, Lingyang; Huang, Haowen, E-mail: hhwn09@163.com; Liu, Fengping [Hunan University of Science and Technology, Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan Provincial University Key Laboratory of QSAR/QSPR, School of Chemistry and Chemical Engineering (China); Liu, Xuanyong, E-mail: xyliu@mail.sic.ac.cn [Chinese Academy of Sciences, State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics (China)

    2014-12-15

    In this paper, a facile approach for preparation of AuAgS/Ag{sub 2}S nanoclusters was developed. The unique AuAgS/Ag{sub 2}S nanoclusters capped with biomolecules exhibit interesting excellent optical and catalytic properties. The fluorescent AuAgS/Ag{sub 2}S nanoclusters show tunable luminescence depending on the nanocluster size. The apoptosis assay demonstrated that the AuAgS/Ag{sub 2}S nanoclusters showed low cytotoxicity and good biocompatibility. Therefore, the nanoclusters can be used not only as a probe for labeling cells but also for their photocatalytic activity for photodegradation of organic dye. Moreover, a highly selective and sensitive assay for detection of mercury including Hg{sup 2+} and undissociated mercury complexes was developed based on the quenching fluorescent AuAgS/Ag{sub 2}S nanoclusters, which provides a promising approach for determining various forms of Hg in the mercury-based compounds in environment. These unique nanoclusters may have potential applications in biological labeling, sensing mercury, and photodegradation of various organic pollutants in waste water.Graphical Abstract.

  11. Simple wet-chemical synthesis of alloyed PdAu nanochain networks with improved electrocatalytic properties

    International Nuclear Information System (INIS)

    Graphical abstract: PdAu alloyed nanochain networks were prepared by a simple and facile one-pot wet-chemical method using allantoin as the structure-directing agent and stabilizing agent. The as-prepared nanocrystals displayed improved catalytic performances for ORR and MOR as compared to commercial Pd black catalyst. - Highlights: • Bimetallic PdAu nanochain networks were synthesized by a simple and facile one-pot wet-chemical approach. • Allantoin was used as the structure-directing agent and stabilizing agent. • The PdAu nanocrystals had large electrochemical active surface area. • The PdAu nanocrystals showed highly catalytic activity and good stability for ORR and MOR. - Abstract: Bimetallic PdAu alloyed nanochain networks (PdAu NCNs) were facilely prepared by a simple wet-chemical method with the assistance of allantoin as the structure-directing agent and stabilizing agent. Allantoin played an important role in the formation of chain-like networks. The products were mainly characterized by transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy. The as-prepared PdAu NCNs had enlarged electrochemical active surface area, and displayed enhanced electrocatalytic activity toward oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR), showing higher resistance to poisoning CO-like intermediates in MOR and more positive onset potential in ORR as compared to commercial Pd black catalyst. This approach provides a promising route for large-scale preparation of desirable bimetallic catalysts with the assistance of small biomolecules

  12. Preparation and characterization of metallic supported thin Pd-Ag membranes for hydrogen separation

    OpenAIRE

    Fernandez, Ekain; Medrano, Jose Antonio; Melendez, Jon; Parco, Maria; Viviente, J.L.; van Sint Annaland, Martin; Gallucci, Fausto; Pacheco Tanaka, David A.

    2015-01-01

    This paper reports the preparation and characterization of thin-film (4-5 µm thick) Pd-Ag metallic supported membranes for high temperature applications. Various thin film membranes have been prepared by depositing a ceramic interdiffusion barrier layer prior to the simultaneous Pd-Ag electroless plating deposition. Two deposition techniques for ceramic layers (made of zirconia and alumina) have been evaluated: atmospheric plasma spraying and dip coating of a powder suspension. Initially, the...

  13. Local structure of disordered Au-Cu and Au-Ag alloys

    International Nuclear Information System (INIS)

    X-ray-absorption fine structure (XAFS) and x-ray-diffraction (XRD) measurements of disordered alloys AuxCu1-x and Au0.5Ag0.5 prepared by melt spinning were performed. In the Au0.5Ag0.5 alloy, no significant local deviations of the atoms from the average fcc lattice were detected while in AuxCu1-x alloys, significant deviations of atoms from the average fcc lattice were found. Mean-square vibrations of the Cu-Cu distances revealed by the XAFS in AuxCu1-x alloys indicate the weakening of contact between Cu atoms in the dilute limit. Our computer simulation for AuxCu1-x clusters of 105 atoms reproduces the main features of both the XAFS and XRD data

  14. Catalysis of oxygen reduction on Au modified by Pd nanoislands in perchloric acid solution

    International Nuclear Information System (INIS)

    Graphical abstract: - Abstract: Oxygen reduction reaction (ORR) was studied on polycrystalline gold, Au(poly), modified by nanosized palladium islands in 0.1 M HClO4 solution using rotating disc electrode technique. Paladium was spontaneously deposited from 1 mM PdSO4·2H2O + 0.5 M H2SO4 solution for various deposition times at a submonolayer coverage. Topography of obtained Pd/Au(poly) surfaces was observed by tapping mode atomic force microscopy (AFM), while chemical surface composition changes were detected by simultaneously performed phase AFM. Deposited Pd islands were nonuniform in size and randomly distributed over the gold substrate. Size and number of Pd islands increase with the increase of the deposition time, and consequently surface coverage increases too. Deposited Pd was also identified by the changes in cyclic voltammetry (CV) profiles from which an active surface area was estimated. Obtained Pd/Au(poly) surfaces have shown a significant catalytic activity towards oxygen reduction reaction which increases with the increase of Pd islands coverage. The initial potential of ORR was shifted positively, while reaction pathway changes from 2e-reduction on pure gold to 4e-reduction on Pd modified gold. Additionally, obtained Pd/Au(poly) surfaces have shown a significant activity towards hydrogen peroxide reduction (HPRR), which appear as an intermediate during ORR. This supports the assumption that ORR on Pd/Au(poly) occurs partly through 4e-series reduction pathway, the fraction of which increases with the increase of Pd coverage.

  15. Direct measurement of time dependent diffusion for Ag and Au under ambient conditions

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Pil Sun; Jo, Han Yeol; Kim, Tae Kyeong [Hankuk University of Foreign Studies, Yongin (Korea, Republic of)

    2014-12-15

    Time-dependent diffusion for Ag and Au metal atoms was measured using the scanning tunneling microscope break-junction technique in ambient conditions. We observed that Ag contacts do not form long single-atomic chains compared to Au contacts during the elongation of each metal electrode, and Ag atoms diffuse more quickly than Au atoms after metal contact rupture. This is consistent with previous results of molecular dynamic simulations. Further, we found a correlation between diffusion length and the evolution time on an atomic scale to reveal the time-dependent diffusion for Ag and Au metal atoms.

  16. Bonding, Luminescence, Metallophilicity in Linear Au3 and Au2Ag Chains Stabilized by Rigid Diphosphanyl NHC Ligands.

    Science.gov (United States)

    Ai, Pengfei; Mauro, Matteo; Gourlaouen, Christophe; Carrara, Serena; De Cola, Luisa; Tobon, Yeny; Giovanella, Umberto; Botta, Chiara; Danopoulos, Andreas A; Braunstein, Pierre

    2016-09-01

    The heterofunctional and rigid ligand N,N'-diphosphanyl-imidazol-2-ylidene (PCNHCP; P = P(t-Bu)2), through its phosphorus and two N-heterocyclic carbene (NHC) donors, stabilizes trinuclear chain complexes, with either Au3 or AgAu2 cores, and dinuclear Au2 complexes. The two oppositely situated PCNHCP (L) ligands that "sandwich" the metal chain can support linear and rigid structures, as found in the known tricationic Au(I) complex [Au3(μ3-PCNHCP,κP,κCNHC,κP)2](OTf)3 (OTf = CF3SO3; [Au3L2](OTf)3; Chem. Commun. 2014, 50, 103-105) now also obtained by transmetalation from [Ag3(μ3-PCNHCP,κP,κCNHC,κP)2](OTf)3 ([Ag3L2](OTf)3), or in the mixed-metal tricationic [Au2Ag(μ3-PCNHCP,κP,κCNHC,κP)2](OTf)3 ([Au2AgL2](OTf)3). The latter was obtained stepwise by the addition of AgOTf to the digold(I) complex [Au2(μ2-PCNHCP,κP,κCNHC)2](OTf)2 ([Au2L2](OTf)2). The latter contains two dangling P donors and displays fluxional behavior in solution, and the Au···Au separation of 2.8320(6) Å in the solid state is consistent with metallophilic interactions. In the solvento complex [Au3Cl2(tht)(μ3-PCNHCP,κP,κCNHC,κP)](OTf)·MeCN ([Au3Cl2(tht)L](OTf)·MeCN), which contains only one L and one tht ligand (tht = tetrahydrothiophene), the metal chain is bent (148.94(2)°), and the longer Au···Au separation (2.9710(4) Å) is in line with relaxation of the rigidity due to a more "open" structure. Similar features were observed in [Au3Cl2(SMe2)L](OTf)·2MeCN. A detailed study of the emission properties of [Au3L2](OTf)3, [Au3Cl2(tht)L](OTf)·MeCN, [Au2L2](OTf)2, and [Au2AgL2](OTf)3 was performed by means of steady state and time-resolved photophysical techniques. The complex [Au3L2](OTf)3 displays a bright (photoluminescence quantum yield = 80%) and narrow emission band centered at 446 nm with a relatively small Stokes' shift and long-lived excited-state lifetime on the microsecond timescale, both in solution and in the solid state. In line with the very narrow emission

  17. Comparative efficiencies of photothermal destruction of malignant cells using antibody-coated silica@Au nanoshells, hollow Au/Ag nanospheres and Au nanorods

    Science.gov (United States)

    Cheng, Fong-Yu; Chen, Chen-Tai; Yeh, Chen-Sheng

    2009-10-01

    Three Au-based nanomaterials (silica@Au nanoshells, hollow Au/Ag nanospheres and Au nanorods) were evaluated for their comparative photothermal efficiencies at killing three types of malignant cells (A549 lung cancer cells, HeLa cervix cancer cells and TCC bladder cancer cells) using a CW NIR laser. Photodestructive efficiency was evaluated as a function of the number of nanoparticles required to destroy the cancer cells under 808 nm laser wavelength at fixed laser power. Of the three nanomaterials, silica@Au nanoshells needed the minimum number of particles to produce effective photodestruction, whereas Au nanorods needed the largest number of particles. Together with the calculated photothermal conversion efficiency, the photothermal efficiency rankings are silica@Au nanoshells > hollow Au/Ag nanospheres > Au nanorods. Additionally, we found that HeLa cells seem to present better heat tolerance than the other two cancer cell lines.

  18. Novel PdAgCu ternary alloy: Hydrogen permeation and surface properties

    Science.gov (United States)

    Tarditi, Ana M.; Braun, Fernando; Cornaglia, Laura M.

    2011-05-01

    Dense PdAgCu ternary alloy composite membranes were synthesized by the sequential electroless plating of Pd, Ag and Cu on top of both disk and tubular porous stainless steel substrates. X-ray diffraction and scanning electron microscopy were employed to study the structure and morphology of the tested samples. The hydrogen permeation performance of these membranes was investigated over a 350-450 °C temperature range and a trans-membrane pressure up to 100 kPa. After annealing at 500 °C in hydrogen stream followed by permeation experiments, the alloy layer presented a FCC crystalline phase with a bulk concentration of 68% Pd, 7% Ag and 25% Cu as revealed by EDS. The PdAgCu tubular membrane was found to be stable during more than 300 h on hydrogen stream. The permeabilities of the PdAgCu ternary alloy samples were higher than the permeabilities of the PdCu alloy membranes with a FCC phase. The co-segregation of silver and copper to the membrane surface was observed after hydrogen permeation experiments at high temperature as determined by XPS.

  19. Novel PdAgCu ternary alloy: Hydrogen permeation and surface properties

    International Nuclear Information System (INIS)

    Dense PdAgCu ternary alloy composite membranes were synthesized by the sequential electroless plating of Pd, Ag and Cu on top of both disk and tubular porous stainless steel substrates. X-ray diffraction and scanning electron microscopy were employed to study the structure and morphology of the tested samples. The hydrogen permeation performance of these membranes was investigated over a 350-450 deg. C temperature range and a trans-membrane pressure up to 100 kPa. After annealing at 500 deg. C in hydrogen stream followed by permeation experiments, the alloy layer presented a FCC crystalline phase with a bulk concentration of 68% Pd, 7% Ag and 25% Cu as revealed by EDS. The PdAgCu tubular membrane was found to be stable during more than 300 h on hydrogen stream. The permeabilities of the PdAgCu ternary alloy samples were higher than the permeabilities of the PdCu alloy membranes with a FCC phase. The co-segregation of silver and copper to the membrane surface was observed after hydrogen permeation experiments at high temperature as determined by XPS.

  20. Novel PdAgCu ternary alloy: Hydrogen permeation and surface properties

    Energy Technology Data Exchange (ETDEWEB)

    Tarditi, Ana M.; Braun, Fernando [Instituto de Investigaciones en Catalisis y Petroquimica (FIQ, UNL-CONICET), Santiago del Estero 2829, 3000 Santa Fe (Argentina); Cornaglia, Laura M., E-mail: lmcornag@fiq.unl.edu.ar [Instituto de Investigaciones en Catalisis y Petroquimica (FIQ, UNL-CONICET), Santiago del Estero 2829, 3000 Santa Fe (Argentina)

    2011-05-15

    Dense PdAgCu ternary alloy composite membranes were synthesized by the sequential electroless plating of Pd, Ag and Cu on top of both disk and tubular porous stainless steel substrates. X-ray diffraction and scanning electron microscopy were employed to study the structure and morphology of the tested samples. The hydrogen permeation performance of these membranes was investigated over a 350-450 deg. C temperature range and a trans-membrane pressure up to 100 kPa. After annealing at 500 deg. C in hydrogen stream followed by permeation experiments, the alloy layer presented a FCC crystalline phase with a bulk concentration of 68% Pd, 7% Ag and 25% Cu as revealed by EDS. The PdAgCu tubular membrane was found to be stable during more than 300 h on hydrogen stream. The permeabilities of the PdAgCu ternary alloy samples were higher than the permeabilities of the PdCu alloy membranes with a FCC phase. The co-segregation of silver and copper to the membrane surface was observed after hydrogen permeation experiments at high temperature as determined by XPS.

  1. Rapidity density distributions in Au+Au and Au+Ag interactions at 11.6 A GeV/c

    International Nuclear Information System (INIS)

    Pseudorapidity density distributions of charged particles in heavy-ion collisions have been studied. The results from EMU01 have been compared to the results from the experiments WA80 and E802. The recently obtained pseudorapidity distributions from Au+Au and Au+Ag interactions have been compared to a linear extrapolation from lighter systems. (orig.)

  2. HCOOH oxidation on thin Pd layers on Au: Self-poisoning by the subsequent reaction of the reaction product

    International Nuclear Information System (INIS)

    Highlights: ► Thin layers of Pd@Au are more active for HCOOH oxidation than pure Pd. ► Pd@Au surfaces are poisoned more rapidly than Pd black. ► Poisoning is caused by COads formed in CO2 electroreduction. -- Abstract: The oxidation of HCOOH has been investigated on thin Pd layers ranging from 1 to 17 ML equivalents electrodeposited on polycrystalline Au substrate (Pd@Au). The results are compared to those on Pd black. Potentiodynamic polarization curves suggest that on both types of catalyst HCOOH oxidizes through dehydrogenation path. The high current densities achieved on 4–17 ML Pd@Au surpass more than three times the activity of Pd black. Chronoamperometric test reveals that the Pd@Au electrodes lose their activity faster than Pd black. In the stripping experiment performed after the chronoamperometry COads is detected on all the surfaces. On the 4 ML Pd@Au, which exhibits the highest deactivation rate, the COads coverage is the largest. After the chronoamperometric test repeated in the CO2 saturated supporting electrolyte, the anodic stripping shows that COads is present on all the electrodes, again with the highest coverage on 4 ML Pd@Au. It is concluded that deactivation of Pd surfaces is caused by the COads formed in the electrochemical reduction of CO2, which is the product of HCOOH oxidation. Electronic modification of Pd by Au substrate causes stronger interactions of Pd with HCOOH and CO, which increases HCOOH oxidation rate, but also accelerates the poisoning by COads

  3. Supported Pd-Au Membrane Reactor for Hydrogen Production: Membrane Preparation, Characterization and Testing.

    Science.gov (United States)

    Iulianelli, Adolfo; Alavi, Marjan; Bagnato, Giuseppe; Liguori, Simona; Wilcox, Jennifer; Rahimpour, Mohammad Reza; Eslamlouyan, Reza; Anzelmo, Bryce; Basile, Angelo

    2016-01-01

    A supported Pd-Au (Au 7wt%) membrane was produced by electroless plating deposition. Permeation tests were performed with pure gas (H₂, H₂, N₂, CO₂, CH₄) for long time operation. After around 400 h under testing, the composite Pd-Au membrane achieved steady state condition, with an H₂/N₂ ideal selectivity of around 500 at 420 °C and 50 kPa as transmembrane pressure, remaining stable up to 1100 h under operation. Afterwards, the membrane was allocated in a membrane reactor module for methane steam reforming reaction tests. As a preliminary application, at 420 °C, 300 kPa of reaction pressure, space velocity of 4100 h(-1), 40% methane conversion and 35% hydrogen recovery were reached using a commercial Ni/Al₂O₃ catalyst. Unfortunately, a severe coke deposition affected irreversibly the composite membrane, determining the loss of the hydrogen permeation characteristics of the supported Pd-Au membrane. PMID:27171067

  4. Enhanced electrocatalytic performance for isopropanol oxidation on Pd-Au nanoparticles dispersed on poly(p-phenylene) prepared from biphenyl

    International Nuclear Information System (INIS)

    Poly(p-phenylene) (PPP) films with good electrochemical activity and good thermal stability were synthesized by a low-potential electrochemical polymerization of biphenyl in pure boron trifluoride diethyl etherate. As-formed PPP film was firstly used as a catalyst support. Pd-Au nanoparticles were successfully electro-deposited on PPP films (namely, Pd-Au/PPP) and used for the electrooxidation of isopropanol in alkaline media. The Pd-Au/PPP composite catalyst shows a high electrochemical active surface area in the hydrogen adsorption potential region. The results for isopropanol oxidation indicate that Pd-Au/PPP have higher catalytic activity and stronger poisoning-resistance than the Pd-Au deposited on the bare electrode. Furthermore, the role of PPP in the composite catalyst and supplemental effect are discussed. The present study evidences that Pd-Au/PPP is a promising choice as a composite catalyst for isopropanol electrooxidation in alkaline medium.

  5. PVP induce self-seeding process for growth of Au@Ag core@shell nanocomposites

    Science.gov (United States)

    Eisa, Wael H.; Al-Ashkar, Emad; El-Mossalamy, S. M.; Ali, Safaa S. M.

    2016-05-01

    A novel self-seeding route is developed for fabrication of metallic nanocomposites of gold (core) and silver (shell) (Au@Ag core@shell). Herein, polyvinylpyrrolidone (PVP) is used as both reducing and stabilizing agent. The surface plasmon resonance (SPR) of Au@Ag core@shell can be tuned by controlling the thickness of the Ag shell. The different growth stages of the Au@Ag core@shell have been traced by in situ UV-vis absorption spectra. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy are used for the characterization of the prepared samples.

  6. Platinum(iv) prodrug conjugated Pd@Au nanoplates for chemotherapy and photothermal therapy

    Science.gov (United States)

    Shi, Saige; Chen, Xiaolan; Wei, Jingping; Huang, Yizhuan; Weng, Jian; Zheng, Nanfeng

    2016-03-01

    Owing to the excellent near infrared (NIR) light absorption and efficient passive targeting toward tumor tissue, two-dimensional (2D) core-shell PEGylated Pd@Au nanoplates have great potential in both photothermal therapy and drug delivery systems. In this work, we successfully conjugate Pd@Au nanoplates with a platinum(iv) prodrug c,c,t-[Pt(NH3)2Cl2(O2CCH2CH2CO2H)2] to obtain a nanocomposite (Pd@Au-PEG-Pt) for combined photothermal-chemotherapy. The prepared Pd@Au-PEG-Pt nanocomposite showed excellent stability in physiological solutions and efficient Pt(iv) prodrug loading. Once injected into biological tissue, the Pt(iv) prodrug was easily reduced by physiological reductants (e.g. ascorbic acid or glutathione) into its cytotoxic and hydrophilic Pt(ii) form and released from the original nanocomposite, and the NIR laser irradiation could accelerate the release of Pt(ii) species. More importantly, Pd@Au-PEG-Pt has high tumor accumulation (29%ID per g), which makes excellent therapeutic efficiency at relatively low power density possible. The in vivo results suggested that, compared with single therapy the combined thermo-chemotherapy treatment with Pd@Au-PEG-Pt resulted in complete destruction of the tumor tissue without recurrence, while chemotherapy using Pd@Au-PEG-Pt without irradiation or photothermal treatment using Pd@Au-PEG alone did not. Our work highlights the prospects of a feasible drug delivery strategy of the Pt prodrug by using 2D Pd@Au nanoplates as drug delivery carriers for multimode cancer treatment.Owing to the excellent near infrared (NIR) light absorption and efficient passive targeting toward tumor tissue, two-dimensional (2D) core-shell PEGylated Pd@Au nanoplates have great potential in both photothermal therapy and drug delivery systems. In this work, we successfully conjugate Pd@Au nanoplates with a platinum(iv) prodrug c,c,t-[Pt(NH3)2Cl2(O2CCH2CH2CO2H)2] to obtain a nanocomposite (Pd@Au-PEG-Pt) for combined photothermal-chemotherapy. The

  7. Thermal diffusivity of nanofluids containing Au/Pd bimetallic nanoparticles of different compositions.

    Science.gov (United States)

    Sánchez-Ramírez, J F; Jiménez Pérez, J L; Cruz Orea, A; Gutierrez Fuentes, R; Bautista-Hernández, A; Pal, U

    2006-03-01

    Colloidal suspensions of bimetallic Au/Pd nanoparticles were prepared by simultaneous reduction of the metal ions from their corresponding chloride salts with polymer (PVP) stabilizer. Thermal properties of water containing bimetallic nanoparticles with different nominal compositions (Au/Pd = 12/1, 5/1, 1/1, 1/5) were measured using the mode mismatched dual-beam thermal lens technique to determine the effect of particle composition on the thermal diffusivity of the nanofluids. The characteristic time constant of the transient thermal lens was estimated by fitting the experimental data to the theoretical expression for transient thermal lens. The thermal diffusivity of the nanofluids (water, containing Au/Pd bimetallic nanoparticles) is seen to be strongly dependent on the composition of the particles. The maximum diffusivity was achieved for the nanoparticles with highest Au/Pd molar ratio. A possible mechanism for such high thermal diffusivity of the nanofluids with bimetallic particles is given. UV-Vis spectroscopy, TEM and high-resolution electron microscopy (HREM) techniques were used to characterize the Au/Pd bimetallic nanoparticles. PMID:16573121

  8. Site-specific growth of Au-Pd alloy horns on Au nanorods: a platform for highly sensitive monitoring of catalytic reactions by surface enhancement Raman spectroscopy.

    Science.gov (United States)

    Huang, Jianfeng; Zhu, Yihan; Lin, Ming; Wang, Qingxiao; Zhao, Lan; Yang, Yang; Yao, Ke Xin; Han, Yu

    2013-06-12

    Surface-enhanced Raman scattering (SERS) is a highly sensitive probe for molecular detection. The aim of this study was to develop an efficient platform for investigating the kinetics of catalytic reactions with SERS. To achieve this, we synthesized a novel Au-Pd bimetallic nanostructure (HIF-AuNR@AuPd) through site-specific epitaxial growth of Au-Pd alloy horns as catalytic sites at the ends of Au nanorods. Using high-resolution electron microscopy and tomography, we successfully reconstructed the complex three-dimensional morphology of HIF-AuNR@AuPd and identified that the horns are bound with high-index {11l} (0.25 facets. With an electron beam probe, we visualized the distribution of surface plasmon over the HIF-AuNR@AuPd nanorods, finding that strong longitudinal surface plasmon resonance concentrated at the rod ends. This unique crystal morphology led to the coupling of high catalytic activity with a strong SERS effect at the rod ends, making HIF-AuNR@AuPd an excellent bifunctional platform for in situ monitoring of surface catalytic reactions. Using the hydrogenation of 4-nitrothiophenol as a model reaction, we demonstrated that its first-order reaction kinetics could be accurately determined from this platform. Moreover, we clearly identified the superior catalytic activity of the rod ends relative to that of the rod bodies, owing to the different SERS activities at the two positions. In comparison with other reported Au-Pd bimetallic nanostructures, HIF-AuNR@AuPd offered both higher catalytic activity and greater detection sensitivity. PMID:23675958

  9. Site-specific growth of Au-Pd alloy horns on Au nanorods: A platform for highly sensitive monitoring of catalytic reactions by surface enhancement raman spectroscopy

    KAUST Repository

    Huang, Jianfeng

    2013-06-12

    Surface-enhanced Raman scattering (SERS) is a highly sensitive probe for molecular detection. The aim of this study was to develop an efficient platform for investigating the kinetics of catalytic reactions with SERS. To achieve this, we synthesized a novel Au-Pd bimetallic nanostructure (HIF-AuNR@AuPd) through site-specific epitaxial growth of Au-Pd alloy horns as catalytic sites at the ends of Au nanorods. Using high-resolution electron microscopy and tomography, we successfully reconstructed the complex three-dimensional morphology of HIF-AuNR@AuPd and identified that the horns are bound with high-index {11l} (0.25 < l < 0.43) facets. With an electron beam probe, we visualized the distribution of surface plasmon over the HIF-AuNR@AuPd nanorods, finding that strong longitudinal surface plasmon resonance concentrated at the rod ends. This unique crystal morphology led to the coupling of high catalytic activity with a strong SERS effect at the rod ends, making HIF-AuNR@AuPd an excellent bifunctional platform for in situ monitoring of surface catalytic reactions. Using the hydrogenation of 4-nitrothiophenol as a model reaction, we demonstrated that its first-order reaction kinetics could be accurately determined from this platform. Moreover, we clearly identified the superior catalytic activity of the rod ends relative to that of the rod bodies, owing to the different SERS activities at the two positions. In comparison with other reported Au-Pd bimetallic nanostructures, HIF-AuNR@AuPd offered both higher catalytic activity and greater detection sensitivity. © 2013 American Chemical Society.

  10. Hydrogen sensing with optical microfibers coated with Pd/Au nanoparticles

    Science.gov (United States)

    Monzón-Hernández, David; Luna-Moreno, Donato; Martínez-Escobar, Dalia; Villatoro, Joel

    2010-10-01

    Optical microfibers decorated with PdAu nanoparticles are proposed for fast hydrogen sensing. The microfibers were obtained by simply tapering conventional telecommunications fiber down to dimensions comparable to the wavelength of the guided light. A few millimeters of the microfiber were coated with a PdAu layer in island form by depositing the layer at low evaporation rate (0.1 Å/s). Then the islands were grown with a thermal annealing process until composite nanoparticles were formed. The PdAu nanoparticles deposited on the optical microfibers experience optical and physical changes when they exposed to hydrogen. This gives rise to reversible transmission changes with an unusual pulsed like behavior which is attributed to scattering of the guided light. The devices are promising for detecting low concentrations of hydrogen (up to 8%) at room temperature with response and recovery times on the order of seconds.

  11. Highly energetic nonequilibrium microstructure fabricated by ion beam manipulation in the Ag-Pd system

    CERN Document Server

    Li, Z C

    2003-01-01

    An artificial ordered layered structure of high energy was obtained by a form of ion beam manipulation, namely interface-assisted ion beam mixing, of appropriately designed nano-sized Ag-Pd multilayered films, in which the interfacial free energy elevated the Ag-Pd multilayered films to near to the corresponding highly energetic state. Diffraction analysis suggested that the ordered layered structure consisted of two overlapped face-centred-cubic lattices with lattice constants smaller than those of both pure Ag and pure Pd. The growth mechanism was also discussed in terms of a dynamic atomic collision, followed by a relaxation lasting for an extremely short time, involved in the irradiation process.

  12. Squeezing and stretching Pd thin films: A high-resolution STM study of Pd/Au(111) and Pd/Cu(111) bimetallics

    Science.gov (United States)

    Blecher, Mishan E.; Lewis, Emily A.; Pronschinske, Alex; Murphy, Colin J.; Mattera, Michael F. G.; Liriano, Melissa L.; Sykes, E. Charles H.

    2016-04-01

    Pd bimetallic alloys are promising catalysts, especially for heterogeneous reactions involving hydrogen, as they exhibit increased activity and reduced demand for expensive precious metals. Using scanning tunneling microscopy, we examine the structure of Pd thin films on Cu(111) and Au(111) and demonstrate compression and expansion, respectively, of the bulk Pd lattice constant in the film. The relative binding strength of H to the two surfaces, inferred via tip-induced diffusion barriers, suggests that the strain in these systems may alter adsorbate binding and corroborates well-known trends in d-band shifts calculated by the density functional theory. Modification to the topography and activity of Pd films based on the choice of substrate metal illustrates the value of bimetallic systems for designing less expensive, tunable catalysts.

  13. Adsorption of Au and Pd on Ruthenium-Supported Bilayer Silica

    OpenAIRE

    Büchner, C.; L. Lichtenstein; Stuckenholz, S.; Heyde, M; Ringleb, F.; Sterrer, M.; Kaden, W.; Giordano, L; G. Pacchioni; H. Freund

    2014-01-01

    Adsorption of Au and Pd over bilayer SiO2/Ru has been investigated using scanning-probe microscopy, X-ray photoemission spectroscopy (XPS), and density functional theory (DFT). Low temperature (∼5 K) atomic force (AFM) and scanning tunneling microscopy (STM) measurements reveal the presence of small adsorption features after exposing the samples to small doses of either metal. In the case of Pd, we note a homogeneous distribution of adsorbates across the entire surface, which consists of both...

  14. Label free detection of DNA on Au/ZnO/Ag hybrid structure based SERS substrate

    Science.gov (United States)

    Pal, Anil Kumar; Mohan, D. Bharathi

    2016-04-01

    Au/ZnO/Ag based SERS substrate was fabricated for the label free detection of DNA of Escherichia Coli bacteria. The SERS substrate was fabricated by growing ZnO nanorod arrays on thermally evaporated ultrathin Ag film of 5 nm thickness using hydrothermal process. Non-spherical like Au nanoparticles were decorated on ZnO nanorod arrays by sputtering technique with sputtering time of 45 sec. The surface of Au/ZnO/Ag was observed to be nearly superhydrophobic exhibiting the contact angle of 144 °. A low volume (5 µl) of aqueous solution of DNA of laboratory strain Escherichia Coli with very low concentration was adsorbed on fabricated SERS substrate by drop casting. The SERS detection of DNA molecules was achieved up to lower concentration of 10-8 M due to strong local electric field enhancement at the nanometer gap among Au nanoparticles and superhydrophobic nature of Au/ZnO/Ag surface.

  15. Solvent and stabilizer free growth of Ag and Pd nanoparticles using metallic salts/cyclotriphosphazenes mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Díaz Valenzuela, C. [Departamento de Química, Facultad de Química, Universidad de Chile, La Palmeras 3425, Nuñoa, Casilla 653, Santiago de Chile (Chile); Valenzuela, M.L., E-mail: mlvalenzuela@unab.cl [Universidad Andres Bello, Departamento de Ciencias Química, Facultad de Ciencias Exactas, Av. Republica 275, Santiago (Chile); Caceres, S.; Diaz, R. [Departamento de Química, Facultad de Química, Universidad de Chile, La Palmeras 3425, Nuñoa, Casilla 653, Santiago de Chile (Chile); O' Dwyer, C. [Applied Nanoscience Group, Department of Chemistry, University College Cork, Cork (Ireland); Micro and Nanoelectronics Centre, Tyndall National Institute, Lee Maltings, Cork (Ireland)

    2013-12-16

    Cyclotriphosphazene is used as a sacrificial solid-state template to synthesize a range of Ag and Pd nanoparticles with diverse geometries by thermal treatment using MLn/N{sub 3}P{sub 3}(O{sub 2}C{sub 12}H{sub 8}){sub 3} mixtures. The Pd and Ag nanoparticles are synthesized by solid-state pyrolysis of AgPPh{sub 3}[CF{sub 3}SO{sub 3}]/N{sub 3}P{sub 3}(O{sub 2}C{sub 12}H{sub 8}){sub 3} and PdCl{sub 2}/N{sub 3}P{sub 3}(O{sub 2}C{sub 12}H{sub 8}){sub 3} mixtures with molar relationships of 1:1, 1:5 and 1:10 respectively, in air and at 800 °C. The morphology of the as-prepared nanoparticles is found to depend on the molar ratio of the precursor mixture, the preparation method and of the nature of the metal. Ag and Pd, microcrystals were thermally grown on Si from the respective 1:1 precursors while that metal foams were grown from 1:5 ratios precursors on SiO{sub 2} wafers. High resolution transmission electron microscopy investigations reveal in most cases small crystals of Pd. HRSTEM measurements indicate that the formation of the Pd and Ag nanoparticles occurs through a phase demixing and dewetting mechanism. This approach has potential to be a useful and facile method to prepare metallic nanoparticles without requiring solutions or surfactants for application in electronic, catalytic and sensor materials and devices. - Highlights: • Pyrolysis MLn/N{sub 3}P{sub 3}(O{sub 2}C{sub 12}H{sub 8}){sub 3} mixtures under air, give Pd and Ag nanoparticles. • AgPPh{sub 3}[CF{sub 3}SO{sub 3}] and PdCl{sub 2} in molar ratios 1:1 and 1:5 were used. • Metal foams were obtained from 1:5 ratios when deposited on SiO{sub 2.} • Using crucible supporting in 1:1 metal/trimer <2 nm Pd nanoparticles were obtained. • The probable mechanism involves a dewetting, nucleation and ripening crystallization.

  16. Enhanced activity and stability of a Au decorated Pt/PdCo/C electrocatalyst toward oxygen reduction reaction

    International Nuclear Information System (INIS)

    Highlights: ► Pt/Au/PdCo/C was obtained by consecutive UPD-replacement on PdCo/C substrate. ► Pt mass activity toward the ORR for Pt/Au/PdCo/C was 4-fold of that for Pt/PdCo/C. ► The stability of Pt/Au/PdCo/C was enhanced significantly via Au decoration. ► The improvements were ascribed to the suppressed OH coverage on Au decorated Pt. - Abstract: Carbon-supported Pt/PdCo and Pt/Au/PdCo catalysts with a low Pt loading were prepared by a combined underpotential deposition and galvanic replacement route. The X-ray diffraction results show that after annealing in H2/Ar atmosphere, the alloy degree of PdCo is enhanced. The average metal particle size of PdCo/C, PdCo/C-H, Pt/PdCo/C and Pt/Au/PdCo/C, characterized by transmission electron microscopy, is about 2.6, 4.1, 5.3 and 5.5 nm, respectively. The electrochemical characterizations show that the Pt/PdCo/C electrocatalyst exhibits a high activity toward the oxygen reduction reaction (ORR) but is unstable in electrochemical environment. After the accelerated aging tests (AAT), the electrochemical surface area (ECSA) for the Pt/PdCo/C catalyst decreases by 48% and the half-wave potential of the ORR polarization curve (E1/2) shifts 35 mV negatively. After decorated by Au, both the catalytic activity and stability of the Pt/PdCo/C catalyst are improved significantly. Compared to Pt/PdCo/C, the E1/2 for Pt/Au/PdCo/C shifts 22 mV toward higher potentials. After the AAT, the ECSA decreases only 26%, and the E1/2 shifts 13 mV negatively for Pt/Au/PdCo/C. The enhanced catalytic activity and stability should be due to the high resistance to be oxidized for Pt and the suppressed OH adsorption on the Au-decorated Pt surface.

  17. A novel TiO2 nanofiber supported PdAg catalyst for methanol electro-oxidation

    International Nuclear Information System (INIS)

    A novel PdAg/TiO2 nanofiber electrocatalyst for methanol oxidation was fabricated by using TiO2 nanofiber as support. The structural and electrochemical properties of the PdAg/TiO2 nanofiber catalyst were characterized by XRD (X-ray diffraction), TEM (the transmission electron microscopy) and electrochemical analysis. The experiment results showed that the large surface area and porous structure of TiO2 nanofiber were preferable to the dispersion of nanosized PdAg alloy on the surface of TiO2 nanofiber support. The electrocatalytic activity for methanol oxidation of the PdAg/TiO2 nanofiber catalyst has shown promising electrocatalytic and anti-poisoning capabilities. The methanol oxidation mechanism of the PdAg/TiO2 nanofiber catalyst was mainly resulted from the photocatalytic function of the composite TiO2 material that had high catalytic activity without UV light illumination. The PdAg/TiO2 catalyst might become a promising candidate for direct methanol fuel cell. - Highlights: • Novel non-Pt catalyst of PdAg/TiO2 nanofiber for methanol oxidation is fabricated. • PdAg alloy is dispersed uniformly on the surface of TiO2 nanofiber support. • The novel catalyst shows promising electrocatalytic activity and anti-poisoning ability. • The methanol oxidation mechanism of the catalyst results from photocatalytic mechanism of TiO2

  18. Pd@Ag Nanosheets in Combination with Amphotericin B Exert a Potent Anti-Cryptococcal Fungicidal Effect

    Science.gov (United States)

    Wang, Guizhen; Fang, Wei; Ye, Chen; Hu, Hanhua; Fa, Zhenzong; Yi, Jiu; Liao, Wan-qing

    2016-01-01

    Silver nanoparticles have received considerable interest as new “nanoantibiotics” with the potential to kill drug-resistant microorganisms. Recently, a class of new core-shell nanostructures, Pd@Ag nanosheets (Pd@Ag NSs), were created using deposition techniques and demonstrated excellent inhibitory effects on various bacteria in vitro. In this study, we evaluated the antifungal activity of Pd@Ag NSs against common invasive fungal pathogens. Among these organisms, Cryptococcus neoformans complex species was most susceptible to Pd@Ag NSs, which exhibited potent antifungal activity against various molecular types or sources of cryptococcal strains including fluconazole-resistant isolates. The anticryptococcal activity of Pd@Ag NSs was significantly greater than fluconazole and similar to that of amphotericin B (AmB). At relatively high concentrations, Pd@Ag NSs exhibited fungicidal activity against Cryptococcus spp., which can likely be attributed to the disruption of cell integrity, intracellular protein synthesis, and energy metabolism. Intriguingly, Pd@Ag NSs also exhibited strong synergistic anti-cryptococcal fungicidal effects at low concentrations in combination with AmB but exhibited much better safety in erythrocytes than AmB, even at the minimal fungicidal concentration. Therefore, Pd@Ag NSs may be a promising adjunctive agent for treating cryptococcosis, and further investigation for clinical applications is required. PMID:27271376

  19. Atomic simulation of amorphization and crystallization of Ag50 Au50 alloy during rapid solidification

    Institute of Scientific and Technical Information of China (English)

    王丽; 杨华; 张均艳; 边秀房; 衣粟

    2002-01-01

    By means of constant temperature and constant pressure molecular dynamic simulation technique, a series of simulations of the glass transition and crystallization processes of Ag50Au50 were performed. The atoms interact via EAM potential function. Pair correlation functions of liquid Ag50Au50 during different cooling rates and temperatures were simulated to reveal the structural features of liquid, super-cooled liquid, glass state and crystal. The thermodynamics and kinetics of structure transition of Ag50Au50 during cooling processes were performed.

  20. Sulfur Tolerant Pd/Cu and Pd/Au Alloy Membranes for H2 Separation with High Pressure CO2 for Sequestration

    Energy Technology Data Exchange (ETDEWEB)

    Yi Hua Ma; Natalie Pomerantz; Chao-Huang Chen

    2008-09-30

    The effect of H{sub 2}S poisoning on Pd, Pd/Cu, and Pd/Au alloy composite membranes prepared by the electroless deposition method on porous Inconel supports was investigated to provide a fundamental understanding of the durability and preparation of sulfur tolerant membranes. X-ray photoelectron spectroscopy (XPS) studies showed that the exposure of pure Pd to 50 ppm H{sub 2}S/H{sub 2} mixtures caused bulk sulfide formation at lower temperatures and surface sulfide formation at higher temperatures. Lower temperatures, longer exposure times, and higher H{sub 2}S concentrations resulted in a higher degree of sulfidation. In a Pd membrane, the bulk sulfide formation caused a drastic irrecoverable H{sub 2} permeance decline and an irreparable loss in selectivity. Pd/Cu and Pd/Au alloy membranes exhibited permeance declines due to surface sulfide formation upon exposure to 50 ppm H{sub 2}S/H{sub 2} gas mixtures. However in contrast to the pure Pd membrane, the permeances of the Pd/Cu and Pd/Au alloy membranes were mostly recovered in pure H{sub 2} and the selectivity of the Pd alloy layers remained essentially intact throughout the characterization in H{sub 2}, He and H{sub 2}S/H{sub 2} mixtures which lasted several thousand hours. The amount of irreversible sulfur poisoning decreased with increasing temperature due to the exothermicity of H{sub 2}S adsorption. Longer exposure times increased the amount of irreversible poisoning of the Pd/Cu membrane but not the Pd/Au membrane. Pd/Au coupon studies of the galvanic displacement method showed that higher Au{sup 3+} concentrations, lower pH values, higher bath temperatures and stirring the bath at a rate of 200 rpm yielded faster displacement rates, more uniform depositions, and a higher Au content within the layers. While 400 C was found to be sufficient to form a Pd/Au alloy on the surface, high temperature X-ray diffraction (HTXRD) studies showed that even after annealing between 500-600 C, the Pd/Cu alloys could have

  1. Final Technical Report: First Principles Investigations for the Ensemble Effects of PdAu and PtAu Bimetallic Nanocatalysts

    Energy Technology Data Exchange (ETDEWEB)

    Ruqian Wu

    2012-05-18

    Bimetallic surfaces with tunable chemical properties have attracted broad attention in recent years due to their ample potential for heterogeneous catalysis applications. The local chemical properties of constituents are strongly altered from their parent metals by 'ligand effect', a term encompassing the influences of charge transfer, orbital rehybridization and lattice strain. In comparison to the aforementioned, the 'ensemble effect' associated with particular arrangements of the active constituents have received much less attention, despite their notable importance towards the determination of reactivity and selectivity of bimetallic catalysts. We performed theoretical studies for understanding the ensemble effects on bimetallic catalysis: (i) simulations for the formation of different ensembles on PdAu and PtAu nanoclusters; (ii) studies of the size, shape, and substrate dependence of their electronic properties; and (iii) simulations for model reactions such as CO oxidation, methanol, ethylene and water dehydrogenation on PdAu and PtAu nanoclusters. In close collaboration with leading experimental groups, our theoretical research elucidated the fundamentals of Au based bimetallic nanocatalysts.

  2. Nanoporous Ag and Pd foam: Redox induced fabrication using electrochemically deposited nanoporous Cu foam with no need to any additive

    International Nuclear Information System (INIS)

    A simple, rapid and green method for fabrication of nanoporous metal (Ag and Pd) foams using electrochemically deposited nanoporous copper foam is presented. Ideally direct electrochemical formation of Ag and Pd foam structures without any additive reagent does not lead to a desired result; however, indirect fabrication starting from electrochemically fabricated Cu foam seems promising. Highly porous copper foam is fabricated electrochemically at a copper sheet and in turn serves as a hard template and a redox inducer for the deposition of Ag or Pd. The redox induced replacement of copper foam with Ag or Pd is done via simple immersion of as-fabricated nanoporous copper foam in cation aqueous solutions of Ag or Pd. The surface morphology of the as-fabricated foam is characterized by scanning electron microscopy (SEM), EDX and X-ray diffraction. The hydrogen evolution reaction is investigated as an example to demonstrate the electrocatalytic ability of as-fabricated foams.

  3. Ethanol electro-oxidation in alkaline medium using Pd/MWCNT and PdAuSn/MWCNT electrocatalysts prepared by electron beam irradiation

    International Nuclear Information System (INIS)

    Environmental problems and the world growing demand for energy has mobilized the scientific community in finding of clean and renewable energy sources. In this context, fuel cells appear as appropriate technology for generating electricity through alcohols electro-oxidation. Multi Wall Carbon Nanotubes (MWCNT)-supported Pd and trimetallic PdAuSn (Pd:Au:Sn 50:10:40 atomic ratio) electrocatalysts were prepared using electron beam irradiation. The obtained materials were characterized by VC, Chronoamperometry, EDX, TEM and XRD. The catalytic activities of electrocatalysts toward ethanol electro-oxidation were evaluated in alkaline medium in a single alkaline direct ethanol fuel cell (ADEFC) in a range temperature 60 to 90 deg C. The best performances were obtained at 85 deg C: 33 mW.cm-2 and 31 mW.cm-2 for Pd/ MWCNT and PdAuSn/MWCNT electrocatalysts, respectively. X-ray diffractograms of electrocatalysts showed the presence of Pd-rich (fcc) and Au-rich (fcc) phases. Cyclic voltammetry and chronoamperometry experiments showed that PdAuSn/MWCNT electrocatalyst demonstrated similar activity toward ethanol electro-oxidation at room temperature, compared to electrocatalyst Pd/MWCNT. (author)

  4. Ethanol electro-oxidation in alkaline medium using Pd/MWCNT and PdAuSn/MWCNT electrocatalysts prepared by electron beam irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Geraldes, Adriana Napoleao; Silva, Dionisio Furtunato da; Andrade e Silva, Leonardo Gondin de; Spinace, Estevam Vitorio; Oliveira Neto, Almir, E-mail: drinager@ig.com.br, E-mail: dfsilva@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Santos, Mauro Coelho dos [Universidade Federal do ABC (LEMN/CCNH/UFABC), Santo Andre, SP (Brazil)

    2015-07-01

    Environmental problems and the world growing demand for energy has mobilized the scientific community in finding of clean and renewable energy sources. In this context, fuel cells appear as appropriate technology for generating electricity through alcohols electro-oxidation. Multi Wall Carbon Nanotubes (MWCNT)-supported Pd and trimetallic PdAuSn (Pd:Au:Sn 50:10:40 atomic ratio) electrocatalysts were prepared using electron beam irradiation. The obtained materials were characterized by VC, Chronoamperometry, EDX, TEM and XRD. The catalytic activities of electrocatalysts toward ethanol electro-oxidation were evaluated in alkaline medium in a single alkaline direct ethanol fuel cell (ADEFC) in a range temperature 60 to 90 deg C. The best performances were obtained at 85 deg C: 33 mW.cm{sup -2} and 31 mW.cm{sup -2} for Pd/ MWCNT and PdAuSn/MWCNT electrocatalysts, respectively. X-ray diffractograms of electrocatalysts showed the presence of Pd-rich (fcc) and Au-rich (fcc) phases. Cyclic voltammetry and chronoamperometry experiments showed that PdAuSn/MWCNT electrocatalyst demonstrated similar activity toward ethanol electro-oxidation at room temperature, compared to electrocatalyst Pd/MWCNT. (author)

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

    Science.gov (United States)

    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

  6. Formation of the heavy fermion ground state in UPt4M1, M=Au, Ag, Cu

    International Nuclear Information System (INIS)

    Based on comparisons of the low temperature specific heat and susceptibility of single phase UPt4M1, where M=Au0.5Pt0.5, Au0.7Ag0.3, Au0.5Ag0.5, Au0.7Cu0.3, and Au0.5Cu0.5, it is found that the formation of large m* in this system is essentially just as dependent on subtle differences of the electronic properties of Au and Ag as on lattice parameter and Pt versus Au differences. ((orig.))

  7. Electrochemical synthesis of reduced graphene sheet-AuPd alloy nanoparticle composites for enzymatic biosensing.

    Science.gov (United States)

    Yang, Jiang; Deng, Shengyuan; Lei, Jianping; Ju, Huangxian; Gunasekaran, Sundaram

    2011-11-15

    A simple, fast, green and controllable approach was developed for electrochemical synthesis of a novel nanocomposite of electrochemically reduced graphene oxide (ERGO) and gold-palladium (1:1) bimetallic nanoparticles (AuPdNPs), without the aid of any reducing reagent. The electrochemical reduction efficiently removed oxygen-containing groups in ERGO, which was then modified with homogeneously dispersed AuPdNPs in a good size distribution. ERGO-AuPdNPs nanocomposite showed excellent biocompatibility, enhanced electron transfer kinetics and large electroactive surface area, and were highly sensitive and stable towards oxygen reduction. A biosensor was constructed by immobilizing glucose oxidase as a model enzyme on the nanocomposites for glucose detection through oxygen consumption during the enzymatic reaction. The biosensor had a detection limit of 6.9μM, a linear range up to 3.5mM and a sensitivity of 266.6μAmM(-1)cm(-2). It exhibited acceptable reproducibility and good accuracy with negligible interferences from common oxidizable interfering species. These characteristics make ERGO-AuPdNPs nanocomposite highly suitable for oxidase-based biosensing. PMID:21903376

  8. Nanoscale electrical characteristics of metal (Au, Pd)-graphene-metal (Cu) contacts

    Science.gov (United States)

    Ruffino, F.; Meli, G.; Grimaldi, M. G.

    2016-01-01

    Free-standing graphene presents exceptional physical properties (as a high carrier mobility) making it the ideal candidate for the next generation nanoelectronics. However, when graphene layers are inserted in real electronics devices, metal contacting is required. The metal-graphene interaction significantly affects the graphene electrical properties, drastically changing its behavior with respect to the free-standing configuration. So, this work presents an experimental study on the nanoscale electric characteristics of metal/graphene/metal contacts. In particular, starting from single-layer graphene grown on Cu foil we deposited on the graphene surface two different metal films (Au or Pd) and the Au/graphene/Cu and Pd/graphene/Cu current-voltage characteristics are acquired, on the nanometric scale, by the conductive atomic force microscopy. Both systems presented a current voltage rectifying behavior. However, the Au/graphene/Cu system conducts significantly at negative applied bias (graphene behaves as a p-type semiconductor in a meta/semiconductor contact), while in the Pd/graphene/Cu at positive applied bias (graphene behaves as a n-type semiconductor in a metal/semiconductor contact). This difference is discussed on the basis of the band energy diagram at the metal/graphene interface and the modification of the graphene Fermi level due to the Au/graphene or Pd/graphene interaction.

  9. Green synthesis of noble nanometals (Au, Pt, Pd) using glycerol under microwave irradiation conditions

    Science.gov (United States)

    A newer application of glycerol in the field of nanomaterials synthesis has been developed from both the economic and environmental points of view. Glycerol can act as a reducing agent for the fabrication of noble nanometals, such as Au, Pt, and Pd, under microwave irradiation. T...

  10. Experimental determination of phase equilibria and reassessment of Ag-Pd system

    Czech Academy of Sciences Publication Activity Database

    Sopoušek, J.; Zemanová, Adéla; Vřešťál, J.; Brož, P.

    2010-01-01

    Roč. 504, č. 2 (2010), s. 431-434. ISSN 0925-8388 Institutional research plan: CEZ:AV0Z20410507 Keywords : Ag-Pd system * thermal analysis * CALPHAD Subject RIV: BJ - Thermodynamics Impact factor: 2.138, year: 2010

  11. Structures of AgPd nanoclusters adsorbed on MgO(100): A computational study

    Czech Academy of Sciences Publication Activity Database

    Negreiros, F. R.; Barcaro, G.; Kuntová, Zdeňka; Rossi, G.; Ferrando, R.; Fortunelli, A.

    2011-01-01

    Roč. 605, 5-6 (2011), s. 483-488. ISSN 0039-6028 Institutional research plan: CEZ:AV0Z10100521 Keywords : AgPd clusters * nanoparticle * bimetallic clusters * superstable polyicosahedra Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.994, year: 2011

  12. Characterization and electrocatalytic properties of sonochemical synthesized PdAg nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Godinez-Garcia, Andres, E-mail: agodinez@qro.cinvestav.mx [Depto. Materiales, Centro de Investigacion y de Estudios Avanzados del IPN, Libramiento norponiente 2000, Fracc. Real de Juriquilla, C.P. 76230 Santiago de Queretaro, Qro. (Mexico); Perez-Robles, Juan Francisco [Depto. Materiales, Centro de Investigacion y de Estudios Avanzados del IPN, Libramiento norponiente 2000, Fracc. Real de Juriquilla, C.P. 76230 Santiago de Queretaro, Qro. (Mexico); Martinez-Tejada, Hader Vladimir [Grupo de Energia y Termodinamica, Universidad Pontificia Bolivariana, Medellin, Antioquia C.P. 050031 (Colombia); Solorza-Feria, Omar [Depto. Quimica, CINVESTAV-IPN, Av. IPN 2508, A. P. 14-740, 07360 D.F. Mexico (Mexico)

    2012-06-15

    High intensity ultrasound was used in the synthesis of PdAg nanoparticles. PdAg nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), scanning transmission electron microscopy (STEM) and high-resolution transmission electron microscopy (HRTEM). Catalytic properties for oxygen reduction reaction (ORR) were determined by electrochemical techniques of cyclic voltammetry (CV) and thin-film rotating disk electrode (TF-RDE). Finally the electrocatalyst was tested as a cathode in a single polymer electrolyte membrane fuel cell (PEMFC). Sonochemical synthesis (SS) decreased the overpotential required for the ORR and increased the double-layer capacitance (DLC) respect to the sodium borohydride reduction method due to a better distribution on vulcan carbon support. The electrocatalytic activity of the nanometric bimetallic electrocatalyst for the ORR in acid media showed a favorable multielectron charge transfer process (n = 4e{sup -}) to water formation. The performance of the membrane electrode assembly (MEA) prepared with dispersed PdAg/C as a cathode catalyst in a single PEMFC is lower in comparison to platinum. - Highlights: Black-Right-Pointing-Pointer Sonochemical synthesized PdAg nanoparticles supported on carbon were produced. Black-Right-Pointing-Pointer The material showed catalytic properties for the oxygen reduction reaction (ORR). Black-Right-Pointing-Pointer The ORR favored the pathway to water formation.

  13. Characterization and electrocatalytic properties of sonochemical synthesized PdAg nanoparticles

    International Nuclear Information System (INIS)

    High intensity ultrasound was used in the synthesis of PdAg nanoparticles. PdAg nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), scanning transmission electron microscopy (STEM) and high-resolution transmission electron microscopy (HRTEM). Catalytic properties for oxygen reduction reaction (ORR) were determined by electrochemical techniques of cyclic voltammetry (CV) and thin-film rotating disk electrode (TF-RDE). Finally the electrocatalyst was tested as a cathode in a single polymer electrolyte membrane fuel cell (PEMFC). Sonochemical synthesis (SS) decreased the overpotential required for the ORR and increased the double-layer capacitance (DLC) respect to the sodium borohydride reduction method due to a better distribution on vulcan carbon support. The electrocatalytic activity of the nanometric bimetallic electrocatalyst for the ORR in acid media showed a favorable multielectron charge transfer process (n = 4e−) to water formation. The performance of the membrane electrode assembly (MEA) prepared with dispersed PdAg/C as a cathode catalyst in a single PEMFC is lower in comparison to platinum. - Highlights: ► Sonochemical synthesized PdAg nanoparticles supported on carbon were produced. ► The material showed catalytic properties for the oxygen reduction reaction (ORR). ► The ORR favored the pathway to water formation.

  14. Morphology and N₂ Permeance of Sputtered Pd-Ag Ultra-Thin Film Membranes.

    Science.gov (United States)

    Fernandez, Ekain; Sanchez-Garcia, Jose Angel; Viviente, Jose Luis; van Sint Annaland, Martin; Gallucci, Fausto; Tanaka, David A Pacheco

    2016-01-01

    The influence of the temperature during the growth of Pd-Ag films by PVD magnetron sputtering onto polished silicon wafers was studied in order to avoid the effect of the support roughness on the layer growth. The surfaces of the Pd-Ag membrane films were analyzed by atomic force microscopy (AFM), and the results indicate an increase of the grain size from 120 to 250-270 nm and film surface roughness from 4-5 to 10-12 nm when increasing the temperature from around 360-510 K. After selecting the conditions for obtaining the smallest grain size onto silicon wafer, thin Pd-Ag (0.5-2-µm thick) films were deposited onto different types of porous supports to study the influence of the porous support, layer thickness and target power on the selective layer microstructure and membrane properties. The Pd-Ag layers deposited onto ZrO₂ 3-nm top layer supports (smallest pore size among all tested) present high N₂ permeance in the order of 10(-6) mol·m(-2)·s(-1)·Pa(-1) at room temperature. PMID:26875977

  15. Morphology and N2 Permeance of Sputtered Pd-Ag Ultra-Thin Film Membranes

    Directory of Open Access Journals (Sweden)

    Ekain Fernandez

    2016-02-01

    Full Text Available The influence of the temperature during the growth of Pd-Ag films by PVD magnetron sputtering onto polished silicon wafers was studied in order to avoid the effect of the support roughness on the layer growth. The surfaces of the Pd-Ag membrane films were analyzed by atomic force microscopy (AFM, and the results indicate an increase of the grain size from 120 to 250–270 nm and film surface roughness from 4–5 to 10–12 nm when increasing the temperature from around 360–510 K. After selecting the conditions for obtaining the smallest grain size onto silicon wafer, thin Pd-Ag (0.5–2-µm thick films were deposited onto different types of porous supports to study the influence of the porous support, layer thickness and target power on the selective layer microstructure and membrane properties. The Pd-Ag layers deposited onto ZrO2 3-nm top layer supports (smallest pore size among all tested present high N2 permeance in the order of 10−6 mol·m−2·s−1·Pa−1 at room temperature.

  16. Spectral Tuning of Plasmon Resonance in a Core/Shell (Au)Ag Nanocomposite

    Science.gov (United States)

    Panarin, A. Yu.; Abakshonok, A. V.; Agabekov, V. E.; Eryomin, A. N.; Terekhov, S. N.

    2015-01-01

    A bimetallic (Au)Ag nanocomposite with a core/shell structure was synthesized in aqueous solution and a H2O/EtOH mixture (1:1) containing polymers (carboxymethylcellulose, sodium polystyrenesulfonate, polyvinylpyrrolidone, dextran). Its structure and optical properties were characterized. The shape and position of scattering bands of colloidal noble-metal nanoparticles with optical density <0.1 were undistorted by solvent absorption. Scattering spectra had to be corrected for solutions of greater optical density. A method for correcting the resonant lightscattering spectra of Au and (Au)Ag nanoparticles was proposed for a single-beam apparatus. The possibility of surface plasmon resonance tuning for (Au)Ag with a short-wavelength shift of ~150 nm for the absorption band maximum and of ~84 nm for the resonant scattering band was demonstrated by varying the AgNO3 concentration during formation of the silver shell on the gold core.

  17. H{sub 2} reduction of surface oxides on Pd-based membrane model systems – The case of Pd(1 0 0) and Pd{sub 75}Ag{sub 25}(1 0 0)

    Energy Technology Data Exchange (ETDEWEB)

    Fernandes, V.R. [Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway); Gustafson, J. [Division of Synchrotron Radiation Research, Lund University, Box 117, SE-221 00 Lund (Sweden); Farstad, M.H.; Walle, L.E. [Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway); Blomberg, S.; Lundgren, E. [Division of Synchrotron Radiation Research, Lund University, Box 117, SE-221 00 Lund (Sweden); Venvik, H.J. [Department of Chemical Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway); Borg, A., E-mail: anne.borg@ntnu.no [Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway)

    2014-09-15

    Highlights: • H{sub 2} reduction of the surface oxide is significantly slower for Pd{sub 75}Ag{sub 25}(1 0 0) compared to Pd(1 0 0). • The reduction behavior shows complex temperature dependence, not well described by Avrami kinetics. • Oxygen spillover effects during the surface oxide reduction are observed for Pd(1 0 0). • For Pd(1 0 0) the observed reduction rate is rather independent of temperature. • For Pd{sub 75}Ag{sub 25}(1 0 0) the reduction rate displays a non-monotonic variation with temperature. - Abstract: Reduction of the (√(5)×√(5))R27° surface oxide on Pd(1 0 0) and Pd{sub 75}Ag{sub 25}(1 0 0) surfaces by H{sub 2} has been studied using high-resolution photoelectron spectroscopy in situ at H{sub 2} pressures 5 × 10{sup −9} mbar and 5 × 10{sup −8} mbar and selected temperatures in the range 30 °C to 170 °C. The reduction is slower on Pd{sub 75}Ag{sub 25}(1 0 0) compared to Pd(1 0 0) for all temperatures and pressures investigated. For Pd(1 0 0), the surface oxide reduction rate is rather independent of temperature, while for Pd{sub 75}Ag{sub 25}(1 0 0) a non-monotonic variation is observed. As indicated by kinetic analysis, the complex reduction behavior is not well described by Avrami kinetics. Oxygen spillover effects contribute to this picture for Pd(1 0 0), while surface compositional effects appear to dominate the performance for Pd{sub 75}Ag{sub 25}(1 0 0). These findings may have implications for understanding the oxidation, reduction and hydrogen transport properties of Pd–Ag membranes.

  18. Characterization of Ag-Pd nanocomposite paste for electrochemical migration resistance.

    Science.gov (United States)

    Kim, Kwang-Seok; Jung, Kwang-Ho; Park, Bum-Geun; Shin, Young-Eui; Jung, Seung-Boo

    2013-11-01

    Direct printing such as inkjet, gravure, and screen printing is an attractive approach for achieving low-cost circuitry in the printed circuit board industry. One of the challenges for direct printing technology, however, is the poor resistance to electrochemical migration (ECM), especially for silver (Ag) which has been widely used in printed electronics. We demonstrate improved resistance to Ag electrochemical migration by adding palladium (Pd) nanoparticles to the Ag nanopaste. Conductive comb-type patterns were fabricated on a bismaleimide-triazine substrate via screen printing. Their ECM characteristics were assessed by water drop test with deionized water. These results showed that the ECM time required for dendritic growth from cathode to anode to cause short-circuit failure was affected by the Pd content and applied voltages: the ECM time of Ag-15wt.% Pd nanopaste was nearly threefold that of Ag nanopaste, and the ECM time decreased by 94.22%, on average, while the applied voltage increased from 3 V to 9 V. PMID:24245303

  19. Admittance Loci Based Design of a Plasmonic Structure Using Ag-Au Bimetallic Alloy Film

    OpenAIRE

    Kaushik Brahmachari; Mina Ray

    2013-01-01

    A theoretical study based on the use of admittance loci method in the design of surface plasmon resonance (SPR) based structure using Ag-Au bimetallic alloy film of different alloy fractions and nanoparticle sizes has been reported along with some interesting performance related simulated results at 633 nm wavelength. The sensitivity and other performance parameter issues of the structure based on the choice of correct alloy fraction and nanoparticle size of Ag-Au bimetallic alloy film have a...

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

    Science.gov (United States)

    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

  1. Hollow raspberry-like PdAg alloy nanospheres: High electrocatalytic activity for ethanol oxidation in alkaline media

    Science.gov (United States)

    Peng, Cheng; Hu, Yongli; Liu, Mingrui; Zheng, Yixiong

    2015-03-01

    Palladium-silver (PdAg) alloy nanospheres with unique structure were prepared using a one-pot procedure based on the galvanic replacement reaction. Their electrocatalytic activity for ethanol oxidation in alkaline media was evaluated. The morphology and crystal structure of the samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Electrochemical characterization techniques, including cyclic voltammetry (CV) and chronoamperometry (CA) measurements were used to analyze the electrochemical performance of the PdAg alloy nanospheres. The SEM and TEM images showed that the PdAg alloy nanospheres exhibit a hierarchical nanostructure with hollow interiors and porous walls. Compared to the commercial Pd/C catalyst, the as-prepared PdAg alloy nanospheres exhibit superior electrocatalytic activity and stability towards ethanol electro-oxidation in alkaline media, showing its potential as a new non-Pt electro-catalyst for direct alcohol fuel cells (DAFCs).

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

    Science.gov (United States)

    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

  3. Bimetallic Au/Pd catalyzed aerobic oxidation of alcohols in the poly(ethylene glycol)/CO2 system

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Bimetallic Au/Pd nanoparticles were prepared and used to catalyze oxidation of alcohols in the poly(ethylene glycol) (PEG)/CO2 biphasic system using O2 as the oxidant without adding any base.The catalytic activity of Au/Pd bimetal with different mole ratios was studied using benzyl alcohol as the substrate.It was found that bimetallic Au/Pd nanoparticles with Au:Pd=1:3.5 had higher catalytic activity than monometallic Au,Pd and the bimetallic Au/Pd nanoparticles with other molar ratios.The effect of CO2 pressure on the oxidation of benzyl alcohol and 1-phenylethanol in PEG/CO2 was investigated.It was demonstrated that CO2 pressure could be used to tune the conversion and selectivity of the reactions effectively.α,β-Unsaturated alcohols were also studied and found to be more reactive than benzyl alcohol and 1-phenylethanol.Recycling experiments showed that the Au/Pd/PEG/CO2 catalytic system could be recycled at least four times without reducing the activity.In addition,the catalytic system is clean and the products can be separated easily.

  4. The bifurcation point of the oxygen reduction reaction on Au-Pd nanoalloys.

    Science.gov (United States)

    Staszak-Jirkovský, Jakub; Ahlberg, Elisabet; Panas, Itai; Schiffrin, David J

    2016-07-01

    The oxygen reduction reaction is of major importance in energy conversion and storage. Controlling electrocatalytic activity and its selectivity remains a challenge of modern electrochemistry. Here, first principles calculations and analysis of experimental data unravel the mechanism of this reaction on Au-Pd nanoalloys in acid media. A mechanistic model is proposed from comparison of the electrocatalysis of oxygen and hydrogen peroxide reduction on different Au-Pd ensembles. A H2O production channel on contiguous Pd sites proceeding through intermediates different from H2O2 and OOH(σ) adsorbate is identified as the bifurcation point for the two reaction pathway alternatives to yield either H2O or H2O2. H2O2 is a leaving group, albeit reduction of H2O2 to H2O can occur by electrocatalytic HO-OH dissociation that is affected by the presence of adsorbed OOH(σ). Similarities and differences between electrochemical and direct synthesis from H2 + O2 reaction on Au-Pd nanoalloys are discussed. PMID:27089504

  5. Phytosynthesis of stable Au, Ag and Au-Ag alloy nanoparticles using J. Sambac leaves extract, and their enhanced antimicrobial activity in presence of organic antimicrobials

    Science.gov (United States)

    Yallappa, S.; Manjanna, J.; Dhananjaya, B. L.

    2015-02-01

    A green chemistry approach for the synthesis of Au, Ag and Au-Ag alloy nanoparticles (NPs) using the corresponding metal precursors and Jasminum sambac leaves extract as both reducing and capping media, under microwave irradiation, is reported. During the formation, as expected, the reaction mixture shows marginal decrease in pH and an increase in solution potential. The formation of NPs is evident from their surface plasmon resonance (SPR) peak observed at ∼555 nm for Au, ∼435 nm for Ag and ∼510 nm for Au-Ag alloy. The XRD pattern shows fcc structure while the FTIR spectra indicate the presence of plant residues adsorbed on these NPs. Such a bio-capping of NPs is characterized by their weight loss, ∼35% due to thermal degradation of biomass, as observed in TG analysis. The colloidal dispersion of NPs is stable for about 6 weeks. The near spherical shape of NPs (ϕ20-50 nm) is observed by FE-SEM/TEM images and EDAX gives the expected elemental composition. Furthermore, these NPs showed enhanced antimicrobial activity (∼1-4-fold increase in zone of inhibition) in combination with antimicrobials against test strains. Thus, the phytosynthesized NPs could be used as effective growth inhibitors for various microorganisms.

  6. Supported Pd-Au Membrane Reactor for Hydrogen Production: Membrane Preparation, Characterization and Testing

    Directory of Open Access Journals (Sweden)

    Adolfo Iulianelli

    2016-05-01

    Full Text Available A supported Pd-Au (Au 7wt% membrane was produced by electroless plating deposition. Permeation tests were performed with pure gas (H2, H2, N2, CO2, CH4 for long time operation. After around 400 h under testing, the composite Pd-Au membrane achieved steady state condition, with an H2/N2 ideal selectivity of around 500 at 420 °C and 50 kPa as transmembrane pressure, remaining stable up to 1100 h under operation. Afterwards, the membrane was allocated in a membrane reactor module for methane steam reforming reaction tests. As a preliminary application, at 420 °C, 300 kPa of reaction pressure, space velocity of 4100 h−1, 40% methane conversion and 35% hydrogen recovery were reached using a commercial Ni/Al2O3 catalyst. Unfortunately, a severe coke deposition affected irreversibly the composite membrane, determining the loss of the hydrogen permeation characteristics of the supported Pd-Au membrane.

  7. Capability of defective graphene-supported Pd13 and Ag13 particles for mercury adsorption

    Science.gov (United States)

    Meeprasert, Jittima; Junkaew, Anchalee; Rungnim, Chompoonut; Kunaseth, Manaschai; Kungwan, Nawee; Promarak, Vinich; Namuangruk, Supawadee

    2016-02-01

    Reactivity of single-vacancy defective graphene (DG) and DG-supported Pdn and Agn (n = 1, 13) for mercury (Hg0) adsorption has been studied using density functional theory calculation. The results show that Pdn binds defective site of DG much stronger than the Agn, while metal nanocluster binds DG stronger than single metal atom. Metal clustering affects the adsorption ability of Pd composite while that of Ag is comparatively less. The binding strength of -8.49 eV was found for Pd13 binding on DG surface, indicating its high stability. Analyses of structure, energy, partial density of states, and d-band center (ɛd) revealed that the adsorbed metal atom or cluster enhances the reactivity of DG toward Hg adsorption. In addition, the Hg adsorption ability of Mn-DG composite is found to be related to the ɛd of the deposited Mn, in which the closer ɛd of Mn to the Fermi level correspond to the higher adsorption strength of Hg on Mn-DG composite. The order of Hg adsorption strength on Mn-DG composite are as follows: Pd13 (-1.68 eV) >> Ag13 (-0.67 eV) ∼ Ag1 (-0.69 eV) > Pd1 (-0.62 eV). Pd13-DG composite is therefore more efficient sorbent for Hg0 removal in terms of high stability and high adsorption reactivity compared to the Ag13. Further design of highly efficient carbon based sorbents should be focused on tailoring the ɛd of deposited metals.

  8. Formation of Ag 2, Au 2 and AgAu particles on MgO(1 0 0): DFT study on the role of support-induced charge transfer in metal-metal interactions

    Science.gov (United States)

    Fuente, Silvia A.; Belelli, Patricia G.; Branda, María M.; Ferullo, Ricardo M.; Castellani, Norberto J.

    2009-05-01

    The formation of Ag 2, Au 2 and AgAu particles oriented perpendicularly to the MgO(1 0 0) surface was studied using the density functional theory. While the support induces a slight enhancement of the Ag-Ag bond (by 0.3-0.4 eV), the Au-Au bond is strongly enhanced (by 0.8-1.1 eV). Concerning the bimetallic particle, the Ag-Au bond stabilization depends on the relative position of each atom. Thus, in general terms, the strength of the metal-metal bond is determined by the nature of the terminal atom; the bond is stronger in Au-terminal particles. The partial electronic charge transfer to the terminal Au atom and its ability to polarize this charge are responsible for this energetic stabilization.

  9. Formation of Ag{sub 2}, Au{sub 2} and AgAu particles on MgO(1 0 0): DFT study on the role of support-induced charge transfer in metal-metal interactions

    Energy Technology Data Exchange (ETDEWEB)

    Fuente, Silvia A.; Belelli, Patricia G.; Branda, Maria M. [Grupo de Materiales y Sistemas Cataliticos, Departamento de Fisica, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca (Argentina); Ferullo, Ricardo M., E-mail: caferull@criba.edu.ar [Grupo de Materiales y Sistemas Cataliticos, Departamento de Fisica, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca (Argentina); Departamento de Quimica, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca (Argentina); Castellani, Norberto J. [Grupo de Materiales y Sistemas Cataliticos, Departamento de Fisica, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca (Argentina)

    2009-05-30

    The formation of Ag{sub 2}, Au{sub 2} and AgAu particles oriented perpendicularly to the MgO(1 0 0) surface was studied using the density functional theory. While the support induces a slight enhancement of the Ag-Ag bond (by 0.3-0.4 eV), the Au-Au bond is strongly enhanced (by 0.8-1.1 eV). Concerning the bimetallic particle, the Ag-Au bond stabilization depends on the relative position of each atom. Thus, in general terms, the strength of the metal-metal bond is determined by the nature of the terminal atom; the bond is stronger in Au-terminal particles. The partial electronic charge transfer to the terminal Au atom and its ability to polarize this charge are responsible for this energetic stabilization.

  10. Formation of Ag2, Au2 and AgAu particles on MgO(1 0 0): DFT study on the role of support-induced charge transfer in metal-metal interactions

    International Nuclear Information System (INIS)

    The formation of Ag2, Au2 and AgAu particles oriented perpendicularly to the MgO(1 0 0) surface was studied using the density functional theory. While the support induces a slight enhancement of the Ag-Ag bond (by 0.3-0.4 eV), the Au-Au bond is strongly enhanced (by 0.8-1.1 eV). Concerning the bimetallic particle, the Ag-Au bond stabilization depends on the relative position of each atom. Thus, in general terms, the strength of the metal-metal bond is determined by the nature of the terminal atom; the bond is stronger in Au-terminal particles. The partial electronic charge transfer to the terminal Au atom and its ability to polarize this charge are responsible for this energetic stabilization.

  11. Optical properties of ZnSe doped with Ag and Au

    Science.gov (United States)

    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.

  12. Biosynthesis and stabilization of Au and Au–Ag alloy nanoparticles by fungus, Fusarium semitectum

    Directory of Open Access Journals (Sweden)

    Balaji Dasaratrao Sawle, Basavaraja Salimath, Raghunandan Deshpande, Mahesh Dhondojirao Bedre, Belawadi Krishnamurthy Prabhakar and Abbaraju Venkataraman

    2008-01-01

    Full Text Available Crystallized and spherical-shaped Au and Au–Ag alloy nanoparticles have been synthesized and stabilized using a fungus, F . semitectum in an aqueous system. Aqueous solutions of chloroaurate ions for Au and chloroaurate and Ag+ ions (1 : 1 ratio for Au–Ag alloy were treated with an extracellular filtrate of F . semitectum biomass for the formation of Au nanoparticles (AuNP and Au–Ag alloy nanoparticles (Au–AgNP. Analysis of the feasibility of the biosynthesized nanoparticles and core–shell alloy nanoparticles from fungal strains is particularly significant. The resultant colloidal suspensions are highly stable for many weeks. The obtained Au and Au–Ag alloy nanoparticles were characterized by the surface plasmon resonance (SPR peaks using a UV-vis spectrophotometer, and the structure, morphology and size were determined by Fourier transform infrared spectroscopy (FTIR, x-ray diffraction (XRD, and transmission electron microscopy (TEM. Possible optoelectronics and medical applications of these nanoparticles are envisaged.

  13. Study of thermal diffusivity of nanofluids with bimetallic nanoparticles with Au(core)/Ag(shell) structure

    Science.gov (United States)

    Gutierrez Fuentes, R.; Pescador Rojas, J. A.; Jiménez-Pérez, J. L.; Sanchez Ramirez, J. F.; Cruz-Orea, A.; Mendoza-Alvarez, J. G.

    2008-11-01

    The thermal diffusivity of Au/Ag nanoparticles with core/shell structure, at different compositions (Au/Ag = 3/1, 1/1, 1/3, 1/6), was measured by using the mismatched mode of the dual-beam thermal lens (TL) technique. This study determines the effect of the bimetallic composition on the thermal diffusivity of the nanofluids. In these results we find a lineal increment of the nanofluid it thermal diffusivity when the Ag shell thickness is increased. Our results show that the nanoparticle structure is an important parameter to improve the heat transport in composites and nanofluids. These results could have importance for applications in therapies and photothermal deliberation of drugs. Complementary measurements with UV-vis spectroscopy and TEM, were used to characterize the Au(core)/Ag(shell) nanoparticles.

  14. Study of thermal diffusivity of nanofluids with bimetallic nanoparticles with Au(core)/Ag(shell) structure

    Energy Technology Data Exchange (ETDEWEB)

    Gutierrez Fuentes, R.; Pescador Rojas, J.A. [CICATA-IPN, Legaria 694, Mexico 11500, D.F. (Mexico); Jimenez-Perez, J.L. [CICATA-IPN, Legaria 694, Mexico 11500, D.F. (Mexico)], E-mail: jimenezp@fis.cinvestav.mx; Sanchez Ramirez, J.F. [CICATA-IPN, Legaria 694, Mexico 11500, D.F. (Mexico); Departamento de Fisica, CINVESTAV-IPN, A.P. 14-740, Mexico 07360, D.F. (Mexico); Cruz-Orea, A.; Mendoza-Alvarez, J.G. [Departamento de Fisica, CINVESTAV-IPN, A.P. 14-740, Mexico 07360, D.F. (Mexico)

    2008-11-30

    The thermal diffusivity of Au/Ag nanoparticles with core/shell structure, at different compositions (Au/Ag = 3/1, 1/1, 1/3, 1/6), was measured by using the mismatched mode of the dual-beam thermal lens (TL) technique. This study determines the effect of the bimetallic composition on the thermal diffusivity of the nanofluids. In these results we find a lineal increment of the nanofluid it thermal diffusivity when the Ag shell thickness is increased. Our results show that the nanoparticle structure is an important parameter to improve the heat transport in composites and nanofluids. These results could have importance for applications in therapies and photothermal deliberation of drugs. Complementary measurements with UV-vis spectroscopy and TEM, were used to characterize the Au(core)/Ag(shell) nanoparticles.

  15. Ore mineralogy of the Serra Pelada Au-Pd-Pt deposit, Carajás, Brazil and implications for ore-forming processes

    Science.gov (United States)

    Berni, Gabriel V.; Heinrich, Christoph A.; Lobato, Lydia M.; Wall, Vic

    2016-01-01

    Serra Pelada is a world-class hydrothermal Au-Pd-Pt deposit located at the eastern border of the Amazon craton, northern Brazil. The rocks at Serra Pelada have experienced intense tropical weathering for about 70 Ma, but drill core samples preserve the primary mineralogy and hydrothermal alteration features, with extreme grades of Au, Pd and Pt individually reaching hundreds of parts per million (ppm) by weight. Mineralization at Serra Pelada occurs in hydrothermally altered metasiltstones and dolomitic metasandstones at the hinge zone of a recumbent syncline, comprising zones of hematite, chlorite-carbon, argillic, and siliceous alteration. The main hydrothermal gangue minerals are quartz, kaolinite, sericite, amesite, hematite, monazite, florencite and variable amounts of highly reflective carbonaceous matter. Hydrothermal carbon input is evident from precipitated carbon occurring along crenulation planes and veinlets associated with the precious metals. Ore and accessory minerals include a variety of sulphide, selenide, arsenide, sulphate and oxide minerals, including gold with variable metal contents, palladian gold, fischesserite, sudovikovite, sperrylite, selenian braggite, isomertieite, mertieite-II and secondary Au-Pt-Pd alloys. The composition of fischesserite varies from the ideal formula (Ag3AuSe2) towards a more Ag-rich composition, indicating a disordered solid solution form that is stable only above 260 °C, consistent with the high thermal maturity of associated carbonaceous matter approaching graphite. Primary ore and gangue minerals at Serra Pelada comprise a suite of elements that are best transported in oxidising conditions and precipitated upon reduction. This suggests that fluid mixing between a highly oxidised (metal carrier) and a reduced fluid was a key process for high-grade noble metal precipitation at Serra Pelada.

  16. Ore mineralogy of the Serra Pelada Au-Pd-Pt deposit, Carajás, Brazil and implications for ore-forming processes

    Science.gov (United States)

    Berni, Gabriel V.; Heinrich, Christoph A.; Lobato, Lydia M.; Wall, Vic

    2016-08-01

    Serra Pelada is a world-class hydrothermal Au-Pd-Pt deposit located at the eastern border of the Amazon craton, northern Brazil. The rocks at Serra Pelada have experienced intense tropical weathering for about 70 Ma, but drill core samples preserve the primary mineralogy and hydrothermal alteration features, with extreme grades of Au, Pd and Pt individually reaching hundreds of parts per million (ppm) by weight. Mineralization at Serra Pelada occurs in hydrothermally altered metasiltstones and dolomitic metasandstones at the hinge zone of a recumbent syncline, comprising zones of hematite, chlorite-carbon, argillic, and siliceous alteration. The main hydrothermal gangue minerals are quartz, kaolinite, sericite, amesite, hematite, monazite, florencite and variable amounts of highly reflective carbonaceous matter. Hydrothermal carbon input is evident from precipitated carbon occurring along crenulation planes and veinlets associated with the precious metals. Ore and accessory minerals include a variety of sulphide, selenide, arsenide, sulphate and oxide minerals, including gold with variable metal contents, palladian gold, fischesserite, sudovikovite, sperrylite, selenian braggite, isomertieite, mertieite-II and secondary Au-Pt-Pd alloys. The composition of fischesserite varies from the ideal formula (Ag3AuSe2) towards a more Ag-rich composition, indicating a disordered solid solution form that is stable only above 260 °C, consistent with the high thermal maturity of associated carbonaceous matter approaching graphite. Primary ore and gangue minerals at Serra Pelada comprise a suite of elements that are best transported in oxidising conditions and precipitated upon reduction. This suggests that fluid mixing between a highly oxidised (metal carrier) and a reduced fluid was a key process for high-grade noble metal precipitation at Serra Pelada.

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

    Science.gov (United States)

    Baldwin, Dylan

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

  18. Synthesis of unidirectional structures of SiO2-Ag using Au nanoparticles as nucleation centers

    International Nuclear Information System (INIS)

    This paper reports a method to synthesize Ag unidirectional structures covered with SiO2 by sol-gel technique using Au nanoparticles as nucleation centers of the unidirectional structures. In the first phase unidirectional structures of SiO2-Ag CI are obtained by sol-gel, using TEOS as a precursor of metallic structures (Ag) and the incorporation of Au nanoparticles as nucleation centers for growth of unidirectional structures. In the second stage, one-way systems are subjected to thermal treatment in H2 atmosphere for obtain AG0 particles through mechanisms that diffusion and coalescence of silver to form structures that have a thin cover of SiO2. Analysis by scanning electron microscopy, transmission and atomic force microscopy allowed to determine the chemical composition and microstructural properties of unidirectional systems SiO2-Ag. (Author)

  19. Effect of Ag addition to L10 FePt and L10 FePd films grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    L10 ordered FePt-Ag (5 nm) and FePd-Ag (5 nm) films were grown on MgO (001) substrate at temperatures of 250–400 °C by using molecular beam epitaxy method, and their crystal and surface structures, perpendicular magnetic anisotropies and Curie temperatures were investigated. In the case of FePt-Ag, Ag addition with the amount of 10–20 at. % was effective to promote L10 ordering and granular growth, resulting in the increase of the perpendicular magnetic anisotropy and coercivity of the FePt-Ag films. On the other hand, in the case of FePd-Ag, Ag addition changed the surface morphology from island to continuous film associated with the reductions of its coercivity and perpendicular anisotropy. The variations of lattice constants and Curie temperature with Ag addition were significantly different between FePt-Ag and FePd-Ag. For FePd-Ag, the c and a axes lattice spacings and Curie temperature gradually changed with increasing Ag content, while they unchanged for FePt-Ag. These results suggest the possibility of the formation of FePdAg alloy in FePd-Ag, while Ag segregation in FePt-Ag

  20. Nanocrystalline Pd alloy films coated by electroless deposition.

    Science.gov (United States)

    Strukov, G V; Strukova, G K; Batov, I E; Sakharov, M K; Kudrenko, E A; Mazilkin, A A

    2011-10-01

    The structures of palladium and palladium alloys thin films deposited from organic electrolytes onto metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005-1 microm thick films with high adhesive strength to the substrate surface. EDX, XRD, SEM and TEM methods were used to determine the composition and structure of alloy coatings of the following binary systems: Pd-Au, Pd-Ag, Pd-Ni, Pd-Pb, and ternary system Pd-Au-Ni. The coatings of Pd-Au, Pd-Ag and Pd-Ni have a solid solution structure, whereas Pd-Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11-35 nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed. PMID:22400291

  1. Hollow Ag-Pd core–shell nanotubes as highly active catalysts for the electro-oxidation of formic acid

    International Nuclear Information System (INIS)

    Ag nanowires are prepared as templates by a polyol reduction process. Then Ag nanotubes coated with a thin layer of Pd are synthesized through sequential reduction accompanied with the galvanic displacement reaction. The products show a hollow core–shell nanotubular structure, as demonstrated by detailed characterizations. The Ag-Pd can significantly improve the electrocatalytic activity towards the electro-oxidation of formic acid and enhance the stability of the Pd component. It is proposed that the enhanced electrochemically active surface area and modulated electron structure of Pd by Ag are responsible for the improvement of electrocatalytic activity and durability. The results obtained in this work are different from those previous reports, in which alloy walls with hollow interiors are usually formed. This work provides a new and simple method for synthesizing novel bimetallic core–shell structure with a hollow interior, which can be applied as high-performance catalysts for the electro-oxidation of formic acid. (paper)

  2. Pd-Au Electrocatalysts for Hydrogen Evolution Reaction at Neutral pH

    OpenAIRE

    Elitsa Chorbadzhiyska; Mario Mitov; Georgi Hristov; Nina Dimcheva; Lori Nalbandian; Antigoni Evdou; Yolina Hubenova

    2014-01-01

    Pd-Au codeposits with different ratio of both metals were electrodeposited on carbon felt, characterized by scanning electron microscopy, and investigated as electrocatalysts towards hydrogen evolution reaction in neutral phosphate buffer solution. The quantities of the produced hydrogen gas with different electrocatalysts, estimated from data obtained by chronoamperometry, were confirmed by mass spectrometry analysis. The highest hydrogen evolution rate was achieved with the electrocatalysts...

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

    International Nuclear Information System (INIS)

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

  4. Third-order optical nonlinearity studies of bilayer Au/Ag metallic films

    Science.gov (United States)

    Mezher, M. H.; Chong, W. Y.; Zakaria, R.

    2016-05-01

    This paper presents nonlinear optical studies of bilayer metallic films of gold (Au) and silver (Ag) on glass substrate prepared using electron beam evaporation. The preparation of Au and Ag nanoparticles (NPs) on the substrate involved the use of electron beam deposition, then thermal annealing at 600 °C and 270 °C, respectively, to produce a randomly distributed layer of Au and a layer of Ag NPs. Observation of field-effect scanning electron microscope images indicated the size of the NPs. Details of the optical properties related to peak absorption of surface plasmon resonance of the nanoparticle were revealed by use of UV-Vis spectroscopy. The Z-scan technique was used to measure the nonlinear absorption and nonlinear refraction of the fabricated NP layers. The third-order nonlinear refractive index coefficients for Au and Ag are (-9.34 and  -1.61)  ×  10-11 cm2 W-1 given lower n 2, in comparison with bilayer (Au and Ag) NPs at  -1.24  ×  10-10 cm2 W-1. The results show bilayer NPs have higher refractive index coefficients thus enhance the nonlinearity effects.

  5. A comparative investigation of the behaviors of H in Au and Ag from first principles

    Science.gov (United States)

    Han, Quan-Fu; Zhou, Zhen-Yu; Ma, Yuming; Liu, Yue-Lin

    2016-05-01

    Hydrogen (H) is a common impurity in metals and has a significant effect on their purification, even at concentrations of only a few parts per million. Here we present a comparative analysis of the behaviors of H in Au and Ag based on first-principles calculations. In bulk Au and Ag, the results demonstrate that the tetrahedral position is energetically more stable for a single H atom than the octahedral site. The concentration of H dissolving in the interstitial sites as a function of temperature is calculated in both metals. To characterize the dynamic behaviors, in bulk Au and Ag we determine the theoretical diffusivity and permeation of H, which are in quantitative agreement with the experimental data. Further, we investigate the role of vacancy on the formation of the H n -vacancy (H n V) via a clustering reaction. One vacancy can accommodate up to 9 H atoms in Au and capture as many as 7 H atoms in Ag. The H2 molecule in the vacancy is energetically unstable in both metals. These research results will provide a very useful reference for the refinement of Ag/Au as noble metals in industry.

  6. A comparison study of oxygen reduction on the supported Pt, Pd, Au monolayer on WC(0001)

    Science.gov (United States)

    Zhang, Xilin; Lu, Zhansheng; Yang, Zongxian

    2016-07-01

    Using the first principles methods, the geometric and electronic structures of the metal monolayers supported on WC(0001) surfaces (MML/WC(0001) (M = Pt, Pd, and Au)) and their catalytic activity toward the oxygen reduction reaction (ORR) were comparatively studied. Both the kinetics and the density of states results demonstrated that the direct dissociation of O2 on all three MML/WC(0001) surfaces are almost impossible. Yet the barriers of the formation and dissociation of OOH on AuML/WC(0001) are much smaller than those on the PtML/WC(0001) and the PdML/WC(0001) surfaces, implying that the AuML/WC(0001) exhibits the highest catalytic activity for ORR via a combination of 2e- hydrogenation of O2 and 4e- dissociation of OOH. The rate-limiting step barrier of 0.83 eV for the hydrogenation of OH forming H2O is also comparable to that on the traditional Pt-based catalysts. The deactivation mechanism of PtML/WC(0001) and the performance of PdML/WC(0001) for ORR were identified. The present study is conductive to designing new efficient catalyst without using of the precious Pt for efficiently promoting ORR.

  7. Centrality definition using mid-rapidity ET distributions from p+Be to Au+Au at AGS energies

    International Nuclear Information System (INIS)

    Measurements by the E802 Collaboration of the A-dependence and pseudorapidity interval (δη) dependence of mid-rapidity ET distributions in a half-azimuth electromagnetic calorimeter are presented for p+Be, p+Au, O+Cu, Si+Au and Au+Au collisions at the BNL-AGS. The issues addressed are 1) whether the shapes of the upper edges of the ET distributions vary with δη similarly to the variation in shapes of mid-rapidity charged particle distributions and 2) how small a δη interval would still give a meaningful characterization of the 'nuclear geometry' of a reaction. A new way of plotting ET distributions was found from which the reaction dynamics could be read directly

  8. Wearout Reliability and Intermetallic Compound Diffusion Kinetics of Au and PdCu Wires Used in Nanoscale Device Packaging

    Directory of Open Access Journals (Sweden)

    C. L. Gan

    2013-01-01

    Full Text Available Wearout reliability and diffusion kinetics of Au and Pd-coated Cu (PdCu ball bonds are useful technical information for Cu wire deployment in nanoscale semiconductor device packaging. This paper discusses the HAST (with bias and UHAST (unbiased HAST wearout reliability performance of Au and PdCu wires used in fine pitch BGA packages. In-depth failure analysis has been carried out to identify the failure mechanism under various wearout conditions. Intermetallic compound (IMC diffusion constants and apparent activation energies (Eaa of both wire types were investigated after high temperature storage life test (HTSL. Au bonds were identified to have faster IMC formation, compared to slower IMC growth of PdCu. PdCu wire was found to exhibit equivalent or better wearout reliability margin compared to conventional Au wire bonds. Failure mechanisms of Au, Cu ball bonds post-HAST and UHAST tests are been proposed, and both Au and PdCu IMC diffusion kinetics and their characteristics are discussed in this paper.

  9. Resonance Scattering Detection of Trace Hg2+ Using Aptamer-modified AuPd Nanoalloy Probe as Catalyst

    Institute of Scientific and Technical Information of China (English)

    刘庆业; 范燕燕; 梁爱惠; 蒋治良

    2011-01-01

    The 5 nm AuPd nanoalloy in mole ratio of Au:Pd=32 : 1 was prepared, using sodium citrate as the stabilizing agent and NaBH4 as the reductant. The AuPd nanoalloy was modified by the aptamer to prepare an aptamer- AuPd (AptAuPd) probe for resonance scattering (RS) detection of 5.(Y-1250 nmol/L Hg2+. The AptAuPd-Hg2+ aptamer reaction solution was filtrated by membrane, and the AptAuPd in the filtrate exhibited strong catalytic ef- fect on the slow NiP particle reaction between NiCI2 and NaHzPO2, and the NiP particles showed a RS peak at 508 nm. The RS intensity decreased when Hg2+ concentration increased. The decreased RS intensity was linear to Hg2+ concentration in the range of 0.5--1250 nmol/L. The RS assays were used to determine Hg2+ in real samples, with good results.

  10. Core-shell Au/Ag nanoparticles embedded in silicate sol-gel network for sensor application towards hydrogen peroxide

    Indian Academy of Sciences (India)

    Shanmugam Manivannan; Ramasamy Ramaraj

    2009-09-01

    The electrocatalytic activity of core-shell Au100-Ag ( = 15, 27, 46, and 60) bimetallic nanoparticles embedded in methyl functionalized silicate MTMOS network towards the reduction of hydrogen peroxide was investigated by using cyclic voltammetry and chronoamperometric techniques. Core-shell Au/Ag bimetallic nanoparticles were characterized by absorption spectra and HRTEM. The MTMOS silicate sol-gel embedded Au73Ag27 core-shell nanoparticles modified electrode showed better synergistic electrocatalytic effect towards the reduction of hydrogen peroxide when compared to monometal MTMOS-Aunps and MTMOS-Agnps modified electrodes. These modified electrodes were studied without immobilizing any enzyme in the MTMOS sol-gel matrix. The present study highlights the influence of molar composition of Ag nanoparticles in the Au/Ag bimetallic composition towards the electrocatalytic reduction and sensing of hydrogen peroxide in comparison to monometal Au and Ag nanoparticles.

  11. Ag@Au core-shell dendrites: a stable, reusable and sensitive surface enhanced Raman scattering substrate

    Science.gov (United States)

    Jun Yin, Hong; Yang Chen, Zhao; Mei Zhao, Yong; Yang Lv, Ming; An Shi, Chun; Long Wu, Zheng; Zhang, Xin; Liu, Luo; Li Wang, Ming; Jun Xu, Hai

    2015-09-01

    Surface enhanced Raman scattering (SERS) substrate based on fabricated Ag@Au core-shell dendrite was achieved. Ag dendrites were grown on Si wafer by the hydrothermal corrosion method and Au nanofilm on the surface of Ag dendritic nanostructure was then fabricated by chemical reduction. With the help of sodium borohydride in water, Au surface absorbates such as thiophene, adenine, rhodamine, small anions (Br- and I-), and a polymer (PVP, poly(N-vinylpyrrolidone)) can be completely and rapidly removed. After four repeatable experiments, the substrate SERS function did not decrease at all, indicating that the Ag@Au dendrite should be of great significance to SERS application because it can save much resource. Six-month-duration stability tests showed that the Ag@Au core-shell dendrite substrate is much more stable than the Ag dendrite substrates. We have also experimented on fast detection of Cd2+ at 10-8  M concentration by decorating single-stranded DNA containing adenine and guanine bases on the surface of this Ag@Au dendrite. Finite-difference time-domain simulations were carried out to investigate the influence of Au nanolayer on Ag dendrites, which showed that the local electric fields and enhancement factor are hardly affected when a 4 nm Au nanolayer is coated on Ag dendrite surface.

  12. Development of Au-Ag nanowire mesh fabrication by UV-induced approach

    Energy Technology Data Exchange (ETDEWEB)

    Saggar, Siddhartha [Laboratory for Molecular Photonics and Electronics, Department of Physics, National Institute of Technology, Calicut, Kerala, India and School of Nanoscience and Technology, National Institute of Technology, Calicut, Kerala (India); Predeep, Padmanabhan, E-mail: predeep@nitc.ac.in

    2014-10-15

    In an attempt to overcome the limitations of the presently prevailing transparent conducting electrode (TCE) - indium tin oxide (ITO) - many materials have been considered for replacing ITO. Recently, a novel method has been reported for the synthesis of Au-Ag nanowire (NW) mesh, and tested successfully for organic-light-emitting-diodes (OLEDs). It employs UV-induced reduction of gold- and silver- precursors to form Au-Ag NW mesh. In this report, Au-Ag NW mesh thin films are synthesized on glass substrates with an objective for use as facing-electrode for Organic Photovoltaics. Various issues and factors affecting the fabrication-process have been improved, and are also discussed here. The electrode showed good transmitivity, of around 95% (excluding that of glass substrate). The advantage of the technique is its simple processing method and cost-effectiveness.

  13. Dissociative adsorption of water on Au/MgO/Ag(001) from first principles calculations

    Science.gov (United States)

    Nevalaita, J.; Häkkinen, H.; Honkala, K.

    2015-10-01

    The molecular and dissociative adsorption of water on a Ag-supported 1 ML, 2 ML and 3 ML-a six atomic layer-thick MgO films with a single Au adatom is investigated using density functional theory calculations. The obtained results are compared to a bulk MgO(001) surface with an Au atom. On thin films the negatively charged Au strengthens the binding of the polar water molecule due to the attractive Au-H interaction. The adsorption energy trends of OH and H with respect to the film thickness depend on an adsorption site. In the case OH or H binds atop Au on MgO/Ag(001), the adsorption becomes more exothermic with the increasing film thickness, while the reverse trend is seen when the adsorption takes place on bare MgO/Ag(001). This behavior can be explained by different bonding mechanisms identified with the Bader analysis. Interestingly, we find that the rumpling of the MgO film and the MgO-Ag interface distance correlate with the charge transfer over the thin film and the interface charge, respectively. Moreover, we employ a modified Born-Haber-cycle to analyze the effect of film thickness to the adsorption energy of isolated Au and OH species on MgO/Ag(001). The analysis shows that the attractive Coulomb interaction between the negatively charged adsorbate and the positive MgO-Ag-interface does not completely account for the weaker binding with increasing film thickness. The redox energy associated with the charge transfer from the interface to the adsorbate is more exothermic with the increasing film thickness and partly compensates the decrease in the attractive Coulomb interaction.

  14. Hollow Ag@Pd core-shell nanotubes as highly active catalysts for the electro-oxidation of formic acid

    DEFF Research Database (Denmark)

    Jiang, Yuanyuan; Lu, Yizhong; Han, Dongxue;

    2012-01-01

    Ag nanowires are prepared as templates by a polyol reduction process. Then Ag nanotubes coated with a thin layer of Pd are synthesized through sequential reduction accompanied with the galvanic displacement reaction. The products show a hollow core-shell nanotubular structure, as demonstrated by...

  15. Topological description of mechanical behavior of Cu, Ag and Au: A first-principle study

    Directory of Open Access Journals (Sweden)

    M Saghayezhian

    2011-12-01

    Full Text Available  Mechanical properties and stress-strain curves of Cu, Ag and Au single crystals are calculated using ab initio methods. Elastic and Plastic regions are scrutinized. Yield stress and slope of these curves can shed light on brittlenesss and ductility of these metals that prove Cu, despite its high ultimate tensile strength, is less ductile than Au and Ag. Analysis of topology of charge density along with stress-strain curves shows that the elastic-plastic transition accompanies topological transition and for these metals, both transitions occur in the same strain. Some charactristics of critical point, especially bond points, are inspected.

  16. Ag and Au atoms intercalated in bilayer heterostructures of transition metal dichalcogenides and graphene

    Directory of Open Access Journals (Sweden)

    F. Iyikanat

    2014-09-01

    Full Text Available The diffusive motion of metal nanoparticles Au and Ag on monolayer and between bilayer heterostructures of transition metal dichalcogenides and graphene are investigated in the framework of density functional theory. We found that the minimum energy barriers for diffusion and the possibility of cluster formation depend strongly on both the type of nanoparticle and the type of monolayers and bilayers. Moreover, the tendency to form clusters of Ag and Au can be tuned by creating various bilayers. Tunability of the diffusion characteristics of adatoms in van der Waals heterostructures holds promise for controllable growth of nanostructures.

  17. Carbon monoxide mediated chemical deposition of Pt or Pd quasi-monolayer on Au surfaces with superior electrocatalysis for ethanol oxidation in alkaline media.

    Science.gov (United States)

    Wang, Han; Jiang, Kun; Chen, Qiaoli; Xie, Zhaoxiong; Cai, Wen-Bin

    2016-01-01

    Electroless deposition of a quasi-monolayer (q-ML) of Pt and/or Pd on different Au substrates is achieved by using CO as both reducing and quenching agents, imparting Au@Pt/C or Au@Pd/C with superior electrocatalytic activity for ethanol oxidation in alkaline media. PMID:26523296

  18. Characterizing the economic value of an epithermal Au-Ag ore with Laser Induced Breakdown Spectroscopy (LIBS)

    NARCIS (Netherlands)

    Dalm, M.; Buxton, M.W.N.

    2016-01-01

    LIBS was applied to 19 Au-Ag ore samples to investigate if this technique can be used to distinguish between economic and sub-economic ore either by direct detection of these elements or by using other elements as indicators. However, the Au and Ag grades of the samples are below the detection limit

  19. Electrical conductivity dependence of thin metallic films of Au and Pd as a top electrode in capacitor applications

    International Nuclear Information System (INIS)

    Electrical conductivity dependence of thin metallic films of Au and Pd over the different perovskites was investigated. It is found from electrical properties that crystallographic growth orientation of Au and Pd thin layers attained from X-ray diffraction results indicate the slop of current (I)-voltage (V) plots. Besides, surface morphology and topography was considered using Field Emission Scanning Electron Microscopy and Atomic Force Microscopy, respectively. Obtained results showed the Stranski-Krastanov growth of the Pd and Au. Indeed, diminishing of the root-mean-square roughness of Pd/BiMnO3/SrTiO3 following by Au deposition should be concerned due to growth of Au onto the crack-like parts of the substrate. These crack-like parts appeared due to parasitic phases of the Bi-Mn-O system mainly Mn3O4 (l 0 l) and Mn3O4 (0 0 4 l). The different response in the electrical properties of heterostructures suggests that electrical conductance of the Au and Pd thin metallic films have the crystallographic orientation dependence. Furthermore, polycrystallinity of the thin metallic films are desired in electrode applications due to increase the conductivity of the metallic layers.

  20. Assemblies of silicate sol-gel matrix encapsulated core/shell Au/Ag nanoparticles: interparticles surface plasmon coupling

    Energy Technology Data Exchange (ETDEWEB)

    Manivannan, Shanmugam; Ramaraj, Ramasamy, E-mail: ramarajr@yahoo.com [Madurai Kamaraj University, Centre for Photoelectrochemistry, School of Chemistry (India)

    2012-06-15

    Cluster-like assemblies of bimetal core/shell Au/Ag nanoparticles were prepared. The Ag shell was deposited on the preformed Au nanoparticles using two different types of preformed Au nanoparticles in the presence of EDAS silane monomer, one stabilized by citrate and other by {beta}-cyclodextrin. The Ag shell was deposited on the preformed Au nanoparticles by the reduction of Ag{sup +} ions by {beta}-cyclodextrin and EDAS silane composite. Interestingly, productive Ag shell deposition occurred only on the {beta}-cyclodextrin-stabilized Au nanoparticles and led to the assembly formation, whereas aggregation occurred with the citrate-stabilized Au nanoparticles. The average particle size of the core/shell Au/Ag nanoparticles was found to be 6.5 nm. Spectral features of this assembly of core/shell Au/Ag nanoparticles resembled the longitudinal surface plasmon resonance behavior of Au nanorod-like structures arising from the interparticles surface plasmon coupling. The assemblies so prepared were characterized by uv-vis absorption spectroscopy and high-resolution transmission electron microscopy.Graphical Abstract.

  1. Plasmonic-induced inhibition and enhancement of the electrocatalytic activity of Pd-Au hetero-nanoraspberries for ethanol oxidation

    Science.gov (United States)

    Wang, Qiyu; Zheng, Weitao; Chen, Hong; Zhang, Bingsen; Su, Dangsheng; Cui, Xiaoqiang

    2016-06-01

    Plasmonic modulation of the catalytic performances of metallic nanostructures shows great potential in the development of novel materials for catalysis. In addition to the challenges of devising new catalysts with high activity while maintaining controllable plasmonic properties, the mechanisms underlying the enhancement of the activity by surface plasmon resonance (SPR) are still under exploration. Here, we design a Pd-Au bimetallic hetero structure and use the well-defined SPR property of the core Au NPs to tune its surface electro catalytic activity. The hot electrons are transferred into the Pd nanopetals from the Au core with visible-light irradiation, resulting in an enhancement of the electrocatalytic oxidation of ethanol on Au concurrent with an inhibition on Pd. The anti-poisoning and stability of the as-prepared heterostructures is also enhanced by visible-light irradiation.

  2. Isolation of atomically precise mixed ligand shell PdAu24 clusters

    Science.gov (United States)

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

    2016-05-01

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

  3. Direct electrochemical oxidation of S-captopril using gold electrodes modified with graphene-AuAg nanocomposites

    Directory of Open Access Journals (Sweden)

    Pogacean F

    2014-02-01

    Full Text Available Florina Pogacean,1 Alexandru R Biris,2 Maria Coros,1 Mihaela Diana Lazar,1 Fumiya Watanabe,3 Ganesh K Kannarpady,3 Said A Farha Al Said,4 Alexandru S Biris,3 Stela Pruneanu1 1Department of Isotopic Physics and Technology, 2Department of Mass Spectrometry, Chromatography, and Applied Physics, National Institute for Research and Development of Isotopic and Molecular Technologies, Cluj-Napoca, Romania; 3Center for Integrative Nanotechnology Sciences, University of Arkansas at Little Rock, Little Rock, Arkansas, USA; 4Department of Physics, College of Science, King Abdulaziz University, Jeddah, Saudi Arabia Abstract: In this paper, we present a novel approach for the electrochemical detection of S-captopril based on graphene AuAg nanostructures used to modify an Au electrode. Multi-layer graphene (Gr sheets decorated with embedded bimetallic AuAg nanoparticles were successfully synthesized catalytically with methane as the carbon source. The two catalytic systems contained 1.0 wt% Ag and 1.0 wt% Au, while the second had a larger concentration of metals (1.5 wt% Ag and 1.5 wt% Au and was used for the synthesis of the Gr-AuAg-1 and Gr-AuAg-1.5 multicomponent samples. High-resolution transmission electron microscopy analysis indicated the presence of graphene flakes that had regular shapes (square or rectangular and dimensions in the tens to hundreds of nanometers. We found that the size of the embedded AuAg nanoparticles varied between 5 and 100 nm, with the majority being smaller than 20 nm. Advanced scanning transmission electron microscopy studies indicated a bimetallic characteristic of the metallic clusters. The resulting Gr-AuAg-1 and Gr-AuAg-1.5 samples were used to modify the surface of commonly used Au substrates and subsequently employed for the direct electrochemical oxidation of S-captopril. By comparing the differential pulse voltammograms recorded with the two modified electrodes at various concentrations of captopril, the peak current

  4. Synthesis and characterization of PdAg as a catalyst for oxygen reduction reaction in acid medium; Sintesis y caracterizacion de PdAg como catalizador para la reaccion de reduccion de oxigeno en medio acido

    Energy Technology Data Exchange (ETDEWEB)

    Martinez-Casillas, D. C.; Vazquez-Huerta, G.; Solorza-Feria, O. [Centro de Investigacion y de Estudios Avanzados del IPN, Mexico D.F. (Mexico)]. E-mail: dcmartinez@cinvestav.mx

    2009-09-15

    This work presents the synthesis of the binary compound PdAg and the electrochemical characterization for oxygen reduction reaction (ORR) in acid medium. The catalyst is obtained from the reduction of Pd(NO{sub 3}){sub 2}·2H{sub 2}O and AgNO{sub 3} with NaBH{sub 4} in THF. The synthesized compound was physically characterized with transmission electron microscopy (TEM), sweep electron microscopy (SEM) and x-ray diffraction (XRD) of powder. Electrochemical studies were conducted to determine the catalytic activity and intrinsic properties of the PdAg material for the ORR in acid medium using cyclic voltamperometry (CV), rotary disc electrode (RDE) and electrochemical impedance spectroscopy (EIS) in a solution of H{sub 2}SO{sub 4} 0.5 M at 25 degrees Celsius. The electrochemical current-potential responses were compared to those of palladium and platinum. The kinetic results showed an increase in the performance of the bimetallic electrocatalyst containing Ag as compared to pure Pd, but less than that obtained with nanometric Pt. The Tafel slopes obtained are roughly120 mV dec-1, similar to that reported for Pt and Pd and for other Ru-based electrocatalysts. [Spanish] En este trabajo se presentan la sintesis del compuesto binario PdAg y su caracterizacion electroquimica para la reaccion de reduccion de oxigeno (RRO) en medio acido. El catalizador se obtuvo a partir de la reduccion de Pd(NO{sub 3}){sub 2}·2H{sub 2}O y AgNO{sub 3} con NaBH{sub 4} en THF. El compuesto sintetizado se caracterizo fisicamente por microscopia electronica de transmision (MET), microscopia electronica de barrido (MEB) y difraccion de rayos X (DRX) de polvos. Se realizaron estudios electroquimicos para determinar la actividad catalitica y las propiedades intrinsecas del material de PdAg para la reaccion de reduccion de oxigeno (RRO) en medio acido, utilizando las tecnicas de voltamperometria ciclica (VC), electrodo disco rotatorio (EDR) y espectroscopia de impedancia electroquimica (EIE), en

  5. Transparent ITO/Ag-Pd-Cu/ITO multilayer cathode use in inverted organic solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyo-Joong; Kim, Han-Ki, E-mail: imdlhkkim@khu.ac.kr [Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, 1 Seocheon-dong, Yongin-si, Gyeonggi-do 446-701 (Korea, Republic of); Lee, Hyun Hwi [Pohang Accelerator Laboratory, POSTECH, Jigokro-127beon-gil, Nam-gu, Pohang 790-784 (Korea, Republic of); Kal, Jinha; Hahn, Jungseok [Future Technology Research Group, Kolon Central Research Park, 154 Mabukro, Giheung-ku, Yongin-si, Kyunggi-do, 16910 (Korea, Republic of)

    2015-10-15

    The characteristics of transparent ITO/Ag-Pd-Cu (APC)/ITO multilayer cathodes were investigated for use in inverted organic solar cells (IOSCs). The insertion of an APC interlayer into the ITO film effectively led to crystallization of the top ITO layer, unlike that in the Ag interlayer, and resulted in a low sheet resistance of 6.55 Ohm/square and a high optical transmittance of 84.14% without post annealing. In addition, the alloying of the Pd and Cu elements into Ag prevented agglomeration and oxidization of the metal interlayer and led to more stable ITO/APC/ITO films under ambient conditions. The microstructure and interfacial structure of the transparent ITO/APC/ITO cathode in the IOSCs were examined in detail by synchrotron X-ray scattering and high resolution transmission electron microscopy. Furthermore, we suggested a possible mechanism to explain the lower PCE of the IOSCs with an ITO/APC/ITO cathode than that of a reference IOSC with a crystalline ITO cathode using the external quantum efficiency of the IOSCs.

  6. Transparent ITO/Ag-Pd-Cu/ITO multilayer cathode use in inverted organic solar cells

    Science.gov (United States)

    Kim, Hyo-Joong; Lee, Hyun Hwi; Kal, Jinha; Hahn, Jungseok; Kim, Han-Ki

    2015-10-01

    The characteristics of transparent ITO/Ag-Pd-Cu (APC)/ITO multilayer cathodes were investigated for use in inverted organic solar cells (IOSCs). The insertion of an APC interlayer into the ITO film effectively led to crystallization of the top ITO layer, unlike that in the Ag interlayer, and resulted in a low sheet resistance of 6.55 Ohm/square and a high optical transmittance of 84.14% without post annealing. In addition, the alloying of the Pd and Cu elements into Ag prevented agglomeration and oxidization of the metal interlayer and led to more stable ITO/APC/ITO films under ambient conditions. The microstructure and interfacial structure of the transparent ITO/APC/ITO cathode in the IOSCs were examined in detail by synchrotron X-ray scattering and high resolution transmission electron microscopy. Furthermore, we suggested a possible mechanism to explain the lower PCE of the IOSCs with an ITO/APC/ITO cathode than that of a reference IOSC with a crystalline ITO cathode using the external quantum efficiency of the IOSCs.

  7. Transparent ITO/Ag-Pd-Cu/ITO multilayer cathode use in inverted organic solar cells

    Directory of Open Access Journals (Sweden)

    Hyo-Joong Kim

    2015-10-01

    Full Text Available The characteristics of transparent ITO/Ag-Pd-Cu (APC/ITO multilayer cathodes were investigated for use in inverted organic solar cells (IOSCs. The insertion of an APC interlayer into the ITO film effectively led to crystallization of the top ITO layer, unlike that in the Ag interlayer, and resulted in a low sheet resistance of 6.55 Ohm/square and a high optical transmittance of 84.14% without post annealing. In addition, the alloying of the Pd and Cu elements into Ag prevented agglomeration and oxidization of the metal interlayer and led to more stable ITO/APC/ITO films under ambient conditions. The microstructure and interfacial structure of the transparent ITO/APC/ITO cathode in the IOSCs were examined in detail by synchrotron X-ray scattering and high resolution transmission electron microscopy. Furthermore, we suggested a possible mechanism to explain the lower PCE of the IOSCs with an ITO/APC/ITO cathode than that of a reference IOSC with a crystalline ITO cathode using the external quantum efficiency of the IOSCs.

  8. Transparent ITO/Ag-Pd-Cu/ITO multilayer cathode use in inverted organic solar cells

    International Nuclear Information System (INIS)

    The characteristics of transparent ITO/Ag-Pd-Cu (APC)/ITO multilayer cathodes were investigated for use in inverted organic solar cells (IOSCs). The insertion of an APC interlayer into the ITO film effectively led to crystallization of the top ITO layer, unlike that in the Ag interlayer, and resulted in a low sheet resistance of 6.55 Ohm/square and a high optical transmittance of 84.14% without post annealing. In addition, the alloying of the Pd and Cu elements into Ag prevented agglomeration and oxidization of the metal interlayer and led to more stable ITO/APC/ITO films under ambient conditions. The microstructure and interfacial structure of the transparent ITO/APC/ITO cathode in the IOSCs were examined in detail by synchrotron X-ray scattering and high resolution transmission electron microscopy. Furthermore, we suggested a possible mechanism to explain the lower PCE of the IOSCs with an ITO/APC/ITO cathode than that of a reference IOSC with a crystalline ITO cathode using the external quantum efficiency of the IOSCs

  9. Dodecahedral Au@Pd nanocrystals with high-index facets and excellent electrocatalytic activity and highly efficient surface-enhanced Raman scattering enhancement

    Science.gov (United States)

    Zhang, Lin-Fei; Zhang, Chun-Yang

    2013-06-01

    We synthesize the three-fold symmetric shield-like Au@Pd core-shell nanocrystals, enclosed predominantly by high-index {541} facets with kinks, through the simultaneous reduction of Au and Pd ions in the presence of triangular Au nanocrystal seeds in aqueous solution at room-temperature. The obtained shield-like Au@Pd core-shell nanocrystals exhibit superior electrocatalytic activity for the oxidation of ethanol and unique near-field enhancement property with a highly sensitive surface-enhanced Raman scattering (SERS) response. These excellent properties can be ascribed to the presence of sharp corners and edges as well as high-index faceted Pd-rich shell in the shield-like Au@Pd core-shell structure. We also investigate the mechanism for the formation of three-fold symmetric shield-like Au@Pd core-shell nanocrystals.We synthesize the three-fold symmetric shield-like Au@Pd core-shell nanocrystals, enclosed predominantly by high-index {541} facets with kinks, through the simultaneous reduction of Au and Pd ions in the presence of triangular Au nanocrystal seeds in aqueous solution at room-temperature. The obtained shield-like Au@Pd core-shell nanocrystals exhibit superior electrocatalytic activity for the oxidation of ethanol and unique near-field enhancement property with a highly sensitive surface-enhanced Raman scattering (SERS) response. These excellent properties can be ascribed to the presence of sharp corners and edges as well as high-index faceted Pd-rich shell in the shield-like Au@Pd core-shell structure. We also investigate the mechanism for the formation of three-fold symmetric shield-like Au@Pd core-shell nanocrystals. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr00695f

  10. Hydrogen adsorption on bimetallic PdAu(111) surface alloys:minimum adsorption ensemble, ligand and ensemble effects, and ensemble confinement

    OpenAIRE

    Takehiro, Naoki; Liu, Ping; Bergbreiter, Andreas; K. Nørskov, Jens; Behm, R. Juergen

    2014-01-01

    The adsorption of hydrogen on structurally well defined PdAu-Pd(111) monolayer surface alloys was investigated in a combined experimental and theoretical study, aiming at a quantitative understanding of the adsorption and desorption properties of individual PdAu nanostructures. Combining the structural information obtained by high resolution scanning tunneling microscopy (STM), in particular on the abundance of specific adsorption ensembles at different Pd surface concentrations, with informa...

  11. Collagen-chitosan scaffold modified with Au and Ag nanoparticles: Synthesis and structure

    Science.gov (United States)

    Rubina, M. S.; Kamitov, E. E.; Zubavichus, Ya. V.; Peters, G. S.; Naumkin, A. V.; Suzer, S.; Vasil'kov, A. Yu.

    2016-03-01

    Nowadays, the dermal biomimetic scaffolds are widely used in regenerative medicine. Collagen-chitosan scaffold one of these materials possesses antibacterial activity, good compatibility with living tissues and has been already used as a wound-healing material. In this article, collagen-chitosan scaffolds modified with Ag and Au nanoparticles have been synthesized using novel method - the metal-vapor synthesis. The nanocomposite materials are characterized by XPS, TEM, SEM and synchrotron radiation-based X-ray techniques. According to XRD data, the mean size of the nanoparticles (NPs) is 10.5 nm and 20.2 nm in Au-Collagen-Chitosan (Au-CollCh) and Ag-Collagen-Chitosan (Ag-CollCh) scaffolds, respectively in fair agreement with the TEM data. SAXS analysis of the composites reveals an asymmetric size distribution peaked at 10 nm for Au-CollCh and 25 nm for Ag-CollCh indicative of particle's aggregation. According to SEM data, the metal-carrying scaffolds have layered structure and the nanoparticles are rather uniformly distributed on the surface material. XPS data indicate that the metallic nanoparticles are in their unoxidized/neutral states and dominantly stabilized within the chitosan-rich domains.

  12. Structural and magnetic phase transitions in CeCu6 -xTx (T =Ag ,Pd )

    Science.gov (United States)

    Poudel, L.; de la Cruz, C.; Payzant, E. A.; May, A. F.; Koehler, M.; Garlea, V. O.; Taylor, A. E.; Parker, D. S.; Cao, H. B.; McGuire, M. A.; Tian, W.; Matsuda, M.; Jeen, H.; Lee, H. N.; Hong, T.; Calder, S.; Zhou, H. D.; Lumsden, M. D.; Keppens, V.; Mandrus, D.; Christianson, A. D.

    2015-12-01

    The structural and the magnetic properties of CeCu6 -xAgx (0 ≤x ≤0.85 ) and CeCu6 -xPdx (0 ≤x ≤0.4 ) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6 -xAgx and CeCu6 -xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (P n m a ) to a monoclinic (P 21/c ) phase at 240 K. In CeCu6 -xAgx , the structural phase transition temperature (Ts) decreases linearly with Ag concentration and extrapolates to zero at xS ≈0.1 . The structural transition in CeCu6 -xPdx remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6 -xAgx and CeCu6 -xPdx , exhibit a magnetic quantum critical point (QCP), at x ≈0.2 and x ≈0.05 , respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (δ10 δ2), where δ1˜0.62 ,δ2˜0.25 ,x =0.125 for CeCu6 -xPdx and δ1˜0.64 ,δ2˜0.3 ,x =0.3 for CeCu6 -xAgx . The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.

  13. AuPd CATALYTIC NANOPARTICLE SIZE EFFECT ON THE FORMATION OF AMORPHOUS SILICON NANOWIRES

    Institute of Scientific and Technical Information of China (English)

    LIU ZU-QIN; SUN LIAN-FENG; TANG DONG-SHENG; ZHOU WEI-YA; LI YU-BAO; Zou XIAO-PING

    2000-01-01

    Amorphous silicon (a-Si) nanowires have been prepared on SiO2/Si substrates by AuPd nanoparticles / silane reaction method. Field-emission scanning electron microscopy and transmission electron microscopy were used to characterize the samples. The typical a-Si nanowires we obtained are of a uniform diameter about 20 nm and length up to several micrometers. The growth mechanism of the nanowires seems to be the vapor-liquid-solid mechanism. The catalytic particle size effect on the formation of the nanowires and the cause of forming amorphous state Si nanowires are discussed.

  14. Preparation of Ag{sub core}/Au{sub shell} bimetallic nanoparticles from physical mixtures of Au clusters and Ag ions under dark conditions and their catalytic activity for aerobic glucose oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Haijun, E-mail: zhanghaijun@wust.edu.cn [College of Materials and Metallurgy, Wuhan University of Science and Technology, Wuhan, Hubei Province 430081 (China); Toshima, Naoki; Takasaki, Kanako [Department of Applied Chemistry, Tokyo University of Science Yamaguchi, SanyoOnoda-shi, Yamaguchi 756-0884 (Japan); Okumura, Mitsutaka [Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)

    2014-02-15

    Graphical abstract: The synthesis, characterization and catalytic activities for glucose oxidation of AgAu bimetallic nanoparticles (BNPs) with size of less than 2 nm are reported. The catalytic activity of Ag{sub 10}Au{sub 90} BNPs was about two times higher than that of Au NPs, even the BNPs have a larger particle size than that of Au NPs. -- Highlights: • Ag{sub core}/Au{sub shell} BNPs with size of less than 2.0 nm were prepared. • No any reducing reagents and lights were used for the preparation of the BNPs. • The catalytic activity of the BNPs is about two times higher than that of Au NPs. -- Abstract: AgAu bimetallic nanoparticles (BNPs), one of the most extensively studied bimetallic systems in the literatures, could have various structures and compositions depending on their preparation conditions. In the present work, catalytically highly active PVP-protected Ag{sub core}/Au{sub shell} BNPs of about 2.5 nm in diameter were fabricated from physical mixtures of aqueous dispersions of Au nanoparticles and Ag{sup +} ions under dark conditions without using any reducing agents. The prepared Ag{sub core}/Au{sub shell} BNP colloidal catalysts, which possessed a high activity for aerobic glucose oxidation, were characterized by Ultraviolet–visible spectrophotometry (UV–Vis), Inductive coupled plasma emission spectrometer (ICP), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Energy disperse spectroscopy (EDS) in High-resolution scanning transmission electron microscopy (HR-STEM). The highest activity (11,360 mol-glucose h{sup −1} mol-metal{sup −1}) was observed for the BNPs with the Ag/Au atomic ratio of 1/9, the TOF value of which is about two times higher than that of Au nanoparticles with the particle size of 1.3 nm. The enhanced catalytic activity of the prepared Ag{sub core}/Au{sub shell} BNPs compared to Au NPs can be ascribed to the presence of negatively charged Au atoms resulted from electron donations

  15. Surface characterization of Pd/Ag23 wt% membranes after different thermal treatments

    International Nuclear Information System (INIS)

    Hydrogen permeation measurements of 1.5-10 μm thick Pd/Ag23 wt% membranes before and after thermal treatments at 300 deg. C in air (both sides) or in the temperature range 300-450 deg. C in N2 (feed side) and Ar (permeate side) were performed. Accompanying changes in surface topography and chemical composition were subsequently investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profiling. For a 2 μm thick membrane, the surface roughness increased for all annealing temperatures applied, while a temperature of 450 deg. C was required for an increase in roughness of both membrane surfaces to occur for the 5 μm membrane. The thickest membrane, of 10 μm, showed changed surface roughness on one side of the membrane only and a slight decrease in hydrogen permeance after all heat treatments in N2/Ar. X-ray photoelectron spectroscopy investigations performed after treatment and subsequent permeation measurements revealed segregation of silver to the membrane surfaces for all annealing temperatures applied. In comparison, heat treatment at 300 deg. C in air resulted in significantly increased hydrogen permeance accompanied by increasing surface roughness. Upon exposure to oxygen, Pd segregates to the surface to form a 2-3 nm thick oxide layer (PdO), with more complex segregation behavior after subsequent reduction and permeance measurements in pure hydrogen. The available permeance data for the Pd/Ag23 wt% membranes after heat treatment in air at 300 deg. C is found to depend linearly on the inverse membrane thickness, implying bulk limited hydrogen permeation for thicknesses down to 1.5-2.0 μm.

  16. Kinetic analysis of the reduction of 4-nitrophenol catalyzed by Au/Pd nanoalloys immobilized in spherical polyelectrolyte brushes.

    Science.gov (United States)

    Gu, Sasa; Lu, Yan; Kaiser, Julian; Albrecht, Martin; Ballauff, Matthias

    2015-11-14

    We present a detailed study of the catalytic activity of Au/Pd nanoalloys with Au : Pd molar ratio 75 : 25 synthesized using spherical polyelectrolyte brushes (SPB) as carrier system. The reduction of 4-nitrophenol (Nip) by sodium borohydride (BH4(-)) has been used as a model reaction. This reaction proceeds in two steps: 4-nitrophenol is first reduced to 4-hydroxylaminophenol which in a second step is reduced to the final product 4-aminophenol. Both steps of the reaction proceed on the surface of the nanoparticles (Langmuir-Hinshelwood-mechanism). We use this model to analyze the experimental data obtained by catalysis with the Au/Pd-nanoalloys. Good agreements between theory and experiments were found up to 30% conversion of Nip. The kinetic parameters were compared with the data derived from neat Au and Pd nanoparticles immobilized in the same SPB carrier system. The addition of 25% molar ratio of Pd to the nanoalloys increases the reaction rate of the first step nearly 10 times compared with that of SPB-Au and 60 times compared with that of SPB-Pd. Analysis of the nanoalloy by high-resolution transmission electron microscopy suggests that the surface defects of the nanoalloys play an important role for the enhanced catalytic activity. PMID:25790094

  17. A comparative study on the bond strength of porcelain to the millingable Pd-Ag alloy

    OpenAIRE

    Hong, Jun-Tae; Shin, Soo-Yeon

    2014-01-01

    PURPOSE The porcelain fused to gold has been widely used as a restoration both with the natural esthetics of the porcelain and durability and marginal fit of metal casting. However, recently, due to the continuous rise in the price of gold, an interest towards materials to replace gold alloy is getting higher. This study compared the bond strength of porcelain to millingable palladium-silver (Pd-Ag) alloy, with that of 3 conventionally used metal-ceramic alloys. MATERIALS AND METHODS Four typ...

  18. Evolution of a defect structure of Pd-Ag alloys during tritium exposure

    Energy Technology Data Exchange (ETDEWEB)

    Tebus, V. E-mail: tebus@bochvar.ru; Rivkis, L.; Dmitrievskaia, E.; Arutunova, G.; Golikov, I.; Ryazantseva, N.; Filin, V.; Kapychev, V.; Bulkin, V

    2002-12-01

    Pd-Ag alloys, a material for palladium diffuser of the ITER fuel clean-up system, were investigated after long-term usage exposition in tritium. Nucleation and evolution of the alloy structure defects as a result of a radiogenic helium-3 accumulation have been examined using electron microscopy, positron annihilation and X-ray analysis. The types of helium containing defects and their characteristics were determined. The early stage of helium bubbles forming was observed. It was shown that the simple defect concentration decreased slowly and helium-3 bubble sizes and concentration increased during the tritium exposure.

  19. Enlace y estereoquímica en compuestos monovalentes de Cu, Ag y Au

    OpenAIRE

    Carvajal Barba, Mª Àngels

    2004-01-01

    [spa] En esta tesis se tratan diversos aspectos de la química de Cu(I), Ag(I) y Au(I). En primer lugar se estudia sistemáticamente la capacidad de los funcionales de la densidad B3LYP, PBE0 y PBE1 para tratar las interacciones d10···d10 y otros tipos de interacciones intermoleculares, tales como enlace de hidrógeno fuerte, débil y moderado e interacciones de Van der Waals. Se estudia el problema del número de coordinación en compuestos de Cu(I), Ag(I) y Au(I): mientras que Cu(I) y Ag(I) forma...

  20. Dependence of the conductance change on the molecular orbitals in Ag and Au electrodes

    Science.gov (United States)

    Kim, Hyun Sung; Kim, Taekyeong

    2016-01-01

    The conductance change in single-molecule junctions due to the molecular orbitals and the metal's Fermi energy was investigated by using a scanning tunneling microscopy break-junction technique with Ag and Au electrodes. 4,4'-diaminobiphenyl and 4,4'-dicyanobiphenyl as the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) junctions were used. The amine-linked HOMO-conducting junction had a lower conductance, and cyano-linked LUMO-conducting junction had a higher conductance for Ag electrode compared to Au electrode. These results are attributed to the difference between the metal electrode Fermi energy and the molecular orbital level in the metal-molecule junction. Furthermore, 2,7-diaminofluorene exhibited a higher conductance but the identical molecular plateau length for the Ag electrodes compared to that of 4,4'-diaminobiphenyl indicating that the twist angle of the molecular backbone affects the conductance.

  1. Highly sensitive electrochemical determination of Sunset Yellow based on the ultrafine Au-Pd and reduced graphene oxide nanocomposites.

    Science.gov (United States)

    Wang, Jin; Yang, Beibei; Zhang, Ke; Bin, Duan; Shiraishi, Yukihide; Yang, Ping; Du, Yukou

    2016-11-01

    A sensitive and novel electrochemical sensor with Au-Pd and reduced graphene oxide (RGO) nanocomposites modified glassy carbon electrode (Au-Pd-RGO/GCE) was successfully fabricated by one-step synthesis method for the detection of Sunset Yellow. The as-prepared composites were uniformly dispersed on the surface of electrode with an average diameter of approximately 3.44nm, and the ultrafine nanoparticles effectively enhanced the electrochemical active surface area of GCE. The modified electrode had been characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and electrochemical tests. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) results showed high stability and outstanding electrocatalytic activity of Au-Pd-RGO/GCE for the detection of SY with low detection limits (1.5 nM, S/N=3) and wide concentration ranges (0.686-331.686μM). The Au-Pd-RGO/GCE was further applied to detect SY in real samples with good recovery. Herein, the fabricated Au-Pd-RGO/GCE showed excellent sensitivity, stability and repeatability for the detection of SY and will be a promising application in electrochemical sensor. PMID:27475710

  2. Photocatalytic degradation of malathion in aqueous solution using an Au-Pd-TiO2 nanotube film

    International Nuclear Information System (INIS)

    The extensive use of pesticides has promoted the agricultural production, but a series of subsequent environmental issues have drawn the concern of governments and people worldwide, such as groundwater and surface water pollutions. In order to remove these pollutants, photocatalysis has emerged as a powerful method. In this paper, the photocatalytic degradation of an organophosphorus pesticide malathion was investigated using an Au-Pd co-modified TiO2 nanotube film (Au-Pd-TiO2). This film was fabricated by simultaneously photo-depositing Au and Pd precursors on a self-organized TiO2 nanotube film. Its morphology and structures were well characterized by a scanning electron microscope (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The photocatalytic experiments revealed that the malathion elimination rate increased by 172% when the photocatalyst of the naked TiO2 nanotube film was replaced by Au-Pd-TiO2. Additionally, the amount of H2O2 yielded on the Au-Pd-TiO2 film in 60 min was 2.89 times that on the naked TiO2. The enhanced photocatalytic performance could be attributed to both the effective separation of photo-generated charge carriers and the higher synthesis rate of H2O2. The possible photocatalytic mechanism was discussed.

  3. Preparation of monolithic foamed Au/Ag alloy with hollow microspheres

    International Nuclear Information System (INIS)

    The polystyrene (PS) microspheres were coated by gold colloid with an average grain size of 4.6 nm by the electrostatic effect, and then electroless plated with gold silver consecutively. The deposited gold layer was 70 to 90 nm thick, almost coating the PS spheres completely. The silver particles deposited subsequently were compact, and larger than the previously de- posited gold particles, forming a 200 to 400 nm-thick layer on the surface of each Au/PS microsphere. The self-supported hollow-sphere Au40 Ag60 alloy was then obtained after the template being removed. Finally, the columniform foamed Au-Ag alloy, 5 mm in diameter, 1.2 g/cm3 in density, was obtained with the hollow spheres of 10 μm diameter after heat treatment. (authors)

  4. Critical Factors Controlling Pd and Pt Potential in Porphyry Cu–Au Deposits: Evidence from the Balkan Peninsula

    Directory of Open Access Journals (Sweden)

    Demetrios G. Eliopoulos

    2014-03-01

    Full Text Available Porphyry Cu–Au–Pd±Pt deposits are significant Au resources, but their Pd and Pt potential is still unknown. Elevated Pd, Pt (hundreds of ppb and Au contents are associated with typical stockwork magnetite-bornite-chalcopyrite assemblages, at the central parts of certain porphyry deposits. Unexpected high grade Cu–(Pd+Pt (up to 6 ppm mineralization with high Pd/Pt ratios at the Elatsite porphyry deposit, which is found in a spatial association with the Chelopech epithermal deposit (Bulgaria and the Skouries porphyry deposit, may have formed during late stages of an evolved hydrothermal system. Estimated Pd, Pt and Au potential for porphyry deposits is consistent with literature model calculations demonstrating the capacity of aqueous vapor and brine to scavenge sufficient quantities of Pt and Pd, and could contribute to the global platinum-group element (PGE production. Critical requirements controlling potential of porphyry deposits may be from the metals contained in magma (metasomatized asthenospheric mantle wedge as indicated by significant Cr, Co, Ni and Re contents. The Cr content may be an indicator for the mantle input.

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

    CERN Document Server

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

    2014-01-01

    Anisotropic Au nanoparticles show unique localized surface plasmon resonance (LSPR) properties, which make it 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 observation and spectral monitoring, we found that the layered epitaxial growth mode (i.e., 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 for the formation of the nanostars. The LSPR properties of the Au nanoparticles have been well investigated with morphology control via precursor amount and growth temperature. The Au nanostars showed improved surface-enhanced Raman spectroscopy (SERS) performance for rhodamine 6G du...

  6. Au+Au reactions at the AGS: Experiments E866 and E917

    Energy Technology Data Exchange (ETDEWEB)

    Ogilvie, C.A.; Ahle, L. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Physics; Akiba, Y. [KEK, Tanashi (Japan)] [and others; E866 Collaboration; E917 Collaboration

    1997-12-01

    Particle production and correlation functions from Au+Au reactions have been measured as a function of both beam energy (2--10.7 AGeV) and impact parameter. These results are used to probe the dynamics of heavy-ion reactions, confront hadronic models over a wide range of conditions and to search for the onset of new phenomena.

  7. In situ biosynthesis of Ag, Au and bimetallic nanoparticles using Piper pedicellatum C.DC: green chemistry approach.

    Science.gov (United States)

    Tamuly, Chandan; Hazarika, Moushumi; Borah, Sarat Ch; Das, Manash R; Boruah, Manas P

    2013-02-01

    The synthesis of Ag, Au and Ag-Au bimetallic nanoparticles using Piper pedicellatum C.DC leaf extract is demonstrated here. The rapid formation of stable Ag and Au nanoparticles has been found using P. pedicellatum C.DC leaf extract in aqueous medium at normal atmospheric condition. Competitive reduction of Ag(+) and Au(3+) ions present simultaneously in solution during exposure to P. pedicellatum C.DC leaf extract leads to the synthesis of bimetallic Ag-Au nanoparticles in solution. Transmission electron microscopy (TEM) analysis revealed that the Ag nanoparticles predominantly form spherical in shape with the size range of 2.0±0.5-30.0±1.2 nm. In case of Au nanoparticles, the particles are spherical in shape along with few triangular, hexagonal and pentagonal shaped nanoparticles also observed. X-ray diffraction (XRD) studies revealed that the nanoparticles were face centered cubic (fcc) in shape. Fourier transform infrared spectroscopy (FTIR) showed nanoparticles were capped with plant compounds. The chemical constituents, viz. catechin, gallic acid, courmaric acid and protocatechuic acid of the leaf extract were identified which may act as a reducing, stabilizing and capping agent. The expected reaction mechanism in the formation of Ag and Au nanoparticles is also reported. PMID:23107941

  8. Influence of Ag-Au microstructure on the photoelectrocatalytic performance of TiO2 nanotube array photocatalysts.

    Science.gov (United States)

    Wang, Qingyao; Wang, Xiaotong; Zhang, Miao; Li, Guihua; Gao, Shanmin; Li, Mingyang; Zhang, Yiqing

    2016-02-01

    In this work, vertically-aligned TiO2 nanotube arrays (TiO2 NTs) were grown on Ti substrates via a facile electrochemical anodization method followed by calcinations. Then, Ag-Au alloy nanoparticles and Ag@Au core-shell nanoparticles were deposited on the obtained TiO2 NTs via UV reduction and displacement reaction, respectively. X-ray diffraction, scanning electron microscopy and transmission electron microscopy indicated that Ag-Au alloy nanoparticles and Ag@Au core-shell nanoparticles grew uniformly on the walls of TiO2 NTs. Investigation results from removal of methyl orange (MO) and Cr(IV) ions indicated that the as-prepared bimetal plasmonic photocatalysts exhibited excellent photoelectrocatalytic (PEC) activities. The influences of Ag-Au alloy and core-shell microstructures on PEC properties of TiO2 NTs were investigated and the TiO2 NTs/Ag@Au photocatalyst showed more outstanding PEC removal efficiency than that of TiO2 NTs/Ag-Au due to the regular core-shell microstructure and low recombination of photogenerated electrons and holes. PMID:26555961

  9. Photochemical synthesis of bimetallic Au-Ag nanoparticles with "core-shell" type structure by seed mediated catalytic growth

    Institute of Scientific and Technical Information of China (English)

    DONG Shou-an; TANG Chun

    2005-01-01

    The colloidal Au core/Ag shell structure composite nanoparticles were synthesized in PEG-acetone solution by photochemical route. The monodispersed Au nanoparticles with average diameter of 3.9 nm were used as growth seeds. The optical property of colloids and the sizes of composite nanoparticles were characterized when the molar ratio of Au to Ag ranges from 4 : 1 to 1 : 4. The results show that a composite nanoparticle structure similar to strawberry shape is formed at the molar ratio of Au to Ag from 4 : 1 to 1 : 1; the composite nanoparticles consisting of a core of Au and shell of Ag were generated at the 1: 4 molar ratio, having a striking feature of forming interconnected network structure.

  10. Hydrodynamic instabilities of thin Au/Pd alloy film induced by tightly focused femtosecond laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Kuchmizhak, Aleksandr, E-mail: ku4mijak@dvo.ru [Institute for Automation and Control Processes, Far Eastern Branch, Russian Academy of Science, 5 Radio str., Vladivostok 690041 (Russian Federation); Gurbatov, Stanislav; Nepomniaschiy, Aleksandr; Mayor, Aleksandr [Institute for Automation and Control Processes, Far Eastern Branch, Russian Academy of Science, 5 Radio str., Vladivostok 690041 (Russian Federation); Kulchin, Yuri; Vitrik, Oleg [Institute for Automation and Control Processes, Far Eastern Branch, Russian Academy of Science, 5 Radio str., Vladivostok 690041 (Russian Federation); Far Eastern Federal University, 8 Sukhanova Str., Vladivostok 690041 (Russian Federation); Makarov, Sergey [Lebedev Physical Institute, Moscow 119991 (Russian Federation); ITMO University, St. Petersburg 197101 (Russian Federation); Kudryashov, Sergey [Lebedev Physical Institute, Moscow 119991 (Russian Federation); National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409 Moscow (Russian Federation); Ionin, Andrey [Lebedev Physical Institute, Moscow 119991 (Russian Federation)

    2015-05-15

    Highlights: • Each type of laser-induced hydrodynamic instabilities results in the formation of corresponding frozen surface relief nanostructure: nanojets, nanocrowns or hybrid structures (a nanojet surrounded by a nanocrown). • The thickness of the metal film as well as the pulse energy were found to be the key parameters determining the type of the resulted surface structure. • Pd addition in the Au film results in the formation of the nanojets and the spherical droplets with a porous internal structure. - Abstract: We report on detailed experimental study of various nanoscale surface hydrodynamic instabilities on thin Au/Pd alloy films induced by tightly focused single femtosecond pulses. Each type of laser-induced hydrodynamic instabilities results in the formation of corresponding resolidified surface relief nanostructure: nanojet, nanocrown or hybrid structure (a nanojet surrounded by a nanocrown), where the hybrid structure is reported for the first time. Thickness of metal films, as well as the laser pulse energy, were found to be the key parameters determining the type of the resulting surface structures. Single nanojets were revealed to appear only on films with sub-100-nm thickness, while irradiation of thicker films (120–240 nm) leads to the formation of nanocrowns at near-threshold energies or hybrid structures at higher energies. The underlying formation mechanisms giving rise to all of these laser-induced nanostructures are also discussed.

  11. Nanometer sized electrodes fabricated by electromigration of Au and Pd nanowires

    Science.gov (United States)

    Vlad, Alexandru; Faniel, Sébastien; Hackens, Benoît; Bayot, Vincent; Melinte, Sorin

    2008-03-01

    Electromigration-driven metallic nanowire failure is presented. Here, Au and Pd nanowires patterned by electron-beam lithography were electrically stressed up to their breaking point. Feedback control and simple voltage sweep techniques have been successfully used to form nanometer-sized gaps. We observe a material- and geometry-dependent behavior. The Au nanowires showed a Joule-induced reversible resistance increase with the applied voltage up to the breaking point. In contrast, Pd nanowires presented an anomalous resistance decrease close to their failure point. This was associated to the melting and agglomeration of metallic grains within the electrically stressed nanowires. The SEM images acquired at intermediate stages of electromigration agree with the electrical data findings. The influence of the nanowire geometry upon the morphology of fabricated nanoelectrodes is considered. Beside the morphological characterization of our break junctions, we also measured their current-voltage characteristics. We observed single electron tunneling effects, probably due to the presence of metallic clusters formed close to the nanoelectrodes during the electromigration. Our results are consistent with recent findings on Coulomb blockade phenomena in electromigrated gold break junctions.

  12. Change of Work Function of Pd, Ag, K on Al(001) as a Function of External Electric Field

    Institute of Scientific and Technical Information of China (English)

    侯柱峰; 黄美纯; 朱梓忠; 黄荣彬; 郑兰荪

    2001-01-01

    We present a local density functional calculation of the effect of an external electric field on the work function change of Pd and Ag adsorption on an Al(001) surface. The adsorption of K has also been considered for comparison. We found that the work functions for all the systems increased linearly when the strength of the external electric field was increased. Since the polarized electrons at the interstitial regions between the adsorbate and substrate for Pd/Al(001) and Ag/Al(001) react to the external electric field differently, the subtle differences between Pd/Al(001) and Ag/Al(001) bondings has been characterized through the comparison of the slopes of the work function change versus electric field.

  13. Magnetic properties of ZnS doped with noble metals (X = Ru, Rh, Pd, and Ag)

    Science.gov (United States)

    Tan, Zhiyun; Xiao, Wenzhi; Wang, Lingling; Yang, Youchang

    2012-12-01

    Density functional theory calculations are carried out to study the electronic structures and magnetic properties in zinc-blende structure ZnS doped with nonmagnetic noble metals (X = Ru, Rh, Pd, and Ag). Results show robust magnetic ground states for X-doped ZnS. The total magnetic moments are about 2.0, 3.0, and 2.0 μB per supercell for the Ru-, Rh-, and Pd-doped ZnS, respectively. As the atomic number of X element increases, the local magnetic moment tends toward delocalize and the hybridization between X-4d and S-3p states become stronger. This trend is strongly related to the difference in electronegativity between the substitutional X and the cation in the ZnS host. For Ag-doped ZnS, both non-spin- and spin-polarized calculations yield nearly equal total energy. The substitution of Zn in ZnS parent material by the nonmagnetic 4d transition-metals may lead to half-metallic ferromagnetism which stems from the hybridization between X-4d and S-3p states and could be attributed to a double-exchange mechanism. Curie temperature values are estimated using mean-field approximation.

  14. Compensation effect in H 2 permeation kinetics of PdAg membranes

    KAUST Repository

    Zeng, Gaofeng

    2012-08-30

    Knowledge about the (inter)dependence of permeation kinetic parameters on the stoichiometry of H 2-selective alloys is still rudimentary, although uncovering the underlying systematic correlations will greatly facilitate current efforts into the design of novel high-performance H 2 separation membranes. Permeation measurements with carefully engineered, 2-7 μm thick supported Pd 100-xAg x membranes reveal that the activation energy and pre-exponential factor of H 2 permeation laws vary systematically with alloy composition, and both kinetic parameters are strongly correlated for x ≤ 50. We show that this permeation kinetic compensation effect corresponds well with similar correlations in the hydrogen solution thermodynamics and diffusion kinetics of PdAg alloys that govern H 2 permeation rates. This effect enables the consistent description of permeation characteristics over wide temperature and alloy stoichiometry ranges, whereas hydrogen solution thermodynamics may play a role, too, as a yet unrecognized source of kinetic compensation in, for example, H 2-involving reactions over metal catalysts or hydrogenation/ dehydrogenation of hydrogen storage materials. © 2012 American Chemical Society.

  15. Electromotive force measurements in liquid Ag-In-Pd lead-free alloys

    Institute of Scientific and Technical Information of China (English)

    Grzegorz Garzel; Leszek A. Zabdyr

    2006-01-01

    Emf technique was employed to determine indium activities in the liquid Ag-In-Pd alloys using galvanic cellswith yttria-stabilised-zirconia as solid electrolyte according to the scheme: kanthal/rhenium, Ag-In-Pd, In2O3 | YSZ | Ni, NiO, Pt. Composition and temperature measurement ranges were limited, because of very steep liquidus surface; 35 compositions for XPd up to 0.3 were investigated and at temperatures from near-liquidus up to 1700 K. High temperature experiments required special moly furnace to be constructed with unique automatic gas supply system for furnace winding protective atmosphere. Emf readings were taken and recorded by automatic data acquisition system. Linear dependence of emf on temperature was observed for all compositions investigated, and results were approximated by straight line equations. Then In activities were calculated using well-known relations and taking into account correction for thermoelectric power between kanthal and platinum. Results are to be used along with other existing data to perform assessment of the ternary system under accord.

  16. Sonochemically synthesized mono and bimetallic Au-Ag reduced graphene oxide based nanocomposites with enhanced catalytic activity.

    Science.gov (United States)

    Neppolian, Bernaurdshaw; Wang, Chang; Ashokkumar, Muthupandian

    2014-11-01

    Graphene oxide (GO) supported Ag and Au mono-metallic and Au-Ag bimetallic catalysts were synthesized using a sonochemical method. Bimetallic catalysts containing different weight ratios of Au and Ag were loaded onto GO utilizing a low frequency horn-type ultrasonicator. High frequency ultrasonication was used to efficiently reduce Ag(I) and Au(III) ions in the presence of polyethylene glycol and 2-propanol. Transmission electron microscopy (TEM-EDX) and X-ray photoelectron spectroscopy were used to analyze the morphology, size, shape and chemical oxidation states of the prepared metallic catalysts on GO. The catalytic efficiency of the prepared catalysts were compared using 4-nitrophenol (4-NP) reduction reaction and the subsequent formation of 4-aminophenol (4-AP) that was also monitored using UV-vis spectrophotometry. The results revealed that Au-Ag-GO bimetallic catalysts showed high activity for the conversion of 4-NP to 4-AP than their monometallic counterparts. Amongst different weight ratios (1:1, 1:2 and 2:1) between Au and Ag, the 1:2 (Au:Ag) catalyst exhibited very good catalytic performance for the conversion of 4-NP to 4-AP. A total reduction of 4-NP took place within a short period of time if Au-GO was reduced first followed by Ag reduction, whereas a lower reduction rate was observed if Ag-GO was reduced first. The same trend was observed for all the ratios of bimetallic catalysts prepared by this method. The initial unfavorable reduction potential of Ag(I) is likely to be responsible for the above order. It was found that applying dual frequency ultrasonication was a highly effective way of preparing bimetallic catalysts requiring relatively low levels of added chemicals and producing bimetallic catalysts with GO with improved catalytic efficiency. PMID:24582660

  17. Blood surface-enhanced Raman spectroscopy based on Ag and Au nanoparticles for nasopharyngeal cancer detection

    Science.gov (United States)

    Lin, Duo; Ge, Xiaosong; Lin, Xueliang; Chen, Guannan; Chen, Rong

    2016-05-01

    This study aims to evaluate and compare the utility of blood surface-enhanced Raman spectroscopy (SERS) based on Au or Ag nanoparticles (NPs), respectively, for detection of nasopharyngeal cancer (NPC). A rapid home-made Raman system was employed for SERS measurement, and high quality SERS spectra can be recorded from blood plasma samples belonging to 60 healthy volunteers and 100 NPC patients, using both metallic NPs. The spectral differences under Ag-SERS measurement between the normal and cancer groups are more significant than Au-SERS. Principal component analysis combined with linear discriminant analysis (PCA-LDA) was used for differentiating the two blood groups with a diagnostic sensitivity and specificity of 90% and 95%, respectively, using Ag-SERS method, which has almost a 20% improvement in diagnostic specificity in comparison to Au-SERS. This exploratory study demonstrates that blood SERS based on Ag NPs is capable of achieving a better diagnostic performance for NPC detection, and has promising potential for improving NPC screening.

  18. Evolution of the quantum well states in Ag layers on Au(111)

    Energy Technology Data Exchange (ETDEWEB)

    Nuber, Andreas; Bendounan, Azzedine [Universitaet Wuerzburg, Experimentelle Physik II, Am Hubland, 97074 Wuerzburg (Germany); Huang, Li [Surface Physics Laboratory, Dept. of Physics, Fudan Univ (China); Oak Ridge National Lab., TN (United States). Materials Science and Technology Div.; Gong, Xingao [Surface Physics Laboratory, Dept. of Physics, Fudan Univ (China); Zhang, Zhenyu [Oak Ridge National Lab., TN (United States). Materials Science and Technology Div.

    2007-07-01

    Electronic quantum well states (QWS) confined in ultrathin films are of great scientific interest. Outside the substrate energy gap the confinement is supressed. They can couple with substrate states and form quantum well resonances (QWR). We present systematic studies on epitaxial layer-by-layer growing Ag films up to 45 ML on Au(111) using angular resolved photoelectron spectroscopy (ARUPS) ({delta}E=3 meV,{delta}{theta}=0.3 ). Our data in combination with density functional theory show the transition from QWR to QWS. We investigated the localization of the states in terms of their center-of-charge, peak position and lineshape. In contrast to comparable systems like Ag/W(110) QWS in Ag/Au(111) are formed not before a thickness of {approx}8 ML. The center-of-charge and the peak position are localized within the Ag overlayer and Au energy gap, respectively, at the same film thickness and hence can be used as criteria for the formation of QWS. Further investigations on their lineshape close to the substrate gap edge allow access to further many-body characteristics of the QWS.

  19. Energy loss of 107Ag, 109Ag and 150Sm in Ni and Au

    International Nuclear Information System (INIS)

    The stopping power of 107Ag, 109Ag and 150Sm in nickel and gold was measured as a preliminary test of a new technique for measuring energy loss based on the γ-ray Dopppler shift. The analysis of the data was based on the theories of Lindhard, Scharff and Schiott for nuclear and electronic stopping. The results are compared with the semi-empirical predictions of Northcliffe and Schilling. (author)

  20. Fe-Au and Fe-Ag composites as candidates for biodegradable stent materials.

    Science.gov (United States)

    Huang, Tao; Cheng, Jian; Bian, Dong; Zheng, Yufeng

    2016-02-01

    In this study, Fe-Ag and Fe-Au composites were fabricated by powder metallurgy using spark plasma sintering. Their microstructures, mechanical properties, and biocorrosion behavior were investigated by using optical microscopy, X-ray diffraction, environment scanning electronic microscopy, compressive test, electrochemical measurements, and immersion tests. Microstructure characterization indicated that the as-sintered iron-based materials obtained much finer grains than that of as-cast pure iron. Phase analysis showed that the Fe-Ag composites were composed of α-Fe and pure Ag phases, and Fe-Au composites consisted of α-Fe and Au phases. Compressive test showed that the improved mechanical strengths were obtained in as-sintered iron-based materials, among which the Fe-5 wt %Ag exhibited the best mechanical properties. The electrochemical and immersion tests revealed that the addition of Ag and Au could increase the corrosion rate of the iron matrix and change the corrosion mode into more uniform one. Based on the results of cytotoxicity evaluation, it was found that all the experimental material extracts performed no significant toxicity on the L-929 cells and EA. hy-926 cells, whereas a considerable inhibition on the proliferation of vascular smooth muscle cells was observed. The hemocompatibility tests showed that the hemolysis of all the experimental materials was within the range of 5%, which is the criteria value of biomaterials with good hemocomaptibility. The amount of platelet adhered on the surface of as-sintered iron-based materials was lower than that of as-cast pure iron, and the morphology of platelets kept smoothly spherical on the surface of all the experimental materials. PMID:25727071

  1. Calculation of Elastic Constants of Ag/Pd Superlattice Thin Films by Molecular Dynamics with Many-Body Potentials

    Institute of Scientific and Technical Information of China (English)

    GAO Ning; LAI Wen-Sheng

    2006-01-01

    @@ The calculation of elastic constants of Ag/Pd superlattice thin films by molecular dynamics simulations with many-body potentials is presented. It reveals that the elastic constants C11 and C55 increase with decreasing modulation wavelength A of the films, which is consistent with experiments. However, the change of C11 and C55 with A is found to be around the values determined by a rule of mixture using bulk elastic constants of metals.No supermodulus effect is observed and it is due to cancellation between enhanced and reduced contributions to elastic constants from Ag and Pd layers subjected to compressive and tensile strains, respectively.

  2. Effect of Thickness and Phosphorus Content on Au/Pd/Ni(P) Metal Finish of Printed Circuit Board

    Science.gov (United States)

    Huang, Chih-Kai; Lin, Keh-Wen; Huang, Yu-Ming; Caparanga, Alvin R.; Leron, Rhoda B.; Li, Meng-Hui

    2013-08-01

    Electroless nickel/electroless palladium/immersion gold [Au/Pd/Ni(P) or ENEPIG] pads consisting of layers of Ni(P) (200 μin), pure palladium (Pd) or palladium phosphorus (PdP) (2 μin, 4 μin or 6 μin), and gold (Au) (2 μin or 4 μin) were prepared using two different processes (wire bonding and lead-free soldering). Each of these processes was done with zero- or two-time reflow. Different tests on solderability, wettability, wire-bonding capacity, and corrosion resistance were performed on different combinations of ENEPIG pads formed using different combinations of processes and conditions. Scanning electron microscopy was also performed to examine the surface characteristics of the pads. It was found that the ENEPIG pad sample with the 4- μin-thick Au and 4- μin-thick PdP layers possessed stable wire-bonding capacity and excellent lead-free solder reliability. In addition, the ENEPIG-PdP systems showed better corrosion resistance, which is attributed to the presence of the amorphous PdP layer protecting the nickel layer.

  3. Diffusion of Ag, Au and Cs implants in MAX phase Ti3SiC2

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Weilin; Henager, Charles H.; Varga, Tamas; Jung, Hee Joon; Overman, Nicole R.; Zhang, Chonghong; Gou, Jie

    2015-05-16

    MAX phases (M: early transition metal; A: elements in group 13 or 14; X: C or N), such as titanium silicon carbide (Ti3SiC2), have a unique combination of both metallic and ceramic properties, which make them attractive for potential nuclear applications. Ti3SiC2 has been considered as a possible fuel cladding material. This study reports on the diffusivities of fission product surrogates (Ag and Cs) and a noble metal Au (with diffusion behavior similar to Ag) in this ternary compound at elevated temperatures, as well as in dual-phase nanocomposite of Ti3SiC2/3C-SiC and polycrystalline CVD 3C-SiC for behavior comparisons. Samples were implanted with Ag, Au or Cs ions and characterized with various methods, including x-ray diffraction, electron backscatter diffraction, energy dispersive x-ray spectroscopy, Rutherford backscattering spectrometry, helium ion microscopy, and transmission electron microscopy. The results show that in contrast to immobile Ag in 3C-SiC, there is a significant outward diffusion of Ag in Ti3SiC2 within the dual-phase nanocomposite during Ag ion implantation at 873 K. Similar behavior of Au in polycrystalline Ti3SiC2 was also observed. Cs out-diffusion and release from Ti3SiC2 occurred during post-implantation thermal annealing at 973 K. This study suggests caution and further studies in consideration of Ti3SiC2 as a fuel cladding material for advanced nuclear reactors operating at very high temperatures.

  4. Diffusion of Ag, Au and Cs implants in MAX phase Ti3SiC2

    Science.gov (United States)

    Jiang, Weilin; Henager, Charles H.; Varga, Tamas; Jung, Hee Joon; Overman, Nicole R.; Zhang, Chonghong; Gou, Jie

    2015-07-01

    MAX phases (M: early transition metal; A: elements in group 13 or 14; X: C or N), such as titanium silicon carbide (Ti3SiC2), have a unique combination of both metallic and ceramic properties, which make them attractive for potential nuclear applications. Ti3SiC2 has been considered as a possible fuel cladding material. This study reports on the diffusivities of fission product surrogates (Ag and Cs) and a noble metal Au (with diffusion behavior similar to Ag) in this ternary compound at elevated temperatures, as well as in dual-phase nanocomposite of Ti3SiC2/3C-SiC and polycrystalline CVD 3C-SiC for behavior comparisons. Samples were implanted with Ag, Au or Cs ions and characterized with various methods, including X-ray diffraction, electron backscatter diffraction, energy dispersive X-ray spectroscopy, Rutherford backscattering spectrometry, helium ion microscopy, and transmission electron microscopy. The results show that in contrast to immobile Ag in 3C-SiC, there is a significant outward diffusion of Ag in Ti3SiC2 within the dual-phase nanocomposite during Ag ion implantation at 873 K. Similar behavior of Au in polycrystalline Ti3SiC2 was also observed. Cs out-diffusion and release from Ti3SiC2 occurred during post-implantation thermal annealing at 973 K. This study suggests caution and further studies in consideration of Ti3SiC2 as a fuel cladding material for advanced nuclear reactors operating at very high temperatures.

  5. A green method to prepare Pd-Ag nanoparticles supported on reduced graphene oxide and their electrochemical catalysis of methanol and ethanol oxidation

    Science.gov (United States)

    Li, Lingzhi; Chen, Mingxi; Huang, Guanbo; Yang, Nian; Zhang, Li; Wang, Huan; Liu, Yu; Wang, Wei; Gao, Jianping

    2014-10-01

    Bimetallic palladium-silver nanoparticles (NPs) supported on reduced oxide graphene (RGO) with different Pd/Ag ratios (Pd-Ag/RGO) were prepared by an easy green method which did not use any additional reducing agents or a dispersing agent. During the process, simultaneous redox reactions between AgNO3, K2PdCl4 and graphene oxide (GO) led to bimetallic Pd-Ag NPs. The morphology and composition of the Pd-Ag/RGO were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis and Raman spectroscopy. Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical activities and stabilities of these Pd-Ag/RGO catalysts for the electro-oxidation of methanol and ethanol in alkaline media. Among the different Pd/Ag ratios, the Pd-Ag (1:1)/RGO had the best catalytic activities and stability. So it is a promising catalyst for direct alcohol fuel cell applications.

  6. PdM (M = Pt, Au) bimetallic alloy nanowires with enhanced electrocatalytic activity for electro-oxidation of small molecules

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Chengzhou; Guo, Shaojun; Dong, Shaojun [State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022 (China)

    2012-05-02

    A facile and general method has been developed to synthesize well-defined PdPt and PdAu alloy nanowires, which exhibit significantly enhanced activity towards small molecules, such as ethanol, methanol, and glucose electro-oxidation in an alkaline medium. Considering the important role of one-dimensional alloy nanowires in electrocatalytic systems, the present Pd-based alloy nanostructures could offer a promising new class of advanced electrocatalysts for direct alcohol fuel cells and electrochemical sensors. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. Mg-AI Mixed Oxides Supported Bimetallic Au-Pd Nanoparticles with Superior Catalytic Properties in Aerobic Oxidation of Benzyl Alcohol and Glycerol

    Institute of Scientific and Technical Information of China (English)

    王亮; 张伟; 曾尚景; 苏党生; 孟祥举; 肖丰收

    2012-01-01

    Nano-sized Au and Pd catalysts are favorable for oxidations with molecular oxygen, and the preparation of this kind of nanoparticles with high catalytic activities is strongly desirable. We report a successful synthesis of bimetal- lic Au-Pd nanoparticles with rich edge and comer sites on unique support of Mg-AI mixed oxides (Au-Pd/MAO), which are favorable for producing metal nanoparticles with high degree of coordinative unsaturation of metal atoms The systematic microscopic characterizations confirm the bimetallic Au-Pd nanoparticles are present as Au-Pd alloy The irregular shape of the bimetallic nanoparticles are directly observed in HRTEM images. As we expected, Au-Pd/MAO gives very excellent catalytic performances in the aerobic oxidation of benzyl alcohol and glycerol. For example, Au-Pd/MAO shows very high TOF of 91000 h i at 433 K with molecular oxygen at air pressure in solvent-free oxidation of benzyl alcohol; this catalyst also shows relatively high selectivity for tartronic acid (TA- RAC, 36.6%) at high conversion (98.5%) in aerobic oxidation of glycerol. The superior catalytic properties of Au-Pd/MAO would be potentially important tbr production of fine chemicals.

  8. Water-dispersable hybrid Au-Pd nanoparticles as catalysts in ethanol oxidation, aqueous phase Suzuki-Miyaura and Heck reactions

    KAUST Repository

    Song, HyonMin

    2012-01-01

    The catalytic activities of water-dispersable Au@Pd core-shell nanoparticles (NPs) and Au-Pd alloy NPs were examined. There is growing interest in Au-Pd hybridized NPs in a supported matrix or non-supported forms as catalysts in various reactions that are not limited to conventional Pd-related reactions. Four different Au@Pd core-shell NPs in this study were prepared at room temperature with help from the emulsion phase surrounding the Au core NPs. Au-Pd alloy NPs were prepared over 90 °C, and underwent phase transfer to aqueous medium for their catalytic use. Au@Pd core-shell NPs show catalytic activity in ethanol oxidation reactions as electrocatalysts, and both core-shell and alloy NPs are good to excellent catalysts in various Suzuki-Miyaura and Heck reactions as heterogeneous catalysts. Specifically, Au@Pd core-shell NPs with sharp branched arms show the highest yield in the reactions tested in this study. A relatively small amount (0.25 mol%) was used throughout the catalytic reactions. © 2012 The Royal Society of Chemistry.

  9. Preparation of Pd-MgO model catalysts by deposition of Pd from aqueous precursor solutions onto Ag(001)-supported MgO(001) thin films

    OpenAIRE

    Ringleb, Franziska; Sterrer, Martin; Freund, Hans-Joachim

    2013-01-01

    The preparation of Pd–MgO model catalysts via liquid-phase deposition of Pd from aqueous Pd precursor solutions was studied. Thin, single-crystalline MgO(0 0 1) films grown on a Ag(0 0 1) substrate were used as support and allowed surface science techniques such as Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning tunneling microscopy, and temperature programmed desorption to be applied for characterization. Thin MgO(0 0 1) films were unstable and rapidly dissolved in ac...

  10. Effects of Ag + and Au 3+ ion implantation of lithium niobate

    Science.gov (United States)

    Amolo, G. O.; Comins, J. D.; Naidoo, S. R.; Connell, S. H.; Witcomb, M. J.; Derry, T. E.

    2006-09-01

    The optical effects of implantation of lithium niobate crystals with 100 keV Ag + and 8 MeV Au 3+ ions with fluences of 1 × 10 17 ions/cm 2 have been investigated. Metal nanoparticle formation has been studied as a function of annealing temperature, and the resulting optical extinction curves have been simulated by the Mie theory in the small particle limit. Transmission electron microscopy (TEM) has provided direct evidence for the MNP sizes allowing comparison with the calculated results. A TEM study of an X-cut sample implanted with Ag + ions show that the implanted region is partially amorphised. The differences in the temperature of Au colloid development in X- and Y-cut faces of the lithium niobate crystal are attributed to restoration of crystallinity as a result of annealing.

  11. Fabrication of AgAu alloy-TiO2 core-shell nanoparticles and their photocatalytic properties

    Science.gov (United States)

    Zhang, Xiao-yu; Yuan, Shu-long; Yuan, Yu-zhen; Li, Xue

    2015-01-01

    In this paper, for improving the photocatalytic efficiency of titania (TiO2) nanoparticles (NPs), AgAu alloy-TiO2 core-shell NPs are fabricated via a sol-gel (SG) process in the presence of AgAu alloy NPs with block copolymer shells as templates. The photocatalytic activities of the AgAu-TiO2 NPs on the photodecomposition of methylene blue (MB) are investigated. The AgAu-TiO2 composite NPs coated with 5.0% titania related to block copolymers show higher photocatalytic activity than the other samples in which the titania contents are larger than 5.0%. The results indicate that the increase of the thickness of the TiO2 shell leads to the decrease of the photocatalytic activity.

  12. Focused-ion-beam-fabricated Au nanorods coupled with Ag nanoparticles used as surface-enhanced Raman scattering-active substrate for analyzing trace melamine constituents in solution.

    Science.gov (United States)

    Sivashanmugan, Kundan; Liao, Jiunn-Der; Liu, Bernard Haochih; Yao, Chih-Kai

    2013-10-24

    A well-ordered Au-nanorod array with a controlled tip ring diameter (Au_NRsd) was fabricated using the focused ion beam method. Au_NRsd was then coupled with Ag nanoparticles (Ag NPs) to bridge the gaps among Au nanorods. The effect of surface-enhanced Raman scattering (SERS) on Au_NRsd and Ag NPs/Au_NRsd was particularly verified using crystal violet (CV) as the molecular probe. Raman intensity obtained from a characteristic peak of CV on Au_NRsd was estimated by an enhancement factor of ≈10(7) in magnitude, which increased ≈10(12) in magnitude for that on Ag NPs/Au_NRsd. A highly SERS-active Ag NPs/Au_NRsd was furthermore applied for the detection of melamine (MEL) at very low concentrations. Raman-active peaks of MEL (10(-3) to 10(-12)M) in water or milk solution upon Au_NRsd or Ag NPs/Au_NRsd were well distinguished. The peaks at 680 and 702 cm(-1) for MEL molecules were found suitable to be used as the index for sensing low-concentration MEL in a varied solution, while that at 1051 cm(-1) was practical to interpret MEL molecules in water or milk solution bonded with Au (i.e., Au_NRsd) or Ag (i.e., Ag NPs/Au_NRsd) surface. At the interface of Ag NPs/Au_NRsd and MEL molecules in milk solution, a laser-induced electromagnetic field or hotspot effect was produced and competent to sense low-concentration MEL molecules interacting with Ag and Au surfaces. Accordingly, Ag NPs/Au_NRsd is very promising to be used as a fast and sensitive tool for screening MEL in complex matrices such as adulteration in e.g., food and pharmaceutical products. PMID:24120168

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

    OpenAIRE

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

    2004-01-01

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

  14. Optical and structural properties of Au-Ag islands films for plasmonic applications

    Energy Technology Data Exchange (ETDEWEB)

    Sancho-Parramon, J.; Janicki, V.; Loncaric, M.; Zorc, H.; Dubcek, P. [Ruder Boskovic Institute, Zagreb (Croatia); Bernstorff, S. [Sincrotrone Trieste, Basovizza Trieste (Italy)

    2011-06-15

    Bimetallic islands films consisting of composite Au-Ag nanoparticles are deposited on glass substrates by electron beam evaporation. Broad tuning of the surface-plasmon resonance (SPR) characteristics can be achieved by controlling film composition, deposition temperature and post-deposition thermal annealing. Optical and structural characterization of the samples enable one to establish the link between the SPR and the morphological and compositional characteristics of nanoparticles. (orig.)

  15. New apparatus for DTA at 2000 bar: thermodynamic studies on Au, Ag, Al and HTSC oxides

    OpenAIRE

    Garnier, V.; Giannini, E.; Hugi, S.; Seeber, B.; Flukiger, R.

    2004-01-01

    A new DTA (Differential Thermal Analysis) device was designed and installed in a Hot Isostatic Pressure (HIP) furnace in order to perform high-pressure thermodynamic investigations up to 2 kbar and 1200C. Thermal analysis can be carried out in inert or oxidising atmosphere up to p(O2) = 400 bar. The calibration of the DTA apparatus under pressure was successfully performed using the melting temperature (Tm) of pure metals (Au, Ag and Al) as standard calibration references. The thermal propert...

  16. Sorption Of Au (III) and Ag (I) on Amino- and Mercapto-Silica Hybrid Columns

    International Nuclear Information System (INIS)

    Adsorption-desorption of Au(III) and Ag(I) ion on amino-silica hybrid (ASH) and mercapto-silica hybrid (MSH) in a column system has been studied. Adsorption was conducted in a 0.5-g adsorbent packed column passing through 30 mL solution of Au(III)/ Ag(I)/ Cu(II) ions 10 mg/ L for MSH and Au(III)/ Ag(I)/ Ni(II) for ASH with three repetitions. Desorption used eluent of thiourea in HCl solution with volume of 10 mL each. Concentration of metal ions in the eluent was analyzed with flame atomic absorption spectroscopy and the amount of metal ions desorbed was calculated. The results showed that metal ions loaded in the columns were adsorbed completely in both adsorbents. However, the amount of metal ions desorbed for first three fractions is depended on the concentration of eluent. Thiourea 1M in 1M HCl solution eluted 96.7 % and 59.1 % of Au(III) ion from MSH and ASH, respectively; and Ag(I) was desorbed 79.2 % from MSH and 97.6 % from ASH. Metal ions of Cu(II) and Ni(II) are not easily eluted with that eluent; only 45.8 % of Cu(II) was eluted from MSH and 5.0 % of Ni(II) from ASH. Repetition of process in three-time use indicates the highly stability of the adsorbents; hence those are potential for solid phase extraction application. (author)

  17. Calculating model of mass action concentrations for Ag-Au-Cu melts

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Based on phase diagrams and measured activities, the calculating model of mass action concentrations for heterogeneous melts Ag-Au-Cu was formulated. Calculated results agree with the improved results of recent research work.showing that the model formulated can reflect the structural characteristics of these melts. In this model, without the help of any empirical parameters, only three equilibrium constants are used, hence it is simple, lear, and favorable to the simplification of calculation.

  18. Laser-Induced, Polarization Dependent Shape Transformation of Au/Ag Nanoparticles in Glass

    OpenAIRE

    Hofmeister H; Haug J; Dubiel M; Seifert G; Stalmashonak A

    2009-01-01

    Abstract Bimetallic, initially spherical Ag/Au nanoparticles in glass prepared by ion implantation have been irradiated with intense femtosecond laser pulses at intensities still below the damage threshold of the material surface. This high-intensity laser processing produces dichroism in the irradiated region, which can be assigned to the observed anisotropic nanoparticle shapes with preferential orientation of the longer particle axis along the direction of laser polarization. In addition, ...

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

    NARCIS (Netherlands)

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

    2002-01-01

    Gold and silver nanoclusters embedded in MgO were created by means of ion implantation of 1.0 MeV Au or 600 keV Ag ions to a dose of 10^16 cm–2 into single crystals of MgO(100) and subsequent annealing at 1473 K for a period of 22 h. The structural properties of the nanoclusters were characterised b

  20. Focused-ion-beam-fabricated Au nanorods coupled with Ag nanoparticles used as surface-enhanced Raman scattering-active substrate for analyzing trace melamine constituents in solution

    International Nuclear Information System (INIS)

    Graphical abstract: -- Highlights: •Well-ordered Au-nanorod array with a controlled tip ring diameter (AuNRsd) is made by focused ion beam. •AuNRsd coupled with Ag nanoparticles (Ag NPs/AuNRsd) is competent to sense target molecules in a solution. •Ag NPs/AuNRsd SERS active substrate can detect a single molecule of crystal violet. •Ag NPs/AuNRsd as a SERS-active substrate can distinguish melamine contaminants at low concentrations (e.g., 10−12 M). -- Abstract: A well-ordered Au-nanorod array with a controlled tip ring diameter (AuNRsd) was fabricated using the focused ion beam method. AuNRsd was then coupled with Ag nanoparticles (Ag NPs) to bridge the gaps among Au nanorods. The effect of surface-enhanced Raman scattering (SERS) on AuNRsd and Ag NPs/AuNRsd was particularly verified using crystal violet (CV) as the molecular probe. Raman intensity obtained from a characteristic peak of CV on AuNRsd was estimated by an enhancement factor of ≈107 in magnitude, which increased ≈1012 in magnitude for that on Ag NPs/AuNRsd. A highly SERS-active Ag NPs/AuNRsd was furthermore applied for the detection of melamine (MEL) at very low concentrations. Raman-active peaks of MEL (10−3 to 10−12 M) in water or milk solution upon AuNRsd or Ag NPs/AuNRsd were well distinguished. The peaks at 680 and 702 cm−1 for MEL molecules were found suitable to be used as the index for sensing low-concentration MEL in a varied solution, while that at 1051 cm−1 was practical to interpret MEL molecules in water or milk solution bonded with Au (i.e., AuNRsd) or Ag (i.e., Ag NPs/AuNRsd) surface. At the interface of Ag NPs/AuNRsd and MEL molecules in milk solution, a laser-induced electromagnetic field or hotspot effect was produced and competent to sense low-concentration MEL molecules interacting with Ag and Au surfaces. Accordingly, Ag NPs/AuNRsd is very promising to be used as a fast and sensitive tool for screening MEL in complex matrices such as adulteration in e.g., food

  1. Highly Stretchable and Transparent Supercapacitor by Ag-Au Core-Shell Nanowire Network with High Electrochemical Stability.

    Science.gov (United States)

    Lee, Habeom; Hong, Sukjoon; Lee, Jinhwan; Suh, Young Duk; Kwon, Jinhyeong; Moon, Hyunjin; Kim, Hyeonseok; Yeo, Junyeob; Ko, Seung Hwan

    2016-06-22

    Stretchable and transparent electronics have steadily attracted huge attention in wearable devices. Although Ag nanowire is the one of the most promising candidates for transparent and stretchable electronics, its electrochemical instability has forbidden its application to the development of electrochemical energy devices such as supercapacitors. Here, we introduce a highly stretchable and transparent supercapacitor based on electrochemically stable Ag-Au core-shell nanowire percolation network electrode. We developed a simple solution process to synthesize the Ag-Au core-shell nanowire with excellent electrical conductivity as well as greatly enhanced chemical and electrochemical stabilities compared to pristine Ag nanowire. The proposed core-shell nanowire-based supercapacitor still possesses fine optical transmittance and outstanding mechanical stability up to 60% strain. The Ag-Au core-shell nanowire can be a strong candidate for future wearable electrochemical energy devices. PMID:27285849

  2. Magnetic and electronic structure of Mn nanostructures on Ag(111) and Au(111)

    Science.gov (United States)

    Cardias, R.; Bezerra-Neto, M. M.; Ribeiro, M. S.; Bergman, A.; Szilva, A.; Eriksson, O.; Klautau, A. B.

    2016-01-01

    We present results of the electronic and magnetic structure of Mn nanowires adsorbed on Ag(111) and Au(111) surfaces. For finite Mn nanowires on Ag(111) and Au(111) surfaces, our ab initio results show that the large difference between the spin-orbit splitting of these two surfaces leads to completely different magnetic configurations. The magnetic ordering for Mn nanowires adsorbed on Ag(111) is governed by the strong exchange interaction between Mn adatoms. For Mn nano-chains on Au(111), the competition between Heisenberg and Dzyaloshinskii-Moriya interactions leads to a complex magnetic structure of the clusters considered here. Among the more conspicuous results we note a spin-spiral helical type for the nanowire with seven atoms, and a complex magnetic configuration incommensurate with the substrate lattice for a double-sized Mn wire. The effect of the structural relaxation is also investigated, showing sensitivity of the exchange interactions to the bond distance to the substrate. We also demonstrate that small changes in the band filling of these Mn chains results in drastically different changes of the interatomic exchange. Finally, we show that dispersion of the electronic energy spectrum is possible even in nanostructures with bounded spatial extension.

  3. Coalescence of heteroclusters Au767 and Ag767:a molecular-dynamics study

    Institute of Scientific and Technical Information of China (English)

    Li Guo-Jian; Wang Qiang; Li Hu-Tian; Wang Kai; He Ji-Cheng

    2008-01-01

    This paper studies the coalescence of heteroclusters Au767 and Ag767 by using molecular dynamics with the embedded atom method,where layer atomic energy is employed to describe the potential energy variation of per atom in different layers along radial direction.The results show that the coalescence is driven by releasing the atomic energy of the coalesced zone.The deformation,which is induced by substitutional and vacancy diffusion during the coalescence,makes the coalesced cluster disorder.If the summation of the thermal energy and the released atomic energy is large enough to keep the disorder state,the clusters form a metastable liquid droplet;otherwise,the clusters coalesce into a solid cluster when the coalesced cluster reaches the equilibrium state,and the coalesced cluster experiences liquid to solid ordering changes during the coalescence of a solid Au767 with a liquid Ag767 and a liquid Au767 with a liquid Ag767.The centre of figure of the cluster system is shifted during the coalescence process,and higher coalescence temperature causes larger shift degree.

  4. Novel high rate Au beam counters for experiments at the AGS

    International Nuclear Information System (INIS)

    A high rate quartz Cerenkov detector is being developed to count incident Au ions for AGS Experiment 864. This detector must operate at beam rates of 107 Hz and deliver excellent timing (σ 2 which is viewed by photomultiplier tubes (PMT's). Due to high beam rates, small beam spot size, and the large dE/dx of 1 1.5 A circ GeV/c Au ions (∼ 11 GeV circ cm2/g), the detector must tolerate an exceptional radiation dose. Two quartz technologies are being considered for the Cerenkov radiator. In one design, a thin quartz plate is used while the other calls for an array of silica fibers. Prototype detectors will be tested in the 1993 Au ion run at the AGS. In preparation for the AGS tests, candidate PMT's and high-rate PM base designs have been evaluated at pulse rates approaching 107 Hz using a laser calibration system (also under development for E864). The results of these in-house tests and critical design parameters will be discussed along with the relative merits of each radiator design

  5. New isotopic evidence bearing on bonanza (Au-Ag) epithermal ore-forming processes

    Science.gov (United States)

    Saunders, James A.; Mathur, Ryan; Kamenov, George D.; Shimizu, Toru; Brueseke, Matthew E.

    2016-01-01

    New Cu, S, and Pb isotope data provide evidence for a magmatic source of metal(loid)s and sulfur in epithermal Au-Ag deposits even though their ore-forming solutions are composed primarily of heated meteoric (ground) waters. The apparent isotopic discrepancy between ore metals and ore-forming solutions, and even between the ore and associated gangue minerals, indicates two different sources of epithermal ore-forming constituents: (1) a shallow geothermal system that not only provides the bulk of water for the ore-forming solutions but also major chemical constituents leached from host rocks (silica, aluminum, potassium, sodium, calcium) to make gangue minerals and (2) metals and metalloids (As, Te, Sb, etc.) and sulfur (±Se) derived from deeper magma bodies. Isotopic data are consistent with either vapor-phase transport of metal(loids) and sulfur and their subsequent absorption by shallow geothermal waters or formation of metallic (Au, Ag, Cu phases) nanoparticles at depth from magmatic fluids prior to encountering the geothermal system. The latter is most consistent with ore textures that indicate physical transport and aggregation of nanoparticles were significant ore-forming processes. The recognition that epithermal Au-Ag ores form in tectonic settings that produce magmas capable of releasing metal-rich fluids necessary to form these deposits can refine exploration strategies that previously often have focused on locating fossil geothermal systems.

  6. Effect of Refractive Index of Substrate on Fabrication and Optical Properties of Hybrid Au-Ag Triangular Nanoparticle Arrays

    OpenAIRE

    Jing Liu; Yushan Chen; Haoyuan Cai; Xiaoyi Chen; Changwei Li; Cheng-Fu Yang

    2015-01-01

    In this study, the nanosphere lithography (NSL) method was used to fabricate hybrid Au-Ag triangular periodic nanoparticle arrays. The Au-Ag triangular periodic arrays were grown on different substrates, and the effect of the refractive index of substrates on fabrication and optical properties was systematically investigated. At first, the optical spectrum was simulated by the discrete dipole approximation (DDA) numerical method as a function of refractive indexes of substrates and mediums. S...

  7. Electron configuration and charge state of electrically active Cu, Ag and Au ions in ZnSe

    International Nuclear Information System (INIS)

    The Hall effect, electrical conductivity and electron mobility are investigated at temperatures between 55 and 500 K in n-ZnSe crystals doped with Cu, Ag or Au. The presence of a small amount of Cu atoms leads to an inversion of the sign of the Hall coefficient at temperatures above 300 K. Anomalous temperature dependence of the electron mobility is observed in the samples with low Cu concentration (Zn+ (d10) and CuZn2+ (d9), and two acceptor levels near the valence band. Silver and gold exist in single-charged states AgZn+ and AuZn+ with d10 electron configuration forming single energy levels near the valence band. Au atoms form mainly interstitial Aui donors at low doping concentrations and substitutional AuZn and AuZn-based acceptors at high doping concentrations. Time stimulation of the amphoteric properties of Ag is discussed

  8. Electron configuration and charge state of electrically active Cu, Ag and Au ions in ZnSe

    Science.gov (United States)

    Nedeoglo, N. D.; Sirkeli, V. P.; Nedeoglo, D. D.; Laiho, R.; Lähderanta, E.

    2006-08-01

    The Hall effect, electrical conductivity and electron mobility are investigated at temperatures between 55 and 500 K in n-ZnSe crystals doped with Cu, Ag or Au. The presence of a small amount of Cu atoms leads to an inversion of the sign of the Hall coefficient at temperatures above 300 K. Anomalous temperature dependence of the electron mobility is observed in the samples with low Cu concentration (AgZn+ and AuZn+ with d10 electron configuration forming single energy levels near the valence band. Au atoms form mainly interstitial Aui donors at low doping concentrations and substitutional AuZn and AuZn-based acceptors at high doping concentrations. Time stimulation of the amphoteric properties of Ag is discussed.

  9. Porous Au-Ag Alloy Particles Inlaid AgCl Membranes As Versatile Plasmonic Catalytic Interfaces with Simultaneous, in Situ SERS Monitoring.

    Science.gov (United States)

    Cao, Qi; Yuan, Kaiping; Liu, Qinghe; Liang, Chongyun; Wang, Xiang; Cheng, Yi-Feng; Li, Qingqing; Wang, Min; Che, Renchao

    2015-08-26

    We present a novel porous Au-Ag alloy particles inlaid AgCl membrane as plasmonic catalytic interfaces with real-time, in situ surface-enhanced Raman spectroscopy (SERS) monitoring. The Au-Ag alloy particles inlaid AgCl membranes were obtained via a facile two-step, air-exposed, and room-temperature immersion reaction with appropriate annealing process. Owing to the designed integration of semiconductor component AgCl and noble metal Au-Ag particles, both the catalytic reduction and visible-light-driven photocatalytic activities toward organic contaminants were attained. Specifically, the efficiencies of about 94% of 4-nitrophenol (4-NP, 5 × 10(-5) M) reduction after 8 min of reaction, and degradation of rhodamine 6G (R6G, 10(-5) M) after 12 min of visible light irradiation were demonstrated. Moreover, efficiencies of above 85% of conversion of 4-NP to 4-aminophenol (4-AP) and 90% of R6G degradation were achieved as well after 6 cycles of reactions, by which robust recyclability was confirmed. Further, with distinct SERS signals generated simultaneously from the surfaces of Au-Ag particles under laser excitation, in situ SERS monitoring of the process of catalytic reactions with superior sensitivity and linearity has been realized. Overall, the capability of the Au-Ag particles inlaid AgCl membranes to provide SERS monitored catalytic and visible-light-driven photocatalytic conversion of organic pollutants, along with their mild and cost-effective fabrication method, would make sense for in-depth understanding of the mechanisms of (photo)catalytic reactions, and also future development of potable, multifunctional and integrated catalytic and sensing devices. PMID:26263301

  10. Dendrite characteristics in directionally solidified Pb-8 pct Au and Pb-3 pct Pd alloys

    Science.gov (United States)

    Tewari, S. N.

    1986-01-01

    An investigation of Pb-8 pct Au and Pb-3 pct Pd alloy specimens which have been partially directionally solidified and then quenched is performed in order to characterize their dendritic microstructural details and solute composition profiles. A controlled sectioning technique is employed to measure dendrite tip radii. It is found that most of the observed behavior is predicted quite well by a modification of the Burden and Hunt (1974) model proposed by Laxmanan (1984), in addition to the models based on the marginal stability approach. Results indicate that quantitative comparison of the primary arm spacing measurements can not form the basis of distinguishing among the various dendrite growth models in a positive temperature gradient.

  11. The adsorption of ethylene on Au/Pd(100) alloy surfaces

    Science.gov (United States)

    Li, Zhenjun; Thuening, Theodore; Tysoe, Wilfred T.

    2016-04-01

    The surface chemistry of ethylene is explored on model Au/Pd(100) alloy surfaces using a combination of temperature-programmed desorption and reflection-absorption infrared spectroscopy. The heat of adsorption of ethylene on the model alloy surface is found to increase monotonically with increasing palladium coverage in the alloy, from ~ 33 kJ/mol for a completely gold-covered surface to ~ 80 kJ/mol as the gold coverage decreases to zero. A large change in heat of adsorption is found for palladium coverages between 0 and ~ 0.35 monolayers, where previous studies have shown that the surface comprises exclusively isolated palladium sites. The heat of adsorption changes more slowly for higher palladium coverages, when palladium-palladium bridge sites appear. Vinyl species are identified for palladium coverages above ~ 0.8 ML from a vibrational mode at ~ 1120 cm- 1, which disappears when the sample is heated to ~ 250 K, due to vinyl decomposition.

  12. Highly sensitive electrochemiluminescenc assay of acetylcholinesterase activity based on dual biomarkers using Pd-Au nanowires as immobilization platform.

    Science.gov (United States)

    Ye, Cui; Wang, Min-Qiang; Zhong, Xia; Chen, Shihong; Chai, Yaqin; Yuan, Ruo

    2016-05-15

    One-dimensional Pd-Au nanowires (Pd-Au NWs) were prepared and applied to fabricate an electrochemiluminescence (ECL) biosensor for the detection of acetylcholinesterase (AChE) activity. Compared with single-component of Pd or Au, the bimetallic nanocomposite of Pd-Au NWs offers a larger surface area for the immobilization of enzyme, and displays superior electrocatalytic activity and efficient electron transport capacity. In the presence of AChE and choline oxidase (ChOx), acetylcholine (ATCl) is hydrolyzed by AChE to generate thiocholine, then thiocholine is catalyzed by ChOx to produce H2O2 in situ, which serves as the coreactant to effectively enhance the ECL intensity in luminol-ECL system. The detection principle is based on the inhibited AChE and reactivated AChE as dual biomarkers, in which AChE was inhibited by organophosphorus (OP) agents, and then reactivated by obidoxime. Such dual biomarkers method can achieve credible evaluation for AChE activity via providing AChE activity before and after reactivation. The liner range for AChE activity detection was from 0.025 U L(-1) to 25 KU L(-1) with a low detection limit down to 0.0083 U L(-1). PMID:26686921

  13. Shape-controlled synthesis of Au@Pd core-shell nanoparticles and their corresponding electrochemical properties

    KAUST Repository

    Song, HyonMin

    2012-01-01

    The shape-controlled synthesis of Au@Pd core-shell nanoparticles (NPs) was successfully achieved through the emulsion phase generated during the phase transfer from organic to aqueous medium. Contrary to conventional epitaxial growth for obtaining core-shell structures, this method does not require high temperatures and does not have shape restrictions. © 2012 The Royal Society of Chemistry.

  14. Synthesis and characterization of Pt, Au or Pd clusters deposited titania-modified mesoporous silicate MCM-41

    International Nuclear Information System (INIS)

    Nanosized metal clusters Pt, Au and Pd were deposited in the mesopore of titania-modified MCM-41 by the photocatalytic reduction method under the mild conditions. The resulting Pt-, Au- or Pd-deposited titania-modified MCM-41 were characterized by using XRD, nitrogen adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS), TEM and diffuse reflectance UV-Vis spectroscopy. The results showed that Pt(IV), Au(III) or Pd(II) was reduced to metallic Pt, Au or Pd efficiently on the surface of titania, which modified over the inner surface of mesopore of the MCM-41 after the UV light irradiation for 4 h, and the metal nanoparticles deposited in the channels of the titania-modified MCM-41. The BET surface areas and pore volumes of the metal deposited samples decreased due to the noble metal clusters in the mesopore. The UV absorption spectra of titania-modified MCM-41 broadened and changed the UV absorption in the range of 190-300 nm after loading the metal clusters

  15. Amphiphilic hollow porous shell encapsulated Au@Pd bimetal nanoparticles for aerobic oxidation of alcohols in water

    KAUST Repository

    Zou, Houbing

    2015-01-01

    © The Royal Society of Chemistry 2015. This work describes the design, synthesis and analysis of an amphiphilic hollow mesoporous shell encapsulating catalytically active Au@Pd bimetal nanoparticles. The particles exhibited excellent catalytic activity and stability in the aerobic oxidation of primary and secondary alcohols to their corresponding aldehydes or ketones in water when using air as an oxidizing agent under atmospheric pressure.

  16. Test of supersymmetry in IBM by high resolution (p,d) and (d-vector,t) studies 196Au

    International Nuclear Information System (INIS)

    Using the Q3D magnetic spectrograph a high resolution (p,d) transfer experiment has been performed with 26 MeV protons on a Au target. The measured deuteron spectrum is presented. The angular distributions and asymmetries of the groundstate doublet are shown. (K.A.)

  17. First principles investigation of the activity of thin film Pt, Pd and Au surface alloys for oxygen reduction

    DEFF Research Database (Denmark)

    Tripkovic, Vladimir; Hansen, Heine Anton; Rossmeisl, Jan;

    2015-01-01

    of Au with mixed Pt/Pd skins. The activity of the binary and ternary catalysts is explained through weakening of the OH binding energy caused by solute elements. However, given the low alloy formation energies it may be difficult to tune and retain the composition under operating conditions. This is...

  18. A green approach to ethyl acetate: Quantitative conversion of ethanol through direct dehydrogenation in a Pd-Ag membrane reactor

    KAUST Repository

    Zeng, Gaofeng

    2012-11-07

    Pincers do the trick: The conversion of ethanol to ethyl acetate and hydrogen was achieved using a pincer-Ru catalyst in a Pd-Ag membrane reactor. Near quantitative conversions and yields could be achieved without the need for acid or base promoters or hydrogen acceptors (see scheme). © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Electrochemical Glucose Oxidation Using Glassy Carbon Electrodes Modified with Au-Ag Nanoparticles: Influence of Ag Content

    Directory of Open Access Journals (Sweden)

    Nancy Gabriela García-Morales

    2015-01-01

    Full Text Available This paper describes the application of glassy carbon modified electrodes bearing Aux-Agy nanoparticles to catalyze the electrochemical oxidation of glucose. In particular, the paper shows the influence of the Ag content on this oxidation process. A simple method was applied to prepare the nanoparticles, which were characterized by transmission electron microscopy, Ultraviolet-Visible spectroscopy, X-ray diffraction spectroscopy, and cyclic voltammetry. These nanoparticles were used to modify glassy carbon electrodes. The effectiveness of these electrodes for electrochemical glucose oxidation was evaluated. The modified glassy carbon electrodes are highly sensitive to glucose oxidation in alkaline media, which could be attributed to the presence of Aux-Agy nanoparticles on the electrode surface. The voltammetric results suggest that the glucose oxidation speed is controlled by the glucose diffusion to the electrode surface. These results also show that the catalytic activity of the electrodes depends on the Ag content of the nanoparticles. Best results were obtained for the Au80-Ag20 nanoparticles modified electrode. This electrode could be used for Gluconic acid (GA production.

  20. A new methodology for the near-surface strain measurement on Pd-Ag-Sn alloy

    International Nuclear Information System (INIS)

    With the development of modern synchrotron sources, high-energy X-ray diffraction plays an important role in the residual stresses analysis of materials. This paper deals with the development of a new high-energy synchrotron X-ray diffraction (HESXRD) stress evaluation method for improving the near-surface strain measurement. For this purpose a new Monte Carlo simulation program has been developed to modelize any synchrotron radiation instrument. Futhermore conventional X-ray diffraction measurements have also been carried out after chemical etching, to define the surface and in-depth stresses of the sample, thus giving a reference to test the synchrotron radiation measurements. It has been shown that the reliability of this method is better than 5 μm. This method has been applied to a machined palladium alloy (Pd-Ag-Sn) plate substrate.

  1. Synthesis of polyol based Ag/Pd nanocomposites for applications in catalysis

    Directory of Open Access Journals (Sweden)

    J.A. Adekoya

    2014-01-01

    Full Text Available The synthesis of polyvinylpyrrolidone seed mediated Ag/Pd allied nanobimetallic particles was successfully carried out by the simultaneous reduction of the metal ions in ethylene glycol, diethylene glycol, glycerol, pentaerythritol and sodium borohydride solution. The optical measurement revealed the existence of peak broadening that causes diffusion processes of the metal sols to decrease making it possible to monitor the changes spectrophotometrically. This, together with X-ray diffraction (XRD, X-ray photoelectron spectroscopy (XPS, transmission electron microscopy (TEM and high resolution TEM measurements strongly support the conclusion that intimately alloyed clusters were formed and the particle growth anisotropy is diffusion limited. Finally, the catalytic potential of the nanocomposites was investigated using 4-nitrophenol in the presence of sodium borohydride at 299 K; a good linear fitting of ln(A/A0 versus the reaction time was obtained, indicating pseudo-first-order kinetics.

  2. Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces

    OpenAIRE

    Nevalaita, Janne

    2011-01-01

    Water dissociation and the energetics of the WGS reaction on a bulk MgO, an Ag supported MgO thin film and Au/MgO/Ag surfaces is studied based on the density functional theory. The literature results for water splitting on MgO and MgO/Ag surfaces with a step type defect are repeated and further analysis on the origin of the energetically favored dissociative water adsorption are made. The reactivity towards water dissociation on the stepped MgO and MgO/Ag surfaces is attribu...

  3. Spectroscopic ellipsometry study of the dielectric response of Au-In and Ag-Sn thin-film couples

    International Nuclear Information System (INIS)

    Optical properties and phase composition of In-Au and Sn-Ag ultra-thin films grown by sequential evaporating and co-depositing of metals in a vacuum were investigated combining X-ray diffraction and spectroscopic ellipsometry methods. The atomic concentration ratios of bilayer and co-deposited samples were the same, i.e. In(Sn):Au(Ag) = 1:2. The XRD patterns indicated creation of AuIn, AuIn2, Au3In2, Au9In4 and Ag3Sn intermetallic compounds at room temperature. The effective complex dielectric functions of the composite layers, =1(E)>+i2(E)>, were determined from ellipsometric quantities Ψ and Δ measured in a photon energy range of 0.6-6.5 eV. The free-carrier parameters (unscreened plasma frequency and free-carrier damping) and optical resistivity were evaluated using a semiclassical Drude-Lorentz model of the effective dielectric function. There was noticed a distinct influence of phase composition and surface morphology on the optical constants and conductivity of the samples: ρop changed from approximately 15 μΩ cm to 37 μΩ cm for Ag-Sn structures, composed of β-Sn and Ag3Sn phases, and from 21 μΩ cm to 83 μΩ cm for Au-In multiphase system. Lower resistivity demonstrated diffusive layers formed after deposition of an In(Sn) thin film on the noble metal underlayer.

  4. SERS-active Ag, Au and Ag–Au alloy nanoparticles obtained by laser ablation in liquids for sensing methylene blue

    Energy Technology Data Exchange (ETDEWEB)

    Olea-Mejía, Oscar, E-mail: oleaoscar@yahoo.com.mx [Centro Conjunto de Investigación en Química Sustentable UAEM-UNAM, Universidad Autónoma del Estado de México, km 14.5 Carretera Toluca-Atlacomulco, San Cayetano 50200, México (Mexico); Fernández-Mondragón, Mariana; Rodríguez-de la Concha, Gabriela [Centro Conjunto de Investigación en Química Sustentable UAEM-UNAM, Universidad Autónoma del Estado de México, km 14.5 Carretera Toluca-Atlacomulco, San Cayetano 50200, México (Mexico); Camacho-López, Marco [Laboratorio de Investigación y Desarrollo de Materiales Avanzados, Universidad Autónoma del Estado de México, Km 14.5 Carretera Toluca-Atlacomulco, San Cayetano 50925, México (Mexico)

    2015-09-01

    Highlights: • We synthesized Ag/Au nanoparticles by laser ablation in liquids. • We characterized such particles by UV–vis, TEM and EDS/STEM. • The SERS effect was studied for the obtained nanoparticles. • Pure silver nanoparticles showed the highest SERS signals. • We can sense methylene blue at a concentration of 10{sup −10} mole/L. - Abstract: We have synthesized Ag–Au nanoparticles by laser ablation in liquids using five different targets: 100% Ag, 80%Ag/20%Au, 50%Ag/50%Au, 20%Ag/80%Au and 100% Au (weight percentages). We used ethanol and methylene blue solutions in ethanol as the liquid media. The nanoparticles were mostly spherical with diameters 15, 19, 18, 23 and 11 nm, respectively. When alloyed targets were used, the resulting nanoparticles were completely alloyed forming solid solutions as evidenced by UV–vis Spectroscopy and Scanning Transmission Electron Microscopy. The obtained nanoparticles were employed to study the SERS effect of the methylene blue molecule. All the samples showed good SERS activity, however the ones composed of pure silver showed the greatest Raman signal enhancement. Finally, pure Ag nanoparticles were used for sensing methylene blue at different concentrations. While almost no signal can be discerned from the Raman spectrum when no particles are used at a concentration of methylene blue of 1 × 10{sup −2} M (∼3000 ppm), when Ag nanoparticles are used one can observe the characteristic peak of the molecule at concentrations as low as 1 × 10{sup −10} M (∼3 × 10{sup −5} ppm)

  5. SERS-active Ag, Au and Ag–Au alloy nanoparticles obtained by laser ablation in liquids for sensing methylene blue

    International Nuclear Information System (INIS)

    Highlights: • We synthesized Ag/Au nanoparticles by laser ablation in liquids. • We characterized such particles by UV–vis, TEM and EDS/STEM. • The SERS effect was studied for the obtained nanoparticles. • Pure silver nanoparticles showed the highest SERS signals. • We can sense methylene blue at a concentration of 10−10 mole/L. - Abstract: We have synthesized Ag–Au nanoparticles by laser ablation in liquids using five different targets: 100% Ag, 80%Ag/20%Au, 50%Ag/50%Au, 20%Ag/80%Au and 100% Au (weight percentages). We used ethanol and methylene blue solutions in ethanol as the liquid media. The nanoparticles were mostly spherical with diameters 15, 19, 18, 23 and 11 nm, respectively. When alloyed targets were used, the resulting nanoparticles were completely alloyed forming solid solutions as evidenced by UV–vis Spectroscopy and Scanning Transmission Electron Microscopy. The obtained nanoparticles were employed to study the SERS effect of the methylene blue molecule. All the samples showed good SERS activity, however the ones composed of pure silver showed the greatest Raman signal enhancement. Finally, pure Ag nanoparticles were used for sensing methylene blue at different concentrations. While almost no signal can be discerned from the Raman spectrum when no particles are used at a concentration of methylene blue of 1 × 10−2 M (∼3000 ppm), when Ag nanoparticles are used one can observe the characteristic peak of the molecule at concentrations as low as 1 × 10−10 M (∼3 × 10−5 ppm)

  6. Particle growth mechanisms in Ag-ZrO2 and Au-ZrO2 granular films obtained by pulsed laser deposition

    International Nuclear Information System (INIS)

    Thin films consisting of Ag and Au nanoparticles embedded in amorphous ZrO2 matrix were grown by pulsed laser deposition in a wide range of metal volume concentrations in the dielectric regime (0.08AgAuc(Ag)∼0.28 and xc(Au)∼0.52)

  7. Determination of Anthracene on Ag-Au Alloy Nanoparticles/Overoxidized-Polypyrrole Composite Modified Glassy Carbon Electrodes

    Directory of Open Access Journals (Sweden)

    Emmanuel I. Iwuoha

    2010-10-01

    Full Text Available A novel electrochemical sensor for the detection of anthracene was prepared by modifying a glassy carbon electrode (GCE with over-oxidized polypyrrole (PPyox and Ag-Au (1:3 bimetallic nanoparticles (Ag-AuNPs. The composite electrode (PPyox/Ag-AuNPs/GCE was prepared by potentiodynamic polymerization of pyrrole on GCE followed by its overoxidation in 0.1 M NaOH. Ag-Au bimetallic nanoparticles were chemically prepared by the reduction of AgNO3 and HAuCl4 using C6H5O7Na3 as the reducing agent as well as the capping agent and then immobilized on the surface of the PPyox/GCE. The nanoparticles were characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the bimetallic alloy nanoparticles. Transmission electron microscopy showed that the synthesized bimetallic nanoparticles were in the range of 20–50 nm. The electrochemical behaviour of anthracene at the PPyox/Ag-AuNPs/GCE with Ag: Au atomic ratio 25:75 (1:3 exhibited a higher electrocatalytic effect compared to that observed when GCE was modified with each constituent of the composite (i.e., PPyox, Ag-AuNPs and bare GCE. A linear relationship between anodic current and anthracene concentration was attained over the range of 3.0 × 10−6 to 3.56 × 10−4 M with a detection limit of 1.69 × 10−7 M. The proposed method was simple, less time consuming and showed a high sensitivity.

  8. Cu-Au-Ag alloy nanoparticles incorporated silica films using a new three-layer deposition technique.

    Science.gov (United States)

    Pal, Sudipto; Bysakh, Sandip; De, Goutam

    2010-02-01

    Formation of Au-Ag-Cu ternary alloy nanoparticles (NPs) is difficult mainly because the system Cu/Ag is immiscible. We present a new synthetic technique to generate such ternary alloy NPs in silica film matrix employing a three-layer (3L) coating design. In this methodology three successive coating layers were deposited on silica glass substrates from separately prepared Cu-, Au- and Ag-ion incorporated inorganic-organic hybrid silica sols by dipping method. The Au layer is kept in the middle because it is miscible with both the Ag and Cu. The 3L film assembly was subjected to UV- and heat-treatment at 450-750 degrees C in H2-N2 atmosphere. UV-treatment generates small Au and Ag NPs in the respective layers and Cu remains as Cu2+; subsequent heat-treatment in H2-N2 induces the formation of ternary alloy NPs by the interlayer diffusion of nanometals. The final heat-treated film (750 degrees C/H2-N2) shows single and sharp plasmon band centered at 480 nm in the UV-visible spectrum indicating the formation of alloy (solid solution) NPs. GIXRD study shows one set of diffraction peaks which are shifted towards higher angle with respect to the Au or Ag diffraction peaks. FESEM, GIXRD, HRTEM, and SAED analyses reveal that the alloy has a composition close to (Au + Ag)0.88Cu0.12. The EDS analyses using the nano probe attached with TEM confirm the presence of Au, Ag and Cu in all the alloy NPs. PMID:20352717

  9. Green Synthesis of Ag and Pd Nanospheres, Nanowires, and Nanorods Using Vitamin B2: Catalytic Polymerisation of Aniline and Pyrrole

    Directory of Open Access Journals (Sweden)

    Mallikarjuna N. Nadagouda

    2008-01-01

    Full Text Available For the first time, we report green chemistry approach using vitamin B2 in the synthesis of silver (Ag and palladium (Pd, nanospheres, nanowires, and nanorods at room temperature without using any harmful reducing agents, such as sodium borohydride (NaBH4 or hydroxylamine hydrochloride and any special capping or dispersing agent. Vitamin B2 was used as reducing agent as well as capping agent due to its high-water solubility, biodegradability, and low-toxicity compared with other reducing agents. The average particle size of nanoprticle was found to be Ag (average size 6.1±0.1 nm and Pd (average size 4.1±0.1 nm nanoparticles in ethylene glycol and Ag (average size 5.9±0.1 nm, and average size 6.1±0.1 nanoparticles in acetic acid and NMP, respectively. The formation of noble multiple shape nanostructures and their self assembly were dependent on the solvent employed for the preparation. When water was used as solvent media, Ag and Pd nanoparticles started to self-assemble into rod-like structures and in isopropanol Ag and Pd nanoparticles yielded wire-like structures with a thickness in the range of 10 to 20 nm and several hundred microns in length. In acetone and acetonitrile medium, the Ag and Pd nanoparticles are self-assembled into a regular pattern making nanorod structures with thicknesses ranging from 100 to 200 nm and lengths of a few microns. The so-synthesized nanostructures were characterized using scanning electron microscopy (SEM, transmission electron microscopy (TEM, energy dispersive X-ray (EDX analysis, and UV spectroscopy. The ensuing Ag and Pd nanoparticles catalyzed the reactions of aniline and pyrrole to generate polyaniline and polypyrrole nanofibers and may find various technological and biological applications. This single-step greener approach is general and can be extended to other noble metals and transition metal oxides.

  10. A comparative study of elemental additives (Ni, Co and Ag) on electrocatalytic activity improvement of PdSn-based catalysts for ethanol and formic acid electro-oxidation

    International Nuclear Information System (INIS)

    In this study, we have synthesized a series of carbon supported PdSn(molar ratio 1:1), PdSnAg(2:2:1), PdSnNi(2:2:1) and PdSnCo(2:2:1) catalysts by a borohydride reduction method. These catalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and chronoamperometry (CA). As compared with PdSn/C, the trimetallic catalysts show a significant activity enhancement for ethanol and formic acid electro-oxidation. Moreover, the PdSnAg/C catalyst exhibits the highest activity together with much better stability. The activity enhancement of PdSnAg/C can be rationalized by the synergistic effect of Pd-SnO2-Ag clusters on the superficial surface of catalyst, such as bi-functional mechanism, superior electronic structure, excellent electric conductivity, etc. In addition, both ethanol and formic acid electro-oxidation reactions on the PdSnAg/C catalyst are diffusion-controlled and represent good linear correlation with ethanol and formic acid concentrations

  11. Effect of Ni and Pd Addition on Mechanical, Thermodynamic, and Electronic Properties of AuSn4-Based Intermetallics: A Density Functional Investigation

    Science.gov (United States)

    Tian, Yali; Zhou, Wei; Wu, Ping

    2016-05-01

    The effects of Ni and Pd addition on the mechanical, thermodynamic, and electronic properties of AuSn4-based intermetallic compounds (IMCs) have been investigated by first-principles calculations to reveal the essence of Au embrittlement. Three kinds of doped (namely Ni-doped, Pd-doped, and Ni/Pd-codoped) IMCs are considered in this work. The polycrystalline elastic properties are deduced from single-crystal elastic constants. It is found that the doped systems together with nondoped AuSn4 are all ductile phases. For Ni-doped AuSn4, the modulus, hardness, brittleness, Debye temperature, and minimum thermal conductivity increase with the Ni fraction, but this is not the case for the Pd-doped material, since Au0.75Pd0.25Sn4 is the more brittle phase. For Au0.5Pd0.25Ni0.25Sn4, the mechanical, thermodynamic, and electronic properties are similar to those of Au0.5Pd0.5Sn4.

  12. Variations of color with alloying elements in Pd-free Au-Pt-based high noble dental alloys

    International Nuclear Information System (INIS)

    The effects of alloying addition of a small amount of base metals (In, Sn, Fe, Zn) on color variations in Pd-free Au-Pt-based high noble dental alloys were investigated in terms of rectilinear and polar color coordinates. The ternary Au-Pt-X (X = In, Sn, Fe, Zn) and quaternary Au-Pt-In-Y (Y = Sn, Fe, Zn) alloys were prepared from high purity component metals. The amount of alloying base metals, X and Y, were restricted up to 2 at.%. The alloying addition of a small amount of Fe, In, Sn, to a binary Au-10 at.% Pt alloy (referred to as AP10) effectively increased chroma, C *. On the other hand, the addition of Zn to the parent alloy AP10 did not change color coordinates greatly. The increase in chroma in the present Au-Pt-based high noble alloys was attributed to the increase in the slope of spectral reflectance curve at its absorption edge near 515 nm. It was found that the addition of a small amount of Fe to the parent alloy AP10 markedly increased lightness, L *, and the addition of Sn gave a very light tint of red to the parent alloy. Although red-green chromaticity index a * contributed to chroma to some extent, contribution of yellow-blue chromaticity index b * was much greater in determining chroma in this Pd-free Au-Pt-based multi-component alloys. The present results are expected to be valuable in case color is to be taken into account in designing Pd-free Au-Pt-based high noble dental alloys

  13. Bimetallic Ag-Pd nanoparticles-decorated graphene oxide: a fascinating three-dimensional nanohybrid as an efficient electrochemical sensing platform for vanillin determination

    International Nuclear Information System (INIS)

    Highlights: • A 3D Ag-Pd/GO nanohybrid was fabricated via a green and in situ chemical route. • Ag-Pd/GO shows excellent electro-catalytic properties for the oxidation of vanillin. • The 3D hybrid-based sensor shows excellent performances for the vanillin detection. • This proposed method was successfully used to detect vanillin in children’s snacks. - Abstract: In this work, a fascinating hybrid based on Ag-Pd bimetallic nanoparticles-decorated graphene oxide (Ag-Pd/GO) has been successfully synthesized by a green and in situ chemical reduction strategy. The resultant hybrid was particularly characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, ultraviolet-visible spectroscopy and electrochemical techniques. The morphological results illustrate that Ag-Pd nanoparticles in microspheric appearances are highly dispersed and embedded on the GO layers, resulting in a rough surface and three-dimensional (3D) microstructure with a high Ag-Pd content in the matrix. The as-synthesized 3D Ag-Pd/GO hybrid displays distinctly enhanced electrocatalytic activity for the vanillin oxidation in comparison with that of the monometal-decorated GO, revealing a synergistic effect of the matrix GO and the doped bimetallic Ag-Pd. Therefore, the Ag-Pd/GO composite can be used as an enhanced electrochemical sensing platform for the sensitive determination of vanillin, and the fabricated sensor displays a wide detection range of 0.02–45 μmol dm−3, low detection limit of 5 nmol dm−3 and satisfactory recoveries between 98.8 % and 103.5 %. All the results demonstrate that the 3D hybrids integrated graphene with bimetallic nanoparticles are promising candidates for the development of high-performance electrochemical sensors

  14. Thermodynamic properties of Ag3AuSe2 from 300 to 500 K by a solid state galvanic cell

    International Nuclear Information System (INIS)

    Highlights: • Experimental thermodynamics data on Ag3AuSe2 compounds are obtained to 500 K. • A new phase transformation of Ag3AuSe2 at low temperature is proposed. • Advanced measurement makes possible to distinguish the phase transformation. -- Abstract: The numerical values of the standard thermodynamic functions of Ag3AuSe2 (fischesserite) in the Ag–Au–Se system were determined by the electromotive force (EMF) method in a solid state galvanic cell with RbAg4I5 as the solid electrolyte below 500 K. Ag3AuSe2 was synthesized from pure elements in stoichiometric composition by evacuated ampoules made of quartz glass. On the basis of EMF vs. temperature experimental data, the analytical equations were obtained, from which the temperature dependent relationships of the Gibbs energy in the relevant reactions and the standard thermodynamic functions of Ag3AuSe2 within the temperature range of 300–500 K were calculated. The results show that there is possible a new polymorphic transformation around 350 K

  15. Synthesis of unidirectional structures of SiO{sub 2}-Ag using Au nanoparticles as nucleation centers; Sintesis de estructuras unidireccionales de SiO{sub 2}-Ag utilizando nanoparticulas de Au como centros de nucleacion

    Energy Technology Data Exchange (ETDEWEB)

    Villa S, G.; Mendoza A, D.; Gutierrez W, C.; Perez H, R. [ININ, Carretera Mexico-Toluca s/n, Ocoyoacac 52750, Estado de Mexico (Mexico)], e-mail: demetrio.mendoza@inin.gob.mx

    2008-07-01

    This paper reports a method to synthesize Ag unidirectional structures covered with SiO{sub 2} by sol-gel technique using Au nanoparticles as nucleation centers of the unidirectional structures. In the first phase unidirectional structures of SiO{sub 2}-Ag CI are obtained by sol-gel, using TEOS as a precursor of metallic structures (Ag) and the incorporation of Au nanoparticles as nucleation centers for growth of unidirectional structures. In the second stage, one-way systems are subjected to thermal treatment in H{sub 2} atmosphere for obtain AG{sup 0} particles through mechanisms that diffusion and coalescence of silver to form structures that have a thin cover of SiO{sub 2}. Analysis by scanning electron microscopy, transmission and atomic force microscopy allowed to determine the chemical composition and microstructural properties of unidirectional systems SiO{sub 2}-Ag. (Author)

  16. Preparation of Au and Ag nanoparticles using Artemisia annua and their in vitro antibacterial and tyrosinase inhibitory activities

    Energy Technology Data Exchange (ETDEWEB)

    Basavegowda, Nagaraj; Idhayadhulla, Akber; Lee, Yong Rok, E-mail: yrlee@yu.ac.kr

    2014-10-01

    This work describes a plant-mediated approach to the preparation of metal nanoparticles using leaf extract of Artemisia annua (A. annua), an ethno-medicinal plant widely found in Asia, which was used as reducing and stabilizing agent. A. annua is used in traditional Chinese medicine to alleviate fever. Au and Ag nanoparticles were prepared using a one-step aqueous method at room temperature without any toxic chemicals. The formation of Au and Ag nanoparticles was monitored by UV–vis spectroscopy. Synthesized nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). TEM analysis of Au nanoparticles showed that they had triangular and spherical shapes with sizes ranging from 15 to 40 nm. The silver nanoparticles were predominantly spherical and uniformly sized (30–50 nm). The Au and Ag nanoparticles produced showed significant tyrosinase inhibitory and antibacterial effects. These results suggest that the synthesized nanoparticles provide good alternatives in varied medical and industrial applications. - Highlights: • Au and Ag nanoparticles were synthesized using Artemisia annua leaf aqueous extract. • Nanoparticles were characterized by UV–vis spectroscopy, FT-IR, TEM, EDX, XRD, and TGA. • Au and Ag nanoparticles were of size 25 and 30 nm respectively, in spherical forms. • Nanoparticles showed significant tyrosinase inhibitory and antibacterial activities.

  17. Preparation of Au and Ag nanoparticles using Artemisia annua and their in vitro antibacterial and tyrosinase inhibitory activities

    International Nuclear Information System (INIS)

    This work describes a plant-mediated approach to the preparation of metal nanoparticles using leaf extract of Artemisia annua (A. annua), an ethno-medicinal plant widely found in Asia, which was used as reducing and stabilizing agent. A. annua is used in traditional Chinese medicine to alleviate fever. Au and Ag nanoparticles were prepared using a one-step aqueous method at room temperature without any toxic chemicals. The formation of Au and Ag nanoparticles was monitored by UV–vis spectroscopy. Synthesized nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). TEM analysis of Au nanoparticles showed that they had triangular and spherical shapes with sizes ranging from 15 to 40 nm. The silver nanoparticles were predominantly spherical and uniformly sized (30–50 nm). The Au and Ag nanoparticles produced showed significant tyrosinase inhibitory and antibacterial effects. These results suggest that the synthesized nanoparticles provide good alternatives in varied medical and industrial applications. - Highlights: • Au and Ag nanoparticles were synthesized using Artemisia annua leaf aqueous extract. • Nanoparticles were characterized by UV–vis spectroscopy, FT-IR, TEM, EDX, XRD, and TGA. • Au and Ag nanoparticles were of size 25 and 30 nm respectively, in spherical forms. • Nanoparticles showed significant tyrosinase inhibitory and antibacterial activities

  18. Physico-chemical and antimicrobial properties of co-sputtered Ag-Au/PTFE nanocomposite coatings

    International Nuclear Information System (INIS)

    In this work, we used co-sputtering of noble metals together with polytetrafluorethylene (PTFE) as a method for producing antibacterial metal/polymer nanocomposite coatings, where the precious metals are only incorporated in a thin surface layer. Moreover, they are finely dispersed as nanoparticles, thus saving additional material and providing a very large effective surface for metal ion release. Nanocomposite films with thickness between 100 and 300 nm were prepared with a wide range of metal filling between 10 and 40%. The antimicrobial effect of the nanocomposite coatings was evaluated by means of two different assays. The bactericidal activity due to silver release from the surface was determined by a modification of conventional disc diffusion methods. Inhibition of bacterial growth on the coated surface was investigated through a modified proliferation assay. Staphylococcus aureus and S. epidermidis were used as test bacteria, as these species commonly cause infections associated with medical polymer devices. The antibacterial efficiency of the coatings against different bacteria was demonstrated at extremely small noble metal consumption: Au: ∼1 mg m-2 and Ag: ∼0.1 g m-2. The maximum ability for having an antibacterial effect was shown by the Ag-Au/PTFE nanocomposite, followed by the Ag/PTFE nanocomposite

  19. Enzyme-free hydrogen peroxide sensor based on Au@Ag@C core-double shell nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yancai, E-mail: liyancai@mnnu.edu.cn [College of Chemistry & Environment, Minnan Normal University, Zhangzhou 363000 (China); Fujian Province Key Laboratory of Modern Analytical Science and Separation Technology, Minnan Normal University, Zhangzhou 363000 (China); Zhang, Yayun; Zhong, Yanmei [College of Chemistry & Environment, Minnan Normal University, Zhangzhou 363000 (China); Li, Shunxing [College of Chemistry & Environment, Minnan Normal University, Zhangzhou 363000 (China); Fujian Province Key Laboratory of Modern Analytical Science and Separation Technology, Minnan Normal University, Zhangzhou 363000 (China)

    2015-08-30

    Graphical abstract: - Highlights: • A facile method was designed to synthesize Au@Ag@C core-double shell nanocomposites. • Carbon nanomaterials at the outermost layer could protect Au and Ag nanoparticles from oxidation and aggregation. • The Au@Ag@C core-double shell nanocomposites showed high sensitivity and selectivity to electrocatalytic reduction of hydrogen peroxide. • The hydrogen peroxide sensor has a wide linear range of 5.0 μM to 4.75 mM and a limit of detection as low as 0.14 μM. - Abstract: The well-designed Au@Ag@C core-double shell nanocomposites were synthesized via a facile method, and were used to fabricate an enzyme-free amperometric hydrogen peroxide (H{sub 2}O{sub 2}) sensor. The size, shape, elementary composition and structure of the nanocomposites were characterized by transmission electron microscope (TEM), energy-dispersed spectrum (EDS) and X-ray diffraction (XRD). The outermost layer of the nanocomposites was amorphous carbon, the second layer was Ag and the core was Au. The Au@Ag@C core-double shell nanocomposites exhibit attractive activity for electrocatalytic reduction of H{sub 2}O{sub 2} according to the electrochemical experiments. It also demonstrates the H{sub 2}O{sub 2} sensor possess well performance with a wide linear range of 5.0 μM to 4.75 mM and a limit of detection (LOD) as low as 0.14 μM (S/N = 3). Furthermore, the interference from the common interfering species, such as glucose, ascorbic acid, dopamine and uric acid can be effectively avoided. In a word, the Au@Ag@C nanocomposites are promising candidates for enzyme-free H{sub 2}O{sub 2} sensor.

  20. Enzyme-free hydrogen peroxide sensor based on Au@Ag@C core-double shell nanocomposites

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • A facile method was designed to synthesize Au@Ag@C core-double shell nanocomposites. • Carbon nanomaterials at the outermost layer could protect Au and Ag nanoparticles from oxidation and aggregation. • The Au@Ag@C core-double shell nanocomposites showed high sensitivity and selectivity to electrocatalytic reduction of hydrogen peroxide. • The hydrogen peroxide sensor has a wide linear range of 5.0 μM to 4.75 mM and a limit of detection as low as 0.14 μM. - Abstract: The well-designed Au@Ag@C core-double shell nanocomposites were synthesized via a facile method, and were used to fabricate an enzyme-free amperometric hydrogen peroxide (H2O2) sensor. The size, shape, elementary composition and structure of the nanocomposites were characterized by transmission electron microscope (TEM), energy-dispersed spectrum (EDS) and X-ray diffraction (XRD). The outermost layer of the nanocomposites was amorphous carbon, the second layer was Ag and the core was Au. The Au@Ag@C core-double shell nanocomposites exhibit attractive activity for electrocatalytic reduction of H2O2 according to the electrochemical experiments. It also demonstrates the H2O2 sensor possess well performance with a wide linear range of 5.0 μM to 4.75 mM and a limit of detection (LOD) as low as 0.14 μM (S/N = 3). Furthermore, the interference from the common interfering species, such as glucose, ascorbic acid, dopamine and uric acid can be effectively avoided. In a word, the Au@Ag@C nanocomposites are promising candidates for enzyme-free H2O2 sensor

  1. Influence of water on the properties of an Au/Mpy/Pd metal/molecule/metal junction

    Directory of Open Access Journals (Sweden)

    Jan Kučera

    2011-07-01

    Full Text Available The geometric and electronic structure of the metal–molecule interface in metal/molecule/metal junctions is of great interest since it affects the functionality of such units in possible nanoelectronic devices. We have investigated the interaction between water and a palladium monolayer of a Au(111/4-mercaptopyridine/Pd junction by means of DFT calculations. A relatively strong bond between water and the palladium monolayer of the Au/Mpy/Pd complex is observed via a one-fold bond between the oxygen atom of the water molecule and a Pd atom. An isolated H2O molecule adsorbs preferentially in a flat-lying geometry on top of a palladium atom that is at the same time also bound to the nitrogen atom of a Mpy molecule of the underlying self-assembled monolayer. The electronic structure of these Pd atoms is considerably modified which is reflected in a reduced local density of states at the Fermi energy. At higher coverages, water can be arranged in a hexagonal ice-like bilayer structure in analogy to water on bulk metal surfaces, but with a much stronger binding which is dominated by O–Pd bonds.

  2. Use of Au-In-Pd and Pd-In electroless deposits for ohmic contacts on n-GaAs

    International Nuclear Information System (INIS)

    Codeposition of gold-palladium-indium and palladium-indium alloys onto n-GaAs substrates is obtained in an acidic medium by the electroless method. The preparation and characteristics of the different baths are presented. For the Pd-In alloys, a crystalline refractory Pd(In)3 compound is initially formed, whereas after a 2 min annealing treatment at 470 degrees C traces of InAs and PdGa are found. A high-quality ohmic contact having ρ = 6.10-6 Ω cm2 is obtained with annealing

  3. Antibacterial Activity of Partially Oxidized Ag/Au Nanoparticles against the Oral Pathogen Porphyromonas gingivalis W83

    Directory of Open Access Journals (Sweden)

    Megan S. Holden

    2016-01-01

    Full Text Available Advances in nanotechnology provide opportunities for the prevention and treatment of periodontal disease. While physicochemical properties of Ag containing nanoparticles (NPs are known to influence the magnitude of their toxicity, it is thought that nanosilver can be made less toxic to eukaryotes by passivation of the NPs with a benign metal. Moreover, the addition of other noble metals to silver nanoparticles, in the alloy formulation, is known to alter the silver dissolution behavior. Thus, we synthesized glutathione capped Ag/Au alloy bimetallic nanoparticles (NPs via the galvanic replacement reaction between maltose coated Ag NPs and chloroauric acid (HAuCl4 in 5% aqueous triblock F127 copolymer solution. We then compared the antibacterial activity of the Ag/Au NPs to pure Ag NPs on Porphyromonas gingivalis W83, a key pathogen in the development of periodontal disease. Only partially oxidized glutathione capped Ag and Ag/Au (Au : Ag ≈ 0.2 NPs inhibited the planktonic growth of P. gingivalis W83. This effect was enhanced in the presence of hydrogen peroxide, which simulates the oxidative stress environment in the periodontal pocket during chronic inflammation.

  4. Digestive ripening facilitated atomic diffusion at nanosize regime: Case of AuIn2 and Ag3In intermetallic nanoparticles

    International Nuclear Information System (INIS)

    Highlights: • A digestive ripening facilitated interatomic diffusion process is presented. • Nearly monodisperse AuIn2 and Ag3In intermetallic nanoparticles were synthesized. • Optimization of reaction temperature facilitates interatomic transfer. • Presence of excess ligand plays a crucial role in the digestive ripening process. - Abstract: Monodisperse colloidal gold–indium (AuIn2) intermetallic nanoparticles have been synthesized from Au and In colloids using the digestive ripening process. Formation of the intermetallic proceeds via digestive ripening facilitated atomic diffusion of Au and In atoms from the Au and In nanoparticles followed simultaneously by their growth in the solution. Optimization of the reaction temperature was found to be crucial for the formation of AuIn2 intermetallic from gold and indium nanoparticles. Transmission electron microscopy revealed the presence of nearly monodisperse nanoparticles of Au and AuIn2 with particle size distribution of 3.7 ± 1.0 nm and 5.0 ± 1.6 nm, respectively. UV–visible spectral studies brought out the absence of SPR band in pure AuIn2 intermetallic nanoparticles. Optical study and electron microscopy, in combination with powder X-ray diffraction established phase pure AuIn2 intermetallic nanoparticles unambiguously. The potential of such an unprecedented approach has been further exploited in the synthesis of Ag3In intermetallic nanoparticles with the dimension of less than 10 nm

  5. The Optical Nonlinearity of Au and Ag Nanoparticle Prepared by the Γ-Radiation Method

    Directory of Open Access Journals (Sweden)

    Esmaeil Shahriari

    2010-01-01

    Full Text Available Problem statement: The third order nonlinear optical properties of metal nanoparticles have been of interest in physical chemistry, medical diagnostics and optical devices. Gold colloidal nanoparticles are responsible for the brilliant reds seen in stained glass windows and silver particles are typically yellow. The purpose of the study was to determine the nonlinear refraction and absorption coefficient of the Au and Ag nanoparticles in PVP solution. Approach: The samples were prepared by Γ-radiation method and the nonlinear optical properties of the composites were investigated using a single beam Z-scan technique with a beam power of 40 mW and operated at wavelength of 532 nm. The measurements were carried out for both Open and closed aperture Z-scan arrangements. Results: For both Au/PVP and Ag/PVP samples the results exhibited reverse saturable absorption. The closed aperture Z-scan of the nano-fluid samples revealed self-defocusing effect while the open aperture Z-scan of the samples show a reversible saturable absorption. Conclusion: The Z-scan measurement showed that silver and gold nano-fluid prepared by gamma radiation exhibited large thermal nonlinear refractive index n2 as -8.78×10-7 and -2.478×10-6 cm2/W, respectively. We have also investigated nonlinear absorption of these samples and we found a large value of nonlinear absorption for Ag nanoparticle and a weak absorption for Au nanoparticle. In conclusion, the experimental result shows a good nonlinear refractive index at low laser power in which encouraging for possible applications in nonlinear optical devices.

  6. Novel electrochemical redox-active species: one-step synthesis of polyaniline derivative-Au/Pd and its application for multiplexed immunoassay

    Science.gov (United States)

    Wang, Liyuan; Feng, Feng; Ma, Zhanfang

    2015-11-01

    Electrochemical redox-active species play crucial role in electrochemically multiplexed immunoassays. A one-pot method for synthesizing four kinds of new electrochemical redox-active species was reported using HAuCl4 and Na2PdCl4 as dual oxidating agents and aniline derivatives as monomers. The synthesized polyaniline derivative-Au/Pd composites, namely poly(N-methyl-o-benzenediamine)-Au/Pd, poly(N-phenyl-o-phenylenediamine)-Au/Pd, poly(N-phenyl-p-phenylenediamine)-Au/Pd and poly(3,3’,5,5’-tetramethylbenzidine)-Au/Pd, exhibited electrochemical redox activity at -0.65 V, -0.3 V, 0.12 V, and 0.5 V, respectively. Meanwhile, these composites showed high H2O2 electrocatalytic activity because of the presence of Au/Pd. The as-prepared composites were used as electrochemical immunoprobes in simultaneous detection of four tumor biomarkers (carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA199), carbohydrate antigen 72-4 (CA724), and alpha fetoprotein (AFP)). This immunoassay shed light on potential applications in simultaneous gastric cancer (related biomarkers: CEA, CA199, CA724) and liver cancer diagnosis (related biomarkers: CEA, CA199, AFP). The present strategy to the synthesize redox species could be easily extended to other polymers such as polypyrrole derivatives and polythiophene derivatives. This would be of great significance in the electrochemical detection of more analytes.

  7. Surface photovoltage of Ag nanoparticles and Au chains on Si(111)

    Energy Technology Data Exchange (ETDEWEB)

    Sell, Kristian; Barke, Ingo; Polei, Stefan; Schumann, Christian; Oeynhausen, Viola von; Meiwes-Broer, Karl-Heinz [Institute of Physics, University of Rostock (Germany)

    2010-05-15

    We present surface photovoltage (SPV) measurements of metal nanostructures on Si(111)-(7 x 7) using scanning tunneling microscopy and spectroscopy (STM/STS). Quantitative results are obtained from spatially resolved I(V) spectra under laser illumination. The SPV data of Ag nanoparticles deposited on Si(111)-(7 x 7) are compared to results of a Si(111) surface partially covered by the quasi one-dimensional Si(111)-(5 x 2)-Au structure. On the latter we determine the SPV as a function of laser power at different locations. An accurate value for the Fermi-level pinning position of Si(111)-(5 x 2)-Au atomic chains is obtained. Based on these results we establish and discuss a simple model for the band topology. It is confirmed by spatially resolved local work function measurements utilizing the image-state derived field-emission resonances. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  8. Novel PdAgCu ternary alloy as promising materials for hydrogen separation membranes: Synthesis and characterization

    Science.gov (United States)

    Tarditi, Ana M.; Cornaglia, Laura M.

    2011-01-01

    The use of the sequential electroless plating method allowed us to obtain the PdAgCu ternary alloy on top of dense stainless steel (SS) 316 L disks. The XRD analysis indicated that initially the nucleation of the two phases of the alloy (FCC and BCC) takes place, but the FCC/BCC ratio increases with the annealing time at 500 °C in H 2 stream. After 162 h, the film contained only the FCC phase, which presents promising properties to be applied in the synthesis of hydrogen selective membranes. SEM cross-section results showed that a dense, continuous, defect-free film was deposited on top of the SS support, and the EDS data indicated that no significant gradient was present on the thickness of the film. XPS and LEIS allowed us to determine that Cu and Ag surface segregation takes place after annealing up to 500 °C/5 days. In the top-most surface layer, Ag enrichment takes place as determined by ARXPS experiments which can be the result of the lower surface tension of Ag compared to that of Cu and Pd. Increasing the annealing temperature results in an increase of the Ag surface segregation while the Cu concentration in the top-most surface layer decreases.

  9. Interaction of bathocuproine with metals (Ca, Mg, Al, Ag, and Au) studied by density functional theory

    International Nuclear Information System (INIS)

    Electronic structure of the interface between a bathocuproine (BCP) molecule and metal surface was studied by density functional theory. The bond energy of BCP with metal surface increased with decreasing work function of metals, that is, Au, Ag, Al, Mg, and Ca in this order. The charge transfer also increased with decreasing metal work function. It was analyzed that the Fermi level and the lowest unoccupied molecular orbital of BCP are composed of both BCP and metal orbital component, and electron transport properties across the BCP and metal is discussed based on these analyses.

  10. Strain and structure in nano Ag films deposited on Au: Molecular dynamics simulation

    International Nuclear Information System (INIS)

    Molecular dynamics simulations are applied to analyze the stress and structure of nano Ag thin films deposited on the Au substrate. The interactions in the system are described by the embedded atom method. The kinematical theory of scattering is employed to identify the structure obtained from simulations data. Results shows that the silver layers are adjusted to the crystalline lattice of the gold buffer layers, and during the deposition process only compressive stress is observed. In all the cases the distribution of stress does not depend on temperature.

  11. Comparison between the fragmentation processes in central Pb + Ag and Pb + Au collisions

    Energy Technology Data Exchange (ETDEWEB)

    Jouault, B.; Royer, G.; Sebille, F.; Haddad, F.; Lecolley, J.F.

    1996-12-31

    The fragmentation processes of a medium mass system and of a very massive one formed in central collisions are compared within the Landau-Vlasov model taking into account both the isospin dependence and the two-body residual interactions. The simulations predict the formation of a roughly ellipsoidal source in the central Pb + Ag reactions while, for the Pb + Au system, the fragmentation occurs from an hollow source, the configuration of which being intermediate between bubble-like and toroidal shapes. This difference shapes explain and allow to reproduce semi-quantitatively the two different profiles of the experimental kinetic energy spectra. (authors).

  12. Synthesis of (Au)Ag core-shell nanocomposite in the water- ethanol mixture and its optical properties

    Science.gov (United States)

    Abakshonok, A. V.; Panarin, A. Yu; Agabekov, V. E.; Eryomin, A. N.; Terekhov, S. N.

    2014-08-01

    The technique of synthesis of (Au)Ag core-shell bimetallic nanocomposite was developed. Gold seed nanoparticles (NPs) were obtained by HAuCl4 reduction with sodium citrate at ultrasonic treatment during 3 hours in a mixture of water - ethanol (1:1). Then, the surface of gold NPs was modified by silver. In the presence of polyvinylpyrrolidone (PVP) K30 (Mw ~ 24000) and K90 (Mw ~ 360000) the coreshell (Au)Ag NPs of spherical shape were formed. They are characterized by aggregate stability and well-defined absorption maximum at 400-514 nm. Composite (Au)Ag, prepared in the solution without a polymer or in the presence of carboxymethylcellulose (CMC), sodium polystyrene sulfonate (PSS), dextran T100 and T500, had a broad band plasmon resonance in the whole range of visible spectrum. The ability to use the (Au)Ag core-shell nanoparticles in absorption nanospectroscopy based on the phenomenon of plasmon resonance energy transfer (PRET) was evaluated. In the presence of 0,1-2,0 μM of water-soluble cationic Cu (II) -5,10,15,20-tetrakis (4-N-methyl pyridinium) porphyrin (CuTMPyP4) distinct dips due to plasmon quenching matched the absorption maximum of CuTMPyP4 were detected in the resonant scattering spectrum of (Au)Ag solution.

  13. Fabrication a new modified electrochemical sensor based on Au-Pd bimetallic nanoparticle decorated graphene for citalopram determination.

    Science.gov (United States)

    Daneshvar, Leili; Rounaghi, Gholam Hossein; Es'haghi, Zarrin; Chamsaz, Mahmoud; Tarahomi, Somayeh

    2016-12-01

    This paper proposes a simple approach for sensing of citalopram (CTL) using gold-palladium bimetallic nanoparticles (Au-PdNPs) decorated graphene modified gold electrode. Au-PdNPs were deposited at the surface of a graphene modified gold electrode with simple electrodeposition method. The morphology and the electrochemical properties of the modified electrode were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), energy dispersion spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave voltammetry (SWV). The novel sensor exhibited an excellent catalytic activity towards the oxidation of CTL. The oxidation peak current of CTL, was linear in the range of 0.5-50μM with a detection limit 0.049μM with respect to concentration of citalopram. The proposed sensor was successfully applied for determination of CTL tablet and human plasma samples with satisfactory results. PMID:27612758

  14. One-Step Synthesis of Pd-M/ZnO (M=Ag, Cu, and Ni) Catalysts by γ-Irradiation and Their Use in Hydrogenation and Suzuki Reaction

    OpenAIRE

    Mi-Ran Kim; Seong-Ho Choi

    2009-01-01

    ZnO-supported Pd, Pd-Ag, Pd-Cu, and Pd-Ni catalysts (Pd-M/ZnO) were prepared in MeOH/H2O mixture (4/1, v/v-%) by γ-irradiation at room temperature. Small mono- and bimetallic nanoparticles were loaded on the surface of ZnO nanopowder as confirmed with TEM, TEM-EDXS, XRD, and ICP-AES data. The catalytic efficiency against Pd-M/ZnO was determined in hydrogenation and Suzuki reaction and compared with the commercial Pd/C catalyst. The Pd-Ag/ZnO showed the highest catalytic efficiency ...

  15. Synthesis of Ag/Pd nanoparticles via reactive micelles as templates and its application to electroless copper deposition.

    Science.gov (United States)

    Yang, Chia-Cheng; Wan, Chi-Chao; Wang, Yung-Yun

    2004-11-15

    Ag/Pd nanoparticles have been synthesized with a reactive alcohol-type surfactant, sodium dodecyl sulfate (SDS), without the presence of an external reducing agent. Both UV-vis absorption spectra and X-ray diffraction patterns for the bimetallic and physical mixtures of individual nanoparticles revealed the formation of a bimetallic structure. Based on this method, an ordered 3D grapelike nanostructure was formed, possibly due to transformation of the liquid crystal phase of the micelles. Data from the energy-dispersive X-ray analysis show that the composition of bimetallic nanoparticle is approximately equal to the feeing solution. Furthermore, the Ag/Pd nanoparticles exhibit distinct catalyst for electroless copper deposition and may be a substitute for the conventional palladium system, which is expensive and unstable in operation. PMID:15464808

  16. Probing the influence of bimetallic composition on the Pd/Au catalysed synthesis of vinyl acetate monomer

    OpenAIRE

    Haire, Andrew Richard

    2010-01-01

    Scanning Tunnelling Microscopy (STM) was utilised together with the high resolution depth-profiling capabilities of Medium Energy Ion Scattering (MEIS), a technique traditionally associated with single crystal substrates, to probe the mean size and depth dependent composition profile of bimetallic PdAu nanoparticles on planar oxide surfaces as functions of the starting composition and annealing temperature. In order to fit composition profiles to experimental MEIS data, a ne...

  17. In situ measurements of change in work function of Pt, Pd and Au surfaces during desorption of oxygen by using photoemission yield spectrometer in air

    Science.gov (United States)

    Yamashita, Daisuke; Ishizaki, Atsushi

    2016-02-01

    We investigated the change in work function of Pt, Pd and Au surfaces during desorption of oxygen by using a photoemission yield spectrometer with an open counter. Oxygen coverage was formed by UV/ozone treatment, and then continuous change in work function with exposure to air was observed at various temperatures. Work function of Pt, Pd and Au surfaces decreased during desorption of oxygen, and finally returned to the initial value of untreated surfaces. Furthermore, temperature dependence on the change in work function was found. These characteristics were explained using chemical kinetics scheme. The exponential decay of work function was well reproduced by the first-order reaction rate equation, and it was confirmed that the order of rate constant, kr, is kr(Au) < kr(Pd) < kr(Pt). The activation energy was estimated to be 36, 38 and 28 kJ/mol for Pt, Pd, Au, respectively.

  18. Green Synthesis of Ag and Pd Nanospheres, Nanowires, and Nanorods Using Vitamin B2: Catalytic Polymerisation of Aniline and Pyrrole

    OpenAIRE

    Mallikarjuna N. Nadagouda; Varma, Rajender S.

    2008-01-01

    For the first time, we report green chemistry approach using vitamin B2 in the synthesis of silver (Ag) and palladium (Pd), nanospheres, nanowires, and nanorods at room temperature without using any harmful reducing agents, such as sodium borohydride (NaBH4) or hydroxylamine hydrochloride and any special capping or dispersing agent. Vitamin B2 was used as reducing agent as well as capping agent due to its high-water solubility, biodegradability, and low-toxicity compared with other reducing a...

  19. Fermi surface study of ScAu2(Al, In) and ScPd2(Sn, Pb) compounds

    International Nuclear Information System (INIS)

    A detailed study on the electronic structure and Fermi surface (FS) of superconducting Heusler compounds ScAu2(Al, In) and ScPd2(Sn, Pb) has been carried out using first principles electronic structure calculations. The spin orbit coupling is found to play a major role in understanding the band structure and FS. Analysis of the data shows the importance of spin orbit coupling effect in the above compounds. The bands which cross Fermi level (EF) are found to be dominated by the Sc dt2g-states. The calculated total density of states are in good agreement with the experimentally reported value for ScPd2Sn. Under compression we find a change in the Fermi surface topology of ScPd2Sn at V/V0 = 0.95 (pressure of≈15 GPa), which is explained using the band structure calculations

  20. Autothermal reforming of ethanol in a Pd-Ag/Ni composite membrane reactor

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Wen-Hsiung [Department of Beauty Science, Chienkuo Technology University, Changhua 500 (China); Liu, Ying-Chi; Chang, Hsin-Fu [Department of Chemical Engineering, Feng Chia University, Taichung 407 (China)

    2010-12-15

    The main objective of this project is to study the hydrogen production reaction from oxidative steam reforming of bio-ethanol in the pertinent characteristics of a palladium-silver alloy membrane reactor. The enhancements of hydrogen permeation and of H{sub 2}/N{sub 2} permselectivity were studied in a Ni-Pd-Ag ternary alloy membrane, which was fabricated by successive electroless plating of palladium and silver on stainless steel (PSS) supports modified with nickel electroplating. XRD, SEM, and EDS were used to characterize the surface morphology of the membranes. Ethanol-water mixture (n{sub water}/n{sub ethanol} = 1 or 3) and oxygen (n{sub oxygen}/n{sub ethanol} = 0.2 or 0.7) were fed concurrently into the membrane reactor packed with Zn-Cu commercial catalyst (MDC-3). The reaction temperatures were set at temperatures of 593-723 K and pressures of 3-10 atm. The amount of oxygen added in the feed has a significant effect on the steam reforming reaction of ethanol. At high pressures, autothermal reaction of ethanol with no need for external heating to the composite membrane reactor to produce high purity hydrogen was easily processed. (author)

  1. Polymer monolithic capillary microextraction on-line coupled with inductively coupled plasma-mass spectrometry for the determination of trace Au and Pd in biological samples

    International Nuclear Information System (INIS)

    A novel method based on on-line polymer monolithic capillary microextraction (CME)-inductively coupled plasma mass spectrometry (ICP-MS) was developed for the determination of trace Au and Pd in biological samples. For this purpose, poly(glycidyl methacrylate-ethylene dimethacrylate) monolith was prepared and functionalized with mercapto groups. The prepared monolith exhibited good selectivity to Au and Pd, and good resistance to strong acid with a long life span. Factors affecting the extraction efficiency of CME, such as sample acidity, sample flow rate, eluent conditions and coexisting ion interference were investigated in detail. Under the optimal conditions, the limits of detection (LODs, 3σ) were 5.9 ng L−1 for Au and 8.3 ng L−1 for Pd, and the relative standard deviations (RSDs, c = 50 ng L−1, n = 7) were 6.5% for Au and 1.1% for Pd, respectively. The developed method was successfully applied to the determination of Au and Pd in human urine and serum samples with the recovery in the range of 84–118% for spiked samples. The developed on-line polymer monolithic CME-ICP-MS method has the advantages of rapidity, simplicity, low sample/reagent consumption, high sensitivity and is suitable for the determination of trace Au and Pd in biological samples with limited amount available and complex matrix. - Highlights: • An on-line CME-ICP-MS method was developed for Au and Pd analysis in human fluids. • Poly(GMA-EDMA-SH) monolith exhibited good selectivity for Au/Pd and acid-resistance. • The method is rapid, simple, and sensitive with low sample/reagents consumption

  2. Molecular dynamics simulation of joining process of Ag-Au nanowires and mechanical properties of the hybrid nanojoint

    International Nuclear Information System (INIS)

    The nanojoining process of Ag-Au hybrid nanowires at 800K was comprehensively studied by virtue of molecular dynamics (MD) simulation. Three kinds of configurations including end-to-end, T-like and X-like were built in the simulation aiming to understand the nanojoining mechanism. The detailed dynamic evolution of atoms, crystal structure transformation and defects development during the nanojoining processes were performed. The results indicate that there are two stages in the nanojoining process of Ag-Au nanowires which are atom diffusion and new bonds formation. Temperature is a key parameter affecting both stages ascribed to the energy supply and the optimum temperature for Ag-Au nanojoint with diameter of 4.08 nm has been discussed. The mechanical properties of the nanojoint were examined with simulation of tensile test on the end-to-end joint. It was revealed that the nanojoint was strong enough to resist fracture at the joining area

  3. Molecular dynamics simulation of joining process of Ag-Au nanowires and mechanical properties of the hybrid nanojoint

    Directory of Open Access Journals (Sweden)

    Su Ding

    2015-05-01

    Full Text Available The nanojoining process of Ag-Au hybrid nanowires at 800K was comprehensively studied by virtue of molecular dynamics (MD simulation. Three kinds of configurations including end-to-end, T-like and X-like were built in the simulation aiming to understand the nanojoining mechanism. The detailed dynamic evolution of atoms, crystal structure transformation and defects development during the nanojoining processes were performed. The results indicate that there are two stages in the nanojoining process of Ag-Au nanowires which are atom diffusion and new bonds formation. Temperature is a key parameter affecting both stages ascribed to the energy supply and the optimum temperature for Ag-Au nanojoint with diameter of 4.08 nm has been discussed. The mechanical properties of the nanojoint were examined with simulation of tensile test on the end-to-end joint. It was revealed that the nanojoint was strong enough to resist fracture at the joining area.

  4. Planar potentiometric sensors based on Au and Ag microelectrodes and conducting polymers for flow-cell analysis

    International Nuclear Information System (INIS)

    Back-side contact Au and Ag microelectrodes were used as transducers to construct planar all-solid-state electrodes suitable for flow-through analysis. The microsensors were based on plasticized PVC potassium-selective membranes containing ion-electron conducting polymer-polypyrrole doped with di(2-ethylhexyl) sulfosuccinate. The proposed technique allowed simple construction of microsensors in one step, by membrane solution casting directly on the surface of the planar metallic transducers. The performance of the microsensors based on Au and Ag transducers were determined and compared with planar sensors based on internal electrolyte immobilized in polyHEMA. The addition of the polypyrrole to the membrane composition did not influence on the selectivity, reproducibility and long-term stability of the microsensors but improved their standard potential stability in time in comparison with coated-wire type sensors. Moreover, all-solid-state microsensors based on Au transducers exhibited better signal stability than Ag based sensors

  5. Influence of quenching on the martensitic transformation temperature in Au-47.5at.%Cd-Ag alloys

    International Nuclear Information System (INIS)

    We determined bccB2, B2L21 and martensitic transformation temperatures in Au-47.5at.%Cd-Ag alloys for a wide range of compositions, and examined changes in martensitic transformation temperatures by quenching from various temperatures for Au-47.5at.%Cd-15at.%Ag and Au-47.5at.%Cd-27at.%Ag alloys. It has been found that in spite of the differences in the long-range β-phase order of both alloys, the quenching behavior of the martensitic transformation temperatures is quite similar for each of them, i.e. the maximum depression of the transformation temperature due to quenching occurs when quenched from temperatures near 773 K corresponding well to the B2 order state. This result suggests that the short-range disorder in the B2 ordered phase causes the martensitic transformation temperature to decrease. (orig.)

  6. Crystal Chemistry of Natural Tellurides. I: Refinement of the Crystal Structure of Sylvanite, AuAgTe4

    International Nuclear Information System (INIS)

    Electron microprobe analyses and the refinement of the crystal structure indicate, that sylvanite, AuAgTe4, from Baia de Aries (=Offenbanya), Romania, has a stoichiometric composition and an ordered crystal structure (a-8.95(1) A, b=4.478(5) A, c=14.62(2) A; β=145.35(5)supo; Z-2; space group P2/c-Csub(2h)4). The Au atom is surrounded by six Te atoms in a [4+2] coordination as characteristic for oxidation state III. Around the Ag atom (oxidation state I) are also six Te atoms, but arranged in a [2+2+2] coordination. Via common edges the AuTe6 and AgTe6 polyhedra build up 'sheets' parallel to (100). These 'sheets' are combined to a network of Te2 dumbbells (Te-Te=2.82 A). (Author)

  7. Half sandwich structures of MCF6- (M = Ag and Au): An experimental and theoretical study

    Science.gov (United States)

    Sun, Zhang; Tang, Zichao; Gao, Zhen

    2013-01-01

    The metal-hexafluorobenzene anionic complexes of [MC6F6]- (M = Ag and Au) were produced from the reactions between metal cluster generated by laser ablation and the hexafluorobenzene seeded in argon carrier gas, and were studied by photoelectron spectroscopy (PES) and density functional theory (DFT). The adiabatic electron affinities (EAs) of these corresponding complexes are measured from the experimental PE spectra at 193 nm photon energy. Also, the calculated EAs and the calculated density of states (DOS) spectra of these complexes in the ground state are conducted, which are in good agreement with their experimental PE spectra. The most possible structures of the anions [AgC6F6]- and [AuC6F6]- are the half-sandwich structures with C6v symmetry, in which the metal atom is above the center of the C6F6 plane. Furthermore, the molecular orbital (MO) analysis of these species indicates that the additional electron of the anions binds on the metal.

  8. Ohmic contacts of Au and Ag metals to n-type GdN thin films

    Directory of Open Access Journals (Sweden)

    Felicia Ullstad

    2015-05-01

    Full Text Available The rare-earth nitrides appear as attractive alternatives to dilute ferromagnetic semiconductors for spintronics device applications. Most of them combine the properties of the ferromagnet and the semiconductor, an exceedingly rare combination. In this work we have grown n-type polycrystalline semiconducting GdN layers between pre-deposited contacts made of Cr/Au and Cr/Ag. The resistivity of the GdN layers ranges from 4.4×10-4 Ωcm to 3.1×10-2 Ωcm depending on the nitrogen pressure during the growth. The electrical properties of metal/n-type GdN/metal planar junctions are investigated as a function of the temperature. The current voltage characteristics of the junctions were linear for temperatures ranging from 300 K down to 5 K, suggesting an ohmic contact between the Au or Ag metal and the n-type GdN layer.

  9. Electrodeposition of Au/Ag bimetallic dendrites assisted by Faradaic AC-electroosmosis flow

    Directory of Open Access Journals (Sweden)

    Jianlong Ji

    2014-03-01

    Full Text Available Au/Ag bimetallic dendrites were synthesized successfully from the corresponding aqueous solution via the AC electrodeposition method. Both of the morphologies and compositions could be tuned by the electrolyte concentration and AC frequency. The prepared bimetallic dendrites were characterized by scanning electron microscopy (SEM, energy dispersive X-ray spectrometer (EDS, transmission electron microscopy (TEM and UV–vis spectroscopy. The underlying dendrite growth mechanism was then proposed in the context of the Directed Electrochemical Nanowires Assembly (DENA models. Owing to the unscreened voltage dropping in the electrolyte bulk, electromigration dominates the species flux process, and cations tend to accumulate in areas with strong electric field intensity, such as electrode edges. Moreover, Faradaic AC-electro-osmosis (ACEO flow could increase the effective diffusion layer thickness in these areas during the electrochemical reaction, and leads to dendrite growth. Further Micro-Raman observations illustrated that the Au/Ag bimetallic dendrites exhibited pronounced surface-enhanced Raman scattering (SERS activity, using 4-mercaptopyridine (4-MP as model molecules.

  10. Au and Pd nanoparticles supported on CeO{sub 2}, TiO{sub 2}, and Mn{sub 2}O{sub 3} oxides

    Energy Technology Data Exchange (ETDEWEB)

    Nascente, P.A.P., E-mail: nascente@ufscar.br [Federal University of Sao Carlos, Department of Materials Engineering, Sao Carlos, SP (Brazil); Maluf, S.S.; Afonso, C.R.M. [Federal University of Sao Carlos, Department of Materials Engineering, Sao Carlos, SP (Brazil); Landers, R. [State University of Campinas, Institute of Physics, Department of Applied Physics, Campinas, SP (Brazil); Pinheiro, A.N.; Leite, E.R. [Federal University of Sao Carlos, Department of Chemistry, Sao Carlos, SP (Brazil)

    2014-10-01

    Highlights: • CeO{sub 2}, TiO{sub 2}, and Mn{sub 2}O{sub 3} supported Au and Pd nanoparticles. • Additions of 0.5 wt% of Au and Pd onto CeO{sub 2}, TiO{sub 2}, and Mn{sub 2}O{sub 3} supports. • Characterization by XRD, XPS, EDS, TEM, HRTEM, STEM, and EFTEM. - Abstract: Gold and palladium nanoparticles were incorporated on CeO{sub 2}, TiO{sub 2}, and Mn{sub 2}O{sub 3} supports prepared by a sol–gel method. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution TEM (HRTEM), scanning TEM (STEM) in high angle annular dark field mode (HAADF), and energy filtered TEM (EFTEM) using electron energy loss spectroscopy (EELS). The XRD diffractograms presented sharp and intense peaks indicating that the samples are highly crystalline, but it did not detected any peak corresponding to Au or Pd phases. This indicates that the Au and Pd NPs were incorporated into the structures of the oxides. It was not possible to obtain an Au 4f spectrum for Au/Mn{sub 2}O{sub 3} due to an overlap with the Mn 3p spectrum. The XPS Au 4f spectra for Au/CeO{sub 2} and Au/TiO{sub 2} present negative chemical shifts that could be attributed to particle-size-related properties. The XPS Pd 3d spectra indicate that for both CeO{sub 2} and TiO{sub 2} substrates, the Pd NPs were in the metallic state, while for the Mn{sub 2}O{sub 3} substrate, the Pd NPs were oxidized. The HRTEM results show the formation of nanocrystalline oxides having particles sizes between 50 and 200 nm. TEM micrographs show that the addition of Au caused the formation of Au clusters in between the CeO{sub 2} NPS, formation of Au NPs for the TiO{sub 2} support, and homogeneous distribution of Au clusters for the Mn{sub 2}O{sub 3} support. The addition of Pd yielded a homogeneous dispersion throughout the CeO{sub 2} and TiO{sub 2}, but caused the formation of Pd clusters for the Mn{sub 2}O

  11. The crystal structures of jaguéite, Cu2Pd3Se4, and chrisstanleyite, Ag2Pd3Se4

    DEFF Research Database (Denmark)

    Topa, Dan; Makovicky, Emil; Balic Zunic, Tonci

    2006-01-01

    equipped with a CCD area-detector. The crystal structure of chrisstanleyite, ideally Ag2Pd3Se4, monoclinic a 5.676(2), b 10.342(4), c 6.341(2) Å, ß 114.996(4)º, space group P21/c, has been solved by direct methods and refi ned to an R1 index of 8.3% for 1203 unique refl ections measured with MoK X......-Cu(Ag)-Pd2 system of metal-metal bonds, help to stabilize the open-work structure composed of PdSe4 squares....

  12. Wear out Reliability and Intermetallic Compound Diffusion Kinetics of Au and PdCu Wires Used in Nano scale Device Packaging

    International Nuclear Information System (INIS)

    Wear out reliability and diffusion kinetics of Au and Pd-coated Cu (PdCu) ball bonds are useful technical information for Cu wire deployment in nano scale semiconductor device packaging. This paper discusses the HAST (with bias) and UHAST (unbiased HAST) wear out reliability performance of Au and PdCu wires used in fine pitch BGA packages. In-depth failure analysis has been carried out to identify the failure mechanism under various wear out conditions. Intermetallic compound (IMC) diffusion constants and apparent activation energies (Eaa) of both wire types were investigated after high temperature storage life test (HTSL). Au bonds were identified to have faster IMC formation, compared to slower IMC growth of PdCu. PdCu wire was found to exhibit equivalent or better wear out reliability margin compared to conventional Au wire bonds. Failure mechanisms of Au, Cu ball bonds post-HAST and UHAST tests are been proposed, and both Au and PdCu IMC diffusion kinetics and their characteristics are discussed in this paper.

  13. Polymer monolithic capillary microextraction on-line coupled with inductively coupled plasma-mass spectrometry for the determination of trace Au and Pd in biological samples

    Science.gov (United States)

    Liu, Xiaolan; He, Man; Chen, Beibei; Hu, Bin

    2014-11-01

    A novel method based on on-line polymer monolithic capillary microextraction (CME)-inductively coupled plasma mass spectrometry (ICP-MS) was developed for the determination of trace Au and Pd in biological samples. For this purpose, poly(glycidyl methacrylate-ethylene dimethacrylate) monolith was prepared and functionalized with mercapto groups. The prepared monolith exhibited good selectivity to Au and Pd, and good resistance to strong acid with a long life span. Factors affecting the extraction efficiency of CME, such as sample acidity, sample flow rate, eluent conditions and coexisting ion interference were investigated in detail. Under the optimal conditions, the limits of detection (LODs, 3σ) were 5.9 ng L- 1 for Au and 8.3 ng L- 1 for Pd, and the relative standard deviations (RSDs, c = 50 ng L -1, n = 7) were 6.5% for Au and 1.1% for Pd, respectively. The developed method was successfully applied to the determination of Au and Pd in human urine and serum samples with the recovery in the range of 84-118% for spiked samples. The developed on-line polymer monolithic CME-ICP-MS method has the advantages of rapidity, simplicity, low sample/reagent consumption, high sensitivity and is suitable for the determination of trace Au and Pd in biological samples with limited amount available and complex matrix.

  14. Au@Ag/Au nanoparticles assembled with activatable aptamer probes as smart ``nano-doctors'' for image-guided cancer thermotherapy

    Science.gov (United States)

    Shi, Hui; Ye, Xiaosheng; He, Xiaoxiao; Wang, Kemin; Cui, Wensi; He, Dinggeng; Li, Duo; Jia, Xuekun

    2014-07-01

    Although nanomaterial-based theranostics have increased positive expectations from cancer treatment, it remains challenging to develop in vivo ``nano-doctors'' that provide high-contrast image-guided site-specific therapy. Here we designed an activatable theranostic nanoprobe (ATNP) via self-assembly of activatable aptamer probes (AAPs) on Au@Ag/Au nanoparticles (NPs). As both quenchers and heaters, novel Au@Ag/Au NPs were prepared, showing excellent fluorescence quenching and more effective near-infrared photothermal therapy than Au nanorods. The AAP comprised a thiolated aptamer and a fluorophore-labeled complementary DNA; thus, the ATNP with quenched fluorescence in the free state could realize signal activation through target binding-induced conformational change of the AAP, and then achieve on-demand treatment under image-guided irradiation. By using S6 aptamer as the model, in vitro and in vivo studies of A549 lung cancer verified that the ATNP greatly improved imaging contrast and specific destruction, suggesting a robust and versatile theranostic strategy for personalized medicine in future.Although nanomaterial-based theranostics have increased positive expectations from cancer treatment, it remains challenging to develop in vivo ``nano-doctors'' that provide high-contrast image-guided site-specific therapy. Here we designed an activatable theranostic nanoprobe (ATNP) via self-assembly of activatable aptamer probes (AAPs) on Au@Ag/Au nanoparticles (NPs). As both quenchers and heaters, novel Au@Ag/Au NPs were prepared, showing excellent fluorescence quenching and more effective near-infrared photothermal therapy than Au nanorods. The AAP comprised a thiolated aptamer and a fluorophore-labeled complementary DNA; thus, the ATNP with quenched fluorescence in the free state could realize signal activation through target binding-induced conformational change of the AAP, and then achieve on-demand treatment under image-guided irradiation. By using S6 aptamer as

  15. Modification of the electronic properties of Au/molecule/Pd junctions by adsorbed hydrogen: a DFT study

    Energy Technology Data Exchange (ETDEWEB)

    Kucera, Jan; Gross, Axel [Institut fuer Theoretische Chemie, Universitaet Ulm, D-89069 Ulm (Germany)

    2011-07-01

    Metal-molecule-metal contacts assembled from a Pd monolayer deposited on a Au-supported self-assembled monolayer (SAM) of 4-mercaptopyridine or 4-aminothiophenol were recently achieved by means of an electrochemical approach. Subsequent photoelectron spectroscopy showed a strongly reduced Pd density of states (DOS) at the Fermi energy. This phenomenon is still not fully comprehended, however, its understanding is crucial for the use of the sandwich design as a platform for future nanoelectronics. Periodic density functional theory (DFT) calculation revealed that the dehydrogenation of the amino group and the subsequent strong bonding of the remaining nitrogen atom to the Pd layer could explain the observed modification of the DOS. We have now extended this study in order to clarify the role of hydrogen atoms for the electronic properties of the Pd layers. In equilibrium, these layers should always show a considerable hydrogen coverage in an aqueous environment. Our calculations demonstrate that indeed the adsorbed hydrogen atoms significantly modify the electronic structure of the Pd layers.

  16. Facile Synthesis of Au or Ag Nanoparticles-Embedded Hollow Carbon Microspheres from Metal-Organic Framework Hybrids and Their Efficient Catalytic Activities.

    Science.gov (United States)

    Choi, Sora; Lee, Hee Jung; Oh, Moonhyun

    2016-05-01

    Au or Ag nanoparticles-embedded hollow carbon spheres, which display outstanding catalytic activity and excellent recyclability, are prepared by a one-step pyrolysis of metal-organic framework (MOF) hybrids consisting of polystyrene cores and MOF shells loaded with noble metal ions (polystyrene@ZIF-8/M(n+) ; M(n+) = Au(3+) or Ag(+) ). PMID:27151828

  17. Facile synthesis and intraparticle self-catalytic oxidation of dextran-coated hollow Au-Ag nanoshell and its application for chemo-thermotherapy.

    Science.gov (United States)

    Jang, Hongje; Kim, Young-Kwan; Huh, Hyun; Min, Dal-Hee

    2014-01-28

    Galvanic replacement reaction is a useful method to prepare various hollow nanostructures. We developed fast and facile preparation of biocompatible and structurally robust hollow Au-Ag nanostructures by using dextran-coated Ag nanoparticles. Oxidation of the surface dextran alcohols was enabled by catalytic activity of the core Au-Ag nanostructure, introducing carbonyl groups that are useful for further bioconjugation. Subsequent doxorubicin (Dox) conjugation via Schiff base formation was achieved, giving high payload of approximately 35 000 Dox per particle. Near-infrared-mediated photothermal conversion showed high efficacy of the Dox-loaded Au-Ag nanoshell as a combinational chemo-thermotherapy to treat cancer cells. PMID:24383549

  18. Preparation and Characterization of Au/Pd Modified-TiO2 Photocatalysts for Phenol and Toluene Degradation under Visible Light—The Effect of Calcination Temperature

    Directory of Open Access Journals (Sweden)

    Anna Cybula

    2014-01-01

    Full Text Available Rutile loaded with Au/Pd nanoparticles was prepared using a water-in-oil microemulsion system of water/AOT/cyclohexane followed by calcination. The effect of calcination temperature (from 350 to 700°C on the structure of Au/Pd nanoparticles deposited at rutile matrix and the photocatalytic properties of Au/Pd-TiO2 was investigated in two model reactions (toluene degradation in gas phase and phenol degradation in aqueous phase. Toluene was irradiated over Au/Pd-TiO2 using light emitting diodes (LEDs, λmax⁡ = 415 nm. The sample 0.5 mol% Pd/TiO2 exhibited the highest activity under visible light irradiation in gas and aqueous phase reaction among all photocatalysts calcined at 350°C, while the sample modified only with gold nanoparticles showed the lowest activity. The Au/Pd-TiO2 sample calcinated at 350°C possesses the highest photocatalytic activity when degrading phenol under visible light, which is 14 times higher than that of the one calcinated at 450°C. It was observed that increasing temperature from 350 to 700°C during calcination step caused segregation of metals and finally resulted in photoactivity drop.

  19. DNA-embedded Au-Ag core-shell nanoparticles assembled on silicon slides as a reliable SERS substrate.

    Science.gov (United States)

    Zhang, Zhong; Zhang, Sha; Lin, Mengshi

    2014-05-01

    This study aimed at developing a sensitive and reliable SERS substrate by assembling DNA-embedded Au-Ag core-shell nanoparticles (NPs) on silicon slides. First, a monolayer of well separated DNA-functionalized Au NPs (40 nm) was decorated on (3-aminopropyl)triethoxysilane modified silicon slides. The DNA-embedded Au-Ag core-shell NPs were assembled on the 40 nm Au-DNA NPs to form a core-satellite structure through DNA hybridization. Using 4-MBA as a Raman dye, the SERS performance of the substrates was evaluated after being cleaned by low oxygen and argon plasma. The Raman intensity of the assembly using DNA-embedded Au-Ag core-shell NPs was 8-10 times higher than the intensity of the assembly using Au NPs as satellites. In addition, the signal-to-noise ratio of the assembly was 2.6 times higher than that of a commercial substrate (Klarite™) when a 785 nm laser was used. The SERS enhancements of the assembled substrates were 2.2 to 2.8 times higher than the Klarite when an acquisition time of 5 s was used at an excitation wavelength of 633 nm. The assembled substrates also show a good spot-to-spot and substrate-to-substrate reproducibility at the excitation wavelengths of 633 and 785 nm. These results demonstrate that the fabrication process is simple and cost-effective for assembling DNA-embedded Au-Ag core-shell NPs on silicon slides that can be used as a reliable SERS substrate. PMID:24627887

  20. Nucleation-mediated synthesis and enhanced catalytic properties of Au-Pd bimetallic tripods and bipyramids with twinned structures and high-energy facets

    Science.gov (United States)

    Zhang, Lei; Chen, Qiaoli; Wang, Xue; Jiang, Zhiyuan

    2016-01-01

    The Au-Pd alloy has been proved to be an excellent catalyst in many applications, such as the electro-oxidation of formic acid, CO oxidation and oxidation of alcohols to aldehydes. However, most of the research has been focused on the shape-controlled Au-Pd alloy NCs with a single-crystal structure. Due to the existence of high-energy atoms on the twin defects, twinned structures usually will further increase their catalytic activities. It is necessary to develop a method to prepare the Au-Pd alloy with twinned structures and investigate their catalytic properties. Herein, we successfully synthesized Au-Pd alloy tripods and bipyramids with twinned structures by the cooperation of cetyltrimethyl ammonium chloride (CTAC) and cetyltrimethyl ammonium bromide (CTAB). The tripods contain one twin plane, while the bipyramids consist of a fivefold-twinned structure. In addition, the tripods and bipyramids are both exposed by high-energy facets. We proposed that the tripods and bipyramids are evolved from bipyramid seeds and fivefold twinned seeds, respectively. The as-prepared Au-Pd tripods and bipyramids performed better activity for electrocatalytic oxidation of formic acid compared to the cubic Au-Pd nanoparticles.The Au-Pd alloy has been proved to be an excellent catalyst in many applications, such as the electro-oxidation of formic acid, CO oxidation and oxidation of alcohols to aldehydes. However, most of the research has been focused on the shape-controlled Au-Pd alloy NCs with a single-crystal structure. Due to the existence of high-energy atoms on the twin defects, twinned structures usually will further increase their catalytic activities. It is necessary to develop a method to prepare the Au-Pd alloy with twinned structures and investigate their catalytic properties. Herein, we successfully synthesized Au-Pd alloy tripods and bipyramids with twinned structures by the cooperation of cetyltrimethyl ammonium chloride (CTAC) and cetyltrimethyl ammonium bromide (CTAB

  1. Atomic scale insights into ethanol oxidation on Pt, Pd and Au metallic nanofilms: A DFT with van der Waals interactions

    International Nuclear Information System (INIS)

    In this work, we use dispersion corrected DFT calculations (DFT + D3) to explore the ethanol decomposition on Pt, Pd and Au metallic nanofilms. The structural and energetic properties of ethanol and the most common intermediate products in ethanol oxidation were investigated, namely acetaldehyde, acetic acid, acetyl and CO. Our results suggests that even when starting from an initial condition very close to the equilibrium geometry it is not possible to obtain the correct adsorption properties from standard DFT calculations; the system is trapped in a local minimum geometry and the correct adsorption geometry cannot be accessed. Therefore, the inclusion of vdW interactions is fundamental to assure correct adsorption properties and agreement with experimental data. By analyzing the adsorption of ethanol and its oxidation products on metallic nanofilms we found that Pt (1 1 1), Pt/Pd (1 1 1), Pt/Au (1 1 1) and Pd/Pt (1 1 1) nanofilms present enhanced adsorption properties and seem to be good candidates for ethanol catalysis.

  2. Total oxidation of VOCs on Pd and/or Au supported on TiO2/ZrO2 followed by ''operando'' Drift

    International Nuclear Information System (INIS)

    Catalytic performances of nano-structured meso-porous TiO2-ZrO2 mixed oxides impregnated by Pd and/or Au were studied in toluene total oxidation in a fixed bed micro-reactor and with 'operando' DRIFT. Meso-porous TiO2-ZrO2 mixed oxides with various Ti:Zr mole ratio of 80/20, 50/50 and 20/80, high surface areas were synthesised using a mixture of zirconium prop-oxide and titanium iso-prop-oxide as Zr and Ti sources and also CTMABr as surfactant. The new supports are impregnated by 0.5 or 1.5 wt% of palladium and 1 wt% of gold using impregnation and Deposition-Precipitation methods. The catalytic activity for the nano-structured meso-porous TiO2-ZrO2 mixed oxides varies depending on the molar ratio of Ti:Zr and also for all series of the studied catalysts impregnated by Pd and/or Au, when the gold is loaded firstly the activity in toluene complete oxidation is higher than when Pd was deposited firstly (PdAu/TZ ≥ 1.5Pd/TZ ≥ AuPd/TZ ≥ Pd/TZ ≥ Au/TZ ≥ TZ). The highest activity of PdAu/TZ (80/20) can be related to the higher acid sites density of the support and also to the presence of a synergetic effect between palladium and gold. 'Operando' DRIFT allowed following the VOCs oxidation but also suggesting an interaction between the adsorbed molecule and the catalyst which decreases when the activity for oxidation reaction increases. (authors)

  3. Hybridization effects in U3T3X4 compounds. (T = Ni, Cu, Pd, Pt, Au and X = Sn, Sb)

    International Nuclear Information System (INIS)

    We report on fabrication and physical properties of ternary uranium compounds U3T3X4 with T = Ni, Cu, Pd, Pt, Au and X = Sn, Sb which crystallize in the cubic Y3Au3Sb4-type structure. A heavy-fermion behavior manifests itself in U3T3Sn4, where the electronic specific-heat coefficient increases from 90 mJ/K2molU for T = Ni and Pt to about 300 mJ/K2molU for T = Cu and Au. On the other hand, U3T3Sb4 compounds with T = Ni, Pd and Pt show a semiconducting behavior with a band gap of about 0.2 eV, whereas U3Cu3Sb4 is a metallic ferromagnet with Tc = 91 K. The wide variety of physical properties is discussed with respect to the variation in the d-f and p-f hybridization, which was deduced from the photoemission study. (author)

  4. Facile Synthesis of Ag Nanorods with No Plasmon Resonance Peak in the Visible Region by Using Pd Decahedra of 16 nm in Size as Seeds.

    Science.gov (United States)

    Luo, Ming; Huang, Hongwen; Choi, Sang-Il; Zhang, Chao; da Silva, Robson Rosa; Peng, Hsin-Chieh; Li, Zhi-Yuan; Liu, Jingyue; He, Zhike; Xia, Younan

    2015-10-27

    This article describes a seed-mediated approach to the synthesis of Ag nanorods with thin diameters and tunable aspect ratios. The success of this method is built upon our recent progress in the synthesis of Pd decahedra as uniform samples, together with controllable sizes. When used as a seed, the Pd decahedron could direct the deposition of Ag atoms along the 5-fold axis to generate a nanorod, with its diameter being determined by the lateral dimension of the seed. We were able to generate Ag nanorods with uniform diameters down to 20 nm. Under the conditions we used for growth, symmetry breaking occurred as the Ag atoms were only deposited along one side of the Pd decahedral seed to generate a Ag nanorod with the Pd seed being positioned at one of its two ends. We also systematically investigated the localized surface plasmon resonance (LSPR) properties of the Ag nanorods. With the transverse mode kept below 400 nm, the longitudinal mode could be readily tuned from the visible to the near-infrared region by varying the aspect ratio. As an important demonstration, we obtained Ag nanorods with no LSPR peak in the visible spectrum (400-800 nm), which are attractive for applications related to the fabrication of touchscreen displays, solar films, and energy-saving smart windows. PMID:26372854

  5. Dextrin-mediated synthesis of Ag NPs for colorimetric assays of Cu(2+) ion and Au NPs for catalytic activity.

    Science.gov (United States)

    Bankura, Kalipada; Rana, Dipak; Mollick, Md Masud Rahaman; Pattanayak, Sutanuka; Bhowmick, Biplab; Saha, Nayan Ranjan; Roy, Indranil; Midya, Tarapada; Barman, Gadadhar; Chattopadhyay, Dipankar

    2015-09-01

    A facile one-pot approach for rapid synthesis of silver and gold nanoparticles (Ag NPs and Au NPs) with narrow size distribution and good stability was described by reducing silver nitrate and chloroauric acid with polysaccharide dextrin. Here, dextrin was used as both a reducing and stabilizing agent for synthesis of NPs. The as-synthesized Ag NPs and Au NPs were characterized by UV-visible absorption spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The Ag NPs and Au NPs exhibited an absorption maxima at 404 and 547 nm respectively. TEM images showed NPs in the range of 8-28 nm. The crystallinity of the NPs was measured by XRD analysis. Furthermore, the as-prepared Ag NPs revealed colorimetric sensor property for detection of Cu(2+) ions based on changes in absorbance resulting from metal ion-induced aggregation of NPs or direct deposition of metal ions onto NPs. The as-prepared Au NPs exhibited a notable catalytic activity toward the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4. PMID:26143120

  6. Fast and facile preparation of CTAB based gels and their applications in Au and Ag nanoparticles synthesis

    Energy Technology Data Exchange (ETDEWEB)

    Upadhyay, Ravi Kant, E-mail: rkupadhyay85@gmail.com [Department of Chemistry, School of Natural Sciences, Shiv Nadar University, Gautam Budh Nagar, 201314 Uttar Pradesh (India); Soin, Navneet, E-mail: n.soin@bolton.ac.uk [Knowledge Centre for Materials Chemistry (KCMC), Institute for Materials Research and Innovation (IMRI), University of Bolton, Deane Road, Bolton BL3 5AB (United Kingdom); Saha, Susmita, E-mail: ssaha@bose.res.in [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700 098 (India); Barman, Anjan, E-mail: abarman@bose.res.in [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700 098 (India); Sinha Roy, Susanta, E-mail: susanta.roy@snu.edu.in [Department of Physics, School of Natural Sciences, Shiv Nadar University, Gautam Budh Nagar, 201314 Uttar Pradesh (India)

    2015-04-15

    We have demonstrated that the gel-like mesophase of Cetyltrimethylammonium bromide (CTAB) can be synthesized by judicial adjustment of water to surfactant molar ratio (W{sub 0}), without using any additional salts, gelating agents or co-surfactants. Gel formation was found to be highly dependent on the water to surfactant molar ratio (W{sub 0}), with the lowest value of W{sub 0} (41.5) resulting in rapid gel formation. Environmental scanning electron microscope (ESEM) analysis revealed that the gel was comprised of interconnected cylindrical structures. The presence of hydrogen bonding in the gel-like mesophase was confirmed by Fourier Transform Infrared spectroscopy (FTIR) analysis. Rheology measurements revealed that all the gel samples were highly viscoelastic in nature. Furthermore, Au and Ag containing CTAB gels were explored as precursors for the preparation of spherical Gold (Au) and Silver (Ag) nanoparticles using Sodium borohydride (NaBH{sub 4}) as reducing agent. The effects of NaBH{sub 4} concentration on the particle size and morphology of the Au and Ag nanoparticles have also been studied. - Highlights: • A facile synthesis of CTAB based gel-like mesophase is reported. • CTAB gels were obtained by adjusting water to surfactant molar ratio (W{sub 0}). • FTIR analysis revealed that hydrogen bonding plays a key role in gel formation. • Au, Ag nanoparticles were synthesized by using CTAB gel and NaBH{sub 4}.

  7. Effect of alloying on the electronic structure and magnetic properties of Fe, Co and Ni with Au and Ag

    Indian Academy of Sciences (India)

    Ashish Bhattacharjee; Mesbahuddin Ahmed; Abhijit Mookerjee; Amal Halder

    2003-01-01

    We use the self-consistent, augmented space recursion technique to study the electronic structure and magnetic properties of alloys of the transition metals, Fe, Co and Ni with the noble metals, Ag and Au. We analyse the effect of local environment and the hybridization between the constituent bands on the electronic and magnetic properties.

  8. Energy Reflection Coefficients for 5-10 keV He Ions Incident on Au, Ag, and Cu

    DEFF Research Database (Denmark)

    Schou, Jørgen; Sørensen, H.; Littmark, U.

    The calorimetric deuterium-film method was used for measurements of the energy reflection coefficient γ for normal incidence of 5-10 keV He ions on Cu, Ag and Au. A theoretical calculation of γ by means of transport theory gives fair agreement with the experimental results. The experimental data ...

  9. Fast and facile preparation of CTAB based gels and their applications in Au and Ag nanoparticles synthesis

    International Nuclear Information System (INIS)

    We have demonstrated that the gel-like mesophase of Cetyltrimethylammonium bromide (CTAB) can be synthesized by judicial adjustment of water to surfactant molar ratio (W0), without using any additional salts, gelating agents or co-surfactants. Gel formation was found to be highly dependent on the water to surfactant molar ratio (W0), with the lowest value of W0 (41.5) resulting in rapid gel formation. Environmental scanning electron microscope (ESEM) analysis revealed that the gel was comprised of interconnected cylindrical structures. The presence of hydrogen bonding in the gel-like mesophase was confirmed by Fourier Transform Infrared spectroscopy (FTIR) analysis. Rheology measurements revealed that all the gel samples were highly viscoelastic in nature. Furthermore, Au and Ag containing CTAB gels were explored as precursors for the preparation of spherical Gold (Au) and Silver (Ag) nanoparticles using Sodium borohydride (NaBH4) as reducing agent. The effects of NaBH4 concentration on the particle size and morphology of the Au and Ag nanoparticles have also been studied. - Highlights: • A facile synthesis of CTAB based gel-like mesophase is reported. • CTAB gels were obtained by adjusting water to surfactant molar ratio (W0). • FTIR analysis revealed that hydrogen bonding plays a key role in gel formation. • Au, Ag nanoparticles were synthesized by using CTAB gel and NaBH4

  10. Enzyme-free hydrogen peroxide sensor based on Au@Ag@C core-double shell nanocomposites

    Science.gov (United States)

    Li, Yancai; Zhang, Yayun; Zhong, Yanmei; Li, Shunxing

    2015-08-01

    The well-designed Au@Ag@C core-double shell nanocomposites were synthesized via a facile method, and were used to fabricate an enzyme-free amperometric hydrogen peroxide (H2O2) sensor. The size, shape, elementary composition and structure of the nanocomposites were characterized by transmission electron microscope (TEM), energy-dispersed spectrum (EDS) and X-ray diffraction (XRD). The outermost layer of the nanocomposites was amorphous carbon, the second layer was Ag and the core was Au. The Au@Ag@C core-double shell nanocomposites exhibit attractive activity for electrocatalytic reduction of H2O2 according to the electrochemical experiments. It also demonstrates the H2O2 sensor possess well performance with a wide linear range of 5.0 μM to 4.75 mM and a limit of detection (LOD) as low as 0.14 μM (S/N = 3). Furthermore, the interference from the common interfering species, such as glucose, ascorbic acid, dopamine and uric acid can be effectively avoided. In a word, the Au@Ag@C nanocomposites are promising candidates for enzyme-free H2O2 sensor.

  11. Effects of plasmon excitation on photocatalytic activity of Ag/TiO 2 and Au/TiO2 nanocomposites

    DEFF Research Database (Denmark)

    Sellappan, Raja; González-Posada, Fernando; Chakarov, Dinko;

    2013-01-01

    Model nanocomposite photocatalysts consisting of undoped TiO2 films with optically active Ag or Au nanoparticles (NPs) were designed, fabricated, and examined to address the role of plasmon excitations in their performance. Different composition configurations were tested in which the NPs were ei...

  12. Direct laser planting of hybrid Au-Ag/C nanostructures - nanoparticles, flakes and flowers

    CERN Document Server

    Manshina, Alina; Bashouti, Muhammad; Povolotskiy, Alexey; Petrov, Yuriy; Koshevoy, Igor; Christiansen, Silke; Tunik, Sergey; Leuchs, Gerd

    2015-01-01

    We demonstrate a new approach for forming hybrid metal/carbonaceous nanostructures in a controlled direct laser planting process. Au-Ag nanoclusters in amorphous or crystalline carbonaceous matrices are formed with different morphology: nanoparticles, nanoflakes, and nanoflowers. In contrast to other generation techniques our approach is simple, involving only a single laser-induced process transforming supramolecular complexes dissolved in solvent such as acetone, acetophenone, or dichloroethane into hybrid nanostructures in the laser-affected area of the substrate. The morphology of the hybrid nanostructures can be steered by controlling the deposition parameters, the composition of the liquid phase and the type of substrate, amorphous or crystalline. The carbonaceous phase of the hybrid nanostructures consists of hydrogenated amorphous carbon in the case of nanoparticles and of crystalline orthorhombic graphite of nanoscale thickness in the case of flakes and flowers. To the best of our knowledge this is t...

  13. Electronic transport properties of carbon chains between Au and Ag electrodes: A first-principles study

    International Nuclear Information System (INIS)

    We report first-principles calculations of the current-voltage characteristic and the conductance of carbon-based molecular wires with different length capped with sulfur ends between two metallic electrodes made of different metals. The optimized molecular structure of carbon chain in the junction is presented on the structure of polyyne. The conductance of the polyyne wires shows oscillatory behavior depending on the number of carbon atoms (triple bonds). Current rectification is found and rectification direction presents inversion with the odd and even number of carbon atoms. -- Highlights: → Au and Ag as two asymmetric electrodes. → Relaxed carbon chain structure is in the form of polyyne. → Oscillatory conductance behavior with the number of carbon atoms. → Current rectification of carbon chains in the asymmetric electrodes. → Rectification inversion with the number of carbon atoms.

  14. Antiproton production at 0 degrees for Si + A and Au + A collisions at the AGS

    International Nuclear Information System (INIS)

    We present results on antiproton production obtained in the AGS experiments E858 and preliminary results of E878. The yields of antiprotons in Si + A collisions are shown to sale with number of first collisions. The rapidity distributions for all targets (Au, Cu and Al) and both beams (si at 14.6 GeV/c and A at 11. GeV/c) have gaussian shapes peaking at yNN and with similar standard deviations. From E878 we report a difference in the shape of the antiproton rapidity distributions obtained from two samples of the data populated with central and peripheral events respectively. In A induced reactions the A dependence of the antiproton yields is small

  15. High stability of the goldalloy fullerenes: A density functional theory investigation of M12@Au20 (M = Na, Al, Ag, Sc, Y, La, Lu, and Au) clusters

    International Nuclear Information System (INIS)

    Discovering highly stable metal fullerenes such as the celebrated C60 is interesting in cluster science as they have potential applications as building blocks in new nanostructures. We here investigated the structural and electronic properties of the fullerenes M12@Au20 (M = Na, Al, Ag, Sc, Y, La, Lu, and Au), using a first-principles investigation with the density functional theory. It is found that these compound clusters possess a similar cage structure to the icosahedral Au32 fullerene. La12@Au20 is found to be particularly stable among these clusters. The binding energy of La12@Au20 is 3.43 eV per atom, 1.05 eV larger than that in Au32. The highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap of La12@Au20 is only 0.31 eV, suggesting that it should be relatively chemically reactive. (condensed matter: structural, mechanical, and thermal properties)

  16. Tailor-made Au-Ag core–shell nanoparticle 2D arrays on protein-coated graphene oxide with assembly enhanced antibacterial activity

    International Nuclear Information System (INIS)

    Water-dispersible two-dimensional (2D) assemblies of Au-Ag core–shell nanoparticles are obtained through a highly selective electroless silver deposition on pre-assembled gold nanoparticles on bovine serum albumin (BSA)-coated graphene oxide (BSA-GO). While neither BSA-GO nor AuNP-decorated BSA-GO shows any antibacterial ability, the silver-coated GO-Au nanosheets (namely GO-Au-Ag) exhibit an enhanced antibacterial activity against Gram-negative Escherichia coli (E. coli) bacteria, superior to unassembled Au-Ag nanoparticles and even ionic Ag. Such an improvement may be attributed to the increased local concentration of silver nanoparticles around a bacterium and a polyvalent interaction with the bacterial surface. In addition, the colloidal stability of this novel nano-antimicrobial against the formation of random nanoparticle aggregates guarantees a minimized activity loss of the Au-Ag nanoparticles. The antibacterial efficacy of GO-Au-Ag is less sensitive to the existence of Cl−, in comparison with silver ions, providing another advantage for wound dressing applications. Our research unambiguously reveals a strong and very specific interaction between the GO-Au-Ag nanoassembly and E. coli, which could be an important clue toward a rational design, synthesis and assembly of innovative and highly active antibacterial nanomaterials. (paper)

  17. Sonochemical synthesis of a PdAg/C electrocatalyst for oxygen reduction reaction; Sintesis sonoquimica de un electrocatalizador de PdAg/C para la reaccion de reduccion de oxigeno

    Energy Technology Data Exchange (ETDEWEB)

    Godinez-Garcia, A.; Perez-Robles, J.F. [Centro de Investigacion y de Estudios Avanzados del IPN. Santiago de Queretaro, Queretaro (Mexico)]. E-mail: jperez@qro.cinvestav.mx; Solorza-Feria, O. [CINVESTAV-IPN, Mexico, D.F. (Mexico)

    2009-09-15

    The synthesis and characterization of nanocatalysts for fuel cells has been a primary line of research for the purpose of obtaining less expensive electrocatalysts with better activity. A large variety of methods exist to synthesize useful nanoparticles as electrocatalysts. Each method generates particles with a different surface morphology and, therefore, the catalytic activity usually varies depending on which is used in the synthesis. In this work, PdAg/C electrocatalysts are synthesized with high-intensity ultrasonic irradiation and compared to those obtained using a conventional method such as reduction by NaBH{sub 4}. The study of this technique is of interest because it produces highly dispersed carbon-supported nanoparticles with very clean surfaces. Each electrocatalyst was evaluated for its oxygen reduction reaction (ORR) in acid medium with cyclic voltamperometry (CV) and rotating disc electrode (RDE). The electrocatalyst was characterized with x-ray diffraction and transmission electron microscopy (TEM). The physical characterization reveals that the electrocatalyst is composed of nanometric bimetallic aggregates. An important characteristic of the PdAg/C alloy obtained using ultrasound is better activity than that obtained by reduction with NaBH{sub 4}. [Spanish] La sintesis y caracterizacion de nanocatalizadores para celdas de combustible ha sido una de las principales lineas de investigacion, con el objetivo de obtener electrocatalizadores mas baratos y con una mejor actividad. Existen una gran variedad de metodos para sintetizar nanoparticulas utiles como electrocatalizadores, cada metodo genera particulas con una morfologia superficial diferente por lo que la actividad catalitica suele variar dependiendo de cual se utilice en la sintesis. En este trabajo se sintetizan electrocatalizadores de PdAg/C con irradiacion ultrasonica de alta intensidad y se comparan con las obtenidas con un metodo convencional como es la reduccion por NaBH{sub 4}. Esta

  18. Studies of the AgM5N45N4.5 spectrum of disordered Ag0.5Pd0.5 alloy by Auger photoelectron coincidence spectroscopy (APECS)

    International Nuclear Information System (INIS)

    Full text: The Auger electron emission process from solids is very complex, with a range of intrinsic processes producing intensity in final spectra. These processes can include the basic Auger process, initial- and final-states, shake-up/off and Coster-Kronig (CK) processes. Auger Photoelectron Coincidence Spectroscopy (APECS) is a technique to detect the Auger electron only when the 'initial' photoelectron also is detected. By counting those Auger electrons that arrive in coincidence with a photoelectron of certain binding energy, the initial state is uniquely determined, thus controlling the magnitude of various satellites of the Auger spectrum. AxPd1-x is a disordered alloy. XPS spectra indicated that the FWHM of Ag 3d5/2 increases from 0.56 eV in pure Ag to 0.77 eV in Ag0.5Pd0.5. The disorder broadening of the Ag 3d core line in AgPd is due to the spread of local potentials in the atomic cores arising from the effects of charge transfer. In this study, an effect of disorder broadening of the core level photoelectron line on the Ag MVV Auger spectra in random substituted Ag0.5Pd0.5 alloy has been investigated by APECS. Data were collected for the AgM5V45V45 Auger line in coincidence with Ag 3d photoelectron lines. It is shown that the broadening of the AgM5V45V45 line is directly associated with the presence of disorder broadening of the Ag 3d5/2 photoelectron line

  19. Brazing of zirconia to titanium using Ag-Cu and Au-Ni filler alloys

    Directory of Open Access Journals (Sweden)

    Jean S. Pimenta

    2013-12-01

    Full Text Available Advanced ceramic is usually joined to metal by the well-known direct brazing process, where costly active filler alloys can be considered a limitation. Brazing using active-metal-free filler alloy as insert between the joint components is an attempt to overcome it. The active metal diffusion from the titanium member through the bulk of molten filler to the ceramic was responsible to produce an active filler alloy in loco and promote reduction of the zirconium oxide to improve wetting on the ceramic surface. Unalloyed titanium was joined in a high-vacuum furnace (<3x10-5 mbar to yttria-tetragonal zirconia polycristals (Y-TZP and zirconia partially stabilized with magnesia (Mg-PSZ, where commercial fillers Ag-28Cu and Au-18Ni with respective thermal cycles were evaluated. Helium gas leak detection test was performed at the ceramic/metal interface at room temperature; samples from reliable vacuum tight joints were examined by microstructural analysis techniques and energy dispersive X-ray analysis at the joint cross-section. Tight joints were produced with eutectic Ag-Cu filler, revealing an intermetallic layer and a dark reaction layer near the ceramic surface; titanium diffusion was efficient for superficial chemical interactions between individual components. Brazing joints were also tested using three-point flexure testing.

  20. Synthesis and Optical Properties of Au-Ag Alloy Nanoclusters with Controlled Composition

    Directory of Open Access Journals (Sweden)

    J. F. Sánchez-Ramírez

    2008-01-01

    Full Text Available Colloidal solid-solution-like Au-Ag alloy nanoclusters of different compositions were synthesized through citrate reduction of mixed metal ions of low concentrations, without using any other protective or capping agents. Optical absorption of the alloy nanoclusters was studied both theoretically and experimentally. The position of the surface plasmon resonance (SPR absorption band of the nanoclusters could be tuned from 419 nm to 521 nm through the variation of their composition. Considering effective dielectric constant of the alloy, optical absorption spectra for the nanoclusters were calculated using Mie theory, and compared with the experimentally obtained spectra. Theoretically obtained optical spectra well resembled the experimental spectra when the true size distribution of the nanoparticles was considered. High-resolution transmission electron microscopy (HREM, high-angle annular dark field (HAADF imaging, and energy dispersive spectroscopy (EDS revealed the true alloy nature of the nanoparticles with nominal composition being preserved. The synthesis technique can be extended to other bimetallic alloy nanoclusters containing Ag.

  1. Focused-ion-beam-fabricated Au nanorods coupled with Ag nanoparticles used as surface-enhanced Raman scattering-active substrate for analyzing trace melamine constituents in solution

    Energy Technology Data Exchange (ETDEWEB)

    Sivashanmugan, Kundan [Department of Materials Science and Engineering, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan (China); Liao, Jiunn-Der, E-mail: jdliao@mail.ncku.edu.tw [Department of Materials Science and Engineering, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan (China); Center for Micro/Nano Science and Technology, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan (China); Liu, Bernard Haochih; Yao, Chih-Kai [Department of Materials Science and Engineering, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan (China)

    2013-10-24

    Graphical abstract: -- Highlights: •Well-ordered Au-nanorod array with a controlled tip ring diameter (Au{sub N}Rs{sub d}) is made by focused ion beam. •Au{sub N}Rs{sub d} coupled with Ag nanoparticles (Ag NPs/Au{sub N}Rs{sub d}) is competent to sense target molecules in a solution. •Ag NPs/Au{sub N}Rs{sub d} SERS active substrate can detect a single molecule of crystal violet. •Ag NPs/Au{sub N}Rs{sub d} as a SERS-active substrate can distinguish melamine contaminants at low concentrations (e.g., 10{sup −12} M). -- Abstract: A well-ordered Au-nanorod array with a controlled tip ring diameter (Au{sub N}Rs{sub d}) was fabricated using the focused ion beam method. Au{sub N}Rs{sub d} was then coupled with Ag nanoparticles (Ag NPs) to bridge the gaps among Au nanorods. The effect of surface-enhanced Raman scattering (SERS) on Au{sub N}Rs{sub d} and Ag NPs/Au{sub N}Rs{sub d} was particularly verified using crystal violet (CV) as the molecular probe. Raman intensity obtained from a characteristic peak of CV on Au{sub N}Rs{sub d} was estimated by an enhancement factor of ≈10{sup 7} in magnitude, which increased ≈10{sup 12} in magnitude for that on Ag NPs/Au{sub N}Rs{sub d}. A highly SERS-active Ag NPs/Au{sub N}Rs{sub d} was furthermore applied for the detection of melamine (MEL) at very low concentrations. Raman-active peaks of MEL (10{sup −3} to 10{sup −12} M) in water or milk solution upon Au{sub N}Rs{sub d} or Ag NPs/Au{sub N}Rs{sub d} were well distinguished. The peaks at 680 and 702 cm{sup −1} for MEL molecules were found suitable to be used as the index for sensing low-concentration MEL in a varied solution, while that at 1051 cm{sup −1} was practical to interpret MEL molecules in water or milk solution bonded with Au (i.e., Au{sub N}Rs{sub d}) or Ag (i.e., Ag NPs/Au{sub N}Rs{sub d}) surface. At the interface of Ag NPs/Au{sub N}Rs{sub d} and MEL molecules in milk solution, a laser-induced electromagnetic field or hotspot effect was produced and

  2. [Au]/[Pd] Multicatalytic Processes: Direct One-Pot Access to Benzo[ c ]chromenes and Benzo[ b ]furans

    KAUST Repository

    Oonishi, Yoshihiro

    2014-08-28

    A new synthetic protocol that combines the advantages offered by eco-friendly solvent-free reactions and sequential transformations is reported. This strategy offers straightforward access to benzo[c]chromenes and benzo[b]furans from commercially available starting materials. This two-step, one-pot strategy consists of an Au-catalyzed hydrophenoxylation process followed by Pd-catalyzed C-H activation or Mizoroki-Heck reactions. The selectivity of the process towards C-H activation or Mizoroki-Heck reaction can be easily tuned. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Investigation of nanostructured Pd-Ag/n-ZnO thin film based Schottky junction for methane sensing

    Science.gov (United States)

    Roy, S.; Das, S.; Sarkar, C. K.

    2016-07-01

    Undoped nanocrystalline n-type ZnO thin film was deposited by chemical deposition technique on a thermally oxidized p-Si (~5 Ω cm resistivity and orientation) substrate. Formation of stable zinc oxide thin film was confirmed by two-dimensional X-Ray Diffraction (XRD) and EDX analysis. The average crystallite size of the ZnO sample was evaluated as ~50 nm. The surface was characterized by Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) that confirm the formation of nanocrystalline (grain size ~50 nm) ZnO thin film with surface roughness of ~100 nm. Good conversion of precursor into ZnO thin film in the chemical deposition method was evident by Fourier Transform Infrared Spectroscopy (FTIR). A small peak at 479 cm-1was observed in the FTIR spectrum confirming the formation of quartzite structure of the ZnO. The band gap (~3.44 eV) of the material was calculated from the optical absorption spectroscopy. To prepare Pd-Ag/n-ZnO Schottky junction, Pd-Ag contacts were taken by electron beam evaporation method. I-V characteristics of the junction were studied at different temperatures in inert and reducing ambient (N2 and N2 + CH4) with turn on voltage of around 0.2 V. The parameters like ideality factor ( η), saturation current ( I 0), series resistance ( Rs), and barrier height ( Φ BO) of the junction were calculated in the temperature range 50-200 °C in N2 as well as in 1 % CH4 + N2 ambient. It was observed that the ideality factor decreases in the temperature range 50-200 °C ( η = 12.34 at 50 °C and η = 1.52 at 200 °C) in N2 ambient and η = 1.18 in N2 +CH4 ambient at 200 °C. Schottky Barrier Height ( Φ BO) of the Pd-Ag/n-ZnO junction was found to increase with temperature. A close observation of Pd-Ag/n-ZnO junction in the presence of methane was performed to appreciate its application as methane sensor. The sensing mechanism was illustrated by a simplified energy band diagram.

  4. Rapid Synthesis of Highly Monodisperse Au x Ag 1− x Alloy Nanoparticles via a Half-Seeding Approach

    KAUST Repository

    Chng, Ting Ting

    2011-05-03

    Gold-silver alloy AuxAg1-x is an important class of functional materials promising new applications across a wide array of technological fields. In this paper, we report a fast and facile synthetic protocol for preparation of highly monodisperse AuxAg1-x alloy nanoparticles in the size range of 3-6 nm. The precursors employed in this work are M(I)-alkanethiolates (M = Au and Ag), which can be easily prepared by mixing common chemicals such as HAuCl4 or AgNO3 with alkanethiols at room temperature. In this half-seeding approach, one of the M(I)-alkanethiolates is first heated and reduced in oleylamine solvent, and freshly formed metal clusters will then act as premature seeds on which both the first and second metals (from M(I)-alkanethiolates, M = Au and Ag) can grow accordingly without additional nucleation and thus achieve high monodispersity for product alloy nanoparticles. Unlike in other prevailing methods, both Au and Ag elements present in these solid precursors are in the same monovalent state and have identical supramolecular structures, which may lead to a more homogeneous reduction and complete interdiffusion at elevated reaction temperatures. When the M(I)-alkanethiolates are reduced to metallic forms, the detached alkanethiolate ligands will serve as capping agent to control the growth. More importantly, composition, particle size, and optical properties of AuxAg1-x alloy nanoparticles can be conveniently tuned with this approach. The optical limiting properties of the prepared particles have also been investigated at 532 and 1064 nm using 7 ns laser pulses, which reveals that the as-prepared alloy nanoparticles exhibit outstanding broadband optical limiting properties with low thresholds. © 2011 American Chemical Society.

  5. Organic-Inorganic Hybrid Nanoparticles for Bacterial Inhibition: Synthesis and Characterization of Doped and Undoped ONPs with Ag/Au NPs

    Directory of Open Access Journals (Sweden)

    Carlos Alberto Huerta Aguilar

    2015-04-01

    Full Text Available Organic nanoparticles (ONPs of lipoic acid and its doped derivatives ONPs/Ag and ONPs/Au were prepared and characterized by UV-Visible, EDS, and TEM analysis. The antibacterial properties of the ONPs ONPs/Ag and ONPs/Au were tested against bacterial strains (Staphylococcus aureus, Bacillus cereus, Escherichia coli and Salmonella typhi. Minimal Inhibitory Concentration (MIC and bacterial growth inhibition tests show that ONPs/Ag are more effective in limiting bacterial growth than other NPs, particularly, for Gram positive than for Gram-negative ones. The order of bacterial cell growth inhibition was ONPs/Ag > ONPs > ONPs/Au. The morphology of the cell membrane for the treated bacteria was analyzed by SEM. The nature of bond formation of LA with Ag or Au was analyzed by molecular orbital and density of state (DOS using DFT.

  6. Bi-SERS sensing and enhancement by Au-Ag bimetallic non-alloyed nanoparticles on amorphous and crystalline silicon substrate.

    Science.gov (United States)

    Tan, Chee Leong; Lee, Soo Kyung; Lee, Yong Tak

    2015-03-01

    We have demonstrated Au-Ag bimetallic non-alloy nanoparticles (BNNPs) on thin a-Si film and c-Si substrate for high SERS enhancement, low cost, high sensitivity and reproducible SERS substrate with bi-SERS sensing properties where two different SERS peak for Au NPs and Ag NPs are observed on single SERS substrate. The isolated Au-Ag bimetallic NPs, with uniform size and spacing distribution, are suitable for uniform high density hotspot SERS enhancement. The SERS enhancement factor of Au-Ag BNNPs is 2.9 times higher compared to Ag NPs on similar substrates due to the increase of the localized surface plasmon resonance effect. However there is a decrement of SERS peak intensity at specific wavenumbers when the surrounding refractive index increases due to out-phase hybridization of Au NPs. The distinct changes of the two different SERS peaks on single Au-Ag BNNPs SERS substrate due to Au and Ag NPs independently show possible application for bi-molecular sensing. PMID:25836846

  7. Strong enhancement of the electrochemiluminescence of luminol by AuAg and PtAg alloy nanoclusters, and its sensitization by phenolic artificial oestrogens

    International Nuclear Information System (INIS)

    This paper reports on the synthesis of AuAg and PtAg alloy nanoclusters (NCs) and their enhancement effect on the electrochemiluminescence (ECL) of luminol. The conditions of synthesis were optimized, and the structure and properties of the NCs were characterized by X-ray diffraction, transmission electron microscopy, electrochemistry, and optical spectroscopy. The NCs are found to intensify (by up to 20 times) the ECL of luminol in solution of pH 8.5. This finding can largely extend the useful pH range of the ECL of luminol. The enhanced ECL is strongly affected by oxygen and hydrogen peroxide, and the mechanism of enhancement is attributed to the accelerated production of reactive oxygen species. The enhanced ECL is also affected by phenolic artificial estrogens, and this was used for their determination with detection limits as low as 700 pg L−1 (with AuAg) and 1.6 ng L−1 (with PtAg). The method was applied to the determination of such estrogens in egg samples using diethylstilbestrol as a reference substance. (author)

  8. Influence of silver on the glycerol electro-oxidation over AuAg/C catalysts in alkaline medium: a cyclic voltammetry and in situ FTIR spectroscopy study

    International Nuclear Information System (INIS)

    In the present work, we investigated the influence of silver on the glycerol electro-oxidation over carbon-supported AuAg catalysts by cyclic voltammetry and in situ FTIR spectroscopy. We observed that the presence of Ag in the bimetallic materials provided a more efficient catalyst in terms of the ability to electro-oxidize glycerol at relatively low potentials. On the other hand, the bimetallic catalysts were found to be less promising than the Au/C catalyst with respect to the reaction rate. Ag addition influenced the mechanism of glycerol electro-oxidation, favoring the C-C-C bond breaking, as evidenced by the selective formation of formic acid on the bimetallic catalysts. The impact of Ag on the glycerol electro-oxidation over AuAg/C may be driven by electronic modifications and Ag segregation on the catalysts surface

  9. Synthesis and photo physical properties of Au - Ag (core - shell) nanoparticles disperse in poly vinyl alcohol matrix

    International Nuclear Information System (INIS)

    Synthesis of core - shell (Au - Ag) nanoparticle with varying silver composition has been carried out in aqueous poly vinyl alcohol (PVA) matrix. Core gold nanoparticle (∼15 nm) has been synthesized through seed-mediated growth process. Synthesis of silver shell with increasing thickness (∼1–5 nm) has been done by reducing Ag+ over the gold sol in the presence of mild reducing ascorbic acid. Characterization of Au - Ag nanoparticles has been done by UV–Vis, High resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDX) spectroscopic study. The blue shift of surface plasmon resonance (SPR) band with increasing mole fraction of silver has been interpreted due to dampening of core, i.e. Au SPR by Ag. The dependence of nonlinear optical response of spherical core - shell nanoparticles has been investigated as a function of relative composition of each metal. Simulation of SPR extinction spectra based on quasi-static theory is done. A comparison of our experimental and the simulated extinction spectra using quasi-static theory of nanoshell suggests that our synthesized bimetallic particles have core - shell structure rather than bimetallic alloy particles.

  10. Ultrasensitive electrochemical sensor for Hg(2+) by using hybridization chain reaction coupled with Ag@Au core-shell nanoparticles.

    Science.gov (United States)

    Li, Zongbing; Miao, Xiangmin; Xing, Ke; Peng, Xue; Zhu, Aihua; Ling, Liansheng

    2016-06-15

    A novel electrochemical biosensor for Hg(2+) detection was reported by using DNA-based hybridization chain reaction (HCR) coupled with positively charged Ag@Au core-shell nanoparticles ((+)Ag@Au CSNPs) amplification. To construct the sensor, capture probe (CP ) was firstly immobilized onto the surface of glass carbon electrode (GCE). In the presence of Hg(2+), the sandwiched complex can be formed between the immobilized CP on the electrode surface and the detection probe (DP) modified on the gold nanoparticles (AuNPs) based on T-Hg(2+)-T coordination chemistry. The carried DP then opened two ferrocene (Fc) modified hairpin DNA (H1 and H2) in sequence and propagated the happen of HCR to form a nicked double-helix. Numerous Fc molecules were formed on the neighboring probe and produced an obvious electrochemical signal. Moreover, (+)Ag@Au CSNPs were assembly onto such dsDNA polymers as electrochemical signal enhancer. Under optimal conditions, such sensor presents good electrochemical responses for Hg(2+) detection with a detection limit of 3.6 pM. Importantly, the methodology has high selectivity for Hg(2+) detection. PMID:26852203

  11. Electrochemical and surface studies on the passivity of a dental Pd-based casting alloy in alkaline sulphide solution

    International Nuclear Information System (INIS)

    The corrosion and tarnish behavior of a dental casting Pd-25Ag-18Cu-12Au alloy in 0.1% Na2S solution at 37 deg. C was investigated using potentiodynamic polarization and spectrocolorimetric techniques. The surface film was characterized by X-ray photoelectron spectroscopy (XPS). This alloy exhibited markedly higher resistance to corrosion and tarnish than did the Ag-20Pd-18Cu-12Au alloy in current clinical use. XPS spectra indicated the presence of a thin sulphide film composed of PdS. It was found that the PdS film is very protective and is responsible for the passivity of the Pd-25Ag-18Cu-12Au alloy in 0.1% Na2S solution

  12. Solvent-Mediated Eco-Friendly Synthesis and Characterization of Monodispersed Bimetallic Ag/Pd Nano composites for Sensing and Raman Scattering Applications

    International Nuclear Information System (INIS)

    The solvent-mediated eco-friendly monodispersed Ag/Pd bimetallic nano composites (BNCs) having thick core and thin shell have been prepared through novel green chemical solvent reduction method. Reducing solvent, dimethyl formamide (DMF) is employed for the controlled green synthesis. Characterization of the synthesized Ag/Pd BNCs has been done by x-ray diffraction (XRD) studies, high-resolution scanning electron microscopy (HR-SEM), energy-dispersive X-ray analysis (EDX), and high-resolution transmission electron microscopy (HR-TEM) with selected area electron diffraction (SAED) pattern. The nature of the interaction of L-cysteine with Ag/Pd BNCs has been studied by using surface plasmon spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), cyclic voltammetry (CV), and theoretical methods.

  13. X-ray fluorescence determination of Au, Pd and Pt from chloride solutions after preconcentration on cellulose filters

    International Nuclear Information System (INIS)

    The aim of this work was synthesis of new sorption cellulose filters for dynamic preconcentration of Au, Pd and Pt from chloride solutions and subsequent XRF determination of these elements on the filters. New filters were prepared by impregnation of a filter paper with solution of tri-n-octylamine and paraffin in hexane (TOA-filters). The effect of paraffin and TOA concentration in hexane on a content of nitrogen in a filter was studied. It was found that Au(III), Pd(II) and Pt(IV) were quantitatively recovered on the TOA-filters (filtering surface diameter of 23 mm, thickness of 0.15 mm) from 0.5 - 1 M HCl at a flow rates of 2-5 ml min-1 from 10-100 ml of solution. The mathematical model of sorption dynamics was offered for the estimation of potential possibilities of new impregnated sorbents and for the evaluation of optimum dynamic conditions allowing to achieve of maximum concentration efficiency (CEmax). The elements were determined directly on the filters by XRF spectrometer. Palladium was also determined on the TOA-filters after formation of coloured compounds of metal with 4-(2-pyridylazo)resorcinol (PAR) by diffuse reflectance spectroscopy with the calculation of calorimetric characteristics and using test-scale. (authors)

  14. Role of different Pd/Pt ensembles in determining CO chemisorption on Au-based bimetallic alloys: A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Ham, Hyung Chul, E-mail: hchahm@kist.re.kr [Department of Chemical Engineering, The University of Texas at Austin, Austin, TX 78712 (United States); Fuel Cell Research Center, Korea Institute of Science and Technology, Seoul (Korea, Republic of); Manogaran, Dhivya [Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, TX 78712 (United States); Hwang, Gyeong S., E-mail: gshwang@che.utexas.edu [Department of Chemical Engineering, The University of Texas at Austin, Austin, TX 78712 (United States); Han, Jonghee; Kim, Hyoung-Juhn; Nam, Suk Woo; Lim, Tae Hoon [Fuel Cell Research Center, Korea Institute of Science and Technology, Seoul (Korea, Republic of)

    2015-03-30

    Graphical abstract: - Highlights: • Pd ensembles greatly reduce CO adsorption energy as compared to Pt ensembles. • The steeper potential energy surface of CO adsorption in Pd(1 1 1) than in Pt(1 1 1). • Switch of binding site preference in ensembles is key to determining CO adsorption. • Opposite electronic (ligand) effect in Pd and Pt ensemble. - Abstract: Using spin-polarized density functional calculations, we investigate the role of different Pd/Pt ensembles in determining CO chemisorption on Au-based bimetallic alloys through a study of the energetics, charge transfer, geometric and electronic structures of CO on various Pd/Pt ensembles (monomer/dimer/trimer/tetramer). We find that the effect of Pd ensembles on the reduction of CO chemisorption energy is much larger than the Pt ensemble case. In particular, small-sized Pd ensembles like monomer show a substantial reduction of CO chemisorption energy compared to the pure Pd (1 1 1) surface, while there are no significant size and shape effects of Pt ensembles on CO chemisorption energy. This is related to two factors: (1) the steeper potential energy surface (PES) of CO in Pd (1 1 1) than in Pt (1 1 1), indicating that the effect of switch of binding site preference on CO chemisorption energy is much larger in Pd ensembles than in Pt ensembles, and (2) down-shift of d-band in Pd ensembles/up-shift of d-band in Pt ensembles as compared to the corresponding pure Pd (1 1 1)/Pt (1 1 1) surfaces, suggesting more reduced activity of Pd ensembles toward CO adsorption than the Pt ensemble case. We also present the different bonding mechanism of CO on Pd/Pt ensembles by the analysis of orbital resolved density of state.

  15. Role of different Pd/Pt ensembles in determining CO chemisorption on Au-based bimetallic alloys: A first-principles study

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Pd ensembles greatly reduce CO adsorption energy as compared to Pt ensembles. • The steeper potential energy surface of CO adsorption in Pd(1 1 1) than in Pt(1 1 1). • Switch of binding site preference in ensembles is key to determining CO adsorption. • Opposite electronic (ligand) effect in Pd and Pt ensemble. - Abstract: Using spin-polarized density functional calculations, we investigate the role of different Pd/Pt ensembles in determining CO chemisorption on Au-based bimetallic alloys through a study of the energetics, charge transfer, geometric and electronic structures of CO on various Pd/Pt ensembles (monomer/dimer/trimer/tetramer). We find that the effect of Pd ensembles on the reduction of CO chemisorption energy is much larger than the Pt ensemble case. In particular, small-sized Pd ensembles like monomer show a substantial reduction of CO chemisorption energy compared to the pure Pd (1 1 1) surface, while there are no significant size and shape effects of Pt ensembles on CO chemisorption energy. This is related to two factors: (1) the steeper potential energy surface (PES) of CO in Pd (1 1 1) than in Pt (1 1 1), indicating that the effect of switch of binding site preference on CO chemisorption energy is much larger in Pd ensembles than in Pt ensembles, and (2) down-shift of d-band in Pd ensembles/up-shift of d-band in Pt ensembles as compared to the corresponding pure Pd (1 1 1)/Pt (1 1 1) surfaces, suggesting more reduced activity of Pd ensembles toward CO adsorption than the Pt ensemble case. We also present the different bonding mechanism of CO on Pd/Pt ensembles by the analysis of orbital resolved density of state

  16. Diffusion of Ag, Au and Cs implants in MAX phase Ti{sub 3}SiC{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Weilin, E-mail: weilin.jiang@pnnl.gov [Pacific Northwest National Laboratory, Richland, WA (United States); Henager, Charles H.; Varga, Tamas; Jung, Hee Joon; Overman, Nicole R. [Pacific Northwest National Laboratory, Richland, WA (United States); Zhang, Chonghong; Gou, Jie [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China)

    2015-07-15

    MAX phases (M: early transition metal; A: elements in group 13 or 14; X: C or N), such as titanium silicon carbide (Ti{sub 3}SiC{sub 2}), have a unique combination of both metallic and ceramic properties, which make them attractive for potential nuclear applications. Ti{sub 3}SiC{sub 2} has been considered as a possible fuel cladding material. This study reports on the diffusivities of fission product surrogates (Ag and Cs) and a noble metal Au (with diffusion behavior similar to Ag) in this ternary compound at elevated temperatures, as well as in dual-phase nanocomposite of Ti{sub 3}SiC{sub 2}/3C-SiC and polycrystalline CVD 3C-SiC for behavior comparisons. Samples were implanted with Ag, Au or Cs ions and characterized with various methods, including X-ray diffraction, electron backscatter diffraction, energy dispersive X-ray spectroscopy, Rutherford backscattering spectrometry, helium ion microscopy, and transmission electron microscopy. The results show that in contrast to immobile Ag in 3C-SiC, there is a significant outward diffusion of Ag in Ti{sub 3}SiC{sub 2} within the dual-phase nanocomposite during Ag ion implantation at 873 K. Similar behavior of Au in polycrystalline Ti{sub 3}SiC{sub 2} was also observed. Cs out-diffusion and release from Ti{sub 3}SiC{sub 2} occurred during post-implantation thermal annealing at 973 K. This study suggests caution and further studies in consideration of Ti{sub 3}SiC{sub 2} as a fuel cladding material for advanced nuclear reactors operating at very high temperatures.

  17. Room temperature hydrogen generation from hydrolysis of ammonia-borane over an efficient NiAgPd/C catalyst

    KAUST Repository

    Hu, Lei

    2014-12-01

    NiAgPd nanoparticles are successfully synthesized by in-situ reduction of Ni, Ag and Pd salts on the surface of carbon. Their catalytic activity was examined in ammonia borane (NH3BH3) hydrolysis to generate hydrogen gas. This nanomaterial exhibits a higher catalytic activity than those of monometallic and bimetallic counterparts and a stoichiometric amount of hydrogen was produced at a high generation rate. Hydrogen production rates were investigated in different concentrations of NH3BH3 solutions, including in the borates saturated solution, showing little influence of the concentrations on the reaction rates. The hydrogen production rate can reach 3.6-3.8 mol H2 molcat -1 min-1 at room temperature (21 °C). The activation energy and TOF value are 38.36 kJ/mol and 93.8 mol H2 molcat -1 min-1, respectively, comparable to those of Pt based catalysts. This nanomaterial catalyst also exhibits excellent chemical stability, and no significant morphology change was observed from TEM after the reaction. Using this catalyst for continuously hydrogen generation, the hydrogen production rate can be kept after generating 6.2 L hydrogen with over 10,000 turnovers and a TOF value of 90.3 mol H2 molcat -1 min-1.

  18. Development of Pd-Ag Compostie Membrane for Separation of Hydrogen at Elevated Temperature

    Energy Technology Data Exchange (ETDEWEB)

    Shamsuddin Ilias

    2009-02-28

    Pd-based membrane reactor offers the possibility of combining reaction and separation in a single operation at high temperatures to overcome the equilibrium limitations experienced in conventional reactor configurations. In this project to develop a defect-free and hermally-stable Pd-film on microporous stainless steel (MPSS) support for H2-separation and membrane reactor applications, the electroless plating process was revisited with an aim to improve the membrane morphology. Specifically, this study includes; (a) an improvement f activation step using Pulse Laser Deposition (PLD), (b) development of a novel surfactant induced electroless plating (SIEP) for depositing robust Pd-film on microporous support, and (c) application of Pd-membrane as membrane reactor in steam methanol reforming (SMR) reactions.

  19. DNA origami based Au-Ag-core-shell nanoparticle dimers with single-molecule SERS sensitivity

    Science.gov (United States)

    Prinz, J.; Heck, C.; Ellerik, L.; Merk, V.; Bald, I.

    2016-03-01

    DNA origami nanostructures are a versatile tool to arrange metal nanostructures and other chemical entities with nanometer precision. In this way gold nanoparticle dimers with defined distance can be constructed, which can be exploited as novel substrates for surface enhanced Raman scattering (SERS). We have optimized the size, composition and arrangement of Au/Ag nanoparticles to create intense SERS hot spots, with Raman enhancement up to 1010, which is sufficient to detect single molecules by Raman scattering. This is demonstrated using single dye molecules (TAMRA and Cy3) placed into the center of the nanoparticle dimers. In conjunction with the DNA origami nanostructures novel SERS substrates are created, which can in the future be applied to the SERS analysis of more complex biomolecular targets, whose position and conformation within the SERS hot spot can be precisely controlled.DNA origami nanostructures are a versatile tool to arrange metal nanostructures and other chemical entities with nanometer precision. In this way gold nanoparticle dimers with defined distance can be constructed, which can be exploited as novel substrates for surface enhanced Raman scattering (SERS). We have optimized the size, composition and arrangement of Au/Ag nanoparticles to create intense SERS hot spots, with Raman enhancement up to 1010, which is sufficient to detect single molecules by Raman scattering. This is demonstrated using single dye molecules (TAMRA and Cy3) placed into the center of the nanoparticle dimers. In conjunction with the DNA origami nanostructures novel SERS substrates are created, which can in the future be applied to the SERS analysis of more complex biomolecular targets, whose position and conformation within the SERS hot spot can be precisely controlled. Electronic supplementary information (ESI) available: Additional information about materials and methods, designs of DNA origami templates, height profiles, additional SERS spectra, assignment of DNA

  20. Effect of long-range order on elastic properties of Pd0.5Ag0.5 alloy from first principles

    International Nuclear Information System (INIS)

    The effect of long-range order on single-crystal elastic constants of Pd0.5Ag0.5 alloy has been investigated using first-principles electronic structure calculations. The lowest energy among the considered ordered, partially ordered, and disordered structures is found to be the L11 layered structure, which is formed by alternate (111) Pd and Ag layers. The ordering effect is found to follow a clear trend: in contrast to the disordered phase, for which the Ka and Kc compressibilities are equal, the L11 structure becomes less compressible along the c axis than along the a axis.

  1. Electrochemical sensor for detection of hydrazine based on Au@Pd core–shell nanoparticles supported on amino-functionalized TiO2 nanotubes

    International Nuclear Information System (INIS)

    In this paper, we reported a simple strategy for synthesizing well-defined TiO2NTs–Au@Pd hybrid nanostructures with prior TiO2 nanotube functionalization (F-TiO2NTs). TiO2NTs with larger surface area (BET surface area is 184.9 m2 g−1) were synthesized by hydrothermal method, and the NTs are anatase phase with a range of 2–3 μm in length and 30–50 nm in diameter after calcined at 400 °C for 3 h. 3-Aminopropyl-trimethoxysilane (APTMS) as a coupling agent was reacted with the surface hydroxyl groups as anchoring sites for flower-shaped bimetallic Au@Pd nanostructures, self-assembling amine functionality on the surface of TiO2NTs. Note that two faces at the interface between F-TiO2NTs with (004) plane and Au@Pd nanostructures with (111) one of cubic Au and Pd nanoparticles are compatible, benefiting to the charge transfer between two components due to their crystalline coordination. The results showed that as-prepared F-TiO2NTs–Au@Pd hybrid nanostructures modified glassy carbon electrode (GCE) exhibits high electrocatalytic activity toward hydrazine (N2H4) at low potential and a linear response from 0.06 to 700 μM with the detection limit for N2H4 was found to be 1.2 × 10−8 M (S/N = 3). Based on scan rate effect during the hydrazine oxidation, it indicates that the number of electrons transferred in the rate-limiting step is 1, and a transfer coefficient (α) is estimated as 0.73. The self-assembled F-TiO2NTs–Au@Pd hybrid nanostructures as enhanced materials present excellent electrocatalytic activity, fast response, highly sensitive and have a promising application potential in nonenzymatic sensing. - Highlights: • Flower Au@Pd nanoparticles -TiO2 nanotubes (NTs) hybrid nanostructures were prepared by a self-assembled technique. • (004) plane of TiO2NTs and (111) one of Au@Pd nanoparticles at the interface are compatible. • The electrochemical sensor exhibits high activity toward hydrazine (N2H4)

  2. Studies of nanocrystalline Pd alloy films coated by electroless deposition

    International Nuclear Information System (INIS)

    The microstructures of thin coating films of pure palladium and palladium alloys deposited from organic electrolytes onto different metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005-1 μm thick films with high adhesive strength to the substrate surface. X-ray spectral analysis, X-ray phase analysis, transmission and scanning electron microscopy were used to determine the composition and structure of alloy coatings of binary systems: Pd-Au, Pd-Ag, Pd-Ni, Pd-Pb, and ternary system Pd-Au-Ni. The coatings of Pd-Au, Pd-Ag, and Pd-Ni have a solid solution structure, whereas Pd-Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11-35 nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed.

  3. In situ spectroscopy of catalytically active surfaces: FTIR and EXAFS studies of CO oxidation on Pd and Au nanoparticles

    International Nuclear Information System (INIS)

    This thesis was aiming at a comprehensive investigation of the reaction mechanism of CO oxidation, applying in situ Fourier Transform Infrared (FTIR) Spectroscopy and X- Ray Absorption Spectroscopy (XAS) under reaction conditions to different industrial-grade noble metal catalysts. For alumina supported palladium nanoparticles (∼2 and 5 nm) variable oxidative pre-treatments were utilized to identify and characterize palladium (sub)oxide species in different oxidation states. In situ EXAFS and in situ FTIR spectroscopy clearly demonstrated that such substoichiometric palladiumoxides PdOx (x<1) were also present during the CO oxidation reaction. Although they may contribute to activity, the highest catalytic activity was assigned to metallic palladium. The relatively high activity of the substoichiometric palladiumoxides (as compared to fully oxidized palladium(II)oxide) was attributed to their reducibility under technically relevant conditions by CO. The study of CO oxidation on Pd/Al2O3 indicated a coexistence of metallic Pd and PdOx under reaction conditions, with metallic palladium being essential for the activation of CO and molecular O2. Under specific reaction conditions this resulted in oscillatory behavior. The mechanism of CO oxidation on titania supported gold nanoparticles (∼4 nm) was also investigated. In situ FTIR spectroscopy identified metallic gold as CO adsorption site, whereas the oxygen adsorption site was located on the titania support. Adsorption experiments with isotopically labelled 13C18O demonstrated the involvement of hydroxyl groups of the titania support in the catalytic reaction. This explained the increase in catalytic activity upon addition of small amounts of water: water dissociates on titania producing an increased number of terminal OH groups on the catalyst surface. The results suggest a 'phase boundary-mechanism' of CO oxidation on Au/TiO2, with the reaction taking place at the oxide/metal interface. (author)

  4. Broadband light absorption enhancement in dye-sensitized solar cells with Au-Ag alloy popcorn nanoparticles

    Science.gov (United States)

    Xu, Qi; Liu, Fang; Liu, Yuxiang; Cui, Kaiyu; Feng, Xue; Zhang, Wei; Huang, Yidong

    2013-07-01

    In this paper, we present an investigation on the use of Au-Ag alloy popcorn-shaped nanoparticles (NPs) to realise the broadband optical absorption enhancement of dye-sensitized solar cells (DSCs). Both simulation and experimental results indicate that compared with regular plasmonic NPs, such as nano-spheres, irregular popcorn-shaped alloy NPs exhibit absorption enhancement over a broad wavelength range due to the excitation of localized surface plasmons (LSPs) at different wavelengths. The power conversion efficiency (PCE) of DSCs is enhanced by 16% from 5.26% to 6.09% by incorporating 2.38 wt% Au-Ag alloy popcorn NPs. Moreover, by adding a scattering layer on the exterior of the counter electrode, the popcorn NPs demonstrate an even stronger ability to increase the PCE by 32% from 5.94% to 7.85%, which results from the more efficient excitation of the LSP mode on the popcorn NPs.

  5. Fano effect in the angle-integrated valence band photoemission of the noble metals Cu, Ag, and Au

    International Nuclear Information System (INIS)

    Results of a combined experimental and theoretical investigation on the Fano-effect in the angle-integrated valence band photoemission of the noble metals are presented. In line with the fact that the Fano-effect is caused by the spin-orbit-coupling, the observed spin polarization of the photocurrent was found to be the more pronounced the higher the atomic number of the element investigated. The ratio of the normalized spin difference curves, however, agreed only for Cu and Ag with the ratio of the corresponding spin-orbit coupling strength parameters. The deviation from this expected behavior in the case of Au could be explained by the properties of individual d-p- and d-f-contributions to the total spin difference curves, that were found to be quite different for Au compared to Cu and Ag

  6. Optimization of Pt and Pd Displacement Process of Au Reduced Solution

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    The question existed in the displacement of platinum and palladium from Au reduced solution was analyzed. The process optimization scheme was put forward and adopted to practice and has achieved a good result.

  7. Broadband light absorption enhancement in dye-sensitized solar cells with Au-Ag alloy popcorn nanoparticles

    OpenAIRE

    Qi Xu; Fang Liu; Yuxiang Liu; Kaiyu Cui; Xue Feng; , Wei Zhang; Yidong Huang

    2013-01-01

    In this paper, we present an investigation on the use of Au-Ag alloy popcorn-shaped nanoparticles (NPs) to realise the broadband optical absorption enhancement of dye-sensitized solar cells (DSCs). Both simulation and experimental results indicate that compared with regular plasmonic NPs, such as nano-spheres, irregular popcorn-shaped alloy NPs exhibit absorption enhancement over a broad wavelength range due to the excitation of localized surface plasmons (LSPs) at different wavelengths. The ...

  8. Fluid inclusion chemistry of adularia-sericite epithermal Au-Ag deposits of the southern Hauraki Goldfield, New Zealand

    Science.gov (United States)

    Simpson, Mark P.; Strmic Palinkas, Sabina; Mauk, Jeffrey L.; Bodnar, Robert J.

    2015-01-01

    Microthermometry, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and Raman spectroscopy have been used to determine the temperature, apparent salinity, and composition of individual fluid inclusions in adularia-sericite Au-Ag epithermal veins from the Karangahake, Martha, Favona, and Waitekauri deposits, southern Hauraki goldfield, New Zealand. Quartz veins contain colloform to crustiform bands that alternate with coarse-grained quartz and amethyst. The ore mineralization occurs only in colloform to crustiform bands.

  9. Stopping Power of Be, Al, Cu, Ag, Pt, and Au for 5-12-MeV Protons and Deuterons

    DEFF Research Database (Denmark)

    Andersen, H.H.; Hanke, C.; Sørensen, H.; Vajda, P.

    1967-01-01

    Recent measurements on stopping power of aluminum have been continued with the stopping materials Be, Cu, Ag, Pt, and Au. The method of measuring stopping powers utilizing a thermometric compensation technique working at liquid-helium temperature has been used. Results are obtained with a standard...... deviation of 0.3%, and agree with other published experimental results and with Bichsel's tabulated values within their stated errors....

  10. Scanning surface-enhanced Raman spectroscopy (SERS) of chemical agent simulants on templated Au-Ag nanowire substrates

    Science.gov (United States)

    Hoffmann, J. A.; Miragliotta, J. A.; Wang, J.; Tyagi, P.; Maddanimath, T.; Gracias, D. H.; Papadakis, S. J.

    2009-05-01

    We report the results of scanning micro-Raman spectroscopy obtained on Au-Ag nanowires for a variety of chemical warfare agent simulants. Rough silver segments embedded in gold nanowires showed enhancement of 105 - 107 and allowed unique identification of 3 of 4 chemical agent simulants tested. These results suggest a promising method for detection of compounds significant for security applications, leading to sensors that are compact and selective.

  11. Characterization of Ag and Au nanoparticles created by nanosecond pulsed laser ablation in double distilled water

    International Nuclear Information System (INIS)

    Pulsed laser ablation of Ag and Au targets, immersed in double-distilled water is used to synthesize metallic nanoparticles (NPs). The targets are irradiated for 20 min by laser pulses at different wavelengths-the fundamental and the second harmonic (SHG) (λ = 1064 and 532 nm, respectively) of a Nd:YAG laser system. The ablation process is performed at a repetition rate of 10 Hz and with pulse duration of 15 ns. Two boundary values of the laser fluence for each wavelength under the experimental conditions chosen were used-it varied from several J/cm2 to tens of J/cm2. Only as-prepared samples were measured not later than two hours after fabrication. The NPs shape and size distribution were evaluated from transmission electron microscopy (TEM) images. The suspensions obtained were investigated by optical transmission spectroscopy in the near UV and in the visible region in order to get information about these parameters. Spherical shape of the NPs at the low laser fluence and appearance of aggregation and building of nanowires at the SHG and high laser fluence was seen. Dependence of the mean particle size at the SHG on the laser fluence was established. Comments on the results obtained have been also presented.

  12. Characterization of Ag and Au nanoparticles created by nanosecond pulsed laser ablation in double distilled water

    Energy Technology Data Exchange (ETDEWEB)

    Nikolov, A.S., E-mail: anastas_nikolov@abv.bg [Institute of Electronics, Bulgarian Academy of Sciences, Tzarigradsko shousse 72, Sofia 1784 (Bulgaria); Nedyalkov, N.N.; Nikov, R.G.; Atanasov, P.A. [Institute of Electronics, Bulgarian Academy of Sciences, Tzarigradsko shousse 72, Sofia 1784 (Bulgaria); Alexandrov, M.T. [Institute of Experimental Pathology and Parasitology, Bulgarian Academy of Sciences, G. Bonchev Street, bl. 25, Sofia 1113 (Bulgaria)

    2011-04-01

    Pulsed laser ablation of Ag and Au targets, immersed in double-distilled water is used to synthesize metallic nanoparticles (NPs). The targets are irradiated for 20 min by laser pulses at different wavelengths-the fundamental and the second harmonic (SHG) ({lambda} = 1064 and 532 nm, respectively) of a Nd:YAG laser system. The ablation process is performed at a repetition rate of 10 Hz and with pulse duration of 15 ns. Two boundary values of the laser fluence for each wavelength under the experimental conditions chosen were used-it varied from several J/cm{sup 2} to tens of J/cm{sup 2}. Only as-prepared samples were measured not later than two hours after fabrication. The NPs shape and size distribution were evaluated from transmission electron microscopy (TEM) images. The suspensions obtained were investigated by optical transmission spectroscopy in the near UV and in the visible region in order to get information about these parameters. Spherical shape of the NPs at the low laser fluence and appearance of aggregation and building of nanowires at the SHG and high laser fluence was seen. Dependence of the mean particle size at the SHG on the laser fluence was established. Comments on the results obtained have been also presented.

  13. Dihydrogen bond interactions as a result of H2 cleavage at Cu, Ag and Au centres.

    Science.gov (United States)

    Grabowski, Sławomir J; Ruipérez, Fernando

    2016-05-14

    A quantum chemical study of H2 activation at fluorides of coinage metals, MF (M = Cu, Ag and Au), and its splitting was performed. The following reaction path was analyzed: FMH2→ FHHM → HMFH, where both the molecular complexes and the corresponding transition states have been characterized at the CCSD(T)/aug-cc-pVQZ//MP2/aug-cc-pVQZ level of theory. Further single-point CASSCF/CASPT2 calculations, including spin-orbit coupling effects, were also performed to analyze the role of non-dynamic correlation. The scalar relativistic effects are included via aug-cc-pVQZ-PP basis sets used for the metals. The dihydrogen-bonded copper (FHHCu) and silver (FHHAg) complexes are observed as a result of H2 cleavage, while the corresponding FHHAu gold complex is not found but the HAuHF arrangement is observed, instead. The energetic and geometrical parameters of the complexes have been analyzed and both the Quantum Theory of Atoms in Molecules approach and the Natural Bond Orbitals method were additionally applied to analyze the intermolecular interactions. PMID:27101741

  14. Electronic structure and conductivity of nanocomposite metal (Au,Ag,Cu,Mo)-containing amorphous carbon films

    Energy Technology Data Exchange (ETDEWEB)

    Endrino, Jose L.; Horwat, David; Gago, Raul; Andersson, Joakim; Liu, Y.S.; Guo, Jinghua; Anders, Andre

    2008-05-14

    In this work, we study the influence of the incorporation of different metals (Me = Au, Ag, Cu, Mo) on the electronic structure of amorphous carbon (a-C:Me) films. The films were produced at room temperature using a novel pulsed dual-cathode arc deposition technique. Compositional analysis was performed with secondary neutral mass spectroscopy whereas X-ray diffraction was used to identify the formation of metal nanoclusters in the carbon matrix. The metal content incorporated in the nanocomposite films induces a drastic increase in the conductivity, in parallel with a decrease in the band gap corrected from Urbach energy. The electronic structure as a function of the Me content has been monitored by x-ray absorption near edge structure (XANES) at the C K-edge. XANES showed that the C host matrix has a dominant graphitic character and that it is not affected significantly by the incorporation of metal impurities, except for the case of Mo, where the modifications in the lineshape spectra indicated the formation of a carbide phase. Subtle modifications of the spectral lineshape are discussed in terms of nanocomposite formation.

  15. The solvent effect on the electrocatalytic cleavage of carbon-halogen bonds on Ag and Au

    International Nuclear Information System (INIS)

    In recent years it has been shown in detail how the electrocatalytic cleavage of carbon-halogen bonds is modulated by (a) the stepwise or concerted nature of the dissociative electron-transfer mechanism, which is influenced by the nature of the electrode surface, the type of halogen atom and the molecular structure of RX as a whole, and (b) the double-layer structure (as a function of the nature and bulkiness of the supporting electrolyte ions). In order to both complete and support the interpretative scheme thus developed, this work is focused on the solvent role. When one compares aprotic with protic organic solvents after appropriate intersolvental normalization, interesting peculiarities emerge, especially concerning protic media. Solvent proticity deeply affects both the reaction mechanism (on both non-catalytic and catalytic electrodes) and the extent of the catalytic effects. These items are discussed on the basis of a complete investigation carried out with a carefully controlled experimental protocol on two chloride and bromide couples, one aromatic and one aliphatic, representative of stepwise and concerted mechanisms, respectively, in four aprotic and four protic solvents, on both non−catalytic GC and catalytic Ag and Au electrodes. The results are discussed in the framework of a recently developed interpretative scheme of the carbon-halogen cleavage mechanism

  16. Ammonia synthesis on Au modified Fe(111) and Ag and Cu modified Fe(100) surfaces

    DEFF Research Database (Denmark)

    Lytken, Ole; Waltenburg, Hanne Neergaard; Chorkendorff, Ib

    In order to investigate any influence of steps and possible positive effects of making surface alloys the ammonia synthesis has been investigated over Au modified Fe(111) and Ag and Cu modified Fe(100) single crystals in the temperature range 603-773 K, using a system combining ultra-high vacuum...... and a high-pressure cell. Ammonia was synthesized from a stoichiometric (N-2:3H(2)) gas mixture at a pressure of 2 bar. By deposition of small amounts of An, the ammonia production activity of the Fe(1 1 1) surface can be enhanced. More important, for the gold modified surface, the reaction order in...... ammonia pressure is less negative. The activity goes through a maximum as the An coverage increases, and then to zero as the coverage approaches 1 ML. At 713 K and 400 ppm NH3, a maximum enhancement of 50% is observed at 0.04 ML An. Based on features in the TPD spectra, the enhancement is suggested to be...

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

    Science.gov (United States)

    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

  18. Carbon nanotube-supported Au-Pd alloy with cooperative effect of metal nanoparticles and organic ketone/quinone groups as a highly efficient catalyst for aerobic oxidation of amines.

    Science.gov (United States)

    Deng, Weiping; Chen, Jiashu; Kang, Jincan; Zhang, Qinghong; Wang, Ye

    2016-05-21

    Functionalised carbon nanotube (CNT)-supported Au-Pd alloy nanoparticles were highly efficient catalysts for the aerobic oxidation of amines. We achieved the highest turnover frequencies (>1000 h(-1)) for the oxidative homocoupling of benzylamine and the oxidative dehydrogenation of dibenzylamine. We discovered a cooperative effect between Au-Pd nanoparticles and ketone/quinone groups on CNTs. PMID:27125360

  19. A label-free amperometric immunosensor for detection of zearalenone based on trimetallic Au-core/AgPt-shell nanorattles and mesoporous carbon

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Lei; Chao, Yingjun; Cao, Wei, E-mail: chm_caow@ujn.edu.cn; Wang, Yulan; Luo, Chuannan; Pang, Xuehui; Fan, Dawei; Wei, Qin, E-mail: sdjndxwq@163.com

    2014-10-17

    Highlights: • Au@AgPt nanorattles have special structure of Au-core and imperfect AgPt-shell. • Au@AgPt are proposed for the first time applied in electrochemical immunosensor. • Substrate materials MC/Au@AgPt possess excellent conductivity and high surface area. • The proposed immunosensor exhibits a low detection limit of 1.7 pg mL{sup −1}. - Abstract: A novel label-free amperometric immunosensor is proposed for the ultrasensitive detection of zearalenone (ZEN) based on mesoporous carbon (MC) and trimetallic nanorattles (core/shell particles with movable cores encapsulated in the shells). The nanorattles are composed of special Au-core and imperfect AgPt-shell structure (Au@AgPt). The Au@AgPt nanorattles are loaded onto the MC by physical adsorption. The structure of the Au@AgPt nanorattles was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDS) confirmed the composition of the synthesized nanorattles. Compared with monometallic and bimetallic nanoparticles (NPs), Au@AgPt nanorattles show a higher electron transfer rate due to the synergistic effect of the Au, Ag and Pt NPs. MC further improves the sensitivity of the immunosensor because of its extraordinarily large specific surface area, suitable pore arrangement and outstanding conductivity. The large specific surface area of MC and MC@Au@AgPt were characterized by the BET method. ZEN antibodies are immobilized onto the nanorattles via Ag–NH{sub 2} bonds and Pt–NH{sub 2} bonds. Cyclic voltammetry and square wave voltammetry were used to characterize the recognizability of ZEN. Under optimum experimental conditions, the proposed immunosensor exhibited a low detection limit (1.7 pg mL{sup −1}), a wide linear range (from 0.005 to 15 ng mL{sup −1}) as well as good stability, reproducibility and selectivity. The sensor can be used in clinical analysis.

  20. Surface Plasmons and Optical Properties of TiO2/X(X = Au and Ag) Nanostructure Thin Films

    Science.gov (United States)

    Zolanvari, A.; Sadeghi, H.; Norouzi, R.; Ranjgar, A.

    2013-09-01

    TiO2/X(X = Au and Ag) nanolayers are fabricated by depositing TiO2 films using rf magnetron sputtering on thin quartz substrates embedded with Au and Ag nanoparticles. Enhancement of light absorption of the nanostructural layers is observed. These plasmonic and non-plasmonic materials are ordered in geometric arrangements with dimensions that are fractions of the wavelength of light. The light absorption enhancement of synthesized structure in comparison to TiO2 is originated from near-field enhancement caused by the plasmonic effect of metallic nanoparticles, which can be demonstrated by the optical absorption spectra. We show that plasmon modes can exist for the infrared region of the optical spectrum. Also, we analyze the optical properties of the metal-insulator films, in order to clarify the role of metal inclusions in the TiO2 dielectric matrix. Optical band gaps of the nanolayer films are calculated by using Tauc's relation, and the n values of optical band gaps with the variation composition are found from 1.80 to 3.69 eV. Band gap narrowing and absorption in the visible spectral region induced by the incorporation of TiO2/X(X=Au and Ag) nanolayers enable the design of nanostructured thin films to be achieved for photocatalysts and solar energy converters.

  1. Effect of Refractive Index of Substrate on Fabrication and Optical Properties of Hybrid Au-Ag Triangular Nanoparticle Arrays

    Directory of Open Access Journals (Sweden)

    Jing Liu

    2015-05-01

    Full Text Available In this study, the nanosphere lithography (NSL method was used to fabricate hybrid Au-Ag triangular periodic nanoparticle arrays. The Au-Ag triangular periodic arrays were grown on different substrates, and the effect of the refractive index of substrates on fabrication and optical properties was systematically investigated. At first, the optical spectrum was simulated by the discrete dipole approximation (DDA numerical method as a function of refractive indexes of substrates and mediums. Simulation results showed that as the substrates had the refractive indexes of 1.43 (quartz and 1.68 (SF5 glass, the nanoparticle arrays would have better refractive index sensitivity (RIS and figure of merit (FOM. Simulation results also showed that the peak wavelength of the extinction spectra had a red shift when the medium’s refractive index n increased. The experimental results also demonstrated that when refractive indexes of substrates were 1.43 and 1.68, the nanoparticle arrays and substrate had better adhesive ability. Meanwhile, we found the nanoparticles formed a large-scale monolayer array with the hexagonally close-packed structure. Finally, the hybrid Au-Ag triangular nanoparticle arrays were fabricated on quartz and SF5 glass substrates and their experiment extinction spectra were compared with the simulated results.

  2. Bio-mimetic Nanostructure Self-assembled from Au@Ag Heterogeneous Nanorods and Phage Fusion Proteins for Targeted Tumor Optical Detection and Photothermal Therapy

    OpenAIRE

    Fei Wang; Pei Liu; Lin Sun; Cuncheng Li; Valery. A. Petrenko; Aihua Liu

    2014-01-01

    Nanomaterials with near-infrared (NIR) absorption have been widely studied in cancer detection and photothermal therapy (PTT), while it remains a great challenge in targeting tumor efficiently with minimal side effects. Herein we report a novel multifunctional phage-mimetic nanostructure, which was prepared by layer-by-layer self-assembly of Au@Ag heterogenous nanorods (NRs) with rhodamine 6G, and specific pVIII fusion proteins. Au@Ag NRs, first being applied for PTT, exhibited excellent stab...

  3. Optimised photocatalytic hydrogen production using core–shell AuPd promoters with controlled shell thickness

    DEFF Research Database (Denmark)

    Jones, Wilm; Su, Ren; Wells, Peter;

    2014-01-01

    of these materials towards the reforming of alcohols for hydrogen production. The core–shell structured Au–Pd bimetallic nanoparticle supported on TiO2 has being of interest as it exhibited extremely high quantum efficiencies for hydrogen production. However, the effect of shell composition and thickness...

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

    Science.gov (United States)

    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

  5. Semiempirical calculation of radiative constants in the spectra of nickel-like ions Kr IX, Sr XI, Y XII, Ru XVII, Pd XIX, and Ag XX

    Science.gov (United States)

    Loginov, A. V.

    2015-03-01

    The probabilities of the electric-dipole transitions 3 d 94 p, 3 d 94 f-3 d 10, 3 d 94 s, and 3 d 94 d in the spectra of nickel-like ions Kr IX, Sr XI, Y XII, Ru XVII, Pd XIX, and Ag XX are calculated semiempirically with the use of published energy levels.

  6. Traces of Z2 vortices in CuCrO2, AgCrO2, and PdCrO2

    International Nuclear Information System (INIS)

    The spin-spin relaxation of the two-dimensional triangular lattice antiferromagnets CuCrO2, AgCrO2, and PdCrO2 is investigated by electron spin resonance spectroscopy. The data proof excellent agreement with very recent predictions for the Z2-vortex ordering scenario in triangular Heisenberg antiferromagnets derived by Okubo and Kawamura. (author)

  7. Ultrasensitive electrochemical aptasensor for the detection of thrombin based on dual signal amplification strategy of Au@GS and DNA-CoPd NPs conjugates.

    Science.gov (United States)

    Wang, Yaoguang; Zhang, Yong; Yan, Tao; Fan, Dawei; Du, Bin; Ma, Hongmin; Wei, Qin

    2016-06-15

    In this work, an ultrasensitive electrochemical aptasensor for the detection of thrombin was developed based on Au nanoparticles decorated graphene sheet (Au@GS) and CoPd binary nanoparticles (CoPd NPs). A sulfydryl-labeled thrombin capture probe (Apt1) and a biotin-labeled thrombin reporter probe (Apt2) were designed to achieve a sandwich-type strategy. Au@GS was used as a sensing platform for the facile immobilization of Apt1 through Au-S bond, forming a sensing interface for thrombin. The specific recognition of thrombin induced the attachment of Apt2-CoPd NPs to the electrode. The labeled CoPd NPs showed good catalytic properties toward the reduction of H2O2, resulting in an amperometric signal. The amperometric response was correlated to the thrombin concentration in sample solutions. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) confirmed the successful fabrication of the aptasensor. A linear response to thrombin in the range of 0.01-2.00ngmL(-1) with a low detection limit (5pgmL(-1)) was achieved. The proposed aptasensor showed good selectivity, good reproducibility and acceptable stability. This proposed strategy may find many potential applications in the detection of other biomolecules. PMID:26908183

  8. A sensitive electrochemiluminescence immunosensor based on luminophore capped Pd@Au core-shell nanoparticles as signal tracers and ferrocenyl compounds as signal enhancers.

    Science.gov (United States)

    Liu, Yuting; Wang, Haijun; Xiong, Chengyi; Yuan, Yali; Chai, Yaqin; Yuan, Ruo

    2016-07-15

    In this work, N-(aminobutyl)-N-(ethylisoluminol) (ABEI), an analogue of luminol, is served as both the reductant and luminescence reagent to synthesize ABEI capped Pd@Au core-shell nanoparticles (ABEI-Pd@AuNPs). The nanoparticles not only exhibit inherent electrochemiluminescence (ECL) property, but also possess advantages of noble-metal nanomaterials such as outstanding electronic property, high specific surface area and good biocompatibility. In order to enhance the luminescence efficiency, ferrocene monocarboxylic acid (Fc) as catalyzer is grafted on the surface of ABEI-Pd@AuNPs with the aid of l-cysteine (l-Cys). When the Fc is electrochemically oxidized to ferricinium cation species (Fc(+)), the decomposition of H2O2 which existed in detection solution can be catalyzed by Fc(+) to generate oxygen-related free radicals, resulting effective signal amplification for ABEI-H2O2 system. For potential applications, the Pd@Au core-shell nanoparticles bifunctionalized by ABEI and catalyzer are employed as nano-carriers to immobilize detection antibody (Ab2). Based on sandwiched immunoreactions, a "signal-on" ECL immunosensor is developed for detection of human collagen type IV (Col IV), a potential biomarker associated with diabetic nephropathy. Consequently, the proposed immunosensor provides a wide linear detection ranging from 1pgmL(-1) to 10ngmL(-1) with a relatively low detection limit of 0.3pgmL(-1) (S/N=3). PMID:26985586

  9. Symmetry character of collective states in 104Pd populated in the EC-β+ decay of 104Ag

    International Nuclear Information System (INIS)

    The states of 104Pd, populated in the EC-β+ decay of the ground (Jπ=5+) and metastable (Jπ=2+) states of 104Ag, have been investigated in the framework of the proton-neutron interacting boson model, extending a previous analysis to take into account the newly appeared experimental data. All positive-parity states up to an excitation energy of 3 MeV and spin in the range J=1-6, fed by more than 0.3% in the decay of the parent nucleus, have been considered. As a result, strong evidence has been found for interpreting most of these states as states of collective nature having a quite pure full- or mixed-symmetry character and, in particular, for identifying the 1+ level at 2276 keV as the lowest 1+ mixed-symmetry state. (orig.)

  10. First-Principles Predictions of Yet-Unobserved Ordered Structures in the Ag-Pd Phase Diagram

    International Nuclear Information System (INIS)

    The complexity of first-principles total energy calculations limits the pool of structure types considered for a ground-state search for a binary alloy system to a rather small, O(10) , group of ''usual suspects.'' We conducted an unbiased search of fcc-based Ag1-xPd x structures consisting of up to many thousand atoms by using a mixed-space cluster expansion. We find an unsuspected ground state at 50%-50% composition -- the L11 structure, currently known in binary metallurgy only for the Cu0.5Pt 0.5 alloy system. We also provide predicted short-range-order profiles and mixing enthalpies for the high temperature, disordered alloy

  11. Atomic data for radiative transitions in the third spectra of rhodium (Rh III), palladium (Pd III) and silver (Ag III)

    International Nuclear Information System (INIS)

    A new set of radiative decay rates in doubly ionized rhodium (Rh III), palladium (Pd III) and silver (Ag III) has been computed by means of the pseudo-relativistic Hartree–Fock method including core-polarization effects (HFR + CPOL) and semi-empirical optimization of radial energy parameters. For these three ions, oscillator strengths and transition probabilities for spectral lines appearing in the ultraviolet region from 70 to 250 nm are reported for the first time. The accuracy of these results has been estimated through the excellent agreement observed between experimental lifetime measurements and similar HFR + CPOL calculations performed recently in isoelectronic ions Ru II and Rh II. (paper)

  12. Sensitive electrochemical sensors for simultaneous determination of ascorbic acid, dopamine, and uric acid based on Au@Pd-reduced graphene oxide nanocomposites

    Science.gov (United States)

    Jiang, Jingjing; Du, Xuezhong

    2014-09-01

    Sensitive electrochemical sensors were fabricated with reduced graphene oxide-supported Au@Pd (Au@Pd-RGO) nanocomposites by one-step synthesis for individual and simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA) with low detection limits and wide concentration ranges. From the Au@Pd-RGO-modified electrodes, well-separated oxidation peaks and enhanced peak currents of AA, DA, and UA were observed owing to the superior conductivity of RGO and the excellent catalytic activity of Au@Pd nanoparticles. For individual detection, the linear responses of AA, DA, and UA were in the concentration ranges of 0.1-1000, 0.01-100, and 0.02-500 μM with detection limits of 0.02, 0.002, and 0.005 μM (S/N = 3), respectively. For simultaneous detection by synchronous change of the concentrations of AA, DA, and UA, the linear response ranges were 1-800, 0.1-100, and 0.1-350 μM with detection limits of 0.28, 0.024, and 0.02 μM (S/N = 3), respectively. The fabricated sensors were further applied to the detection of AA, DA, and UA in urine samples. The Au@Pd-RGO nanocomposites have promising applications in highly sensitive and selective electrochemical sensing.Sensitive electrochemical sensors were fabricated with reduced graphene oxide-supported Au@Pd (Au@Pd-RGO) nanocomposites by one-step synthesis for individual and simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA) with low detection limits and wide concentration ranges. From the Au@Pd-RGO-modified electrodes, well-separated oxidation peaks and enhanced peak currents of AA, DA, and UA were observed owing to the superior conductivity of RGO and the excellent catalytic activity of Au@Pd nanoparticles. For individual detection, the linear responses of AA, DA, and UA were in the concentration ranges of 0.1-1000, 0.01-100, and 0.02-500 μM with detection limits of 0.02, 0.002, and 0.005 μM (S/N = 3), respectively. For simultaneous detection by synchronous change of the

  13. Ag and Au nanoparticles for SERS substrates produced by pulsed laser ablation

    Energy Technology Data Exchange (ETDEWEB)

    Agarwal, N.R.; Castiglioni, C.; Lucotti, A. [DCMIC, Politecnico di Milano, Milano (Italy); Fazio, E.; Neri, F. [Dip. Fisica della Materia e Ingegneria Elettronica, Universita di Messina, Messina (Italy); Trusso, S. [CNR- Istituto per i Processi Chimico-Fisici, Messina (Italy); Santo, N. [Centro Interdipartimentale Microscopia Avanzata, Universita degli Studi di Milano, Milano (Italy); Ossi, P.M. [Dip. Energia, Politecnico di Milano, Milano (Italy)

    2011-08-15

    A method for the growth of films consisting of Nanoparticles (NP) of Ag and Au is presented. Nanostructured films were obtained by means of nanosecond pulsed laser ablation of a metallic target in presence of a controlled Ar atmosphere. The morphology of these films from island structures to isolated nanoparticles, measured by SEM, depends on the varying gas pressure (10-100 Pa) and on the number of laser pulses (500-30000), keeping other deposition parameters such as the target to substrate distance, incidence angle, laser wavelength, laser fluence constant. Fast imaging of the plasma, performed using a intensified and gateable CCD camera at different time delays with respect to the arrival of the laser pulse, allows revelation of the propagation regime of the ablation plume and inference of plasma initial velocity. This data along with the measured average ablated mass per pulse were taken as inputs to a model to estimate the average size of NPs grown in the expanding plume. The theoretical NP sizes were compared with sizes measured from TEM images. These images indicate narrow gradients of NP sizes. Hence strict control of growth parameters aids fine tuning of NP size that is essential for many applications, including Surface Enhanced Raman Spectroscopy (SERS) active substrates. UV-Visible Spectroscopy helped in determination of appropriate laser wavelength for resonant excitation of the localized surface plasmon. SERS Spectra obtained with increasingly lower concentrations of reference dye Rhodamin 6G (Rh6G) and medical drug Apomorphine, are discussed as a perspective of application to biomedical sensors. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Sensitive determination of dopamine in the presence of uric acid and ascorbic acid using TiO2 nanotubes modified with Pd, Pt and Au nanoparticles.

    Science.gov (United States)

    Mahshid, Sara; Li, Chengcheng; Mahshid, Sahar Sadat; Askari, Masoud; Dolati, Abolghasem; Yang, Lixia; Luo, Shenglian; Cai, Qingyun

    2011-06-01

    A simple modified TiO(2) nanotubes electrode was fabricated by electrodeposition of Pd, Pt and Au nanoparticles. The TiO(2) nanotubes electrode was prepared using the anodizing method, followed by modifying Pd nanoparticles onto the tubes surface, offering a uniform conductive surface for electrodeposition of Pt and Au. The performance of the modified electrode was characterized by cyclic voltammetry and differential pulse voltammetry methods. The Au/Pt/Pd/TiO(2) NTs modified electrode represented a high sensitivity towards individual detection of dopamine as well as simultaneous detection of dopamine and uric acid using 0.1 M phosphate buffer solution (pH 7.00) as the base solution. In both case, electro-oxidation peak currents of dopamine were linearly related to accumulated concentration over a wide concentration range of 5.0 × 10(-8) to 3.0 × 10(-5) M. However in the same range of dopamine concentration, the sensitivity had a significant loss at Pt/Pd/TiO(2) NTs electrode, suggesting the necessity for Au nanoparticles in modified electrode. The limit of the detection was determined as 3 × 10(-8) M for dopamine at signal-to-noise ratio equal to 3. Furthermore, the Au/Pt/Pd/TiO(2) NTs modified electrode was able to distinguish the oxidation response of dopamine, uric acid and ascorbic acid in mixture solution of different acidity. It was shown that the modified electrode possessed a very good reproducibility and long-term stability. The method was also successfully applied for determination of DA in human urine samples with satisfactory results. PMID:21494708

  15. Electronic Structure and Bonding of Icosahedral Core-Shell Gold-Silver Nanoalloy Clusters Au_(144-x)Ag_x(SR)_60

    OpenAIRE

    Malola, Sami; Häkkinen, Hannu

    2011-01-01

    Atomically precise thiolate-stabilized gold nanoclusters are currently of interest for many cross-disciplinary applications in chemistry, physics and molecular biology. Very recently, synthesis and electronic properties of "nanoalloy" clusters Au_(144-x)Ag_x(SR)_60 were reported. Here, density functional theory is used for electronic structure and bonding in Au_(144-x)Ag_x(SR)_60 based on a structural model of the icosahedral Au_144(SR)_60 that features a 114-atom metal core with 60 symmetry-...

  16. Rapidity densities and their fluctuations in central 200 A GeV 32S interactions with Au and Ag, Br nuclei

    International Nuclear Information System (INIS)

    The pseudo-rapidity density distributions of shower particles (ns) are measured in central inelastic S+Au and S+Ag, Br interactions. The extracted maximum energy densities, while being higher for Au than for Ag,Br interactions, were found to be similar to those obtained for oxygen emulsion interactions. The correlation between rapidity density and shower particle multiplicity shows a small deviation from the Lund Model Fritiof for the highest energy densities in S+Au interactions, whereas the bulk of the data yields satisfactory agreement. (orig.)

  17. Thermodynamic properties of Ag{sub 3}AuSe{sub 2} from 300 to 500 K by a solid state galvanic cell

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Dawei, E-mail: dawei.feng@aalto.fi; Taskinen, Pekka, E-mail: pekka.taskinen@aalto.fi

    2014-01-15

    Highlights: • Experimental thermodynamics data on Ag{sub 3}AuSe{sub 2} compounds are obtained to 500 K. • A new phase transformation of Ag{sub 3}AuSe{sub 2} at low temperature is proposed. • Advanced measurement makes possible to distinguish the phase transformation. -- Abstract: The numerical values of the standard thermodynamic functions of Ag{sub 3}AuSe{sub 2} (fischesserite) in the Ag–Au–Se system were determined by the electromotive force (EMF) method in a solid state galvanic cell with RbAg{sub 4}I{sub 5} as the solid electrolyte below 500 K. Ag{sub 3}AuSe{sub 2} was synthesized from pure elements in stoichiometric composition by evacuated ampoules made of quartz glass. On the basis of EMF vs. temperature experimental data, the analytical equations were obtained, from which the temperature dependent relationships of the Gibbs energy in the relevant reactions and the standard thermodynamic functions of Ag{sub 3}AuSe{sub 2} within the temperature range of 300–500 K were calculated. The results show that there is possible a new polymorphic transformation around 350 K.

  18. Electronic Structure and Bonding of Icosahedral Core-Shell Gold-Silver Nanoalloy Clusters Au_(144-x)Ag_x(SR)_60

    CERN Document Server

    Malola, Sami

    2011-01-01

    Atomically precise thiolate-stabilized gold nanoclusters are currently of interest for many cross-disciplinary applications in chemistry, physics and molecular biology. Very recently, synthesis and electronic properties of "nanoalloy" clusters Au_(144-x)Ag_x(SR)_60 were reported. Here, density functional theory is used for electronic structure and bonding in Au_(144-x)Ag_x(SR)_60 based on a structural model of the icosahedral Au_144(SR)_60 that features a 114-atom metal core with 60 symmetry-equivalent surface sites, and a protecting layer of 30 RSAuSR units. In the optimal configuration the 60 surface sites of the core are occupied by silver in Au_84Ag_60(SR)_60. Silver enhances the electron shell structure around the Fermi level in the metal core, which predicts a structured absorption spectrum around the onset (about 0.8 eV) of electronic metal-to-metal transitions. The calculations also imply element-dependent absorption edges for Au(5d) \\rightarrow Au(6sp) and Ag(4d) \\rightarrow Ag(5sp) interband transit...

  19. Sensitive Glycoprotein Sandwich Assays by the Synergistic Effect of In Situ Generation of Raman Probes and Plasmonic Coupling of Ag Core-Au Satellite Nanostructures.

    Science.gov (United States)

    Bi, Xiaoshuang; Li, Xueyuan; Chen, Dong; Du, Xuezhong

    2016-05-01

    Sensitive surface-enhanced Raman scattering (SERS) assays of glycoproteins have been proposed using p-aminothiophenol (PATP)-embedded Ag core-Au satellite nanostructures modified with p-mercaptophenylboronic acid (PMBA) and the self-assembled monolayer of PMBA on a smooth gold-coated wafer. The apparent Raman probe PATP on the surfaces of the Ag cores underwent a photodimerization to generate 4,4'-dimercaptoazobenzene (DMAB) in situ upon excitation of laser, and the in situ generated DMAB acted as the actual Raman probe with considerably strong SERS signals, which was further enhanced by the plasmonic coupling of the Ag core-Au satellite nanostructures due to the synergistic effect. The sandwich assays of glycoproteins showed high sensitivity and excellent selectivity against nonglycoproteins. The Ag core-Au satellite SERS nanostructures can be used for highly sensitive SERS assays of other analytes. PMID:27064515

  20. Invoking Direct Exciton-Plasmon Interactions by Catalytic Ag Deposition on Au Nanoparticles: Photoelectrochemical Bioanalysis with High Efficiency.

    Science.gov (United States)

    Ma, Zheng-Yuan; Xu, Fei; Qin, Yu; Zhao, Wei-Wei; Xu, Jing-Juan; Chen, Hong-Yuan

    2016-04-19

    In this work, direct exciton-plasmon interactions (EPI) between CdS quantum dots (QDs) and Ag nanoparticles (NPs) were invoked ingeniously by catalytic Ag deposition on Au NPs for the stimulation of high efficient damping effect toward the excitonic responses in CdS QDs, on the basis of which a novel photoelectrochemical (PEC) bioanalytical format was achieved for sensitive microRNA detection. Specifically, upon the configurational change from the hairpin probe DNA to the "Y"-shaped ternary conjugate consisting of the original probe DNA, assistant DNA, and the target microRNA, the alkaline phosphatase (ALP) catalytic chemistry would then trigger the transition of the interparticle interplay from the CdS QDs-Au NPs to the CdS QDs-Ag NPs systems for the microRNA detection due to the dependence of the photocurrent quenching on the target concentration. This work not only provided a unique method for EPI generation among the PEC nanosystems but also offered a versatile and general protocol for future PEC bioanalysis development. PMID:27023112

  1. STM of photoemission studies of Au and Pd on TiO2

    International Nuclear Information System (INIS)

    This thesis presents the first scanning tunnelling microscopy (STM) images of metals dispersed on metal oxide supports recorded at high temperatures. Thermal deposition in ultra-high vacuum (UHV) of a sub-monolayer quantity of metal onto single crystal rutile titanium dioxide produces metal nanoparticles on the surface, which are known to be an effective laboratory model of metal/TiO2 powdered commercial catalysts. By acquiring real space nanoscale images of the surface in real time at elevated temperature, we gain direct insight into the mechanism of thermal sintering of these catalysts. Chapter 1 introduces the necessary background to this work, whilst the principles and implementations of the experimental techniques are discussed in the second chapter. In chapter 3 we describe experiments where valence level and shallow core states of gold nanoclusters on TiO2(110) have been studied by synchrotron excited photoemission. The shift to high binding energy and broadening of the Au 4f peaks with decreasing Au surface coverage can be understood in terms of decreasing cluster size and the associated effects of charge on the cluster in the final state. Shifts in the photoemission onset are much more pronounced than the core level shifts and show a strong dependence on the degree of reduction of the TiO2(110) substrate. These observations suggest that the photoemission onset is influenced by an initial state effect involving charge transfer from defect states into cluster states. In chapter 4 STM is used to demonstrate that deposition of Au on TiO2(110) at room temperature leads to nucleation of Au nanoparticles whose initial mean diameter varies between about 20A and 50A depending on the surface coverage. Studying the behaviour of these clusters at elevated temperatures with STM, it is found that at 750K there is growth of the larger clusters, but above 873K evaporation of gold from the surface competes with this ripening process. At 750K the Au coverage remains

  2. New constraints on the origin of the Skaergaard intrusion Cu-Pd-Au mineralization: Insights from high-resolution X-ray computed tomography

    Science.gov (United States)

    Godel, Bélinda; Rudashevsky, Nikolay S.; Nielsen, Troels F. D.; Barnes, Stephen J.; Rudashevsky, Vladimir N.

    2014-03-01

    This contribution presents the first detailed three-dimensional (3D) in situ analysis of samples from the Platinova Reef using high-resolution X-ray computed tomography (HRXCT) and 3D image processing and quantification coupled with microscopic and mineralogical investigations. Our HRXCT analyses reveal the complex textural relationships between Cu-rich sulfides (bulk composition close to bornite), skaergaardite (PdCu), Au-rich phases, silicates and Fe-Ti oxides and provide unequivocal textural evidences, not observed previously. The association in 3D between Cu-rich sulfide globules, PdCu alloy and ilmenite is inconsistent with a hydrothermal origin of the Cu-Pd mineralization. In contrast, our results combined with phase diagrams strongly support a primary magmatic origin for the Cu-Pd mineralization where Cu and Pd-rich, Fe-poor sulfide liquid represents a cumulus phase that forms by in-situ nucleation. These sulfide droplets and attached skaergaardite grains were trapped during the formation and crystallization of the Fe-Ti oxides. Subsequent, post-cumulus processes led to the partial to total dissolution of the sulfide not entirely enclosed by the Fe-Ti oxides (i.e., not protected from reaction) leading to the observed variability in Cu and Pd composition at the aggregate (sulfide + PdCu) scale and to the occurrence of free PdCu alloys. In contrast to the PdCu alloy, gold-bearing minerals are never observed entirely enclosed within the Fe-Ti oxide. Two hypotheses can be envisaged for the formation of the gold enriched layer in the upper part of the section. Gold may have either precipitated from high-temperature late magmatic Cl-rich fluids. Alternatively, gold may have been enriched during fractional crystallization after sulfide had been suppressed from the liquidus after the Pd layer crystallized and then deposited along redox barriers.

  3. Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters

    Science.gov (United States)

    Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; Nobusada, Katsuyuki; Jin, Rongchao

    2016-03-01

    Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared

  4. Target-specific near-IR induced drug release and photothermal therapy with accumulated Au/Ag hollow nanoshells on pulmonary cancer cell membranes.

    Science.gov (United States)

    Noh, Mi Suk; Lee, Somin; Kang, Homan; Yang, Jin-Kyoung; Lee, Hyunmi; Hwang, Doyk; Lee, Jong Woo; Jeong, Sinyoung; Jang, Yoonjeong; Jun, Bong-Hyun; Jeong, Dae Hong; Kim, Seong Keun; Lee, Yoon-Sik; Cho, Myung-Haing

    2015-03-01

    Au/Ag hollow nanoshells (AuHNSs) were developed as multifunctional therapeutic agents for effective, targeted, photothermally induced drug delivery under near-infrared (NIR) light. AuHNSs were synthesized by galvanic replacement reaction. We further conjugated antibodies against the epidermal growth factor receptor (EGFR) to the PEGylated AuHNS, followed by loading with the antitumor drug doxorubicin (AuHNS-EGFR-DOX) for lung cancer treatment. AuHNSs showed similar photothermal efficiency to gold nanorods under optimized NIR laser power. The targeting of AuHNS-EGFR-DOX was confirmed by light-scattering images of A549 cells, and doxorubicin release from the AuHNSs was evaluated under low pH and NIR-irradiated conditions. Multifunctional AuHNS-EGFR-DOX induced photothermal ablation of the targeted lung cancer cells and rapid doxorubicin release following irradiation with NIR laser. Furthermore, we evaluated the effectiveness of AuHNS-EGFR-DOX drug delivery by comparing two drug delivery methods: receptor-mediated endocytosis and cell-surface targeting. Accumulation of the AuHNS-EGFR-DOX on the cell surfaces by targeting EGFR turned out to be more effective for lung cancer treatments than uptake of AuHNS-EGFR-DOX. Taken together, our data suggest a new and optimal method of NIR-induced drug release via the accumulation of targeted AuHNS-EGFR-DOX on cancer cell membranes. PMID:25662498

  5. Digestive ripening facilitated atomic diffusion at nanosize regime: Case of AuIn{sub 2} and Ag{sub 3}In intermetallic nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Arora, Neha [Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012 (India); Jagirdar, Balaji R., E-mail: jagirdar@ipc.iisc.ernet.in [Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012 (India); Klabunde, Kenneth J. [Department of Chemistry, Kansas State University, Manhattan, KS 66506 (United States)

    2014-10-15

    Highlights: • A digestive ripening facilitated interatomic diffusion process is presented. • Nearly monodisperse AuIn{sub 2} and Ag{sub 3}In intermetallic nanoparticles were synthesized. • Optimization of reaction temperature facilitates interatomic transfer. • Presence of excess ligand plays a crucial role in the digestive ripening process. - Abstract: Monodisperse colloidal gold–indium (AuIn{sub 2}) intermetallic nanoparticles have been synthesized from Au and In colloids using the digestive ripening process. Formation of the intermetallic proceeds via digestive ripening facilitated atomic diffusion of Au and In atoms from the Au and In nanoparticles followed simultaneously by their growth in the solution. Optimization of the reaction temperature was found to be crucial for the formation of AuIn{sub 2} intermetallic from gold and indium nanoparticles. Transmission electron microscopy revealed the presence of nearly monodisperse nanoparticles of Au and AuIn{sub 2} with particle size distribution of 3.7 ± 1.0 nm and 5.0 ± 1.6 nm, respectively. UV–visible spectral studies brought out the absence of SPR band in pure AuIn{sub 2} intermetallic nanoparticles. Optical study and electron microscopy, in combination with powder X-ray diffraction established phase pure AuIn{sub 2} intermetallic nanoparticles unambiguously. The potential of such an unprecedented approach has been further exploited in the synthesis of Ag{sub 3}In intermetallic nanoparticles with the dimension of less than 10 nm.

  6. Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters.

    Science.gov (United States)

    Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y; Nobusada, Katsuyuki; Jin, Rongchao

    2016-03-24

    Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications. PMID:26967673

  7. Theoretical study of PTCDA adsorbed on the coinage metal surfaces, Ag(111), Au(111) and Cu(111)

    Energy Technology Data Exchange (ETDEWEB)

    Romaner, L; Nabok, D; Puschnig, P; Ambrosch-Draxl, C [Chair of Atomistic Modelling and Design of Materials, University of Leoben, Franz-Josef-Strasse 18, A-8700 Leoben (Austria); Zojer, E [Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz (Austria)], E-mail: lorenz.romaner@unileoben.ac.at

    2009-05-15

    A thorough understanding of the adsorption of molecules on metallic surfaces is a crucial prerequisite for the development and improvement of functionalized materials. A prominent representative within the class of {pi}-conjugated molecules is 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) which, adsorbed on the Ag(111), Au(111) or Cu(111) surfaces, shows characteristic trends for work-function modification, alignment of molecular levels with the substrate Fermi energy and binding distances. We carried out density functional theory (DFT) calculations to investigate to what extent these trends can be rationalized on a theoretical basis. We used different density functionals (DF) including a fully non-local van der Waals (vdW) DF capable of describing dispersion interactions. We show that, rather independent of the DF, the calculations yield level alignments and work-function modifications consistent with ultra-violet photoelectron spectroscopy when the monolayer is placed onto the surfaces at the experimental distances (as determined from x-ray standing wave experiments). The lowest unoccupied molecular orbital is occupied on the Ag and Cu surfaces, whereas it remains unoccupied on the Au surface. Simultaneously, the work function increases for Ag but decreases for Cu and Au. Adsorption distances and energies, on the other hand, depend very sensitively on the choice of the DF. While calculations in the local density approximation bind the monolayer consistently with the experimental trends, the generalized gradient approximation in several flavors fails to reproduce realistic distances and energies. Calculations employing the vdW-DF reveal that substantial bonding contributions arise from dispersive interactions. They yield reasonable binding energies but larger binding distances than the experiments.

  8. Theoretical study of PTCDA adsorbed on the coinage metal surfaces, Ag(111), Au(111) and Cu(111)

    International Nuclear Information System (INIS)

    A thorough understanding of the adsorption of molecules on metallic surfaces is a crucial prerequisite for the development and improvement of functionalized materials. A prominent representative within the class of π-conjugated molecules is 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) which, adsorbed on the Ag(111), Au(111) or Cu(111) surfaces, shows characteristic trends for work-function modification, alignment of molecular levels with the substrate Fermi energy and binding distances. We carried out density functional theory (DFT) calculations to investigate to what extent these trends can be rationalized on a theoretical basis. We used different density functionals (DF) including a fully non-local van der Waals (vdW) DF capable of describing dispersion interactions. We show that, rather independent of the DF, the calculations yield level alignments and work-function modifications consistent with ultra-violet photoelectron spectroscopy when the monolayer is placed onto the surfaces at the experimental distances (as determined from x-ray standing wave experiments). The lowest unoccupied molecular orbital is occupied on the Ag and Cu surfaces, whereas it remains unoccupied on the Au surface. Simultaneously, the work function increases for Ag but decreases for Cu and Au. Adsorption distances and energies, on the other hand, depend very sensitively on the choice of the DF. While calculations in the local density approximation bind the monolayer consistently with the experimental trends, the generalized gradient approximation in several flavors fails to reproduce realistic distances and energies. Calculations employing the vdW-DF reveal that substantial bonding contributions arise from dispersive interactions. They yield reasonable binding energies but larger binding distances than the experiments.

  9. Origin and shape evolution of core-shell nanoparticles in Au-Pd: from few atoms to high Miller index facets

    Energy Technology Data Exchange (ETDEWEB)

    Bhattarai, Nabraj; Casillas, Gilberto; Khanal, Subarna; Velazquez Salazar, J. Jesus; Ponce, Arturo; Jose-Yacaman, Miguel, E-mail: miguel.yacaman@utsa.edu [University of Texas at San Antonio, Department of Physics and Astronomy (United States)

    2013-06-15

    Au-Pd core-shell nanocubes and triangular nanoparticles were systematically synthesized from a few Pd layers up to fully grown morphologies by a modified seed-mediated growth method. The shape evolution of Au-Pd core-shell nanoparticles from single crystal and singly twinned seed to final concave nanocube and triangular plates are presented at atomic level by Cs-corrected scanning transmission electron microscopy (STEM). The growth mechanism of both morphologies was studied throughout different sizes. It was found that the concave nanocubes grew from octahedral Au seeds due to fast growth along Left-Pointing-Angle-Bracket 111 Right-Pointing-Angle-Bracket directions; while the triangular nanoparticles grew from singly twinned Au seeds, growing twice as fast in Left-Pointing-Angle-Bracket 110 Right-Pointing-Angle-Bracket directions along the twin boundary; compared to the Left-Pointing-Angle-Bracket 111 Right-Pointing-Angle-Bracket direction perpendicular to the twin boundary. Both the concave nanocubes and triangular nanoparticles presented high index facet (HIF) surfaces that will increase the catalytic activity of different reactions.

  10. Swift heavy ion (SHI) modification of Ag/Au-TiO2 nanocomposite thin films prepared by co-sputtering

    International Nuclear Information System (INIS)

    Ag-TiO2 and Au-TiO2 nanocomposites with different volume fractions of metal nanoparticles were prepared by co-sputtering. The morphology of these nanocomposites was investigated by transmission electron microscopy (TEM). Metal volume fractions were determined by SEM-EDX. Optical characterization of these nanocomposites was carried out using UV/Vis/NIR spectroscopy. The nanocomposites were then irradiated by swift heavy ions (SHI) with 100 MeV (Ag8+ ions) at different fluences ranging from 1 X 1012 to 1 X 1013 ions/cm2. The extinction spectra of the pristine samples show plasmon resonances at wavelengths which depend on the volume fraction of metal, particle size and morphology of the composites. The influence of the SHI fluences, on the microstructure and the extinction spectra were observed. The changes in the properties of these nanocomposites are discussed in terms of ion-material interactions

  11. Growth behavior and field emission property of ZnO nanowire arrays on Au and Ag films

    Directory of Open Access Journals (Sweden)

    Sung Hyun Kim

    2013-09-01

    Full Text Available We propose a facile method to control the growth and areal density of zinc-oxide (ZnO nanowire arrays using gold or silver films deposited on aluminum-doped ZnO (AZO layers coated on glass substrates. Nanowires exceeding 5 μm in length grew on both the glass/AZO-layer and on the glass/AZO-layer/Au-film where the areal array density was controlled primarily by changing the annealing temperature. In contrast, the nanowire arrays grew only on the AZO surface but not on the Ag film owing to the formation of an Ag-oxide layer. We fabricated field emitter devices with density controlled ZnO nanowire arrays and low turn-on electric field of ∼6 V/μm and a field enhancement factor of up to 1188 were obtained with density controlled ZnO nanowire arrays.

  12. The effect of intermetallic compound evolution on the fracture behavior of Au stud bumps joined with Sn-3.5Ag solder

    Science.gov (United States)

    Lee, Young-Kyu; Ko, Yong-Ho; Kim, Jun-Ki; Lee, Chang-Woo; Yoo, Sehoon

    2013-01-01

    The microstructure and joint properties of Au stud bumps joined with Sn-3.5Ag solder were investigated as functions of flip chip bonding temperature and aging time. Au stud bumps were bonded on solder-onpad (SOP) at bonding temperature of 260°C and 300°C for 10 s, respectively. Aging treatment was carried out at 150°C for 100 h, 300 h, and 500 h, respectively. After flip chip bonding, intermetallic compounds (IMCs) of AuSn, AuSn2, and AuSn4 were formed at the interface between the Au stud bump and Sn-3.5Ag solder. At a bonding temperature of 300°C, AuSn2 IMC clusters, which were surrounded by AuSn4 IMCs, were observed in the Sn-3.5Ag solder bump. After flip chip bonding, bonding strength was approximately 220.5mN/bump. As aging time increased, the bonding strength decreased. After 100 h of aging treatment, the bonding strength of the joint bonded at 300°C was lower than that bonded at 260°C due to the fast growth rate of the AuSn2 IMCs. The main failure modes were interface fractures between the AuSn2 IMCs and AuSn4 IMCs, fractures through the AuSn2 IMCs and pad lift. Initial joint microstructures after flip chip bonding strongly affected the bonding strengths of aged samples.

  13. Superior effect of Ni-substitution on the hydrogenation kinetics of Mg6Pd1−xTMx (TM = Ag, Cu, Ni) pseudo-binary compounds

    International Nuclear Information System (INIS)

    Highlights: • Kinetics of (de)hydrogenation of Mg6(Pd,TM) TM = Ag, Cu and Ni compared. • Faster hydrogenation kinetics for the Ni compound. • Faster H-desorption for the Ni compound due to MgH2/Mg2NiH4 synergy. - Abstract: In this investigation, the H-sorption kinetics of Mg6Pd and Mg6Pd1−xTMx (TM = Ag, Cu, Ni) pseudo-binary compounds at the TM solubility limit have been studied by isothermal hydrogen absorption, thermal desorption spectroscopy and in situ neutron diffraction. Among all studied compounds, the fastest absorption kinetics takes place for the Ni-substituted one. The fit of the absorption curves to established model equations for solid–gas reaction shows that hydrogenation is controlled by diffusion. As for desorption, the peak temperature for the Ni-substituted compound is 90 K below that of MgH2/Mg system and is characterised by a low activation energy of 68 kJ/molH2. To better understand these results, neutron diffraction experiments during in situ thermal desorption of deuterated Mg6Pd and Mg6Pd0.25Ni0.75 compounds were carried out. These experiments demonstrate a synergetic effect between MgH2 and Mg2NiH4 hydrides as responsible for the remarkable kinetics of the Ni-containing compound

  14. Structural control and K/Ar dating of the Au-Ag epithermal veins in the Shila Cordillera, southern Peru

    International Nuclear Information System (INIS)

    The Au-Ag epithermal mineralization of the Shila Cordillera is dated at about 10.7 Ma (K/Ar on adularia). The vein system is characterized by the association of a major ≅ east-west vein and N120-135 deg. E secondary fractures. The strike-slip faults controlling the veins indicate an initial NE-SW to ENE-WSW Shortening direction, which is compatible with that generally accepted for this period. These structures were reopened during a second phase and channeled mineralizing fluids, the circulation of which may have began at the end of stage 1. (authors)

  15. Multifragmentation in the 4.8-GeV 3He+ natAg, 197Au reactions

    International Nuclear Information System (INIS)

    Multifragmentation of natAg and 197Au nuclei induced by a 4.8-GeV 3He ions has been studied with the Indiana Silicon Sphere 4π detector array. Rapidity and moving source analyses are consistent with thermal emission from a source in approximate kinetic equilibrium. For the most dissipative collisions, the spectral Coulomb peaks are broadened to very low energies, indicative of emission from an extended nuclear system. Predictions of a model with an intranuclear cascade and an expanding, emitting source compare well with experimental multiplicity distributions and the evolution of fragment spectral shapes

  16. Multifragmentation in the 4.8-GeV {sup 3}He+ {sup nat}Ag, {sup 197}Au reactions

    Energy Technology Data Exchange (ETDEWEB)

    Kwiatkowski, K.; Morley, K.B.; Foxford, E.R.; Bracken, D.S.; Viola, V.E.; Yoder, N.R.; Legrain, R.; Pollacco, E.C.; Volant, C.; Friedman, W.A.; Korteling, R.G.; Brzychczyk, J.; Breuer, H. [Department of Chemistry and Physics and IUCF, Indiana University, Bloomington, Indiana 47405 (United States)]|[Commissariat a l`Energie Atomique DAPNIA/Service de Physique des Particles, Centre d`Etudes de Saclay, 91191 Gif-sur-Yvette Cedex (France)]|[Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1SG (Canada)]|[Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)]|[Institute of Physics, Jagiellonian University, 30-059 Krakow (Poland)]|[Department of Physics, University of Maryland, College Park, Maryland 20742 (United States)

    1995-05-08

    Multifragmentation of {sup nat}Ag and {sup 197}Au nuclei induced by a 4.8-GeV {sup 3}He ions has been studied with the Indiana Silicon Sphere 4{pi} detector array. Rapidity and moving source analyses are consistent with thermal emission from a source in approximate kinetic equilibrium. For the most dissipative collisions, the spectral Coulomb peaks are broadened to very low energies, indicative of emission from an extended nuclear system. Predictions of a model with an intranuclear cascade and an expanding, emitting source compare well with experimental multiplicity distributions and the evolution of fragment spectral shapes.

  17. One-pot synthesis of Au@Pd core-shell nanocrystals with multiple high- and low-index facets and their high electrocatalytic performance

    Science.gov (United States)

    Park, Yangsun; Lee, Young Wook; Kang, Shin Wook; Han, Sang Woo

    2014-07-01

    Bimetallic nanocrystals (NCs) enclosed by high-surface energy facets have been of enormous interest due to their pronounced catalytic performance in numerous chemical and electrochemical reactions. However, it remains a significant challenge to develop a facile method to synthesize bimetallic NCs with high-surface energy facets in the form of finely tuned structures due to the difficulties in manipulating the nucleation and growth kinetics of NCs in the presence of multiple metal precursors. In the present work, a facile one-pot aqueous synthesis method is developed for the production of bimetallic Au@Pd core-shell NCs with an unusual truncated hexoctahedral (THOH) shape without pre-synthesized seeds. The THOH Au@Pd NCs are bound by multiple high- and low-index facets. The formation of this unique structure is realized through co-reduction of Au and Pd precursors under precisely controlled kinetic conditions. The prepared THOH NCs exhibit a prominent electrocatalytic performance for ethanol oxidation, which is attributed to their characteristic structural features. This study significantly expands the understanding of NC growth and will lead to fabricating novel nanomaterials with desired morphologies and functions.Bimetallic nanocrystals (NCs) enclosed by high-surface energy facets have been of enormous interest due to their pronounced catalytic performance in numerous chemical and electrochemical reactions. However, it remains a significant challenge to develop a facile method to synthesize bimetallic NCs with high-surface energy facets in the form of finely tuned structures due to the difficulties in manipulating the nucleation and growth kinetics of NCs in the presence of multiple metal precursors. In the present work, a facile one-pot aqueous synthesis method is developed for the production of bimetallic Au@Pd core-shell NCs with an unusual truncated hexoctahedral (THOH) shape without pre-synthesized seeds. The THOH Au@Pd NCs are bound by multiple high- and

  18. Study of the effects of MeV Ag, Cu, Au, and Sn implantation on the optical properties of LiNbO3

    International Nuclear Information System (INIS)

    The authors present the results of characterization of linear absorption and nonlinear refractive index of Au, Ag, Cu and Sn ion implantation into LiNbO3. Ag was implanted at 1.5 MeV to fluences of 2 to 17 x 10 16/cm2 at room temperature. Au and Cu were implanted to fluences of 5 to 20 x 1016/cm2 at an energy of 2.0 MeV. Sn was implanted to a fluence of 1.6 x 1017/cm2 at 160 kV. Optical absorption spectrometry indicated an absorption peak for the Au implanted samples after heat treatment at 1,000 C at 620 nm. The Ag implanted samples absorption peaks shifted from 450 nm before heat treatment to 550 nm after 500 C for 1h. Heat treatment at 800 C returned the Ag implanted crystals to a clear state. Cu nanocluster absorption peaks disappears at 500 C. No Sn clusters were observed by optical absorption or XRD. The size of the Ag and Au clusters as a function of heat treatment were determined from the absorption peaks. The Ag clusters did not change appreciably in size with heat treatment. The Au clusters increased from 3 to 9 nm diameter upon heat treatment at 1000 deg C. TEM analysis performed on a Au implanted crystal indicated the formation of Au nanocrystals with facets normal to the c-axis. Measurements of the nonlinear refractive indices were carried out using the Z-scan method with a tunable dye laser pumped by a frequency doubled mode-locked Nd:YAG laser. The dye laser had a 4.5 ps pulse duration time and 76 MHz pulse repetition rate (575 nm)

  19. Changes in the microbiological and chemical characteristics of white bread during storage in paper packages modified with Ag/TiO2-SiO2, Ag/N-TiO2 or Au/TiO2.

    Science.gov (United States)

    Peter, Anca; Mihaly-Cozmuta, Leonard; Mihaly-Cozmuta, Anca; Nicula, Camelia; Ziemkowska, Wanda; Basiak, Dariusz; Danciu, Virginia; Vulpoi, Adriana; Baia, Lucian; Falup, Anca; Craciun, Grigore; Ciric, Alexandru; Begea, Mihaela; Kiss, Claudia; Vatuiu, Daniela

    2016-04-15

    Microbiological and chemical characteristics of white bread during storage in paper-packages modified with Ag/TiO2-SiO2, Ag/N-TiO2 or Au/TiO2 were investigated. The whiteness and the water retention of the modified packages were slightly superior to those exhibited by the reference sample, as the color of the composite was lighter. The water retention was very good especially for the Ag/TiO2-SiO2-paper. These improvements can be associated with the high specific surface area and with the low agglomeration tendency of Ag nanoparticles in comparison with the Au ones. The preservation activity of the composites for the bread storage is positively influenced by photoactivity and presence of nano-Ag. Packages Ag/TiO2-SiO2-paper and Ag/N-TiO2-paper can find their applicability for extending the shelf life of bread by 2 days as compared with the unmodified paper-package. No influence of the Au/TiO2 on the extending the shelf life of bread was observed. PMID:26617018

  20. Autothermal reforming of methane for producing high-purity hydrogen in a Pd/Ag membrane reactor

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Hsin-Fu; Pai, Wen-Ju; Chen, Ying-Ju [Department of Chemical Engineering, Feng Chia University, Taichung 407 (China); Lin, Wen-Hsiung [Department of Beauty Science, Chienkuo Technology University, Changhua 500 (China)

    2010-12-15

    Autothermal reforming of methane includes steam reforming and partial oxidizing methane. Theoretically, the required endothermic heat of steam reforming of methane could be provided by adding oxygen to partially oxidize the methane. Therefore, combining the steam reforming of methane with partial oxidation may help in achieving a heat balance that can obtain better heat efficacy. Membrane reactors offer the possibility of overcoming the equilibrium conversion through selectively removing one of the products from the reaction zone. For instance, only can hydrogen products permeate through a palladium membrane, which shifts the equilibrium toward conversions that are higher than the thermodynamic equilibrium. In this study, autothermal reforming of methane was carried out in a traditional reactor and a Pd/Ag membrane reactor, which were packed with an appropriate amount of commercial Ni/MgO/Al{sub 2}O{sub 3} catalyst. A power analyzer was employed to measure the power consumption and to check the autothermicity. The average dense Pd/Ag membrane thickness is 24.3 {mu}m, which was coated on a porous stainless steel tube via the electroless palladium/silver plating procedure. The experimental operating conditions had temperatures that were between 350 C and 470 C, pressures that were between 3 atm and 7 atm, and O{sub 2}/CH{sub 4} = 0-0.5. The effects of the operating conditions on methane conversion, permeance of hydrogen, H{sub 2}/CO, selectivities of CO{sub x}, amount of power supply, and the carbon deposition of the catalyst after the reaction is thoroughly discussed in this paper. The experimental results indicate that an optimum methane conversion of 95%, with a hydrogen production rate of 0.093 mol/m{sup 2}. S, can be obtained from the autothermal reforming of methane at H{sub 2}O/CH{sub 4} = 1.3 and O{sub 2}/CH{sub 4} near 0.4, at which the reaction does not consume power, and the catalysts are not subject to any carbon deposition. (author)

  1. Reactivity towards nitriles, cyanamides, and carbodiimides of palladium complexes derived from benzyl alcohol. Synthesis of a mixed Pd2Ag complex.

    Science.gov (United States)

    Fernández-Rodríguez, María-José; Martínez-Viviente, Eloísa; Vicente, José; Jones, Peter G

    2016-01-14

    The chelate complex [Pd(κ(2)-C,O-C6H4CH2O-2)(bpy)] () reacts with acetonitrile, cyanamides, or carbodiimides, in the presence of AgOTf (1 : 5 : 1 molar ratio) and residual water, to form complexes [Pd{κ(2)-C,N-C6H4{CH2OC([double bond, length as m-dash]NX)Y}-2}(bpy)](OTf), where X = H, Y = Me (), NMe2 (), NEt2 (), X = R, Y = NHR (R = (i)Pr (), Tol ()), as a result of the insertion of the unsaturated reagent into the O-Pd bond of and the protonation of one of the N atoms. In the absence of AgOTf the reaction of with TolN[double bond, length as m-dash]C[double bond, length as m-dash]NTol (Tol = p-Tolyl) results in the formation of the neutral complex [Pd{κ(2)-C,N-C6H4{CH2OC([double bond, length as m-dash]NTol)NTol}-2}(bpy)] (). Complexes and can be interconverted by deprotonation ( + KO(t)Bu) or protonation ( + KOTf + HOTf) reactions. When the reaction of with TolN[double bond, length as m-dash]C[double bond, length as m-dash]NTol in the presence of AgOTf is carried out in a 1 : 1 : 1 stoichiometric ratio, or for a short period of time, a mixture of and a mixed heterometallic Ag2Pd complex is obtained ( = [Ag(N-)2](OTf)). Complex is the major product when the AgOTf is added before the carbodiimide, and the reaction is stopped immediately. can also be obtained by reaction of with 0.5 equiv. of AgOTf. When complex [PdI(C6H4CH2OH-2)(bpy)] () reacts with (i)PrN[double bond, length as m-dash]C[double bond, length as m-dash]N(i)Pr in the presence of TlOTf, instead of AgOTf, a ca. 1 : 1 mixture of and [Pd{κ(2)-O,N-OCH2{C6H4{C([double bond, length as m-dash]NH(i)Pr)N(i)Pr}-2}}(bpy)](OTf) () forms. Complex is the result of the insertion of the carbodiimide into the C-Pd bond. Complexes have been extensively characterized by NMR spectroscopy, and the crystal structures of , , and ·2.5CHCl3·0.5Et2O have been determined by X-ray diffraction studies. PMID:26646443

  2. Environmentally benign synthesis of amides and ureas via catalytic dehydrogenation coupling of volatile alcohols and amines in a Pd-Ag membrane reactor

    KAUST Repository

    Chen, Tao

    2016-05-31

    In this study, we report the direct synthesis of amides and ureas via the catalytic dehydrogenation of volatile alcohols and amines using the Milstein catalyst in a Pd-Ag/ceramic membrane reactor. A series of amides and ureas, which could not be synthesized in an open system by catalytic dehydrogenation coupling, were obtained in moderate to high yields via catalytic dehydrogenation of volatile alcohols and amines. This process could be monitored by the hydrogen produced. Compared to the traditional method of condensation, this catalytic system avoids the stoichiometric pre-activation or in situ activation of reagents, and is a much cleaner process with high atom economy. This methodology, only possible by employing the Pd-Ag/ceramic membrane reactor, not only provides a new environmentally benign synthetic approach of amides and ureas, but is also a potential method for hydrogen storage.

  3. The fabrication of stable superhydrophobic surfaces using a thin Au/Pd coating over a hydrophilic 3C-SiC nanorod network

    Science.gov (United States)

    Khan, Afzal; Sohail, Shiraz; Jacob, Chacko

    2015-10-01

    In this work, it has been demonstrated that for hydrophilic materials, like SiC, etc., superhydrophobicity can be achieved by coating them with a material like Au/Pd with surface adsorbed organic contaminants, rather than modifying them by fluoropolymers as is usually done. Dense and randomly aligned 3C-SiC nanorods were grown in a cold-wall APCVD reactor using Ni as a catalyst which formed a network of micro/nano air pockets and exhibited superhydrophobic behavior when modified by an Au/Pd metal alloy coating by forming hierarchical nanostructures with surface adsorbed organic contaminants. A high water contact angle (160°), very low sliding angle (atmosphere at room temperature, which demonstrates the long term stability of these superhydrophobic surfaces.

  4. Quantitative detection of uric acid by electrochemical-surface enhanced Raman spectroscopy using a multilayered Au/Ag substrate.

    Science.gov (United States)

    Zhao, Lili; Blackburn, Jonathan; Brosseau, Christa L

    2015-01-01

    Uric acid is a potential important biomarker in urine and serum samples for early diagnosis of preeclampsia, a life-threatening hypertensive disorder that occurs during pregnancy. Preeclampsia is a leading cause of maternal death, especially in developing nation settings. Quantitative detection of uric acid for rapid and routine diagnosis of early preeclampsia using electrochemical-surface enhanced Raman spectroscopy (EC-SERS) is presented herein. A uniform EC-SERS active Au/Ag substrate was developed by depositing nearly monodisperse gold and silver nanoparticles on the carbon working electrode surface of screen printed electrodes. The multilayered Au/Ag substrates were characterized by electron microscopy and used for quantitative detection of uric acid in 0.1 M NaF and synthetic urine at clinically relevant concentrations. These results showed a linear relationship between the EC-SERS signal intensity and the uric acid concentration. Relative errors calculated for selected concentrations were all within the Clinical Laboratory Improvement Amendments (CLIA) criterion for uric acid analysis (±17%). It is believed that routine and early diagnosis of disease could be possible through such quantitative detection of biomarkers in patient samples using this EC-SERS method. PMID:25483146

  5. Excitation function of squared speed-of-sound extracted from (net-)proton rapidity spectra in Au-Au and Pb-Pb collisions over an energy range from AGS to RHIC

    CERN Document Server

    Gao, Li-Na; Sun, Yan; Sun, Zhu; Lacey, Roy A

    2016-01-01

    Experimental results of the rapidity distributions of protons and net-protons (protons minus antiprotons) emitted in gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions, measured by a few collaborations at the alternating gradient synchrotron (AGS), super proton synchrotron (SPS), and relativistic heavy ion collider (RHIC), are described by a revised Landau hydrodynamic model. The values of squared speed-of-sound parameter $c^2_s$ are then extracted from the rapidity distribution widths of (net-)protons. The excitation function of $c^2_s$ of the interacting system in Au-Au and Pb-Pb collisions over an energy range from AGS to RHIC is obtained to show a local minimum or softest point in the equation of state (EoS) at the center-of-mass energy per nucleon pair $\\sqrt{s_{NN}}=8.8$ GeV which confirms our previous result.

  6. Interface controlled growth of nanostructures in discontinuous Ag and Au thin films fabricated by ion beam sputter deposition for plasmonic applications

    Indian Academy of Sciences (India)

    R Brahma; M Ghanashyam Krishna

    2012-08-01

    The growth of discontinuous thin films of Ag and Au by low energy ion beam sputter deposition is reported. The study focuses on the role of the film–substrate in determining the shape and size of nanostructures achieved in such films. Ag films were deposited using Ar ion energy of 150 eV while the Au films were deposited with Ar ion energies of 250–450 eV. Three types of interfaces were investigated in this study. The first set of film–substrate interfaces consisted of Ag and Au films grown on borosilicate glass and carbon coated Cu grids used as substrates. The second set of films was metallic bilayers in which one of the metals (Ag or Au) was grown on a continuous film of the other metal (Au or Ag). The third set of interfaces comprised of discontinuous Ag and Au films deposited on different dielectrics such as SiO2, TiO2 and ZrO2. In each case, a rich variety of nanostructures including self organized arrays of nanoparticles, nanoclusters and nanoneedles have been achieved. The role of the film–substrate interface is discussed within the framework of existing theories of thin film nucleation and growth. Interfacial nanostructuring of thin films is demonstrated to be a viable technique to realize a variety of nanostructures. The use of interfacial nanostructuring for plasmonic applications is demonstrated. It is shown that the surface Plasmon resonance of the metal nanostructures can be tuned over a wide range of wavelengths from 400 to 700 nm by controlling the film–substrate interface.

  7. Enhancement of chitosan-graphene oxide SPR sensor with a multi-metallic layers of Au-Ag-Au nanostructure for lead(II) ion detection

    Science.gov (United States)

    Kamaruddin, Nur Hasiba; Bakar, Ahmad Ashrif A.; Yaacob, Mohd Hanif; Mahdi, Mohd Adzir; Zan, Mohd Saiful Dzulkefly; Shaari, Sahbudin

    2016-01-01

    We demonstrate the enhancement of surface plasmon resonance (SPR) technique by implementing a multi-metallic layers of Au-Ag-Au nanostructure in the chitosan-graphene oxide (CS-GO) SPR sensor for lead(II) ion detection. The performance of the sensor is analyzed via SPR measurements, from which the sensitivity, signal-to-noise ratio and repeatability are determined. The nanostructure layers are characterized using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). We showed that the proposed structure has increased the shift in the SPR angle up to 3.5° within the range of 0.1-1 ppm due to the enhanced evanescent field at the sensing layer-analyte interface. This sensor also exhibits great repeatability which benefits from the stable multi-metallic nanostructure. The SNR value of 0.92 for 5 ppm lead(II) ion solution and reasonable linearity range up to that concentration shows that the tri-metallic CS-GO SPR sensor gives a good response towards the lead(II) ion solution. The CS-GO SPR sensor is also sensitive to at least a 10-5 change in the refractive index. The results prove that our proposed tri-metallic CS-GO SPR sensor demonstrates a strong performance and reliability for lead(II) ion detection in accordance with the standardized lead safety level for wastewater.

  8. Composite particle production in relativistic Au+Au collisions at AGS: First results from the E866 forward spectrometer at sign 2, 4, and 10.8 A·GeV

    International Nuclear Information System (INIS)

    Particle spectra were measured for Au + Au collisions at 2, 4, and 10. 8 A·GeV using the E866 spectrometers. Recent results on proton emission and composite particle production form the E866 forward spectrometer data taken in 1994 together with the first results from the 1995/6 AGS running period are presented. Preliminary results indicate a decrease in the coalescence scaling coefficient with increasing projectile energy and centrality

  9. Hardening by cooling rate control and post-firing heat treatment in Pd-Ag-Sn alloy for bonding porcelain.

    Science.gov (United States)

    Yu, Young-Jun; Seol, Hyo-Joung; Cho, Mi-Hyang; Kim, Hyung-Il; Kwon, Yong Hoon

    2016-01-01

    The aim of this study was to determine the hardening effect by controlling the cooling rate during the porcelain firing process and performing an additional post-firing heat treatment in a Pd-Ag-Sn alloy. The most effective cooling rate for alloy hardening was determined by cooling the specimens at various cooling rates after oxidation treatment. A subsequent porcelain firing simulation followed by cooling at the selected cooling rate was performed. A post-firing heat treatment was then done at 600°C in a porcelain furnace. The hardening mechanism was characterized by a hardness test, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Alloy softening occurred during the porcelain firing process followed by cooling at a controlled cooling rate. A post-firing heat treatment allowed apparent precipitation hardening. It is advisable to perform a postfiring heat treatment at 600°C in a porcelain furnace by annealing metal substructure after porcelain fusing. PMID:27041022

  10. Quantitative description of short-range order and its influence on the electronic structure in Ag-Pd alloys.

    Science.gov (United States)

    Hoffmann, M; Marmodoro, A; Ernst, A; Hergert, W; Dahl, J; Lång, J; Laukkanen, P; Punkkinen, M P J; Kokko, K

    2016-08-01

    We investigate the effect of short-range order (SRO) on the electronic structure in alloys from the theoretical point of view using density of states (DOS) data. In particular, the interaction between the atoms at different lattice sites is affected by chemical disorder, which in turn is reflected in the fine structure of the DOS and, hence, in the outcome of spectroscopic measurements. We aim at quantifying the degree of potential SRO with a proper parameter. The theoretical modeling is done with the Korringa-Kohn-Rostoker Green's function method. Therein, the extended multi-sublattice non-local coherent potential approximation is used to include SRO. As a model system, we use the binary solid solution Ag c Pd1-c at three representative concentrations c  =  0.25, 0.5 and 0.75. The degree of SRO is varied from local ordering to local segregation through an intermediate completely uncorrelated state. We observe some pronounced features, which change over the whole energy range of the valence bands as a function of SRO in the alloy. These spectral variations should be traceable in modern photoemission experiments. PMID:27269809

  11. Comparative Study on The Photocatalytic Hydrogen Production from Methanol over Cu-, Pd-, Co- and Au-Loaded TiO2

    Directory of Open Access Journals (Sweden)

    Udani P.P.C.

    2015-09-01

    Full Text Available Photocatalytic hydrogen production from a methanol-water solution was investigated in a semi-continuous reactor over different metal-loaded TiO2 catalysts under UltraViolet (UV light irradiation. The catalysts were mainly prepared by the incipient wetness impregnation method by varying the metal weight ratio in the range of 1-10 wt%. The effects of metal loading and H2 pre-treatment on the photocatalytic activity were investigated. In addition, the activity of the catalysts was also compared with a reference Au-TiO2 catalyst from the World Gold Council (WGC. The photocatalysts were characterized by using X-Ray Diffraction (XRD and N2 physisorption before and after the activity measurements. The photocatalytic activity decreased in the order of Pd > Au > Cu > Co in the comparative study of Cu-TiO2, Co-TiO2, Au-TiO2 and Pd-TiO2. Optimum hydrogen evolution was achieved with 5 wt% Pd-TiO2 and 5 wt% Cu-TiO2.

  12. Electrical and structural properties of (Pd/Au) Schottky contact to as grown and rapid thermally annealed GaN grown by MBE

    Science.gov (United States)

    Nirwal, Varun Singh; Singh, Joginder; Gautam, Khyati; Peta, Koteswara Rao

    2016-05-01

    We studied effect of thermally annealed GaN surface on the electrical and structural properties of (Pd/Au) Schottky contact to Ga-polar GaN grown by molecular beam epitaxy on Si substrate. Current voltage (I-V) measurement was used to study electrical properties while X-ray diffraction (XRD) measurement was used to study structural properties. The Schottky barrier height calculated using I-V characteristics was 0.59 eV for (Pd/Au) Schottky contact on as grown GaN, which increased to 0.73 eV for the Schottky contact fabricated on 700 °C annealed GaN film. The reverse bias leakage current at -1 V was also significantly reduced from 6.42×10-5 A to 7.31×10-7 A after annealing. The value of series resistance (Rs) was extracted from Cheung method and the value of Rs decreased from 373 Ω to 172 Ω after annealing. XRD results revealed the formation of gallide phases at the interface of (Pd/Au) and GaN for annealed sample, which could be the reason for improvement in the electrical properties of Schottky contact after annealing.

  13. Ultrasensitive electrochemical immunoassay for surface array protein, a Bacillus anthracis biomarker using Au-Pd nanocrystals loaded on boron-nitride nanosheets as catalytic labels.

    Science.gov (United States)

    Sharma, Mukesh Kumar; Narayanan, J; Pardasani, Deepak; Srivastava, Divesh N; Upadhyay, Sanjay; Goel, Ajay Kumar

    2016-06-15

    Bacillus anthracis, the causative agent of anthrax, is a well known bioterrorism agent. The determination of surface array protein (Sap), a unique biomarker for B. anthracis can offer an opportunity for specific detection of B. anthracis in culture broth. In this study, we designed a new catalytic bionanolabel and fabricated a novel electrochemical immunosensor for ultrasensitive detection of B. anthracis Sap antigen. Bimetallic gold-palladium nanoparticles were in-situ grown on poly (diallyldimethylammonium chloride) functionalized boron nitride nanosheets (Au-Pd NPs@BNNSs) and conjugated with the mouse anti-B. anthracis Sap antibodies (Ab2); named Au-Pd NPs@BNNSs/Ab2. The resulting Au-Pd NPs@BNNSs/Ab2 bionanolabel demonstrated high catalytic activity towards reduction of 4-nitrophenol. The sensitivity of the electrochemical immunosensor along with redox cycling of 4-aminophenol to 4-quinoneimine was improved to a great extent. Under optimal conditions, the proposed immunosensor exhibited a wide working range from 5 pg/mL to 100 ng/mL with a minimum detection limit of 1 pg/mL B. anthracis Sap antigen. The practical applicability of the immunosensor was demonstrated by specific detection of Sap secreted by the B. anthracis in culture broth just after 1h of growth. These labels open a new direction for the ultrasensitive detection of different biological warfare agents and their markers in different matrices. PMID:26874112

  14. Magneto-optical Properties of (Pt/Co/X/IZO (X = Ta, Au, Pt, Ru and Ag Structures for Magneto-optical Spatial Light Modulators

    Directory of Open Access Journals (Sweden)

    Ishibashi T.

    2013-01-01

    Full Text Available Magneto-optical properties of Si sub./(Ta/Cu2/(Pt/Co multilayer/X/indium zinc oxide (IZO (X = Ta, Au, Pt, Ru, and Ag are studied. Kerr rotations, reflectivities and figures of merit of the structures are compared with those of (Ta/Cu2/(Pt/Co multilayer/X (X = Ta, Au, Pt, Ru, and Ag with IZO layers calculated by the virtual optical constant method. Two peaks caused by interference are confirmed in both of those spectra, and the Kerr rotation of the samples with Ta, Au, and Pt capping layer reached 1.2 degrees at approximately 2.7 eV. The sample with Au capping layer gave the highest figure of merit.

  15. Highly sensitive colorimetric detection of glucose in a serum based on DNA-embeded Au@Ag core-shell nanoparticles

    Science.gov (United States)

    Kang, Fei; Hou, Xiangshu; Xu, Kun

    2015-10-01

    Glucose is a key energy substance in diverse biology and closely related to the life activities of the organism. To develop a simple and sensitive method for glucose detection is extremely urgent but still remains a key challenge. Herein, we report a colorimetric glucose sensor in a homogeneous system based on DNA-embedded core-shell Au@Ag nanoparticles. In this assay, a glucose substrate was first catalytically oxidized by glucose oxidase to produce H2O2 which would further oxidize and gradually etch the outer silver shell of Au@Ag nanoparticles. Afterwards, the solution color changed from yellow to red and the surface plasmon resonance (SPR) band of Au@Ag nanoparticles declined and red-shifted from 430 to 516 nm. Compared with previous silver-based glucose colorimetric detection strategies, the distinctive SPR band change is superior to the color variation, which is critical to the high sensitivity of this assay. Benefiting from the outstanding optical property, robust stability and well-dispersion of the core-shell Au@AgNPs hybrid, this colorimetric assay obtained a detection limit of glucose as low as 10 nM, which is at least a 10-fold improvement over other AgNPs-based procedures. Moreover, this optical biosensor was successfully employed to the determination of glucose in fetal bovine serum.

  16. First principles calculations of the optical and plasmonic response of Au alloys and intermetallic compounds.

    Science.gov (United States)

    Keast, V J; Barnett, R L; Cortie, M B

    2014-07-30

    Pure Au is widely used in plasmonic applications even though its use is compromised by significant losses due to damping. There are some elements that are less lossy than Au (e.g. Ag or Al) but they will normally oxidize or corrode under ambient conditions. Here we examine whether alloying Au with a second element would be beneficial for plasmonic applications. In order to evaluate potential alternatives to pure Au, the density of states (DOS), dielectric function and plasmon quality factor have been calculated for alloys and compounds of Au with Al, Cd, Mg, Pd, Pt, Sn, Ti, Zn and Zr. Substitutional alloying of Au with Al, Cd, Mg and Zn was found to slightly improve the plasmonic response. Of the large number of intermetallic compounds studied, only AuAl2, Au3Cd, AuMg, AuCd and AuZn were found to be suitable for plasmonic applications. PMID:25001413

  17. A simple approach to uniform PdAg alloy membranes: Comparative study of conventional and silver concentration-controlled co-plating

    KAUST Repository

    Zeng, Gaofeng

    2014-03-01

    An Ag-controlled co-plating method was developed for the preparation of palladium/silver alloy membranes on porous tubular alumina supports. By controlling the feed rate of Ag to the Pd bath, the concentration of the silver in the plating bath was restricted during the course of plating. As a result, preferential deposition of silver at the beginning was suppressed and uniform dispersion of silver inside the membrane with silver composition in the desired range was achieved. Ultrathin (∼2.5 μm) PdAg alloy membranes with uniform silver composition of ∼25% were successfully obtained. The membrane showed a hydrogen permeance of 0.88 mol m-2 s-1 and pure-gas H2/N2 selectivity of 2140 at 823 K with ΔP = 100 kPa. Only one hydride phase existed in the studied temperature range from 373 to 823 K with ΔPH=100kPa. Direct comparisons with the conventional simply-mixed co-plating method showed that membranes made by the novel Ag-controlled co-plating method had much more uniform silver distribution, smoother surface, denser membrane structure, higher utilization rate of metal sources, and shorter alloying time. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

  18. Energetic consideration of the conduction type of Mg2Si doped with Cu, Ag, or Au using first-principle calculations

    International Nuclear Information System (INIS)

    Highlights: ► Energetic consideration of Cu-, Ag-, and Au-doped Mg2Si has been performed using first-principle calculations. ► Cu will be inserted into 4b site of Mg2Si, resulting in making a p-type compound. ► Au will substitute Si of the Mg2Si lattice, resulting in making an n-type compound. ► Difference in number of sites to be substituted or inserted by Ag causes p-type conduction of Ag-doped Mg2Si. - Abstract: Electronic energy calculations of Cu-, Ag-, or Au-doped Mg2Si, expected thermoelectric energy conversion materials, have been performed using a density-functional theory assuming that doped elements will work as either (1), substitutional impurities of Mg or Si sites of the Mg2Si lattice, or (2), inserted impurities into its 4b sites. From the energetic point of view, it was found that Cu will be most favorably inserted into the 4b site of Mg2Si, resulting in making a p-type compound. Au will substitute Si of Mg2Si lattice to make an n-type compound. Ag will make both of an interstitial compound and a substitutional compound where Mg and Si are almost equally replaced, but the overall conduction type would be p-type. These predictions agrees well to the observed facts for Ag- and Au- doped Mg2Si but does not for Cu-doped Mg2Si, perhaps because of insufficient solubility of Cu into Mg2Si to compensate the n-type carriers of undoped Mg2Si.

  19. A further discussion of the factors controlling the distribution of Pt, Pd, Rh and Au in road dust, gullies, road sweeper and gully flusher sediment in the city of Sheffield, UK.

    Science.gov (United States)

    Prichard, H M; Sampson, J; Jackson, M

    2009-02-15

    Forty paired road dust and gully sediments from the city of Sheffield in NE England show that high platinum, palladium and rhodium concentrations derived from catalytic converters depend on proximity to both roundabouts rather than traffic lights and to topographic lows. Road dust outside schools and control samples, further away on the same road, show that Pt, Pd and Rh concentrations are dependent on passing traffic flow rather than numbers of stopping vehicles. Highest values of Pt+Pd in road dust are 852 ppb and 694 ppb in gullies. Rh has maximum values of 113 ppb in road dust and 49 ppb in gullies. Pt and Pd values of a few ppb to just over 100 ppb occur in road dust where traffic does not stop, on roads away from junctions. Pt, Pd, Rh and Au are all picked up by road sweepers and gully flushers both with maximum values of just over 100 ppb Pt and Pd. High Au values (maximum 610 ppb in a road dust) were located on pavements, in suburbs, outside schools and in road sweepers collecting in residential areas rather than on high traffic flow roads. Stratification of Pt and Pd in gullies was not observed whereas a high Au value was recorded at the bottom of a gully suggesting gravity concentration for Au. Anomalous Pd grades of 1050 ppb in road dust from a school entrance and 2040 ppb in a street sweeper sample were recorded. These high Pd- and Au-bearing samples do not have anomalous Pt or Rh values and may be sourced from jewellery or dental fillings. However, most samples have consistent Pt/Pd ratios of about 1 and Pt/Rh values of 4 to 5 indicating a catalytic converter source. Pt and Pd are concentrated in road dust at levels well above background in all the samples, including on high and low traffic flow roads. PMID:19081605

  20. ⁶⁴Cu-Doped PdCu@Au Tripods: A Multifunctional Nanomaterial for Positron Emission Tomography and Image-Guided Photothermal Cancer Treatment.

    Science.gov (United States)

    Pang, Bo; Zhao, Yongfeng; Luehmann, Hannah; Yang, Xuan; Detering, Lisa; You, Meng; Zhang, Chao; Zhang, Lei; Li, Zhi-Yuan; Ren, Qiushi; Liu, Yongjian; Xia, Younan

    2016-03-22

    This article reports a facile synthesis of radiolabeled PdCu@Au core-shell tripods for use in positron emission tomography (PET) and image-guided photothermal cancer treatment by directly incorporating radioactive (64)Cu atoms into the crystal lattice. The tripod had a unique morphology determined by the PdCu tripod that served as a template for the coating of Au shell, in addition to well-controlled specific activity and physical dimensions. The Au shell provided the nanostructure with strong absorption in the near-infrared region and effectively prevented the Cu and (64)Cu atoms in the core from oxidization and dissolution. When conjugated with D-Ala1-peptide T-amide (DAPTA), the core-shell tripods showed great enhancement in targeting the C-C chemokine receptor 5 (CCR5), a newly identified theranostic target up-regulated in triple negative breast cancer (TNBC). Specifically, the CCR5-targeted tripods with an arm length of about 45 nm showed 2- and 6-fold increase in tumor-to-blood and tumor-to-muscle uptake ratios, respectively, relative to their nontargeted counterpart in an orthotopic mouse 4T1 TNBC model at 24 h postinjection. The targeting specificity was further validated via a competitive receptor blocking study. We also demonstrated the use of these targeted, radioactive tripods for effective photothermal treatment in the 4T1 tumor model as guided by PET imaging. The efficacy of treatment was confirmed by the significant reduction in tumor metabolic activity revealed through the use of (18)F-fluorodeoxyglucose PET/CT imaging. Taken together, we believe that the (64)Cu-doped PdCu@Au tripods could serve as a multifunctional platform for both PET imaging and image-guided photothermal cancer therapy. PMID:26824412

  1. Self-standing corrugated Ag and Au-nanorods for plasmonic applications

    DEFF Research Database (Denmark)

    Habouti, S.; Mátéfi-Tempfli, M.; Solterbeck, C.-H.;

    2011-01-01

    of the NR arrays as substrates for molecular detection using Raman scattering and Rhodamine 6G (R6G) as a model dye strongly depends on noble metal. R6G concentrations down to 1 pM are detected on the corrugated arrays yielding an effective enhancement factor (EF) of approximately 2 × 10 for Ag...

  2. Applicability of near-infrared hyperspectral imagery (NIR-HI) for sensor based sorting of an epithermal Au-Ag ore

    NARCIS (Netherlands)

    Dalm, M.; Buxton, M.W.N.; Van Ruitenbeek, F.J.A.

    2015-01-01

    In the presented study test work was performed with near-infrared hyperspectral imagery (NIR-HI) on 36 ore samples from a South-American epithermal Au-Ag mine. The aim of the test work was to investigate if NIR-HI provides information about the alteration mineralogy of samples that can be used to pr

  3. Effect of alloying on the electronic structure and magnetic properties of AgFe, AuFe and CuFe

    International Nuclear Information System (INIS)

    We use the self-consistent, augmented space recursion technique to study the electronic structure and magnetic properties of alloys of the transition metal Fe with the noble metals Cu, Ag and Au. We analyze the effect of hybridization between the constituent bands on the electronic and magnetic properties. (author)

  4. {sup 3}He induced reactions on {sup nat}Ag and {sup 197}Au at 1.8, 3.6 and 4.8 GeV

    Energy Technology Data Exchange (ETDEWEB)

    Brzychczyk, J. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Dept. d`Astrophysique, de la Physique des Particules, de la Physique Nucleaire et de l`Instrumentation Associee]|[Jagiellonian Univ., Krakow (Poland). Inst. of Physics; Pollacco, E.C.; Volant, C.; Legrain, R. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Dept. d`Astrophysique, de la Physique des Particules, de la Physique Nucleaire et de l`Instrumentation Associee; Kwiatkowski, K.; Morley, K.B.; Renshaw-Foxford, E.; Bracken, D.S.; Viola, V.E.; Yoder, N.R. [Indiana Univ., Bloomington, IN (United States). Dept. of Chemistry] [and others

    1995-03-01

    The {sup 3}He induced reactions on Ag and Au are studied using a large solid angle and low energy threshold detector array. The data show consistency with intranuclear cascade and expanding emitting source description. Charge moment analysis is presented. (author). 18 refs., 8 figs.

  5. 3He induced reactions on natAg and 197Au at 1.8, 3.6 and 4.8 GeV

    International Nuclear Information System (INIS)

    The 3He induced reactions on Ag and Au are studied using a large solid angle and low energy threshold detector array. The data show consistency with intranuclear cascade and expanding emitting source description. Charge moment analysis is presented. (author). 18 refs., 8 figs

  6. Mass and velocity of fragments from the reaction 17-115 MeV/u 40Ar + Cu, Ag and Au

    International Nuclear Information System (INIS)

    Measurements are reported for fragment masses and velocities from the reactions 17-115 MeV/u 40Ar + Cu, Ag and Au. High momentum and energy deposition are reported for selected events, even for higher incident energy. Further study is needed to understand their origin. (authors)

  7. Spin and orbital magnetism of coinage metal trimers (Cu3, Ag3, Au3: A relativistic density functional theory study

    Directory of Open Access Journals (Sweden)

    Mahdi Afshar

    2013-11-01

    Full Text Available We have demonstrated electronic structure and magnetic properties of Cu3, Ag3 and Au3 trimers using a full potential local orbital method in the framework of relativistic density functional theory. We have also shown that the non-relativistic generalized gradient approximation for the exchange-correlation energy functional gives reliable magnetic properties in coinage metal trimers compared to experiment. In addition we have indicated that the spin-orbit coupling changes the structure and magnetic properties of gold trimer while the structure and magnetic properties of copper and silver trimers are marginally affected. A significant orbital moment of 0.21μB was found for most stable geometry of the gold trimer whereas orbital magnetism is almost quenched in the copper and silver trimers.

  8. Energy reflection coefficents for 5-10 keV He ions incident on Au, Ag and Cu

    International Nuclear Information System (INIS)

    The calorimetric deuterium-film method was used for measurements of the energy reflection coefficient γ for normal incidence of 5-10 keV He ions on Cu, Ag and Au. A theoretical calculation of β by means of transport theory gives fair agreement with the experimental results. The experimental data for all three materials lie on a single curve, if depicted as a function of the reduced entry epsilon, γ varies from 0.14 to 0.04 with epsilon varying from 0.2 to 1.6. The calculated data do not show similar behaviour, and the position of each curve depends on the specific beam-target combination. Both the experimental and theoretical results for the He ions are in acceptable agreement with other experimental and theoretical results. For He ions, the experimental γ-values are 20-30% above the values for hydrogen ions for the same value of epsilon. (Auth.)

  9. 4π studies of the 1.8-4.8 GeV 3He+natAg, 197Au reactions. I. Energy deposition

    International Nuclear Information System (INIS)

    The 4π detector ISiS has been used to measure light-charged particles and intermediate-mass-fragments emitted in the 1.8-4.8 GeV 3He+natAg, 197Au reactions. Ejectile multiplicity and total event kinetic energy distribution scale systematically with projectile energy and target mass, except for the natAg target at 3.6 and 4.8 GeV. For this system, a saturation in deposition energy is indicated by the data, suggesting the upper projectile energy for stopping has been reached. Maximum deposition energies of ∼950 MeV for the natAg target and ∼1600 MeV for the 197Au target are inferred from the data. Comparison of the experimental distributions with intranuclear cascade predictions shows qualitative agreement. (author)

  10. 4{pi} studies of the 1.8-4.8 GeV {sup 3}He+{sup nat}Ag, {sup 197}Au reactions. I. Energy deposition

    Energy Technology Data Exchange (ETDEWEB)

    Morley, K.B.; Kwiatkowski, K.; Bracken, D.S.; Renshaw Foxford, E. [Indiana Univ., Bloomington, IN (United States). Dept. of Chemistry; Legrain, R.; Pollacco, E.C.; Volant, C. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Dept. d`Astrophysique, de la Physique des Particules, de la Physique Nucleaire et de l`Instrumentation Associee; Korteling, R.G. [Simon Fraser Univ., Burnaby, BC (Canada). Dept. of Chemistry; Breuer, H. [Maryland Univ., College Park, MD (United States). Dept. of Physics; Brzychczyk, J. [Jagellonian Univ., Krakow (Poland). Inst. of Physics

    1996-01-01

    The 4{pi} detector ISiS has been used to measure light-charged particles and intermediate-mass-fragments emitted in the 1.8-4.8 GeV {sup 3}He+{sup nat}Ag, {sup 197}Au reactions. Ejectile multiplicity and total event kinetic energy distribution scale systematically with projectile energy and target mass, except for the {sup nat}Ag target at 3.6 and 4.8 GeV. For this system, a saturation in deposition energy is indicated by the data, suggesting the upper projectile energy for stopping has been reached. Maximum deposition energies of {approx}950 MeV for the {sup nat}Ag target and {approx}1600 MeV for the {sup 197}Au target are inferred from the data. Comparison of the experimental distributions with intranuclear cascade predictions shows qualitative agreement. (author). Submitted to Physical Review, C (US); 46 refs.

  11. Total oxidation of VOCs on Pd and/or Au supported on TiO{sub 2}/ZrO{sub 2} followed by ''operando'' Drift

    Energy Technology Data Exchange (ETDEWEB)

    Hosseini, M.; Siffert, St.; Cousin, R.; Aboukais, A. [Universite du Littoral-Cote d' Opale, Lab. de Catalyse et Environnement, E.A. 2598, 59 - Dunkerque (France); Hadj-Sadok, Z.; Bao-Lian, Su [Namur Univ., Lab. de Chimie des Materiaux Inorganiques, Namur (Belgium)

    2009-06-15

    Catalytic performances of nano-structured meso-porous TiO{sub 2}-ZrO{sub 2} mixed oxides impregnated by Pd and/or Au were studied in toluene total oxidation in a fixed bed micro-reactor and with 'operando' DRIFT. Meso-porous TiO{sub 2}-ZrO{sub 2} mixed oxides with various Ti:Zr mole ratio of 80/20, 50/50 and 20/80, high surface areas were synthesised using a mixture of zirconium prop-oxide and titanium iso-prop-oxide as Zr and Ti sources and also CTMABr as surfactant. The new supports are impregnated by 0.5 or 1.5 wt% of palladium and 1 wt% of gold using impregnation and Deposition-Precipitation methods. The catalytic activity for the nano-structured meso-porous TiO{sub 2}-ZrO{sub 2} mixed oxides varies depending on the molar ratio of Ti:Zr and also for all series of the studied catalysts impregnated by Pd and/or Au, when the gold is loaded firstly the activity in toluene complete oxidation is higher than when Pd was deposited firstly (PdAu/TZ {>=} 1.5Pd/TZ {>=} AuPd/TZ {>=} Pd/TZ {>=} Au/TZ {>=} TZ). The highest activity of PdAu/TZ (80/20) can be related to the higher acid sites density of the support and also to the presence of a synergetic effect between palladium and gold. 'Operando' DRIFT allowed following the VOCs oxidation but also suggesting an interaction between the adsorbed molecule and the catalyst which decreases when the activity for oxidation reaction increases. (authors)

  12. Changes in the real structure and magnetoresistance of Co90Fe10/Cu and Co90Fe10/Cu85Ag10Au5 multilayers after annealing

    International Nuclear Information System (INIS)

    Annealing of the (1.1 nm Co90Fe10/2.2 nm Cu)x20 and (1.1 nm Co90Fe10/2.2 nm Cu85Ag10Au5)x20 multilayers at 235 deg. C improved their magnetoresistance as compared to the virgin samples. Annealing at higher temperatures resulted in degradation of the magnetoresistance effect. This observation raised the motivation of a detailed structural study using small-angle X-ray scattering, wide-angle X-ray diffraction, electron diffraction and transmission electron microscopy with the aim to link the structural changes in the system to the changes in the magnetoresistance. The structure studies have shown that the maximum of the magnetoresistance observed after annealing at 235 deg. C is related to the separation of Co90Fe10 and Cu, which are partly intermixed at interfaces after the deposition process. The decay of the GMR effect at higher annealing temperatures is caused by an increase of the interface roughness, which led in the Co90Fe10/Cu multilayers to occurrence of non-continuous interfaces and to short-circuiting of magnetic layers. In the Cu85Ag10Au5 multilayers, the combination of small-angle X-ray scattering and wide-angle X-ray diffraction has shown that Cu85Ag10Au5 did not form an alloy with the nominal composition: Only a part of Au and Ag was dissolved in the copper structure; the remainder of Ag and Au formed precipitates

  13. Exchange interaction between magnetic impurities on surfaces of CuxPd1−x and CuxAu1−x random substitutional alloys

    International Nuclear Information System (INIS)

    We present fully relativistic first principles calculations of the exchange interactions between magnetic impurities deposited on the (1 1 1) surfaces of CuxPd1−x and CuxAu1−x random substitutional alloys, described using the coherent potential approximation. We show that as with pure surfaces of Cu and Au, where Shockley-type surface states mediate an RKKY-type interaction, a surface state and its dispersion can be obtained from studying the Bloch spectral function. In the second part of the paper we show how the details of the interaction are determined by the properties and dispersion of the surface states of the host material. We find an extra exponential decay in the range of the interactions compared to the 1/R2 decay on surfaces of pure metals. The similar topology of the Fermi surface of Cu and Au allows us to scale the spin–orbit coupling and to study the Bychkov–Rashba splitting. Alternatively, the entirely different topology of the Cu and Pd Fermi surfaces allows us to study changes in the surface-state dispersion of the RKKY interaction between surface impurities. (paper)

  14. Relativistic and correlated all-electron calculations on the ground and excited states of AgH and AuH

    Science.gov (United States)

    Witek, Henryk A.; Nakijima, Takahito; Hirao, Kimihiko

    2000-11-01

    We report relativistic all-electron multireference based perturbation calculations on the low-lying excited states of gold and silver hydrides. For AuH, we consider all molecular states dissociating to the Au(2S)+H(2S) and Au(2D)+H(2S) atomic limits, and for AgH, the states corresponding to the Ag(2S)+H(2S), Ag(2P)+H(2S), and Ag(2D)+H(2S) dissociation channels. Spin-free relativistic effects and the correlation effects are treated on the same footing through the relativistic scheme of eliminating small components (RESC). Spin-orbit effects are included perturbatively. The calculated potential energy curves for AgH are the first reported in the literature. The computed spectroscopic properties agree well with experimental findings; however, the assignment of states does not correspond to our calculations. Therefore, we give a reinterpretation of the experimentally observed C 1Π, a 3Π, B 1Σ+, b(3Δ1)1, D 1Π, c13Π1, and c0(3Π0) states. A labeling suggested by us is a1, C0+, b0-, c2, B3Π0+, d3Π1, e1, f1 and g1, respectively. The spin-orbit states corresponding to Ag(2D)+H(2S) have not well defined the Λ and S quantum numbers, and therefore, they probably correspond to Hund's coupling case c. For AuH, we present a comparison of the calculated potential energy curves and spectroscopic parameters with the previous configuration interaction study and the experiment.

  15. Nano-Crystal Formation and Growth from High-Fluence Ion Implantation of Au, Ag or Cu in Silica

    Science.gov (United States)

    Ila, D.; Baglin, J. E. E.; Zimmerman, R. L.

    The linear and non-linear optical properties of silica may be tailored by the introduction of a random distribution of nanocrystallites of an immiscible metal within a near-surface region. The size, size distribution, and spatial distribution of these crystallites must be controllable in order to optimize the functional properties for device applications. In this paper, we present a novel fabrication technique that offers such control. Energetic metal ions are implanted in silica at room temperature. Subsequent heat treatment leads to diffusion of the implanted atoms, nucleation and growth of metal crystallites, and Ostwald ripening of the resulting clusters. We have observed the kinetics and effective activation energies describing the multiple processes involved, for the cases of Au, Ag or Cu implanted at MeV energies, at various fluences, and then annealed at fixed temperatures in the range 500 °C-1000 °C. Effective activation energies found for nanocrystal nucleation and growth at temperatures below 800 °C (e.g. 64 meV for Ag) are replaced above this temperature range by much higher activation energies (e.g. 400 meV for Ag). We may attribute this to the depletion of un-attached mobile metal atoms (so that ripening of clusters will be limited by energy barriers for escape of such mobile atoms from small crystallites), and/or the annealing of implant-caused stress in the silica structure at high temperatures, that creates new channels for thermal diffusion of metal atoms within the silica host.

  16. Factors determining the structure of Au, Ag and Cr thin layers deposited on alkaline halogen substrates

    International Nuclear Information System (INIS)

    Metal thin layer deposited on dielectric substrates, in general, and on alkaline halogen substrates, in particular, have been thoroughly studied in order to make clear the phenomenology of the formation and development processes, to set out fundamental factors in determining their structure and to determine optimum conditions for the obtaining of monocrystal thin layers or metastable structured thin layers in view of their practical applications. Starting from a systematic programme of experimental investigations, an attempt has been made to investigate the influence of substrate composition, of defects within alkaline halogen substrates and of deposition conditions on the orientated formation and development of Au layer and on the formation of metastable Cr-delta structures in the case of thin Cr layers. A systematic study on the influence of deposition conditions and on alkaline halogen substrates with colloidal centres is carried out in view of elaborating a method for the development of monocrystal Au layers for ''channeling targets''. A correlation between characteristic parameters which define the atomic theory of nucleation including deposition conditions and material parameters, Au parameters for the case of epitaxial layers deposited on KBr, KCl and NaCl substrates has been attempted. (author)

  17. Ultra-thin L10-FePt for perpendicular anisotropy L10-FePt/Ag/[Co/Pd]30 pseudo spin valves

    International Nuclear Information System (INIS)

    Perpendicular anisotropy L10-FePt/Ag/[Co/Pd]30 pseudo spin valves (PSVs) with ultra-thin L10-FePt alloy free layer possessing high anisotropy and thermal stability have been fabricated and studied. The thickness of the L10-FePt layer was varied between 2 and 4 nm. The PSV became increasingly decoupled with reduced L10-FePt thickness due to the larger difference between the coercivity of the L10-FePt and [Co/Pd]30 films. The PSV with an ultra-thin L10-FePt free layer of 2 nm displayed a high Ku of 2.21 × 107 ergs/cm3, high thermal stability of 84 and a largest giant magnetoresistance of 0.54%

  18. Characterization of electroless Au, Pt and Pd contacts on CdTe and ZnTe by RBS and SIMS techniques

    International Nuclear Information System (INIS)

    Rutherford backscattering spectrometry (RBS) was applied to characterize Au, Pt and Pd contacts on II-VI semiconductor materials, CdTe and ZnTe, used as nuclear detectors. Electroless thin film depositions were prepared by changing the concentration of the reaction solution. Contrary to the deposition reaction time, it was observed that the amount of solution dilution degree had a considerable effect on increasing the thickness of the metal layer. Furthermore, PICTS electrical measurements confirmed the depth profile analysis performed by RBS and SIMS

  19. Hydrogen Dissociation and Diffusion on Transition Metal(=Ti,Zr,V,Fe,Ru,Co,Rh,Ni,Pd,Cu,Ag)-doped Mg(0001) Surfaces

    OpenAIRE

    Pozzo, Monica; Alfe`, Dario

    2008-01-01

    The kinetics of hydrogen absorption by magnesium bulk is affected by two main activated processes: the dissociation of the H$_2$ molecule and the diffusion of atomic H into the bulk. In order to have fast absorption kinetics both activated processed need to have a low barrier. Here we report a systematic ab-initio density functional theory investigation of H$_2$ dissociation and subsequent atomic H diffusion on TM(=Ti,V,Zr,Fe,Ru,Co,Rh,Ni,Pd,Cu,Ag)-doped Mg(0001) surfaces. The calculations sho...

  20. Research on the performance of AuPdPt-WC/C as a composite catalyst on cathode reaction of DMFC%AuPdPt-WC/C复合材料作为直接甲醇燃料电池阴极催化剂的性能研究

    Institute of Scientific and Technical Information of China (English)

    郑仓晟; 聂明; 李庆; 王宏煜; 袁宇; 刘晓卫; 杜胜娟; 刘其阳; 王孝益

    2015-01-01

    本实验以碳化钨(WC)增强的AuPdPt-WC/C复合催化剂作为直接甲醇燃料电池(DMFC)的阴极催化剂,选取了各组元比例,温度为变量,测试了其作为 DMFC催化剂的性能。首先,采用了间歇微波加热法(IHM)制备了纳米级的碳化钨(WC)颗粒,并采用还原法和真空干燥法制备了 AuPdPt-WC/C 复合催化剂,控制 Au、Pd、Pt的比例,制备了两组催化剂。通过循环伏安扫描,线性伏安扫描等手段进行电化学测试,表征其氧还原的性能。结果显示,复合催化剂具有高于传统 Pt/C催化剂的性能,并且与实验条件息息相关。%Our research mainly focuses on the preparation and characterization of tungsten carbide (WC) enhanced AuPdPt-WC/C composite catalyst of the cathode oxygen reduction reaction of direct methanol fuel cells (DMFC). By using intermittent mi-crowave heating method, we firstly synthesized nano tungsten carbide particle, then we prepared two AuPdPt-WC/C catalyst of different composition through reduction method and vacuum drying method. For characterization, we controlled composition and temperature as variable and used cyclic voltammetry and linear sweep voltammetry for electrochemistry test. The results indicated that the composite catalyst has a better performance than common single Pt catalyst and its performance is influenced by operating conditions.