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Sample records for ag au cd

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

    NASA Astrophysics Data System (ADS)

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

    2008-09-01

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

  2. Synthesis and photoeletrochemical performance of AuAg@CdS double-walled nanotubes

    NASA Astrophysics Data System (ADS)

    Guan, Shundong; Fu, Xiuli; Tang, Ying; Peng, Zhijian

    2017-08-01

    Uniform CdS coated AuAg alloyed double-walled nanotubes were successfully fabricated by solvothermal process using Ag nanowires as the template. UV-vis-NIR extinction spectra revealed that the obtained double-walled nanotubes can present an enhanced light absorption ability compared with both pure AuAg alloyed nanotubes and CdS nanowires. Photocurrent and electrochemical impedance spectroscopy measurements indicated that such double-walled structure could significantly extend the lifetime of photo-generated carriers and increase the light-harvesting efficiency of CdS, due to the low charge transfer resistance and a high carrier transfer rate of the double-walled structure. The growth mechanism of such kind of nanotubes was also proposed.

  3. Ternary Solid Phase Equilibria in the Systems (Ag,In,Au)-(Cd,He)-Te

    DTIC Science & Technology

    1988-07-22

    thermochemnical data. In closed thermodynamic systems Ag,In, and Au were shown to be stable with respect to stoichiometric CdTe and Ag, In reactive towards...compositions within Codes Avail and/or 2lit Specilal the six ternary systems. Thermodynamic calculations were performed using the data collected in... Thermodynamic Properties of the Elements, (Amer.Chem.Soc., Washington, D.C., 1956) 11) John H. Pugh, Masters Thesis, UCLA, 1986-unpublished. 12) W.G

  4. Atomic-scale structure and chemistry of ceramic/metal interfaces -- 2: Solute segregation at MgO/Cu (Ag) and CdO/Ag (Au) interfaces

    SciTech Connect

    Shashkov, D.A.; Muller, D.A.; Seidman, D.N.

    1999-11-12

    The first quantitative measurements of solute segregation at ceramic/metal (C/M) heterophase interfaces are presented for the MgO/Cu (Ag) and CdO/Ag (Au) systems. Interfaces are produced by internal oxidation of ternary alloys. Solute segregation at C/M interfaces is induced by intermediate-temperature annealing treatments. The Gibbsian interfacial excess of solute, {Gamma}{sub solute}, at these interfaces is determined in a direct, quantitative manner by atom-probe field-ion microscopy (APFIM). These measurements are complemented in the MgO/Cu (Ag) system by a composition analysis of this interface employing electron energy loss spectroscopy (EELS). Analyses of 15 {l{underscore}brace}222{r{underscore}brace} MgO/Cu (Ag) interfaces by APFIM show an average segregation level of (4.0 {+-} 1.9) x 10{sup 14} atoms/cm{sup 2} or 0.22 {+-} 0.10 effective monolayers at 500 C. Analyses of three {l{underscore}brace}222{r{underscore}brace} CdO/Ag (Au) interfaces show an average segregation level of (3.0 {+-} 1.0) x 10{sup 14} atoms/cm{sup 2} or 0.22 {+-} 0.07 effective monolayers at 400 C. Whereas {l{underscore}brace}222{r{underscore}brace} CdO/Ag (Au) interfaces in unannealed specimens show no evidence of gold segregation. These results are discussed in view of recent models of interfacial segregation.

  5. @AuAg nanostructures

    NASA Astrophysics Data System (ADS)

    Singh, Rina; Soni, R. K.

    2014-09-01

    Bimetallic and trimetallic nanoparticles have attracted significant attention in recent times due to their enhanced electrochemical and catalytic properties compared to monometallic nanoparticles. The numerical calculations using Mie theory has been carried out for three-layered metal nanoshell dielectric-metal-metal (DMM) system consisting of a particle with a dielectric core (Al@Al2O3), a middle metal Ag (Au) layer and an outer metal Au (Ag) shell. The results have been interpreted using plasmon hybridization theory. We have also prepared Al@Al2O3@Ag@Au and Al@Al2O3@AgAu triple-layered core-shell or alloy nanostructure by two-step laser ablation method and compared with calculated results. The synthesis involves temporal separations of Al, Ag, and Au deposition for step-by-step formation of triple-layered core-shell structure. To form Al@Ag nanoparticles, we ablated silver for 40 min in aluminium nanoparticle colloidal solution. As aluminium oxidizes easily in water to form alumina, the resulting structure is core-shell Al@Al2O3. The Al@Al2O3 particle acts as a seed for the incoming energetic silver particles for multilayered Al@Al2O3@Ag nanoparticles is formed. The silver target was then replaced by gold target and ablation was carried out for different ablation time using different laser energy for generation of Al@Al2O3@Ag@Au core-shell or Al@Al2O3@AgAu alloy. The formation of core-shell and alloy nanostructure was confirmed by UV-visible spectroscopy. The absorption spectra show shift in plasmon resonance peak of silver to gold in the range 400-520 nm with increasing ablation time suggesting formation of Ag-Au alloy in the presence of alumina particles in the solution.

  6. Radiochemical neutron activation analysis for 36 elements in geological material: Au, Ag, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Sn, Te, Tl, U, and Zn as well as Sc, Y, and REE

    SciTech Connect

    Anders, E; Wolf, R; Morgan, J W; Ebihara, M; Woodrow, A B; Janssens, M J; Hertogen, J

    1988-01-01

    In lunar and terrestrial rocks and in meteorites, the radiochemical neutron activation method decribed here enables determination of the 21 trace and ultratrace elements Ag, Au, Bi, Br, Cd, Cs, Ga, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Te, Tl, U, Zn, as well as 13 rare earth elements (REE), Sc and Y. Materials, techniques and procedures are discussed. 81 refs.

  7. Optical nonlinearities of Au nanoparticles and Au/Ag coreshells.

    PubMed

    Seo, Jae Tae; Yang, Qiguang; Kim, Wan-Joong; Heo, Jinhwa; Ma, Seong-Min; Austin, Jasmine; Yun, Wan Soo; Jung, Sung Soo; Han, Sang Woo; Tabibi, Bagher; Temple, Doyle

    2009-02-01

    Au nanoparticles exhibited both negative and positive nonlinear absorptions with ground-state plasmon bleaching and free-carrier absorption that could be origins of the saturable and reverse-saturable optical properties. Au/Ag coreshells displayed only positive nonlinear absorption and reverse-saturable optical properties as a function of excitation intensity at the edge of surface-plasmon resonance, which implies no ground-state plasmon bleaching and the existence of two-photon absorption.

  8. Isomorphism and solid solutions among Ag- and Au-selenides

    SciTech Connect

    Palyanova, Galina A.; Seryotkin, Yurii V.; Kokh, Konstantin A.; Bakakin, Vladimir V.

    2016-09-15

    Au-Ag selenides were synthesized by heating stoichiometric mixtures of elementary substances of initial compositions Ag{sub 2−x}Au{sub x}Se with a step of x=0.25 (0≤x≤2) to 1050 °C and annealing at 500 °C. Scanning electron microscopy, optical microscopy, electron microprobe analysis and X-ray powder diffraction methods have been applied to study synthesized samples. Results of studies of synthesized products revealed the existence of three solid solutions with limited isomorphism Ag↔Au: naumannite Ag{sub 2}Se – Ag{sub 1.94}Au{sub 0.06}Se, fischesserite Ag{sub 3}AuSe{sub 2} - Ag{sub 3.2}Au{sub 0.8}Se{sub 2} and gold selenide AuSe - Au{sub 0.94}Ag{sub 0.06}Se. Solid solutions and AgAuSe phases were added to the phase diagram of Ag-Au-Se system. Crystal-chemical interpretation of Ag-Au isomorphism in selenides was made on the basis of structural features of fischesserite, naumannite, and AuSe. - Highlights: • Au-Ag selenides were synthesized. • Limited Ag-Au isomorphism in the selenides is affected by structural features. • Some new phases were introduced to the phase diagram Ag-Au-Se.

  9. Comparative toxicity study of Ag, Au, and Ag-Au bimetallic nanoparticles on Daphnia magna.

    PubMed

    Li, Ting; Albee, Brian; Alemayehu, Matti; Diaz, Rocio; Ingham, Leigha; Kamal, Shawn; Rodriguez, Maritza; Bishnoi, Sandra Whaley

    2010-09-01

    A comparative assessment of the 48-h acute toxicity of aqueous nanoparticles synthesized using the same methodology, including Au, Ag, and Ag-Au bimetallic nanoparticles, was conducted to determine their ecological effect in freshwater environments through the use of Daphnia magna, using their mortality as a toxicological endpoint. D. magna are one of the standard organisms used for ecotoxicity studies due to their sensitivity to chemical toxicants. Particle suspensions used in toxicity testing were well-characterized through a combination of absorbance measurements, atomic force or electron microscopy, flame atomic absorption spectrometry, and dynamic light scattering to determine composition, aggregation state, and particle size. The toxicity of all nanoparticles tested was found to be dose and composition dependent. The concentration of Au nanoparticles that killed 50% of the test organisms (LC(50)) ranged from 65-75 mg/L. In addition, three different sized Ag nanoparticles (diameters = 36, 52, and 66 nm) were studied to analyze the toxicological effects of particle size on D. magna; however, it was found that toxicity was not a function of size and ranged from 3-4 μg/L for all three sets of Ag nanoparticles tested. This was possibly due to the large degree of aggregation when these nanoparticles were suspended in standard synthetic freshwater. Moreover, the LC(50) values for Ag-Au bimetallic nanoparticles were found to be between that of Ag and Au but much closer to that of Ag. The bimetallic particles containing 80% Ag and 20% Au were found to have a significantly lower toxicity to Daphnia (LC(50) of 15 μg/L) compared to Ag nanoparticles, while the toxicity of the nanoparticles containing 20% Ag and 80% Au was greater than expected at 12 μg/L. The comparison results confirm that Ag nanoparticles were much more toxic than Au nanoparticles, and that the introduction of gold into silver nanoparticles may lower their environmental impact by lowering the amount

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Effects of metal-bearing nanoparticles (Ag, Au, CdS, ZnO, SiO2) on developing zebrafish embryos

    NASA Astrophysics Data System (ADS)

    María Lacave, José; Retuerto, Ander; Vicario-Parés, Unai; Gilliland, Douglas; Oron, Miriam; Cajaraville, Miren P.; Orbea, Amaia

    2016-08-01

    Due to the increasing commercialization of consumer and industrial products containing nanoparticles (NPs), an increase in the introduction of these materials into the environment is expected. NP toxicity to aquatic organisms depends on multiple biotic and abiotic factors, resulting in an unlimited number of combinations impossible to test in practice. The zebrafish embryo model offers a useful screening tool to test and rank the toxicity of nanomaterials according to those diverse factors. This work aims to study the acute and sublethal toxicity of a set of metal-bearing NPs displaying different properties, in comparison to that of the ionic and bulk forms of the metals, in order to establish a toxicity ranking. Soluble NPs (Ag, CdS and ZnO) showed the highest acute and sublethal toxicity, with LC50 values as low as 0.529 mg Ag l-1 for Ag NPs of 20 nm, and a significant increase in the malformation prevalence in embryos exposed to 0.1 mg Cd l-1 of CdS NPs of ˜4 nm. For insoluble NPs, like SiO2 NPs, acute effects were not observed during early embryo development due to the protective effect of the chorion. But effects on larvae could be expected, since deposition of fluorescent SiO2 NPs over the gill lamella and excretion through the intestine were observed after hatching. In other cases, such as for gold NPs, the toxicity could be attributed to the presence of additives (sodium citrate) in the NP suspension, as they displayed a similar toxicity when tested separately. Overall, the results indicated that toxicity to zebrafish embryos depends primarily on the chemical composition and, thus, the solubility of the NPs. Other characteristics, such as size, played a secondary role. This was supported by the observation that ionic forms of the metals were always more toxic than the nano forms, and bulk forms were the least toxic to the developing zebrafish embryos.

  12. Effect of Ag Templates on the Formation of Au-Ag Hollow/Core-Shell Nanostructures.

    PubMed

    Tsai, Chi-Hang; Chen, Shih-Yun; Song, Jenn-Ming; Haruta, Mitsutaka; Kurata, Hiroki

    2015-12-01

    Au-Ag alloy nanostructures with various shapes were synthesized using a successive reduction method in this study. By means of galvanic replacement, twined Ag nanoparticles (NPs) and single-crystalline Ag nanowires (NWs) were adopted as templates, respectively, and alloyed with the same amount of Au(+) ions. High angle annular dark field-scanning TEM (HAADF-STEM) images observed from different rotation angles confirm that Ag NPs turned into AuAg alloy rings with an Au/Ag ratio of 1. The shifts of surface plasmon resonance and chemical composition reveal the evolution of the alloy ring formation. On the other hand, single-crystalline Ag NWs became Ag@AuAg core-shell wires instead of hollow nanostructure through a process of galvanic replacement. It is proposed that in addition to the ratio of Ag templates and Au ion additives, the twin boundaries of the Ag templates were the dominating factor causing hollow alloy nanostructures.

  13. Isomorphism and solid solutions among Ag- and Au-selenides

    NASA Astrophysics Data System (ADS)

    Palyanova, Galina A.; Seryotkin, Yurii V.; Kokh, Konstantin A.; Bakakin, Vladimir V.

    2016-09-01

    Au-Ag selenides were synthesized by heating stoichiometric mixtures of elementary substances of initial compositions Ag2-xAuxSe with a step of x=0.25 (0≤x≤2) to 1050 °C and annealing at 500 °C. Scanning electron microscopy, optical microscopy, electron microprobe analysis and X-ray powder diffraction methods have been applied to study synthesized samples. Results of studies of synthesized products revealed the existence of three solid solutions with limited isomorphism Ag↔Au: naumannite Ag2Se - Ag1.94Au0.06Se, fischesserite Ag3AuSe2 - Ag3.2Au0.8Se2 and gold selenide AuSe - Au0.94Ag0.06Se. Solid solutions and AgAuSe phases were added to the phase diagram of Ag-Au-Se system. Crystal-chemical interpretation of Ag-Au isomorphism in selenides was made on the basis of structural features of fischesserite, naumannite, and AuSe.

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

    NASA Astrophysics Data System (ADS)

    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

  15. Laser generated Ag and Ag-Au composite nanoparticles for refractive index sensor

    NASA Astrophysics Data System (ADS)

    Navas, M. P.; Soni, R. K.

    2014-09-01

    Localized surface plasmon resonance (LSPR) wavelength of metal nanoparticles (NPs) is highly sensitive to size, shape and the surrounding medium. Metal targets were laser ablated in liquid for preparation of spherical Ag and Ag@Au core-shell NP colloidal solution for refractive index sensing. The LSPR peak wavelength and broadening of the NPs were monitored in different refractive index liquid. Quasi-static Mie theory simulation results show that refractive index sensitivity of Ag, Ag-Au alloy and Ag@Au core-shell NPs increases nearly linearly with size and shell thickness. However, the increased broadening of the LSPR peak with size, alloy concentration and Au shell thickness restricts the sensing resolution of these NPs. Figure-of-merit (FOM) was calculated to optimize the size of Ag NPs, concentration of Ag-Au alloy NPs and Au shell thickness of Ag@Au core-shell NPs. The refractive index sensitivity (RIS) and FOM were optimum in the size range 20-40 nm for Ag NPs. Laser generated Ag@Au NPs of Au shell thickness in the range of 1-2 nm showed optimum FOM, where thin layer of Au coating can improve the stability of Ag NPs.

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

    PubMed Central

    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

    2015-01-01

    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. PMID:26412773

  17. Synthesis, characterization and SERS activity of Au-Ag nanorods.

    PubMed

    Philip, Daizy; Gopchandran, K G; Unni, C; Nissamudeen, K M

    2008-09-01

    The formation mechanism and morphology of Au-Ag bimetallic colloidal nanoparticles depend on the composition. Ag coated Au colloidal nanoparticles have been prepared by deposition of Ag through chemical reduction on performed Au colloid. The composition of the Au100-x-Agx particles was varied from x=0 to 50. The obtained colloids were characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). The Au80-Ag20 colloid consists of alloy nanorods with dimension of 25nm x 100nm. The activity of these nanorods in surface enhanced Raman spectroscopy (SERS) was checked by using sodium salicylate as an adsorbate probe. Intense SERS bands are observed indicating its usefulness as a SERS substrate in near infrared (NIR) laser excitation.

  18. Biosynthesis of Au, Ag and Au-Ag nanoparticles using edible mushroom extract

    NASA Astrophysics Data System (ADS)

    Philip, Daizy

    2009-07-01

    Integration of green chemistry principles to nanotechnology is one of the key issues in nanoscience research. There is growing need to develop environmentally benign metal nanoparticle synthesis process that do not use toxic chemicals in the synthesis protocols to avoid adverse effects in medical applications. Here, it is a report on extracellular synthesis method for the preparation of Au, Ag and Au-Ag nanoparticles in water, using the extract of Volvariella volvacea, a naturally occurring edible mushroom, as reducing and protecting agents. Gold nanoparticles of different sizes (20-150 nm) and shapes from triangular nanoprisms to nearly spherical and hexagonal are obtained by this novel method. The size and shape of gold nanoparticles are also found to depend on temperature of the extract. The silver nanoparticles are spherical with size ˜15 nm. There is increased productivity of nanoparticles as shown by sharp and intense surface plasmon resonance bands for the nanoparticles prepared using an excess of the extract. The Au-Ag nanoparticles prepared by co-reduction has only one plasmon band due to alloying of the constituents. All the synthesized nanoparticles are found to be photoluminescent and are highly crystalline as shown by SAED and XRD patterns with fcc phase oriented along the (1 1 1) plane. FTIR measurements were carried out to identify the possible biomolecules responsible for capping and efficient stabilization of the nanoparticles. It is found that Au nanoparticles are bound to proteins through free amino groups and silver nanoparticles through the carboxylate group of the amino acid residues. The position and intensity of the emission band is found to depend on composition of the nanoparticles indicating the possible use in therapeutic applications.

  19. Melting curve of metals Cu, Ag and Au under pressure

    NASA Astrophysics Data System (ADS)

    Tam, Pham Dinh; Hoc, Nguyen Quang; Tinh, Bui Duc; Tan, Pham Duy

    2016-01-01

    In this paper, the dependence of the melting temperature of metals Cu, Ag and Au under pressure in the interval from 0 kbar to 40 kbar is studied by the statistical moment method (SMM). This dependence has the form of near linearity and the calculated slopes of melting curve are 3.9 for Cu, 5.7 for Ag and 6 for Au. These results are in good agreement with the experimental data.

  20. The extraction characteristic of Au-Ag from Au concentrate by thiourea solution

    NASA Astrophysics Data System (ADS)

    Kim, Bongju; Cho, Kanghee; On, Hyunsung; Choi, Nagchoul; Park, Cheonyoung

    2013-04-01

    The cyanidation process has been used commercially for the past 100 years, there are ores that are not amenable to treatment by cyanide. Interest in alternative lixiviants, such as thiourea, halogens, thiosulfate and malononitrile, has been revived as a result of a major increase in gold price, which has stimulated new developments in extraction technology, combined with environmental concern. The Au extraction process using the thiourea solvent has many advantages over the cyanidation process, including higher leaching rates, faster extraction time and less than toxicity. The purpose of this study was investigated to the extraction characteristic of Au-Ag from two different Au concentrate (sulfuric acid washing and roasting) under various experiment conditions (thiourea concentration, pH of solvent, temperature) by thiourea solvent. The result of extraction experiment showed that the Au-Ag extraction was a fast extraction process, reaching equilibrium (maximum extraction rate) within 30 min. The Au-Ag extraction rate was higher in the roasted concentrate than in the sulfuric acid washing. The higher the Au-Ag extraction rate (Au - 70.87%, Ag - 98.12%) from roasted concentrate was found when the more concentration of thiourea increased, pH decreased and extraction temperature increased. This study informs extraction method basic knowledge when thiourea was a possibility to eco-/economic resources of Au-Ag utilization studies including the hydrometallurgy.

  1. An Au/AgBr-Ag heterostructure plasmonic photocatalyst with enhanced catalytic activity under visible light.

    PubMed

    Purbia, Rahul; Paria, Santanu

    2017-01-17

    This study reports an easy synthesis protocol of a novel bimetallic silver halide (Au/AgBr-Ag) plasmonic heterostructure as a visible light induced photocatalyst. In this process, first CTAB capped Au NPs were coated with AgBr, and then Ag nanoparticles were formed on the surface of AgBr by photoreduction, while exposing to daylight at room temperature. The presence of Au and Ag improves the visible absorption ability of NPs and avoids charge recombination of the semiconductor AgBr during photoexcitation, which in turn enhances 16 and 8.9 fold the photocatalytic efficiency of Rhodamine B dye degradation under visible light irradiation compared to that of pure AgBr and AgBr/Ag, respectively. The recycling tests of the photocatalyst show only ∼8.7% decrease in efficiency after the 5(th) cycle of reuse without changing the morphology. During the photocatalytic process, active superoxide radicals (O2˙(-)) play a major role, proved through scavenger trapping and photoluminescence experiments. The presence of two plasmonic metals (Au and Ag) in the heterostructure helps to improve visible light absorption as well as avoid charge recombination of the semiconductor AgBr to act as a better photocatalyst. Since this heteronanostructure can be easily synthesized by a one-step method, this study could provide a new approach for the development of efficient bimetallic/semiconductor halide plasmonic photocatalysts with enhanced visible absorption and better charge separation.

  2. Au-Ag@Au Hollow Nanostructure with Enhanced Chemical Stability and Improved Photothermal Transduction Efficiency for Cancer Treatment.

    PubMed

    Jiang, Tongtong; Song, Jiangluqi; Zhang, Wenting; Wang, Hao; Li, Xiaodong; Xia, Ruixiang; Zhu, Lixin; Xu, Xiaoliang

    2015-10-07

    Despite the fact that Au-Ag hollow nanoparticles (HNPs) have gained much attention as ablation agents for photothermal therapy, the instability of the Ag element limits their applications. Herein, excess Au atoms were deposited on the surface of a Au-Ag HNP by improving the reduction power of l-ascorbic acid (AA) and thereby preventing the reaction between HAuCl4 and the Ag element in the Au-Ag alloy nanostructure. Significantly, the obtained Au-Ag@Au HNPs show excellent chemical stability in an oxidative environment, together with remarkable increase in extinction peak intensity and obvious narrowing in peak width. Moreover, finite-difference time-domain (FDTD) was used to simulate the optical properties and electric field distribution of HNPs. The calculated results show that the proportion of absorption cross section in total extinction cross section increases with the improvement of Au content in HNP. As predicted by the theoretical calculation results, Au-Ag@Au nanocages (NCs) exhibit a photothermal transduction efficiency (η) as high as 36.5% at 808 nm, which is higher than that of Au-Ag NCs (31.2%). Irradiated by 808 nm laser at power densities of 1 W/cm(2), MCF-7 breast cancer cells incubated with PEGylated Au-Ag@Au NCs were seriously destroyed. Combined together, Au-Ag@Au HNPs with enhanced chemical stability and improved photothermal transduction efficiency show superior competitiveness as photothermal agents.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. Facile synthesis of Ag@Au core-sheath nanowires with greatly improved stability against oxidation.

    PubMed

    Yang, Miaoxin; Hood, Zachary D; Yang, Xuan; Chi, Miaofang; Xia, Younan

    2017-02-07

    We report a facile synthesis of Ag@Au core-sheath nanowires through the conformal deposition of Au atoms onto the surface of pre-synthesized Ag nanowires. The resulting Ag@Au nanowires showed morphology and optical properties almost identical to the pristine Ag nanowires, but with greatly improved stability under different corrosive environments.

  6. Biogenic synthesis of Ag, Au and bimetallic Au/Ag alloy nanoparticles using aqueous extract of mahogany (Swietenia mahogani JACQ.) leaves.

    PubMed

    Mondal, Samiran; Roy, Nayan; Laskar, Rajibul A; Sk, Ismail; Basu, Saswati; Mandal, Debabrata; Begum, Naznin Ara

    2011-02-01

    In this paper, we have demonstrated for the first time, the superb efficiency of aqueous extract of dried leaves of mahogany (Swietenia mahogani JACQ.) in the rapid synthesis of stable monometallic Au and Ag nanoparticles and also Au/Ag bimetallic alloy nanoparticles having spectacular morphologies. Our method was clean, nontoxic and environment friendly. When exposed to aqueous mahogany leaf extract, competitive reduction of Au(III) and Ag(I) ions present simultaneously in same solution leads to the production of bimetallic Au/Ag alloy nanoparticles. UV-visible spectroscopy was used to monitor the kinetics of nanoparticles formation. UV-visible spectroscopic data and TEM images revealed the formation of bimetallic Au/Ag alloy nanoparticles. Mahogany leaf extract contains various polyhydroxy limonoids which are responsible for the reduction of Au(III) and Ag(I) ions leading to the formation and stabilization of Au and Ag nanopaticles. Copyright © 2010 Elsevier B.V. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

  8. Dielectric function dependence on temperature for Au and Ag

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Jen; Lee, Meng-Chang; Wang, Chih-Ming

    2014-08-01

    The dielectric functions of Au and Ag are measured using a spectral ellipsometer. The temperature dependence parameters ωp, τ, and ɛ∞, in the Drude-Sommerfeld model have been studied. Furthermore, we provide an empirical function to describe the temperature dependence of the dielectric function for Au and Ag. The empirical function shows a good agreement with previous results. Through the empirical function, one can obtain the dielectric constant at arbitrary temperature and wavelength. This database is useful for the applications that use surface plasmon (SP) resonance at high temperatures, such as the plasmonic thermal emitter, SP-assisted thermal cancer treatment and so on.

  9. Restructuring hollow Au-Ag nanostructures for improved SERS activity

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    Hollow Au-Ag nanostructures with improved SERS performance were prepared by using a modified galvanic replacement reaction. The plasmon characteristics of the hollow structures are found to be highly sensitive to the volume of cathode, whether or not a co-reductant was used in the synthesis. It is found that the presence of a co-reductant viz., ascorbic acid (AA) during the reaction make the hollow structures capable to maintain its physical structure even after addition of excess cathode and also it transformes sacrificial templates into highly efficient hollow Au-Ag SERS substrates. In the galvanic replacement reaction conducted in presence of AA, where on one side the removal of Ag atoms make cavities to occur and on the other side a coating on the surface with Au and Ag atoms due to co-reduction take place simultaneously. Morphological observations indicated that it is possible to control the competition between these two mechanisms and to make Au-Ag hollow structures in tune with applications by optimizing the volume of cathode or AA. The SERS activity of these substrates were tested with crystal violet molecule as probe, using two different laser lines, 514 and 784.8 nm. In this report, the enhancement observed for hollow structures fabricated under optimum conditions are in the order of 106. SERS measurements have shown that for a specific volume of cathode, substrates fabricated in presence of AA are superior to the other type and also the increase in enhancement factor is ˜10 fold.

  10. Interfacial reactions in the Sn-Ag/Au couples

    NASA Astrophysics Data System (ADS)

    Chen, Sinn-Wen; Yen, Yee-Wen

    2001-09-01

    Ag-Sn alloys are one of the most promising lead-free solders. Their reactions with Au substrates have been examined by using the reaction couple technique. Sn-3.5wt.%Ag/Au and Sn-25wt.%Ag/Au couples have been prepared and reacted at 120, 150, 180 and 200 C for various lengths of time. Three phases, δ-AuSn, ɛ2-AuSn2, and η-AuSn4, are found in all the couples. The thickness of the reaction layers inccreases with higher temperatures and longer reaction time, and their growth rates are described by using the parabolic law. Arrhenius equation is used to describe the temperature dependence of the growth rates. The activation energy of the growth of the intermetallic layers in both kinds of the reaction couples is similar and is determined to be 76.74 KJ/mole. Based on the reaction path knowledge and interfacial morphology, it is concluded that Sn is the fastest diffusion species in the couples.

  11. Ion-exchange synthesis and improved photovoltaic performance of CdS/Ag2S heterostructures for inorganic-organic hybrid solar cells

    NASA Astrophysics Data System (ADS)

    Xu, Xiaoyun; Wang, Xiong; Zhang, Yange; Li, Pinjiang

    2016-11-01

    A facile ultrasound-assisted ion exchange route was developed for the synthesis of CdS/Ag2S heterojunctions by ion exchange between the nanostructured CdS film and [Ag(NH3)2]+ under ultrasonication. The CdS/Ag2S heterojunction film was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis DRS spectroscopy, photoelectrochemical measurements, and the transient photovoltage (TPV) technique. CdSsbnd Ag2S heterojunctions exhibit a dense morphology, enhanced visible light absorption and stronger photocurrent response than the pure CdS films. Poly(3-hexylthiophene) (P3HT) was then spin coated into the CdS/Ag2S framework. Hybrid solar cells constructed with FTO/CdS/Ag2S/P3HT/Au display relatively higher power conversion efficiency than FTO/CdS/P3HT/Au.

  12. Nanoporous Au structures by dealloying Au/Ag thermal- or laser-dewetted bilayers on surfaces

    NASA Astrophysics Data System (ADS)

    Ruffino, F.; Torrisi, V.; Grillo, R.; Cacciato, G.; Zimbone, M.; Piccitto, G.; Grimaldi, M. G.

    2017-03-01

    Nanoporous Au attracts great technological interest and it is a promising candidate for optical and electrochemical sensors. In addition to nanoporous Au leafs and films, recently, interest was focused on nanoporous Au micro- and nano-structures on surfaces. In this work we report on the study of the characteristics of nanoporous Au structures produced on surfaces. We developed the following procedures to fabricate the nanoporous Au structures: we deposited thin Au/Ag bilayers on SiO2 or FTO (fluorine-doped tin oxide) substrates with thickness xAu and xAg of the Au and Ag layers; we induced the alloying and dewetting processes of the bilayers by furnace annealing processes of the bilayers deposited on SiO2 and by laser irradiations of the bilayers deposited on FTO; the alloying and dewetting processes result in the formation of AuxAgy alloy sub-micron particles being x and y tunable by xAu and xAg. These particles are dealloyed in HNO3 solution to remove the Ag atoms. We obtain, so, nanoporous sub-micron Au particles on the substrates. Analyzing the characteristics of these particles we find that: a) the size and shape of the particles depend on the nature of the dewetting process (solid-state dewetting on SiO2, molten-state dewetting on FTO); b) the porosity fraction of the particles depends on how the alloying process is reached: about 32% of porosity for the particles fabricated by the furnace annealing at 900 °C, about 45% of porosity for the particles fabricated by the laser irradiation at 0.5 J/cm2, in both cases independently on the Ag concentration in the alloy; c) After the dealloying process the mean volume of the Au particles shrinks of about 39%; d) After an annealing at 400 °C the nanoporous Au particles reprise their initial volume while the porosity fraction is reduced. Arguments to justify these behaviors are presented.

  13. Chemical stability and degradation mechanisms of triangular Ag, Ag@Au, and Au nanoprisms.

    PubMed

    Lee, Kee Eun; Hesketh, Amelia V; Kelly, Timothy L

    2014-06-28

    Anisotropic metal nanoparticles have found use in a variety of plasmonic applications because of the large near-field enhancements associated with them; however, the very features that give rise to these enhancements (e.g., sharply curved edges and tips) often have high surface energies and are easily degraded. This paper describes the stability and degradation mechanisms of triangular silver, gold-coated silver, and gold nanoprisms upon exposure to a wide variety of adverse conditions, including halide ions, thiols, amines and elevated temperatures. The silver nanoprisms were immediately and irreversibly degraded under all of the conditions studied. In contrast, the core-shell Ag@Au nanoprisms were less susceptible to etching by chlorides and bromides, but were rapidly degraded by iodides, amines and thiols by a different degradation pathway. Only the pure gold nanoprisms were stable to all of the conditions tested. These results have important implications for the suitability of triangular nanoprisms in many applications; this is particularly true in biological or environmental fields, where the nanoparticles would inevitably be exposed to a wide variety of chemical stimuli.

  14. Rough surface Au@Ag core-shell nanoparticles to fabricating high sensitivity SERS immunochromatographic sensors.

    PubMed

    Fu, Qiangqiang; Liu, Hongwu Liu; Wu, Ze; Liu, An; Yao, Cuize; Li, Xiuqing; Xiao, Wei; Yu, Shiting; Luo, Zhi; Tang, Yong

    2015-11-14

    Immunochromatographic sensors (ICSs) are inexpensive, simple, portable, and robust, thus making ICSs commonplace in clinical diagnoses, food testing, and environmental monitoring. However, commonly used gold nanoparticles (AuNPs) ICSs have low sensitivity. Therefore, we developed highly sensitive surface enhanced Raman scattering (SERS) ICSs. To enhance the sensitivity of SERS ICSs, rough surface core-shell Au@Ag nanoparticles (RSAu@AgNPs) were prepared by coating silver on the surface of gold nanoflowers (AuNFs). Then these nanoparticles were used as SERS substrate in the SERS ICSs, after which the SERS ICSs were implemented to detect haemoglobin and heavy metal cadmium ion (Cd(2+)). The limit of detection (LOD) of the SERS ICSs for detecting haemoglobin was 8 ng/mL, and the linear range of the SERS ICSs was from 31.3 to 2000 ng/mL. The LOD of the SERS ICSs for detecting Cd(2+) was 0.05 ng/mL and the linear analysis range was from 0.05 to 25 ng/mL. The cross reactivity of the SERS ICSs was studied and results showed that the SERS ICSs exhibited highly specific for detection of haemoglobin and Cd(2+), respectively. The SERS ICSs were then used to detect haemoglobin (spiked in serum and in stool) and Cd(2+) (spiked in tap water, river water, and soil leaching water), and the results showed high recovery. These characteristics indicated that SERS ICSs were ideal tools for clinical diagnosis and environmental pollution monitoring.

  15. Au-Ag hollow nanostructures with tunable SERS properties

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  16. Toward hybrid Au nanorods @ M (Au, Ag, Pd and Pt) core-shell heterostructures for ultrasensitive SERS probes

    NASA Astrophysics Data System (ADS)

    Xie, Xiaobin; Gao, Guanhui; Kang, Shendong; Lei, Yanhua; Pan, Zhengyin; Shibayama, Tamaki; Cai, Lintao

    2017-06-01

    Being able to precisely control the morphologies of noble metallic nanostructures is of essential significance for promoting the surface-enhanced Raman scattering (SERS) effect. Herein, we demonstrate an overgrowth strategy for synthesizing Au @ M (M = Au, Ag, Pd, Pt) core-shell heterogeneous nanocrystals with an orientated structural evolution and highly improved properties by using Au nanorods as seeds. With the same reaction condition system applied, we obtain four well-designed heterostructures with diverse shapes, including Au concave nanocuboids (Au CNs), Au @ Ag crystalizing face central cube nanopeanuts, Au @ Pd porous nanocuboids and Au @ Pt nanotrepangs. Subsequently, the exact overgrowth mechanism of the above heterostructural building blocks is further analysed via the systematic optimiziation of a series of fabrications. Remarkably, the well-defined Au CNs and Au @ Ag nanopeanuts both exhibit highly promoted SERS activity. We expect to be able to supply a facile strategy for the fabrication of multimetallic heterogeneous nanostructures, exploring the high SERS effect and catalytic activities.

  17. Plasmon Mapping in Au@Ag Nanocube Assemblies

    PubMed Central

    2014-01-01

    Surface plasmon modes in metallic nanostructures largely determine their optoelectronic properties. Such plasmon modes can be manipulated by changing the morphology of the nanoparticles or by bringing plasmonic nanoparticle building blocks close to each other within organized assemblies. We report the EELS mapping of such plasmon modes in pure Ag nanocubes, Au@Ag core–shell nanocubes, and arrays of Au@Ag nanocubes. We show that these arrays enable the creation of interesting plasmonic structures starting from elementary building blocks. Special attention will be dedicated to the plasmon modes in a triangular array formed by three nanocubes. Because of hybridization, a combination of such nanotriangles is shown to provide an antenna effect, resulting in strong electrical field enhancement at the narrow gap between the nanotriangles. PMID:25067991

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

    PubMed

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

    2017-09-04

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

  19. Dependence of SERS enhancement on the chemical composition and structure of Ag/Au hybrid nanoparticles

    NASA Astrophysics Data System (ADS)

    Chaffin, Elise; O'Connor, Ryan T.; Barr, James; Huang, Xiaohua; Wang, Yongmei

    2016-08-01

    Noble metal nanoparticles (NPs) such as silver (Ag) and gold (Au) have unique plasmonic properties that give rise to surface enhanced Raman scattering (SERS). Generally, Ag NPs have much stronger plasmonic properties and, hence, provide stronger SERS signals than Au NPs. However, Ag NPs lack the chemical stability and biocompatibility of comparable Au NPs and typically exhibit the most intense plasmonic resonance at wavelengths much shorter than the optimal spectral region for many biomedical applications. To overcome these issues, various experimental efforts have been devoted to the synthesis of Ag/Au hybrid NPs for the purpose of SERS detections. However, a complete understanding on how the SERS enhancement depends on the chemical composition and structure of these nanoparticles has not been achieved. In this study, Mie theory and the discrete dipole approximation have been used to calculate the plasmonic spectra and near-field electromagnetic enhancements of Ag/Au hybrid NPs. In particular, we discuss how the electromagnetic enhancement depends on the mole fraction of Au in Ag/Au alloy NPs and how one may use extinction spectra to distinguish between Ag/Au alloyed NPs and Ag-Au core-shell NPs. We also show that for incident laser wavelengths between ˜410 nm and 520 nm, Ag/Au alloyed NPs provide better electromagnetic enhancement than pure Ag, pure Au, or Ag-Au core-shell structured NPs. Finally, we show that silica-core Ag/Au alloy shelled NPs provide even better performance than pure Ag/Au alloy or pure solid Ag and pure solid Au NPs. The theoretical results presented will be beneficial to the experimental efforts in optimizing the design of Ag/Au hybrid NPs for SERS-based detection methods.

  20. Annealing of Au, Ag and Au-Ag alloy nanoparticle arrays on GaAs (100) and (111)B.

    PubMed

    Whiticar, Alexander M; Mårtensson, Erik K; Nygård, Jesper; Dick, Kimberly A; Bolinsson, Jessica

    2017-05-19

    Metal nanoparticles (NPs), in particular gold NPs, are often used in the fabrication process of semiconductor nanowires. Besides being able to induce the 1D crystallization of new material, it is highly beneficial if the NPs can be used to dictate the position and diameter of the final nanowire structure. To achieve well-defined NP arrays of varying diameter and pitch distances for nanowire growth, it is necessary to understand and control the effect that a pre-growth annealing process may have on the pre-defined NP arrays. Recently, it has been demonstrated that silver (Ag) may be an alternative to using gold (Au) NPs as seed for particle-seeded nanowire fabrication. This work brings light onto the effect of annealing of Au, Ag and Au-Ag alloy metal NP arrays in two commonly used epitaxial systems, the molecular beam epitaxy (MBE) and the metalorganic vapor phase epitaxy (MOVPE). The metal NP arrays are fabricated with the aid of electron beam lithography on GaAs 100 and 111B wafers and the evolution of the NPs with respect to shape, size and position on the surfaces is studied after annealing using scanning electron microscopy. We find that while the Au NP arrays are found to be stable when annealed up to 600 °C in a MOVPE system, a diameter and pitch dependent splitting of the particles is seen for annealing in a MBE system. The Ag NP arrays are found to be less stable, with smaller diameters (≤50 nm) dissolving during the annealing process in both epitaxial systems. In general, the mobility of the NPs is observed to differ between the two the GaAs 100 and 111B surfaces. Finally, our observations on the effect of annealing on Au-Ag alloy NP arrays suggest that these NP can withstand necessary annealing conditions for a complete de-oxidation of GaAs surfaces in both MOVPE and MBE.

  1. Annealing of Au, Ag and Au-Ag alloy nanoparticle arrays on GaAs (100) and (111)B

    NASA Astrophysics Data System (ADS)

    Whiticar, Alexander M.; Mårtensson, Erik K.; Nygård, Jesper; Dick, Kimberly A.; Bolinsson, Jessica

    2017-05-01

    Metal nanoparticles (NPs), in particular gold NPs, are often used in the fabrication process of semiconductor nanowires. Besides being able to induce the 1D crystallization of new material, it is highly beneficial if the NPs can be used to dictate the position and diameter of the final nanowire structure. To achieve well-defined NP arrays of varying diameter and pitch distances for nanowire growth, it is necessary to understand and control the effect that a pre-growth annealing process may have on the pre-defined NP arrays. Recently, it has been demonstrated that silver (Ag) may be an alternative to using gold (Au) NPs as seed for particle-seeded nanowire fabrication. This work brings light onto the effect of annealing of Au, Ag and Au-Ag alloy metal NP arrays in two commonly used epitaxial systems, the molecular beam epitaxy (MBE) and the metalorganic vapor phase epitaxy (MOVPE). The metal NP arrays are fabricated with the aid of electron beam lithography on GaAs 100 and 111B wafers and the evolution of the NPs with respect to shape, size and position on the surfaces is studied after annealing using scanning electron microscopy. We find that while the Au NP arrays are found to be stable when annealed up to 600 °C in a MOVPE system, a diameter and pitch dependent splitting of the particles is seen for annealing in a MBE system. The Ag NP arrays are found to be less stable, with smaller diameters (≤50 nm) dissolving during the annealing process in both epitaxial systems. In general, the mobility of the NPs is observed to differ between the two the GaAs 100 and 111B surfaces. Finally, our observations on the effect of annealing on Au-Ag alloy NP arrays suggest that these NP can withstand necessary annealing conditions for a complete de-oxidation of GaAs surfaces in both MOVPE and MBE.

  2. Time Dependent Universal Conductance Fluctuations In AuPd, Ag, And Au Wires

    NASA Astrophysics Data System (ADS)

    Trionfi, A.; Lee, S.; Natelson, D.

    2006-09-01

    Quantum transport phenomena allow experimental determinations of the phase coherence information in metals. We report quantitative comparisons of inferred coherence lengths from independent measurements of the weak localization magnetoresistance and time-dependent universal conductance fluctuations' magnetic field dependence. Strong agreement is observed in both quasi-2D and quasi-1D AuPd samples. However, quantitative agreement is not seen in quasi-1D Ag wires below 10 K and quasi-1D Au wires below 14 K. A possible explanation for this disagreement will be discussed. Attempts to produce changes in the coherence length in Au by annealing have also been made and results will be reported.

  3. On the structure of the thiolated Au6Ag7 cluster.

    PubMed

    Tlahuice-Flores, Alfredo

    2014-09-14

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

  4. Nanoscale Wire Bonding of Individual Ag Nanowires on Au Substrate at Room Temperature

    NASA Astrophysics Data System (ADS)

    Peng, Peng; Guo, Wei; Zhu, Ying; Liu, Lei; Zou, Guisheng; Zhou, Y. Norman

    2017-07-01

    The controllable wire bonding of individual Ag nanowires onto a Au electrode was achieved at room temperature. The plastic deformation induced by pressure using nanoindentation could break the protective organic shell on the surface of the Ag nanowires and cause atomic contact to promote the diffusion and nanojoining at the Ag and Au interface. Severe slip bands were observed in the Ag nanowires after the deformation. A metallic bond was formed at the interface, with the Ag diffusing into the Au more than the Au diffused into the Ag. This nanoscale wire bonding might present opportunities for nanoscale packaging and nanodevice design.

  5. Spectral and thermodynamic properties of Ag(I), Au(III), Cd(II), Co(II), Fe(III), Hg(II), Mn(II), Ni(II), Pb(II), U(IV), and Zn(II) binding by methanobactin from Methylosinus trichosporium OB3b.

    PubMed

    Choi, Dong W; Do, Young S; Zea, Corbin J; McEllistrem, Marcus T; Lee, Sung-W; Semrau, Jeremy D; Pohl, Nicola L; Kisting, Clint J; Scardino, Lori L; Hartsel, Scott C; Boyd, Eric S; Geesey, Gill G; Riedel, Theran P; Shafe, Peter H; Kranski, Kim A; Tritsch, John R; Antholine, William E; DiSpirito, Alan A

    2006-12-01

    Methanobactin (mb) is a novel chromopeptide that appears to function as the extracellular component of a copper acquisition system in methanotrophic bacteria. To examine this potential physiological role, and to distinguish it from iron binding siderophores, the spectral (UV-visible absorption, circular dichroism, fluorescence, and X-ray photoelectron) and thermodynamic properties of metal binding by mb were examined. In the absence of Cu(II) or Cu(I), mb will bind Ag(I), Au(III), Co(II), Cd(II), Fe(III), Hg(II), Mn(II), Ni(II), Pb(II), U(VI), or Zn(II), but not Ba(II), Ca(II), La(II), Mg(II), and Sr(II). The results suggest metals such as Ag(I), Au(III), Hg(II), Pb(II) and possibly U(VI) are bound by a mechanism similar to Cu, whereas the coordination of Co(II), Cd(II), Fe(III), Mn(II), Ni(II) and Zn(II) by mb differs from Cu(II). Consistent with its role as a copper-binding compound or chalkophore, the binding constants of all the metals examined were less than those observed with Cu(II) and copper displaced other metals except Ag(I) and Au(III) bound to mb. However, the binding of different metals by mb suggests that methanotrophic activity also may play a role in either the solubilization or immobilization of many metals in situ.

  6. Nanocap array of Au:Ag composite for surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Zhang, Yongjun; Wang, Cong; Wang, Jinpeng; Chen, Lei; Li, Jia; Liu, Yang; Zhao, Xiaoyu; Wang, Yaxin; Yang, Jinghai

    2016-01-01

    We fabricated Au:Ag nanocap arrays by co-sputtering Au and Ag onto two-dimensional polystyrene (PS) colloidal sphere templates in a magnetron sputtering system for the surface-enhanced Raman scattering (SERS) substrate. In contrast to the bilayer Au/Ag, the co-sputtering Au:Ag bimetal array formed the protrusion network of Ag and Au nanoparticles, which contributed to Raman enhancement in the waxberry-like structure. The metal protrusions formed waxberry-like shell in which the PS beads were encapsulated. At the same time, the Au:Ag bimetal arrays exhibit 4-fold more enhancement in the SERS signal intensity of Rhodamine 6G at the 1649 cm-1 than Au/Ag bilayer array, which is ascribed to the plasmon coupling between the nanoparticles of Au and Ag on the sample. When the PS colloidal particle templates were etched by O2-plasma before sputtering process, the nanogaps affected the surface plasmon resonance (SPR), and the optimal gaps between adjacent Au:Ag nanocaps generated even stronger SERS enhancements. This SERS substrate of Au:Ag showed high sensitivity and reproducibility. The EF of Au:Ag nanocap array substrate onto which Rhodamine 6G (R6G) were adsorbed was evaluated as 6.72 × 1010.

  7. Laccase/AuAg Hybrid Glucose Microfludic Fuel Cell

    NASA Astrophysics Data System (ADS)

    López-González, B.; Cuevas-Muñiz, F. M.; Guerra-Balcázar, M.; Déctor, A.; Arjona, N.; Ledesma-García, J.; Arriaga, L. G.

    2013-12-01

    In this work a hybrid microfluidic fuel cell was fabricated and evaluated with a AuAg/C bimetallic material for the anode and an enzymatic cathode. The cathodic catalyst was prepared adsorbing laccase and ABTS on Vulcan carbon (Lac-ABTS/C). This material was characterized by FTIR-ATR, the results shows the presence of absorption bands corresponding to the amide bounds. The electrochemical evaluation for the materials consisted in cyclic voltammetry (CV). The glucose electrooxidation reaction in AuAg/C occurs around - 0.3 V vs. NHE. Both electrocatalytic materials were placed in a microfluidic fuel cell. The fuel cell was fed with PBS pH 5 oxygen saturated solution in the cathodic compartment and 5 mM glucose + 0.3 M KOH in the anodic side. Several polarization curves were performed and the maximum power density obtained was 0.3 mWcm-2 .

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

    PubMed Central

    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. Synthesis of triangular Au core-Ag shell nanoparticles

    SciTech Connect

    Rai, Akhilesh; Chaudhary, Minakshi; Ahmad, Absar; Bhargava, Suresh; Sastry, Murali . E-mail: msastry@tatachemicals.com

    2007-07-03

    In this paper, we demonstrate a simple and reproducible method for the synthesis of triangular Au core-Ag shell nanoparticles. The triangular gold core is obtained by the reduction of gold ions by lemongrass extract. Utilizing the negative charge on the gold nanotriangles, silver ions are bound to their surface and thereafter reduced by ascorbic acid under alkaline conditions. The thickness of the silver shell may be modulated by varying the pH of the reaction medium. The formation of the Au core-Ag shell triangular nanostructures has been followed by UV-vis-NIR Spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements. The sharp vertices of the triangles coupled with the core-shell structure is expected to have potential for application in surface enhanced Raman spectroscopy and in the sensitive detection of biomolecules.

  10. Injection and acceleration of Au31+ in the BNL AGS.

    SciTech Connect

    Fischer,W.; Ahrens, L.; Brown, K.; Gardner, C.; Glenn, W.; Huang, H.; Mapes, M.; Smart, L.; Thieberger, P.; Tsoupas, N.; Zhang, S.Y.; Zeno, K.; Omet, C.; Spiller, P.

    2008-06-23

    Injection and acceleration of ions in a lower charge state reduces space charge effects, and, if further elcctron stripping is needed, may allow elimination of a stripping stage and the associated beam losses. The former is of interest to the accelerators in the GSI FAIR complex, the latter for BNL RHIC collider operation at energies lower than the current injection energy. Lower charge state ions, however, have a higher likelihood of electron stripping which can lead to dynamic pressures rises and subsequent beam losses. We report on experiments in the AGS where Au{sup 31+} ions were injected and accelerated instead of the normally used Au{sup 77+} ions. Beam intensities and the average pressure in the AGS ring are recorded, and compared with calculations for dynamic pressures and beam losses. The experimental results will be used to benchmark the StrahlSim dynamic vacuum code and will be incorporated in the GSI FAIR SIS100 design.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Conversion of Ag nanowires to AgCI nanowires decorated with Au nanoparticles and their photocatalytic activity.

    SciTech Connect

    Sun, Y.; Center for Nanoscale Materials

    2010-02-11

    A two-step approach has been developed to synthesize AgCl nanowires decorated with Au nanoparticles by using Ag nanowires as chemical templates. In the first step, the Ag nanowires are oxidized with FeCl{sub 3} followed by a simultaneous precipitation reaction between Ag{sup +} and Cl{sup -} ions at room temperature, resulting in conversion of the Ag nanowires to AgCl nanowires as well as reduction of Fe{sup 3+} to Fe{sup 2+} ions. In the second step, the Fe{sup 2+} ions generated in the first step reduce Au precursors (e.g., NaAuCl{sub 4}) to deposit Au nanoparticles on the surfaces of the AgCl nanowires, resulting in the formation of AgCl:Au composite nanowires. Because of strong surface plasmon resonance and chemical inertness of Au nanoparticles, the as-synthesized AgCl:Au nanowires exhibit enhanced absorption coefficient in the visible region and enhanced chemical stability to prevent them from degradation and aggregation. These unique properties enable the AgCl:Au nanowires to be used as a class of promising plasmonic photocatalysts driven by visible light. Preliminary results demonstrate these composite nanowires can efficiently decompose organics, such as methylene blue molecules, under illumination of white light.

  13. A facile and green strategy for the synthesis of Au, Ag and Au-Ag alloy nanoparticles using aerial parts of R. hypocrateriformis extract and their biological evaluation.

    PubMed

    Godipurge, S S; Yallappa, S; Biradar, Naveen J; Biradar, J S; Dhananjaya, B L; Hegde, Gajanan; Jagadish, K; Hegde, Gurumurthy

    2016-12-01

    A facile and green strategy is reported here to synthesize gold (Au), silver (Ag) and gold-silver (Au-Ag) alloy nanoparticles (NPs) through bio-reduction reactions of aqueous corresponding metal precursors mediated by extracts of aerial parts of R. hypocrateriformis, which act as both reducing and stabilizing agents, under microwave irradiation. UV-vis spectrophotometer, XRD, FT-IR, FESEM/TEM, TGA and EDAX analysis were used to characterize the obtained NPs. The formation of NPs is evident from their surface plasmon resonance peak observed at λmax=∼550, 450 and 500nm for Au, Ag and Au-Ag alloy NPs respectively. XRD pattern revealed that fcc structure, while FT-IR spectra signify the presence of phytochemicals adsorbed on NPs. Such a biofunctionalized NPs were characterized by their weight loss, 30% due to thermal degradation of plant phytochemicals observed in TG analysis. The spherical shape of Au, Ag and Au-Ag alloy NPs (∼10-50nm) is observed by FE-SEM/TEM images. EDAX analysis confirms the expected elemental composition. Moreover, these NPs showed enhanced antimicrobial, antioxidant, and anticancer activities, though it is more pronounced for Au-Ag alloy NPs, which is due to the combining effect of phytochemicals, Au and Ag metals. Thus, the biosynthesized NPs could be applied as effective growth inhibitors for various biomedical applications.

  14. Ag/Au/Pt trimetallic nanoparticles with defects: preparation, characterization, and electrocatalytic activity in methanol oxidation

    NASA Astrophysics Data System (ADS)

    Thongthai, Kontee; Pakawanit, Phakkhananan; Chanlek, Narong; Kim, Jun-Hyun; Ananta, Supon; Srisombat, Laongnuan

    2017-09-01

    Two series of Ag x /Au/Pt y trimetallic nanoparticles (Ag x Au1Pt2 with x ranging from 1-5 and Ag4Au1Pt y with y ranging from 1-3) were prepared by a sequential chemical reduction method that involved the deposition of Pt on preformed Ag/Au core-shell particles by systematically controlling the amount of Ag, Au, and Pt metal precursor solutions. The structural changes (the diameters and increased surface roughness from the defective features) and absorption patterns (the significant reduction of the peak intensities) of the nanoparticles examined with TEM and UV-vis spectroscopy indicated the selective incorporation of Pt on the Ag/Au nanoparticles regardless of their compositions. In addition, a combination of WDX, XRD, and XPS analyses quantitatively and qualitatively confirmed the successful formation of the Ag x Au1Pt2 and Ag4Au1Pt y trimetallic nanoparticles. Subsequently, these series of nanoparticles were deposited on multi-wall carbon nanotubes (MWCNTs) to evaluate their electrocatalytic property in the methanol oxidation reaction (MOR) as a function of their metal compositions. The results showed that the electrocatalytic activities of all Ag4/Au1/Pt y systems were higher than those of typical Pt on the MWCNTs. In particular, the Ag4Au1Pt2 nanoparticles exhibited the highest electrocatalytic property for the MOR, suggesting the importance of the proper combination of metal constituents and structures to regulate the activity in electrocatalytic systems.

  15. Ag/Au/Pt trimetallic nanoparticles with defects: preparation, characterization, and electrocatalytic activity in methanol oxidation.

    PubMed

    Thongthai, Kontee; Pakawanit, Phakkhananan; Chanlek, Narong; Kim, Jun-Hyun; Ananta, Supon; Srisombat, Laongnuan

    2017-09-15

    Two series of Ag x /Au/Pt y trimetallic nanoparticles (Ag x Au1Pt2 with x ranging from 1-5 and Ag4Au1Pt y with y ranging from 1-3) were prepared by a sequential chemical reduction method that involved the deposition of Pt on preformed Ag/Au core-shell particles by systematically controlling the amount of Ag, Au, and Pt metal precursor solutions. The structural changes (the diameters and increased surface roughness from the defective features) and absorption patterns (the significant reduction of the peak intensities) of the nanoparticles examined with TEM and UV-vis spectroscopy indicated the selective incorporation of Pt on the Ag/Au nanoparticles regardless of their compositions. In addition, a combination of WDX, XRD, and XPS analyses quantitatively and qualitatively confirmed the successful formation of the Ag x Au1Pt2 and Ag4Au1Pt y trimetallic nanoparticles. Subsequently, these series of nanoparticles were deposited on multi-wall carbon nanotubes (MWCNTs) to evaluate their electrocatalytic property in the methanol oxidation reaction (MOR) as a function of their metal compositions. The results showed that the electrocatalytic activities of all Ag4/Au1/Pt y systems were higher than those of typical Pt on the MWCNTs. In particular, the Ag4Au1Pt2 nanoparticles exhibited the highest electrocatalytic property for the MOR, suggesting the importance of the proper combination of metal constituents and structures to regulate the activity in electrocatalytic systems.

  16. Production of {phi} mesons in Au-Au collisions at the AGS.

    SciTech Connect

    Back, B. B.; Betts, R. R.; Chang, J.; E917 Collaboration; Gillitzer, A.; Henning, W. F.; Hofman, D. J.; Nanal, V.; Seto, R. K.; Wuosmaa, A. H.; Xiang, H.

    1999-08-10

    The first measurements of {phi} meson production in Au-Au collisions at AGS energies are presented via the decay to K{sup +} K{sup {minus}}. A measurement of the centrality dependence of the yield shows an increase similar to that seen for the K{sup {minus}} with a spectral shape consistent with a relativistic Breit-Wigner distribution within the statistical errors of the present data set. Future analysis using the full data set with 4 times the statistics will allow a more accurate determination of the yields, slopes and spectral shapes.

  17. High Visible Photoelectrochemical Activity of Ag Nanoparticle-Sandwiched CdS/Ag/ZnO Nanorods.

    PubMed

    Yang, Xu; Li, Hui; Zhang, Wu; Sun, Mingxuan; Li, Lequn; Xu, Ning; Wu, Jiada; Sun, Jian

    2017-01-11

    We report on the sensitizing of CdS-coated ZnO (CdS/ZnO) nanorods (NRs) by Ag nanoparticles (NPs) embedded between the CdS coating and the ZnO nanorod and the improved optical and photoelectrochemical properties of the Ag NP-sandwiched nanostructure CdS/Ag/ZnO NRs. The CdS/Ag/ZnO NRs were fabricated by growing Ag NPs on hydrothermally grown ZnO NRs and subsequently depositing CdS coatings followed by subsequent N2 annealing. The structure of the fabricated CdS/Ag/ZnO NRs was characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman backscattering, revealing that the ZnO NRs and the CdS coatings are both structured with hexagonal wurtzite and the Ag NPs contact well with ZnO and CdS. Optical properties were evaluated by measuring optical absorption and photoluminescence, showing that the Ag NPs behave well as sensitizers for optical property improvement and the CdS/Ag/ZnO NRs exhibit better photoresponse in a wide spectral region than CdS/ZnO because of plasmon-enhanced absorption due to the embedment of Ag NPs. The Ag NPs also serve as electron relays from CdS to ZnO, facilitating electron transfer from the CdS coatings to the ZnO NRs. The excellent photoresponse and efficient electron transfer make the CdS/Ag/ZnO NRs highly photoelectrochemically active. The CdS/Ag/ZnO NRs fabricated on indium-tin oxide present much better photoelectrochemical performance as photoanodes working in the visible region than CdS/ZnO NRs without Ag NPs. Under visible illumination, a maximum optical-to-chemical conversion efficiency of 3.13% is obtained for CdS/Ag/ZnO NR photoanodes against 1.35% for CdS/ZnO NR photoanodes.

  18. Growth of large aspect ratio AuAg bimetallic nanowires on Si(110) substrate

    NASA Astrophysics Data System (ADS)

    Bhukta, Anjan; Guha, Puspendu; Satpati, Biswarup; Maiti, Paramita; Satyam, Parlapalli V.

    2017-06-01

    Large aspect ratio bimetallic nanowire structures comprise potential applications in areas such as higher catalytic activity and surface Raman enhancement spectroscopy (SERS) substrates. By using the highly anisotropic ultra-clean Si(110) surface and with initial growth of sub monolayer (ML) Ag on such surface, a high aspect ratio AuAg bimetallic nanostructures can be formed. We report on the formation of large aspect ratio (>7.2 ± 0.8) AuAg nanowires on ultra-clean Si(110) surfaces using 0.5 ML Ag followed by 3.0 ML Au using molecular beam epitaxy (MBE) at a growth temperature of 300 °C. Under similar growth conditions without pre-deposition of Ag and only with deposition of 3.0 ML of Au consequences smaller aspect ratio (2.1 ± 0.1) monometallic Au nanostructures. The enhancement in aspect ratio of the nanostructures is attributed to the formation of one dimensional Ag layer (prior to Au growth) and Au-Ag bimetallic intermixing at elevated temperature. Considering deposition of 3.0 ML Au, a regime of substrate temperature ≈ 270-330 °C is found to be optimum to growth some of high aspect ratio (>25.0) AuAg nanowires as well. Exterior of this regime, at lower temperature due to low mobility of the ad-atoms and at higher temperature due to probable inter-diffusion of Ag, such extremely high aspect ratio AuAg nanowires found to be infrequent to grow. For growth at substrate temperature 300 °C, mean aspect ratio of the AuAg nanostructures is gradually increased in accordance with Au thickness up to 3.0 ML due to preferential accumulation of ad-atoms (Au, Ag) along Si < 1 1 bar 0 > and thereafter reduces for adequate accumulation along Si < 001 > .

  19. Inner shell excitation of Cu, Ag and Au

    NASA Astrophysics Data System (ADS)

    Stauffer, Allan; McEachran, Robert

    2016-09-01

    The ground states of Cu, Ag and Au have the configuration nd10(n +1)s with n = 3, 4 and 5. The lowest excited manifold for Cu and Au has the configuration nd9(n +1)s2 which is well separated from the next excited manifold nd10(n +1)p. However, for Ag, the lowest 4d95s2 level with J = 5/2 lies between the two levels of the 4d105p manifold. In we compared our Relativistic Distorted Wave calculations for the excitation of the 4d105p manifold with experimental measurements which would have included a contribution from the 4d95s2 J = 5/2 level. While we do not expect the cross section for this forbidden transition to be large compared to the optical allowed transitions of the P levels, we decided to investigate excitation of these inner shell levels, in part because they are the lowest excited levels in Cu and Au, We will discuss the theoretical expressions for these excitations as well as give numerical results of our cross section calculations.

  20. A new photothermal therapeutic agent: core-free nanostructured Au x Ag1-x dendrites.

    PubMed

    Hu, Kuo-Wei; Huang, Chih-Chia; Hwu, Jih-Ru; Su, Wu-Chou; Shieh, Dar-Bin; Yeh, Chen-Sheng

    2008-01-01

    A new class of Au(x)Ag(1-x) nanostructures with dendrite morphology and a hollow interior were synthesized by using a replacement reaction between Ag dendrites and an aqueous solution of HAuCl(4). The Ag nanostructured dendrites were generated by the reaction of AgNO(3) with ascorbic acid in a methanol/water system. The dendrites resemble a coral shape and are built up of many stems with an asymmetric arrangement. Each stem is approximately 400 nm in length and 65 nm in diameter. The bimetallic composition of Au(x)Ag(1-x) can be tuned by the addition of different amounts of HAuCl(4) to the Ag dendritic solution. The hollowing process resulted in tubular structures with a wall thickness of 10.5 nm in Au(0.3)Ag(0.7) dendrites. The UV/Vis spectra indicate that the strongest NIR absorption among the resulting hollow Au(x)Ag(1-x) dendrites was in Au(0.3)Ag(0.7). The MTT assay was conducted to evaluate the cytotoxicity of Ag dendrites, hollow Au(0.06)Ag(0.94) and Au(0.3)Ag(0.7) dendrites, and Au nanorods. It was found that hollow Au(0.06)Ag(0.94) and Au(0.3)Ag(0.7) dendrites exhibited good biocompatibility, while both Ag dendrites and Au nanorods showed dose-dependent toxicity. Because of absorption in the NIR region, hollow Au(0.3)Ag(0.7) dendrites were used as photothermal absorbers for destroying A549 lung cancer cells. Their photothermal performance was compared to that of Au nanorod photothermal therapeutic agents. As a result, the particle concentration and laser power required for efficient cancer cell damage were significantly reduced for hollow Au(0.3)Ag(0.7) dendrites relative to those used for Au nanorods. The hollow Au(0.3)Ag(0.7) nanostructured dendrites show potential in photothermolysis for killing cancer cells.

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

    NASA Astrophysics Data System (ADS)

    Frenkel, A. I.; Machavariani, V. Sh.; Rubshtein, A.; Rosenberg, Yu.; Voronel, A.; Stern, E. A.

    2000-10-01

    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.

  2. Theoretical study of CO oxidation on cationic, neutral, and anionic AuM dimers (M = Pd and Ag).

    PubMed

    Chen, Xuan; Lu, Rui-Feng; Kan, Er-Jun; Liu, Yu-Zhen; Xiao, Chuan-Yun; Deng, Kai-Ming

    2014-06-01

    The CO and O2 adsorption as well as CO oxidation on cationic, neutral, and anionic AuM dimers (M = Pd, Ag) are studied by density functional calculations. Our results show that CO and O2 are adsorbed more stably on AuPd dimers than on AuAg dimers with corresponding charge state. O2 is favorable to be adsorbed on Pd atom in AuPd(+), AuPd and AuPd(-) dimers. CO is adsorbed on Pd in AuPd and AuPd(-), while it is favorable to be adsorbed on Au in AuPd(+). For AuAg dimers, O2 is adsorbed on Ag in AuAg and AuAg(-), and it is adsorbed on Au in AuAg(+). CO is adsorbed on Ag in AuPd(-), while it is adsorbed on Au in AuAg and AuAg(+). The CO oxidation reaction is explored along two possible pathways: path-1 involves CO attacking the initial complexes of AuM dimers and O2, and path-2 is related to O2 interacting with the complexes of AuM dimers and CO. The charge state of AuM dimers has a substantial effect on CO oxidation. The reaction on AuPd(-) prefers path-1, and AuPd(+) mediated reaction proceeds along path-2, while CO oxidation on AuPd is difficult along both paths. For AuAg, both pathways are viable for AuAg(-) mediated reactions, while AuAg and AuAg(+) mediated reactions prefer path-2. Moreover, the energy barriers of CO oxidation on neutral AuAg is comparable with those on AuPd in all charge states while the energy barriers for AuAg(-) and AuAg(+) are considerably lower than those for all AuPd dimmers, indicating the impurity atom also plays a significant role in the catalytic activity. Furthermore, AuAg(-) is proposed to be the most active species due to the lowest barrier involved in the reaction.

  3. Ab initio study of He point defects in fcc Au-Ag alloys

    SciTech Connect

    Zhu, Zi Qiang; Yang, Li; Nie, JL; Peng, SM; Long, XG; Zhou, X. S.; Zu, Xiaotao; Gao, Fei

    2013-04-25

    The relative stabilities of He defects in two fcc Au-Ag alloys (Au3Ag2 and AuAg) are investigated using ab initio method based on density functional theory. The results show that the stabilities of He defects in the two alloys mainly depend on the atomic arrangements of the nearest neighboring host metals. A He interstitial prefers to stay at a site with more Ag neighboring atoms, while the favorable substitutional site has more Au neighboring atoms in Au-Ag alloys. Moreover, the substitutional He defects are the most stable configurations in both the alloys, and the octahedral He interstitials are energetically more favorable than the tetrahedral interstitials. It is of interest to note that the properties of He defects slightly depend on the mass-density of Au-Ag alloys. The results also demonstrate that the relative stabilities of He defects are primarily attributed to the hybridization between metals d states and He p states.

  4. Plasmonic enhancements of photocatalytic activity of Pt/n-Si/Ag photodiodes using Au/Ag core/shell nanorods.

    PubMed

    Qu, Yongquan; Cheng, Rui; Su, Qiao; Duan, Xiangfeng

    2011-10-26

    We report the plasmonic enhancement of the photocatalytic properties of Pt/n-Si/Ag photodiode photocatalysts using Au/Ag core/shell nanorods. We show that Au/Ag core/shell nanorods can be synthesized with tunable plasmon resonance frequencies and then conjugated onto Pt/n-Si/Ag photodiodes using well-defined chemistry. Photocatalytic studies showed that the conjugation with Au/Ag core/shell nanorods can significantly enhance the photocatalytic activity by more than a factor of 3. Spectral dependence studies further revealed that the photocatalytic enhancement is strongly correlated with the plasmonic absorption spectra of the Au/Ag core/shell nanorods, unambiguously demonstrating the plasmonic enhancement effect.

  5. Corrosion resistance evaluation of Pd-free Ag-Au-Pt-Cu dental alloys.

    PubMed

    Fujita, Takeshi; Shiraishi, Takanobu; Takuma, Yasuko; Hisatsune, Kunihiro

    2011-01-01

    The corrosion resistance of nine experimental Pd-free Ag-Au-Pt-Cu dental alloys in a 0.9% NaCl solution was investigated using cyclic voltammetry (CV), optical microscopy, and scanning electron microscopy (SEM). CV measurements revealed that the breakdown potential (E(bd)) and zero current potential (E(zc)) increased with increasing Au/(Au+Ag) atomic ratio. Thus, the Au/(Au+Ag) atomic ratio, but not the Cu content, influenced the corrosion resistance of Ag-Au-Pt-Cu alloys. After the forward scan of CV, both optical and scanning electron microscope images showed that in all the experimental alloys, the matrix phase was corroded but not the second phase. From corrosion resistance viewpoint, the Ag-Au-Pt-Cu alloys seemed to be suitable for clinical application.

  6. Growth of Au nanocrystals on CdS nanorods

    NASA Astrophysics Data System (ADS)

    Yang, Heesun

    2006-08-01

    Nanorods of S2- rich CdS were synthesized by a reaction of excess S versus Cd precursors in the presence of ethylene diamine. The photoluminescence (PL) emission from the S2- rich CdS nanorods was broad with a peak at ˜710 nm, which was 40 nm longer in wavelength than the PL peak from Cd2+ rich CdS (˜670 nm) nanorods. The influence of surface electron or hole trap states on the luminescent pathway of CdS nanorods will be discussed to explain these shifts in wavelength. Nanocrystals of Au ˜2 nm in size were grown on S2- rich surfaces of CdS nanorods. Significant luminescence quenching was observed from the Au nanocrystals on the CdS nanorods due to interfacial charge separation. Change separation by the Au nanocrystals on the CdS resulted in enhanced photocatalytic degradation of Procion red mix-5B (PRB) dye in an aqueous solution under UV light irradiation.

  7. Corrosion behavior of Au and Ag modified Cu-Ni-Mn alloys.

    PubMed

    Wright, S R; Cocks, F H; Gettleman, L

    1980-04-01

    The linear electrochemical polarization method was used to provide quantitative in vitro measurements of corrosion rates as a function of exposure time for Cu-Ni-Mn, Cu-Ni-Mn-Au, Cu-Ni-Mn-Ag, and Cu-Ni-Mn-Au-Ag alloys in artificial saliva. Both Au and Ag additives to dental-cast Cu-Ni-Mn alloys lowered the corrosion rate significantly.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

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

    2016-09-06

    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

  10. Enhanced plasmonic behavior of bimetallic (Ag-Au) multilayered spheres

    NASA Astrophysics Data System (ADS)

    Peña-Rodríguez, Ovidio; Pal, Umapada

    2011-12-01

    In this article we study the plasmonic behavior of some stable, highly biocompatible bimetallic metal-dielectric-metal (MDM) and double concentric nanoshell (DCN) structures. By simply switching the material of the inner structure from Au to Ag, the intensity of their surface plasmon resonance could be increased in the optical transparency region of the human tissues up to 20 and 60 percent for the MDM and DCN, respectively, while the biocompatibility is retained. The obtained results indicate that these novel structures could be highly suitable for surface enhanced Raman scattering and photothermal cancer therapy.

  11. Anisotropic syntheses of boat-shaped core shell Au Ag nanocrystals and nanowires

    NASA Astrophysics Data System (ADS)

    Yang, Zusing; Chang, Huan-Tsung

    2006-05-01

    This paper describes the syntheses of boat-shaped core-shell Au-Ag bimetallic nanoparticles (NPs) and Au-Ag bimetallic nanowires (NWs). Initially, gold nanorods (AuNRs) having lengths and widths of 70 ± 18 and 12 ± 2 nm, respectively, were prepared from gold seeds in the presence of hexadecyltrimethylammonium bromide (CTAB), benzyldimethylammonium chloride (BDAC), NaAuCl4, AgNO3, and ascorbic acid. The thus-prepared AuNRs were then used to prepare boat-shaped core-shell Au-Ag bimetallic NPs in a glycine solution (pH 8.0) containing CTAB, AgNO3, and ascorbic acid. The CTAB/BDAC molar ratio and the AgNO3 concentration were important parameters affecting the anisotropy of the products. Silver atoms were deposited at both ends of the AuNRs to form the boat-shaped core-shell Au-Ag bimetallic NPs. Upon coalescence of the NPs at 88 ± 2 °C, the boat-shaped core-shell Au-Ag bimetallic NPs assembled into the form of NWs. These NWs, which were stable in solution at room temperature for at least 3 weeks, formed nanomaterials containing AuNRs after being heated at 210 °C for 15 min, i.e. as a result of the melting of the BDAC and silver shells.

  12. Hollow Au-Ag Nanoparticles Labeled Immunochromatography Strip for Highly Sensitive Detection of Clenbuterol

    PubMed Central

    Wang, Jingyun; Zhang, Lei; Huang, Youju; Dandapat, Anirban; Dai, Liwei; Zhang, Ganggang; Lu, Xuefei; Zhang, Jiawei; Lai, Weihua; Chen, Tao

    2017-01-01

    The probe materials play a significant role in improving the detection efficiency and sensitivity of lateral-flow immunochromatographic test strip (ICTS). Unlike conventional ICTS assay usually uses single-component, solid gold nanoparticles as labeled probes, in our present study, a bimetallic, hollow Au-Ag nanoparticles (NPs) labeled ICTS was successfully developed for the detection of clenbuterol (CLE). The hollow Au-Ag NPs with different Au/Ag mole ratio and tunable size were synthesized by varying the volume ratio of [HAuCl4]:[Ag NPs] via the galvanic replacement reaction. The surface of hollow Ag-Au NPs was functionalized with 11-mercaptoundecanoic acid (MUA) for further covalently bonded with anti-CLE monoclonal antibody. Overall size of the Au-Ag NPs, size of the holes within individual NPs and also Au/Ag mole ratio have been systematically optimized to amplify both the visual inspection signals and the quantitative data. The sensitivity of optimized hollow Au-Ag NPs probes has been achieved even as low as 2 ppb in a short time (within 15 min), which is superior over the detection performance of conventional test strip using Au NPs. The optimized hollow Au-Ag NPs labeled test strip can be used as an ideal candidate for the rapid screening of CLE in food samples. PMID:28134263

  13. Hollow Au-Ag Nanoparticles Labeled Immunochromatography Strip for Highly Sensitive Detection of Clenbuterol.

    PubMed

    Wang, Jingyun; Zhang, Lei; Huang, Youju; Dandapat, Anirban; Dai, Liwei; Zhang, Ganggang; Lu, Xuefei; Zhang, Jiawei; Lai, Weihua; Chen, Tao

    2017-01-30

    The probe materials play a significant role in improving the detection efficiency and sensitivity of lateral-flow immunochromatographic test strip (ICTS). Unlike conventional ICTS assay usually uses single-component, solid gold nanoparticles as labeled probes, in our present study, a bimetallic, hollow Au-Ag nanoparticles (NPs) labeled ICTS was successfully developed for the detection of clenbuterol (CLE). The hollow Au-Ag NPs with different Au/Ag mole ratio and tunable size were synthesized by varying the volume ratio of [HAuCl4]:[Ag NPs] via the galvanic replacement reaction. The surface of hollow Ag-Au NPs was functionalized with 11-mercaptoundecanoic acid (MUA) for further covalently bonded with anti-CLE monoclonal antibody. Overall size of the Au-Ag NPs, size of the holes within individual NPs and also Au/Ag mole ratio have been systematically optimized to amplify both the visual inspection signals and the quantitative data. The sensitivity of optimized hollow Au-Ag NPs probes has been achieved even as low as 2 ppb in a short time (within 15 min), which is superior over the detection performance of conventional test strip using Au NPs. The optimized hollow Au-Ag NPs labeled test strip can be used as an ideal candidate for the rapid screening of CLE in food samples.

  14. Hollow Au-Ag Nanoparticles Labeled Immunochromatography Strip for Highly Sensitive Detection of Clenbuterol

    NASA Astrophysics Data System (ADS)

    Wang, Jingyun; Zhang, Lei; Huang, Youju; Dandapat, Anirban; Dai, Liwei; Zhang, Ganggang; Lu, Xuefei; Zhang, Jiawei; Lai, Weihua; Chen, Tao

    2017-01-01

    The probe materials play a significant role in improving the detection efficiency and sensitivity of lateral-flow immunochromatographic test strip (ICTS). Unlike conventional ICTS assay usually uses single-component, solid gold nanoparticles as labeled probes, in our present study, a bimetallic, hollow Au-Ag nanoparticles (NPs) labeled ICTS was successfully developed for the detection of clenbuterol (CLE). The hollow Au-Ag NPs with different Au/Ag mole ratio and tunable size were synthesized by varying the volume ratio of [HAuCl4]:[Ag NPs] via the galvanic replacement reaction. The surface of hollow Ag-Au NPs was functionalized with 11-mercaptoundecanoic acid (MUA) for further covalently bonded with anti-CLE monoclonal antibody. Overall size of the Au-Ag NPs, size of the holes within individual NPs and also Au/Ag mole ratio have been systematically optimized to amplify both the visual inspection signals and the quantitative data. The sensitivity of optimized hollow Au-Ag NPs probes has been achieved even as low as 2 ppb in a short time (within 15 min), which is superior over the detection performance of conventional test strip using Au NPs. The optimized hollow Au-Ag NPs labeled test strip can be used as an ideal candidate for the rapid screening of CLE in food samples.

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

    NASA Astrophysics Data System (ADS)

    Zhao, Qian; Chen, Shenna; Zhang, Lingyang; Huang, Haowen; Liu, Fengping; Liu, Xuanyong

    2014-12-01

    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.

  16. Formation of one-dimensional Ag-Au solid solution colloids with Au nanorods as seeds, their alloying mechanisms, and surface plasmon resonances

    NASA Astrophysics Data System (ADS)

    Guo, Tao; Tan, Yiwei

    2012-12-01

    In this work, one dimensional (1D) Ag-Au solid solution nanoalloys were synthesized by rapidly diffusing Ag into the preformed Au nanorod (AuNR) seeds at ambient temperature in aqueous solution. By varying the molar ratio of AgCl/AuNR (in gold atoms), two kinds of 1D Ag-Au alloy nanostructures with a narrow size distribution--AgAu nanowires and Ag33Au67 nanorods--could be obtained in high yields when NaCl and polyvinylpyrrolidone (PVP) were used as an additive and capping reagent, respectively. Based on HRTEM imaging combined with a series of control experiments, it is conceivable that vacancy/defect-motivated interdiffusion of Ag and Au atoms coupled with oxidative etching is a crucial stage in the mechanism responsible for this room-temperature alloying process, and the subsequent conjugation of the fused Ag-Au alloyed nanostructures is associated with the formation of the AgAu nanowires. The resulting 1D Ag-Au nanoalloys form stable colloidal dispersions and show unique localized surface plasmon resonance (LSPR) peaks in the ensemble extinction spectra.In this work, one dimensional (1D) Ag-Au solid solution nanoalloys were synthesized by rapidly diffusing Ag into the preformed Au nanorod (AuNR) seeds at ambient temperature in aqueous solution. By varying the molar ratio of AgCl/AuNR (in gold atoms), two kinds of 1D Ag-Au alloy nanostructures with a narrow size distribution--AgAu nanowires and Ag33Au67 nanorods--could be obtained in high yields when NaCl and polyvinylpyrrolidone (PVP) were used as an additive and capping reagent, respectively. Based on HRTEM imaging combined with a series of control experiments, it is conceivable that vacancy/defect-motivated interdiffusion of Ag and Au atoms coupled with oxidative etching is a crucial stage in the mechanism responsible for this room-temperature alloying process, and the subsequent conjugation of the fused Ag-Au alloyed nanostructures is associated with the formation of the AgAu nanowires. The resulting 1D Ag-Au

  17. Size-dependent spontaneous alloying of Au-Ag nanoparticles.

    PubMed

    Shibata, Tomohiro; Bunker, Bruce A; Zhang, Zhenyuan; Meisel, Dan; Vardeman, Charles F; Gezelter, J Daniel

    2002-10-09

    We report on systematic studies of size-dependent alloy formation of silver-coated gold nanoparticles (NPs) in aqueous solution at ambient temperature using X-ray absorption fine structure spectroscopy (XAFS). Various Au-core sizes (2.5-20 nm diameter) and Ag shell thicknesses were synthesized using radiolytic wet techniques. The equilibrium structures (alloy versus core-shell) of these NPs were determined in the suspensions. We observed remarkable size dependence in the room temperature interdiffusion of the two metals. The interdiffusion is limited to the subinterface layers of the bimetallic NPs and depends on both the core size and the total particle size. For the very small particles (< or =4.6 nm initial Au-core size), the two metals are nearly randomly distributed within the particle. However, even for these small Au-core NPs, the interdiffusion occurs primarily in the vicinity of the original interface. Features from the Ag shells do remain. For the larger particles, the boundary is maintained to within one monolayer. These results cannot be explained either by enhanced self-diffusion that results from depression of the melting point with size or by surface melting of the NPs. We propose that defects, such as vacancies, at the bimetallic interface enhance the radial migration (as well as displacement around the interface) of one metal into the other. Molecular dynamics calculations correctly predict the activation energy for diffusion of the metals in the absence of vacancies and show an enormous dependence of the rate of mixing on defect levels. They also suggest that a few percent of the interfacial lattice sites need to be vacant to explain the observed mixing.

  18. Cu-Ag sulfides as indicators of pre-porphyritic epithermal Au-Ag deposits in Northeastern Russia

    NASA Astrophysics Data System (ADS)

    Savva, N. E.; Sidorov, A. A.; Volkov, A. V.

    2016-08-01

    Au-Ag mineralization of the Olcha and Teploe epithermal deposits underwent thermal metamorphism due to porphyritic intrusions. The presence of Bi-bearing galena and matildite in the ores (Teploe), Cu-Te-bearing naumannite (Olcha), the occurrence of middle- and high-temperature facies of metasomatic rocks (epidote and actinolite), and temperature formation conditions are related, firstly, to the influence of granitoids on the ore process, which supplied not only Cu and Mo, but also Bi, Te, and, secondly, to the heating of host rocks containing pre-porphyritic epithermal Au-Ag mineralization. The abundance of Cu-Ag sulfides and Cu-acanthite resulted from the enrichment of later mineral phases in Cu and Ag under the substance redistribution with the formation of Ag-acanthite ores. The data considered in the paper are of practical importance for regional forecasting of metallogenic constructions, exploration, and evaluation of the epithermal Au-Ag deposits.

  19. Simulation of Electric Field in Semi Insulating Au/CdTe/Au Detector under Flux

    SciTech Connect

    Franc, J.; James, R.; Grill, R.; Kubat, J.; Belas, E.; Hoschl, P.; Moravec, P.; Praus, P.

    2009-08-02

    We report our simulations on the profile of the electric field in semi insulating CdTe and CdZnTe with Au contacts under radiation flux. The type of the space charge and electric field distribution in the Au/CdTe/Au structure is at high fluxes result of a combined influence of charge formed due to band bending at the electrodes and from photo generated carriers, which are trapped at deep levels. Simultaneous solution of drift-diffusion and Poisson equations is used for the calculation. We show, that the space charge originating from trapped photo-carriers starts to dominate at fluxes 10{sup 15}-10{sup 16}cm{sup -2}s{sup -1}, when the influence of contacts starts to be negligible.

  20. Synthesis and biosensor application of Ag@Au bimetallic nanoparticles based on localized surface plasmon resonance

    NASA Astrophysics Data System (ADS)

    Ghodselahi, T.; Arsalani, S.; Neishaboorynejad, T.

    2014-05-01

    This work demonstrates a simple method for synthesizing gold-silver bimetallic nanoparticles (Ag@Au BNPs). Ag@Au BNPs on the carbon thin film are prepared by co-deposition of RF-sputtering and RF-PECVD using acetylene gas and gold-silver target. X-ray diffraction analysis indicates that Au and Ag NPs with FCC crystal structure are formed in our samples. From AFM image and data, average particles size of gold and silver are estimated to be about 5 and 8 nm, respectively. XRD profile and localized surface plasmon resonance (LSPR) spectroscopy indicate that Ag NPs in Ag@Au BNPs composite have a more chemical activity with respect to bare Ag NPs. Biosensor application of Ag@Au BNPs without probe immobilization is introduced too. The change in LSPR absorption peak of Ag@Au BNPs in presence of DNA primer decamer (ten-deoxycytosine) at fM concentrations is investigated. The LSPR absorption peak of Au NPs has a blue shift and the LSPR absorption peak of Ag NPs has a red shift by addition of DNA primer and under DNA exposure up to 1 h. Our sample shows a good response to low concentration of DNA and has a short response time. Both of these are prerequisite for applying this sample as LSPR biosensor chip.

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

    PubMed

    Nigam, Sandeep; Majumder, Chiranjib

    2010-11-03

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

  2. Catalysis by Nanostructures: Methane, Ethylene Oxide, and Propylene Oxide Synthesis on Ag, Cu or Au Nanoclusters

    DTIC Science & Technology

    2008-02-07

    GRANT NUMBER Propylene Oxide Synthesis on Ag , Cu or Au nanoclusters F49620-01-1-0459 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Horia...Nanostructures: Methane, Ethylene Oxide, and Propylene Oxide Synthesis on Ag , Cu or Au nanoclusters, F49620-01-1-0459 Final Performance Report (for the period 07...andthe mobility of Ag clusters and Au clusters on TiO 2(1 10) have been published " . We found that Au atoms are very mobile and form large clusters at

  3. Synthesis and characterization of Au core-Au-Ag shell nanoparticles from gold seeds: impacts of glycine concentration and pH.

    PubMed

    Huang, Yu-Fen; Huang, Kuan-Ming; Chang, Huan-Tsung

    2006-09-01

    This paper describes the preparation of Au core-Au-Ag shell nanoparticles (NPs) in different morphologies by controlling both the pH and the glycine concentration. Using a seed-growth method, we prepared high-quality Au core-Au-Ag shell NPs from a glycine solution under alkaline conditions (pH>8.5). By controlling both the pH and the glycine concentration, we prepared dumbbell-shaped and peanut-shaped Au core-Au-Ag shell NPs readily by depositing gold and silver, reduced by ascorbate, onto the gold nanorods. We have found that the glycine concentration that is optimal for preparing high-quality Au core-Au-Ag shell NPs differs at the various values of pH. At pH<8.5, the glycine concentration is not important, but, when preparing dumbbell- and peanut-shaped Au core-Au-Ag shell NPs, it should be greater than 50 mM and greater than 20 mM at pH 9.5 and 10.5, respectively. Glycine plays a number of roles during the synthesis of the Au core-Au-Ag shell NPs by controlling the solution pH, altering the reduction potentials of gold and silver ions through forming complexes with metal ions (Au(+) and Ag(+)), minimizing the formation of Ag(2)O, AgCl, and AgBr precipitates, and stabilizing the thus-prepared NPs. At pH 9.7, we observed the changes in the morphologies of the Au core-Au-Ag shell NPs-from regular (rectangular) to peanut- and dumbbell-shaped, and finally to jewel-, diamond-, and/or sphere-shaped-that occurred during the course of a 60-min reaction. In addition, we were able to affect the shapes and sizes of the Au core-Au-Ag shell NPs by controlling the reaction time.

  4. High density Ag nanobranches decorated with sputtered Au nanoparticles for surface-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Kim, Yong-Tae; Schilling, Joerg; Schweizer, Stefan L.; Wehrspohn, Ralf B.

    2017-07-01

    High density Ag nanobranches (NBs) decorated with Au nanoparticles (NPs) have been fabricated through pulsed electrodeposition using porous anodic aluminum oxide (AAO) as a template, followed by a metal sputtering process. Au NP-decorated Ag NBs show higher surface-enhanced Raman scattering (SERS) intensity than pure Ag NBs due to tiny Au NPs creating additional hot spots which contribute to the increased Raman enhancement. High density Ag NBs protruding from planar AAO templates function not only as an effective plasmonic material but also as an indispensable platform for loading a large amount of Au NPs with a narrow size distribution. Moreover, the long term stability of the SERS substrates significantly improved by decorating Ag NBs with Au NPs resulting in high SERS intensity even after several months of storage in air.

  5. A SERS and fluorescence dual mode cancer cell targeting probe based on silica coated Au@Ag core-shell nanorods.

    PubMed

    Zong, Shenfei; Wang, Zhuyuan; Yang, Jing; Wang, Chunlei; Xu, Shuhong; Cui, Yiping

    2012-08-15

    We report a dual mode cancer cell targeting probe based on CdTe quantum dots (QDs) conjugated, silica coated Au@Ag core-shell nanorods (Au@Ag NRs), which can generate both surface enhanced Raman scattering (SERS) and fluorescence signals. In such a probe, folic acid (FA) is used as a targeting ligand for folate receptors (FRs) overexpressed cancer cells. To synthesize the probe, Au@Ag NRs were first prepared to serve as the SERS substrates by coating an Ag shell on the gold nanorods. Then the Au@Ag NRs were labeled with 4-mercaptobenzoic acid (4MBA) to generate SERS signals, followed by being coated with a silica shell through a modified Stöber method. Finally, CdTe QDs and FA were conjugated to the silica coated Au@Ag NRs by the carbodiimide chemistry to yield fluorescence and the targeting ability, respectively. To validate the targeting capability of the probe, in vitro experiments were conducted, using HeLa cells with overexpressed FRs as the model target cells and MRC-5 cells with a low folate receptor expression level as the negative control. Both the fluorescence imaging and the SERS mapping results confirmed that the proposed probe can be used as an efficient cancer cell targeting agent. This kind of multifunctional probe has great potential in the diagnosis and therapeutics of cancerous diseases due to its specific targeting and multiplex imaging abilities, especially in the simultaneous tracking of multiple components in a hybrid bio-system.

  6. Effect of Au thickness on AuAg bimetallic growth on reconstructed Si(5 5 12) surfaces

    NASA Astrophysics Data System (ADS)

    Bhukta, Anjan; Ghosh, Arnab; Guha, Puspendu; Maiti, Paramita; Satpati, Biswarup; Satyam, Parlapalli Venkata

    2017-03-01

    Large, stable and single domain unit cell with row-like structures makes reconstructed Si(5 5 12) surface an important one-dimensional growth template of nanostructures. We report on the morphological aspects of the growth of AuAg bimetallic nanostructures on a reconstructed Si(5 5 12) surface that has been deposited with a 0.5 monolayer (ML) Ag and various Au thicknesses (0.5 to 5.0 ML) to determine the optimum gold thickness for a growth of high aspect ratio of AuAg nanostructures. The mean aspect ratio of AuAg nanostructures increases up to Au thickness of 3.0 ML and for larger thickness the mean aspect ratio decreases. The prior growth of 0.5 ML Ag on reconstructed surface result in the formation of one-dimensional Ag strips which are helping for preferential nucleation sites along Si< 1bar{1}0 rangle to form AuAg bimetallic long aspect ratio structures. Followed by these early processes of growth, for Au thickness >3.0 ML, excess Au ad-atoms begin to accumulate along Si< 66bar{5} rangle and consequences reduction of mean aspect ratio of bimetallic nanostructures. Nanostructures are grown using molecular beam epitaxy method under ultra-high vacuum conditions and in situ scanning tunneling microscopy has been used to investigate the morphological variations. Determination of structural aspects and compositional analysis has been carried out using Rutherford backscattering spectrometry and high-resolution (scanning) transmission electron microscopy methods.

  7. Optimizing Au/Ag core-shell nanorods: purification, stability, and surface modification

    NASA Astrophysics Data System (ADS)

    Ma, Yanan; Zhou, Jun; Shu, Lei; Li, Tianhua; Petti, Lucia; Mormile, Pasquale

    2014-06-01

    The purification, stability, and surface modification of Au/Ag core-shell nanorods (Au/Ag NRs) in a biological buffer solution were systematically studied for the first time. In this study, Au/Ag NRs were synthesized by chemically reducing silver on the surface of gold nanorods using cetyltrimethylammonium bromide as surfactant and then purified by centrifugation washing. Based on the analysis of UV-Vis absorption spectra, TEM images, Raman spectra, and the ξ-potential, it was observed that after the second washing step, the Au/Ag NRs displayed good stability and high surface-enhanced Raman scattering (SERS) enhancement. When the as-prepared Au/Ag NRs were centrifuged more than twice, a structural transition in the surfactant layer was manifested with a sudden increase in the Raman signal intensities at 760 and 1,455 cm-1. Moreover, 4-mercaptobenzoic acid (4MBA) was used as a Raman reporter molecule to investigate the SERS characteristics of the purified Au/Ag NRs. The Raman signal intensity was enhanced with increasing the concentration of 4MBA and reached its highest intensity at the saturation concentration of 1.0 µM 4MBA in a 5 ml solution of the purified Au/Ag NRs. To prevent significant aggregation of the 4MBA-tagged Au/Ag NRs, a poly(styrenesulfonate) (PSS) layer was assembled on the nanorod surfaces by electrostatic adsorption for further surface modification, which made the 4MBA-tagged Au/Ag NRs suitable for the labeled biosensing. Subsequently, the characteristics of the PSS-coated Au/Ag NRs were demonstrated for the potential applications of label-free biosensing.

  8. Polymers effects on synthesis of AuNPs, and Au/Ag nanoalloys: indirectly generated AuNPs and versatile sensing applications including anti-leukemic agent.

    PubMed

    Jahan, Shanaz; Mansoor, Farrukh; Kanwal, Shamsa

    2014-03-15

    Polymers either serve as shielding or capping agents to restrict the nanoparticle size. This study demonstrates the polymer depositions and their effects in synthesis and sharp stabilization of gold nanoparticles (AuNPs) and to develop gold/silver nanoalloys (Au/Ag nanoalloys). Effects of different polymers are tested to justify their role in synthesis and stability of phloroglucinol (PG) coated AuNPs and Au/Ag nanoalloys. Cationic and anionic i.e. [Polydiallyldimethylammonium](+) (PDDA), [Polyethyleneimine](+) (PEI), [Polystyrene sulfonate](2-) (PSS) and neutral polymer Polychlorotriflouroethylene (PCTFE) produce praiseworthy stable AuNPs and Au/Ag nanoalloy. To prove polymer effects characterization protocols including UV-vis, Fluorescence (PL), IR and AFM imaging are performed to fully investigate the mechanism and size characteristics of these nanoparticles/nanoalloys. In this study sharp size controlling/sheilding effects were observed particularly with cationic polymers simply through the favorable electrostatic interactions with the terminal ends of PG Potent/significant detection of doxorubicin (DOX, an antileukemic agent) via fluorescence resonance energy transfer (FRET) between PEI shielded AuNPs (AuNPEI) and DOX was achieved upto 10 pM level, while PDDA protected AuNPs facilitated the detection of ascorbic acid based on fluorescence enhancement effects in wide range (10-200 nM) and with detection limit of 200 pM. Similarly sensing performance of PEI stabilized Au/Ag nanoalloys on addition of halides (Cl(-), Br(-), I(-)) is evaluated through red shifted SPR along with continuous increase in absorbance and also through AFM. Moreover the addition of halide ions also helped the regeneration of AuNPs by taking away silver from the Au/Ag nanoalloys enabling their detections upto subnanomolar levels.

  9. Invoking Direct Exciton-Plasmon Interactions by Catalytic Ag Deposition on Au Nanoparticles: Photoelectrochemical Bioanalysis with High Efficiency.

    PubMed

    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.

  10. Formation of one-dimensional Ag-Au solid solution colloids with Au nanorods as seeds, their alloying mechanisms, and surface plasmon resonances.

    PubMed

    Guo, Tao; Tan, Yiwei

    2013-01-21

    In this work, one dimensional (1D) Ag-Au solid solution nanoalloys were synthesized by rapidly diffusing Ag into the preformed Au nanorod (AuNR) seeds at ambient temperature in aqueous solution. By varying the molar ratio of AgCl/AuNR (in gold atoms), two kinds of 1D Ag-Au alloy nanostructures with a narrow size distribution--AgAu nanowires and Ag(33)Au(67) nanorods--could be obtained in high yields when NaCl and polyvinylpyrrolidone (PVP) were used as an additive and capping reagent, respectively. Based on HRTEM imaging combined with a series of control experiments, it is conceivable that vacancy/defect-motivated interdiffusion of Ag and Au atoms coupled with oxidative etching is a crucial stage in the mechanism responsible for this room-temperature alloying process, and the subsequent conjugation of the fused Ag-Au alloyed nanostructures is associated with the formation of the AgAu nanowires. The resulting 1D Ag-Au nanoalloys form stable colloidal dispersions and show unique localized surface plasmon resonance (LSPR) peaks in the ensemble extinction spectra.

  11. Preparation of biaxially cube textured Ag, Cu-Au and Cu-Au-Ag films on Cu substrates for HTS coated conductor applications

    NASA Astrophysics Data System (ADS)

    Díaz, J.; Segarra, M.; Espiell, F.; Piñol, S.

    2001-08-01

    Copper (100) cube textured tapes have been covered successfully with biaxially textured thin and thick films of silver, gold and gold-silver by electrodeposition techniques for high temperature superconductors (HTS) coated conductor applications. The cube texture of Cu was promoted by recrystallization after smooth cold rolling. The biaxially cube textured Ag films were obtained by the electro-epitaxial deposition technique using no post-deposition heat treatment. Intermediate gold buffer layers were prepared in order to increase the thermal stability of the cube-textured Ag-buffered Cu substrates. The as-electrodeposited Au buffer layers were polycrystalline, but after an annealing treatment at high temperature the Au is absorbed by diffusion mechanism into the Cu tapes and a biaxially solid solution of Au-Cu(100) is formed on the surface. Ag thin films deposited on Cu-Au substrates form the same biaxial cube texture as the rolled Cu tapes after recrystallization at high temperature.

  12. Study of Ag induced bimetallic (Au-Ag) nanowires on silicon (5 5 12) surfaces: Experiment and theoretical aspects

    NASA Astrophysics Data System (ADS)

    Bhukta, Anjan; Bagarti, Trilochan; Guha, Puspendu; Ravulapalli, Sathyavathi; Satpati, Biswarup; Rakshit, Bipul; Maiti, Paramita; Parlapalli, Venkata Satyam

    2017-10-01

    The reconstructed vicinal (high index) silicon surfaces, such as, Si (5 5 12) composes row-like structures that can be used as templates for growing aligned nanowires. By using a sub-monolayers of Ag, prior to Au deposition on reconstructed Si (5 512) surface, intermixing of Au and Ag, enhancement of aspect ratio of bimetallic Au-Ag nanowires with tunable morphology is reported. This is attributed to a combined effect of pre-grown Ag strips as nucleation centers for incoming Au ad-atoms and anisotropic Au-Ag intermixing. To achieve optimum conditions for the growth of larger aspect ratio Au-Ag nanostructures, the growth kinetics have been studied by varying growth and annealing temperatures. At ≈400 °C, the Ag diffused into silicon substrate and the inter-diffusion found to inhibit the formation of Au-Ag bimetallic nanostructures. Controlled experiments under ultra-high vacuum condition in a molecular beam epitaxy system and in-situ scanning tunneling microscopy measurements along with ex-situ scanning transmission and secondary electron microscopy measurements have been carried out to understand the bimetallic nanostructure growth. Kinetic Monte Carlo (KMC) simulations based on kinematics of ad-atoms on an anisotropic template with a solid on solid model in which the relative ratios of binding energies (that are obtained from the Density Functional Theory) have been used and the KMC simulations results agree with the experimental observations. Advantage of having bimetallic structures as effective substrates for Surface enhanced Raman spectroscopy application is demonstrated by detecting Rhodamine 6 G (R6G) molecule at the concentration of 10-7M.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    Zhao, G F; Zeng, Z

    2006-07-07

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

  15. Phase diagram and structural evolution of Ag-Au bimetallic nanoparticles: molecular dynamics simulations.

    PubMed

    Yeo, Sang Chul; Kim, Da Hye; Shin, Kihyun; Lee, Hyuck Mo

    2012-02-28

    We studied the structural evolution of a 270-atom Ag-Au bimetallic nanoparticle (2 nm in size) with varying composition and temperature. The liquid to solid transition region and the solid-state structure were investigated using molecular dynamics simulations. To determine the exact transition temperature region, we applied the mean square displacement and structure deviation methods, as well as the generally used caloric curve of potential energy versus temperature. The results showed that a complete solid-solution phase diagram of the binary Ag-Au system was obtained. Irrespective of the composition, the freezing temperature of a Ag-Au bimetallic nanoparticle was lower than that of the bulk state by a margin of several hundred degrees, and three different solid-state structures are proposed in relation to the Au composition. Our phase diagram offers guidance for the application of Ag-Au nanoparticles.

  16. Structure and electronic behavior of 26-atom Cu-Ag and Cu-Au nanoalloys

    NASA Astrophysics Data System (ADS)

    Guzmán-Ramírez, Gregorio; Robles, Juvencio; Aguilera-Granja, Faustino

    2016-09-01

    We hereby present a density functional theory (DFT) study of the structural, energetic, and electronic properties of the binary clusters Cu n X26- n (with X = Ag and Au). Our electronic calculations were performed with the DFT package GAUSSIAN 09, and we chose the BPW91 exchange correlation functional in combination with an effective core potential LANL2DZ basis set as our level of theory. We find that in the case of these clusters and in a completely different way - as compared to the bulk chemical order observed in both alloys CuAg (segregation) and CuAu (ordering) -, for small n both Ag and Au clusters exhibit a similar chemical order, finding the Cu atoms in the center of the cluster with the tendency to form core shell structures. On the other hand, for large n values the Ag and Au atoms tend to occupy surface positions forming separated surface islands that keep the two metal atoms separated as long as the concentration allows it. Concerning the structural properties, a clear increase in the interatomic distance of the Ag-Ag and Au-Au surface pairs is observed, particularly in the equiatomic region. In conclusion, both nanoalloys CuAg and CuAu behave quite similarly in contrast to their respective bulk cases.

  17. The Ag shell thickness effect of Au@Ag@SiO2 core-shell nanoparticles on the optoelectronic performance of dye sensitized solar cells.

    PubMed

    Wang, Yang; Zhai, Jin; Song, Yanlin; He, Ling

    2016-02-07

    To tailor the Au@Ag@SiO2 LSPR effect by varying the Ag shell thickness, the Au@Ag@SiO2 core-ultra-thin shell nanoparticles are fabricated and introduced into DSSC for improving light harvesting and decreasing the recombination of photo-carriers. The Au@Ag@SiO2 electrode exhibits a photo-conversion efficiency of 23.42% (486.7 nm, 10 mW cm(-2)).

  18. Fabrication of Porous Ag/TiO2/Au Coatings with Excellent Multipactor Suppression

    PubMed Central

    Wu, Duoduo; Ma, Jianzhong; Bao, Yan; Cui, Wanzhao; Hu, Tiancun; Yang, Jing; Bai, Yuanrui

    2017-01-01

    Porous Ag/TiO2/Au coatings with excellent multipactor suppression were prepared by fabrication of porous Ag surface through two-step wet chemical etching, synthesis of TiO2 coatings by electroless-plating-like solution deposition and deposition of Au coatings via electroless plating. Porous structure of Ag surface, TiO2 coatings on porous Ag surface and Au coatings on porous Ag/TiO2 surface were verified by field-emission scanning electron microscopy, the composition and crystal type of TiO2 coatings was characterized by X-ray photoelectron spectroscopy and X-ray diffraction. Secondary electron yield (SEY) measurement was used to monitor the SEY coefficient of the porous Ag coatings and Ag/TiO2/Au coatings. The as-obtained porous Ag coatings were proved exhibiting low SEY below 1.2, and the process was highly reproducible. In addition, the porous Ag/TiO2/Au coatings showed excellent multipactor suppression with the SEY 1.23 and good environmental stability. It is worth mentioning that the whole preparation process is simple and feasible, which would provide a promising application in RF devices. PMID:28281546

  19. Fabrication of Porous Ag/TiO2/Au Coatings with Excellent Multipactor Suppression.

    PubMed

    Wu, Duoduo; Ma, Jianzhong; Bao, Yan; Cui, Wanzhao; Hu, Tiancun; Yang, Jing; Bai, Yuanrui

    2017-03-10

    Porous Ag/TiO2/Au coatings with excellent multipactor suppression were prepared by fabrication of porous Ag surface through two-step wet chemical etching, synthesis of TiO2 coatings by electroless-plating-like solution deposition and deposition of Au coatings via electroless plating. Porous structure of Ag surface, TiO2 coatings on porous Ag surface and Au coatings on porous Ag/TiO2 surface were verified by field-emission scanning electron microscopy, the composition and crystal type of TiO2 coatings was characterized by X-ray photoelectron spectroscopy and X-ray diffraction. Secondary electron yield (SEY) measurement was used to monitor the SEY coefficient of the porous Ag coatings and Ag/TiO2/Au coatings. The as-obtained porous Ag coatings were proved exhibiting low SEY below 1.2, and the process was highly reproducible. In addition, the porous Ag/TiO2/Au coatings showed excellent multipactor suppression with the SEY 1.23 and good environmental stability. It is worth mentioning that the whole preparation process is simple and feasible, which would provide a promising application in RF devices.

  20. Fabrication of Porous Ag/TiO2/Au Coatings with Excellent Multipactor Suppression

    NASA Astrophysics Data System (ADS)

    Wu, Duoduo; Ma, Jianzhong; Bao, Yan; Cui, Wanzhao; Hu, Tiancun; Yang, Jing; Bai, Yuanrui

    2017-03-01

    Porous Ag/TiO2/Au coatings with excellent multipactor suppression were prepared by fabrication of porous Ag surface through two-step wet chemical etching, synthesis of TiO2 coatings by electroless-plating-like solution deposition and deposition of Au coatings via electroless plating. Porous structure of Ag surface, TiO2 coatings on porous Ag surface and Au coatings on porous Ag/TiO2 surface were verified by field-emission scanning electron microscopy, the composition and crystal type of TiO2 coatings was characterized by X-ray photoelectron spectroscopy and X-ray diffraction. Secondary electron yield (SEY) measurement was used to monitor the SEY coefficient of the porous Ag coatings and Ag/TiO2/Au coatings. The as-obtained porous Ag coatings were proved exhibiting low SEY below 1.2, and the process was highly reproducible. In addition, the porous Ag/TiO2/Au coatings showed excellent multipactor suppression with the SEY 1.23 and good environmental stability. It is worth mentioning that the whole preparation process is simple and feasible, which would provide a promising application in RF devices.

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

    PubMed

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

    2014-12-24

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

  2. Selective growth of Ag nanodewdrops on Au nanostructures: a new type of bimetallic heterostructure.

    PubMed

    Gao, Li; Fan, Louzhen; Zhang, Jian

    2009-10-06

    A new type of bimetallic Au-Ag heterostructured material was prepared by a selective growing strategy of a Ag nanodewdrop on the petal tip of a Au flower using an electrochemical method. The whole process was strictly controlled by forming the reactive tip of the flower petal and passivating the facet along the body of the metal petal using poly(vinyl pyrrolidone) (PVP) coating film. The formed Au-Ag heterostructured flowers (HSFs) were observed to be about 2 microm in diameter and have the Ag particles of about 50 nm settled on the tips of Au petals. The Au-Ag HSFs were found to display the superior properties on the surface-enhanced Raman scattering (SERS). The presence of Ag nanodewdrops could also facilitate the oxidation of Ru(bpy)3(2+) complex in electrogenerated chemiluminescence (ECL) measurements and dramatically enhance the emission intensity. The features of Au-Ag HSFs can promise a new type of heterogeneous bimetallic alloy material for the potential applications in chemical and biological sensors.

  3. Selective Growth of Ag Nanodewdrop on Au Nanostructure: A New Type of Bimetallic Heterostructure

    PubMed Central

    Gao, Li

    2009-01-01

    A new type of bimetallic Au-Ag heterostructured material was prepared by a selective growing strategy of Ag nanodewdrop on the petal tip of Au flower using electrochemical method. The whole process was strictly controlled by forming the reactive tip of flower petal and passivating the facet along the body of metal petal using poly(vinyl pyrrolidone)(PVP) coating film. The formed Au-Ag HSFs were observed to be about 2 μm in diameter and have the Ag particles of about 50 nm settled on the tips of Au petals. The Au-Ag HSFs were found to display the superior properties on the surface-enhanced Raman scattering (SERS). The presence of Ag nanodewdrops could also facilitate the oxidation of Ru(bpy)32+ complex in electrogenerated chemiluminescence (ECL) measurements and dramatically enhance the emission intensity. The features of Au-Ag HSFs can promise a new type of heterogeneous bimetallic alloy material for the potential applications in chemical and biological sensors. PMID:19788230

  4. Fabrication and surface enhanced Raman scattering effect of centimeter level AgCuAu composite nanowires

    NASA Astrophysics Data System (ADS)

    Xu, Dapeng; Zhang, Song; Yang, Wei; Chen, Jian

    2017-10-01

    Centimeter level AgCuAu composite nanowires were prepared by a solid-state ionics method under a direct current electric field (DCEF) using fast ionic conductor RbAg4I5 films and vacuum thermal evaporation method. The surface morphology and chemical composition of the AuAgCu composite nanowires were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), respectively. Raman enhancement performance of the AgCuAu composite nanowires substrates was detected by Rhodamine 6G (R6G) aqueous solutions as probe molecules. Long-range order and short-range order AgCuAu composite nanowires with the length of 1 cm were prepared. The nanowires were bamboo-shaped with high surface roughness and the diameters of nanowires ranged from 60 to 100 nm. The molar ratio of Ag:Cu:Au in composite nanowires is 15:2:1. The intrinsic Raman peaks of 10-16 mol/L R6G at 612, 773, 1125, 1182, 1307, 1361, 1418, 1506, 1545, 1575, 1597, 1650 cm-1 are all present when AgCuAu composite nanowires were used as the SERS substrates.

  5. SERS activity studies of Ag/Au bimetallic films prepared by galvanic replacement.

    PubMed

    Wang, Chaonan; Fang, Jinghuai; Jin, Yonglong

    2012-10-01

    Ag films on Si substrates were fabricated by immersion plating, which served as sacrificial materials for preparation of Ag/Au bimetallic films by galvanic replacement method. SEM images displayed that the sacrificial Ag films presenting island morphology experienced interesting structural evolution process during galvanic replacement reaction, and nano-scaled holes were formed in the resultant bimetallic films. SERS measurements using crystal violet as an analyte showed that SERS intensities of bimetallic films were enhanced significantly compared with that of pure Ag films and related mechanisms were discussed. Immersion plating experiment carried out on Ag films on PEN substrates fabricated by photoinduced reduction method further confirmed that galvanic replacement is an easy method to fabricate Ag/Au bimetallic and a potential approach to improve the SERS performance of Ag films.

  6. Optical spectroscopy of arrays of Ag-Au nanoparticles obtained by vacuum-thermal evaporation

    NASA Astrophysics Data System (ADS)

    Gromov, D. G.; Mel'nikov, I. V.; Savitskii, A. I.; Trifonov, A. Yu.; Redichev, E. N.; Astapenko, V. A.

    2017-03-01

    The possibility of creating irregular arrays of bimetallic Ag-Au nanoparticles is investigated. The ability to manipulate their optical properties based on the simple engineering processes of thermal spraying followed by low-temperature annealing is demonstrated.

  7. Studies on plasmon characteristics and the local density of states of Au and Ag based nanoparticles

    NASA Astrophysics Data System (ADS)

    Vinod, M.; Biju, V.; Gopchandran, K. G.

    2016-01-01

    Knowledge about the conductive properties and the local density of states of chemically pure Au, Ag, Ag@Au core-shell and Au-Ag bimetallic nanoparticles is technologically important. Herein, the I-V characteristics and the density of states derived from scanning tunneling microscopy measurements made under atmospheric conditions is reported. The nanoparticles in thin film form used in this study were prepared by laser ablation in water followed by drop and evaporation. The morphology of the surface of the nanostructures was observed from optimizing tunneling current in each case. The monometallic Au and Ag particles shows almost similar current characteristics as well as discrete energy states but the slope of I-V characteristics was different for bimetallic structures. An attempt has also been made to compare the current measurements done in the nanoscale with the surface plasmon characteristics.

  8. Huge enhancement of optical nonlinearities in coupled Au and Ag nanoparticles induced by conjugated polymers

    NASA Astrophysics Data System (ADS)

    Polavarapu, Lakshminarayana; Mamidala, Venkatesh; Guan, Zhenping; Ji, Wei; Xu, Qing-Hua

    2012-01-01

    Exceptional optical limiting properties were observed in coupled Au and Ag nanoparticles that are induced by conjugated polymers. Fluence-dependent transmission measurements using 7-ns laser pulses of 532-nm wavelength showed that the optical limiting properties of Au and Ag nanoparticles were significantly enhanced upon assembly induced by addition of cationic conjugated polymers. The optical limiting performances of coupled Au and Ag nanoparticles (with optical limiting threshold as low as 2.8 J/cm2 and 2.6 J/cm2, respectively) are even better than that of the benchmark optical limiter-carbon nanotube suspensions (with threshold of 3.6 J/cm2). In addition, these coupled Au and Ag nanoparticle solutions are very stable and suitable for practical applications. Input fluence and angle-dependent scattering experiments suggested that nonlinear scattering should play an important role in the observed optical limiting effects.

  9. A facile strategy to synthesize bimetallic Au/Ag nanocomposite film by layer-by-layer assembly technique

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Wang, Cong; Zhang, Yi

    2012-05-01

    A facile strategy has been developed for the preparation of bimetallic gold-silver (Au-Ag) nanocomposite films by alternating absorption of poly-(ethyleneimine)-silver ions and Au onto substrates and subsequent reduction of the silver ions. The composition, micro-structure and properties of the {PEI-Ag/Au}n nanocomposite films were characterized by ultraviolet visible spectroscopy (UV-vis), transmisson electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), surface enhanced Raman scattering (SERS) and cyclic voltammetry (CV). The UV-vis characteristic absorbances of {PEI-Ag/Au}n nanocomposite thin film increase almost linear with the number of bilayers, which indicates a process of uniform assembling. Appearance of a double plasmon bands in the visible region and the lack of apparent core-shell structures in the TEM images confirm the formation of bimetallic Au-Ag nanoparticles. The result of XPS also demonstrates the existence of Ag and Au nanoparticles in the nanocomposite films. TEM and FESEM images show that these Ag and Au nanoparticles in the films possess sphere structure with the size of 20-25 nm. The resulting {PEI-Ag/Au}n films inherit the properties from both the metal Ag and Au, which exhibits a unique performance in SERS and electrocatalytic activities to the oxidation of dopamine. As a result, the {PEI-Ag/Au}n films are more attractive compared to {PEI-Ag/PSS}n and {PEI/Au}n films.

  10. The unusual effect of AgNO3 on the growth of Au nanostructures and their catalytic performance.

    PubMed

    Li, Xingliang; Yang, Yun; Zhou, Guangju; Han, Shuhua; Wang, Wenfang; Zhang, Lijie; Chen, Wei; Zou, Chao; Huang, Shaoming

    2013-06-07

    Au nanostructures attract much attention due to their potential applications in many fields. The controlled synthesis is critical to their properties modulation and applications. AgNO3-assisted synthesis is a widely used method for controllably preparing Au nanostructures in aqueous system. Herein, the effect of AgNO3 on the growth of Au nanostructures in polyol is studied. We observe an unusual effect that AgNO3 can induce the formation of pentatwinned Au nanostructures (nanorods and decahedra) and block the growth of Au nanorods. More interestingly, this blocking effect can be tuned through controlling the amount of AgNO3. A moderate amount of AgNO3 facilitates the formation of Au nanorods. A large amount of AgNO3 completely blocks the growth of nanorods and favors the formation of high quality decahedra (decahedra can be considered as nanorods with 0 nm longitudinal length). Besides, this blocking effect also allows preparation of different high-index-faceted Au nanobipyramids. These prepared Au nanostructures further serve as starting templates to fabricate other heterostructured Au/Ag nanomaterials, such as Ag-Au-Ag segmental nanorods, Au@Ag core-shelled nanostructures. The prepared nanostructures exhibit size- and structure-dependent catalytic performance in the reduction of p-nitrophenol to p-aminophenol by sodium borohydride.

  11. Revisiting the geometry of nd10 (n+1)s0 [M(H2O)]p+ complexes using four-component relativistic DFT calculations and scalar relativistic correlated CSOV energy decompositions (M(p+) = Cu+, Zn2+, Ag+, Cd2+, Au+, Hg2+).

    PubMed

    Gourlaouen, Christophe; Piquemal, Jean-Philip; Saue, Trond; Parisel, Olivier

    2006-01-30

    Hartree-Fock and DFT (B3LYP) nonrelativistic (scalar relativistic pseudopotentials for the metallic cation) and relativistic (molecular four-component approach coupled to an all-electron basis set) calculations are performed on a series of six nd10 (n+1)s0 [M(H2O)]p+ complexes to investigate their geometry, either planar C2v or nonplanar C(s). These complexes are, formally, entities originating from the complexation of a water molecule to a metallic cation: in the present study, no internal reorganization has been found, which ensures that the complexes can be regarded as a water molecule interacting with a metallic cation. For [Au(H2O)]+ and [Hg(H2O)]2+, it is observed that both electronic correlation and relativistic effects are required to recover the C(s) structures predicted by the four-component relativistic all-electron DFT calculations. However, including the zero-point energy corrections makes these shallow C(s) minima vanish and the systems become floppy. In all other systems, namely [Cu(H2O)]+, [Zn(H2O)]2+, [Ag(H2O)]+, and [Cd(H2O)]2+, all calculations predict a C2v geometry arising from especially flat potential energy surfaces related to the out-of-plane wagging vibration mode. In all cases, our computations point to the quasi-perfect transferability of the atomic pseudopotentials considered toward the molecular species investigated. A rationalization of the shape of the wagging potential energy surfaces (i.e., single well vs. double well) is proposed based on the Constrained Space Orbital Variation decompositions of the complexation energies. Any way of stabilizing the lowest unoccupied orbital of the metallic cation is expected to favor charge-transfer (from the highest occupied orbital(s) of the water ligand), covalence, and, consequently, C(s) structures. The CSOV complexation energy decompositions unambiguously reveal that such stabilizations are achieved by means of relativistic effects for [Au(H2O)]+, and, to a lesser extent, for [Hg(H2O)]2

  12. Core-shell Au@Pd nanoparticles with enhanced catalytic activity for oxygen reduction reaction via core-shell Au@Ag/Pd constructions

    PubMed Central

    Chen, Dong; Li, Chengyin; Liu, Hui; Ye, Feng; Yang, Jun

    2015-01-01

    Core-shell nanoparticles often exhibit improved catalytic properties due to the lattice strain created in these core-shell particles. Herein, we demonstrate the synthesis of core-shell Au@Pd nanoparticles from their core-shell Au@Ag/Pd parents. This strategy begins with the preparation of core-shell Au@Ag nanoparticles in an organic solvent. Then, the pure Ag shells are converted into the shells made of Ag/Pd alloy by galvanic replacement reaction between the Ag shells and Pd2+ precursors. Subsequently, the Ag component is removed from the alloy shell using saturated NaCl solution to form core-shell Au@Pd nanoparticles with an Au core and a Pd shell. In comparison with the core-shell Au@Pd nanoparticles upon directly depositing Pd shell on the Au seeds and commercial Pd/C catalysts, the core-shell Au@Pd nanoparticles via their core-shell Au@Ag/Pd templates display superior activity and durability in catalyzing oxygen reduction reaction, mainly due to the larger lattice tensile effect in Pd shell induced by the Au core and Ag removal. PMID:26144550

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  14. Real-time imaging and elemental mapping of AgAu nanoparticle transformations.

    PubMed

    Lewis, E A; Slater, T J A; Prestat, E; Macedo, A; O'Brien, P; Camargo, P H C; Haigh, S J

    2014-11-21

    We report the controlled alloying, oxidation, and subsequent reduction of individual AgAu nanoparticles in the scanning transmission electron microscope (STEM). Through sequential application of electron beam induced oxidation and in situ heating and quenching, we demonstrate the transformation of Ag-Au core-shell nanoparticles into: AgAu alloyed, Au-Ag core-shell, hollow Au-Ag2O core-shell, and Au-Ag2O yolk-shell nanoparticles. We are able to directly image these morphological transformations in real-time at atomic resolution and perform energy dispersive X-ray (EDX) spectrum imaging to map changing elemental distributions with sub-nanometre resolution. By combining aberration corrected STEM imaging and high efficiency EDX spectroscopy we are able to quantify not only the growth and coalescence of Kirkendall voids during oxidation but also the compositional changes occurring during this reaction. This is the first time that it has been possible to track the changing distribution of elements in an individual nanoparticle undergoing oxidation driven shell growth and hollowing.

  15. Templated Atom-Precise Galvanic Synthesis and Structure Elucidation of a [Ag24Au(SR)18](-) Nanocluster.

    PubMed

    Bootharaju, Megalamane S; Joshi, Chakra P; Parida, Manas R; Mohammed, Omar F; Bakr, Osman M

    2016-01-18

    Synthesis of atom-precise alloy nanoclusters with uniform composition is challenging when the alloying atoms are similar in size (for example, Ag and Au). A galvanic exchange strategy has been devised to produce a compositionally uniform [Ag24Au(SR)18](-) cluster (SR: thiolate) using a pure [Ag25(SR)18](-) cluster as a template. Conversely, the direct synthesis of Ag24Au cluster leads to a mixture of [Ag(25-x)Au(x)(SR)18](-), x=1-8. Mass spectrometry and crystallography of [Ag24Au(SR)18](-) reveal the presence of the Au heteroatom at the Ag25 center, forming Ag24Au. The successful exchange of the central Ag of Ag25 with Au causes perturbations in the Ag25 crystal structure, which are reflected in the absorption, luminescence, and ambient stability of the particle. These properties are compared with those of Ag25 and Ag24Pd clusters with same ligand and structural framework, providing new insights into the modulation of cluster properties with dopants at the single-atom level.

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

    PubMed

    Pogacean, Florina; Biris, Alexandru R; Coros, Maria; Lazar, Mihaela Diana; Watanabe, Fumiya; Kannarpady, Ganesh K; Al Said, Said A Farha; Biris, Alexandru S; Pruneanu, Stela

    2014-01-01

    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 was determined to be well-defined, even at relatively low concentration (10(-5) M), for the Au/Gr-AuAg-1.5 electrode. In contrast, the signals recorded with the Au/Gr-AuAg-1 electrode were poorly defined within a 5×10(-6) to 5×10(-3) M concentration range, and many of them overlapped with the background. Such composite materials could find significant applications in nanotechnology, sensing, or nanomedicine.

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

    PubMed Central

    Pogacean, Florina; Biris, Alexandru R; Coros, Maria; Lazar, Mihaela Diana; Watanabe, Fumiya; Kannarpady, Ganesh K; Al Said, Said A Farha; Biris, Alexandru S; Pruneanu, Stela

    2014-01-01

    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 was determined to be well-defined, even at relatively low concentration (10−5 M), for the Au/Gr-AuAg-1.5 electrode. In contrast, the signals recorded with the Au/Gr-AuAg-1 electrode were poorly defined within a 5×10−6 to 5×10−3 M concentration range, and many of them overlapped with the background. Such composite materials could find significant applications in nanotechnology, sensing, or nanomedicine. PMID:24596464

  18. Theoretical studies of diatomic and triatomic systems containing the group IB atoms Cu, Ag, and Au

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1986-01-01

    Selected portions of the ground state potential energy surfaces of the Cu3, Ag3, AgCu2, and AuCu2 trimers are studied at the single-reference singles plus doubles configuration interaction and couple pair functional levels correlating 33 electrons. The calculations use the effective core potentials of Hay and Wadt (1985) to replace the deep core levels. The Cu3 and Ag3 molecules are found to have 2B2 obtuse-angled ground states, with low-lying 2A1 acute-angled excited states. The AgCu2 and AuCu2 molecules have 2A1 acute-angled ground states. The Cu3 molecule has a smaller 3d population than Ag3, and Cu3 has a smaller s electron density in the open-shell orbital than does Ag3, in agreement with recent ESR experiments.

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

    PubMed

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

    2005-05-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

  1. Intriguing centrality dependence of the Au-Au source size at the AGS

    SciTech Connect

    Baker, M.D.; The E802 Collaboration

    1996-06-01

    One of the main goals of high energy heavy ion physics is to establish the existence of a deconfined phase of nuclear matter--the quark-gluon plasma--at high temperatures or densities. One possible signature of such a phase transition, especially if it were first order, would be a larger source size or lifetime than a similar hadronic system. At current AGS energies, we attempt to form a quark- gluon plasma by achieving a high baryon density for a period of time in the center of the collision region. For a given density threshold, the size of this high density region should be a strong function of the impact parameter: the more central the event, the larger the high density region. Therefore, one possible signature of a quark-gluon plasma would be a sudden change in system lifetime or size as a function of the centrality of the collision. In this talk we present an intriguing effect which was not predicted for simple hadronic systems: a rapid increase of the HBT-measured source radius parameter for pion pairs with increasing centrality for Au-Au collisions at a beam momentum of 11.45 A GeV/c on a fixed target. Experience has shown, however, that we must be cautious in our interpretation. A complete understanding of the collision dynamics at a given energy must be built up from several measurements and new, but conventional, hadronic explanations must be considered for such unexpected effects. More study is needed, therefore, before any strong conclusions can be reached.

  2. Egg White Templated Synthesis of Ag and Au@Ag Alloy Microspheres for Surface-Enhanced Raman Spectroscopy Research.

    PubMed

    Li, Min; Zhang, Ying; Wang, Xiansong; Cui, Daxiang

    2016-01-01

    Herein, we report the green synthesis of Ag and Au@Ag microspheres by using the aqueous extracts of the egg white as well as their application as substrates for surface-enhanced Raman spectroscopy (SERS) detection. Both microspheres are prepared via the green synthesis method (room temperature, in aqueous solution and a benign reducer). The as-prepared urchin-like Ag microspheres have an average diameter of 600-800 nm, which is made up of some nanopricks with an average length of 10-40 nm. Meanwhile, the Au@Ag architectures prepared by galvanic replacement keep nearly similar size, which is also composed of some compact nanoparticles with an average diameter of about 10-40 nm. These products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscopy (TEM), and Fourier transform infrared spectrophotometer (FTIR). The study on SERS activities is also carried out for both microspheres. It is found that Au@Ag microspheres possess much higher SERS activity than Ag microspheres. Our work may shed light on the design and synthesis of self-assembled 3D micro/nano-architectures for the use of SERS, catalysis, biosensors, nanomedicine, etc.

  3. 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

    NASA Astrophysics Data System (ADS)

    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.

  4. 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.

    PubMed

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

    2015-02-25

    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.

  5. Ag-Au alloy nanoparticles prepared by electro-exploding wire technique

    NASA Astrophysics Data System (ADS)

    Alqudami, Abdullah; Annapoorni, S.; Govind; Shivaprasad, S. M.

    2008-08-01

    Homogenous Ag-Au alloy nanoparticles having an average size of 12 ± 2 nm were successfully prepared by the exploding wire technique comprising of a wire-plate system and using 12 V batteries. The X-ray photoelectron spectroscopy data reveal the formation of alloy nanoparticles with Ag80-Au20 composition, which agrees with the absorption data, obtained using UV-Visible spectroscopy. XPS also reveals a thin metal-oxide shell on the metallic alloy core. These alloy nanoparticles show visible fluorescence emission that was compared with the observed fluorescence from pure Ag nanoparticles. A mechanism for the observed fluorescence is also provided.

  6. TiO2 coated Au/Ag nanorods with enhanced photocatalytic activity under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Zhou, Na; Polavarapu, Lakshminarayana; Gao, Nengyue; Pan, Yanlin; Yuan, Peiyan; Wang, Qing; Xu, Qing-Hua

    2013-05-01

    A facile method was used to prepare uniform Au NR/TiO2 and Au/Ag NR/TiO2 core-shell composite nanoparticles. Au/Ag NR/TiO2 nanoparticles were found to display significantly enhanced visible light photo-catalytic activity compared to Au NR/TiO2 and the commercially available TiO2 nanoparticles. The enhancement mechanism was ascribed to injection of hot electrons of photo-excited Au/Ag NRs to TiO2, which was confirmed by 633 nm laser induced reduction of silver ions on the surface of Au/Ag NR/TiO2 composite nanoparticles.A facile method was used to prepare uniform Au NR/TiO2 and Au/Ag NR/TiO2 core-shell composite nanoparticles. Au/Ag NR/TiO2 nanoparticles were found to display significantly enhanced visible light photo-catalytic activity compared to Au NR/TiO2 and the commercially available TiO2 nanoparticles. The enhancement mechanism was ascribed to injection of hot electrons of photo-excited Au/Ag NRs to TiO2, which was confirmed by 633 nm laser induced reduction of silver ions on the surface of Au/Ag NR/TiO2 composite nanoparticles. Electronic supplementary information (ESI) available: The details of experimental procedures, SEM and TEM images of various nanoparticles prepared, photographs of the samples, control experiments, reusability test, wavelength dependent photocatalytic activities of Au/Ag/TiO2 nanoparticles, and UV-Vis spectra of a Ag nanoparticle formed on the surface of Au/Ag/TiO2 under visible light irradiation. See DOI: 10.1039/c3nr00517h

  7. Synthesis and characterization of Au-core Ag-shell nanoparticles from unmodified apoferritin

    SciTech Connect

    Li, T.; Chattopadhyay, S.; Shibata, T.; Cook, R. E.; Miller, J. T.; Suthiwangcharoen, N.; Lee, S.; Winans, R. E.; Lee, B.

    2012-01-01

    Narrow-size distributed, water-soluble Au-core Ag-shell nanoparticles with a size range from 1 to 5 nm are synthesized using unmodified apoferritin as a template. Fast protein liquid chromatography reveals that the nanoparticles are formed inside the apoferritin cavity and are stable in aqueous solution. Electron microscopy shows that the particles are uniform in size and composed of both Au and Ag. In addition, extended X-ray absorption fine structure confirms that the particles have a core-shell structure with a Au core covered with a Ag shell. By varying the loading amounts of the silver precursor, the Ag shell thickness is controlled from one layer to several layers.

  8. Nanoporous Au-Ag shell with fast kinetics: integrating chemical and plasmonic catalysis.

    PubMed

    Yang, Wenpeng; Wu, Ke; Yang, Weimin; Wang, Hailing; Lv, Xianglong; Qian, Lihua; Yu, Tianshui; Li, Zengquan; Zhou, Xiangji; Barasa, Godfrey Okumu; Yuan, S L; Jiang, Yingtao; Yang, Zhilin

    2017-08-07

    Nanoporous noble metals and alloys are widely utilized as efficient catalysts, because they have high surface-to-volume ratios for surfficient active sites and induce molecule polarization through plasmon excitation as well. Herein we demonstrate one approach to fabricate nanoporous Au-Ag shell. Such material represents the dual functions serving as efficient catalysts and high-performance surface-enhanced Raman scattering (SERS) substrate. In-situ spectrum acquisition can track the conversion of p-nitrothiophenol to 4, 4'-dimercapto-azobenzene at ambient temperature. In particular, as a result of chemcial catalysis of Ag elements and strong plasmon-molecule coupling, catalytic kinetics of nanoporous Au-Ag shell is 79.2-123.8 times faster than Au nanoparticles, and 2.2-3.3 times faster than Ag nanoparticles. This investigation offers a route to design superior catalysts to integrate chemical and plasmonic catalysis. © 2017 IOP Publishing Ltd.

  9. Nanoporous Au-Ag shell with fast kinetics: integrating chemical and plasmonic catalysis

    NASA Astrophysics Data System (ADS)

    Yang, Wenpeng; Wu, Ke; Yang, Weimin; Wang, Hailing; Lv, Xianglong; Qian, Lihua; Yu, Tianshui; Li, Zengquan; Zhou, Xiangji; Okumu Barasa, Godfrey; Yuan, Songliu; Jiang, Yingtao; Yang, Zhilin

    2017-10-01

    Nanoporous noble metals and alloys are widely utilized as efficient catalysts, because they have high surface-to-volume ratios for sufficient active sites and induce molecule polarization through plasmon excitation as well. Herein, we demonstrate one approach to fabricate nanoporous Au-Ag shell. Such material represents the dual functions serving as efficient catalysts and high-performance surface-enhanced Raman scattering substrate. In situ spectrum acquisition can track the conversion of p-nitrothiophenol to 4, 4‧-dimercapto-azobenzene at ambient temperature. In particular, as a result of chemical catalysis of Ag elements and strong plasmon-molecule coupling, catalytic kinetics of nanoporous Au-Ag shell is 79.2–123.8 times faster than Au nanoparticles (NPs), and 2.2–3.3 times faster than Ag NPs. This investigation offers a route to design superior catalysts to integrate chemical and plasmonic catalysis.

  10. Enlarge the biologic coating-induced absorbance enhancement of Au-Ag bimetallic nanoshells by tuning the metal composition.

    PubMed

    Zhu, Jian; Li, Xin; Li, Jian-Jun; Zhao, Jun-Wu

    2018-01-15

    Surface plasmon resonance (SPR) absorption properties of biologic layer-coated Au-Ag core-shell nanoparticle have been studied theoretically. By comparing with pure Au and Ag nanoparticles, the absorption peak intensity of Au-Ag bimetallic nanoparticle is more dependent on the dielectric coating, and the longer wavelength peak corresponding to the Au-Ag interface is more sensitive to the coating thickness. As the Au-Ag composition ratio is increased, the dielectric coating-dependent peak intensity change is always non-monotonous, and the critical Au-Ag composition ratio corresponding to the greatest peak intensity increase could be further tuned by changing the dielectric constant of the coated dielectric layer. The physical mechanism of the non-monotonous sensitivity change has been attributed to the Au-Ag composition ratio-dependent separation and overlap of the two SPR peaks from Au-Ag interface and outer Ag surface. These results indicate that the plasmonic absorption intensity of Au-Ag core-shell nanoparticle could be used in refractive index sensing and biologic detection. Copyright © 2017 Elsevier B.V. All rights reserved.

  11. Tuning the SERS Response with Ag-Au Nanoparticle-Embedded Polymer Thin Film Substrates.

    PubMed

    Rao, V Kesava; Radhakrishnan, T P

    2015-06-17

    Development of facile routes to the fabrication of thin film substrates with tunable surface enhanced Raman scattering (SERS) efficiency and identification of the optimal conditions for maximizing the enhancement factor (EF) are significant in terms of both fundamental and application aspects of SERS. In the present work, polymer thin films with embedded bimetallic nanoparticles of Ag-Au are fabricated by a simple two-stage protocol. Ag nanoparticles are formed in the first stage, by the in situ reduction of silver nitrate by the poly(vinyl alcohol) (PVA) film through mild thermal annealing, without any additional reducing agent. In the second stage, aqueous solutions of chloroauric acid spread on the Ag-PVA thin film under ambient conditions, lead to the galvanic displacement of Ag by Au in situ inside the film, and the formation of Ag-Au particles. Evolution of the morphology of the bimetallic nanoparticles into hollow cage structures and the distribution of Au on the nanoparticles are revealed through electron microscopy and energy dispersive X-ray spectroscopy. The localized surface plasmon resonance (LSPR) extinction of the nanocomposite thin film evolves with the Ag-Au composition; theoretical simulation of the extinction spectra provides insight into the observed trends. The Ag-Au-PVA thin films are found to be efficient substrates for SERS. The EF follows the variation of the LSPR extinction vis-à-vis the excitation laser wavelength, but with an offset, and the maximum SERS effect is obtained at very low Au content; experiments with Rhodamine 6G showed EFs on the order of 10(8) and a limit of detection of 0.6 pmol. The present study describes a facile and simple fabrication of a nanocomposite thin film that can be conveniently deployed in SERS investigations, and the utility of the bimetallic system to tune and maximize the EF.

  12. Synthesis of hollow Ag-Au bimetallic nanoparticles in polyelectrolyte multilayers.

    PubMed

    Zhang, Xin; Zhang, Guangyu; Zhang, Bodong; Su, Zhaohui

    2013-06-04

    Ag nanoparticles of ~20 nm size and rather uniform size distribution were synthesized in polyelectrolyte multilayers (PEMs) via an ion-exchange/reduction process in two stages (seeding and growth), which were used as sacrificial templates to fabricate Ag-Au bimetallic hollow nanoparticles via galvanic replacement reaction. The reaction process was monitored by UV-vis spectroscopy. The morphology and structure of the nanoparticles were characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy, which confirmed the formation of hollow Ag-Au bimetallic nanoparticles. UV-vis absorbance spectroscopy and TEM results indicated that both size and optical properties of the Ag nanoparticles in the PEM can be controlled by manipulating ion content in the PEM and the number of the ion-exchange/reduction cycle, whereas that of Ag-Au bimetallic nanoparticles were dependent on size of the Ag templates and the replacement reaction kinetics. The hollow Ag-Au bimetallic nanoparticles exhibited a significant red shift in the surface plasmon resonance to the near-infrared region. The strategy enables facile preparation of hollow bimetallic nanoparticles in situ in polymer matrixes.

  13. Solar hydrogen generation by a CdS-Au-TiO2 sandwich nanorod array enhanced with Au nanoparticle as electron relay and plasmonic photosensitizer.

    PubMed

    Li, Jiangtian; Cushing, Scott K; Zheng, Peng; Senty, Tess; Meng, Fanke; Bristow, Alan D; Manivannan, Ayyakkannu; Wu, Nianqiang

    2014-06-11

    This paper presents a sandwich-structured CdS-Au-TiO2 nanorod array as the photoanode in a photoelectrochemical cell (PEC) for hydrogen generation via splitting water. The gold nanoparticles sandwiched between the TiO2 nanorod and the CdS quantum dot (QD) layer play a dual role in enhancing the solar-to-chemical energy conversion efficiency. First, the Au nanoparticles serve as an electron relay, which facilitates the charge transfer between CdS and TiO2 when the CdS QDs are photoexcited by wavelengths shorter than 525 nm. Second, the Au nanoparticles act as a plasmonic photosensitizer, which enables the solar-to-hydrogen conversion at wavelengths longer than the band edge of CdS, extending the photoconversion wavelength from 525 to 725 nm. The dual role of Au leads to a photocurrent of 4.07 mA/cm(2) at 0 V (vs Ag|AgCl) under full solar spectrum irradiation and a maximum solar-to-chemical energy conversion efficiency of 2.8%. An inversion analysis is applied to the transient absorption spectroscopy data, tracking the transfer of electrons and holes in the heterostructure, relating the relaxation dynamics to the underlying coupled rate equation and revealing that trap-state Auger recombination is a dominant factor in interfacial charge transfer. It is found that addition of Au nanoparticles increases the charge-transfer lifetime, reduces the trap-state Auger rate, suppresses the long-time scale back transfer, and partially compensates the negative effects of the surface trap states. Finally, the plasmonic energy-transfer mechanism is identified as direct transfer of the plasmonic hot carriers, and the interfacial Schottky barrier height is shown to modulate the plasmonic hot electron transfer and back transfer. Transient absorption characterization of the charge transfer shows defect states cannot be ignored when designing QD-sensitized solar cells. This facile sandwich structure combines both the electrical and the optical functions of Au nanoparticles into a

  14. Centrality definition using mid-rapidity E T distributions from p+Be to Au+Au at AGS energies

    NASA Astrophysics Data System (ADS)

    Tannenbaum, M. J.; E802 Collaboration

    1999-12-01

    Measurements by the E802 Collaboration of the A-dependence and pseudorapidity interval (δη) dependence of mid-rapidity E T 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 E T 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 E T distributions was found from which the reaction dynamics could be read directly.

  15. Centrality and collision system dependence of antiproton production from p+A to Au+Au collisions at AGS energies

    NASA Technical Reports Server (NTRS)

    Sako, H.; Ahle, L.; Akiba, Y.; Ashktorab, K.; Baker, M. D.; Beavis, D.; Britt, H. C.; Chang, J.; Chasman, C.; Chen, Z.; hide

    1997-01-01

    Antiproton production in heavy ion collisions reflects subtle interplay between initial production and absorption by nucleons. Because the AGS energies (10--20 A(center-dot)GeV/c) are close to the antiproton production threshold, antiproton may be sensitive to cooperative processes such as QGP and hadronic multi-step processes. On the other hand, antiproton has been proposed as a probe of baryon density due to large N(anti N) annihilation cross sections. Cascade models predict the maximum baryon density reaches about 10 times the normal nucleus density in central Au+Au collisions, where the strong antiproton absorption is expected. In this paper, the authors show systematic studies of antiproton production from p+A to Au+Au collisions.

  16. Ultrasound-assisted microwave preparation of Ag-doped CdS nanoparticles.

    PubMed

    Ma, Jun; Tai, Guo'an; Guo, Wanlin

    2010-03-01

    Ag-doped CdS nanoparticles were synthesized by an ultrasound-assisted microwave synthesis method. The X-ray diffraction patterns reveal a structural evolution from cubic to hexagonal with increasing molar ratios of Ag(+)/Cd(2+) from 0% to 5%. It shows that the Ag-doped hexagonal CdS nanoparticles are polycrystal. The X-ray photoelectron spectroscopy of the CdS nanoparticles doping with 5% Ag(+) shows that the doped Ag in CdS is metallic. Simultaneously, the characteristic Raman peaks of the CdS nanoparticles enhance with increasing Ag(+) concentrations. The photocatalytic activity of different Ag-doped samples show a reasonable change due to different ratios of Ag which doped into CdS. Copyright 2009 Elsevier B.V. All rights reserved.

  17. An electrochemical and multispectroscopic study of corrosion of Ag-Pd-Cu-Au alloys.

    PubMed

    Niemi, L; Minni, E; Ivaska, A

    1986-06-01

    Corrosion of a multi-phase Ag-Pd-Cu-Au-based commercial dental casting alloy and a Cu-Pd-rich and Ag-rich single-phase alloy was studied by open-circuit potential measurements, atomic absorption spectrometry, and electron spectroscopy. The alloys were immersed in an artificial saliva solution for 24 hr while the open-circuit potentials of the alloys were measured. The potentials were found to stabilize at certain levels after a steep rise during the first hours of the experiment. Cu was found to dissolve considerably from the Cu-Pd-rich alloy, with simultaneous enrichment of Pd in the surface layer of the alloy. Ag dissolved slightly from the Ag-rich alloy, but both Cu and Ag were found to dissolve from the multi-phase alloy. Neither Pd nor Au dissolved from any of the alloys studied.

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

    PubMed

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

    2014-04-21

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  20. Photochemically controlled electrochemical deposition and dissolution of Ag0 nanoclusters on au electrode surfaces.

    PubMed

    Riskin, Michael; Katz, Eugenii; Gutkin, Vitaly; Willner, Itamar

    2006-12-05

    A photoisomerizable thiolated nitrospiropyran SP, (1a), monolayer is assembled on a Au electrode by the primary deposition of thiolated nitromerocyanine isomer 1b as a monolayer on the electrode, followed by the irradiation of the surface with visible light, lambda > 475 nm. The surface coverage of nitrospiropyran units (1a) on the electrode is 2 x 10-10 mole cm-2. Irradiation of the electrode with UV light, 320 nm < lambda < 360 nm, results in the nitromerocyanine, MR, monolayer on the electrode that binds Ag+ ions to the phenolate units. The Ag+ ions associated with the MR monolayer undergo cyclic reduction to surface-confined Ag0 nanoclusters, and reoxidation and dissolution of the Ag0 nanoclusters to Ag+ ions associated with the monolayer are demonstrated. The electron-transfer rate constants for the reduction of Ag+ to Ag0 and for the dissolution of Ag0 were determined by chronoamperometry and correspond to ketred = 12.7 s-1 and ketox = 10.5 s-1, respectively. The nanoclustering rate was characterized by surface plasmon resonance measurements, and it proceeds on a time scale of 10 min. The size of the Ag0 nanoclusters is in the range of 2 to 20 nm. The electrochemically induced reduction of the MR-Ag+ monolayer to the MR-Ag0 surface and the reoxidation of the MR-Ag0 surface control the hydrophilic-hydrophobic properties of the surface. The advancing contact angle of the MR-Ag0-functionalized surface is 59 degrees , and the contact angle of the MR-Ag+-monolayer-functionalized surface is 74 degrees . Photoisomerization of the Ag0-MR surface to the Ag0-SP state, followed by the oxidation of the Ag0 nanoclusters, results in the dissolution of the Ag+ ions into the electrolyte solution.

  1. Near infrared Ag/Au alloy nanoclusters: tunable photoluminescence and cellular imaging.

    PubMed

    Wang, Chuanxi; Xu, Lin; Xu, Xiaowei; Cheng, Hao; Sun, Hongchen; Lin, Quan; Zhang, Chi

    2014-02-15

    The fluorescent nanomaterials play an important role in cellular imaging. Although the synthesis of fluorescent metal nanoclusters (NCs) have been developing rapidly, there are many technical issues in preparing metal alloy NCs. Herein, we used a facile galvanic replacement reaction to prepare Ag/Au alloy NCs. The characterizations of UV, PL, HRTEM, EDX and XPS confirm one fact the Ag/Au alloy NCs are carried out. As-prepared Ag/Au alloy NCs display near-infrared (NIR) fluorescence centered at 716 nm and show tunable luminescence from visible red (614 nm) to NIR (716 nm) by controlling the experimental Ag/Au ratios. Moreover, as-prepared Ag/Au alloy NCs are protected by glutathione (GSH) whose some functional groups including thiol, carboxyl and amino groups make the as-prepared alloy NCs exhibit good dispersion in aqueous solution, high physiological stability and favorable biocompatibility. Together with NIR fluorescence, these advantages make alloy NCs be promising candidate in biological labeling.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Study on surface-enhanced Raman scattering efficiency of Ag core-Au shell bimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Dong, Xiao; Gu, Huaimin; Kang, Jian; Yuan, Xiaojuan

    2009-08-01

    In this article, the relationship between the states of Ag core-Au shell (core-shell) nanoparticles (NP) and the intensity of Raman scattering of analytes dissolved in the water and adsorbed on the NP was studied. The core-shell NP were synthesised by coating Au layers over Ag seeds by the method of "seed-growth". To highlight the advantage of the core-shell NP, Ag colloid and Au colloid were chosen for contrasting. The analyte that were chosen for this testing were methylene blue (MB) for the reason that MB has very strong signal in surface-enhanced Raman scattering (SERS). The SERS activity of optimalizing states of Ag and Au colloids were compared with that of core-shell NP when MB was used as analyte. In this study, sodium chloride, sodium sulfate and sodium nitrate were used as aggregating agents for Ag, Au colloids and core-shell NP, because anions have a strong influence on the SERS efficiency and the stability of colloids. The results indicate that core-shell NP can obviously enhance the SERS of MB. The aim of this study is to prove that compared with the metal colloid, the core-shell NP is a high efficiency SERS active substrate.

  4. Tarnish resistance evaluation of experimental Pd-free Ag-Au-Pt-Cu dental alloys.

    PubMed

    Takuma, Yasuko; Shiraishi, Takanobu; Fujita, Takeshi; Hisatsune, Kunihiro

    2010-05-01

    This study evaluated the tarnish resistance of eight experimental Pd-free Ag-Au-Pt-Cu dental alloys in a 0.1% Na(2)S aqueous solution at 37 degrees C. Color measurements of the plate samples were made using a computerized spectrophotometer before and after immersion in the test solution for up to 72 hours. Tarnish discoloration was evaluated using the color difference vector, DeltaE*, in the CIELAB color space. Microstructural observation of each sample through an optical microscope revealed the matrix phase as the major constituent and second-phase small grains in the matrix phase. Selective tarnish discoloration occurred in the matrix, and fractional area of the matrix to the whole surface area was influenced by the sum of Au and Ag concentrations. The DeltaE* value significantly decreased with increasing Au/(Au+Ag) atomic ratio. In conclusion, the Au/(Au+Ag) ratio in an alloy and the fractional area of the matrix were found to be primary and auxiliary factors affecting the tarnish resistance of the experimental alloys.

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

    NASA Astrophysics Data System (ADS)

    Stoica, Maria; Lo, Cynthia S.

    2012-09-01

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

  6. Superior photoluminescence and photocatalytic activity of CdS (core)-SiO2 (shell) nanostructures obtained by CdS photoetching and Au deposition.

    PubMed

    Gupta, Nidhi; Pal, Bonamali

    2013-07-01

    Core-shell morphology of silica (SiO2) coated CdS nanocomposites (SiO2@CdS) of different shapes have been made for better stability, luminescence and photochemical activity of CdS nanoparticles. A thin layer (thickness 1-1.4 nm) of SiO2 shell is deposited over CdS nanorods (CdS-NR) of aspect ratio = 21 and CdS nanospheres (CdS-NS) of size 6-8 nm by alkyl silane agents. Synthesized nanostructures were characterized by diffuse reflectance spectra, HR-TEM, BET surface measurement, LB surface film, and absorption and photoluminescence analysis. Photoetching (PE) of CdS core led to blue shift of the absorbance onset of SiO2@CdS-NR along with the appearance of an exciton band at 485 nm due to the quantum confinement effect. Photodissolution of CdS core shifts the band gap energy from initial 2.4 to 2.6 eV for CdS-NR and 2.5 to 2.67 eV for CdS-NS. TEM images reveal the increase in aspect ratio of NR from 21 to 31 and decrease in the spherical core to 2.5 nm from 6-8 nm after PE. Photoetched SiO2@CdS-NC displayed highly intense fluorescence emission (SiO2@CdS-NS > SiO2@CdS-NR) than unetched SiO2@CdS-NC at 488 nm corresponding to band edge position. The Au (0.5 wt.%) deposition onto photoetched SiO2@CdS-NR(PE) composites highly enhanced the fluorescence intensity in comparison to 1 wt.% of Au and Ag loading. SiO2@CdS-NC(PE) displayed improved photocatalytic activity during benzaldehyde photooxidation under UV (125 W, Hg-arc, 10.4 mW/cm2) irradiation. Silica coating onto CdS particles improves the photostability and photoactivity of CdS upon long UV irradiation.

  7. A dealloying process of core-shell Au@AuAg nanorods for porous nanorods with enhanced catalytic activity

    NASA Astrophysics Data System (ADS)

    Guo, Xia; Ye, Wei; Sun, Hongyan; Zhang, Qiao; Yang, Jian

    2013-11-01

    One-dimensional porous metallic nanomaterials have attracted much attention due to their unique shape and hollow structure. Herein, the gold nanorods in a porous shell of an AuAg alloy are synthesized via a dealloying process of the core-shell Au@AuAg nanorods at room temperature. The formation of tiny pores in the shell results in the huge red-shift, sharp decrease and drastic broadening of longitudinal surface plasmon resonance absorption. The continuous removal of silver from the porous nanorods leads to the breakage of tiny pores and leaves a rough surface on the nanorods behind. The rough surface gradually becomes smooth in the subsequent dealloying process. The surface structures of these intermediates are correlated with their absorption spectra and catalytic activities for the catalytic reduction of p-nitrophenol. The porous nanorods show a higher catalytic efficiency than the gold nanorods, the core-shell nanorods and the rough nanorods. The results indicate that the dealloying of anisotropic bimetal nanomaterials not only provides an effective pathway to carve the structures on the nanoscale but also offers numerous opportunities to observe novel optical properties and enhanced catalysis performances.One-dimensional porous metallic nanomaterials have attracted much attention due to their unique shape and hollow structure. Herein, the gold nanorods in a porous shell of an AuAg alloy are synthesized via a dealloying process of the core-shell Au@AuAg nanorods at room temperature. The formation of tiny pores in the shell results in the huge red-shift, sharp decrease and drastic broadening of longitudinal surface plasmon resonance absorption. The continuous removal of silver from the porous nanorods leads to the breakage of tiny pores and leaves a rough surface on the nanorods behind. The rough surface gradually becomes smooth in the subsequent dealloying process. The surface structures of these intermediates are correlated with their absorption spectra and

  8. Localized surface plasmon resonance and surface enhanced Raman scattering responses of Au@Ag core-shell nanorods with different thickness of Ag shell.

    PubMed

    Ma, Yanan; Zhou, Jun; Zou, Weibo; Jia, Zhenhong; Petti, Lucia; Mormile, Pasquale

    2014-06-01

    The properties of the localized surface plasmon resonance (LSPR) and the surface enhanced Raman scattering (SERS) of the core-shell bimetallic nanostructures, that is the monodisperse Au@Ag core-shell nanorods with different thickness of Ag shell, are theoretically and experimental researched. The UV-vis-NIR absorption spectra of the Au@Ag core-shell nanorods are measured and displayed their blue-shifts of the longitudinal plasmon resonance peaks with increasing of Ag concentrations in the colloidal solution. And the absorption spectra of the Au@Ag core-shell nanorods are simulated by the Finite Element Method (FEM), which are in agreement with the experimental measurements and reveal their LSPR mechanism as the varying structures. In addition, Rhodamine 6G, as a Raman reporter molecule, is used to investigate SERS of gold nanorods and Au@Ag core-shell nanorods. It is found that Au@Ag core-shell nanorods have better SERS responses, comparing with those of Au nanorods, and their SERS intensities are increased with the increases of the Ag shell thickness, which demonstrate that the chemisorptive bond effect and the morphology of the nanoparticle play key roles to the SERS signals. It is significant to design the biosensor based on the properties of Au@Ag core-shell nanorods.

  9. Guazuma ulmifolia bark-synthesized Ag, Au and Ag/Au alloy nanoparticles: Photocatalytic potential, DNA/protein interactions, anticancer activity and toxicity against 14 species of microbial pathogens.

    PubMed

    Karthika, Viswanathan; Arumugam, Ayyakannu; Gopinath, Kasi; Kaleeswarran, Periyannan; Govindarajan, Marimuthu; Alharbi, Naiyf S; Kadaikunnan, Shine; Khaled, Jamal M; Benelli, Giovanni

    2017-02-01

    In the present study, we focused on a quick and green method to fabricate Ag, Au and Ag/Au alloy nanoparticles (NPs) using the bark extract of Guazuma ulmifolia L. Green synthesized metal NPs were characterized using different techniques, including UV-Vis spectroscopy, FT-IR, XRD, AFM and HR-TEM analyses. The production of Ag, Au and Ag/Au alloy NPs was observed monitoring color change from colorless to brown, followed by pink and dark brown, as confirmed by UV-Vis spectroscopy characteristic peaks at 436, 522 and 510nm, respectively. TEM shed light on the spherical shapes of NPs with size ranges of 10-15, 20-25 and 10-20nm. Biosynthesized NPs showed good catalytic activity reducing two organic dyes, 4-nitrophenol (4-NP) and Congo red (CR). UV-vis spectroscopy, fluorescence, circular dichroism spectroscopy and viscosity analyses were used to investigate the NP binding with calf thymus DNA. The binding constant of NPs with DNA calculated in UV-Vis absorption studies were 1.18×10(4), 1.83×10(4) and 2.91×10(4)M(-1), respectively, indicating that NPs were able to bind DNA with variable binding affinity: Ag/Au alloy NPs>Ag NPs>Au NPs. Ag/Au alloy NPs also showed binding activity to bovine serum albumin (BSA) over the other NPs. Ag and Ag/Au alloy NPs exhibited good antimicrobial activity on 14 species of microbial pathogens. In addition, the cytotoxic effects of Ag/Au alloy NPs were studied on human cervical cancer cells (HeLa) using MTT assay. Overall, our work showed the promising potential of bark-synthesized Ag and Ag/Au alloy NPs as cheap sources to develop novel and safer photocatalytic, antimicrobial and anticancer agents. Copyright © 2017. Published by Elsevier B.V.

  10. Antibacterial activity of microstructured Ag/Au sacrificial anode thin films.

    PubMed

    Köller, Manfred; Sengstock, Christina; Motemani, Yahya; Khare, Chinmay; Buenconsejo, Pio J S; Geukes, Jonathan; Schildhauer, Thomas A; Ludwig, Alfred

    2015-01-01

    Ten different Ag dot arrays (16 to 625 microstructured dots per square mm) were fabricated on a continuous Au thin film and for comparison also on Ti film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Escherichia coli and Staphylococcus aureus were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards both bacterial strains was induced by Ag dot arrays on fabricated Au thin film (sacrificial anode system for Ag), due to the release of Ag ions from dissolution of Ag dots in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag) which remained intact to the original dot shape. The required number of Ag dots on gold film to achieve complete bactericidal effects for both bacterial strains was seven times lower than that observed with Ag dot arrays on Ti film. Copyright © 2014 Elsevier B.V. All rights reserved.

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

    SciTech Connect

    Saggar, Siddhartha; Predeep, Padmanabhan

    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.

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

    PubMed

    Chen, Fuyi; Johnston, Roy L

    2008-01-01

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

  13. Studies on polishing of Ti and Ag-Pd-Cu-Au alloy with five dental abrasives.

    PubMed

    Hirata, T; Nakamura, T; Takashima, F; Maruyama, T; Taira, M; Takahashi, J

    2001-08-01

    Titanium (Ti) and Ag-Pd-Cu-Au alloy were examined for their polishing behaviour by conducting manually controlled polishing tests using five dental abrasives [carborundum point (CR) and silicone points (R1 and R2)] driven by a high torque micromotor with rotational speeds ranging from 2000 to 15 000 r.p.m. Polishing of Ti resulted in less volume of removal upon polishing, a rougher surface and larger loss of abrasives, compared with polishing of Ag-Pd-Cu-Au alloy. Polishing of Ti with a rotational speed of 15 000 r.p.m. led to the largest volume of removal upon polishing, whilst that of 10 000 r.p.m. produced the optimal volume for Ag-Pd-Cu-Au alloy. It was concluded that Ti was much more difficult to polish, requiring special care (e.g. frequent exchange of abrasives). Development of new abrasives for polishing Ti is required.

  14. Structure and bonding of the MCN molecules, M=Cu,Ag,Au,Rg.

    PubMed

    Zaleski-Ejgierd, Patryk; Patzschke, Michael; Pyykkö, Pekka

    2008-06-14

    High-precision calculations are reported for the title series with M=Cu, Ag, Au, using CCSD(T) with the latest pseudopotentials and basis sets up to cc-pVQZ. The bond lengths for M=Cu, Ag, Au agree with experiment within better than 1 pm. The role of deep-core excitations is studied. The second-order spin-orbit effects are evaluated at the density functional theory level, including M=Rg. A qualitative bonding analysis suggests multiple M-C bonding. The calculated vibrational frequencies are expected to be more accurate than the available experimental estimates. The M-C bond lengths obey CuAu.

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  16. An Atomically Precise Au10 Ag2 Nanocluster with Red-Near-IR Dual Emission.

    PubMed

    Lei, Zhen; Guan, Zong-Jie; Pei, Xiao-Li; Yuan, Shang-Fu; Wan, Xian-Kai; Zhang, Jin-Yuan; Wang, Quan-Ming

    2016-08-01

    A red-near-IR dual-emissive nanocluster with the composition [Au10 Ag2 (2-py-C≡C)3 (dppy)6 ](BF4 )5 (1; 2-py-C≡C is 2-pyridylethynyl, dppy=2-pyridyldiphenylphosphine) has been synthesized. Single-crystal X-ray structural analysis reveals that 1 has a trigonal bipyramidal Au10 Ag2 core that contains a planar Au4 (2-py-C≡C)3 unit sandwiched by two Au3 Ag(dppy)3 motifs. Cluster 1 shows intense red-NIR dual emission in solution. The visible emission originates from metal-to-ligand charge transfer (MLCT) from silver atoms to phosphine ligands in the Au3 Ag(dppy)3 motifs, and the intense NIR emission is associated with the participation of 2-pyridylethynyl in the frontier orbitals of the cluster, which is confirmed by a time-dependent density functional theory (TD-DFT) calculation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Ru-Ag and Ru-Au dicarbene complexes from an abnormal carbene ruthenium system.

    PubMed

    Bitzer, Mario J; Pöthig, Alexander; Jandl, Christian; Kühn, Fritz E; Baratta, Walter

    2015-07-14

    Reaction of [Ru(OAc)2(PPh3)2] with a P-functionalized imidazolium bromide easily affords a cationic abnormal carbene Ru system. Metalation with Ag2O yields a Ru-Ag complex containing an anionic dicarbene ligand, while subsequent transmetalation with Au(tht)Cl leads to the corresponding Ru-Au system. The bimetallic complexes were characterized by single crystal X-ray diffraction and are the first examples of complexes bearing anionic dicarbene ligands connecting two different d-block elements.

  18. Nanoalloy composition-temperature phase diagram for catalyst design: Case study of Ag-Au

    SciTech Connect

    Wang, Lin-Lin; Tan, Teck L.; Johnson, Duane D.

    2012-07-23

    By coupling a cluster expansion with density functional theory (DFT) calculations, we determine the configurational thermodynamics (site preferences and occupations) for alloyed nanoparticles (NPs) as functions of composition (c) and temperature (T), exemplified using a 55-atom Ag-Au truncated cuboctahedron NP. The c-T phase diagram for site occupations gives detailed design information for alloyed NP, especially the thermodynamically stable active sites for catalysis and how they change with stoichiometry and processing temperature. Generally, Ag prefers core and Au prefers shell, agreeing with our universal core-shell preference assessed from DFT impurity segregation energies but with interesting multishell configurations having specific active sites.

  19. Effect of Annealing Twins on Electromigration in Ag-8Au-3Pd Bonding Wires

    NASA Astrophysics Data System (ADS)

    Chuang, Tung-Han; Wang, Hsi-Ching; Chuang, Chien-Hsun; Lee, Jun-Der; Tsai, Hsing-Hua

    2013-03-01

    An innovative Ag-8Au-3Pd bonding wire with a high twin density has been produced. The grain size of this annealing-twinned wire changes moderately during electrical stressing, unlike that of the conventional grained wire, which increases drastically and even leads to a bamboo structure. In addition, the durability against electromigration of the annealing-twinned Ag-8Au-3Pd alloy wire is higher than that of the conventional grained wire. This higher durability can be ascribed to the surface reconstruction of a stepwise morphology and slow grain growth resulting from the abundance of annealing twins in this wire.

  20. The unusual effect of AgNO3 on the growth of Au nanostructures and their catalytic performance

    NASA Astrophysics Data System (ADS)

    Li, Xingliang; Yang, Yun; Zhou, Guangju; Han, Shuhua; Wang, Wenfang; Zhang, Lijie; Chen, Wei; Zou, Chao; Huang, Shaoming

    2013-05-01

    Au nanostructures attract much attention due to their potential applications in many fields. The controlled synthesis is critical to their properties modulation and applications. AgNO3-assisted synthesis is a widely used method for controllably preparing Au nanostructures in aqueous system. Herein, the effect of AgNO3 on the growth of Au nanostructures in polyol is studied. We observe an unusual effect that AgNO3 can induce the formation of pentatwinned Au nanostructures (nanorods and decahedra) and block the growth of Au nanorods. More interestingly, this blocking effect can be tuned through controlling the amount of AgNO3. A moderate amount of AgNO3 facilitates the formation of Au nanorods. A large amount of AgNO3 completely blocks the growth of nanorods and favors the formation of high quality decahedra (decahedra can be considered as nanorods with 0 nm longitudinal length). Besides, this blocking effect also allows preparation of different high-index-faceted Au nanobipyramids. These prepared Au nanostructures further serve as starting templates to fabricate other heterostructured Au/Ag nanomaterials, such as Ag-Au-Ag segmental nanorods, Au@Ag core-shelled nanostructures. The prepared nanostructures exhibit size- and structure-dependent catalytic performance in the reduction of p-nitrophenol to p-aminophenol by sodium borohydride.Au nanostructures attract much attention due to their potential applications in many fields. The controlled synthesis is critical to their properties modulation and applications. AgNO3-assisted synthesis is a widely used method for controllably preparing Au nanostructures in aqueous system. Herein, the effect of AgNO3 on the growth of Au nanostructures in polyol is studied. We observe an unusual effect that AgNO3 can induce the formation of pentatwinned Au nanostructures (nanorods and decahedra) and block the growth of Au nanorods. More interestingly, this blocking effect can be tuned through controlling the amount of AgNO3. A moderate

  1. Hollow Au/Ag nanostars displaying broad plasmonic resonance and high surface-enhanced Raman sensitivity

    NASA Astrophysics Data System (ADS)

    Garcia-Leis, Adianez; Torreggiani, Armida; Garcia-Ramos, Jose Vicente; Sanchez-Cortes, Santiago

    2015-08-01

    Bimetallic Au/Ag hollow nanostar (HNS) nanoparticles with different morphologies were prepared in this work. These nanoplatforms were obtained by changing the experimental conditions (concentration of silver and chemical reductors, hydroxylamine and citrate) and by using Ag nanostars as template nanoparticles (NPs) through galvanic replacement. The goal of this research was to create bimetallic Au/Ag star-shaped nanoparticles with advanced properties displaying a broader plasmonic resonance, a cleaner exposed surface, and a high concentration of electromagnetic hot spots on the surface provided by the special morphology of nanostars. The size, shape, and composition of Ag as well as their optical properties were studied by extinction spectroscopy, hyperspectral dark field microscopy, transmission and scanning electron microscopy (TEM and SEM), and energy dispersive X-ray spectroscopy (EDX). Finally, the surface-enhanced Raman scattering (SERS) activity of these HNS was investigated by using thioflavin T, a biomarker of the β-amyloid fibril formation, responsible for Alzheimer's disease. Lucigenin, a molecule displaying different SERS activities on Au and Ag, was also used to explore the presence of these metals on the NP surface. Thus, a relationship between the morphology, plasmon resonance and SERS activity of these new NPs was made.Bimetallic Au/Ag hollow nanostar (HNS) nanoparticles with different morphologies were prepared in this work. These nanoplatforms were obtained by changing the experimental conditions (concentration of silver and chemical reductors, hydroxylamine and citrate) and by using Ag nanostars as template nanoparticles (NPs) through galvanic replacement. The goal of this research was to create bimetallic Au/Ag star-shaped nanoparticles with advanced properties displaying a broader plasmonic resonance, a cleaner exposed surface, and a high concentration of electromagnetic hot spots on the surface provided by the special morphology of nanostars

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

    PubMed

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

    2012-09-07

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

  3. Complex structures in the Au - Cd alloy system: Hume-Rothery mechanism as origin

    NASA Astrophysics Data System (ADS)

    Degtyareva, Valentina F.; Afonikova, Nataliya S.

    2015-11-01

    The binary (simple metal) phase diagram Au-Cd contains a number of intermetallic compounds with various distortions, superlattices and vacancies. To understand the reasons of these structural complexities and their phase stability, we analyze these crystal structures within the nearly free-electron model in the frame of Fermi sphere - Brillouin zone interactions. Examination of the Brillouin-Jones configuration in relation to the nearly-free electron Fermi sphere provides insights for significance of the valence electron energy contribution to the phase stability. Representation of these complex structures in the reciprocal space clarifies their relationship to simple basic cells. This approach shows the importance of the additional planes for the stability of superlattices. The AuCd-hP18, AuCd3-hP24 and AuCd4-hP273 structures are shown to be related to the AuCd-cP2 via rhombohedral distortion with superlattices and vacancies.

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

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    Manivannan, Shanmugam; Ramaraj, Ramasamy

    2012-06-01

    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 β-cyclodextrin. The Ag shell was deposited on the preformed Au nanoparticles by the reduction of Ag+ ions by β-cyclodextrin and EDAS silane composite. Interestingly, productive Ag shell deposition occurred only on the β-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.

  6. Two-Photon Imaging of 3D Organization of Bimetallic AuAg Nanoclusters in DNA Matrix.

    PubMed

    Brach, Katarzyna; Waszkielewicz, Magdalena; Olesiak-Banska, Joanna; Samoc, Marek; Matczyszyn, Katarzyna

    2017-09-12

    We report on two-photon excitation properties of small silver-doped gold nanoclusters (AuAgNCs) and on their three-dimensional arrangement in a hybrid system composed of DNA liquid crystals (LCs) and AuAgNCs. UV-vis and fluorescence spectroscopy, transmission electron microscopy (TEM), and multiphoton excitation spectroscopy were used to characterize the nanoparticles. We show that AuAgNCs exhibit two-photon excited luminescence (2PL) emission and second-harmonic generation (SHG) and that these properties remain the same in liquid crystalline matrix. The results are described in detail and discussed in the context of possible imaging application of AuAgNC and specific AuAgNCs organization induced by liquid crystalline ordering of DNA molecules.

  7. TiO2 coated Au/Ag nanorods with enhanced photocatalytic activity under visible light irradiation.

    PubMed

    Zhou, Na; Polavarapu, Lakshminarayana; Gao, Nengyue; Pan, Yanlin; Yuan, Peiyan; Wang, Qing; Xu, Qing-Hua

    2013-05-21

    A facile method was used to prepare uniform Au NR/TiO2 and Au/Ag NR/TiO2 core-shell composite nanoparticles. Au/Ag NR/TiO2 nanoparticles were found to display significantly enhanced visible light photo-catalytic activity compared to Au NR/TiO2 and the commercially available TiO2 nanoparticles. The enhancement mechanism was ascribed to injection of hot electrons of photo-excited Au/Ag NRs to TiO2, which was confirmed by 633 nm laser induced reduction of silver ions on the surface of Au/Ag NR/TiO2 composite nanoparticles.

  8. A dry method to synthesize dendritic Ag2Se nanostructures utilizing CdSe quantum dots and Ag thin films

    NASA Astrophysics Data System (ADS)

    Hu, Lian; Zhang, Bingpo; Xu, Tianning; Li, Ruifeng; Wu, Huizhen

    2015-01-01

    Dendritic Ag2Se nanostructures are synthesized in a dry environment by UV irradiating the hybrids composed of CdSe quantum dots (QDs) and silver (Ag). UV irradiation on CdSe QDs induces a photooxidation effect on the QD surface and leads to the formation of SeO2 components. Then SeO2 reacts with the Ag atoms in either Ag film or QD layer to produce the Ag2Se. The growth mechanism of Ag2Se dendrites on solid Ag films is explored and explained by a diffusion limited aggregation model in which the QD layer provides enough freedom for Ag2Se motion. Since the oxidation of the CdSe QDs is the critical step for the Ag2Se dendrites formation this dry chemical interaction between QDs and Ag film can be applied in the study of the QD surface chemical properties. With this dry synthesis method, the Ag2Se dendrites can also be facilely formed at the designed area on Ag substrates.

  9. A dry method to synthesize dendritic Ag2Se nanostructures utilizing CdSe quantum dots and Ag thin films.

    PubMed

    Hu, Lian; Zhang, Bingpo; Xu, Tianning; Li, Ruifeng; Wu, Huizhen

    2015-01-09

    Dendritic Ag2Se nanostructures are synthesized in a dry environment by UV irradiating the hybrids composed of CdSe quantum dots (QDs) and silver (Ag). UV irradiation on CdSe QDs induces a photooxidation effect on the QD surface and leads to the formation of SeO2 components. Then SeO2 reacts with the Ag atoms in either Ag film or QD layer to produce the Ag2Se. The growth mechanism of Ag2Se dendrites on solid Ag films is explored and explained by a diffusion limited aggregation model in which the QD layer provides enough freedom for Ag2Se motion. Since the oxidation of the CdSe QDs is the critical step for the Ag2Se dendrites formation this dry chemical interaction between QDs and Ag film can be applied in the study of the QD surface chemical properties. With this dry synthesis method, the Ag2Se dendrites can also be facilely formed at the designed area on Ag substrates.

  10. Ag@Au concave cuboctahedra: A unique probe for monitoring Au-catalyzed reduction and oxidation reactions by surface-enhanced Raman spectroscopy

    SciTech Connect

    Zhang, Jiawei; Winget, Sarah A.; Wu, Yiren; Su, Dong; Sun, Xiaojun; Xie, Zhao -Xiong; Qin, Dong

    2016-01-26

    In this paper, we report a facile synthesis of Ag@Au concave cuboctahedra by titrating aqueous HAuCl4 into a suspension of Ag cuboctahedra in the presence of ascorbic acid (AA), NaOH, and poly(vinylpyrrolidone) (PVP) at room temperature. Initially, the Au atoms derived from the reduction of Au3+ by AA are conformally deposited on the entire surface of a Ag cuboctahedron. Upon the formation of a complete Au shell, however, the subsequently formed Au atoms are preferentially deposited onto the Au{100} facets, resulting in the formation of a Ag@Au cuboctahedron with concave structures at the sites of {111} facets. The concave cuboctahedra embrace excellent SERS activity that is more than 70-fold stronger than that of the original Ag cuboctahedra at an excitation wavelength of 785 nm. The concave cuboctahedra also exhibit remarkable stability in the presence of an oxidant such as H2O2 because of the protection by a complete Au shell. These two unique attributes enable in-situ SERS monitoring of the reduction of 4-nitrothiophenol (4-NTP) to 4-aminothiophenol (4-ATP) by NaBH4 through a 4,4'-dimercaptoazobenzene (trans-DMAB) intermediate and the subsequent oxidation of 4-ATP back to trans-DMAB upon the introduction of H2O2.

  11. Ag@Au concave cuboctahedra: A unique probe for monitoring Au-catalyzed reduction and oxidation reactions by surface-enhanced Raman spectroscopy

    DOE PAGES

    Zhang, Jiawei; Winget, Sarah A.; Wu, Yiren; ...

    2016-01-26

    In this paper, we report a facile synthesis of Ag@Au concave cuboctahedra by titrating aqueous HAuCl4 into a suspension of Ag cuboctahedra in the presence of ascorbic acid (AA), NaOH, and poly(vinylpyrrolidone) (PVP) at room temperature. Initially, the Au atoms derived from the reduction of Au3+ by AA are conformally deposited on the entire surface of a Ag cuboctahedron. Upon the formation of a complete Au shell, however, the subsequently formed Au atoms are preferentially deposited onto the Au{100} facets, resulting in the formation of a Ag@Au cuboctahedron with concave structures at the sites of {111} facets. The concave cuboctahedramore » embrace excellent SERS activity that is more than 70-fold stronger than that of the original Ag cuboctahedra at an excitation wavelength of 785 nm. The concave cuboctahedra also exhibit remarkable stability in the presence of an oxidant such as H2O2 because of the protection by a complete Au shell. These two unique attributes enable in-situ SERS monitoring of the reduction of 4-nitrothiophenol (4-NTP) to 4-aminothiophenol (4-ATP) by NaBH4 through a 4,4'-dimercaptoazobenzene (trans-DMAB) intermediate and the subsequent oxidation of 4-ATP back to trans-DMAB upon the introduction of H2O2.« less

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

    NASA Astrophysics Data System (ADS)

    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.

  13. Investigation of the ratio of proton-stopping cross sections in Ag and Au

    SciTech Connect

    Semrad, D.; Golser, R.

    1987-06-01

    Knowledge of the ratio of stopping cross sections may help in determining best values from measurements. The case of Ag and Au is discussed, where theoretical considerations show that this ratio always has a value smaller than 1. This is confirmed experimentally for proton energies larger than 70 keV, in contradiction to all published stopping-power tabulations.

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

    NASA Astrophysics Data System (ADS)

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

    2002-05-01

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

  15. Phase equilibria in the Ag-Au-In system at 500°C

    NASA Astrophysics Data System (ADS)

    Ptashkina, E. A.; Romanova, A. G.; Pavlenko, A. S.; Kabanova, E. G.; Kuznetsov, V. N.

    2017-02-01

    Phase equilibria in Ag-Au-In system at 500°C are investigated by means of electron microscopy, electron probe microanalysis, and X-ray powder diffraction. The part of the system's isothermal cross section with an indium content of up to 50 at % is constructed.

  16. Antitumor Activity of Alloy and Core-Shell-Type Bimetallic AgAu Nanoparticles

    NASA Astrophysics Data System (ADS)

    Shmarakov, Igor; Mukha, Iuliia; Vityuk, Nadiia; Borschovetska, Vira; Zhyshchynska, Nelya; Grodzyuk, Galyna; Eremenko, Anna

    2017-05-01

    Nanoparticles (NPs) of noble metals, namely gold and silver, remain promising anticancer agents capable of enhancing current surgery- and chemotherapeutic-based approaches in cancer treatment. Bimetallic AgAu composition can be used as a more effective agent due to the synergetic effect. Among the physicochemical parameters affecting gold and silver nanoparticle biological activity, a primary concern relates to their size, shape, composition, charge, etc. However, the impact of metal components/composition as well as metal topological distribution within NPs is incompletely characterized and remains to be further elucidated and clarified. In the present work, we tested a series of colloidal solutions of AgAu NPs of alloy and core-shell type for an antitumor activity depending on metal molar ratios (Ag:Au = 1:1; 1:3; 3:1) and topological distribution of gold and silver within NPs (AucoreAgshell; AgcoreAushell). The efficacy at which an administration of the gold and silver NPs inhibits mouse Lewis lung carcinoma (LLC) growth in vivo was compared. The data suggest that in vivo antitumor activity of the studied NPs strongly depends on gold and silver interaction arising from their ordered topological distribution. NPs with Ag core covered by Au shell were the most effective among the NPs tested towards LLC tumor growth and metastasizing inhibition. Our data show that among the NPs tested in this study, AgcoreAushell NPs may serve as a suitable anticancerous prototype.

  17. Theoretical investigation on reactivity of Ag and Au atoms toward CS2 in gas phase

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Yang, Ling; Tian, An-Min; Wong, Ning-Bew

    2008-02-01

    The reaction mechanisms of Ag and Au atoms with CS2 on both doublet and quartet potential energy surfaces (PESs) have been investigated using UBPW91 and UCCSD(T) methods. The two studied reactions proceed via a similar insertion-elimination mechanism instead of a direct abstract mechanism. The reaction Ag + CS2 --> SAgCS is endothermic by about 21E0 kcal/mol. But another reaction Au + CS2 --> SAuCS is slightly exothermic by about 8.8 kcal/mol, which is different from the previous theoretical prediction. In the overall reactions, the rate-determining step is found to be the C-S bond cleavage step with a high-activation barrier of about 40 kcal/mol. The calculated vibration frequencies are in good agreement with the experiment values and show that the BPW91 method is very good for the calculation of small molecules containing Ag and Au. The reactivity of the two atoms toward CS2 is compared with those of the first-row transition-metal atoms. The present study provides a detailed picture of the C-S bond activation and cleavage in carbon disulfide mediated by second and the third row transition-metal atoms Ag and Au.

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

    PubMed

    Jana, Partha P; Lidin, Sven

    2015-02-02

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

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

    PubMed

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

    2016-01-28

    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.

  20. SERS-active Au@Ag nanorod dimers for ultrasensitive dopamine detection.

    PubMed

    Tang, Lijuan; Li, Si; Han, Fei; Liu, Liqiang; Xu, Liguang; Ma, Wei; Kuang, Hua; Li, Aike; Wang, Libing; Xu, Chuanlai

    2015-09-15

    Dopamine (DA) is a neurotransmitter which plays a key role in the life science. Self-assembled Au@Ag nanorod dimers based on aptamers were developed for ultrasensitive dopamine detection. The electronic field was significantly enhanced by the addition of silver shell coating on the surface of Au NR dimer. The results displayed that Au@Ag NR dimers were ideal building blocks for constructing the SERS substrates with prominent Raman enhancement effects. It was found that with using this Surface-enhanced Raman scattering (SERS)-encoded this sensing system, a limit of detection of 0.006 pM and a wide linear range of 0.01-10 pM for dopamine detection were obtained. Our work open up a new avenue for the diagnosis and drug-discovery programs.

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

    PubMed

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

    2014-07-17

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

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

    NASA Astrophysics Data System (ADS)

    Baldwin, Dylan

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

  3. Heavy metals contamination and their risk assessment around the abandoned base metals and Au-Ag mines in Korea

    NASA Astrophysics Data System (ADS)

    Chon, Hyo-Taek

    2017-04-01

    Heavy metals contamination in the areas of abandoned Au-Ag and base metal mines in Korea was investigated in order to assess the level of metal pollution, and to draw general summaries about the fate of toxic heavy metals in different environments. Efforts have been made to compare the level of heavy metals, chemical forms, and plant uptake of heavy metals in each mine site. In the base-metals mine areas, significant levels of Cd, Cu, Pb and Zn were found in mine dump soils developed over mine waste materials and tailings. Leafy vegetables tend to accumulate heavy metals(in particular, Cd and Zn) higher than other crop plants, and high metal concentrations in rice crops may affect the local residents' health. In the Au-Ag mining areas, arsenic would be the most characteristic contaminant in the nearby environment. Arsenic and heavy metals were found to be mainly associated with sulfide gangue minerals, and the mobility of these metals would be enhanced by the effect of continuing weathering and oxidation. According to the sequential extraction of metals in soils, most heavy metals were identified as non-residual chemical forms, and those are very susceptible to the change of ambient conditions of a nearby environment. The concept of pollution index(PI) of soils gives important information on the extent and degree of multi-element contamination, and can be applied to the evaluation of mine soils before their agricultural use and remediation. The risk assessment process comprising exposure assessment, dose-response assessment, and risk characterization was discussed, and the results of non-cancer risk of As, Cd, and Zn, and those of cancer risk of As were suggested.

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

    NASA Astrophysics Data System (ADS)

    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

  5. Strangeness production in Au+Au collisions at the AGS: recent results from E917.

    SciTech Connect

    Chang, W.-C.; Back, B. B.; Betts, R. R.; Britt, H. C.; Chang, W. C.; Gillitzer, A.; Henning, W. F.; Hofman, D. J.; Holzman, B.; Nanal, V.; Wuosmaa, A. H.

    1999-03-30

    Strangeness production in Au+Au collisions has been measured via the yields of K{sup +} , K{sup {minus}} at 6, 8 AGeV and of {bar {Lambda}} at 10.8 AGeV beam kinetic energy in experiment E917. By varying the collision centrally and beam energy, a systematic search for indications of new phenomena and in-medium effects under high baryon density is undertaken.

  6. Cyclic voltammetry and near edge X-ray absorption fine structure spectroscopy at the Ag L3-edge on electrochemical halogenation of Ag layers on Au(111)

    NASA Astrophysics Data System (ADS)

    Endo, Osamu; Nakamura, Masashi

    2011-05-01

    One to three layers of Ag grown on a Au(111) electrode were studied by cyclic voltammetry in chloride and bromide solutions and by ex-situ near-edge X-ray absorption fine structure spectroscopy at the Ag L3-edge (Ag L3-NEXAFS). The one and two layers obtained by underpotential deposition exhibited reduced intensity at the absorption edge in the Ag L3-NEXAFS spectra, which suggests the gain of d-electrons in these layers. The cyclic voltammograms and the Ag L3-NEXAFS spectra indicate that the second and third layers of Ag halogenated at positive potentials, whereas the first layer remained in metallic form.

  7. Converting Ag₂S-CdS and Ag₂S-ZnS into Ag-CdS and Ag-ZnS nanoheterostructures by selective extraction of sulfur.

    PubMed

    Zhou, Jiangcong; Huang, Feng; Xu, Ju; Wang, Yuansheng

    2014-11-01

    A mild three-step solution strategy is developed to prepare Ag-MS (M=Zn, Cd) nanoheterostructures composed of MS nanorods with silver tips. First, Ag2S-MS heterostructures are synthesized by following a solution-liquid-solid mechanism with Ag2S nanoparticles as catalysts, then the Ag2S sections of the heterostructures are converted into silver nanoparticles by selective extraction of sulfur. Notably, for the prepared Ag-CdS heterostructures, the localized surface plasmon resonance of silver remarkably intensifies the photoluminescence of CdS by enhancing the excitation light absorption, which is beneficial for potential applications of CdS nanoparticles in the fields of biolabeling, light-emitting diodes, and so forth. The strategy reported herein would be useful for designing and fabricating other metal-semiconductor hybrid nanostructures with desirable performances.

  8. Au-Ag-Au double shell nanoparticles-based localized surface plasmon resonance and surface-enhanced Raman scattering biosensor for sensitive detection of 2-mercapto-1-methylimidazole.

    PubMed

    Liao, Xue; Chen, Yanhua; Qin, Meihong; Chen, Yang; Yang, Lei; Zhang, Hanqi; Tian, Yuan

    2013-12-15

    In this paper, Au-Ag-Au double shell nanoparticles were prepared based on the reduction of the metal salts HAuCl4 and AgNO3 at the surface of seed particles. Due to the synergistic effect between Au and Ag, the hybrid nanoparticles are particularly stable and show excellent performances on the detection of 2-mercapto-1-methylimidazole (methimazole). The binding of target molecule at the surface of Au-Ag-Au double shell nanoparticles was demonstrated based on both localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS) spectra. The LSPR intensity is directly proportional to the methimazole concentration in the range of 0.10-3.00×10(-7) mol L(-1). The SERS spectrum can be applied in identification of methimazole molecule. The LSPR coupled with SERS based on the Au-Ag-Au double shell nanoparticles would be very attractive for the quantitative determination and qualitative analysis of the analytes in medicines.

  9. XPS profile analysis on CdS thin film modified with Ag by an ion exchange

    NASA Astrophysics Data System (ADS)

    Ristova, M.; Ristov, M.

    2001-09-01

    Thin CdS films were produced by the method of chemical bath deposition. The composition of the film surface was modified with Ag by their immersion in 0.025 M thiosulfate Ag + complex solution for 60 s. After 3-4 months, films underwent XPS analysis. The peaks on the Auger electron spectrum were identified to originate from Cd, Ag, S, O and C electrons. Depth profile electron spectra were taken for 15 different depths of the film profile. AgMNN and CdMNN, Cd3d, S2p, Ag3d and O1s peaks were subject to detailed qualitative and quantitative analysis. Results of the quantitative profile analysis showed that the Ag +-ions from the ion exchange solution, introduced into the CdS thin film by this method, displace the Cd +2 ions during the substitution diffusion by a kick-out mechanism, forming Ag 2S. The distribution of Ag 2S in the film profile could be fitted to a exponential curve. The overall Ag 2S concentration in the thin CdS film was calculated from the integral of the normalized fitted curve over the entire film thickness. The data from the film profile was related to the optical and electrical properties of the Ag modified CdS films, which were the subject of study in our previous research.

  10. Ag nanoparticle mediated growth of CdS nanobelts

    NASA Astrophysics Data System (ADS)

    Sreejith, K.; Nuwad, J.; Thinaharan, C.; Dey, G. K.; Pillai, C. G. S.

    2007-06-01

    Catalytic growth of CdS have been carried out on large scale by evaporation of bulk CdS on Ag deposited Si (1 1 1) at atmospheric pressure. The as prepared CdS had wurtzite structure as evidenced by X-ray diffraction. The nanostructures were beltlike with several tens of micrometers length, several micrometers width and few nanometers to tens of nanometers thick as seen by scanning electron microscope and confirmed by TEM studies. The nanobelts were single crystalline in nature and showed reflection corresponding to (1 1 2) and (0 0 2) planes in SAED. The PL studies revealed the green band due to band gap emission and red band due to emission from the surface states. The higher intensity of the defect emission indicated the presence of considerable concentration of surface defects in the as prepared sample. The deposition of CdS could be explained on the basis of catalyst assisted vapor-liquid-solid and vapor-solid mechanism.

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

    PubMed

    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. Copyright © 2012 Elsevier B.V. All rights reserved.

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

    PubMed

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

    2012-12-07

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

  13. Hydroquinone-assisted synthesis of branched au-ag nanoparticles with polydopamine coating as highly efficient photothermal agents.

    PubMed

    Li, Jing; Wang, Wenjing; Zhao, Liang; Rong, Li; Lan, Shijie; Sun, Hongchen; Zhang, Hao; Yang, Bai

    2015-06-03

    Despite the success of galvanic replacement in preparing hollow nanostructures with diversified morphologies via the replacement reaction between sacrificial metal nanoparticles (NPs) seeds and less active metal ions, limited advances are made for producing branched alloy nanostructures. In this paper, we report an extended galvanic replacement for preparing branched Au-Ag NPs with Au-rich core and Ag branches using hydroquinone (HQ) as the reductant. In the presence of HQ, the preformed Ag seeds are replaceable by Au and, in turn, supply the growth of Ag branches. By altering the feed ratio of Ag seeds, HAuCl4, and HQ, the size and morphology of the NPs are tunable. Accordingly, the surface plasmon resonance absorption is tuned to near-infrared (NIR) region, making the branched NPs as potential materials in photothermal therapy. The branched NPs are further coated with polydopamine (PDA) shell via dopamine polymerization at room temperature. In comparison with bare NPs, PDA-coated branched Au-Ag (Au-Ag@PDA) NPs exhibit improved stability, biocompatibility, and photothermal performance. In vitro experiments indicate that the branched Au-Ag@PDA NPs are competitive agents for photothermal ablation of cancer cells.

  14. Corrosion properties of Ag-Au-Cu-Pd system alloys containing indium.

    PubMed

    Hattori, Masayuki; Tokizaki, Teruhiko; Matsumoto, Michihiko; Oda, Yutaka

    2010-01-01

    In this study, the corrosion resistance of Ag-Au-Cu-Pd system alloys consisting of 5 or 10 mass% indium was evaluated. Levels of element release and tarnish were determined and electrochemical measurements performed. Results were compared with those for commercial silver-palladium-gold alloy. In terms of electrochemical behavior, the transpassive potential of these experimental alloys was 168-248mV. Experimental alloys with 25 mass% Au showed similar corrosion resistance to control gold-silver-palladium alloy. Amount of released elements was 14-130microg/cm(2) at 7 days, which is in the allowable range for dental alloys. Addition of indium to Ag-Au-Cu-10mass%Pd system alloys was effective in increasing resistance to tarnish and alloys containing 10 mass% of indium showed a minimal decrease in L(*) values after immersion. These findings indicate that 25Au-37.5Ag-15Cu-10Pd-2Zn-10In-0.5Ir alloy is applicable in dental practice.

  15. Chloroplasts-mediated biosynthesis of nanoscale Au-Ag alloy for 2-butanone assay based on electrochemical sensor

    NASA Astrophysics Data System (ADS)

    Zhang, Yixia; Gao, Guo; Qian, Qirong; Cui, Daxiang

    2012-08-01

    We reported a one-pot, environmentally friendly method for biosynthesizing nanoscale Au-Ag alloy using chloroplasts as reducers and stabilizers. The prepared nanoscale Au-Ag alloy was characterized by UV-visible spectroscopy, X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM). Fourier transform infrared spectroscopy (FTIR) analysis was further used to identify the possible biomolecules from chloroplasts that are responsible for the formation and stabilization of Au-Ag alloy. The FTIR results showed that chloroplast proteins bound to the nanoscale Au-Ag alloy through free amino groups. The bimetallic Au-Ag nanoparticles have only one plasmon band, indicating the formation of an alloy structure. HR-TEM images showed that the prepared Au-Ag alloy was spherical and 15 to 20 nm in diameter. The high crystallinity of the Au-Ag alloy was confirmed by SAED and XRD patterns. The prepared Au-Ag alloy was dispersed into multiwalled carbon nanotubes (MWNTs) to form a nanosensing film. The nanosensing film exhibited high electrocatalytic activity for 2-butanone oxidation at room temperature. The anodic peak current (Ip) has a linear relationship with the concentrations of 2-butanone over the range of 0.01% to 0.075% (v/v), when analyzed by cyclic voltammetry. The excellent electronic catalytic characteristics might be attributed to the synergistic electron transfer effects of Au-Ag alloy and MWNTs. It can reasonably be expected that this electrochemical biosensor provided a promising platform for developing a breath sensor to screen and pre-warn of early cancer, especially gastric cancer.

  16. Antitumor Activity of Alloy and Core-Shell-Type Bimetallic AgAu Nanoparticles.

    PubMed

    Shmarakov, Igor; Mukha, Iuliia; Vityuk, Nadiia; Borschovetska, Vira; Zhyshchynska, Nelya; Grodzyuk, Galyna; Eremenko, Anna

    2017-12-01

    Nanoparticles (NPs) of noble metals, namely gold and silver, remain promising anticancer agents capable of enhancing current surgery- and chemotherapeutic-based approaches in cancer treatment. Bimetallic AgAu composition can be used as a more effective agent due to the synergetic effect. Among the physicochemical parameters affecting gold and silver nanoparticle biological activity, a primary concern relates to their size, shape, composition, charge, etc. However, the impact of metal components/composition as well as metal topological distribution within NPs is incompletely characterized and remains to be further elucidated and clarified. In the present work, we tested a series of colloidal solutions of AgAu NPs of alloy and core-shell type for an antitumor activity depending on metal molar ratios (Ag:Au = 1:1; 1:3; 3:1) and topological distribution of gold and silver within NPs (AucoreAgshell; AgcoreAushell). The efficacy at which an administration of the gold and silver NPs inhibits mouse Lewis lung carcinoma (LLC) growth in vivo was compared. The data suggest that in vivo antitumor activity of the studied NPs strongly depends on gold and silver interaction arising from their ordered topological distribution. NPs with Ag core covered by Au shell were the most effective among the NPs tested towards LLC tumor growth and metastasizing inhibition. Our data show that among the NPs tested in this study, AgcoreAushell NPs may serve as a suitable anticancerous prototype.

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

    NASA Astrophysics Data System (ADS)

    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. Aqueous synthesis and characterization of Ag and Ag-Au nanoparticles: addressing challenges in size, monodispersity and structure.

    PubMed

    Mott, Derrick; Thuy, Nguyen T B; Aoki, Yoshiya; Maenosono, Shinya

    2010-09-28

    In this paper, we demonstrate the synthesis of monodispersed silver nanoparticles (NPs) of controlled size (20.5 +/- 3.3 nm) in aqueous phase from a silver hydroxide precursor with sodium acrylate as dual reducing-capping agent. We then coat these NPs in a layer of gold with controllable thickness through a reduction-deposition process. The materials are characterized using several techniques including high-resolution transmission electron microscopy, ultraviolet-visible spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The results show that we were able to synthesize not only monodispersed Ag NPs but also core-shell Ag-Au NPs with a discrete structure, which is significant because of the challenges associated with the creation of such materials, namely the propensity of metallic Ag to be oxidized by the presence of ionic Au. The NPs are of interest for use in a wide range of potential applications, including biomedical diagnostics and biomolecular detection as well as many others.

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

    PubMed

    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.

  20. Ferritin-mediated biomimetic synthesis of bimetallic Au-Ag nanoparticles on graphene nanosheets for electrochemical detection of hydrogen peroxide

    NASA Astrophysics Data System (ADS)

    Wang, Li; Wang, Jiku; Ni, Pengjuan; Li, Zhuang

    2015-03-01

    We demonstrated a biomimetic green synthesis of bimetallic Au-Ag nanoparticles (NPs) on graphene nanosheets (GNs). The spherical protein, ferritin (Fr), was bound onto GNs and served as the template for the synthesis of GN/Au-Ag nanohybrids. The created GN/Au-Ag nanohybrids were further utilized to fabricate a non-enzymatic amperometric biosensor for the sensitive detection of hydrogen peroxide (H2O2), and this biosensor displayed high performances to determine H2O2 with a detection limit of 20.0 × 10-6 M and a linear detection range from 2.0 μM to 7.0 mM.

  1. Interfacial band bending in Au-tipped Cd-chalcogenides hybrid nanostructures

    NASA Astrophysics Data System (ADS)

    Saad, Mahmoud M.; Abdallah, Tamer; Negm, Sohair; Talaat, Hassan

    2015-12-01

    The interfacial electronic structure of Au-tipped CdX (X = S, Se and Te) hybrid nanostructures (HNSs) have been studied by UHV scanning tunneling spectroscopy (STS) at room temperature. Au-tipped CdX (X = S, Se and Te) HNSs were synthesized by phase transfer chemical methods. The dimensions were determined by the scanning tunneling microscope (STM), the high resolution transmission electron microscope (HRTEM) and the optical absorption. The measured dimensions using these techniques are consistent, giving Au tip average size within the range of [2.5, 3.5] nm and Cd-chalcogenides quantum dots (QDs) nanoparticles (NPs) average size within the range of [3.5, 4] nm. The STS at the interface of Au-tipped CdS and CdSe HNSs detects a downward band bending towards the interface ∼0.25 ± 0.01 eV and 0.18 ± 0.03 eV respectively, indicating an electron accumulation at these interfaces. However, an upward band bending towards the interface of ∼0.78 ± 0.01 eV is measured by the STS at the interface of Au-tipped CdTe HNS, indicating electron depletion at the interface. The band bending values were also confirmed using the corresponding calculated models of the energy band diagrams. These different behaviors were also observed in the UV-vis absorption of Au-tipped CdS and CdSe HNSs, which shows exciton bleaching features, but an exciton increasing feature is observed in the case of Au-tipped CdTe HNS. These later results are explained as a result of the presence of electron accumulation at the interface of Au-tipped CdS and CdSe HNSs, and also an electron depletion at the interface of Au-tipped CdTe HNS. Such determinations of the interfacial band bending in Au-tipped Cd-chalcogenides HNSs have significant consequences on the charge separation efficiency and the photo-response behavior. Furthermore, the presence of these bands has a direct impact in the field of applying plasmonics for improved photovoltaic solarcells.

  2. An intermetallic Au24Ag20 superatom nanocluster stabilized by labile ligands.

    PubMed

    Wang, Yu; Su, Haifeng; Xu, Chaofa; Li, Gang; Gell, Lars; Lin, Shuichao; Tang, Zichao; Häkkinen, Hannu; Zheng, Nanfeng

    2015-04-08

    An intermetallic nanocluster containing 44 metal atoms, Au24Ag20(2-SPy)4(PhC≡C)20Cl2, was successfully synthesized and structurally characterized by single-crystal analysis and density funtional theory computations. The 44 metal atoms in the cluster are arranged as a concentric three-shell Au12@Ag20@Au12 Keplerate structure having a high symmetry. For the first time, the co-presence of three different types of anionic ligands (i.e., phenylalkynyl, 2-pyridylthiolate, and chloride) was revealed on the surface of metal nanoclusters. Similar to thiolates, alkynyls bind linearly to surface Au atoms using their σ-bonds, leading to the formation of two types of surface staple units (PhC≡C-Au-L, L = PhC≡C(-) or 2-pyridylthiolate) on the cluster. The co-presence of three different surface ligands allows the site-specific surface and functional modification of the cluster. The lability of PhC≡C(-) ligands on the cluster was demonstrated, making it possible to keep the metal core intact while removing partial surface capping. Moreover, it was found that ligand exchange on the cluster occurs easily to offer various derivatives with the same metal core but different surface functionality and thus different solubility.

  3. Atomic structure of water/Au, Ag, Cu and Pt atomic junctions.

    PubMed

    Li, Yu; Kaneko, Satoshi; Fujii, Shintaro; Nishino, Tomoaki; Kiguchi, Manabu

    2017-02-08

    Much progress has been made in understanding the transport properties of atomic-scale conductors. We prepared atomic-scale metal contacts of Cu, Ag, Au and Pt using a mechanically controllable break junction method at 10 K in a cryogenic vacuum. Water molecules were exposed to the metal atomic contacts and the effect of molecular adsorption was investigated by electronic conductance measurements. Statistical analysis of the electronic conductance showed that the water molecule(s) interacted with the surface of the inert Au contact and the reactive Cu ant Pt contacts, where molecular adsorption decreased the electronic conductance. A clear conductance signature of water adsorption was not apparent at the Ag contact. Detailed analysis of the conductance behaviour during a contact-stretching process indicated that metal atomic wires were formed for the Au and Pt contacts. The formation of an Au atomic wire consisting of low coordination number atoms leads to increased reactivity of the inert Au surface towards the adsorption of water.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    SciTech Connect

    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.

  6. A facile fabrication of Ag-Au-Ag nanostructures with nanogaps for intensified surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Jin, Liangliang; She, Guangwei; Li, Jing; Xia, Jing; Wang, Xiaotian; Mu, Lixuan; Shi, Wensheng

    2016-12-01

    Nanogap between two metallic nanostructures has been demonstrated to be able to efficiently concentrate an incident electromagnetic field into a small space. As a result, the formed strong field localization could extraordinarily enhance the surface-enhanced Raman scattering (SERS). In this study, controllable plasmonic nanogaps are formed by separating two layers of plasmonic Ag nanoparticles (50-100 nm) with small Au nanoparticles (2.5-6 nm). The size of the nanogaps can be readily tuned by altering the size of the Au nanoparticles. Utilizing an SERS substrate with such nanogaps, the SERS performance can be significantly improved. Such improvement could be attributed to the strongly enhanced electric field within the nanogaps, which is demonstrated by the Finite-difference time-domain simulations. The present work provides a facile strategy to rationally fabricate SERS substrates with controllable nanogaps and intensified SERS signals.

  7. Visible and "invisible" forms of gold and silver in the crystallization products of melts in the Fe-S-Ag-Au system: experimental data

    NASA Astrophysics Data System (ADS)

    Palyanova, G. A.; Mikhlin, Yu. L.; Karmanov, N. S.; Kokh, K. A.; Seryotkin, Yu. V.

    2017-06-01

    The forms of Au and Ag occurrence in the crystallization products of melts in the Fe-S-Ag-Au system depending on the proportions of Fe/S and Ag/Au have been studied at (Fe + S)/(Ag + Au) = 0.1. It is shown that the S-rich systems with S/Fe = 2 contain Au-Ag sulfides and Au-Ag alloys. The systems depleted in S with S/Fe = 1 contain only Au-Ag alloys. The results of XPS provide evidence for the sulfide and metallic components of Au and Ag among the crystallization products of melts in the system studied at S/Fe = 2 and a metallic component with S/Fe = 1. According to the data of electron microprobe analysis, the content of "invisible" forms of noble metals in pyrite and pyrrhotite is < 0.024 wt % for Au and <0.030 wt % for Ag; the contents of "invisible" Au and Ag in troilites are 0.040 ± 0.013 wt % Au and 0.079 ± 0.016 wt % Ag.

  8. Identification of Au-Sn phase in Ag3Sn alloys containing gold.

    PubMed

    Malhotra, M L; Lawless, K R

    1975-03-01

    Substitution of gold in part for silver in Ag3Sn alloys is found to result in two separate phases: gamma (Ag3Sn particles) grains with a uniform distribution of gold within the grain and an Au-Sn phase in a form of ring surrounding the gamma grain. The thickness of this ring increases with increasing gold concentration. The phases were identified by using the techniques of x-ray diffraction, optical metallography, scanning electron microscopy, and x-ray energy dispersive spectroscopy.

  9. Pulsed Electrodeposition of Two-Dimensional Ag Nanostructures on Au(111)

    NASA Astrophysics Data System (ADS)

    Borissov, D.; Tsekov, R.; Freyland, W.

    2006-07-01

    One-step pulsed potential electrodeposition of Ag on Au(111) in the underpotential deposition (UPD) region has been studied in 0.5 mM Ag2SO4 + 0.1 M H2SO4 aqueous electrolyte at various pulse durations from 0.2 to 500 ms. Evolution of the deposited Ag nanostructures was followed by in situ scanning tunneling microscopy (STM) and by measurement of the respective current transients. At short pulse durations a relatively high number density (4 × 10^11 cm-2) of two-dimensional Ag clusters with a narrow size and distance distribution is observed. They exhibit a remarkably high stability characterized by a dissolution potential which lies about 200 mV more anodically than the typical potential of Ag-(1 × 1) monolayer dissolution. To elucidate the underlying nucleation and growth mechanism, two models have been considered: two-dimensional lattice incorporation and a newly developed coupled diffusion-adsorption model. The first one yields a qualitative description of the current transients, whereas the second one is in nearly quantitative agreement with the experimental data. In this model the transformation of a Ag-(3 × 3) into a Ag-(1 × 1) structure indicated in the cyclic voltammogram (peaks at 520 vs 20 mV) is taken into account.

  10. Highly sensitive immunoassay based on SERS using nano-Au immune probes and a nano-Ag immune substrate.

    PubMed

    Shu, Lei; Zhou, Jun; Yuan, Xiaocong; Petti, Lucia; Chen, Jinping; Jia, Zhenhong; Mormile, Pasquale

    2014-06-01

    A super-high-sensitivity immunoassay based on surface-enhanced Raman scattering (SERS) was implemented using the nano-Au immune probes and nano-Ag immune substrate. Ultraviolet-visible extinction spectra, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images, and SERS spectra were used to characterise the nano-Au immune probes and the nano-Ag immune substrate. The nano-Ag immune substrate was prepared by the in situ growth of Ag nanoparticles and the subsequent linkage of these nanoparticles with anti-apolipoprotein B on a silicon wafer. The nano-Ag immune substrate exhibited strong SERS activity, excellent reproducibility, and high biospecificity. The nano-Au immune probes were prepared by immobilising 4-mercaptobenzoic acid (4MBA) molecules as a Raman reporter and anti-apolipoprotein B onto the surfaces of Au nanoparticles. It was found that 4MBA induced the aggregation of Au nanoparticles, resulting in the generation of vast hot spots. Moreover, the nano-Au immune probes exhibited strong SERS activity and high biospecificity. A sandwich-type immunoassay structure consisting of the nano-Au immune probes and nano-Ag immune substrate was used to detect the concentration of apolipoprotein B, where the detection limit was as low as 2 fg/mL (3.878×10(-18) mol/L). Taken together, the experimental results indicate that the proposed immunoassay protocol has a great potential application in biological sensing and clinical diagnostics.

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

    NASA Astrophysics Data System (ADS)

    Ribas, R. V.; Seale, W. A.; Roney, W. A.; Szanto, E. M.

    1980-04-01

    The stopping pow´er 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 Doppler 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 semiempirical predictions of Northcliffe and Schilling and the Lindhard-Scharff-Schiott theory.

  12. Au@Ag core-shell nanocubes for efficient plasmonic light scattering effect in low bandgap organic solar cells.

    PubMed

    Baek, Se-Woong; Park, Garam; Noh, Jonghyeon; Cho, Changsoon; Lee, Chun-Ho; Seo, Min-Kyo; Song, Hyunjoon; Lee, Jung-Yong

    2014-04-22

    In this report, we propose a metal-metal core-shell nanocube (NC) as an advanced plasmonic material for highly efficient organic solar cells (OSCs). We covered an Au core with a thin Ag shell as a scattering enhancer to build Au@Ag NCs, which showed stronger scattering efficiency than Au nanoparticles (AuNPs) throughout the visible range. Highly efficient plasmonic organic solar cells were fabricated by embedding Au@Ag NCs into an anodic buffer layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and the power conversion efficiency was enhanced to 6.3% from 5.3% in poly[N-9-hepta-decanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PCDTBT):[6,6]-phenyl C71-butyric acid methyl ester (PC70BM) based OSCs and 9.2% from 7.9% in polythieno[3,4-b]thiophene/benzodithiophene (PTB7):PC70BM based OSCs. The Au@Ag NC plasmonic PCDTBT:PC70BM-based organic solar cells showed 2.2-fold higher external quantum efficiency enhancement compared to AuNPs devices at a wavelength of 450-700 nm due to the amplified plasmonic scattering effect. Finally, we proved the strongly enhanced plasmonic scattering efficiency of Au@Ag NCs embedded in organic solar cells via theoretical calculations and detailed optical measurements.

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

    PubMed

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

    2016-11-07

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

  14. Collective global dynamics in Au+Au collisions at the BNL AGS

    NASA Astrophysics Data System (ADS)

    Bravina, L.; Csernai, L. P.; Lévai, P.; Strottman, D.

    1994-10-01

    Signatures of collective effects are studied in the quark gluon string model and in the fluid dynamical model for Au+Au collisions at 11.6A GeV/c. In the fluid dynamical model the dependence of observables on the quark-gluon plasma (QGP) formation in the equation of state is pointed out although the maximal total amount of pure QGP formed is only about 8 fm3 in these reactions. In contrast to the baryon rapidity distribution, the in-plane transverse flow and especially the squeeze-out effect are particularly sensitive to the EOS. In the QGSM the lifetime and extent of baryon density in strings are studied. The QGSM picture is very similar to the one obtained in the fluid dynamical model with a pure hadronic EOS.

  15. Nonlinear optical properties of Au-Ag core-shell nanorods for all-optical switching

    NASA Astrophysics Data System (ADS)

    Zhang, Luman; Dai, Hongwei; Wang, Xia; Yao, Linhua; Ma, Zongwei; Han, Jun-Bo

    2017-09-01

    Au-Ag core-shell nanorods with surface plasmon resonance wavelengths of 760-840 nm were prepared. Wavelength-dependent nonlinear absorption coefficients (β) and nonlinear refractive indices (γ) of the nanorods were measured by using Z-scan techniques. The corresponding one-photon and two-photon figures of merit (W and T) were calculated from β and γ. The results show that the requirements of W  >  1 and T  <  1 for the application of all-optical switching could be achieved for all the samples over a broad wavelength range. These observations make the Au-Ag core-shell nanorods a good candidate for all-optical switching devices.

  16. Polynuclear Gold [AuI]4, [AuI]8, and Bimetallic [AuI 4AgI] Complexes: C−H Functionalization of Carbonyl Compounds and Homogeneous Carbonylation of Amines

    PubMed Central

    Smirnova, Ekaterina S.; Muñoz Molina, José M.; Johnson, Alice; Bandeira, Nuno A. G.; Bo, Carles

    2016-01-01

    Abstract The synthesis of tetranuclear gold complexes, a structurally unprecedented octanuclear complex with a planar [AuI 8] core, and pentanuclear [AuI 4MI] (M=Cu, Ag) complexes is presented. The linear [AuI 4] complex undergoes C−H functionalization of carbonyl compounds under mild reaction conditions. In addition, [AuI 4AgI] catalyzes the carbonylation of primary amines to form ureas under homogeneous conditions with efficiencies higher than those achieved by gold nanoparticles. PMID:27167611

  17. 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.

    PubMed

    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.

  18. Plasmonic effects of au/ag bimetallic multispiked nanoparticles for photovoltaic applications.

    PubMed

    Sharma, Manisha; Pudasaini, Pushpa Raj; Ruiz-Zepeda, Francisco; Vinogradova, Ekaterina; Ayon, Arturo A

    2014-09-10

    In recent years, there has been considerable interest in the use of plasmons, that is, free electron oscillations in conductors, to boost the performance of both organic and inorganic thin film solar cells. This has been driven by the possibility of employing thin active layers in solar cells in order to reduce materials costs, and is enabled by significant advances in fabrication technology. The ability of surface plasmons in metallic nanostructures to guide and confine light in the nanometer scale has opened up new design possibilities for solar cell devices. Here, we report the synthesis and characterization of highly monodisperse, reasonably stable, multipode Au/Ag bimetallic nanostructures using an inorganic additive as a ligand for photovoltaic applications. A promising surface enhanced Raman scattering (SERS) effect has been observed for the synthesized bimetallic Au/Ag multispiked nanoparticles, which compare favorably well with their Au and Ag spherical nanoparticle counterparts. The synthesized plasmonic nanostructures were incorporated on the rear surface of an ultrathin planar c-silicon/organic polymer hybrid solar cell, and the overall effect on photovoltaic performance was investigated. A promising enhancement in solar cell performance parameters, including both the open circuit voltage (VOC) and short circuit current density (JSC), has been observed by employing the aforementioned bimetallic multispiked nanoparticles on the rear surface of solar cell devices. A power conversion efficiency (PCE) value as high as 7.70% has been measured in a hybrid device with Au/Ag multispiked nanoparticles on the rear surface of an ultrathin, crystalline silicon (c-Si) membrane (∼ 12 μm). This value compares well to the measured PCE value of 6.72% for a similar device without nanoparticles. The experimental observations support the hope for a sizable PCE increase, due to plasmon effects, in thin-film, c-Si solar cells in the near future.

  19. Anchoring of Ag-Au alloy nanoparticles on reduced graphene oxide sheets for the reduction of 4-nitrophenol

    NASA Astrophysics Data System (ADS)

    Hareesh, K.; Joshi, R. P.; D. V., Sunitha; Bhoraskar, V. N.; Dhole, S. D.

    2016-12-01

    One-step gamma radiation assisted method has been used for the synthesis of Silver-Gold (Ag-Au) alloy nanoparticles with simultaneous reduction of graphene oxide (GO). UV-vis spectroscopic results along with X-ray diffraction analysis, X-ray Photoelectron spectroscopy and Transmission electron microscopy confirmed the decoration face centered cubic structured Ag-Au nanoparticles of size (5-19) nm on reduced graphene oxide (rGO) sheets. The increase in disorder parameter in Raman spectroscopy indicates the formation of more number of small sp2 domains. The synthesized Ag-Au-rGO nanocomposite showed enhanced catalytic activity towards the reduction of 4-Nitrophenol compared to individual Ag-Au and rGO components.

  20. AuAg bimetallic nonalloyed nanoparticles on a periodically nanostructured GaAs substrate for enhancing light trapping.

    PubMed

    Lee, Soo Kyung; Tan, Chee Leong; Ju, Gun Wu; Song, Jae Hong; Yeo, Chan Il; Lee, Yong Tak

    2015-12-15

    We present a light trapping structure consisting of AuAg bimetallic nonalloyed nanoparticles (BNNPs) on cone-shaped GaAs subwavelength structures (SWSs), combining the advantages of plasmonic structures and SWSs for GaAs-based solar cell applications. To obtain efficient light trapping in solar cells, the optical properties' dependence on the size and composition of the Ag and Au metal nanoparticles was systematically investigated. Cone-shaped GaAs SWSs with AuAg BNNPs formed from an Au film of 12 nm and an Ag film of 10 nm exhibited the extremely low average reflectance (R(avg)) of 2.43% and the solar-weighted reflectance (SWR) of 2.38%, compared to that of a bare GaAs substrate (R(avg), 37.50%; SWR, 36.72%) in the wavelength range of 300 to 870 nm.

  1. Determining the Concentration Dependent Transformations of Ag Nanoparticles in Complex Media: Using SP-ICP-MS and Au@Ag Core-Shell Nanoparticles as Tracers.

    PubMed

    Merrifield, Ruth C; Stephan, Chady; Lead, Jamie

    2017-03-21

    The fate, behavior, and impact of engineered nanoparticles (NPs) in toxicological and environmental media are driven by complex processes which are difficult to quantify. A key limitation is the ability to perform measurements at low and environmentally relevant concentrations, since concentration may be a key factor determining fate and effects. Here, we use single particle inductively coupled mass spectroscopy (SP-ICP-MS) to measure directly NP diameter and particle number concentration of suspensions containing gold-silver core-shell (Au@Ag) NPs in EPA moderately hard water (MHW) and MHW containing 2.5 mg L(-1) Suwannee River fulvic acid. The Au core of the Au@Ag NPs acts as an internal standard, and aids in the analysis of the complex Ag transformations. The high sensitivity of SP-ICP-MS, along with the Au@Ag NPs, enabled us to track the NP transformations in the range 0.01 and 50 μg L(-1), without further sample preparation. On the basis of the analysis of both Au and Ag parameters (size, size distribution, and particle number), concentration was shown to be a key factor in NP behavior. At higher concentration, NPs were in an aggregation-dominated regime, while at the lower and environmentally representative concentrations, dissolution of Ag was dominant and aggregation was negligible. In addition, further formation of ionic silver as Ag NPs in the form of AgS or AgCl was shown to occur. Between 1 and 10 μg L(-1), both aggregation and dissolution were important. The results suggest that, under realistic conditions, the role of NP homoaggregation may be minimal. In addition, the complexity of exposure and dose in dose-response relationships is highlighted.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Wilcoxon, Jess; Martin, James

    2001-03-01

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

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

    NASA Astrophysics Data System (ADS)

    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.

  6. First principles investigation of the diffusion of interstitial Cu, Ag and Au in ZnTe

    NASA Astrophysics Data System (ADS)

    Chen, Li An; Zhu, Xing Feng; Chen, Ling Fu

    2015-07-01

    The diffusion is of great significance in many applications when the impurities are employed to tune the semiconductor's electrical or optical properties. It is necessary to understand how dopant defects diffuse in semiconductors. Using first-principles calculations, we consider interstitial diffusion mechanisms and calculate the migration barrier energies of interstitial Cu, Ag and Au atoms in II-VI compounds ZnTe. We find that the relative size of dopant and bulk atoms is an important factor which affects the diffusion behavior. The high symmetry Tc site, which is tetrahedrally coordinated by four cation atoms, is the global minimum energy location for Ag and Au interstitials. The size of Cu adatom is small, so Cu is more stable when it locates at the Ta site which is tetrahedrally coordinated by four anion atoms. But the global minimum energy location for Cu interstitials is M site which is of smaller space than Ta. Cu adatoms show an asymmetric curve of energy diffusion barrier with two energetically distinct extremum in the pathway. Ag diffuses along nearly straight line paths along [111] or equivalent directions. Diffusion for Cu or Au deviates from the straight line paths along <111> avoiding high symmetric sites.

  7. Cooperative plasmonic effect of Ag and Au nanoparticles on enhancing performance of polymer solar cells.

    PubMed

    Lu, Luyao; Luo, Zhiqiang; Xu, Tao; Yu, Luping

    2013-01-09

    This article describes a cooperative plasmonic effect on improving the performance of polymer bulk heterojunction solar cells. When mixed Ag and Au nanoparticles are incorporated into the anode buffer layer, dual nanoparticles show superior behavior on enhancing light absorption in comparison with single nanoparticles, which led to the realization of a polymer solar cell with a power conversion efficiency of 8.67%, accounting for a 20% enhancement. The cooperative plasmonic effect aroused from dual resonance enhancement of two different nanoparticles. The idea was further unraveled by comparing Au nanorods with Au nanoparticles for solar cell application. Detailed studies shed light into the influence of plasmonic nanostructures on exciton generation, dissociation, and charge recombination and transport inside thin film devices.

  8. Crystalline monolayer surface of liquid Au-Cu-Si-Ag-Pd: Metallic glass former

    SciTech Connect

    Mechler, S; Yahel, E; Pershan, P S; Meron, M; Lin, B

    2012-02-06

    It is demonstrated by means of x-ray synchrotron reflectivity and diffraction that the surface of the liquid phase of the bulk metallic glass forming alloy Au49Cu26.9Si16.3Ag5.5Pd2.3 consists of a two-dimensional crystalline monolayer phase for temperatures of up to about 50 K above the eutectic temperature. The present alloy as well as glass forming Au82Si18 and Au-Si-Ge alloys containing small amounts of Ge are the only metallic liquids to exhibit surface freezing well above the melting temperature. This suggests that the phenomena of surface freezing in metallic liquids and glass forming ability are related and probably governed by similar physical properties.

  9. Loading Ag nanoparticles on Cd(II) boron imidazolate framework for photocatalysis

    SciTech Connect

    Liu, Min; Zhang, De-Xiang; Chen, Shumei; Wen, Tian

    2016-05-15

    An amine-functionalized Cd(II) boron imidazolate framework (BIF-77) with three-dimensional open structure has been successfully synthesized, which can load Ag nanoparticles (NPs) for photocatalytic degradation of methylene blue (MB). - Graphical abstract: An amine-functionalized neutral Cd(II) boron imidazolate framework can load Ag NPs and show excellent photocatalytic degradation behavious for MB. - Highlights: • Amine-functionalization. • Neutral boron imidazolate framework. • Loading Ag nanoparticles (NPs). • Photocatalytic degradation of methylene blue.

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

    PubMed

    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.

  11. Raman scattering of 4-aminobenzenethiol sandwiched between Ag nanoparticle and macroscopically smooth Au substrate: effects of size of Ag nanoparticles and the excitation wavelength.

    PubMed

    Kim, Kwan; Choi, Jeong-Yong; Lee, Hyang Bong; Shin, Kuan Soo

    2011-09-28

    A nanogap formed by a metal nanoparticle and a flat metal substrate is one kind of "hot site" for surface-enhanced Raman scattering (SERS). Accordingly, although no Raman signal is observable when 4-aminobenzenethiol (4-ABT), for instance, is self-assembled on a flat Au substrate, a distinct spectrum is obtained when Ag or Au nanoparticles are adsorbed on the pendent amine groups of 4-ABT. This is definitely due to the electromagnetic coupling between the localized surface plasmon of Ag or Au nanoparticle with the surface plasmon polariton of the planar Au substrate, allowing an intense electric field to be induced in the gap even by visible light. To appreciate the Raman scattering enhancement and also to seek the optimal condition for SERS at the nanogap, we have thoroughly examined the size effect of Ag nanoparticles, along with the excitation wavelength dependence, by assembling 4-ABT between planar Au and a variable-size Ag nanoparticle (from 20- to 80-nm in diameter). Regarding the size dependence, a higher Raman signal was observed when larger Ag nanoparticles were attached onto 4-ABT, irrespective of the excitation wavelength. Regarding the excitation wavelength, the highest Raman signal was measured at 568 nm excitation, slightly larger than that at 632.8 nm excitation. The Raman signal measured at 514.5 and 488 nm excitation was an order of magnitude weaker than that at 568 nm excitation, in agreement with the finite-difference time domain simulation. It is noteworthy that placing an Au nanoparticle on 4-ABT, instead of an Ag nanoparticle, the enhancement at the 568 nm excitation was several tens of times weaker than that at the 632.8 nm excitation, suggesting the importance of the localized surface plasmon resonance of the Ag nanoparticles for an effective coupling with the surface plasmon polariton of the planar Au substrate to induce a very intense electric field at the nanogap.

  12. Redox-Robust Pentamethylferrocene Polymers and Supramolecular Polymers, and Controlled Self-Assembly of Pentamethylferricenium Polymer-Embedded Ag, AgI, and Au Nanoparticles.

    PubMed

    Gu, Haibin; Ciganda, Roberto; Castel, Patricia; Vax, Amélie; Gregurec, Danijela; Irigoyen, Joseba; Moya, Sergio; Salmon, Lionel; Zhao, Pengxiang; Ruiz, Jaime; Hernández, Ricardo; Astruc, Didier

    2015-12-07

    We report the first pentamethylferrocene (PMF) polymers and the redox chemistry of their robust polycationic pentamethylferricenium (PMFium) analogues. The PMF polymers were synthesized by ring-opening metathesis polymerization (ROMP) of a PMF-containing norbornene derivative by using the third-generation Grubbs ruthenium metathesis catalyst. Cyclic voltammetry studies allowed us to determine confidently the number of monomer units in the polymers through the Bard-Anson method. Stoichiometric oxidation by using ferricenium hexafluorophosphate quantitatively and instantaneously provided fully stable (even in aerobic solutions) blue d(5) Fe(III) metallopolymers. Alternatively, oxidation of the PMF-containing polymers was conducted by reactions with Ag(I) or Au(III) , to give PMFium polymer-embedded Ag and Au nanoparticles (NPs). In the presence of I2 , oxidation by using Ag(I) gave polymer-embedded Ag/AgI NPs and AgNPs at the surface of AgI NPs. Oxidation by using Au(III) also produced an Au(I) intermediate that was trapped and characterized. Engineered single-electron transfer reactions of these redox-robust nanomaterial precursors appear to be a new way to control their formation, size, and environment in a supramolecular way. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Synthesis of multifunctional Ag@Au@phenol formaldehyde resin particles loaded with folic acids for photothermal therapy.

    PubMed

    Yang, Ping; Xu, Qi-Zhi; Jin, Sheng-Yu; Lu, Yang; Zhao, Yang; Yu, Shu-Hong

    2012-07-23

    Multifunctional Ag@Au@ phenol formaldehyde resin (PFR) particles loaded with folic acids (FA) have been designed for killing tumor cells through photothermy conversion under the irradiation of near-infrared (NIR) light. Possessing the virtue of good fluorescence, low toxicity, and good targeting, the nanocomposite consists of an Ag core, an Au layer, a PFR shell, and folic acids on the PFR shell. The Ag@PFR core-shell structure can be prepared with a simple hydrothermal method after preheating. We then filled the PFR shell with a layer of Au by heating and modified the shell with polyelectrolyte to change its surface charge state. To capture tumor cells actively, FA molecules were attached onto the surface of the Ag@Au@PFR particles in the presence of 1-ethyl-3-(3-dimethly aminopropyl) carbodiimide (EDAC) and N-hydroxysuccinimide (NHS). Owing to the excellent property of Au NPs and Ag NPs as photothermal conversion agents, the Ag@Au@ PFR@FA particles can be utilized to kill tumor cells when exposed to NIR light.

  14. Enhanced photocatalytic degradation of sulfamethoxazole by deposition of Au, Ag and Cu metallic nanoparticles on TiO2.

    PubMed

    Zanella, Rodolfo; Avella, Edwin; Ramírez-Zamora, Rosa María; Castillón-Barraza, Felipe; Durán-Álvarez, Juan C

    2017-07-26

    Mono- (Au, Ag and Cu) and bi-metallic (Au-Ag and Au-Cu) nanoparticles were deposited on TiO2 and tested for the photocatalytic degradation of sulfamethoxazole using either UV-C or simulated sunlight. The optimal loading of metallic nanoparticles was determined as 1.5 wt% for Au and Ag, and 1.0 wt% for Cu. In the case of bi-metallic nanoparticles, only the ratio 1:0.5 wt% for both Au-Ag and Au-Cu was tested. In experiments using UV-C light, the highest degradation performance was found for Ag/TiO2, while bi-metallic nanoparticles supported on TiO2 also showed increased photocatalytic activity compared with unmodified TiO2. In simulated sunlight irradiation tests, Au/TiO2 showed to be the most efficient material. Complete mineralization of sulfamethoxazole was achieved when surface-modified materials were tested in both UV-C and simulated sunlight experiments. Photolysis was efficient to fully degrade sulfamethoxazole, although mineralization was lower than 10% for both luminic sources. The main by-products of sulfamethoxazole were determined in photolysis and photocatalysis tests using UV-C light, and degradation paths were proposed. By-products showed non-toxicity and low antibiotic activity. Reuse of the catalysts upon three reaction cycles did not result in the loss of activity.

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

    PubMed

    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.

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

    EPA Science Inventory

    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...

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

    EPA Science Inventory

    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...

  18. Enhanced photoluminescence of CdSe quantum dots by the coupling of Ag nanocube and Ag film

    NASA Astrophysics Data System (ADS)

    Jiang, Tong-Tong; Shao, Wei-Jia; Yin, Nai-Qiang; Liu, Ling; Song, Jiang-Lu-Qi; Zhu, Li-Xin; Xu, Xiao-Liang

    2014-08-01

    The coupling of local surface plasmon (LSP) of nanoparticle and surface plasmon (SP) mode produced by metal film can lead to the enhanced electromagnetic field, which has an important application in enhancing the fluorescence of quantum dots (QDs). Herein, the Ag nanocube and Ag film are used to enhance the fluorescence of CdSe QDs. The enhancement is found to relate to the sizes of the Ag nanocube and the thickness of the Ag film. Moreover, we also present the fluorescence enhancement caused by only SP. The result shows that the coupling between metal nanoparticles and metal film can realize larger field enhancement. Numerical simulation verifies that a nanocube can localize a strong electric field around its corner. All the results indicate that the fluorescence of QDs can be efficiently improved by optimizing the parameters of Ag film and Ag cubes.

  19. All-thiol-stabilized Ag44 and Au12Ag32 nanoparticles with single-crystal structures.

    PubMed

    Yang, Huayan; Wang, Yu; Huang, Huaqi; Gell, Lars; Lehtovaara, Lauri; Malola, Sami; Häkkinen, Hannu; Zheng, Nanfeng

    2013-01-01

    Noble metal nanoparticles stabilized by organic ligands are important for applications in assembly, site-specific bioconjugate labelling and sensing, drug delivery and medical therapy, molecular recognition and molecular electronics, and catalysis. Here we report crystal structures and theoretical analysis of three Ag44(SR)30 and three Au12Ag32(SR)30 intermetallic nanoclusters stabilized with fluorinated arylthiols (SR=SPhF, SPhF2 or SPhCF3). The nanocluster forms a Keplerate solid of concentric icosahedral and dodecahedral atom shells, protected by six Ag2(SR)5 units. Positive counterions in the crystal indicate a high negative charge of 4(-) per nanoparticle, and density functional theory calculations explain the stability as an 18-electron superatom shell closure in the metal core. Highly featured optical absorption spectra in the ultraviolet-visible region are analysed using time-dependent density functional perturbation theory. This work forms a basis for further understanding, engineering and controlling of stability as well as electronic and optical properties of these novel nanomaterials.

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

    PubMed Central

    Mailu, Stephen N.; Waryo, Tesfaye T.; Ndangili, Peter M.; Ngece, Fanelwa R.; Baleg, Abd A.; Baker, Priscilla G.; Iwuoha, Emmanuel I.

    2010-01-01

    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. PMID:22163419

  1. Determination of anthracene on Ag-Au alloy nanoparticles/overoxidized-polypyrrole composite modified glassy carbon electrodes.

    PubMed

    Mailu, Stephen N; Waryo, Tesfaye T; Ndangili, Peter M; Ngece, Fanelwa R; Baleg, Abd A; Baker, Priscilla G; Iwuoha, Emmanuel I

    2010-01-01

    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 AgNO(3) and HAuCl(4) using C(6)H(5)O(7)Na(3) 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.

  2. A coherent phase diagram of the [(AuCu)0.86Ag0.14]1-XPtX pseudobinary section in Au-Cu-Ag-Pt quaternary system.

    PubMed

    Sakrana, A A; Tanaka, Y; Udoh, K; Hisatsune, K; Atsuta, M; Yasuda, K

    1997-12-01

    In order to determine a coherent phase diagram of the [(AuCu)0.86Ag0.14]1-XPtX pseudobinary system, phase identifications and analyses of the microstructural configurations were performed by means of transmission electron microscopy. Various phase regions were detected in the coherent phase diagram as follows; (1) alpha 0 (fcc) single phase region, (2) two-phase region (alpha 1 + alpha 2), (3) AuCu I (L10) + alpha 0, (4) AuCu I + alpha 2, (5) AuCu II (L10-S) + alpha 2, (6) AuCu I + AuCu II + alpha 2, (7) AuCu I single phase region. Microstructural features of these regions relating to the phase transformations were described.

  3. Lithogeochemistry and fluid inclusions of an Au-Ag vein deposit in a granodiorite intrusive

    SciTech Connect

    Hahn, R.; Ikramuddin, M.

    1985-01-01

    Forty-eight samples of altered and unaltered rocks and quartz veins from the Acme mine in northeast Washington, an Au-Ag vein deposit in a granodiorite intrusive, have been analyzed for SiO/sub 2/, Al/sub 2/O/sub 3/, Fe/sub 2/O/sub 3/, Feo, MgO, CaO, Na/sub 2/O, K/sub 2/O, TiO/sub 2/, MnO, P/sub 2/O/sub 5/, H/sub 2/O, CO/sub 2/, Ag, Au, Ba, Cu, Pb, Rb, Sr, Tl, and Zn. A comparison of major and trace elements shows that the altered granodiorite is enriched in SiO/sub 2/, Fe/sub 2/O/sub 3/, K/sub 2/O, Ag, Au, Ba, Cu, Pb, Rb, Tl, and Zn and depleted in Al/sub 2/O/sub 3/, FeO, MgO, CaO, Na/sub 2/O, TiO/sub 2/, MnO, P/sub 2/O/sub 5/, and Sr. The average contents of Au in unaltered and altered granodiorite and quartz veins are 9 ppb. 270 ppb and 1020 ppb respectively. The average Ba/Tl ratio in the altered samples decrease and average Rb/Sr and Tl/Sr ratios increase. K, Rb, and Tl are enriched in the altered granodiorite by factors of 1.5, 1.6, and 1.4 respectively. Tl is not enriched relative to Rb and K in the altered samples due to the high temperature of the deposit. The Ba/Tl, K/Tl and K/Rb ratios do not show complete separation of altered from unaltered samples. However, the Ba/Tl and K/Tl ratios in the quartz vein are significantly lower than the unaltered and altered granodiorite. This is due to the enrichment of Tl over K and Rb in the quartz veins. The Rb/Sr and Tl/Sr ratios are higher in the altered granodiorite and quartz veins compared to unaltered samples. The enrichment of Tl and presence of low Ba/Tl and high Rb/Sr and Tl/Sr ratios in a granodiorite indicate that the rocks are hydrothermally altered and represent a possible Au-Ag target.

  4. Ehrlich-Schwöbel barriers and adsorption of Au, Cu and Ag stepped (100) surfaces

    NASA Astrophysics Data System (ADS)

    Benlattar, M.; Elkoraychy, E.; Sbiaai, K.; Mazroui, M.; Boughaleb, Y.

    2017-02-01

    We use a combination of quenched molecular dynamics and embedded atom method to calculate the activation energy barriers for the hopping and exchange mechanisms of Au, Ag or Cu on Au(100), Ag(100) or Cu(100) stepped surfaces. Our findings show that the Ehrlich-Schwöbel (ES) barriers for an adatom to undergo jump or exchange at a step edge are found to be dependent of the nature of substrate stepped surfaces. We also find that the ES barriers for the hopping processes are too high, except for Cu/Au(100). While for exchange process the Ehrlich-Schwöbel barriers are found to be very low and even negative. These ES barriers can explain the difference in the growth modes for the different systems. On the other hand, we calculated the adsorption energies at the most stable adsorption sites near step edges. In particular, we wish to clarify the relation between the adatom diffusion energy barriers and the adatom adsorption energies. These results may serve as some guiding rules for studying stepped surface morphologies, which are of importance to surface nanoengineering.

  5. Cysteamine coated Ag and Au nanorods for improved surface enhanced Raman scattering from dinitrotoluene and trinitrotoluene

    NASA Astrophysics Data System (ADS)

    Glembocki, O. J.; Gowda, M.; Geng, S.; Prokes, S. M.; Garces, N. Y.; Cushen, J.; Caldwell, J. D.

    2010-08-01

    Surface-enhanced Raman scattering (SERS) from trinitrotoluene and other nitro-based explosives is important for the development of a reliable detection scheme exhibiting low false-positive rates. However, the interaction of these compounds with Ag and Au causes the molecules to orient in ways such that the primary vibrations of the nitro groups, the main identifying Raman marker of these compounds, are inhibited in addition to causing a reduction in the SERS response. It has recently been shown that cysteamine, which contains amine functional end groups, will electrostatically attract the nitro groups of TNT. Therefore, as the thiol functional group of cysteamine chemically bonds this molecule to the plasmonically-active Au and Ag nanoparticles studied, SERS of TNT can be obtained following the nitro-amine functional group complex formation. It is observed that the cysteamine adsorbs in one of two configurations on the metal surface, with the trans configuration consisting of bonding at the S end of the molecule and the cysteamine is perpendicular to the metal surface, while in the Gauche configuration S bonding occurs, but the molecule bends over towards the metal film surface, approaching the parallel configuration allowing the amine groups interact with the surface. We find that the trans configuration is best for the detection of SERS from TNT. Experiments compare well with DFT calculations of the cysteamine and TNT complex and their adsorption on Ag.

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

    NASA Astrophysics Data System (ADS)

    Zaporojtchenko, V.; Podschun, R.; Schürmann, U.; Kulkarni, A.; Faupel, F.

    2006-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Kaur, Gagandeep; Gupta, Shuchi; Dharamvir, Keya

    2013-06-01

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

  8. Properties of Ag layered in Te/Cd stack prepared by stacked elemental layer method

    NASA Astrophysics Data System (ADS)

    Subramani, Shanmugan; Devarajan, Mutharasu; Ibrahim, Kamarulazizi

    2012-06-01

    Ag layered Te/Cd stack thin films (<1 µm thick) were prepared by the Stacked Elemental Layer (SEL) method. The XRD results revealed that the synthesized films had a polycrystalline nature. The synthesized films were preferentially oriented with (111) directions with a cubic phase. Structural studies were evidenced the formation of Ag related alloys at high annealing temperatures as a result of thermal diffusion in elemental stack. Optical and photo-resistivity studies revealed the influence of Ag on the CdTe lattice at high annealing temperatures. Surface morphology and the influence of Ag atoms on surface roughness are also presented.

  9. A novel intermediate layer for Au/CdZnTe/FTO photoconductive structure

    NASA Astrophysics Data System (ADS)

    Zhang, Yuelu; Wang, Linjun; Xu, Run; Huang, Jian; Tao, Jun; Meng, Hua; Zhang, Jijun; Min, Jiahua

    2016-12-01

    In this work, graphene is tried to use to improve the performance of polycrystalline CdZnTe high-energy radiation and photon detectors. A graphene intermediate layer is prepared by spin-coating process on the surface of polycrystalline CdZnTe film, which forms a photoconductive Au/graphene/CdZnTe/FTO structure. XRD, Raman, photoelectric response and other characterisation methods are adopted to investigate the effect of graphene layer on the electrical characteristics and UV photo-response performance of CdZnTe photoconductive structure. It is demonstrated that graphene layer can significantly improve the contact property of Au/CdZnTe structure, and obviously enhance its UV photo-response and the UV sensitivity increased with one order of magnitude.

  10. Luminescent Di and Polynuclear Organometallic Gold(I)-M (Au2, {Au2Ag}n and {Au2Cu}n) Compounds Containing Bidentate Phosphanes as Active Antimicrobial Agents

    PubMed Central

    Frik, Malgorzata; Jiménez, Josefina; Gracia, Ismael; Falvello, Larry R.; Abi-Habib, Sarya; Suriel, Karina; Muth, Theodore R.

    2012-01-01

    The reaction of new dinuclear gold(I) organometallic complexes containing mesityl ligands and bridging bidentate phosphanes [Au2(mes)2(μ-LL)] (LL = dppe: 1,2-Bis(di-phenylphosphano)ethane 1a, and water-soluble dppy: 1,2-Bis(di-3-pyridylphosphano)ethane 1b) with Ag+ and Cu+ lead to the formation of a family of heterometallic clusters with mesityl bridging ligands of the general formula [Au2M(μ-mes)2(μ-LL)]A (M = Ag, A = ClO4−, L-L = dppe 2a, dppy 2b; M = Ag, A = SO3CF3−, L-L = dppe 3a, dppy 3b; M = Cu, A = PF6−, L-L = dppe 4a, dppy 4b). The new compounds were characterized by different spectroscopic techniques and mass spectrometry The crystal structures of [Au2(mes)2(μ-dppy)] 1b and [Au2Ag(μ-mes)2(μ-dppe)]SO3CF3 3a were determined by a single-crystal X-ray diffraction study. 3a in solid state is not a cyclic trinuclear Au2Ag derivative but it gives an open polymeric structure instead, with the {Au2(μ-dppe)} fragments “linked” by Ag(μ-mes)2 units. The very short distances of 2.7559(6) Å (Au-Ag) and 2.9229(8) Å (Au-Au) are indicative of gold-silver (metallophillic) and aurophilic interactions. A systematic study of their luminescence properties revealed that all compounds are brightly luminescent in solid state, at room temperature (RT) and at 77 K, or in frozen DMSO solutions with lifetimes in the microsecond range and probably due to the self-aggregation of [Au2M(μ-mes)2(μ-LL)]+ units (M= Ag or Cu; LL= dppe or dppy) into an extended chain structure, through Au-Au and/or Au-M metallophylic interactions, as that observed for 3a. In solid state the heterometallic Au2M complexes with dppe (2a–4a) show a shift of emission maxima (from ca. 430 to the range of 520–540 nm) as compared to the parent dinuclear organometallic product 1a while the complexes with dppy (2b–4b) display a more moderate shift (505 for 1b to a max of 563 nm for 4b). More importantly, compound [Au2Ag(μ-mes)2(μ-dppy)]ClO4 2b resulted luminescent in diluted DMSO solution

  11. Relativistic Effects and Gold Site Distributions: Synthesis, Structure, and Bonding in a Polar Intermetallic Na6Cd16Au7

    SciTech Connect

    Samal, Saroj L.; Corbett, John D.

    2011-07-05

    Na{sub 6}Cd{sub 16}Au{sub 7} has been synthesized via typical high-temperature reactions, and its structure refined by single crystal X-ray diffraction as cubic, Fm{bar 3}m, a = 13.589(1) {angstrom}, Z = 4. The structure consists of Cd{sub 8} tetrahedral star (TS) building blocks that are face capped by six shared gold (Au2) vertexes and further diagonally bridged via Au1 to generate an orthogonal, three-dimensional framework [Cd{sub 8}(Au2){sub 6/2}(Au1){sub 4/8}], an ordered ternary derivative of Mn{sub 6}Th{sub 23}. Linear muffin-tin-orbital (LMTO)-atomic sphere approximation (ASA) electronic structure calculations indicate that Na{sub 6}Cd{sub 16}Au{sub 7} is metallic and that {approx}76% of the total crystal orbital Hamilton populations (-ICOHP) originate from polar Cd-Au bonding with 18% more from fewer Cd-Cd contacts. Na{sub 6}Cd{sub 16}Au{sub 7} (45 valence electron count (vec)) is isotypic with the older electron-richer Mg{sub 6}Cu{sub 16}Si{sub 7} (56 vec) in which the atom types are switched and bonding characteristics among the network elements are altered considerably (Si for Au, Cu for Cd, Mg for Na). The earlier and more electronegative element Au now occupies the Si site, in accord with the larger relativistic bonding contributions from polar Cd-Au versus Cu-Si bonds with the neighboring Cd in the former Cu positions. Substantial electronic differences in partial densities-of-states (PDOS) and COHP data for all atoms emphasize these. Strong contributions of nearby Au 5d{sup 10} to bonding states without altering the formal vec are the likely origin of these effects.

  12. The chemistry and structure of ?222? CdO/Ag heterophase interfaces on an atomic scale

    NASA Astrophysics Data System (ADS)

    Chan, D. K.; Seidman, D. N.; Merkle, K. L.

    1996-03-01

    The chemistry and structure of {222} CdO/Ag (ceramic/metal) heterophase interfaces are determined with sub-nanometer chemical and structural spatial resolution employing atom-probe field-ion and high-resolution electron microscopies. The interfaces are produced in a controlled manner via internal oxidation of a Ag1.62at%Cd alloy, which results in the formation of CdO precipitates in a Ag matrix. The CdO precipitates are octahedral-shaped with facets on the {222} polar planes, and have a cube-on-cube orientation relationship with the Ag matrix. Atom-probe analyses are made along the chemically-ordered CdO <111>-type directions, thereby perpendicularly intersecting the {222} interfaces. A total of 35 {222} heterophase interfaces is chemically analyzed, of which 19 have the chemical sequence Ag|O|Cd|… and 16 the sequence Ag|Cd|O|…. High resolution electron microscopy analyses reveal that the {222} facet planes of the CdO precipitates con atomic height ledges, therefore indicating that the preciptates were in a coarsening stage. The combined atom-probe and high-resolution electron microscope results demonstrate that the chemistry of the terminating {222} facet plane of CdO is controlled by coarsening kinetics.

  13. First Principles Calculations on the Diffusion of Cu, Ag and Au Atoms or Aggregates on the Bulk and Surface of Titania

    DTIC Science & Technology

    2011-04-01

    AFRL-AFOSR-UK-TR-2011-0002 First Principles Calculations on the Diffusion of Cu, Ag and Au Atoms or Aggregates on the Bulk and...SUBTITLE First Principles Calculations on the Diffusion of Cu, Ag and Au Atoms or Aggregates on the Bulk and Surface of Titania 5a. CONTRACT...093072 Final report First principles calculations on the diffusion of Cu, Ag and Au atoms or aggregates on the bulk and surface of titania List

  14. Relativistic effects on the nuclear magnetic shielding in the MF (M=Cu, Ag, Au) series

    SciTech Connect

    David, Jorge; Restrepo, Albeiro

    2007-11-15

    Relativistic effects on the nuclear magnetic shielding {sigma}(M) of the series of diatomics MF (M=Cu, Ag, Au) are calculated and analyzed using the Dirac-Hartree-Fock (DHF) method in the random phase approximation (RPA). Significant differences due to relativistic effects on the shielding constant {sigma}(M) are found in this series of atoms. The high electronegativity of the fluorine atom works in conjunction with the spin-orbit coupling to increase the calculated value for {sigma}(Au). An unusually large diamagnetic contribution to the shielding constant is observed. Nonrelativistic nuclear magnetic shielding [{sigma}{sup NR}(M)] shows very good linear correlation with the nuclear charge (Z) of the metal, while the relativistic shielding [{sigma}{sup rel}(M)] varies as Z{sup 2.26}.

  15. Chitosan stabilized Ag-Au nanoalloy for colorimetric sensing and 5-Fluorouracil delivery.

    PubMed

    E A K, Nivethaa; S, Dhanavel; Narayanan, V; A, Stephen

    2017-02-01

    Fluorescent CS/Ag-Au (chitosan/silver-gold) nanocomposite containing different weight percentage of Ag and Au was synthesized using the chemical reduction method. 5-Fluorouracil (5-FU) encapsulated nanocomposite was also synthesized and its cytotoxicity towards breast cancer cell lines (MCF-7) studied. The XRD pattern of the nanocomposite shows peaks of chitosan, silver and gold. The peaks corresponding to gold and silver indicate the face centered cubic structure of silver and gold nanoparticles. The polymer matrix nanocomposite structure with chitosan as the matrix and silver-gold as the filler phase is evident from the high resolution transmission electron microscopy (HRTEM) images and an increase in particle size from∼5nm to about 12nm is noticeable on encapsulation of 5-Fluorouracil (5-FU). The presence of fluorine in the case of 5-FU encapsulated nanocomposite and the presence of reflections corresponding to 5-FU in the SAED pattern confirms the encapsulation of 5-FU into the nanocomposite, which is also confirmed by elemental mapping. The presence of a single surface plasmon resonance (SPR) peak in the case of the nanocomposite in a position in between the SPR bands of pure silver and gold nanoparticles confirms the formation of Ag-Au alloy and the elemental mapping results obtained for the nanocomposite also supports the UV-vis results. The photoluminescence (PL) spectrum clearly shows an emission peak in the near infrared region (700-900nm), which makes the nanocomposite suitable for use in cellular imaging. The application of the nanocomposite as a colorimetric sensor was also studied and it was found to be useful for the specific detection of mercury (Hg) without much interference and the detection limit was found to be 5.0×10(-8)M. Copyright © 2016 Elsevier B.V. All rights reserved.

  16. The IP6 micelle-stabilized small Ag cluster for synthesizing Ag-Au alloy nanoparticles and the tunable surface plasmon resonance effect

    NASA Astrophysics Data System (ADS)

    Wang, Na; Wen, Ying; Wang, Yao; Zhang, Rui; Chen, Xiyao; Ling, Bo; Huan, Shuangyan; Yang, Haifeng

    2012-04-01

    The stable small Ag seeds (size in diameter < 10 nm) were obtained in the presence of inositol hexakisphosphoric (IP6) micelles. Then Ag-Au bimetallic nanoparticles were synthesized through a replacement reaction with the rapid interdiffusion process between such small Ag seeds in nanoclusters and HAuCl4. Adjusting the dosage of HAuCl4 resulted in different products, which possessed unique surface plasmon resonances (SPR). The morphologies of the as-made nanoparticles were observed using transmission electron microscopy and field emission scanning electron microscopy and their compositions were determined by energy-dispersive x-ray spectroscopy. Among them, the Ag-Au alloy nanoparticles with the cauliflower-like structure had a suitable SPR for highly sensitive Raman detection application as a surface-enhanced Raman scattering (SERS) substrate with a long-term stability of six months.

  17. Preparation of Ag/Au bimetallic nanostructures and their application in surface-enhanced fluorescence.

    PubMed

    Dong, Jun; Ye, Yanyan; Zhang, Wenhui; Ren, Zebin; Huo, Yiping; Zheng, Hairong

    2015-11-01

    An effective substrate for surface-enhanced fluorescence, which consists of cluster Ag/Au bimetallic nanostructures on a copper surface, was synthesized via a multi-stage galvanic replacement reaction of a Ag cluster in a chlorauric acid (HAuCl4) solution at room temperature. The fabricated silver/gold bimetallic cluster were found to yield large surface-enhanced fluorescence (SEF) enhancement factors for rhodamine 6G probe molecules deposited on the substrate, and also the fluorescence efficiency is critically dependent on the period of nanostructure growth. With the help of proper control reaction conditions, such as the reaction time, and concentration of reaction solutions, the maximum fluorescence enhanced effect was obtained. Therefore, the bimetallic nanostructure substrate also can be adapted to studies in SEF, which will expand the application of SEF.

  18. Femtosecond spectroscopy of electron-electron and electron-phonon energy relaxation in Ag and Au

    NASA Astrophysics Data System (ADS)

    Groeneveld, Rogier H. M.; Sprik, Rudolf; Lagendijk, Ad

    1995-05-01

    We show experimentally that the electron distribution of a laser-heated metal is a nonthermal distribution on the time scale of the electron-phonon (e-ph) energy relaxation time τE. We measured τE in 45-nm Ag and 30-nm Au thin films as a function of lattice temperature (Ti=10-300 K) and laser-energy density (Ul=0.3-1.3 J cm-3), combining femtosecond optical transient-reflection techniques with the surface-plasmon polariton resonance. The experimental effective e-ph energy relaxation time decreased from 710-530 fs and 830-530 fs for Ag and Au, respectively, when temperature is lowered from 300 to 10 K. At various temperatures we varied Ul between 0.3-1.3 J cm-3 and observed that τE is independent from Ul within the given range. The results were first compared to theoretical predictions of the two-temperature model (TTM). The TTM is the generally accepted model for e-ph energy relaxation and is based on the assumption that electrons and lattice can be described by two different time-dependent temperatures Te and Ti, implying that the two subsystems each have a thermal distribution. The TTM predicts a quasiproportional relation between τE and Ti in the perturbative regime where τE is not affected by Ul. Hence, it is shown that the measured dependencies of τE on lattice temperature and energy density are incompatible with the TTM. It is proven that the TTM assumption of a thermal electron distribution does not hold especially under our experimental conditions of low laser power and lattice temperature. The electron distribution is a nonthermal distribution on the picosecond time scale of e-ph energy relaxation. We developed a new model, the nonthermal electron model (NEM), in which we account for the (finite) electron-electron (e-e) and electron-phonon dynamics simultaneously. It is demonstrated that incomplete electron thermalization yields a slower e-ph energy relaxation in comparison to the thermalized limit. With the NEM we are able to give a consistent

  19. Heterodiffusion of Ag adatoms on imperfect Au(1 1 0) surfaces

    NASA Astrophysics Data System (ADS)

    El koraychy, E.; Sbiaai, K.; Mazroui, M.; Ferrando, R.; Boughaleb, Y.

    2017-02-01

    The hetero-diffusion of Ag adatoms on imperfect Au(1 1 0) surfaces is studied using Molecular Dynamics (MD) simulations. The atomic interactions are described by an Embedded Atom Method (EAM) potential. Static activation energies governing various diffusion processes (jumps and exchanges) are calculated by quenched MD, finding that activation energies for interlayer mobility at straight step edges are somewhat larger than those on the flat surface in the cross-channel [1 0 0]-direction, while interlayer barriers at kinks are considerably lower. Dynamic activation energies are calculated at high temperature from the Arrhenius plots of different diffusion mechanisms and compared to static barriers.

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

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; He, Xiao

    2017-10-01

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

  1. Hyperspectral reflected light microscopy of plasmonic Au/Ag alloy nanoparticles incubated as multiplex chromatic biomarkers with cancer cells.

    PubMed

    Patskovsky, Sergiy; Bergeron, Eric; Rioux, David; Simard, Mikaël; Meunier, Michel

    2014-10-21

    A hyperspectral microscopy system based on a reflected light method for plasmonic nanoparticle (NP) imaging was designed and compared with a conventional darkfield method for spatial localization and spectroscopic identification of single Au, Ag and Au/Ag alloy NPs incubated with fixed human cancer cell preparations. A new synthesis protocol based on co-reduction of Au and Ag salts combined with the seeded growth technique was used for the fabrication of monodispersed alloy NPs with sizes ranging from 30 to 100 nm in diameter. We validated theoretically and experimentally the performance of 60 nm Au, Ag and Au/Ag (50 : 50) NPs as multiplexed biological chromatic markers for biomedical diagnostics and optical biosensing. The advantages of the proposed reflected light microscopy method are presented for NP imaging in a complex and highly diffusing medium such as a cellular environment. The obtained information is essential for the development of a high throughput, selective and efficient strategy for cancer detection and treatment.

  2. Fabrication of Au@Ag core-shell NPs as enhanced CT contrast agents with broad antibacterial properties.

    PubMed

    Huo, Da; He, Jian; Li, Hui; Yu, Haiping; Shi, Tingting; Feng, Yahui; Zhou, Zhengyang; Hu, Yong

    2014-05-01

    Au@Ag core-shell nanoparticles (NPs) integrating both antibacterial and X-ray attenuation capabilities were facilely synthesized in aqueous solution. These NPs modified with methoxy-PEG-SH (m-PEG) on the surface rendered them favorable dispersity and stability in water, resulting in enhancement of their blood circulation time. X-ray photoelectron spectroscope (XPS) and high-resolution transmission electron microscope (HRTEM) results confirmed the core-shell structure of m-PEG-Au@Ag NPs. The m-PEG-Au@Ag NPs showed low cytotoxicity and strong X-ray absorption potency in vitro. Further in vivo study showed that as-synthesized NPs offered a pronounced contrast and prolonged their circulation time in the blood stream with negligible toxic effect in vivo. Besides, m-PEG-Au@Ag NPs had significant bacteriostatic effect toward common bacteria like Escherichia coli and Staphylococcus aureus as demonstrated by broth dilution assay. Given their low-cytotoxicity and high CT attenuation efficacy, m-PEG-Au@Ag NPs had a promising potential for use as CT enhancing and antibacterial agents.

  3. Bifunctional Ag@SiO 2 /Au Nanoparticles for Probing Sequential Catalytic Reactions by Surface-Enhanced Raman Spectroscopy

    DOE PAGES

    Wu, Yiren; Su, Dong; Qin, Dong

    2017-02-22

    Here, we report the synthesis of bifunctional Ag@SiO2/Au nanoparticles with an “islands in the sea” configuration by titrating HAuCl4 solution into an aqueous suspension of Ag@SiO2 core–shell nanocubes in the presence of NaOH, ascorbic acid, and poly(vinyl pyrrolidone) at pH 11.9. The NaOH plays an essential role in generating small pores in the SiO2 shell in situ, followed by the epitaxial deposition of Au from the Ag surface through the pores, leading to the formation of Au islands (6–12 nm in size) immersed in a SiO2 sea. Furthermore, by controlling the amount of HAuCl4 titrated into the reaction system, themore » Au islands can be made to pass through and protrude from the SiO2 shell, embracing catalytic activity toward the reduction of 4-nitrophenol to 4-aminophenol by NaBH4. And while the Ag in the core provides a strong surface-enhanced Raman scattering activity, the SiO2 sea helps maintain the Au component as compact, isolated, and stabilized islands. The Ag@SiO2/Au nanoparticles can serve as a bifunctional probe to monitor the stepwise Au-catalyzed reduction of 4-nitrothiophenol to 4-aminothiophenol by NaBH4 and Ag-catalyzed oxidation of 4-aminothiophenol to trans-4,4'-dimercaptoazobenzene by the O2 from air in the same reaction system.« less

  4. Surface enhanced Raman spectroscopy of self-assembled layers of lipid molecules on nanostructured Au and Ag substrates.

    PubMed

    Slekiene, Nora; Ramanauskaite, Lina; Snitka, Valentinas

    2017-03-01

    In this work surface enhanced Raman spectroscopy (SERS) has been used for the investigation of the self-assembled layers of lipid molecules (SALLMs) deposited on the nanostructured Au and Ag surfaces. The SALLMs were prepared from one part of 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) and four parts of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipids. The synthesis of Au and Ag SERS substrates was based on the direct gold and silver ions reduction onto HF etched silicon wafers. Au SERS substrates were not suitable for the formation of SALLMs because of the inappropriate contact angle of surface. It was found that the formation of the SALLM does not take place on Au SERS substrate. However, it has been shown that the modification of Au SERS substrate with 1-dodecanothiol layer allows building the SALLM on its surface. In the case of Ag SERS substrate, the SALLM was deposited directly on its surface. The SERS spectra of the SALLMs were recorded in the CH stretching (2800-3000cm(-1)) and the fingerprint (<1.800cm(-1)) regions. It has been demonstrated that the SERS spectra of the SALLM recorded on Au substrate differs from that one recorded on Ag SERS substrate. These spectral differences were found to be determined by the different interaction mechanisms of the lipid molecules with nanostructured surfaces.

  5. Tautomerism of a thiabendazole fungicide on Ag and Au nanoparticles investigated by Raman spectroscopy and density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Singh, Dheeraj K.; Ganbold, Erdene-Ochir; Cho, Eun-Min; Lee, Cheol Min; Yang, Sung Ik; Joo, Sang-Woo

    2013-10-01

    The energetic stabilities of a fungicide, thiobendazole (TBZ) on the Au and Ag atoms were analyzed by density functional theory (DFT) calculations at the levels of B3LYP/LANL2DZ. The most stable configuration on Au occurred when the metal atom was close to the N1 atom of TBZ in the same plane. There are two conformers of TBZ, N1-deprotonated and N3-deprotonated tautomers, depending on the hydrogen position of the benzimidazole in TBZ. Due to the planar geometry of the N1-deprotonated tautomer, it is more stable (ΔG = 6.31 kcal/mol) than the N3-deprotonated tautomer, which exhibits N1-C2-C10-C14 and N3-C2-C10-N11 dihedral angles of 30° and 28°, respectively. On the other hand, the most stable geometry of TBZ on Ag was formed when the N3 and N11 atoms of TBZ make a bridged configuration with the Ag atom. The binding energy of TBZ on Au was found larger than that of Ag. Spectral features of TBZ are compared on silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) by means of Raman spectroscopy. The presence of an Ag-N and an Au-N stretching band at 227 and 239 cm-1 in the Raman spectrum indicated that the nitrogen atoms of TBZ may be involved in the binding of the adsorbate on the surfaces of the AgNPs and AuNPs.

  6. Influence of Ag doping concentration on structural and optical properties of CdS thin film

    SciTech Connect

    Kumar, Pragati; Saxena, Nupur; Gupta, Vinay; Agarwal, Avinash

    2015-05-15

    This work shows the influence of Ag concentration on structural properties of pulsed laser deposited nanocrystalline CdS thin film. X-ray photoelectron spectroscopy (XPS) studies confirm the dopant concentration in CdS films and atomic concentration of elements. XPS studies show that the samples are slightly sulfur deficient. GAXRD scan reveals the structural phase transformation from cubic to hexagonal phase of CdS without appearance of any phase of CdO, Ag{sub 2}O or Ag{sub 2}S suggesting the substitutional doping of Ag ions. Photoluminescence studies illustrate that emission intensity increases with increase in dopant concentration upto 5% and then decreases for higher dopant concentration.

  7. Loading Ag nanoparticles on Cd(II) boron imidazolate framework for photocatalysis

    NASA Astrophysics Data System (ADS)

    Liu, Min; Zhang, De-Xiang; Chen, Shumei; Wen, Tian

    2016-05-01

    An amine-functionalized Cd(II) boron imidazolate framework (BIF-77) with three-dimensional open structure has been successfully synthesized, which can load Ag nanoparticles (NPs) for photocatalytic degradation of methylene blue (MB).

  8. Localized surface plasmon resonance-based hybrid Au-Ag nanoparticles for detection of Staphylococcus aureus enterotoxin B

    NASA Astrophysics Data System (ADS)

    Zhu, Shaoli; Du, ChunLei; Fu, Yongqi

    2009-09-01

    A triangular hybrid Au-Ag nanoparticles array was proposed for the purpose of biosensing in this paper. Constructing the hybrid nanoparticles, an Au thin film is capped on the Ag nanoparticles which are attached on glass substrate. The hybrid nanoparticles array was designed by means of finite-difference and time-domain (FDTD) algorithm-based computational numerical calculation and optimization. Sensitivity of refractive index of the hybrid nanoparticles array was obtained by the computational calculation and experimental detection. Moreover, the hybrid nanoparticles array can prevent oxidation of the pure Ag nanoparticles from atmosphere environment because the Au protective layer was deposited on top of the Ag nanoparticles so as to isolate the Ag particles from the atmosphere. We presented a novel surface covalent link method between the localized surface plasmon resonance (LSPR) effect-based biosensors with hybrid nanoparticles array and the detected target molecules. The generated surface plasmon wave from the array carries the biological interaction message into the corresponding spectra. Staphylococcus aureus enterotoxin B (SEB), a small protein toxin was directly detected at nanogramme per milliliter level using the triangular hybrid Au-Ag nanoparticles. Hence one more option for the SEB detection is provided by this way.

  9. Arrays of Ag and Au Nanoparticles with Terpyridine- and Thiophene-Based Ligands: Morphology and Optical Responses.

    PubMed

    Prusková, Markéta; Sutrová, Veronika; Šlouf, Miroslav; Vlčková, Blanka; Vohlídal, Jiří; Šloufová, Ivana

    2017-05-02

    The assembly of Ag and Au nanoparticles (NPs) into nanoparticulate arrays mediated by terpyridine (tpy), 4'-(2-thienyl)terpyridine (T-tpy), and short α,ω-bis(tpy)oligothiophene ligands has been accomplished at the interface between the Ag or Au NP hydrosol and a solution of the molecular species in dichloromethane. The relationship between the morphology and the optical responses of the arrays has been investigated by advanced methods of TEM (transmission electron microscopy) image analysis and surface plasmon extinction (SPE) spectra. It has been established that the size of islands of closely spaced NPs rather than the average interparticle distance affects the extent of delocalization of the surface plasmon excitations and thus also the SPE spectra. Furthermore, the structure of surface-adsorbate complexes formed in these arrays has been investigated by SERS spectral measurements carried out as a function of the excitation wavelength. Photoinduced charge transfer (CT) transitions from the neutral Ags(0) and Aus(0) adsorption sites on metal NPs to antibonding orbitals of the adsorbates have been identified for Ag/tpy, Ag/T-tpy, Au/tpy, and Au/T-tpy nanoparticulate arrays. Although the surface-adsorbate complexes displaying a photoinduced CT are known for Ag NPs, the Aus(0) surface complexes with this CT are newly reported. Bis(tpy)oligothiophenes were found to be attached to both Ag and Au NPs via the tpy group(s). The match between the interparticle distances within the NP islands and the lengths of the oligomers molecules indicates that the molecules act as interparticle linkers. In this case, unequivocal spectral marker band evidence of the Ags(0) as well as Aus(0) surface complex formation has not been obtained.

  10. Au@Ag/Au nanoparticles assembled with activatable aptamer probes as smart ``nano-doctors'' for image-guided cancer thermotherapy

    NASA Astrophysics Data System (ADS)

    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

  11. Hybrid microfluidic fuel cell based on Laccase/C and AuAg/C electrodes.

    PubMed

    López-González, B; Dector, A; Cuevas-Muñiz, F M; Arjona, N; Cruz-Madrid, C; Arana-Cuenca, A; Guerra-Balcázar, M; Arriaga, L G; Ledesma-García, J

    2014-12-15

    A hybrid glucose microfluidic fuel cell composed of an enzymatic cathode (Laccase/ABTS/C) and an inorganic anode (AuAg/C) was developed and tested. The enzymatic cathode was prepared by adsorption of 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and Laccase on Vulcan XC-72, which act as a redox mediator, enzymatic catalyst and support, respectively. The Laccase/ABTS/C composite was characterised by Fourier Transform Infrared (FTIR) Spectroscopy, streaming current measurements (Zeta potential) and cyclic voltammetry. The AuAg/C anode catalyst was characterised by Transmission electron microscopy (TEM) and cyclic voltammetry. The hybrid microfluidic fuel cell exhibited excellent performance with a maximum power density value (i.e., 0.45 mW cm(-2)) that is the highest reported to date. The cell also exhibited acceptable stability over the course of several days. In addition, a Mexican endemic Laccase was used as the biocathode electrode and evaluated in the hybrid microfluidic fuel cell generating 0.5 mW cm(-2) of maximum power density.

  12. Electrodeposition of Au/Ag bimetallic dendrites assisted by Faradaic AC-electroosmosis flow

    NASA Astrophysics Data System (ADS)

    Ji, Jianlong; Li, Pengwei; Sang, Shengbo; Zhang, Wendong; Zhou, Zhaoying; Yang, Xing; Dong, Hualai; Li, Gang; Hu, Jie

    2014-03-01

    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.

  13. Electrodeposition of Au/Ag bimetallic dendrites assisted by Faradaic AC-electroosmosis flow

    SciTech Connect

    Ji, Jianlong; Li, Pengwei; Sang, Shengbo Zhang, Wendong Li, Gang; Hu, Jie; Zhou, Zhaoying Yang, Xing; Dong, Hualai

    2014-03-15

    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.

  14. A microscopic study of strongly plasmonic Au and Ag island thin films

    NASA Astrophysics Data System (ADS)

    Pavaskar, Prathamesh; Hsu, I.-Kai; Theiss, Jesse; Hsuan Hung, Wei; Cronin, Stephen B.

    2013-01-01

    Thin Au and Ag evaporated films (˜5 nm) are known to form island-like growth, which exhibit a strong plasmonic response under visible illumination. In this work, evaporated thin films are imaged with high resolution transmission electron microscopy, to reveal the structure of the semicontinuous metal island film with sub-nm resolution. The electric field distributions and the absorption spectra of these semicontinuous island film geometries are then simulated numerically using the finite difference time domain method and compared with the experimentally measured absorption spectra. We find surface enhanced Raman scattering (SERS) enhancement factors as high as 108 in the regions of small gaps (≤2 nm), which dominate the electromagnetic response of these films. The small gap enhancement is further substantiated by a statistical analysis of the electric field intensity as a function of the nanogap size. Areal SERS enhancement factors of 4.2 × 104 are obtained for these films. These plasmonic films can also enhance the performance of photocatalytic and photovoltaic phenomena, through near-field coupling. For TiO2 photocatalysis, we calculate enhancement factors of 16 and 19 for Au and Ag, respectively. We study the effect of annealing on these films, which results in a large reduction in electric field strength due to increased nanoparticle spacing.

  15. Nanowire networks and hollow nanospheres of Ag-Au bimetallic alloys at room temperature

    NASA Astrophysics Data System (ADS)

    Britto Hurtado, R.; Cortez-Valadez, M.; Arizpe-Chávez, H.; Flores-Lopez, N. S.; Álvarez, Ramón A. B.; Flores-Acosta, M.

    2017-03-01

    Due to their physicochemical properties, metallic nanoalloys have potential applications in biomedicine, electrocatalysis and electrochemical sensors, among many other fields. New alternative procedures have emerged in order to reduce production costs and the use of toxic substances. In this study we present a novel low-toxicity synthesis method for the fabrication of nanowire networks (NWNs) and Ag-Au hollow nanospheres. The synthesis process is performed at room temperature without any sophisticated equipment, such as special cameras or furnaces, etc. Transmission electron microscopy showed that the NWNs contain random alloys with a diameter of between 10-13 nm. The radius for the hollow nanospheres is approximately located between 70-130 nm. The absorption bands in the UV-vis spectrum associated with the surface plasmon in Ag-Au bimetallic nanoparticles are highlighted at 385 nm for the NWNs and 643 nm for the hollow nanospheres. The study was performed with low-toxicity substances, such as rongalite, ascorbic acid and sucrose, and showed high efficiency for the fabrication of these types of nanostructures, as well as good stability for long periods of time.

  16. Synthesis, fractionation, and optical characterization of Au-Ag composite nanorods

    NASA Astrophysics Data System (ADS)

    Alekseeva, Anna V.; Bogatyrev, Vladimir A.; Trachuk, Lyubov A.; Khlebtsov, Nikolai G.

    2005-06-01

    We report on a synthesis procedure and optical properties of composite Au-Ag spherical and rod-like nanoparticles. The synthesis protocol is based on a seed-mediated growth in the presence of soft templates in micellar aqueous solution of ionic surfactant (CTAB). Variation of Au/Ag molar ratio allows one to produce nanorods (NRs) with different aspect ratio. The disadvantage of the method is formation of appreciable amount of spherical nanoparticles. To separate rod-like particles from spheres and surfactant, we used a fractionation procedure that involves centrifugatiori of samples in the density gradient of glycerol. The separated NRs were suspended in water or 25% glycerol solutions and their extinction and differential light scattering (at 900) spectra were recorded for 450-850 ni-n wavelengths. Theoretical spectra were calculated by T-matrix method as applied to randomly oriented gold cylinders with semispherical ends. The simulated spectra for water and glycerol suspensions can be brought in close agreement with experimental observations if the aspect ratio is used as a fitting parameter. We discuss also the absorption and light scattering contribution to the total extinction spectra and deviation of the exact solution from the classical electrostatic approximation by Gans.

  17. Fully alloyed Ag/Au nanorods with tunable surface plasmon resonance and high chemical stability.

    PubMed

    Bai, Yaocai; Gao, Chuanbo; Yin, Yadong

    2017-10-12

    Limited success has been achieved in preparing nanorods of silver with uniform sizes and tunable localized surface plasmon resonances. Also, the practical applications of silver nanostructures have been hindered by their poor chemical stability in a corrosive environment. Here we address these issues by converting Au@Ag core/shell nanorods into fully alloyed ones through controlled high-temperature annealing in confined spaces. Compared with their core/shell counterparts, the obtained alloy nanorods demonstrated significantly enhanced stability toward oxidative etching. We also systematically investigated their novel plasmonic properties, and revealed that the band positions of both longitudinal and transverse modes can be readily tuned by either manipulating the Ag/Au ratio or starting with gold cores of different aspect ratios. Moreover, we have achieved widely adjusted peak intensity ratios between the transverse and longitudinal bands from 0.14 to 1.22, which is impossible for nonalloyed nanorods. The alloy nanorods developed in this work are believed to find great uses in fundamental spectroscopic studies as well as many attractive plasmonic applications.

  18. Ultrasensitive MicroRNA Assay via Surface Plasmon Resonance Responses of Au@Ag Nanorods Etching.

    PubMed

    Gu, Yu; Song, Juan; Li, Mei-Xing; Zhang, Ting-Ting; Zhao, Wei; Xu, Jing-Juan; Liu, Maili; Chen, Hong-Yuan

    2017-10-03

    Quantification of trace serum circulate microRNAs is extremely important in clinical diagnosis but remains a great challenge. Herein we developed an ultrasensitive platform for microRNA 141 (miR-141) detection based on a silver coated gold nanorods (Au@Ag NRs) etching process accompanied by surface plasmon resonance (SPR) shift. Both SPR absorption and scattering responses were monitored. Combined amplification cascades of catalyzed hairpin assembly (CHA) and hybridization chain reaction (HCR) with the sensitive SPR responses of plasmonic Au@Ag NRs, the proposed bioassay exhibited ultrahigh sensitivity toward miRNA-141 with dynamic range from 5.0 × 10(-17) M to 1.0 × 10(-11) M. With target concentration higher than 1.0 × 10(-13) M, the color of the solution changed obviously that could be observed with naked eyes. Under dark-field microscopy observation of individual particle, a limit of detection down to 50 aM could be achieved. Owing to the superior sensitivity and selectivity, the proposed method was applied to detecting trace microRNA in serum. Similar SPR assays could be developed simply by redesigning the switching aptamer for the detections of other microRNAs or targets such as small molecule, DNA, or protein. Considering the convenient operation, good performance and simple observation modes of this method, it may have great potential in trace bioanalysis for clinical applications.

  19. Nanowire networks and hollow nanospheres of Ag-Au bimetallic alloys at room temperature.

    PubMed

    Hurtado, R Britto; Cortez-Valadez, M; Arizpe-Chávez, H; Flores-Lopez, N S; Álvarez, Ramón A B; Flores-Acosta, M

    2017-03-17

    Due to their physicochemical properties, metallic nanoalloys have potential applications in biomedicine, electrocatalysis and electrochemical sensors, among many other fields. New alternative procedures have emerged in order to reduce production costs and the use of toxic substances. In this study we present a novel low-toxicity synthesis method for the fabrication of nanowire networks (NWNs) and Ag-Au hollow nanospheres. The synthesis process is performed at room temperature without any sophisticated equipment, such as special cameras or furnaces, etc. Transmission electron microscopy showed that the NWNs contain random alloys with a diameter of between 10-13 nm. The radius for the hollow nanospheres is approximately located between 70-130 nm. The absorption bands in the UV-vis spectrum associated with the surface plasmon in Ag-Au bimetallic nanoparticles are highlighted at 385 nm for the NWNs and 643 nm for the hollow nanospheres. The study was performed with low-toxicity substances, such as rongalite, ascorbic acid and sucrose, and showed high efficiency for the fabrication of these types of nanostructures, as well as good stability for long periods of time.

  20. Valence band studies of the RTX (R=Pr, Nd; T=Cu, Ag, Au; X=Ge, Sn) compounds

    NASA Astrophysics Data System (ADS)

    Szytuła, A.; Jezierski, A.; Penc, B.; Fus, D.

    2000-12-01

    The valence band in the RTX (R=Pr, Nd; T=Cu, Ag, Au; X=Ge, Sn) compounds was studied by the X-ray photoemission spectroscopy. The XPS data were compared with the ones calculated using the spin-polarized tight-binding linear muffin-tin orbital (TB LMTO) method. The obtained results show that the valence bands are determined mainly by the Cu 3d, Ag 4d and Au 5d bands. The calculation of the total energy for two models of the crystal structure: an ordered of the LiGaGe-type and a disordered one of the CaIn 2-type indicates that in the RTSn (T=Cu, Ag ,Au) compounds the LiGaGe-type structure is stable. Calculated value of the Pr magnetic moment is smaller than that of the free Pr 3+ ion value, whereas the Nd magnetic moment is equal to the free Nd 3+ ion value.

  1. Hexagonal core-shell and alloy Au/Ag nanodisks on ZnO nanorods and their optical enhancement effect

    NASA Astrophysics Data System (ADS)

    Zhang, Junming; Lai, Boya; Chen, Zuxin; Chu, Sheng; Chu, Guang; Peng, Rufang

    2014-05-01

    Au and Ag hybrid hexagonal nanodisks were synthesized on ZnO nanorods' (0002) surface via a new two-step deposition-annealing method. The structural, compositional, as well as optical investigations were carried out systematically to find out the nanodisks' formation mechanism and optical enhancement effect. It was shown that the core-shell Au/Ag nanodisk can be formed under rapid annealing temperature of 500°C, while Au/Ag alloy nanodisks are formed if higher temperatures (>550°C) are applied. The optical effect from these nanodisks was studied through photoluminescence and absorption spectroscopy. It was found that the carrier-plasmon coupling together and carrier transfer between metal and ZnO contribute to the emission enhancement. Furthermore, the results suggest that the composition of nanodisk on the vicinity of metal/ZnO interface plays an important role in terms of the enhancement factors.

  2. Synthesis of MoS2/Graphene hybrid supported Au and Ag nanoparticles with multi-functional catalytic properties.

    PubMed

    Chen, Ying; Peng, Wenchao; Li, Xiaoyan

    2017-03-30

    The detection and removal of nitroaromatic compounds are important issues for environment protection. In this study, the hybrid of molybdenum disulfide (MoS2) and graphene (GR) was first synthesized using a facile hydrothermal method. Au and Ag nanoparticles were then deposited on the surface of MoS2/GR hybrid with sodium citrate as stabilizer and reductant. Compared to using pure MoS2 as the support, the obtained Au (Ag)-MoS2/GR composites showed improved activity for electrochemical detection and chemical reduction of 4-nitrophenol. The activity enhancement should be due to the addition of GR, which could improve the conductivity as well as provide more active sites. The successful synthesis of Au (Ag)-MoS2/GR composites could provide new multi-function catalysts for environment protection.

  3. Molecular dynamics simulation of joining process of Ag-Au nanowires and mechanical properties of the hybrid nanojoint

    SciTech Connect

    Ding, Su; Tian, Yanhong Jiang, Zhi; He, Xiaobin

    2015-05-15

    The nanojoining process of Ag-Au hybrid nanowires at 800K was comprehensively studied by virtue of molecular dynamics (MD) simulation. Three kinds of configurations including end-to-end, T-like and X-like were built in the simulation aiming to understand the nanojoining mechanism. The detailed dynamic evolution of atoms, crystal structure transformation and defects development during the nanojoining processes were performed. The results indicate that there are two stages in the nanojoining process of Ag-Au nanowires which are atom diffusion and new bonds formation. Temperature is a key parameter affecting both stages ascribed to the energy supply and the optimum temperature for Ag-Au nanojoint with diameter of 4.08 nm has been discussed. The mechanical properties of the nanojoint were examined with simulation of tensile test on the end-to-end joint. It was revealed that the nanojoint was strong enough to resist fracture at the joining area.

  4. Au-Ag Alloy Static High Pressure EOS measurements: FY09 summary of results

    SciTech Connect

    Evans, W J; Jenei, Z

    2009-09-17

    Static high-pressure measurements of the equation of state of a Gold-Silver alloy (23.5 wt-% Ag) at room temperature were performed up to a pressure of approximately 100 GPA (1 megabar). Measurements were made using an energy-dispersive x-ray diffraction method. The data was analyzed, yielding crystal structure lattice constants and volume/density as a function of pressure. The results are extremely precise yielding accuracy of better than 1%. The experiments were carried out at the HPCAT 16BM-D beamline at the Advanced Photon Source. Two experiments on separate samples were carried out using conventional membrane diamond anvil cells. To achieve hydrostatic conditions, we loaded a 50-100 micron piece of the Au-Ag alloy into the cell and surrounded it with neon and mineral oil pressure media in the respective experiments. The differing pressure media demonstrated no measurable difference on the resultant crystal structures, lattice constants or pressure-volume curves. Results of our work are shown in the figures below. Up to the maximum pressure of 100 GPa the sample remained in the face-centered cubic structure, e.g., we observed no change in crystal structure. EOS curves of silver and gold, taken from the literature, are shown for comparison. We fit our data to a Vinet EOS functional form, and the parameters for this EOS were found to be, Reference (ambient pressure) volume, V{sub 0} = 16.965435 {angstrom}{sup 3}; Reference (ambient pressure) density, {rho}{sub 0} = 16.14584 g/cm{sup 3}; Bulk Modulus, K{sub 0} = 144 GPa; and Bulk Mod Derivative, K{prime}{sub 0} = 5.66. As one might expect the Au-Ag alloy lies between the gold and silver EOS curves, and tracks more closely to the gold EOS. These data are useful in validating and developing predictive EOS models of the pressure-dependent behavior of Au-Ag alloys.

  5. Self -organization of Au-CdSe hybrid nanoflowers at different length scales via bi-functional diamine linkers

    NASA Astrophysics Data System (ADS)

    AbouZeid, Khaled Mohamed; Mohamed, Mona Bakr; El-Shall, M. Samy

    2016-01-01

    This work introduces a series of molecular bridging bi-functional linkers to produce laterally self-assembled nanostructures of the Au-CdSe nanoflowers on different length scales ranging from 10 nm to 100 microns. Assembly of Au nanocrystals within amorphous CdSe rods is found in the early stages of the growth of the Au-CdSe nanoflowers. The Au-CdSe nanoflowers are formed through a one-pot low temperature (150 °C) process where CdSe clusters are adsorbed on the surface of the Au cores, and they then start to form multiple arms and branches resulting in flower-shaped hybrid nanostructures. More complex assembly at a micron length scale can be achieved by means of bi-functional capping agents with appropriate alkyl chain lengths, such as 1,12-diaminododecane.

  6. Operating mechanism of electrically bistable memory device based on Ag doped CdSe/PVA nanocomposite

    NASA Astrophysics Data System (ADS)

    Kaur, Ramneek; Tripathi, S. K.

    2015-06-01

    This paper reports the fabrication and characterization of electrically bistable memory device with device structure Al/Ag doped CdSe/PVA nanocomposite/Ag. Current-Voltage (I-V) measurements show two conductivity states at the same applied voltage indicating the bistability behavior. The possible operating mechanism for the memory effects has been described. During transition from the low resistance state to high resistance state, the current follows the change from the injection emission to the space charge limited conduction mechanism. The achieved results demonstrate that the device based on Ag doped CdSe/PVA nanocomposite has a potential for future non-volatile memory devices.

  7. Degradation mechanisms studies in CdS/CdTe solar cells with ZnTe:Cu/Au back contact

    NASA Astrophysics Data System (ADS)

    Morgan, D.; Tang, J.; Kaydanov, V.; Ohno, T. R.; Trefny, J. U.

    1999-03-01

    CdS/CdTe/ZnTe:Cu/Au solar cells were fabricated and tested under stressed conditions including enhanced temperature, forward and reverse bias, open circuit, dark and light. Discussion of results was focused mostly on the development of the back contact Schottky diode (increase in series resistance). Changes in the cell parameters were detected based on the analysis of the dynamic resistance of a cell (dV/dJ) at forward biases. A possible role of electromigration of the Cu dopant was discussed.

  8. An ab-initio study of silicon adsorption on metallic surfaces (Au/Ag): Novel perspective to explore chemical bonding

    NASA Astrophysics Data System (ADS)

    Chakraborty, S.; Ghaisas, S. V.; Majumder, C.

    2012-07-01

    We report a first-principle investigation of the structure and electronic properties of small Sin (n = 1-6,9) clusters deposited on the Au(111) and Ag(111) surfaces. The calculations were performed using a plane wave based pseudopotential method under the framework of density functional theory. The results reveal the preference of Si atom to be adsorbed on the h.c.p. site of the metal (111) surfaces with strong binding energy. We study monolayer (ML) deposition as well as the cluster deposition on both the surfaces. The clusters introduce interlayer forces in the adsorbate. Based on PDOS (projected density of states) analysis it is found that Si atoms acquire charges from the Au/Ag surface. The binding energies are consistent with the known cohesive energy of Ag and Au silicides. The planar Sin cluster deposition on metal surfaces show that Au provides an adjustable surface with relatively strong Au-Si interaction while Ag-Si relatively weak interaction leading to dimerization of Si. The strong bonding with the surface atoms is a result of p-d hybridization. Some of the 3-D clusters show shape distortions after deposition on metal surfaces. This leads to internal stresses after deposition. A statistical parameter is defined over PDOS. It helps to measure the state delocalization in energy. Implications of the Si-Metal interaction on the initial stages of growth are discussed.

  9. A grazing incidence surface X-ray absorption fine structure (GIXAFS) study of alkanethiols adsorbed on Au, Ag, and Cu

    NASA Astrophysics Data System (ADS)

    Floriano, Pierre N.; Schlieben, Olaf; Doomes, Edward E.; Klein, Ingo; Janssen, J.; Hormes, Josef; Poliakoff, E. D.; McCarley, Robin L.

    2000-04-01

    Self-assembled monolayers of n-alkanethiols, CH 3-(CH 2) x-SH, on Au, Ag, and Cu have been studied with GIXAFS at the sulfur K-edge. For both pentanethiol and decanethiol monolayers on Ag and Cu, the three-fold hollow site is found to be the most probable sulfur binding site. However, observations for octadecanethiol indicate that the three-fold hollow site is not the exclusive binding site. In addition, the possible existence of disulfide bonds on the metal surface (adsorbed dialkyldisulfides) is not supported by the data. Preliminary results from monolayers on Au are also reported.

  10. Sandwiched ZnO@Au@CdS Nanorod Arrays with Enhanced Visible-Light-Driven Photocatalytical Performance.

    PubMed

    Ren, Shoutian; Wang, Yingying; Fan, Guanghua; Gao, Renxi; Liu, Wenjun

    2017-09-18

    The development of high-performance photocatalysts is central to take advantage of solar energy to overcome environmental and energy crises. Integrating different functional materials artfully into nanostructures can acquire more efficient photocatalytic activity. Here sandwiched ZnO@Au@CdS nanorod films were synthesized via successive ZnO nanorod electrodeposition, Au sputtering and CdS electrodeposition. The as-synthesized composites were characterized by UV-vis spectrophotometer, x-ray diffractometer, scanning and transmission electron microscopy. Their photocatalytic activity was assessed by degrading Rhodamine B solution under visible light irradiation. ZnO@Au@CdS exhibited better photocatalytic performance than ZnO@CdS throughout the visible light region, and the corresponding enhancement factor of Au nanoparticles was measured as a function of CdS loading amount, and it could reach 190% with CdS deposition for 1 min. The normalized rate constant could reach 0.387 h-1 for ZnO@Au@CdS-1min, which was equivalent to or better than results in reference photocatalysts. The enhancement mechanism of Au nanoparticles was estimated by comparing the monochromatic photocatalytic action spectra with the absorption spectrum of ZnO@Au@CdS, and it was mainly determined by incident photon energy. With selective excitation of Au nanoparticles by incident photons, the excited hot electrons in Au NPs are transferred to the conduction band of ZnO to boost photocatalytic reaction. With selective excitation of CdS, the enhanced interband absorption of CdS and relay station effect of Au nanoparticles should be responsible for the enhanced photocatalytic performance. Our work not only opens the door to the design of efficient supported photocatalysts, but also helps to understand the enhancement mechanism of LSPR effect on the photoelectric conversion of semiconductors. © 2017 IOP Publishing Ltd.

  11. Flexible nonvolatile memory devices based on Au/PMMA nanocomposites deposited on PEDOT:PSS/Ag nanowire hybrid electrodes

    NASA Astrophysics Data System (ADS)

    Sung, Sihyun; Kim, Tae Whan

    2017-07-01

    Flexible nonvolatile memory (NVM) devices fabricated utilizing Au nanoparticles (AuNPs) embedded in a poly(methylmethacrylate) (PMMA) layer were fabricated on a silver nanowire (AgNW) or a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/AgNW coated on poly(ethylene terephthalate) (PET) substrates. The transmittance and the sheet resistance of the PEDOT:PSS/AgNW hybrid layer were approximately 89% and 50 Ω/sq, respectively, which were comparable to the values for commercial indium-tin-oxide (ITO) electrodes. Current-voltage curves for the Al/PMMA:AuNP/PEDOT:PSS/AgNW/PET devices at 300 K showed clockwise current hysteresis behaviors due to the existence of the AuNPs. The endurance number of ON/OFF switching for the NVM devices was above 30 cycles. An ON/OFF ratio of 1 × 103 was maintained for retention times longer than 1 × 104 s. The maximum memory margins of the NVM devices before and after bending were approximately 3.4 × 103 and 1.4 × 103, respectively. The retention times of the devices before and after bending remained same 1 × 104 s. The memory margin and the stability of flexible NVMs fabricated on AgNW electrodes were enhanced due to the embedded PEDOT:PSS buffer layer.

  12. Au@Ag nanorods based electrochemical immunoassay for immunoglobulin G with signal enhancement using carbon nanofibers-polyamidoamine dendrimer nanocomposite.

    PubMed

    Ma, Lina; Ning, Danlei; Zhang, Hongfang; Zheng, Jianbin

    2015-06-15

    Au@Ag nanorods (Au@AgNRs) was utilized to construct a novel sandwich-type electrochemical immunosensor for the detection of immunoglobulin G (IgG). The sensor was prepared by immoblizing capture antibodies on the amine-terminated nanocomposite of carbon nanofibers-polyamidoamine dendrimer (CNFs-PAMAM), whilst the trace tag was prepared by loading anti-human IgG on Au@AgNRs. The "built-in" Ag layer on Au nanorods was characterized by UV-vis extinction spectra, transmission electron microscopy and energy dispersive spectroscopy. The results of cyclic voltammetry indicated that modifying CNFs-PAMAM nanocomposite on glassy carbon electrode enabled 177 times of peak current increase of Ag in the bimetallic nanorods. The peak current was quantitatively related with the concentration of the target protein IgG via the formation of immunocomplex. After the parameter optimization, the oxidative peak current of silver was proportional to the concentration of IgG in a wide linear range of six orders of magnitude with a low detection limit of 0.5 fg mL(-1). Besides, this sensor showed acceptable reproducibility and stability, and thus the strategy reported here has great promise for extension to the other disease biomarkers.

  13. Photochemical green synthesis of calcium-alginate-stabilized Ag and Au nanoparticles and their catalytic application to 4-nitrophenol reduction.

    PubMed

    Saha, Sandip; Pal, Anjali; Kundu, Subrata; Basu, Soumen; Pal, Tarasankar

    2010-02-16

    Silver and gold nanoparticles have been grown on calcium alginate gel beads using a green photochemical approach. The gel served as both a reductant and a stabilizer. The nanoparticles were characterized using UV-visible spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), energy dispersive X-ray (EDS), and selected area electron diffraction (SAED) analyses. The particles are spherical, crystalline, and the size ranges for both Ag and Au nanoparticles are <10 nm. It is noticed from the sorption experiment that the loading of gold on calcium alginate beads is much more compared to that of Ag. The effectiveness of the as-prepared dried alginate-stabilized Ag and Au nanoparticles as a solid phase heterogeneous catalyst has been evaluated, for the first time, on the well-known 4-nitrophenol (4-NP) reduction to 4-aminophenol (4-AP) in the presence of excess borohydride. The reduction was very efficient and followed zero-order kinetics for both Ag and Au nanocomposites. The effects of borohydride, initial 4-NP concentration, and catalyst dose were evaluated. The catalyst efficiency was examined on the basis of turnover frequency (TOF) and recyclability. The catalytic efficiency of alginate-based Ag catalyst was much more compared to that of the Au catalyst. The as-prepared new solid-phase biopolymer-based catalysts are very efficient, stable, easy to prepare, eco-friendly, and cost-effective, and they have the potential for industrial applications.

  14. Thermal Expansion Behavior of M(I)[AuX2(CN)2]-Based Coordination Polymers (M = Ag, Cu; X = CN, Cl, Br).

    PubMed

    Ovens, Jeffrey S; Leznoff, Daniel B

    2017-07-03

    Two sets of trans-[AuX2(CN)2](-)-based coordination polymer materials-M[AuX2(CN)2] (M = Ag; X = Cl, Br or M = Cu; X = Br) and M[Au(CN)4] (M = Ag, Cu)-were synthesized and structurally characterized and their dielectric constants and thermal expansion behavior explored. The M[AuX2(CN)2] series crystallized in a tightly packed, mineral-like structure featuring 1-D trans-[AuX2(CN)2](-)-bridged chains interconnected via a series of intermolecular Au···X and M···X (M = Ag, Cu) interactions. The M[Au(CN)4] series adopted a 2-fold interpenetrated 3-D cyano-bound framework lacking any weak intermolecular interactions. Despite the tight packing and the presence of intermolecular interactions, these materials exhibited decreased thermal stability over unbound trans-[AuX2(CN)2](-) in [(n)Bu4N][AuX2(CN)2]. A significant dielectric constant of up to εr = 36 for Ag[AuCl2(CN)2] (1 kHz) and a lower εr = 9.6 (1 kHz) for Ag[Au(CN)4] were measured and interpreted in terms of their structures and composition. A systematic analysis of the thermal expansion properties of the M[AuX2(CN)2] series revealed a negative thermal expansion (NTE) component along the cyano-bridged chains with a thermal expansion coefficient (αCN) of -13.7(11), -14.3(5), and -11.36(18) ppm·K(-1) for Ag[AuCl2(CN)2], Ag[AuBr2(CN)2], and Cu[AuBr2(CN)2], respectively. The Au···X and Ag···X interactions affect the thermal expansion similarly to metallophilic Au···Au interactions in M[Au(CN)2] and AuCN; replacing X = Cl with the larger Br atoms has a less significant effect. A similar analysis for the M[Au(CN)4] series (where the volume thermal expansion coefficient, αV, is 41(3) and 68.7(19) ppm·K(-1) for M = Ag, Cu, respectively) underscored the significance of the effect of the atomic radius on the flexibility of the framework and, thus, the thermal expansion properties.

  15. Controlled protein embedment onto Au/Ag core-shell nanoparticles for immuno-labeling of nanosilver surface.

    PubMed

    Lee, In Hwan; Lee, Jeong Min; Jung, Yongwon

    2014-05-28

    Difficulties in stable conjugation of biomolecules to nanosilver surfaces have severely limited the use of silver nanostructures in biological applications. Here, we report a facile antibody conjugation onto gold/silver (Au/Ag) core-shell nanoparticles by stable and uniform embedment of an antibody binding protein, protein G, in silver nanoshells. A rigid helical peptide linker with a terminal cysteine residue was fused to protein G. A mixture of the peptide-fused protein G and space-filling free peptide was reacted with gold nanoparticles (AuNPs) to form a protein G-linked peptide layer on the particle surface. Uniform silver nanoshells were successfully formed on these protein G-AuNPs, while stably embedding protein G-linked peptide layers. Protein G specifically targets the Fc region of an antibody and thus affords properly orientated antibodies on the particle surface. Compared to Au nanoparticles of similar size with randomly adsorbed antibodies, the present immuno-labeled Au/Ag core-shell nanoparticles offered nearly 10-fold higher sensitivities for naked-eye detection of surface bound antigens. In addition, small dye molecules that were bonded to the peptide layer on Au nanoparticles exhibited highly enhanced surface-enhanced Raman scattering (SERS) signals upon Ag shell formation. The present strategy provides a simple but efficient way to conjugate antibodies to nanosilver surfaces, which will greatly facilitate wider use of the superior optical properties of silver nanostructures in biological applications.

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

    PubMed

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

    2014-07-30

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

  17. An ultrasensitive, uniform and large-area surface-enhanced Raman scattering substrate based on Ag or Ag/Au nanoparticles decorated Si nanocone arrays

    NASA Astrophysics Data System (ADS)

    Zhang, P. P.; Gao, J.; Sun, X. H.

    2015-01-01

    Large-area and highly ordered Si nanocone arrays decorated with Ag or Au/Ag nanoparticles have been fabricated via a mask-free lithography with reaction ion etching, followed by metal deposition process. Ultrasensitive surface enhanced Raman scattering signals with an enhancement factor of 1012 were achieved even at the concentration of the Rhodamine 6G as low as 10-15 M. The surface-enhanced Raman spectroscopy (SERS) substrate was also applied on the detection of Sudan I dye and the Raman signals were substantially enhanced as well. The stability of the SERS substrate can be significantly improved by covering Ag nanoparticles with Au thin layer, which maintain a high SERS performance even after one month storage. This nanofabrication process appears to be a feasible approach to prepare uniform and reproducible SERS-active substrates with high sensitivity and stability for practical SERS applications.

  18. Reflow soldering and isothermal solid-state aging of Sn-Ag eutectic solder on Au/Ni surface finish

    NASA Astrophysics Data System (ADS)

    Liu, C. M.; Ho, C. E.; Chen, W. T.; Kao, C. R.

    2001-09-01

    The reaction between the eutectic Sn-3.5Ag solder and the Au/Ni surface finish during reflow as well as during isothermal aging was studied. The Au layer was electroplated and had a thickness of the one μm. The peak reflow temperature was fixed at 250 C while the reflow time was varied between 10 sec and one h. Samples that went through 90 sec reflow time were then subjected to 160 C isothermal aging for up to 875 h. It was found that during reflow the Au layer reacted very quickly with the solder to form AuSn4. One μm of Au layer was consumed in less than 10 sec. As the aging time increased, AuSn4 grains began to separate themselves from the Ni layer at the roots of the grains and started to fall into the solder. When, the reflow time reached 30 sec, all the Au intermetallic head left the interface, and Ni3Sn4 started, to form at the interface. The Ni3Sn4 growth rate followed linear kinetics initially (<240 sec), but the growth rate slowed down afterward. During the isothermal aging, only a small amount of (AuxNi1-x)Sn4 resettled back to the interface, and a continuous (Au0.45Ni0.55)Sn4 layer did not form at the interface, unlike the case for the Sn-37Pb solder. This is an important advantage for Sn-3.5 Ag over Sn-37Pb because a continuous (Au0.45Ni0.55)Sn4 layer inevitably will weaken a solder joint. Our observation indicated that many (AuxNi1-x)Sn4 particles were trapped by the Ag3Sn particles, and were hindered from resettling back to the interface.

  19. A nanocomposite of Au-AgI core/shell dimer as a dual-modality contrast agent for x-ray computed tomography and photoacoustic imaging

    PubMed Central

    Orza, Anamaria; Yang, Yi; Feng, Ting; Wang, Xueding; Wu, Hui; Li, Yuancheng; Yang, Lily; Tang, Xiangyang; Mao, Hui

    2016-01-01

    Purpose: To develop a core/shell nanodimer of gold (core) and silver iodine (shell) as a dual-modal contrast-enhancing agent for biomarker targeted x-ray computed tomography (CT) and photoacoustic imaging (PAI) applications. Methods: The gold and silver iodine core/shell nanodimer (Au/AgICSD) was prepared by fusing together components of gold, silver, and iodine. The physicochemical properties of Au/AgICSD were then characterized using different optical and imaging techniques (e.g., HR- transmission electron microscope, scanning transmission electron microscope, x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, Z-potential, and UV-vis). The CT and PAI contrast-enhancing effects were tested and then compared with a clinically used CT contrast agent and Au nanoparticles. To confer biocompatibility and the capability for efficient biomarker targeting, the surface of the Au/AgICSD nanodimer was modified with the amphiphilic diblock polymer and then functionalized with transferrin for targeting transferrin receptor that is overexpressed in various cancer cells. Cytotoxicity of the prepared Au/AgICSD nanodimer was also tested with both normal and cancer cell lines. Results: The characterizations of prepared Au/AgI core/shell nanostructure confirmed the formation of Au/AgICSD nanodimers. Au/AgICSD nanodimer is stable in physiological conditions for in vivo applications. Au/AgICSD nanodimer exhibited higher contrast enhancement in both CT and PAI for dual-modality imaging. Moreover, transferrin functionalized Au/AgICSD nanodimer showed specific binding to the tumor cells that have a high level of expression of the transferrin receptor. Conclusions: The developed Au/AgICSD nanodimer can be used as a potential biomarker targeted dual-modal contrast agent for both or combined CT and PAI molecular imaging. PMID:26745951

  20. A nanocomposite of Au-AgI core/shell dimer as a dual-modality contrast agent for x-ray computed tomography and photoacoustic imaging.

    PubMed

    Orza, Anamaria; Yang, Yi; Feng, Ting; Wang, Xueding; Wu, Hui; Li, Yuancheng; Yang, Lily; Tang, Xiangyang; Mao, Hui

    2016-01-01

    To develop a core/shell nanodimer of gold (core) and silver iodine (shell) as a dual-modal contrast-enhancing agent for biomarker targeted x-ray computed tomography (CT) and photoacoustic imaging (PAI) applications. The gold and silver iodine core/shell nanodimer (Au/AgICSD) was prepared by fusing together components of gold, silver, and iodine. The physicochemical properties of Au/AgICSD were then characterized using different optical and imaging techniques (e.g., HR- transmission electron microscope, scanning transmission electron microscope, x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, Z-potential, and UV-vis). The CT and PAI contrast-enhancing effects were tested and then compared with a clinically used CT contrast agent and Au nanoparticles. To confer biocompatibility and the capability for efficient biomarker targeting, the surface of the Au/AgICSD nanodimer was modified with the amphiphilic diblock polymer and then functionalized with transferrin for targeting transferrin receptor that is overexpressed in various cancer cells. Cytotoxicity of the prepared Au/AgICSD nanodimer was also tested with both normal and cancer cell lines. The characterizations of prepared Au/AgI core/shell nanostructure confirmed the formation of Au/AgICSD nanodimers. Au/AgICSD nanodimer is stable in physiological conditions for in vivo applications. Au/AgICSD nanodimer exhibited higher contrast enhancement in both CT and PAI for dual-modality imaging. Moreover, transferrin functionalized Au/AgICSD nanodimer showed specific binding to the tumor cells that have a high level of expression of the transferrin receptor. The developed Au/AgICSD nanodimer can be used as a potential biomarker targeted dual-modal contrast agent for both or combined CT and PAI molecular imaging.

  1. A nanocomposite of Au-AgI core/shell dimer as a dual-modality contrast agent for x-ray computed tomography and photoacoustic imaging

    SciTech Connect

    Orza, Anamaria; Wu, Hui; Li, Yuancheng; Mao, Hui E-mail: Xiangyang.Tang@emory.edu; Yang, Yi; Tang, Xiangyang E-mail: Xiangyang.Tang@emory.edu; Feng, Ting; Wang, Xueding; Yang, Lily

    2016-01-15

    Purpose: To develop a core/shell nanodimer of gold (core) and silver iodine (shell) as a dual-modal contrast-enhancing agent for biomarker targeted x-ray computed tomography (CT) and photoacoustic imaging (PAI) applications. Methods: The gold and silver iodine core/shell nanodimer (Au/AgICSD) was prepared by fusing together components of gold, silver, and iodine. The physicochemical properties of Au/AgICSD were then characterized using different optical and imaging techniques (e.g., HR- transmission electron microscope, scanning transmission electron microscope, x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, Z-potential, and UV-vis). The CT and PAI contrast-enhancing effects were tested and then compared with a clinically used CT contrast agent and Au nanoparticles. To confer biocompatibility and the capability for efficient biomarker targeting, the surface of the Au/AgICSD nanodimer was modified with the amphiphilic diblock polymer and then functionalized with transferrin for targeting transferrin receptor that is overexpressed in various cancer cells. Cytotoxicity of the prepared Au/AgICSD nanodimer was also tested with both normal and cancer cell lines. Results: The characterizations of prepared Au/AgI core/shell nanostructure confirmed the formation of Au/AgICSD nanodimers. Au/AgICSD nanodimer is stable in physiological conditions for in vivo applications. Au/AgICSD nanodimer exhibited higher contrast enhancement in both CT and PAI for dual-modality imaging. Moreover, transferrin functionalized Au/AgICSD nanodimer showed specific binding to the tumor cells that have a high level of expression of the transferrin receptor. Conclusions: The developed Au/AgICSD nanodimer can be used as a potential biomarker targeted dual-modal contrast agent for both or combined CT and PAI molecular imaging.

  2. Wetting reaction of Sn-Ag based solder systems on Cu substrates plated with Au and/or Pd layer

    NASA Astrophysics Data System (ADS)

    Liu, C. Y.; Li, Jian; Vandentop, G. J.; Choi, W. J.; Tu, K. N.

    2001-05-01

    The wetting behavior of SnAg based Pb-free solders on Cu and Cu substrates plated with Au, Pd, and Au/Pd thin films have been studied. The wetting angle and kinetics of interfacial reaction were measured. The Au-plated substrates exhibit better wetting than the Pd-plated substrates. In the case of SnAg on Pd-plated Cu, SEM observation revealed that the solder cap was surrounded by an innerring of Cu-Sn compound and an outer ring of Pd-Sn compound. This implies that the molten SnAg solder had removed the Pd and wetted the Cu directly in the equilibrium state. The effects of pre-doping Cu in the SnAg solder on wetting behavior were also investigated. We found that wettability decreases with increasing Cu content in the solder. We also observed that the SnAgCu solders have a lower Cu consumption rate than the SnAg solder.

  3. Underpotential deposition of Cd on Ag(1 1 1): an in situ STM study

    NASA Astrophysics Data System (ADS)

    García, S. G.; Salinas, D. R.; Staikov, G.

    2005-02-01

    The kinetics and mechanism of Cd underpotential deposition (UPD) and involved surface alloy formation processes in the system Ag(1 1 1)/Cd 2+, SO42-, are studied by means of combined electrochemical measurements and in situ scanning tunneling microscopy (STM). The results show that the UPD process starts with a formation of an expanded (diluted) adlayer with a superlattice structure Ag(1 1 1)- (√{3}×√{19})R23.4°. In the underpotential range 50 mV < Δ E < 80 mV this adlayer transforms to a condensed close packed Cd monolayer via a first order phase transition. At long polarization times the condensed monolayer undergoes structural changes involving place exchange processes between Cd atoms and surface Ag atoms. A formation of a second Cd monolayer and a significant Ag-Cd surface alloying take place at lower underpotentials (Δ E < 50 mV). The kinetics of surface alloying are analyzed on the basis of a recently proposed diffusion model including a relatively fast initial formation of a very thin surface alloy film and a subsequent slow alloy growth controlled by solid state diffusion. The anodic dealloying results in an appearance of monatomically deep pits, which disappear quickly at relatively high underpotentials (Δ E > 550 mV) indicating a high mobility of surface Ag atoms.

  4. Fabrication of Au@Ag core/shell nanoparticles decorated TiO2 hollow structure for efficient light-harvesting in dye-sensitized solar cells.

    PubMed

    Yun, Juyoung; Hwang, Sun Hye; Jang, Jyongsik

    2015-01-28

    Improving the light-harvesting properties of photoanodes is promising way to enhance the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). We synthesized Au@Ag core/shell nanoparticles decorated TiO2 hollow nanoparticles (Au@Ag/TiO2 HNPs) via sol-gel reaction and chemical deposition. The Au@Ag/TiO2 HNPs exhibited multifunctions from Au@Ag core/shell NPs (Au@Ag CSNPs) and TiO2 hollow nanoparticles (TiO2 HNPs). These Au@Ag CSNPs exhibited strong and broadened localized surface plasmon resonance (LSPR), together with a large specific surface area of 129 m(2) g(-1), light scattering effect, and facile oxidation-reduction reaction of electrolyte from TiO2 HNPs, which resulted in enhancement of the light harvesting. The optimum PCE of η = 9.7% was achieved for the DSSCs using photoanode materials based on TiO2 HNPs containing Au@Ag/TiO2 HNPs (0.2 wt % Au@Ag CSNPs with respect to TiO2 HNPs), which outperformed by 24% enhancement that of conventional photoanodes formed using P25 (η = 7.8%).

  5. Au@Ag/Au nanoparticles assembled with activatable aptamer probes as smart "nano-doctors" for image-guided cancer thermotherapy.

    PubMed

    Shi, Hui; Ye, Xiaosheng; He, Xiaoxiao; Wang, Kemin; Cui, Wensi; He, Dinggeng; Li, Duo; Jia, Xuekun

    2014-08-07

    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.

  6. PdAgAu alloy with high resistance to corrosion by H2S

    SciTech Connect

    Braun, Fernando; Miller, James B.; Gellman, Andrew J.; Tarditi, Ana M.; Fleutot, Benoit; Kondratyuk, Petro; Cornaglia, Laura M.

    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.

  7. Development of Ag-Pd-Au-Cu alloys for multiple dental applications. Part 2. Mechanical properties of experimental Ag-Pd-Au-Cu alloys containing Sn or Ga for ceramic-metal restorations.

    PubMed

    Goto, S; Nakai, A; Miyagawa, Y; Ogura, H

    2001-06-01

    Eighteen Ag-Pd-Au-Cu alloys, consisting of nine Ag-Pd-Au-Cu mother compositions (Pd: 20, 30 or 40%, Au: 20%, Cu: 10, 15 or 20%, Ag: balance) containing either 5% Sn or 5% Ga as an additive metal, were experimentally prepared. Tensile strength, proof stress, elongation, elastic modulus, and Vickers hardness of these alloys were evaluated to clarify the potential of these alloys for use as ceramic-metal restorations as well as the effects of the Pd and Cu contents on their mechanical properties. The tensile strength, proof stress, elongation, elastic modulus and Vickers hardness of the 18 experimental alloys were in the range of 410.0-984.0 MPa, 289.7-774.3 MPa, 2.2-23.7%, 81.3-123.0 GPa and 135.7-332.3 HV1, respectively. Ten of the 18 experimental alloys can be used for ultra-low fusing ceramics based on their proof stress, elastic modulus, elongation and hardness. Between the Ga- and Sn-added alloys, differences in tensile strength, proof stress, elongation and hardness were found at several Ag-Pd-Au-Cu compositions.

  8. Plasmonic Au nanoparticles embedding enhances the activity and stability of CdS for photocatalytic hydrogen evolution

    SciTech Connect

    Yu, Guiyang; Wang, Xiang; Cao, Jungang; Wu, Shujie; Yan, Wenfu; Liu, Gang

    2016-01-01

    A composite photocatalyst of embedding plasmonic Au nanoparticle into CdS (Au@CdS) was prepared with a cysteine-assisted hydrothermal approach. This structure could take fully advantage of electromagnetic fields at the surface of the Au nanoparticles under visible light illumination. The photocatalytic hydrogen evolution activity of CdS could be significantly improved. Without the use of any other metal or metal oxide as cocatalysts, the quantum efficiency can reach 12.1 % over 0.5%Au@CdS at 420 nm. When using 0.1%Pt as a cocatalyst, the quantum efficiency of 0.5%Au@CdS can be further improved to 45.6%. This efficiency can be maintained more than 100 h in the test 12 days, exhibiting a relatively high stability. Photoluminescence (PL) characterization shows that the formation rate of photoexcited e-/h+ was dramatically increased when Au nanoparticles were embedded into CdS. Time-resolved PL measurement shows that Au@CdS also has a longer luminescence lifetime than that of CdS, reflecting that the photoexcited electrons in Au@CdS be with much longer lifetime to reduce H+ forming H2. All these enhancements can be attributed to the effective energy transfer between the Au surface and CdS due to the well matched composite nanostructure. Dr. Xiang Wang gratefully acknowledges the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division for the support of this work.

  9. Growth of periodic nano-layers of nano-crystals of Au, Ag, Cu by ion beam

    NASA Technical Reports Server (NTRS)

    Smith, Cydale C.; Zheng, B.; Muntele, C. I.; Muntele, I. C.; Ila, D.

    2005-01-01

    Multilayered thin films of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/, were grown by deposition. We have previously shown that MeV ion Bombardment of multi-nano-layers of SiO2/AU+ SiO2/ produces Au nanocrystals in the AU+ SiO2 layers. An increased number of nano-layers followed by MeV ion bombardment produces a wide optical absorption band, of which its FWHM depends on the number of nano-layers of SiO2/AU+ SiO2/. We have successfully repeated this process for nano-layers of SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/. In this work we used 5 MeV Si as the post deposition bombardment ion and monitored the location as well as the optical absorption's FWHM for each layered structure using Optical Absorption Photospectrometry. The concentration and location of the metal nano-crystals were measured by Rutherford Backscattering Spectrometry. We will report on the results obtained for nano-layered structures produced by post deposition bombardment of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/ layered systems as well as the results obtained from a system containing a periodic combination of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/.

  10. DNA-embedded Au-Ag core-shell nanoparticles assembled on silicon slides as a reliable SERS substrate.

    PubMed

    Zhang, Zhong; Zhang, Sha; Lin, Mengshi

    2014-05-07

    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.

  11. Growth of periodic nano-layers of nano-crystals of Au, Ag, Cu by ion beam

    NASA Technical Reports Server (NTRS)

    Smith, Cydale C.; Zheng, B.; Muntele, C. I.; Muntele, I. C.; Ila, D.

    2005-01-01

    Multilayered thin films of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/, were grown by deposition. We have previously shown that MeV ion Bombardment of multi-nano-layers of SiO2/AU+ SiO2/ produces Au nanocrystals in the AU+ SiO2 layers. An increased number of nano-layers followed by MeV ion bombardment produces a wide optical absorption band, of which its FWHM depends on the number of nano-layers of SiO2/AU+ SiO2/. We have successfully repeated this process for nano-layers of SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/. In this work we used 5 MeV Si as the post deposition bombardment ion and monitored the location as well as the optical absorption's FWHM for each layered structure using Optical Absorption Photospectrometry. The concentration and location of the metal nano-crystals were measured by Rutherford Backscattering Spectrometry. We will report on the results obtained for nano-layered structures produced by post deposition bombardment of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/ layered systems as well as the results obtained from a system containing a periodic combination of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/.

  12. Controlled preparation of Au/Ag/SnO2 core-shell nanoparticles using a photochemical method and applications in LSPR based sensing

    NASA Astrophysics Data System (ADS)

    Zhou, Na; Ye, Chen; Polavarapu, Lakshminarayana; Xu, Qing-Hua

    2015-05-01

    A photochemical method for the controlled preparation of core-shell Au/Ag/SnO2 nanorods (NRs) and nanospheres (NSs) has been developed based on photo-induced electron transfer processes in the plasmonic metal-semiconductor system. Au/AgNR/SnO2 and Au/AgNS/SnO2 were prepared by the UV irradiation of a mixture of mesoporous SnO2 coated AuNRs, or AuNSs, and AgNO3, in which AgNO3 was reduced by electrons transferred from the photo-excited mesoporous SnO2 (semiconductor) to the gold (metal). This method allows precise control over the composition and optical properties of the obtained nanoparticles. The LSPR refractive index sensitivity of the obtained Au/AgNR/SnO2 nanoparticles has been optimized to obtain a refractive index sensitivity of ~442 nm RIU-1. The optimized nanoparticles were subsequently chosen for the LSPR based sensing of glutathione (GSH) with the limit of detection of ~7.5 × 10-7 M. This photochemical method allows the controlled preparation of various Au/Ag/SnO2 nanoparticles to adjust their LSPR to suit various applications.A photochemical method for the controlled preparation of core-shell Au/Ag/SnO2 nanorods (NRs) and nanospheres (NSs) has been developed based on photo-induced electron transfer processes in the plasmonic metal-semiconductor system. Au/AgNR/SnO2 and Au/AgNS/SnO2 were prepared by the UV irradiation of a mixture of mesoporous SnO2 coated AuNRs, or AuNSs, and AgNO3, in which AgNO3 was reduced by electrons transferred from the photo-excited mesoporous SnO2 (semiconductor) to the gold (metal). This method allows precise control over the composition and optical properties of the obtained nanoparticles. The LSPR refractive index sensitivity of the obtained Au/AgNR/SnO2 nanoparticles has been optimized to obtain a refractive index sensitivity of ~442 nm RIU-1. The optimized nanoparticles were subsequently chosen for the LSPR based sensing of glutathione (GSH) with the limit of detection of ~7.5 × 10-7 M. This photochemical method allows

  13. Polymicrobial sepsis alters Ag-dependent and -independent memory CD8 T cell functions1

    PubMed Central

    Duong, Sean; Condotta, Stephanie A.; Rai, Deepa; Martin, Matthew D.; Griffith, Thomas S.; Badovinac, Vladimir P.

    2014-01-01

    Mortality from sepsis frequently results from secondary infections, and the extent to which sepsis affects pathogen-specific memory CD8 T cell responses remains unknown. Using the cecal-ligation and puncture (CLP) model of polymicrobial sepsis, we observed rapid apoptosis of pre-existing memory CD8 T cells after sepsis induction that led to a loss in CD8 T cell-mediated protection. Ag-sensitivity (functional avidity) and Ag-driven secondary expansion of memory CD8 T cells were decreased after sepsis, further contributing to the observed loss in CD8 T cell-mediated immunity. Moreover, Ag-independent bystander activation of memory CD8 T cells in response to heterologous infection was also significantly impaired early after sepsis induction. The reduced sensitivity of pre-existing memory CD8 T cells to sense inflammation and respond to heterologous infection by IFN-γ production was observed in inbred and outbred hosts and controlled by extrinsic (but not cell intrinsic) factors suggesting that sepsis-induced changes in the environment regulates innate functions of memory CD8 T cells. Taken together, the data in this study revealed a previously unappreciated role of sepsis in shaping the quantity and functionality of infection- or vaccine-induced memory CD8 T cells and will help further define the decline in T cell-mediated immunity during the sepsis-induced phase of immunosuppression. PMID:24646738

  14. Facile synthesis and intraparticle self-catalytic oxidation of dextran-coated hollow Au-Ag nanoshell and its application for chemo-thermotherapy.

    PubMed

    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.

  15. Simulation of 6 to 3 to 1 merge and squeeze of Au77+ bunches in AGS

    SciTech Connect

    Gardner, C. J.

    2016-05-09

    In order to increase the intensity per Au77+ bunch at AGS extraction, a 6 to 3 to 1 merge scheme was developed and implemented by K. Zeno during the 2016 RHIC run [1]. For this scheme, 12 Booster loads, each consisting of a single bunch, are delivered to AGS per AGS magnetic cycle. The bunch from Booster is itself the result of a 4 to 2 to 1 merge which is carried out on a at porch during the Booster magnetic cycle [2]. Each Booster bunch is injected into a harmonic 24 bucket on the AGS injection porch. In order to t into the buckets and allow for the AGS injection kicker rise time, the bunch width must be reduced by exciting quadrupole oscillations just before extraction from Booster [1]. The bunches are injected into two groups of six adjacent harmonic 24 buckets. In each group the 6 bunches are merged into 3 by bringing on RF harmonic 12 while reducing harmonic 24. This is a straightforward 2 to 1 merge (in which two adjacent bunches are merged into one). One ends up with two groups of three adjacent bunches sitting in harmonic 12 buckets. These bunches are accelerated to an intermediate porch for further merging. Doing the merge on a porch that sits above injection energy helps reduce losses that are believed to be due to the space-charge force acting on the bunched particles [3]. (The 6 to 3 merge is done on the injection porch because the harmonic 24 frequency on the intermediate porch would be too high for the AGS RF cavities.) On the intermediate porch each group of 3 bunches is merged into one by bringing on RF harmonics 8 and 4 and then reducing harmonics 12 and 8. One ends up with 2 bunches, each the result of a 6 to 3 to 1 merge and each sitting in a harmonic 4 bucket. This puts 6 Booster loads into each bunch. Each merged bunch needs to be squeezed into a harmonic 12 bucket for subsequent acceleration. This is done by again bringing on harmonic 8 and then harmonic 12.

  16. EC-STM study of the initial stages of the electrochemical Au(1 1 1)-Cd alloy formation

    NASA Astrophysics Data System (ADS)

    Schlaup, Christian; Horch, Sebastian

    2015-02-01

    We have studied the formation of an Au(1 1 1)-Cd alloy in a H2SO4 electrolyte by means of electrochemical STM (EC-STM). To this end, we first characterized the underpotential deposited (upd) Cd overlayers on Au(1 1 1) electrodes. We confirmed the existence of two upd phases on the reconstructed Au(1 1 1) surface, of which the first can be described with a (4 ×√{ 3}) unit cell and the second one with a (3 ×√{ 3}) unit cell in coexistence with a (2 ×√{ 3}) unit cell. At more negative potentials, an alloy with the Au(1 1 1) substrate is formed. In order to obtain a deeper insight into the alloying process, we had to avoid further Cd deposition at these potentials. This was achieved by exchanging the electrolyte after Cd deposition for a Cd-free solution under potential control. We found that the Au-Cd alloy exhibits an atomic structure with a close to square unit cell and locally interferes with the pattern of the Au(1 1 1) "herringbone" reconstruction. This Au-Cd alloy increases the overpotential for the hydrogen evolution reaction (HER) by about 130 mV.

  17. Effect of grain boundary structure on grain boundary diffusivities in the Au/Ag system

    SciTech Connect

    Ma, Qing, Balluffi, R.W.

    1990-12-01

    Grain boundary chemical diffusivities for a series of symmetric (001) tilt boundaries in the Au/Ag system were measured by the surface accumulation method using newly developed thin-film multi-crystal specimens, in which the grain boundaries feeding the accumulation surface were all of the same type. Possible effects due to segregation at the grain boundaries and surfaces were avoided. CSL boundaries of low-{Sigma} (i.e., 5, 13, 17, 25) and also more general boundaries with tilt angles between the low-{Sigma} orientations were selected. The diffusivities were found to vary monotonically with tilt angle (i.e., no cusps at low-{Sigma}'s were found) in a manner consistent with the Structural Unit model. 8 refs., 7 figs.

  18. [Au]/[Ag]-catalysed expedient synthesis of branched heneicosafuranosyl arabinogalactan motif of Mycobacterium tuberculosis cell wall.

    PubMed

    Thadke, Shivaji A; Mishra, Bijoyananda; Islam, Maidul; Pasari, Sandip; Manmode, Sujit; Rao, Boddu Venkateswara; Neralkar, Mahesh; Shinde, Ganesh P; Walke, Gulab; Hotha, Srinivas

    2017-01-25

    Emergence of multidrug-resistant and extreme-drug-resistant strains of Mycobacterium tuberculosis (MTb) can cause serious socioeconomic burdens. Arabinogalactan present on the cellular envelope of MTb is unique and is required for its survival; access to arabinogalactan is essential for understanding the biosynthetic machinery that assembles it. Isolation from Nature is a herculean task and, as a result, chemical synthesis is the most sought after technique. Here we report a convergent synthesis of branched heneicosafuranosyl arabinogalactan (HAG) of MTb. Key furanosylations are performed using [Au]/[Ag] catalysts. The synthesis of HAG is achieved by the repetitive use of three reactions namely 1,2-trans furanoside synthesis by propargyl 1,2-orthoester donors, unmasking of silyl ether, and conversion of n-pentenyl furanosides into 1,2-orthoesters. Synthesis of HAG is achieved in 47 steps (with an overall yield of 0.09%) of which 21 are installation of furanosidic linkages in a stereoselective manner.

  19. Intracellular and in Vivo Cyanide Mapping via Surface Plasmon Spectroscopy of Single Au-Ag Nanoboxes.

    PubMed

    Wang, Peiyuan; Bai, Yujie; Yao, Chi; Li, Xiaomin; Zhou, Lei; Wang, Wenxing; El-Toni, Ahmed Mohamed; Zi, Jian; Zhao, Dongyuan; Shi, Lei; Zhang, Fan

    2017-02-21

    Cyanide is extremely toxic to organisms but difficult to detect in living biological specimens. Here, we report a new CN(-) sensing platform based on unmodified Au-Ag alloy nanoboxes that etch in the presence of this analyte, yielding a shift in plasmon frequency that correlates with the analyte concentration. Significantly, when combined with dark field microscopy, these particle probes can be used to measure CN(-) concentrations in HeLa cells and in vivo in Zebra fish embryos. The limit of detection (LOD) of the novel method is 1 nM (below the acceptable limit defined by the World Health Organization), and finite-difference time-domain (FDTD) calculations are used to understand the CN(-) induced spectral shifts.

  20. [Au]/[Ag]-catalysed expedient synthesis of branched heneicosafuranosyl arabinogalactan motif of Mycobacterium tuberculosis cell wall

    NASA Astrophysics Data System (ADS)

    Thadke, Shivaji A.; Mishra, Bijoyananda; Islam, Maidul; Pasari, Sandip; Manmode, Sujit; Rao, Boddu Venkateswara; Neralkar, Mahesh; Shinde, Ganesh P.; Walke, Gulab; Hotha, Srinivas

    2017-01-01

    Emergence of multidrug-resistant and extreme-drug-resistant strains of Mycobacterium tuberculosis (MTb) can cause serious socioeconomic burdens. Arabinogalactan present on the cellular envelope of MTb is unique and is required for its survival; access to arabinogalactan is essential for understanding the biosynthetic machinery that assembles it. Isolation from Nature is a herculean task and, as a result, chemical synthesis is the most sought after technique. Here we report a convergent synthesis of branched heneicosafuranosyl arabinogalactan (HAG) of MTb. Key furanosylations are performed using [Au]/[Ag] catalysts. The synthesis of HAG is achieved by the repetitive use of three reactions namely 1,2-trans furanoside synthesis by propargyl 1,2-orthoester donors, unmasking of silyl ether, and conversion of n-pentenyl furanosides into 1,2-orthoesters. Synthesis of HAG is achieved in 47 steps (with an overall yield of 0.09%) of which 21 are installation of furanosidic linkages in a stereoselective manner.

  1. Measurement of antiproton annihilation on Cu, Ag and Au with emulsion films

    NASA Astrophysics Data System (ADS)

    Aghion, S.; Amsler, C.; Ariga, A.; Ariga, T.; Bonomi, G.; Bräunig, P.; Brusa, R. S.; Cabaret, L.; Caccia, M.; Caravita, R.; Castelli, F.; Cerchiari, G.; Comparat, D.; Consolati, G.; Demetrio, A.; Di Noto, L.; Doser, M.; Ereditato, A.; Evans, C.; Ferragut, R.; Fesel, J.; Fontana, A.; Gerber, S.; Giammarchi, M.; Gligorova, A.; Guatieri, F.; Haider, S.; Hinterberger, A.; Holmestad, H.; Huse, T.; Kawada, J.; Kellerbauer, A.; Kimura, M.; Krasnický, D.; Lagomarsino, V.; Lansonneur, P.; Lebrun, P.; Malbrunot, C.; Mariazzi, S.; Matveev, V.; Mazzotta, Z.; Müller, S. R.; Nebbia, G.; Nedelec, P.; Oberthaler, M.; Pacifico, N.; Pagano, D.; Penasa, L.; Petracek, V.; Pistillo, C.; Prelz, F.; Prevedelli, M.; Ravelli, L.; Rienaecker, B.; RØhne, O. M.; Rotondi, A.; Sacerdoti, M.; Sandaker, H.; Santoro, R.; Scampoli, P.; Simon, M.; Smestad, L.; Sorrentino, F.; Testera, G.; Tietje, I. C.; Vamosi, S.; Vladymyrov, M.; Widmann, E.; Yzombard, P.; Zimmer, C.; Zmeskal, J.; Zurlo, N.

    2017-04-01

    The characteristics of low energy antiproton annihilations on nuclei (e.g. hadronization and product multiplicities) are not well known, and Monte Carlo simulation packages that use different models provide different descriptions of the annihilation events. In this study, we measured the particle multiplicities resulting from antiproton annihilations on nuclei. The results were compared with predictions obtained using different models in the simulation tools GEANT4 and FLUKA. For this study, we exposed thin targets (Cu, Ag and Au) to a very low energy antiproton beam from CERN's Antiproton Decelerator, exploiting the secondary beamline available in the AEgIS experimental zone. The antiproton annihilation products were detected using emulsion films developed at the Laboratory of High Energy Physics in Bern, where they were analysed at the automatic microscope facility. The fragment multiplicity measured in this study is in good agreement with results obtained with FLUKA simulations for both minimally and heavily ionizing particles.

  2. [Au]/[Ag]-catalysed expedient synthesis of branched heneicosafuranosyl arabinogalactan motif of Mycobacterium tuberculosis cell wall

    PubMed Central

    Thadke, Shivaji A.; Mishra, Bijoyananda; Islam, Maidul; Pasari, Sandip; Manmode, Sujit; Rao, Boddu Venkateswara; Neralkar, Mahesh; Shinde, Ganesh P.; Walke, Gulab; Hotha, Srinivas

    2017-01-01

    Emergence of multidrug-resistant and extreme-drug-resistant strains of Mycobacterium tuberculosis (MTb) can cause serious socioeconomic burdens. Arabinogalactan present on the cellular envelope of MTb is unique and is required for its survival; access to arabinogalactan is essential for understanding the biosynthetic machinery that assembles it. Isolation from Nature is a herculean task and, as a result, chemical synthesis is the most sought after technique. Here we report a convergent synthesis of branched heneicosafuranosyl arabinogalactan (HAG) of MTb. Key furanosylations are performed using [Au]/[Ag] catalysts. The synthesis of HAG is achieved by the repetitive use of three reactions namely 1,2-trans furanoside synthesis by propargyl 1,2-orthoester donors, unmasking of silyl ether, and conversion of n-pentenyl furanosides into 1,2-orthoesters. Synthesis of HAG is achieved in 47 steps (with an overall yield of 0.09%) of which 21 are installation of furanosidic linkages in a stereoselective manner. PMID:28120821

  3. Controlling Structural Transitions in AuAg Nanoparticles through Precise Compositional Design.

    PubMed

    Gould, Anna L; Rossi, Kevin; Catlow, C Richard A; Baletto, Francesca; Logsdail, Andrew J

    2016-11-03

    We present a study of the transitional pathways between high-symmetry structural motifs for AgAu nanoparticles, with a specific focus on controlling the energetic barriers through chemical design. We show that the barriers can be altered by careful control of the elemental composition and chemical arrangement, with core@shell and vertex-decorated arrangements being specifically influential on the barrier heights. We also highlight the complexity of the potential and free energy landscapes for systems where there are low-symmetry geometric motifs that are energetically competitive to the high-symmetry arrangements. In particular, we highlight that some core@shell arrangements preferentially transition through multistep restructuring of low-symmetry truncated octahedra and rosette-icosahedra, instead of via the more straightforward square-diamond transformations, due to lower energy barriers and competitive energetic minima. Our results have promising implications for the continuing efforts in bespoke nanoparticle design for catalytic and plasmonic applications.

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

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

  5. Novel Au-Ag hybrid device for electrochemical SE(R)R spectroscopy in a wide potential and spectral range.

    PubMed

    Feng, Jiu-Ju; Gernert, Ulrich; Sezer, Murat; Kuhlmann, Uwe; Murgida, Daniel H; David, Christin; Richter, Marten; Knorr, Andreas; Hildebrandt, Peter; Weidinger, Inez M

    2009-01-01

    A nanostructured gold-silver-hybrid electrode for SER spectroelectrochemistry was developed which advantageously combines the electrochemical properties and chemical stability of Au and the strong surface enhancement of (resonance) Raman scattering by Ag. The layered device consists of a massive nanoscopically rough Ag electrode, a thin (2 nm) organic layer, and a ca. 20 nm thick Au film that may be coated by self-assembled monolayers for protein adsorption. The SERR-spectroscopic and electrochemical performance of this device is demonstrated using the heme protein cytochrome c as a benchmark model system, thereby extending, for the first time, SE(R)R studies of molecules on Au surfaces to excitation in the violet spectral range. The enhancement factor is only slightly lower than for Ag electrodes which can be rationalized in terms of an efficient transfer of plasmon resonance excitation from the Ag to the Au coating. This mechanism, which requires a thin dielectric layer between the two metals, is supported by theoretical calculations.

  6. Interfacial assembly of mussel-inspired au@ag@ polydopamine core-shell nanoparticles for recyclable nanocatalysts.

    PubMed

    Zhou, Jiajing; Duan, Bo; Fang, Zheng; Song, Jibin; Wang, Chenxu; Messersmith, Phillip B; Duan, Hongwei

    2014-02-01

    Recyclable nanocatalysts of core-shell bimetallic nanocrystals are developed through polydopamine coating-directed one-step seeded growth, interfacial assembly, and substrate-immobilization of Au@Ag core-shell nanocrystals. This strategy provides new opportunities to design and optimize heterogeneous nanocatalysts with tailored size, morphology, chemical configuration, and supporting substrates for metal-catalyzed reactions.

  7. Chitosan nanocomposite films based on Ag-NP and Au-NP biosynthesis by Bacillus Subtilis as packaging materials.

    PubMed

    Youssef, Ahmed M; Abdel-Aziz, Mohamed S; El-Sayed, Samah M

    2014-08-01

    Chitosan-silver (CS-Ag) and Chitosan-gold (CS-Au) nanocomposites films were synthesized by a simple chemical method. A local bacterial isolate identified as Bacillus subtilis ss subtilis was found to be capable to synthesize both silver nanoparticles (Ag-NP) and gold nanoparticles (Au-NP) from silver nitrate (AgNO3) and chloroauric acid (AuCl(4-)) solutions, respectively. The biosynthesis of both Ag-NP and Au-NP characterize using UV/vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), and then added to chitosan by different ratios (0.5, 1 and 2%). The prepared chitosan nanocomposites films were characterize using UV, XRD, SEM and TEM. Moreover, the antibacterial activity of the prepared films was evaluated against gram positive (Staphylococcus aureus) and gram negative bacteria (Pseudomonas aerugenosa), fungi (Aspergillus niger) and yeast (Candida albicans). Therefore, these materials can be potential used as antimicrobial agents in packaging applications.

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

    NASA Astrophysics Data System (ADS)

    Wu, Xia; Sun, Yan

    2017-06-01

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

  9. Enhanced Raman and luminescence spectra from co-encapsulated silicon quantum dots and Au-Ag nanoalloys.

    PubMed

    Harun, Noor Aniza; Horrocks, Benjamin R; Fulton, David A

    2014-10-21

    We report an approach to enhance simultaneously luminescence and SERS signals with a single excitation wavelength by co-encapsulating silicon quantum dots and Au-Ag alloy nanoparticles encoded with Raman reporter molecules inside polymeric nanoparticles. The SERS-luminescence enhancement exploits the large Stokes shift of silicon quantum dots, which allows 'room' for the display of a Raman spectrum.

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

    NASA Astrophysics Data System (ADS)

    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. Synthesis of highly fluorescent metal (Ag, Au, Pt, and Cu) nanoclusters by electrostatically induced reversible phase transfer.

    PubMed

    Yuan, Xun; Luo, Zhentao; Zhang, Qingbo; Zhang, Xinhai; Zheng, Yuangang; Lee, Jim Yang; Xie, Jianping

    2011-11-22

    This paper reports a simple and scalable method for the synthesis of highly fluorescent Ag, Au, Pt, and Cu nanoclusters (NCs) based on a mild etching environment made possible by phase transfer via electrostatic interactions. Using Ag as a model metal, a simple and fast (total synthesis time < 3 h) phase transfer cycle (aqueous → organic (2 h incubation) → aqueous) has been developed to process originally polydisperse, nonfluorescent, and unstable Ag NCs into monodisperse, highly fluorescent, and extremely stable Ag NCs in the same phase (aqueous) and protected by the same thiol ligand. The synthetic protocol was successfully extended to fabricate highly fluorescent Ag NCs protected by custom-designed peptides with desired functionalities (e.g., carboxyl, hydroxyl, and amine). The facile synthetic method developed in this study should largely contribute to the practical applications of this new class of fluorescence probes.

  12. Large stokes shift of Ag doped CdSe quantum dots via aqueous route.

    PubMed

    Huang, Jian; Jiang, Yang; Duan, Hongyan; Liu, Chao; Mi, Longfei; Lan, Xinzheng; Zhou, Hongyang; Zhong, Honghai

    2013-10-01

    Monodispersed and luminescent Ag-doped CdSe semiconductor quantum dots (d-dots) were synthesized by an aqueous route assisted with electrochemical preparation of Se source with 3-mercaptopropionic acid as stabilizer. The silver dopants were incorporated into the host crystals via cation-exchange mechanism. X-ray diffraction patterns revealed that the as-synthesized CdSe:Ag d-dots were well retained in the zinc blende structure. The CdSe:Ag d-dots that exhibited uniform size distribution and good crystallnity could be observed by High-resolution transmission electron microscopy (HRTEM), with average diameter of 2.7 nm. Successful doping was confirmed by X-ray photoelectron spectroscopy survey spectra. The peculiar Ag-related photoluminescence showed strong intensity, and at the same time, intrinsic band-edge exciton emission of CdSe QDs was suppressed. The dopant emission exhibited larger Stockes shift of - 0.51 eV than that of the band-gap emission, and varied from 546 to 583 nm by changing electrolytic time. Possible radiative recombination mechanism of the aqueous Ag-doped CdSe d-dots was discussed. The results demonstrated that doping can be an effective way to manipulate the optical properties of semiconductor nanocrystals.

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

    Genetic algorithm global optimization of Ag-Pd, Ag-Au, and Pd-Pt clusters is performed. The 34- and 38-atom clusters are optimized for all compositions. The atom-atom interactions are modeled by a semiempirical potential. All three systems are characterized by a small size mismatch and a weak tendency of the larger atoms to segregate at the surface of the smaller ones. As a result, the global minimum structures exhibit a larger mixing than in Ag-Cu and Ag-Ni clusters. Polyicosahedral structures present generally favorable energetic configurations, even though they are less favorable than in the case of the size-mismatched systems. A comparison between all the systems studied here and in the previous paper (on size-mismatched systems) is presented.

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

    PubMed

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

    2005-05-15

    Genetic algorithm global optimization of Ag-Pd, Ag-Au, and Pd-Pt clusters is performed. The 34- and 38-atom clusters are optimized for all compositions. The atom-atom interactions are modeled by a semiempirical potential. All three systems are characterized by a small size mismatch and a weak tendency of the larger atoms to segregate at the surface of the smaller ones. As a result, the global minimum structures exhibit a larger mixing than in Ag-Cu and Ag-Ni clusters. Polyicosahedral structures present generally favorable energetic configurations, even though they are less favorable than in the case of the size-mismatched systems. A comparison between all the systems studied here and in the previous paper (on size-mismatched systems) is presented.

  15. Pyrazine functionalized Ag(I) and Au(I)-NHC complexes are potential antibacterial agents.

    PubMed

    Roymahapatra, G; Mandal, S M; Porto, W F; Samanta, T; Giri, S; Dinda, J; Franco, O L; Chattaraj, P K

    2012-01-01

    Antimicrobial resistance is an ever-increasing problem throughout the world and has already reached severe proportions. Bacteria can develop ways to render traditional antibiotics ineffective, raising a crucial need to find new antimicrobials with novel mode of action. We demonstrate here a novel class of pyrazine functionalized Ag(I) and Au(I)-NHC complexes as antibacterial agents against human pathogens that are resistant to several antibiotics. Complete synthetic and structural studies of Au(I) and Ag(I) complexes of 2-(1-methylimidazolium) pyrimidinechloride (L-1), 2,6-bis(1-methylimidazol)pyrazinechloride (L-2) and 2,6-bis(1-methyl imidazol) pyrazinehexa-fluorophosphate (L-3) are reported herein. Chloro[2,6-bis(1-methyl imidazol)pyrazine]gold(I), 2b and chloro [2,6-bis(1-methyl imidazol)pyrazine]silver(I), 2a complexes are found to have more potent antimicrobial activity than other synthesized compounds and several conventionally used antibiotics. Complexes 2b and 2a also inhibit the biofilm formation by Gram-positive bacteria, Streptococcus mutans and Gram-negative bacteria, Escherichia coli, causing drastic damage to the bacterial cell wall and increasing membrane permeability. Complexes 2b and 2a strongly binds to both Lys and Dap-Type peptidoglycan layers, which may be the reason for damage to the bacterial cell wall. Theoretical studies of all the complexes reveal that 2b and 2a are more reactive than other complexes, and this may be the cause of differences in antibacterial activity. These findings will pave the way towards developing a new class of antibiotics against different groups of conventional antibiotic-resistant bacteria.

  16. Chemical stability at noble metal M/YBa 2Cu 3O 6.8 interfaces (M = Pt, Ag, Au)

    NASA Astrophysics Data System (ADS)

    Bohnenkamp-Weiss, Ruth; Schmid-Fetzer, Rainer

    1994-02-01

    The chemical compatibility between YBa 2Cu 3O 6.8 (Y123) and Pt, Ag or Au was studied using quasi-infinite diffusion couples which were encapsulated and annealed at 650 to 800°C for 5 to 80 h. The phase formation at the interface was analyzed in cross sections of these couples using optical and scanning electron microscopy together with energy- and wavelength dispersive X-ray microanalysis. In addition, bulk powder mixtures of Y123 with Pt, Ag or Au were annealed at 800°C for 100 h and phase analysis was performed using X-ray diffraction. At the Pt/Y123 interface a reaction zone grows slowly but decisively at 800°C. Its microstructure is multiphase with YCu-oxides and a fine-grained dispersion of Y 2BaCuO 5 (Y211) with BaCu-oxides. Additional BaPt oxides and other phases are seen in powder mixtures annealed for longer times. Barium is suspected to diffuse out from the superconductor along grain boundaries from as deep as 1 mm, causing the decomposition of Y123 into YCu-oxides in the depleted regions. Ag and Au form a stable contact at the interface to Y123 with no reaction zone or new phases. Interdiffusion at the Ag/Y123 interface at 800°C was too low to be clearly detected. In contrast, Au diffuses very fast into Y123 and at 800°C the solubility is 4.2 mass% Au. Yttrium and barium diffuse much slower into the (Au) phase, Cu diffusion was not detected. Weak traces of decomposition products, mostly Y211 and BaCu-oxides, were observed in bulk powder mixtures of Y123 with Ag or Au annealed at 800°C for 100 h in closed capsules. These decomposition products are considered to be due to the high oxygen pressure in the closed capsule, exceeding the stability limit of Y123, and not due to the reduction of Y123. Both Ag and Au are virtually non-reactive with Y123.

  17. Tailor-made Au@Ag core-shell nanoparticle 2D arrays on protein-coated graphene oxide with assembly enhanced antibacterial activity

    NASA Astrophysics Data System (ADS)

    Wang, Huiqiao; Liu, Jinbin; Wu, Xuan; Tong, Zhonghua; Deng, Zhaoxiang

    2013-05-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-10-01

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

  19. Ultrafine Au and Ag Nanoparticles Synthesized from Self-Assembled Peptide Fibers and Their Excellent Catalytic Activity.

    PubMed

    Xu, Wenlong; Hong, Yue; Hu, Yuanyuan; Hao, Jingcheng; Song, Aixin

    2016-07-18

    The self-assembly of an amphiphilic peptide molecule to form nanofibers facilitated by Ag(+) ions was investigated. Ultrafine AgNPs (NPs=nanoparticles) with an average size of 1.67 nm were synthesized in situ along the fibers due to the weak reducibility of the -SH group on the peptide molecule. By adding NaBH4 to the peptide solution, ultrafine AgNPs and AuNPs were synthesized with an average size of 1.35 and 1.18 nm, respectively. The AuNPs, AgNPs, and AgNPs/nanofibers all exhibited excellent catalytic activity toward the reduction of 4-nitrophenol, with turnover frequency (TOF) values of 720, 188, and 96 h(-1) , respectively. Three dyes were selected for catalytic degradation by the prepared nanoparticles and the nanoparticles showed selective catalysis activity toward the different dyes. It was a surprising discovery that the ultrafine AuNPs in this work had an extremely high catalytic activity toward methylene blue, with a reaction rate constant of 0.21 s(-1) and a TOF value of 1899 h(-1) .

  20. Au-Ag template stripped pattern for scanning probe investigations of DNA arrays produced by dip pen nanolithography.

    PubMed

    Baserga, Andrea; Viganò, Marco; Casari, Carlo S; Turri, Stefano; Li Bassi, Andrea; Levi, Marinella; Bottani, Carlo E

    2008-11-18

    We report on DNA arrays produced by dip pen nanolithography (DPN) on a novel Au-Ag micropatterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting multi-instrument and multitechnique local detection and analysis. Moreover the smooth surface of the Au squares ( approximately 5-10 A roughness) allows AFM/STM to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label-free detection methods for DNA nanoarrays based on the use of scanning probes.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  2. Gold-doped silver nanocluster [Au3Ag38(SCH2Ph)24X5](2-) (X = Cl or Br).

    PubMed

    Wang, Zhi; Senanayake, Ravithree; Aikens, Christine M; Chen, Wen-Miao; Tung, Chen-Ho; Sun, Di

    2016-12-07

    Here we report the single-crystal structure, experimental and theoretical characterization of a 41-metal atom Au-Ag alloy nanocluster [Au3Ag38(SCH2Ph)24X5](2-) (1, X = Cl or Br). The nanocluster 1 is co-protected by thiolate and halogen atoms and features an all-metallic face-fused biicosahedral Au2@AuAg20 rod-like kernel enwrapped by the outermost Ag18(SCH2Ph)24X3 shell. Two sites on the surface of the biicosahedral kernel are partially occupied by Au and Ag atoms. The outer Ag18(SCH2Ph)24X3 shell is composed of two Ag6S6 cycles at the two poles and one Ag6S2X3 arc at the equator with both 2- and 3-coordinated Ag atoms, which has not been observed in gold or silver nanoclusters ever before. Theoretical calculations elucidate its electronic structure as well as optical properties, thus producing informative correlations between its structure and properties. This nanocluster exhibits near-infrared (NIR) emission around 825 nm. This work (i) snapshots a rare crystal structure of an Au-doped silver alloyed nanocluster; (ii) gives a deep insight to understand how the capping ligand or anions affect the structure of the alloy nanocluster; and (iii) provides precise information about gold atom doping site that is very significant in the recognition of potential active catalytic sites of the alloy nanoparticles.

  3. Dual-frequency plasmon lasing modes in active three-layered bimetallic Ag/Au nanoshells

    NASA Astrophysics Data System (ADS)

    Wu, DaJian; Wu, XueWei; Cheng, Ying; Jin, BiaoBing; Liu, XiaoJun

    2015-11-01

    The optical properties of three-layered silver-gold-silica (SGS) nanoshells with gain have been investigated theoretically by using Mie theory. Surface plasmon amplification by stimulated emission of radiation (spaser) phenomena can be observed at two plasmon modes of the active SGS nanoshell in the visible region. It is found with the decrease in the radius of the inner Ag core that the critical value of ɛg″(ωg ) for the super-resonance of the low-energy mode increases first and then decreases while that for the high-energy mode decreases. An interesting overlap between the two curves for the critical value of ɛg″(ωg ) can be found at a special core radius. At this point, two super-resonances can be achieved concurrently at the low- and high-energy modes of the active SGS nanoshell with the same gain coefficient. This dual-frequency spaser based on the bimetallic Ag/Au nanoshell may be an efficient candidate for designing the nanolaser.

  4. Chemical noise produced by equilibrium adsorption/desorption of surface pyridine at Au-Ag-Au bimetallic atom-scale junctions studied by fluctuation spectroscopy.

    PubMed

    Hwang, Tai-Wei; Branagan, Sean P; Bohn, Paul W

    2013-03-20

    The chemical noise contained in conductance fluctuations resulting from adsorption and desorption of pyridine at Au-Ag-Au bimetallic atom-scale junctions (ASJs) exhibiting ballistic electron transport is studied using fluctuation spectroscopy. ASJs are fabricated by electrochemical Ag deposition in a Au nanogap to produce a high-conductance Ag quantum wire, followed by electromigration-induced thinning in pyridine solution to create stable ASJs. The conductance behavior of the resulting ASJs is analyzed by sequential autocorrelation and Fourier transform of the current-time data to yield the power spectral density (PSD). In these experiments the PSDs from Ag ASJs in pyridine exhibit two main frequency regions: 1/f noise originating from resistance fluctuations of the junction itself at low frequencies, and a Lorentzian noise component arising from molecular adsorption/desorption fluctuations at higher frequencies. The characteristic cutoff frequency of the Lorentzian noise component determines the relaxation time of molecular fluctuations, which, in turn, is sensitive to the kinetics of the adsorption/desorption process. The kinetics are found to depend on concentration and on the adsorption binding energy. The junction size (<5G0), on the other hand, does not affect the kinetics, as the cutoff frequency remains unchanged. Concentration-dependent adsorption free energies are interpreted as arising from a distribution of binding energies, N(E(b)), on the Ag ASJ. Other observations, such as long lifetime ASJs and two-level fluctuations in conductance, provide additional evidence for the integral role of the adsorbate in determining ASJ reorganization dynamics.

  5. Real-Time Ab Initio KMC Simulation of the Self-Assembly and Sintering of Bimetallic Epitaxial Nanoclusters: Au + Ag on Ag(100)

    SciTech Connect

    Han, Yong; Liu, Da-Jiang; Evans, James W

    2014-08-13

    Far-from-equilibrium shape and structure evolution during formation and post-assembly sintering of bimetallic nanoclusters is extremely sensitive to the periphery diffusion and intermixing kinetics. Precise characterization of the many distinct local-environment-dependent diffusion barriers is achieved for epitaxial nanoclusters using density functional theory to assess interaction energies both with atoms at adsorption sites and at transition states. Kinetic Monte Carlo simulation incorporating these barriers then captures structure evolution on the appropriate time scale for two-dimensional core-ring and intermixed Au-Ag nanoclusters on Ag(100).

  6. Ag adsorption on Cd-terminated CdS (0 0 0 1) and S-terminated CdS (0 0 0 1-bar) surfaces: First-principles investigations

    SciTech Connect

    Ma, Yandong; Dai, Ying; Wei, Wei; Liu, Xianghong; Huang, Baibiao

    2011-04-15

    First-principles calculations are performed to study the adsorption of Ag at Cd-terminated CdS (0 0 0 1) and S-terminated CdS (0 0 0 1-bar) surfaces as a function of Ag coverage. Our results reveal that Ag adsorption at Cd-terminated (0 0 0 1) has a large binging energy than at S-terminated (0 0 0 1-bar) surface. For Ag adsorption at Cd-terminated (0 0 0 1) surface, T4 structure is more favorable and the Ag-Cd bond posses an ionic-like character. While for Ag adsorption at S-terminated (0 0 0 1-bar) surface, the H3 structure is most stable and the bonding between Ag-S is covalent. It is found that the magnitude and the sign of surface dipole moment are partly determined by the difference between the electronegativities of Ag and the host atom bonding with Ag. The adsorption energy changes as a function of Ag coverage. In addition, related properties of Ag cluster adsorption at Cd-terminated (0 0 0 1) surface are also discussed. -- Graphical abstract: We studied the adsorption of Ag at Cd-terminated CdS (0 0 0 1) and S-terminated CdS (0 0 0 1-bar) surfaces as a function of Ag coverage by means of the first-principles calculations. In addition, related properties of Ag cluster adsorption at Cd-terminated (0 0 0 1) surface are also discussed. Our ab initio calculations are useful complement to the intense experimental studies for Ag-CdS interface. Display Omitted Research highlights: {yields} Ag adsorption effects on electronic structure and associated physics properties of CdS is systemically studied. {yields} The surface dipole moment is partly determined by the difference between the electronegativities of silver and the host atom bonding with silver. {yields} The characteristic of Ag cluster (Ag{sub 2}, Ag{sub 4}, and Ag{sub 7}) adsorption on the CdS (0 0 0 1) surface is discussed.

  7. Plasmonic effect in Au(core)-CdS(shell) quantum dot-sensitized photoelectrochemical cell for hydrogen generation from water

    NASA Astrophysics Data System (ADS)

    Ikeda, Takuya; Akashi, Ryo; Fujishima, Musashi; Tada, Hiroaki

    2017-09-01

    UV-light irradiation of Au nanoparticle (NP)-loaded mesoporous TiO2 nanocrystalline films in an ethanol solution of Cd(NO3)2 and S8 at 298 K gives rise to selective CdS deposition on Au NPs to yield Au(core)-CdS(shell) hybrid quantum dots (Au@CdS/mp-TiO2). Two-electrode quantum dot-sensitized photoelectrochemical cells with the structure of photoanode|0.25 M Na2S, 0.35 M Na2SO3 (solvent = water)|cathode were fabricated. The Au@CdS/mp-TiO2 photoanode cell yields hydrogen (H2) with a rate of 0.18 ml h-1 [solar-to-current efficiency (STCE) = 0.028%] without external bias far surpassing the rate of 0.028 ml h-1 (solar-to-current efficiency = 0.006%) for the CdS/mp-TiO2 photoanode cell under illumination of simulated sunlight (λ > 430 nm, AM 1.5, one sun). The 3D finite-difference time-domain calculations for a model Au@CdS/TiO2 system indicate that an intense local electric field with an enhancement factor of ˜103 is generated at the Au-CdS-TiO2 three-phase interface. The striking effect of the Au core stems from the enhancement of the excitation of the CdS shell and subsequent charge separation by the intense local electric field.

  8. Hot-electron transfer from the semiconductor domain to the metal domain in CdSe@CdS{Au} nano-heterostructures.

    PubMed

    Dana, Jayanta; Maity, Partha; Ghosh, Hirendra N

    2017-07-13

    Semiconductor-metal hybrid nanostructures are recognized as great materials due to their high level of light-induced charge separation, which has direct relevance in photocatalysis and solar energy conversion. To understand the mechanism of charge separation processes, hybrid CdSe@CdS{Au} nano-heterostructures containing Au nanoparticles (NPs) with different sizes were synthesized, and the ultrafast charge-transfer dynamics were monitored using femtosecond transient absorption spectroscopy. Steady-state optical absorption studies suggest the formation of charge-transfer complexes between core shell nanocrystals (NCs) and Au NPs. Steady-state and time-resolved luminescence spectroscopy suggest electron transfer from the photo-excited CdSe@CdS core shell QDs NCs to the Au NPs within the heterostructure. The ultrafast interfacial electron-transfer dynamics in the heterostructures were monitored by femtosecond transient absorption spectroscopy. The results revealed that both hot and thermalized electrons are transferred from the core shell QDs to the metal NPs with time constants of 150 and 300 fs, respectively. Hot-electron transfer from QDs to Au NPs was found to take place predominantly in the heterostructures depending on the sizes of the metal NPs. The photo-degradation of rhodamin B in the presence of the CdSe@CdS{Au} heterostructures under visible-light radiation suggests that the hot electrons in the heterostructures play a major role in photocatalytic degradation.

  9. Size evolution of nanomagnetic particles and magnetotransport properties of (Co90Fe10)20Ag80 nanogranular films: influence of Cu80Ag15Au5 underlayer

    NASA Astrophysics Data System (ADS)

    Öksüzoğlu, Ramis Mustafa; Meshcheryakov, Vladimir F.; Ayas, Erhan

    2012-06-01

    The influence of (Co90Fe10)20Ag80 film thickness and of Cu80Ag15Au5 underlayer on nanomagnetic, magnetotransport and structural properties of (Co90Fe10)20Ag80 nanogranular films prepared by ultra-high vacuum ion beam sputtering technique have been investigated using X-ray diffraction, X-ray reflectivity and vibrating sample magnetometer. Films indicate a superparamagnetic behavior. The evolution of the magnetic particle size in (Co90Fe10)20Ag80 film with different thicknesses was calculated by fit of magnetization curves using Langevin equation. A parallel resistance model has been used to determine particle size distribution. The average (mean) particle sizes range from 1.6 to 2.1 nm. A linear dependence of giant magnetoresistance (GMR) on the particle size has been found. This result is also supported by the observed linear correlation between the square root of the effective magnetization and the particle size. Furthermore, a linear correlation between the square of GMR and the distance between particles has been found. This remains unchanged also in (Co90Fe10)20Ag80 films with Cu80Ag15Au5 underlayer. Using of the underlayer leads to an enhancement of the mean particle size (1.8-2.5 nm) and GMR; however, to a reduction of distances between particles accompanied by the destruction of the <111> texture in the Ag matrix structure. The reason of the GMR effect in the nanogranular films is discussed by means of the obtained results.

  10. Controlled preparation of Au/Ag/SnO2 core-shell nanoparticles using a photochemical method and applications in LSPR based sensing.

    PubMed

    Zhou, Na; Ye, Chen; Polavarapu, Lakshminarayana; Xu, Qing-Hua

    2015-05-21

    A photochemical method for the controlled preparation of core-shell Au/Ag/SnO2 nanorods (NRs) and nanospheres (NSs) has been developed based on photo-induced electron transfer processes in the plasmonic metal-semiconductor system. Au/AgNR/SnO2 and Au/AgNS/SnO2 were prepared by the UV irradiation of a mixture of mesoporous SnO2 coated AuNRs, or AuNSs, and AgNO3, in which AgNO3 was reduced by electrons transferred from the photo-excited mesoporous SnO2 (semiconductor) to the gold (metal). This method allows precise control over the composition and optical properties of the obtained nanoparticles. The LSPR refractive index sensitivity of the obtained Au/AgNR/SnO2 nanoparticles has been optimized to obtain a refractive index sensitivity of ∼442 nm RIU(-1). The optimized nanoparticles were subsequently chosen for the LSPR based sensing of glutathione (GSH) with the limit of detection of ∼7.5 × 10(-7) M. This photochemical method allows the controlled preparation of various Au/Ag/SnO2 nanoparticles to adjust their LSPR to suit various applications.

  11. Resonance scattering spectral detection of catalase activity using Au@Ag nanoparticle as probe and coupling catalase catalytic reaction with Fenton reaction.

    PubMed

    Liang, Aihui; Liang, Yueyuan; Jiang, Zhiliang; Jiang, Hesheng

    2009-11-01

    The Au(core)Ag(shell) (Au@Ag) nanoparticles in size of 30 nm were prepared using 10 nm gold nanoparticles as seeds at 90 degrees C, and were purified by high-speed centrifugation to remove the excess trisodium citrate to obtain Au@Ag nanoprobe. In the medium of pH 4.0 acetate buffer solution--7.2 micromol/L H2O2--67 micromol/L Fe(II), Au@Ag nanoparticles exhibited a resonance scattering (RS) peak at 538 nm. Upon addition of Catalase (Ct), the system produced hydroxyl radical that oxidized the Au@Ag nanoprobe to form the AuAg nanoparticles with partly bare nanogold. Those AuAg nanoparticles aggregated to large nanoclusters that led to the RS peak wavelength red-shift and its RS peak intensity enhanced. The catalase activity (C) is linear to the enhanced RS intensity (DeltaI) in the range of 6 to 2,800 U/L, with regression equation of DeltaI = 0.168 C-0.2, the correlation coefficient of 0.9952, and detection limit of 2.8 U/L. This method was applied to the detection of serum samples, and the results were agreement with that of the spectrophotometry. A new catalytic mechanism of catalase was proposed with oxywater principle that was agreement with the results of resonance scattering spectroscopy, absorption spectrophotometry, transmission electron microscopy and laser scattering.

  12. Total structure determination of surface doping [Ag46Au24(SR)32](BPh4)2 nanocluster and its structure-related catalytic property

    PubMed Central

    Wang, Shuxin; Jin, Shan; Yang, Sha; Chen, Shuang; Song, Yongbo; Zhang, Jun; Zhu, Manzhou

    2015-01-01

    The structure effect is widely present in the catalysis of alloy systems. However, the surface structure of this system is still ambiguous because of the limitations of the current surface characterization tools. We reported the x-ray crystallographic structure of the first and the largest AgAu alloy nanocluster with a doping shell formulated as [Ag46Au24(SR)32](BPh4)2. This nanocluster consists of an achiral bimetallic Ag2@Au18@Ag20 core protected by a chiral Ag24Au6(SR)32 shell. The catalysis experiments further revealed that the surface structure affects the selectivity of products significantly. This is the first case to find the structure effect in atomically precise alloy nanoclusters. Our work will benefit the basic understanding of bimetal distribution, as well as the structure-related catalytic property of alloy nanoclusters at the atomic level. PMID:26601236

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

    PubMed

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

    2017-08-17

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

  14. Ultrasensitive electrochemical sensor for Hg(2+) by using hybridization chain reaction coupled with Ag@Au core-shell nanoparticles.

    PubMed

    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.

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

    PubMed

    Basavegowda, Nagaraj; Idhayadhulla, Akber; Lee, Yong Rok

    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. Copyright © 2014 Elsevier B.V. All rights reserved.

  16. On the Effect of Native SiO2 on Si over the SPR-mediated Photocatalytic Activities of Au and Ag Nanoparticles.

    PubMed

    Wang, Jiale; de Freitas, Isabel C; Alves, Tiago V; Ando, Romulo A; Fang, Zebo; Camargo, Pedro H C

    2017-05-29

    In hybrid materials containing plasmonic nanoparticles such as Au and Ag, charge-transfer processes from and to Au or Ag can affect both activities and selectivity in plasmonic catalysis. Inspired by the widespread utilization of commercial Si wafers in surface-enhanced Raman spectroscopy (SERS) studies, we investigated herein the effect of the native SiO2 layer on Si wafers over the surface plasmon resonance (SPR)-mediated activities of the Au and Ag nanoparticles (NPs). We prepared SERS-active plasmonic comprised of Au and Ag NPs deposited onto a Si wafer. Here, two kinds of Si wafers were employed: Si with a native oxide surface layer (Si/SiO2 ) and Si without a native oxide surface layer (Si). This led to Si/SiO2 /Au, Si/SiO2 /Ag, Si/Au, and Si/Ag NPs. The SPR-mediated oxidation of p-aminothiophenol (PATP) to p,p'-dimercaptoazobenzene (DMAB) was employed as a model transformation. By comparing the performances and band structures for the Si/Au and Si/Ag relative to Si/SiO2 /Au and Si/SiO2 /Ag NPs, it was found that the presence of a SiO2 layer was crucial to enable higher SPR-mediated PATP to DMAB conversions. The SiO2 layer acts to prevent the charge transfer of SPR-excited hot electrons from Au or Ag nanoparticles to the Si substrate. This enabled SPR-excited hot electrons to be transferred to adsorbed O2 molecules, which then participate in the selective oxidation of PATP to DMAB. In the absence of a SiO2 layer, SPR-excited hot electrons are preferentially transferred to Si instead of adsorbed O2 molecules, leading to much lower PATP oxidation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Autoclave mediated one-pot-one-minute synthesis of AgNPs and Au-Ag nanocomposite from Melia azedarach bark extract with antimicrobial activity against food pathogens.

    PubMed

    Pani, Alok; Lee, Joong Hee; Yun, Soon-Ii

    2016-01-01

    The increasing use of nanoparticles and nanocomposite in pharmaceutical and processed food industry have increased the demand for nontoxic and inert metallic nanostructures. Chemical and physical method of synthesis of nanostructures is most popular in industrial production, despite the fact that these methods are labor intensive and/or generate toxic effluents. There has been an increasing demand for rapid, ecofriendly and relatively cheaper synthesis of nanostructures. Here, we propose a strategy, for one-minute green synthesis of AgNPs and a one-pot one-minute green synthesis of Au-Ag nanocomposite, using Melia azedarach bark aqueous extract as reducing agent. The hydrothermal mechanism of the autoclave technology has been successfully used in this study to accelerate the nucleation and growth of nano-crystals. The study also presents high antimicrobial potential of the synthesized nano solutions against common food and water born pathogens. The multistep characterization and analysis of the synthesized nanomaterial samples, using UV-visible spectroscopy, ICP-MS, FT-IR, EDX, XRD, HR-TEM and FE-SEM, also reveal the reaction dynamics of AgNO3, AuCl3 and plant extract in synthesis of the nanoparticles and nanocomposite. The antimicrobial effectiveness of the synthesized Au-Ag nanocomposite, with high gold to silver ratio, reduces the dependency on the AgNPs, which is considered to be environmentally more toxic than the gold counterpart. We hope that this new strategy will change the present course of green synthesis. The rapidity of synthesis will also help in industrial scale green production of nanostructures using Melia azedarach.

  18. Ag/Au/Polypyrrole Core-shell Nanowire Network for Transparent, Stretchable and Flexible Supercapacitor in Wearable Energy Devices

    PubMed Central

    Moon, Hyunjin; Lee, Habeom; Kwon, Jinhyeong; Suh, Young Duk; Kim, Dong Kwan; Ha, Inho; Yeo, Junyeob; Hong, Sukjoon; Ko, Seung Hwan

    2017-01-01

    Transparent and stretchable energy storage devices have attracted significant interest due to their potential to be applied to biocompatible and wearable electronics. Supercapacitors that use the reversible faradaic redox reaction of conducting polymer have a higher specific capacitance as compared with electrical double-layer capacitors. Typically, the conducting polymer electrode is fabricated through direct electropolymerization on the current collector. However, no research have been conducted on metal nanowires as current collectors for the direct electropolymerization, even though the metal nanowire network structure has proven to be superior as a transparent, flexible, and stretchable electrode platform because the conducting polymer’s redox potential for polymerization is higher than that of widely studied metal nanowires such as silver and copper. In this study, we demonstrated a highly transparent and stretchable supercapacitor by developing Ag/Au/Polypyrrole core-shell nanowire networks as electrode by coating the surface of Ag NWs with a thin layer of gold, which provide higher redox potential than the electropolymerizable monomer. The Ag/Au/Polypyrrole core-shell nanowire networks demonstrated superior mechanical stability under various mechanical bending and stretching. In addition, proposed supercapacitors showed fine optical transmittance together with fivefold improved areal capacitance compared to pristine Ag/Au core-shell nanowire mesh-based supercapacitors. PMID:28155913

  19. Ag/Au/Polypyrrole Core-shell Nanowire Network for Transparent, Stretchable and Flexible Supercapacitor in Wearable Energy Devices.

    PubMed

    Moon, Hyunjin; Lee, Habeom; Kwon, Jinhyeong; Suh, Young Duk; Kim, Dong Kwan; Ha, Inho; Yeo, Junyeob; Hong, Sukjoon; Ko, Seung Hwan

    2017-02-03

    Transparent and stretchable energy storage devices have attracted significant interest due to their potential to be applied to biocompatible and wearable electronics. Supercapacitors that use the reversible faradaic redox reaction of conducting polymer have a higher specific capacitance as compared with electrical double-layer capacitors. Typically, the conducting polymer electrode is fabricated through direct electropolymerization on the current collector. However, no research have been conducted on metal nanowires as current collectors for the direct electropolymerization, even though the metal nanowire network structure has proven to be superior as a transparent, flexible, and stretchable electrode platform because the conducting polymer's redox potential for polymerization is higher than that of widely studied metal nanowires such as silver and copper. In this study, we demonstrated a highly transparent and stretchable supercapacitor by developing Ag/Au/Polypyrrole core-shell nanowire networks as electrode by coating the surface of Ag NWs with a thin layer of gold, which provide higher redox potential than the electropolymerizable monomer. The Ag/Au/Polypyrrole core-shell nanowire networks demonstrated superior mechanical stability under various mechanical bending and stretching. In addition, proposed supercapacitors showed fine optical transmittance together with fivefold improved areal capacitance compared to pristine Ag/Au core-shell nanowire mesh-based supercapacitors.

  20. Ag/Au/Polypyrrole Core-shell Nanowire Network for Transparent, Stretchable and Flexible Supercapacitor in Wearable Energy Devices

    NASA Astrophysics Data System (ADS)

    Moon, Hyunjin; Lee, Habeom; Kwon, Jinhyeong; Suh, Young Duk; Kim, Dong Kwan; Ha, Inho; Yeo, Junyeob; Hong, Sukjoon; Ko, Seung Hwan

    2017-02-01

    Transparent and stretchable energy storage devices have attracted significant interest due to their potential to be applied to biocompatible and wearable electronics. Supercapacitors that use the reversible faradaic redox reaction of conducting polymer have a higher specific capacitance as compared with electrical double-layer capacitors. Typically, the conducting polymer electrode is fabricated through direct electropolymerization on the current collector. However, no research have been conducted on metal nanowires as current collectors for the direct electropolymerization, even though the metal nanowire network structure has proven to be superior as a transparent, flexible, and stretchable electrode platform because the conducting polymer’s redox potential for polymerization is higher than that of widely studied metal nanowires such as silver and copper. In this study, we demonstrated a highly transparent and stretchable supercapacitor by developing Ag/Au/Polypyrrole core-shell nanowire networks as electrode by coating the surface of Ag NWs with a thin layer of gold, which provide higher redox potential than the electropolymerizable monomer. The Ag/Au/Polypyrrole core-shell nanowire networks demonstrated superior mechanical stability under various mechanical bending and stretching. In addition, proposed supercapacitors showed fine optical transmittance together with fivefold improved areal capacitance compared to pristine Ag/Au core-shell nanowire mesh-based supercapacitors.

  1. Highly efficient and porous TiO2-coated Ag@Fe3O4@C-Au microspheres for degradation of organic pollutants

    NASA Astrophysics Data System (ADS)

    Shen, Mao; Chen, Suqing; Jia, Wenping; Fan, Guodong; Jin, Yanxian; Liang, Huading

    2016-12-01

    In this paper, we reported a novel hierarchical porous Ag@Fe3O4@C-Au@TiO2 core@shell microspheres with a highly photocatalytic activity and magnetically separable properties. The synthesis method is included of a Fe3O4 magnetic embedded Ag core (Ag@Fe3O4), an interlayer of carbon modified by PEI to form sufficient amounts of amine functional groups (Ag@Fe3O4@C-PEI), the grafting of Au nanoparticles on the surface of Ag@Fe3O4@C-PEI (Ag@Fe3O4@C-Au), and an ordered porous TiO2 structured shell. As an example of the applications, the photocatalytic activities of the samples were investigated by the reduction of Rhodamine B (RhB) under visible-light irradiation. The results show that the porous Ag@Fe3O4@C-Au@TiO2 core@shell microspheres display higher adsorption and photocatalytic activities compared to the pure porous TiO2 and Ag@Fe3O4@C@TiO2 microspheres, which are attributed to the local surface plasmon resonance (LSPR) by the Ag and Au nanoparticles and the high specific surface area.

  2. Realization of Red Plasmon Shifts up to ∼900 nm by AgPd-Tipping Elongated Au Nanocrystals.

    PubMed

    Zhu, Xingzhong; Yip, Hang Kuen; Zhuo, Xiaolu; Jiang, Ruibin; Chen, Jianli; Zhu, Xiao-Ming; Yang, Zhi; Wang, Jianfang

    2017-10-04

    The synthesis of metal nanostructures with plasmon wavelengths beyond ∼1000 nm is strongly desired, especially for those with small sizes. Herein we report on a AgPd-tipping process on Au nanobipyramids with the resultant red plasmon shifts reaching up to ∼900 nm. The large red plasmon shifts are ascribed to the deposition of the metal at the tips of Au nanobipyramids, which is verified by electrodynamic simulations. The method has been successfully applied to Au nanobipyramids and nanorods with different longitudinal dipolar plasmon wavelengths, demonstrating that the plasmon wavelengths of these Au nanocrystals can be extended to the entire near-infrared region. Pt can also induce the tipping on Au nanobipyramids and nanorods to realize red plasmon shifts, suggesting the generality of our approach. We have further shown that the metal-tipped Au nanobipyramids possess a high photothermal conversion efficiency and good photothermal therapy performance. This study opens up a route to the construction of Au nanostructures with plasmon resonance in a broad spectral region for plasmon-enabled technological applications.

  3. Overpotential deposition of Ag monolayer and bilayer on Au(1 1 1) mediated by Pb adlayer underpotential deposition/stripping cycles

    NASA Astrophysics Data System (ADS)

    Wang, J. X.; Ocko, B. M.; Adzic, R. R.

    2003-08-01

    Ultra-thin Ag films on the Au(1 1 1) surface were prepared via overpotential deposition (OPD) in the presence of Pb 2+ ions. By carrying out repetitive Pb adlayer underpotential deposition (UPD) and stripping cycles during Ag bulk deposition, the two-dimensional growth of Ag films was significantly enhanced in high OPD. The Ag monolayer sample was made by comparing the voltammetry curves, in which the signatures for Pb adlayer UPD on Au(1 1 1) changed to that on Ag(1 1 1). As demonstrated by the X-ray specular reflectivity measurements, nearly complete monolayer and bilayer films can be made with optimized deposition procedures. On subatomic scale, however, we found that these films have significant higher root-mean-square displacement amplitudes than those underpotentially deposited Ag monolayer and bilayer on either Au(1 1 1) or Pt(1 1 1).

  4. Au-Ag polymetallic mineralization within tectonically weak zones along the southwestern edge of the Colorado Plateau

    SciTech Connect

    Wenrich, K.J.; Silberman, M.L. )

    1993-04-01

    The Music Mountain mining district lies at the base of the Grand Wash Cliffs, a major fault-line scarp along the Grand Wash fault, which marks the SW margin of the Colorado Plateau. Nearly vertical Au-Ag polymetallic quartz veins parallel, and are in contact with, altered diabase and granite porphyry dikes that cut Proterozoic granite, schist, and gneiss. The gold-bearing veins range in thickness from an inch to several feet and contain significant amounts of sulfide minerals. Diabase dikes and quartz veins in the district and to the north consistently strike N42[degree]W to N57[degree]W, which is one of the most prevalent fracture orientation throughout NW Arizona. In the Gold Basin-Lost Basin districts to the north, the Au occurs in such pegmatite-quartz veins that strike NE. Thirty miles east along Diamond Creek, quartz veins and diabase dikes strike N45[degree]E and are associated with Au and Ag anomalies in stream-sediments and panned concentrates. To the west major Au-Ag polymetallic quartz veins of the Wallapai mining district show consistent strikes from N30[degree] to 60[degree]W. K-Ar ages of hydrothermal alterations of 4 NW oriented diabase dikes that have quartz veins along them, range from 935 [+-] 35 to 755 [+-] 21 Ma. Sericite from altered granite porphyry, adjacent to a mineralized vein, gave a K-Ar age of 72 [+-]2 Ma. All geochemical sites (within a 1,000 mi[sup 2] area) determined to be anomalous in Au lie within 2 mi of either the Grand Wash or Hurricane faults. The Hurricane and Grand Wash faults, major Precambrian fault zones that were reactivated in the Phanerozoic, appear to be good exploration targets for Au-rich quartz veins associated with pegmatite or diabase dikes, many of which may be buried beneath the thick alluvium of Hualapai Valley.

  5. Ultrasensitive photoelectrochemical immunoassay for CA19-9 detection based on CdSe@ZnS quantum dots sensitized TiO2NWs/Au hybrid structure amplified by quenching effect of Ab2@V(2+) conjugates.

    PubMed

    Zhu, Hua; Fan, Gao-Chao; Abdel-Halim, E S; Zhang, Jian-Rong; Zhu, Jun-Jie

    2016-03-15

    A novel, enhanced photoelectrochemical immunoassay was established for sensitive and specific detection of carbohydrate antigen 19-9 (CA19-9, Ag). In this protocol, TiO2 nanowires (TiO2NWs) were first decorated with Au nanoparticles to form TiO2NWs/Au hybrid structure, and then coated with CdSe@ZnS quantum dots (QDs) via the layer-by-layer method, producing TiO2NWs/Au/CdSe@ZnS sensitized structure, which was employed as the photoelectrochemical matrix to immobilize capture CA19-9 antibodies (Ab1); whereas, bipyridinium (V(2+)) molecules were labeled on signal CA19-9 antibodies (Ab2) to form Ab2@V(2+) conjugates, which were used as signal amplification elements. The TiO2NWs/Au/CdSe@ZnS sensitized structure could adequately absorb light energy and dramatically depress electron-hole recombination, resulting in evidently enhanced photocurrent intensity of the immunosensing electrode. While target Ag were detected, the Ab2@V(2+) conjugates could significantly decrease the photocurrent detection signal because of strong electron-withdrawing property of V(2+) coupled with evident steric hindrance of Ab2. Thanks to synergy effect of TiO2NWs/Au/CdSe@ZnS sensitized structure and quenching effect of Ab2@V(2+) conjugates, the well-established photoelectrochemical immunoassay exhibited a low detection limit of 0.0039 U/mL with a wide linear range from 0.01 U/mL to 200 U/mL for target Ag detection. This proposed photoelectrochemical protocol also showed good reproducibility, specificity and stability, and might be applied to detect other important biomarkers.

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

    PubMed

    Iida, Kenji; Yasuike, Tomokazu; Nobusada, Katsuyuki

    2013-09-14

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

  7. Characteristics and Distribution of Mineral Textures and Fluid Inclusions in the Epithermal Ag-Au Deposits at Guanajuato, Mexico

    NASA Astrophysics Data System (ADS)

    Moncada, D.; Bodnar, R. J.; Reynolds, T. J.; Rimstidt, J. D.; Mutchler, S.

    2009-05-01

    Fluid inclusion and mineralogical features indicative of boiling have been characterized in 855 samples from epithermal precious metals deposits along the Veta Madre at Guanajuato, Mexico. Features associated with boiling that have been identified include colloform texture silica, plumose texture silica, moss texture silica, ghost-sphere texture silica, lattice-bladed calcite, lattice-bladed calcite replaced by quartz and pseudo-acicular quartz after calcite and coexisting liquid-rich and vapor-rich fluid inclusions. Samples were assayed for Au, Ag, Cu, Pb, Zn, As and Sb, and were divided into high-grade and low-grade samples based on the gold and silver concentrations. For silver, the cutoff for high grade was 100 ppm, and for gold the cutoff was 1 ppm. The feature that is most closely associated with high grades of both gold and silver is colloform texture silica, and this feature also shows the largest difference in grade based on the presence or absence of that feature (178.8 ppm Ag versus 17.2 ppm Ag, and 1.1 ppm Au versus 0.2 ppm Au). For both Ag and Au, there is no significant difference in average grade in samples that contain coexisting liquid-rich and vapor-rich fluid inclusions and those where this feature is absent. The textural and fluid inclusion data were analyzed using the binary classifier within SPSS Clementine. The models that correctly distinguish between high and low grade samples most consistently (˜70-75% of the tests) for both Ag and Au were the neural network, the C5 decision tree and Quest decision tree models. For both Au and Ag, the presence of colloform silica texture is the variable with the greatest importance, i.e., the variable that has the greatest predictive power. Boiling features are absent or rare in samples collected along a traverse perpendicular to the Veta Madre. This suggests that if an explorationist observes these features in samples collected during exploration, an environment favorable to precious metal mineralization

  8. Hotspots engineering by grafting Au@Ag core-shell nanoparticles on the Au film over slightly etched nanoparticles substrate for on-site paraquat sensing.

    PubMed

    Wang, Chaoguang; Wu, Xuezhong; Dong, Peitao; Chen, Jian; Xiao, Rui

    2016-12-15

    Paraquat (PQ) pollutions are ultra-toxic to human beings and hard to be decomposed in the environment, thus requiring an on-site detection strategy. Herein, we developed a robust and rapid PQ sensing strategy based on the surface-enhanced Raman scattering (SERS) technique. A hybrid SERS substrate was prepared by grafting the Au@Ag core-shell nanoparticles (NPs) on the Au film over slightly etched nanoparticles (Au FOSEN). Hotspots were engineered at the junctions as indicated by the finite difference time domain calculation. SERS performance of the hybrid substrate was explored using p-ATP as the Raman probe. The hybrid substrate gives higher enhancement factor comparing to either the Au FOSEN substrate or the Au@Ag core-shell NPs, and exhibits excellent reproducibility, homogeneity and stability. The proposed SERS substrates were prepared in batches for the practical PQ sensing. The total analysis time for a single sample, including the pre-treatment and measurement, was less than 5min with a PQ detection limit of 10nM. Peak intensities of the SERS signal were plotted as a function of the PQ concentrations to calibrate the sensitivity by fitting the Hill's equation. The plotted calibration curve showed a good log-log linearity with the coefficient of determination of 0.98. The selectivity of the sensing proposal was based on the "finger print" Raman spectra of the analyte. The proposed substrate exhibited good recovery when it applied to real water samples, including lab tap water, bottled water, and commercially obtained apple juice and grape juice. This SERS-based PQ detection method is simple, rapid, sensitive and selective, which shows great potential in pesticide residue and additives abuse monitoring.

  9. M-Au/TiO2 (M = Ag, Pd, and Pt) nanophotocatalyst for overall solar water splitting: role of interfaces

    NASA Astrophysics Data System (ADS)

    Melvin, Ambrose A.; Illath, Kavya; Das, Tanmay; Raja, Thirumalaiswamy; Bhattacharyya, Somnath; Gopinath, Chinnakonda S.

    2015-08-01

    M-Au/TiO2 (M = Ag, Pd, Pt) composites were prepared through a facile one-pot photodeposition synthesis and evaluated for solar water splitting (SWS) with and without a sacrificial agent. The M-Au combination exhibits a dominant role in augmenting the H2 generation activity by forming a bi-metallic system. Degussa P25 was used as a TiO2 substrate to photodeposit Au followed by Au + M (M = Ag/Pd/Pt). The SWS activity of the M-Au/TiO2 was determined through photocatalytic H2 production in the presence of methanol as a sacrificial agent under one sun conditions with an AM1.5 filter. The highest H2 yield was observed for Pt0.5-Au1/TiO2 and was around 1.3 +/- 0.07 mmol h-1 g-1, with an apparent quantum yield (AQY) of 6.4%. Pt0.5-Au1/TiO2 also demonstrated the same activity for 25 cycles of five hours each for 125 h. Critically, the same Pt0.5-Au1/TiO2 catalyst was active in overall SWS (OSWS) without any sacrificial agent, with an AQY = 0.8%. The amount of Au and/or Pt was varied to obtain the optimum composition and it was found that the Pt0.5-Au1/TiO2 composition exhibits the best activity. Detailed characterization by physico-chemical, spectral and microscopy measurements was carried out to obtain an in-depth understanding of the origin of the photocatalytic activity of Pt0.5-Au1/TiO2. These in-depth studies show that gold interacts predominantly with oxygen vacancies present on titania surfaces, and Pt preferentially interacts with gold for an effective electron-hole pair separation at Pt-Au interfaces and electron storage in metal particles. The Pt in Pt0.5-Au1/TiO2 is electronically and catalytically different from the Pt in Pt/TiO2 and it is predicted that the former suppresses the oxygen reduction reaction.M-Au/TiO2 (M = Ag, Pd, Pt) composites were prepared through a facile one-pot photodeposition synthesis and evaluated for solar water splitting (SWS) with and without a sacrificial agent. The M-Au combination exhibits a dominant role in augmenting the H2

  10. The Tuscarora Au-Ag district: Eocene volcanic-hosted epithermal deposits in the Carlin gold region, Nevada

    USGS Publications Warehouse

    Castor, S.B.; Boden, D.R.; Henry, C.D.; Cline, J.S.; Hofstra, A.H.; McIntosh, W.C.; Tosdal, R.M.; Wooden, J.P.

    2003-01-01

    The Tuscarora mining district contains the oldest and the only productive Eocene epithermal deposits in Nevada. The district is a particularly clear example of association of low-sulfidation deposits with igneous activity and structure, and it is unusual in that it consists of two adjoining but physically and chemically distinct types of low-sulfidation deposits. Moreover, Tuscarora deposits are of interest because they formed contemporaneously with nearby, giant Carlin-type gold deposits. The Tuscarora deposits formed within the 39.9 to 39.3 Ma Tuscarora volcanic field, along and just outside the southeastern margin of the caldera-like Mount Blitzen volcanic center. Both deposit types formed at 39.3 Ma, contemporaneous with the only major intrusive activity in the volcanic field. No deposits are known to have formed during any of the intense volcanic phases of the field. Intrusions were the apparent heat source, and structures related to the Mount Blitzen center were conduits for hydrothermal circulation. The ore-forming fluids interacted dominantly with Eocene igneous rocks. The two deposit types occur in a northern silver-rich zone that is characterized by relatively high Ag/Au ratios (110-150), narrow alteration zones, and quartz and carbonate veins developed mostly in intrusive dacite, and in a southern gold-rich zone that is typified by relatively low Ag/Au ratios (4-14), more widespread alteration, and quartz-fissure and stockwork veins commonly developed in tuffaceous sedimentary rocks. The deposit types have similar fluid inclusion and Pb and S isotope characteristics but different geochemical signatures. Quartz veins from both zones have similar thermal and paragenetic histories and contain fluid inclusions that indicate that fluids cooled from between 260?? and 230??C to less than 200??C. Fluid boiling may have contributed to precious-metal deposition. Veins in both zones have relatively high As and Sb and low Bi, Te, and W. The silver zone has high Ca

  11. Measurements of the stopping forces for heavy ions in Ge, Ag and Au using novel ‘polka-dot’ detectors

    NASA Astrophysics Data System (ADS)

    Weijers-Dall, T. D. M.; Timmers, H.; Stenström, K.; Persson, P.; Pergjegjaj, A.; Wang, X.; Graczyk, M.; Osipowicz, T.; Ren, M. Q.; O'Connor, D. J.; Whitlow, H. J.

    2006-10-01

    Measurements of the stopping forces for 14C, 14N and 16O ions in Ge and Au, for 14N and 19F ions in Ag, as well as for 19F ions in Au have been made, respectively. A novel technique, reported recently, using PIN diodes coated directly with the stopping medium in a polka dot pattern was used. This provided a set of precise, self-consistent measurements on the same stopping medium. Results show small but significant deviations from SRIM stopping predictions and are also compared to a recently-developed empirical stopping force predictor.

  12. DNA origami based Au-Ag-core-shell nanoparticle dimers with single-molecule SERS sensitivity

    NASA Astrophysics Data System (ADS)

    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

  13. Enhanced photocatalytic performance of vertically grown ZnO nanorods decorated with metals (Al, Ag, Au, and Au-Pd) for degradation of industrial dye

    NASA Astrophysics Data System (ADS)

    Singh Chauhan, Pankaj; Rai, Ashutosh; Gupta, Ankur; Bhattacharya, Shantanu

    2017-05-01

    In this work we have fabricated vertically grown novel rod type nanostructures of zinc oxide on a silicon substrate which are decorated with metals (Al, Ag, Au, and Au-Pd) using sputtering technique. These structures have been utilized in remediation of industrial dyes through solar light photo-catalysis with enhanced efficacy. The obtained structures have been thoroughly characterized using x-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), and Fourier transform infrared spectroscopy (FTIR) analysis etc. The decorating elements have been compared for the photo-catalytic performance relative to the pristine zinc oxide structures and they are found to act as electron sink for the electrons generated by redox reaction on the surface of the ZnO nanostructure. This is attributed as a main reason for increasing the photocatalytic yield by the decorated structures. Approximately 20-45 % (maximum in case of Au-Pd and minimum in case of Ag) enhancement in dye degradation (concentration basis) was achieved by decoration of metals in comparison with undecorated ZnO nanorod. A theoretical model comprising of governing equations associated with the mechanism of the catalysis process was developed for proper understanding of the experimental data.

  14. Modelling of zircaloy dissolution by molten (Ag, In, Cd) absorber alloy

    NASA Astrophysics Data System (ADS)

    Veshchunov, M. S.; Hofmann, P.

    1996-04-01

    Solid Zircaloy (Zry) is dissolved by molten (Ag, In, Cd) alloy at high temperatures. Results of detailed chemical-analytical examinations (integral and point analysis) of (Ag, In, Cd)/Zry reaction couples annealed at temperatures of 1100, 1150 and 1200°C in crucible tests demonstrate a homogeneous composition of the resulting liquid phase and prove that strong convective mixing of the liquid takes place in the course of the interactions. The theoretical model developed on the basis of the measured data explains the reasons for the observed convective mixing of the liquid phase and describes the kinetics of the (Ag, In, Cd)/Zry interactions leading to the saturation of the liquid phase with Zr. Two main parameters of the model are calculated: Zr concentration in the saturated melt and convective mass transfer coefficient in the liquid phase. The influence of an oxide layer on the (Ag, In, Cd)/Zry interactions is additionally studied and described by the developed model.

  15. Synthesis and enhanced fluorescence of Ag doped CdTe semiconductor quantum dots.

    PubMed

    Ding, Si-Jing; Liang, Shan; Nan, Fan; Liu, Xiao-Li; Wang, Jia-Hong; Zhou, Li; Yu, Xue-Feng; Hao, Zhong-Hua; Wang, Qu-Quan

    2015-02-07

    Doping with intentional impurities is an intriguing way to tune the properties of semiconductor nanocrystals. However, the synthesis of some specific doped semiconductor nanocrystals remains a challenge and the doping mechanism in this strongly confined system is still not clearly understood. In this work, we report, for the first time, the synthesis of stable and water-soluble Ag-doped CdTe semiconductor quantum dots (SQDs) via a facile aqueous approach. Experimental characterization demonstrated the efficient doping of the Ag impurities into the CdTe SQDs with an appropriate reaction time. By doping 0.3% Ag impurities, the Stokes shift is decreased by 120 meV, the fluorescence intensity is enhanced more than 3 times, the radiative rate is enhanced 4.2 times, and the non-radiative rate is efficiently suppressed. These observations reveal that the fluorescence enhancement in Ag-doped CdTe SQDs is mainly attributed to the minimization of surface defects, filling of the trap states, and the enhancement of the radiative rate by the silver dopants. Our results suggest that the silver doping is an efficient method for tuning the optical properties of the CdTe SQDs.

  16. Hardening behavior after high-temperature solution treatment of Ag-20Pd-12Au-xCu alloys with different Cu contents for dental prosthetic restorations.

    PubMed

    Kim, Yonghwan; Niinomi, Mitsuo; Hieda, Junko; Nakai, Masaaki; Cho, Ken; Fukui, Hisao

    2014-07-01

    Ag-Pd-Au-Cu alloys have been used widely for dental prosthetic applications. Significant enhancement of the mechanical properties of the Ag-20Pd-12Au-14.5Cu alloy as a result of the precipitation of the β' phase through high-temperature solution treatment (ST), which is different from conventional aging treatment in these alloys, has been reported. The relationship between the unique hardening behavior and precipitation of the β' phase in Ag-20Pd-12Au-xCu alloys (x=6.5, 13, 14.5, 17, and 20mass%) subjected to the high-temperature ST at 1123K for 3.6ks was investigated in this study. Unique hardening behavior after the high-temperature ST also occurs in Ag-20Pd-12Au-xCu alloys (x=13, 17, and 20) with precipitation of the β' phase. However, hardening is not observed and the β' phase does not precipitate in the Ag-20Pd-12Au-6.5Cu alloy after the same ST. The tensile strength and 0.2% proof stress also increase in Ag-20Pd-12Au-xCu alloys (x=13, 14.5, 17, and 20) after the high-temperature ST. In addition, these values after the high-temperature ST increase with increasing Cu content in Ag-20Pd-12Au-xCu alloys (x=14.5, 17, and 20). The formation process of the β' phase can be explained in terms of diffusion of Ag and Cu atoms and precipitation of the β' phase. Clarification of the relationship between hardening and precipitation of the β' phase via high-temperature ST is expected to help the development of more effective heat treatments for hardening in Ag-20Pd-12Au-xCu alloys. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. Integrated logic gate for fluorescence turn-on detection of histidine and cysteine based on Ag/Au bimetallic nanoclusters-Cu²⁺ ensemble.

    PubMed

    Sun, Jian; Yang, Fan; Zhao, Dan; Chen, Chuanxia; Yang, Xiurong

    2015-04-01

    By means of employing 11-mercaptoundecanoic acid (11-MUA) as a reducing agent and protecting ligand, we present straightforward one-pot preparation of fluorescent Ag/Au bimetallic nanoclusters (namely AgAuNCs@11-MUA) from AgNO3 and HAuCl4 in alkaline aqueous solution at room temperature. It is found that the fluorescence of AgAuNCs@11-MUA has been selectively quenched by Cu(2+) ions, and the nonfluorescence off-state of the as-prepared AgAuNCs@11-MUA-Cu(2+) ensemble can be effectively switched on upon the addition of histidine and cysteine. By incorporating Ni(2+) ions and N-ethylmaleimide, this phenomenon is further exploited as an integrated logic gate and a specific fluorescence turn-on assay for selectively and sensitively sensing histidine and cysteine has been designed and established based on the original noncovalent AgAuNCs@11-MUA-Cu(2+) ensemble. Under the optimal conditions, histidine and cysteine can be detected in the concentration ranges of 0.25-9 and 0.25-7 μM; besides, the detection limits are found to be 87 and 111 nM (S/N = 3), respectively. Furthermore, we demonstrate that the proposed AgAuNCs@11-MUA-based fluorescent assay can be successfully utilized for biological fluids sample analysis.

  18. Ag2S/CdS/TiO2 Nanotube Array Films with High Photocurrent Density by Spotting Sample Method

    NASA Astrophysics Data System (ADS)

    Sun, Hong; Zhao, Peini; Zhang, Fanjun; Liu, Yuliang; Hao, Jingcheng

    2015-10-01

    Ag2S/CdS/TiO2 hybrid nanotube array films (Ag2S/CdS/TNTs) were prepared by selectively depositing a narrow-gap semiconductor—Ag2S (0.9 eV) quantum dots (QDs)—in the local domain of the CdS/TiO2 nanotube array films by spotting sample method (SSM). The improvement of sunlight absorption ability and photocurrent density of titanium dioxide (TiO2) nanotube array films (TNTs) which were obtained by anodic oxidation method was realized because of modifying semiconductor QDs. The CdS/TNTs, Ag2S/TNTs, and Ag2S/CdS/TNTs fabricated by uniformly depositing the QDs into the TNTs via the successive ionic layer adsorption and reaction (SILAR) method were synthesized, respectively. The X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS) results demonstrated that the Ag2S/CdS/TNTs prepared by SSM and other films were successfully prepared. In comparison with the four films of TNTs, CdS/TNTs, Ag2S/TNTs, and Ag2S/CdS/TNTs by SILAR, the Ag2S/CdS/TNTs prepared by SSM showed much better absorption capability and the highest photocurrent density in UV-vis range (320~800 nm). The cycles of local deposition have great influence on their photoelectric properties. The photocurrent density of Ag2S/CdS/TNTs by SSM with optimum deposition cycles of 6 was about 37 times that of TNTs without modification, demonstrating their great prospective applications in solar energy utilization fields.

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

    SciTech Connect

    Xiu, Fu-Rong; Qi, Yingying; Zhang, Fu-Shen

    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.

  20. Fano effect in the angle-integrated valence band photoemission of the noble metals Cu, Ag, and Au

    SciTech Connect

    De Nadaie, C.; Brookes, N.B.; Minar, J.; Ebert, H.; Ghiringhelli, G.; Tagliaferri, A.

    2004-10-01

    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.

  1. Crystallization-induced emission enhancement: A novel fluorescent Au-Ag bimetallic nanocluster with precise atomic structure

    PubMed Central

    Chen, Tao; Yang, Sha; Chai, Jinsong; Song, Yongbo; Fan, Jiqiang; Rao, Bo; Sheng, Hongting; Yu, Haizhu; Zhu, Manzhou

    2017-01-01

    We report the first noble metal nanocluster with a formula of Au4Ag13(DPPM)3(SR)9 exhibiting crystallization-induced emission enhancement (CIEE), where DPPM denotes bis(diphenylphosphino)methane and HSR denotes 2,5-dimethylbenzenethiol. The precise atomic structure is determined by x-ray crystallography. The crystalline state of Au4Ag13 shows strong luminescence at 695 nm, in striking contrast to the weak emission of the amorphous state and hardly any emission in solution phase. The structural analysis and the density functional theory calculations imply that the compact C–H⋯π interactions significantly restrict the intramolecular rotations and vibrations and thus considerably enhance the radiative transitions in the crystalline state. Because the noncovalent interactions can be easily modulated via varying the chemical environments, the CIEE phenomenon might represent a general strategy to amplify the fluorescence from weakly (or even non-) emissive nanoclusters. PMID:28835926

  2. Surface plasmon dispersion engineering via double-metallic AU/AG layers for nitride light-emitting diodes

    DOEpatents

    Tansu, Nelson; Zhao, Hongping; Zhang, Jing; Liu, Guangyu

    2014-04-01

    A double-metallic deposition process is used whereby adjacent layers of different metals are deposited on a substrate. The surface plasmon frequency of a base layer of a first metal is tuned by the surface plasmon frequency of a second layer of a second metal formed thereon. The amount of tuning is dependent upon the thickness of the metallic layers, and thus tuning can be achieved by varying the thicknesses of one or both of the metallic layers. In a preferred embodiment directed to enhanced LED technology in the green spectrum regime, a double-metallic Au/Ag layer comprising a base layer of gold (Au) followed by a second layer of silver (Ag) formed thereon is deposited on top of InGaN/GaN quantum wells (QWs) on a sapphire/GaN substrate.

  3. Broadband light absorption enhancement in dye-sensitized solar cells with Au-Ag alloy popcorn nanoparticles.

    PubMed

    Xu, Qi; Liu, Fang; Liu, Yuxiang; Cui, Kaiyu; Feng, Xue; Zhang, Wei; Huang, Yidong

    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 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.

  4. Broadband light absorption enhancement in dye-sensitized solar cells with Au-Ag alloy popcorn nanoparticles

    NASA Astrophysics Data System (ADS)

    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. Broadband light absorption enhancement in dye-sensitized solar cells with Au-Ag alloy popcorn nanoparticles

    PubMed Central

    Xu, Qi; Liu, Fang; Liu, Yuxiang; Cui, Kaiyu; Feng, Xue; Zhang, Wei; Huang, Yidong

    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 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. PMID:23817586

  6. Surface enhanced Raman scattering effect of CdSe/ZnS quantum dots hybridized with Au nanowire

    NASA Astrophysics Data System (ADS)

    Lee, Yong-baek; Ho Lee, Seok; Lee, Sunmi; Lee, Hyunsoo; Kim, Jeongyong; Joo, Jinsoo

    2013-01-01

    Functionalized CdSe/ZnS quantum dots (QDs) were attached to the surface of Au nanowire (NW). Analysis of optical absorption spectra disclosed surface plasmon bands of Au NWs at 562 and 627 nm and showing an overlap with the QD absorption band. Micro Raman spectra (λex = 514 nm) of the QDs/Au single NW exhibited surface enhanced Raman scattering (SERS) peaks at 180, 205, and 277 cm-1, corresponding to surface, longitudinal, and transverse optical phonon modes, respectively. From time-resolved fluorescence spectra, the exciton lifetime of QDs decreased after hybridization with Au NW due to the energy transfer, supporting the SERS effect.

  7. Formation of recent Pb-Ag-Au mineralization by potential sub-surface microbial activity.

    PubMed

    Tornos, Fernando; Velasco, Francisco; Menor-Salván, César; Delgado, Antonio; Slack, John F; Escobar, Juan Manuel

    2014-08-06

    Las Cruces is a base-metal deposit in the Iberian Pyrite Belt, one of the world's best-known ore provinces. Here we report the occurrence of major Pb-Ag-Au mineralization resulting from recent sub-surface replacement of supergene oxyhydroxides by carbonate and sulphide minerals. This is probably the largest documented occurrence of recent microbial activity producing an ore assemblage previously unknown in supergene mineralizing environments. The presence of microbial features in the sulphides suggests that these may be the first-described natural bacteriomorphs of galena. The low δ(13)C values of the carbonate minerals indicate formation by deep anaerobic microbial processes. Sulphur isotope values of sulphides are interpreted here as reflecting microbial reduction in a system impoverished in sulphate. We suggest that biogenic activity has produced around 3.1 × 10(9) moles of reduced sulphur and 10(10) moles of CO2, promoting the formation of ca. 1.19 Mt of carbonates, 114,000 t of galena, 638 t of silver sulphides and 6.5 t of gold.

  8. Formation of recent Pb-Ag-Au mineralization by potential sub-surface microbial activity

    NASA Astrophysics Data System (ADS)

    Tornos, Fernando; Velasco, Francisco; Menor-Salván, César; Delgado, Antonio; Slack, John F.; Escobar, Juan Manuel

    2014-08-01

    Las Cruces is a base-metal deposit in the Iberian Pyrite Belt, one of the world’s best-known ore provinces. Here we report the occurrence of major Pb-Ag-Au mineralization resulting from recent sub-surface replacement of supergene oxyhydroxides by carbonate and sulphide minerals. This is probably the largest documented occurrence of recent microbial activity producing an ore assemblage previously unknown in supergene mineralizing environments. The presence of microbial features in the sulphides suggests that these may be the first-described natural bacteriomorphs of galena. The low δ13C values of the carbonate minerals indicate formation by deep anaerobic microbial processes. Sulphur isotope values of sulphides are interpreted here as reflecting microbial reduction in a system impoverished in sulphate. We suggest that biogenic activity has produced around 3.1 × 109 moles of reduced sulphur and 1010 moles of CO2, promoting the formation of ca. 1.19 Mt of carbonates, 114,000 t of galena, 638 t of silver sulphides and 6.5 t of gold.

  9. Electronic structure and conductivity of nanocomposite metal (Au,Ag,Cu,Mo)-containing amorphous carbon films

    SciTech Connect

    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.

  10. In situ liquid cell electron microscopy of Ag-Au galvanic replacement reactions.

    PubMed

    Sutter, Eli A; Sutter, Peter W

    2017-01-19

    Galvanic replacement reactions are important as they transform nanoparticle templates into complex porous and hollow metal or alloy nanostructures with interesting properties for a variety of applications. Real-time liquid cell electron microscopy (LCEM) observations of the transformation of solid nanoparticles into hollow shell and cage bimetallic nanostructures are challenging because the high-energy electron beam strongly affects the galvanic process via species such as aqueous electrons and hydroxyl radicals generated through the radiolysis of water in the liquid cell. As a result the galvanic reactions are modified by the introduction of additional pathways that can decouple the oxidation of the nanoparticles from the reduction of the metal ion complexes in solution. Here we demonstrate that changing the pH of the solution provides an effective approach to alter the balance of radiolysis products. In situ observations of the transformation of Ag nanocubes in Au salt containing neutral and acidic aqueous solutions demonstrate that a lowering of the pH by addition of H2SO4 significantly lessens radical-induced modifications of redox reactions by avoiding the excessive reduction of metal-chloro complexes by aqueous electrons (eaq(-)) and making the process sufficiently slow to be observed. As a result, the different stages of galvanic replacement reactions on nanoparticles can be imaged in real-time by LCEM.

  11. AgCl-doped CdSe quantum dots with near-IR photoluminescence.

    PubMed

    Kotin, Pavel Aleksandrovich; Bubenov, Sergey Sergeevich; Mordvinova, Natalia Evgenievna; Dorofeev, Sergey Gennadievich

    2017-01-01

    We report the synthesis of colloidal CdSe quantum dots doped with a novel Ag precursor: AgCl. The addition of AgCl causes dramatic changes in the morphology of synthesized nanocrystals from spherical nanoparticles to tetrapods and finally to large ellipsoidal nanoparticles. Ellipsoidal nanoparticles possess an intensive near-IR photoluminescence ranging up to 0.9 eV (ca. 1400 nm). In this article, we explain the reasons for the formation of the ellipsoidal nanoparticles as well as the peculiarities of the process. The structure, Ag content, and optical properties of quantum dots are also investigated. The optimal conditions for maximizing both the reaction yield and IR photoluminescence quantum yield are found.

  12. AgCl-doped CdSe quantum dots with near-IR photoluminescence

    PubMed Central

    Bubenov, Sergey Sergeevich; Mordvinova, Natalia Evgenievna; Dorofeev, Sergey Gennadievich

    2017-01-01

    We report the synthesis of colloidal CdSe quantum dots doped with a novel Ag precursor: AgCl. The addition of AgCl causes dramatic changes in the morphology of synthesized nanocrystals from spherical nanoparticles to tetrapods and finally to large ellipsoidal nanoparticles. Ellipsoidal nanoparticles possess an intensive near-IR photoluminescence ranging up to 0.9 eV (ca. 1400 nm). In this article, we explain the reasons for the formation of the ellipsoidal nanoparticles as well as the peculiarities of the process. The structure, Ag content, and optical properties of quantum dots are also investigated. The optimal conditions for maximizing both the reaction yield and IR photoluminescence quantum yield are found. PMID:28685116

  13. Effects of the Au/CdTe back contact on IV and CV characteristics of Au/CdTe/CdS/TCO solar cells

    NASA Astrophysics Data System (ADS)

    Niemegeers, Alex; Burgelman, Marc

    1997-03-01

    A simple analytical theory is presented to explain the measured roll over and cross over behaviour of the IV characteristics of thin film CdTe solar cells. It involves a classical description of the CdS/CdTe junction and the CdTe/back contact structure and is extended with a new description of minority carrier current in the CdTe contact region. This extension is crucial in describing the light dependence of the forward IV curves, and hence cross over. The same model also explains the measured CV curves. It is shown that analysis of the capacitance measurement can yield additional information about the doping density of CdTe in the vicinity of the contact. A relationship between the fill factor of the solar cell and the barrier height of the back contact is derived; this relation is useful as a new, practical criterion for the quality of the back contact. The results of this simple analytical model are confirmed by full numerical calculations of the dc and ac characteristics.

  14. Uniform and controllable preparation of Au-Ag core-shell nanorods using anisotropic silver shell formation on gold nanorods.

    PubMed

    Okuno, Yoshifumi; Nishioka, Koji; Kiya, Ayaka; Nakashima, Naotoshi; Ishibashi, Ayumu; Niidome, Yasuro

    2010-08-01

    Anisotropic and controllable silver shell formation on gold nanorods was realized in a micellar solution of hexadecytrimethylammonium chloride. Uniformity of the anisotropic Au-Ag core-shell particles contributes separation of four extinction bands. The ability to manipulate the shapes and sizes of these nanoparticles offers a wide-range control of the surface extinction from the visible to the near infrared regions (450-800 nm).

  15. Enzymatic plasmonic engineering of Ag/Au bimetallic nanoshells and their use for sensitive optical glucose sensing.

    PubMed

    He, Haili; Xu, Xiaolong; Wu, Haoxi; Jin, Yongdong

    2012-04-03

    Enzyme works for plasmonic nanostructure: an interesting enzyme-responsive hybrid Ag/Au-GOx bimetallic nanoshell (NS) system is reported, in which control over the enzyme reaction of glucose oxidase (GOx) can automatically fine-tune the morphology (from complete NS to porous NS) and optical properties of the hybrid nanostructure. The phenomenon is further exploited as a new platform for sensitive optical glucose sensing.

  16. Local field-induced optical properties of Ag-coated CdS quantum dots.

    PubMed

    Je, Koo-Chul; Ju, Honglyoul; Treguer, Mona; Cardinal, Thierry; Park, Seung-Han

    2006-08-21

    Local field-induced optical properties of Ag-coated CdS quantum dot structures are investigated. We experimentally observe a clear exciton peak due to the quantum confinement effect in uncoated CdS quantum dots, and surface plasmon resonance and red-shifted exciton peak in Ag-coated CdS composite quantum dot structures. We have calculated the Stark shift of the exciton peak as a function of the local field for different silver thicknesses and various sizes of quantum dots based on the effective-mass Hamiltonian using the numerical-matrix-diagonalization method. Our theoretical calculations strongly indicate that the exciton peak is red-shifted in the metal-semiconductor composite quantum dots due to a strong local field, i.e., the quantum confined Stark effect.

  17. The effect of Zn, Ag and Au substitution for Cu in Finemet on the crystallization and magnetic properties

    NASA Astrophysics Data System (ADS)

    Chau, N.; Hoa, N. Q.; The, N. D.; Vu, L. V.

    2006-08-01

    Soft magnetic ribbons of Finemet compound with Zn, Ag and Au substituted for Cu: Fe 73.5Si 13.5B 9Nb 3Cu 1-xM x (M=Zn, Ag, Au; x=0.5, 1.0) have been fabricated by rapid quenching technique with wheel speeds of 10, 25 and 30 m/s, respectively. The crystallization evolution of samples examined by DSC measurements showed that the high cooling rates make the ribbons in amorphous state whereas the samples with M=Zn; x=0.5, 1.0 showed to be partly crystallized when they fabricated by the wheel speed of 10 m/s. In the case of Zn ( x=0.5, 1.0) and Ag ( x=1.0) substitution there is a sharp peak in the DSC curve corresponding to crystallization of α-Fe(Si) phase. However, the role of Au is similar to that of Cu. Hysteresis loops of as-cast samples exhibited square form which relates to the pinning centers in domain wall displacement. After appropriate annealing, the ultrasoft magnetic properties of studied ribbons are obtained.

  18. DNA biosensor-based on fluorescence detection of E. coli O157:H7 by Au@Ag nanorods.

    PubMed

    Sun, Jiadi; Ji, Jian; Sun, Yanqing; Abdalhai, Mandour H; Zhang, Yinzhi; Sun, Xiulan

    2015-08-15

    A novel DNA sensor for the detection of the Escherichia coli O157:H7 (E. coli O157:H7) eaeA gene was constructed using surface enhanced fluorescence (SEF). The spacing distance dependence nature of Au@Ag nanorods surface enhanced fluorescence was investigated when the cy3-labled single strand DNA(ssDNA) and the stem-loop DNA probe modified on the nanorods was co-hybridized. The result revealed that the fluorescence intensity reached the maximum value with the spacing distance of about 10nm between cy3 and the Au@Ag nanorods surface. Based on this result, a fluorescence "ON/OFF" switch for detecting the eaeA gene of E. coli O157:H7 was constructed. Under optimal conditions, the DNA sensor produced a linear range from 10(-17) to 10(-11) M with a correlation coefficient of 0.9947 and a detection limit of 3.33×10(-18) M, and was also found to be specific in targeting eaeA. The DNA sensor demonstrated a new strategy of combining eaeA recognition and Au@Ag nanorods for fluorescence signal enhancement, and increased sensitivity in the detection of bacterial specific genes.

  19. Quantitative surface-enhanced Raman spectroscopy for kinetic analysis of aldol condensation using Ag-Au core-shell nanocubes.

    PubMed

    Weatherston, Joshua D; Worstell, Nolan C; Wu, Hung-Jen

    2016-10-17

    Surface-enhanced Raman spectroscopy (SERS) is a powerful tool with high potential for multiplexed detection of dilute analytes. However, quantitative SERS of kinetic assays can be difficult due to the variation in enhancement factors caused by changing reaction conditions. We report a method for quantitative SERS kinetic analysis using colloidal Ag-Au core-shell nanocubes (Ag@AuNCs) as the SERS substrate. This substrate is mass producible, possesses large SERS enhancement, and is resistant to degradation in most environments. The SERS enhancement of the Ag@AuNCs was evaluated both experimentally and computationally. Quantitation was achieved by covalently attaching a non-reactive internal standard (IS) to substrate surfaces and normalizing SERS spectra to the IS signal. We demonstrated that IS normalization corrects for temporal variations in enhancement factor and particle concentration. Quantitation was demonstrated by monitoring the base-catalyzed aldol condensation of surface-bound 4-(methylthio)benzaldehyde with free acetone. The kinetic model of this reaction was fitted to IS normalized SERS data, resulting in kinetic parameters that agreed well with published values. This SERS platform is a robust and sensitive method for quantitative analysis of kinetic assays, with potential applications in many fields.

  20. Probing the mechanism of plasma protein adsorption on Au and Ag nanoparticles with FT-IR spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Mengmeng; Fu, Cuiping; Liu, Xingang; Lin, Zhipeng; Yang, Ning; Yu, Shaoning

    2015-09-01

    Protein-nanoparticle interactions are important in biomedical applications of nanoparticles and for growing biosafety concerns about nanomaterials. In this study, the interactions of four plasma proteins, human serum albumin (HSA), myoglobin (MB), hemoglobin (HB), and trypsin (TRP), with Au and Ag nanoparticles were investigated by FT-IR spectroscopy. The secondary structure of thio-proteins changed with time during incubation with Au and Ag nanoparticles, but the secondary structures of non-thio-proteins remained unchanged. The incubation time for structural changes depended on the sulfur-metal bond energy; the stronger the sulfur-metal energy, the less the time needed. H/D exchange experiments revealed that protein-NP complexes with thio-proteins were less dynamic than free proteins. No measurable dynamic differences were found between free non-thio-proteins and the protein-Au (or Ag) nanoparticle complex. Therefore, the impact of covalent bonds on the protein structure is greater than that of the electrostatic force.

  1. The enhancing of Au-Ag-Te content in tellurium-bearing ore mineral by bio-oxidation-leaching

    NASA Astrophysics Data System (ADS)

    Kim, PyeongMan; Kim, HyunSoo; Myung, EunJi; Kim, YoonJung; Lee, YongBum; Park*, CheonYoung

    2015-04-01

    The purpose of this study is to enhance the content of valuable metals such as Au-Ag-Te in tellurium-bearing minerals by bio-oxidation-leaching. It was confirmed that pyrite, chalcopyrite, sphalerite and galena were produced together with tellurium-bearing minerals including hessite, sylvanite and tellurobismuthite from ore minerals and concentrates through microscopic observation and SEM/EDS analysis. In a bio-oxidation-leaching experiment, with regard to Au, Ag, Te, Cu and Fe, the changes in the amount of leaching and the content of leaching residues were compared and analyzed with each other depending on the adaptation of an indigenous microbe identified as Acidithiobacillus ferrooxidans. As a result of the experiment, the Au-Ag-Te content in tellurium-bearing ore mineral was enhanced in the order of physical oxidation leaching, physical/non-adaptive bio-oxidation-leaching and physical/adaptive biological leaching. It suggests that the bio-oxidation-leaching using microbes adapted in tellurium-bearing ore mineral can be used as a pre-treatment and a main process in a recovery process of valuable metals. "This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(NRF-2013R1A1A2004898)"

  2. Plasmon coupling-enhanced two-photon photoluminescence of Au@Ag core-shell nanoparticles and applications in the nuclease assay

    NASA Astrophysics Data System (ADS)

    Yuan, Peiyan; Ma, Rizhao; Gao, Nengyue; Garai, Monalisa; Xu, Qing-Hua

    2015-05-01

    Au and Ag nanoparticles (NPs) have been known to display significantly enhanced two-photon photoluminescence (2PPL) upon the formation of nanoparticle aggregates. The enhancement effect of the core-shell nanoparticles has not been explored so far. Here we have prepared Au@Ag bimetallic core-shell nanoparticles with different thicknesses (1.1, 2.1, 3.5, 4.5, and 5.5 nm) of silver coating on 19 nm Au NPs to investigate the composition effects on plasmon coupling-enhanced 2PPL. A maximum 2PPL enhancement factor (IcoupledNPs/IisolatedNPs) of up to 840-fold was obtained for Au@Ag NPs with ~3.5 nm Ag nanoshells. These Au@Ag NPs were subsequently utilized in two-photon detection of S1 nuclease as a photoluminescence turn on probe. This method displayed high sensitivity with the limit of detection of 1.4 × 10-6 U μL-1 and an excellent selectivity.Au and Ag nanoparticles (NPs) have been known to display significantly enhanced two-photon photoluminescence (2PPL) upon the formation of nanoparticle aggregates. The enhancement effect of the core-shell nanoparticles has not been explored so far. Here we have prepared Au@Ag bimetallic core-shell nanoparticles with different thicknesses (1.1, 2.1, 3.5, 4.5, and 5.5 nm) of silver coating on 19 nm Au NPs to investigate the composition effects on plasmon coupling-enhanced 2PPL. A maximum 2PPL enhancement factor (IcoupledNPs/IisolatedNPs) of up to 840-fold was obtained for Au@Ag NPs with ~3.5 nm Ag nanoshells. These Au@Ag NPs were subsequently utilized in two-photon detection of S1 nuclease as a photoluminescence turn on probe. This method displayed high sensitivity with the limit of detection of 1.4 × 10-6 U μL-1 and an excellent selectivity. Electronic supplementary information (ESI) available: TEM images, histograms of the sizes of Au@Ag NPs; extinction, 2PPL spectra of aggregated NPs, cysteamine, ssDNA and S1 nuclease; 2-photon action cross section of aggregated NPs; lengths of ssDNA and [NaCl] effect; excitation power

  3. Ab initio study of MXe{sub n}{sup +} (M=Cu, Ag, and Au; n=1,2)

    SciTech Connect

    Li Xinying; Cao Xue

    2008-02-15

    The equilibrium geometries, vibrational frequencies, dissociation energies, and populations of the title species were studied at Hartree-Fock (HF), second-order Moeller-Plesset (MP2), and coupled-cluster singles-doubles (triples) [CCSD(T)] levels. The electron correlation effects and relativistic effects on the geometry and stability were investigated at the CCSD(T) level. Both effects stabilize title species. The populations analyses show that M-Xe bonding is dominated by electrostatic interactions and the best theoretical estimate of the dissociation energies are 1.104 and 2.260 eV for AuXe{sup +} and AuXe{sub 2}{sup +}, respectively. The Cu and Ag are weakly bonded to Xe compared to Au.

  4. Interaction of Au, Ag, and Bi ions with Ba2YCu3O(7-y) - Implications for superconductor applications

    NASA Technical Reports Server (NTRS)

    Hepp, A. F.; Gaier, J. R.; Pouch, J. J.; Hambourger, P. D.

    1988-01-01

    Results are presented on the reactions of Au, Ag, and Bi ions with Ba2YCu3O(7-y) oxides and on the properties of the resultant materials. The results indicate that Au(3+) structural chemistry makes gold an excellent candidate for multiphase structures of the Ba2Y(Cu/1-x/Au/x/)3O(7-y)-type substituted superconductors. Silver is structurally and chemically compatible with the perovskite structure, but when it forms a second phase, it does so without the destruction of the superconducting phase, making silver a useful metal for metal/ceramic applications. On the other hand, bismuth was shown to degrade Tc phase or to form other phases, indicating that it may not be useful in applications with rare-earth-based superconductors.

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

    PubMed

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

    2011-02-10

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

  6. Tunable Visible Emission of Ag-Doped CdZnS Alloy Quantum Dots

    PubMed Central

    2010-01-01

    Highly luminescent Ag-ion-doped Cd1−xZnxS (0 ≤ x ≤ 1) alloy nanocrystals were successfully synthesized by a novel wet chemical precipitation method. Influence of dopant concentration and the Zn/Cd stoichiometric variations in doped alloy nanocrystals have been investigated. The samples were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) to investigate the size and structure of the as prepared nanocrystals. A shift in LO phonon modes from micro-Raman investigations and the elemental analysis from the energy dispersive X-ray analysis (EDAX) confirms the stoichiometry of the final product. The average crystallite size was found increasing from 1.0 to 1.4 nm with gradual increase in Ag doping. It was observed that photoluminescence (PL) intensity corresponding to Ag impurity (570 nm), relative to the other two bands 480 and 520 nm that originates due to native defects, enhanced and showed slight red shift with increasing silver doping. In addition, decrease in the band gap energy of the doped nanocrystals indicates that the introduction of dopant ion in the host material influence the particle size of the nanocrystals. The composition dependent bandgap engineering in CdZnS:Ag was achieved to attain the deliberate color tunability and demonstrated successfully, which are potentially important for white light generation. PMID:20652135

  7. Tunable Visible Emission of Ag-Doped CdZnS Alloy Quantum Dots

    NASA Astrophysics Data System (ADS)

    Sethi, Ruchi; Kumar, Lokendra; Sharma, Prashant K.; Pandey, A. C.

    2010-01-01

    Highly luminescent Ag-ion-doped Cd1-xZnxS (0 ≤ x ≤ 1) alloy nanocrystals were successfully synthesized by a novel wet chemical precipitation method. Influence of dopant concentration and the Zn/Cd stoichiometric variations in doped alloy nanocrystals have been investigated. The samples were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) to investigate the size and structure of the as prepared nanocrystals. A shift in LO phonon modes from micro-Raman investigations and the elemental analysis from the energy dispersive X-ray analysis (EDAX) confirms the stoichiometry of the final product. The average crystallite size was found increasing from 1.0 to 1.4 nm with gradual increase in Ag doping. It was observed that photoluminescence (PL) intensity corresponding to Ag impurity (570 nm), relative to the other two bands 480 and 520 nm that originates due to native defects, enhanced and showed slight red shift with increasing silver doping. In addition, decrease in the band gap energy of the doped nanocrystals indicates that the introduction of dopant ion in the host material influence the particle size of the nanocrystals. The composition dependent bandgap engineering in CdZnS:Ag was achieved to attain the deliberate color tunability and demonstrated successfully, which are potentially important for white light generation.

  8. Tunable Visible Emission of Ag-Doped CdZnS Alloy Quantum Dots.

    PubMed

    Sethi, Ruchi; Kumar, Lokendra; Sharma, Prashant K; Pandey, Ac

    2009-10-13

    Highly luminescent Ag-ion-doped Cd1-xZnxS (0 ≤ x ≤ 1) alloy nanocrystals were successfully synthesized by a novel wet chemical precipitation method. Influence of dopant concentration and the Zn/Cd stoichiometric variations in doped alloy nanocrystals have been investigated. The samples were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) to investigate the size and structure of the as prepared nanocrystals. A shift in LO phonon modes from micro-Raman investigations and the elemental analysis from the energy dispersive X-ray analysis (EDAX) confirms the stoichiometry of the final product. The average crystallite size was found increasing from 1.0 to 1.4 nm with gradual increase in Ag doping. It was observed that photoluminescence (PL) intensity corresponding to Ag impurity (570 nm), relative to the other two bands 480 and 520 nm that originates due to native defects, enhanced and showed slight red shift with increasing silver doping. In addition, decrease in the band gap energy of the doped nanocrystals indicates that the introduction of dopant ion in the host material influence the particle size of the nanocrystals. The composition dependent bandgap engineering in CdZnS:Ag was achieved to attain the deliberate color tunability and demonstrated successfully, which are potentially important for white light generation.

  9. One step hydrothermal synthesis of transition metal based coordination polymers along with magnetic and electrical conductive Ag and Au nanospheres and rods

    NASA Astrophysics Data System (ADS)

    Agarwal, Rashmi A.

    2017-07-01

    Herein, a one step in situ co-synthesis of porous coordination polymers of Ni(II), Co(II) and Mn(II) encapsulating Ag/Ag2O and Au/Au2O3 nanoparticle clusters (spheres and rods) is reported by employing precursors of metal and PCPs, under hydrothermal conditions. No surfactant and reductant have been used. After synthesis of these clusters at high temperature they come out from the cavities of polymers and nucleation process continues inside the cavities. These Ag/Ag2O and Au/Au2O3 nanoclusters encapsulated frameworks show strong paramagnetic and ferromagnetic (soft) properties respectively at room temperature. While electrical characterization data shows that Ag/Ag2O/PCP displays very high conductivity in the range of 1.80×104 S/m which represents the higher end of semiconductance in comparison to Au/Au2O3/PCP which has conductance of 5.9×10-4 S/m representing semiconductivity in the lower mid range at room temperature.

  10. Antimicrobial activity of CdS and Ag2S quantum dots immobilized on poly(amidoamine) grafted carbon nanotubes.

    PubMed

    Neelgund, Gururaj M; Oki, Aderemi; Luo, Zhiping

    2012-12-01

    Herein we report the design of antimicrobial nanohybrids, f-MWCNTs-CdS and f-MWCNTs-Ag(2)S developed by covalent grafting of cationic hyperbranched dendritic polyamidoamine (PAMAM) onto multiwalled carbon nanotubes (MWCNTs) and successive deposition of CdS and Ag(2)S quantum dots (QDs). The CdS and Ag(2)S QDs were in situ deposited on PAMAM grafted MWCNTs instead of anchoring the pre-synthesized QDs. The fourth generation, amine terminated hyperbranched PAMAM was grafted on MWCNTs, which was achieved through repetitive reactions of Michael addition of methylmethacrylate to the surface amino groups and amidation of terminal ester groups with ethylenediamine. The covalent grafting of PAMAM onto MWCNTs and the consecutive conjugation of CdS and Ag(2)S QDs were characterized using Fourier transform infrared spectroscopy, elemental analysis, powder X-ray diffraction, Raman spectroscopy, transmission electron microscopy and energy dispersive spectroscopy. The antibacterial activity of f-MWCNTs-CdS and f-MWCNTs-Ag(2)S nanohybrids was evaluated against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus and the results were compared with the activity of carboxylated MWCNTs, PAMAM grafted MWCNTs, PAMAM dendrimer, and CdS and Ag(2)S QDs. It was found that the germicidal action of MWCNTs was enhanced by grafting of PAMAM, which was further improved with immobilization of CdS and Ag(2)S QDs.

  11. Desulfinylation of Ag(I) Sulfinyl Mesoionic Carbenes: Preparation of C-Unsubstituted Au(I)-1,2,3-Triazole Carbene Complexes.

    PubMed

    Frutos, María; Ortuño, Manuel A; Lledos, Agustí; Viso, Alma; Fernández de la Pradilla, Roberto; de la Torre, María C; Sierra, Miguel A; Gornitzka, Heinz; Hemmert, Catherine

    2017-02-17

    New and well-characterized Ag-bis(1,2,3-triazolylidene) complexes having enantiopure (S)-sulfoxides upon sequential treatment with alcohols and Au(I) form separable mixtures of regioisomeric C-unsubstituted Au-1,2,3-triazolylidene complexes. Mechanistic studies and DFT calculations support a desulfinylation process for in situ generated free triazolylidene salts.

  12. Exploration and geology of the Karangahake and Rahu epithermal Au-Ag deposits, Hauraki Goldfield

    USGS Publications Warehouse

    Simpson, Mark P.; Stevens, Murray R; Mauk, Jeffrey L.; Harris, Matthew C; Stuart, Alistair G J

    2016-01-01

    Karangahake was the third largest gold producer in the Hauraki goldfield. In 2009, New Talisman Gold mines was granted a mining permit, and plans are underway to commence underground mine development of the Maria vein, which has a maiden Ore Reserve (consistent with the 2012 JORC Code) of 28 800 oz Au and 127 800 oz Ag. Exploration drilling at Rahu, located 2 km north of Karangahake has identified polymictic hydrothermal breccias and quartz veins that are strongly gold anomalous. Some quartz vein clasts within the breccia have up to 8.7 g/t Au, suggesting the presence of higher grade quartz vein(s) either below or directly adjacent to the breccias. A controlled source audio-frequency magnetotelluric (CSAMT) survey at Rahu revealed that strongly resistive zones extend below the Barbara and Eunice anomalies to at least 300 m depth and likely correspond to areas of increased silicification, breccias and/or veins. Future drilling will focus on these targets. Detailed geophysical, alteration and fluid inclusion studies have been undertaken at Karangahake, Rahu and Ascot (c 1 km NW of Rahu). Karangahake and Rahu both occur within a broad demagnetised zone, c 4.2 × 2.7 km, in which magnetite has been destroyed by strong hydrothermal alteration. At Karangahake, andesite and overlying minor rhyolite are replaced by adularia, chlorite, illite, pyrite, plus minor albite, epidote and calcite, which have formed from upwelling chloride waters that at depth were hotter than 280°C. At Rahu, localised adularia coupled with complex distributions of illite and interstratified illite-smectite, suggest cooler (c 180° to 240°C) and more focused fluid flow, as well as inferred cool groundwater influx. Fluid inclusion data suggest veins at Karangahake, Rahu and Ascot formed beneath palaeowater tables at 920 m, 440 m and 430 m relative to current sea level (asl), respectively. At Ascot, the presence of silica sinter at 135 m asl, which formed at the palaeosurface, is shallower compared

  13. Controlled preparation of M(Ag, Au)/TiO2 through Sulfydryl -Assisted method for enhanced photocatalysis.

    PubMed

    Xia, Hongbo; Wu, Suli; Bi, Jiajie; Zhang, Shufen

    2017-09-19

    Here a simple and effective method was explored to fabricate M/TiO<sub>2</sub> (M=Ag, Au) composites, which required neither pre-treatment of TiO<sub>2</sub> nor any additives as reducing agent. Using amorphous TiO<sub>2</sub> spheres functionalized with SH groups as starting materials, the noble metallic ions (Ag, Au) can be adsorbed by TiO<sub>2</sub> due to their special affinity with SH groups, which is beneficial to the uniform dispersion of metallic ions on the surface of TiO<sub>2</sub>. Then the adsorbed ions were reduced to form noble metal nanoparticles by heating process (95<sup>o</sup>C) directly without additive as reduction agent. Meanwhile, the amorphous TiO<sub>2</sub> was transformed into anatase phase during the heating process. Thus, the transformation of TiO<sub>2</sub> along with the reduction of noble metallic ions (Ag, Au) was simultaneously carried out by heating. The XRD patterns proved the formation of anatase TiO<sub>2</sub> after heating. The characterizations of XPS and TEM proved the formation of Ag and Au nanoparticles on the surface of TiO<sub>2</sub>. The element mapping indicated that Ag nanoparticles are dispersed uniformly on the surface of TiO<sub>2</sub>. The photocatalytic activity of the composites has been investigated by the degradation of methyl orange under visible light irradiation. The results showed that when Ag/TiO<sub>2</sub> (2.8 wt%) was used as photocatalyst, about 98% of the MO molecules were degraded in 70 min. © 2017 IOP Publishing Ltd.

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

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

  15. Au@CdS Core–Shell Nanoparticles‐Modified ZnO Nanowires Photoanode for Efficient Photoelectrochemical Water Splitting

    PubMed Central

    Guo, Chun Xian; Xie, Jiale; Yang, Hongbin

    2015-01-01

    Hydrogen production from water splitting using solar energy based on photoelectrochemical (PEC) cells has attracted increasing attention because it leaves less of a carbon footprint and has economic superiority of solar and hydrogen energy. Oxide semiconductors such as ZnO possessing high stability against photocorrosion in hole scavenger systems have been widely used to build photoanodes of PEC cells but under visible light their conversion efficiencies with respect to incident‐photon‐to‐current conversion efficiency (IPCE) measured without external bias are still not satisfied. An innovative way is presented here to significantly improve the conversion efficiency of PEC cells by constructing a core–shell structure‐based photoanode comprising Au@CdS core–shell nanoparticles on ZnO nanowires (Au@CdS‐ZnO). The Au core offers strong electronic interactions with both CdS and ZnO resulting in a unique nanojunction to facilitate charge transfer. The Au@CdS‐ZnO PEC cell under 400 nm light irradiation without any applied bias provides an IPCE of 14.8%. Under AM1.5 light illumination with a bias of 0.4 V, the Au@CdS‐ZnO PEC cell produces H2 at a constant rate of 11.5 μmol h−1 as long as 10 h. This work provides a fundamental insight to improve the conversion efficiency for visible light in water splitting. PMID:27980921

  16. Determining the boundaries of second-type phase transitions in Ag-Mg-Cd alloys by means of diffusion couples

    NASA Astrophysics Data System (ADS)

    Kalmykov, K. B.; Dmitrieva, N. E.; Dunaev, S. F.

    2017-02-01

    The interaction between elements in the transition zones of diffusion couples Mg + AgCd-alloy are studied. Isothermal sections of the Ag-Mg-Cd ternary system at 573 K are constructed. The existence of a Heusler phase based on H-Ag2MgCd compound is found in the field of the solid β'-solution. It is shown that the interdiffusion of components prevents the formation of ordered phases in the transition zones of bimetals, allowing us to determine the boundaries of second-type phase transitions in solid solutions.

  17. A ternary functional Ag@GO@Au sandwiched hybrid as an ultrasensitive and stable surface enhanced Raman scattering platform

    NASA Astrophysics Data System (ADS)

    Zhang, Cong-yun; Hao, Rui; Zhao, Bin; Hao, Yao-wu; Liu, Ya-qing

    2017-07-01

    The graphene-mediated surface enhanced Raman scattering (SERS) substrates by virtues of plasmonic metal nanostructures and graphene or its derivatives have attracted tremendous interests which are expected to make up the deficiency of traditional plasmonic metal substrates. Herein, we designed and fabricated a novel ternary Ag@GO@Au sandwich hybrid wherein the ultrathin graphene oxide (GO) films were seamlessly wrapped around the hierarchical flower-like Ag particle core and meanwhile provided two-dimensional anchoring scaffold for the coating of Au nanoparticles (NPs). The surface coverage density of loading Au NPs could be readily controlled by tuning the dosage amount of Au particle solutions. These features endowed the sandwiched structures high enrichment capability for analytes such as aromatic molecules and astonishing SERS performance. The Raman signals were enormously enhanced with an ultrasensitive detection limit of rhodamine-6G (R6G) as low as 10-13 M based on the chemical enhancement from GO and multi-dimensional plasmonic coupling between the metal nanoparticles. In addition, the GO interlayer as an isolating shell could effectively prevent the metal-molecule direct interaction and suppress the oxidation of Ag after exposure at ambient condition which enabled the substrates excellent reproducibility with less than 6% signal variations and prolonged life-time. To evaluate the feasibility and the practical application for SERS detection in real-world samples based on GO sandwiched hybrid as SERS-active substrate, three different prohibited colorants with a series of concentrations were measured with a minimum detected concentration down to 10-9 M. Furthermore, the prepared GO sandwiched nanostructures can be used to identify different types of colorants existing in red wine, implying the great potential applications for single-particle SERS sensing of biotechnology and on-site monitoring in food security.

  18. Elastic moduli of cast Ti-Au, Ti-Ag, and Ti-Cu alloys.

    PubMed

    Kikuchi, Masafumi; Takahashi, Masatoshi; Okuno, Osamu

    2006-07-01

    This study investigated the effect of alloying titanium with gold, silver, or copper on the elastic properties of the alloys. A series of binary titanium alloys was made with four concentrations of gold, silver, or copper (5, 10, 20, and 30 mass%) in an argon-arc melting furnace. The Young's moduli and Poisson's ratios of the alloy castings were determined with an ultrasonic-pulse method. The density of each alloy was previously measured by the Archimedes' principle. Results were analyzed using one-way ANOVA and the Scheffé's test. The densities of Ti-Au, Ti-Ag, and Ti-Cu alloys monotonically increased as the concentration of alloying elements increased. As the concentration of gold or silver increased to 20%, the Young's modulus significantly decreased, followed by a subsequent increase in value. As the concentration of copper increased, the Young's modulus monotonically increased. The Young's moduli of all the Ti-Cu alloys were significantly higher than that of the titanium. The density of all the experimental alloys was virtually independent of the alloy phases, while the Young's moduli and Poisson's ratios of the alloys were dependent. The addition of gold or silver slightly reduced the Young's modulus of the titanium when the alloy phase was single alpha. The increase in the Young's modulus of the Ti-Cu alloys is probably due to the precipitation of intermetallic compound Ti2Cu. Copper turned out to be a moderate stiffener that gains a Young's modulus of titanium up to 20% at the copper concentration of 30 mass%.

  19. Nanoengineering the antibacterial activity of biosynthesized nanoparticles of TiO2, Ag, and Au and their nanohybrids with Portobello mushroom spore (PMS) (TiOx/PMS, Ag/PMS and Au/PMS) and making them optically self-indicating

    NASA Astrophysics Data System (ADS)

    Jaffer Al-Timimi, Iman A.; Sermon, Paul A.; Burghal, Ahmed A.; Salih, Afrodet A.; Alrubaya, Inaam M. N.

    2016-09-01

    Results show that nanoparticles (NPs) can be biosynthesized at room temperature on the reductive and chelating surfaces of Portobello mushroom spores (PMS). Using this green approach TiOx, Ag, Au, Ag-TiOx and Au-TiOx NPs have been prepared. These were characterized by TEM, SIMS and μFTIR-FTIR. TiOx/PMS, Ag-TiOx/PMS, Au-TiOx/PMS and Ag/PMS were active in bacterial inhibition towards Eschericia coli and Staphylococcus aureus, but Au/PMS was not active (suggesting a strong Au-PMS interaction). TiOx/PMS, Ag/PMS and Ag-TiOx/PMS were equally active in an antibacterial and an antifungal sense when tested against Asperillus and Candide. All samples (except Ag-TiOx/PMS and Au-TiOx/PMS) showed an interesting interaction with DNA. We report on the process of fine-tuning these antibacterial properties, progress on making these nanomaterials optically self-indicating and movement towards optical control of their antibacterial activity. Au-TiOx/PMS shows a surface plasmon resonance (SPR) with a maximum at 518 nm that might be useful in following its anti-bacterial properties (i.e. making the bionanomaterial self-indicating). The future of such green bio-nanomaterials is strong.

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

    PubMed

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

    2014-10-14

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

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

    PubMed

    Xiu, Fu-Rong; Qi, Yingying; Zhang, Fu-Shen

    2015-07-01

    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 60min for Au and Pd, and 410°C and 30min for Ag. The optimum dissolution parameters for Au, Pd, and Ag in (SCWO+HL)-treated PCBs with iodine-iodide system were leaching time of 120min (90min for Ag), iodine/iodide mole ratio of 1:5 (1:6 for Ag), solid-to-liquid ratio (S/L) of 1:10g/mL (1:8g/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. Copyright © 2015 Elsevier Ltd. All rights reserved.

  2. Formation of heteroepitaxy in different shapes of Au-CdSe metal-semiconductor hybrid nanostructures.

    PubMed

    Haldar, Krishna Kanta; Pradhan, Narayan; Patra, Amitava

    2013-10-25

    Formation of heteroepitaxy and designing different-shaped heterostructured nanomaterials of metal and semiconductor in solution remains a frontier area of research. However, it is evident that the synthesis of such materials is not straightforward and needs a selective approach to retain both metal and semiconductor identities in the reaction system during heterostructure formation. Herein, the epitaxial growth of semiconductor CdSe on selected facets of metal Au seeds is reported and different shapes (flower, tetrapod, and core/shell) hetero-nanostructures are designed. These results are achieved by controlling the reaction parameters, and by changing the sequence and timing for introduction of different reactant precursors. Direct evidence of the formation of heteroepitaxy between {111} facets of Au and (0001) of wurtzite CdSe is observed during the formation of these three heterostructures. The mechanism of the evolution of these hetero-nanostructures and formation of their heteroepitaxy with the planes having minimum lattice mismatch are also discussed. This shape-control growth mechanism in hetero-nanostructures should be helpful to provide more information for establishing the fundamental study of heteroepitaxial growth for designing new nanomaterials. Such metal-semiconductor nanostructures may have great potential for nonlinear optical properties, in photovoltaic devices, and as chemical sensors.

  3. Effects of Au and Pd Additions on Joint Strength, Electrical Resistivity, and Ion-Migration Tolerance in Low-Temperature Sintering Bonding Using Ag2O Paste

    NASA Astrophysics Data System (ADS)

    Ito, Takeyasu; Ogura, Tomo; Hirose, Akio

    2012-09-01

    A new bonding process using an Ag2O paste consisting of Ag2O particles mixed with a triethylene glycol reducing agent has been proposed as an alternative joining approach for microsoldering in electronics assembly, which currently uses Pb-rich, high-temperature solders. Ag nanoparticles were formed at approximately 130°C to 160°C through a reduction process, sintered to one another immediately, and bonded to a metal substrate. An Au-coated Cu specimen was successfully bonded using the Ag2O paste. The resulting joint exhibited superior strength compared with joints fabricated using conventional Pb-rich solders. To improve ion-migration tolerance, the Ag2O paste was mixed with Au and Pd microparticles to form sintered Ag-Au and Ag-Pd layers, respectively. The additions of Au and Pd improved the ion-migration tolerance of the joint. Regarding the mechanical properties of the joints, addition of secondary Au and Pd both resulted in decreased joint strength. To match the joint strength of conventional Pb-10Sn solder, the mixing ratios of Au and Pd were estimated to be limited to 16 vol.% and 7 vol.%, respectively. The electrical resistivities of the sintered layers consisting of 16 vol.% Au and 7 vol.% Pd were lower than that of Pb-10Sn solder. Thus, the additive fractions of Au and Pd to the Ag2O paste should be less than 16 vol.% and 7 vol.%, respectively, to avoid compromising the mechanical and electrical properties of the sintered layer relative to those of contemporary Pb-10Sn solder. Following the addition of Au and Pd to the paste, the ion-migration tolerances of the sintered layers were approximately 3 and 2 times higher than that of pure Ag, respectively. Thus, the addition of Au was found to improve the ion-migration tolerance of the sintered Ag layer more effectively and with less sacrifice of the mechanical and electrical properties of the sintered layer than the addition of Pd.

  4. A general approach to fabricate diverse noble-metal (Au, Pt, Ag, Pt/Au)/Fe2O3 hybrid nanomaterials.

    PubMed

    Zhang, Jun; Liu, Xianghong; Guo, Xianzhi; Wu, Shihua; Wang, Shurong

    2010-07-19

    A novel, facile, and general one-pot strategy is explored for the synthesis of diverse noble-metal (Au, Pt, Ag, or Pt/Au)/Fe(2)O(3) hybrid nanoparticles with the assistance of lysine (which is a nontoxic, user friendly amino acid that is compatible with organisms) and without using any other functionalization reagents. Control experiments show that lysine, which contains both amino and carboxylic groups, plays dual and crucial roles as both linker and capping agents in attaching noble metals with a small size and uniform distribution onto an Fe(2)O(3) support. Considering the perfect compatibility of lysine with organism, this approach may find potentials in biochemistry and biological applications. Furthermore, this novel route is also an attractive alternative and supplement to the current methods using a silane coupling agent or polyelectrolyte for preparing hybrid nanomaterials. To demonstrate the usage of such hybrid nanomaterials, a chemical gas sensor has been fabricated from the as-synthesized Au/Fe(2)O(3) nanoparticles and investigated for ethanol detection. Results show that the hybrid sensor exhibits significantly improved sensor performances in terms of high sensitivity, low detection limit, better selectivity, and good reproducibility in comparison with pristine Fe(2)O(3). Most importantly, this general approach can be further employed to fabricate other hybrid nanomaterials based on different support materials.

  5. The design of novel visible light driven Ag/CdO as smart nanocomposite for photodegradation of different dye contaminants.

    PubMed

    Saravanakumar, K; Muthuraj, V; Jeyaraj, M

    2018-01-05

    In this paper, we report a novel visible light driven Ag/CdO photocatalyst, fabricated for the first time via one pot hydrothermal method and further applied for the photodegradation of two important exemplar water contaminants, Malachite green and Acid Orange 7. The microstructure, composition and optical properties of Ag/CdO nanocomposites were thoroughly investigated by various techniques. Scanning electron microscopy clearly shows that Ag NPs were strongly embedded between the CdO nanoparticles. Among the series of synthesized Ag/CdO nanocomposites, (5%) Ag/CdO nanocomposite possesses enhanced photocatalytic activity. This result was attributed to the synergistic effect between Ag and CdO, and mainly Ag NPs can act as an electron trap site, which could reduce the recombination of the electron-hole and induce the visible light absorption. The active species trapping experiments implicate OH and O2(-) radicals as the respective primary and secondary reactive species responsible for oxidative photodegradation of organic pollutants. On the basis of the results, a possible photocatalytic mechanism has also been proposed. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. ZnO/Ag/CdO nanocomposite for visible light-induced photocatalytic degradation of industrial textile effluents.

    PubMed

    Saravanan, R; Mansoob Khan, M; Gupta, Vinod Kumar; Mosquera, E; Gracia, F; Narayanan, V; Stephen, A

    2015-08-15

    A ternary ZnO/Ag/CdO nanocomposite was synthesized using thermal decomposition method. The resulting nanocomposite was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopy, and X-ray photoelectron spectroscopy. The ZnO/Ag/CdO nanocomposite exhibited enhanced photocatalytic activity under visible light irradiation for the degradation of methyl orange and methylene blue compared with binary ZnO/Ag and ZnO/CdO nanocomposites. The ZnO/Ag/CdO nanocomposite was also used for the degradation of the industrial textile effluent (real sample analysis) and degraded more than 90% in 210 min under visible light irradiation. The small size, high surface area and synergistic effect in the ZnO/Ag/CdO nanocomposite is responsible for high photocatalytic activity. These results also showed that the Ag nanoparticles induced visible light activity and facilitated efficient charge separation in the ZnO/Ag/CdO nanocomposite, thereby improving the photocatalytic performance.

  7. Raman studies on Ag-ion doped CdZnS luminescent alloy quantum dots

    NASA Astrophysics Data System (ADS)

    Sethi, Ruchi; Sharma, Prashant K.; Pandey, A. C.; Kumar, Lokendra

    2010-07-01

    Un-doped and Ag-ion doped CdZnS alloy nanocrystals were synthesized using methaacrylic acid (MAA) as a capping agent. A continuous higher frequency shift in optical phonon modes was observed in the Raman spectra of the samples with increasing Zn composition demonstrating a typical 'one-mode' type behavior of the alloy material. Furthermore, the influence of MAA concentration on the optical and vibrational properties was also investigated. Transmission electron micrograph (TEM) of the samples shows that the CdZnS nanocrystals were embedded in the matrix of MAA. In addition, tremendous attention was paid towards the power induced Raman shift in the alloy nanocrystals.

  8. Phase Transition and Second Harmonic Generation in Thiophosphates Ag2Cd(P2S6) and AgCd3(PS4)S2 Containing Two Second-Order Jahn-Teller Distorted Cations.

    PubMed

    Fan, Yu-Hang; Jiang, Xiao-Ming; Liu, Bin-Wen; Li, Shu-Fang; Guo, Wei-Huan; Zeng, Hui-Yi; Guo, Guo-Cong; Huang, Jin-Shun

    2017-01-03

    Two new phases in the Ag-Cd-P-S system containing two second-order Jahn-Teller (SOJT) distorted d(10) cations (Cd(2+) and Ag(+)), namely, Ag2Cd(P2S6) (1) and AgCd3(PS4)S2 (2), are obtained via medium-temperature solid-state synthesis. Compound 1 exhibits a two-dimensional layered structure and undergoes a first-order structural phase transition at approximately 280 °C. This outcome can be ascribed to the significant mismatch in the expansion coefficients between Cd-S (Ag-S) and P-P (P-S) bonds evaluated through bond valence theory. The three-dimensional non-centrosymmetric (NCS) framework of 2 is constructed by two types of tetrahedral layers consisting of corner-shared CdS4, AgS4, and PS4 tetrahedra. Compound 2 exhibits second harmonic generation (SHG) intensity of 0.45 times that of commercial AgGaS2 (AGS) at a laser irradiation of 1.85 μm and an optical band gap of 2.56 eV, and no intrinsic vibrational absorption of chemical bonds is observed in the range of 2.5-18.2 μm. Both phase transition in 1 and SHG properties in 2 are closely related to the SOJT distorted d(10) cations and diverse phosphorus-sulfur polyanions (PaSb)(n-), which together can easily result in NCS distorted structures and interesting properties.

  9. Target-specific near-IR induced drug release and photothermal therapy with accumulated Au/Ag hollow nanoshells on pulmonary cancer cell membranes.

    PubMed

    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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  10. Bi-, tetra-, and hexanuclear AuI and binuclear AgI complexes and AgI coordination polymers containing phenylaminobis(phosphonite), PhN{P(OC6H4OMe-o)2}2, and pyridyl ligands.

    PubMed

    Ganesamoorthy, Chelladurai; Balakrishna, Maravanji S; Mague, Joel T; Tuononen, Heikki M

    2008-04-07

    The reactions of phenylaminobis(phosphonite), PhN{P(OC6H4OMe-o)2}2 (1) (PNP), with [AuCl(SMe2)] in appropriate ratios, afford the bi- and mononuclear complexes, [(AuCl)2(micro-PNP)] (2) and [(AuCl)(PNP)]2 (3) in good yield. Treatment of 2 with 2 equiv of AgX (X = OTf or ClO4) followed by the addition of 1 or 2,2'-bipyridine affords [Au2(micro-PNP)2](OTf)2 (4) and [Au2(C10H8N2)2(micro-PNP)](ClO4)2 (5), respectively. Similarly, the macrocycles [Au4(C4H4N2)2(micro-PNP)2](ClO4)4 (6), [Au4(C10H8N2)2(micro-PNP)2](ClO4)4 (7), and [Au6(C3H3N3)2(micro-PNP)3](ClO4)6 (8) are obtained by treating 2 with pyrazine, 4,4'-bipyridine, or 1,3,5-triazine in the presence of AgClO 4. The reaction of 1 with AgOTf in a 1:2 molar ratio produces [Ag2(micro-OTf)2(micro-PNP)] (9). The displacement of triflate ions in 9 by 1 leads to a disubstituted derivative, [Ag2(micro-PNP)3](OTf)2 (10). The equimolar reaction of 1 with AgClO4 in THF affords [Ag2(C4H8O)2(micro-PNP)2](ClO4)2 (11). Treatment of 1 with AgClO4 followed by the addition of 2,2'-bipyridine affords a discrete binuclear complex, [Ag2(C10H8N2)2(micro-PNP)](ClO4)2 (12), whereas similar reactions with 4,4'-bipyridine or pyrazine produce one-dimensional zigzag Ag (I) coordination polymers, [Ag2(C10H8N2)(micro-ClO4)(ClO4)(micro-PNP)]n (13) and [Ag2(C4H4N2)(micro-ClO4)(ClO4)(micro-PNP)]n (14) in good yield. The nature of metal-metal interactions in compounds 2, 4, 5, and 12 was analyzed theoretically by performing HF and CC calculations. The structures of the complexes 2, 4, 5, 7, 9, 12, and 14 are confirmed by single crystal X-ray diffraction studies.

  11. Genesis of Middle Miocene Yellowstone hotspot-related bonanza epithermal Au-Ag deposits, Northern Great Basin, USA

    NASA Astrophysics Data System (ADS)

    Saunders, J. A.; Unger, D. L.; Kamenov, G. D.; Fayek, M.; Hames, W. E.; Utterback, W. C.

    2008-09-01

    Epithermal deposits with bonanza Au-Ag veins in the northern Great Basin (NGB) are spatially and temporally associated with Middle Miocene bimodal volcanism that was related to a mantle plume that has now migrated to the Yellowstone National Park area. The Au-Ag deposits formed between 16.5 and 14 Ma, but exhibit different mineralogical compositions, the latter due to the nature of the country rocks hosting the deposits. Where host rocks were primarily of meta-sedimentary or granitic origin, adularia-rich gold mineralization formed. Where glassy rhyolitic country rocks host veins, colloidal silica textures and precious metal-colloid aggregation textures resulted. Where basalts are the country rocks, clay-rich mineralization (with silica minerals, adularia, and carbonate) developed. Oxygen isotope data from quartz (originally amorphous silica and gels) from super-high-grade banded ores from the Sleeper deposit show that ore-forming solutions had δ 18O values up to 10‰ heavier than mid-Miocene meteoric water. The geochemical signature of the ores (including their Se-rich nature) is interpreted here to reflect a mantle source for the “epithermal suite” elements (Au, Ag, Se, Te, As, Sb, Hg) and that signature is preserved to shallow crustal levels because of the similar volatility and aqueous geochemical behavior of the “epithermal suite” elements. A mantle source for the gold in the deposits is further supported by the Pb isotopic signature of the gold ores. Apparently the host rocks control the mineralization style and gangue mineralogy of ores. However, all deposits are considered to have derived precious metals and metalloids from mafic magmas related to the initial emergence of the Yellowstone hotspot. Basalt-derived volatiles and metal(loid)s are inferred to have been absorbed by meteoric-water-dominated geothermal systems heated by shallow rhyolitic magma chambers. Episodic discharge of volatiles and metal(loid)s from deep basaltic magmas mixed with

  12. Preparation of PdAg and PdAu nanoparticle-loaded carbon black catalysts and their electrocatalytic activity for the glycerol oxidation reaction in alkaline medium

    NASA Astrophysics Data System (ADS)

    Lam, Binh Thi Xuan; Chiku, Masanobu; Higuchi, Eiji; Inoue, Hiroshi

    2015-11-01

    PdAg and PdAu alloy nanoparticle catalysts for the glycerol oxidation reaction (GOR) were prepared at room temperature by a wet method. The molar ratio of the precursors controlled the bulk composition of the PdAg and PdAu alloys, and their surface composition was Ag-enriched and Pd-enriched, respectively. On PdAg-loaded carbon black (PdAg/CB) electrodes, the onset potential of GOR was 0.10-0.15 V more negative than on the Pd/CB electrode due to the electronic effect. The ratio of GOR peak current densities in the backward and forward sweeps of CVs (ib/if) was smaller because of the improved tolerance to the poisoning species. The ratio of the GOR current density at 60 and 5 min (i60/i5) for the PdAg/CB electrodes was higher for more negative potentials than the Pd/CB electrode. In contrast, the PdAu-loaded CB (PdAu/CB) electrodes had an onset potential of GOR similar to the Pd/CB electrode and a higher GOR peak current density owing to the bi-functional effect. However, the ib/if ratio was higher for PdAu/CB because of the increase in ib as the Pd surface was recovered, and the i60/i5 ratio was higher for more positive potentials, similar to the Pd/CB electrode.

  13. A 200-fold quantum yield boost in the photoluminescence of silver-doped Ag(x)Au(25-x) nanoclusters: the 13th silver atom matters.

    PubMed

    Wang, Shuxin; Meng, Xiangming; Das, Anindita; Li, Tao; Song, Yongbo; Cao, Tiantian; Zhu, Xiuyi; Zhu, Manzhou; Jin, Rongchao

    2014-02-24

    The rod-shaped Au25 nanocluster possesses a low photoluminescence quantum yield (QY=0.1%) and hence is not of practical use in bioimaging and related applications. Herein, we show that substituting silver atoms for gold in the 25-atom matrix can drastically enhance the photoluminescence. The obtained Ag(x)Au(25-x) (x=1-13) nanoclusters exhibit high quantum yield (QY=40.1%), which is in striking contrast with the normally weakly luminescent Ag(x)Au(25-x) species (x=1-12, QY=0.21%). X-ray crystallography further determines the substitution sites of Ag atoms in the Ag(x)Au(25-x) cluster through partial occupancy analysis, which provides further insight into the mechanism of photoluminescence enhancement. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Ag@Au core-shell nanoparticles synthesized by pulsed laser ablation in water: Effect of plasmon coupling and their SERS performance.

    PubMed

    Vinod, M; Gopchandran, K G

    2015-01-01

    Ag@Au core-shell nanoparticles are synthesised by pulsed laser ablation in water using low energy laser pulses. The plasmon characteristics of these core-shell nanoparticles are found to be highly sensitive to the thickness of Au coating. In the synthesis, at first silver nanocolloid was prepared by ablating Ag target and then it is followed by ablation of Au target for different time durations to form Ag@Au core-shell nanostructures. The effect of plasmon-plasmon coupling on the absorption spectra is investigated by decreasing the effective distance between the nanoparticles. This is achieved by reducing the total volume of the colloidal suspension by simple evaporation of water, the solvent used. The suitability of these core-shell nanostructures for application as surface enhanced Raman scattering substrates are tested with crystal violet as probe molecules. Influence of plasmon coupling on the enhancement of Raman bands is found to be different for different bands.

  15. [Determination of Ag, Cu, Zn and Cd in silver brazing filler metals by ICP-AES].

    PubMed

    Yang, X

    1997-06-01

    A method of simultaneous and direct determination for Ag, Cu, Zn and Cd in silver brazing filler metals by ICP-AES is reported. The spectral interferences and effect of acidity have been investigated. Working conditions were optimized. The method has been applied to the analysis of silver brazing filler metals with RSD of 4-7% and recovery of 94-105%. This method was accurate, simple and rapid.

  16. Ag-Au bimetallic nanoclusters formed from a homogeneous gas phase: a new thermodynamic expression confirmed by molecular dynamics simulation.

    PubMed

    Akbarzadeh, H; Shamkhali, A N; Mehrjouei, E

    2017-02-01

    In this work, two probabilistic and thermodynamic limits for formation of a bimetallic nanocluster from a homogeneous gas phase were obtained in order to investigate the related phenomena using molecular dynamics simulation. Therefore, by application of some simple assumptions from thermodynamics and statistical mechanics, a new expression for composition of the nanocluster was derived which depends only on the initial conditions of the system and one adjustable parameter. This expression can be easily fitted to the results of molecular dynamics and can be used as a measure of the thermodynamic contribution in the cluster formation process. Then, molecular dynamics simulations were performed for several systems containing the same total number of metallic atoms and different concentrations of Ag and Au atoms. The results of this study exhibited that depending on different initial compositions of Ag and Au types, fcc and icosahedral structures are formed. Moreover, increase of the initial Ag concentration leads to products whose compositions are more controlled by probability limits. However, longer simulation times indicated that creation of more thermodynamically favoured nanoclusters depends on the formation of more probable ones in the early stages of the simulation.

  17. Kinetically controlled overgrowth of Ag or Au on Pd nanocrystal seeds: from hybrid dimers to nonconcentric and concentric bimetallic nanocrystals.

    PubMed

    Zhu, Cun; Zeng, Jie; Tao, Jing; Johnson, Matthew C; Schmidt-Krey, Ingeborg; Blubaugh, Lynn; Zhu, Yimei; Gu, Zhongze; Xia, Younan

    2012-09-26

    This article describes a systematic study of the nucleation and growth of Ag (and Au) on Pd nanocrystal seeds. By carefully controlling the reaction kinetics, the newly formed Ag atoms could be directed to selectively nucleate and then epitaxially grow on a specific number (ranging from one to six) of the six faces on a cubic Pd seed, leading to the formation of bimetallic nanocrystals with a variety of different structures. In addition to changing the injection rate of precursor, we also systematically investigated other reaction parameters including the capping agent, reductant, and reaction temperature. Our results suggest that the site-selective growth of Ag on cubic Pd seeds could be readily realized by optimizing these reaction parameters. On the basis of the positions of Pd seeds inside the bimetallic nanocrystals as revealed by TEM imaging and elemental mapping, we could identify the exact growth pathways and achieve a clear and thorough understanding of the mechanisms. We have successfully applied the same strategy based on kinetic control to cubic Pd seeds with different sizes and octahedral Pd seeds of one size to generate an array of novel bimetallic nanocrystals with well-controlled structures. With cubic Pd seeds as an example, we have also extended this strategy to the Pd-Au system. We believe this work will provide a promising route to the fabrication of bimetallic nanocrystals with novel structures and properties for applications in plasmonics, catalysis, and other areas.

  18. Selective turn-on fluorescence sensor for Ag+ using cysteamine capped CdS quantum dots: determination of free Ag+ in silver nanoparticles solution.

    PubMed

    Khantaw, Thitima; Boonmee, Chanida; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2013-10-15

    Cadmium sulfide quantum dots capped with cysteamine (Cys-CdS QDs) were demonstrated as a selective fluorescence probe for sensing of free trace silver ions. The fluorescence intensity of the Cys-CdS QDs can be enhanced only in the presence of free Ag(+) and the fluorescence spectrum was slightly red shift from the original spectra. In addition, the fluorescence intensities were linearly increased upon increasing Ag(+) concentration. At the optimized condition for Ag(+) detection, when adding other metal ions to the Cys-CdS QDs solution, fluorescence spectra of Cys-CdS QDs did not change significantly revealing good selectivity of the sensors towards Ag(+). The working linear concentration range was found to be 0.1-1.5 µM with LOD of 68 nM. The proposed sensor was then applied to detect free Ag(+) in the silver nanoparticles solution. The results showed that the proposed sensor can be efficiently used with good accuracy and precision providing the simple method for detection of free Ag(+) in silver nanoparticles of quality control products.

  19. Synthesis and characterisations of Au-nanoparticle-doped TiO2 and CdO thin films

    NASA Astrophysics Data System (ADS)

    Gültekin, Aytaç; Karanfil, Gamze; Özel, Faruk; Kuş, Mahmut; Say, Ridvan; Sönmezoğlu, Savaş

    2014-06-01

    In the present study, pure and gold nanoparticle (Au NP)-doped titanium dioxide (TiO2) and cadmium oxide (CdO) thin film were prepared by the sol-gel method, and the effect of Au NP doping on the optical, structural and morphological properties of these thin films was investigated. The prepared thin films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet-visible-near infrared (UV-Vis-NIR) spectra. While the optical band increases from 3.62 to 3.73 for TiO2 thin films, it decreases from 2.20 to 1.55 for CdO thin films with increasing Au doping concentration. Analysis of XRD indicates that the intensities of peaks of the crystalline phase have increased with the increasing Au NP concentrations in all thin films. SEM images demonstrate that the surface morphologies of the samples were affected by the incorporation of Au NPs. Consequently, the most significant results of the present study are that the Au NPs can be used to modify the optical, structural and morphological properties of TiO2 and CdO thin films.

  20. Red to blue high electrochromic contrast and rapid switching poly(3,4-ethylenedioxypyrrole)-Au/Ag nanocomposite devices for smart windows.

    PubMed

    Kharkwal, Aneeta; Deepa, Melepurath; Joshi, Amish G; Srivastava, Avanish Kumar

    2011-04-18

    Poly(3,4-ethylenedioxypyrrole) (PEDOP)-Ag and PEDOP-Au nanocomposite films have been synthesized for the first time by electropolymerization of the conducting-polymer precursor in a waterproof ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, followed by Ag/Au nanoparticle incorporation. That the Ag/Au nanoparticles are not adventitious entities in the film is confirmed by a) X-ray photoelectron spectroscopy, which provides evidence of Ag/Au-PEDOP interactions through chemical shifts of the Ag/Au core levels and new signals due to Ag-N(H) and Au-N(H) components, and b) electron microscopy, which reveals Au nanoparticles with a face-centered-cubic crystalline structure associated with the amorphous polymer. Spectroelectrochemistry of electrochromic devices based on PEDOP-Au show a large coloring efficiency (η(max) =270 cm(2) C(-1), λ=458 nm) in the visible region, for an orange/red to blue reversible transition, followed by a second, remarkably high η(max) of 490 cm(2) C(-1) (λ=1000 nm) in the near-infrared region as compared to the much lower values achieved for the neat PEDOP analogue. Electrochemical impedance spectroscopy studies reveal that the metal nanoparticles lower charge-transfer resistance and facilitate ion intercalation-deintercalation, which manifests in enhanced performance characteristics. In addition, significantly faster color-bleach kinetics (five times of that of neat PEDOP!) and a larger electrochemical ion insertion capacity unambiguously demonstrate the potential such conducting-polymer nanocomposites have for smart window applications. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Synthesis of 4H/fcc-Au@Metal Sulfide Core-Shell Nanoribbons.

    PubMed

    Fan, Zhanxi; Zhang, Xiao; Yang, Jian; Wu, Xue-Jun; Liu, Zhengdong; Huang, Wei; Zhang, Hua

    2015-09-02

    Although great advances on the synthesis of Au-semiconductor heteronanostructures have been achieved, the crystal structure of Au components is limited to the common face-centered cubic (fcc) phase. Herein, we report the synthesis of 4H/fcc-Au@Ag2S core-shell nanoribbon (NRB) heterostructures from the 4H/fcc Au@Ag NRBs via the sulfurization of Ag. Remarkably, the obtained 4H/fcc-Au@Ag2S NRBs can be further converted to a novel class of 4H/fcc-Au@metal sulfide core-shell NRB heterostructures, referred to as 4H/fcc-Au@MS (M = Cd, Pb or Zn), through the cation exchange. We believe that these novel 4H/fcc-Au@metal sulfide NRB heteronanostructures may show some promising applications in catalysis, surface enhanced Raman scattering, solar cells, photothermal therapy, etc.

  2. The visible light photocatalytic activity enhancement of cotton cellulose nanofibers/In2S3/Ag-CdS nanocomposites

    NASA Astrophysics Data System (ADS)

    Pan, Jiaqi; Li, Jing; Zhang, Xiufang; Zheng, Yingying; Cui, Can; Zhu, Zhiyan; Li, Chaorong

    2016-07-01

    Cotton cellulose nanofibers (CCNFs)/In2S3/Ag-CdS nanocomposites were prepared by a typical technical route which combined electrospinning and a chemical method. The results showed that the CCNFs/In2S3/Ag-CdS nanocomposites had a remarkable visible light photocatalytic property and cycling stability, which displayed a significant enhancement compared with that of pure In2S3. Through analysis, this enhancement could be mainly attributed to the multilevel structure of the composites.

  3. Efficient electrostatic self-assembly of one-dimensional CdS-Au nanocomposites with enhanced photoactivity, not the surface plasmon resonance effect

    NASA Astrophysics Data System (ADS)

    Liu, Siqi; Xu, Yi-Jun

    2013-09-01

    A series of CdS nanowire-Au nanocomposites (CdS NW-Au NCs) with different weight addition ratios of Au nanoparticles (NPs) are successfully synthesized by using a simple and efficient electrostatic self-assembly method at room temperature for utilizing the natural surface charge properties of the CdS NWs and Au NPs. These natural surface charge properties are dependent on the synthesis approaches. The probe reactions for photocatalytic selective reduction of nitroaromatic compounds in the aqueous phase under visible light irradiation are utilized to evaluate the photoactivity of this series of as-prepared CdS NW-Au NCs. The CdS NW-Au NCs exhibit significantly enhanced photoactivity as compared to the CdS nanowires (CdS NWs). The addition of Au NPs into the CdS NW domain enables efficient enhancement of the lifetime and transfer of photogenerated charge carriers from CdS NWs under visible light irradiation. However, the addition of excess amounts of Au NPs not only influences the penetration of light but the Au NPs also become the recombination centers, and result in decreased photoactivity. The optimal proportion of the Au NPs is proved to be 1 wt%, which indicates the synergistic effect between the CdS NWs and Au NPs. In addition, the surface plasmon resonance (SPR) effect of Au NPs is proved to not play an efficient role in the reaction and the possible photocatalytic reaction mechanism is proposed. It is hoped that this work could aid in the fabrication of 1-D semiconductor-metal nanocomposites by using such a simple and efficient electrostatic self-assembly strategy. In addition, it is also expected to enrich and supplement their application as visible light photocatalysts toward selective organic transformations through our investigation.A series of CdS nanowire-Au nanocomposites (CdS NW-Au NCs) with different weight addition ratios of Au nanoparticles (NPs) are successfully synthesized by using a simple and efficient electrostatic self-assembly method at room

  4. Enhanced selective photocatalytic CO2 reduction into CO over Ag/CdS nanocomposites under visible light

    NASA Astrophysics Data System (ADS)

    Zhu, Zezhou; Qin, Jiani; Jiang, Min; Ding, Zhengxin; Hou, Yidong

    2017-01-01

    Photocatalytic reduction of carbon dioxide can convert chemically inert carbon dioxide into useful chemical fuel in a mild manner. Herein, Ag-CdS nanocomposites were prepared by photodeposition method and examined for photocatalytic CO2 reduction under visible light. Meanwhile, the nanocomposites were characterized by XRD, SEM, TEM, XPS, DRS and PL in detail. The results show that, the deposition of Ag improves the photocatalytic performance of CdS, especially in the selectivity of CO2-to-CO. The highest photocatalytic activity is achieved over 1.0 wt.% Ag/CdS, with an increase by 3 times in comparison to CdS. In this reaction system, Ag can serve as electron trap as well as active site for CO2 reduction, which is probably responsible for the enhanced activity and selectivity of CO2 to CO over Ag/CdS. The possible mechanism of CO2 photoreduction over Ag/CdS was proposed in view of the abovementioned analysis.

  5. Synthesis and characterization of AgI nanoparticles in β-CD/PAN nanofibers by electrospinning method

    NASA Astrophysics Data System (ADS)

    Liang, Haiou; Li, Chunping; Bai, Jie; Zhang, Lijuan; Guo, Liping; Huang, Yarong

    2013-04-01

    AgI nanoparticles/β-cyclodextrin (β-CD)/polyacrylonitrile (PAN) composite nanofibers film were prepared via a new route which combined electrospinning technology with the reaction of solid-liquid process. In this article, AgI nanoparticles were successfully prepared in β-CD/PAN nanofibers which contained different concentration β-CD by the new route. Firstly, the AgNO3-β-CD/PAN nanofibers were obtained via electrospinning method, then put the nanofibers into the solution of potassium iodide to prepare AgI-β-CD/PAN nanofibers. The morphology and structure of the composite nanofibers and nanoparticles have been investigated by scanning electron microscopy (SEM) and transmission electro microscopy (TEM). The existence of the AgI nanoparticles was proved by X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD) patterns. The results of various characterizations indicated that the sample of AgI-β-CD (2 wt%)/PAN have the optimum morphology and structure.

  6. Effect of Ag doping on the electrical properties of thermally deposited CdS-La2O3 TFTs

    NASA Astrophysics Data System (ADS)

    Gogoi, Paragjyoti; Saikia, Rajib

    2012-06-01

    In this article, we have reported the fabrication of CdS thin film transistors (TFTs) doped with Ag by thermal evaporation technique on chemically cleaned glass substrates using multiple pumps down process. High-k rare earth oxide La2O3 is used as gate dielectric in CdS TFTs. Some important electrical parameters have been evaluated using Weimer's model. The electrical parameters are compared with the parameters of undoped CdS TFTs. The Ag-doped CdS TFTs exhibit a high mobility of 6.1 cm2 V-1 s-1 than that of the undoped CdS TFTs, mobility of which is found as 6.25 × 10-2 cm2 V-1 s-1. The TFTs also exhibit low threshold voltage. Both Ag-doped and undoped TFTs are characterised using Levinson et al. model.

  7. Effect of cross-sectional shape on the propagation characteristics of fundamental plasmon mode guided along Au and Ag nanowires

    NASA Astrophysics Data System (ADS)

    Jitender; Kumar, Arun

    2017-01-01

    We numerically examine the effect of the cross-sectional shape on the propagation characteristics of the fundamental surface plasmon polariton (SPP) mode guided along Au and Ag nanowires. It is observed that as the cross-sectional symmetry decreases from circular to triangular via pentagonal and square, the modal confinement, loss and dispersion increases. Further the difference in propagation characteristics between circular and other cross-sections increases rapidly as the wavelength of operation decreases. The study should be useful for selecting the cross-sectional shape of the nanowire for a particular application.

  8. New one-pot synthesis of Au and Ag nanoparticles using green rust reactive particle as a micro-reactor

    NASA Astrophysics Data System (ADS)

    Ayadi, Sondra; Perca, Cristian; Legrand, Ludovic

    2013-02-01

    A new, simple, and fast one-pot synthesis of supported Au or Ag nanoparticles is implemented, for which a reactive Fe(II)-bearing green rust inorganic particle is used as an individual micro-reactor acting as both the reducing agent and support for the resulting metal nanoparticles. The mechanism involves both the solid-state oxidation of the green rust support (sulfate or carbonate) and the reduction-precipitation of soluble metal precursor. The resulting nanohybrids have a platy inorganic part supporting about one to ten nanoparticles with sizes in the 20 to 120 nm range.

  9. Cross sections for interactions of 8.8 GeV α particles with Ag, Au, Bi and Th

    NASA Astrophysics Data System (ADS)

    Lazić, D. L.; Todorović, Ž.

    1990-03-01

    Makrofol was used as 4π track detector to determine reaction cross sections of Ag, Au, Bi and Th induced by 8.8 GeV α particles. The variation of cross sections as functions of the Z 2/A parameter of the target has been investigated. Data concerning geometry of events, momentum transfer and fission probabilities were discussed in order to discern fission products from those originating from more violent processes. Comparison with proton data has been done and differences were discussed.

  10. Dirac and Weyl Semimetal in XYBi (X = Ba, Eu; Y = Cu, Ag and Au)

    PubMed Central

    Du, Yongping; Wan, Bo; Wang, Di; Sheng, Li; Duan, Chun-Gang; Wan, Xiangang

    2015-01-01

    Weyl and Dirac semimetals recently stimulate intense research activities due to their novel properties. Combining first-principles calculations and effective model analysis, we predict that nonmagnetic compounds BaYBi (Y = Au, Ag and Cu) are Dirac semimetals. As for the magnetic compound EuYBi, although the time reversal symmetry is broken, their long-range magnetic ordering cannot split the Dirac point into pairs of Weyl points. However, we propose that partially substitute Eu ions by Ba ions will realize the Weyl semimetal. PMID:26399742

  11. Nonresonant surface-enhanced Raman scattering of ZnO quantum dots with Au and Ag nanoparticles.

    PubMed

    Rumyantseva, Anna; Kostcheev, Sergey; Adam, Pierre-Michel; Gaponenko, Sergey V; Vaschenko, Svetlana V; Kulakovich, Olga S; Ramanenka, Andrey A; Guzatov, Dmitry V; Korbutyak, Dmytro; Dzhagan, Volodymyr; Stroyuk, Alexander; Shvalagin, Vitaliy

    2013-04-23

    Pronounced 10(4)-fold enhancement of Raman scattering has been obtained for ZnO nanocrystals on substrates coated with 50 nm Ag nanoparticles under nonresonant excitation with a commercial red-emitting laser. This makes feasible beyond 10(-18) mole detection of ZnO nanocrystals with a commercial setup using a 0.1 mW continuous wave laser and can be purposefully used in analytical applications where conjugated nanocrystals serve as Raman markers. For Au-coated surfaces the enhancement is much lower and the heating effects in the course of Raman experiments are pronounced.

  12. CdS/CdSe quantum dots and ZnPc dye co-sensitized solar cells with Au nanoparticles/graphene oxide as efficient modified layer.

    PubMed

    Chen, Cong; Cheng, Yu; Jin, Junjie; Dai, Qilin; Song, Hongwei

    2016-10-15

    Co-sensitization by using two or more sensitizers with complementary absorption spectra to expand the spectral response range is an effective approach to enhance device performance of quantum dot sensitized solar cells (QDSSCs). To improve the light-harvesting in the visible/near-infrared (NIR) region, organic dye zinc phthalocyanine (ZnPc) was combined with CdS/CdSe quantum dots (QDs) for co-sensitized solar cells based on ZnO inverse opals (IOs) as photoanode. The resulting co-sensitized device shows an efficient panchromatic spectral response feature to ∼750nm and presents an overall conversion efficiency of 4.01%, which is superior to that of the individual ZnPc-sensitized solar cells and CdS/CdSe-sensitized solar cells. Meanwhile, an Au nanoparticles/graphene oxide (Au NPs/GO) composite layer was successfully prepared to modify Cu2S counter electrode for the co-sensitized solar cells. Reducing the carrier recombination process by GO and catalytic process of Au NPs leads to increased power conversion efficiency(PCE) from 4.01 to 4.60% and sustainable stability remains ∼85% of its original value after 60min light exposure. In this paper, introduction of the organic dyes as co-sensitizer and Au NPs/GO as counter electrode modified layer has been proved to be an effective route to improve the performance of QDSSCs. Copyright © 2016 Elsevier Inc. All rights reserved.

  13. Real-time wetting dynamics and interfacial chemistry in low-melting 57Bi-42Sn-1Ag solder paste on Ni-Au

    NASA Astrophysics Data System (ADS)

    Bozack, M. J.

    2004-11-01

    We report the observation of real-time, in situ, wetting and spreading dynamics for 57Bi-42Sn-1Ag solder paste on Ni-Au surfaces during melting in a scanning electron microscope. The 57Bi-42Sn-1Ag is a low melting (139 °C) Pb-free eutectic alloy currently under consideration by automobile manufacturers for use in instrument displays. We find that, while there is excellent wetting of 57Bi-42Sn-1Ag solder paste on Ni-Au, there is almost no spreading. A large amount of Bi segregates to the surface of 57Bi-42Sn-1Ag solder balls during the sintering process. At melting, excessive flux outgassing and pooling are observed, several melted solder balls float on top of the flux, and substantial elemental segregation occurs during the first minutes of wetting. Neither Ni nor Au fully intermixes throughout the alloy at the interface within seconds of wetting. Bi does not move outward with the expanding alloy front. This combination of detrimental effects forms voids in the solder paste, contributes to low reliability of solder joints, and complicates the materials science at the solder-substrate interface as shown by Auger electron spectroscopy. Reliability work in progress (3000 cycles) shows that 57Bi-42Sn-1Ag on Ni-Au is less reliable than eutectic Sn-37Pb on Ni-Au for 2512 chip resistors cycled from -40 to 125 °C.

  14. Quantitative analysis of trace Pb(II) by a DNAzyme cracking-rhodamine 6G SERRS probe on Au(core)Ag(shell) nanosol substrate.

    PubMed

    Liu, Qingye; Wei, Yanyan; Luo, Yanghe; Liang, Aihui; Jiang, Zhiliang

    2014-07-15

    In pH 7.2 Tris-HCl buffer solution containing 0.09 mol/L NaCl at 80°C, the single-stranded substrate DNA hybrids with the enzyme DNA to form double-stranded DNA (dsDNA). The substrate chain of dsDNA could be cracked catalytically by Pb(2+) to produce a short single-stranded DNA (ssDNA) that adsorbed on the Au(core)Ag(shell) nanoparticle (Au/AgNP) surface to form stable Au/AgNP-ssDNA conjugate to prevent aggregation by NaCl, and it combined with rhodamine 6G (RhG) to form RhG-Au/AgNP-ssDNA probe that exhibited a strong surface-enhanced resonance Raman scattering (SERRS) peak at 1510 cm(-1). With the increase of Pb(2+) concentration, the SERRS peak increased linearly due to the more RhG-Au/AgNP-ssDNA probe forming. Under the selected conditions, the increased SERRS intensity ΔI was linear to Pb(2+) concentration in the range of 5.0×10(-8)-7.0×10(-7) mol/L, with a detection limit of 7×10(-9) mol/L Pb(2+). Copyright © 2014 Elsevier B.V. All rights reserved.

  15. Photoelectric properties of ITO/CdS/chlorophyll a/Ag heterojunction solar cells

    SciTech Connect

    Segui, J.; Hotchandani, S.; Baddou, D.; Leblanc, R.M. )

    1991-10-31

    The heterojunction ITO/CdS/Chl a/Ag (Chl a = chlorophyll a) solar cells have been prepared by sequential electrodeposition of CdS and Chl a onto conductive indium-tin oxide (ITO) electrode followed by vacuum deposition of Ag, and their photovoltaic studies have been carried out. The dark J-V and photovoltaic characteristics, especially the action spectra, suggest the presence of a barrier at CdS/CFhl a interface. Various photovoltaic parameters of the cells obtained for the incident light power of 20 {mu}W/Cm{sup 2} at 740 nm, the maximum of Chl a absorption in red region, are as follows: J{sub SC} {approx equal} 150-200 nA/cm{sup 2}, V{sub OC} {approx} 0.35-0.40 V, ff = 0.26, and {eta} (%) = 0.17. The measurements performed at three wavelengths, namely, 740, 680, and 560 nm, indicate that the cells (illuminated through CdS electrode) perform better for weakly absorbed light at 560 nm. The results further show that the use of CdS instead of Al as rectifying electrode has definitely led to an improvement in the performance of CdS/Chl a over Al/Chl a cells in terms of the decreased internal resistances, decreased dark current and voltage, increased fill factors, and increased power conversion efficiencies. This has been attributed to the elimination of insulating layer of Al{sub 2}O{sub 3} existing at Al/Chl a interface.

  16. Study of the effects of MeV Ag, Cu, Au, and Sn implantation on the optical properties of LiNbO3

    NASA Technical Reports Server (NTRS)

    Williams, E. K.; Ila, D.; Sarkisov, S.; Curley, M.; Poker, D. B.; Hensley, D. K.; Borel, C.

    1998-01-01

    The authors present the results of characterization of linear absorption and nonlinear refractive index of Au, Ag, Cu and Sn ion implantation into LiNbO3. Ag was implanted at 1.5 MeV to fluences of 2 to 17 x 17(exp 16)/sq cm at room temperature. Au and Cu were implanted to fluences of 5 to 20 x 10(exp 16)/sq cm at an energy of 2.0 MeV. Sn was implanted to a fluence of 1.6 x 10(exp 17)/sq cm at 160 kV. Optical absorption spectrometry indicated an absorption peak for the Au implanted samples after heat treatment at 1,000 C at approx. 620 nm. The Ag implanted samples absorption peaks shifted from approx. 450 nm before heat treatment to 550 nm after 500 C for 1h. Heat treatment at 800 C returned the Ag implanted crystals to a clear state. Cu nanocluster absorption peaks disappears at 500 C. No Sn clusters were observed by optical absorption or XRD. The size of the Ag and Au clusters as a function of heat treatment were determined from the absorption peaks. The Ag clusters did not change appreciably in size with heat treatment. The Au clusters increased from 3 to 9 nm diameter upon heat treatment at 1000 C. TEM analysis performed on a Au implanted crystal indicated the formation of Au nanocrystals with facets normal to the c-axis. Measurements of the nonlinear refractive indices were carried out using the Z-scan method with a tunable dye laser pumped by a frequency doubled mode-locked Nd:YAG laser. The dye laser had a 4.5 ps pulse duration time and 76 MHz pulse repetition rate (575 nm).

  17. (Ca/Sr)Au xCd 1- x: Stacking variants of the CrB-FeB series

    NASA Astrophysics Data System (ADS)

    Harms, Wiebke; Dürr, Ines; Daub, Michael; Röhr, Caroline

    2010-01-01

    The structural chemistry of binary 1:1 alkaline earth metallides AIIM ( M=p-block or late transition element) is dominated by planar M zig-zag chains, which are stacked in different orientations (CrB ( c) to FeB ( h) type) and with variable stacking distances (types I and II). As a case study of the electronic influences, the substitution of Au against Cd in the respective Ca and Sr aurides was examined by means of experimental, crystallographic and computational methods. Starting from CaAu, up to 11% of Au can be substituted by Cd without a change in the CrB structure type (orthorhombic, space group Cmcm, a=398.2(1), b=1122.6(6), c=460.9(2) pm, Z=4, R1=0.0303). Starting from SrAu (stacking sequence (hc)2(h2c)2), depending on the proportion of the Cd substitution a successive change to structures with increased hexagonality is observed: In SrAu0.93Cd0.07 (monoclinic, space group P21/m, a=621.3(4), b=472.4(2), c=1216.1(9) pm, β=96.97(5)∘, Z=6, R1=0.0467) the stacking sequence is h2 c, i.e. the hexagonality is 66.67%. A slightly more increased Cd content in SrAu0.78Cd0.22 (orthorhombic, space group Pnma, a=3243.3(8), b=474.17(8), c=626.20(9) pm, Z=16, R1=0.0682) drives the hexagonality to 75%, with a (h3c)2 stacking sequence known from several rare earth nickel compounds. Further Cd substitution is not possible. However, in the Cd-rich section of the two series, where the CsCl/β-brass structure type occurs for both alkaline earth elements, a small Au substitution, as determined from powder data by Rietveld refinements, is possible. The substitution limit and the stability ranges of the CsCl and the CrB type can be rationalized from the calculated band structures. Geometrical and electronic criteria are used to compare and discuss the stability ranges in a structural map.

  18. Approaching the N=82 shell closure with mass measurements of Ag and Cd isotopes

    SciTech Connect

    Breitenfeldt, M.; Baruah, S.; Rosenbusch, M.; Schweikhard, L.; Borgmann, Ch.; Boehm, Ch.; George, S.; Audi, G.; Lunney, D.; Minaya-Ramirez, E.; Naimi, S.; Beck, D.; Dworschak, M.; Herfurth, F.; Savreux, R.; Yazidjian, C.; Blaum, K.; Cakirli, R. B.; Casten, R. F.; Delahaye, P.

    2010-03-15

    Mass measurements of neutron-rich Cd and Ag isotopes were performed with the Penning trap mass spectrometer ISOLTRAP. The masses of {sup 112,114-124}Ag and {sup 114,120,122-124,126,128}Cd, determined with relative uncertainties between 2x10{sup -8} and 2x10{sup -7}, resulted in significant corrections and improvements of the mass surface. In particular, the mass of {sup 124}Ag was previously unknown. In addition, other masses that had to be inferred from Q values of nuclear decays and reactions have now been measured directly. The analysis includes various mass differences, namely the two-neutron separation energies, the applicability of the Garvey-Kelson relations, double differences of masses deltaV{sub pn}, which give empirical proton-neutron interaction strengths, as well as a comparison with recent microscopic calculations. The deltaV{sub pn} results reveal that for even-even nuclides around {sup 132}Sn the trends are similar to those in the {sup 208}Pb region.

  19. Enhancement of chitosan-graphene oxide SPR sensor with a multi-metallic layers of Au-Ag-Au nanostructure for lead(II) ion detection

    NASA Astrophysics Data System (ADS)

    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.

  20. Weakened negative effect of Au/TiO2 photocatalytic activity by CdS quantum dots deposited under UV-vis light illumination at different intensity ratios.

    PubMed

    Song, Kang; Wang, Xiaohong; Xiang, Qun; Xu, Jiaqiang

    2016-10-26

    Herein, we demonstrate experimentally the coexistence of photocatalytic dual opposite roles of Au nanoparticles in a UV-vis light irradiated Au/TiO2 system. We have investigated that the photocatalytic performance curves of Au/TiO2 and CdS/Au/TiO2 for degradation of methylene blue (MB) all present a V-shape with different radiation power ratios. However, through the comparison of photocatalytic activities of Au/TiO2 and CdS/Au/TiO2 by statistics and mathematical simulation, we propose qualitatively that the deposition of CdS used as a photosensitizer could extend the Au/TiO2 light absorption range and weaken the negative effect of Au/TiO2. Compared with Au/TiO2, it is proven indirectly that the photo-excited electrons of CdS/Au/TiO2 transfer from CdS to Au, and then to TiO2. Furthermore, we discuss the photocatalytic dual opposite roles of Au nanoparticles between CdS and TiO2, the positive effect includes localized surface plasmon resonance (LSPR) and Schottky barrier (SB), and the negative effect is that Au nanoparticles can be used as a new charge-carrier recombination center. In addition, we have analyzed that the dual opposite relationship of Au/TiO2 under the irradiation of mixed-light could be regulated by changing the intensity ratio of visible to UV light as well.

  1. Facile in situ synthesis of hydrophilic RGO-CD-Ag supramolecular hybrid and its enhanced antibacterial properties.

    PubMed

    Li, Tie; Shen, Jianfeng; Li, Na; Ye, Mingxin

    2014-06-01

    In this study, a novel hydrophilic RGO-CD-Ag hybrid with the supramolecular β-cyclodextrin (CD) as a conjugation interface was fabricated successfully by a facile in situ synthesis process. The results of several characterizations confirmed that the in situ reaction provided a straightforward approach to deposit the CD wrapped Ag nanoparticles onto the CD chemical functionalized RGO sheets through the head-to-head H-bond interactions between the linker CD molecules. Moreover, it was also found that the CD interface that existed indeed influences the structure and performances of RGO-CD-Ag nanocomposite. The analysis of the static contact angle revealed that the surface property of the hybrid could be transformed from hydrophobic to hydrophilic feature, which highly improved the aqueous dispersibility. And then, the bactericidal test of RGO-CD-Ag was demonstrated and clearly showed the strongest antibacterial activity against Gram-negative and Gram-positive bacteria among all samples. In short, this method may readily provide a new family of supramolecular based materials expected to find applications beyond the bactericidal field.

  2. Dissolution-reprecipitation versus solid state diffusion: mechanism of mineral transformations in sylvanite, (AuAg)2Te4, under hydrothermal conditions.

    NASA Astrophysics Data System (ADS)

    Zhao, J.; Brugger, J.; Pring, A.

    2012-04-01

    The transformation behaviour of the sylvannite (AuAgTe4) under hydrothermal conditions has been explored. At temperatures between 160 and 220 °C, under autogenious vapour pressure, sylvannite transforms to Au-Ag alloy, calaverite (AuTe2), petzite (AuAg3Te2) and hessite (Ag2Te). At the same temperature, in the absences of a hydrothermal fluid, no reaction occurs. The range and proportions of transformation products depends on the hydrothermal reaction conditions. The texturesof the products of the transformation of sylvannite to Au-Ag alloy are consistent with an interface coupled dissolution-reprecipitation reaction mechanism as is the transformation of sylvannite to Ag-rich-Te-depleted calaverite. The break-down of the Ag-rich-Te-depleted calaverite ((Au0.78Ag0.22)Te1.74 ) to stoichiometric calaverite and phase X (Ag3+xAu1-xTe2, 0.1 < x < 0.55 ) via exsolution. Phase X in turn breaks down to a fine intergrowth of petzite and hessite also via exsolution. Up until the current study, chalcogenide transformations studied under hydrothermal conditions, have been at temperatures such that the mobility of the metal ions, due to self-diffusion, was low and the kinetics of any solid state diffusion driven process was very sluggish when compared to the kinetics of ICDR reactions. It is clear, however, that in more mobile systems, such as some Ag or Cu chalcogenides, solid state diffusion may be significant, and solid state reactions may compete kinetically with the ICDR mechanism. Given that sylvanite melts at 354 °C it is reasonable to expect that cation diffusion in this mineral will be significant at temperatures above 145 °C (two thirds of the melting point in kelvin) for experiments on a laboratory time scale (days to months). One aim of this work is to establish the reaction texture and mechanism of mineral replacement of a gold silver telluride and to compare these to our previous studies on the replacement of calaverite (Zhao et al 2009).

  3. Thermodynamic-temperature determinations of the Ag and Au freezing temperatures using a detector-based radiation thermometer

    SciTech Connect

    Yoon, Howard W.; Allen, David W.; Gibson, Charles E.; Litorja, Maritoni; Saunders, Robert D.; Brown, Steven W.; Eppeldauer, George P.; Lykke, Keith R

    2007-05-20

    The development of a radiation thermometer calibrated for spectral radiance responsivity using cryogenic, electrical-substitution radiometry to determine the thermodynamic temperatures of the Ag- and Au-freezing temperatures is described. The absolute spectral radiance responsivity of the radiation thermometer is measured in the NIST Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) facility with a total uncertainty of0.15% (k=2) and is traceable to the electrical watt, and thus the thermodynamic temperature of any blackbody can be determined by using Planck radiation law and the measured optical power. The thermodynamic temperatures of the Ag- and Au-freezing temperatures are determined to be1234.956 K ({+-}0.110 K) (k=2) and1337.344 K({+-}0.129 K) (k=2) differing from the International Temperature Scale of 1990 (ITS-90) assignments by 26 mK and 14 mK, respectively,within the stated uncertainties. The temperatures were systematically corrected for the size-of-source effect, the nonlinearity of the preamplifier and the emissivity of the blackbody.The ultimate goal of these thermodynamic temperature measurements is to disseminate temperature scales with lower uncertainties than those of the ITS-90. These results indicate that direct disseminations of thermodynamic temperature scales are possible.

  4. Investigation of interfacial reaction between Sn-Ag eutectic solder and Au/Ni/Cu/Ti thin film metallization

    NASA Astrophysics Data System (ADS)

    Park, J. Y.; Yang, C. W.; Ha, J. S.; Kim, C.-U.; Kwon, E. J.; Jung, S. B.; Kang, C. S.

    2001-09-01

    This paper reports the formation of intermetallic compounds in Au/Ni/Cu/Ti under-bump-metallization (UBM) structure reacted with Ag-Sn eutectic solder. In this study, UBM is prepared by evaporating Au(500 Å)/Ni(1000 Å)/Cu(7500 Å) /Ti (700 Å) thin films on top of Si substrates. It is then reacted with Ag-Sn eutectic solder at 260 C for various times to induce different stages of the interfacial reaction. Microstructural examination of the interface, using both chemical and crystallographic analysis, indicates that two types of intermetallic compounds are formed during the interfacial reaction. The first phase, formed at the intial stage of the reaction, is predominantly Ni3Sn4. At longer times the Ni3Sn4 phase transforms into (Cu, Ni)6Sn6, probably induced by interdiffusion of Cu and Ni. At this stage, the underlying Cu layer also reacts with Sn and forms the same phase, (Cu,Ni)6Sn5. As a result, the fully reacted interface is found to consist of two intermetallic layers with the same phase but different morphologies.

  5. Gamma Spectra Resulting From the Annihilation of Positrons with Electrons in Single, Selected Core Levels of Cu, Ag and Au

    SciTech Connect

    Kim, S; Eshed, A; Goktepeli, S; Sterne, P A; Koymen, A R; Chen, W C; Weiss, A H

    2005-07-25

    The {gamma}-ray energy spectra due to positron annihilation with the 3p core-level of Cu, the 4p core-level of Ag, and 5p core level of Au were obtained separately from the total annihilation spectrum by measuring the energies of {gamma}-rays time coincident with Auger electrons emitted as a result of filling the core-hole left by annihilation. The results of these measurements are compared to the total annihilation spectra and with LDA based theoretical calculations. A comparison of area normalized momentum distributions with the individual cores extracted from the Doppler measurements shows good qualitative agreement, however, in all three spectra, the calculated values of the momentum density appears to fall below the measured values as the momentum increases. The discrepancies between theory and experiment are well outside the statistical uncertainties of the experiment and become more pronounced with increasing Z going down the column from Cu to Ag to Au. The comparison with the experimental results clearly indicates that the calculations are not predicting the correct ratio of high momentum to low momentum spectral weight and suggest the need to improve the treatment of many body electron-positron correlation effects in annihilation as they pertain to core levels.

  6. Effects of Ga addition on the mechanical properties of 35Ag-30Pd-20Au-15Cu alloy.

    PubMed

    Yamanaka, Masahiko; Goto, Shin-ichi; Churnjitapirom, Pornkiat; Ogura, Hideo

    2002-12-01

    Ten 35Ag-30Pd-20Au-15Cu alloys containing 0.00, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 2.00, 4.00, or 6.00% Ga were experimentally prepared to investigate the effect of Ga on their mechanical properties in addition to their use for denture frameworks, connectors and clasps. The effect of Ga addition on the mechanical properties was marked with a significant increase in the tensile strength, 0.2% off-set proof stress (proof stress) and Vickers hardness observed at low Ga contents (0.25-2.00%). On the other hand, the elongation significantly decreased with the addition of Ga at all contents used in this study. The tensile strength, proof stress and Vickers hardness of the 35Ag-30Pd-20Au-15Cu alloys containing 0.25-2.00% Ga were in the range of 809-957 MPa, 669-857 MPa and 260-301 MPa, respectively. These values are similar to those of Co-Cr alloys, suggesting that 0.25-2.00% Ga alloys can be used for denture frameworks, clasps and connectors.

  7. Schottky Diodes Prepared with Ag, Au, or Pd Contacts on a MgZnO/ZnO Heterostructure

    NASA Astrophysics Data System (ADS)

    Lee, Jong Hoon; Kim, Chang Hoi; Kim, Ah Ra; Kim, Hong Seung; Jang, Nak Won; Yun, Young; Kim, Jin-Gyu; Pin, Min Wook; Lee, Won Jae

    2012-09-01

    We successfully fabricated lateral Schottky diodes with a thin MgZnO layer inserted between the ZnO and Schottky contact metal layers. The MgZnO/ZnO heterostructure was deposited onto a c-sapphire substrate by pulsed laser deposition using Mg0.3Zn0.7O and ZnO targets. Ti/Au was used to achieve ohmic contact with the Mg0.3Zn0.7O thin film layer, whereas Schottky contacts were prepared using silver (Ag), gold (Au), and palladium (Pd). The Ag Schottky diode devices exhibited rectification ratios as high as ˜103 at a bias voltage of ±1 V, with an ideality factor of 2.37 and a work function of 0.73 eV. The possibility of preparing Schottky contacts with a high carrier concentration on the ZnO layer is discussed as a function of the presence or absence of a MgZnO thin layer and in terms of the measured current-voltage properties.

  8. Magnetic instability and f-d hybridization in CeFe2 on substituting Cr, Ag, and Au for Fe

    NASA Astrophysics Data System (ADS)

    Das, Rakesh; Gupta, Mukul; Srivastava, S. K.

    2017-07-01

    Hybridization between Ce f and conduction d states has been speculatively known to be one of the mechanisms responsible for magnetic instability of the ferromagnetic ground state of CeFe2. Substituting Fe by small amounts of certain elements stabilizes it to an antiferromagnetic state below the Curie temperature via a first-order second phase transition. In the present work, we seek any direct relation between the f-d hybridization and the second transition by measuring primarily dc magnetization and Ce M4,5 edge X-ray absorption spectra of Ce(Fe1-xMx) 2 pseudobinaries, with M = Cr, Ag, and Au. X-ray diffraction and X-ray photoelectron spectroscopy measurements are also performed essentially to monitor the quality of the samples. Whereas Cr impurity is found to cause the second transition, Ag and Au apparently do not induce any. In the former, the Curie and second transition temperatures vary systematically, but differently, with x. Our results imply that there is a definite proportionality between the x dependences of the second transition temperature and the f-d hybridization strength estimated qualitatively from the absorption spectra.

  9. Ag/Au bi-metallic film based color surface plasmon resonance biosensor with enhanced sensitivity, color contrast and great linearity.

    PubMed

    Li, Chung-Tien; Lo, Kun-Chi; Chang, Hsin-Yun; Wu, Hsieh-Ting; Ho, Jennifer H; Yen, Ta-Jen

    2012-01-01

    In wavelength surface plasmon resonance (SPR) biosensor, the manipulation of SPR dispersion relation by Ag/Au bi-metallic film was first time implemented. Due to the enhanced resonant wavelength shift and the sharper SPR slope of using Ag/Au bi-metallic film, the illuminated color of reflection shows one order of magnitude greater contrast than conventional SPR biosensors. Such an Ag/Au bi-metallic film based color SPR biosensor (CSPRB) allows the detail bio-interactions, for example 100 nM streptavidin, to be distinguished by directly observing the color change of reflection through naked eyes rather than the analysis of spectrometer. In addition to the enhanced sensitivity and color contrast, this CSPRB also possesses a great linear detection range up to 0.0254 RIU, which leading to the application of point-of-care tests.

  10. 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.

    PubMed

    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.

  11. β-CD Dimer-immobilized Ag Assembly Embedded Silica Nanoparticles for Sensitive Detection of Polycyclic Aromatic Hydrocarbons

    PubMed Central

    Hahm, Eunil; Jeong, Daham; Cha, Myeong Geun; Choi, Jae Min; Pham, Xuan-Hung; Kim, Hyung-Mo; Kim, Hwanhee; Lee, Yoon-Sik; Jeong, Dae Hong; Jung, Seunho; Jun, Bong-Hyun

    2016-01-01

    We designed a β-CD dimer on silver nanoparticles embedded with silica nanoparticles (Ag@SiO2 NPs) structure to detect polycyclic aromatic hydrocarbons (PAHs). Silica NPs were utilized as a template for embedding silver NPs to create hot spot structures and enhance the surface-enhanced Raman scattering (SERS) signal, and a thioether-bridged dimeric β-CD was immobilized on Ag NPs to capture PAHs. The assembled Ag NPs on silica NPs were confirmed by TEM and the presence of β-CD dimer on Ag@SiO2 was confirmed by UV-vis and attenuated total reflection-Fourier transform infrared spectroscopy. The β-CD dimer@Ag@SiO2 NPs were used as SERS substrate for detecting perylene, a PAH, directly and in a wide linearity range of 10−7 M to 10−2 M with a low detection limit of 10−8 M. Also, the β-CD dimer@Ag@SiO2 NPs exhibited 1000-fold greater sensitivity than Ag@SiO2 NPs in terms of their perylene detection limit. Furthermore, we demonstrated the possibility of detecting various PAH compounds using the β-CD dimer@Ag@SiO2 NPs as a multiplex detection tool. Various PAH compounds with the NPs exhibited their distinct SERS bands by the ratio of each PAHs. This approach of utilizing the assembled structure and the ligands to recognize target has potential for use in sensitive analytical sensors. PMID:27184729

  12. β-CD Dimer-immobilized Ag Assembly Embedded Silica Nanoparticles for Sensitive Detection of Polycyclic Aromatic Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Hahm, Eunil; Jeong, Daham; Cha, Myeong Geun; Choi, Jae Min; Pham, Xuan-Hung; Kim, Hyung-Mo; Kim, Hwanhee; Lee, Yoon-Sik; Jeong, Dae Hong; Jung, Seunho; Jun, Bong-Hyun

    2016-05-01

    We designed a β-CD dimer on silver nanoparticles embedded with silica nanoparticles (Ag@SiO2 NPs) structure to detect polycyclic aromatic hydrocarbons (PAHs). Silica NPs were utilized as a template for embedding silver NPs to create hot spot structures and enhance the surface-enhanced Raman scattering (SERS) signal, and a thioether-bridged dimeric β-CD was immobilized on Ag NPs to capture PAHs. The assembled Ag NPs on silica NPs were confirmed by TEM and the presence of β-CD dimer on Ag@SiO2 was confirmed by UV-vis and attenuated total reflection-Fourier transform infrared spectroscopy. The β-CD dimer@Ag@SiO2 NPs were used as SERS substrate for detecting perylene, a PAH, directly and in a wide linearity range of 10‑7 M to 10‑2 M with a low detection limit of 10‑8 M. Also, the β-CD dimer@Ag@SiO2 NPs exhibited 1000-fold greater sensitivity than Ag@SiO2 NPs in terms of their perylene detection limit. Furthermore, we demonstrated the possibility of detecting various PAH compounds using the β-CD dimer@Ag@SiO2 NPs as a multiplex detection tool. Various PAH compounds with the NPs exhibited their distinct SERS bands by the ratio of each PAHs. This approach of utilizing the assembled structure and the ligands to recognize target has potential for use in sensitive analytical sensors.

  13. Decorating CdTe QD-Embedded Mesoporous Silica Nanospheres with Ag NPs to Prevent Bacteria Invasion for Enhanced Anticounterfeit Applications.

    PubMed

    Gao, Yangyang; Dong, Qigeqi; Lan, Shi; Cai, Qian; Simalou, Oudjaniyobi; Zhang, Shiqi; Gao, Ge; Chokto, Harnoode; Dong, Alideertu

    2015-05-13

    Quantum dots (QDs) as potent candidates possess advantageous superiority in fluorescence imaging applications, but they are susceptible to the biological circumstances (e.g., bacterial environment), leading to fluorescence quenching or lose of fluorescent properties. In this work, CdTe QDs were embedded into mesoporous silica nanospheres (m-SiO2 NSs) for preventing QD agglomeration, and then CdTe QD-embedded m-SiO2 NSs (m-SiO2/CdTe NSs) were modified with Ag nanoparticles (Ag NPs) to prevent bacteria invasion for enhanced anticounterfeit applications. The m-SiO2 NSs, which serve as intermediate layers to combine CdTe QDs with Ag NPs, help us establish a highly fluorescent and long-term antibacterial system (i.e., m-SiO2/CdTe/Ag NSs). More importantly, CdTe QD-embedded m-SiO2 NSs showed fluorescence quenching when they encounter bacteria, which was avoided by attaching Ag NPs outside. Ag NPs are superior to CdTe QDs for preventing bacteria invasion because of the structure (well-dispersed Ag NPs), size (small diameter), and surface charge (positive zeta potentials) of Ag NPs. The plausible antibacterial mechanisms of m-SiO2/CdTe/Ag NSs toward both Gram-positive and Gram-negative bacteria were established. As for potential applications, m-SiO2/CdTe/Ag NSs were developed as fluorescent anticounterfeiting ink for enhanced imaging applications.

  14. Density functional theory study of the carbonyl-ene reaction of encapsulated formaldehyde in Cu(I), Ag(I), and Au(I) exchanged FAU zeolites.

    PubMed

    Wannakao, Sippakorn; Khongpracha, Pipat; Limtrakul, Jumras

    2011-11-17

    Carbonyl-ene reactions, which involve C-C bond formation, are essential in many chemical syntheses. The formaldehyde-propene reaction catalyzed by several of the group 11 metal cations, Cu(+), Ag(+), and Au(+) exchanged on the faujasite zeolite (metal-FAU) has been investigated by density functional theory at the M06-L/6-31G(d,p) level. The Au-FAU exhibits a higher activity than the others due to the high charge transfer between the Au and the reactant molecules, even though it is located at a negatively charged site of the zeolite. This site enables it to compensate for the charge of the Au(+) ion. The NBO analysis reveals that the 6s orbital of the Au atom plays an important role, inducing a charge on the probe molecules. Moreover, the effect of the zeolite framework makes the Au-FAU more active than the others by stabilizing the high charge induced transition structure. The activation energy of the reaction catalyzed by Au-FAU is 13.0 kcal/mol whereas that of Cu and Ag-FAU is found to be around 17 kcal/mol. The product desorption needs to be improved for Au-FAU; however, we suggest that catalysts with high charge transfer might provide a promising activity.

  15. Metal arsonate polymers of Cd, Zn, Ag and Pb supported by 4-aminophenylarsonic acid

    NASA Astrophysics Data System (ADS)

    Lesikar-Parrish, Leslie A.; Neilson, Robert H.; Richards, Anne F.

    2013-02-01

    The coordination preferences of 4-aminophenylarsonic acid, 4-NH2C6H4AsO3H2, (p-arsanilic acid) with CdCl2·2.5H2O, ZnCl2, Ag(SO3CF3) and Pb(NO3)2 have been investigated affording five new metal arsonate polymers. The reaction between 4-aminophenylarsonic acid and CdCl2·2.5H2O resulted in a one-dimensional polymer, [{Cd(4-NH3C6H4AsO3H)(Cl)2}(H2O)2]n, 1, in which the polymeric chain is propagated by bridging chlorides. Exchange of CdCl2 for ZnCl2 afforded [{Zn2(4-NH3C6H4AsO3)(Cl)2}(H2O)2(Cl)]n, 2, featuring interlinked 6- and 8-membered [Zn-O-As] ring systems. The reaction of Ag(SO3CF3) with 4-aminophenylarsonic acid, afforded polymeric 3, [Ag(4-NH2C6H4AsO3H)(4-NH2C6H4AsO3H2)]n where coordination of the amino group to the silver center is observed and [{Ag2(4-NH3C6H4AsO3H)(4-NH3C6H4AsO3)(μ2-SO3CF3)2}(SO3CF3)2]n, 4. By comparison, the reaction of p-arsanilic acid with Pb(NO3)2 yielded a polymeric chain [Pb(4-NH3C6H4AsO3H)(NO3)2]n, 5 of similar topology to 1. The structures of 1-5 have been indiscriminately characterized by single crystal X-ray diffraction and their composition supported by relevant spectroscopic techniques. A comparison of the structural features of these polymers is used to determine the coordination preference of the ligand and factors influencing structural motifs, for example, the role of the anion.

  16. Experimental and theoretical spectroscopic studies of Ag-, Cd- and Pb-sodalite

    NASA Astrophysics Data System (ADS)

    Mikuła, A.; Król, M.; Koleżyński, A.

    2016-12-01

    Synthetic sodalite structures containing silver, cadmium and lead cations have been obtained and structurally identified. In order to examine the changes in sodalite spectra envelope resulting from the substitution of initial sodium cations by Ag+, Cd2+ and Pb2+, a series of theoretical sodalite model structures with various Me/Na ratio and different anions have been prepared. Based on ab initio calculations and experimental results, it has been determined how the type and amount of both extra framework cations and anions affect the vibrational spectra and structural properties of sodalite. Additionally, an attempt to identified of bands associated with the individual cations and anions vibration has been undertaken.

  17. Highly sensitive colorimetric detection of glucose in a serum based on DNA-embeded Au@Ag core-shell nanoparticles

    NASA Astrophysics Data System (ADS)

    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.

  18. RuSi@Ru(bpy)3(2+)/Au@Ag2S nanoparticles electrochemiluminescence resonance energy transfer system for sensitive DNA detection.

    PubMed

    Wu, Mei-Sheng; He, Li-Jing; Xu, Jing-Juan; Chen, Hong-Yuan

    2014-05-06

    This work describes a new electrochemiluminescence resonance energy transfer (ECL-RET) system with graphene oxide(GO)-Au/RuSi@Ru(bpy)3(2+)/chitosan (CS) composites as the ECL donor and Au@Ag2S nanoparticles (NPs) as ECL the acceptor for the first time. The ECL signal observed by the application of GO-Au/RuSi@Ru(bpy)3(2+)/CS composites was enhanced for 5-fold compared to that of RuSi@Ru(bpy)3(2+)/CS in the presence of coreactant tripropylamine (TPA) due to the increased surface area and improved electrical conductivity by using graphene oxide-gold nanoparticles (GO-Au) composite materials. In addition, we synthesized Au@Ag2S core-shell NPs, whose UV-vis absorption spectrum shows good spectral overlap with the ECL spectrum of GO-Au/RuSi@Ru(bpy)3(2+)/CS composites by adjusting the amount of Na2S and AgNO3 in the process of synthesis. The distance between energy donor and acceptor was studied to get the highly effective ECL-RET. Then, this ECL-RET system was developed for sensitive and specific detection of target DNA, and the ECL quenching efficiency (ΔI/I0, ΔI = I0 - I) was found to be logarithmically related to the concentration of the target DNA in the range from 10 aM to 10 pM.

  19. Photoluminescence of Cu:ZnS, Ag:ZnS, and Au:ZnS nanoparticles applied in Bio-LED

    NASA Astrophysics Data System (ADS)

    Lin, Kuan Bo; Su, Yen Hsun

    2013-12-01

    In this work, transition elements, including Cu2+, Ag+, and Au3+, were used to dope in zinc sulfide (ZnS) by chemical solution synthesis to prepare Cu:ZnS, Ag:ZnS, and Au:ZnS nanoparticles, respectively. Transition elements doping ZnS nanoparticles form the electronic energy level between the conduction band and valance band, which will result in the green light emission. There is a zinc sulfide emission shift from blue (~3.01 eV) to green light (~2.15 eV). We also found that Au:ZnS nanoparticles will emit a green light (~2.3 eV) and a blue light (~2.92 eV) at the same time because the mechanism of blue light emission was not broken after Au element had been doped. Furthermore, we used sodium chlorophyllin copper salt to simulate chlorophyll in biological light emission devices (Bio-LED). We combined copper chlorophyll with Cu:ZnS, Ag:ZnS, and Au:ZnS nanoparticles by a self-assembly method. Then, we measured its photoluminescence spectroscopy and X-ray photoelectron spectroscopy to study its emission spectrum and bonding mode. We found that Au:ZnS nanoparticles are able to emit green and blue light to excite the red light emission of copper chlorophyll, which is a potential application of Bio-LED.