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Sample records for nucleaires application au

  1. Au Based Nanocomposites Towards Plasmonic Applications

    NASA Astrophysics Data System (ADS)

    Panniello, A.; Curri, M. L.; Placido, T.; Reboud, V.; Kehagias, N.; Sotomayor Torres, C. M.; Mecerreyes, D.; Agostiano, A.; Striccoli, M.

    2010-06-01

    Incorporation of nano-sized metals in polymers can transfer their unique features to the host matrix, providing nanocomposite materials with improved optical, electric, magnetic and mechanical properties. In this work, colloidal Au nanorods have been incorporated into PMMA based random co-polymer, properly functionalized with amino groups and the optical and morphological properties of the resulting nanocomposite have been investigated by spectroscopic and AFM measurements. Au nanorods have demonstrated to preserve the plasmon absorption and to retain morphological features upon the incorporation, thus making the final metal modified polymer composite exploitable for the fabrication of plasmonic devices. The prepared nanocomposites have been then patterned by Nano Imprint Lithography technique in order to demonstrate the viability of the materials towards optical applications.

  2. New ideally absorbing Au plasmonic nanostructures for biomedical applications

    NASA Astrophysics Data System (ADS)

    Zakomirnyi, Vadim I.; Rasskazov, Ilia L.; Karpov, Sergey V.; Polyutov, Sergey P.

    2017-01-01

    In this paper a new set of plasmonic nanostructures operating at the conditions of an ideal absorption (Grigoriev et al., 2015 [1]) was proposed for novel biomedical applications. We consider spherical x/Au nanoshells and Au/x/Au nanomatryoshkas, where 'x' changes from conventional Si and SiO2 to alternative plasmonic materials (Naik and Shalaev, 2013 [2]), such as zinc oxide doped with aluminum, gallium and indium tin oxide. The absorption peak of proposed nanostructures lies within 700-1100 nm wavelength region and corresponds to the maximal optical transparency of hemoglobin and melanin as well as to the radiation frequency of available pulsed medical lasers. It was shown that the ideal absorption takes place in a given wavelength region for Au coatings with thickness less than 12 nm. In this case finite quantum size effects for metallic nanoshells play a significant role. The mathematical model for the search of the ideal absorption conditions was modified by taking into account the finite quantum size effects.

  3. Fe/Au Core-Shell Nanoparticles for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Sra, Amandeep; Leslie-Pelecky, Diandra

    2009-10-01

    The physical properties of nanoparticles, including size, composition and surface chemistry, greatly influence biological and pharmacological properties and, ultimately, their clinical applications. Superparamagnetic iron oxide nanoparticles are widely used for applications such as MRI contrast agents, drug delivery via magnetic targeting and hyperthermia due to their chemical stability and biocompatibility; however, enhancing the saturation magnetization (Ms) of nanoparticles would produce greater sensitivity. Our design strategy involves a bottom-up wet chemistry approach to the synthesis of Fe nanoparticles. Specific advantages of Fe are the high value of Ms (210 emu/g in bulk) coupled with low toxicity; however, Fe nanoparticles must be protected from oxidation, which causes a dramatic reduction in Ms. To circumvent oxidation, Fe nanoparticles are coated with a Au shell that prevents the oxidation of the magnetic core and also provides the nanoparticles with plasmonic properties for optical stimulation. Ligands of various functionalities can be introduced through the well established Au-thiol surface chemistry for different biomedical applications while maintaining the magnetic functionality of the Fe core. In this presentation, we will discuss the physical, chemical and magnetic properties of our Fe/Au nanoparticles and their resistance to oxidation.

  4. Development of Pt-Au-Graphene-Carbon Nanotube Composite for Fuel Cells and Biosensors Applications

    DTIC Science & Technology

    2011-02-11

    1 Project Title:- Development of Pt-Au-Graphene- Carbon nanotube composites for fuel cells and biosensors applications Objectives:- This...project addresses the architectures needed for the processing of Pt-Au-graphene- carbon nanotube (Pt-Au/f-G/f-CNT) nanocomposites and aims at the...05-2010 4. TITLE AND SUBTITLE Development of Pt-Au-Graphene- Carbon nanotube composite for fuel cells and biosensors applications 5a. CONTRACT

  5. Enzymatic deposition of Au nanoparticles on the designed electrode surface and its application in glucose detection.

    PubMed

    Zhang, Hongfang; Liu, Ruixiao; Sheng, Qinglin; Zheng, Jianbin

    2011-02-01

    This paper reported the enzymatic deposition of Au nanoparticles (AuNPs) on the designed 3-mercapto-propionic acid/glucose oxidase/chitosan (MPA/GOD/Chit) modified glassy carbon electrode and its application in glucose detection. Chit served as GOD immobilization matrix and interacted with MPA through electrostatic attraction. AuNPs, without nano-seeds presented on the electrode surface, was produced through the glucose oxidase catalyzed oxidation of glucose. The mechanism of production of AuNPs was confirmed to be that enzymatic reaction products H(2)O(2) in the solution reduce gold complex to AuNPs. The characterizations of the electrode modified after each assembly step was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy showed the average particle size of the AuNPs is 40nm with a narrow particle size distribution. The content of AuNPs on the electrode surfaces was measured by differential pulse stripping voltammetry. The electrochemical signals on voltammogram showed a linear increase with the glucose concentration in the range of 0.010-0.12mM with a detection limit of 4μM. This provided a method to the determination of glucose. Copyright © 2010 Elsevier B.V. All rights reserved.

  6. Highly selective ratiometric fluorescent probe for Au3+ and its application to bioimaging.

    PubMed

    Choi, Ji Young; Kim, Gun-Hee; Guo, Zhiqian; Lee, Hye Yeon; Swamy, K M K; Pai, Jaeyoung; Shin, Seunghoon; Shin, Injae; Yoon, Juyoung

    2013-11-15

    The 4-propargylamino-1,8-naphthalimide based fluorescent probe 1 has been explored as a sensor for selective detection of Au(3+). 4-Amino-1,8-naphthalimides, that possess typical intramolecular charge transfer (ICT) electronic characteristics, have been widely used as versatile platforms for fluorescent probes. The newly designed probe 1 contains a propargylamine moiety at C-4 of the naphthalimide chromophore that reacts with Au(3+) to generate a product that has distinctly different electronic properties from 1. Specifically, the probe undergoes a remarkable change in its absorption spectrum upon addition of Au(3+) that is associated with a distinct color change from yellow to light pink. In addition, a blue shift of ca. 56 nm also takes place in the emission spectra of the probe. Consequently, 1 serves as a reaction-based sensor or so called chemodosimeter for Au(3+). Importantly, surfactants enhance the rate of reaction of 1 with Au(3+), thus, enhancing its use as a real time sensor. Finally, the results of studies probing its application to bioimaging of Au(3+) in live cells show that the probe 1 has a unique ability to sense Au(3+) in cells and, in particular, in lipid droplets within cells. Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

  7. 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.

  8. Very high temperature measurements: Applications to nuclear reactor safety tests; Mesures des tres hautes temperatures: Applications a des essais de surete des reacteurs nucleaires

    SciTech Connect

    Parga, Clemente-Jose

    2013-09-27

    This PhD dissertation focuses on the improvement of very high temperature thermometry (1100 deg. C to 2480 deg. C), with special emphasis on the application to the field of nuclear reactor safety and severe accident research. Two main projects were undertaken to achieve this objective: - The development, testing and transposition of high-temperature fixed point (HTFP) metal-carbon eutectic cells, from metrology laboratory precision (±0.001 deg. C) to applied research with a reasonable degradation of uncertainties (±3-5 deg. C). - The corrosion study and metallurgical characterization of Type-C thermocouple (service temp. 2300 deg. C) prospective sheath material was undertaken to extend the survivability of TCs used for molten metallic/oxide corium thermometry (below 2000 deg. C)

  9. Nitrite ion-induced fluorescence quenching of luminescent BSA-Au(25) nanoclusters: mechanism and application.

    PubMed

    Unnikrishnan, Binesh; Wei, Shih-Chun; Chiu, Wei-Jane; Cang, Jinshun; Hsu, Pang-Hung; Huang, Chih-Ching

    2014-05-07

    Fluorescence quenching is an interesting phenomenon which is highly useful in developing fluorescence based sensors. A thorough understanding of the fluorescence quenching mechanism is essential to develop efficient sensors. In this work, we investigate different aspects governing the nitrite ion-induced fluorescence quenching of luminescent bovine serum albumin stabilized gold nanoclusters (BSA-Au NCs) and their application for detection of nitrite in urine. The probable events leading to photoluminescence (PL) quenching by nitrite ions were discussed on the basis of the results obtained from ultraviolet-visible (UV-Vis) absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), fluorescence measurements, circular dichroism (CD) spectroscopy, zeta potential and dynamic light scattering (DLS) studies. These studies suggested that PL quenching mainly occurred through the oxidation of Au(0) atoms to Au(i) atoms in the core of BSA-Au NCs mediated by nitrite ions. The interference caused by certain species such as Hg(2+), Cu(2+), CN(-), S(2-), glutathione, cysteine, etc. during the nitrite determination by fluorescence quenching was eliminated by using masking agents and optimising the conditions. Based on these findings we proposed a BSA-Au NC-modified membrane based sensor which would be more convenient for the real life applications such as nitrite detection in urine samples. The BSA-Au NC-modified nitrocellulose membrane (NCM) enabled the detection of nitrite at a level as low as 100 nM in aqueous solutions. This Au NC-based paper probe was validated to exhibit good performance for nitrite analysis in environmental water and urine samples, which makes it useful in practical applications.

  10. 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.

  11. Core-shell Au-Pd nanoparticles as cathode catalysts for microbial fuel cell applications

    NASA Astrophysics Data System (ADS)

    Yang, Gaixiu; Chen, Dong; Lv, Pengmei; Kong, Xiaoying; Sun, Yongming; Wang, Zhongming; Yuan, Zhenhong; Liu, Hui; Yang, Jun

    2016-10-01

    Bimetallic nanoparticles with core-shell structures usually display enhanced catalytic properties due to the lattice strain created between the core and shell regions. In this study, we demonstrate the application of bimetallic Au-Pd nanoparticles with an Au core and a thin Pd shell as cathode catalysts in microbial fuel cells, which represent a promising technology for wastewater treatment, while directly generating electrical energy. In specific, in comparison with the hollow structured Pt nanoparticles, a benchmark for the electrocatalysis, the bimetallic core-shell Au-Pd nanoparticles are found to have superior activity and stability for oxygen reduction reaction in a neutral condition due to the strong electronic interaction and lattice strain effect between the Au core and the Pd shell domains. The maximum power density generated in a membraneless single-chamber microbial fuel cell running on wastewater with core-shell Au-Pd as cathode catalysts is ca. 16.0 W m-3 and remains stable over 150 days, clearly illustrating the potential of core-shell nanostructures in the applications of microbial fuel cells.

  12. Core-shell Au-Pd nanoparticles as cathode catalysts for microbial fuel cell applications

    PubMed Central

    Yang, Gaixiu; Chen, Dong; Lv, Pengmei; Kong, Xiaoying; Sun, Yongming; Wang, Zhongming; Yuan, Zhenhong; Liu, Hui; Yang, Jun

    2016-01-01

    Bimetallic nanoparticles with core-shell structures usually display enhanced catalytic properties due to the lattice strain created between the core and shell regions. In this study, we demonstrate the application of bimetallic Au-Pd nanoparticles with an Au core and a thin Pd shell as cathode catalysts in microbial fuel cells, which represent a promising technology for wastewater treatment, while directly generating electrical energy. In specific, in comparison with the hollow structured Pt nanoparticles, a benchmark for the electrocatalysis, the bimetallic core-shell Au-Pd nanoparticles are found to have superior activity and stability for oxygen reduction reaction in a neutral condition due to the strong electronic interaction and lattice strain effect between the Au core and the Pd shell domains. The maximum power density generated in a membraneless single-chamber microbial fuel cell running on wastewater with core-shell Au-Pd as cathode catalysts is ca. 16.0 W m−3 and remains stable over 150 days, clearly illustrating the potential of core-shell nanostructures in the applications of microbial fuel cells. PMID:27734945

  13. Core-shell Au-Pd nanoparticles as cathode catalysts for microbial fuel cell applications.

    PubMed

    Yang, Gaixiu; Chen, Dong; Lv, Pengmei; Kong, Xiaoying; Sun, Yongming; Wang, Zhongming; Yuan, Zhenhong; Liu, Hui; Yang, Jun

    2016-10-13

    Bimetallic nanoparticles with core-shell structures usually display enhanced catalytic properties due to the lattice strain created between the core and shell regions. In this study, we demonstrate the application of bimetallic Au-Pd nanoparticles with an Au core and a thin Pd shell as cathode catalysts in microbial fuel cells, which represent a promising technology for wastewater treatment, while directly generating electrical energy. In specific, in comparison with the hollow structured Pt nanoparticles, a benchmark for the electrocatalysis, the bimetallic core-shell Au-Pd nanoparticles are found to have superior activity and stability for oxygen reduction reaction in a neutral condition due to the strong electronic interaction and lattice strain effect between the Au core and the Pd shell domains. The maximum power density generated in a membraneless single-chamber microbial fuel cell running on wastewater with core-shell Au-Pd as cathode catalysts is ca. 16.0 W m(-3) and remains stable over 150 days, clearly illustrating the potential of core-shell nanostructures in the applications of microbial fuel cells.

  14. 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.

  15. Magnetic susceptibility and hardness of Au-xPt-yNb alloys for biomedical applications.

    PubMed

    Uyama, Emi; Inui, Shihoko; Hamada, Kenichi; Honda, Eiichi; Asaoka, Kenzo

    2013-09-01

    Metal devices in the human body induce serious metal artifacts in magnetic resonance imaging (MRI). Metals artifacts are mainly caused by a volume magnetic susceptibility (χv) mismatch between a metal device and human tissue. In this research, Au-xPt-yNb alloys were developed for fabricating MRI artifact-free biomedical metal devices. The magnetic properties, hardness and phase constitutions of these alloys were investigated. The Au-xPt-8Nb alloys showed satisfactory χv values. Heat treatments did not clearly change the χv values for Au-xPt-8Nb alloys. The Vickers hardness (HV) of these two alloys was much higher than that of high-Pt alloys; moreover, aging at 700°C increased the HV values of these two alloys. A dual phase structure consisting of face-centered cubic α1 and α2 phases was observed and aging at 700°C promoted phase separation. The Au-5Pt-8Nb and Au-10Pt-8Nb alloys showed satisfactory χv values and high hardness and are thus suggested as candidates for MRI artifact-free alloys for biomedical applications. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  16. Au dotted magnetic network nanostructure and its application for on-site monitoring femtomolar level pesticide.

    PubMed

    Yang, Tianxi; Guo, Xiaoyu; Wang, Hui; Fu, Shuyue; Yu, Jie; Wen, Ying; Yang, Haifeng

    2014-04-09

    A novel magnetically responsive and surface-enhanced Raman spectroscopy (SERS) active nanocomposite is designed and prepared by direct grafting of Au nanoparticles onto the surface of magnetic network nanostructure (MNN) with the help of a nontoxic and environmentally friendly reagent of inositol hexakisphosphate shortly named as IP6. The presence of IP6 as a stabilizer and a bridging agent could weave Fe3O4 nanoparticles (NPs) into magnetic network nanostructure, which is easily dotted with Au nanoparticles (Au NPs). It has been shown firstly that the huge Raman enhancement of Au-MNN is reached by an external magnetic collection. Au-MNN presenting the large surface and high detection sensitivity enables it to exhibit multifunctional applications involving sufficient adsorption of dissolved chemical species for enrichment, separation, as well as a Raman amplifier for the analysis of trace pesticide residues at femtomolar level by a portable Raman spectrometer. Therefore, such multifunctional nanocomposites can be developed as a smart and promising nanosystem that integrates SERS approach with an easy assay for concentration by an external magnet for the effective on-site assessments of agricultural and environmental safety.

  17. High resolution transmission electron microscopy of age-hardenable Au-Cu-Zn alloys for dental applications.

    PubMed

    Seol, Hyo Joung; Shiraishi, Takanobu; Tanaka, Yasuhiro; Miura, Eri; Hisatsune, Kunihiro

    2003-05-01

    Microstructures of age-hardenable AuCu-Zn pseudobinary alloys for dental applications were studied by means of high resolution transmission electron microscopic (HRTEM) observation and X-ray diffraction study. HRTEM study revealed that the appearance frequency of antiphase boundaries (APBs) per unit volume of the AuCu II superstructure effectively increased by Zn addition to AuCu, which may be the reason for that high hardness was maintained for a long time in AuCu-Zn alloys. The disordered APBs zone in the AuCu II superstructure had wavy characteristics and fluctuated within regular range. With increasing Zn content in AuCu-Zn alloys, the fluctuation range of APBs' width became narrower, thus random APBs' spacing and irregular APBs' shape of AuCu II superstructure changed to comparatively regular APBs' spacing and shape. Due to the APBs' wavy characteristics, spacing between successive APBs, M, was not constant but scattered, and the magnitude of the scattering of M value decreased with increasing Zn content. By Zn addition to AuCu, phase transformation from a disordered alpha phase to AuCu II phase was greatly accelerated, which made it possible for the AuCu-Zn alloy to have excellent age-hardenability at relatively low temperature like intraoral temperature.

  18. Green synthesis and applications of Au-Ag bimetallic nanoparticles.

    PubMed

    Meena Kumari, M; Jacob, John; Philip, Daizy

    2015-02-25

    This paper reports for the first time the synthesis of bimetallic nanoparticles at room temperature using the fruit juice of pomegranate. Simultaneous reduction of gold and silver ions in different molar ratios leads to the formation of alloy as well as core-shell nanostructures. The nanoparticles have been characterized using UV-vis spectroscopy, transmission electron microscopy, Fourier Transform Infrared Spectroscopy and X-ray diffraction. The synthesized alloy particles are used as catalysts in the reduction of 2-, 3-, 4-nitrophenols to the corresponding amines and in the degradation of methyl orange. The reduction kinetics for all the reactions follows pseudo-first order. The rate constants follow the order k4-nitrophenolapplication. The nitric oxide and hydroxyl radical scavenging activity shown by the nanoparticles promise the potential application in biomedical field. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. Green synthesis and applications of Au-Ag bimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Meena Kumari, M.; Jacob, John; Philip, Daizy

    2015-02-01

    This paper reports for the first time the synthesis of bimetallic nanoparticles at room temperature using the fruit juice of pomegranate. Simultaneous reduction of gold and silver ions in different molar ratios leads to the formation of alloy as well as core-shell nanostructures. The nanoparticles have been characterized using UV-vis spectroscopy, transmission electron microscopy, Fourier Transform Infrared Spectroscopy and X-ray diffraction. The synthesized alloy particles are used as catalysts in the reduction of 2-, 3-, 4-nitrophenols to the corresponding amines and in the degradation of methyl orange. The reduction kinetics for all the reactions follows pseudo-first order. The rate constants follow the order k4-nitrophenol < k2-nitrophenol < k3-nitrophenol. Thermal conductivity is measured as a function of volume fraction and it is observed that the incorporation of the alloy nanoparticles enhances the thermal conductivity of the base fluid (water) showing nanofluid application. The nitric oxide and hydroxyl radical scavenging activity shown by the nanoparticles promise the potential application in biomedical field.

  20. Colloidal Au-enhanced surface plasmon resonance imaging: application in a DNA hybridization process

    NASA Astrophysics Data System (ADS)

    Manera, M. G.; Spadavecchia, J.; Taurino, A.; Rella, R.

    2010-03-01

    The detection of the DNA hybridization mechanism using monodispersed gold nanoparticles as labels is an interesting alternative to increase the sensitivity of the SPR imaging technique. DNA-modified Au nanoparticles (DNA-Au NPs) containing single-stranded (ss) portions of DNA were prepared by monitoring their monolayer formation by UV-vis spectroscopy. The hybridization process between specific thio-oligonucleotides immobilized on the DNA-Au NPs and the corresponding complementary strands is reported and compared with the traditional hybridization process on properly self-assembled thin gold films deposited on glass substrates. A remarkable signal amplification is observed, following the incorporation of colloidal Au into a SPR biosensing experiment, resulting in an increased SPR response to DNA-DNA interactions. In particular Fusarium thiolated DNA (5'HS poly(T)15ATC CCT CAA AAA CTG CCG CT-3) and trichothecenes complementary DNA (5'-AGC GGC AGT TTT TGA GGG AT-3') sequences have been explored due to their possible application to agro-industry for the control of food quality.

  1. Selective Au-Si eutectic bonding for Si-based MEMS applications

    SciTech Connect

    Lee, A.; Lehew, S.; Yu, C.

    1995-05-22

    A novel method of fabricating three-dimensional silicon micro electromechanical systems (MEMS) is presented, using selectivity thin film deposited Au-Si eutectic bond pads. Utilizing this process, complicated structures such as microgrippers and microchannels are fabricated. Bond strengths are higher than the silicon fracture strength and the bond areas can be localized and aligned to the processed wafer. The process and the applications are described in this paper.

  2. Au/(Ti-W) and Au/Cr metallization of chemically vapor-deposited diamond substrates for multichip module applications

    NASA Astrophysics Data System (ADS)

    Meyyappan, Ilango; Malshe, A. P.; Naseem, H. A.; Brown, W. D.

    1994-12-01

    Since diamond obtained by chemical vapor deposition (CVD) has an extremely high thermal conductivity, it holds great promise in solving thermal management problems in high performance multichip modules (MCMs). Consequently, there is a need to develop a reliable metallization system for CVD diamond. Refractory metals such as Ti, Mo, Ta and W are known to form adhering carbide layers at high temperatures. Also, transition metals such as Cr, Ni and Ni-Cr are widely used in other MCM technologies involving Si, AlN, SiC and alumina substrates. In the work reported here, adherent Au/Cr and Au/(Ti-W) metallization systems were produced at low temperatures using d.c. magnetron sputtering and electron beam evaporation techniques. Adhesion at low temperature is essential since CVD diamond could lose its thermal and electrical properties at high temperatures. Furthermore, interaction between metal layers may cause an increase in conductor trace resistivity and delamination. Adhesion was measured using a Sebastian V-A thin film stud pull tester. The deposition parameters were optimized to give maximum adhesion using a statistical design software package, echip. In the case of the sputtered metallization, pre-sputter cleaning of diamond surface improved adhesion significantly. Values above 9 klbf/sq in were obtained in the case of Au/(Ti-W) and 11.8 klbf/sq in in the case of Au/Cr. Post-deposition annealing was performed in nitrogen ambient to investigate the effect of post-metallization processing on adhesion and also to test for any possible interaction between the metals at high temperatures. Annealing temperatures were limited to 450 C since MCM substrates are seldom exposed to temperatures higher than these. Energy-dispersive spectroscopy (EDS) analysis indicated outdiffusion of W through Au at 400 deg C. No interdiffusion was observed in the case of Au/Cr as per optical microscopy and EDS analysis. Auger electron spectroscopy results indicate interaction between the

  3. Analysis of the applicability of Ni, Cu, Au, Pt, and Pd nanoclusters for data recording

    NASA Astrophysics Data System (ADS)

    Redel', L. V.; Gafner, S. L.; Gafner, Yu. Ya.; Zamulin, I. S.; Goloven'ko, Zh. V.

    2017-02-01

    The applicability of individual Ni, Cu, Au, Pt, and Pd nanoclusters as data bits in next generation memory devices constructed on the phase-change carrier principle is studied. To this end, based on the modified tight-binding potential (TB-SMA), structure formation from the melt of nanoparticles of these metals to 10 nm in diameter was simulated by the molecular dynamics method. The effect of various crystallization conditions on the formation of the internal structures of Ni, Cu, Au, Pt, and Pd nanoclusters is studied. The stability boundaries of various crystalline isomers are analyzed. The obtained systematic features are compared for nanoparticles of copper, nickel, gold, platinum, and palladium of identical sizes. It is concluded that platinum nanoclusters of diameter D > 8 nm are the best materials among studied metals for producing memory elements based on phase transitions.

  4. Antitumor therapeutic application of self-assembled RNAi-AuNP nanoconstructs: Combination of VEGF-RNAi and photothermal ablation

    PubMed Central

    Son, Sejin; Kim, Namho; You, Dong Gil; Yoon, Hong Yeol; Yhee, Ji Young; Kim, Kwangmeyung; Kwon, Ick Chan; Kim, Sun Hwa

    2017-01-01

    Nucleic acid-directed self-assembly provides an attractive method to fabricate prerequisite nanoscale structures for a wide range of technological applications due to the remarkable programmability of DNA/RNA molecules. In this study, exquisite RNAi-AuNP nanoconstructs with various geometries were developed by utilizing anti-VEGF siRNA molecules as RNAi-based therapeutics in addition to their role as building blocks for programmed self-assembly. In particular, the anti-VEGF siRNA-functionalized AuNP nanoconstructs can take additional advantage of gold-nanoclusters for photothermal cancer therapeutic agent. A noticeable technical aspect of self-assembled RNAi-AuNP nanoconstructs in this study is the precise conjugation and separation of designated numbers of therapeutic siRNA onto AuNP to develop highly sophisticated RNA-based building blocks capable of creating various geometries of RNAi-AuNP nano-assemblies. The therapeutic potential of RNAi-AuNP nanoconstructs was validated in vivo as well as in vitro by combining heat generation capability of AuNP and anti-angiogenesis mechanism of siRNA. This strategy of combining anti-VEGF mechanism for depleting angiogenesis process at initial tumor progression and complete ablation of residual tumors with photothermal activity of AuNP at later tumor stage showed effective tumor growth inhibition and tumor ablation with PC-3 tumor bearing mice. PMID:28042312

  5. Ionic liquid functionalized graphene/Au nanocomposites and its application for electrochemical immunosensor.

    PubMed

    Liu, Na; Chen, Xia; Ma, Zhanfang

    2013-10-15

    In this work, a new nanocomposite, which was composed of ionic liquid functionalized graphene sheet (IL-GS) loaded gold nanoparticles (AuNPs), was prepared. The IL-GS was directly synthesized by the electrochemical exfoliation of graphite in ionic liquid (IL). Due to the modification of the IL, IL-GS can not only be dispersed easily in aqueous solution to form a homogeneous colloidal suspension of individual sheet, but also exhibits an improved conductivity. Meanwhile, the loaded AuNPs on the nanocomposites can increase the specific surface area to capture a large amount of antibodies as well as improve the capability of electron transfer. The IL-GS-Au nanocomposites were successfully employed for the fabrication of a facile and sensitive electrochemical immunosensor. Carcinoembryonic antigen (CEA) was used as a model protein. The proposed immunosensor exhibits a wide linear detection range (LDR) from 1 fg mL⁻¹ to 100 ng mL⁻¹, and an ultralow limit of detection (LOD) of 0.1 fg mL⁻¹ (S/N=3). In addition, for the detection of clinical serum samples, it is well consistent with the data determined by the developed immunoassay and ELISA, indicating that the immunosensor provides a possible application for the detection of CEA in clinical diagnostics. Copyright © 2013 Elsevier B.V. All rights reserved.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  8. Suitability of Au- and self-assisted GaAs nanowires for optoelectronic applications.

    PubMed

    Breuer, Steffen; Pfüller, Carsten; Flissikowski, Timur; Brandt, Oliver; Grahn, Holger T; Geelhaar, Lutz; Riechert, Henning

    2011-03-09

    The incorporation of Au during vapor-liquid-solid nanowire growth might inherently limit the performance of nanowire-based devices. Here, we assess the material quality of Au-assisted and Au-free grown GaAs/(Al,Ga)As core-shell nanowires using photoluminescence spectroscopy. We show that at room temperature, the internal quantum efficiency is systematically much lower for the Au-assisted nanowires than for the Au-free ones. In contrast, the optoelectronic material quality of the latter is comparable to that of state-of-the-art planar double heterostructures.

  9. 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.

  10. 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.

  11. Application of cellulose acetate to the selective adsorption and recovery of Au(III).

    PubMed

    Yang, Jian; Kubota, Fukiko; Baba, Yuzo; Kamiya, Noriho; Goto, Masahiro

    2014-10-13

    Cellulose acetyl derivatives were examined for the selective recovery of Au(III) from acidic chloride solutions as an adsorbent, and cellulose acetate fibers (CAF) were found to be effective for the separation of Au(III) from other metal ions, including the precious metal ions Pt(IV) and Pd(II). The amount of Au(III) adsorbed by the fibers increased with an increase in the hydrochloric acid concentration, but decreased with an increase in the ionic strength of the solution. The adsorption of Au(III) onto CAF took place quickly and an adsorption equilibrium was reached within 1h. The maximum adsorption capacity of Au(III) was determined to be 110 mg/g at 2M hydrochloric acid. The loaded Au(III) was readily recovered by incineration.

  12. Formation of Au nanoparticles on CNTs three dimensional structure for LSPR biosensor application

    NASA Astrophysics Data System (ADS)

    Yang, Ming; Shimizu, Tetsuhide

    2017-02-01

    A 3D LSPR sensor was fabricated by using CNTs as support and depositing AuNPs on the support in this study. We proposed a simple process to arrange AuNPs to CNTs by using vacuum deposition and annealing for 3D LSPR sensor. In order to fabricate 3D LSPR sensor, CNTs was synthesized and patterned on quartz glass substrate by CVD method and photolithography. For the synthesis of AuNPs, Au thin film was deposited on glass and CNTs by vacuum deposition. After deposition, Au thin film on glass and CNTs was particulated by annealing. The performance of 3D LSPR sensor was confirmed using BSA for bio analysis. LSPR characteristics was measured and compared before and after adsorption of BSA. The detection limit was 100ng/ml and detection sensitivity was 10 times in comparison with 2D LSPR sensor of same AuNPs formation condition.

  13. Solid-state ionics method fabricated centimeter level CuAu alloy nanowires: Application in SERS.

    PubMed

    Xu, Dapeng; Dong, Jing; Yang, Wei; Zhang, Song; Peng, Yuli; Chen, Jian

    2017-04-08

    CuAu alloy nanowires were prepared by a solid-state ionics method under a direct current electric field (DCEF) using fast ionic conductor Rb4Cu16Cl13I7 films. The surface morphology, chemical composition and crystal structures of the CuAu alloy nanowires were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. Raman enhancement performance of the CuAu alloy nanowires substrates was detected by Rhodamine 6G (R6G) aqueous solutions as probe molecules. Long-range disorder and short-range order CuAu alloy nanowires with the length of 1 cm were prepared by a solid-state ionics method. The nanowires were bamboo-shaped and the diameters of nanowires ranged from 40 to 100nm. The molar ratio of Cu to Au is 16:1. The crystal structure of the CuAu alloy nanowires is crystallized. A part of Cu and Au formed Au3Cu alloy structure. The limiting concentrations of R6G for the prepared CuAu alloy nanowires SERS substrates is 10(-15)mol/L.

  14. 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.

  15. Pd-on-Au Supra-nanostructures Decorated Graphene Oxide: An Advanced Electrocatalyst for Fuel Cell Application.

    PubMed

    Tao, Yingzhou; Dandapat, Anirban; Chen, Liming; Huang, Youju; Sasson, Yoel; Lin, Zhenyu; Zhang, Jiawei; Guo, Longhua; Chen, Tao

    2016-08-30

    We report a very easy and effective approach for synthesizing unique palladium-on-gold supra-nanostructure (Au@Pd-SprNS)-decorated graphene oxide (GO) nanosheets. The SprNSs comprising Au nanorods as core and a unique close-packed assembly of tiny anisotropic Pd nanoparticles (NPs) as shell were homogeneously distributed on the GO surface via electrostatic self-assembly. Compared with the traditional one-pot method for synthesis of metal NPs on GO sheets, the size and shape of core-shell Au@Pd SprNSs can be finely controlled and uniformly distributed on the GO carrier. Interestingly, this Au@Pd-SprNSs/GO nanocomposite displayed high electrocatalytic activities toward the oxidation of methanol, ethanol, and formic acid, which can be attributed to the abundance of intrinsic active sites including high density of atomic steps, ledges and kinks, Au-Pd heterojunctions and cooperative action of the two metals of the SprNSs. Additionally, uniform dispersion of the SprNSs over the GO nanosheets prevent agglomeration between the SprNSs, which is of great significance to enhance the long-term stability of catalyst. This work will introduce a highly efficient Pd-based nanoelectrocatalyst to be used in fuel cell application.

  16. Sonophotodeposition of bimetallic photocatalysts Pd-Au/TiO2 : application to selective oxidation of methanol to methyl formate.

    PubMed

    Colmenares, Juan C; Lisowski, Paweł; Łomot, Dariusz; Chernyayeva, Olga; Lisovytskiy, Dmytro

    2015-05-22

    The aim of this work is to develop bimetallic Pd-Au/TiO2 P90 systems, which are highly active and selective for the photocatalytic oxidation of methanol to form methyl formate. Modification of commercial TiO2 P90 with Pd-Au nanoparticles was successfully achieved for the first time by means of a sonophotodeposition (SPD) method. The prepared materials were characterized by TEM, UV/Vis spectroscopy, X-ray photoelectron spectroscopy, and powder XRD. The Pd-Au bimetallic nanoparticles supported on titania exhibited remarkably enhanced catalytic activity in selective methanol oxidation to form methyl formate due to the synergism of Au and Pd particles, as well as the strong interaction between TiO2 and Pd-Au. SPD is a green methodology that can be used to prepare well-defined bimetallic surfaces on semiconductor supports with great promise for catalytic applications, in which selectivity can be tuned through adjustment of the surface composition. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Single gold nanowire electrodes and single Pt@Au nanowire electrodes: electrochemistry and applications.

    PubMed

    Zhang, Yaoyao; Xu, Shen; Xiao, Xiaoqing; Liu, Yong; Qian, Yuanyuan; Li, Yongxin

    2017-03-02

    Single Au nanowire electrodes and single Pt@Au nanowire electrodes showed steady-state voltammetric responses and a fast electron-transfer rate, which have been used to fabricate an E-DNA sensor and investigate the oxygen reduction reaction at the single nanowire level.

  18. Electrical performance of Ti-ZnO-Au thin film composite structure for device application

    NASA Astrophysics Data System (ADS)

    Joshi, Priyanka; Singh, Jitendra; Das, Surajit; Desai, J. V.; Akhtar, Jamil

    2016-04-01

    Thin film layers of Au/Ti approximately 2200 Å thick and ZnO approximately 2.24 µm thick were sputtered sequentially onto silicon dioxide coated <100> Si-wafer. Conventional wisdom confirms the adhesion of gold over zinc oxide (ZnO) by an intermediate layer of titanium for better adhesion. But, in Au/Ti/ZnO/Au/Ti structure, it was observed that with the passing of time the gold diffused into ZnO thin film at room temperature, making a very low resistance between the two gold layers eventually making a conductive path in ZnO. Therefore, electrical connectivity was found between the metal layers. A detailed experimental analysis has been carried out in support of the observed Au diffusion. In the present work, reliability of Ti/Au metallisation and anomalous electrical behavior due to gold diffusion has been studied.

  19. Preparation of Au coated polystyrene beads and their application in an immunoassay.

    PubMed

    Cao, Yuan-Cheng; Hua, Xiao-Feng; Zhu, Xiao-Xia; Wang, Zhan; Huang, Zhen-Li; Zhao, Yuan-Di; Chen, Hong; Liu, Man-Xi

    2006-12-20

    A novel immunoassay method based on polystyrene beads coated with Au nanoparticles (Au@PS) is described. Au nanoparticles were prepared by reductive reaction, and then deposited on the surface of polystyrene beads to form Au coatings. Results indicated that the Au coatings had good stability and that human IgG was immobilized at a concentration of 16 microg/g Au@PS. FITC-labeled rabbit-anti-human IgG and FITC-labeled rabbit-anti-goat IgG were employed to react with the human IgG on Au@PS. Fluorescence imaging results showed that the reaction had good immuno-specificity. In addition, further experiments at the single-bead level indicated that the linear range was 0.05-15 microg/ml, and that the FITC signal could be detected even when the target antibody concentration was as low as 0.01 microg/ml. The assay results were compared with an enzyme-linked immunosorbent assay (ELISA), and showed relatively good reliability.

  20. Application of Turkevich Method for Gold Nanoparticles Synthesis to Fabrication of SiO2@Au and TiO2@Au Core-Shell Nanostructures

    PubMed Central

    Dobrowolska, Paulina; Krajewska, Aleksandra; Gajda-Rączka, Magdalena; Bartosewicz, Bartosz; Nyga, Piotr; Jankiewicz, Bartłomiej J.

    2015-01-01

    The Turkevich synthesis method of Au nanoparticles (AuNPs) was adopted for direct fabrication of SiO2@Au and TiO2@Au core-shell nanostructures. In this method, chloroauric acid was reduced with trisodium citrate in the presence of amine-functionalized silica or titania submicroparticles. Core-shells obtained in this way were compared to structures fabricated by mixing of Turkevich AuNPs with amine-functionalized silica or titania submicroparticles. It was found that by modification of reaction conditions of the first method, such as temperature and concentration of reagents, control over gold coverage on silicon dioxide particles has been achieved. Described method under certain conditions allows fabrication of semicontinuous gold films on the surface of silicon dioxide particles. To the best of our knowledge, this is the first report describing use of Turkevich method to direct fabrication of TiO2@Au core-shell nanostructures.

  1. Tuning the Composition of AuPt Bimetallic Nanoparticles for Antibacterial Application**

    PubMed Central

    Zhao, Yuyun; Ye, Chunjie; Liu, Wenwen; Chen, Rong; Jiang, Xingyu

    2014-01-01

    We show that bimetallic nanoparticles (NPs) of AuPt without any surface modification are potent antibiotic reagents, while pure Au NPs or pure Pt NPs display no antibiotic activities. The most potent antibacterial AuPt NPs happen to be the most effective catalysts for chemical transformations. The mechanism of antibiotic action includes the dissipation of membrane potential and the elevation of adenosine triphosphate (ATP) levels. These bimetallic NPs are unique in that they do not produce reactive oxygen species as most antibiotics do. Being non-toxic to human cells, these bimetallic noble NPs might open an entry to a new class of antibiotics. PMID:24828967

  2. Facile Synthesis of Quasi-One-Dimensional Au/PtAu Heterojunction Nanotubes and Their Application as Catalysts in an Oxygen-Reduction Reaction.

    PubMed

    Cai, Kai; Liu, Jiawei; Zhang, Huan; Huang, Zhao; Lu, Zhicheng; Foda, Mohamed F; Li, Tingting; Han, Heyou

    2015-05-11

    An intermediate-template-directed method has been developed for the synthesis of quasi-one-dimensional Au/PtAu heterojunction nanotubes by the heterogeneous nucleation and growth of Au on Te/Pt core-shell nanostructures in aqueous solution. The synthesized porous Au/PtAu bimetallic nanotubes (PABNTs) consist of porous tubular framework and attached Au nanoparticles (AuNPs). The reaction intermediates played an important role in the preparation, which fabricated the framework and provided a localized reducing agent for the reduction of the Au and Pt precursors. The Pt7 Au PABNTs showed higher electrocatalytic activity and durability in the oxygen-reduction reaction (ORR) in 0.1 M HClO4 than porous Pt nanotubes (PtNTs) and commercially available Pt/C. The mass activity of PABNTs was 218 % that of commercial Pt/C after an accelerated durability test. This study demonstrates the potential of PABNTs as highly efficient electrocatalysts. In addition, this method provides a facile strategy for the synthesis of desirable hetero-nanostructures with controlled size and shape by utilizing an intermediate template.

  3. 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.

  4. Fabrication of Te and Te-Au Nanowires-Based Carbon Fiber Fabrics for Antibacterial Applications

    PubMed Central

    Chou, Ting-Mao; Ke, Yi-Yun; Tsao, Yu-Hsiang; Li, Ying-Chun; Lin, Zong-Hong

    2016-01-01

    Pathogenic bacteria that give rise to diseases every year remain a major health concern. In recent years, tellurium-based nanomaterials have been approved as new and efficient antibacterial agents. In this paper, we developed the approach to directly grow tellurium nanowires (Te NWs) onto commercial carbon fiber fabrics and demonstrated their antibacterial activity. Those Te NWs can serve as templates and reducing agents for gold nanoparticles (Au NPs) to deposit. Three different Te-Au NWs with varied concentration of Au NPs were synthesized and showed superior antibacterial activity and biocompability. These results indicate that the as-prepared carbon fiber fabrics with Te and Te-Au NWs can become antimicrobial clothing products in the near future. PMID:26861380

  5. Fabrication of Te and Te-Au Nanowires-Based Carbon Fiber Fabrics for Antibacterial Applications.

    PubMed

    Chou, Ting-Mao; Ke, Yi-Yun; Tsao, Yu-Hsiang; Li, Ying-Chun; Lin, Zong-Hong

    2016-02-06

    Pathogenic bacteria that give rise to diseases every year remain a major health concern. In recent years, tellurium-based nanomaterials have been approved as new and efficient antibacterial agents. In this paper, we developed the approach to directly grow tellurium nanowires (Te NWs) onto commercial carbon fiber fabrics and demonstrated their antibacterial activity. Those Te NWs can serve as templates and reducing agents for gold nanoparticles (Au NPs) to deposit. Three different Te-Au NWs with varied concentration of Au NPs were synthesized and showed superior antibacterial activity and biocompability. These results indicate that the as-prepared carbon fiber fabrics with Te and Te-Au NWs can become antimicrobial clothing products in the near future.

  6. Synthesis and characterization of ferrocene modified Fe3O4@Au magnetic nanoparticles and its application.

    PubMed

    Qiu, Jian-Ding; Xiong, Meng; Liang, Ru-Ping; Peng, Hua-Ping; Liu, Fen

    2009-04-15

    A novel dopamine sensor was fabricated by forming the 6-ferrocenylhexanethiol (HS(CH(2))(6)Fc) functionalized Fe(3)O(4)@Au nanoparticles (NPs) films on the surface of a carbon paste electrode with the aid of a permanent magnet. HS(CH(2))(6)Fc, which acted as the redox mediator, was self-assembled to Fe(3)O(4)@Au NPs via Au-S bond. Transmission electron microscopy, UV-visible absorption spectroscopy, Fourier transform infrared spectra, and cyclic voltammetry were used to characterize the properties of the Fe(3)O(4)@Au NPs/HS(CH(2))(6)Fc nanocomposite. It is shown that the prepared ferrocene-functionalized Fe(3)O(4)@Au NPs composite shuttled electrons between analyte and electrode, increased the mediator loading, and more importantly prevented the leakage of the mediator during measurements, which resulted in the substantially enhanced stability and reproducibility of the modified electrode. The electrooxidation of dopamine could be catalyzed by Fc/Fc(+) couple as a mediator and had a higher electrochemical response due to the unique performance of Fe(3)O(4)@Au NPs. The nanocomposite modified electrode exhibited fast response (3 s) and the linear range was from 2.0x10(-6) to 9.2x10(-4) M with a detection limit of 0.64 microM. This immobilization approach effectively improved the stability of the electron transfer mediator and is promising for construction of other sensors and bioelectronic devices.

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

    PubMed

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

    2007-11-01

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

  8. Realization of improved metallization-Ti/Al/Ti/W/Au ohmic contacts to n-GaN for high temperature application

    NASA Astrophysics Data System (ADS)

    Motayed, A.; Davydov, A. V.; Boettinger, W. J.; Josell, D.; Shapiro, A. J.; Levin, I.; Zheleva, T.; Harris, G. L.

    2005-05-01

    Tungsten metal layer was used for the first time as an effective diffusion barrier for the standard Ti/Al/Ti/Au ohmic metallization scheme to obtain thermally stable ohmic contact suitable for high temperature applications. Comparative studies were performed on three distinct metallization schemes: 1) standard GaN/Ti/Al/Ti/Au, 2) GaN/Ti/Al/W/Au, and 3) GaN/Ti/Al/Ti/W/Au. For the GaN with doping level of 5 × 1017 cm-3, the lowest specific contact resistance for the Ti/Al/Ti/W/Au metallization scheme annealed in argon at 750 °C for 30 sec was 5 × 10-6 .cm2, which is comparable to the standard Ti/Al/Ti/Au scheme. X-ray diffractions (XRD), auger electron spectroscopy (AES) depth profiling, field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (TEM) revealed that the Ti/Al/Ti/W/Au metallization has superior morphology and microstructural properties compared to standard Ti/Al/Ti/Au metallizations. Remarkably, this metallization was able to withstand thermal aging at 500 °C for 50 hrs with only marginal morphological and electrical deterioration. These studies revealed that the utilization of a compound diffusion barrier stack, as in the Ti/Al/Ti/W/Au metallization, yields electrically, structurally, and morphologically superior metallizations with exceptional thermal stability.

  9. TEM characterization of Au-based alloys to join YSZ to steel for SOFC applications

    SciTech Connect

    Lin, Kun-Lin; Singh, Mrityunjay; Asthana, Rajiv

    2012-01-15

    The microstructures of two gold-based alloys with compositions (in wt.%) of 96.4Au-3Ni-0.6Ti and 97.5Au-0.75Ni-1.75V following oxidation at 850 Degree-Sign C for 200 min were characterized by analytical transmission electron microscopy with energy dispersive spectroscopy and by scanning electron microscopy. In the oxidized 96.4Au-3Ni-0.6Ti interlayer, a dense scale composed of nickel oxide (NiO) and nickel titanate (NiTiO{sub 3}) formed at the alloy surface. No evidence of titanium oxide was found because there was not enough Ti present to form titanium oxide. In the oxidized 97.5Au-0.75Ni-1.75V interlayer, loose vanadium oxide (V{sub 2}O{sub 5}) and nickel vanadate (Ni{sub 2}V{sub 2}O{sub 7}) formed and were distributed within the oxidized 97.5Au-0.75Ni-1.75V interlayer. Similarly, because of the low Ni content in the alloys, no NiO formed. The oxide products in the 96.4Au-3Ni-0.6Ti and 97.5Au-0.75Ni-1.75V interlayers after oxidation are consistent with the Pilling-Bedworth (PB) ratio considerations. - Highlights: Black-Right-Pointing-Pointer Two commercial Au-based reactive metallic interlayers were oxidized at 850 Degree-Sign C for 200 min. Black-Right-Pointing-Pointer The oxidized products at the surface were characterized by TEM/EDS and SEM. Black-Right-Pointing-Pointer NiO and NiTiO{sub 3} formed at the oxidized 96.4Au-3Ni-0.6Ti interlayer. Black-Right-Pointing-Pointer V{sub 2}O{sub 5} and Ni{sub 2}V{sub 2}O{sub 7} were found in the oxidized 97.5Au-0.75Ni-1.75V interlayer. Black-Right-Pointing-Pointer These oxide products are consistent with the Pilling-Bedworth (PB) ratio considerations.

  10. Au nanostructure arrays for plasmonic applications: annealed island films versus nanoimprint lithography

    NASA Astrophysics Data System (ADS)

    Lopatynskyi, Andrii M.; Lytvyn, Vitalii K.; Nazarenko, Volodymyr I.; Guo, L. Jay; Lucas, Brandon D.; Chegel, Volodymyr I.

    2015-03-01

    This paper attempts to compare the main features of random and highly ordered gold nanostructure arrays (NSA) prepared by thermally annealed island film and nanoimprint lithography (NIL) techniques, respectively. Each substrate possesses different morphology in terms of plasmonic enhancement. Both methods allow such important features as spectral tuning of plasmon resonance position depending on size and shape of nanostructures; however, the time and cost is quite different. The respective comparison was performed experimentally and theoretically for a number of samples with different geometrical parameters. Spectral characteristics of fabricated NSA exhibited an expressed plasmon peak in the range from 576 to 809 nm for thermally annealed samples and from 606 to 783 nm for samples prepared by NIL. Modelling of the optical response for nanostructures with typical shapes associated with these techniques (parallelepiped for NIL and semi-ellipsoid for annealed island films) was performed using finite-difference time-domain calculations. Mathematical simulations have indicated the dependence of electric field enhancement on the shape and size of the nanoparticles. As an important point, the distribution of electric field at so-called `hot spots' was considered. Parallelepiped-shaped nanoparticles were shown to yield maximal enhancement values by an order of magnitude greater than their semi-ellipsoid-shaped counterparts; however, both nanoparticle shapes have demonstrated comparable effective electrical field enhancement values. Optimized Au nanostructures with equivalent diameters ranging from 85 to 143 nm and height equal to 35 nm were obtained for both techniques, resulting in the largest electrical field enhancement. The application of island film thermal annealing method for nanochips fabrication can be considered as a possible cost-effective platform for various surface-enhanced spectroscopies; while the NIL-fabricated NSA looks like more effective for sensing of

  11. Binary self-assembled monolayers modified Au nanoparticles as carriers in biological applications.

    PubMed

    Chang, Hsun-Yun; You, Yun-Wen; Liao, Hua-Yang; Shyue, Jing-Jong

    2014-12-01

    Gold nanoparticles (AuNPs) are good nonviral carriers because of their ease of synthesis and conjugation in biochemistry, and self-assembled monolayers (SAMs) provide a tunable system to change their interfacial properties. Using homogeneously mixed carboxylic acid and amine functional groups, a series of surface potentials and isoelectric points (IEPs) could be obtained and allow systematic study of the effect of surface potential. In this work, the result of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay revealed that binary-SAM modified AuNPs have high biocompatibility with HEK293T cells. The amount of AuNPs ingested by the cells was found to increase with increasing surface potential and the difference was also confirmed with a scanning transmission electron microscope. The ability of binary-SAM modified AuNPs as carriers was examined, and the plasmid deoxyribose nucleic acid (DNA)-containing eGFP reporter gene was used as the model cargo. Fluorescence imaging revealed that the transfection efficiency generally increased with increasing surface potential. More importantly, when the IEP of the AuNPs was higher than that of the environment of the endosome but lower than that of the cytoplasm, the plasmid DNA can be protected better and released more easily during the endocytosis process hence higher efficiency is obtained with 60% NH2 and 40% COOH in the binary-SAM.

  12. Corrosion Protection of Al/Au/ZnO Anode for Hybrid Cell Application

    PubMed Central

    Slaughter, Gymama; Stevens, Brian

    2015-01-01

    Effective protection of power sources from corrosion is critical in the development of abiotic fuel cells, biofuel cells, hybrid cells and biobateries for implantable bioelectronics. Corrosion of these bioelectronic devices result in device inability to generate bioelectricity. In this paper Al/Au/ZnO was considered as a possible anodic substrate for the development of a hybrid cell. The protective abilities of corrosive resistant aluminum hydroxide and zinc phosphite composite films formed on the surface of Al/Au/ZnO anode in various electrolyte environments were examined by electrochemical methods. The presence of phosphate buffer and physiological saline (NaCl) buffer allows for the formation of aluminum hyrdroxide and zinc phosphite composite films on the surface of the Al/Au/ZnO anode that prevent further corrosion of the anode. The highly protective films formed on the Al/Au/ZnO anode during energy harvesting in a physiological saline environment resulted in 98.5% corrosion protective efficiency, thereby demonstrating that the formation of aluminum hydroxide and zinc phosphite composite films are effective in the prevention of anode corrosion during energy harvesting. A cell assembly consisting of the Al/Au/ZnO anode and platinum cathode resulted in an open circuit voltage of 1.03 V. A maximum power density of 955.3 μW/ cm2 in physiological saline buffer at a cell voltage and current density of 345 mV and 2.89 mA/ cm2, respectively. PMID:26580661

  13. Synthesis, characterization and potential application of MnZn ferrite and MnZn ferrite @ Au nanoparticles.

    PubMed

    Wang, Xin; Wang, Lingyan; Lim, I-Im S; Bao, Kun; Mott, Derrick; Park, Hye-Young; Luo, Jin; Hao, Shunli; Zhong, Chuan-Jian

    2009-05-01

    The ability to tune the magnetic properties of magnetic nanoparticles by manipulating the composition or surface properties of the nanoparticles is important for exploiting the application of the nanomaterials. This report describes preliminary findings of an investigation of the viability of synthesizing MnZn ferrite and core @ shell MnZn ferrite @ Au nanoparticles as potentially magnetization-tunable nanomaterials. The synthesis of the core-shell magnetic nanoparticles involved a simple combination of seed formation of the MnZn ferrite magnetic nanoparticles and surface coating of the seeds with gold shells. Water-soluble MnZn ferrite nanoparticles of 20-40 nm diameters and MnZn ferrite @ Au nanoparticles of 30-60 nm have been obtained. The MnZn ferrite @ Au nanoparticles have been demonstrated to be viable in magnetic separation of nanoparticles via interparticle antibody-specific binding reactivity between antibodies on the gold shells of the core-shell magnetic particles and proteins on gold nanoparticles. These findings have significant implications to the design of the core @ shell magnetic nanomaterials with core composition tuned magnetization for bioassay application.

  14. 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

  15. Production of radio-gold {sup 199}Au for diagnostic and therapeutic applications

    SciTech Connect

    Khandaker, Mayeen Uddin Kassim, Hasan Abu; Haba, Hiromitsu

    2016-01-22

    Production cross-sections of the {sup nat}Pt(d,x){sup 199}Au reactions have been measured from a 24-MeV deuteron energy down to the threshold by using a stacked-foil activation technique combined with HPGe γ-ray spectrometry. Only a partial agreement is obtained with the existing literature data. Theoretical data extracted from the TENDL-2013 library shows large discrepancy with the measured ones. Physical thick target yield for the {sup 199}Au radionuclide was deduced using the measured cross-sections, and found a general agreement with the directly measured yield available in the literature. This study reveals that a low deuteron energy (<15 MeV) cyclotron and an enriched {sup 198}Pt (100%) target could be used to obtain {sup 199}Au in no carrier added form.

  16. Production of radio-gold 199Au for diagnostic and therapeutic applications

    NASA Astrophysics Data System (ADS)

    Khandaker, Mayeen Uddin; Haba, Hiromitsu; Kassim, Hasan Abu

    2016-01-01

    Production cross-sections of the natPt(d,x)199Au reactions have been measured from a 24-MeV deuteron energy down to the threshold by using a stacked-foil activation technique combined with HPGe γ-ray spectrometry. Only a partial agreement is obtained with the existing literature data. Theoretical data extracted from the TENDL-2013 library shows large discrepancy with the measured ones. Physical thick target yield for the 199Au radionuclide was deduced using the measured cross-sections, and found a general agreement with the directly measured yield available in the literature. This study reveals that a low deuteron energy (<15 MeV) cyclotron and an enriched 198Pt (100%) target could be used to obtain 199Au in no carrier added form.

  17. Cyclotron produced 198gAu, a potential radionuclide for diagnostic and therapeutic applications

    NASA Astrophysics Data System (ADS)

    Khandaker, Mayeen Uddin; Haba, Hiromitsu; Kassim, Hasan Abu

    2016-02-01

    Production cross-sections of the natPt(d,x)198Au reactions have been measured from a 24-MeV deuteron energy down to the threshold by using a stacked-foil activation technique combined with HPGe γ-ray spectrometry. Only a partial agreement is obtained with the existing literature data and the theoretical data extracted from the TENDL-2013 library. Physical thick target yield for the 198Au radionuclide was deduced using the measured cross-sections, and found a general agreement with the directly measured yield available in the literature. This study reveals that a low deuteron energy (<15 MeV) cyclotron and an enriched 198Pt (100%) target could be used to obtain 198Au in no carrier added form.

  18. Nonlinear stability of solar type 3 radio bursts. 2: Application to observations near 1 AU

    NASA Technical Reports Server (NTRS)

    Goldstein, M. L.; Smith, R. A.; Papadopoulos, K.

    1978-01-01

    A set of rate equations including strong turbulence effects and anomalous resitivity are solved using parmeters which model several solar type 3 bursts. Exciter distributions observed at 1 AU are excitation of the linear bump-in-tail instability, amplifying Langmuir waves above the threshold for the oscillating two stream instability (OTSI). The OTSI, and the attendant anomalous resistivity produce a rapid spectral transfer of Langmuir waves to short wavelengths, out of resonance with the electron exciter. Further energy loss of the beam is thus precluded. The various parameters needed to model the bursts are extrapolated inside 1 AU with similar results. Again, the OTSI is excited and decouples the electron beam from the Langmuir radiation. Reabsorption of the Langmuir waves by the beam is shown to be unimportant in all cases, even at 0.1 AU. The theory provides a natural explanation for the observed realationship between radio flux, and the electron flux.

  19. Enhancement of the transverse magneto-optical Kerr effect via resonant tunneling in Au/Ce:YIG/Au trilayers and its application

    NASA Astrophysics Data System (ADS)

    Li, Jie; Tang, Tingting; Zhang, Yanfen; Luo, Li

    2017-02-01

    We propose a new structure to enhance the transverse magneto-optical Kerr effect (TMOKE) via resonant photon tunneling. In trilayer structures with a magnetic dielectric layer sandwiched between non-magnetic metal layers, an enhanced TMOKE can be observed. The TMOKE in Au/Ce:YIG/Au trilayers with different widths of magnetic dielectric layers are calculated using a 4  ×  4 transfer-matrix method, in which the maximum absolute value reaches 0.7. Based on the enhanced TMOKE, we apply the structure proposed above in magnetic field sensing, and TMOKE values are calculated when the external magnetic field intensity is increasing. Compared with other magnetic field sensing methods, the Au/Ce:YIG/Au trilayer possesses a very simple structure and shows high sensitivity to magnetic field variation, which is promising as a highly integrated and sensitive magneto-optical device.

  20. Simultaneous Au(III) Extraction and In Situ Formation of Polymeric Membrane-Supported Au Nanoparticles: A Sustainable Process with Application in Catalysis.

    PubMed

    Mora-Tamez, Lucía; Esquivel-Peña, Vicente; Ocampo, Ana L; Rodríguez de San Miguel, Eduardo; Grande, Daniel; de Gyves, Josefina

    2017-04-10

    A polymeric membrane-supported catalyst with immobilized gold nanoparticles (AuNPs) was prepared through the extraction and in situ reduction of Au(III) salts in a one-step strategy. Polymeric inclusion membranes (PIMs) and polymeric nanoporous membranes (PNMs) were tested as different membrane-support systems. Transport experiments indicated that PIMs composed of cellulose triacetate, 2-nitrophenyloctyl ether, and an aliphatic tertiary amine (Adogen 364 or Alamine 336) were the most efficient supports for Au(III) extraction. The simultaneous extraction and reduction processes were proven to be the result of a synergic phenomenon in which all the membrane components were involved. Scanning electron microscopy characterization of cross-sectional samples suggested a distribution of AuNPs throughout the membrane. Transmission electron microscopy characterization of the AuNPs indicated average particle sizes of 36.7 and 2.9 nm for the PIMs and PNMs, respectively. AuNPs supported on PIMs allowed for >95.4 % reduction of a 0.05 mmol L(-1) 4-nitrophenol aqueous solution with 10 mmol L(-1) NaBH4 solution within 25 min. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Synthesis of Photoswitchable Magnetic Au-Fullerosome Hybrid Nanomaterials for Permittivity Enhancement Applications.

    PubMed

    Wang, Min; Jeon, Seaho; Su, Chefu; Yu, Tzuyang; Tan, Loon-Seng; Chiang, Long Y

    2015-08-13

    We designed and synthesized several nanomaterials 3 of three-layered core-shell (γ-FeOx@AuNP)@[C60(>DPAF-C9) 1 or 2]n nanoparticles (NPs). These NPs having e(-)-polarizable fullerosome structures located at the outer layer were fabricated from highly magnetic core-shell γ-FeOx@AuNPs. Fullerosomic polarization of 3 was found to be capable of causing a large amplification of material permittivity that is also associated with the photoswitching effect in the frequency range of 0.5-4.0 GHz. Multilayered synthetic construction allows Förster resonance energy transfer (FRET) of photoinduced accumulative surface plasmon resonance (SPR) energy in the gold layer to the partially bilayered C60(>DPAF-C9) 1 or 2-derived fullerosome membrane shell layer in a near-field of direct contact without producing radiation heat, which is commonly associated with SPR.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    PubMed

    Xian, Jiawei; Baroni, Stefano; Umari, P

    2014-03-28

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

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

    SciTech Connect

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

    2014-03-28

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

  5. Tuning the composition of AuPt bimetallic nanoparticles for antibacterial application.

    PubMed

    Zhao, Yuyun; Ye, Chunjie; Liu, Wenwen; Chen, Rong; Jiang, Xingyu

    2014-07-28

    We show that bimetallic nanoparticles (NPs) of AuPt without any surface modification are potent antibiotic reagents, while pure Au NPs or pure Pt NPs display no antibiotic activities. The most potent antibacterial AuPt NPs happen to be the most effective catalysts for chemical transformations. The mechanism of antibiotic action includes the dissipation of membrane potential and the elevation of adenosine triphosphate (ATP) levels. These bimetallic NPs are unique in that they do not produce reactive oxygen species as most antibiotics do. Being non-toxic to human cells, these bimetallic noble NPs might open an entry to a new class of antibiotics. © 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution Non-Commercial NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

  6. Nanostructuring of thin Au films deposited on ordered Ti templates for applications in SERS

    NASA Astrophysics Data System (ADS)

    Grochowska, Katarzyna; Siuzdak, Katarzyna; Macewicz, Łukasz; Skiba, Franciszek; Szkoda, Mariusz; Karczewski, Jakub; Burczyk, Łukasz; Śliwiński, Gerard

    2017-10-01

    In this work the results on thermal nanostructuring of the Au films on Ti templates as well as morphology and optical properties of the obtained structures are reported. The bimetal nanostructures are fabricated in a multi-step process. First, the titania nanotubes are produced on the surface of Ti foil by anodization in an ethylene glycol-water solution containing fluoride ions. This is followed by chemical etching in oxalic acid and results in a highly ordered dimpled surface. Subsequently, thin gold films (5-20 nm) are deposited onto prepared Ti substrates by magnetron sputtering. The as-prepared layers are then dewetted by the UV nanosecond laser pulses or alternatively in the furnace (temperature < 500 °C). The SEM inspection reveals formation of honeycomb nanostructures (cavity diameter: ∼100 nm) covered with Au nanoparticles (NPs). It is observed that both the laser annealing and continuous thermal treatment in furnace can lead to the creation of NPs inside every Ti dimple and result in uniform coating of the whole area of structured templates. The size and localization of NPs obtained via both dewetting processes as well as their shape can be tuned by the annealing time and the laser processing parameters and also by initial thickness of Au layer and presence of the dimples themselves in the substrate. Results confirm that the prepared material can be used as substrate for SERS (Surface Enhanced Raman Spectroscopy).

  7. ZnO/Au-based surface plasmon resonance for CO2 gas sensing application

    NASA Astrophysics Data System (ADS)

    Nuryadi, Ratno; Mayasari, Rina Dewi

    2016-01-01

    We fabricate surface plasmon resonance (SPR) device using a modified ZnO/Au-Kretschmann configuration to investigate the possibility of using ZnO for CO2 gas sensing at room temperature. Here, nanostructured ZnO/Au layer was deposited on the flat surface of the prism and then gas chamber was placed on the ZnO/Au surface to observe the gas response. The ZnO structures were characterized by X-ray diffraction, scanning electron microscope, and energy dispersive spectroscopy. We found that ZnO structures have two types of nanostructures, i.e., individual nanorods and flower-like structures, which have hexagonal crystal structure. The ZnO nanorod has a diameter ranged from 200 to 300 nm and length ranged from 3 to 5 μm. The effect of gas response is demonstrated by a shift of SPR spectra and a change in light reflectance. It is found that the adsorption of gas molecules on the ZnO nanorods produces the shift of SPR angle to the lower light incident angle. A consistent sensing behavior over repetitive circles is also demonstrated.

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

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

    PubMed

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

    2015-12-21

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

  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. Electrogenerated Chemiluminescence Behavior of Au nanoparticles-hybridized Pb (II) metal-organic framework and its application in selective sensing hexavalent chromium

    PubMed Central

    Ma, Hongmin; Li, Xiaojian; Yan, Tao; Li, Yan; Liu, Haiyang; Zhang, Yong; Wu, Dan; Du, Bin; Wei, Qin

    2016-01-01

    In this work, a novel electrochemiluminescence (ECL) sensor based on Au nanoparticles-hybridized Pb (II)-β-cyclodextrin (Pb-β-CD) metal-organic framework for detecting hexavalent chromium (Cr(VI)) was developed. Pb-β-CD shows excellent ECL behavior and unexpected reducing ability towards Au ions. Au nanoparticles could massively form on the surface of Pb-β-CD (Au@Pb-β-CD) without use of any additional reducing agent. In the presence of coreactant K2S2O8, the ECL emission of Pb-β-CD was enhanced by the formation of Au nanoparticles. Cr(VI) can collisionally quench the ECL behavior of Au@Pb-β-CD/S2O82− system and the detection mechanism was investigated. This ECL sensor is found to have a linear response in the range of 0.01–100 μM and a low detection limit of 3.43 nM (S/N = 3) under the optimal conditions. These results suggest that metal-organic framework Au@Pb-β-CD has great potential in extending the application in the ECL field as an efficient luminophore. PMID:26902375

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  13. Highly narrow nanogap-containing Au@Au core-shell SERS nanoparticles: size-dependent Raman enhancement and applications in cancer cell imaging

    NASA Astrophysics Data System (ADS)

    Hu, Chongya; Shen, Jianlei; Yan, Juan; Zhong, Jian; Qin, Weiwei; Liu, Rui; Aldalbahi, Ali; Zuo, Xiaolei; Song, Shiping; Fan, Chunhai; He, Dannong

    2016-01-01

    Cellular imaging technologies employing metallic surface-enhanced Raman scattering (SERS) tags have gained much interest toward clinical diagnostics, but they are still suffering from poor controlled distribution of hot spots and reproducibility of SERS signals. Here, we report the fabrication and characterization of high narrow nanogap-containing Au@Au core-shell SERS nanoparticles (GCNPs) for the identification and imaging of proteins overexpressed on the surface of cancer cells. First, plasmonic nanostructures are made of gold nanoparticles (~15 nm) coated with gold shells, between which a highly narrow and uniform nanogap (~1.1 nm) is formed owing to polyA anchored on the Au cores. The well controlled distribution of Raman reporter molecules, such as 4,4'-dipyridyl (44DP) and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), are readily encoded in the nanogap and can generate strong, reproducible SERS signals. In addition, we have investigated the size-dependent SERS activity of GCNPs and found that with the same laser wavelength, the Raman enhancement discriminated between particle sizes. The maximum Raman enhancement was achieved at a certain threshold of particle size (~76 nm). High narrow nanogap-containing Au@Au core-shell SERS tags (GCTs) were prepared via the functionalization of hyaluronic acid (HA) on GCNPs, which recognized the CD44 receptor, a tumor-associated surface biomarker. And it was shown that GCTs have a good targeting ability to tumour cells and promising prospects for multiplex biomarker detection.Cellular imaging technologies employing metallic surface-enhanced Raman scattering (SERS) tags have gained much interest toward clinical diagnostics, but they are still suffering from poor controlled distribution of hot spots and reproducibility of SERS signals. Here, we report the fabrication and characterization of high narrow nanogap-containing Au@Au core-shell SERS nanoparticles (GCNPs) for the identification and imaging of proteins overexpressed on

  14. Transfert radiatif entre une petite particule et un diélectrique: application au chauffage local

    NASA Astrophysics Data System (ADS)

    Mulet, J.-P.; Joulain, K.; Carminati, R.; Greffet, J. J.

    2002-06-01

    nous montrons dans cette étude que le transfert radiatif entre une particule de taille nanométrique et un diélectrique petit être très important lorsque les distances mises en jeu sont petites devant la longueur d'onde caractéristique du rayonnement thermique. Ce transfert peut devenir dominant lorsque les matériaux utilisés sont polaires. Nous discuterons de la possibilité d'appliquer ces résultats au chauffage local dans les nano-structures.

  15. Cu2O and Au/Cu2O particles: surface properties and applications in glucose sensing.

    PubMed

    Won, Yu-Ho; Stanciu, Lia A

    2012-09-26

    In this work we investigated the surface and facet-dependent catalytic properties of metal oxide particles as well as noble metal/metal oxide heterogeneous structures, with cuprous oxide (Cu(2)O) and Au/Cu(2)O being selected as model systems. As an example of application, we explored the potential of these materials in developing electrocatalytic devices. Cu(2)O particles were synthesized in various shapes, then used for testing their morphology-dependent electrochemical properties applied to the detection of glucose. While we did not attempt to obtain the best detection limit reported to date, the octahedral and hexapod Cu(2)O particles showed reasonable detection limits of 0.51 and 0.60 mM, respectively, which are physiologically relevant concentrations. However, detection limit seems to be less affected by particle shapes than sensitivity. Heterogeneous systems where Au NPs were deposited on the surface of Cu(2)O particles were also tested with similar results in terms of the effect of surface orientation.

  16. Crystallographic investigation of Au nanoparticles embedded in a SrTiO{sub 3} thin film for plasmonics applications by means of synchrotron radiation

    SciTech Connect

    Pincini, Davide; Mazzoli, Claudio; Bernhardt, Hendrik; Katzer, Christian; Schmidl, Frank; Uschmann, Ingo; Detlefs, Carsten

    2015-03-14

    Self-organized monocrystalline Au nanoparticles with potential applications in plasmonics are grown in a SrTiO{sub 3} matrix by a novel two-step deposition process. The crystalline preferred orientation of these Au nanoparticles is investigated by synchrotron hard x-ray diffraction. Nanoparticles preferentially align with the (111) direction along the substrate normal (001), whereas two in-plane orientations are found with [110]{sub SrTiO{sub 3}}∥[110]{sub Au} and [100]{sub SrTiO{sub 3}}∥[110]{sub Au}. Additionally, a smaller diffraction signal from nanoparticles with the (001) direction parallel to the substrate normal (001) is observed; once again, two in-plane orientations are found, with [100]{sub SrTiO{sub 3}}∥[100]{sub Au} and [100]{sub SrTiO{sub 3}}∥[110]{sub Au}. The populations of the two in-plane orientations are found to depend on the thickness of the gold film deposited in the first step of the growth.

  17. Novel electrochemical redox-active species: one-step synthesis of polyaniline derivative-Au/Pd and its application for multiplexed immunoassay.

    PubMed

    Wang, Liyuan; Feng, Feng; Ma, Zhanfang

    2015-11-18

    Electrochemical redox-active species play crucial role in electrochemically multiplexed immunoassays. A one-pot method for synthesizing four kinds of new electrochemical redox-active species was reported using HAuCl4 and Na2PdCl4 as dual oxidating agents and aniline derivatives as monomers. The synthesized polyaniline derivative-Au/Pd composites, namely poly(N-methyl-o-benzenediamine)-Au/Pd, poly(N-phenyl-o-phenylenediamine)-Au/Pd, poly(N-phenyl-p-phenylenediamine)-Au/Pd and poly(3,3',5,5'-tetramethylbenzidine)-Au/Pd, exhibited electrochemical redox activity at -0.65 V, -0.3 V, 0.12 V, and 0.5 V, respectively. Meanwhile, these composites showed high H2O2 electrocatalytic activity because of the presence of Au/Pd. The as-prepared composites were used as electrochemical immunoprobes in simultaneous detection of four tumor biomarkers (carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA199), carbohydrate antigen 72-4 (CA724), and alpha fetoprotein (AFP)). This immunoassay shed light on potential applications in simultaneous gastric cancer (related biomarkers: CEA, CA199, CA724) and liver cancer diagnosis (related biomarkers: CEA, CA199, AFP). The present strategy to the synthesize redox species could be easily extended to other polymers such as polypyrrole derivatives and polythiophene derivatives. This would be of great significance in the electrochemical detection of more analytes.

  18. Novel electrochemical redox-active species: one-step synthesis of polyaniline derivative-Au/Pd and its application for multiplexed immunoassay

    PubMed Central

    Wang, Liyuan; Feng, Feng; Ma, Zhanfang

    2015-01-01

    Electrochemical redox-active species play crucial role in electrochemically multiplexed immunoassays. A one-pot method for synthesizing four kinds of new electrochemical redox-active species was reported using HAuCl4 and Na2PdCl4 as dual oxidating agents and aniline derivatives as monomers. The synthesized polyaniline derivative-Au/Pd composites, namely poly(N-methyl-o-benzenediamine)-Au/Pd, poly(N-phenyl-o-phenylenediamine)-Au/Pd, poly(N-phenyl-p-phenylenediamine)-Au/Pd and poly(3,3’,5,5’-tetramethylbenzidine)-Au/Pd, exhibited electrochemical redox activity at −0.65 V, −0.3 V, 0.12 V, and 0.5 V, respectively. Meanwhile, these composites showed high H2O2 electrocatalytic activity because of the presence of Au/Pd. The as-prepared composites were used as electrochemical immunoprobes in simultaneous detection of four tumor biomarkers (carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA199), carbohydrate antigen 72-4 (CA724), and alpha fetoprotein (AFP)). This immunoassay shed light on potential applications in simultaneous gastric cancer (related biomarkers: CEA, CA199, CA724) and liver cancer diagnosis (related biomarkers: CEA, CA199, AFP). The present strategy to the synthesize redox species could be easily extended to other polymers such as polypyrrole derivatives and polythiophene derivatives. This would be of great significance in the electrochemical detection of more analytes. PMID:26577799

  19. Novel electrochemical redox-active species: one-step synthesis of polyaniline derivative-Au/Pd and its application for multiplexed immunoassay

    NASA Astrophysics Data System (ADS)

    Wang, Liyuan; Feng, Feng; Ma, Zhanfang

    2015-11-01

    Electrochemical redox-active species play crucial role in electrochemically multiplexed immunoassays. A one-pot method for synthesizing four kinds of new electrochemical redox-active species was reported using HAuCl4 and Na2PdCl4 as dual oxidating agents and aniline derivatives as monomers. The synthesized polyaniline derivative-Au/Pd composites, namely poly(N-methyl-o-benzenediamine)-Au/Pd, poly(N-phenyl-o-phenylenediamine)-Au/Pd, poly(N-phenyl-p-phenylenediamine)-Au/Pd and poly(3,3’,5,5’-tetramethylbenzidine)-Au/Pd, exhibited electrochemical redox activity at -0.65 V, -0.3 V, 0.12 V, and 0.5 V, respectively. Meanwhile, these composites showed high H2O2 electrocatalytic activity because of the presence of Au/Pd. The as-prepared composites were used as electrochemical immunoprobes in simultaneous detection of four tumor biomarkers (carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA199), carbohydrate antigen 72-4 (CA724), and alpha fetoprotein (AFP)). This immunoassay shed light on potential applications in simultaneous gastric cancer (related biomarkers: CEA, CA199, CA724) and liver cancer diagnosis (related biomarkers: CEA, CA199, AFP). The present strategy to the synthesize redox species could be easily extended to other polymers such as polypyrrole derivatives and polythiophene derivatives. This would be of great significance in the electrochemical detection of more analytes.

  20. Highly efficient and stable Au/CeO2-TiO2 photocatalyst for nitric oxide abatement: potential application in flue gas treatment.

    PubMed

    Zhu, Wei; Xiao, Shuning; Zhang, Dieqing; Liu, Peijue; Zhou, Hongjun; Dai, Wenrui; Liu, Fanfan; Li, Hexing

    2015-10-06

    In the present work, highly efficient and stable Au/CeO2-TiO2 photocatalysts were prepared by a microwave-assisted solution approach. The Au/CeO2-TiO2 composites with optimal molar ratio of Au/Ce/Ti of 0.004:0.1:1 delivered a remarkably high and stable NO conversion rate of 85% in a continuous flow reactor system under simulated solar light irradiation, which far exceeded the rate of 48% over pure TiO2. The tiny Au nanocrystals (∼1.1 nm) were well stabilized by CeO2 via strong metal-support bonding even it was subjected to calcinations at 550 °C for 6 h. These Au nanocrystals served as the very active sites for activating the molecule of nitric oxide and reducing the transmission time of the photogenerated electrons to accelerate O2 transforming to reactive oxygen species. Moreover, the Au-Ce(3+) interface formed and served as an anchoring site of O2 molecule. Then more adsorbed oxygen could react with photogenerated electrons on TiO2 surfaces to produce more superoxide radicals for NO oxidation, resulting in the improved efficiency. Meanwhile, O2 was also captured at the Au/TiO2 perimeter site and the NO molecules on TiO2 sites were initially delivered to the active perimeter site via diffusion on the TiO2 surface, where they assisted O-O bond dissociation and reacted with oxygen at these perimeter sites. Therefore, these finite Au nanocrystals can consecutively expose active sites for oxidizing NO. These synergistic effects created an efficient and stable system for breaking down NO pollutants. Furthermore, the excellent antisintering property of the catalyst will allow them for the potential application in photocatalytic treatment of high-temperature flue gas from power plant.

  1. Applications de la tranformee en ondelettes au traitement de l'information optique

    NASA Astrophysics Data System (ADS)

    Deschenes, Sylvain

    La these presente l'apport d'un outil mathematique recemment decouvert, la transformee en ondelettes, au traitement de l'information optique. Les ondelettes continues sont d'abords introduites et leur realisation optique est presentee. Ensuite, une ondelette repondant aux equations de Maxwell est developpee. Cette derniere permet de tisser des liens entre la transformee en ondelettes et le principe de Huygens utilise pour etudier la diffraction scalaire. La possibilite d'utiliser cette ondelette pour generer des faisceaux non diffractants est egalement discutee. Dans un deuxieme temps, les ondelettes discretes sont utilisees dans le but d'extraire des informations pertinentes dans une banque d'images infrarouges. Ces images representent les vues de vehicules prises a tous les cinq degres. La transformee en ondelettes genere une analyse multiresolution permettant d'extraire des contours moins bruites. Cette information est alors traitee par de nouveaux algorithmes de reconnaissance de forme dans un espace qui caracterise de facon invariante les objets 3-D.

  2. Rapid synthesis and characterization of hybrid ZnO@Au core-shell nanorods for high performance, low temperature NO2 gas sensor applications

    NASA Astrophysics Data System (ADS)

    Ponnuvelu, Dinesh Veeran; Pullithadathil, Biji; Prasad, Arun K.; Dhara, Sandip; Ashok, Anuradha; Mohamed, Kamruddin; Tyagi, Ashok Kumar; Raj, Baldev

    2015-11-01

    A rapid synthesis route for hybrid ZnO@Au core-shell nanorods has been realized for ultrasensitive, trace-level NO2 gas sensor applications. ZnO nanorods and hybrid ZnO@Au core-shell nanorods are structurally analyzed using X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Optical characterization using UV-visible (UV-vis), photoluminescence (PL) and Raman spectroscopies elucidate alteration in the percentage of defect and charge transport properties of ZnO@Au core-shell nanorods. The study reveals the accumulation of electrons at metal-semiconductor junctions leading to upward band bending for ZnO and thus favors direct electron transfer from ZnO to Au nanoclusters, which mitigates charge carrier recombination process. The operating temperature of ZnO@Au core-shell nanorods based sensor significantly decreased to 150 °C compared to alternate NO2 sensors (300 °C). Moreover, a linear sensor response in the range of 0.5-5 ppm of NO2 concentration was observed with a lowest detection limit of 500 ppb using conventional electrodes. The defects with deep level, observed in ZnO nanorods and hybrid ZnO@Au core-shell nanorods influences local electron density, which in-turn indirectly influence the gas sensing properties. The ZnO@Au core-shell nanorods based sensor exhibited good selectivity toward NO2 and was found to be very stable.

  3. Graphene decorated with PtAu alloy nanoparticles: facile synthesis and promising application for formic acid oxidation

    SciTech Connect

    Zhang, Sheng; Shao, Yuyan; Liao, Honggang; Liu, Jun; Aksay, Ilhan A.; Yin, Geping; Lin, Yuehe

    2011-03-01

    PtAu alloy nanoparticles (~ 3.2 nm in diameter) are synthesized in poly(diallyldimethylammonium chloride) (PDDA) aqueous solution and uniformly dispersed on graphene nanosheets. PtAu/graphene exhibits high electrocatalytic activity and stability for formic acid oxidation, which is attributed to the high dispersion of PtAu nanoparticles and the specific interaction between PtAu and graphene, indicating a promising catalyst for direct formic acid fuel cells. The facile method can be readily extended to the synthesis of other alloy nanoparticles.

  4. Au-nanoparticle-loaded graphitic carbon nitride nanosheets: green photocatalytic synthesis and application toward the degradation of organic pollutants.

    PubMed

    Cheng, Ningyan; Tian, Jingqi; Liu, Qian; Ge, Chenjiao; Qusti, Abdullah H; Asiri, Abdullah M; Al-Youbi, Abdulrahman O; Sun, Xuping

    2013-08-14

    Au nanoparticles (AuNPs) were loaded on graphitic carbon nitride (g-C3N4) nanosheets prepared by ultrasonication-assisted liquid exfoliation of bulk g-C3N4 via green photoreduction of Au(III) under visible light irradiation using g-C3N4 as an effective photocatalyst. The nanohybrids show superior photocatalytic activities for the decomposition of methyl orange under visible-light irradiation to bulk g-C3N4, g-C3N4 nanosheets, and AuNP/bulk g-C3N4 hybrids.

  5. The Preparation of Au@TiO2 Yolk-Shell Nanostructure and its Applications for Degradation and Detection of Methylene Blue.

    PubMed

    Wan, Gengping; Peng, Xiange; Zeng, Min; Yu, Lei; Wang, Kan; Li, Xinyue; Wang, Guizhen

    2017-09-18

    This paper reports the synthesis of a new type of Au@TiO2 yolk-shell nanostructures by integrating ion sputtering method with atomic layer deposition (ALD) technique and its applications as visible light-driven photocatalyst and surface-enhanced Raman spectroscopy (SERS) substrate. Both the size and amount of gold nanoparticles confined in TiO2 nanotubes could be facilely controlled via properly adjusting the sputtering time. The unique structure and morphology of the resulting Au@TiO2 samples were investigated by using various spectroscopic and microscopic techniques in detail. It is found that all tested samples can absorb visible light with a maximum absorption at localized surface plasmon resonance (LSPR) wavelengths (550-590 nm) which are determined by the size of gold nanoparticles. The Au@TiO2 yolk-shell composites were used as the photocatalyst for the degradation of methylene blue (MB). As compared with pure TiO2 nanotubes, Au@TiO2 composites exhibit improved photocatalytic properties towards the degradation of MB. The SERS effect of Au@TiO2 yolk-shell composites was also performed to investigate the detection sensitivity of MB.

  6. A Grand Avenue to Au Nanocluster Electrochemiluminescence.

    PubMed

    Hesari, Mahdi; Ding, Zhifeng

    2017-02-21

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

  7. Au-Pt bimetallic nanoparticles supported on nest-like MnO2: synthesis and application in HCHO decomposition

    NASA Astrophysics Data System (ADS)

    Yu, Xuehua; He, Junhui; Wang, Donghui; Hu, Yucai; Tian, Hua; Dong, Tongxin; He, Zhicheng

    2012-11-01

    Facile synthesis of Au-Pt bimetallic nanoparticles (Au1- x Pt x NPs) and mixtures of Au NPs and Pt NPs ((100 % - y)Au/ yPt NPs) and their subsequent deposition on nest-like MnO2 nanostructures were presented. The as-prepared products were characterized by means of UV-visible spectroscopy, X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive spectroscopy. TEM analyses showed that noble metal NPs were evenly dispersed on the surface of nest-like MnO2 nanostructures and no agglomeration was observed. The as-prepared metal NPs supported catalysts showed higher catalytic activities than MnO2 nanostructures for oxidative decomposition of formaldehyde (HCHO). The forms of noble metal NPs and Au/Pt molar ratio have significant effects on the catalytic performance, and Au0.5Pt0.5/MnO2 has the highest catalytic activity among all the as-prepared metal NPs supported MnO2 catalysts, and the temperature for complete decomposition of HCHO reached as low as 313 K. The high catalytic activities of Au1- x Pt x /MnO2 catalysts resulted from the synergistic effect between Au1- x Pt x NPs and MnO2 nanostructure, as well as the synergistic effect between Au and Pt. The current Au1- x Pt x /MnO2 catalysts are among the first trials to apply bimetallic NP-supported catalysts to the decomposition of HCHO, and proved that the Au1- x Pt x /MnO2 catalysts are promising for indoor decomposition of formaldehyde due to their easy synthesis, low cost, and excellent catalytic performance.

  8. Isolation of humic acid from peat soil and its application as an adsorbent for AuCl4- in solution

    NASA Astrophysics Data System (ADS)

    Lestari, Puji

    2017-03-01

    Humic acid (HA) has been isolated from South Kalimantan (Indonesia) peat soil using alkali extraction method. The isolated HA then was applied on the adsorption process of AuCl4- in solution. Parameters investigated in the adsorption process consisted of the effect of initial pH, adsorption rate constant (k) and the adsorption capacity of AuCl4- on peat soil HA. The adsorption rate constant was determined according to the kinetic model proposed by Santosa (2007). The adsorption of AuCl4- on peat soil HA was optimum at pH 2. The adsorption rate constant (k) was 1.11 × 10-3 min-1. Adsorption of AuCl4- on peat soil HA fitted the Langmuir isotherm with the adsorption capacity of 90.91 mg.g-1. The adsorption of AuCl4- on peat soil HA was accompanied by the reduction of AuCl4- to Au(0), clarified by the existence of several peaks belonging to Au(0) in the XRD pattern of HA after the adsorption process.

  9. Application of an asymmetric flow field flow fractionation multi-detector approach for metallic engineered nanoparticle characterization--prospects and limitations demonstrated on Au nanoparticles.

    PubMed

    Hagendorfer, Harald; Kaegi, Ralf; Traber, Jacqueline; Mertens, Stijn F L; Scherrers, Roger; Ludwig, Christian; Ulrich, Andrea

    2011-11-14

    In this work we discuss about the method development, applicability and limitations of an asymmetric flow field flow fractionation (A4F) system in combination with a multi-detector setup consisting of UV/vis, light scattering, and inductively coupled plasma mass spectrometry (ICPMS). The overall aim was to obtain a size dependent-, element specific-, and quantitative method appropriate for the characterization of metallic engineered nanoparticle (ENP) dispersions. Thus, systematic investigations of crucial method parameters were performed by employing well characterized Au nanoparticles (Au-NPs) as a defined model system. For good separation performance, the A4F flow-, membrane-, and carrier conditions were optimized. To obtain reliable size information, the use of laser light scattering based detectors was evaluated, where an online dynamic light scattering (DLS) detector showed good results for the investigated Au-NP up to a size of 80 nm in hydrodynamic diameter. To adapt large sensitivity differences of the various detectors, as well as to guarantee long term stability and minimum contamination of the mass spectrometer a split-flow concept for coupling ICPMS was evaluated. To test for reliable quantification, the ICPMS signal response of ionic Au standards was compared to that of Au-NP. Using proper stabilization with surfactants, no difference for concentrations of 1-50 μg Au L(-1) in the size range from 5 to 80 nm for citrate stabilized dispersions was observed. However, studies using different A4F channel membranes showed unspecific particle-membrane interaction resulting in retention time shifts and unspecific loss of nanoparticles, depending on the Au-NP system as well as membrane batch and type. Thus, reliable quantification and discrimination of ionic and particular species was performed using ICPMS in combination with ultracentrifugation instead of direct quantification with the A4F multi-detector setup. Figures of merit were obtained, by comparing the

  10. Au102(p-MBA)44 nanocluster, a superatom suitable for bio-applications

    NASA Astrophysics Data System (ADS)

    Häkkinen, Hannu

    2016-12-01

    Inorganic nanoparticles, including metals, semiconductors and metal oxides, comprise a common set of structures exhibiting an inorganic core `passivated' by an organic shell. Ligated inorganic nanoparticles currently provoke widespread fundamental interest in their structural, optical and magnetic properties, which differ fundamentally from bulk counterparts. These nanomaterials are already finding applications in biology, medicine, solar energy, and display panels. 1-6 Conjugating inorganic nanoparticles with organic (biological) material for applications in nanobiology and nanomedicine creates significant challenges for controlling the effects on the environment, particularly regarding toxicity. Chemical reactions of almost identical substances can lead to drastically different outcomes in a biological environment. As a simplistic example one can consider the case of ethanol vs. methanol. Ethanol (CH3CH2OH) can be consumed by humans while even a small dose of methanol (CH3OH) can be fatal, yet the difference between the molecular formulas of these substances is just the smallest meaningful hydrocarbon unit CH2. This illuminates the fact that minute differences in the size and structure of molecular compounds can have drastically different end effects in a biological environment due to the way the compounds start to react with the environment. In recent years, gold nanoparticles covered by ligands that make them water-soluble have become a popular target for research in nanobiology and nanomedicine. 1,2 In most cases up to now, colloidal nanoparticles (5 nm and larger) have been used for sensing and photothermal applications. However, this class of gold-based nanomaterials still has large uncertainties regarding the atomic composition of the nanoparticle surface and particularly the metal-ligand interface. A simple example illuminates the facts. The density of atoms in the fcc lattice of macrosocopic gold metal is about 59 atoms/nm3. This means that a spherical

  11. Seed-induced growth of flower-like Au-Ni-ZnO metal-semiconductor hybrid nanocrystals for photocatalytic applications.

    PubMed

    Chen, Yuanzhi; Zeng, Deqian; Cortie, Michael B; Dowd, Annette; Guo, Huizhang; Wang, Junbao; Peng, Dong-Liang

    2015-03-25

    The combination of metal and semiconductor components in nanoscale to form a hybrid nanocrystal provides an important approach for achieving advanced functional materials with special optical, magnetic and photocatalytic functionalities. Here, a facile solution method is reported for the synthesis of Au-Ni-ZnO metal-semiconductor hybrid nanocrystals with a flower-like morphology and multifunctional properties. This synthetic strategy uses noble and magnetic metal Au@Ni nanocrystal seeds formed in situ to induce the heteroepitaxial growth of semiconducting ZnO nanopyramids onto the surface of metal cores. Evidence of epitaxial growth of ZnO{0001} facets on Ni {111} facets is observed on the heterojunction, even though there is a large lattice mismatch between the semiconducting and magnetic components. Adjustment of the amount of Au and Ni precursors can control the size and composition of the metal core, and consequently modify the surface plasmon resonance (SPR) and magnetic properties. Room-temperature superparamagnetic properties can be achieved by tuning the size of Ni core. The as-prepared Au-Ni-ZnO nanocrystals are strongly photocatalytic and can be separated and re-cycled by virtue of their magnetic properties. The simultaneous combination of plasmonic, semiconducting and magnetic components within a single hybrid nanocrystal furnishes it multifunctionalities that may find wide potential applications.

  12. A rapid green strategy for the synthesis of Au "meatball"-like nanoparticles using green tea for SERS applications

    NASA Astrophysics Data System (ADS)

    Wu, Shichao; Zhou, Xi; Yang, Xiangrui; Hou, Zhenqing; Shi, Yanfeng; Zhong, Lubin; Jiang, Qian; Zhang, Qiqing

    2014-09-01

    We report a simple and rapid biological approach to synthesize water-soluble and highly roughened "meatball"-like Au nanoparticles using green tea extract under microwave irradiation. The synthesized Au meatball-like nanoparticles possess excellent monodispersity and uniform size (250 nm in diameter). Raman measurements show that these tea-generated meatball-like gold nanostructures with high active surface areas exhibit a high enhancement of surface-enhanced Raman scattering. In addition, the Au meatball-like nanoparticles demonstrate good biocompatibility and remarkable in vitro stability at the biological temperature. Meanwhile, the factors that influence the Au meatball-like nanoparticles morphology are investigated, and the mechanisms behind the nonspherical shape evolution are discussed.

  13. An enhanced photocatalytic response of nanometric TiO2 wrapping of Au nanoparticles for eco-friendly water applications.

    PubMed

    Scuderi, Viviana; Impellizzeri, Giuliana; Romano, Lucia; Scuderi, Mario; Brundo, Maria V; Bergum, Kristin; Zimbone, Massimo; Sanz, Ruy; Buccheri, Maria A; Simone, Francesca; Nicotra, Giuseppe; Svensson, Bengt G; Grimaldi, Maria G; Privitera, Vittorio

    2014-10-07

    We propose a ground-breaking approach by an upside-down vision of the Au/TiO2 nano-system in order to obtain an enhanced photocatalytic response. The system was synthesized by wrapping Au nanoparticles (∼8 nm mean diameter) with a thin layer of TiO2 (∼4 nm thick). The novel idea of embedding Au nanoparticles with titanium dioxide takes advantage of the presence of metal nanoparticles, in terms of electron trapping, without losing any of the TiO2 exposed surface, so as to favor the photocatalytic performance of titanium dioxide. A complete structural characterization was made by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The remarkable photocatalytic performance together with the stability of the nano-system was demonstrated by degradation of the methylene blue dye in water. The non-toxicity of the nano-system was established by testing the effect of the material on the reproductive cycle of Mytilus galloprovincialis in an aquatic environment. The originally synthesized material was also compared to conventional TiO2 with Au nanoparticles on top. The latter system showed a dispersion of Au nanoparticles in the liquid environment, due to their instability in the aqueous solution that clearly represents an environmental contamination issue. Thus, the results show that nanometric TiO2 wrapping of Au nanoparticles has great potential in eco-friendly water/wastewater purification.

  14. An enhanced photocatalytic response of nanometric TiO2 wrapping of Au nanoparticles for eco-friendly water applications

    NASA Astrophysics Data System (ADS)

    Scuderi, Viviana; Impellizzeri, Giuliana; Romano, Lucia; Scuderi, Mario; Brundo, Maria V.; Bergum, Kristin; Zimbone, Massimo; Sanz, Ruy; Buccheri, Maria A.; Simone, Francesca; Nicotra, Giuseppe; Svensson, Bengt G.; Grimaldi, Maria G.; Privitera, Vittorio

    2014-09-01

    We propose a ground-breaking approach by an upside-down vision of the Au/TiO2 nano-system in order to obtain an enhanced photocatalytic response. The system was synthesized by wrapping Au nanoparticles (~8 nm mean diameter) with a thin layer of TiO2 (~4 nm thick). The novel idea of embedding Au nanoparticles with titanium dioxide takes advantage of the presence of metal nanoparticles, in terms of electron trapping, without losing any of the TiO2 exposed surface, so as to favor the photocatalytic performance of titanium dioxide. A complete structural characterization was made by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The remarkable photocatalytic performance together with the stability of the nano-system was demonstrated by degradation of the methylene blue dye in water. The non-toxicity of the nano-system was established by testing the effect of the material on the reproductive cycle of Mytilus galloprovincialis in an aquatic environment. The originally synthesized material was also compared to conventional TiO2 with Au nanoparticles on top. The latter system showed a dispersion of Au nanoparticles in the liquid environment, due to their instability in the aqueous solution that clearly represents an environmental contamination issue. Thus, the results show that nanometric TiO2 wrapping of Au nanoparticles has great potential in eco-friendly water/wastewater purification.

  15. Pulse electrodeposition to prepare core-shell structured AuPt@Pd/C catalyst for formic acid fuel cell application

    NASA Astrophysics Data System (ADS)

    Lu, Xueyi; Luo, Fan; Song, Huiyu; Liao, Shijun; Li, Hualing

    2014-01-01

    A novel core-shell structured AuPt@Pd/C catalyst for the electrooxidation of formic acid is synthesized by a pulse electrodeposition process, and the AuPt core nanoparticles are obtained by a NaBH4 reduction method. The catalyst is characterized with X-ray powder diffraction and transmission electron microscopy, thermogravimetric analysis, cyclic voltammetry, CO stripping and X-ray photoelectron spectroscopy. The core-shell structure of the catalyst is revealed by the increase in particle size resulting from a Pd layer covering the AuPt core, and by a negative shift in the CO stripping peaks. The addition of a small amount of Pt improves the dispersion of Au and results in smaller core particles. The catalyst's activity is evaluated by cyclic voltammetry in formic acid solution. The catalyst shows excellent activity towards the anodic oxidation of formic acid, the mass activity reaches 4.4 A mg-1Pd and 0.83 A mg-1metal, which are 8.5 and 1.6 times that of commercial Pd/C. This enhanced electrocatalytic activity could be ascribed to the good dispersion of Au core particles resulting from the addition of Pt, as well as to the interaction between the Pd shell layer and the Au and Pt in the core nanoparticles.

  16. DNA-templated synthesis of PtAu bimetallic nanoparticle/graphene nanocomposites and their application in glucose biosensor

    PubMed Central

    2014-01-01

    In this paper, single-stranded DNA (ss-DNA) is demonstrated to functionalize graphene (GR) and to further guide the growth of PtAu bimetallic nanoparticles (PtAuNPs) on GR with high densities and dispersion. The obtained nanocomposites (PtAuNPs/ss-DNA/GR) were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDS), and electrochemical techniques. Then, an enzyme nanoassembly was prepared by self-assembling glucose oxidase (GOD) on PtAuNP/ss-DNA/GR nanocomposites (GOD/PtAuNPs/ss-DNA/GR). The nanocomposites provided a suitable microenvironment for GOD to retain its biological activity. The direct and reversible electron transfer process between the active site of GOD and the modified electrode was realized without any extra electron mediator. Thus, the prepared GOD/PtAuNP/ss-DNA/GR electrode was proposed as a biosensor for the quantification of glucose. The effects of pH, applied potential, and temperature on the performance of the biosensor were discussed in detail and were optimized. Under optimal conditions, the biosensor showed a linearity with glucose concentration in the range of 1.0 to 1,800 μM with a detection limit of 0.3 μM (S/N = 3). The results demonstrate that the developed approach provides a promising strategy to improve the sensitivity and enzyme activity of electrochemical biosensors. PMID:24572068

  17. Photoelectrochemical studies of DNA-tagged biomolecules on Au and Au/Ni/Au multilayer nanowires

    PubMed Central

    2011-01-01

    The use of nanowires (NWs) for labeling, sensing, and sorting is the basis of detecting biomolecules attached on NWs by optical and magnetic properties. In spite of many advantages, the use of biomolecules-attached NWs sensing by photoelectrochemical (PEC) study is almost non-existent. In this article, the PEC study of dye-attached single-stranded DNA on Au NWs and Au-Ni-Au multilayer NWs prepared by pulse electrodeposition are investigated. Owing to quantum-quenching effect, the multilayer Au NWs exhibit low optical absorbance when compared with Au NWs. The tagged Au NWs show good fluorescence (emission) at 570 nm, indicating significant improvement in the reflectivity. Optimum results obtained for tagged Au NWs attached on functionalized carbon electrodes and its PEC behavior is also presented. A twofold enhancement in photocurrent is observed with an average dark current of 10 μA for Au NWs coated on functionalized sensing electrode. The importance of these PEC and optical studies provides an inexpensive and facile processing platform for Au NWs that may be suitable for biolabeling applications. PMID:21961940

  18. Application de la methode des sous-groupes au calcul Monte-Carlo multigroupe

    NASA Astrophysics Data System (ADS)

    Martin, Nicolas

    This thesis is dedicated to the development of a Monte Carlo neutron transport solver based on the subgroup (or multiband) method. In this formalism, cross sections for resonant isotopes are represented in the form of probability tables on the whole energy spectrum. This study is intended in order to test and validate this approach in lattice physics and criticality-safety applications. The probability table method seems promising since it introduces an alternative computational way between the legacy continuous-energy representation and the multigroup method. In the first case, the amount of data invoked in continuous-energy Monte Carlo calculations can be very important and tend to slow down the overall computational time. In addition, this model preserves the quality of the physical laws present in the ENDF format. Due to its cheap computational cost, the multigroup Monte Carlo way is usually at the basis of production codes in criticality-safety studies. However, the use of a multigroup representation of the cross sections implies a preliminary calculation to take into account self-shielding effects for resonant isotopes. This is generally performed by deterministic lattice codes relying on the collision probability method. Using cross-section probability tables on the whole energy range permits to directly take into account self-shielding effects and can be employed in both lattice physics and criticality-safety calculations. Several aspects have been thoroughly studied: (1) The consistent computation of probability tables with a energy grid comprising only 295 or 361 groups. The CALENDF moment approach conducted to probability tables suitable for a Monte Carlo code. (2) The combination of the probability table sampling for the energy variable with the delta-tracking rejection technique for the space variable, and its impact on the overall efficiency of the proposed Monte Carlo algorithm. (3) The derivation of a model for taking into account anisotropic

  19. Intense fluorescence of Au20

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

  20. Eco-friendly synthesis of TiO2, Au and Pt doped TiO2 nanoparticles for dye sensitized solar cell applications and evaluation of toxicity

    NASA Astrophysics Data System (ADS)

    Gopinath, K.; Kumaraguru, S.; Bhakyaraj, K.; Thirumal, S.; Arumugam, A.

    2016-04-01

    Driven by the demand of pure TiO2, Au and Pt doped TiO2 NPs were successfully synthesized using Terminalia arjuna bark extract. The eco-friendly synthesized NPs were characterized by UV-Vis-DRS, ATR-FT-IR, PL, XRD, Raman, SEM with EDX and TEM analysis. The synthesized NPs were investigation for dye sensitized solar cell applications. UV-Vis-Diffused Reflectance Spectra clearly showed that the expected TiO2 inter band absorption below 306 nm, incorporation of gold shows surface plasma resonant (SPR) near 555 nm and platinum incorporated TiO2 NPs shows absorbance at 460 nm. The energy conversion efficiency for Au doped TiO2 NPs when compared to pure and Pt doped TiO2 NPs. In addition to that, Au noble metal present TiO2 matrix and an improve open-circuit voltage (Voc) of DSSC. Synthesized NPs was evaluated into antibacterial and antifungal activities by disk diffusion method. It is observed that NPs have not shown any activities in all tested bacterial and fungal strains. In this eco-friendly synthesis method to provide non toxic and environmental friendly nanomaterials can be used for solar energy device application.

  1. Controllable growth and transfer of monolayer MoS2 on Au foils and its potential application in hydrogen evolution reaction.

    PubMed

    Shi, Jianping; Ma, Donglin; Han, Gao-Feng; Zhang, Yu; Ji, Qingqing; Gao, Teng; Sun, Jingyu; Song, Xiuju; Li, Cong; Zhang, Yanshuo; Lang, Xing-You; Zhang, Yanfeng; Liu, Zhongfan

    2014-10-28

    Controllable synthesis of monolayer MoS2 is essential for fulfilling the application potentials of MoS2 in optoelectronics and valleytronics, etc. Herein, we report the scalable growth of high quality, domain size tunable (edge length from ∼ 200 nm to 50 μm), strictly monolayer MoS2 flakes or even complete films on commercially available Au foils, via low pressure chemical vapor deposition method. The as-grown MoS2 samples can be transferred onto arbitrary substrates like SiO2/Si and quartz with a perfect preservation of the crystal quality, thus probably facilitating its versatile applications. Of particular interest, the nanosized triangular MoS2 flakes on Au foils are proven to be excellent electrocatalysts for hydrogen evolution reaction, featured by a rather low Tafel slope (61 mV/decade) and a relative high exchange current density (38.1 μA/cm(2)). The excellent electron coupling between MoS2 and Au foils is considered to account for the extraordinary hydrogen evolution reaction activity. Our work reports the synthesis of monolayer MoS2 when introducing metal foils as substrates, and presents sound proof that monolayer MoS2 assembled on a well selected electrode can manifest a hydrogen evolution reaction property comparable with that of nanoparticles or few-layer MoS2 electrocatalysts.

  2. Low temperature activation of Au/Ti getter film for application to wafer-level vacuum packaging

    NASA Astrophysics Data System (ADS)

    Wu, Ming; Moulin, Johan; Lani, Sébastien; Hallais, Géraldine; Renard, Charles; Bosseboeuf, Alain

    2015-03-01

    Non-evaporable getter (NEG) thin films based on alloys of transition metals have been studied by various authors for vacuum control in wafer-level packages of micro electro mechanical systems (MEMS). These materials have typically a relatively high activation temperature (300-450 °C) which is incompatible with some temperature sensitive MEMS devices. In this work we investigate the potential of Au/Ti system with a thin or ultrathin non oxidizable Au layer as a low activation temperature getter material. In this bilayer system, gettering activation is produced by thermal outdiffusion of titanium atoms through the gold film. The outdiffusion kinetics of titanium was modelled and characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Rutherford backscattering spectrometry (RBS) at various temperatures. Results confirm that Au/Ti bilayer is a promising getter material for wafer-level packaging with an activation temperature below 300 °C for 1 h annealing time.

  3. Magnetic gold nanocatalyst (nanocat-Fe–Au): catalytic applications for the oxidative esterification and hydrogen transfer reactions

    EPA Science Inventory

    An efficient and sustainable protocol is described for the oxidative esterification of aldehydes and the reduction of aromatic nitro compounds that uses magnetically separable and reusable maghemite-supported gold nanocatalyst (nanocat-Fe-Au) under mild conditions. The complex ch...

  4. Adsorption between TC-stabilized AuNPs and the phosphate group: application of the PTP1B activity assay.

    PubMed

    Lv, Jun; Wang, Xiaonan; Zhang, Yuanyuan; Li, Defeng; Zhang, Juan; Sun, Lizhou

    2015-12-07

    Based on the adsorption between tetracycline (TC) and phosphate groups, a general colorimetric method is explored in this work by using TC-stabilized gold nanoparticles (TC/AuNPs) and 4-aminophenyl phosphate-functionalized Fe3O4 magnetic nanoparticles (APP/MNPs). Taking protein tyrosine phosphatase 1B (PTP1B) as an example, 4-aminophenyl phosphate (APP) can be hydrolyzed into 4-aminophenol (AP) by PTP1B, resulting in the disappearance of the phosphate group on the outer layer of MNPs and the loss of corresponding adsorptive ability. Upon addition of TC/AuNP solution, TC/AuNPs will remain in the supernatant solution after magnetic separation and a high absorbance value can be observed. So PTP1B activity is related to the concentrations of TC/AuNPs in the supernatant solution. In this work, the enzyme activity can be determined at levels as low as 0.0885 U mL(-1) and over a linear detection range as wide as 0.1 U mL(-1) to 0.9 U mL(-1). Moreover, using the proposed method, the inhibition effect of betulinic acid (BA) and sodium orthovanadate (Na3VO4) on PTP1B activity can be tested with IC50 values of 30 μM and 4 μM, respectively. Therefore, a universal platform for the accurate colorimetric analysis of kinase and phosphatase activities can be established through the adsorption between TC and phosphate groups.

  5. Synthesis of Au-decorated tripod-shaped Te hybrids for applications in the ultrasensitive detection of arsenic.

    PubMed

    Wang, Demeng; Zhao, Yuewu; Jin, Huile; Zhuang, Jinxia; Zhang, Weiming; Wang, Shun; Wang, Jichang

    2013-06-26

    Novel Au-decorated Te hybrids with a tripod-shaped planar microstructure were prepared through a two-step hydrothermal process: the synthesis of Te single crystals and the subsequent self-sacrificial reaction of Te template with HAuCl4. Based on the influences of reaction temperature and solvent compositions on the as-obtained microstructures, a plausible mechanism was proposed to account for the formation of the tripod-shaped Te and Au/Te crystals. The as-prepared Au/Te hybrids have the sensitivity of 6.35 μA/ppb in the electrochemical detection of As(III), which represents the highest sensitivity reported in literature. The Au/Te sensor also has a low detection limit of 0.0026 ppb and could work in complex mixtures containing As(III), Cu(II) and other heavy metal ions, exhibiting excellent selectivity on As(III) and Cu(II) ions. The enhanced electrocatalytic property may be attributed to the synergetic interactions between the noble metal and semiconductor and the presence of a large number of active sites on the hybrids surface.

  6. Magnetic gold nanocatalyst (nanocat-Fe–Au): catalytic applications for the oxidative esterification and hydrogen transfer reactions

    EPA Science Inventory

    An efficient and sustainable protocol is described for the oxidative esterification of aldehydes and the reduction of aromatic nitro compounds that uses magnetically separable and reusable maghemite-supported gold nanocatalyst (nanocat-Fe-Au) under mild conditions. The complex ch...

  7. Fabrication of Lab-on-Paper Using Porous Au-Paper Electrode: Application to Tumor Marker Electrochemical Immunoassays.

    PubMed

    Ge, Shenguang; Zhang, Yan; Yan, Mei; Huang, Jiadong; Yu, Jinghua

    2017-01-01

    A simple, low-cost, and sensitive electrochemical lab-on-paper assay is developed based on a novel gold nanoparticle modified porous paper working electrode for use in point-of-care testing (POCT). Electrochemical methods are introduced for lab-on-paper based on screen-printed paper electrodes. To further improve specificity, performance, and sensitivity for point-of-care testing, a novel porous Au-paper working electrode (Au-PWE) is designed for lab-on-paper using growth of an interconnected Au nanoparticle (NP) layer on the surface of cellulose fibers in order to enhance the conductivity of the paper sample zone and immobilize the primary antibodies (Ab1). With a sandwich-type immunoassay format, Pd-Au bimetallic nanoparticles possessing peroxidase-like activity are used as a matrix to immobilize secondary antibodies (Ab2) for rapid detection of targets. This lab-on-paper based immunodevice is applied to the diagnosis of a cancer biomarker in clinical serum samples.

  8. MO-FG-303-08: PET-Detectable Bimetallic (Zn@Au) Nanoparticles for Radiotherapy and Molecular Imaging Applications

    SciTech Connect

    Cho, J; Cho, S; Wang, M; Zubarev, E; Gonzalez-Lepera, C

    2015-06-15

    Purpose: A technical challenge in clinical translation of GNP-mediated radiotherapy is lack of in-vivo imaging tools for monitoring biodistribution of GNPs. While several modalities (x-ray fluorescence, photoacoustic, etc.) are investigated, we propose a potentially more effective technique based on PET imaging. We developed Zn@Au NPs whose Zn core acts as positron emitters when activated by protons, while the Au shell plays the original role for GNP-mediated radiosensitization. Methods: Spherical Zn NPs (∼7nm diameter) were synthesized and then coated with ∼7nm thick Au layer to make Zn@Au NPs (∼20nm diameter). A water slurry containing 29mg of Zn@Au NPs was deposited (<10µm thickness) on a thin cellulose target and subsequently baked to remove the water. The cellulose matrix was placed in an aluminum target holder and irradiated with 14.5MeV protons from a GE PETtrace cyclotron with 4µA for 5min. After irradiation the cellulose matrix with the NPs was placed in a dose calibrator to assay radioactivity. Gamma spectroscopy using a HPGe detector was conducted on a very small fraction (<1mg) of the irradiated NPs. Results: We measured 158µCi of activity 32min after end of bombardment (EOB) using 66Ga setting on the dose calibrator (contribution from the cellulose matrix is negligible) which decreased to 2µCi over a 24hrs period. A gamma spectrum started one hour after EOB on the small fraction and acquired for 700sec showed a strong peak at 511keV (∼40,000 counts) with several other peaks (highest peak <1200 counts) of smaller magnitude. Conclusion: Strong 511keV gamma emission from proton-activated Zn cores can potentially be utilized to image the biodistribution of Zn@Au NPs using a PET scanner. The developed Zn@Au NPs are expected to retain radiosensitizing capability similar to solid GNPs, while observable through PET imaging for human-sized objects. Moreover, bioconjugated PET-detectable GNPs would allow a new option to perform molecular imaging.

  9. Preparation of Au-polydopamine functionalized carbon encapsulated Fe₃O₄ magnetic nanocomposites and their application for ultrasensitive detection of carcino-embryonic antigen.

    PubMed

    Ji, Lei; Yan, Tao; Li, Yan; Gao, Jian; Wang, Qi; Hu, Lihua; Wu, Dan; Wei, Qin; Du, Bin

    2016-02-12

    A novel carbon encapsulated Fe3O4 nanoparticles embedded in two-dimensional (2D) porous graphitic carbon nanocomposites (Fe3O4@C@PGC nanocomposites) were synthesized by situ synthesis strategy, which provided a sensor platform owing to a large aspect ratio and porous structure. Polydopamine (PDA) were modified on the surface of Fe3O4@C@PGC nanocomposites through self-polymerization of dopamine, acting as both the reductant and template for one-step synthesis of gold nanoparticles. The prepared Au/PDA/Fe3O4@C@PGC nanocomposites show ferromagnetic features, extremely excellent electron transfer, large specific surface area and excellent dispersing property. These are conducive to the electrochemical signal output and the immobilization of antibody. In this work, a highly label-free sensitive magnetic immunosensor was developed based on Au/PDA/Fe3O4@C@PGC nanocomposites for the detection of carcino-embryonic antigen (CEA). The magnetic glassy carbon electrode was used to fix the Au/PDA/Fe3O4@C@PGC nanocomposites with the help of magnetic force. Under the optimal conditions, the immunosensor exhibited a wide linear range (0.001 ng/mL-20.0 ng/mL), a low detection limit (0.33 pg/mL), good reproducibility, selectivity and acceptable stability. The proposed sensing strategy may provide a potential application in the detection of other cancer biomarkers.

  10. Development of ultrafine multichannel microfluidic mixer for synthesis of bimetallic nanoclusters: catalytic application of highly monodisperse AuPd nanoclusters stabilized by poly(N-vinylpyrrolidone).

    PubMed

    Hayashi, Naoto; Sakai, Yuka; Tsunoyama, Hironori; Nakajima, Atsushi

    2014-09-02

    On account of their novel properties, bimetallic nanoparticles and nanoclusters (NCs) are strong potential candidates for optical, magnetic, and catalytic functional materials. These properties depend on the chemical composition and size (number of constituent atoms) of the NCs. Control of size, structure, and composition is particularly important for fabricating highly functional materials based on bimetallic NCs. Size- and structure-controlled synthesis of two-element alloys can reveal their intrinsic electronic synergistic effects. However, because synergistic enhancement of activity is strongly affected by composition as well as by size and structure, controlled synthesis is a challenging task, particularly in catalytic applications. To investigate catalytic synergistic effects, we have synthesized highly monodisperse, sub-2 nm, solid-solution AuPd NCs stabilized with poly(N-vinylpyrrolidone) (AuPd:PVP) using a newly developed ultrafine microfluidic mixing device with 15 μm wide multiple lamination channels. The synergistic enhancement for catalytic aerobic oxidation of benzyl alcohol exhibited a volcano-shaped trend, with a maximum at 20-65 at. % Pd. From X-ray photoelectron spectroscopic measurements, we confirmed that the enhanced activity originates from the enhanced electron density at the Au sites, donated by Pd sites.

  11. Preparation of Au-polydopamine functionalized carbon encapsulated Fe3O4 magnetic nanocomposites and their application for ultrasensitive detection of carcino-embryonic antigen

    PubMed Central

    Ji, Lei; Yan, Tao; Li, Yan; Gao, Jian; Wang, Qi; Hu, Lihua; Wu, Dan; Wei, Qin; Du, Bin

    2016-01-01

    A novel carbon encapsulated Fe3O4 nanoparticles embedded in two-dimensional (2D) porous graphitic carbon nanocomposites (Fe3O4@C@PGC nanocomposites) were synthesized by situ synthesis strategy, which provided a sensor platform owing to a large aspect ratio and porous structure. Polydopamine (PDA) were modified on the surface of Fe3O4@C@PGC nanocomposites through self-polymerization of dopamine, acting as both the reductant and template for one-step synthesis of gold nanoparticles. The prepared Au/PDA/Fe3O4@C@PGC nanocomposites show ferromagnetic features, extremely excellent electron transfer, large specific surface area and excellent dispersing property. These are conducive to the electrochemical signal output and the immobilization of antibody. In this work, a highly label-free sensitive magnetic immunosensor was developed based on Au/PDA/Fe3O4@C@PGC nanocomposites for the detection of carcino-embryonic antigen (CEA). The magnetic glassy carbon electrode was used to fix the Au/PDA/Fe3O4@C@PGC nanocomposites with the help of magnetic force. Under the optimal conditions, the immunosensor exhibited a wide linear range (0.001 ng/mL–20.0 ng/mL), a low detection limit (0.33 pg/mL), good reproducibility, selectivity and acceptable stability. The proposed sensing strategy may provide a potential application in the detection of other cancer biomarkers. PMID:26868035

  12. Tailored synthesis of photoactive TiO ₂ nanofibers and Au/TiO ₂ nanofiber composites: structure and reactivity optimization for water treatment applications.

    PubMed

    Nalbandian, Michael J; Greenstein, Katherine E; Shuai, Danmeng; Zhang, Miluo; Choa, Yong-Ho; Parkin, Gene F; Myung, Nosang V; Cwiertny, David M

    2015-02-03

    Titanium dioxide (TiO2) nanofibers with tailored structure and composition were synthesized by electrospinning to optimize photocatalytic treatment efficiency. Nanofibers of controlled diameter (30-210 nm), crystal structure (anatase, rutile, mixed phases), and grain size (20-50 nm) were developed along with composite nanofibers with either surface-deposited or bulk-integrated Au nanoparticle cocatalysts. Their reactivity was then examined in batch suspensions toward model (phenol) and emerging (pharmaceuticals, personal care products) pollutants across various water qualities. Optimized TiO2 nanofibers meet or exceed the performance of traditional nanoparticulate photocatalysts (e.g., Aeroxide P25) with the greatest reactivity enhancements arising from (i) decreasing diameter (i.e., increasing surface area), (ii) mixed phase composition [74/26 (±0.5) % anatase/rutile], and (iii) small amounts (1.5 wt %) of surface-deposited, more so than bulk-integrated, Au nanoparticles. Surface Au deposition consistently enhanced photoactivity by 5- to 10-fold across our micropollutant suite independent of their solution concentration, behavior that we attribute to higher photocatalytic efficiency from improved charge separation. However, the practical value of Au/TiO2 nanofibers was limited by their greater degree of inhibition by solution-phase radical scavengers and higher rate of reactivity loss from surface fouling in nonidealized matrixes (e.g., partially treated surface water). Ultimately, unmodified TiO2 nanofibers appear most promising for use as reactive filtration materials because their performance was less influenced by water quality, although future efforts must increase the strength of TiO2 nanofiber mats to realize such applications.

  13. A simple approach to the synthesis of eccentric Au@SiO2 Janus nanostructures and their catalytic applications

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Yang, Di; Hu, Huicheng; Chen, Lei; Xu, Yong; Qu, Lili; Yang, Peipei; Zhang, Qiao

    2016-06-01

    In this paper, we present a simple method to synthesize eccentric Au@SiO2 Janus nanoparticles. By simply tuning the concentration of poly(vinyl pyrrolidone) (PVP), the surface of gold nanoparticle can be partially or fully wrapped with the amphiphilic ligand. As a result, Janus nanoparticle or concentric core-shell nanostructures can be obtained, respectively. A systematic study has been carried out to confirm the function of PVP molecules. The as-prepared Janus nanoparticle can act as a catalyst to catalyze the reduction of 4-nitrophenol, while the core-shell nanostructure is not active due to the coverage of dense silica shell. This work provides a robust and scalable method to produce Au@SiO2 Janus nanoparticles.

  14. Computational criterion for application of the characteristic effective medium approximation to ultrathin Co Au multi-bilayer structures

    NASA Astrophysics Data System (ADS)

    Haija, A. J.; Larry Freeman, W.; DeNinno, Matthew

    2008-11-01

    The basic optical properties, reflectivity and transmissivity, of three sets of Co-Au bilayer structures are calculated for normal incidence in the wavelength range 300-700 nm. Each set consists of a total number of bilayer identity periods m=1, 2, 3, 4, 5, 6. The thickness of the bilayer in each set is 5, 7, and 9 nm. The composition of the bilayer is kept fixed: 40% Co and 60% Au. The calculations are done for ideal layered Co-Au stacks using the characteristic matrix technique. Calculations for each stack based on the thicknesses of the two composite layers and their optical constants are contrasted against calculations using the characteristic effective medium approximation, CEMA. A third calculation of the optical properties for each stack is performed, again using the CEMA, but when the whole stack, called the effective stack, ES, is treated as one uniform medium of effective optical constants. The comparison of the three sets of calculations for all sets is intended to shed more light onto the validity of the CEMA approximation that has been established for thin bilayer structures whose constituents have thicknesses much less than the wavelength of the incident radiation. The study establishes a limit based on the product of the number of layers m and the identity period of the stack h, beyond which the CEMA approximation cannot be applied. This limit is consistent with a previous study carried out on Ag-SiO ultrathin stacks.

  15. Performance-Enhancing Methods for Au Film over Nanosphere Surface-Enhanced Raman Scattering Substrate and Melamine Detection Application

    PubMed Central

    Wang, Jun Feng; Wu, Xue Zhong; Xiao, Rui; Dong, Pei Tao; Wang, Chao Guang

    2014-01-01

    A new high-performance surface-enhanced Raman scattering (SERS) substrate with extremely high SERS activity was produced. This SERS substrate combines the advantages of Au film over nanosphere (AuFON) substrate and Ag nanoparticles (AgNPs). A three order enhancement of SERS was observed when Rhodamine 6G (R6G) was used as a probe molecule to compare the SERS effects of the new substrate and commonly used AuFON substrate. These new SERS substrates can detect R6G down to 1 nM. The new substrate was also utilized to detect melamine, and the limit of detection (LOD) is 1 ppb. A linear relationship was also observed between the SERS intensity at Raman peak 682 cm−1 and the logarithm of melamine concentrations ranging from 10 ppm to 1 ppb. This ultrasensitive SERS substrate is a promising tool for detecting trace chemical molecules because of its simple and effective fabrication procedure, high sensitivity and high reproducibility of the SERS effect. PMID:24886913

  16. Fixed-frequency and Frequency-agile (au, HTS) Microstrip Bandstop Filters for L-band Applications

    NASA Technical Reports Server (NTRS)

    Saenz, Eileen M.; Subramanyam, Guru; VanKeuls, Fred W.; Chen, Chonglin; Miranda, Felix A.

    2001-01-01

    In this work, we report on the performance of a highly selective, compact 1.83 x 2.08 cm(exp 2) (approx. 0.72 x 0.82 in(exp 2) microstrip line bandstop filter of YBa2CU3O(7-delta) (YBCO) on LaAlO3 (LAO) substrate. The filter is designed for a center frequency of 1.623 GHz for a bandwidth at 3 dB from reference baseline of less than 5.15 MHz, and a bandstop rejection of 30 dB or better. The design and optimization of the filter was performed using Zeland's IE3D circuit simulator. The optimized design was used to fabricate gold (Au) and High-Temperature Superconductor (HTS) versions of the filter. We have also studied an electronically tunable version of the same filter. Tunability of the bandstop characteristics is achieved by the integration of a thin film conductor (Au or HTS) and the nonlinear dielectric ferroelectric SrTiO3 in a conductor/ferroelectric/dielectric modified microstrip configuration. The performance of these filters and comparison with the simulated data will be presented.

  17. Design and application of Au decorated ZnO/TiO2 as a stable photocatalyst for wide spectral coverage.

    PubMed

    Mukhopadhyay, Soumita; Maiti, Debabrata; Chatterjee, Sabyasachi; Devi, Parukuttyamma Sujatha; Suresh Kumar, Gopinatha

    2016-11-23

    A ternary nanostructured photocatalyst consisting of ZnO/TiO2/Au was designed to achieve an enhanced solar absorption due to the coupling of surface enhanced plasmonic absorption of metal and semiconductor excitons. TiO2 coated ZnO rods with an aspect ratio of 8-12 were decorated with citrate capped gold nanoparticles for photocatalytic degradation of organic pollutants in simulated waste water under solar irradiation. Simulated waste water was prepared so as to get a mixture exhibiting a wide range of spectral distribution in the UV-visible region by deliberately mixing congo red, methylene blue and malachite green. Photo-oxidation of few phenolic compounds such as phenol, 4-chlorophenol and polycyclic aromatic hydrocarbons viz. anthracene and phenanthrene were also investigated in order to rule out the visible light sensitization of the dye molecules and confirm the photocatalytic efficacy of the ternary composite for a wide range of water pollutants under simulated solar irradiation. The composite exhibited enhanced photocatalytic activity and photoelectrochemical stability upon UV and visible light exposure. This enhanced efficiency was also corroborated with the photocarrier lifetime and chronoamperometric studies. Under simulated solar irradiation, UV light induced well separated charge carriers coupled with the visible light induced local surface plasmon resonance of AuNPs to exert significantly enhanced photocatalytic activity in a broad spectral region. This type of material may evolve as a novel photocatalyst for the efficient removal of organic contaminants in waste water and photoelectrochemical water splitting under the solar spectrum.

  18. Study of an Au colloid self-assembled electrode and its application to the determination of carbon monoxide.

    PubMed

    Shi, G; Luo, M; Xue, J; Xu, F; Jin, L; Jin, J

    2001-08-01

    A novel electrochemical sensor has been developed for the detection of carbon monoxide. The chemically modified electrode, prepared by reaction of cysteine and then an Au colloid of size approximately 15 nm with a platinum microelectrode, has excellent catalytic activity toward carbon monoxide, with an oxidation potential of +600 mV relative to the Ag/AgCl electrode. The CO gas sensor is based on an Au colloid self-assembled modified electrode as working electrode, an Ag/AgCl electrode as reference electrode, a Pt electrode as counter electrode, and a porous film which is in direct contact with the gas-containing atmosphere. The effects on the determination of CO of different internal electrolyte solutions of perchloric acid, hydrochloric acid, sulfuric acid, nitric acid, and phosphate buffer of different concentrations were also studied. The sensor is characterized by a short response time and highly reproducible detection of CO. This sensor can be used in the field of environmental monitoring and control.

  19. Identification and characterization of a new member of the SINE Au retroposon family (GmAu1) in the soybean, Glycine max (L.) Merr., genome and its potential application.

    PubMed

    Shu, Yongjun; Li, Yong; Bai, Xi; Cai, Hua; Ji, Wei; Ji, Zuojun; Guo, Changhong; Zhu, Yanming

    2011-12-01

    A plant short interspersed element (SINE) was identified in Glycine max after re-sequencing of the soybean sequence characterized amplified region (SCAR) markers. Detailed analysis revealed that this newly recognized SINE element consisted of a tRNA-related region, a tRNA non-related region, direct flanking repeat sequences, and a short stretch of Ts at the 3'-terminal region. These features are similar to previously characterized SINEs. To investigate the evolution of the SINE retroposon, BLASTN was used to search against genome sequences of other plants. Since it is homologous with the retroposon Au in Aegilops umbellulata (wheat) and its homology in soybean, the SINE is named as GmAu1. Genome analysis of the Glycine max var. Willimas 82 uncovered more than 847 copies of GmAu1 per haploid genome of soybean. Examination of the regions flanking the inserted GmAu1 sequences indicated a preference for introns over exons or other noncoding regions. Considering the flanking insertion sequences, 146 primers were designed in order to detect insertion mutations by a PCR-based method. Seventy-seven primers displayed polymorphism and were used to develop corresponding GmAu1-based SCAR markers. The retroposon GmAu1 and its related SCAR markers identified in this study will prove valuable to future investigations into the genetic mapping, phylogeny, and evolution of the Glycine genus.

  20. Precursor polymers for the carbon coating of Au@ZnO multipods for application as active material in lithium-ion batteries.

    PubMed

    Oschmann, Bernd; Tahir, Muhammad Nawaz; Mueller, Franziska; Bresser, Dominic; Lieberwirth, Ingo; Tremel, Wolfgang; Passerini, Stefano; Zentel, Rudolf

    2015-06-01

    The synthesis of statistical and block copolymers based on polyacrylonitrile, as a source for carbonaceous materials, and thiol-containing repeating units as inorganic nanoparticle anchoring groups is reported. These polymers are used to coat Au@ZnO multipod heteroparticles with polymer brushes. IR spectroscopy and transmission electron microscopy prove the successful binding of the polymer onto the inorganic nanostructures. Thermogravimetric analysis is applied to compare the binding ability of the block and statistical copolymers. Subsequently, the polymer coating is transformed into a carbonaceous (partially graphitic) coating by pyrolysis. The obtained carbon coating is characterized by Raman spectroscopy and energy-dispersive X-ray (EDX) spectroscopy. The benefit of the conformal carbon coating of the Au@ZnO multipods regarding its application as lithium-ion anode material is revealed by performing galvanostatic cycling, showing a highly enhanced and stabilized electrochemical performance of the carbon-coated particles (still 831 mAh g(-1) after 150 cycles) with respect to the uncoated ones (only 353 mAh g(-1) after 10 cycles).

  1. Synthesis of Au microwires by selective oxidation of Au-W thin-film composition spreads.

    PubMed

    Hamann, Sven; Brunken, Hayo; Salomon, Steffen; Meyer, Robert; Savan, Alan; Ludwig, Alfred

    2013-02-01

    We report on the stress-induced growth of Au microwires out of a surrounding Au-W matrix by selective oxidation, in view of a possible application as 'micro-Velcro'. The Au wires are extruded due to the high compressive stress in the tungsten oxide formed by oxidation of elemental W. The samples were fabricated as a thin-film materials library using combinatorial sputter deposition followed by thermal oxidation. Sizes and shapes of the Au microwires were investigated as a function of the W to Au ratio. The coherence length and stress state of the Au microwires were related to their shape and plastic deformation. Depending on the composition of the Au-W precursor, the oxidized samples showed regions with differently shaped Au microwires. The Au48W52 composition yielded wires with the maximum length to diameter ratio due to the high compressive stress in the tungsten oxide matrix. The values of wire length (35 μm) and diameter (2 μm) achieved at the Au48W52 composition are suitable for micro-Velcro applications.

  2. Self-assembly of thiolated cyanine aggregates on Au(111) and Au nanoparticle surfaces

    NASA Astrophysics Data System (ADS)

    Menéndez, Guillermo O.; Cortés, Emiliano; Grumelli, Doris; Méndez de Leo, Lucila P.; Williams, Federico J.; Tognalli, Nicolás G.; Fainstein, Alejandro; Vela, María Elena; Jares-Erijman, Elizabeth A.; Salvarezza, Roberto C.

    2012-01-01

    Heptamethinecyanine J-aggregates display sharp, intense fluorescence emission making them attractive candidates for developing a variety of chem-bio-sensing applications. They have been immobilized on planar thiol-covered Au surfaces and thiol-capped Au nanoparticles by weak molecular interactions. In this work the self-assembly of novel thiolated cyanine (CNN) on Au(111) and citrate-capped AuNPs from solutions containing monomers and J-aggregates has been studied by using STM, XPS, PM-IRRAS, electrochemical techniques and Raman spectroscopy. Data show that CNN species adsorb on the Au surfaces by forming thiolate-Au bonds. We found that the J-aggregates are preferentially adsorbed on the Au(111) surface directly from the solution while adsorbed CNN monomers cannot organize into aggregates on the substrate surface. These results indicate that the CNN-Au interaction is not able to disorganize the large J-aggregates stabilized by π-π stacking to optimize the S-Au binding site but it is strong enough to hinder the π-π stacking when CNNs are chemisorbed as monomers. The optical properties of the J-aggregates remain active after adsorption. The possibility of covalently bonding CNN J-aggregates to Au planar surfaces and Au nanoparticles controlling the J-aggregate/Au distance opens a new path regarding their improved stability and the wide range of biological applications of both CNN and AuNP biocompatible systems.Heptamethinecyanine J-aggregates display sharp, intense fluorescence emission making them attractive candidates for developing a variety of chem-bio-sensing applications. They have been immobilized on planar thiol-covered Au surfaces and thiol-capped Au nanoparticles by weak molecular interactions. In this work the self-assembly of novel thiolated cyanine (CNN) on Au(111) and citrate-capped AuNPs from solutions containing monomers and J-aggregates has been studied by using STM, XPS, PM-IRRAS, electrochemical techniques and Raman spectroscopy. Data show

  3. Catalysis of aptamer-modified AuPd nanoalloy probe and its application to resonance scattering detection of trace UO22+

    NASA Astrophysics Data System (ADS)

    Liang, Aihui; Zhang, Yi; Fan, Yanyan; Chen, Chunqiang; Wen, Guiqing; Liu, Qingye; Kang, Caiyan; Jiang, Zhiliang

    2011-08-01

    AuPd nanoalloy and nanopalladium with a diameter of 5 nm were prepared, using sodium citrate as the stabilizing agent and NaBH4 as the reductant. The nanocatalyst containing palladium on the surface exhibited a strong catalytic effect on the slow NiP particle reaction between NiCl2 and NaH2PO2, and the NiP particle system showed a resonance scattering (RS) peak at 508 nm. The RS results showed that the Pd atom on AuPd nanoalloy surface is the catalytic center. Combining the aptamer cracking reaction of double-stranded DNA (dsDNA)-UO22+, AuPd nanoalloy aggregation, and AuPd nanoalloy catalysis, both AuPd nanoalloy RS probe and AuPd nanoalloy catalytic RS assays were developed for the determination of 40-250 pmol L-1 UO22+ and 5.0-50 pmol L-1 UO22+, respectively.

  4. 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.

  5. Fabrication and spectroscopic studies of folic acid-conjugated Fe3O4@Au core-shell for targeted drug delivery application

    NASA Astrophysics Data System (ADS)

    Karamipour, Sh.; Sadjadi, M. S.; Farhadyar, N.

    2015-09-01

    Gold coated magnetite core shell is a kind of nanoparticle that include magnetic iron oxide core with a thin layer nanogold. Fe3O4-gold core-shell nanostructure can be used in biomedical applications such as magnetic bioseparation, bioimaging, targeting drug delivery and cancer treatment. In this study, the synthesis and characterization of gold coated magnetite nanoparticles were discussed. Magnetite nanoparticles with an average size of 6 nm in diameter were synthesized by the chemical co-precipitation method and gold-coated Fe3O4 core-shell nanostructures were produced with an average size of 11.5 nm in diameter by reduction of Au3+ with citrate ion in the presence of Fe3O4. Folate-conjugated gold coated magnetite nanoparticles were synthesized to targeting folate receptor that is overexpressed on the surface of cancerous cells. For this purpose, we used L-cysteine, as a bi-functional linker for attachment to gold surface and it was linked to the gold nanoparticles surface through its thiol group. Then, we conjugated amino-terminated nanoparticles to folic acid with an amide-linkage formation. These gold magnetic nanoparticles were characterized by various techniques such as X-ray powder diffraction (XRD) analysis, Fourier transform infrared spectrometer (FT-IR), UV-visible spectroscopy, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), dispersive analysis of X-ray (EDAX) and vibrating sample magnetometer (VSM) analysis. The magnetic and optical properties of Fe3O4 nanostructure were changed by gold coating and attachment of L-cysteine and folic acid to Fe3O4@Au nanoparticles.

  6. 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.

  7. Transport de particules massives dans un fluide turbulent: Application a l'erosion due au sable sur les parois d'une turbine hydraulique

    NASA Astrophysics Data System (ADS)

    Bergeron, Stephen

    Le transport de particules massives par un champ turbulent est un vaste domaine de la mécanique des fluides. Il possède de nombreuses applications comme par exemple le transport de sable dans une turbine hydraulique. En raison de la dureté des grains de quartz et des grandes vitesses de collision avec les parois métalliques, un phénomène d'érosion intensif se produit. Les dommages résultants peuvent diminuer le rendement de la turbine au cours des quelques mois suivant la mise en opération. L'objectif de cette thèse est de mettre au point un outil permettant de prédire ces zones d'érosion. Ce projet de recherche en contexte industriel a été réalisé en collaboration avec la compagnie General Electric Hydro du Canada. Dans un régime hautement turbulent, il est possible d'obtenir une expression suffisamment générale en utilisant une formulation partiellement empirique: l'équation de Basset- Boussinesq-Oseen modifiée. Ce choix de modèle tient compte du niveau de précision recherché et de la méthode numérique employée afin de résoudre la phase fluide. Il permet aussi d'éliminer plusieurs ambiguïtés fréquemment rencontrées dans la littérature et implementées dans certains codes commerciaux courants. La formulation mathématique du problème est effectuée dans un espace mixte Euler-Lagrange. Les paramètres dynamiques sont relies au type de particules et à l'intensité de la turbulence. Le code numérique résultant est le plus performant développé à ce jour (août 1998). Les trajectoires de plusieurs centaines de milliers de particules peuvent être simulées et visualisées de manière interactive sur une station de travail (SGI R4K, R8K et R10K). L'utilisateur du logiciel est libre de se déplacer dans l'espace à l'aide d'un environnement similaire a un ``simulateur de vol''. Il peut ainsi analyser les détails du processus d'érosion de même que l'écoulement du fluide dans la turbine. Les zones d'érosion obtenues à l

  8. Au nanorod helical superstructures with designed chirality.

    PubMed

    Lan, Xiang; Lu, Xuxing; Shen, Chenqi; Ke, Yonggang; Ni, Weihai; Wang, Qiangbin

    2015-01-14

    A great challenge for nanotechnology is to controllably organize anisotropic nanomaterials into well-defined three-dimensional superstructures with customized properties. Here we successfully constructed anisotropic Au nanorod (AuNR) helical superstructures (helices) with tailored chirality in a programmable manner. By designing the 'X' pattern of the arrangement of DNA capturing strands (15nt) on both sides of a two-dimensional DNA origami template, AuNRs functionalized with the complementary DNA sequences were positioned on the origami and were assembled into AuNR helices with the origami intercalated between neighboring AuNRs. Left-handed (LH) and right-handed (RH) AuNR helices were conveniently accomplished by solely tuning the mirrored-symmetric 'X' patterns of capturing strands on the origami. The inter-rod distance was precisely defined as 14 nm and inter-rod angle as 45°, thus a full helix contains 9 AuNRs with its length up to about 220 nm. By changing the AuNR/origami molar ratio in the assembly system, the average number of AuNR in the helices was tuned from 2 to 4 and 9. Intense chiroptical activities arose from the longest AuNR helices with a maximum anisotropy factor of ∼0.02, which is highly comparable to the reported macroscopic AuNR assemblies. We expect that our strategy of origami templated assembly of anisotropic chiral superstructures would inspire the bottom-up fabrication of optically active nanostructures and shed light on a variety of applications, such as chiral fluids, chiral signal amplification, and fluorescence combined chiral spectroscopy.

  9. One-step synthesis of graphene-AuNPs by HMTA and the electrocatalytical application for O2 and H2O2.

    PubMed

    Hu, Jianguo; Li, Fenghua; Wang, Kaikai; Han, Dongxue; Zhang, Qixian; Yuan, Junhua; Niu, Li

    2012-05-15

    A green, one-step method for synthesis of graphene-Au nanoparticles (graphene-AuNPs) was introduced in this article, using an environmentally benign hexamethylenetetramine (HMTA) as reducing and stabilizing agent. HMTA slowly was hydrolyzed to generate aldehyde ammonia to reduce graphene oxides (GO) and hydrogen tetrachloroaurate (Au precursor). The structure and composition of the graphene-AuNPs nanocomposites were studied by means of ultraviolet visible (UV) absorption spectra, X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM). The AuNPs are well-dispersed on graphene nanosheets in narrow size range. The nanocomposites have excellent electrocatalytical properties for catalytic reduction of O(2) and H(2)O(2).

  10. AuPdFe ternary solution model and applications to understanding the fO2 of hydrous, high-pressure experiments

    NASA Astrophysics Data System (ADS)

    Barr, Jay A.; Grove, Timothy L.

    2010-11-01

    This study provides an experimental calibration of the equilibrium constant for AuPdFe alloys with Fe-bearing silicate melts. The ideal metal capsules for H2O-bearing experiments are pure Au, because of its slow hydrogen diffusivity. However, above the melting point of Au, other materials must be used. The solution to this problem is to use AuPd alloy capsules. However, under most relevant fO2 conditions, this alloy absorbs Fe from the coexisting silicate melt, thus changing the bulk composition of the experimental charge. This study combines previous work on the Au-Pd, Pd-Fe, and Au-Fe binary systems to develop a ternary thermodynamic solution model for AuPdFe. This solution model is used with experiments to calculate an equilibrium reaction coefficient for the FeOmelt → Fealloy + 1/2O2 exchange reaction. Using a non-ideal ternary solution model, the fO2 conditions of hydrous, piston cylinder experiments can be estimated by analyzing the sample capsule alloy and the coexisting liquid composition.

  11. CO-free hydrogen production for fuel cell applications over Au/CeO2 catalysts: FTIR insight into the role of dopant.

    PubMed

    Tabakova, Tatyana; Manzoli, Maela; Vindigni, Floriana; Idakiev, Vasko; Boccuzzi, Flora

    2010-03-25

    The impact of ceria doping by Zn (atomic ratio Zn/(Zn + Ce) = 0.05) on the structural and catalytic properties of Au/CeO(2) catalyst was studied. The ceria modification influenced the catalytic activity toward purification of hydrogen via water-gas shift (WGS) and preferential CO oxidation (PROX) reactions in a different way: it diminished the WGS activity and improved the PROX performance. A characterization by FTIR spectroscopy was conducted to explain differences in the catalytic performance. The nature of gold active species after different pretreatments, under different atmospheres (H(2), D(2)), and after admission of CO and its subsequent interaction with (18)O(2) was investigated. Evidence has been found of the dissociation of hydrogen at room temperature on gold, producing on the oxidized sample a broad absorption assigned to Au-OH vibrations, whereas on the reduced one, bands at 3200 and 1800 cm(-1) ascribed, respectively, to Au-OH and Au-H species have been detected. For the first time, the formation of Au-hydride on supported heterogeneous catalysts was proposed. These features were stronger on the Au/CeO(2) sample than on the Au/Zn-CeO(2) sample. The availability of highly dispersed gold clusters in contact with oxygen vacancies on the ceria surface could contribute to higher WGS activity, whereas the steps of small gold particles are the active sites for both CO and oxygen activation during the PROX reaction.

  12. Conceptual design study of concentrator enhanced solar arrays for space applications. 2kW Si and GaAs systems at 1 AU

    NASA Technical Reports Server (NTRS)

    1980-01-01

    The effect of concentration level on the specific power for a deployable, thin, gallium arsenide cell array in geosynchronous orbit for 10 years in conjunction with a two dimensional flat plate trough concentrator (V trough) and also with a multiple flat plate concentrator was investigated as well as the effects for a conventional silicon cell array on a rigid substrate. For application to a thin GaAs array at 1 AU for 10 years, the V trough produces a 19% benefit in specific power and a dramatic reduction in array area, while the multiple flat plate collector design is not only of no benefit, but is a considerable detriment. The benefit it achieves by reducing array area is duplicated by the 2D design. For the silicon array on a rigid substrate, improvement in performance due to a concentrator with ordinary mirror coating is quite small: 9% increase in specific power, and 13% reduction in array area. When the concentrator mirrors are coated with an improved cold mirror coating, somewhat more significant results are obtained: 31% specific power improvement; and 27% area reduction. In both cases, a 10 year exposure reduces BOL output by 23%.

  13. Modelisation et commande des redresseurs triphases fonctionnant a haut rendement et a faible taux de distorsion harmonique: Application au redresseur triphase de vienne

    NASA Astrophysics Data System (ADS)

    Belhadj Youssef, Nesrine

    Les problemes de la qualite de l'onde electrique constituent l'une des preoccupations majeures des fournisseurs de l'energie et des organismes specialises en qualite d'energie. Ce sujet a gagne davantage d'ampleur avec l'utilisation ascendante des convertisseurs de l'energie electrique dans la majorite des applications industrielles et domestiques. Dans le cadre de cette these, on s'interesse plus particulierement au type des convertisseurs alternatif/continu, dont le fonctionnement adequat implique la parfaite regulation du bus DC de tension, l'attenuation des harmoniques de courants, la compensation de l'energie reactive et la maximisation du rendement energetique. Ces differents criteres doivent etre maintenus pour diverses conditions de fonctionnement, c'est-a-dire independamment des variations parametriques auxquelles le systeme peut etre sujet. Il s'avere donc indispensable d'adopter des techniques de commande efficaces, ce qui passe par une modelisation correcte du convertisseur. L'optimisation du nombre de capteurs dans le circuit est egalement un facteur cle a prendre en consideration.

  14. Advanced Characterization Techniques for Nanoparticles for Cancer Research: Applications of SEM and NanoSIMS for Locating Au Nanoparticles in Cells

    PubMed Central

    Kempen, Paul J; Hitzman, Chuck; Sasportas, Laura S; Gambhir, Sanjiv S; Sinclair, Robert

    2014-01-01

    The ability of nano secondary ion mass spectrometry (NanoSIMS) to locate and analyze Raman active gold core nanoparticles (R-AuNPs) in a biological system is compared with the standard analysis using the scanning electron microscope (SEM). The same cell with R-AuNPs on and inside the macrophage was analyzed with both techniques to directly compare them. SEM analysis showed a large number of nanoparticles within the cell. Subsequent NanoSIMS analysis showed fewer R-AuNPs with lower spatial resolution. SEM was determined to be superior to NanoSIMS for the analysis of inorganic nanoparticles in complex biological systems. PMID:25364091

  15. Advanced Characterization Techniques for Nanoparticles for Cancer Research: Applications of SEM and NanoSIMS for Locating Au Nanoparticles in Cells.

    PubMed

    Kempen, Paul J; Hitzman, Chuck; Sasportas, Laura S; Gambhir, Sanjiv S; Sinclair, Robert

    2013-05-13

    The ability of nano secondary ion mass spectrometry (NanoSIMS) to locate and analyze Raman active gold core nanoparticles (R-AuNPs) in a biological system is compared with the standard analysis using the scanning electron microscope (SEM). The same cell with R-AuNPs on and inside the macrophage was analyzed with both techniques to directly compare them. SEM analysis showed a large number of nanoparticles within the cell. Subsequent NanoSIMS analysis showed fewer R-AuNPs with lower spatial resolution. SEM was determined to be superior to NanoSIMS for the analysis of inorganic nanoparticles in complex biological systems.

  16. 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.

  17. Au20Si12: A hollow Catalan pentakis dodecahedron.

    PubMed

    Guo, J J; Zhao, H Y; Wang, J; Ai, L Y; Liu, Y

    2017-02-14

    A stable hollow Au20Si12 cage with Ih symmetry has been predicted using first-principles density functional theory. The stability of the cage-like Au20Si12 structure is verified by vibrational frequency analysis and molecular dynamics simulations. A relatively large highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.057 eV is found. Electronic structure analysis shows that clearly p-d hybridizations between Si atoms and Au atoms are of great importance for the stability of Au20Si12 cage. The cage-like Au20Si12 structure may have potential applications in semiconductor industry and microelectronics.

  18. Au20Si12: A hollow Catalan pentakis dodecahedron

    NASA Astrophysics Data System (ADS)

    Guo, J. J.; Zhao, H. Y.; Wang, J.; Ai, L. Y.; Liu, Y.

    2017-02-01

    A stable hollow Au20Si12 cage with Ih symmetry has been predicted using first-principles density functional theory. The stability of the cage-like Au20Si12 structure is verified by vibrational frequency analysis and molecular dynamics simulations. A relatively large highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.057 eV is found. Electronic structure analysis shows that clearly p-d hybridizations between Si atoms and Au atoms are of great importance for the stability of Au20Si12 cage. The cage-like Au20Si12 structure may have potential applications in semiconductor industry and microelectronics.

  19. Effects of soft beam energy on the microstructure of Pb37Sn, Au20Sn, and Sn3.5Ag0.5Cu solder joints in lensed-SM-fiber to laser-diode-affixing application

    NASA Astrophysics Data System (ADS)

    Tan, C. W.; Chan, Y. C.; Leung, Bernard; Liu, H. D.

    2008-01-01

    This paper reports on the effectiveness of soft beam energy as a heat source to form an optimum solder joint to fix a lensed fiber permanently on a Ni/Au-plated substrate. Solders, i.e., Pb37Sn, Au20Sn, and Sn3.5Ag0.5Cu (SAC) [wt%] were evaluated for this fluxless application. The microstructures of the solder joints have been examined using scanning electron microscopy (SEM), in order to understand the response of these solder materials to the focussed white light. Obviously, the exposure time has a greater effect on the soldering temperature before reaching the peak temperature, which is determined by the power. A power setting of 40 W can reach approximately 340 °C, 30 W can reach about 310 °C while 25 W can easily reach 260 °C. In general, a higher soldering temperature than the melting temperature is required to form good wetting solder joints for fluxless applications. However, too high an input thermal energy may result in premature aging for the cases of Pb37Sn and SAC, and lateral cracks for the case of Au20Sn. The thermal cracks and voids observed in Au20Sn solder joint were attributed to the fact that the soft beam heating profile does not suit the AuSn preform. Out of these three solder types, SAC demonstrated just the right response to the soft beam, i.e., good wetting, fine and homogeneous structure, and no cracks or other visible failures.

  20. 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

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

    SciTech Connect

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

    2016-05-23

    We present electronic properties of atomic layer of Au, Au{sub 2}-N, Au{sub 2}-O and Au{sub 2}-F in graphene-like structure within the framework of density functional theory (DFT). The lattice constant of derived monolayers are found to be higher than the pristine Au monolayer. Au monolayer is metallic in nature with quantum ballistic conductance calculated as 4G{sub 0}. Similarly, Au{sub 2}-N and Au{sub 2}-F monolayers show 4G{sub 0} and 2G{sub 0} quantum conductance respectively while semiconducting nature with calculated band gap of 0.28 eV has been observed for Au{sub 2}-O monolayer. Most interestingly, half metalicity has been predicted for Au{sub 2}-N and Au{sub 2}-F monolayers. Our findings may have importance for the application of these monolayers in nanoelectronic and spintronics.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  3. Synthesis of double-shelled sea urchin-like yolk-shell Fe3O4/TiO2/Au microspheres and their catalytic applications

    NASA Astrophysics Data System (ADS)

    Li, Jie; Tan, Li; Wang, Ge; Yang, Mu

    2015-03-01

    Double-shelled sea urchin-like yolk-shell Fe3O4/TiO2/Au microspheres were successfully synthesized through loading Au nanoparticles on the Fe3O4/TiO2 support by a in situ reduction of HAuCl4 with NaBH4 aqueous solution. These microspheres possess tunable cavity size, adjustable shell layers, high structural stability and large specific surface area. The Au nanoparticles of approximately 5 nm in diameter were loaded both on the TiO2 nanofibers and inside the cavities of sea urchin-like yolk-shell Fe3O4/TiO2 microspheres. The sea urchin-like structure composed of TiO2 nanofibers ensure the good distribution of the Au nanoparticles, while the novel double-shelled yolk-shell structure guarantees the high stability of the Au nanoparticles. Furthermore, the Fe3O4 magnetic core facilitates the convenient recovery of the catalyst by applying an external magnetic field. The Fe3O4/TiO2/Au microspheres display excellent activities and recycling properties in the catalytic reduction of 4-nitrophenol (4-NP): the rate constant is 1.84 min-1 and turnover frequency is 5457 h-1.

  4. A study on the effect of low energy ion beam irradiation on Au/TiO2 system for its application in photoelectrochemical splitting of water

    NASA Astrophysics Data System (ADS)

    Verma, Anuradha; Srivastav, Anupam; Sharma, Dipika; Banerjee, Anamika; Sharma, Shailja; Satsangi, Vibha Rani; Shrivastav, Rohit; Avasthi, Devesh Kumar; Dass, Sahab

    2016-07-01

    Nanostructured TiO2 thin films were deposited on indium tin oxide (ITO) substrate via sol-gel technique and were modified by plasmonic Au layer. The plasmonic Au modified TiO2 (Au/TiO2) thin films were then irradiated with 500 keV Ar2+ ion beam at different ion fluences viz. 1 × 1016, 3 × 1016 and 1 × 1017 to study the effect of nuclear energy deposition on the morphology, crystallinity, band gap, surface plasmon resonance (SPR) peak exhibited by Au particles and photoelectrochemical properties of the system. Prepared thin films were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS) measurements and UV-visible spectroscopy. The photoelectrochemical measurements revealed that both Au/TiO2 and Au/TiO2 thin film irradiated at 1 × 1016 fluence exhibits enhanced photoelectrochemical response in comparison to pristine TiO2. The film irradiated at 1 × 1016 fluence offered maximum applied bias photon-to-current efficiency (ABPE) and shows 6 times increment in photocurrent density which was attributed to more negative flat band potential, maximum decrease in band gap, high open circuit voltage (Voc) and reduced charge transfer resistance.

  5. Β-cyclodextrin polymer as a linker to fabricate ternary nanocomposites AuNPs/pATP-β-CDP/rGO and their electrochemical application.

    PubMed

    Chen, Ming; Shen, Xiao; Liu, Peipei; Wei, Ying; Meng, Yang; Zheng, Gang; Diao, Guowang

    2015-03-30

    Based on the self-assembly strategy, β-cyclodextrin polymer (β-CDP) was used as a linker to connect reduced graphene oxide (rGO) and p-aminothiophenol (pATP). Then, pre-prepared gold nanoparticles (AuNPs) can self-assemble onto the surface of pATP-β-CDP/rGO to obtain new ternary nanocomposites AuNPs/pATP-β-CDP/rGO. The amount or the density of AuNPs can be adjusted by changing the concentration of pATP. UV-vis and (1)H NMR spectra confirmed the formation of inclusion complex between pATP and β-CDP. β-CDP might improve the dispersity of rGO in aqueous and the surface property of rGO. AuNPs/pATP-β-CDP/rGO modified electrode displayed high electrochemical response toward a pesticide-imidacloprid (IDP). The enrichment capability and molecular recognition of β-CDP and the catalytic property of AuNPs for IDP molecules synergistically promoted the electrochemical response of rGO modified electrode. Additionally, ternary nanocomposites exhibited the good electrocatalytic performance for oxygen reduction in O2-saturated 0.1M H2SO4 solution. The proposed synthesis strategy provided a facile, feasible and effective method for development of electrochemical sensors and Au-based catalysts for fuel cells. Copyright © 2014 Elsevier Ltd. All rights reserved.

  6. Catalysis of aptamer-modified AuPd nanoalloy probe and its application to resonance scattering detection of trace UO(2)2+.

    PubMed

    Liang, Aihui; Zhang, Yi; Fan, Yanyan; Chen, Chunqiang; Wen, Guiqing; Liu, Qingye; Kang, Caiyan; Jiang, Zhiliang

    2011-08-01

    AuPd nanoalloy and nanopalladium with a diameter of 5 nm were prepared, using sodium citrate as the stabilizing agent and NaBH(4) as the reductant. The nanocatalyst containing palladium on the surface exhibited a strong catalytic effect on the slow NiP particle reaction between NiCl(2) and NaH(2)PO(2), and the NiP particle system showed a resonance scattering (RS) peak at 508 nm. The RS results showed that the Pd atom on AuPd nanoalloy surface is the catalytic center. Combining the aptamer cracking reaction of double-stranded DNA (dsDNA)-UO(2)(2+), AuPd nanoalloy aggregation, and AuPd nanoalloy catalysis, both AuPd nanoalloy RS probe and AuPd nanoalloy catalytic RS assays were developed for the determination of 40-250 pmol L(-1) UO(2)(2+) and 5.0-50 pmol L(-1) UO(2)(2+), respectively.

  7. Growth of cedar-like Au nanoparticles coating on an etched stainless steel wire and its application for selective solid-phase microextraction.

    PubMed

    Zhang, Yida; Yang, Yaoxia; Li, Yi; Zhang, Min; Wang, Xuemei; Du, Xinzhen

    2015-05-30

    A novel cedar-like Au nanoparticles (AuNPs) coating was fabricated on an etched stainless steel (SS) wire by direct chemical deposition and used as an efficient and unbreakable solid phase microextraction (SPME) fiber. The etched SS wire offers a rough surface structure for subsequent growth of AuNPs in chloroauric acid solution. As a result, the uniform cedar-like AuNPs coating with larger surface area was tightly attached to the etched SS wire substrate. The AuNPs coated etched SS fiber (AuNPs/SS) was examined for SPME of ultraviolet (UV) filters, phthalate esters and aromatic hydrocarbons coupled to high-performance liquid chromatography with UV detection. The fabricated fiber exclusively exhibited excellent extraction efficiency and selectivity for some aromatic hydrocarbons. Influential parameters of extraction and desorption time, temperature, stirring rate and ionic strength were investigated and optimized. The limits of detection ranged from 0.008 μg L(-1) to 0.037 μg L(-1). The single fiber repeatability varied from 3.90% to 4.50% and the fiber-to-fiber reproducibility ranged from 5.15% to 6.87%. The recovery of aromatic hydrocarbons in real water samples spiked at 2.0 μg L(-1) and 20 μg L(-1) ranged from 94.38% to 106.2% with the relative standard deviations below 6.44%. Furthermore the growth of the cedar-like AuNPs coating can be performed in a highly reproducible manner. This fabricated fiber exhibits good stability and withstands at least 200 extraction and desorption replicates. Copyright © 2015. Published by Elsevier B.V.

  8. Au@Ag Heterogeneous Nanorods as Nanozyme Interfaces with Peroxidase-Like Activity and Their Application for One-Pot Analysis of Glucose at Nearly Neutral pH.

    PubMed

    Han, Lei; Li, Cuncheng; Zhang, Tao; Lang, Qiaolin; Liu, Aihua

    2015-07-08

    As substitutes for natural peroxidases, most nanomaterial-based enzyme mimetics (nanozymes) have unique properties such as high stability, low-cost, large surface area, and high catalytic activity. However, they usually work in acidic conditions and thus impede their real applications. In this work, by modulating the nanostructure, composition, and surface property of the bimetallic materials, the positively charged poly(diallyldimethylammonium)-stabilized Au@Ag heterogeneous nanorods (NRs) were developed as synergistic peroxidase-like interfaces, which exhibited high activity over a wide pH range (pH 4.0-6.5) using 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) as the chromogenic substrate. At pH 6.5, the peroxidase-like activity for the Au@Ag heterogeneous NRs was stable and optimal within 20-40 °C. Moreover, the Au@Ag heterogeneous NRs showed excellent temperature stability and long-term storage stability. Given these characters, the detection of H2O2 at pH 6.5 was proposed on the basis of the Au@Ag heterogeneous NRs catalyzing the colorimetric reaction of H2O2 and ABTS, where the oxidized ABTS showed a typical absorption peak at 414 nm. The absorbance at 414 nm was linear with H2O2 concentration from 0.01 to 10 mM. Further, considering that Au@Ag heterogeneous NRs and glucose oxidase (GOx) have similar optimal pH for catalytic activities, a novel one-pot method for the detection of glucose was developed by the coupled catalytic reaction using GOx, Au@Ag heterogeneous NRs, and ABTS at nearly neutral pH (pH 6.5) and 37 °C. This proposed method had simple and rapid processes, wide linear range (0.05-20 mM), and reliability for the successful analysis of real samples. On the basis of these attractive and unique characteristics, Au@Ag heterogeneous NRs can become promising substitutes for peroxidase in analytical chemistry and environmental science.

  9. Directional light scattering from individual Au nanocup

    NASA Astrophysics Data System (ADS)

    Bai, Jinjun; Li, Yong; Zhao, Bo

    2017-03-01

    We investigate the optical scattering properties of gold nanocup with different orientation and fractional height by full vector finite element method. All of the scattering cross section, the distribution of electric field intensity, and the ability of directional light scattering are simulated, respectively. It is demonstrated that the scattering cross section of Au nanocup is a superposition of scattering spectrum of a transverse mode and an axial mode. The wavelength and the intensity of the maximum value of the scattering cross section increase initially then reduce with the fractional height increasing for transverse mode, while they increase monotonously with the fractional height increasing for axial mode. Furthermore, the calculation results show that the ability of redirecting incident light of Au nanocup mainly depends on the transverse mode. And the deflected angle of scattering increases with the fractional height of Au nanocup decreasing. These results indicate that Au nanocup has a promising application in the planar plasmon devices.

  10. Observation of DNA pinning at laser focal point on Au surface and its application to single DNA nanowire and cross-wire formation.

    PubMed

    Fujii, Sho; Kobayashi, Katsuaki; Kanaizuka, Katsuhiko; Okamoto, Tetsuaki; Toyabe, Shoichi; Muneyuki, Eiro; Haga, Masa-Aki

    2010-11-01

    We report a new technique for fabricating a single DNA nanowire at a desired position in a sequential manner using the micronanobubble generated by laser local heating at the Au/water interface. In our previous report, we found the reversible pull-in/shrinkage of one end immobilized DNA strands near a Nd:YAG laser focal point on an Au surface. In further experiments, the pinning of DNA strands in the stretched state was observed on the Au surface only when the bubble has touched the free end of DNA. This pinning phenomenon was observed even on the alkane thiol modified Au surface as self-assembled monolayers (SAMs) such as hexanethiol, mercaptohexanol, and hexadecanethiol. However, no pinning was observed on the bovine serum albumin (BSA) modified surface. Since optical tweezers can manipulate a DNA modified bead (radius=1.87 μm), the bead was firstly fixed on a solid surface by being compressed with the optical tweezers, and the pulling and pinning of DNA on the bead were achieved. As a consequence, the laser local heating on the Au surface enables us to control the number and position of the one end immobilized DNA strands as DNA nanowires. Copyright © 2010 Elsevier B.V. All rights reserved.

  11. A simple way to prepare Au@polypyrrole/Fe3O4 hollow capsules with high stability and their application in catalytic reduction of methylene blue dye

    NASA Astrophysics Data System (ADS)

    Yao, Tongjie; Cui, Tieyu; Wang, Hao; Xu, Linxu; Cui, Fang; Wu, Jie

    2014-06-01

    Metal nanoparticles are promising catalysts for dye degradation in treating wastewater despite the challenges of recycling and stability. In this study, we have introduced a simple way to prepare Au@polypyrrole (PPy)/Fe3O4 catalysts with Au nanoparticles embedded in a PPy/Fe3O4 capsule shell. The PPy/Fe3O4 capsule shell used as a support was constructed in one-step, which not only dramatically simplified the preparation process, but also easily controlled the magnetic properties of the catalysts through adjusting the dosage of FeCl2.4H2O. The component Au nanoparticles could catalyze the reduction of methylene blue dye with NaBH4 as a reducing agent and the reaction rate constant was calculated through the pseudo-first-order reaction equation. The Fe3O4 nanoparticles permitted quick recycling of the catalysts with a magnet due to their room-temperature superparamagnetic properties; therefore, the catalysts exhibited good reusability. In addition to catalytic activity and reusability, stability is also an important property for catalysts. Because both Au and Fe3O4 nanoparticles were wrapped in the PPy shell, compared with precursor polystyrene/Au composites and bare Fe3O4 nanoparticles, the stability of Au@PPy/Fe3O4 hollow capsules was greatly enhanced. Since the current method is simple and flexible to create recyclable catalysts with high stability, it would promote the practicability of metal nanoparticle catalysts in industrial polluted water treatment.Metal nanoparticles are promising catalysts for dye degradation in treating wastewater despite the challenges of recycling and stability. In this study, we have introduced a simple way to prepare Au@polypyrrole (PPy)/Fe3O4 catalysts with Au nanoparticles embedded in a PPy/Fe3O4 capsule shell. The PPy/Fe3O4 capsule shell used as a support was constructed in one-step, which not only dramatically simplified the preparation process, but also easily controlled the magnetic properties of the catalysts through adjusting

  12. A simple way to prepare Au@polypyrrole/Fe3O4 hollow capsules with high stability and their application in catalytic reduction of methylene blue dye.

    PubMed

    Yao, Tongjie; Cui, Tieyu; Wang, Hao; Xu, Linxu; Cui, Fang; Wu, Jie

    2014-07-07

    Metal nanoparticles are promising catalysts for dye degradation in treating wastewater despite the challenges of recycling and stability. In this study, we have introduced a simple way to prepare Au@polypyrrole (PPy)/Fe3O4 catalysts with Au nanoparticles embedded in a PPy/Fe3O4 capsule shell. The PPy/Fe3O4 capsule shell used as a support was constructed in one-step, which not only dramatically simplified the preparation process, but also easily controlled the magnetic properties of the catalysts through adjusting the dosage of FeCl2·4H2O. The component Au nanoparticles could catalyze the reduction of methylene blue dye with NaBH4 as a reducing agent and the reaction rate constant was calculated through the pseudo-first-order reaction equation. The Fe3O4 nanoparticles permitted quick recycling of the catalysts with a magnet due to their room-temperature superparamagnetic properties; therefore, the catalysts exhibited good reusability. In addition to catalytic activity and reusability, stability is also an important property for catalysts. Because both Au and Fe3O4 nanoparticles were wrapped in the PPy shell, compared with precursor polystyrene/Au composites and bare Fe3O4 nanoparticles, the stability of Au@PPy/Fe3O4 hollow capsules was greatly enhanced. Since the current method is simple and flexible to create recyclable catalysts with high stability, it would promote the practicability of metal nanoparticle catalysts in industrial polluted water treatment.

  13. Catalytic effect of ReAu nanoalloy on the Te particle reaction and its application to resonance scattering spectral assay of CA125.

    PubMed

    Cai, Wei; Liang, Aihui; Liu, Qingye; Liao, Xianjiu; Jiang, Zhiliang; Shang, Guangyi

    2011-01-01

    ReAu nanoparticles with a molar ratio of 2:8 Re and Te nanoparticles were prepared by NaBH₄ reduction. In HCl medium at 65°C, ultratrace Re, Te and ReAu bimetallic nanoparticles strongly catalyzed the slow reaction between Sn(II) and Te(VI) to form Te particles, which exhibited the strongest resonance scattering (RS) peak at 782 nm. As the amount of nanocatalyst increased, the RS intensity at 782 nm (I(782 nm) ) increased linearly, and the increase in intensity ΔI(782 nm) was linear to the ReAu, Re and Te concentrations in the ranges 0.07-9.0, 0.01-4.5 and 30-1200 nM, respectively. As a model, a ReAu immunonanoprobe catalytic Te-particle resonance scattering spectral (RSS) method was established for detection of CA125, using ReAu nanoparticle labeling CA125 antibody (CA125Ab) to obtain an immunonanoprobe (ReAuCA125Ab) for CA125. In pH 7.6 citric acid-Na₂HPO₄ buffer solution, ReAuCA125Ab aggregated nonspecifically. Upon addition of CA125, the immunonanoprobe reacted with it to form ReAuCA125Ab-CA125 dispersive immunocomplex in the solution. After the centrifugation, the supernatant containing the immunocomplex was used to catalyze the reaction of Te(VI)-Sn(II) to produce the Te particles that resulted in the I(782 nm) increasing. The ΔI(782 nm) was linear to CA125 concentration (C(CA125)) in the range 0.1-240 mU/mL. The regression equation, correlation coefficient and detection limit were ΔI(782 nm) = 1.61 C(CA125) + 1.5, 0.9978 and 0.02 mU/mL, respectively. The proposed method was applied to detect CA125 in serum samples, with satisfactory results.

  14. Au/ZnO nanoarchitectures with Au as both supporter and antenna of visible-light

    NASA Astrophysics Data System (ADS)

    Liu, Tianyu; Chen, Wei; Hua, Yuxiang; Liu, Xiaoheng

    2017-01-01

    In this paper, we fabricate Au/ZnO nanostructure with smaller ZnO nanoparticles loaded onto bigger gold nanoparticles via combining seed-mediated method and sol-gel method. The obtained Au/ZnO nanocomposites exhibit excellent properties in photocatalysis process like methyl orange (MO) degradation and oxidative conversion of methanol into formaldehyde under visible light irradiation. The enhanced properties were ascribed to the surface plasmon resonance (SPR) effect of Au nanoparticles, which could contribute to the separation of photo-excited electrons and holes and facilitate the process of absorbing visible light. This paper contributes to the emergence of multi-functional nanocomposites with possible applications in visible-light driven photocatalysts and makes the Au/ZnO photocatalyst an exceptional choice for practical applications such as environmental purification of organic pollutants in aqueous solution and the synthesis of fine chemicals and intermediates.

  15. @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.

  16. Technical Evaluation Report on Knowledge Based System Applications for Guidance and Control (Application des Systemes a Base de Connaissances au Guidage-Pilotage),

    DTIC Science & Technology

    1991-07-01

    Sanz-Aranguez SP ProfessorJohn T.Shcpherd UK Dr Elihu Zimet us HOST PAINEL COORDINATOR Mdr Carlos A. Garriga. Lopez SENER Ingenieria y Sistemas SA...real-time expert systems. This problem arises when the prototype phase is finished and the goal is to produce an industrialized system. A methodology...meaningful in terms of industrial applications. The industrial exploitation of AI technology is strictly associated with the combination of both

  17. The application of Au nanoclusters in the fluorescence imaging of human serum proteins after native PAGE: enhancing detection by low-temperature plasma treatment.

    PubMed

    Zhang, Jing; Sajid, Muhammad; Na, Na; Huang, Lingyun; He, Dacheng; Ouyang, Jin

    2012-05-15

    Proteins in human serum are increasingly being studied for their roles in a wide variety of biochemical interactions. To improve the sensitivity of the detection of human serum proteins after native polyacrylamide gel electrophoresis (PAGE), we have developed a fluorescence imaging detection technique for the detection. BSA (bovine serum albumin)-stabilized Au nanoclusters (NCs) were applied as fluorescent probes for imaging, and low-temperature plasma (LTP) treatment of the Au NCs was introduced to enhance the fluorescence imaging. Here, a series of optimization experiments (e.g. those to optimize for pH) were conducted for protein detection after 1-DE and 2-DE, and several types of discharge gases (He, O(2), and N(2)) were selected for the LTP treatment. The possible mechanism of interaction between the proteins and the Au NCs was demonstrated by an isothermal titration calorimetry experiment. Using the present method, a sensitivity of 7-14 times higher than that of traditional staining detection methods was observed in the oxygen LTP-treated Au NCs fluorescence images, and some relatively low abundance proteins (identified by the MS/MS technique) were easily detected. In addition, this fluorescence imaging method was applied to distinguish between the serum samples of patients with liver diseases and those of healthy people. Thus, this fluorescence imaging method is suitable for the highly sensitive detection of various serum proteins, and it shows potential capabilities for clinical diagnosis. Copyright © 2012 Elsevier B.V. All rights reserved.

  18. Preparation and Characterization of Au-ZrO2-SiO2 Nanocomposite Spheres and Their Application in Enrichment and Detection of Organophosphorus Agents

    SciTech Connect

    Yang, Yuqi; Tu, Haiyang; Zhang, Aidong; Du, Dan; Lin, Yuehe

    2012-03-01

    Au-ZrO{sub 2}-SiO{sub 2} nanocomposite spheres were synthesized and used as selective sorbents for the solid-phase extraction (SPE) of orananophosphorous agents. A non-enzymatic electrochemical sensor based on an Au-ZrO{sub 2}-SiO{sub 2} modified electrode was developed for selective detection of orananophosphorous pesticides (OPs). The Au-ZrO{sub 2}-SiO{sub 2} nanocomposite spheres were synthesized by hydrolysis and condensation of zirconia n-butoxide (TBOZ) on the surface of SiO{sub 2} spheres and then introduction of gold nanoparticles on the surface. Transmission electron microscope and X-ray photoelectron spectroscopy were performed to characterize the formation of the nanocomposite sphere. Fast extraction of OP was achieved by Au-ZrO{sub 2}-SiO{sub 2} modified electrode within 5 min via the specific affinity between zirconia and phosphoric group. The assay yields a broad concentration range of paraoxon-ethyl from 1.0 to 500 ng/mL{sup -1} with a detection limit 0.5 ng/mL{sup -1}. This selective and sensitive method holds great promise for the enrichment and detection of OPs.

  19. Bioinspired polydopamine as the scaffold for the active AuNPs anchoring and the chemical simultaneously reduced graphene oxide: characterization and the enhanced biosensing application.

    PubMed

    Tian, Juan; Deng, Sheng-Yuan; Li, Da-Li; Shan, Dan; He, Wei; Zhang, Xue-Ji; Shi, You

    2013-11-15

    We report here an efficient approach to enhance the performance of biosensing platform based on graphene or graphene derivate. Initially, graphene oxides (GO) nanosheets were reduced and surface functionalized by one-step oxidative polymerization of dopamine in basic solution at environment friendly condition to obtain the polydopamine (Pdop) modified reduced graphene oxides (PDRGO). The bioinspired surface was further used as a support to anchor active gold nanoparticles (AuNPs). The morphology and structure of the as-prepared AuNPs/PDRGO nanocomposite were investigated by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform-infrared spectroscopy (FT-IR). Electrochemical studies demonstrate that the as-prepared AuNPs/PDRGO hybrid materials possess excellent electrochemical properties and electrocatalytic activity toward the oxidation of NADH at low potential (0.1 V vs. SCE) with the fast response (15s) and the broad linear range (5.0 × 10(-8)-4.2 × 10(-5)M). Thus, this AuNPs/PDRGO nanocomposite can be further used to fabricate a sensitive alcohol biosensor using alcohol dehydrogenase (ADH), by simply incorporating the specific enzyme within the composite matrix with the aid of chitosan (Chit). Copyright © 2013 Elsevier B.V. All rights reserved.

  20. Synthesis of Au-BiVO4 nanocomposite through anodic electrodeposition followed by galvanic replacement and its application to the photocatalytic decomposition of methyl orange.

    PubMed

    Myung, Noseung; Lee, Wooju; Lee, Changhyun; Jeong, Seonghan; Rajeshwar, Krishnan

    2014-07-21

    A Au-BiVO(4) nanocomposite is synthesized by a two-step strategy involving anodic electrodeposition combined with in situ galvanic replacement. First, a BiVO(4) layer is prepared by the anodic oxidation of pre-electrodeposited Bi film in a VO(4)(3-) containing electrolyte. Thus-prepared BiVO(4) film contains excess metallic Bi, which is then galvanically replaced with Au from an aqueous HAuCl(4) solution, resulting in the Au-BiVO(4) composite in the second step. Optical, photoelectrochemical and photocatalytic properties are investigated by using X-ray diffraction, energy-dispersive X-ray analysis, diffuse reflectance spectrometry, and photoelectrochemical analyses. The visible-light photocatalytic activity of the Au-BiVO(4) composite is evaluated using the decomposition of methyl orange dye and is superior to the bare BiVO(4) film counterpart. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. The synthesis of Au@C@Pt core-double shell nanocomposite and its application in enzyme-free hydrogen peroxide sensing

    NASA Astrophysics Data System (ADS)

    Zhang, Yayun; Li, Yuhui; Jiang, Yingying; Li, Yancai; Li, Shunxing

    2016-08-01

    A novel Au@C@Pt core-double shell nanocomposite was synthesized and used to fabricate enzyme-free electrochemical sensor for rapid and sensitive detection of hydrogen peroxide (H2O2). The well-designed Au@C@Pt core-double shell nanocomposite was characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM) and energy-dispersed spectrum (EDS). The Au@C@Pt core-double shell nanocomposite modified glassy carbon electrode (Au@C@Pt/GCE) exhibits good electrocatalytic activity towards H2O2 reduction at 0.0 V and can be used as H2O2 sensor. The sensor displays two wide linear ranges towards H2O2 detection. The one is 9.0 μM-1.86 mM with high sensitivity of 144.7 μA mM-1 cm-2, and the other is 1.86 mM-7.11 mM with sensitivity of 80.1 μA mM-1 cm-2. When signal to noise (S/N) is 3, the calculated detection limit (LOD) is 0.13 μM. Furthermore, the interference from the common interfering species such as glucose, ascorbic acid, dopamine and uric acid can be effectively avoided to H2O2 detection. Additionally, the H2O2 sensor also displays good stability and reproducibility.

  2. Photoemission study of Au on a-Si:H

    NASA Astrophysics Data System (ADS)

    Pi, Tun-Wen; Yang, A.-B.; Olson, C. G.; Lynch, D. W.

    1990-11-01

    We report a high-resolution photoemission study of Au evaporated on rf-sputtered a-Si:H at room temperature. Three regions of coverage can be classified according to the behavior of the valence-band and core-level spectra: an unreacted region with an equivalent thickness of 2 Å, followed by an intermixed Au/a-Si overlayer (~9 Å), and a dual-phase region at higher coverage. Au adatoms are dispersed in the unreacted region. They subsequently cluster in the intermixed region, where they attach to Si atoms that are not hydrogen bonded, suggesting that the intermixed Si is mainly from those that have dangling bonds. In the dual-phase region, two sets of Au 4f core levels evolve with higher binding energy, one from Au intermixed with Si, and the lower one exhibiting pure gold character. The interface eventually ends up with the sequence: a-Si:H(sub.)+(pure Au mixed with intermixed Au/Si)+(vac). This is unlike the case of Au on c-Si, which has a pure gold layer sandwiched by intermixed Au/Si complexes along the surface normal. Traces of silicon atoms on top of composite surfaces appear even at the highest coverage, 205 Å, of the gold deposit. The applicability of the four models previously used for the Au/c-Si interface is also briefly discussed.

  3. Design of Au/SPIO composite nanoparticle for facile and biocompatible surface functionalization via Au-S bond

    NASA Astrophysics Data System (ADS)

    Seino, Satoshi; Shibata, Yujin; Yamanaka, Masayuki; Nakagawa, Takashi; Mukai, Yohei; Nakagawa, Shinsaku; Yamamoto, Takao A.

    2013-01-01

    Immobilization of Au nanoparticles on super-paramagnetic iron-oxide (SPIO) enables facile and biocompatible surface functionalization via Au-S bond. Au/SPIO composite nanoparticle is easily modified by thiol-modified polyethylene glycol (PEG-SH), and they are successfully applied on MR tumor imaging. However, its large hydrodynamic size ( 150 nm) still causes the accumulation to liver in vivo. In this study, we controlled the hydrodynamic size of Au/SPIO by testing different raw SPIOs and stabilizing polymers. As the best candidate, Au/Molday-ION which was synthesized from Molday-ION and polyvinyl alcohol comprised the hydrodynamic size of 56 nm. Moreover, PEGylated Au/Molday-ION showed excellent dispersibility in blood serum, with the hydrodynamic size of 65 nm. This surface functionalization strategy is effective for the constructions of magnetic nanocarriers for in vivo applications.

  4. Selection of a new Mycobacterium tuberculosis H37Rv aptamer and its application in the construction of a SWCNT/aptamer/Au-IDE MSPQC H37Rv sensor.

    PubMed

    Zhang, XiaoQing; Feng, Ye; Yao, QiongQiong; He, Fengjiao

    2017-12-15

    A rapid and accurate detection method for Mycobacterium tuberculosis (M. tuberculosis) is essential for effectively treating tuberculosis. However, current detection methods cannot meet these clinical requirements because the methods are slow or of low specificity. Consequently, a new highly specific ssDNA aptamer against M. tuberculosis reference strain H37Rv was selected by using the whole-cell systematic evolution of ligands by exponential enrichment technique. The selected aptamer was used to construct a fast and highly specific H37Rv sensor. The probe was produced by immobilizing thiol-modified aptamer on an Au interdigital electrode (Au-IDE) of a multichannel series piezoelectric quartz crystal (MSPQC) through Au-S bonding, and then single-walled carbon nanotubes (SWCNTs) were bonded on the aptamer by π-π stacking. SWCNTs were used as a signal indicator because of their considerable difference in conductivity compared with H37Rv. When H37Rv is present, it replaces the SWCNTs because it binds to the aptamer much more strongly than SWCNTs do. The replacement of SWCNTs by H37Rv resulted in a large change in the electrical properties, and this change was detected by the MSPQC. The proposed sensor is highly selective and can distinguish H37Rv from Mycobacterium smegmatis (M. smegmatis) and Bacillus Calmette-Guerin vaccine (BCG). The detection time was 70min and the detection limit was 100cfu/mL. Compared with conventional methods, this new SWCNT/aptamer/Au-IDE MSPQC H37Rv sensor was specific, rapid, and sensitive, and it holds great potential for the early detection of H37Rv in clinical diagnosis. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. The vital function of Fe3O4@Au nanocomposites for hydrolase biosensor design and its application in detection of methyl parathion.

    PubMed

    Zhao, Yuting; Zhang, Weiying; Lin, Yuehe; Du, Dan

    2013-02-07

    A nanocomposite of gold nanoparticles (AuNPs) decorating a magnetic Fe(3)O(4) core was synthesized using cysteamine (SH-NH(2)) as linker, and characterized by TEM, XPS, UV and electrochemistry. Then a hydrolase biosensor, based on self-assembly of methyl parathion hydrolase (MPH) on the Fe(3)O(4)@Au nanocomposite, was developed for sensitive and selective detection of the organophosphorus pesticide (OP) methyl parathion. The magnetic nanocomposite provides an easy way to construct the enzyme biosensor by simply exerting an external magnetic field, and also provides a simple way to renew the electrode surface by removing the magnet. Unlike inhibition-based enzyme biosensors, the hydrolase is not poisoned by OPs and thus is reusable for continuous measurement. AuNPs not only provide a large surface area, high loading efficiency and fast electron transfer, but also stabilize the enzyme through electrostatic interactions. The MPH biosensor shows rapid response and high selectivity for detection of methyl parathion, with a linear range from 0.5 to 1000 ng mL(-1) and a detection limit of 0.1 ng mL(-1). It also shows acceptable reproducibility and stability. The simplicity and ease of operation of the proposed method has great potential for on-site detection of P-S containing pesticides and provides a promising strategy to construct a robust biosensor.

  6. Contribution of β' and β precipitates to hardening in as-solutionized Ag-20Pd-12Au-14.5Cu alloys for dental prosthesis applications.

    PubMed

    Kim, Yonghwan; Niinomi, Mitsuo; Hieda, Junko; Nakai, Masaaki; Cho, Ken; Fukui, Hisao

    2014-04-01

    Dental Ag-20Pd-12Au-14.5Cu alloys exhibit a unique hardening behavior, which the mechanical strengths enhance significantly which enhances the mechanical strength significantly after high-temperature (1123K) solution treatment without aging treatment. The mechanism of the unique hardening is not clear. The contribution of two precipitates (β' and β phases) to the unique hardening behavior in the as-solutionized Ag-20Pd-12Au-14.5Cu alloys was investigated. In addition, the chemical composition of the β' phase was investigated. The fine β' phase densely precipitates in a matrix. The β' phase (semi-coherent precipitate), which causes lattice strain, contributes greatly to the unique hardening behavior. On the other hand, the coarse β phase sparsely precipitates in the matrix. The contribution of the β phase (incoherent precipitate), which does not cause lattice strain, is small. The chemical composition of the β' phase was determined. This study reveals that the fine β' phase precipitated by high-temperature solution treatment leads to the unique hardening behavior in dental Ag-20Pd-12Au-14.5Cu alloys in the viewpoints of the lattice strain contrast and interface coherency. It is expected to make the heat treatment process more practical for hardening. The determined chemical composition of β' phase would be helpful to study an unknown formation process of β' phase.

  7. The Vital Function of Fe3O4@Au nanocomposites for Hydrolase Biosensor Design and Its Application in Detection of Methyl Parathion

    SciTech Connect

    Zhao, Yuting; Zhang, Weiying; Lin, Yuehe; Du, Dan

    2013-02-04

    A nanocomposite of gold nanoparticles (AuNPs) decorating a magnetic Fe3O4 core was synthesized using cysteamine (SH–NH2) as linker, and characterized by TEM, XPS, UV and electrochemistry. Then a hydrolase biosensor, based on self-assembly of methyl parathion hydrolase (MPH) on the Fe3O4@Au nanocomposite, was developed for sensitive and selective detection of the organophosphorus pesticide (OP) methyl parathion. The magnetic nanocomposite provides an easy way to construct the enzyme biosensor by simply exerting an external magnetic field, and also provides a simple way to renew the electrode surface by removing the magnet. Unlike inhibition-based enzyme biosensors, the hydrolase is not poisoned by OPs and thus is reusable for continuous measurement. AuNPs not only provide a large surface area, high loading efficiency and fast electron transfer, but also stabilize the enzyme through electrostatic interactions. The MPH biosensor shows rapid response and high selectivity for detection of methyl parathion, with a linear range from 0.5 to 1000 ng/mL and a detection limit of 0.1 ng/mL. It also shows acceptable reproducibility and stability. The simplicity and ease of operation of the proposed method has great potential for on-site detection of P–S containing pesticides and provides a promising strategy to construct a robust biosensor.

  8. High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures

    PubMed Central

    Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S.; Weidner, Donald J.

    2016-01-01

    We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10–15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K–B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source. PMID:26902122

  9. Green synthesis, characterization of Au-Ag core-shell nanoparticles using gripe water and their applications in nonlinear optics and surface enhanced Raman studies

    NASA Astrophysics Data System (ADS)

    Kirubha, E.; Palanisamy, P. K.

    2014-12-01

    In recent years there has been excessive progress in the ‘green’ chemistry approach for the synthesis of gold and silver nanoparticles. Bimetallic nanoparticles have gained special significance due to their unique tunable optical properties. Herein we report a facile one-pot, eco-friendly synthesis of Au-Ag bimetallic core-shell nanoparticles using gripe water as reducing as well as stabilizing agent. The as-synthesized Au-Ag nanoparticles are characterized using UV-Vis spectroscopy to determine the surface plasmon resonance, and using transmission electron microscopy to study the morphology and the particle size. The optical nonlinearity of the bimetallic nanoparticles investigated by z-scan technique using femtosecond Ti:sapphire is in the order of 109. The nonlinear optical parameters such as the nonlinear refractive index n2, nonlinear absorption coefficient β and the third order nonlinear susceptibility χ3 are measured for various wavelengths from 700 nm to 950 nm. The Au-Ag nanoparticles are also used in surface enhanced Raman spectroscopic studies to enhance the Raman signals of rhodamine 6G.

  10. High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures

    DOE PAGES

    Hong, Xinguo; Ehm, Lars; Zhong, Zhong; ...

    2016-02-23

    We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10–15 μm) has been achieved at energies of 66 and 81keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DACmore » can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. In conclusion, the coupling of sagittally bent Laue crystals with K–B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source.« less

  11. High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures

    SciTech Connect

    Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S.; Weidner, Donald J.

    2016-02-23

    We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10–15 μm) has been achieved at energies of 66 and 81keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. In conclusion, the coupling of sagittally bent Laue crystals with K–B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source.

  12. High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures

    NASA Astrophysics Data System (ADS)

    Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S.; Weidner, Donald J.

    2016-02-01

    We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10–15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K–B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source.

  13. Pd-Au@carbon dots nanocomposite: Facile synthesis and application as an ultrasensitive electrochemical biosensor for determination of colitoxin DNA in human serum.

    PubMed

    Huang, Qitong; Lin, Xiaofeng; Zhu, Jie-Ji; Tong, Qing-Xiao

    2017-03-22

    In this study, a green and fast method was developed to synthesize high-yield carbon dots (CDs) via one-pot microwave treatment of banana peels without using any other surface passivation agents. Then the as-prepared CDs was used as the reducing agent and stabilizer to synthesize a Pd-Au@CDs nanocomposite by a simple sequential reduction strategy. Finally, Pd-Au@CDs nanocomposite modified glassy carbon electrode (Pd-Au@CDs/GCE) was obtained as a biosensor for target DNA after being immobilized a single-stranded probe DNA by a carboxyl ammonia condensation reaction. Under the optimal conditions, the sensor could detect target DNA concentrations in the range from 5.0×10(-16) to 1.0×10(-1)°molL(-1). The detection limit (LD) was estimated to be 1.82×10(-17)molL(-1), which showed higher sensitivity than other electrochemical biosensors reported. In addition, the DNA sensor was also successfully applied to detect colitoxin DNA in human serum.

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

    NASA Astrophysics Data System (ADS)

    Fangyuan, Wang; Guiqin, Li

    2016-07-01

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

  16. The vital function of Fe3O4@Au nanocomposites for hydrolase biosensor design and its application in detection of methyl parathion

    NASA Astrophysics Data System (ADS)

    Zhao, Yuting; Zhang, Weiying; Lin, Yuehe; Du, Dan

    2013-01-01

    A nanocomposite of gold nanoparticles (AuNPs) decorating a magnetic Fe3O4 core was synthesized using cysteamine (SH-NH2) as linker, and characterized by TEM, XPS, UV and electrochemistry. Then a hydrolase biosensor, based on self-assembly of methyl parathion hydrolase (MPH) on the Fe3O4@Au nanocomposite, was developed for sensitive and selective detection of the organophosphorus pesticide (OP) methyl parathion. The magnetic nanocomposite provides an easy way to construct the enzyme biosensor by simply exerting an external magnetic field, and also provides a simple way to renew the electrode surface by removing the magnet. Unlike inhibition-based enzyme biosensors, the hydrolase is not poisoned by OPs and thus is reusable for continuous measurement. AuNPs not only provide a large surface area, high loading efficiency and fast electron transfer, but also stabilize the enzyme through electrostatic interactions. The MPH biosensor shows rapid response and high selectivity for detection of methyl parathion, with a linear range from 0.5 to 1000 ng mL-1 and a detection limit of 0.1 ng mL-1. It also shows acceptable reproducibility and stability. The simplicity and ease of operation of the proposed method has great potential for on-site detection of P-S containing pesticides and provides a promising strategy to construct a robust biosensor.A nanocomposite of gold nanoparticles (AuNPs) decorating a magnetic Fe3O4 core was synthesized using cysteamine (SH-NH2) as linker, and characterized by TEM, XPS, UV and electrochemistry. Then a hydrolase biosensor, based on self-assembly of methyl parathion hydrolase (MPH) on the Fe3O4@Au nanocomposite, was developed for sensitive and selective detection of the organophosphorus pesticide (OP) methyl parathion. The magnetic nanocomposite provides an easy way to construct the enzyme biosensor by simply exerting an external magnetic field, and also provides a simple way to renew the electrode surface by removing the magnet. Unlike

  17. Magnetic susceptibilities of liquid Cr-Au, Mn-Au and Fe-Au alloys

    SciTech Connect

    Ohno, S.; Shimakura, H.; Tahara, S.; Okada, T.

    2015-08-17

    The magnetic susceptibility of liquid Cr-Au, Mn-Au, Fe-Au and Cu-Au alloys was investigated as a function of temperature and composition. Liquid Cr{sub 1-c}Au{sub c} with 0.5 ≤ c and Mn{sub 1-c}Au{sub c} with 0.3≤c obeyed the Curie-Weiss law with regard to their dependence of χ on temperature. The magnetic susceptibilities of liquid Fe-Au alloys also exhibited Curie-Weiss behavior with a reasonable value for the effective number of Bohr magneton. On the Au-rich side, the composition dependence of χ for liquid TM-Au (TM=Cr, Mn, Fe) alloys increased rapidly with increasing TM content, respectively. Additionally, the composition dependences of χ for liquid Cr-Au, Mn-Au, and Fe-Au alloys had maxima at compositions of 50 at% Cr, 70 at% Mn, and 85 at% Fe, respectively. We compared the composition dependences of χ{sub 3d} due to 3d electrons for liquid binary TM-M (M=Au, Al, Si, Sb), and investigated the relationship between χ{sub 3d} and E{sub F} in liquid binary TM-M alloys at a composition of 50 at% TM.

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

    SciTech Connect

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

    2016-05-23

    We report stability and electronic properties of benzene molecule adsorbed on the Au atomic layer within the framework of density function theory (DFT). Horizontal configuration of benzene on the top site of Au monolayer prefers energetically over other studied configurations. On the adsorption of benzene, the ballistic conductance of Au monolayer is found to decrease from 4G{sub 0} to 2G{sub 0} suggesting its applications for the fabrications of organic sensor devices based on the Au atomic layers.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  20. Reduction of Fermi level pinning at Au-MoS2 interfaces by atomic passivation on Au surface

    NASA Astrophysics Data System (ADS)

    Min, Kyung-Ah; Park, Jinwoo; Wallace, Robert M.; Cho, Kyeongjae; Hong, Suklyun

    2017-03-01

    Monolayer molybdenum disulfide (MoS2), which is a semiconducting material with direct band gap of ˜1.8 eV, has drawn much attention for application in field effect transistors (FETs). In this connection, it is very important to understand the Fermi level pinning (FLP) which occurs at metal-semiconductor interfaces. It is known that MoS2 has an n-type contact with Au, which is a high work function metal, representing the strong FLP at Au-MoS2 interfaces. However, such FLP can obstruct the attainment of high performance of field effect devices. In this study, we investigate the reduction of FLP at Au-MoS2 interfaces by atomic passivation on Au(111) using first-principles calculations. To reduce the FLP at Au-MoS2 interfaces, we consider sulfur, oxygen, nitrogen, fluorine, and hydrogen atoms that can passivate the surface of Au(111). Calculations show that passivating atoms prevent the direct contact between Au(111) and MoS2, and thus FLP at Au-MoS2 interfaces is reduced by weak interaction between atom-passivated Au(111) and MoS2. Especially, FLP is greatly reduced at sulfur-passivated Au-MoS2 interfaces with the smallest binding energy. Furthermore, fluorine-passivated Au(111) can form ohmic contact with MoS2, representing almost zero Schottky barrier height (SBH). We suggest that SBH can be controlled depending on the passivating atoms on Au(111).

  1. Solid-Phase Equilibria in the Au-As, Au-Ga-Sb, Au-In-As, and Au-In-Sb Ternaries.

    DTIC Science & Technology

    1986-02-28

    AD6i5 469 SOLID- PHASE EQUILIBRIA IN THE Ru-As AU-GA-SB AU-IN-AS- 1/17 AND AU-IN-SB TERNAR (U) CALIFORNIA UNIV LOS ANGELES DEPT OF CHEMISTRY AND...REPORT & PERIOD COVERED SOLID- PHASE EQUILIBRIA IN THE Au-Ga-As, Au-Ga-Sb Thchnical Report Au-In-As, and Au-In-Sb TEARIEIS S. PERFORMING ORG. REPORT NUMBER...CLASSIFICATION OF THIS PAGEMI*n Does Entepd) 4./ lie- . .- - - - - -- -- Solid Phase Equilibria in the Au-Ga-As, Au-Ga-Sb, Au-In-As, and Au-In-Sb Ternaries C

  2. M\\TiO₂ (M=Au, Ag) transparent aqueous sols and its application on polymeric surface antibacterial post-treatment.

    PubMed

    Wu, Liangzhuan; Yu, Yuan; Song, Le; Zhi, Jinfang

    2015-05-15

    In this paper, we reported a simple and mild chemical method for synthesis of crystalline metal\\TiO2 (M=Au, Ag) transparent aqueous sols at low temperature (80°C). It should be found that the as-synthesized metal\\TiO2 sols could easily be coated on the flexible PET surfaces of the through the as-developed electroless-plating-like solution deposition (EPLSD) procedure. The as-prepared metal\\TiO2 sols and related flexible thin film were characterized by TEM, SEM, XRD, UV-vis, and FTIR analysis. The results showed that the Au and Ag nanoparticles can significantly improve the optical absorption properties of TiO2 due to the surface plasmon generated by the noble metal, which in turn enhanced the photo-induced antibacterial performance of the as-prepared metal\\TiO2 flexible film. Moreover, the photo-generated electrons could transfer between the metal and titanium dioxide under different irradiation (ultraviolet or visible light), which could significantly reduce the recombination of photo-induced electrons and holes, resulting in the better photo-induced antibacterial performance. Therefore, the EPLSD procedure may be used as a general polymeric surface antibacterial post-treatment procedure for preparing the metal\\TiO2 flexible film because of the noble metal enhanced antibacterial performance. Copyright © 2015 Elsevier Inc. All rights reserved.

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

    PubMed

    Iida, Kenji; Yasuike, Tomokazu; Nobusada, Katsuyuki

    2013-09-14

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

  4. Development of Ag-Pd-Au-Cu alloy for multiple dental applications. Part 1. Effects of Pd and Cu contents, and addition of Ga or Sn on physical properties and bond with ultra-low fusing ceramic.

    PubMed

    Goto, S; Miyagawa, Y; Ogura, H

    2000-09-01

    Ag-Pd-Au-Cu quaternary alloys consisting of 30-50% Ag, 20-40% Pd, 10-20% Cu and 20% Au (mother alloys) were prepared. Then 5% Sn or 5% Ga was added to the mother alloy compositions, and another two alloy systems (Sn-added alloys and Ga-added alloys) were also prepared. The bond between the prepared alloys and an ultra-low fusing ceramic as well as their physical properties such as the solidus point, liquidus point and the coefficient of thermal expansion were evaluated. The solidus point and liquidus point of the prepared alloys ranged from 802 degrees C to 1142 degrees C and from 931 degrees C to 1223 degrees C, respectively. The coefficient of thermal expansion ranged from 14.6 to 17.1 x 10(-6)/degrees C for the Sn- and Ga-added alloys. In most cases, the Pd and Cu contents significantly influenced the solidus point, liquidus point and coefficient of thermal expansion. All Sn- and Ga-added alloys showed high area fractions of retained ceramic (92.1-100%), while the mother alloy showed relatively low area fractions (82.3%) with a high standard deviation (20.5%). Based on the evaluated properties, six Sn-added alloys and four Ga-added alloys among the prepared alloys were suitable for the application of the tested ultra-low fusing ceramic.

  5. Magnetoresistance of Au films

    SciTech Connect

    Zhang, D. L.; Song, X. H.; Zhang, X.; Zhang, Xiaoguang

    2014-12-10

    Measurement of the magnetoresistance (MR) of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler s rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms.

  6. Magnetoresistance of Au films

    DOE PAGES

    Zhang, D. L.; Song, X. H.; Zhang, X.; ...

    2014-12-10

    Measurement of the magnetoresistance (MR) of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler s rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms.

  7. 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.

  8. Plasmon assisted enhanced second-harmonic generation in single hybrid Au/ZnS nanowires

    NASA Astrophysics Data System (ADS)

    Jassim, Nadia M.; Wang, Kai; Han, Xiaobo; Long, Hua; Wang, Bing; Lu, Peixiang

    2017-02-01

    We demonstrate the enhanced second-harmonic generation (SHG) in single ZnS nanowires (NWs) attached with gold nanoparticles (Au NPs). The hybrid Au/ZnS NWs with different densities of the attached Au NPs were prepared by a simple solution impregnation method. By comparing with bare ZnS NWs, ∼1.3, ∼6.6, ∼7 and ∼2 times enhancement of SH intensity was achieved in the hybrid Au/ZnS NWs with low, moderate, high and ultrahigh densities of the attached Au NPs, respectively. The enhanced SHG in the hybrid Au/ZnS NWs is attributed to the strong local-fields from the Au cluster under the near-resonant condition, which is supported by the related dark-field scattering spectra. This hybrid Au/ZnS NWs provide a simple platform for enhancing nonlinear optical responses, which have potential applications in nano-probing and nano-sensing.

  9. Novel photoswitchable dielectric properties on nanomaterials of electronic core-shell γ-FeOx@Au@fullerosomes for GHz frequency applications

    NASA Astrophysics Data System (ADS)

    Wang, Min; Su, Chefu; Yu, Tzuyang; Tan, Loon-Seng; Hu, Bin; Urbas, Augustine; Chiang, Long Y.

    2016-03-01

    We unexpectedly observed a large amplification of the dielectric properties associated with the photoswitching effect and the new unusual phenomenon of delayed photoinduced capacitor-like (i.e. electric polarization) behavior at the interface on samples of three-layered core-shell (γ-FeOx@AuNP)@[C60(>DPAF-C9)]n2 nanoparticles (NPs) in frequencies of 0.5-4.0 GHz. The detected relative dielectric constant amplification was initiated upon switching off the light followed by relaxation to give an excellent recyclability. These NPs having e--polarizable fullerosomic structures located at the outer layer were fabricated from highly magnetic core-shell γ-FeOx@AuNPs. Surface-stabilized 2 in a core-shell structure was found to be capable of photoinducing the surface plasmonic resonance (SPR) effect by white LED light. The accumulated SPR energy was subsequently transferred to the partially bilayered C60(>DPAF-C9) fullerosomic membrane layer in a near-field (~1.5 nm) region without producing radiation heat. Since the monostatic SAR signal is dielectric property-dependent, we used these measurements to provide evidence of derived reflectivity changes on a surface coated with 2 at 0.5-4.0 GHz upon illumination of LED white light. We found that a high, >99%, efficiency of response amplification in image amplitude can be achieved.We unexpectedly observed a large amplification of the dielectric properties associated with the photoswitching effect and the new unusual phenomenon of delayed photoinduced capacitor-like (i.e. electric polarization) behavior at the interface on samples of three-layered core-shell (γ-FeOx@AuNP)@[C60(>DPAF-C9)]n2 nanoparticles (NPs) in frequencies of 0.5-4.0 GHz. The detected relative dielectric constant amplification was initiated upon switching off the light followed by relaxation to give an excellent recyclability. These NPs having e--polarizable fullerosomic structures located at the outer layer were fabricated from highly magnetic core-shell γ-FeOx@Au

  10. The transport of gold and molybdenum through hydration in aqueous vapor and vapor-like fluids: Application to porphyry Au and Mo deposits

    NASA Astrophysics Data System (ADS)

    Hurtig, N. C.; Williams-Jones, A. E.

    2013-12-01

    The hypothesis that vapor is a viable medium for the transport of gold and molybdenum in ore forming magmatic-hydrothermal systems is supported by fluid inclusion data, analyses of volcanic gas condensates and the occurrence of metal-rich incrustations around fumaroles. Experiments have shown that hydration of metal species in water vapor is an essential factor in making such transport possible [1,2,3]. Indeed, hydration has been shown to increase concentrations of Au and Mo in the aqueous vapor phase by several orders of magnitude over those calculated using volatility data. Nevertheless metal concentrations determined experimentally in previous studies are substantially lower than those reported for vapor inclusions in magmatic hydrothermal systems, and are limited to one or two dominant hydrated metal species. To bridge this gap, we performed a series of new experiments extending the density-range to near critical vapor density, and intermediate-density in the case of supercritical fluids. Experiments were carried out in batch-type Ti autoclaves at temperatures between 300 and 500 °C and pressures up to 366 bar in HCl-bearing water vapor. Oxygen fugacity was buffered either by the assemblage MoO2/MoO3 or WO2/WO3 or graphite. Gold and molybdenum concentrations measured in the experimental condensates ranged from 0.9 ppb and 3 ppm in low-density vapor at 300 °C to 4.6 ppm and 481 ppm at 297 bar and 400 °C, respectively. The fugacity of both metals increased exponentially with increasing water fugacity, resulting in an increase in metal solubility between 1 and 3 orders of magnitude from the lowest pressures investigated. Curves representing the experimentally determined relationship between metal fugacity and fH2O were fitted to a step-wise hydration model to extract a set of logarithmic equilibrium constants for P and T extrapolation. We have used the above data to model Au and Mo mobilization in magmatic-hydrothermal vapor plumes. This modeling shows that the

  11. Growth of GaN@InGaN Core-Shell and Au-GaN Hybrid Nanostructures for Energy Applications

    DOE PAGES

    Kuykendall, Tevye; Aloni, Shaul; Jen-La Plante, Ilan; ...

    2009-01-01

    We demonstrated a method to control the bandgap energy of GaN nanowires by forming GaN@InGaN core-shell hybrid structures using metal organic chemical vapor deposition (MOCVD). Furthermore, we show the growth of Au nanoparticles on the surface of GaN nanowires in solution at room temperature. The work shown here is a first step toward engineering properties that are crucial for the rational design and synthesis of a new class of photocatalytic materials. The hybrid structures were characterized by various techniques, including photoluminescence (PL), energy dispersive x-ray spectroscopy (EDS), transmission and scanning electron microscopy (TEM and SEM), and x-ray diffraction (XRD).

  12. Effect of Silicon on Activity Coefficients of Siderophile Elements (P, Au, Pd, As, Ge, Sb, and In) in Liquid Fe, with Application to Core Formation

    NASA Technical Reports Server (NTRS)

    Righter, K.; Pando, K.; Danielson, L. R.; Humayun, M.; Righter, M.; Lapen, T.; Boujibar, A.

    2016-01-01

    Earth's core contains approximately 10 percent light elements that are likely a combination of S, C, Si, and O, with Si possibly being the most abundant. Si dissolved into Fe liquids can have a large effect on the magnitude of the activity coefficient of siderophile elements (SE) in Fe liquids, and thus the partitioning behavior of those elements between core and mantle. The effect of Si can be small such as for Ni and Co, or large such as for Mo, Ge, Sb, As. The effect of Si on many siderophile elements is unknown yet could be an important, and as yet unquantified, influence on the core-mantle partitioning of SE. Here we report new experiments designed to quantify the effect of Si on the partitioning of P, Au, Pd, and many other SE between metal and silicate melt. The results will be applied to Earth, for which we have excellent constraints on the mantle siderophile element concentrations.

  13. Charge optimized many body (COMB) potentials for Pt and Au

    NASA Astrophysics Data System (ADS)

    Antony, A. C.; Akhade, S. A.; Lu, Z.; Liang, T.; Janik, M. J.; Phillpot, S. R.; Sinnott, S. B.

    2017-06-01

    Interatomic potentials for Pt and Au are developed within the third generation charge optimized many-body (COMB3) formalism. The potentials are capable of reproducing phase order, lattice constants, and elastic constants of Pt and Au systems as experimentally measured or calculated by density functional theory. We also fit defect formation energies, surface energies and stacking fault energies for Pt and Au metals. The resulting potentials are used to map a 2D contour of the gamma surface and simulate the tensile test of 16-grain polycrystalline Pt and Au structures at 300 K. The stress-strain behaviour is investigated and the primary slip systems {1 1 1}<1 \\bar{1}  0> are identified. In addition, we perform high temperature (1800 K for Au and 2300 K for Pt) molecular dynamics simulations of 30 nm Pt and Au truncated octahedron nanoparticles and examine morphological changes of each particle. We further calculate the activation energy barrier for surface diffusion during simulations of several nanoseconds and report energies of 0.62+/- 0.16 eV for Pt and 1.44+/- 0.06 eV for Au. This initial parameterization and application of the Pt and Au potentials demonstrates a starting point for the extension of these potentials to multicomponent systems within the COMB3 framework.

  14. meson production in Au+Au collisions at in STAR

    NASA Astrophysics Data System (ADS)

    Zhou, Long; STAR collaboration

    2017-01-01

    In this article, we report the measurements of the nuclear modification factor (R AA) and elliptic flow (v 2) for in Au+Au collisions at from the STAR experiment. These results are compared with the results of other open charm mesons to study the hadronization mechanism of the charm quarks and disentangle the transport properties of quark-gluon plasma and hadronic phase [1]. We found that the nuclear modification factor for D s are systematically higher than unity and D 0 R AA. The ratio of D s /D 0 for 10-40% central Au+Au collisions is also higher than that in p+p collisions as predicted by PYTHIA. The D s /D 0 ratio is also compared to that in Pb+Pb collisions at measured by the ALICE experiment. Our results indicate an enhancement of D s meson production in Au+Au collisions.

  15. Multiple surface plasmon resonances of square lattice nanohole arrays in Au-SiO2-Au multilayer films

    NASA Astrophysics Data System (ADS)

    Yi, Zao; Liu, Miao; Luo, Jiangshan; Zhao, Yulin; Zhang, Weibin; Yi, Yougen; Yi, Yong; Duan, Tao; Wang, Chaoyang; Tang, Yongjian

    2017-05-01

    The optical properties and the local electromagnetic field enhancement of a multilayer structure with square lattice nanohole arrays in Au-SiO2-Au multilayer films are numerically studied using finite-difference time domain method. Simulation results demonstrate that the multiple surface plasmons (SP) resonances consist of SP on the air/Au interface, SiO2/Au interfaces (the middle layers), Au/SiO2 interface (the lower layer) and coupling modes on the Au film and Au film. We investigated some of structure parameters that influence the SP resonances of the multilayer nanostructure. Adjustment of the thickness of SiO2 film (H2), the diameter (R) of circular nanoholes, the periods (C) of square lattice and the thickness of Au film (H1) could change the absorption intensity and the SP resonances. The simulation of the electromagnetic field distributions shows that the location of the local electromagnetic field enhancement can specify the different SP resonances patterns. Dipole, quadrupole, and twelve-pole SP resonances modes can be found in the multilayer nanostructure. These studies are important for applications using multiple SP resonances.

  16. Dynamic features of rod-shaped Au nanoclusters

    NASA Astrophysics Data System (ADS)

    So, Woong Young; Das, Anindita; Wang, Shuxin; Zhao, Shuo; Byun, Hee Young; Lee, Dana; Kumar, Santosh; Jin, Rongchao; Peteanu, Linda A.

    2015-08-01

    Gold nanoclusters hold many potential applications such as biosensing and optics due to their emission characteristics, small size, and non-toxicity. However, their low quantum yields remain problematic for further applications, and their fluorescence mechanism is still unclear. To increase the low quantum yields, various methods have been performed: doping, tuning structures, and changing number of gold atoms. In the past, most characterizations have been performed on spherical shaped nanoclusters; in this paper, several characterizations of various rod-shaped Au nanoclusters specifically on Au25 are shown. It has been determined that the central gold atom in Au25 nano-rod is crucial in fluorescence. Furthermore, single molecule analysis of silver doped Au25 nano-rod revealed that it has more photo-stability than conjugated polymers and quantum dots.

  17. Antibacterial Au nanostructured surfaces

    NASA Astrophysics Data System (ADS)

    Wu, Songmei; Zuber, Flavia; Brugger, Juergen; Maniura-Weber, Katharina; Ren, Qun

    2016-01-01

    We present here a technological platform for engineering Au nanotopographies by templated electrodeposition on antibacterial surfaces. Three different types of nanostructures were fabricated: nanopillars, nanorings and nanonuggets. The nanopillars are the basic structures and are 50 nm in diameter and 100 nm in height. Particular arrangement of the nanopillars in various geometries formed nanorings and nanonuggets. Flat surfaces, rough substrate surfaces, and various nanostructured surfaces were compared for their abilities to attach and kill bacterial cells. Methicillin-resistant Staphylococcus aureus, a Gram-positive bacterial strain responsible for many infections in health care system, was used as the model bacterial strain. It was found that all the Au nanostructures, regardless their shapes, exhibited similar excellent antibacterial properties. A comparison of live cells attached to nanotopographic surfaces showed that the number of live S. aureus cells was <1% of that from flat and rough reference surfaces. Our micro/nanofabrication process is a scalable approach based on cost-efficient self-organization and provides potential for further developing functional surfaces to study the behavior of microbes on nanoscale topographies.We present here a technological platform for engineering Au nanotopographies by templated electrodeposition on antibacterial surfaces. Three different types of nanostructures were fabricated: nanopillars, nanorings and nanonuggets. The nanopillars are the basic structures and are 50 nm in diameter and 100 nm in height. Particular arrangement of the nanopillars in various geometries formed nanorings and nanonuggets. Flat surfaces, rough substrate surfaces, and various nanostructured surfaces were compared for their abilities to attach and kill bacterial cells. Methicillin-resistant Staphylococcus aureus, a Gram-positive bacterial strain responsible for many infections in health care system, was used as the model bacterial strain. It

  18. Voltammogram spikes interpreted as envelopes of spikes resulting from electrode crystals of various sizes: Application to the UPD of Cu on Au(111)

    NASA Astrophysics Data System (ADS)

    Medved', Igor; Huckaby, Dale A.

    2003-06-01

    We study and explain shapes of voltammogram spikes, observed during underpotential deposition (UPD) on electrode surfaces, as averaged envelopes of mutually shifted spikes associated with first-order phase transitions that occur in crystalline domains of various sizes that are formed on the electrode surface. This concept, already used in our previous work for two-phase systems and symmetric voltammogram spike shapes, is here substantially generalized to systems with multiple-phase coexistence and asymmetric spike shapes, using the rigorous statistical mechanical techniques of Borgs and Kotecký. Rather than mere numerical plots, we extract explicit functions that accurately describe the spike shapes. For the sake of clarity, we present our analysis and apply our results to fit the voltammogram of the UPD of Cu on Au(111) in sulfuric acid medium. This voltammogram shows two distinct spikes with a broad foot region near the spike at higher potentials. As was done in earlier treatments, we explain each of the two spikes as a result of a first-order transition. Here, though, the spikes are obtained as envelopes of closely spaced spikes resulting from crystals of various sizes. In contrast to earlier studies, however, we also explain the foot region in the same way. The foot's shape, despite its large width and small height, can be equally well obtained as an envelope of shifted crystal spikes that are broader and smaller than those giving rise to the two distinct spikes. We achieve very good agreement with experiment.

  19. DNA nanocages swallow gold nanoparticles (AuNPs) to form AuNP@DNA cage core-shell structures.

    PubMed

    Zhang, Chuan; Li, Xiang; Tian, Cheng; Yu, Guimei; Li, Yulin; Jiang, Wen; Mao, Chengde

    2014-02-25

    DNA offers excellent programming properties to nanomaterials syntheses. Host-guest interaction between DNA nanostructures and inorganic nanoparticles (NPs) is of particular interest because the resulting complexes would possess both programming properties intrinsic to DNA and physical properties associated with inorganic NPs, such as plasmonic and magnetic features. Here, we report a class of core-shell complexes (AuNP@DNA cages): hard gold NPs (AuNPs) are encapsulated in geometrically well-defined soft DNA nanocages. The AuNP guest can be further controllably released from the host (DNA nanocages), pointing to potential applications in surface engineering of inorganic NPs and cargo delivery of DNA nanocages.

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

    PubMed Central

    2013-01-01

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

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

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

  3. Fluctuations Magnetiques des Gaz D'electrons Bidimensionnels: Application AU Compose Supraconducteur LANTHANE(2-X) Strontium(x) Cuivre OXYGENE(4)

    NASA Astrophysics Data System (ADS)

    Benard, Pierre

    Nous presentons une etude des fluctuations magnetiques de la phase normale de l'oxyde de cuivre supraconducteur La_{2-x}Sr _{x}CuO_4 . Le compose est modelise par le Hamiltonien de Hubbard bidimensionnel avec un terme de saut vers les deuxiemes voisins (modele tt'U). Le modele est etudie en utilisant l'approximation de la GRPA (Generalized Random Phase Approximation) et en incluant les effets de la renormalisation de l'interaction de Hubbard par les diagrammes de Brueckner-Kanamori. Dans l'approche presentee dans ce travail, les maximums du facteur de structure magnetique observes par les experiences de diffusion de neutrons sont associes aux anomalies 2k _{F} de reseau du facteur de structure des gaz d'electrons bidimensionnels sans interaction. Ces anomalies proviennent de la diffusion entre particules situees a des points de la surface de Fermi ou les vitesses de Fermi sont tangentes, et conduisent a des divergences dont la nature depend de la geometrie de la surface de Fermi au voisinage de ces points. Ces resultats sont ensuite appliques au modele tt'U, dont le modele de Hubbard usuel tU est un cas particulier. Dans la majorite des cas, les interactions ne determinent pas la position des maximums du facteur de structure. Le role de l'interaction est d'augmenter l'intensite des structures du facteur de structure magnetique associees a l'instabilite magnetique du systeme. Ces structures sont souvent deja presentes dans la partie imaginaire de la susceptibilite sans interaction. Le rapport d'intensite entre les maximums absolus et les autres structures du facteur de structure magnetique permet de determiner le rapport U_ {rn}/U_{c} qui mesure la proximite d'une instabilite magnetique. Le diagramme de phase est ensuite etudie afin de delimiter la plage de validite de l'approximation. Apres avoir discute des modes collectifs et de l'effet d'une partie imaginaire non-nulle de la self-energie, l'origine de l'echelle d'energie des fluctuations magnetiques est examinee

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  5. Effects of cooling treatment and glutaraldehyde on the morphology of Au nanostructures synthesized from chitosan.

    PubMed

    Wei, Dongwei; Qian, Weiping; Shi, Yi; Ding, Shaohua; Xia, Yan

    2008-02-25

    A facile approach for the synthesis of chitosan-based Au nanostructures that have interesting absorptions in the near-infrared (NIR) region is presented. The effects of cooling treatment and the cross-linking agent glutaraldehyde on the formation of Au nanostructures based on chitosan were investigated. It has been demonstrated that the size and shape, and thus the optical properties of Au nanostructures, could be modulated via cooling treatment. The optical absorption extension of these Au nanostructures in the NIR region is promising in biomedical applications. The presence of a cross-linking agent, glutaraldehyde, during synthesis accelerated the reduction of the Au precursor and favored the growth of isotropic Au nanoparticles. A possible mechanism for the change in growth modality of Au nanostructures with and without glutaraldehyde was elucidated.

  6. 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.

  7. Significant Broadband Photocurrent Enhancement by Au-CZTS Core-Shell Nanostructured Photocathodes

    NASA Astrophysics Data System (ADS)

    Zhang, Xuemei; Wu, Xu; Centeno, Anthony; Ryan, Mary P.; Alford, Neil M.; Riley, D. Jason; Xie, Fang

    2016-03-01

    Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon resonance (LSPR) peak of the Au and the semiconductor bandgap.

  8. Significant Broadband Photocurrent Enhancement by Au-CZTS Core-Shell Nanostructured Photocathodes.

    PubMed

    Zhang, Xuemei; Wu, Xu; Centeno, Anthony; Ryan, Mary P; Alford, Neil M; Riley, D Jason; Xie, Fang

    2016-03-21

    Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon resonance (LSPR) peak of the Au and the semiconductor bandgap.

  9. Magnetoresistance of Au films

    SciTech Connect

    Zhang, D. L. Song, X. H.; Zhang, X.; Zhang, X.-G.

    2014-12-14

    Classical magnetoresistance (MR) in nonmagnetic metals are conventionally understood in terms of the Kohler rule, with violation usually viewed as anomalous electron transport, in particular, as evidence of non-Fermi liquid behavior. Measurement of the MR of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms. Consequently, the Kohler rule should not be used to distinguish normal and anomalous electron transport in solids.

  10. On the electron affinity of Au3

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.

    1989-01-01

    The EA of Au3 is estimated to be 3.93 eV. The calculations also show that the feature in the photodetachment spectrum at about 2 eV electron binding energy is due to a two-photon process involving fragmentation of Au3(-) to Au and Au2(-) and subsequent photodetachment of Au2(-). Au3 is found to have a 2B2 ground state that is only slightly distorted from an equilateral triangle.

  11. Studies of the structure and phase transitions of nano-confined pentanedithiol and its application in directing hierarchical molecular assemblies on Au(1 1 1)

    NASA Astrophysics Data System (ADS)

    Pawlicki, Alison; Avery, Erin; Jurow, Matthew; Ewers, Bradley; Vilan, Ayelet; Drain, Charles Michael; Batteas, James

    2016-03-01

    Directing molecular devices into pre-designed integrated electronic circuits while enforcing selectivity and hierarchy is an inherent challenge for molecular electronics. Here we explore ways to direct the assembly of electrically-active molecular monolayers into specific locations as well as controlling their internal organization. We have accomplished this by two consecutive surface reactions: (1) forming pentanedithiol (C5DT) domains within an inert alkanethiol self-assembled monolayer (SAM) on Au; and (2) selectively binding porphyrin derivatives to the C5DT domains. The C5DT domains were fabricated by phase segregation during co-adsorption from a mixed C5DT/dodecanethiol (C12) solution and nanografting with Atomic Force Microscopy (AFM). AFM revealed that co-absorbed and nanografted C5DT domains were in a standing-up phase and scanning tunneling microscopy (STM) showed that their molecular organization within about 5 nm, 40 nm, 50 nm and 120 nm domains, was dependent upon the size of the domain, such that structure of the C5DT transitions from (\\sqrt{3}   ×  \\sqrt{3} ) R30°, to (2  ×  2), and ultimately to a disordered phase with increasing domain size. This is due to the varying degrees of influence of the surrounding C12; providing sufficient van der Waals interactions as well as a geometric confinement to stabilize the standing-up phase of the C5DT. Understanding the molecular configuration of dithiol SAMs affords their use as a reactive template to subsequently bind active head groups. As a proof of principle, porphyrins with a pendant pentafluorophenyl ring were attached to the C5DT domains by a ‘click’ reaction between the fluorinated ring and the free thiol on the surface. From AFM and STM, these porphyrin derivatives reacted selectively with the C5DT domains with some porphyrins binding directly to the C5DT, subsequently allowing additional localized porphyrin deposition through pi-stacking.

  12. Analyse multiechelle d'images radar: Application au filtrage, a la classification et a la fusion d'images radar et optique

    NASA Astrophysics Data System (ADS)

    Foucher, Samuel

    Les images radar sont perturbees par un bruit multiplicatif (chatoiement) reduisant sensiblement la resolution radiometrique des cibles homogenes etendues. Le but de cette these est d'etudier l'apport de l'analyse multiechelle, plus particulierement de la transformee en ondelettes, dans le probleme de la reduction du chatoiement et de la classification non dirigee des images radar. Dans le cadre de la transformee en ondelettes stationnaire, garantissant l'invariance par translation de la representation, les techniques usuelles de filtrage adaptatif sont etendues au domaine multiechelle. Nous proposons de prendre en compte les specificites statistiques de l'image radar (modele multiplicatif, loi K) afin de separer les coefficients d'ondelettes engendres par le bruit seul de ceux engendres par les structures significatives de l'image. Le systeme de distribution de Pearson est applique afin de modeliser la distribution de probabilites des coefficients d'ondelettes. Lorsque l'intensite observee obeit a une loi K, le systeme de Pearson conduit a une loi de type IV (loi Beta complexe). Le type IV de Pearson est mis en oeuvre dans une ponderation de type MAP (Maximum A Posteriori). L'influence de la correlation du chatoiement sur les moments d'ordre superieur est ensuite evaluee quantitativement a partir d'une modelisation MA ("Moving Average") de l'image radar correlee. Les resultats obtenus sur un ensemble d'images artificielles montrent que l'approche multiechelle permet d'atteindre un meilleur compromis entre preservation des details et lissage des regions homogenes par rapport aux methodes de filtrage traditionnelles. En classification, la representation multiechelle permet de faire fluctuer le compromis precision spatiale/incertitude radiometrique. La theorie des croyances fournit un cadre theorique afin de manipuler les notions d'incertitude et d'imprecision. Nous proposons de combiner directement les decisions multiechelles par la regle de Dempster en integrant l

  13. Synthesis of Au@Pt bimetallic nanoparticles with concave Au nanocuboids as seeds and their enhanced electrocatalytic properties in the ethanol oxidation reaction

    NASA Astrophysics Data System (ADS)

    Tan, Lingyu; Li, Lidong; Peng, Yi; Guo, Lin

    2015-12-01

    Herein, a new type of uniform and well-structured Au@Pt bimetallic nanoparticles (BNPs) with highly active concave Au nanocuboids (NCs) as seeds was successfully synthesized by using the classic seed-mediated method. Electrochemical measurements were conducted to demonstrate their greatly enhanced catalytic performance in the ethanol oxidation reaction (EOR). It was found that the electrochemical performance for Au@Pt BNPs with the concave Au NCs as seeds, which were enclosed by {611} high-index facets, could be seven times higher than that of the Au@Pt bimetallic nanoparticles with regular spherical Au NPs as seeds. Furthermore, our findings show that the morphology and electrocatalytic activity of the Au@Pt BNPs can be tuned simply by changing the compositional ratios of the growth solution. The lower the amount of H2PtCl6 used in the growth solution, the thinner the Pt shell grew, and the more high-index facets of concave Au NCs seeds were exposed in Au@Pt BNPs, leading to higher electrochemical activity. These as-prepared concave Au@Pt BNPs will open up new strategies for improving catalytic efficiency and reducing the use of the expensive and scarce resource of platinum in the ethanol oxidation reaction, and are potentially applicable as electrochemical catalysts for direct ethanol fuel cells.

  14. Synthesis of Au@Pt bimetallic nanoparticles with concave Au nanocuboids as seeds and their enhanced electrocatalytic properties in the ethanol oxidation reaction.

    PubMed

    Tan, Lingyu; Li, Lidong; Peng, Yi; Guo, Lin

    2015-12-18

    Herein, a new type of uniform and well-structured Au@Pt bimetallic nanoparticles (BNPs) with highly active concave Au nanocuboids (NCs) as seeds was successfully synthesized by using the classic seed-mediated method. Electrochemical measurements were conducted to demonstrate their greatly enhanced catalytic performance in the ethanol oxidation reaction (EOR). It was found that the electrochemical performance for Au@Pt BNPs with the concave Au NCs as seeds, which were enclosed by {611} high-index facets, could be seven times higher than that of the Au@Pt bimetallic nanoparticles with regular spherical Au NPs as seeds. Furthermore, our findings show that the morphology and electrocatalytic activity of the Au@Pt BNPs can be tuned simply by changing the compositional ratios of the growth solution. The lower the amount of H2PtCl6 used in the growth solution, the thinner the Pt shell grew, and the more high-index facets of concave Au NCs seeds were exposed in Au@Pt BNPs, leading to higher electrochemical activity. These as-prepared concave Au@Pt BNPs will open up new strategies for improving catalytic efficiency and reducing the use of the expensive and scarce resource of platinum in the ethanol oxidation reaction, and are potentially applicable as electrochemical catalysts for direct ethanol fuel cells.

  15. Determination of relative sensitivity factors during secondary ion sputtering of silicate glasses by Au+, Au2+ and Au3+ ions.

    PubMed

    King, Ashley; Henkel, Torsten; Rost, Detlef; Lyon, Ian C

    2010-01-01

    In recent years, Au-cluster ions have been successfully used for organic analysis in secondary ion mass spectrometry. Cluster ions, such as Au(2)(+) and Au(3)(+), can produce secondary ion yield enhancements of up to a factor of 300 for high mass organic molecules with minimal sample damage. In this study, the potential for using Au(+), Au(2)(+) and Au(3)(+) primary ions for the analysis of inorganic samples is investigated by analyzing a range of silicate glass standards. Practical secondary ion yields for both Au(2)(+) and Au(3)(+) ions are enhanced relative to those for Au(+), consistent with their increased sputter rates. No elevation in ionization efficiency was found for the cluster primary ions. Relative sensitivity factors for major and trace elements in the standards showed no improvement in quantification with Au(2)(+) and Au(3)(+) ions over the use of Au(+) ions. Higher achievable primary ion currents for Au(+) ions than for Au(2)(+) and Au(3)(+) allow for more precise analyses of elemental abundances within inorganic samples, making them the preferred choice, in contrast to the choice of Au(2)(+) and Au(3)(+) for the analysis of organic samples. The use of delayed secondary ion extraction can also boost secondary ion signals, although there is a loss of overall sensitivity.

  16. Intrinsic catalytic activity of Au nanoparticles with respect to hydrogen peroxide decomposition and superoxide scavenging.

    PubMed

    He, Weiwei; Zhou, Yu-Ting; Wamer, Wayne G; Hu, Xiaona; Wu, Xiaochun; Zheng, Zhi; Boudreau, Mary D; Yin, Jun-Jie

    2013-01-01

    Gold nanoparticles have received a great deal of interest due to their unique optical and catalytic properties and biomedical applications. Developing applications as well as assessing associated risks requires an understanding of the interactions between Au nanoparticles (NPs) and biologically active substances. In this paper, electron spin resonance spectroscopy (ESR) was used to investigate the catalytic activity of Au NPs in biologically relevant reactions. We report here that Au NPs can catalyze the rapid decomposition of hydrogen peroxide. Decomposition of hydrogen peroxide is accompanied by the formation of hydroxyl radicals at lower pH and oxygen at higher pH. In addition, we found that, mimicking SOD, Au NPs efficiently catalyze the decomposition of superoxide. These results demonstrate that Au NPs can act as SOD and catalase mimetics. Since reactive oxygen species are biologically relevant products being continuously generated in cells, these results obtained under conditions resembling different biological microenvironments may provide insights for evaluating risks associated with Au NPs.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

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

    PubMed Central

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

    2014-01-01

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

  19. ETUDE AU MICROSCOPE ELECTRONIQUE DES TRANSFORMATIONS NUCLEAIRES DE E. COLI K12 S ET K12 S (λ26) APRES IRRADIATION AUX RAYONS ULTRAVIOLETS ET AUX RAYONS X

    PubMed Central

    Ryter, Antoinette

    1960-01-01

    Nuclear transformations induced in E. coli K12S and K12S(λ26) by ultraviolet radiations and x-rays have been studied with ultrathin sections in the electron microscope. The nucleoplasm keeps its normal aspect during "fragmentation" and during "condensation" of the nucleus into the "vesicular" form. Serial sections show that the "fragmented" nucleus consists in reality of only one very tortuous vacuole. No difference either in the shape or in the fine structure of the nucleus could be observed between the lysogenic strain and the non-lysogenic strain. A high concentration of NaCl has a "condensation" effect on the fragmented nuclei and decreases the induction rate. PMID:13745076

  20. Formation of Pd/Au Nanostructures from Pd Nanowires via Galvanic Replacement Reaction

    SciTech Connect

    Teng,X.; Wang, Q.; Liu, P.; Han, W.; Frenkel, A.; Wen, W.; Marinkovic, N.; Hanson, J.; Rodriguez, J.

    2008-01-01

    Bimetallic nanostructures with non-random metal atoms distribution are very important for various applications. To synthesize such structures via benign wet chemistry approach remains challenging. This paper reports a synthesis of a Au/Pd alloy nanostructure through the galvanic replacement reaction between Pd ultrathin nanowires (2.4 {+-} 0.2 nm in width, over 30 nm in length) and AuCl3 in toluene. Both morphological and structural changes were monitored during the reaction up to 10 h. Continuous changes of chemical composition and crystalline structure from Pd nanowires to Pd68Au32 and Pd45Au55 alloys, and to Au nanoparticles were observed. More interestingly, by using combined techniques such as high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), UV-vis absorption, and extended X-ray absorption fine structure (EXAFS) spectroscopy, we found the formation of Pd68Au32 non-random alloy with Au-rich core and Pd-rich shell, and random Pd45Au55 alloy with uniformly mixed Pd and Au atom inside the nanoparticles, respectively. Density functional theory (DFT) calculations indicated that alkylamine will strongly stabilize Pd to the surface, resulting in diffusion of Au atoms into the core region to form a non-random alloy. We believe such benign synthetic techniques can also enable the large scale preparation of various types of non-random alloys for several technically important catalysis applications.

  1. 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.

  2. Photoionization of Au+ ions and developments in the synthesis of the metallofullerene Au@C60

    NASA Astrophysics Data System (ADS)

    Bogolub, Kyren; Macaluso, David; Mueller, Allison; Johnson, Andrea; Müller, Alfred; Schippers, Stefan; Hellhund, Jonas; Borovik, Alexander; Anders, Andre; Aguilar, Alex; Kilcoyne, A. L. David

    2014-05-01

    Single photoionization of Au+ ions was investigated via the merged-beams technique at AMO Beamline 10.0.1.2 of the Advanced Light Source at Lawrence Berkeley National Laboratory. The relative single photoionization yield was measured as a function of photon energy in the 45 eV to 120 eV energy range. These measurements were made in preparation for future photoionization studies of the endohedral metallofullerene Au@C60, the production of which was also investigated. In proof-of-principle measurements a mass-resolved beam of Au@C60+was produced with a primary ion beam current in the single picoamp range without optimization of the ion source or synthesis parameters. Plans are presented for improved metallofullere production yield to be used in photoionization measurements of the endohedral fullerene ions in conjunction with the continuing study of pure Au. We would like to acknowledge the generous sharing of equipment vital to this work by Andre Anders, the Plasma Applications group leader at the Advanced Light Source, LBNL.

  3. Mn2Au: body-centered-tetragonal bimetallic antiferromagnets grown by molecular beam epitaxy.

    PubMed

    Wu, Han-Chun; Liao, Zhi-Min; Sofin, R G Sumesh; Feng, Gen; Ma, Xiu-Mei; Shick, Alexander B; Mryasov, Oleg N; Shvets, Igor V

    2012-12-11

    Mn(2)Au, a layered bimetal, is successfully grown using molecular beam epitaxy (MBE). The experiments and theoretical calculations presented suggest that Mn(2)Au film is antiferromagnetic with a very low critical temperature. The antiferromagnetic nature is demonstrated by measuring the exchange-bias effect of Mn(2)Au/Fe bilayers. This study establishes a primary basis for further research of this new antiferromagnet in spin-electronic device applications.

  4. Port-au-Prince, Haiti

    NASA Image and Video Library

    2010-01-14

    This image, produced from instrument data aboard NASA Space Shuttle Endeavour, is a perspective view of the topography of Port-au-Prince, Haiti where a magnitude 7.0 earthquake occurred on January 12, 2010.

  5. Gold-rich ligament nanostructure by dealloying Au-based metallic glass ribbon for surface-enhanced Raman scattering.

    PubMed

    Chao, Bo-Kai; Xu, Yi; Ho, Hsin-Chia; Yiu, Pakman; Lai, Yi-Chen; Shek, Chan-Hung; Hsueh, Chun-Hway

    2017-08-08

    A new method to fabricate an Au-rich interconnected ligament substrate by dealloying the Au-based metallic glass ribbon for surface-enhanced Raman scattering (SERS) applications was investigated in this study. Specifically, three substrates, Au film, Au-based metallic glass ribbon, and dealloyed Au-based metallic glass ribbon, were studied. The dealloyed surface showed ligament nanostructure with protruding micro-islands. Based on the field emission scanning electron microscopy, reflection and scattering measurements, the dealloyed Au-based metallic glass provided a large surface area, multiple reflections, and numerous fine interstices to produce hot spots for SERS enhancements. The SERS signal of analyte, p-aminothiophenol, in the micro-island region of dealloyed Au-based metallic glass was about 2 orders of magnitude larger than the flat Au film. Our work provides a new method to fabricate the inexpensive and high SERS enhancements substrates.

  6. Al-Au-La (010)

    NASA Astrophysics Data System (ADS)

    Carow-Watamura, U.; Louzguine, D. V.; Takeuchi, A.

    This document is part of Part 1 http://dx.doi.org/10.1007/9getType="URL"/> 'Systems from Ag-Al-Ca to Au-Pd-Si' of Subvolume B 'Physical Properties of Ternary Amorphous Alloys' of Volume 37 'Phase Diagrams and Physical Properties of Nonequilibrium Alloys' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains the Chapter 'Al-Au-La (010)' with the content:

  7. State-Sensitive Monitoring of Active and Promoter Sites. Applications to Au/Titania and Pt-Sn/Silica Catalysts by XAFS Combined with X-Ray Fluorescence Spectrometry

    SciTech Connect

    Izumi, Yasuo; Masih, Dilshad; Candy, Jean-Pierre; Yoshitake, Hideaki; Terada, Yasuko; Tanida, Hajime; Uruga, Tomoya

    2007-02-02

    State-sensitive XAFS was enabled combined with high-energy-resolution ({delta}E = 0.3 eV-5.5 keV) X-ray fluorescence spectrometry and applied to Au sites of Au/TiO2 and Sn promoter sites of Pt-Sn/SiO2. Each state of interfacial Au sites located on Ti/O atoms and negatively/positively charged Aun clusters was discriminated. Feasibility of more direct information of on-site catalysis via frontier orbital-sensitive XAFS was demonstrated.

  8. Architecture effects of glucose oxidase/Au nanoparticle composite Langmuir-Blodgett films on glucose sensing performance

    NASA Astrophysics Data System (ADS)

    Wang, Ke-Hsuan; Wu, Jau-Yann; Chen, Liang-Huei; Lee, Yuh-Lang

    2016-03-01

    The Langmuir-Blodgett (LB) deposition technique is employed to prepare nano-composite films consisting of glucose oxidase (GOx) and gold nanoparticles (AuNPs) for glucose sensing applications. The GOx and AuNPs are co-adsorbed from an aqueous solution onto an air/liquid interface in the presence of an octadecylamine (ODA) template monolayer, forming a mixed (GOx-AuNP) monolayer. Alternatively, a composite film with a cascade architecture (AuNP/GOx) is also prepared by sequentially depositing monolayers of AuNPs and GOx. The architecture effects of the composite LB films on the glucose sensing are studied. The results show that the presence of AuNPs in the co-adsorption system does not affect the adsorption amount and preferred conformation (α-helix) of GOx. Furthermore, the incorporation of AuNPs in both composite films can significantly improve the sensing performance. However, the enhancement effects of the AuNPs in the two architectures are distinct. The major effect of the AuNPs is on the facilitation of charge-transfer in the (GOx-AuNP) film, but on the increase of catalytic activity in the (AuNP/GOx) one. Therefore, the sensing performance can be greatly improved by utilizing a film combining both architectures (AuNP/GOx-AuNP).

  9. Rotating Au nanorod and nanowire driven by circularly polarized light.

    PubMed

    Liaw, Jiunn-Woei; Chen, Ying-Syuan; Kuo, Mao-Kuen

    2014-10-20

    The wavelength-dependent optical torques provided by a circularly polarized (CP) plane wave driving Au nanorod (NR) and nanowire (NW) to rotate constantly were studied theoretically. Using the multiple multipole method, the resultant torque in terms of Maxwell's stress tensor was analyzed. Numerical results show that the optical torque spectrum is in accordance with the absorption spectrum of Au NR/NW. Under the same fluence, the maximum optical torque occurs at the longitudinal surface plasmon resonance (LSPR) of Au NR/NW, accompanied by a severe plasmonic heating. The rotation direction of the light-driven NR/NW depends on the handedness of CP light. In contrast, the optical torque exerted on Au NR/NW illuminated by a linearly polarized light is null at LSPR. Due to the plasmonic effect, the optical torque on Au NR/NW by CP light is two orders of magnitude larger than that on a dielectric NR/NW of the same size. The steady-state rotation of NR/NW in water, resulting from the balance of optical torque and viscous torque, was also discussed. Our finding shed some light on manipulating a CP light-driven Au NR/NW as a rotating nanomotor for a variety of applications in optofluidics and biophysics.

  10. Enhanced photocatalytic performance of Au/TiO2 nanofibers by precisely manipulating the dosage of uniform-sized Au nanoparticles

    NASA Astrophysics Data System (ADS)

    Feng, Cong; Yu, Zhichao; Liu, Hongjing; Yuan, Kangkang; Wang, Xinqiang; Zhu, Luyi; Zhang, Guanghui; Xu, Dong

    2017-08-01

    The drawback of using TiO2 in photocatalytic applications lies in the wide band gap and high recombination rate of charge carriers. To solve the above problems, modification of TiO2 with Au nanoparticles (NPs) has received considerable attention. Here, TiO2 nanofibers uniformly deposited with Au NPs which have a narrow size distribution (16 nm) were synthesized. We demonstrate that the photocatalytic performance of Au/TiO2 heterostructured nanofibers can be effectively enhanced under UV and visible light irradiation by manipulating the dosage of decorated Au NPs. The effect of metal dosage on the photocatalytic performance has been systematically investigated. The enhanced photocatalytic properties are ascribed to the increase of visible light absorption from the Au NP's surface and the enhancement of separation of electron-hole charge pairs at the interface of Au/TiO2 junctions. Besides, the decrease of photoactivity with more addition of Au NPs is due to the fact that redundant Au NPs reduce the photon flux reaching the TiO2 surface and also act as recombination centers for electron-hole pairs. The present work provides guidance toward the fabrication of more efficient Au/TiO2 photocatalysts.

  11. Sulfur-induced mobilization of Au surface atoms on Au(1 1 1) studied by real-time STM

    NASA Astrophysics Data System (ADS)

    Biener, Monika M.; Biener, Juergen; Friend, Cynthia M.

    2007-04-01

    The interaction of sulfur with gold surfaces has attracted considerable interest due to numerous technological applications such as the formation of self-assembled monolayers and as a chemical sensor. Here, we report on the interaction of sulfur with Au(1 1 1) at two different temperatures (300 K and 420 K) studied by real-time scanning tunnelling microscopy, low energy electron diffraction and Auger electron spectroscopy. In the low coverage regime (<0.1 ML), S adsorption lifts the herringbone reconstruction of the clean Au(1 1 1) surface indicating a lateral expansion of the surface layer. An ordered (√3 × √3) R30° sulfur adlayer develops as the coverage reaches ˜0.3 ML. At higher S coverages (>0.3 ML) gold surface atoms are removed from regular terrace sites and incorporated into a growing gold sulfide phase. At 300 K this process leads to the formation of a rough pit and mound surface morphology. This gold sulfide exhibits short-range order and an incommensurate, long-range ordered AuS phase develops upon annealing at 450-525 K. In contrast, formation of an ordered AuS phase via rapid step-retraction rather than etch pit formation is observed during S-interaction with Au(1 1 1) surfaces at 420 K. Our results shed new light on the S-Au(1 1 1) interaction.

  12. Heterojunction metal-oxide-metal Au-Fe{sub 3}O{sub 4}-Au single nanowire device for spintronics

    SciTech Connect

    Reddy, K. M. Punnoose, Alex; Hanna, Charles; Padture, Nitin P.

    2015-05-07

    In this report, we present the synthesis of heterojunction magnetite nanowires in alumina template and describe magnetic and electrical properties from a single nanowire device for spintronics applications. Heterojunction Au-Fe-Au nanowire arrays were electrodeposited in porous aluminum oxide templates, and an extensive and controlled heat treatment process converted Fe segment to nanocrystalline cubic magnetite phase with well-defined Au-Fe{sub 3}O{sub 4} interfaces as confirmed by the transmission electron microscopy. Magnetic measurements revealed Verwey transition shoulder around 120 K and a room temperature coercive field of 90 Oe. Current–voltage (I-V) characteristics of a single Au-Fe{sub 3}O{sub 4}-Au nanowire have exhibited Ohmic behavior. Anomalous positive magnetoresistance of about 0.5% is observed on a single nanowire, which is attributed to the high spin polarization in nanowire device with pure Fe{sub 3}O{sub 4} phase and nanocontact barrier. This work demonstrates the ability to preserve the pristine Fe{sub 3}O{sub 4} and well defined electrode contact metal (Au)–magnetite interface, which helps in attaining high spin polarized current.

  13. Controlled electrodeposition of Au monolayer film on ionic liquid

    NASA Astrophysics Data System (ADS)

    Ma, Qiang; Pang, Liuqing; Li, Man; Zhang, Yunxia; Ren, Xianpei; Liu, Shengzhong Frank

    2016-05-01

    Gold (Au) nanoparticles have been attractive for centuries for their vibrant appearance enhanced by their interaction with sunlight. Nowadays, there have been tremendous research efforts to develop them for high-tech applications including therapeutic agents, sensors, organic photovoltaics, medical applications, electronics and catalysis. However, there remains to be a challenge to fabricate a monolayer Au coating with complete coverage in controlled fashion. Here we present a facile method to deposit a uniform Au monolayer (ML) film on the [BMIM][PF6] ionic liquid substrate using an electrochemical deposition process. It demonstrates that it is feasible to prepare a solid phase coating on the liquid-based substrate. Moreover, the thickness of the monolayer coating can be controlled to a layer-by-layer accuracy.

  14. Fundamental interaction between Au quantum dots and DNA

    NASA Astrophysics Data System (ADS)

    Karna, Molleshree; Mallick, Govind; Karna, Shashi

    2010-03-01

    Semiconductor quantum dots (QDs) and metal nanoparticles (NPs) have attracted a great deal of attention in biology community due to their application as fluorescent labels and sensors. The optical properties of QDs and NPs allow them to be effective imaging agents. However, QDs have the potential to be used as more than just sensors and labels. Their biological sensing abilities include identifying target DNA through a linker followed by color change and electrical signaling. If this property can be combined with the direct binding of QDs with DNA, many other applications in bio-nanotechnological field are possible. In this paper, we investigate the interaction between colloidal Au QDs and 30-base sequence single strand DNA. Our preliminary results indicate that the DNA strand tend to form different structures in the presence of Au QDs. Furthermore, small as well as large agglomerated Au particles appear to be linked along the DNA strand.

  15. Interface effects on tunneling magnetoresistance in organic spintronics with flexible amine-Au links.

    PubMed

    Gorjizadeh, Narjes; Quek, Su Ying

    2013-10-18

    Organic spintronics is a promising emerging field, but the sign of the tunneling magnetoresistance (TMR) is highly sensitive to interface effects, a crucial hindrance to applications. A key breakthrough in molecular electronics was the discovery of amine-Au link groups that give a reproducible conductance. Using first-principles calculations, we predict that amine-Au links give improved reproducibility in organic spintronics junctions with Au-covered Fe leads. The Au layers allow only states with sp character to tunnel into the molecule, and the flexibility of amine-Au links results in a narrow range of TMR for a fixed number of Au layers. Even as the Au thickness changes, the TMR remains positive as long as the number of Au layers is the same on both sides of the junction. Since the number of Au layers on Fe surfaces or Fe nanoparticles can now be experimentally controlled, amine-Au links provide a route towards robust TMR in organic spintronics.

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

    PubMed

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

    2009-09-30

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

  17. Methylene blue and neutral red electropolymerisation on AuQCM and on modified AuQCM electrodes: an electrochemical and gravimetric study.

    PubMed

    Barsan, Madalina M; Pinto, Edilson M; Brett, Christopher M A

    2011-03-28

    The phenazine monomers neutral red (NR) and methylene blue (MB) have been electropolymerised on different quartz crystal microbalance (QCM) substrates: MB at AuQCM and nanostructured ultrathin sputtered carbon AuQCM (AuQCM/C), and NR on AuQCM and on layer-by-layer films of hyaluronic acid with myoglobin deposited on AuQCM (AuQCM-{HA/Mb}(6)). The surface of the electrode substrates was characterised by atomic force microscopy (AFM), and the frequency changes during potential cycling electropolymerisation of the monomer were monitored by the QCM. The study investigates how the monomer chemical structure together with the electrode morphology and surface structure can influence the electropolymerisation process and the electrochemical properties of the phenazine-modified electrodes. Differences between MB and NR polymerisation, as well as between the different substrates were found. The electrochemical properties of the PNR-modified electrodes were analysed by cyclic voltammetry and electrochemical impedance spectroscopy and compared with the unmodified AuQCM. The results are valuable for future applications of modified AuQCM as substrates for electroactive polymer film deposition and applications in redox-mediated electrochemical sensors and biosensors.

  18. Electrografting of thionine diazonium cation onto the graphene edges and decorating with Au nano-dendrites or glucose oxidase: Characterization and electrocatalytic applications.

    PubMed

    Shervedani, Reza Karimi; Amini, Akbar; Sadeghi, Nima

    2016-03-15

    Thionine (Th) diazonium cation is covalently attached onto the glassy carbon (GC) electrode via graphene nanosheets (GNs) (GC-GNs-Th). The GC-GNs-Th electrode is subjected to further modifications to fabricate (i) glucose and (ii) nitrite sensors. Further modifications include: (i) direct immobilization of glucose oxidase (GOx) and (ii) electrodeposition of gold dendrite-like nanostructures (DGNs) on the GC-GNs-Th surface, constructing GC-GNs-Th-GOx and GC-GNs-Th-DGNs modified electrodes, respectively. The GC-GNs-Th-GOx biosensor exhibited a linear response range to glucose, from 0.5 to 6.0mM, with a limit of detection (LOD) of 9.6 μM and high sensitivity of 43.2 µAcm(-2)mM(-1). Also, the GC-GNs-Th-DGNs sensor showed a wide dynamic response range for NO2(-) ion with two linear parts, from 0.05 μM to 1.0 μM and 30.0 μM to 1.0mM, a sensitivity of 263.2 μAmM(-1) and a LOD of 0.01 μM. Applicability of the modified electrodes was successfully tested by determination of glucose in human blood serum and nitrite in water based on addition/recovery tests.

  19. Characterization of Au/PbTi0.5Fe0.5O3/Si structure for possible multiferroic based non-volatile memory applications

    NASA Astrophysics Data System (ADS)

    Nawaz, S.; Roy, S.; Tulapurkar, A. A.; Palkar, V. R.

    2017-03-01

    Magnetoelectric multiferroic PbTi0.5Fe0.5O3 films are deposited on a ⟨100⟩ conducting p-Si substrate without any buffer layer by using pulsed laser deposition and characterized for possible non-volatile memory applications. Their crystalline structure and surface morphology were characterized by using x-ray diffraction and AFM techniques. HRTEM was employed to determine the film-substrate interface. The electronic structure of the film was investigated by XPS, and no signature of metal was found for all the elements. The chemical shift of the Ti 2p XPS peak is attributed to the replacement of Ti with Fe in the PbTiO3 matrix. Piezoelectric force microscopy (PFM) results indicate the 180° phase shift of ferroelectric polarization. The upward self-polarization phenomenon is also observed in the PFM study. Magnetic and magneto-electric coupling measurements were carried out to confirm the magnetic nature and electro-magnetic coupling characteristics. C-V measurements exhibit clock-wise hysteresis loops with a maximum memory window of 1.2 V and a sweep voltage of ±7 V. This study could influence the fabrication of silicon compatible multiple memory device structures.

  20. Spectroscopically forbidden infra-red emission in Au-vertical graphene hybrid nanostructures.

    PubMed

    Sivadasan, A K; Parida, Santanu; Ghosh, Subrata; Pandian, Ramanathaswamy; Dhara, Sandip

    2017-09-19

    Implementation of Au nanoparticles (NPs) is a subject for frontier plasmonic research due to its fascinating optical properties. Herein, the present study deals with plasmonic assisted emission properties of Au NPs-vertical graphene (VG) hybrid nanostructures. The influence of effective polarizability of Au NPs on the surface enhanced Raman scattering and luminescence properties is investigated. In addition, a remarkable infra-red (IR) emission in the hybrid nanostructures is observed and interpreted on the basis of intra-band transitions in Au NPs. The flake-like nanoporous VG structure is invoked for the generation of additional confined photons to impart additional momentum and a gradient of confined excitation energy towards initiating the intra-band transitions of Au NPs. Integrating Au plasmonic materials in three-dimensional VG nanostructures enhances the light-matter interactions. The present study provides a new adaptable plasmonic assisted pathway for optoelectronic and sensing applications. © 2017 IOP Publishing Ltd.

  1. Photoluminescence enhancement in few-layer WS{sub 2} films via Au nanoparticles

    SciTech Connect

    Choi, Sin Yuk; Yip, Cho Tung; Li, Guang-Can; Lei, Dang Yuan; Fung, Kin Hung; Yu, Siu Fung E-mail: jh.hao@polyu.edu.hk; Hao, Jianhua E-mail: jh.hao@polyu.edu.hk

    2015-06-15

    Nano-composites of two-dimensional atomic layered WS{sub 2} and Au nanoparticles (AuNPs) have been fabricated by sulfurization of sputtered W films followed by immersing into HAuCl{sub 4} aqueous solution. The morphology, structure and AuNPs distribution have been characterized by electron microscopy. The decorated AuNPs can be more densely formed on the edge and defective sites of triangle WS{sub 2}. We have compared the optical absorption and photoluminescence of bare WS{sub 2} and Au-decorated WS{sub 2} layers. Enhancement in the photoluminescence is observed in the Au-WS{sub 2} nano-composites, attributed to localized surface plasmonic effect. This work provides the possibility to develop photonic application in two-dimensional materials.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  3. Au nanoinjectors for electrotriggered gene delivery into the cell nucleus.

    PubMed

    Kang, Mijeong; Kim, Bongsoo

    2015-01-01

    Intracellular delivery of exogenous materials is an essential technique required for many fundamental biological researches and medical treatments. As our understanding of cell structure and function has been improved and diverse therapeutic agents with a subcellular site of action have been continuously developed, there is a demand to enhance the performance of delivering devices. Ideal intracellular delivery devices should convey various kinds of exogenous materials without deteriorating cell viability regardless of cell type and, furthermore, precisely control the location and the timing of delivery as well as the amount of delivered materials for advanced researches.In this chapter the development of a new intracellular delivery device, a nanoinjector made of a Au (gold) nanowire (a Au nanoinjector) is described in which delivery is triggered by external application of an electric pulse. As a model study, a gene was delivered directly into the nucleus of a neuroblastoma cell, and successful delivery without cell damage was confirmed by the expression of the delivered gene. The insertion of a Au nanoinjector directly into a cell can be generally applied to any kind of cell, and a high degree of surface modification of Au allows attachment of diverse materials such as proteins, small molecules, or nanoparticles as well as genes on Au nanoinjectors. This expands their applicability, and it is expected that they will provide important information on the effects of delivered exogenous materials and consequently contribute to the development of related therapeutic or clinical technologies.

  4. 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 > .

  5. 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.

  6. Au/Si Nanorod-Based Biosensor for Salmonella Detection

    USDA-ARS?s Scientific Manuscript database

    Among several potentials of nanotechnology applications for food industry, development of nanoscale sensors for food safety and quality measurement are emerging. A novel biosensor for Salmonella detection was developed using Au/Si/ nanorods. The Si nanorods were fabricated by glancing angle depositi...

  7. Nitrogen mineralization from 'AU Golden' sunn hemp residue

    USDA-ARS?s Scientific Manuscript database

    The tropical legume sunn hemp (Crotalaria juncea) cultivar ‘AU Golden’ has the potential to provide substantial amounts of nitrogen (N) to subsequent crops that could reduce recommended application rates of synthetic N fertilizers. Nitrogen fertilization problems via legumes are often due to asynch...

  8. Photogenerated charge carriers and reactive oxygen species in ZnO/Au hybrid nanostructures with enhanced photocatalytic and antibacterial activity.

    PubMed

    He, Weiwei; Kim, Hyun-Kyung; Wamer, Wayne G; Melka, David; Callahan, John H; Yin, Jun-Jie

    2014-01-15

    Semiconductor nanostructures with photocatalytic activity have the potential for many applications including remediation of environmental pollutants and use in antibacterial products. An effective way for promoting photocatalytic activity is depositing noble metal nanoparticles (NPs) on a semiconductor. In this paper, we demonstrated the successful deposition of Au NPs, having sizes smaller than 3 nm, onto ZnO NPs. ZnO/Au hybrid nanostructures having different molar ratios of Au to ZnO were synthesized. It was found that Au nanocomponents even at a very low Au/ZnO molar ratio of 0.2% can greatly enhance the photocatalytic and antibacterial activity of ZnO. Electron spin resonance spectroscopy with spin trapping and spin labeling was used to investigate the enhancing effect of Au NPs on the generation of reactive oxygen species and photoinduced charge carriers. Deposition of Au NPs onto ZnO resulted in a dramatic increase in light-induced generation of hydroxyl radical, superoxide and singlet oxygen, and production of holes and electrons. The enhancing effect of Au was dependent on the molar ratio of Au present in the ZnO/Au nanostructures. Consistent with these results from ESR measurements, ZnO/Au nanostructures also exhibited enhanced photocatalytic and antibacterial activity. These results unveiled the enhanced mechanism of Au on ZnO and these materials have great potential for use in water purification and antibacterial products.

  9. Suppression of Υ production in d + Au + and Au + Au collisions at √sNN =200 GeV

    DOE PAGES

    None

    2014-07-01

    We report measurements of Upsilon meson production in p + p, d +Au, and Au+Au collisions using the STAR detector at RHIC. We compare the Upsilon yield to the measured cross section in p + p collisions in order to quantify any modifications of the yield in cold nuclear matter using d +Au data and in hot nuclear matter using Au+Au data separated into three centrality classes. Our p +p measurement is based on three times the statistics of our previous result. We obtain a nuclear modification factor for Upsilon (1S + 2S + 3S) in the rapidity range |y|more » < 1 in d + Au collisions of RdAu = 0.79 ± 0.24(stat.) ± 0.03(syst.) ± 0.10(p + p syst.). A comparison with models including shadowing and initial state part on energy loss indicates the presence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au + Au collisions, we measure a nuclear modification factor of R AA = 0.49 ±0.1(stat.) ±0.02(syst.) ±0.06(p + p syst.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are consistent with complete suppression of excited-state Upsilon mesons in Au + Au collisions. The additional suppression in Au + Au is consistent with the level expected in model calculations that include the presence of a hot, deconfined Quark–Gluon Plasma. However, understanding the suppression seen in d + Au is still needed before any definitive statements about the nature of the suppression in Au + Au can be made.« less

  10. Optical Spectroscopy of AU Mon

    NASA Astrophysics Data System (ADS)

    Barría, D.; Mennickent, R. E.

    2011-09-01

    We have carried out a series of spectroscopic observations of the Double Periodic Variable system AU Monocerotis since 2008. Most data were taken at the DuPont telescope in Las Campanas Observatory using the Echelle spectrograph. We present preliminary results of our spectroscopic analysis of AU Mon. With an orbital period of 11.1 days and long period of 417 days, AU Mon is a bright galactic system (V = 8.4) formed by a Be-type primary (gainer) and a G-type secondary (donor). We show Balmer and Helium line profiles in different phases of the orbital and long period as diagnostic of mass loss processes and dynamics of the rotating gas envelope.

  11. 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.

  12. Graphene nanoribbons synthesized from molecular precursor polymerization on Au(110)

    SciTech Connect

    Massimi, Lorenzo; Ourdjini, Oualid; Della Pia, Ada; Mariani, Carlo; Betti, Maria Grazia; Cavaliere, Emanuele; Gavioli, Luca

    2015-06-23

    A spectroscopic study of 10,10-dibromo-9,9 bianthracene (DBBA) molecules deposited on the Au(110) surface is presented, by means of ultraviolet and X-ray photoemission, and X-ray absorption spectroscopy. Through a thermally activated procedure, these molecular precursors polymerize and eventually form graphene nanoribbons (GNRs) with atomically controlled shape and width, very important building blocks for several technological applications. The GNRs observed by scanning tunneling microscopy (STM) appear as short segments on top of the gold surface reconstruction, pointing out the delicate balance among surface diffusion and surface corrugation in their synthesis on the Au(110) surface.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Kumar, Santosh; Jin, Rongchao

    2012-06-01

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

  15. The adsorption of CO on charged and neutral Au and Au2: a comparison between wave-function based and density functional theory.

    PubMed

    Schwerdtfeger, Peter; Lein, Matthias; Krawczyk, Robert P; Jacob, Christoph R

    2008-03-28

    Quantum theoretical calculations are presented for CO attached to charged and neutral Au and Au(2) with the aim to test the performance of currently applied density functional theory (DFT) by comparison with accurate wave-function based results. For this, we developed a compact sized correlation-consistent valence basis set which accompanies a small-core energy-consistent scalar relativistic pseudopotential for gold. The properties analyzed are geometries, dissociation energies, vibrational frequencies, ionization potentials, and electron affinities. The important role of the basis-set superposition error is addressed which can be substantial for the negatively charged systems. The dissociation energies decrease along the series Au(+)-CO, Au-CO, and Au(-)-CO and as well as along the series Au(2)(+)-CO, Au(2)-CO, and Au(2)(-)-CO. As one expects, a negative charge on gold weakens the carbon oxygen bond considerably, with a consequent redshift in the CO stretching frequency when moving from the positively charged to the neutral and the negatively charged gold atom or dimer. We find that the different density functional approximations applied are not able to correctly describe the rather weak interaction between CO and gold, thus questioning the application of DFT to CO adsorption on larger gold clusters or surfaces.

  16. Slow Relaxation of Surface Plasmon Excitations in Au55: The Key to Efficient Plasmonic Heating in Au/TiO2.

    PubMed

    Ranasingha, Oshadha; Wang, Hong; Zobač, Vladimír; Jelínek, Pavel; Panapitiya, Gihan; Neukirch, Amanda J; Prezhdo, Oleg V; Lewis, James P

    2016-04-21

    Gold nanoparticles distinguish themselves from other nanoparticles due to their unique surface plasmon resonance properties that can be exploited for a multiplicity of applications. The promise of plasmonic heating in systems of Au nanoparticles on transition metal oxide supports, for example, Au/TiO2, rests with the ability of the surface plasmon in Au nanoparticles to effectively transfer energy into the transition metal oxide. Here, we report a critical observation regarding Au nanoparticle (Au55) surface plasmon excitations, that is, the relaxation of the surface plasmon excitation is very slow, on the order of several picoseconds. Starting from five plasmon states in Au55 nanoparticles using nonadiabatic molecular dynamics simulations, we find that the relaxation time constant resulting from these simulations is ∼6.8 ps, mainly resulting from a long-lived intermediate state found at around -0.8 eV. This long-lived intermediate state aligns with the conduction band edge of TiO2, thereby facilitating energy transfer injection from the Au55 nanoparticle into the TiO2. The current results rule out the previously reported molecular-like relaxation dynamics for Au55.

  17. 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.

  18. Surfactant assisted Au nanoparticle layering in titanium oxide thin films

    NASA Astrophysics Data System (ADS)

    Mukherjee, Smita; Das, Pradip Shekhar; Choudhuri, Madhumita; Datta, Alokmay; Ghosh, Jiten; Mukhopadhyay, Anoop Kr.

    2017-05-01

    Au Nanoparticle (NP) decorated TiO2 thin films, prepared by a unique surfactant assisted 2D self-assembling technique with molecular level control, showed significant decrease in optical band gap as well as enhanced crystallinity compared to its sol-gel prepared pristine counterpart. Spin coated Au NP overlayers on titania in absence of surfactant, on the other hand, had no appreciable effect on either band gap or crystal structure compared to undoped TiO2 films. Apart from exhibiting band gap tuning of TiO2, this cheap, scalable technique of surfactant aided deposition of 2D layers of Au NPs on semiconducting oxides, may be used for development of multilayered structures with promising light harvesting and unidirectional energy transfer (LUET) applications.

  19. 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.

  20. Crystallography of Martensite in TiAu Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Inamura, T.; Hosoda, H.

    2011-01-01

    The twin structure, habit plane orientation, and morphology of B19 martensite in TiAu, which is a candidate shape memory alloy (SMA) for high-temperature and biomedical applications, were investigated by conventional transmission electron microscopy. Almost all internal twins were {111} type I twins as lattice-invariant deformation (LID). The <211> type II twin was scarcely observed in TiAu, unlike in TiPd and TiPt SMAs. The habit plane roughly corresponded to the twinning plane ( K 1 plane) of the <211> type II twin because of the superb lattice parameter ratio of TiAu. As a result, an energy-minimizing microstructure referred to as "twins within twins" appears as the major microstructure. The selection rules for the twinning of LID are also discussed considering the results of extensive studies on LID in SMAs.

  1. New systematic features in the neutron-deficient Au isotopes

    NASA Astrophysics Data System (ADS)

    Venhart, M.; Wood, J. L.; Sedlák, M.; Balogh, M.; Bírová, M.; Boston, A. J.; Cocolios, T. E.; Harkness-Brennan, L. J.; Herzberg, R.-D.; Holub, L.; Joss, D. T.; Judson, D. S.; Kliman, J.; Klimo, J.; Krupa, L.; Lušnák, J.; Makhathini, L.; Matoušek, V.; Motyčák, Š.; Page, R. D.; Patel, A.; Petrík, K.; Podshibyakin, A. V.; Prajapati, P. M.; Rodin, A. M.; Špaček, A.; Urban, R.; Unsworth, C.; Veselský, M.

    2017-07-01

    A recently developed portable, on-line capability for γ-ray and conversion-electron spectroscopy, HIGH-TATRA is demonstrated with its application to the study of 183Hg \\to 183Au at ISOLDE. Key details of the low-energy level scheme of the neutron-deficient nuclide 183Au populated in this decay are presented. A broad energy germanium detector is employed to achieve this (the first-ever use of such a device in decay-scheme spectroscopy), by way of a combination of high-gain γ-ray singles spectroscopy and γ–γ coincidence spectroscopy. Further, by combining the γ-ray detectors with a liquid-nitrogen-cooled Si(Li) detector operated under high vacuum, conversion-electron singles and e–γ coincidences are obtained. These data lead to the determination of transition multipolarities and the location of a highly converted (E0 + M1 + E2) transition in the 183Au decay scheme, suggesting a possible new shape coexisting structure in this nucleus. Identification of new intruder and normal states fixes their relative energies in 183Au for the first time. New systematic features in the odd-Au isotopes are presented.

  2. CeO2-modified Au@SBA-15 nanocatalysts for liquid-phase selective oxidation of benzyl alcohol

    NASA Astrophysics Data System (ADS)

    Wang, Tuo; Yuan, Xiang; Li, Shuirong; Zeng, Liang; Gong, Jinlong

    2015-04-01

    Tuning the interfacial perimeter and structure is crucial to understanding the origin of catalytic performance. This paper describes the design, characterization, and application of CeO2 modified Au@SBA-15 (Au-CeO2@SBA-15) catalysts in selective oxidation of benzyl alcohol. The reaction results showed that Au-CeO2@SBA-15 catalysts exhibited higher catalytic activity compared with Au@SBA-15 and Au/CeO2 catalysts under identical conditions along with the high selectivity towards benzaldehyde (>99%). The turnover frequency of benzyl alcohol over the Au-100CeO2@SBA-15 catalyst is about nine-fold and four-fold higher than those of Au@SBA-15 and Au/CeO2 catalysts, respectively. The supported catalysts were characterized by N2 adsorption-desorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, scanning transmission electron microscopy-energy dispersive spectrometry, and X-ray photoelectron spectroscopy. It was found that the Au and small CeO2 nanoparticles (~5 nm) were homogeneously mixed in the channels of SBA-15, which led to an increase in the interfacial area between Au and CeO2 and consequently a better catalytic performance of Au-CeO2@SBA-15 catalysts for the selective oxidation of benzyl alcohol to benzaldehyde compared with that of Au/CeO2. The prevention of agglomeration and leaching of Au nanoparticles by restricting them inside the mesopores of SBA-15 was conducive to the stable existence of large quantities of Au-CeO2 interface, which leads to high stability of the Au-CeO2@SBA-15 catalyst.Tuning the interfacial perimeter and structure is crucial to understanding the origin of catalytic performance. This paper describes the design, characterization, and application of CeO2 modified Au@SBA-15 (Au-CeO2@SBA-15) catalysts in selective oxidation of benzyl alcohol. The reaction results showed that Au-CeO2@SBA-15 catalysts

  3. Au-TiO(2) nanoscale heterodimers synthesis from an ambient spark discharge for efficient photocatalytic and photothermal activity.

    PubMed

    Byeon, Jeong Hoon; Kim, Young-Woo

    2014-01-22

    Ultrafine Au particles incorporating TiO2 heterodimers were synthesized using an ambient heterogeneous spark discharge and the resultant materials were employed both in oxidizing photocatalytically CO gas and killing photothermally cancerous cells. Ti-Au spark configuration was employed to vaporize Ti and Au components into an airflow and finally ultrafine Au particles (∼2 nm in lateral dimension) were incorporated with TiO2 nanoparticles in the form of Au-TiO2 heterodimers (∼38 nm in lateral dimension) with enhanced photocatalytic (in CO oxidation) and photothermal activity (in cancerous cell killing) under visible light. We propose that the localized surface plasmon resonance of ultrafine Au particles on TiO2 supports, induced by the visible light, would promote the adsorption-oxidation of CO and photothermal killing of HeLa cells. The present strategy may be suitable to fabricate other Au-metal oxide nanocomposites for catalytic and biomedical applications.

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

  5. A combined experimental and computational study of AuPd nanoparticles

    NASA Astrophysics Data System (ADS)

    Bruma, Alina

    The thesis is focused on the investigation of structural properties of AuPd nanoparticles via theoretical and experimental studies. For the first system, the 98-atom AuPd nanoclusters, a theoretical analysis has been employed to study the energetics and segregation effects and to assess how typical is the Leary Tetrahedron (LT). Although this motif is the most stable at the empirical level, it loses stability at the DFT level against FCC or Marks Decahedron. The second system is the Au24Pd1 nanoclusters. Theoretically, by performing a search at the DFT level using Basin Hopping Monte Carlo, we identified pyramidal cage structures as putative global minima, where Pd sits in the core and Au occupies surface positions. The Lowdin analysis emphasized charge transfer between Pd and Au, explaining the enhanced catalytic activity with respect to Au25 clusters. Experimentally, STEM has been employed for the structural characterization of Au24Pd1 clusters supported on Multiwall Carbon Nanotubes. Whenever possible, we have tried to link the experimental analysis to the theoretical findings. The third system has been the evaporated AuPd nanoparticles. We observed that the annealing process led to the formation of L12 ordered phases as well as layered and core-shell structures. This study aimed to bring an insight on the segregation and energetics effects of AuPd nanoparticles with potential applications in nanocatalysis.

  6. Facile synthesis of fluorescent Au/Ce nanoclusters for high-sensitive bioimaging.

    PubMed

    Ge, Wei; Zhang, Yuanyuan; Ye, Jing; Chen, Donghua; Rehman, Fawad Ur; Li, Qiwei; Chen, Yun; Jiang, Hui; Wang, Xuemei

    2015-02-03

    Tumor-target fluorescence bioimaging is an important means of early diagnosis, metal nanoclusters have been used as an excellent fluorescent probe for marking tumor cells due to their targeted absorption. We have developed a new strategy for facile synthesis of Au/Ce nanoclusters (NCs) by doping trivalent cerium ion into seed crystal growth process of gold. Au/Ce NCs have bright fluorescence which could be used as fluorescent probe for bioimaging. In this study, we synthesized fluorescent Au/Ce NCs through two-step hydrothermal reaction. The concentration range of 25-350 μM, Au/Ce NCs have no obvious cell cytotoxicity effect on HeLa, HepG2 and L02 cells. Furthermore, normal cells (L02) have no obvious absorption of Au/Ce NCs. Characterization of synthesized Au/Ce NCs was done by using TEM, EDS and XPS. Then these prepared Au/Ce NCs were applied for in vitro/in vivo tumor-target bioimaging due to its prolonged fluorescence lifetime and bright luminescence properties. The glutathione stabilized Au/Ce NCs synthesized through hydrothermal reaction possess stable and bright fluorescence that can be readily utilized for high sensitive fluorescence probe. Our results suggest that Au/Ce NCs are useful candidate for in vitro/in vivo tumor bioimaging in potential clinical application.

  7. Photoneutron cross sections for Au

    SciTech Connect

    Itoh, O.; Utsunomiya, H.; Akimune, H.; Yamagata, T.; Kondo, T.; Kamata, M.; Toyokawa, H.; Harada, H.; Kitatani, F.; Goko, S.; Nair, C.; Lui, Y.-W.

    2011-10-28

    Photoneutron cross sections were measured for Au in the entire energy range of the ({gamma},n) channel based on a direct neutron-counting technique with quasimonochromatic {gamma} rays produced in inverse Compton-scattering of laser photons with relativistic electrons. We present results of the measurement in comparison with the past data.

  8. Biological synthesis of Au nanoparticles using liquefied mash of cassava starch and their functionalization for enhanced hydrolysis of xylan by recombinant xylanase.

    PubMed

    Zeng, Sumei; Du, Liangwei; Huang, Meiying; Feng, Jia-Xun

    2016-05-01

    Au nanoparticles (AuNPs) have shown the potential for a variety of applications due to their unique physical and chemical properties. In this study, a facile and affordable method for the synthesis of AuNPs via the liquefied mash of cassava starch has been described and the functionalized AuNPs by L-cysteine improved activity of recombinant xylanase was demonstrated. UV-Vis absorption spectroscopy, transmission electron microscopy, and zeta potential measurements were performed to characterize the AuNPs and monitor their synthesis. The presence of Au was confirmed by energy-dispersive X-ray spectroscopy (EDX) and the X-ray diffraction patterns showed that Au nanocrystals were face-centered cubic. The C=O stretching vibration in the Fourier transform infrared spectrum of AuNPs suggested that the hemiacetal C-OH of sugar molecules performed the reduction of Au³⁺ to Au⁰. The presence of C and O in the EDX spectrum and the negative zeta potential of AuNPs suggested that the biomolecules present in liquefied cassava mash were responsible for the stabilization of AuNPs. The surface of AuNPs was easily functionalized by L-cysteine, which improved the stability of AuNPs. Moreover, cysteine-functionalized AuNPs could significantly improve recombinant xylanase efficiency and stability.

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

    SciTech Connect

    Ruqian Wu

    2012-05-18

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

  10. CeO2-modified Au@SBA-15 nanocatalysts for liquid-phase selective oxidation of benzyl alcohol.

    PubMed

    Wang, Tuo; Yuan, Xiang; Li, Shuirong; Zeng, Liang; Gong, Jinlong

    2015-05-07

    Tuning the interfacial perimeter and structure is crucial to understanding the origin of catalytic performance. This paper describes the design, characterization, and application of CeO2 modified Au@SBA-15 (Au-CeO2@SBA-15) catalysts in selective oxidation of benzyl alcohol. The reaction results showed that Au-CeO2@SBA-15 catalysts exhibited higher catalytic activity compared with Au@SBA-15 and Au/CeO2 catalysts under identical conditions along with the high selectivity towards benzaldehyde (>99%). The turnover frequency of benzyl alcohol over the Au-100CeO2@SBA-15 catalyst is about nine-fold and four-fold higher than those of Au@SBA-15 and Au/CeO2 catalysts, respectively. The supported catalysts were characterized by N2 adsorption-desorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, scanning transmission electron microscopy-energy dispersive spectrometry, and X-ray photoelectron spectroscopy. It was found that the Au and small CeO2 nanoparticles (∼5 nm) were homogeneously mixed in the channels of SBA-15, which led to an increase in the interfacial area between Au and CeO2 and consequently a better catalytic performance of Au-CeO2@SBA-15 catalysts for the selective oxidation of benzyl alcohol to benzaldehyde compared with that of Au/CeO2. The prevention of agglomeration and leaching of Au nanoparticles by restricting them inside the mesopores of SBA-15 was conducive to the stable existence of large quantities of Au-CeO2 interface, which leads to high stability of the Au-CeO2@SBA-15 catalyst.

  11. 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.

  12. 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

  13. Dewetting process of Au films on SiO2 nanowires: Activation energy evaluation

    NASA Astrophysics Data System (ADS)

    Ruffino, F.; Grimaldi, M. G.

    2015-05-01

    SiO2 nanowires gain scientific and technological interest in application fields ranging from nano-electronics, optics and photonics to bio-sensing. Furthermore, the SiO2 nanowires chemical and physical properties, and so their performances in devices, can be enhanced if decorated by metal nanoparticles (such Au) due to local plasmonic effects. In the present paper, we propose a simple, low-cost and high-throughput three-steps methodology for the mass-production of Au nanoparticles coated SiO2 nanowires. It is based on (1) production of the SiO2 nanowires on Si surface by solid state reaction of an Au film with the Si substrate at high temperature; (2) sputtering deposition of Au on the SiO2 nanowires to obtain the nanowires coated by an Au film; and (3) furnace annealing processes to induce the Au film dewetting on the SiO2 nanowires surface. Using scanning electron microscopy analyses, we followed the change of the Au nanoparticles mean versus the annealing time extracting values for the characteristic activation energy of the dewetting process of the Au film on the SiO2 nanowires surface. Such a study can allow the tuning of the nanowires/nanoparticles sizes for desired technological applications.

  14. Spiral Patterning of Au Nanoparticles on Au Nanorod Surface to Form Chiral AuNR@AuNP Helical Superstructures Templated by DNA Origami.

    PubMed

    Shen, Chenqi; Lan, Xiang; Zhu, Chenggan; Zhang, Wei; Wang, Leyu; Wang, Qiangbin

    2017-02-20

    Plasmonic motifs with precise surface recognition sites are crucial for assembling defined nanostructures with novel functionalities and properties. In this work, a unique and effective strategy is successfully developed to pattern DNA recognition sites in a helical arrangement around a gold nanorod (AuNR), and a new set of heterogeneous AuNR@AuNP plasmonic helices is fabricated by attaching complementary-DNA-modified gold nanoparticles (AuNPs) to the predesigned sites on the AuNR surface. AuNR is first assembled to one side of a bifacial rectangular DNA origami, where eight groups of capture strands are selectively patterned on the other side. The subsequently added link strands make the rectangular DNA origami roll up around the AuNR into a tubular shape, therefore giving birth to a chiral patterning of DNA recognition sites on the surface of AuNR. Following the hybridization with the AuNPs capped with the complementary strands to the capture strands on the DNA origami, left-handed and right-handed AuNR@AuNP helical superstructures are precisely formed by tuning the pattern of the recognition sites on the AuNR surface. Our strategy of nanoparticle surface patterning innovatively realizes hierarchical self-assembly of plasmonic superstructures with tunable chiroptical responses, and will certainly broaden the horizon of bottom-up construction of other functional nanoarchitectures with growing complexity.

  15. New Structure Model of Au22(SR)18: Bitetrahederon Golden Kernel Enclosed by [Au6(SR)6] Au(I) Complex.

    PubMed

    Pei, Yong; Tang, Jian; Tang, Xianqiong; Huang, Yunqing; Zeng, Xiao Cheng

    2015-04-16

    The study of atomic structure of thiolate-protected gold with decreased core size is important to explore the structural evolution from Au(I) complex to Au nanoclusters. In this work, we theoretically predicted the structure of recently synthesized four valence electron (4e) Au22(SR)18 cluster. The Au22(SR)18 cluster is proposed to possess a bitetrahedron Au7 kernel that is surrounded by a unique [Au6(SR)6] Au(I) complex and three Au3(SR)4 staple motifs. More interestingly, the Au22(SR)18 exhibits structural connections with Au24(SR)20 and Au20(SR)16. The stability of Au22(SR)18 can be understood from the superatom electronic configuration of the Au kernel as well as the formation of superatomic network. The present study can offer new insight into the structural evolution as well as electronic structure of thiolate-protected Au nanoclusters.

  16. Evolution of Self-Assembled Au NPs by Controlling Annealing Temperature and Dwelling Time on Sapphire (0001).

    PubMed

    Lee, Jihoon; Pandey, Puran; Sui, Mao; Li, Ming-Yu; Zhang, Quanzhen; Kunwar, Sundar

    2015-12-01

    Au nanoparticles (NPs) have been utilized in a wide range of device applications as well as catalysts for the fabrication of nanopores and nanowires, in which the performance of the associated devices and morphology of nanopores and nanowires are strongly dependent on the size, density, and configuration of the Au NPs. In this paper, the evolution of the self-assembled Au nanostructures and NPs on sapphire (0001) is systematically investigated with the variation of annealing temperature (AT) and dwelling time (DT). At the low-temperature range between 300 and 600 °C, three distinct regimes of the Au nanostructure configuration are observed, i.e., the vermiform-like Au piles, irregular Au nano-mounds, and Au islands. Subsequently, being provided with relatively high thermal energy between 700 and 900 °C, the round dome-shaped Au NPs are fabricated based on the Volmer-Weber growth model. With the increased AT, the size of the Au NPs is gradually increased due to a more favorable surface diffusion while the density is gradually decreased as a compensation. On the other hand, with the increased DT, the size and density of Au NPs decrease due to the evaporation of Au at relatively high annealing temperature at 950 °C.

  17. Onset of nuclear matter expansion in Au+Au collisions

    NASA Astrophysics Data System (ADS)

    Crochet, P.; Rami, F.; Gobbi, A.; Dona, R.; Coffin, J. P.; Fintz, P.; Guillaume, G.; Jundt, F.; Kuhn, C.; Roy, C.; de Schauenburg, B.; Tizniti, L.; Wagner, P.; Alard, J. P.; Amouroux, V.; Andronic, A.; Basrak, Z.; Bastid, N.; Belyaev, I.; Best, D.; Biegansky, J.; Buta, A.; Čaplar, R.; Cindro, N.; Dupieux, P.; Dželalija, M.; Fan, Z. G.; Fodor, Z.; Fraysse, L.; Freifelder, R. P.; Berrmann, N.; Hildenbrand, K. D.; Hong, B.; Jeong, S. C.; Kecskemeti, J.; Kirejczyk, M.; Koncz, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Manko, V.; Moisa, D.; Mösner, J.; Neubert, W.; Pelte, D.; Petrovici, M.; Pinkenburg, C.; Pras, P.; Ramillien, V.; Reisdorf, W.; Ritman, J. L.; Sadchikov, A. G.; Schüll, D.; Seres, Z.; Sikora, B.; Simion, V.; Siwek-Wilczyńska, K.; Sodan, U.; Teh, K. M.; Trzaska, M.; Vasiliev, M.; Wang, G. S.; Wessels, J. P.; Wienold, T.; Wisniewski, K.; Wohlfarth, D.; Zhilin, A.; FOPI Collaboration

    1997-02-01

    Using the FOPI detector at GSI Darmstadt, excitation functions of collective flow components were measured for the Au+Au system, in the reaction plane and out of this plane, at seven incident energies ranging from 100 A MeV to 800 A MeV. The threshold energies, corresponding to the onset of sideward-flow (balance energy) and squeeze-out effect (transition energy), are extracted from extrapolations of these excitation functions toward lower beam energies for charged products with Z ⩾ 2. The transition energy is found to be larger than the balance energy. The impact parameter dependence of both balance and transition energies, when extrapolated to central collisions, suggests comparable although slightly higher values than the threshold energy for the radial flow. The relevant parameter seems to be the energy deposited into the system in order to overcome the attractive nuclear forces.

  18. Global polarization measurement in Au+Au collisions

    SciTech Connect

    Abelev, B.I.; Adams, J.; Aggarwal, M.M.; Ahammed, Z.; Amonett,J.; Anderson, B.D.; Anderson, M.; Arkhipkin, D.; Averichev, G.S.; Bai,Y.; Balewski, J.; Barannikova, O.; Barnby, L.S.; Baudot, J.; Bekele, S.; Belaga, V.V.; Bellingeri-Laurikainen, A.; Bellwied, R.; Benedosso, F.; Bhardwaj, S.; Bhasin, A.; Bhati, A.K.; Bichsel, H.; Bielcik, J.; Bielcikova, J.; Bland, L.C.; Blyth, S.-L.; Bonner, B.E.; Botje, M.; Bouchet, J.; Brandin, A.V.; Bravar, A.; Bystersky, M.; Cadman, R.V.; Cai,X.Z.; Caines, H.; Calderon de la Barca Sanchez, M.; Castillo, J.; Catu,O.; Cebra, D.; Chajecki, Z.; Chaloupka, P.; Chattopadhyay, S.; Chen,H.F.; Chen, J.H.; Cheng, J.; Cherney, M.; Chikanian, A.; Christie, W.; Coffin, J.P.; Cormier, T.M.; Cosentino, M.R.; Cramer, J.G.; Crawford,H.J.; Das, D.; Das, S.; Daugherity, M.; de Moura, M.M.; Dedovich, T.G.; DePhillips, M.; Derevschikov, A.A.; Didenko, L.; Dietel, T.; Djawotho,P.; Dogra, S.M.; Dong, W.J.; Dong, X.; Draper, J.E.; Du, F.; Dunin, V.B.; Dunlop, J.C.; Dutta Mazumdar, M.R.; Eckardt, V.; Edwards, W.R.; Efimov,L.G.; Emelianov, V.; Engelage, J.; Eppley, G.; Erazmus, B.; Estienne, M.; Fachini, P.; Fatemi, R.; Fedorisin, J.; Filimonov, K.; Filip, P.; Finch,E.; Fine, V.; Fisyak, Y.; Fu, J.; Gagliardi, C.A.; Gaillard, L.; Ganti,M.S.; Ghazikhanian, V.; Ghosh, P.; Gonzalez, J.S.; Gorbunov, Y.G.; Gos,H.; Grebenyuk, O.; Grosnick, D.; Guertin, S.M.; Guimaraes, K.S.F.F.; Guo,Y.; Gupta, N.; Gutierrez, T.D.; Haag, B.; Hallman, T.J.; Hamed, A.; Harris, J.W.; He, W.; Heinz, M.; Henry, T.W.; Hepplemann, S.; Hippolyte,B.; Hirsch, A.; Hjort, E.; Hoffman, A.M.; Hoffmann, G.W.; Horner, M.J.; Huang, H.Z.; Huang, S.L.; Hughes, E.W.; Humanic, T.J.; Igo, G.; Jacobs,P.; Jacobs, W.W.; Jakl, P.; Jia, F.; Jiang, H.; Jones, P.G.; Judd, E.G.; Kabana, S.; Kang, K.; Kapitan, J.; Kaplan, M.; Keane, D.; Kechechyan, A.; Khodyrev,V.Yu.; Kim, B.C.; Kiryluk, J.; Kisiel, A.; Kislov, E.M.; Klein,S.R.; Kocoloski, A.; Koetke, D.D.; et al.

    2007-08-02

    The system created in non-central relativisticnucleus-nucleus collisions possesses large orbital angular momentum. Dueto spin-orbit coupling, particles produced in such a system could becomeglobally polarized along the direction of the system angular momentum. Wepresent the results of Lambda and anti-Lambda hyperon global polarizationmeasurements in Au+Au collisions at sqrt sNN=62.4 GeV and 200 GeVperformed with the STAR detector at RHIC. The observed globalpolarization of Lambda and anti-Lambda hyperons in the STAR acceptance isconsistent with zero within the precision of the measurements. Theobtained upper limit, lbar P Lambda, anti-Lambda rbar<= 0.02, iscompared to the theoretical values discussed recently in theliterature.

  19. Universality in fragment inclusive yields from Au+Au collisions

    NASA Astrophysics Data System (ADS)

    Insolia, A.; Tuvè, C.; Albergo, S.; Bieser, F.; Brady, F. P.; Caccia, Z.; Cebra, D.; Chacon, A. D.; Chance, J. L.; Choi, Y.; Costa, S.; Elliott, J. B.; Gilkes, M.; Hauger, J. A.; Hirsch, A. S.; Hjort, E. L.; Justice, M.; Keane, D.; Kintner, J.; Lisa, M.; Matis, H. S.; McMahan, M.; McParland, C.; Olson, D. L.; Partlan, M. D.; Porile, N. T.; Potenza, R.; Rai, G.; Rasmussen, J.; Ritter, H. G.; Romero, J. L.; Russo, G. V.; Scharenberg, R.; Scott, A.; Shao, Y.; Srivastava, B. K.; Symons, T. J. M.; Tincknell, M. L.; Wang, S.; Warren, P. G.; Wieman, H. H.; Wolf, K. L.

    2001-11-01

    The inclusive light fragment (Z⩽7) yield data in Au+Au reactions, measured by the EOS Collaboration at the LBNL Bevalac, are presented and discussed. For peripheral collisions the measured charge distributions develop progressively according to a power law which can be fitted by a single τ exponent independently of the bombarding energy in the range 250-1200 A MeV. In addition to this universal feature, we observe that the location of the maximum in the individual yields of different charged fragments shift towards lower multiplicity as the fragment charge increases from Z=3 to Z=7. This trend is common to all six measured beam energies. Moments of charge distributions and correlations among different moments are reported. Finally, the THe,DT thermometer has been constructed for central and peripheral collisions using the double yield ratios of He and D, T projectile fragments. The measured nuclear temperatures are in agreement with experimental findings in other fragmentation reactions.

  20. Successful synthesis and thermal stability of immiscible metal Au-Rh, Au-Ir and Au-Ir-Rh nanoalloys.

    PubMed

    Shubin, Yury; Plusnin, Pavel; Sharafutdinov, Marat; Makotchenko, Evgenia; Korenev, Sergey

    2017-04-06

    We successfully prepared face-centred cubic nanoalloys in systems of Au-Ir, Au-Rh and Au-Ir-Rh, with large bulk miscibility gaps, in one-run reactions under thermal decomposition of specially synthesised single-source precursors, namely, [AuEn2][Ir(NO2)6], [AuEn2][Ir(NO2)6]х[Rh(NO2)6]1-х and [AuEn2][Rh(NO2)6]. The precursors employed contain all desired metals "mixed" at the molecular level, thus providing significant advantages for obtaining alloys. The observations using HR TEM show that the nanoalloy structures are composed of well-dispersed aggregates of crystalline domains with a mean size of 5±3 nm. EDX and XRD measurements confirm the formation of AuIr, AuRh, AuIr0.75Rh0.25, AuIr0.50Rh0.50 and AuIr0.25Rh0.75 metastable solid solutions. In-situ real-time synchrotron XRD was used to study the formation mechanism of nanoalloys. The observed transformations are described by the "conversion chemistry" mechanism characterised by the primary development of particles comprising atoms of only one type, followed by a chemical reaction resulting in the final formation of a nanoalloy. The obtained metastable nanoalloys exhibit essential thermal stability. Exposure to 180 ºC for 30 h does not cause any dealloying process.

  1. Theoretical prediction of thermodynamic activities of liquid Au-Sn-X (X=Bi, Sb, Zn) solder systems

    NASA Astrophysics Data System (ADS)

    Awe, O. E.; Oshakuade, O. M.

    2017-02-01

    Molecular interaction volume model has been theoretically used to predict the thermodynamic activities of tin in Au-Sn-Bi and Au-Sn-Sb and the thermodynamic activity of zinc in Au-Sn-Zn at experimental temperatures 800 K, 873 K and 973 K, respectively. On the premise of agreement between the predicted and experimental values, we predicted the activities of the remaining two components in each of the three systems. This prediction was extended from three cross-sections to five cross-sections, and to temperature range 400-600 K, relevant for applications. Iso-activities were plotted. Results show that addition of tin reduces the tendency for chemical short range order in both Au-Sb and Au-Zn systems, while addition of gold and bismuth, respectively, reduce the tendency for chemical short range order in Sn-Sb and Au-Sn systems. Also, we found that, in the desired high-temperature region for applications, while a combination of chemical order and miscibility of components exist in both Au-Sn-Bi and Au-Sn-Zn systems, only chemical order exist in the Au-Sn-Sb system. Results, further show that increase in temperature reduces the phase separation tendency in Au-Sn-Bi system.

  2. Co-Determination of Crystal Structures at High Pressure: Combined Application of Theory and Experiment to the AuGa2 Intermetallic analog to High-Pressure SiO2

    NASA Astrophysics Data System (ADS)

    Godwal, B. K.; Stackhouse, S.; Yan, J.; Speziale, S.; Militzer, B.; Jeanloz, R.

    2012-12-01

    The intermetallic compounds AuX2 (X = In, Ga, Al) crystallize in the calcium fluorite (CaF2) structure, making them analogs for SiO2 at TPa pressures. A combination of high-pressure x-ray diffraction experiments and first-principles calculations reveals the sequence of crystal-structural phase transitions in AuGa2 from cubic (Fm3m) to orthorhombic (Pnma) at 10 (± 4) GPa, and then to monoclinic (P21/n) at 33 (± 6) GPa. The post-cotunnite (P1121/a) phase identified as the final step in the phase-transition sequence for other AX2 compounds is found to be unstable. As the structural sequence followed by AuGa2 is similar to that observed in ACl2 (A = Pb, Sn) compounds it implies that AX2 compounds iso-structural to PbCl2 will acquire the monoclinic (P21/n) structure at extreme pressures. Neither theory nor experiment would have been adequate, on their own, in documenting this sequence of phases, but together they confirm a sequence differing from the Fm3m → Pnma → P63/mmc transitions predicted for CaF2, and observed for the intermetallic analog compounds AuIn2 and AuAl2 under pressure. Experimental [and theoretical] values of zero-pressure volume and bulk modulus are 224.5 (± 0.2) [219.5] Å3 and 81 (± 5) [95] GPa; 204.0 (± 1) [204.8] Å3 and 112 (± 12) [96] GPa; and 192 (± 4) [201.1] Å3 and 157 (± 5) [99] GPa for the cubic, orthorhombic and monoclinic phases, respectively.

  3. d + Au hadron correlation measurements at PHENIX

    SciTech Connect

    Anne M. Sickles

    2014-05-13

    In these proceedings, we discuss recent results from d + Au collisions in PHENIX ridge related measurements and their possible hydrodynamic origin. We present the v2 at midrapidity and measurements of the pseudorapidity dependence of the ridge, distinguishing between the d-going and Au-going directions. We investigate the possible geometrical origin by comparing v2 in d + Au to that in p + Pb, Au + Au and Pb + Pb collisions. Future plans to clarify the role of geometry in small collision systems at RHIC are discussed.

  4. Observation of dynamic water microadsorption on Au surface

    SciTech Connect

    Huang, Xiaokang Gupta, Gaurav; Gao, Weixiang; Tran, Van; Nguyen, Bang; McCormick, Eric; Cui, Yongjie; Yang, Yinbao; Hall, Craig; Isom, Harold

    2014-05-15

    Experimental and theoretical research on water wettability, adsorption, and condensation on solid surfaces has been ongoing for many decades because of the availability of new materials, new detection and measurement techniques, novel applications, and different scales of dimensions. Au is a metal of special interest because it is chemically inert, has a high surface energy, is highly conductive, and has a relatively high melting point. It has wide applications in semiconductor integrated circuitry, microelectromechanical systems, microfluidics, biochips, jewelry, coinage, and even dental restoration. Therefore, its surface condition, wettability, wear resistance, lubrication, and friction attract a lot of attention from both scientists and engineers. In this paper, the authors experimentally investigated Au{sub 2}O{sub 3} growth, wettability, roughness, and adsorption utilizing atomic force microscopy, scanning electron microscopy, reflectance spectrometry, and contact angle measurement. Samples were made using a GaAs substrate. Utilizing a super-hydrophilic Au surface and the proper surface conditions of the surrounding GaAs, dynamic microadsorption of water on the Au surface was observed in a clean room environment. The Au surface area can be as small as 12 μm{sup 2}. The adsorbed water was collected by the GaAs groove structure and then redistributed around the structure. A model was developed to qualitatively describe the dynamic microadsorption process. The effective adsorption rate was estimated by modeling and experimental data. Devices for moisture collection and a liquid channel can be made by properly arranging the wettabilities or contact angles of different materials. These novel devices will be very useful in microfluid applications or biochips.

  5. Direct chemical synthesis of L1(0)-FePtAu nanoparticles with high coercivity.

    PubMed

    Yu, Yongsheng; Mukherjee, P; Tian, Yuan; Li, X-Z; Shield, J E; Sellmyer, D J

    2014-10-21

    We report a facile synthesis of hard magnetic L10-FePtAu nanoparticles by coreduction of Fe(acac)3, Pt(acac)2 (acac = acetylacetonate) and gold acetate in oleylamine. In the current reaction condition, NP sizes are controlled to be 5.5 to 11.0 nm by changing the amount of Au doping. When the Au composition in the NPs is higher than 14%, the hard magnetic NPs are directly obtained without any annealing. The highest coercivity of 12.15 kOe at room temperature could be achieved for the NPs with 32% Au doping, which is much higher than the coercivities reported by the previous studies on solution-synthesized FePt nanoparticles. The reported one-pot synthesis of L10-FePtAu NPs may help to build superstrong magnets for magnetic or data-storage applications.

  6. Electrotriggered, spatioselective, quantitative gene delivery into a single cell nucleus by Au nanowire nanoinjector.

    PubMed

    Yoo, Seung Min; Kang, Mijeong; Kang, Taejoon; Kim, Dong Min; Lee, Sang Yup; Kim, Bongsoo

    2013-06-12

    Delivery of bioactive materials into a cell is highly important in the study of cell biology and medical treatments. Ideal nanoinjectors should be able to deliver biomaterials with high spatial resolution while causing minimum cell damage. We developed a Au nanowire (NW) nanoinjector that has the thinnest diameter (100–150 nm) among the DNA delivering devices as well as optimum mechanical properties, minimizing cell damage. Well-defined (111) single-crystalline Au surface and high electric conductivity of a Au NW nanoinjector allow precisely timed and efficient electrochemical release of DNA molecules attached on a Au NW surface. Both linear DNA and plasmid DNA were delivered separately and showed successful expression. The Au NW nanoinjector would find important biomedical applications in the fields such as gene therapy, DNA vaccination, targeted drug delivery, and probe/control of cell signaling events.

  7. Optical readout of hydrogen storage in films of Au and Pd

    NASA Astrophysics Data System (ADS)

    Nishijima, Yoshiaki; Shimizu, Shogo; Kurihara, Keisuke; Hashimoto, Yoshikazu; Takahashi, Hajime; Balčytis, Armandas; Seniutinas, Gediminas; Okazaki, Shinji; Juodkazytė, Jurga; Iwasa, Takeshi; Taketsugu, Tetsuya; Tominaga, Yoriko; Juodkazis, Saulius

    2017-10-01

    For hydrogen sensor and storage applications, films of Au and Pd were (i) co-sputtered at different rates or (ii) deposited in a sequential layer-by-layer fashion on a cover glass. Peculiarities of hydrogen uptake and release were optically monitored using 1.3 micrometers wavelength light. Increase of optical transmission was observed for hydrogenated Pd-rich films of 10-30 nm thickness. Up to a three times slower hydrogen release took place as compared with the hydrogen uptake. Composition ratio of Au:Pd and thermal treatment of films provided control over the optical extinction changes and hydrogen uptake/release time constants. Higher uptake and release rates were observed in the annealed Au:Pd films as compared to those deposited at room temperature and were faster for the Au-richer films. Three main parameters relevant for sensors: sensitivity, selectivity, stability (reproducibility) are discussed together with the hydrogenation mechanism in Au:Pd alloys.

  8. Time-resolved optical sensing of oligonucleotide hybridization via Au colloidal nanoparticles.

    PubMed

    Liu, Gang L; Rodriguez, Victoria B; Lee, Luke P

    2005-11-01

    Au nanoparticles have distinctive absorption spectra whose peak position or particle plasmon resonance wavelength is highly sensitive to molecule adsorption on their surfaces. Spherical Au nanoparticles are surface-modified by amino-functionalized self-assembly-monolayer and used as optical probes in the fluorescence-label-free spectroscopic detection of sub-nanomole oligonucleotides. Time-resolved studies of the immobilization and hybridization of oligonucleotides on the surface of Au nanoparticles were carried out. By measuring peak shift of absorption spectra of the Au colloidal nanoparticles over time, the samples of 15 nM 20 mer target and mismatched oligonucleotides are distinguished by their different influences on the particle plasmon resonance wavelength. The approach presented in this paper extends the application of Au nanoparticles as the optical probe in oligonucleotide recognitions without prior sample labeling.

  9. Sugar determination via the homogeneous reduction of Au salts: a novel optical measurement.

    PubMed

    Scampicchio, Matteo; Fuenmayor, Carlos Alberto; Mannino, Saverio

    2009-07-15

    A novel optical assay for sugar determination based on the catalytic and biocatalytic growth of gold nanoparticles (AuNPs) is presented. The reaction of carbohydrates with these Au salts in alkaline media generates AuNPs at room temperature (RT) without the need for Au seeds in the solution or fibrous mesh. The optical properties of the resulting AuNPs relates to the total reducing sugar content of the samples analyzed. The development of such inexpensive optical assay was evaluated qualitatively and quantitatively on food beverages and honey samples. Its application can be of help to control the glucose content of the diet or easily extended in a host of industrial, biomedical and clinical fields.

  10. Generation of composite Au/TiO2 nanoparticles by pulsed laser ablation in aqueous media

    NASA Astrophysics Data System (ADS)

    Kawai, Shota; Mardis, Mardiansyah; Takada, Noriharu; Diono, Wahyu; Kanda, Hideki; Goto, Motonobu; Goto lab. Team

    2016-09-01

    Composite nanoparticles have been known for their potential applications in photocatalysis, medical and optical limiters. In particular, Au/TiO2 composite nanoparticles have attracted attention because of its remarkable properties. However, commonly Au/TiO2 composite nanoparticles are synthesized by chemical method using toxic precursor and reducing agents, and problems by their residue arised. Here, we examined a new synthesis method of composite nanoparticles by pulsed laser ablation (PLA) without any chemical agents, but only with distilled water. Au/TiO2 composite nanoparticles were obtained by PLA of Ti plate covered with Au and TiO2 nanoparticles, which were preliminarily synthesized by PLA in distilled water. The synthesized nanoparticles were characterized by using TEM, UV-vis absorption spectroscopy, dynamic light scattering and XRD. The TEM images showed that composite nanoparticles including Au-TiO2 core-shell nanoparticles were successfully generated with diameter around 100 nm.

  11. 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.

  12. Direct chemical synthesis of L10-FePtAu nanoparticles with high coercivity

    NASA Astrophysics Data System (ADS)

    Yu, Yongsheng; Mukherjee, P.; Tian, Yuan; Li, X.-Z.; Shield, J. E.; Sellmyer, D. J.

    2014-09-01

    We report a facile synthesis of hard magnetic L10-FePtAu nanoparticles by coreduction of Fe(acac)3, Pt(acac)2 (acac = acetylacetonate) and gold acetate in oleylamine. In the current reaction condition, NP sizes are controlled to be 5.5 to 11.0 nm by changing the amount of Au doping. When the Au composition in the NPs is higher than 14%, the hard magnetic NPs are directly obtained without any annealing. The highest coercivity of 12.15 kOe at room temperature could be achieved for the NPs with 32% Au doping, which is much higher than the coercivities reported by the previous studies on solution-synthesized FePt nanoparticles. The reported one-pot synthesis of L10-FePtAu NPs may help to build superstrong magnets for magnetic or data-storage applications.We report a facile synthesis of hard magnetic L10-FePtAu nanoparticles by coreduction of Fe(acac)3, Pt(acac)2 (acac = acetylacetonate) and gold acetate in oleylamine. In the current reaction condition, NP sizes are controlled to be 5.5 to 11.0 nm by changing the amount of Au doping. When the Au composition in the NPs is higher than 14%, the hard magnetic NPs are directly obtained without any annealing. The highest coercivity of 12.15 kOe at room temperature could be achieved for the NPs with 32% Au doping, which is much higher than the coercivities reported by the previous studies on solution-synthesized FePt nanoparticles. The reported one-pot synthesis of L10-FePtAu NPs may help to build superstrong magnets for magnetic or data-storage applications. Electronic supplementary information (ESI) available: Fig. S1 to S3. See DOI: 10.1039/c4nr02345e

  13. Structural and morphological peculiarities of hybrid Au/nanodiamond engineered nanostructures.

    PubMed

    Matassa, Roberto; Orlanducci, Silvia; Reina, Giacomo; Cassani, Maria Cristina; Passeri, Daniele; Terranova, Maria Letizia; Rossi, Marco

    2016-08-12

    Nanostructured Au nano-platelets have been synthesized from an Au(III) complex by growth process triggered by nanodiamond (ND). An electroless synthetic route has been used to obtain 2D Au/ND architectures, where individual nanodiamond particles are intimately embedded into face-centered cubic Au platelets. The combined use of high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED), was able to reveal the unusual organization of these hybrid nanoparticles, ascertaining the existence of preferential crystallographic orientations for both nanocrystalline species and highlighting their mutual locations. Detailed information on the sample microstructure have been gathered by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) of HR-TEM images, allowing us to figure out the role of Au defects, able to anchor ND crystallites and to provide specific sites for heteroepitaxial Au growth. Aggregates constituted by coupled ND and Au, represent interesting systems conjugating the best optoelectronics and plasmonics properties of the two different materials. In order to promote realistically the applications of such outstanding Au/ND materials, the cooperative mechanisms at the basis of material synthesis and their influence on the details of the hybrid nanostructures have to be deeply understood.

  14. Structural and morphological peculiarities of hybrid Au/nanodiamond engineered nanostructures

    PubMed Central

    Matassa, Roberto; Orlanducci, Silvia; Reina, Giacomo; Cassani, Maria Cristina; Passeri, Daniele; Terranova, Maria Letizia; Rossi, Marco

    2016-01-01

    Nanostructured Au nano-platelets have been synthesized from an Au(III) complex by growth process triggered by nanodiamond (ND). An electroless synthetic route has been used to obtain 2D Au/ND architectures, where individual nanodiamond particles are intimately embedded into face-centered cubic Au platelets. The combined use of high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED), was able to reveal the unusual organization of these hybrid nanoparticles, ascertaining the existence of preferential crystallographic orientations for both nanocrystalline species and highlighting their mutual locations. Detailed information on the sample microstructure have been gathered by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) of HR-TEM images, allowing us to figure out the role of Au defects, able to anchor ND crystallites and to provide specific sites for heteroepitaxial Au growth. Aggregates constituted by coupled ND and Au, represent interesting systems conjugating the best optoelectronics and plasmonics properties of the two different materials. In order to promote realistically the applications of such outstanding Au/ND materials, the cooperative mechanisms at the basis of material synthesis and their influence on the details of the hybrid nanostructures have to be deeply understood. PMID:27514638

  15. Ultrasensitive and recyclable SERS substrate based on Au-decorated Si nanowire arrays.

    PubMed

    Yang, Xiaoling; Zhong, Hua; Zhu, Yihua; Shen, Jianhua; Li, Chunzhong

    2013-10-21

    Metallic nanoparticle (NP) decorated silicon nanowire (SiNW) heterostructures show significant promise in enhanced optical and opto-electrical properties due to the coupling of surface plasmon to nanowires. Here, recyclable Au-decorated silicon nanowire arrays (Au-SiNWAs) as surface-enhanced Raman scattering (SERS) substrates were successfully fabricated by a simple galvanic displacement reaction. The influence of different average size and aggregation level of Au NPs on SERS activity was explored. The SERS activity of the substrates strongly depends on the average size and aggregation level of Au NPs on the surface of the SiNWs, and the most optimal size and separation of AuNPs on the SiNWs can be achieved by controlling the reaction time. The optimized Au-SiNWA substrate exhibits ultrahigh sensitivity with an enhancement factor of 10(9), and is able to detect the analyte molecule at a concentration as low as 10(-11) M. More importantly, the SERS substrate is recyclable, as enabled by a self-cleaning function due to UV light photocatalytic degradation of the analyte molecules. The high sensitivity and recyclability of the Au-SiNWA SERS substrate is demonstrated by the detection of a model molecule rhodamine B (RhB). Our studies show that the unique Au-SiNWA SERS substrates have significant potential to put SERS into wider application.

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

    NASA Astrophysics Data System (ADS)

    Reinke, Petra; Liu, Hui

    2007-03-01

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

  17. In Vitro Study of Influence of Au Nanoparticles on HT29 and SPEV Cell Lines

    NASA Astrophysics Data System (ADS)

    Pavlovich, Elena; Volkova, Nataliia; Yakymchuk, Elena; Perepelitsyna, Olena; Sydorenko, Michail; Goltsev, Anatoliy

    2017-08-01

    Cell culture models are excellent tools for potential toxicity of nanoparticles and fundamental investigations in cancer research. Thus, information about AuNP potential toxicity and effects on human health is necessary for the use of nanomaterials in clinical settings. The aim of our research is to examine the effects of AuNPs on the epithelial origin cell lines: continuous and oncogenic. Embryonic porcine kidney epithelial inoculated (SPEV) cell line and colorectal carcinoma cell line (HT29) were used. In the test cultures, the cell proliferation, necrosis/apoptosis, and multicellular spheroids generation were evaluated. We demonstrated that AuNP concentrations of 6-12 μg/ml reduced the proliferation of SPEV and HT29 cells and increased the cell number at early and late stages of apoptosis and necrosis. It was shown that small concentrations of AuNPs (1-3 μg/ml) stimulate multicellular spheroid formation by HT29 and SPEV cells. However, higher AuNP concentrations (6-12 μg/ml) had both cytotoxic and anti-cohesive effects on cell in suspension. The large sensitiveness to the action of AuNPs was shown by the line of HT29 (6 μg/ml) as compared to the SPEV cells (12 μg/ml). This experimental study of the effect of AuNPs on SPEV and HT29 cell lines will justify their further application in AuNP-mediated anticancer treatment.

  18. Structural and morphological peculiarities of hybrid Au/nanodiamond engineered nanostructures

    NASA Astrophysics Data System (ADS)

    Matassa, Roberto; Orlanducci, Silvia; Reina, Giacomo; Cassani, Maria Cristina; Passeri, Daniele; Terranova, Maria Letizia; Rossi, Marco

    2016-08-01

    Nanostructured Au nano-platelets have been synthesized from an Au(III) complex by growth process triggered by nanodiamond (ND). An electroless synthetic route has been used to obtain 2D Au/ND architectures, where individual nanodiamond particles are intimately embedded into face-centered cubic Au platelets. The combined use of high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED), was able to reveal the unusual organization of these hybrid nanoparticles, ascertaining the existence of preferential crystallographic orientations for both nanocrystalline species and highlighting their mutual locations. Detailed information on the sample microstructure have been gathered by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) of HR-TEM images, allowing us to figure out the role of Au defects, able to anchor ND crystallites and to provide specific sites for heteroepitaxial Au growth. Aggregates constituted by coupled ND and Au, represent interesting systems conjugating the best optoelectronics and plasmonics properties of the two different materials. In order to promote realistically the applications of such outstanding Au/ND materials, the cooperative mechanisms at the basis of material synthesis and their influence on the details of the hybrid nanostructures have to be deeply understood.

  19. Dendritic Au/TiO2 nanorod arrays for visible-light driven photoelectrochemical water splitting

    NASA Astrophysics Data System (ADS)

    Su, Fengli; Wang, Tuo; Lv, Rui; Zhang, Jijie; Zhang, Peng; Lu, Jianwei; Gong, Jinlong

    2013-09-01

    This paper describes the synthesis of TiO2 branched nanorod arrays (TiO2 BNRs) with plasmonic Au nanoparticles attached on the surface. Such Au/TiO2 BNR composites exhibit high photocatalytic activity in photoelectrochemical (PEC) water splitting. The unique structure of Au/TiO2 BNRs shows enhanced activity with a photocurrent of 0.125 mA cm-2 under visible light (>=420 nm) and 2.32 +/- 0.1 mA cm-2 under AM 1.5 G illumination (100 mW cm-2). The obtained photocurrent is comparable to the highest value ever reported. Furthermore, the Au/TiO2 BNRs achieve the highest efficiency of ~1.27% at a low bias of 0.50 V vs. RHE, indicating elevated charge separation and transportation efficiencies. The high PEC performance is mainly due to the plasmonic effect of Au nanoparticles, which enhances the visible light absorption, together with the large surface area, efficient charge separation and high carrier mobility of the TiO2 BNRs. The carrier density of Au/TiO2 BNRs is nearly 6 times higher than the pristine TiO2 BNRs as calculated by the Mott-Schottky plot. Based on the analysis by UV-Vis spectroscopy, electrochemical impedance spectroscopy, and photoluminescence, a mechanism was proposed to explain the high activity of Au/TiO2 BNRs in PEC water splitting. The capability of synthesizing highly visible light active Au/TiO2 BNR based photocatalysts is useful for solar conversion applications, such as PEC water splitting, dye-sensitized solar cells and photovoltaic devices.This paper describes the synthesis of TiO2 branched nanorod arrays (TiO2 BNRs) with plasmonic Au nanoparticles attached on the surface. Such Au/TiO2 BNR composites exhibit high photocatalytic activity in photoelectrochemical (PEC) water splitting. The unique structure of Au/TiO2 BNRs shows enhanced activity with a photocurrent of 0.125 mA cm-2 under visible light (>=420 nm) and 2.32 +/- 0.1 mA cm-2 under AM 1.5 G illumination (100 mW cm-2). The obtained photocurrent is comparable to the highest value ever

  20. Polarization properties of fluorescent BSA protected Au25 nanoclusters

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  1. Ultrafast Relaxation Dynamics of Au 38 (SC 2 H 4 Ph) 24 Nanoclusters and Effects of Structural Isomerism

    DOE PAGES

    Zhou, Meng; Tian, Shubo; Zeng, Chenjie; ...

    2016-12-22

    Structural isomerism in nanoparticles has recently emerged as a new topic and stimulated research interest because the atomic structures of ultrasmall nanoparticles may have great impact on their fundamental properties and applications. We report the correlation between ultrafast relaxation dynamics and atomic structures of two isomers of thiolate-protected Au38(SC2H4Ph)24. The bi-icosahedral Au38 (denoted as Au38Q) with a Au23 inner core in its atomic structure shows rapid decay (1.5 ps) followed by nanosecond relaxation to the ground state, whereas its structural isomer (Au38T) exhibits similar relaxation processes, but the rapid decay is accelerated by ~50% (1.0 ps). The picosecond relaxations inmore » both cases can be assigned to core–shell charge transfer or electronic rearrangement within the metal core. The acceleration of the fast decay in Au38T is ascribed to its unique core structure, which is made up of a mono-icosahedral Au13 capped by a Au12 tri-tetrahedron by sharing two atoms. Interestingly, coherent phonon emissions (25 cm–1 for Au38Q, 27 and 60 cm–1 for Au38T) are observed in both isomers with pumping in the NIR region. These results illustrate for the first time the importance of atomic structures in the photophysics of same sized gold nanoclusters.« less

  2. Factors Influencing the Stability of Au-Incorporated Metal-Oxide Supported Thin Films for Optical Gas Sensing

    DOE PAGES

    Baltrus, John P.; Holcomb, Gordon R.; Tylczak, Joseph H.; ...

    2017-02-24

    There is interest in using Au-nanoparticle incorporated oxide films as functional sensor layers for high-temperature applications in optical-based sensors for measurements in both highly-oxidizing and highly-reducing atmospheres at temperatures approaching 900°C-1000°C because of a relatively high melting temperature combined with the inert nature of Au nanoparticles. This study includes a systematic series of experiments and theoretical calculations targeted at further understanding stability of Au-nanoparticle incorporated TiO2 films as archetype sensing materials. A combination of thermodynamic modeling and long-term exposure tests were utilized to unambiguously determine that gas stream composition-dependent reactive evaporation of Au (to form predominately Au(g) or AuH(g), dependingmore » upon the environment) at the surface of the nanoparticles is the dominant mechanism for mass loss of Au. Primary factors dictating the rate of reactive evaporation, and hence the associated film stability, were determined to be the gas stream temperature and the concentration of H2, with the former playing a more significant role over the ranges of temperatures (700°C - 800°C) and H2 concentrations (1% to 29% H2 by volume) explored. The mitigation of Au-mass loss through reactive evaporation was also successfully demonstrated by depositing a SiO2 overlayer on the Au-nanoparticle embedded films to prevent direct Au-nanoparticle/vapor-phase contact.« less

  3. Controlled growth and multi-photon luminescence of hexagonal arrays of Au nanoparticles on anodic aluminum oxide templates

    SciTech Connect

    Li Jianbo; Yu Ying; Peng Xiaoniu; Yang Zhongjian; Zhou Li; Zhou Zhangkai

    2012-06-15

    Au nanoparticles were deposited onto anodic aluminum oxide (AAO) templates by using a rotating sputtering technique. Interestingly, hexagonal arrays of Au nanoparticles were obtained at an appropriate rotating rate and deposition time. Strong three-photon luminescence was observed from the hexagonally arrayed Au nanoparticles, which is attributed to the strong enhancements of local electromagnetic fields at both excitation and emission wavelengths. Our findings provide a new method to prepare Au nanoparticle arrays with large field enhancements and could have prospective applications in plasmonic nanodevices, such as surface-enhanced Raman scattering substrates, and biosensors.

  4. High-p(T) Tomography of d+Au and Au+Au at SPS, RHIC, and LHC.

    PubMed

    Vitev, Ivan; Gyulassy, Miklos

    2002-12-16

    The interplay of nuclear effects on the p(T)>2 GeV inclusive hadron spectra in d+Au and Au+Au reactions at sqrt[s(NN)]=17, 200, and 5500 GeV is compared to leading order perturbative QCD calculations for elementary p+p (p+p) collisions. The competition between nuclear shadowing, Cronin effect, and jet energy loss due to medium-induced gluon radiation is predicted to lead to a striking energy dependence of the nuclear suppression/enhancement pattern in A+A reactions. We show that future d+Au data can be used to disentangle the initial and final state effects.

  5. Effect of Thiolated Ligands in Au Nanowire Synthesis.

    PubMed

    Wang, Yawen; He, Jiating; Yu, Suzhu; Chen, Hongyu

    2017-08-30

    Thiolated ligands are seldom used as morphology-directing reagent in the synthesis of Au nanostructures due to their low selectivity toward the different facets. Recently, we developed a thiolated ligands-induced synthesis of nanowires where the selective Au deposition only occurs at the ligand-deficient Au-substrate interface. Herein, the structural effect of thiolated ligands in this active surface growth is systematically investigated. It is revealed that their ability of rendering surface is closely related to the molecular structure. Ligands with aromatic backbones are capable of inducing nanowire formation, whereas those with aliphatic backbones cannot, likely because the former can pack better at short time scale of the rapid growth. The substituents of the ligands are critical for the colloidal stability of the final structure. It is further demonstrated that aromatic and aliphatic ligands could be mixed to turn on the continual lateral growth, leading to nanowires with tapered ends. The ligand generality in this growth mode also allows the creation of superhydrophobic surface, with the nanowire forest providing the nanoscale surface roughness and the hydrophobic ligand offering the surface property. These applications of the thiolated ligands in the nanosynthesis open a new approach for controlled synthesis of Au-based nanostructures with various morphologies and properties. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Investigation of Metal Free Naphthalocyanine Vapor Deposited on Au(111)

    SciTech Connect

    Wiggins, Bryan C.; Hipps, Kerry W.

    2014-02-27

    Naphthalocyanines (Ncs) are promising candidates for future components in electronic devices and applications. To maximize the efficiency of Nc devices, it is critical to understand their structural and electronic properties and how these are impacted by deposition methods. The formation of a metal free naphthalocyanine (H2Nc) self-assembled monolayer on a Au(111) crystal was investigated by scanning tunneling microscopy under ultra-high-vacuum conditions at room temperature. A rigorous purification and processing procedure was developed to produce high purity, low defect, and well-ordered monolayers. High-resolution STM images reveal epitaxial growth of H2Nc on Au(111) with the observed structure having a molecular spacing of 1.6 ± 0.05 nm, with molecules orientated slightly off (roughly 2.5°) the low density packing direction of Au(111). A commensurate structure having 4 molecules per unit cell and unit cell parameters of A = 3.25 ± 0.05 nm, B = 3.17 ± 0.05 nm, and α = 87.5 ± 2° is proposed. Orbital-mediated tunneling spectroscopy was used to examine the electronic properties of individual molecules within the thin film. The first ionization potential and electron affinity of H2Nc adsorbed on Au(111) were measured to be -0.68 ± 0.03 and 1.12 ± 0.02 eV, relative to the Fermi energy.

  7. 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.

  8. Fluorogenic Gold Nanoparticle (AuNP) Substrate: A Model for the Controlled Release of Molecules from AuNP Nanocarriers via Interfacial Staudinger-Bertozzi Ligation.

    PubMed

    Luo, Wilson; Gobbo, Pierangelo; Gunawardene, Praveen N; Workentin, Mark S

    2017-02-28

    The ability to regulate small-molecule release from metallic nanoparticle substrates offers unprecedented opportunities for nanocarrier-based imaging, sensing, and drug-delivery applications. Herein we report a novel and highly specific release methodology off gold nanoparticle (AuNP) surfaces based on the bioorthogonal Staudinger-Bertozzi ligation. A thiol ligand bearing the molecular cargo, a Rhodamine B dye derivative, was synthesized and used to modify small water-soluble 5 nm AuNPs. Upon incorporation into the AuNP monolayer, we observed efficient quenching of the dye emission, resulting in a very low level of fluorescence emission that provided the baseline from which cargo release was monitored. We examined the ability of these AuNPs to react with azide molecules via Staudinger-Bertozzi ligation on the nanoparticle surface by monitoring the fluorescence emission after the introduction of an organic azide. We observed an immediate increase in emission intensity upon azide addition, which corresponded to the release of the dye into the bulk solution. The (31)P NMR spectrum of the AuNP product also agrees with the formation of the ligation product. Thus this system represents a novel and highly specific release methodology off AuNP surfaces that can have potential applications in drug delivery, sensing, and materials science.

  9. Au-assisted fabrication of nano-holes on c-plane sapphire via thermal treatment guided by Au nanoparticles as catalysts

    NASA Astrophysics Data System (ADS)

    Sui, Mao; Pandey, Puran; Li, Ming-Yu; Zhang, Quanzhen; Kunwar, Sundar; Lee, Jihoon

    2017-01-01

    Nanoscale patterning of sapphires is a challenging task due to the high mechanical strength, chemical stability as well as thermal durability. In this paper, we demonstrate a gold droplet assisted approach of nano-hole fabrication on c-plane sapphire via a thermal treatment. Uniformly distributed nano-holes are fabricated on the sapphire surface guided by dome shaped Au nanoparticles (NPs) as catalysts and the patterning process is discussed based on the disequilibrium of vapor, liquid, solid interface energies at the Au NP/sapphire interface induced by the Au evaporation at high temperature. Followed by the re-equilibration of interface energy, transport of alumina from the beneath of NPs to the sapphire surface can occur along the NP/sapphire interface resulting in the formation of nano-holes. The fabrication of nano-holes using Au NPs as catalysts is a flexible, economical and convenient approach and can find applications in various optoelectronics.

  10. A general and high-yield galvanic displacement approach to Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells and enhanced electrocatalytic performances.

    PubMed

    Kuai, Long; Geng, Baoyou; Wang, Shaozhen; Sang, Yan

    2012-07-23

    In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au-Au, Au-Pd, and Au-Pt core-shell nanostructures with typical porous shells. Moreover, the Au-Au isomeric core-shell nanostructure is reported for the first time. The lower oxidation states of Au(I), Pd(II), and Pt(II) are supposed to contribute to the formation of porous core-shell nanostructures instead of yolk-shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au-Pd core-shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core-shell nanostructures. As expected, the Au-Pd core-shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44 mV and 32 mV), a much improved CO tolerance (I(f)/I(b) is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au-M (M = Au, Pd, and Pt) core-shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface-enhanced Raman scattering, and so forth. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Ultrasmall NHC-coated gold nanoparticles obtained through solvent free thermolysis of organometallic Au(i) complexes.

    PubMed

    Crespo, Julián; Guari, Yannick; Ibarra, Alfonso; Larionova, Joulia; Lasanta, Tania; Laurencin, Danielle; López-de-Luzuriaga, José M; Monge, Miguel; Olmos, M Elena; Richeter, Sébastien

    2014-11-14

    Ultrasmall gold nanoparticles (Au UNPs) represent a unique class of nanomaterials making them very attractive for certain applications. Herein, we developed an organometallic approach to the synthesis of Au UNPs stabilized with the C18H37-NHC ligand by the solvent free thermolysis of [RMIM][Au(C6F5)2] () or [Au(C6F5)(RNHC)] () (with R = C18H37-), by controlling the reactivity of pentafluorophenyl ligands as deprotonating or reductive elimination agents; Au UNPs can be achieved by solvent free thermolysis. Pentafluorophenyl Au(i) complexes and are synthesized from the corresponding ionic and neutral precursors. The presence of long alkyl chain imidazolium or carbene species in the complexes makes them to behave as isotropic liquids at moderate temperatures. The use of multinuclear NMR allows the description of the mechanism of formation of the UNPs as well as the surface state of the UNPs.

  12. Surface plasmon resonance of Au-Cu bimetallic nanoparticles predicted by a quasi-chemical model

    NASA Astrophysics Data System (ADS)

    Su, Yen-Hsun; Wang, Wen-Lin

    2013-10-01

    Au-Cu alloys are functional materials with nonlinear optical applications. However, the optical properties of such alloys are difficult to predict due to the random mixing of materials. In this paper, we present a quasi-chemical model to simulate the optical properties of Au-Cu alloy systems based on the mixing of Gibbs free energy. This model is also able to predict the position of the surface plasmon resonance peaks for Au-Cu alloy nanoparticles. The model can be applied to predict the optical properties of alloy systems in the fields of plasmonics and nanophotonics.

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

    DTIC Science & Technology

    2001-01-01

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

  14. Topological Insulators as Substrates for CO Oxidation Catalysis by Ultrathin Au Films

    NASA Astrophysics Data System (ADS)

    Chen, Hua; Zhu, Wenguang; Xiao, Di; Zhang, Zhenyu

    2011-03-01

    We propose a novel application of three dimensional topological insulators (3DTIs) in heterogeneous catalysis based on first- principles calculations within density functional theory. We use a Bi 2 Se 3 substrate as the support of an ultrathin Au film, and show that the Au adatoms are strongly bound to and able to wet the surface of Bi 2 Se 3 . More importantly, we find the topological surface states of Bi 2 Se 3 are robust against Au deposition, and it can enhance the interaction between Au and CO, O2 molecules by acting as an electron bath . The present study may broaden the potential technological applications of 3DTIs, and shine some new light on the understanding of the role of surface states in heterogeneous catalysis. Supported by DMSE/BES of USDOE, USNSF, and NNSFC.

  15. Tunable VO2/Au Hyperbolic Metamaterial

    DTIC Science & Technology

    2016-02-12

    United States Government.   Tunable VO2/Au hyperbolic metamaterial S. Prayakarao1, B. Mendoza2,3, A. Devine2,3, C. Kyaw2, R. B. Van Dover2, V...can be used as a tunable component of an active metamaterial . The lamellar metamaterial studied in this work is composed of subwavelength VO2 and Au...Au lamellar metamaterial stacks have been fabricated and studied in the electrical conductivity and optical (transmission and reflection

  16. 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.

  17. Split resonance modes of a AuBRC plasmonic nanosystem caused by the coupling effect

    NASA Astrophysics Data System (ADS)

    Ni, Yuan; Kan, Caixia; Xu, Haiying; Wang, Changshun

    2016-12-01

    A plasmonic nanosystem can give rise to particular optical responses due to a coupling effect. In this work, we investigate the optical properties and field distributions of a novel ‘matrioska’ nanocavity structure composed of a Au nanorod (AuNR) within a nanobox (AuNB) via finite-difference time-domain (FDTD) simulation. This nanocavity can be fabricated by a two-step wet-chemical method. The multiple SPR modes of optical spectrum for nanocavity are caused by the strong interaction between the AuNR-core and AuNB-shell when the incident light is perpendicular or parallel to the long axis of the Au box/rod nanocavity (AuBRC). The SPR modes are known as the dipole-dipole bonding resonance mode in the lower-energy region and the antibonding resonance mode in the higher-energy region. It is proposed that AuBRC can escape the orientation confinement of AuNR because the multiple modes occur and provide a potential application for the enhancement of the photoluminescence signal. Additionally, the SPR modes red-shift with increasing the offset of the AuNR-core, whereas the SPR mode dramatically blue-shifts when the conductive coupling is formed. The intense ‘hot-spot’ could be induced within a small interaction region in the conductive coupled system. The SPR line-shape of high quality would also be promoted. The SPR is highly sensitive to the medium, which is promising in the sensing and detecting devices.

  18. Sulfur-induced corrosion of Au(111) studied by real-time STM

    SciTech Connect

    Biener, M; Biener, J; Friend, C

    2004-11-02

    The interaction of sulfur with gold surfaces has attracted considerable interest due to numerous technological applications such as the formation of self-assembled monolayers (SAMs), use as a corrosion inhibitor, and as a chemical sensor. In this work, the interaction of sulfur with Au(111) at two different temperatures (300 K and 420 K) was studied by real-time scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). In the low coverage regime (< 0.1 monolayer), S modifies the surface stress leading to a lateral expansion of the Au surface layer. An ordered ({radical}3 x {radical}3)R30{sup o} sulfur adlayer develops as the coverage reaches {approx}0.3 ML. With further increasing S coverage the Au(111) surface undergoes a dynamic rearrangement while forming a two-dimensional AuS phase: gold surface atoms are removed from regular terrace sites and incorporated into the growing gold sulfide phase resulting in the appearance of pits and irregularly shaped AuS islands. Gold sulfide prepared at room temperature exhibits short-range order; an incommensurate, long-range ordered AuS phase develops upon annealing at 450-525 K. Higher temperatures lead to decomposition of the AuS corrosion film. Formation of an ordered AuS phase via rapid step retraction rather than etch pit formation is observed during S-interaction with Au(111) surfaces at 420 K. Our results shed new light on the S-Au(111) interaction.

  19. Interface effects between germanene and Au(1 1 1) from first principles

    NASA Astrophysics Data System (ADS)

    Li, Fengping; Wei, Wei; Yu, Lin; Huang, Baibiao; Dai, Ying

    2017-03-01

    We study two-dimensional (2D) germanene supported on Au(1 1 1) to determine the structural, electronic and interface interaction properties on the basis of first-principles electronic calculations. In light of the lattice commensurability, (2  ×  2)/(√7  ×  √7) and (√3  ×  √3)/(√7  ×  √7) germanene/Au(1 1 1) superstructures are obtained with low-binding energy. We find that the interface effects between germanene and Au(1 1 1) break the inversion symmetry of germanene to a significant extent. The electron accumulation layer between germanene and Au(1 1 1) bonds the adlayer and substrate together, indicating strong adsorption behavior. Charge transfer occurs from Au(1 1 1) to germanene with the formation of a dipole layer. In addition, the intense electronic orbital hybridization effects between germanene and Au(1 1 1) are revealed through the atomic projected band structures. Clearly, resonant behavior occurs between germanene p orbitals and Au(1 1 1) s orbitals. As germanene is peeled off from Au(1 1 1), the band structures are characterized as metallic, and in the absence of the Au(1 1 1) substrate the band structure of (√3  ×  √3) single layer germanene demonstrates a lower effective mass due to its higher geometrical symmetry, which is similar to that of planar graphene. This paper shows that Au(1 1 1) is a suitable candidate for the growth of germanene, and our results offer useful information for the application of germanene in electronic devices.

  20. A novel method to encapsulate a Au nanorod array in 15 nm radius multiwalled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Liao, Gaomin; Pan, Yuanyuan; Wu, Qiang; Li, Shaoyun; Weng, Yuyan; Zhang, Xiaohua; Yang, Zhaohui; Guo, Jun; Chen, Muzi; Tang, Minghua; Tsui, Ophelia K. C.

    2014-11-01

    In this paper we demonstrate a novel complex array structure comprising well-aligned Au nanorods (10 nm in diameter) encapsulated inside 15 nm radius multiwalled carbon nanotubes (MWCNTs). A pre-aligned and open-ended nanoporous MWCNT membrane is used as the starting material. Au nanorods are precisely deposited and aligned inside the hollow channels of CNTs by inter-diffusing the HAuCl4 precursor and the reductant solution. Ultra-long Au nanowires and spherical Au nanoparticles are also observed in the CNT cavity with the same diameter in special cases. Using high-resolution TEM (HRTEM), scanning transmission electron microscopy (STEM), 3-dimensional TEM (3D-TEM) and energy dispersive X-ray spectroscopy (EDX), the precise location and composition of the encapsulated Au components with various structures are confirmed. This aligned Au@CNT endohedral material has important potential applications in nanocatalysis, waveguides, as well as in novel plasmonic devices.In this paper we demonstrate a novel complex array structure comprising well-aligned Au nanorods (10 nm in diameter) encapsulated inside 15 nm radius multiwalled carbon nanotubes (MWCNTs). A pre-aligned and open-ended nanoporous MWCNT membrane is used as the starting material. Au nanorods are precisely deposited and aligned inside the hollow channels of CNTs by inter-diffusing the HAuCl4 precursor and the reductant solution. Ultra-long Au nanowires and spherical Au nanoparticles are also observed in the CNT cavity with the same diameter in special cases. Using high-resolution TEM (HRTEM), scanning transmission electron microscopy (STEM), 3-dimensional TEM (3D-TEM) and energy dispersive X-ray spectroscopy (EDX), the precise location and composition of the encapsulated Au components with various structures are confirmed. This aligned Au@CNT endohedral material has important potential applications in nanocatalysis, waveguides, as well as in novel plasmonic devices. Electronic supplementary information (ESI

  1. Successful synthesis and thermal stability of immiscible metal Au-Rh, Au-Ir andAu-Ir-Rh nanoalloys

    NASA Astrophysics Data System (ADS)

    Shubin, Yury; Plyusnin, Pavel; Sharafutdinov, Marat; Makotchenko, Evgenia; Korenev, Sergey

    2017-05-01

    We successfully prepared face-centred cubic nanoalloys in systems of Au-Ir, Au-Rh and Au-Ir-Rh, with large bulk miscibility gaps, in one-run reactions under thermal decomposition of specially synthesised single-source precursors, namely, [AuEn2][Ir(NO2)6], [AuEn2][Ir(NO2)6] х [Rh(NO2)6]1-х and [AuEn2][Rh(NO2)6]. The precursors employed contain all desired metals ‘mixed’ at the atomic level, thus providing significant advantages for obtaining alloys. The observations using high-resolution transmission electron microscopy show that the nanoalloy structures are composed of well-dispersed aggregates of crystalline domains with a mean size of 5 ± 3 nm. Еnergy dispersive x-ray spectroscopy and x-ray powder diffraction (XRD) measurements confirm the formation of AuIr, AuRh, AuIr0.75Rh0.25, AuIr0.50Rh0.50 and AuIr0.25Rh0.75 metastable solid solutions. In situ high-temperature synchrotron XRD (HTXRD) was used to study the formation mechanism of nanoalloys. The observed transformations are described by the ‘conversion chemistry’ mechanism characterised by the primary development of particles comprising atoms of only one type, followed by a chemical reaction resulting in the final formation of a nanoalloy. The obtained metastable nanoalloys exhibit essential thermal stability. Exposure to 180 °C for 30 h does not cause any dealloying process.

  2. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Enhanced nonlinear optical absorption of Au/SiO2 nano-composite thin films

    NASA Astrophysics Data System (ADS)

    Zhao, Cui-Hua; Zhang, Bo-Ping; Shang, Peng-Peng

    2009-12-01

    Nano metal-particle dispersed glasses are the attractive candidates for nonlinear optical material applications. Au/SiO2 nano-composite thin films with 3 vol% to 65 vol% Au are prepared by inductively coupled plasma sputtering. Au particles as perfect spheres with diameters between 10 nm and 30 nm are uniformly dispersed in the SiO2 matrix. Optical absorption peaks due to the surface plasmon resonance of Au particles are observed. The absorption property is enhanced with the increase of Au content, showing a maximum value in the films with 37 vol% Au. The absorption curves of the Au/SiO2 thin films with 3 vol% to 37 vol% Au accord well with the theoretical optical absorption spectra obtained from Mie resonance theory. Increasing Au content over 37 vol% results in the partial connection of Au particles, whereby the intensity of the absorption peak is weakened and ultimately replaced by the optical absorption of the bulk. The band gap decreases with Au content increasing from 3 vol% to 37 vol% but increases as Au content further increases.

  3. The Electronic Properties and L3 XANES of Au and Nano-Au

    SciTech Connect

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

    2004-04-20

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

  4. Graphene/AuNPs/chitosan nanocomposites film for glucose biosensing.

    PubMed

    Shan, Changsheng; Yang, Huafeng; Han, Dongxue; Zhang, Qixian; Ivaska, Ari; Niu, Li

    2010-01-15

    A novel glucose biosensor based on immobilization of glucose oxidase in thin films of chitosan containing nanocomposites of graphene and gold nanoparticles (AuNPs) at a gold electrode was developed. The resulting graphene/AuNPs/chitosan composites film exhibited good electrocatalytical activity toward H(2)O(2) and O(2). The wide linear response to H(2)O(2) ranging from 0.2 to 4.2 mM (R=0.998) at -0.2V, high sensitivity of 99.5 microA mM(-1) cm(-2) and good reproducibility were obtained. The good electrocatalytical activity might be attributed to the synergistic effect of graphene and AuNPs. With glucose oxidase (GOD) as a model, the graphene/AuNPs/GOD/chitosan composite-modified electrode was constructed through a simple casting method. The resulting biosensor exhibited good amperometric response to glucose with linear range from 2 to 10 mM (R=0.999) at -0.2V and from 2 to 14 mM (R=0.999) at 0.5 V, good reproducibility and detection limit of 180 microM. Glucose concentration in human blood was studied preliminarily. From 2.5 to 7.5 mM, the cathodic peak currents of the biosensor decrease linearly with increasing the glucose concentrations. The graphene/AuNPs/GOD/chitosan composites film shows prominent electrochemical response to glucose, which makes a promising application for electrochemical detection of glucose. Copyright 2009 Elsevier B.V. All rights reserved.

  5. Enhancing near IR luminescence of thiolate Au nanoclusters by thermo treatments and heterogeneous subcellular distributions.

    PubMed

    Conroy, Cecil V; Jiang, Jie; Zhang, Chen; Ahuja, Tarushee; Tang, Zhenghua; Prickett, Cherish A; Yang, Jenny J; Wang, Gangli

    2014-07-07

    A five-to-ten fold enhancement, up to ca. 5-10% quantum efficiency, of near IR luminescence from monothiolate protected gold nanoclusters was achieved by heating in the presence of excess ligand thiols. An emission maximum in the 700-900 nm range makes these Au nanoclusters superior for bioimaging applications over other emissions centered below 650 nm due to reduced background interference, albeit visible emissions could have higher quantum efficiency. The heating procedure is shown to be effective to improve the luminescence of Au nanoclusters synthesized under a variety of conditions using two types of monothiols: mercaptosuccinic acid and tiopronin. Therefore, this heating method is believed to be a generalizable approach to improve the near IR luminescence of aqueous soluble Au nanoclusters, which enables better bioimaging applications. The high quantum yield is found relatively stable over a wide pH range. PEGylation of the Au nanoclusters reduces their quantum efficiency but improves their permeation into the cytoplasm. Interestingly, z-stack confocal analysis clearly reveals the presence of Au nanoclusters inside the cell nucleus in single cell imaging. The finding addresses controversial literature reports and demonstrates the internalization and heterogeneous subcellular distributions, particularly inside the nucleus. The high luminescence intensity, small overall dimension, cell and nuclear distribution, chemical stability and low-to-non toxicity make these Au nanoclusters promising probes for broad cell dynamics and imaging applications.

  6. Theranostic Au cubic nano-aggregates as potential photoacoustic contrast and photothermal therapeutic agents.

    PubMed

    Hu, Juan; Zhu, Xianglong; Li, Hui; Zhao, Zhenghuan; Chi, Xiaoqin; Huang, Guoming; Huang, Dengtong; Liu, Gang; Wang, Xiaomin; Gao, Jinhao

    2014-01-01

    Multifunctional nanostructures combining diagnosis and therapy modalities into one entity have drawn much attention in the biomedical applications. Herein, we report a simple and cost-effective method to synthesize a novel cubic Au nano-aggregates structure with edge-length of 80 nm (Au-80 CNAs), which display strong near-infrared (NIR) absorption, excellent water-solubility, good photothermal stability, and high biocompatibility. Under 808 nm laser irradiation for 5 min, the temperature of the solution containing Au-80 CNAs (100 μg/mL) increased by ~38 °C. The in vitro and in vivo studies demonstrated that Au-80 CNAs could act as both photothermal therapeutic (PTT) agents and photoacoustic imaging (PAI) contrast agents, indicating that the only one nano-entity of Au-80 CNAs shows great potentials for theranostic applications. Moreover, this facile and cost-effective synthetic method provides a new strategy to prepare stable Au nanomaterials with excellent optical properties for biomedical applications.

  7. Anisotropic flow nu2 in Au + Au collisions at RHIC

    SciTech Connect

    Lu, Y.; Bleicher, M.; Liu, F.; Kiu, Z.; Sorensen, P.; Stocker,H.; Xu, N.; Zhu, X.

    2005-08-20

    Using the RQMD model, transverse momentum dependence of the anisotropic flow v{sub 2} for {pi}, K, nucleon, {phi}, and {lambda}, are studied for Au + Au collisions at {radical}s{sub NN} = 200 GeV. Both hydrodynamic hadron-mass hiragracy (hhmh) at low p{sub T} region and particle type dependence (baryon versus meson) at the intermediate p{sub T} region are reproduced with the model calculations although the model underpredicted the overall values of v{sub 2} by a factor of 2-3. As expected, when the rescatterings are turned off, all v{sub 2} becomes zero. The failure of the hadronic model in predicting the absolute values of hadron v{sub 2} clearly demonstrate the need of early dense partonic interaction in heavy-ion collisions at RHIC. At the intermediate p{sub T}, the hadron type dependence cold also be explained by the vacume hadronic cross sections within the frame of the model. The measurements of collective motion of hadrons from high-energy nuclear collisions can provide information on the dynamical equation of state information of the system [1, 2, 3]. Specifically, the strange and multi-strange hadron flow results have demonstrated the partonic collectivity [5] and the heavy-flavor flow will test the hypothesis of early thermalization in such collisions [4]. At RHIC, the measurements [6, 7] of elliptic flow v{sub 2} and nuclear modification factor r{sub AA} has lead to the conclusion that hadrons were formed via the coalescence/recombination of massive quarks [8, 9, 10]. This finding is directly related to the key issue in high-energy nuclear collisions such as deconfinement and chiral symmetry restoration. In addition, it also touched the important problem of hadronization process in high-energy collisions. Therefore a systematic study with different approaches becomes necessary. In this report, using a hadronic transport model UrQMD(v2.2)/RQMD(v2.4) [11, 12], we study the v{sub 2} of {pi}, K, p, {phi}, and {Lambda} from Au + Au collisions at 200 Ge

  8. 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.

  9. Synthesis and properties of Au-Fe3O4 heterostructured nanoparticles.

    PubMed

    Sheng, Yang; Xue, Junmin

    2012-05-15

    Au-Fe(3)O(4) composite nanoparticles have received much research interest due to their promising biomedical applications. In this work, Au-Fe(3)O(4) composites with well-defined dimer-like nanostructure were synthesized via thermal decomposition route. The surfactant 1,2-hexandicandiol has proved to be critical for the formation of the Au-Fe(3)O(4) hetero-dimers. The hetero-dimers production yield could be significantly improved to be 90% when the 1,2-hexandicandiol concentration was optimized at 0.6 M. The obtained Au-Fe(3)O(4) hetero-dimers possess dual-functionalities of plasmon resonance and magnetization. Moreover, the Fe(3)O(4) domain of the hetero-dimers can be tuned readily by adjusting the molar ratio between Fe and Au sources. Furthermore, it was demonstrated that these Au-Fe(3)O(4) hetero-dimers could be further developed into star-like Au-Fe(3)O(4) nanoparticles which showed plasmon absorption at NIR region. Copyright © 2012 Elsevier Inc. All rights reserved.

  10. Synthesis of Au/Graphene Oxide Composites for Selective and Sensitive Electrochemical Detection of Ascorbic Acid

    NASA Astrophysics Data System (ADS)

    Song, Jian; Xu, Lin; Xing, Ruiqing; Li, Qingling; Zhou, Chunyang; Liu, Dali; Song, Hongwei

    2014-12-01

    In this work, we present a novel ascorbic acid (AA) sensor applied to the detection of AA in human sera and pharmaceuticals. A series of Au nanoparticles (NPs) and graphene oxide sheets (Au NP/GO) composites were successfully synthesized by reduction of gold (III) using sodium citrate. Then the Au NP/GO composites were used to construct nonenzymatic electrodes in practical AA measurement. The electrode that has the best performance presents attractive analytical features, such as a low working potential of +0.15 V, a high sensitivity of 101.86 μA mM-1 cm-2 to AA, a low detection limit of 100 nM, good reproducibility and excellent selectivity. And more,it was also employed to accurately and practically detect AA in human serum and clinical vitamin C tablet with the existence of some food additive. The enhanced AA electrochemical properties of the Au NP/GO modified electrode in our work can be attributed to the improvement of electroactive surface area of Au NPs and the synergistic effect from the combination of Au NPs and GO sheets. This work shows that the Au NP/GO/GCEs hold the prospect for sensitive and selective determination of AA in practical clinical application.

  11. Large extrinsic spin Hall effect in Au-Cu alloys by extensive atomic disorder scattering

    NASA Astrophysics Data System (ADS)

    Zou, L. K.; Wang, S. H.; Zhang, Y.; Sun, J. R.; Cai, J. W.; Kang, S. S.

    2016-01-01

    Spin Hall angle, which denotes the conversion efficiency between spin and charge current, is a key parameter in the pure spin current phenomenon. The search for materials with large spin Hall angle is indeed important for scientific interest and potential application in spintronics. Here the large enhanced spin Hall effect (SHE) of Au-Cu alloy is reported by investigating the spin Seebeck effect, spin Hall anomalous Hall effect, and spin Hall magnetoresistance of the Y3F e5O12 (YIG)/A uxC u1 -x hybrid structure over the full composition. At the near equiatomic Au-Cu composition with maximum atomic disorder scattering, the spin Hall angle of the Au-Cu alloy increases by two to three times together with a moderate spin diffusion length in comparison with Au. The longitudinal spin Seebeck voltage and the spin Hall magnetoresistance ratio also increase by two to three times. More importantly, no evidence of anomalous Hall effect is observed in all YIG/Au-Cu samples, in contrast to the cases of other giant SHE materials Pt(Pd), Ta, and W. This behavior makes Au-Cu free from any suspicion of the magnetic proximity effect involved in the hybrid structure, and thus the Au-Cu alloy can be an ideal material for pure spin current study.

  12. Significant Broadband Photocurrent Enhancement by Au-CZTS Core-Shell Nanostructured Photocathodes

    PubMed Central

    Zhang, Xuemei; Wu, Xu; Centeno, Anthony; Ryan, Mary P.; Alford, Neil M.; Riley, D. Jason; Xie, Fang

    2016-01-01

    Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon resonance (LSPR) peak of the Au and the semiconductor bandgap. PMID:26997140

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

    PubMed Central

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

    2015-01-01

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

  14. a High-Performance Glucose Biosensor Based on Zno Nanorod Arrays Modified with AU Nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhang, Gong; Lei, Yang; Yan, Xiaoqin

    2012-08-01

    An amperometric glucose biosensor based on vertically aligned ZnO nanorod (NR) arrays modified with Au nanoparticles (NPs) was constructed in a channel-limited way. Au NPs with diameters in the range of 8-10 nm have been successfully synthesized by photoreduction method and were uniformly loaded onto the surface of ZnO NRs that was hydrothermally deposited on the Fluorine doped SnO2 conductive glass (FTO) via electrostatic self-assembly technique. The morphology and structure of Au/ZnO NR arrays were characterized by field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectrum analyzer (XPS). The electrocatalytic properties of glucose oxidase (GOD)- immobilized Au/ZnO NR arrays were evaluated by amperometry. Compared with the biosensor based on ZnO NR arrays, the resulting Au/ZnO NR arrays modified biosensor exhibited an expanded linear range from 3 μM to 3 mM with the detection limit of 30 nM and a smaller Michaelis-Menten constant of 0.7836 mM. All these results suggest that the Au NPs can greatly improve the biosensing properties of ZnO NR arrays and therefore Au/ZnO NR arrays provide a promising material for the biosensor designs and other biological applications.

  15. Synthesis of Au/Graphene Oxide Composites for Selective and Sensitive Electrochemical Detection of Ascorbic Acid

    PubMed Central

    Song, Jian; Xu, Lin; Xing, Ruiqing; Li, Qingling; Zhou, Chunyang; Liu, Dali; Song, Hongwei

    2014-01-01

    In this work, we present a novel ascorbic acid (AA) sensor applied to the detection of AA in human sera and pharmaceuticals. A series of Au nanoparticles (NPs) and graphene oxide sheets (Au NP/GO) composites were successfully synthesized by reduction of gold (III) using sodium citrate. Then the Au NP/GO composites were used to construct nonenzymatic electrodes in practical AA measurement. The electrode that has the best performance presents attractive analytical features, such as a low working potential of +0.15 V, a high sensitivity of 101.86 μA mM−1 cm−2 to AA, a low detection limit of 100 nM, good reproducibility and excellent selectivity. And more,it was also employed to accurately and practically detect AA in human serum and clinical vitamin C tablet with the existence of some food additive. The enhanced AA electrochemical properties of the Au NP/GO modified electrode in our work can be attributed to the improvement of electroactive surface area of Au NPs and the synergistic effect from the combination of Au NPs and GO sheets. This work shows that the Au NP/GO/GCEs hold the prospect for sensitive and selective determination of AA in practical clinical application. PMID:25515430

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

    PubMed

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

    2015-09-10

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

  17. Au@MoS2 Core-Shell Heterostructures with Strong Light-Matter Interactions.

    PubMed

    Li, Yuan; Cain, Jeffrey D; Hanson, Eve D; Murthy, Akshay A; Hao, Shiqiang; Shi, Fengyuan; Li, Qianqian; Wolverton, Chris; Chen, Xinqi; Dravid, Vinayak P

    2016-12-14

    There are emerging opportunities to harness diverse and complex geometric architectures based on nominal two-dimensional atomically layered structures. Herein we report synthesis and properties of a new core-shell heterostructure, termed Au@MoS2, where the Au nanoparticle is snugly and contiguously encapsulated by few shells of MoS2 atomic layers. The heterostructures were synthesized by direct growth of multilayer fullerene-like MoS2 shell on Au nanoparticle cores. The Au@MoS2 heterostructures exhibit interesting light-matter interactions due to the structural curvature of MoS2 shell and the plasmonic effect from the underlying Au nanoparticle core. We observed significantly enhanced Raman scattering and photoluminescence emission on these heterostructures. We attribute these enhancements to the surface plasmon-induced electric field, which simulations show to mainly localize within the MoS2 shell. We also found potential evidence for the charge transfer-induced doping effect on the MoS2 shell. The DFT calculations further reveal that the structural curvature of MoS2 shell results in a modification of its electronic structure, which may facilitate the charge transfer from MoS2 to Au. Such Au@MoS2 core-shell heterostructures have the potential for future optoelectronic devices, optical imaging, and other energy-environmental applications.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  19. First-principles study of SF6 decomposed gas adsorbed on Au-decorated graphene

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoxing; Yu, Lei; Gui, Yingang; Hu, Weihua

    2016-03-01

    We theoretically investigated the decomposed gaseous components of sulfur hexafluoride (SF6), namely, H2S, SO2, SOF2, and SO2F2, adsorbed on pristine and Au-embedded graphene based on the revised Perdew-Burke-Ernzerhof calculation, which empirically includes a dispersion correction (DFT-D) for van der Waals interaction with standard generalized gradient approximation. Pristine graphene exhibits weak adsorption and absence of charge transfer, which indicates barely satisfactory sensing for decomposed components. The Au atom introduces magnetism to the pristine graphene after metal-embedded decoration as well as enhances conductivity. All four molecules induce certain hybridization between the molecules and Au-graphene, which results in chemical interactions. SOF2 and SO2F2 exhibit a strong chemisorption interaction with Au-graphene, while H2S and SO2 exhibit quasi-molecular binding effects. Only H2S exhibits n-type doping to Au-graphene, whereas the rest gases exhibit p-type doping. Magnetic moments fluctuate substantially in the original Au-graphene when H2S and SO2 are adsorbed. While the adsorption effects of SOF2 and SO2F2 generate magnetism quenching. The charge transfer mechanism is also discussed in this paper. These results will shed light on the valuable application of Au-embedded graphene for selective gas sensing and spintronics.

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

    SciTech Connect

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

    1995-12-31

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

  1. Efficient H{sub 2} production over Au/graphene/TiO{sub 2} induced by surface plasmon resonance of Au and band-gap excitation of TiO{sub 2}

    SciTech Connect

    Liu, Yang; Yu, Hongtao; Wang, Hua; Chen, Shuo; Quan, Xie

    2014-11-15

    Highlights: • Both surface plasmon resonance and band-gap excitation were used for H{sub 2} production. • Au/Gr/TiO{sub 2} composite photocatalyst was synthesized. • Au/Gr/TiO{sub 2} exhibited enhancement of light absorption and charge separation. • H{sub 2} production rate of Au/Gr/TiO{sub 2} was about 2 times as high as that of Au/TiO{sub 2}. - Abstract: H{sub 2} production over Au/Gr/TiO{sub 2} composite photocatalyst induced by surface plasmon resonance of Au and band-gap excitation of TiO{sub 2} using graphene (Gr) as an electron acceptor has been investigated. Electron paramagnetic resonance study indicated that, in this composite, Gr collected electrons not only from Au with surface plasmon resonance but also from TiO{sub 2} with band-gap excitation. Surface photovoltage and UV–vis absorption measurements revealed that compared with Au/TiO{sub 2}, Au/Gr/TiO{sub 2} displayed more effective photogenerated charge separation and higher optical absorption. Benefiting from these advantages, the H{sub 2} production rate of Au/Gr/TiO{sub 2} composite with Gr content of 1.0 wt% and Au content of 2.0 wt% was about 2 times as high as that of Au/TiO{sub 2}. This work represents an important step toward the efficient application of both surface plasmon resonance and band-gap excitation on the way to converting solar light into chemical energy.

  2. Chitosan-induced Au/Ag nanoalloy dispersed in IL and application in fabricating an ultrasensitive glucose biosensor based on luminol-H₂O₂-Cu²⁺/IL chemiluminescence system.

    PubMed

    Chaichi, M J; Alijanpour, S O

    2014-11-01

    A novel glucose biosensor based on the chemiluminescence (CL) detection of enzymatically generated hydrogen peroxide (H₂O₂) was constructed by one covalent immobilization of glucose oxidase (GOD) in glutaraldehyde-functionalized glass cell. In following, chitosan-induced Au/Ag nanoparticles dispersed in ion liquid (IL) were synthesised and immobilized on it. Herein, chitosan molecules acted as both the reducing and stabilizing agent for the preparation of NPs and also, as a coupling agent GOD and Au/Ag alloy NPs. In addition to catalyze luminol CL reaction, these NPs offered excellent catalytic activity toward hydrogen peroxide generation in enzymatic reaction between GOD and glucose. The used IL in fabrication of biosensor increased its stability. Also, IL alongside Cu(2+) accelerated enzymatic and CL reaction kinetic, and decreased luminol CL reaction optimum pH to 7.5 which would enable sensitive and precision determination of glucose. Under optimum condition, linear response range of glucose was found to be 1.0 × 10(-6)-7.5 × 10(-3)M, and detection limit was 4.0 × 10(-7)M. The CL biosensor exhibited good storage stability, i.e., 90% of its initial response was retained after 2 months storage at pH 7.0. The present CL biosensor has been applied satisfactory to analysis of glucose in real serum and urine samples.

  3. Preparation of Au-Pt nanostructures by combining top-down with bottom-up strategies and application in label-free electrochemical immunosensor for detection of NMP22.

    PubMed

    Jia, Hongying; Gao, Picheng; Ma, Hongmin; Wu, Dan; Du, Bin; Wei, Qin

    2015-02-01

    A novel label-free amperometric immunosensor for sensitive detection of nuclear matrix protein 22 (NMP22) was developed based on Au-Pt bimetallic nanostructures, which were prepared by combining top-down with bottom-up strategies. Nanoporous gold (NPG) was prepared by "top-down" dealloying of commercial Au/Ag alloy film. After deposition of NPG on an electrode, Pt nanoparticles (PtNPs) were further decorated on NPG by "bottom-up" electrodeposition. The prepared bimetallic nanostructures combine the merits of both NPG and PtNPs, and show a high electrocatalytic activity towards the reduction of H2O2. The label-free immunosensor was constructed by directly immobilizing antibody of NMP22 (anti-NMP22) on the surface of bimetallic nanostructures. The immunoreaction induced amperometric response could be detected and negatively correlated to the concentration of NMP22. Bimetallic nanostructure morphologies and detection conditions were investigated to obtain the best sensing performance. Under the optimal conditions, a linear range from 0.01ng/mL to 10ng/mL and a detection limit of 3.33pg/mL were obtained. The proposed immunosensor showed high sensitivity, good selectivity, stability, reproducibility, and regeneration for the detection of NMP22, and it was evaluated in urine samples, receiving satisfactory results.

  4. 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

  5. Au25(SG)18 as a fluorescent iodide sensor

    NASA Astrophysics Data System (ADS)

    Wang, Man; Wu, Zhikun; Yang, Jiao; Wang, Guozhong; Wang, Hongzhi; Cai, Weiping

    2012-06-01

    The recently emerging gold nanoclusters (GNC) are of major importance for both basic science studies and practical applications. Based on its surface-induced fluorescence properties, we investigated the potential use of Au25(SG)18 (GSH: glutathione) as a fluorescent iodide sensor. The current detection limit of 400 nM, which can possibly be further enhanced by optimizing the conditions, and excellent selectivity among 12 types of anion (F-, Cl-, Br-, I-, NO3-, ClO4-, HCO3-, IO3-, SO42-, SO32-, CH3COO- and C6H5O73-) make Au25(SG)18 a good candidate for iodide sensing. Furthermore, our work has revealed the particular sensing mechanism, which was found to be affinity-induced ratiometric and enhanced fluorescence (abbreviated to AIREF), which has rarely been reported previously and may provide an alternative strategy for devising nanoparticle-based sensors.The recently emerging gold nanoclusters (GNC) are of major importance for both basic science studies and practical applications. Based on its surface-induced fluorescence properties, we investigated the potential use of Au25(SG)18 (GSH: glutathione) as a fluorescent iodide sensor. The current detection limit of 400 nM, which can possibly be further enhanced by optimizing the conditions, and excellent selectivity among 12 types of anion (F-, Cl-, Br-, I-, NO3-, ClO4-, HCO3-, IO3-, SO42-, SO32-, CH3COO- and C6H5O73-) make Au25(SG)18 a good candidate for iodide sensing. Furthermore, our work has revealed the particular sensing mechanism, which was found to be affinity-induced ratiometric and enhanced fluorescence (abbreviated to AIREF), which has rarely been reported previously and may provide an alternative strategy for devising nanoparticle-based sensors. Electronic supplementary information (ESI) available: fluorescence spectra of Au25(SG)18 (1.6 μM in H2O) with successive titration of I- and the time-dependent fluorescence of Au25(SG)18. See DOI: 10.1039/c2nr30169e.

  6. The effects of colorimetric detection of heavy metal ions based on Au nanoparticles (NPs): size and shape—a case of Co2+

    NASA Astrophysics Data System (ADS)

    Leng, Yumin; He, Junbao; Li, Bo; Xing, Xiaojing; Guo, Yongming; Ye, Liqun; Lu, Zhiwen

    2017-09-01

    The different sized and shaped Au NPs have intrigued considerable attention, because they possess different surface plasma resonance (SPR) absorption bands and thus result in many colorimetric Au NP-based detection applications. In this article, four different sized and shaped Au NPs of nanodots/rods were prepared and characterized. The as-prepared Au NPs were modified by the negatively charged anions of [SCH2CO2]2- to investigate both the size and shape effects of modified Au NPs on colorimetric detection of Co2+ and the corresponding SPR absorption properties. The different-shaped Au NPs possess different SPR absorption properties. The Au nanorods appeared to be colorimetric sensitive for Co2+ sensing.

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

    PubMed

    Yudanov, Ilya V; Neyman, Konstantin M

    2010-05-21

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

  8. Well-defined linear Au n (n = 2-4) chains encapsulated in SWCNTs: a DFT study.

    PubMed

    Liu, Yiliang; Hua, Yawen; Yan, Anying; Wu, Shuang; Kong, Fanjie

    2017-01-01

    One-dimensional (1D) gold nanostructures have been extensively studied due to their potential applications in nanoelectronic devices. Using first-principles calculations, composites consisting of a well-defined linear Au n (n = 2-4) chain encapsulated in a (9,0) single-walled carbon nanotube (SWCNT) were studied. The translational energy barrier of a single Au atom in a (9,0) SWCNT was found to be 0.03 eV. This low barrier guaranteed the formation of Au n @ (9,0) SWCNT (n = 1-4) composites. Bond lengths, differential charge densities, and electronic band structures of the composites were studied. The average Au-Au bond lengths in the composites were found to be almost the same as those in the corresponding free-standing linear Au n . The average bond length increased as the number of Au atoms increased. Charge transfer in all of these composites was slight, although a few valence electrons were transferred from the (9,0) SWCNT and the Au chains to intercalations. The conductivities of the encapsulated linear Au n (n = 2-4) chains were enhanced to some extent by encapsulating them in the SWCNT.

  9. Ordered binary arrays of Au nanoparticles derived from colloidal lithography.

    PubMed

    Zhang, Gang; Wang, Dayang; Möhwald, Helmuth

    2007-01-01

    By using angle-resolved colloidal lithography and O2-plasma etched bilayers of hexagonally packed spheres as templates, we succeeded in fabrication of highly ordered binary arrays of gold nanoparticles with varied shapes, for instance, with a shuttlecock-like shape composed of a small crescent-shaped nanoparticle and a big fan-shaped one. The size and shape of both small and big nanoparticles obtained were manipulated by the plasma etching period and the incidence angle of Au vapor flow. The subsequent thermal annealing led to binary arrays of round Au nanoparticles with a rather narrow distribution in terms of size and shape. Our approach should pave a simple and versatile colloidal way to form binary nanoparticle arrays, holding immense promise for technical applications such as nanoelectronics and nanophotonics.

  10. 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.

  11. 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.

  12. Crystal structures and new perspectives on Y3Au4 and Y14Au51.

    PubMed

    Celania, Chris; Smetana, Volodymyr; Mudring, Anja Verena

    2017-09-01

    Y3Au4 (triyttrium tetragold) and Y14Au51 (tetradecayttrium henpentacontagold), two binary representatives of Au-rich rare earth (R) systems crystallize with the space groups R-3 and P6/m, adopting the Pu3Pd4 and Gd14Ag51 structure types, respectively (Pearson symbols hR42 and hP65). A variety of binary R-Au compounds have been reported, although only a few have been investigated thoroughly. Many reports lack information or misinterpret known compounds reported elsewhere. The Pu3Pd4 type is fairly common for group 10 elements Ni, Pd, and Pt, while Au representatives are restricted to just five examples, i.e. Ca3Au4, Pr3Au4, Nd3Au4, Gd3Au4, and Th3Au4. Sm6Au7 is suspected to be Sm3Au4 due to identical symmetry and close unit-cell parameters. The Pu3Pd4 structure type allows for full substitution of the position of the rare earth atom by more electronegative and smaller elements, i.e. Ti and Zr. The Gd14Ag51 type instead is more common for the group 11 metals, while rare representatives of group 12 are known. Y3Au4 can be represented as a tunnel structure with encapsulated cations and anionic chains. Though tunnels are present in Y14Au51, this structure is more complex and is best described in terms of polyhedral `pinwheels' around the tunnel forming polyhedra along the c axis.

  13. Impact of Ni/Ge/Au/Ti/Au and Ti/Pt/Au collector metal on GaInP/GaAs HBT characteristics

    NASA Astrophysics Data System (ADS)

    Park, Jae-Woo; Mohammadi, Saeed; Pavlidis, Dimitris

    2000-10-01

    The collector-emitter offset voltage of GaInP/GaAs HBTs grown by chemical-beam epitaxy with reduced toxicity precursors is investigated for Ni/Ge/Au/Ti/Au and Ti/Pt/Au collector contact metals. The offset voltage for HBTs with Ti/Pt/Au collector metal is increased by 0.26 V compared to Ni/Ge/Au/Ti/Au due to the 0.26 eV barrier existing between the n-GaAs subcollector and the Ti/Pt/Au contact metal. Other parameters affected by the collector contact barrier and impacting transistor performance include DC gain, microwave and power performance.

  14. Heterostructured CIGS-Au nanoparticles: from Au-CIGS side-by-side structure to Au-core/CIGS-shell configuration.

    PubMed

    Xu, Yeming; Li, Quan

    2011-08-01

    Heterostructured Au-Copper Indium Gallium Selenide (CIGS) nanoparticles (nps) with Au-CIGS side-by-side and Au-core/CIGS-shell configurations have been synthesized in a controllable manner using seed mediated growth. Detailed microstructure analysis reveals that (112) planes in the tetragonal chalcopyrite CIGS serve as the predominant termination surfaces during single phase CIGS nanoparticle growth. Preferential nucleation of Au on such planes determines the Au-CIGS side-by-side configuration when the pre-synthesized CIGS nps are used as the seeds for further Au growth. Reversing the growth sequence by employing Au nano-seeds results in Au-core/CIGS-shell configuration, as determined by the non-preferential nucleation of CIGS on the spherical Au nanoparticle surface. The different morphological configurations of the heterostructures are found to modify the surface plasmon resonance of Au in the corresponding samples. This journal is © The Royal Society of Chemistry 2011

  15. Cu-Au Alloys Using Monte Carlo Simulations and the BFS Method for Alloys

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Good, Brian; Ferrante, John

    1996-01-01

    Semi empirical methods have shown considerable promise in aiding in the calculation of many properties of materials. Materials used in engineering applications have defects that occur for various reasons including processing. In this work we present the first application of the BFS method for alloys to describe some aspects of microstructure due to processing for the Cu-Au system (Cu-Au, CuAu3, and Cu3Au). We use finite temperature Monte Carlo calculations, in order to show the influence of 'heat treatment' in the low-temperature phase of the alloy. Although relatively simple, it has enough features that could be used as a first test of the reliability of the technique. The main questions to be answered in this work relate to the existence of low temperature ordered structures for specific concentrations, for example, the ability to distinguish between rather similar phases for equiatomic alloys (CuAu I and CuAu II, the latter characterized by an antiphase boundary separating two identical phases).

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

    PubMed

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

    2016-05-09

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

  17. Formation and Stabilization of Single-Crystalline Metastable AuGe Phases in Ge Nanowires

    SciTech Connect

    Sutter, E.; Sutter, P.

    2011-07-22

    We use in situ observations by variable temperature transmission electron microscopy on AuGe alloy drops at the tips of Ge nanowires (NWs) with systematically varying composition to demonstrate the controlled formation of metastable solid phases integrated in NWs. The process, which operates in the regime of vapor-liquid-solid growth, involves a size-dependent depression of the alloy liquidus at the nanoscale that leads to extremely Ge-rich AuGe melts at low temperatures. During slow cooling, these liquid AuGe alloy drops show pronounced departures from equilibrium, i.e., a frustrated phase separation of Ge into the adjacent solid NW, and ultimately crystallize as single-crystalline segments of metastable {gamma}-AuGe. Our findings demonstrate a general avenue for synthesizing NW heterostructures containing stable and metastable solid phases, applicable to a wide range of materials of which NWs form by the vapor-liquid-solid method.

  18. Ultrasensitive IL-6 electrochemical immunosensor based on Au nanoparticles-graphene-silica biointerface.

    PubMed

    Wang, Guangfeng; He, Xiuping; Chen, Ling; Zhu, Yanhong; Zhang, Xiaojun

    2014-04-01

    An Interleukin-6 (IL-6) electrochemical immunosensor was fabricated based on the Au nanoparticles (AuNP)-graphene-silica sol-gel as immobilization biointerface and AuNP-polydopamine (PDA)@carbon nanotubes (CNT) as the label of HRP-bound antibodies. The AuNP-graphene-silica sol-gel film was prepared in situ and modified on the ITO electrode, providing a stable network for the immobilization of antibody and exhibiting a dynamic working range of 1-40 pg/mL with a low detection limit of 0.3 pg/mL IL-6 (at 3s). The results of serum samples with the sensor received an acceptable agreement with the ELISA method. Importantly, this method provided a promising ultrasensitive assay strategy for clinical applications. Copyright © 2013 Elsevier B.V. All rights reserved.

  19. Structure-induced enhancement in electrooxidation of trimetallic FePtAu nanoparticles.

    PubMed

    Zhang, Sen; Guo, Shaojun; Zhu, Huiyuan; Su, Dong; Sun, Shouheng

    2012-03-21

    Using FePtAu nanoparticles (NPs) as an example, this Communication demonstrates a new structure-control strategy to tune and optimize NP catalysis. The presence of Au in FePtAu facilitates FePt structure transformation from chemically disordered face-centered cubic (fcc) structure to chemically ordered face-centered tetragonal (fct) structure, and further promotes formic acid oxidation reaction (FAOR). The fct-FePtAu NPs have mass activity as high as 2809.9 mA/mg Pt and retain 92.5% of this activity after a 13 h stability test. They become the most efficient NP catalyst ever reported for FAOR. This structure-control strategy can be extended to other multimetallic NP systems, providing a general approach to advanced NP catalysts with desired activity and durability control for practical applications.

  20. Ballistic-electron-emission microscopy of subsurface defects at the Au-GaAs(100) interface

    NASA Technical Reports Server (NTRS)

    Hecht, M. H.; Bell, L. D.; Kaiser, W. J.

    1989-01-01

    The application of ballistic-electron-emission microscopy (BEEM) to a study of the influence of GaAs(100) substrate conditions on the formation of a multidefect structure at the Au-GaAs(100) Schottky barrier interface is described. Interfaces prepared on both melt-grown GaAs(100) wafer substrates and MBF-deposited GaAs(100) buffer layers are considered. As a comparison to the study of Au-GaAs(100) interfaces, BEEM imaging is performed on Au-Si(100) interfaces. It is noted that Au-GaAs(100) interface formation is relatively insensitive to the effects of substrate surface condition and substrate bulk defect density, and that the combination of BEEM imaging and BEEM spectroscopy indicates that the heterogeneous interface defects are the result of diffusion between the Schottky barrier electrodes.

  1. Ballistic-electron-emission microscopy of subsurface defects at the Au-GaAs(100) interface

    NASA Technical Reports Server (NTRS)

    Hecht, M. H.; Bell, L. D.; Kaiser, W. J.

    1989-01-01

    The application of ballistic-electron-emission microscopy (BEEM) to a study of the influence of GaAs(100) substrate conditions on the formation of a multidefect structure at the Au-GaAs(100) Schottky barrier interface is described. Interfaces prepared on both melt-grown GaAs(100) wafer substrates and MBF-deposited GaAs(100) buffer layers are considered. As a comparison to the study of Au-GaAs(100) interfaces, BEEM imaging is performed on Au-Si(100) interfaces. It is noted that Au-GaAs(100) interface formation is relatively insensitive to the effects of substrate surface condition and substrate bulk defect density, and that the combination of BEEM imaging and BEEM spectroscopy indicates that the heterogeneous interface defects are the result of diffusion between the Schottky barrier electrodes.

  2. Water-Dispersed Hydrophobic Au Nanocrystal Assemblies with a Plasmon Fingerprint.

    PubMed

    Yang, Nailiang; Deeb, Claire; Pelouard, Jean-Luc; Felidj, Nordin; Pileni, Marie-Paule

    2017-08-22

    Hydrophobic Au nanocrystal assemblies (both ordered and amorphous) were dispersed in aqueous solution via the assistance of lipid vesicles. The intertwine between vesicles and Au assemblies was made possible through a careful selection of the length of alkyl chains on Au nanocrystals. Extinction spectra of Au assemblies showed two peaks that were assigned to a scattering mode that red-shifted with increasing the assembly size and an absorption mode associated with localized surface plasmon that was independent of their size. This plasmon fingerprint could be used as a probe for investigating the optical properties of such assemblies. Our water-soluble assemblies enable exploring a variety of potential applications including solar energy and biomedicine.

  3. 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.

  4. Colloidal domain lithography for regularly arranged artificial magnetic out-of-plane monodomains in Au/Co/Au layers.

    PubMed

    Kuświk, Piotr; Ehresmann, Arno; Tekielak, Maria; Szymański, Bogdan; Sveklo, Iosif; Mazalski, Piotr; Engel, Dieter; Kisielewski, Jan; Lengemann, Daniel; Urbaniak, Maciej; Schmidt, Christoph; Maziewski, Andrzej; Stobiecki, Feliks

    2011-03-04

    Regularly arranged magnetic out-of-plane patterns in continuous and flat films are promising for applications in data storage technology (bit patterned media) or transport of individual magnetic particles. Whereas topographic magnetic structures are fabricated by standard lithographical techniques, the fabrication of regularly arranged artificial domains in topographically flat films is difficult, since the free energy minimization determines the existence, shape, and regularity of domains. Here we show that keV He(+) ion bombardment of Au/Co/Au layer systems through a colloidal mask of hexagonally arranged spherical polystyrene beads enables magnetic patterning of regularly arranged cylindrical magnetic monodomains with out-of-plane magnetization embedded in a ferromagnetic matrix with easy-plane anisotropy. This colloidal domain lithography creates artificial domains via periodic lateral anisotropy variations induced by periodic defect density modulations. Magnetization reversal of the layer system observed by magnetic force microscopy shows individual disc switching indicating monodomain states.

  5. Functionalized silicate sol-gel-supported TiO2-Au core-shell nanomaterials and their photoelectrocatalytic activity.

    PubMed

    Pandikumar, Alagarsamy; Murugesan, Sepperumal; Ramaraj, Ramasamy

    2010-07-01

    The N-[3-(trimethoxysilyl)propyl]ethylenediamine (EDAS) derived silicate matrix supported core-shell TiO(2)-Au nanoparticles (EDAS/(TiO(2)-Au)(nps)) were prepared by NaBH(4) reduction of HAuCl(4) precursor on preformed TiO(2) nanoparticles in the presence of EDAS monomer. The core-shell (TiO(2)-Au)(nps) nanoparticles were stabilized by the amine functional group of the EDAS silicate sol-gel network. The potential application of this EDAS/(TiO(2)-Au)(nps) modified electrode toward the photoelectrochemical oxidation of methanol was explored. The EDAS/(TiO(2)-Au)(nps) modified electrode showed a 12-fold enhancement in the catalytic activity toward photoelectrooxidation of methanol when compared to TiO(2) dispersed in EDAS silicate sol-gel matrix. This improved photoelectrochemical performance is explained on the basis of beneficial promotion of interfacial charge transfer processes of the EDAS/(TiO(2)-Au)(nps) nanocomposite. A methanol oxidation peak current density of 12.3 mA cm(-2) was achieved at an optimum loading of Au(nps) on TiO(2) particles. This novel amine functionalized EDAS silicate sol-gel stabilized core-shell (TiO(2)-Au)(nps) nanomaterial could be an excellent candidate for the photocatalytic and photoelectrochemical applications.

  6. Complete Au@ZnO core-shell nanoparticles with enhanced plasmonic absorption enabling significantly improved photocatalysis.

    PubMed

    Sun, Yiqiang; Sun, Yugang; Zhang, Tao; Chen, Guozhu; Zhang, Fengshou; Liu, Dilong; Cai, Weiping; Li, Yue; Yang, Xianfeng; Li, Cuncheng

    2016-05-19

    Nanostructured ZnO exhibits high chemical stability and unique optical properties, representing a promising candidate among photocatalysts in the field of environmental remediation and solar energy conversion. However, ZnO only absorbs the UV light, which accounts for less than 5% of total solar irradiation, significantly limiting its applications. In this article, we report a facile and efficient approach to overcome the poor wettability between ZnO and Au by carefully modulating the surface charge density on Au nanoparticles (NPs), enabling rapid synthesis of Au@ZnO core-shell NPs at room temperature. The resulting Au@ZnO core-shell NPs exhibit a significantly enhanced plasmonic absorption in the visible range due to the Au NP cores. They also show a significantly improved photocatalytic performance in comparison with their single-component counterparts, i.e., the Au NPs and ZnO NPs. Moreover, the high catalytic activity of the as-synthesized Au@ZnO core-shell NPs can be maintained even after many cycles of photocatalytic reaction. Our results shed light on the fact that the Au@ZnO core-shell NPs represent a promising class of candidates for applications in plasmonics, surface-enhanced spectroscopy, light harvest devices, solar energy conversion, and degradation of organic pollutants.

  7. Mono- and Bis-Terpyridine-Based Dimer and Metallo-Organic Polymers as Ionic Templates for Preparation of Multi-Metallic Au Nanocluster and Nanowires.

    PubMed

    Liu, Die; Cao, Hongda; Jiang, Zhilong; Wu, Tun; Sun, Xiaoyi; Wang, Pingshan; Moorefield, Charles N; Dai, Liming; Newkome, George R

    2016-03-01

    The preparation of multi-metallic Au nanocluster and nanowires has been achieved using terpyridine-based metallo-organic polymers as multi-ionic templates through a straightforward counterion exchange with aqueous NaAuCl4 followed by a mild reduction in-situ with sodium citrate. The mild reduction of the [TpyFeTpy]2+ x 2[AuCl4]- complex, derived from [TpyFeTpy]2+ x 2Cl- 1 (tpy = 2,2':6',2"-terpyridine), led to the formation of Au nanoclusters (Au NC) with diameters ranging from 7.5-88 nm. Each Au NC alone contained multiple nanoparticles, with diameters ranging from 2.5-4.5 nm. 1,4-bis-terpyridine based metallo-oraganic polymer [-TpyFeTpy-TpyFeTpy-]n(2n+) x [Cl]2n- 2 was found to generate a multi-ionic metallo-polymer with AuCl4- as the counterion, after mild reduction with sodium citrate, resulting in irregular zigzag shaped Au nanowires (Au NW). The prepared Au NW from the di-metallic complex 3 should find applications within electronic devices. Both Au NC and NW were also found to possess excellent catalytic properties.

  8. Photoionization of Au+, Au2+, and Au3+ ions and developments in the synthesis of the metallofullerene Au@C60

    NASA Astrophysics Data System (ADS)

    Kilcoyne, A. L. David; Muller, Alfred; Schippers, Stefan; Hellhund, Jonas; Borovik, Alexander; Mueller, Allison; Gross, Dylan; Johnson, Andrea; Macaluso, David; A. L. D. Kilcoyne Collaboration

    2015-05-01

    Absolute single photoionization of Au+, Au2+, and Au3+ ions was investigated via the merged-beams technique at AMO Beamline 10.0.1.2 of the Advanced Light Source at Lawrence Berkeley National Laboratory. The absolute single photoionization yield was measured as a function of photon energy for each species from the metastable state ionization threshold region to well above the ground state ionization potential. Additional high-resolution measurements were performed for Au+ and Au2+ ions in the region of the ground and metastable state ionization thresholds to better resolve the detailed resonant structure found therein. This structure was used, along with the reported excited state energy levels of Au+, to preliminarily identify previously unreported excitation levels in all three ions. In addition and as a component of the same program, photoionization studies of the endohedral metallofullerene Au@C60+were performed using endohedral fullerene samples synthesized on-site at Beamline 10.0.1.2 of the ALS.

  9. Au Fixed Point Development at NRC

    NASA Astrophysics Data System (ADS)

    Dedyulin, S. N.; Gotoh, M.; Todd, A. D. W.

    2017-04-01

    Two Au fixed points filled using metal of different nominal purities in carbon crucibles have been developed at the National Research Council Canada (NRC). The primary motivation behind this project was to provide the means for direct thermocouple calibrations at the Au freezing point (1064.18°C). Using a Au fixed point filled with the metal of maximum available purity [99.9997 % pure according to glow discharge mass spectroscopy (GDMS)], multiple freezing plateaus were measured in a commercial high-temperature furnace. Four Pt/Pd thermocouples constructed and calibrated in-house were used to measure the freezing plateaus. From the calibration at Sn, Zn, Al and Ag fixed points, the linear deviation function from the NIST-IMGC reference function (IEC 62460:2008 Standard) was determined and extrapolated to the freezing temperature of Au. For all the Pt/Pd thermocouples used in this study, the measured EMF values agree with the extrapolated values within expanded uncertainty, thus substantiating the use of 99.9997 % pure Au fixed point cell for thermocouple calibrations at NRC. Using the Au fixed point filled with metal of lower purity (99.99 % pure according to GDMS), the effect of impurities on the Au freezing temperature measured with Pt/Pd thermocouple was further investigated.

  10. Significant surface flattening effect by Au addition for Cu growth on Cu3Au(001)

    NASA Astrophysics Data System (ADS)

    Kojima, Takayuki; Mizuguchi, Masaki; Takanashi, Koki

    2014-01-01

    To prepare a flat surface of Cu film on Cu3Au(001), we utilized the effect of Au addition to Cu, and investigated the dependence of the growth mode on the amount of Au added. We grew Cu-x%Au (x = 0-20) films on Cu3Au(001) underlayers by co-deposition and observed the surface morphology by scanning tunneling microscopy. For Cu film without Au addition, three-dimensional islands were observed on the surface while flat two-dimensional surfaces were observed for Cu film with only 2.5%Au addition. This difference in the growth mode was found to be due to surface segregation of Au revealed by in situ Auger electron spectroscopy. It was considered that the Au atoms acted like a surfactant and avoided three-dimensional island growth by suppression of the accumulation of epitaxial strain in Cu-x%Au films. However, the terrace size decreased with x. This decrease was thought to be due to an increase in an effective Ehrlich-Schwoebel barrier. The surface flattening effect by addition of another element would be obtained in other systems as well by employing a suitable element.

  11. Au/Au@polythiophene core/shell nanospheres for heterogeneous catalysis of nitroarenes.

    PubMed

    Shin, Hye-Seon; Huh, Seong

    2012-11-01

    Monodisperse Au/Au@polythiophene core/shell nanospheres were facilely prepared through the reduction of gold precursor, AuCl₄⁻, by 2-thiopheneacetonitrile in an aqueous solution. Concomitantly, 2-thiopheneacetonitrile polymerized during this redox process. As a result, Au nanoparticle was encapsulated by conductive polymer shell to afford novel core/shell nanospheres. Interestingly, the shell was composed of very tiny Au nanoparticles surrounded with thiophene polymers. Thus, the new material is best described as Au/Au@polythiophene core/shell nanospheres. FT-IR spectroscopy revealed that the Au nanoparticles were coordinated by the C≡N groups of the polythiophene shell. Some of the C≡N groups were partially hydrolyzed into COOH groups during the redox process because of the acidic reaction condition. The shell was conductive based on the typical ohmic behavior found in electrical measurement. The Au/Au@polythiophene core/shell nanospheres were found to be very active catalysts for the hydrogenation of various nitroarene compounds into corresponding aminoarene compounds in the presence of NaBH₄. Both hydrophilic and hydrophobic nitroarenes were efficiently hydrogenated under mild conditions.

  12. Au40: A Large Tetrahedral Magic Cluster

    SciTech Connect

    Jiang, Deen; Walter, Michael

    2011-01-01

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

  13. Regulating the surface plasmon resonance coupling between Au-nanoparticle and Au-film

    NASA Astrophysics Data System (ADS)

    Wang, Shuang; Li, Kewu; Zhang, Rui; Jing, Ning; Chen, Youhua; Chen, Yuanyuan; Wang, Zhibin

    2017-01-01

    In this paper, we report the coupling between the localized surface plasmon resonance (LSPR) of Au-nanoparticles and surface plasmon resonance (SPR) of the Au-film. According to the conditions for SPR excitation of the classical Kretschmann-Raether structure with 50nm Au thin film, the commonly used classes of spherical Au-nanoparticle is studied and optimized. We used the finite element analysis (COMSOL Multiphysics 5.0), to simulate the coupling. The results from calculation and simulation indicate that the resonant plasmonic coupling between Au-nanoparticles and Au-film could lead to a large field enhancement and thus improve SPR. We demonstrate that the resonant plasmonic coupling could be regulated by the size of nanoparticles, the distance between nanoparticles .

  14. Ir-induced activation of Au towards CO adsorption: Ir films deposited on Au{111}

    NASA Astrophysics Data System (ADS)

    Zhang, Tianfu; Driver, Stephen M.; Pratt, Stephanie J.; Jenkins, Stephen J.; King, David A.

    2016-06-01

    We have investigated the interaction of CO with Ir/Au{111} bimetallic surfaces, and the influence of morphology changes as Ir moves sub-surface into the Au bulk, using reflection-absorption infrared spectroscopy (RAIRS). The presence of Ir stabilises CO on exposed regions of the Au surface at temperatures up to around 200 K: we attribute this to low-coordinated Au sites, probably associated with lifting of the clean-surface 'herringbone' reconstruction by Ir deposition. The highest density of active Au sites is obtained after annealing the bimetallic surface to 500-600 K: we attribute this to morphology changes associated with the movement of Ir into bulk Au.

  15. Substrate effects on the analysis of biomolecular layers using Au +, Au 3+ and C 60+ bombardments

    NASA Astrophysics Data System (ADS)

    Kordys, Jeanette; Fletcher, John S.; Lockyer, Nicholas P.; Vickerman, John C.

    2008-12-01

    Effects of platinum silicon, graphite and PET substrates on the secondary ion yield of sub-monolayer and multilayer samples of Cyclosporin A following 20 keV Au +, Au 3+and C 60+ impacts have been investigated. The obtained results of sub-monolayer samples show that platinum enhances the yield of the pseudo-molecular ion following Au + and Au 3+ impacts due to the high density of the substrate that enables the energy of the primary ions to be deposited near the surface. C 60+ impacts on sub-monolayer samples are less effective, but there is an enhancement on PET substrates. Impacts of 20 keV Au + and Au 3+ are not very efficient on multilayer samples. 20 keV C 60+ impacts enhance the yields significantly, especially for the relatively high molecular weight [M+H] + ion.

  16. Surface composition tuning of Au-Pt bimetallic nanoparticles for enhanced carbon monoxide and methanol electro-oxidation.

    PubMed

    Suntivich, Jin; Xu, Zhichuan; Carlton, Christopher E; Kim, Junhyung; Han, Binghong; Lee, Seung Woo; Bonnet, Nicéphore; Marzari, Nicola; Allard, Lawrence F; Gasteiger, Hubert A; Hamad-Schifferli, Kimberly; Shao-Horn, Yang

    2013-05-29

    The ability to direct bimetallic nanoparticles to express desirable surface composition is a crucial step toward effective heterogeneous catalysis, sensing, and bionanotechnology applications. Here we report surface composition tuning of bimetallic Au-Pt electrocatalysts for carbon monoxide and methanol oxidation reactions. We establish a direct correlation between the surface composition of Au-Pt nanoparticles and their catalytic activities. We find that the intrinsic activities of Au-Pt nanoparticles with the same bulk composition of Au0.5Pt0.5 can be enhanced by orders of magnitude by simply controlling the surface composition. We attribute this enhancement to the weakened CO binding on Pt in discrete Pt or Pt-rich clusters surrounded by surface Au atoms. Our finding demonstrates the importance of surface composition control at the nanoscale in harnessing the true electrocatalytic potential of bimetallic nanoparticles and opens up strategies for the development of highly active bimetallic nanoparticles for electrochemical energy conversion.

  17. 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.

  18. Controlled synthesis of FePt-Au hybrid nanoparticles triggered by reaction atmosphere and FePt seeds.

    PubMed

    Zhu, Jinghan; Wu, Jiajia; Liu, Fei; Xing, Ruijun; Zhang, Chenzhen; Yang, Ce; Yin, Han; Hou, Yanglong

    2013-10-07

    We report an effective and facile method for synthesis of FePt-Au hybrid nanoparticles (HNPs). The typical secondary growth of Au proceeded in the presence of FePt seeds in organic solvents under a specific atmosphere. Interestingly, the type of atmosphere (Ar or Ar-H₂) and the size of selected FePt seeds were two major parameters determining the final morphology of FePt-Au HNPs. Enhancement of catalytic activity and stability of FePt-Au HNPs in methanol oxidation were achieved owing to interactions between Au and FePt. The optical properties of the resulting products can be steadily tuned which sheds light on their potential application in optical devices and bioimaging. The novel synthetic strategy offers an important tool towards multifunctional nanomaterials with designed architectures.

  19. Rhodamine B immobilized on hollow Au-HMS material for naked-eye detection of Hg2+ in aqueous media.

    PubMed

    Zhang, Na; Li, Gang; Cheng, Zhuhong; Zuo, Xiujin

    2012-08-30

    A simple, effective method has been demonstrated to immobilize Rhodamine B (RhB) probes on mesoporous silica (Au-HMS). The prepared chemosensor (Au-HMS-Probe) was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-vis spectrum and Fourier transform infrared spectroscopy (FT-IR). Further application of Au-HMS-Probe in sensing Hg(2+) was confirmed by fluorescence titration experiment. Au-HMS-Probe afforded "turn-on" fluorescence enhancement and displayed high brightness in water, and it also showed excellent selectivity for Hg(2+) over alkali (Na(+), K(+)), alkaline earth (Mg(2+), Ca(2+)) and other heavy metal ions (Ag(+), Cd(2+), Co(2+), Pb(2+), Ni(2+), Cu(2+), Fe(2+)). Importantly, Au-HMS-Probe could be regenerated by treatment with tetrapropylammonium hydroxide solution. Crown Copyright © 2012. Published by Elsevier B.V. All rights reserved.

  20. An ultrafast look at Au nanoclusters.

    PubMed

    Yau, Sung Hei; Varnavski, Oleg; Goodson, Theodore

    2013-07-16

    In the past 20 years, researchers studying nanomaterials have uncovered many new and interesting properties not found in bulk materials. Extensive research has focused on metal nanoparticles (>3 nm) because of their potential applications, such as in molecular electronics, image markers, and catalysts. In particular, the discovery of metal nanoclusters (<3 nm) has greatly expanded the horizon of nanomaterial research. These nanosystems exhibit molecular-like characteristics as their size approaches the Fermi-wavelength of an electron. The relationships between size and physical properties for nanomaterials are intriguing, because for metal nanosystems in this size regime both size and shape determine electronic properties. Remarkably, changes in the optical properties of nanomaterials have provided tremendous insight into the electronic structure of nanoclusters. The success of synthesizing monolayer protected clusters (MPCs) in the condensed phase has allowed scientists to probe the metal core directly. Au MPCs have become the "gold" standard in nanocluster science, thanks to the rigorous structural characterization already accomplished. The use of ultrafast laser spectroscopy on MPCs in solution provides the benefit of directly studying the chemical dynamics of metal nanoclusters (core), and their nonlinear optical properties. In this Account, we investigate the optical properties of MPCs in the visible region using ultrafast spectroscopy. Based on fluorescence up-conversion spectroscopy, we propose an emission mechanism for these nanoclusters. These clusters behave differently from nanoparticles in terms of emission lifetimes as well as two-photon cross sections. Through further investigation of the transient (excited state) absorption, we have found many unique phenomena of nanoclusters, such as quantum confinement effects and vibrational breathing modes. In summary, based on the differences in the optical properties, the distinction between nanoclusters and

  1. 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.

  2. Experimental evidences of a large extrinsic spin Hall effect in AuW alloy

    SciTech Connect

    Laczkowski, P.; Rojas-Sánchez, J.-C.

    2014-04-07

    We report an experimental study of a gold-tungsten alloy (7 at. % W concentration in Au host) displaying remarkable properties for spintronics applications using both magneto-transport in lateral spin valve devices and spin-pumping with inverse spin Hall effect experiments. A very large spin Hall angle of about 10% is consistently found using both techniques with the reliable spin diffusion length of 2 nm estimated by the spin sink experiments in the lateral spin valves. With its chemical stability, high resistivity, and small induced damping, this AuW alloy may find applications in the nearest future.

  3. Thermal Expansion of AuIn2

    SciTech Connect

    Saw, C K; Siekhaus, W J

    2004-07-12

    The thermal expansion of AuIn{sub 2} gold is of great interest in soldering technology. Indium containing solders have been used to make gold wire interconnects at low soldering temperature and over time, AuIn{sub 2} is formed between the gold wire and the solder due to the high heat of formation and the high inter-metallic diffusion of indium. Hence, the thermal expansion of AuIn{sub 2} alloy in comparison with that of the gold wire and the indium-containing solder is critical in determining the integrity of the connection. We present the results of x-ray diffraction measurement of the coefficient of linear expansion of AuIn{sub 2} as well as the bulk expansion and density changes over the temperature range of 30 to 500 C.

  4. PHENIX results on jets in d + Au

    NASA Astrophysics Data System (ADS)

    Hanks, J. Ali

    2016-12-01

    We present recently published results [A. Adare, et al., arxiv:arXiv:1509.04657] on fully reconstructed R=0.3 anti-kt jets measured in p+p and d+Au collisions at 200 GeV center-of-mass energy. The jet yields for four centrality classes along with the p+p reference are presented, as well as both the minimum bias RdAu and centrality dependent RdAu and RCP. We find that while the minimum bias RdA is consistent with unity, providing a strong constraint on models including cold-nuclear-matter effects or energy loss in small systems, the centrality dependent RdAu show a striking variation which presents a challenge to models attempting to describe the interplay between soft and hard processes in these systems.

  5. RHIC Au beam in Run 2014

    SciTech Connect

    Zhang, S. Y.

    2014-09-15

    Au beam at the RHIC ramp in run 2014 is reviewed together with the run 2011 and run 2012. Observed bunch length and longitudinal emittance are compared with the IBS simulations. The IBS growth rate of the longitudinal emittance in run 2014 is similar to run 2011, and both are larger than run 2012. This is explained by the large transverse emittance at high intensity observed in run 2012, but not in run 2014. The big improvement of the AGS ramping in run 2014 might be related to this change. The importance of the injector intensity improvement in run 2014 is emphasized, which gives rise to the initial luminosity improvement of 50% in run 2014, compared with the previous Au-Au run 2011. In addition, a modified IBS model, which is calibrated using the RHIC Au runs from 9.8 GeV/n to 100 GeV/n, is presented and used in the study.

  6. 3D Interdigital Au/MnO2 /Au Stacked Hybrid Electrodes for On-Chip Microsupercapacitors.

    PubMed

    Hu, Haibo; Pei, Zhibin; Fan, Hongjin; Ye, Changhui

    2016-06-01

    On-chip microsupercapacitors (MSCs) have application in powering microelectronic devices. Most of previous MSCs are made from carbon materials, which have high power but low energy density. In this work, 3D interdigital Au/MnO2 /Au stacked MSCs have been fabricated based on laser printed flexible templates. This vertical-stacked electrode configuration can effectively increase the contact area between MnO2 active layer and Au conductive layer, and thus improve the electron transport and electrolyte ion diffusion, resulting in enhanced pseudocapacitive performance of MnO2 . The stacked electrode can achieve an areal capacitance up to 11.9 mF cm(-2) . Flexible and all-solid-state MSCs are assembled based on the sandwich hybrid electrodes and PVA/LiClO4 gel electrolyte and show outstanding high-rate capacity and mechanical flexibility. The laser printing technique in this work combined with the physical sputtering and electrodeposition allows fabrication of MSC array with random sizes and patterns, making them promising power sources for small-scale flexible microelectronic energy storage systems (e.g., next-generation smart phones).

  7. Counterion-Mediated Assembly of Spherical Nucleic Acid-Au Nanoparticle Conjugates (SNA-AuNPs)

    NASA Astrophysics Data System (ADS)

    Kewalramani, Sumit; Moreau, Liane; Guerrero-García, Guillermo; Mirkin, Chad; Olvera de La Cruz, Monica; Bedzyk, Michael; Afosr Muri Team

    2015-03-01

    Controlled crystallization of colloids from solution has been a goal of material scientists for decades. Recently, nucleic acid functionalized spherical Au nanoparticles (SNA-AuNPs) have been programmed to assemble in a wide variety of crystal structures. In this approach, the assembly is driven by Watson-Crick hybridization between DNAs coating the AuNPs. Here, we show that counterions can induce ordered assembly of SNA-AuNPs in bulk solutions, even in the absence of base pairing interactions. The electrostatics-driven assembly of spherical nucleic acid-Au nanoparticle conjugates (SNA-AuNPs) is probed as a function of counterion concentration and counterion valency [ +1 (Na+) or +2 (Ca2+) ] by in situ solution X-ray scattering. Assemblies of AuNPs capped with single-stranded (ss-) or double-stranded (ds-) DNA are examined. SAXS reveals disordered (gas-like) --> face-centered-cubic (FCC) --> glass-like phase transitions with increasing solution ionic strength. These studies demonstrate how non-base-pairing interactions can be tuned to create crystalline assemblies of SNA-AuNPs. The dependence of the inter-SNA-AuNP interactions on counterion valency and stiffness of the DNA corona will be discussed.

  8. DFT study on cysteine adsorption mechanism on Au(111) and Au(110)

    SciTech Connect

    Buimaga-Iarinca, Luiza; Floare, Calin G.; Calborean, Adrian; Turcu, Ioan

    2013-11-13

    Periodic density functional theory calculations were used to investigate relevant aspects of adsorption mechanisms of cysteine dimers in protonated form on Au(111) and Au(110) surfaces. The projected densities of states are explicitly discussed for all main chemical groups of cysteine, i.e. the amino group (NH2), the thiol group (SH) and the carboxylic group (COOH) to identify differences in adsorption mechanism. Special emphasis is put on the analysis of changes in the electronic structure of molecules adsorbed on Au(111) and Au(110) surfaces as well as the accompanying charge transfer mechanisms at molecule-substrate interaction.

  9. Thermal expansion anomalies at the magnetic transition temperatures of Au 4Mn and Au 2Mn

    NASA Astrophysics Data System (ADS)

    Abe, S.; Matsumoto, M.; Yoshida, H.; Mori, S.; Kanomata, T.; Kaneko, T.

    1992-02-01

    Measurements of the thermal expansion and specific heat are carried out for the ferromagnetic ordered alloy Au 4Mn and the antiferromagnetic one Au 2Mn at temperatures including the Curie temperature Tc and Néel temperature TN. The pressure effect on TC and TN is also measured. It is found that both Au 4Mn and Au 2Mn have positive exchange strictions and d TC/d p and d TN/d p are positive. The results are discussed in terms of the MnMn distance dependence of the exchange interactions in AuMn alloys.

  10. The French Mess Nucleaire

    SciTech Connect

    Davis, M.B.

    1994-07-01

    Nuclear weapons production has contaminated parts of France, and measures to counter this contamination may be as much cover-up as cleanup. The nuclear weapons industry is trying to remedy some of the problems it created. But until France lifts military secrecy from weapons production matters that affect the environment, the public has no way to gauge the cleanup. No institution outside the Atomic Energy Commission (CEA) and the Ministry of Defense has control over waste disposal, decontamination, and dismantlement at military nuclear sites. The major generators of weapons production waste in France are the CEA and Cogema, one of its many subsidiaries. Regular operations in military production sites produce environmental contamination. The authors also discuss some accidents causing further contamination. The clean-up measures that the industry is known to be taking, diluting the waste and minimizing the amount of waste, are suspect. The earth`s atmosphere has been considered a prime medium for diluting waste by open air burning of radioactive materials. Releases of mercury to the atmosphere, 260 kilograms per year as of 1984, contributed to water pollution as rain washed the mercury out of the air. Ocean dumping was the CEA`s answer to disposal of sold as well as liquid wastes. Injection liquids into the soil has been a temptation at sites not near substantial bodies of water. Burial of solid wastes has been common. The nuclear industry and the military must make public where and in what form wastes are stored. They must allow independent experts and institutions to examine their research, fabrication, and waste disposal sites. 48 refs.

  11. 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.

  12. 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

  13. Inhibition of gold nanoparticles (AuNPs) on pathogenic biofilm formation and invasion to host cells

    PubMed Central

    Yu, Qilin; Li, Jianrong; Zhang, Yueqi; Wang, Yufan; Liu, Lu; Li, Mingchun

    2016-01-01

    Owing to the growing infectious diseases caused by eukaryotic and prokaryotic pathogens, it is urgent to develop novel antimicrobial agents against clinical pathogenic infections. Biofilm formation and invasion into the host cells are vital processes during pathogenic colonization and infection. In this study, we tested the inhibitory effect of Au nanoparticles (AuNPs) on pathogenic growth, biofilm formation and invasion. Interestingly, although the synthesized AuNPs had no significant toxicity to the tested pathogens, Candida albicans and Pseudomonas aeruginosa, the nanoparticles strongly inhibited pathogenic biofilm formation and invasion to dental pulp stem cells (DPSCs). Further investigations revealed that AuNPs abundantly bound to the pathogen cells, which likely contributed to their inhibitory effect on biofilm formation and invasion. Moreover, treatment of AuNPs led to activation of immune response-related genes in DPSCs, which may enhance the activity of host immune system against the pathogens. Zeta potential analysis and polyethylene glycol (PEG)/polyethyleneimine (PEI) coating tests further showed that the interaction between pathogen cells and AuNPs is associated with electrostatic attractions. Our findings shed novel light on the application of nanomaterials in fighting against clinical pathogens, and imply that the traditional growth inhibition test is not the only way to evaluate the drug effect during the screening of antimicrobial agents. PMID:27220400

  14. Highly Efficient AuPd/Carbon Nanotube Nanocatalysts for the Electro-Fenton Process.

    PubMed

    Sun, Meng; Zhang, Gong; Liu, Yang; Liu, Huijuan; Qu, Jiuhui; Li, Jinghong

    2015-05-11

    Development of novel nanocatalysts for the highly efficient in situ synthesis of H2 O2 from H2 and O2 in the electro-Fenton (EF) process has potential for the remediation of water pollution. In this work, AuPd/carbon nanotube (CNT) nanocatalysts were successfully synthesized by the facile aggregation of AuPd bimetals on CNTs. Characterization by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy indicated that pure AuPd bimetallic heterogeneous nanospheres (≈20 nm) were well dispersed outside the CNTs, which resulted in better catalytic performance than Pd/CNTs alone: 0.36 M H2 O2 was synthesized; 0.05 M Fe(2+) optimally initiated the EF process due to the superior in situ Fe(2+) regeneration; and the organic pollutant removal reached 100 % at 37 min, with a pseudo-first-order kinetic constant k1 =0.051 min(-1) . Moreover, structural insights before/after catalysis revealed that Au strengthened the construction of the nanocrystals, avoided negative deactivation caused by AuPd agglomeration, and immobilized the active Pd(111). The catalytic stability of AuPd/CNTs over ten cycles implied long durability and promising applications of this material.

  15. Evidence for Bioavailability of Au Nanoparticles from Soil and Biodistribution within Earthworms (Eisenia fetida)

    SciTech Connect

    J Unrine; S Hunyadi; O Tsyusko; W Rao; A Shoults-Wilson; P Bertsch

    2011-12-31

    Because Au nanoparticles (NPs) are resistant to oxidative dissolution and are easily detected, they have been used as stable probes for the behavior of nanomaterials within biological systems. Previous studies provide somewhat limited evidence for bioavailability of Au NPs in food webs, because the spatial distribution within tissues and the speciation of Au was not determined. In this study, we provide multiple lines of evidence, including orthogonal microspectroscopic techniques, as well as evidence from biological responses, that Au NPs are bioavailable from soil to a model detritivore (Eisenia fetida). We also present limited evidence that Au NPs may cause adverse effects on earthworm reproduction. This is perhaps the first study to demonstrate that Au NPs can be taken up by detritivores from soil and distributed among tissues. We found that primary particle size (20 or 55 nm) did not consistently influence accumulated concentrations on a mass concentration basis; however, on a particle number basis the 20 nm particles were more bioavailable. Differences in bioavailability between the treatments may have been explained by aggregation behavior in pore water. The results suggest that nanoparticles present in soil from activities such as biosolids application have the potential to enter terrestrial food webs.

  16. Photoelectrochemical sensing of 4-chlorophenol based on Au/BiOCl nanocomposites.

    PubMed

    Yan, Pengcheng; Xu, Li; Xia, Jiexiang; Huang, Yan; Qiu, Jingxia; Xu, Qian; Zhang, Qi; Li, Huaming

    2016-08-15

    The Au/BiOCl composites have been prepared by a facile one-pot ethylene glycol (EG) assisted solvothermal reaction in the presence of ionic liquid 1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl). During the synthesis procedure, the [C16mim]Cl has been used as Cl source, solvent of this system, and dispersing agent to effectively disperse Au on the surface of BiOCl. The as-prepared samples have been systematically characterized by multiple instruments to investigate the structure, morphology, and photoelectrochemical properties. According to the photoelectrochemical data, the Au/BiOCl composites exhibit better photoelectrochemical performance toward the detection of 4-chlorophenol than that of the pure BiOCl. The photocurrent response of Au/BiOCl modified electrode is high and stable under light irradiation. The proposed Au/BiOCl modified electrode shows a wide linear response ranging from 0.16 to 20mgL(-1) with detection limit of 0.05mgL(-1). It indicates a dramatically promising application of bismuth oxyhalides in photoelectrochemical detection. It will be expected that the present study may be lightly extended to the monitor of other organic pollutants by photoelectrochemical detection of the Au/BiOCl composites.

  17. The impact of fabrication conditions on the quality of Au nanoparticle arrays on dimpled Ta templates

    NASA Astrophysics Data System (ADS)

    El-Sayed, Hany A.; Molero, Hebert M.; Birss, Viola I.

    2012-11-01

    Highly ordered dimpled Ta (DT) nanotemplates, prepared by electrochemical anodization of Ta, were recently reported to be ideally suited for the fabrication of a Au nanoparticle (NP) array using a Au thin film dewetting method. Here, we provide guidance and understanding of the effect of the DT fabrication and Au film deposition steps on the characteristics of the resulting NP array. Specifically, the optimum anodization time, voltage and solution composition are established, and the thickness of the sputter-deposited metal film is shown to be a very important parameter in achieving the desired single Au NP per dimple. The resulting high quality Au NP arrays are demonstrated to be electrochemically addressable, with the total Au surface area, measured electrochemically for large-scale samples, agreeing with the calculated area, based on scanning electron microscope determination of average particle shape and distribution. As the NP formation process proceeds via confined thin film dewetting, the protocol developed here should be applicable to the formation of NP arrays of a range of other metals and alloys.

  18. Fabrication of photoactive heterostructures based on quantum dots decorated with Au nanoparticles

    PubMed Central

    Fanizza, Elisabetta; Urso, Carmine; Iacobazzi, R. Maria; Depalo, Nicoletta; Corricelli, Michela; Panniello, Annamaria; Agostiano, Angela; Denora, Nunzio; Laquintana, Valentino; Striccoli, Marinella; Curri, M. Lucia

    2016-01-01

    Abstract Silica based multifunctional heterostructures, exhibiting near infrared (NIR) absorption (650–1200 nm) and luminescence in the visible region, represent innovative nanosystems useful for diagnostic or theranostic applications. Herein, colloidal synthetic procedures are applied to design a photoactive multifunctional nanosystem. Luminescent silica (SiO2) coated quantum dots (QDs) have been used as versatile nanoplatforms to assemble on their surface gold (Au) seeds, further grown into Au spackled structures. The synthesized nanostructures combine the QD emission in the visible region, and, concomitantly, the distinctive NIR absorption of Au nanodomains. The possibility of having multiple QDs in a single heterostructure, the SiO2 shell thickness, and the extent of Au deposition onto SiO2 surface have been carefully controlled. The work shows that a single QD entrapped in 16 nm thick SiO2 shell, coated with Au speckles, represents the most suitable geometry to preserve the QD emission in the visible region and to generate NIR absorption from metal NPs. The resulting architectures present a biomedical potential as an effective optical multimodal probes and as promising therapeutic agents due to the Au NP mediated photothermal effect. PMID:27877861

  19. 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.

  20. Advanced catalytic performance of Au-Pt double-walled nanotubes and their fabrication through galvanic replacement reaction.

    PubMed

    Chen, Lu; Kuai, Long; Yu, Xue; Li, Wenzheng; Geng, Baoyou

    2013-08-26

    Bimetallic tubular nanostructures have been the focus of intensive research as they have very interesting potential applications in various fields including catalysis and electronics. In this paper, we demonstrate a facile method for the fabrication of Au-Pt double-walled nanotubes (Au-Pt DWNTs). The DWNTs are fabricated through the galvanic displacement reaction between Ag nanowires and various metal ions, and the Au-Pt DWNT catalysts exhibit high active catalytic performances toward both methanol electro-oxidation and 4-nitrophenol (4-NP) reduction. First, they have a high electrochemically active surface area of 61.66 m(2)  g(-1), which is close to the value of commercial Pt/C catalysts (64.76 m(2) g(-1)), and the peak current density of Au-Pt DWNTs in methanol oxidation is recorded as 138.25 mA mg(-1), whereas those of Pt nanotubes, Au/Pt nanotubes (simple mixture), and commercial Pt/C are 24.12, 40.95, and 120.65 mA mg(-1), respectively. The Au-Pt DWNTs show a markedly enhanced electrocatalytic activity for methanol oxidation compared with the other three catalysts. They also show an excellent catalytic performance in comparison with common Au nanotubes for 4-nitrophenol (4-NP) reduction. The attractive performance exhibited by these prepared Au-Pt DWNTs can be attributed to their unique structures, which make them promising candidates as high-performance catalysts.

  1. 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

  2. Systematic Measurements of Identified Particle Spectra in pp, d+Au and Au+Au Collisions from STAR

    SciTech Connect

    STAR Coll

    2009-04-11

    Identified charged particle spectra of {pi}{sup {+-}}, K{sup {+-}}, p and {bar p} at mid-rapidity (|y| < 0.1) measured by the dE/dx method in the STAR-TPC are reported for pp and d + Au collisions at {radical}s{sub NN} = 200 GeV and for Au + Au collisions at 62.4 GeV, 130 GeV, and 200 GeV. Average transverse momenta, total particle production, particle yield ratios, strangeness and baryon production rates are investigated as a function of the collision system and centrality. The transverse momentum spectra are found to be flatter for heavy particles than for light particles in all collision systems; the effect is more prominent for more central collisions. The extracted average transverse momentum of each particle species follows a trend determined by the total charged particle multiplicity density. The Bjorken energy density estimate is at least several GeV/fm{sub 3} for a formation time less than 1 fm/c. A significantly larger net-baryon density and a stronger increase of the net-baryon density with centrality are found in Au + Au collisions at 62.4 GeV than at the two higher energies. Antibaryon production relative to total particle multiplicity is found to be constant over centrality, but increases with the collision energy. Strangeness production relative to total particle multiplicity is similar at the three measured RHIC energies. Relative strangeness production increases quickly with centrality in peripheral Au + Au collisions, to a value about 50% above the pp value, and remains rather constant in more central collisions. Bulk freeze-out properties are extracted from thermal equilibrium model and hydrodynamics-motivated blast-wave model fits to the data. Resonance decays are found to have little effect on the extracted kinetic freeze-out parameters due to the transverse momentum range of our measurements. The extracted chemical freeze-out temperature is constant, independent of collision system or centrality; its value is close to the predicted phase

  3. Efficient Removal of Methane over Cobalt-Monoxide-Doped AuPd Nanocatalysts.

    PubMed

    Xie, Shaohua; Liu, Yuxi; Deng, Jiguang; Zang, Simiao; Zhang, Zhenhua; Arandiyan, Hamidreza; Dai, Hongxing

    2017-02-21

    To overcome deactivation of Pd-based catalysts at high temperatures, we herein design a novel pathway by introducing a certain amount of CoO to the supported Au-Pd alloy nanoparticles (NPs) to generate high-performance Au-Pd-xCoO/three-dimensionally ordered macroporous (3DOM) Co3O4 (x is the Co/Pd molar ratio) catalysts. The doping of CoO induced the formation of PdO-CoO active sites, which was beneficial for the improvement in adsorption and activation of CH4 and catalytic performance. The Au-Pd-0.40CoO/3DOM Co3O4 sample performed the best (T90% = 341 °C at a space velocity of 20 000 mL g(-1) h(-1)). Deactivation of the 3DOM Co3O4-supported Au-Pd, Pd-CoO, and Au-Pd-xCoO nanocatalysts resulting from water vapor addition was due to the formation and accumulation of hydroxyl on the catalyst surface, whereas deactivation of the Pd-CoO/3DOM Co3O4 catalyst at high temperatures (680-800 °C) might be due to decomposition of the PdOy active phase into aggregated Pd(0) NPs. The Au-Pd-xCoO/3DOM Co3O4 nanocatalysts exhibited better thermal stability and water tolerance ability compared to the 3DOM Co3O4-supported Au-Pd and Pd-CoO nanocatalysts. We believe that the supported Au-Pd-xCoO nanomaterials are promising catalysts in practical applications for organic combustion.

  4. Dendritic Au/TiO₂ nanorod arrays for visible-light driven photoelectrochemical water splitting.

    PubMed

    Su, Fengli; Wang, Tuo; Lv, Rui; Zhang, Jijie; Zhang, Peng; Lu, Jianwei; Gong, Jinlong

    2013-10-07

    This paper describes the synthesis of TiO₂ branched nanorod arrays (TiO₂ BNRs) with plasmonic Au nanoparticles attached on the surface. Such Au/TiO₂ BNR composites exhibit high photocatalytic activity in photoelectrochemical (PEC) water splitting. The unique structure of Au/TiO₂ BNRs shows enhanced activity with a photocurrent of 0.125 mA cm(-2) under visible light (≥420 nm) and 2.32 ± 0.1 mA cm(-2) under AM 1.5 G illumination (100 mW cm(-2)). The obtained photocurrent is comparable to the highest value ever reported. Furthermore, the Au/TiO₂ BNRs achieve the highest efficiency of ∼1.27% at a low bias of 0.50 V vs. RHE, indicating elevated charge separation and transportation efficiencies. The high PEC performance is mainly due to the plasmonic effect of Au nanoparticles, which enhances the visible light absorption, together with the large surface area, efficient charge separation and high carrier mobility of the TiO₂ BNRs. The carrier density of Au/TiO₂ BNRs is nearly 6 times higher than the pristine TiO₂ BNRs as calculated by the Mott-Schottky plot. Based on the analysis by UV-Vis spectroscopy, electrochemical impedance spectroscopy, and photoluminescence, a mechanism was proposed to explain the high activity of Au/TiO₂ BNRs in PEC water splitting. The capability of synthesizing highly visible light active Au/TiO₂ BNR based photocatalysts is useful for solar conversion applications, such as PEC water splitting, dye-sensitized solar cells and photovoltaic devices.

  5. One-pot synthesis of M (M = Ag, Au)@SiO2 yolk-shell structures via an organosilane-assisted method: preparation, formation mechanism and application in heterogeneous catalysis.

    PubMed

    Chen, Yu; Wang, Qihua; Wang, Tingmei

    2015-05-21

    We demonstrate the fabrication of yolk-shell catalysts consisting of a single M (M = Ag, Au) nanoparticle encapsulated within a hollow mesoporous organosilica shell via an organosilane-assisted strategy. The advantages of our method lie in its good controllability of the void space as well as the thickness of the mesoporous shell. The M@CTAB/SiO2 synthesized through a modified Stöber method can transform to yolk-shell structures after adding (3-aminopropyl)trimethoxysilane (APTMS)/TEOS or (3-aminopropyl)triethoxysilane (APTES)/TEOS into the synthetic medium. We give unambiguous evidence that the middle CTAB/SiO2 layer transforms into a less dense APTMS-rich organic-inorganic layer which was selectively removed in alkaline aqueous solution, while the amino-functionalized hybrid shells remain intact. Moreover, we discuss the role of alkylamino groups in the shell in the transformation from Ag@SiO2 nanorattles to hollow structures when impregnating the as-synthesized Ag@SiO2 nanorattles in HAuCl4 aqueous solution. The nanorattles also exhibit high catalytic activity for the catalytic reduction of p-nitrophenol.

  6. Gold nanoparticles production using reactor and cyclotron based methods in assessment of (196,198)Au production yields by (197)Au neutron absorption for therapeutic purposes.

    PubMed

    Khorshidi, Abdollah

    2016-11-01

    Medical nano-gold radioisotopes is produced regularly using high-flux nuclear reactors, and an accelerator-driven neutron activator can turn out higher yield of (197)Au(n,γ)(196,198)Au reactions. Here, nano-gold production via radiative/neutron capture was investigated using irradiated Tehran Research Reactor flux and also simulated proton beam of Karaj cyclotron in Iran. (197)Au nano-solution, including 20nm shaped spherical gold and water, was irradiated under Tehran reactor flux at 2.5E+13n/cm(2)/s for (196,198)Au activity and production yield estimations. Meanwhile, the yield was examined using 30MeV proton beam of Karaj cyclotron via simulated new neutron activator containing beryllium target, bismuth moderator around the target, and also PbF2 reflector enclosed the moderator region. Transmutation in (197)Au nano-solution samples were explored at 15 and 25cm distances from the target. The neutron flux behavior inside the water and bismuth moderators was investigated for nano-gold particles transmutation. The transport of fast neutrons inside bismuth material as heavy nuclei with a lesser lethargy can be contributed in enhanced nano-gold transmutation with long duration time than the water moderator in reactor-based method. Cyclotron-driven production of βeta-emitting radioisotopes for brachytherapy applications can complete the nano-gold production technology as a safer approach as compared to the reactor-based method.

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

    PubMed

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

    2016-10-06

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

  8. Visualizing Au-Au bond formation in solution with femtosecond X-ray scattering

    NASA Astrophysics Data System (ADS)

    Adachi, Shin-Ichi

    2015-05-01

    Bond formation is an essential process in chemical reactions, but it is challenging to keep track of detailed atomic movements associated with bond formation because of its bimolecular nature. Bond formation in solution phase has been especially elusive because it is difficult to initiate and follow such diffusion-limited bimolecular processes with ultrafast time resolution. In this regard, a Au oligomer complex, [Au(CN)]n-, offers a good model system in which to study the dynamics of bond formation in solution.Using femtosecond time-resolved X-ray scattering, we successfully visualized in real time the birth of a gold trimer complex, [Au(CN)2-]3,that occurs via photoinduced formation of Au-Au covalent bonds. The ground state of the trimer has Au atoms that are weakly bound to each other by aurophilic interaction and aligned in a bent geometry. Upon photoexcitation, the ground state rapidly converts into the first excited state where Au-Au covalent bonds are formed among Au atoms aligned in a linear geometry. Subsequently, the state transforms to a triplet state in 1.6 ps while accompanying further contraction of Au-Au bonds by 0.1 Å. Later, the triplet state of the trimer converts to a tetramer on nanosecond time scale. This work showcases the possibility of tracking detailed structural changes in solution with sub-ps temporal and sub-angstrom spatial resolutions, thanks to the advent of X-ray free electron lasers and the advance of data analysis of time-resolved solution scattering data.

  9. Suppression of ϒ production in d +Au and Au+Au collisions at √{sNN}=200 GeV

    NASA Astrophysics Data System (ADS)

    Adamczyk, L.; Adkins, J. K.; Agakishiev, G.; Aggarwal, M. M.; Ahammed, Z.; Alekseev, I.; Alford, J.; Anson, C. D.; Aparin, A.; Arkhipkin, D.; Aschenauer, E. C.; Averichev, G. S.; Balewski, J.; Banerjee, A.; Barnovska, Z.; Beavis, D. R.; Bellwied, R.; Bhasin, A.; Bhati, A. K.; Bhattarai, P.; Bichsel, H.; Bielcik, J.; Bielcikova, J.; Bland, L. C.; Bordyuzhin, I. G.; Borowski, W.; Bouchet, J.; Brandin, A. V.; Brovko, S. G.; Bültmann, S.; Bunzarov, I.; Burton, T. P.; Butterworth, J.; Caines, H.; Calderón de la Barca Sánchez, M.; Cebra, D.; Cendejas, R.; Cervantes, M. C.; Chaloupka, P.; Chang, Z.; Chattopadhyay, S.; Chen, H. F.; Chen, J. H.; Chen, L.; Cheng, J.; Cherney, M.; Chikanian, A.; Christie, W.; Chwastowski, J.; Codrington, M. J. M.; Corliss, R.; Cramer, J. G.; Crawford, H. J.; Cui, X.; Das, S.; Davila Leyva, A.; De Silva, L. C.; Debbe, R. R.; Dedovich, T. G.; Deng, J.; Derevschikov, A. A.; Derradi de Souza, R.; Dhamija, S.; di Ruzza, B.; Didenko, L.; Dilks, C.; Ding, F.; Djawotho, P.; Dong, X.; Drachenberg, J. L.; Draper, J. E.; Du, C. M.; Dunkelberger, L. E.; Dunlop, J. C.; Efimov, L. G.; Engelage, J.; Engle, K. S.; Eppley, G.; Eun, L.; Evdokimov, O.; Fatemi, R.; Fazio, S.; Fedorisin, J.; Filip, P.; Finch, E.; Fisyak, Y.; Flores, C. E.; Gagliardi, C. A.; Gangadharan, D. R.; Garand, D.; Geurts, F.; Gibson, A.; Girard, M.; Gliske, S.; Grosnick, D.; Guo, Y.; Gupta, A.; Gupta, S.; Guryn, W.; Haag, B.; Hajkova, O.; Hamed, A.; Han, L.-X.; Haque, R.; Harris, J. W.; Hays-Wehle, J. P.; Heppelmann, S.; Hill, K.; Hirsch, A.; Hoffmann, G. W.; Hofman, D. J.; Horvat, S.; Huang, B.; Huang, H. Z.; Huck, P.; Humanic, T. J.; Igo, G.; Jacobs, W. W.; Jang, H.; Judd, E. G.; Kabana, S.; Kalinkin, D.; Kang, K.; Kauder, K.; Ke, H. W.; Keane, D.; Kechechyan, A.; Kesich, A.; Khan, Z. H.; Kikola, D. P.; Kisel, I.; Kisiel, A.; Koetke, D. D.; Kollegger, T.; Konzer, J.; Koralt, I.; Korsch, W.; Kotchenda, L.; Kravtsov, P.; Krueger, K.; Kulakov, I.; Kumar, L.; Kycia, R. A.; Lamont, M. A. C.; Landgraf, J. M.; Landry, K. D.; Lauret, J.; Lebedev, A.; Lednicky, R.; Lee, J. H.; Leight, W.; LeVine, M. J.; Li, C.; Li, W.; Li, X.; Li, X.; Li, Y.; Li, Z. M.; Lima, L. M.; Lisa, M. A.; Liu, F.; Ljubicic, T.; Llope, W. J.; Longacre, R. S.; Luo, X.; Ma, G. L.; Ma, Y. G.; Madagodagettige Don, D. M. M. D.; Mahapatra, D. P.; Majka, R.; Margetis, S.; Markert, C.; Masui, H.; Matis, H. S.; McDonald, D.; McShane, T. S.; Minaev, N. G.; Mioduszewski, S.; Mohanty, B.; Mondal, M. M.; Morozov, D. A.; Munhoz, M. G.; Mustafa, M. K.; Nandi, B. K.; Nasim, Md.; Nayak, T. K.; Nelson, J. M.; Nogach, L. V.; Noh, S. Y.; Novak, J.; Nurushev, S. B.; Odyniec, G.; Ogawa, A.; Oh, K.; Ohlson, A.; Okorokov, V.; Oldag, E. W.; Oliveira, R. A. N.; Pachr, M.; Page, B. S.; Pal, S. K.; Pan, Y. X.; Pandit, Y.; Panebratsev, Y.; Pawlak, T.; Pawlik, B.; Pei, H.; Perkins, C.; Peryt, W.; Peterson, A.; Pile, P.; Planinic, M.; Pluta, J.; Plyku, D.; Poljak, N.; Porter, J.; Poskanzer, A. M.; Pruthi, N. K.; Przybycien, M.; Pujahari, P. R.; Qiu, H.; Quintero, A.; Ramachandran, S.; Raniwala, R.; Raniwala, S.; Ray, R. L.; Riley, C. K.; Ritter, H. G.; Roberts, J. B.; Rogachevskiy, O. V.; Romero, J. L.; Ross, J. F.; Roy, A.; Ruan, L.; Rusnak, J.; Sahoo, N. R.; Sahu, P. K.; Sakrejda, I.; Salur, S.; Sandacz, A.; Sandweiss, J.; Sangaline, E.; Sarkar, A.; Schambach, J.; Scharenberg, R. P.; Schmah, A. M.; Schmidke, W. B.; Schmitz, N.; Seger, J.; Seyboth, P.; Shah, N.; Shahaliev, E.; Shanmuganathan, P. V.; Shao, M.; Sharma, B.; Shen, W. Q.; Shi, S. S.; Shou, Q. Y.; Sichtermann, E. P.; Singaraju, R. N.; Skoby, M. J.; Smirnov, D.; Smirnov, N.; Solanki, D.; Sorensen, P.; deSouza, U. G.; Spinka, H. M.; Srivastava, B.; Stanislaus, T. D. S.; Stevens, J. R.; Stock, R.; Strikhanov, M.; Stringfellow, B.; Suaide, A. A. P.; Sumbera, M.; Sun, X.; Sun, X. M.; Sun, Y.; Sun, Z.; Surrow, B.; Svirida, D. N.; Symons, T. J. M.; Szanto de Toledo, A.; Takahashi, J.; Tang, A. H.; Tang, Z.; Tarnowsky, T.; Thomas, J. H.; Timmins, A. R.; Tlusty, D.; Tokarev, M.; Trentalange, S.; Tribble, R. E.; Tribedy, P.; Trzeciak, B. A.; Tsai, O. D.; Turnau, J.; Ullrich, T.; Underwood, D. G.; Van Buren, G.; van Nieuwenhuizen, G.; Vanfossen, J. A.; Varma, R.; Vasconcelos, G. M. S.; Vasiliev, A. N.; Vertesi, R.; Videbæk, F.; Viyogi, Y. P.; Vokal, S.; Vossen, A.; Wada, M.; Walker, M.; Wang, F.; Wang, G.; Wang, H.; Wang, J. S.; Wang, X. L.; Wang, Y.; Wang, Y.; Webb, G.; Webb, J. C.; Westfall, G. D.; Wieman, H.; Wimsatt, G.; Wissink, S. W.; Witt, R.; Wu, Y. F.; Xiao, Z.; Xie, W.; Xin, K.; Xu, H.; Xu, N.; Xu, Q. H.; Xu, Y.; Xu, Z.; Yan, W.; Yang, C.; Yang, Y.; Yang, Y.; Ye, Z.; Yepes, P.; Yi, L.; Yip, K.; Yoo, I.-K.; Zawisza, Y.; Zbroszczyk, H.; Zha, W.; Zhang, J. B.; Zhang, J. L.; Zhang, S.; Zhang, X. P.; Zhang, Y.; Zhang, Z. P.; Zhao, F.; Zhao, J.; Zhong, C.; Zhu, X.; Zhu, Y. H.; Zoulkarneeva, Y.; Zyzak, M.

    2014-07-01

    We report measurements of ϒ meson production in p + p, d +Au, and Au +Au collisions using the STAR detector at RHIC. We compare the ϒ yield to the measured cross section in p + p collisions in order to quantify any modifications of the yield in cold nuclear matter using d +Au data and in hot nuclear matter using Au +Au data separated into three centrality classes. Our p + p measurement is based on three times the statistics of our previous result. We obtain a nuclear modification factor for ϒ (1 S + 2 S + 3 S) in the rapidity range | y | < 1 in d +Au collisions of RdAu = 0.79 ± 0.24 (stat.) ± 0.03 (syst.) ± 0.10 (p + p syst.). A comparison with models including shadowing and initial state parton energy loss indicates the presence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au +Au collisions, we measure a nuclear modification factor of RAA = 0.49 ± 0.1 (stat.) ± 0.02 (syst.) ± 0.06 (p + psyst.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are consistent with complete suppression of excited-state ϒ mesons in Au +Au collisions. The additional suppression in Au +Au is consistent with the level expected in model calculations that include the presence of a hot, deconfined Quark-Gluon Plasma. However, understanding the suppression seen in d +Au is still needed before any definitive statements about the nature of the suppression in Au +Au can be made.

  10. High hardness in the biocompatible intermetallic compound β-Ti3Au.

    PubMed

    Svanidze, Eteri; Besara, Tiglet; Ozaydin, M Fevsi; Tiwary, Chandra Sekhar; Wang, Jiakui K; Radhakrishnan, Sruthi; Mani, Sendurai; Xin, Yan; Han, Ke; Liang, Hong; Siegrist, Theo; Ajayan, Pulickel M; Morosan, E

    2016-07-01

    The search for new hard materials is often challenging, but strongly motivated by the vast application potential such materials hold. Ti3Au exhibits high hardness values (about four times those of pure Ti and most steel alloys), reduced coefficient of friction and wear rates, and biocompatibility, all of which are optimal traits for orthopedic, dental, and prosthetic applications. In addition, the ability of this compound to adhere to ceramic parts can reduce both the weight and the cost of medical components. The fourfold increase in the hardness of Ti3Au compared to other Ti-Au alloys and compounds can be attributed to the elevated valence electron density, the reduced bond length, and the pseudogap formation. Understanding the origin of hardness in this intermetallic compound provides an avenue toward designing superior biocompatible, hard materials.

  11. High hardness in the biocompatible intermetallic compound β-Ti3Au

    PubMed Central

    Svanidze, Eteri; Besara, Tiglet; Ozaydin, M. Fevsi; Tiwary, Chandra Sekhar; Wang, Jiakui K.; Radhakrishnan, Sruthi; Mani, Sendurai; Xin, Yan; Han, Ke; Liang, Hong; Siegrist, Theo; Ajayan, Pulickel M.; Morosan, E.

    2016-01-01

    The search for new hard materials is often challenging, but strongly motivated by the vast application potential such materials hold. Ti3Au exhibits high hardness values (about four times those of pure Ti and most steel alloys), reduced coefficient of friction and wear rates, and biocompatibility, all of which are optimal traits for orthopedic, dental, and prosthetic applications. In addition, the ability of this compound to adhere to ceramic parts can reduce both the weight and the cost of medical components. The fourfold increase in the hardness of Ti3Au compared to other Ti–Au alloys and compounds can be attributed to the elevated valence electron density, the reduced bond length, and the pseudogap formation. Understanding the origin of hardness in this intermetallic compound provides an avenue toward designing superior biocompatible, hard materials. PMID:27453942

  12. 76 FR 14395 - Ocean Transportation Intermediary License Applicants

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-16

    ... Au dba ABC Logistics Company (NVO), 2250 Gellert Blvd., South San Francisco, CA 94080. Officer: Geoffrey Au, Owner (Qualifying Individual), Application Type: New NVO License. Icon North America, Inc...

  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. Multifunctional compact hybrid Au nanoshells: a new generation of nanoplasmonic probes for biosensing, imaging, and controlled release.

    PubMed

    Jin, Yongdong

    2014-01-21

    Gold nanoshells (AuNSs) with tunable localized surface plasmon resonance (LSPR) peaks in the near-infrared (NIR) region possess unique optical properties-particularly that soft tissues are "transparent" at these wavelengths-making them of great interest in cancer diagnosis and treatment. Since 1998 when Halas and co-workers invented the first generation of AuNS, with a silica core and Au shell, researchers have studied and designed AuNSs for theranostic-individualized, combination diagnosis and therapy-nanomedicine. As demand has increased for more powerful and practical theranostic applications, so has demand for the next generation of AuNSs-compact yet complex multifunctional AuNSs with finely integrated plasmonic and nonplasmonic inorganic components. For in vivo biomedical applications, such a hybrid AuNS offers the desirable optical properties of NIR LSPR. Size, however, has proved a more challenging parameter to control in hybrid AuNSs. The ideal size of therapeutic NPs is 10-100 nm. Larger particles have limited diffusion in the extracellular space, while particles less than 5 nm are rapidly cleared from the circulation through extravasation or renal clearance. Conventional methods of preparing AuNS have failed to obtain small-sized hybrid AuNSs with NIR LSPR responses. In this Account, we present a new class of multifunctional hybrid AuNSs with ultrathin AuNSs and varied, functional (nonplasmonic) core components ranging from "hard" semiconductor quantum dots (QDs), to superparamagnetic NPs, to "soft" liposomes made using poly-l-histidine as a template to direct Au deposition. The resultant hybrid AuNSs are uniform and compact (typically 15-60 nm) but also preserve the optical properties and shell-type NIR response necessary for biomedical use. We also demonstrate these particles' innovative plasmonic applications in biosensing, multimodal imaging and controlled release. More importantly, the magnetic-plasmonic Fe3O4/Au core-shell NP enables a new

  15. 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.

  16. 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.

  17. Transparent, conductive, and SERS-active Au nanofiber films assembled on an amphiphilic peptide template

    NASA Astrophysics Data System (ADS)

    Vinod, T. P.; Zarzhitsky, Shlomo; Morag, Ahiud; Zeiri, Leila; Levi-Kalisman, Yael; Rapaport, Hanna; Jelinek, Raz

    2013-10-01

    The use of biological materials as templates for functional molecular assemblies is an active research field at the interface between chemistry, biology, and materials science. We demonstrate the formation of gold nanofiber films on β-sheet peptide domains assembled at the air/water interface. The gold deposition scheme employed a recently discovered chemical process involving spontaneous crystallization and reduction of water-soluble Au(SCN)41- upon anchoring to surface-displayed amine moieties. Here we show that an interlinked network of crystalline Au nanofibers is readily formed upon incubation of the Au(iii) thiocyanate complex with the peptide monolayers. Intriguingly, the resultant films were optically transparent, enabled electrical conductivity, and displayed pronounced surface enhanced Raman spectroscopy (SERS) activity, making the approach a promising avenue for construction of nano-structured films exhibiting practical applications.The use of biological materials as templates for functional molecular assemblies is an active research field at the interface between chemistry, biology, and materials science. We demonstrate the formation of gold nanofiber films on β-sheet peptide domains assembled at the air/water interface. The gold deposition scheme employed a recently discovered chemical process involving spontaneous crystallization and reduction of water-soluble Au(SCN)41- upon anchoring to surface-displayed amine moieties. Here we show that an interlinked network of crystalline Au nanofibers is readily formed upon incubation of the Au(iii) thiocyanate complex with the peptide monolayers. Intriguingly, the resultant films were optically transparent, enabled electrical conductivity, and displayed pronounced surface enhanced Raman spectroscopy (SERS) activity, making the approach a promising avenue for construction of nano-structured films exhibiting practical applications. Electronic supplementary information (ESI) available: AFM analysis of the

  18. 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.

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

    PubMed

    Villa, Alberto; Wang, Di; Su, Dangsheng; Veith, Gabriel M; Prati, Laura

    2010-03-07

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

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

    SciTech Connect

    Villa, Alberto; Prati, Laura; Su, Dangshen; Wang, Di; Veith, Gabriel M

    2010-01-01

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

  1. LaAu2 and CeAu2 surface intermetallic compounds grown by high-temperature deposition on Au(111)

    NASA Astrophysics Data System (ADS)

    Ormaza, M.; Fernández, L.; Lafuente, S.; Corso, M.; Schiller, F.; Xu, B.; Diakhate, M.; Verstraete, M. J.; Ortega, J. E.

    2013-09-01

    We report on the crystal structure and electronic bands of LaAu2 and CeAu2 surface intermetallic compounds grown by high-temperature deposition on Au(111). By scanning-tunneling microscopy we study the formation of different alloy phases as a function of growth temperature and lanthanide coverage. We determine the specific growth conditions to achieve monolayers and bilayers of LaAu2 and CeAu2 with high crystalline quality. Due to lattice mismatch with the underlying Au substrate, both LaAu2 and CeAu2 exhibit long-range moiré patterns, which can serve as templates for further nanostructure growth. By angle-resolved photoemission we map the two-dimensional band structure of these surface alloys, discussing the nature of the different spectral features in the light of first-principles calculations.

  2. Self-grown Ni(OH)(2) layer on bimodal nanoporous AuNi alloys for enhanced electrocatalytic activity and stability.

    PubMed

    Han, Gao-Feng; Xiao, Bei-Bei; Lang, Xing-You; Wen, Zi; Zhu, Yong-Fu; Zhao, Ming; Li, Jian-Chen; Jiang, Qing

    2014-10-08

    Au nanostructures as catalysts toward electrooxidation of small molecules generally suffer from ultralow surface adsorption capability and stability. Here, we report Ni(OH)2 layer decorated nanoporous (NP) AuNi alloys with a three-dimensional and bimodal porous architecture, which are facilely fabricated by a combination of chemical dealloying and in situ surface segregation, for the enhanced electrocatalytic performance in biosensors. As a result of the self-grown Ni(OH)2 on the AuNi alloys with a coherent interface, which not only enhances adsorption energy of Au and electron transfer of AuNi/Ni(OH)2 but also prohibits the surface diffusion of Au atoms, the NP composites are enlisted to exhibit significant enhancement in both electrocatalytic activity and stability toward glucose electrooxidation. The highly reliable glucose biosensing with exceptional reproducibility and selectivity as well as quick response makes it a promising candidate as electrode materials for the application in nonenzymatic glucose biosensors.

  3. Fabrication of Au nanoparticle composite TiO2 shell arrays by controlled decomposition of polymer particles

    NASA Astrophysics Data System (ADS)

    Yan, Wei-Guo; Luo, Chun-Li; Zhao, Jian; Guo, Mei-Li; Ye, Qing; Li, Zu-Bin; Tian, Jian-Guo

    2014-11-01

    In the paper, the novel TiO2 nanoshell arrays coated with Au nanoparticles (NPs) were prepared by a simple and effective fabrication method with thermal decomposing polymer particles. Surface structure and composition of these arrays were evaluated by Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). The results indicated that TiO2 nanoshell coated with Au NPs was changed into Au@TiO2 composite NPs with the rise of annealing temperature. These novel nanostructures have the potential applications in some research fields, such as photocatalysis, single molecule detection, and novel optoelectronic devices.

  4. Superior Plasmonic Photodetectors Based on Au@MoS2 Core-Shell Heterostructures.

    PubMed

    Li, Yuan; DiStefano, Jennifer G; Murthy, Akshay A; Cain, Jeffrey D; Hanson, Eve D; Li, Qianqian; Castro, Fernando C; Chen, Xinqi; Dravid, Vinayak P

    2017-09-21

    Integrating plasmonic materials into semiconductor media provides a promising approach for applications such as photo-sensing and solar energy conversion. The resulting structures introduce enhanced light-matter interactions, additional charge trap states, and efficient charge-transfer pathways for light-harvesting devices, especially when an intimate interface is built between the plasmonic nanostructure and semiconductor. Herein, we report the development of plasmonic photodetectors using Au@MoS2 heterostructures - an Au nanoparticle core that is encapsulated by a CVD-grown multilayer MoS2 shell, which perfectly realizes the intimate and direct interfacing of Au and MoS2. We explored their favorable applications in different types of photo-sensing devices. The first involves the development of a large-area interdigitated field-effect phototransistor, which shows a photoresponsivity of ~10 times higher than that of planar MoS2 transistors. The other type of device geometry is a Si-supported Au@MoS2 heterojunction gateless photodiode. We demonstrated its superior photo-response and recovery ability, with a photoresponsivity as high as 22.3 A/W, which is beyond the most distinguished values of previously reported similar gateless photodetectors. The improvement of photo-sensing performance can be a combined result of multiple factors, including enhanced light absorption, creation of more trap states, and, possibly, the formation of interfacial charge-transfer transition, benefiting from the intimate connection of Au and MoS2.

  5. Immobilization of a human epidermal growth factor receptor 2 mimotope-derived synthetic peptide on Au and its potential application for detection of herceptin in human serum by quartz crystal microbalance.

    PubMed

    Shang, Yuqin; Singh, Pankaj R; Chisti, Mohammad M; Mernaugh, Ray; Zeng, Xiangqun

    2011-12-01

    Therapeutic antibodies are antigenically similar to human antibodies and are difficult to detect in assays of human serum samples without the use of the therapeutic antibody's complementary antigen. Herein for the first time, we established a platform to detect Herceptin in solutions by using a small (<2.2 kDa), inexpensive, highly stable human epidermal growth factor receptor (HER2) mimotope-derived synthetic peptide immobilized on the surface of a Au quartz electrode. We used the HER2 mimotope as a substitute for the HER2 receptor protein in piezoimmunosensor or quartz crystal microbalance (QCM) assays to detect Herceptin in human serum. We demonstrated that assay sensitivity was dependent upon the amino acids used to tether and link the peptide to the sensor surface and the buffers used to carry out the assays. The detection limit of the piezoimmunosensor assay was 0.038 nM with a linear operating range of 0.038-0.859 nM. Little nonspecific binding to other therapeutic antibodies (Avastin and Rituxan) was observed. Levels of Herceptin in serum samples obtained from treated patients, as ascertained using the synthetic peptide-based QCM assay, were typical for those treated with Herceptin. The findings of this study are significant in that low-cost synthetic peptides could be used in a QCM assay, in lieu of native or recombinant antigens or capture antibodies, to rapidly detect a therapeutic antibody in human serum. The results suggested that a synthetic peptide bearing a particular functional sequence could be applied for developing a new generation of affinity-based immunosensors to detect a broad range of clinical biomarkers.

  6. Adsorbate-modified Electron Relaxation in Au-Au_2S Nanoshells

    NASA Astrophysics Data System (ADS)

    Westcott, Sarah; Averitt, Richard; Wolfgang, John; Nordlander, Peter; Halas, Naomi

    2001-03-01

    Au-Au_2S nanoshells are 50 nm nanoparticles consisting of an Au_2S core encapsulated by a thin (<5 nm) Au shell. Their optical properties are determined by the metallic shell layer, whose inner and outer radii control plasmon frequency and whose thickness determines plasmon linewidth[1]. We studied the time-resolved relaxation of hot electrons in the Au shell, using degenerate pump-probe spectroscopy. The electron relaxation for nanoshells in solution was appreciably slower than relaxation for bulk gold, moreover, adsorbed molecules on the nanoshell surface strongly modify this relaxation. Density functional theory calculations indicate that the molecules providing the strongest modification of relaxation possess the largest induced dipole moments above a metal surface, indicating that the adsorbate-induced perturbation of the nanoshell electron dynamics appears to be primarily electronic in nature. [1] R. D. Averitt, D. Sarkar and N. J. Halas, Phys. Rev. Lett. 78, 4217 (1997).

  7. Surface plasmon resonance-induced photocatalysis by Au nanoparticles decorated mesoporous g-C{sub 3}N{sub 4} nanosheets under direct sunlight irradiation

    SciTech Connect

    Tonda, Surendar; Kumar, Santosh; Shanker, Vishnu

    2016-03-15

    Highlights: • The Au/mp-g-C{sub 3}N{sub 4} was synthesized via a template-free and green in situ strategy. • Au/mp-g-C{sub 3}N{sub 4} nanosheets possesses high surface area and porous structure. • Au/mp-g-C{sub 3}N{sub 4} showed dramatic photocurrent response and photocatalytic activity. • The high performance is due to SPR of Au and mesoporous structure. • Au/mp-g-C{sub 3}N{sub 4} nanosheets exhibited high photostability. - Abstract: In recent years, surface plasmon-induced photocatalytic materials with tunable mesoporous framework have attracted considerable attention in energy conversion and environmental remediation. Herein we report a novel Au nanoparticles decorated mesoporous graphitic carbon nitride (Au/mp-g-C{sub 3}N{sub 4}) nanosheets via a template-free and green in situ photo-reduction method. The synthesized Au/mp-g-C{sub 3}N{sub 4} nanosheets exhibit a strong absorption edge in visible and near-IR region owing to the surface plasmon resonance effect of Au nanoparticles. More attractively, Au/mp-g-C{sub 3}N{sub 4} exhibited much higher photocatalytic activity than that of pure mesoporous and bulk g-C{sub 3}N{sub 4} for the degradation of rhodamine B under sunlight irradiation. Furthermore, the photocurrent and photoluminescence studies demonstrated that the deposition of Au nanoparticles on the surface of mesoporous g-C{sub 3}N{sub 4} could effectively inhibit the recombination of photogenerated charge carriers leading to the enhanced photocatalytic activity. More importantly, the synthesized Au/mp-g-C{sub 3}N{sub 4} nanosheets possess high reusability. Hence, Au/mp-g-C{sub 3}N{sub 4} could be promising photoactive material for energy and environmental applications.

  8. Superparamagnetic Au-Fe3O4 nanoparticles: one-pot synthesis, biofunctionalization and toxicity evaluation

    NASA Astrophysics Data System (ADS)

    Pariti, A.; Desai, P.; Maddirala, S. K. Y.; Ercal, N.; Katti, K. V.; Liang, X.; Nath, M.

    2014-09-01

    Superparamagnetic Au-Fe3O4 bifunctional nanoparticles have been synthesized using a single step hot-injection precipitation method. The synthesis involved using Fe(CO)5 as iron precursor and HAuCl4 as gold precursor in the presence of oleylamine and oleic acid. Oleylamine helps in reducing Au3+ to Au0 seeds which simultaneously oxidizes Fe(0) to form Au-Fe3O4 bifunctional nanoparticles. Triton® X-100 was employed as a highly viscous solvent to prevent agglomeration of Fe3O4 nanoparticles. Detailed characterization of these nanoparticles was performed by using x-ray powder diffraction, transmission electron microscopy, scanning tunneling electron microscopy, UV-visible spectroscopy, Mössbauer and magnetometry studies. To evaluate these nanoparticles’ applicability in biomedical applications, L-cysteine was attached to the Au-Fe3O4 nanoparticles and cytotoxicity of Au-Fe3O4 nanoparticles was tested using CHO cells by employing MTS assay. L-cysteine modified Au-Fe3O4 nanoparticles were qualitatively characterized using Fourier transform infrared spectroscopy and Raman spectroscopy; and quantitatively using acid ninhydrin assay. Investigations reveal that that this approach yields Au-Fe3O4 bifunctional nanoparticles with an average particle size of 80 nm. Mössbauer studies indicated the presence of Fe in Fe3+ in A and B sites (tetrahedral and octahedral, respectively) and Fe2+ in B sites (octahedral). Magnetic measurements also indicated that these nanoparticles were superparamagnetic in nature due to Fe3O4 region. The saturation magnetization for the bifunctional nanoparticles was observed to be ˜74 emu g-1, which is significantly higher than the previously reported Fe3O4 nanoparticles. Mössbauer studies indicated that there was no significant Fe(0) impurity that could be responsible for the superparamagnetic nature of these nanoparticles. None of the investigations showed any presence of other impurities such as Fe2O3 and FeOOH. These Au-Fe3O4 bifunctional

  9. Jets and dijets in Au+Au and p+p collisions at RHIC

    SciTech Connect

    Hardtke, D.; STAR Collaboration

    2002-12-09

    Recent data from RHIC suggest novel nuclear effects in the production of high p{sub T} hadrons. We present results from the STAR detector on high p{sub T} angular correlations in Au+Au and p+p collisions at {radical}S = 200 GeV/c. These two-particle angular correlation measurements verify the presence of a partonic hard scattering and fragmentation component at high p{sub T} in both central and peripheral Au+Au collisions. When triggering on a leading hadron with p{sub T}>4 GeV, we observe a quantitative agreement between the jet cone properties in p+p and all centralities of Au+Au collisions. This quantitative agreement indicates that nearly all hadrons with p{sub T}>4 GeV/c come from jet fragmentation and that jet fragmentation properties are not substantially modified in Au+Au collisions. STAR has also measured the strength of back-to-back high p{sub T} charged hadron correlations, and observes a small suppression of the back-to-back correlation strength in peripheral collisions, and a nearly complete disappearance o f back-to-back correlations in central Au+Au events. These phenomena, together with the observed strong suppression of inclusive yields and large value of elliptic flow at high p{sub T}, are consistent with a model where high p{sub T} hadrons come from partons created near the surface of the collision region, and where partons that originate or propagate towards the center of the collision region are substantially slowed or completely absorbed.

  10. Synthesis and characterization in AuCu–Si nanostructures

    SciTech Connect

    Novelo, T.E.; Amézaga-Madrid, P.; Maldonado, R.D.; Oliva, A.I.; Alonzo-Medina, G.M.

    2015-03-15

    Au/Cu bilayers with different Au:Cu concentrations (25:75, 50:50 and 75:25 at.%) were deposited on Si(100) substrates by thermal evaporation. The thicknesses of all Au/Cu bilayers were 150 nm. The alloys were prepared by thermal diffusion into a vacuum oven with argon atmosphere at 690 K during 1 h. X-ray diffraction analysis revealed different phases of AuCu and CuSi alloys in the samples after annealing process. CuSi alloys were mainly obtained for 25:75 at.% samples, meanwhile the AuCuII phase dominates for samples prepared with 50:50 at.%. Additionally, the Au:Cu alloys with 75:25 at.%, produce Au{sub 2}Cu{sub 3} and Au{sub 3}Cu phases. The formed alloys were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) to study the morphology and the elemental concentration of the formed alloys. - Highlights: • AuCu/Si alloy thin films were prepared by thermal diffusion. • Alloys prepared with 50 at.% of Au produce the AuCuII phase. • Alloys prepared with 75 at.% of Au produce Au{sub 3}Cu and Au{sub 2}Cu{sub 3} phases. • All alloys present diffusion of Si and Cu through the CuSi alloy formation.

  11. Au/Si Hetero-nanorod-based Biosensor for Salmonella Detection

    USDA-ARS?s Scientific Manuscript database

    Among several potentials of nanotechnology applications for food industry, development of nanoscale sensors for food safety and biosecurity measurement are emerging. A novel biosensor for Salmonella detection was developed using Au/Si nanorods. The Si nanorods were fabricated by glancing angle depo...

  12. Au/Si nanorod-based biosensor for food pathogen detection

    USDA-ARS?s Scientific Manuscript database

    Technical Abstract Among several potentials of nanotechnology applications for food industry, development of nanoscale sensors for food safety and quality measurement are emerging. A novel biosensor for Salmonella detection was developed using Au/Si nanorods. The Si nanorods were fabricated by gla...

  13. Au/Si Hetero-Nanorod-based Biosensor for Salmonella Detection

    USDA-ARS?s Scientific Manuscript database

    Technical Abstract Among several potentials of nanotechnology applications for food industry, development of nanoscale sensors for food safety and biosecurity measurement are emerging. A novel biosensor for Salmonella detection was developed using Au/Si nanorods. The Si nanorods were fabricated by...

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

    EPA Science Inventory

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

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

    EPA Science Inventory

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

  16. Brillouin Oscillations from Single Au Nanoplate Opto-Acoustic Transducers.

    PubMed

    Yu, Kuai; Devkota, Tuphan; Beane, Gary; Wang, Guo Ping; Hartland, Gregory V

    2017-08-22

    Brillouin oscillations, which are GHz frequency waves that arise from the interaction of light with acoustic waves, are experiencing increasing applications in biology and materials science. They provide information about the speed of sound and refractive index of the material they propagate in, and have recently been used in imaging applications. In the current study, Brillouin oscillations are observed through ultrafast transient reflectivity measurements using chemically synthesized Au nanoplates as opto-acoustic transducers. The Au nanoplates are semitransparent, which allows the Brillouin oscillations to be observed from material on both sides of the plate. The measured frequencies are consistent with the values expected from the speeds of sound in the different materials, however, the attenuation constants are much larger than those reported in previous studies. The increased damping is attributed to diffraction of the acoustic wave as it propagates away from the excitation region. This effect is more significant for experiments with high numerical aperture objectives. These results are important for understanding the relationship between frequency and spatial resolution in Brillouin oscillation microscopy.

  17. Au nanoparticles films used in biological sensing

    NASA Astrophysics Data System (ADS)

    Rosales Pérez, M.; Delgado Macuil, R.; Rojas López, M.; Gayou, V. L.; Sánchez Ramírez, J. F.

    2009-05-01

    Lactobacillus para paracasei are used commonly as functional food and probiotic substances. In this work Au nanoparticles self-assembled films were used for Lactobacillus para paracasei determination at five different concentrations. Functionalized substrates were immersed in a colloidal solution for one and a half hour at room temperature and dried at room temperature during four hours. After that, drops of Lactobacillus para paracasei in aqueous solution were put into the Au nanoparticles film and let dry at room temperature for another two hours. Infrared spectroscopy in attenuated total reflectance sampling mode was used to observe generation peaks due to substrate silanization, enhancement of Si-O band intensity due to the Au colloids added to silanized substrate and also to observe the enhancement of Lactobacillus para paracasei infrared intensity of the characteristic frequencies at 1650, 1534 and 1450 cm-1 due to surface enhancement infrared absorption.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  19. Electrophoretic deposition of fluorescent Cu and Au sheets for light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Liu, Jiale; Wu, Zhennan; Li, Tingting; Zhou, Ding; Zhang, Kai; Sheng, Yu; Cui, Jianli; Zhang, Hao; Yang, Bai

    2015-12-01

    Electrophoretic deposition (EPD) is a conventional method for fabricating film materials from nanometer-sized building blocks, and exhibits the advantages of low-cost, high-efficiency, wide-range thickness adjustment, and uniform deposition. Inspired by the interest in the application of two-dimensional (2D) nanomaterials, the EPD technique has been recently extended to building blocks with 2D features. However, the studies are mainly focused on simplex building blocks. The utilization of multiplex building blocks is rarely reported. In this work, we demonstrate a controlled EPD of Cu and Au sheets, which are 2D assemblies of luminescent Cu and Au nanoclusters. Systematic investigations reveal that both the deposition efficiency and the thickness are determined by the lateral size of the sheets. For Cu sheets with a large lateral size, a high ζ-potential and strong face-to-face van der Waals interactions facilitate the deposition with high efficiency. However, for Au sheets, the small lateral size and ζ-potential limit the formation of a thick film. To solve this problem, the deposition dynamics are controlled by increasing the concentration of the Au sheets and adding acetone. This understanding permits the fabrication of a binary EPD film by the stepwise deposition of Cu and Au sheets, thus producing a luminescent film with both Cu green emission and Au red emission. A white light-emitting diode prototype with color coordinates (x, y) = (0.31, 0.36) is fabricated by employing the EPD film as a color conversion layer on a 365 nm GaN clip and further tuning the amount of deposited Cu and Au sheets.Electrophoretic deposition (EPD) is a conventional method for fabricating film materials from nanometer-sized building blocks, and exhibits the advantages of low-cost, high-efficiency, wide-range thickness adjustment, and uniform deposition. Inspired by the interest in the application of two-dimensional (2D) nanomaterials, the EPD technique has been recently extended to

  20. The role of interfaces in the magnetoresistance of Au/Fe/Au/Fe/GaAs(001)

    SciTech Connect

    Enders, A.; Monchesky, T. L.; Myrtle, K.; Urban, R.; Heinrich, B.; Kirschner, J.; Zhang, X.-G.; Butler, W. H.

    2001-06-01

    The electron transport and magnetoresistance (MR) were investigated in high quality crystalline epitaxial Fe(001) and Au(001) films and exchange coupled Au/Fe/Au/Fe/GaAs(001) trilayer structures. Fits to the experimental data were based on the semiclassical Boltzmann equation, which incorporates the electronic properties obtained from first-principles local density functional calculations. The fits require a surprisingly high asymmetry for the spin dependent electron lifetimes in Fe, {tau}{sup {down_arrow}}/{tau}{sup {up_arrow}}=10 at room temperature. Despite the large atomic terraces at the Au/vacuum and Fe/GaAs interfaces the scattering at the outer interfaces was found to be diffuse. The origin of MR in Au/Fe/Au/Fe/GaAs(001) structures is due to electron channeling in the Au spacer layer. The measured MR is consistent with the diffusivity parameters s{sup {up_arrow}}=0.55, s{sup {down_arrow}}=0.77 at the metal{endash}metal interfaces. {copyright} 2001 American Institute of Physics.

  1. Toxicity of citrate-capped AuNPs: an in vitro and in vivo assessment

    NASA Astrophysics Data System (ADS)

    Sabella, Stefania; Brunetti, Virgilio; Vecchio, Giuseppe; Galeone, Antonio; Maiorano, Gabriele; Cingolani, Roberto; Pompa, Pier Paolo

    2011-12-01

    In this study, we show that 15 nm citrate-capped AuNPs exert a remarkable toxicity in living systems. The assessment was performed by using well-characterized AuNPs, the combination of in vitro and in vivo models (namely two different cell lines and Drosophila melanogaster), exposure to low dosages of nanoparticles (in the sub-nanomolar concentration range), along with the application of several biological assays to monitor different aspects of the toxic effects, such as viability, genotoxicity, and molecular biomarkers.

  2. Conducting shrinkable nanocomposite based on au-nanoparticle implanted plastic sheet: tunable thermally induced surface wrinkling.

    PubMed

    Greco, Francesco; Bellacicca, Andrea; Gemmi, Mauro; Cappello, Valentina; Mattoli, Virgilio; Milani, Paolo

    2015-04-08

    A thermally shrinkable and conductive nanocomposite material is prepared by supersonic cluster beam implantation (SCBI) of neutral Au nanoparticles (Au NPs) into a commercially available thermo-retractable polystyrene (PS) sheet. Micronanowrinkling is obtained during shrinking, which is studied by means of SEM, TEM and AFM imaging. Characteristic periodicity is determined and correlated with nanoparticle implantation dose, which permits us to tune the topographic pattern. Remarkable differences emerged with respect to the well-known case of wrinkling of bilayer metal-polymer. Wrinkled composite surfaces are characterized by a peculiar multiscale structuring that promises potential technological applications in the field of catalytic surfaces, sensors, biointerfaces, and optics, among others.

  3. Metal-insulator transition in Au-NiO-Ni dual Schottky nanojunctions.

    PubMed

    Sun, Jia-Lin; Zhao, Xingchen; Zhu, Jia-Lin

    2009-11-11

    Ni nanowire arrays were fabricated through electrochemical deposition on a template. After a nanoscale NiO layer was formed on the top of the nanowires, a layer of Au paint was coated on the top of the nanowire arrays to construct Au-NiO-Ni dual Schottky nanojunctions, and the structure was characterized at different scales. Within a small range of voltages, extraordinary current jumps were observed at room temperature and at 77 K. The resistance switch effect can be repeated at room temperature, while switching is irreversible at low temperature. The significant change in resistance of the samples does not require doping and may find future applications.

  4. Plasmonic effect of spray-deposited Au nanoparticles on the performance of inverted organic solar cells.

    PubMed

    Chaturvedi, Neha; Swami, Sanjay Kumar; Dutta, Viresh

    2014-09-21

    Gold nanoparticles with varying sizes were prepared by the spray process under an electric field (DC voltages of 0 V and 1 kV applied to the nozzle) for studying their role in inverted organic solar cells (ITO/Au/ZnO/P3HT:PCBM/Ag). The application of electric field during the spray process resulted in a smaller size (35 nm as compared to 70 nm without the electric field) of the nanoparticles with more uniform distribution. This gave rise to a difference in the surface plasmon resonance (SPR) effect created by the gold nanoparticles (Au NPs), which then affected the solar cell performance. The photovoltaic performances of plasmonic inverted organic solar cells (ITO/Au/ZnO/P3HT:PCBM/Ag) using spray-deposited Au and ZnO layers (both at 1 kV) showed improved efficiency. Fast exciton quenching in the P3HT:PCBM layer was achieved by using a spray-deposited Au layer in between ITO and ZnO layers. The absorption spectra and internal power conversion efficiency (IPCE) curve showed that the Au nanoparticles provide significant plasmonic broadband light absorption enhancement which resulted in the enhancement of the JSC value. Maximum efficiency of 3.6% was achieved for the inverted organic solar cell (IOSC) with an exceptionally high short circuit current density of ∼15 mA cm(-2) which is due to the additional photon absorption and the corresponding increase observed in the IPCE spectrum. The spray technique can be easily applied for the direct formation of Au nanoparticles in the fabrication of IOSC with improved performance over a large area.

  5. Plasmonic effect of spray-deposited Au nanoparticles on the performance of inverted organic solar cells

    NASA Astrophysics Data System (ADS)

    Chaturvedi, Neha; Swami, Sanjay Kumar; Dutta, Viresh

    2014-08-01

    Gold nanoparticles with varying sizes were prepared by the spray process under an electric field (DC voltages of 0 V and 1 kV applied to the nozzle) for studying their role in inverted organic solar cells (ITO/Au/ZnO/P3HT:PCBM/Ag). The application of electric field during the spray process resulted in a smaller size (35 nm as compared to 70 nm without the electric field) of the nanoparticles with more uniform distribution. This gave rise to a difference in the surface plasmon resonance (SPR) effect created by the gold nanoparticles (Au NPs), which then affected the solar cell performance. The photovoltaic performances of plasmonic inverted organic solar cells (ITO/Au/ZnO/P3HT:PCBM/Ag) using spray-deposited Au and ZnO layers (both at 1 kV) showed improved efficiency. Fast exciton quenching in the P3HT:PCBM layer was achieved by using a spray-deposited Au layer in between ITO and ZnO layers. The absorption spectra and internal power conversion efficiency (IPCE) curve showed that the Au nanoparticles provide significant plasmonic broadband light absorption enhancement which resulted in the enhancement of the JSC value. Maximum efficiency of 3.6% was achieved for the inverted organic solar cell (IOSC) with an exceptionally high short circuit current density of ~15 mA cm-2 which is due to the additional photon absorption and the corresponding increase observed in the IPCE spectrum. The spray technique can be easily applied for the direct formation of Au nanoparticles in the fabrication of IOSC with improved performance over a large area.

  6. 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.

  7. Synthesis of ultrathin face-centered-cubic au@pt and au@pd core-shell nanoplates from hexagonal-close-packed au square sheets.

    PubMed

    Fan, Zhanxi; Zhu, Yihan; Huang, Xiao; Han, Yu; Wang, Qingxiao; Liu, Qing; Huang, Ying; Gan, Chee Lip; Zhang, Hua

    2015-05-04

    The synthesis of ultrathin face-centered-cubic (fcc) Au@Pt rhombic nanoplates is reported through the epitaxial growth of Pt on hexagonal-close-packed (hcp) Au square sheets (AuSSs). The Pt-layer growth results in a hcp-to-fcc phase transformation of the AuSSs under ambient conditions. Interestingly, the obtained fcc Au@Pt rhombic nanoplates demonstrate a unique (101)f orientation with the same atomic arrangement extending from the Au core to the Pt shell. Importantly, this method can be extended to the epitaxial growth of Pd on hcp AuSSs, resulting in the unprecedented formation of fcc Au@Pd rhombic nanoplates with (101)f orientation. Additionally, a small amount of fcc (100)f -oriented Au@Pt and Au@Pd square nanoplates are obtained with the Au@Pt and Au@Pd rhombic nanoplates, respectively. We believe that these findings will shed new light on the synthesis of novel noble bimetallic nanostructures.

  8. Enhanced NO2 sensing characteristics of Au modified porous silicon/thorn-sphere-like tungsten oxide composites

    NASA Astrophysics Data System (ADS)

    Yuan, Lin; Hu, Ming; Wei, Yulong; Ma, Wenfeng

    2016-12-01

    The thorn-sphere-like tungsten oxide (WO3) made up by 1D nanorods has been successfully synthesized through hydrothermal method on the Au-modified porous silicon (PS) substrates with seed-layer induction. By using XRD, EDS, FESEM and TEM techniques, we tested and verified that the crystal structure and morphology evolution of WO3 hierarchical nanostructure on the Au-modified PS strongly depend on the Au-sputtering time and hydrothermal reaction time. In addition, by comparing the NO2-sensing properties of the prepared products, we found that the 10 s-Au decorated PS/WO3-3 h (sputtering Au for 10 s and hydrothermal reaction for 3 h) composites sensor behaving as a typical p-type semiconductor and operating at room temperature (RT) exhibits high sensitivity and response characteristics even to ppb-level NO2, which makes this kind of sensor a competitive candidate for NO2-sensing applications. Moreover, the enhanced response may not only due to the high specific surface area but the Au nanoparticles acting as promoters for the spillover effect and forming metal-semiconductor heterojunctions with the PS and WO3. The transmission of electrons and holes in the heterogeneous interface generated among PS, WO3 and Au is proposed to illustrate the p-type response mechanism.

  9. Multifunctional Au-ZnO plasmonic nanostructures for enhanced UV photodetector and room temperature NO sensing devices.

    PubMed

    Gogurla, Narendar; Sinha, Arun Kumar; Santra, Sumita; Manna, Santanu; Ray, Samit Kumar

    2014-09-26

    In this study we report the enhancement of UV photodetection and wavelength tunable light induced NO gas sensing at room temperature using Au-ZnO nanocomposites synthesized by a simple photochemical process. Plasmonic Au-ZnO nanostructures with a size less than the incident wavelength have been found to exhibit a localized surface plasmon resonance (LSPR) that leads to a strong absorption, scattering and local field enhancement. The photoresponse of Au-ZnO nanocomposite can be effectively enhanced by 80 times at 335 nm over control ZnO. We also demonstrated Au-ZnO nanocomposite's application to wavelength tunable gas sensor operating at room temperature. The sensing response of Au-ZnO nancomposite is enhanced both in UV and visible region, as compared to control ZnO. The sensitivity is observed to be higher in the visible region due to the LSPR effect of Au NPs. The selectivity is found to be higher for NO gas over CO and some other volatile organic compounds (VOCs), with a minimum detection limit of 0.1 ppb for Au-ZnO sensor at 335 nm.

  10. 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.

  11. AuPt Alloy Nanostructures with Tunable Composition and Enzyme-like Activities for Colorimetric Detection of Bisulfide

    NASA Astrophysics Data System (ADS)

    He, Weiwei; Han, Xiangna; Jia, Huimin; Cai, Junhui; Zhou, Yunlong; Zheng, Zhi

    2017-01-01

    Tuning the enzyme-like activity and studying the interaction between biologically relevant species and nano-enzymes may facilitate the applications of nanostructures in mimicking natural enzymes. In this work, AuPt alloy nanoparticles (NPs) with varying compositions were prepared through a facile method by co-reduction of Au3+ and Pt2+ in aqueous solutions. The composition could be tuned easily by adjusting the molar ratios of added Pt2+ to Au3+. It was found that both peroxidase-like and oxidase-like activity of AuPt alloy NPs were highly dependent on the alloy compositions, which thus suggesting an effective way to tailor their catalytic properties. By investigating the inhibitory effects of HS‑ on the enzyme-like activity of AuPt alloy NPs and natural enzyme, we have developed a method for colorimetric detection of HS‑ and evaluation of the inhibiting effects of inhibitors on natural and artificial enzymes. In addition, the responsive ability of this method was influenced largely by the composition: AuPt alloy NPs show much lower limit of detection for HS‑ than Pt NPs while Pt NPs show wider linear range than AuPt alloy NPs. This study suggests the facile way not only for synthesis of alloy nanostructures, but also for tuning their catalytic activities and for use in bioanalysis.

  12. Multifunctional Au-ZnO Plasmonic Nanostructures for Enhanced UV Photodetector and Room Temperature NO Sensing Devices

    PubMed Central

    Gogurla, Narendar; Sinha, Arun Kumar; Santra, Sumita; Manna, Santanu; Ray, Samit Kumar

    2014-01-01

    In this study we report the enhancement of UV photodetection and wavelength tunable light induced NO gas sensing at room temperature using Au-ZnO nanocomposites synthesized by a simple photochemical process. Plasmonic Au-ZnO nanostructures with a size less than the incident wavelength have been found to exhibit a localized surface plasmon resonance (LSPR) that leads to a strong absorption, scattering and local field enhancement. The photoresponse of Au-ZnO nanocomposite can be effectively enhanced by 80 times at 335 nm over control ZnO. We also demonstrated Au-ZnO nanocomposite's application to wavelength tunable gas sensor operating at room temperature. The sensing response of Au-ZnO nancomposite is enhanced both in UV and visible region, as compared to control ZnO. The sensitivity is observed to be higher in the visible region due to the LSPR effect of Au NPs. The selectivity is found to be higher for NO gas over CO and some other volatile organic compounds (VOCs), with a minimum detection limit of 0.1 ppb for Au-ZnO sensor at 335 nm. PMID:25255700

  13. AuPt Alloy Nanostructures with Tunable Composition and Enzyme-like Activities for Colorimetric Detection of Bisulfide

    PubMed Central

    He, Weiwei; Han, Xiangna; Jia, Huimin; Cai, Junhui; Zhou, Yunlong; Zheng, Zhi

    2017-01-01

    Tuning the enzyme-like activity and studying the interaction between biologically relevant species and nano-enzymes may facilitate the applications of nanostructures in mimicking natural enzymes. In this work, AuPt alloy nanoparticles (NPs) with varying compositions were prepared through a facile method by co-reduction of Au3+ and Pt2+ in aqueous solutions. The composition could be tuned easily by adjusting the molar ratios of added Pt2+ to Au3+. It was found that both peroxidase-like and oxidase-like activity of AuPt alloy NPs were highly dependent on the alloy compositions, which thus suggesting an effective way to tailor their catalytic properties. By investigating the inhibitory effects of HS− on the enzyme-like activity of AuPt alloy NPs and natural enzyme, we have developed a method for colorimetric detection of HS− and evaluation of the inhibiting effects of inhibitors on natural and artificial enzymes. In addition, the responsive ability of this method was influenced largely by the composition: AuPt alloy NPs show much lower limit of detection for HS− than Pt NPs while Pt NPs show wider linear range than AuPt alloy NPs. This study suggests the facile way not only for synthesis of alloy nanostructures, but also for tuning their catalytic activities and for use in bioanalysis. PMID:28051159

  14. 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.

  15. 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.

  16. SHG anisotropy in Au/Co/Au/Cu/vicinal Si(1 1 1)

    NASA Astrophysics Data System (ADS)

    Cheikh-Rouhou, W.; Sampaio, L. C.; Bartenlian, B.; Beauvillain, P.; Brun, A.; Ferré, J.; Georges, P.; Jamet, J.-P.; Mathet, V.; Stupakewicz, Andrei

    2002-02-01

    The second harmonic generation (SHG) reflectivity on magnetic multilayers is a very sensitive technique to reveal the crystallography of buried interfaces. We have used the azimuthal anisotropy of SHG to demonstrate that the vicinal character of Si(1 1 1) substrate is duplicated in the metallic multilayer Au/Co/Au/Cu. The magnetic properties of these multilayers as anisotropy and magneto-optic polar Kerr rotation were studied by linear magneto-optic effects in correlation with SHG experiments, by varying the Co and Au buffer thicknesses as well as the Cu buffer deposition condition.

  17. 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.

  18. Revisiting the S-Au(111) interaction: Static or Dynamic?

    SciTech Connect

    Biener, M M; Biener, J; Friend, C M

    2004-08-17

    The chemical inertness typically observed for Au does not imply a general inability to form stable bonds with non-metals but is rather a consequence of high reaction barriers. The Au-S interaction is probably the most intensively studied interaction of Au surfaces with non-metals as, for example, it plays an important role in Au ore formation, and controls the structure and dynamics of thiol-based self-assembled-monolayers (SAMs). In recent years a quite complex picture of the interaction of sulfur with Au(111) surfaces emerged, and a variety of S-induced surface structures was reported under different conditions. The majority of these structures were interpreted in terms of a static Au surface, where the positions of the Au atoms remain essentially unperturbed. Here we demonstrate that the Au(111) surface exhibits a very dynamic character upon interaction with adsorbed sulfur: low sulfur coverages modify the surface stress of the Au surface leading to lateral expansion of the surface layer; large-scale surface restructuring and incorporation of Au atoms into a growing two-dimensional AuS phase were observed with increasing sulfur coverage. These results provide new insight into the Au-S surface chemistry, and reveal the dynamic character of the Au(111) surface.

  19. 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.

  20. Localized surface plasmon resonances after selective oxidization of AuCu solid solution nanocrystalline films

    NASA Astrophysics Data System (ADS)

    Sousanis, A.; Grammatikopoulos, S.; Delimitis, A.; Dracopoulos, V.; Poulopoulos, P.

    2015-07-01

    AuxCu100-x, 4 ≤ x ≤ 12 at.%, solid solution nanocrystalline films with thickness between 1.5 and 100 nm were grown on Si(100) and Corning glass substrates at room temperature by radio frequency magnetron sputtering. After post annealing at 430 °C in a furnace with air, phase separation occurred between CuO and Au. The Au nanoparticles showed intense localized surface plasmon resonances with an amplitude increasing with Au concentration. We show the evolution of these resonances with the annealing time and correlate the structure to optical properties. The controllable tuning of position and intensity of plasmon resonances render this system a good candidate for applications.

  1. AuNP-CTG based probing system targeting CAG repeat DNA and RNA sequences.

    PubMed

    Le, Binh Huy; Joo, Han Na; Hwang, Do Won; Kim, Kyu Wan; Seo, Young Jun

    2017-08-15

    We have developed a AuNP-CTG based probing system that is applicable to the detection of many units of CAG repeat sequences which was synthesized by a rolling circle amplification (RCA) system with changes in fluorescence. We also demonstrate that our AuNP-CTG based probing system could transfect without using transfection reagent and detect target CAG repeat sequences in HeLa cells with dramatic changes in fluorescence. This AuNP-CTG based probing system could also be used, in conjunction with the CAG repeat RCA system, to detect target DNA. This system was so sensitive to the target DNA that it could detect even picomolar amounts with amplification of the fluorescence signal. Furthermore, we have used our gold-based CAG probing system for the detection of RNA CAG repeat sequences. Copyright © 2017 Elsevier Ltd. All rights reserved.

  2. Photonic gene circuits by optically addressable siRNA-Au nanoantennas.

    PubMed

    Lee, Somin Eunice; Sasaki, Darryl Y; Park, Younggeun; Xu, Ren; Brennan, James S; Bissell, Mina J; Lee, Luke P

    2012-09-25

    The precise perturbation of gene circuits and the direct observation of signaling pathways in living cells are essential for both fundamental biology and translational medicine. Current optogenetic technology offers a new paradigm of optical control for cells; however, this technology relies on permanent genomic modifications with light-responsive genes, thus limiting dynamic reconfiguration of gene circuits. Here, we report precise control of perturbation and reconfiguration of gene circuits in living cells by optically addressable siRNA-Au nanoantennas. The siRNA-Au nanoantennas fulfill dual functions as selectively addressable optical receivers and biomolecular emitters of small interfering RNA (siRNA). Using siRNA-Au nanoantennas as optical inputs to existing circuit connections, photonic gene circuits are constructed in living cells. We show that photonic gene circuits are modular, enabling subcircuits to be combined on-demand. Photonic gene circuits open new avenues for engineering functional gene circuits useful for fundamental bioscience, bioengineering, and medical applications.

  3. A highly crystalline single Au wire network as a high temperature transparent heater.

    PubMed

    Rao, K D M; Kulkarni, Giridhar U

    2014-06-07

    A transparent conductor which can generate high temperatures finds important applications in optoelectronics. In this article, a wire network made of Au on quartz is shown to serve as an effective high temperature transparent heater. The heater has been fabricated by depositing Au onto a cracked sacrificial template. The highly interconnected Au wire network thus formed exhibited a transmittance of ∼87% in a wide spectral range with a sheet resistance of 5.4 Ω □(-1). By passing current through the network, it could be joule heated to ∼600 °C within a few seconds. The extraordinary thermal performance and stability owe much to the seamless junctions present in the wire network. Furthermore, the wire network gets self-annealed through joule heating as seen from its increased crystallinity. Interestingly, both transmittance and sheet resistance improved following annealing to 92% and 3.2 Ω □(-1), respectively.

  4. Highly sensitive and rapid bacteria detection using molecular beacon-Au nanoparticles hybrid nanoprobes.

    PubMed

    Cao, Jing; Feng, Chao; Liu, Yan; Wang, Shouyu; Liu, Fei

    2014-07-15

    Since many diseases are caused by pathogenic bacterial infections, accurate and rapid detection of pathogenic bacteria is in urgent need to timely apply appropriate treatments and to reduce economic costs. To end this, we designed molecular beacon-Au nanoparticle hybrid nanoprobes to improve the bacterial detection efficiency and sensitivity. Here, we show that the designed molecular beacon modified Au nanoparticles could specifically recognize synthetic DNAs targets and can readily detect targets in clinical samples. Moreover, the hybrid nanoprobes can recognize Escherichia coli within an hour at a concentration of 10(2) cfu/ml, which is 1000-folds sensitive than using molecular beacon directly. Our results show that the molecular beacon-Au nanoparticle hybrid nanoprobes have great potential in medical and biological applications. Copyright © 2014 Elsevier B.V. All rights reserved.

  5. Suppression of Upsilon production in d + Au and Au + Au collisions at root s(NN) = 200 GeV (vol 735, pg 127, 2014)

    SciTech Connect

    Adamczyk, L.; Adkins, J. K.; Agakishiev, G.; Aggarwal, M. M.; Ahammed, Z.; Alekseev, I.; Alford, J.; Anson, C. D.; Aparin, A.; Arkhipkin, D.; Gliske, S.; Krueger, K.; Spinka, H. M.; Underwood, D. G.

    2014-07-30

    We report measurements of Υ meson production in p + p, d +Au, and Au+Aucollisions using the STAR detector at RHIC. We compare the Υ yield to the measured cross section in p + p collisions in order to quantify any modifications of the yield in cold nuclear matter using d +Au data and in hot nuclear matter using Au+Au data separated into three centrality classes. Our p +p measurement is based on three times the statistics of our previous result. We obtain a nuclear modification factor for Υ (1S + 2S + 3S) in the rapidity range |y| < 1 in d + Aucollisions of RdAu = 0.79 ± 0.24(stat.) ± 0.03(syst.) ± 0.10(p + p syst.). A comparison with models including shadowing and initial state parton energy loss indicates the presence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au + Au collisions, we measure a nuclear modification factor of R AA = 0.49 ±0.1(stat.) ±0.02(syst.) ±0.06(p + p syst.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are consistent with complete suppression of excited-state Υ mesons in Au + Aucollisions. The additional suppression in Au + Au is consistent with the level expected in model calculations that include the presence of a hot, deconfined Quark–Gluon Plasma. However, understanding the suppression seen in d + Au is still needed before any definitive statements about the nature of the suppression in Au + Au can be made.

  6. Magnetic two-dimensional organic topological insulator: Au-1,3,5-triethynylbenzene framework

    NASA Astrophysics Data System (ADS)

    Chen, Yu; Sun, Qiang

    2017-09-01

    Based on first-principles calculations, we demonstrate that the recently-synthesized 2D organometallic framework consisting of Au atoms and 1,3,5-triethynylbenzene (Au-TEB) is a magnetic 2D organic topological insulator (OTI). The charge transfer and covalent bonding character lead to ferromagnetism and half-metallicity in the framework, and the weak spin-orbit coupling (SOC) of C pz orbitals mediated by Au d orbitals opens modest bandgaps in the vicinity of the Fermi level. Moreover, using tight-binding model simulations, we further characterize the nonzero Chern number and edge states of Au-TEB to confirm its topological nontriviality that remains intact when the framework is supported on an insulating substrate, and applying an external strain can increase the magnitude of SOC gaps, leading to an enhanced topological nontriviality. Our results suggest that the Au-TEB organometallic framework is promising for the potential applications in quantum spintronics with the merits of low cost and easy synthesis.

  7. 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

  8. 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.

  9. Magnetic two-dimensional organic topological insulator: Au-1,3,5-triethynylbenzene framework.

    PubMed

    Chen, Yu; Sun, Qiang

    2017-09-14

    Based on first-principles calculations, we demonstrate that the recently-synthesized 2D organometallic framework consisting of Au atoms and 1,3,5-triethynylbenzene (Au-TEB) is a magnetic 2D organic topological insulator (OTI). The charge transfer and covalent bonding character lead to ferromagnetism and half-metallicity in the framework, and the weak spin-orbit coupling (SOC) of C pz orbitals mediated by Au d orbitals opens modest bandgaps in the vicinity of the Fermi level. Moreover, using tight-binding model simulations, we further characterize the nonzero Chern number and edge states of Au-TEB to confirm its topological nontriviality that remains intact when the framework is supported on an insulating substrate, and applying an external strain can increase the magnitude of SOC gaps, leading to an enhanced topological nontriviality. Our results suggest that the Au-TEB organometallic framework is promising for the potential applications in quantum spintronics with the merits of low cost and easy synthesis.

  10. Multifunctional BSA-Au nanostars for photoacoustic imaging and X-ray computed tomography.

    PubMed

    Zu, Lihui; Liu, Lin; Qin, Yeshan; Liu, Hongguang; Yang, Haishan

    2016-10-01

    We report the synthesis and characterization of bovine serum albumin-capped Au nanostars (BSA-AuNSs) for dual-modal computed tomography (CT)/photoacoustic (PA) imaging application. The BSA-AuNSs have an average size of 85nm, and a surface plasmon resonance (SPR) peak at approximately 770nm. They have excellent biocompatibility, good X-ray attenuation, and great PA contrast enhancement properties. When injected intravenously, liver signal markedly increases in both CT and PA modalities. The in vivo biodistribution studies and pathology results showed that the BSA-AuNSs were mainly excreted through the liver and intestines with no obvious biotoxicity. These results indicate that BSA-AuNSs have high potential to be used as dual-modal CT/PA imaging contrast agents or further used to develop targeted probes. This preliminary study suggests that PA tomography may be used to non-invasively trace the kinetics and biodistribution of the nanoparticles. Copyright © 2016 Elsevier Inc. All rights reserved.

  11. Au/CeO2-chitosan composite film for hydrogen peroxide sensing

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Xie, Guoming; Li, Shenfeng; Lu, Lingsong; Liu, Bei

    2012-08-01

    Au nanoparticles (AuNPs) were in situ synthesized at the cerium dioxide nanoparticles (CeO2NPs)-chitosan (CS) composite film by one-step direct chemical reduction, and the resulting Au/CeO2-CS composite were further modified for enzyme immobilization and hydrogen peroxide (H2O2) biosensing. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), UV-vis spectra and electrochemical techniques have been utilized for characterization of the prepared composite. The stepwise assembly process and electrochemical performances of the biosensor were characterized by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and typical amperometric response (i-t). The Au/CeO2-CS composite exhibited good conductibility and biocompatibility, and the developed biosensor exhibited excellent response to hydrogen peroxide in the linear range of 0.05-2.5 mM (r = 0.998) with the detection limit of 7 μM (S/N = 3). Moreover, the biosensor presented high affinity (Kmapp=1.93 mM), good reproducibility and storage stability. All these results demonstrate that the Au/CeO2-CS composite film can provide a promising biointerface for the biosensor designs and other biological applications.

  12. 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.

  13. Structural studies of Au-Pd bimetallic nanoparticles by a genetic algorithm method

    NASA Astrophysics Data System (ADS)

    Shao, Gui-Fang; Tu, Na-Na; Liu, Tun-Dong; Xu, Liang-You; Wen, Yu-Hua

    2015-06-01

    Metallic nanoparticles have attracted particular interests due to their excellent electronic, catalytic and optical properties over the past decades. Atomic-level understanding of structural characteristics of metallic nanoparticles is of great importance for their syntheses and applications because the structural characteristics strongly determine their chemical and physical properties. In this article, we systematically investigated the structural stability and structural features of Au-Pd nanoparticles by using the genetic algorithm with the quantum correction Sutton-Chen potentials. Layered coordinate ranking method and an effective fitness function have been introduced into the genetic algorithm to enhance its searching ability of low-energy configurations. Here were addressed eight representative nanoshapes including single-crystalline and multiple-twinned structures. The results reveal that the developed genetic algorithm exhibits superior searching ability. In all polyhedra, the truncated octahedron possessed the best stability, while the icosahedron did the worst. Moreover, segregation of Au to the surface and that of Pd to the core were disclosed in these polyhedral Au-Pd nanoparticles. Particularly, for Au composition of 50%, the optimized structures of Au-Pd nanoparticles were predicted to exhibit core-shell structures.

  14. Nanoporous bimetallic Pt-Au alloy nanocomposites with superior catalytic activity towards electro-oxidation of methanol and formic acid

    NASA Astrophysics Data System (ADS)

    Zhang, Zhonghua; Wang, Yan; Wang, Xiaoguang

    2011-04-01

    We present a facile route to fabricate novel nanoporous bimetallic Pt-Au alloy nanocomposites by dealloying a rapidly solidified Al75Pt15Au10 precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray (EDX) analysis. The Al75Pt15Au10 precursor is composed of a single-phase Al2(Au,Pt) intermetallic compound, and can be fully dealloyed in a 20 wt.% NaOH or 5 wt.% HCl aqueous solution. The dealloying leads to the formation of the nanoporous Pt60Au40 nanocomposites (np-Pt60Au40 NCs) with an fcc structure. The morphology, size and crystal orientation of grains in the precursor can be conserved in the resultant nanoporous alloy. The np-Pt60Au40 NCs consist of two zones with distinct ligament/channel sizes and compositions. The formation mechanism of these np-Pt60Au40 NCs can be rationalized based upon surface diffusion of more noble elements and spinodal decomposition during dealloying. Electrochemical measurements demonstrate that the np-Pt60Au40 NCs show superior catalytic activity towards the electro-oxidation of methanol and formic acid in the acid media compared to the commercial JM-Pt/C catalyst. This material can find potential applications in catalysis related areas, such as direct methanol or formic acidfuelcells. Our findings demonstrate that dealloying is an effective and simple strategy to realize the alloying of immiscible systems under mild conditions, and to fabricate novel nanostructures with superior performance.We present a facile route to fabricate novel nanoporous bimetallic Pt-Au alloy nanocomposites by dealloying a rapidly solidified Al75Pt15Au10 precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron

  15. The sandwich-type electrochemiluminescence immunosensor for α-fetoprotein based on enrichment by Fe3O4-Au magnetic nano probes and signal amplification by CdS-Au composite nanoparticles labeled anti-AFP.

    PubMed

    Zhou, Hankun; Gan, Ning; Li, Tianhua; Cao, Yuting; Zeng, Saolin; Zheng, Lei; Guo, Zhiyong

    2012-10-09

    A novel and sensitive sandwich-type electrochemiluminescence (ECL) immunosensor was fabricated on a glassy carbon electrode (GCE) for ultra trace levels of α-fetoprotein (AFP) based on sandwich immunoreaction strategy by enrichment using magnetic capture probes and quantum dots coated with Au shell (CdS-Au) as the signal tag. The capture probe was prepared by immobilizing the primary antibody of AFP (Ab1) on the core/shell Fe(3)O(4)-Au nanoparticles, which was first employed to capture AFP antigens to form Fe(3)O(4)-Au/Ab1/AFP complex from the serum after incubation. The product can be separated from the background solution through the magnetic separation. Then the CdS-Au labeled secondary antibody (Ab2) as signal tag (CdS-Au/Ab2) was conjugated successfully with Fe(3)O(4)-Au/Ab1/AFP complex to form a sandwich-type immunocomplex (Fe(3)O(4)-Au/Ab1/AFP/Ab2/CdS-Au), which can be further separated by an external magnetic field and produce ECL signals at a fixed voltage. The signal was proportional to a certain concentration range of AFP for quantification. Thus, an easy-to-use immunosensor with magnetic probes and a quantum dots signal tag was obtained. The immunosensor performed at a level of high sensitivity and a broad concentration range for AFP between 0.0005 and 5.0 ng mL(-1) with a detection limit of 0.2 pg mL(-1). The use of magnetic probes was combined with pre-concentration and separation for trace levels of tumor markers in the serum. Due to the amplification of the signal tag, the immunosensor is highly sensitive, which can offer great promise for rapid, simple, selective and cost-effective detection of effective biomonitoring for clinical application.

  16. 22 CFR 62.31 - Au pairs.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... pair participant with child development and child safety instruction, as follows: (1) Prior to... development instruction of which no less than 4 shall be devoted to specific training for children under the... and participate directly in the home life of the host family. All au pair participants provide...

  17. 22 CFR 62.31 - Au pairs.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... pair participant with child development and child safety instruction, as follows: (1) Prior to... development instruction of which no less than 4 shall be devoted to specific training for children under the... and participate directly in the home life of the host family. All au pair participants provide...

  18. 22 CFR 62.31 - Au pairs.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... pair participant with child development and child safety instruction, as follows: (1) Prior to... development instruction of which no less than 4 shall be devoted to specific training for children under the... and participate directly in the home life of the host family. All au pair participants provide...

  19. 22 CFR 62.31 - Au pairs.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... pair participant with child development and child safety instruction, as follows: (1) Prior to... development instruction of which no less than 4 shall be devoted to specific training for children under the... and participate directly in the home life of the host family. All au pair participants provide...

  20. 22 CFR 62.31 - Au pairs.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... pair participant with child development and child safety instruction, as follows: (1) Prior to... development instruction of which no less than 4 shall be devoted to specific training for children under the... and participate directly in the home life of the host family. All au pair participants provide...

  1. The fast diffusion of Au IN Pb

    NASA Technical Reports Server (NTRS)

    Mclellan, R. B.; Ko, C.; Brotzen, F. R.

    1990-01-01

    A treatment of the phenomenon of fast diffusion in lead is presented. The model used is based upon the fast diffusion of free solute interstitials. The very large negative enhancement coefficients found in the Pb-(Au, Ag) systems is explained by the formation of first and second order clusters of vacancies and substitutional solute atoms.

  2. Synthesis and electron microscopy characterization of bimetallic nanoparticles and atomically controlled Au nanoclusters

    NASA Astrophysics Data System (ADS)

    Bhattarai, Nabraj

    The properties of metal nanoparticles are controlled by their composition, shape, size and crystalline structure. Nanoparticles and nanoclusters with controlled shape and size were synthesized and investigated using atomic resolution images from aberration corrected scanning/transmission electron microscopy (STEM) and mass spectrometry (MS). Gold-palladium (Au-Pd) core-shell nanocube and triangular nanoparticles were prepared by a seed-mediated growth process and the growth mechanism was studied by varying the volume of Pd precursors added to the Au seed solution. The atomic resolution STEM images revealed that the nanocube is formed from a single-crystal Au seed with rapid growth along <111> directions while the triangular nanoparticles were obtained with growth preferentially along <110> directions rather than <111> direction. The strain generated by the lattice mismatch between fcc-Au and fcc-Pd, is released by Shockley partial dislocations (SPD), combined with stacking faults (SF) that appear at the final (outer) Pd layer. Then, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations, which finally diffuse to the free surfaces due to the alloying of Au into the Pd shell. In related work, magneto-plasmonic gold-cobalt (Au-Co) nanoparticles of diameter 4-nm were generated by a phase-transfer process and investigated by STEM, where the Z-contrast imaging and energy dispersive x-ray spectroscopy (EDS) showed inhomogeneous alloying between Au and Co at the nanoscale. The observed ferromagnetic behavior carries significance in biomedical applications. In addition, selected metallic (Au144(SR)60) and bimetallic (CuAu144) nanoclusters were obtained with thiolate-ligand protection and characterized using optical, MS, and STEM techniques. The optical spectrum and MS results established the monodispersity and purity of the nanoclusters. Another important aspect is that the emergence of broad strong plasmonic band centered near 520

  3. Characterization of Au and Bimetallic PtAu Nanoparticles on PDDA-Graphene Sheets as Electrocatalysts for Formic Acid Oxidation.

    PubMed

    Yung, Tung-Yuan; Liu, Ting-Yu; Huang, Li-Ying; Wang, Kuan-Syun; Tzou, Huei-Ming; Chen, Po-Tuan; Chao, Chi-Yang; Liu, Ling-Kang

    2015-12-01

    Nanocomposite materials of the Au nanoparticles (Au/PDDA-G) and the bimetallic PtAu nanoparticles on poly-(diallyldimethylammonium chloride) (PDDA)-modified graphene sheets (PtAu/PDDA-G) were prepared with hydrothermal method at 90 °C for 24 h. The composite materials Au/PDDA-G and PtAu/PDDA-G were evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) for exploring the structural characterization for the electrochemical catalysis. According to TEM results, the diameter of Au and bimetallic PtAu nanoparticles is about 20-50 and 5-10 nm, respectively. X-ray diffraction (XRD) results indicate that both of PtAu and Au nanoparticles exhibit the crystalline plane of (111), (200), (210), and (311). Furthermore, XRD data also show the 2°-3° difference between pristine graphene sheets and the PDDA-modified graphene sheets. For the catalytic activity tests of Au/PDDA-G and PtAu/PDDA-G, the mixture of 0.5 M aqueous H2SO4 and 0.5 M aqueous formic acid was used as model to evaluate the electrochemical characterizations. The catalytic activities of the novel bimetallic PtAu/graphene electrocatalyst would be anticipated to be superior to the previous electrocatalyst of the cubic Pt/graphene.

  4. Characterization of Au and Bimetallic PtAu Nanoparticles on PDDA-Graphene Sheets as Electrocatalysts for Formic Acid Oxidation

    NASA Astrophysics Data System (ADS)

    Yung, Tung-Yuan; Liu, Ting-Yu; Huang, Li-Ying; Wang, Kuan-Syun; Tzou, Huei-Ming; Chen, Po-Tuan; Chao, Chi-Yang; Liu, Ling-Kang

    2015-09-01

    Nanocomposite materials of the Au nanoparticles (Au/PDDA-G) and the bimetallic PtAu nanoparticles on poly-(diallyldimethylammonium chloride) (PDDA)-modified graphene sheets (PtAu/PDDA-G) were prepared with hydrothermal method at 90 °C for 24 h. The composite materials Au/PDDA-G and PtAu/PDDA-G were evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) for exploring the structural characterization for the electrochemical catalysis. According to TEM results, the diameter of Au and bimetallic PtAu nanoparticles is about 20-50 and 5-10 nm, respectively. X-ray diffraction (XRD) results indicate that both of PtAu and Au nanoparticles exhibit the crystalline plane of (111), (200), (210), and (311). Furthermore, XRD data also show the 2°-3° difference between pristine graphene sheets and the PDDA-modified graphene sheets. For the catalytic activity tests of Au/PDDA-G and PtAu/PDDA-G, the mixture of 0.5 M aqueous H2SO4 and 0.5 M aqueous formic acid was used as model to evaluate the electrochemical characterizations. The catalytic activities of the novel bimetallic PtAu/graphene electrocatalyst would be anticipated to be superior to the previous electrocatalyst of the cubic Pt/graphene.

  5. High Resolution Photoelectron Spectroscopy of Au_2^- and Au_4^- by Photoelectron Imaging

    NASA Astrophysics Data System (ADS)

    Leon, Iker; Yang, Zheng; Wang, Lai-Sheng

    2013-06-01

    We report high resolution photoelectron spectra of Au_2^- and Au_4^- obtained with a newly-built photoelectron imaging apparatus. Gold anions are produced by laser vaporization and the desired specie is mass selected and focused into the collinear velocity-map imaging (VMI) lens assembly. The design of the imaging lens has allowed us to obtain less than 0.9% energy resolution for high kinetic energy electrons ( > 1eV) while maintaining wavenumber resolution for low kinetic energy electrons. Although gold dimer and tetramer have been studied in the past, we present spectroscopic results under high resolution. For Au_2^-, we report high resolution spectra with an accurate determination of the electron affinity together with a complete vibrational assignment, for both the anion and neutral ground states, while for Au_4^-, we are able to resolve a low frequency mode and obtain accurately the adiabatic detachment energy.

  6. Magnetic disorder in nanostructured Fe7Au93 films and Fe14Au86 powders

    NASA Astrophysics Data System (ADS)

    Alba Venero, D.; Fernández Barquín, L.; Alonso, J.; Svalov, A.; Fdez-Gubieda, M. L.

    2010-01-01

    Thin films and powders of dilute Fe-Au alloys have been produced by DC-magnetron sputtering and high-energy milling, respectively. Energy disperse X-ray spectroscopy gives Fe7Au93 for the films and Fe14Au86 for the powders. The film, with a thickness below 200 nm measured by atomic force microscopy, was deposited onto a Si(100) substrate. X-ray diffraction reveals a major presence of fcc-Au peaks masking the bcc-Fe phase. The (1 0-300 K) DC-susceptibility (H = 100-1000 Oe) shows a clear cusp in the films in contrast to the powders, with a reentrant spin glass-like behavior.

  7. Systematics of Global Observables in Cu+Cu and Au+Au Collisions at RHIC Energies

    SciTech Connect

    Nouicer, Rachid

    2006-07-11

    Charged particles produced in Cu+Cu collisions at {radical}(s{sub NN}) = 200 and 62.4 GeV have been measured in the PHOBOS experiment at RHIC. The comparison of the results for Cu+Cu and Au+Au for the most central collisions at the same energy reveals that the particle density per nucleon participant pair and the extended longitudinal scaling behavior are similar in both systems. This implies that for the most central events in symmetric nucleus-nucleus collisions the particle density per nucleon participant pair does not depend on the size of the two colliding nuclei but only on the collision energy. Also the extended longitudinal scaling seems independent of the colliding energy and species for central collisions. In addition, there is an overall factorization of dNch/d{eta} shapes as a function of collision centraliry between Au+Au and Cu+Cu collisions at the same energy.

  8. Charged-Particle Pseudorapidity Density Distributions from Au+Au Collisions at

    SciTech Connect

    Back, B. B.; Baker, M. D.; Barton, D. S.; Betts, R. R.; Bindel, R.; Budzanowski, A.; Busza, W.; Carroll, A.; Decowski, M. P.; Garcia, E.

    2001-09-03

    The charged-particle pseudorapidity density dN{sub ch}/d{eta} has been measured for Au+Au collisions at s{sub NN}=130 GeV at RHIC, using the PHOBOS apparatus. The total number of charged particles produced for the 3% most-central Au+Au collisions for |{eta}|{<=}5.4 is found to be 4200{+-}470 . The evolution of dN{sub ch}/d{eta} with centrality is discussed, and compared to model calculations and to data from proton-induced collisions. The data show an enhancement in charged-particle production at midrapidity, while in the fragmentation regions, the results are consistent with expectations from pp and pA scattering.

  9. Ohmic Contacts to p-GaAs with Au/Zn/Au Structure

    NASA Astrophysics Data System (ADS)

    Sanada, Tatsuyuki; Wada, Osamu

    1980-08-01

    A reproducible technique for forming ohmic contacts with low contact resistances to p-GaAs is presented. A Au/Zn/Au multilayer structure, which is deposited by sequential evaporation of Au, Zn and Au, is found to realize a satisfactorily low specific contact resistance rc. The value of rc is minimized when the initial thickness of Zn layer is larger than 200 Å and the alloying temperature is around 400°C. The minimum value of rc in Ω-cm2 is expressed as rc{=}1.8× 1018{\\cdot}p-1.3, where p is the net hole concentration in cm-3. It is also confirmed by Auger spectroscopy that the reduction of rc is caused by the preferential incorporation of Zn atoms into the GaAs bulk during alloying.

  10. Charge-dependent azimuthal correlations from AuAu to UU collisions