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Sample records for monolayer modified ag

  1. Oxidized Monolayers of Epitaxial Silicene on Ag(111)

    PubMed Central

    Johnson, Neil W.; Muir, David I.; Moewes, Alexander

    2016-01-01

    The properties of epitaxial silicene monolayers on Ag(111) at various levels of oxidation are determined through complementary density functional theory calculations and soft X-ray spectroscopy experiments. Our calculations indicate that moderate levels of oxidation do not cause a significant bandgap opening in the epitaxial silicene monolayer, suggesting that oxygen functionalization is not a viable mechanism for bandgap tuning while the silicene monolayer remains on its metallic substrate. In addition, moderate oxidation is calculated to strongly distort the hexagonal Si lattice, causing it to cluster in regions of highest oxygen adatom concentration but retain its 2D sheet structure. However, our experiments reveal that beam-induced oxidation is consistent with the formation of islands of bulk-like SiO2. Complete exposure of the monolayer to ambient conditions results in a fully oxidized sample that closely resembles bulk SiO2, of which a significant portion is completely detached from the substrate. PMID:26936144

  2. Oxidized Monolayers of Epitaxial Silicene on Ag(111)

    NASA Astrophysics Data System (ADS)

    Johnson, Neil W.; Muir, David I.; Moewes, Alexander

    2016-03-01

    The properties of epitaxial silicene monolayers on Ag(111) at various levels of oxidation are determined through complementary density functional theory calculations and soft X-ray spectroscopy experiments. Our calculations indicate that moderate levels of oxidation do not cause a significant bandgap opening in the epitaxial silicene monolayer, suggesting that oxygen functionalization is not a viable mechanism for bandgap tuning while the silicene monolayer remains on its metallic substrate. In addition, moderate oxidation is calculated to strongly distort the hexagonal Si lattice, causing it to cluster in regions of highest oxygen adatom concentration but retain its 2D sheet structure. However, our experiments reveal that beam-induced oxidation is consistent with the formation of islands of bulk-like SiO2. Complete exposure of the monolayer to ambient conditions results in a fully oxidized sample that closely resembles bulk SiO2, of which a significant portion is completely detached from the substrate.

  3. A Binder-Free Ag Paste Using a Chemically Adsorbed Monolayer

    NASA Astrophysics Data System (ADS)

    Onishi, Shogo; Ohkubo, Yuji; Soejima, Kazuhiro; Ogawa, Kazufumi

    2009-06-01

    We developed a binder-free Ag paste using reactive chemically absorbed monolayers (CAMs), such as epoxy-terminated CAMs. Ag paste was prepared by forming an epoxy-terminated CAM with 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (ECHxES) on the surface of Ag particles, followed by adding 2-methyl-imidazole (2-MeIm) as a cross-linker into a suspension of dispersed Ag particles modified with ECHxES. To increase electrical conductivity, a mixture of large (average diameter D = 1.0 µm) and small (D = 0.5 µm) Ag particles was used. When the ratio in the mixture of large: small was 7:3, the best conductivity, 4.0 ×104 S/cm, was obtained. To prepare rigid wires from Ag paste, a cross-linker of a copper imidazole complex, instead of 2-MeIm, was added to the mixture of the Ag particles covered with ECHxES CAMs. The best pencil hardness and the best electrical conductivity obtained with the Ag paste wire were F and 2.5 ×105 S/cm, respectively, which exceeded the values of commercially available Ag pastes.

  4. High Temperature Ferromagnetism in a GdAg2 Monolayer.

    PubMed

    Ormaza, M; Fernández, L; Ilyn, M; Magaña, A; Xu, B; Verstraete, M J; Gastaldo, M; Valbuena, M A; Gargiani, P; Mugarza, A; Ayuela, A; Vitali, L; Blanco-Rey, M; Schiller, F; Ortega, J E

    2016-07-13

    Materials that exhibit ferromagnetism, interfacial stability, and tunability are highly desired for the realization of emerging magnetoelectronic phenomena in heterostructures. Here we present the GdAg2 monolayer alloy, which possesses all such qualities. By combining X-ray absorption, Kerr effect, and angle-resolved photoemission with ab initio calculations, we have investigated the ferromagnetic nature of this class of Gd-based alloys. The Curie temperature can increase from 19 K in GdAu2 to a remarkably high 85 K in GdAg2. We find that the exchange coupling between Gd atoms is barely affected by their full coordination with noble metal atoms, and instead, magnetic coupling is effectively mediated by noble metal-Gd hybrid s,p-d bands. The direct comparison between isostructural GdAu2 and GdAg2 monolayers explains how the higher degree of surface confinement and electron occupation of such hybrid s,p-d bands promote the high Curie temperature in the latter. Finally, the chemical composition and structural robustness of the GdAg2 alloy has been demonstrated by interfacing them with organic semiconductors or magnetic nanodots. These results encourage systematic investigations of rare-earth/noble metal surface alloys and interfaces, in order to exploit them in magnetoelectronic applications. PMID:27247988

  5. Comparison of electronic structure between monolayer silicenes on Ag (111)

    NASA Astrophysics Data System (ADS)

    Chun-Liang, Lin; Ryuichi, Arafune; Maki, Kawai; Noriaki, Takagi

    2015-08-01

    The electronic structures of monolayer silicenes (4 × 4 and ) grown on Ag (111) surface are studied by scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. While both phases have similar electronic structures around the Fermi level, significant differences are observed in the higher energy unoccupied states. The DFT calculations show that the contributions of Si 3pz orbitals to the unoccupied states are different because of their different buckled configurations. Project supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) through Grants-in-Aid for Scientific Research (Grant Nos. 24241040 and 25110008) and the World Premier International Research Center Initiative (WPI), MEXT, Japan.

  6. Exploring Ag(111) Substrate for Epitaxially Growing Monolayer Stanene: A First-Principles Study

    PubMed Central

    Gao, Junfeng; Zhang, Gang; Zhang, Yong-Wei

    2016-01-01

    Stanene, a two-dimensional topological insulator composed of Sn atoms in a hexagonal lattice, is a promising contender to Si in nanoelectronics. Currently it is still a significant challenge to achieve large-area, high-quality monolayer stanene. We explore the potential of Ag(111) surface as an ideal substrate for the epitaxial growth of monolayer stanene. Using first-principles calculations, we study the stability of the structure of stanene in different epitaxial relations with respect to Ag(111) surface, and also the diffusion behavior of Sn adatom on Ag(111) surface. Our study reveals that: (1) the hexagonal structure of stanene monolayer is well reserved on Ag(111) surface; (2) the height of epitaxial stanene monolayer is comparable to the step height of the substrate, enabling the growth to cross the surface step and achieve a large-area stanene; (3) the perfect lattice structure of free-standing stanene can be achieved once the epitaxial stanene monolayer is detached from Ag(111) surface; and finally (4) the diffusion barrier of Sn adatom on Ag(111) surface is found to be only 0.041 eV, allowing the epitaxial growth of stanene monolayer even at low temperatures. Our above revelations strongly suggest that Ag(111) surface is an ideal candidate for growing large-area, high-quality monolayer stanene. PMID:27373464

  7. Exploring Ag(111) Substrate for Epitaxially Growing Monolayer Stanene: A First-Principles Study

    NASA Astrophysics Data System (ADS)

    Gao, Junfeng; Zhang, Gang; Zhang, Yong-Wei

    2016-07-01

    Stanene, a two-dimensional topological insulator composed of Sn atoms in a hexagonal lattice, is a promising contender to Si in nanoelectronics. Currently it is still a significant challenge to achieve large-area, high-quality monolayer stanene. We explore the potential of Ag(111) surface as an ideal substrate for the epitaxial growth of monolayer stanene. Using first-principles calculations, we study the stability of the structure of stanene in different epitaxial relations with respect to Ag(111) surface, and also the diffusion behavior of Sn adatom on Ag(111) surface. Our study reveals that: (1) the hexagonal structure of stanene monolayer is well reserved on Ag(111) surface; (2) the height of epitaxial stanene monolayer is comparable to the step height of the substrate, enabling the growth to cross the surface step and achieve a large-area stanene; (3) the perfect lattice structure of free-standing stanene can be achieved once the epitaxial stanene monolayer is detached from Ag(111) surface; and finally (4) the diffusion barrier of Sn adatom on Ag(111) surface is found to be only 0.041 eV, allowing the epitaxial growth of stanene monolayer even at low temperatures. Our above revelations strongly suggest that Ag(111) surface is an ideal candidate for growing large-area, high-quality monolayer stanene.

  8. Exploring Ag(111) Substrate for Epitaxially Growing Monolayer Stanene: A First-Principles Study.

    PubMed

    Gao, Junfeng; Zhang, Gang; Zhang, Yong-Wei

    2016-01-01

    Stanene, a two-dimensional topological insulator composed of Sn atoms in a hexagonal lattice, is a promising contender to Si in nanoelectronics. Currently it is still a significant challenge to achieve large-area, high-quality monolayer stanene. We explore the potential of Ag(111) surface as an ideal substrate for the epitaxial growth of monolayer stanene. Using first-principles calculations, we study the stability of the structure of stanene in different epitaxial relations with respect to Ag(111) surface, and also the diffusion behavior of Sn adatom on Ag(111) surface. Our study reveals that: (1) the hexagonal structure of stanene monolayer is well reserved on Ag(111) surface; (2) the height of epitaxial stanene monolayer is comparable to the step height of the substrate, enabling the growth to cross the surface step and achieve a large-area stanene; (3) the perfect lattice structure of free-standing stanene can be achieved once the epitaxial stanene monolayer is detached from Ag(111) surface; and finally (4) the diffusion barrier of Sn adatom on Ag(111) surface is found to be only 0.041 eV, allowing the epitaxial growth of stanene monolayer even at low temperatures. Our above revelations strongly suggest that Ag(111) surface is an ideal candidate for growing large-area, high-quality monolayer stanene. PMID:27373464

  9. Comparison of a Fluorinated Aryl Thiol Self-Assembled Monolayer with Its Hydrogenated Counterpart on Polycrystalline Ag Substrates

    SciTech Connect

    Schalnat, Matthew C.; Pemberton, Jeanne E.

    2010-07-20

    The effects of perfluorination of aryl thiols on surface coverage, surface electronic properties, and molecular orientation of self-assembled monolayers of thiophenol (TP) and pentafluorothiophenol (F5TP) on polycrystalline Ag were evaluated using linear sweep voltammetry, ultraviolet photoelectron spectroscopy (UPS), and surface Raman spectroscopy, respectively. Electrochemical reductive desorption by linear sweep voltammetry indicates a surface coverage for the TP monolayer of (5.07 ± 1.29) × 10-10 mol/cm2, equating to a molecular area of 32.8 ± 8.3 Å2, and a surface coverage for the F5TP monolayer of (1.95 ± 0.59) × 10-10 mol/cm2, equating to an area of 85.2 ± 25.8 Å2/molecule. TP-modified Ag exhibits a change in work function (ΔΦ) of -0.64 eV relative to bare Ag, whereas F5TP-modified Ag exhibits a ΔΦ of +0.54 eV relative to bare Ag. Quantitative analysis of the UPS and reductive desorption results yields molecular pictures of the proposed interfaces with TP molecules tilted <20° from the surface normal in a herringbone pattern spaced 6.4 Å apart and F5TP molecules in a more disordered arrangement tilted 67° from the surface normal with an intermolecular distance of 10.4 Å. Qualitative surface Raman spectroscopic analysis of in-plane and out-of-plane modes for these systems confirms that TP molecules are oriented more vertical than F5TP molecules in these monolayers.

  10. ELECTROCATALYSIS ON SURFACES MODIFIED BY METAL MONOLAYERS DEPOSITED AT UNDERPOTENTIALS.

    SciTech Connect

    ADZIC,R.

    2000-12-01

    The remarkable catalytic properties of electrode surfaces modified by monolayer amounts of metal adatoms obtained by underpotential deposition (UPD) have been the subject of a large number of studies during the last couple of decades. This interest stems from the possibility of implementing strictly surface modifications of electrocatalysts in an elegant, well-controlled way, and these bi-metallic surfaces can serve as models for the design of new catalysts. In addition, some of these systems may have potential for practical applications. The UPD of metals, which in general involves the deposition of up to a monolayer of metal on a foreign substrate at potentials positive to the reversible thermodynamic potential, facilitates this type of surface modification, which can be performed repeatedly by potential control. Recent studies of these surfaces and their catalytic properties by new in situ surface structure sensitive techniques have greatly improved the understanding of these systems.

  11. Scanning Electrochemical Microscopy of DNA Monolayers Modified with Nile Blue

    PubMed Central

    Gorodetsky, Alon A.; Hammond, William J.; Hill, Michael G.; Slowinski, Krzysztof; Barton, Jacqueline K.

    2009-01-01

    Scanning electrochemical microscopy (SECM) is used to probe long-range charge transport (CT) through DNA monolayers containing the redox-active Nile Blue (NB) intercalator covalently affixed at a specific location in the DNA film. At substrate potentials negative of the formal potential of covalently attached NB, the electrocatalytic reduction of Fe(CN)63− generated at the SECM tip is observed only when NB is located at the DNA/solution interface; for DNA films containing NB in close proximity to the DNA/electrode interface, the electrocatalytic effect is absent. This behavior is consistent with both rapid DNA-mediated CT between the NB intercalator and the gold electrode as well as a rate-limiting electron transfer between NB and the solution phase Fe(CN)63−. The DNA-mediated nature of the catalytic cycle is confirmed through sequence-specific and localized detection of attomoles of TATA-binding protein, a transcription factor that severely distorts DNA upon binding. Importantly, the strategy outlined here is general and allows for the local investigation of the surface characteristics of DNA monolayers both in the absence and in the presence of DNA binding proteins. These experiments highlight the utility of DNA-modified electrodes as versatile platforms for SECM detection schemes that take advantage of CT mediated by the DNA base pair stack. PMID:19053641

  12. Ordered structure upon deposition of Ge on the monolayer silicene on Ag(111)

    NASA Astrophysics Data System (ADS)

    Chen, Han-De; Lin, Dengsung

    The growth of monolayer silicene on Ag (111) has been a hot research in recent years. The akin structure of the same group IV element: Germanene, has also been grown successfully on different metal substrates. In this investigation, Ge has been deposited by molecular beam epitaxy on the monolayer-thick silicene grown on Ag(111). Low-temperature scanning tunneling microscopy (LT-STM) has been employed to observed the surface morphology and atomic structure. On the (3 x 3)Si phase, only one Ge adatom is found on each (3 x 3)Si unit cell on two different sites, A and B. The deposited Ge adatoms prefer to settle around a unit cell that has already incorporated one Ge adatom, thereby forming two domains (3 x 3)A and (3 x 3)B. Results on (r7 x r7)Si superstructure showing local ordering will also be presented.

  13. Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface

    NASA Astrophysics Data System (ADS)

    Yan, Ling-Hao; Wu, Rong-Ting; Bao, De-Liang; Ren, Jun-Hai; Zhang, Yan-Fang; Zhang, Hai-Gang; Huang, Li; Wang, Ye-Liang; Du, Shi-Xuan; Huan, Qing; Gao, Hong-Jun

    2015-07-01

    Adsorption behavior of Fe atoms on a metal-free naphthalocyanine (H2Nc) monolayer on Ag(111) surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory (DFT) based calculations. We found that the Fe atoms were adsorbed on the centers of H2Nc molecules and formed Fe-H2Nc complexes at low coverage. DFT calculations show that Fe sited in the center of the molecule is the most stable configuration, in good agreement with the experimental observations. After an Fe-H2Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe-H2Nc complex monolayer. Therefore, the H2Nc monolayer grown on Ag(111) could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties. Project supported by the National Natural Science Foundation of China (Grant Nos. 61390501, 51325204, and 11204361), the National Basic Research Program of China (Grant Nos. 2011CB808401 and 2011CB921702), the National Key Scientific Instrument and Equipment Development Project of China (Grant No. 2013YQ1203451), the National Supercomputing Center in Tianjin, China, and the Chinese Academy of Sciences.

  14. Superconducting properties of multilayered Ag/Bi(Pb)-2223 tapes prepared using pretextured monolayered tapes

    NASA Astrophysics Data System (ADS)

    Syamaprasad, U.; Sarma, M. S.; Guruswamy, P.; Pillai, S. G. K.; Warrier, K. G. K.; Damodaran, A. D.

    1997-02-01

    Multilayered Ag/Bi(Pb)-2223 tapes with high critical current densities 0953-2048/10/2/005/img1 have been fabricated using partially heat treated, textured monolayered tapes. Cut sections of the monolayered tapes have been stacked one over the other and folded together using high-purity silver foil and further rolled and heat treated to obtain multilayered tapes of different thickness with an HTS layer thickness varying from 9 to 0953-2048/10/2/005/img2. A comparison of the superconducting properties of the multilayered tapes with those of monolayered tapes prepared under identical heat treatment conditions shows that the 0953-2048/10/2/005/img3 ratio at 77 K is as high as 0.57. The ratio is found to decrease with a decrease in the HTS core thickness of the multilayered tapes. XRD studies of `banana peeled' samples show that the monolayered tapes at the folding stage acquire a good degree of texturing. The relatively high value of the 0953-2048/10/2/005/img3 ratio obtained in the present case compared with those reported by the existing techniques is attributed to the use of pretextured monolayered tapes.

  15. Bimetallic PdAg nanoparticle arrays from monolayer films of diblock copolymer micelles

    NASA Astrophysics Data System (ADS)

    Ehret, E.; Beyou, E.; Mamontov, G. V.; Bugrova, T. A.; Prakash, S.; Aouine, M.; Domenichini, B.; Cadete Santos Aires, F. J.

    2015-07-01

    The self-assembly technique provides a highly efficient route to generate well-ordered structures on a nanometer scale. In this paper, well-ordered arrays of PdAg alloy nanoparticles on flat substrates with narrow distributions of particle size (6-7 nm) and interparticle spacing (about 60 nm) were synthesized by the block copolymer micelle approach. A home-made PS-b-P4VP diblock copolymer was prepared to obtain a micellar structure in toluene. Pd and Ag salts were then successfully loaded in the micellar core of the PS-b-P4VP copolymer. A self-assembled monolayer of the loaded micelles was obtained by dipping the flat substrate in the solution. At this stage, the core of the micelles was still loaded with the metal precursor rather than with a metal. Physical and chemical reducing methods were used to reduce the metal salts embedded in the P4VP core into PdAg nanoparticles. HRTEM and EDX indicated that Pd-rich PdAg alloy nanoparticles were synthesized by chemical or physical reduction; UV-visible spectroscopy observations confirmed that metallic PdAg nanoparticles were quickly formed after chemical reduction; XPS measurements revealed that the PdAg alloy nanoparticles were in a metallic state after a short time of exposure to O2 plasma and after hydrazine reduction.

  16. Manipulation resolves non-trivial structure of corrole monolayer on Ag(111).

    PubMed

    Tebi, Stefano; Aldahhak, Hazem; Serrano, Giulia; Schöfberger, Wolfgang; Rauls, Eva; Schmidt, Wolf Gero; Koch, Reinhold; Müllegger, Stefan

    2016-01-15

    Non-trivial arrangement of molecules within a molecular network complicates structure determination due to interdigitation, partial overlap, or stacking. We demonstrate that combined imaging and lateral manipulation with a scanning tunneling microscope resolves the intricate structure of a molecular network in two-dimensions in a straightforward manner. The network, formed by a monolayer of 5,10,15-tris(pentafluorophenyl)-corrole molecules on Ag(111), is manipulated for the first time with single-molecule precision. Our results reveal a shingle-like packing of partially overlapping corrole molecules. Density functional theory calculations support our findings. PMID:26629708

  17. Manipulation resolves non-trivial structure of corrole monolayer on Ag(111)

    NASA Astrophysics Data System (ADS)

    Tebi, Stefano; Aldahhak, Hazem; Serrano, Giulia; Schöfberger, Wolfgang; Rauls, Eva; Gero Schmidt, Wolf; Koch, Reinhold; Müllegger, Stefan

    2016-01-01

    Non-trivial arrangement of molecules within a molecular network complicates structure determination due to interdigitation, partial overlap, or stacking. We demonstrate that combined imaging and lateral manipulation with a scanning tunneling microscope resolves the intricate structure of a molecular network in two-dimensions in a straightforward manner. The network, formed by a monolayer of 5,10,15-tris(pentafluorophenyl)-corrole molecules on Ag(111), is manipulated for the first time with single-molecule precision. Our results reveal a shingle-like packing of partially overlapping corrole molecules. Density functional theory calculations support our findings.

  18. Computer simulations of the Adsorption of Xenon onto a C60 monolayer on Ag (111)

    NASA Astrophysics Data System (ADS)

    Gatica, Silvina; Cole, Milton; Diehl, Renee

    2007-03-01

    We performed Grand Canonical Monte Carlo simulations to study the adsorption of Xenon on a substrate composed of C60 molecules placed on top of a Ag(111) surface. The C60 molecules form a commensurate structure at a distance of 0.227 nm above the Ag surface. The interaction potential between the Xe atoms and the substrate has two contributions: from the C60 molecules and from the Ag atoms. In the simulations, the interaction with the Ag surface was computed using an ab initio van der Waals potential, varying as 1/d^3. The interaction between the Xe atoms and each C60 molecule was computed using a potential previously developed by Hernandez et.al. (E. S. Hernandez, M. W. Cole and M. Boninsegni, ``Wetting of spherical surfaces by quantum fluids'', J. Low Temp. Phys. 134, 309-314 (2004)), who integrated the Lennard Jones interaction over the surface of a spherical buckyball. The total potential has especially attractive 3-fold sites, positioned 0.4 nm above the point between each three buckyballs. The low coverage uptake populates those sites, and then continues forming a monolayer. The adsorption isotherms show several steps, typical of substrates that have distinct adsorption sites. We compare the results with the experimental data.

  19. Ordered array of Ag semishells on different diameter monolayer polystyrene colloidal crystals: An ultrasensitive and reproducible SERS substrate.

    PubMed

    Yi, Zao; Niu, Gao; Luo, Jiangshan; Kang, Xiaoli; Yao, Weitang; Zhang, Weibin; Yi, Yougen; Yi, Yong; Ye, Xin; Duan, Tao; Tang, Yongjian

    2016-01-01

    Ag semishells (AgSS) ordered arrays for surface-enhanced Raman scattering (SERS) spectroscopy have been prepared by depositing Ag film onto polystyrene colloidal particle (PSCP) monolayer templates array. The diversified activity for SERS activity with the ordered AgSS arrays mainly depends on the PSCP diameter and Ag film thickness. The high SERS sensitivity and reproducibility are proved by the detection of rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP) molecules. The prominent enhancements of SERS are mainly from the "V"-shaped or "U"-shaped nanogaps on AgSS, which are experimentally and theoretically investigated. The higher SERS activity, stability and reproducibility make the ordered AgSS a promising choice for practical SERS low concentration detection applications. PMID:27586562

  20. Ordered array of Ag semishells on different diameter monolayer polystyrene colloidal crystals: An ultrasensitive and reproducible SERS substrate

    PubMed Central

    Yi, Zao; Niu, Gao; Luo, Jiangshan; Kang, Xiaoli; Yao, Weitang; Zhang, Weibin; Yi, Yougen; Yi, Yong; Ye, Xin; Duan, Tao; Tang, Yongjian

    2016-01-01

    Ag semishells (AgSS) ordered arrays for surface-enhanced Raman scattering (SERS) spectroscopy have been prepared by depositing Ag film onto polystyrene colloidal particle (PSCP) monolayer templates array. The diversified activity for SERS activity with the ordered AgSS arrays mainly depends on the PSCP diameter and Ag film thickness. The high SERS sensitivity and reproducibility are proved by the detection of rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP) molecules. The prominent enhancements of SERS are mainly from the “V”-shaped or “U”-shaped nanogaps on AgSS, which are experimentally and theoretically investigated. The higher SERS activity, stability and reproducibility make the ordered AgSS a promising choice for practical SERS low concentration detection applications. PMID:27586562

  1. From monomer to monolayer: a global optimisation study of (ZnO)n nanoclusters on the Ag surface.

    PubMed

    Demiroglu, Ilker; Woodley, Scott M; Sokol, Alexey A; Bromley, Stefan T

    2014-12-21

    We employ global optimisation to investigate how oxide nanoclusters of increasing size can best adapt their structure to lower the system energy when interacting with a realistic extended metal support. Specifically, we focus on the (ZnO)@Ag(111) system where experiment has shown that the infinite Ag(111)-supported ZnO monolayer limit corresponds to an epitaxially 7 : 8 matched graphene-like (Zn(3)O(3))-based hexagonal sheet. Using a two-stage search method based on classical interatomic potentials and then on more accurate density functional theory, we report global minina candidate structures for Ag-supported (ZnO)n cluster with sizes ranging from n = 1-24. Comparison with the respective global minina structure of free space (ZnO)n clusters reveals that the surface interaction plays a decisive role in determining the lowest energy Ag-supported (ZnO)n cluster structures. Whereas free space (ZnO)n clusters tend to adopt cage-like bubble structures as they grow larger, Ag-supported (ZnO)n clusters of increasing size become progressively more like planar cuts from the infinite graphene-like ZnO single monolayer. This energetic favourability for planar hexagonal Ag-supported clusters over their 3D counterparts can be partly rationalised by the ZnO-Ag(111) epitaxial matching and the increased number of close interactions with the Ag surface. Detailed analysis shows that this tendency can also be attributed to the capacity of 2D clusters to distort to improve their interaction with the Ag surface relative to more rigid 3D bubble cluster isomers. For the larger sized clusters we find that the adsorption energies and most stable structural types appear to be rather converged confirming that our study makes a bridge between the Ag-supported ZnO monomer and the infinite Ag-supported ZnO monolayer. PMID:25354937

  2. A SERS study of the molecular structure of alkanethiol monolayers on Ag nanocubes in the presence of aqueous glucose

    NASA Astrophysics Data System (ADS)

    Rycenga, Matthew; McLellan, Joseph M.; Xia, Younan

    2008-09-01

    We report progress towards the surface-enhanced Raman scattering (SERS) characterization of self-assembled monolayers (SAMs) on uniform Ag nanocubes. This study quantifies changes in the SAMs induced by the presence of aqueous glucose. The SAMs were prepared from dodecanethiol and they were representative of highly ordered monolayers as indicated by SERS analysis. We examined the SAMs' response to glucose and observed conformational changes in the alkanethiolate SAMs. Analysis of the trans and gauche bands as well as the C-H stretching modes of the SAMs suggests that the analyte-SAM interactions were superficial and there was no penetration for the glucose molecules into the monolayers.

  3. A SERS study of the molecular structure of alkanethiol monolayers on Ag nanocubes in the presence of aqueous glucose

    PubMed Central

    Rycenga, Matthew; McLellan, Joseph M.; Xia, Younan

    2008-01-01

    We report progress towards the surface-enhanced Raman scattering (SERS) characterization of self-assembled monolayers (SAMs) on uniform Ag nanocubes. This study quantifies changes in the SAMs induced by the presence of aqueous glucose. The SAMs were prepared from dodecanethiol and they were representative of highly ordered monolayers as indicated by SERS analysis. We examined the SAMs response to glucose and observed conformational changes in the alkanethiolate SAMs. Analysis of the trans and gauche bands as well as the C-H stretching modes of the SAMs suggest that the analyte-SAM interactions were superficial and there was no penetration for the glucose molecules into the monolayers. PMID:20160847

  4. Evolution of pentacene films on Ag(1 1 1): Growth beyond the first monolayer

    NASA Astrophysics Data System (ADS)

    Käfer, Daniel; Witte, Gregor

    2007-07-01

    The formation and structure of pentacene films upon molecular beam deposition at room temperature onto a Ag(1 1 1) surface have been studied by means of SEM, XRD, TDS and NEXAFS. It is shown that multilayer films actually consist of separate crystalline islands revealing a bulk structure reported before by Siegrist et al. [T. Siegrist, C. Kloc, J.H. Schon, B. Batlogg, R.C. Haddon, S. Berg, G.A. Thomas, Angew. Chem. Int. Ed. 40 (2001) 1732]. Distinctly different π ∗-resonances were observed in the C1s NEXAFS spectra of pentacene for the first monolayer and the crystalline films reflecting differences in the electronic coupling and the molecular orientation. Moreover, such characteristic π ∗-signatures were used to monitor in situ the film evolution upon deposition indicating an immediate formation of crystalline islands on top of a chemisorbed wetting layer.

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

    SciTech Connect

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

    2012-02-06

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

  6. Morphology of Monolayer MgO Films on Ag(100): Switching from Corrugated Islands to Extended Flat Terraces

    NASA Astrophysics Data System (ADS)

    Pal, Jagriti; Smerieri, Marco; Celasco, Edvige; Savio, Letizia; Vattuone, Luca; Rocca, Mario

    2014-03-01

    The ability to engineer nearly perfect ultrathin oxide layers, up to the limit of monolayer thickness, is a key issue for nanotechnological applications. Here we face the difficult and important case of ultrathin MgO films on Ag(100), for which no extended and well-ordered layers could thus far be produced in the monolayer limit. We demonstrate that their final morphology depends not only on the usual growth parameters (crystal temperature, metal flux, and oxygen partial pressure), but also on aftergrowth treatments controlling so far neglected thermodynamics constraints. We thus succeed in tuning the shape of the oxide films from irregular, nanometer-sized, monolayer-thick islands to slightly larger, perfectly squared, bilayer islands, to extended monolayers limited apparently only by substrate steps.

  7. Morphology of monolayer MgO films on Ag(100): switching from corrugated islands to extended flat terraces.

    PubMed

    Pal, Jagriti; Smerieri, Marco; Celasco, Edvige; Savio, Letizia; Vattuone, Luca; Rocca, Mario

    2014-03-28

    The ability to engineer nearly perfect ultrathin oxide layers, up to the limit of monolayer thickness, is a key issue for nanotechnological applications. Here we face the difficult and important case of ultrathin MgO films on Ag(100), for which no extended and well-ordered layers could thus far be produced in the monolayer limit. We demonstrate that their final morphology depends not only on the usual growth parameters (crystal temperature, metal flux, and oxygen partial pressure), but also on aftergrowth treatments controlling so far neglected thermodynamics constraints. We thus succeed in tuning the shape of the oxide films from irregular, nanometer-sized, monolayer-thick islands to slightly larger, perfectly squared, bilayer islands, to extended monolayers limited apparently only by substrate steps. PMID:24724662

  8. Characteristics of localized surface plasmons excited on mixed monolayers composed of self-assembled Ag and Au nanoparticles.

    PubMed

    Tanaka, Daisuke; Imazu, Keisuke; Sung, Jinwoo; Park, Cheolmin; Okamoto, Koichi; Tamada, Kaoru

    2015-10-01

    The fundamental characteristics of localized surface plasmon resonance (LSPR) excited on mixed monolayers composed of self-assembled Ag and Au nanoparticles (AgNPs and AuNPs, respectively) were investigated. Mixed monolayered films were fabricated at the air-water interface at different mixing ratios. The films retained their phase-segregated morphologies in which AuNPs formed several 10 to 100 nm island domains in a homogeneous AgNP matrix phase. The LSPR bands originating from the self-assembled domains shifted to longer wavelengths as the domain size increased, as predicted by a finite-difference time-domain (FDTD) simulation. The FDTD simulation also revealed that even an alternating-lattice-structured two-dimensional (2D) AgNP/AuNP film retained two isolated LSPR bands, revealing that the plasmon resonances excited on each particle did not couple even in a continuous 2D sheet, unlike in the homologous NP system. The fluorescence quenching test of Cy3 and Cy5 dyes confirmed that the independent functions of AuNPs and AgNPs remained in the mixed films, whereas the AuNPs exhibited significantly higher quenching efficiency for the Cy3 dye compared with AgNPs due to the overlap of the excitation/emission bands of the dyes with the AuNP LSPR band. Various applications can be considered using this nanoheterostructured plasmonic assembly to excite spatially designed, high-density LSPR on macroscopic surfaces. PMID:26332039

  9. Characterization of two oxidatively modified phospholipids in mixed monolayers with DPPC.

    PubMed

    Sabatini, Karen; Mattila, Juha-Pekka; Megli, Francesco M; Kinnunen, Paavo K J

    2006-06-15

    The properties of two oxidatively modified phospholipids viz. 1-palmitoyl-2-(9'-oxo-nonanoyl)-sn-glycero-3-phosphocholine (PoxnoPC) and 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC), were investigated using a Langmuir balance, recording force-area (pi-A) isotherms and surface potential psi. In mixed monolayers with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) a progressive disappearance of the liquid expanded-liquid condensed transition and film expansion was observed with increasing content of the oxidized phospholipids. The above is in agreement with fluorescence microscopy of the monolayers, which revealed an increase in the liquid expanded region of DPPC monolayers. At a critical pressure pi(s) approximately 42 mN/m both Poxo- and PazePC induced a deflection in the pi-A isotherms, which could be rationalized in terms of reorientation of the oxidatively modified acyl chains into aqueous phase (adaptation of the so-called extended conformation), followed upon further film compression by solubilization of the oxidized phospholipids into the aqueous phase. Surface potential displayed a discontinuity at the same value of area/molecule, corresponding to the loss of the oxidized phospholipids from the monolayers. Our data support the view that lipid oxidation modifies both the small-scale structural dynamics of biological membranes as well as their more macroscopic lateral organization. Accordingly, oxidatively modified lipids can be expected to influence the organization and functions of membrane associated proteins. PMID:16581831

  10. Characterization of Two Oxidatively Modified Phospholipids in Mixed Monolayers with DPPC

    PubMed Central

    Sabatini, Karen; Mattila, Juha-Pekka; Megli, Francesco M.; Kinnunen, Paavo K. J.

    2006-01-01

    The properties of two oxidatively modified phospholipids viz. 1-palmitoyl-2-(9′-oxo-nonanoyl)-sn-glycero-3-phosphocholine (PoxnoPC) and 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC), were investigated using a Langmuir balance, recording force-area (π-A) isotherms and surface potential ψ. In mixed monolayers with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) a progressive disappearance of the liquid expanded-liquid condensed transition and film expansion was observed with increasing content of the oxidized phospholipids. The above is in agreement with fluorescence microscopy of the monolayers, which revealed an increase in the liquid expanded region of DPPC monolayers. At a critical pressure πs ∼ 42 mN/m both Poxo- and PazePC induced a deflection in the π-A isotherms, which could be rationalized in terms of reorientation of the oxidatively modified acyl chains into aqueous phase (adaptation of the so-called extended conformation), followed upon further film compression by solubilization of the oxidized phospholipids into the aqueous phase. Surface potential displayed a discontinuity at the same value of area/molecule, corresponding to the loss of the oxidized phospholipids from the monolayers. Our data support the view that lipid oxidation modifies both the small-scale structural dynamics of biological membranes as well as their more macroscopic lateral organization. Accordingly, oxidatively modified lipids can be expected to influence the organization and functions of membrane associated proteins. PMID:16581831

  11. Self-Assembly of Tetraphenyldibenzoperiflanthene (DBP) Films on Ag(111) in the Monolayer Regime.

    PubMed

    Kirchhuebel, Tino; Gruenewald, Marco; Sojka, Falko; Kera, Satoshi; Bussolotti, Fabio; Ueba, Takahiro; Ueno, Nobuo; Rouillé, Gaël; Forker, Roman; Fritz, Torsten

    2016-03-01

    Tetraphenyldibenzoperiflanthene (DBP) is a promising candidate as a component of highly efficient organic photovoltaic cells and organic light-emitting diodes. The structural properties of thin films of this particular lander-type molecule on Ag(111) were investigated by complementary techniques. Highly ordered structures were obtained, and their mutual alignment was characterized by means of low-energy electron diffraction (LEED). Scanning tunneling microscopy (STM) images reveal two slightly different arrangements within the first monolayer (ML), both describable as specific herringbone patterns with two molecules per unit cell whose dibenzoperiflanthene framework is parallel to the surface. In contrast, single DBP molecules in the second ML were imaged with much higher intramolecular resolution, resembling the shape of the frontier orbitals in the gas phase as calculated by means of density functional theory (DFT). Further deposition leads to the growth of highly ordered bilayer islands on top of the first ML with identical unit cell dimensions and orientation but slightly inclined molecules. This suggests that the first ML acts as a template for the epitaxial growth of further layers. Simultaneously, a significant number of second-layer molecules mainly located at step edges or scattered over narrow terraces do not form highly ordered aggregates. PMID:26844381

  12. From monomer to monolayer: a global optimisation study of (ZnO)n nanoclusters on the Ag surface

    NASA Astrophysics Data System (ADS)

    Demiroglu, Ilker; Woodley, Scott M.; Sokol, Alexey A.; Bromley, Stefan T.

    2014-11-01

    We employ global optimisation to investigate how oxide nanoclusters of increasing size can best adapt their structure to lower the system energy when interacting with a realistic extended metal support. Specifically, we focus on the (ZnO)@Ag(111) system where experiment has shown that the infinite Ag(111)-supported ZnO monolayer limit corresponds to an epitaxially 7 : 8 matched graphene-like (Zn3O3)-based hexagonal sheet. Using a two-stage search method based on classical interatomic potentials and then on more accurate density functional theory, we report global minina candidate structures for Ag-supported (ZnO)n cluster with sizes ranging from n = 1-24. Comparison with the respective global minina structure of free space (ZnO)n clusters reveals that the surface interaction plays a decisive role in determining the lowest energy Ag-supported (ZnO)n cluster structures. Whereas free space (ZnO)n clusters tend to adopt cage-like bubble structures as they grow larger, Ag-supported (ZnO)n clusters of increasing size become progressively more like planar cuts from the infinite graphene-like ZnO single monolayer. This energetic favourability for planar hexagonal Ag-supported clusters over their 3D counterparts can be partly rationalised by the ZnO-Ag(111) epitaxial matching and the increased number of close interactions with the Ag surface. Detailed analysis shows that this tendency can also be attributed to the capacity of 2D clusters to distort to improve their interaction with the Ag surface relative to more rigid 3D bubble cluster isomers. For the larger sized clusters we find that the adsorption energies and most stable structural types appear to be rather converged confirming that our study makes a bridge between the Ag-supported ZnO monomer and the infinite Ag-supported ZnO monolayer.We employ global optimisation to investigate how oxide nanoclusters of increasing size can best adapt their structure to lower the system energy when interacting with a realistic

  13. Raman gas sensing of modified Ag nanoparticle SERS

    NASA Astrophysics Data System (ADS)

    Myoung, NoSoung; Yoo, Hyung Keun; Hwang, In-Wook

    2014-03-01

    Recent progress in modified Surface Enhanced Raman Scattering (SERS) using Ag nanoparticles makes them promising optical technique for direct gas sensing of interest. However, SERS has been shown to provide sub ppb level detection of the compounds in the vapor phase. The major problem with the sensitivity scaling-up was in the development of fabrication technology for stability and reproducibility of SERS substrates. We report an optimization of 1-propanethiol coated multiple Ag nanoparticle layers on SiO2 substrate as well as new records of real-time, simultaneous vapor phase detection of toluene and 1-2 dichlorobenzene by the radiation of fiber optic coupled 785 nm diode laser and spectrograph. Multiple depositions of Ag NPs were loaded on SiO2 and soaked in 1-propanethiol solution for 24 hours to modify the surface into hydrophobic due to the characteristics of vapor phase of our interests. Raman bands at 1003 cm-1 and 1130 cm-1 for toluene and 12DCB, respectively were compared to 1089 cm-1 and each gas concentration in 1000 mL flask were calculated as a function of each vapor phase ratio. The saturation of toluene and 12DCB were limited only by 800 ppm and the detectable range was 0.6-800 ppm.

  14. Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED.

    PubMed

    Murphy, B E; Krasnikov, S A; Cafolla, A A; Sergeeva, N N; Vinogradov, N A; Beggan, J P; Lübben, O; Senge, M O; Shvets, I V

    2012-02-01

    The room temperature self-assembly and ordering of (5,15-diphenylporphyrinato)nickel(II) (NiDPP) on the Ag(111) and Ag/Si(111)-(√3 × √3)R30° surfaces have been investigated using scanning tunnelling microscopy and low-energy electron diffraction. The self-assembled structures and lattice parameters of the NiDPP monolayer are shown to be extremely dependent on the reactivity of the substrate, and probable molecular binding sites are proposed. The NiDPP overlayer on Ag(111) grows from the substrate step edges, which results in a single-domain structure. This close-packed structure has an oblique unit cell and consists of molecular rows. The molecules in adjacent rows are rotated by approximately 17° with respect to each other. In turn, the NiDPP molecules form three equivalent domains on the Ag/Si(111)-(√3 × √3)R30° surface, which follow the three-fold symmetry of the substrate. The molecules adopt one of three equivalent orientations on the surface, acting as nucleation sites for these domains, due to the stronger molecule-substrate interaction compared to the case of the Ag(111). The results are explained in terms of the substrate reactivity and the lattice mismatch between the substrate and the molecular overlayer. PMID:22223550

  15. High sensitive self-assembled monolayer modified solid mounted resonator for organophosphate vapor detection

    NASA Astrophysics Data System (ADS)

    Wang, Jingjing; Chen, Da; Gan, Yaoguo; Sun, Xuejun; Jin, Yingying

    2011-02-01

    We fabricated a self-assembled monolayer (SAM) modified solid mounted resonator (SMR) for organophosphate vapor detection. The SMR device consisted of a piezoelectric stack and an all-metal Bragg's reflector. The electrode surface is chemically modified with a Cu2+/11-mercaptoundecanoic acid SAM to capture organophosphate compounds. After chemical modification, both the resonance frequency and the Q-factor decrease. Fourier transform infrared external reflection spectroscopy was performed to verify the formation of SAM. Adsorption of organophosphate compounds onto the SAM increases its mass, and the resonance frequency proportionally goes down. The testing results show that the modified SMR can yield a rapid, sensitive, reversible and reproducible response to nerve-agent (dimethyl methyl phosphonate) vapor. This study proves that using the SAM modified SMR to detect trace organophosphate vapor is feasibility.

  16. Comparative Study of Electroless Copper Film on Different Self-Assembled Monolayers Modified ABS Substrate

    PubMed Central

    Xu, Jiushuai; Fan, Ruibin; Wang, Jiaolong; Jia, Mengke; Xiong, Xuanrui; Wang, Fang

    2014-01-01

    Copper films were grown on (3-Mercaptopropyl)trimethoxysilane (MPTMS), (3-Aminopropyl)triethoxysilane (APTES) and 6-(3-(triethoxysilyl)propylamino)-1,3,5- triazine-2,4-dithiol monosodium (TES) self-assembled monolayers (SAMs) modified acrylonitrile-butadiene-styrene (ABS) substrate via electroless copper plating. The copper films were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their individual deposition rate and contact angle were also investigated to compare the properties of SAMs and electroless copper films. The results indicated that the formation of copper nuclei on the TES-SAMs modified ABS substrate was faster than those on the MPTMS-SAMs and APTES-SAMs modified ABS substrate. SEM images revealed that the copper film on TES-SAM modified ABS substrate was smooth and uniform, and the density of copper nuclei was much higher. Compared with that of TES-SAMs modified resin, the coverage of copper nuclei on MPTMS and APTES modified ABS substrate was very limited and the copper particle size was too big. The adhesion property test demonstrated that all the SAMs enhanced the interfacial interaction between copper plating and ABS substrate. XRD analysis showed that the copper film deposited on SAM-modified ABS substrate had a structure with Cu(111) preferred orientation, and the copper film deposited on TES-SAMs modified ABS substrate is better than that deposited on MPTMS-SAMs or APTES-SAMs modified ABS resins in electromigrtion resistance. PMID:24739812

  17. Infrared spectroscopy of organic semiconductors modified by self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Khatib, O.; Lee, B.; Podzorov, V.; Yuen, J.; Heeger, A. J.; Li, Z. Q.; di Ventra, M.; Basov, D. N.

    2009-03-01

    Recently, self-assembled monolayers (SAMs) were used to modify electronic surface properties of organic single crystals, leading to several orders of magnitude increase in the electrical conductivity^1. Motivated by this discovery, the same technique was applied to polymers. Here we present a thorough spectroscopic investigation of organic semiconductors based on poly(3-hexlthiophene) (P3HT) that have been treated with a fluorinated trichlorosilane SAM. Infrared spectroscopy offers access to details of charge injection, electrostatic doping, and the electronic structure that are not always available from transport measurements, which can be dominated by defects and contact effects. In polymer films, the SAM molecules penetrate into the bulk, leading to a rich spectrum of electronic excitations in the mid-infrared energy range. ^1 M. F. Calhoun, J. Sanchez, D. Olaya, M. E. Gershenson, V. Podzorov, Electronic functionalization of the surface of organic semiconductors with self-assembled monolayers, Nature Mater. 7, 84--89 (2008)

  18. Mixed azide-terminated monolayers: a platform for modifying electrode surfaces.

    PubMed

    Collman, James P; Devaraj, Neal K; Eberspacher, Todd P A; Chidsey, Christopher E D

    2006-03-14

    We have prepared and characterized mixed self-assembled monolayers (SAM) on gold electrodes from azido alkane thiols and various omega-functionalized alkane thiols. In the presence of copper(I) catalysts, these azide-modified surfaces are shown to react rapidly and quantitatively with terminal acetylenes forming 1,2,3-triazoles, via "click" chemistry. The initial azide substituents can be identified and monitored using both grazing-angle infrared (IR) and X-ray photoelectron spectrosopies. Acetylenes possessing redox-active ferrocene substituents react with the azide-terminated mixed SAMs and electrochemical measurements of the ferrocene-modified SAM electrodes have been used to quantify the redox centers attached to these platforms. Time-resolved electrochemical measurements have enabled us to follow the formation of these ferrocene centers and thus to measure the rate of the surface "click" reaction. Under optimal conditions this well-behaved second-order reaction takes place with a rate constant of 1 x 10(3) M(-)(1) s(-)(1). Typical reaction times of several minutes were realized using micromolar concentrations of acetylene. These techniques have been used to construct well-characterized, covalently modified monolayers that can be employed as functional electrode surfaces. PMID:16519441

  19. Mixed Azide-Terminated Monolayers: A Platform for Modifying Electrode Surfaces

    PubMed Central

    Collman, James P.; Devaraj, Neal K.; Eberspacher, Todd P. A.; Chidsey, Christopher E. D.

    2006-01-01

    We have prepared and characterized mixed self-assembled-monolayers (SAM) on gold electrodes from azido alkane thiols and various ω-functionalized alkane thiols. In the presence of copper(I) catalysts these azide-modified surfaces are shown to react rapidly and quantitatively with terminal acetylenes forming 1,2,3-triazoles, via “click” chemistry. The initial azide substituents can be identified and monitored using both grazing-angle infrared (IR) and X-ray photoelectron spectrosopies. Acetylenes possessing redox-active ferrocene substituents react with the azide-terminated mixed SAMs and electrochemical measurements of the ferrocene-modified SAM electrodes have been used to quantify the redox centers attached to these platforms. Time-resolved electrochemical measurements have enabled us to follow the formation of these ferrocene centers and thus to measure the rate of the surface “click” reaction. Under optimal conditions this well-behaved second-order reaction takes place with a rate constant of 1×103 M-1sec-1. Typical reaction times of several minutes were realized using micromolar concentrations of acetylene. These techniques have been used to construct well-characterized, covalently-modified monolayers that can be employed as functional electrode surfaces. PMID:16519441

  20. Calculation of Electrochemical Reorganization Energies for Redox Molecules at Self-Assembled Monolayer Modified Electrodes.

    PubMed

    Ghosh, Soumya; Hammes-Schiffer, Sharon

    2015-01-01

    Electrochemical electron transfer reactions play an important role in energy conversion processes with many technological applications. Electrodes modified by self-assembled monolayers (SAMs) exhibit reduced double layer effects and are used in molecular electronics. An important quantity for calculating the electron transfer rate constant is the reorganization energy, which is associated with changes in the solute geometry and the environment. In this Letter, an approach for calculating the electrochemical reorganization energy for a redox molecule attached to or near a SAM modified electrode is presented. This integral equations formalism polarizable continuum model (IEF-PCM) approach accounts for the detailed electronic structure of the molecule, as well as the contributions from the electrode, SAM, and electronic and inertial solvent responses. The calculated total reorganization energies are in good agreement with experimental data for a series of metal complexes in aqueous solution. This approach will be useful for calculating electron transfer rate constants for molecular electrocatalysts. PMID:26263083

  1. Induction and characterization of suppressor T cells and soluble factors with modified timothy grass pollen AgB.

    PubMed

    Malley, A; Deppe, L B; Brandt, C J

    1981-01-01

    Previous studies demonstrated that antigen B (AgB), a major antigen of timothy grass pollen, modified by photooxidation (Ox-AgB) does not react with rabbit, human, or mouse antibodies directed against AgB and does not induce antibodies reactive with either native or modified AgB. However, immunization of mice with Ox-AgB in alum induces significant T helper cell activity. In this review, we describe the conditions and kinetics for Ox-AgB induction of T suppressor cells, the secretion of AgB-specific T suppressor factor (TSF), and the partial purification of AgB-specific TSF. PMID:6453098

  2. A perfect wetting of Mg monolayer on Ag(111) under atomic scale investigation: First principles calculations, scanning tunneling microscopy, and Auger spectroscopy

    NASA Astrophysics Data System (ADS)

    Migaou, Amani; Sarpi, Brice; Guiltat, Mathilde; Payen, Kevin; Daineche, Rachid; Landa, Georges; Vizzini, Sébastien; Hémeryck, Anne

    2016-05-01

    First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally.

  3. A perfect wetting of Mg monolayer on Ag(111) under atomic scale investigation: First principles calculations, scanning tunneling microscopy, and Auger spectroscopy.

    PubMed

    Migaou, Amani; Sarpi, Brice; Guiltat, Mathilde; Payen, Kevin; Daineche, Rachid; Landa, Georges; Vizzini, Sébastien; Hémeryck, Anne

    2016-05-21

    First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally. PMID:27208966

  4. Dual-loss-modulated Q-switched Tm:LuAG laser with AOM and monolayer graphene.

    PubMed

    Luan, Chao; Yang, Ke Jian; Zhao, Jia; Zhao, Sheng Zhi; Qiao, Wen Chao; Li, Tao; Feng, Tian Li; Liu, Cheng; Qiao, Jun Peng; Zheng, Li He; Xu, Jun; Wang, Qing Guo; Su, Liang Bi

    2015-09-20

    A laser-diode-pumped dual-loss-modulated Q-switching Tm:LuAG laser with an acousto-optic modulator (AOM) and monolayer graphene saturable absorber (SA) around 2 μm is presented for the first time to the best of our knowledge. The average output power and the pulse widths for different repetition rates have been measured. In comparison with the singly Q-switching laser with AOM or with monolayer graphene SA, the dual-loss-modulated Q-switching laser could generate shorter pulse width and higher peak power. The maximum pulse width compression ratio was found to be 3.11, and the highest peak power was enhanced 97.4 times. The experimental results show that the dual-loss-modulated technology is an efficient method for compressing the pulse width, improving the peak power, and enhancing the pulse stability for the Q-switched lasers at 2 μm. PMID:26406500

  5. Zinc oxide growth morphology on self-assembled monolayer modified silver surfaces.

    PubMed

    Hsu, Julia W P; Clift, W Miles; Brewer, Luke N

    2008-05-20

    Using organic molecules to direct inorganic crystal growth has opened up new avenues for controlled synthesis on surfaces. Combined with soft lithography to form patterned templates, self-assembled monolayers (SAMs) have been shown to be a powerful approach for the assembly of inorganic nanostructures. In this work, we show that the surface free energy of SAM-modified silver, which depends on end groups and deposition method of SAMs, has a dramatic effect on the nucleation and growth of crystalline ZnO, a technologically important material, from supersaturated solutions. For SAMs with inert methyl end groups, ZnO nucleation is inhibited. For SAMs with chemically active (carboxylic or thiol) end groups, the ZnO morphology is found to be three-dimensional nanorods on low-surface-energy surfaces and two-dimensional thin films on high-energy surfaces. PMID:18399664

  6. Gold Electrodes Modified with Self-Assembled Monolayers for Measuring L-Ascorbic Acid: An Undergraduate Analytical Chemistry Laboratory Experiment

    ERIC Educational Resources Information Center

    Ito, Takashi; Perera, D. M. Neluni T.; Nagasaka, Shinobu

    2008-01-01

    This article describes an undergraduate electrochemistry laboratory experiment in which the students measure the L-ascorbic acid content of a real sample. Gold electrodes modified with self-assembled monolayers (SAMs) of thioctic acid and cysteamine are prepared to study the effects of surface modification on the electrode reaction of L-ascorbic…

  7. Calculation of Electrochemical Reorganization Energies for Redox Molecules at Self-Assembled Monolayer Modified Electrodes

    SciTech Connect

    Ghosh, Soumya; Hammes-Schiffer, Sharon

    2015-01-02

    Electrochemical electron transfer reactions play an important role in energy conversion processes with many technological applications. Electrodes modified by self-assembled monolayers (SAMs) are useful because the double layer effects are reduced. An important quantity for calculating the electron transfer rate constant is the reorganization energy, which is associated with changes in solute geometry and solvent configuration. In this Letter, an approach for calculating the electrochemical solvent reorganization energy for a redox molecule attached to or near a SAM modified electrode is presented. This integral equations formalism polarizable continuum model (IEF-PCM) approach accounts for the detailed electronic structure of the molecule, as well as the contributions from the electrode, SAM, and electronic and inertial solvent responses. The calculated total reorganization energies are in good agreement with experimental data for a series of metal complex in aqueous solution. This approach will be useful for calculating electron transfer rate constants for molecular electrocatalysts. This work was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

  8. Modified fabrication process of protein chips using a short-chain self-assembled monolayer.

    PubMed

    Jang, Ling-Sheng; Keng, Hao-Kai

    2008-04-01

    In previous work a short chain SAM, 4,4-Dithiodibutyric Acid (DTBA) was found to be a thin monolayer in protein chips. However, obtaining uniform fluorescent intensity remains difficult because water-soluble carbodiimides (EDC) in an aqueous system cause the hydrolysis of N-hydroxysuccinimide ester (NHS esters). The hydrolysis of NHS esters reduces coupling yields and therefore reduces the fluorescent intensity of protein chips. The NHS can increase the stability of active intermediate resulting from the reaction of EDC and NHS, but the ratio of the concentration of EDC to that of NHS strongly affects this stability. The effects of the solvents used in the washing step are studied to solve this problem. The results reveal that PBST (PBS + 5% Tween20) is more effective in reducing the hydrolysis of NHS esters than deionized water. Additionally, the effects of 3:1 and 5:2 EDC/NHS ratios on the chips are examined. The 3:1 EDC/NHS ratio yields a higher fluorescent intensity than the 5:2 ratio. The effects on the chips of dissolving EDC in DI water, DI water + 0.1 M MES and alcohol are also investigated. The results show that alcohol provides higher fluorescent intensity than other solvents and the reaction time of 4 h yields a high fluorescent intensity with 3:1 EDC/NHS ratio. A modified fabrication process of protein chips using 4,4-DTBA is developed. In this work, 160 mM 4,4-DTBA is used as a self-assembled monolayer in the fabrication of protein chips. Experiments to characterize 4,4-DTBA are performed by contact angle goniometry and Fourier transform infrared spectroscopy (FTIR). Furthermore, the immobilized protein A-FITC (fluorescein isothiocyanate) is adopted in fluorescent assays. PMID:17849186

  9. Thermoelectric properties of CuS/Ag2S nanocomposites synthesed by modified polyol method

    NASA Astrophysics Data System (ADS)

    Tarachand, Sharma, Vikash; Ganesan, V.; Okram, Gunadhor S.

    2016-05-01

    This is the report on successful synthesis of Ag doped CuS nanostructures by modified polyol method. The resulting samples were characterized by powder X-ray diffraction (XRD), energy dispersive X-ray (EDX), atomic force microscopy (AFM) and dynamic light scattering (DLS). Particle size of pure CuS nanoparticles (NPs) was 17 nm, 38 nm and 97 nm as determined from Scherrer formula, AFM and DLS, respectively. Introduction of Ag led to formation of CuS/Ag2S composites. A transition at 55 K in thermopower is ascribed to structural transformation from hexagonal to orthorhombic structure. Further, their thermoelectric properties exhibit remarkable change owing to Ag doping in CuS nanostructures. The power factor improves with increasing Ag content. They reveal that CuS/Ag2S nanocomposites are some of the potential candidates for generation of thermoelectricity in future.

  10. MoOx modified Ag anode for top-emitting organic light-emitting devices

    NASA Astrophysics Data System (ADS)

    Cao, Jin; Jiang, XueYin; Zhang, ZhiLin

    2006-12-01

    Efficient top-emitting organic light-emitting devices (TOLEDs) using a thin MoOx layer modified Ag as the effective hole-injection anode are demonstrated. With tris-(8-hydroxy quinoline)aluminum as emitting layer and trilayer LiF /Al/Ag as semitransparent cathode, the Ag /MoOx based TOLED shows a tune-on voltage of 2.67V and a maximum current efficiency of 7.27cd/A, which are much better than those (3.92V, 6.12cd/A) obtained from Ag /Ag2O based TOLED and those (5.25V, 3.5cd/A) obtained from the corresponding bottom-emitting organic light-emitting devices. Contact potential difference measurement shows that the work function of Ag /MoOx is higher than those of Ag /Ag2O and ozone-treated indium tin oxide, leading to a stronger hole injection. The good performance of Ag /MoOx based TOLED is attributed to the efficient hole injection from the Ag /MoOx anode as well as a microcavity effect.

  11. Dithiocarbamate Self-Assembled Monolayers as Efficient Surface Modifiers for Low Work Function Noble Metals.

    PubMed

    Meyer, Dominik; Schäfer, Tobias; Schulz, Philip; Jung, Sebastian; Rittich, Julia; Mokros, Daniel; Segger, Ingolf; Maercks, Franziska; Effertz, Christian; Mazzarello, Riccardo; Wuttig, Matthias

    2016-09-01

    Tuning the work function of the electrode is one of the crucial steps to improve charge extraction in organic electronic devices. Here, we show that N,N-dialkyl dithiocarbamates (DTC) can be effectively employed to produce low work function noble metal electrodes. Work functions between 3.1 and 3.5 eV are observed for all metals investigated (Cu, Ag, and Au). Ultraviolet photoemission spectroscopy (UPS) reveals a maximum decrease in work function by 2.1 eV as compared to the bare metal surface. Electronic structure calculations elucidate how the complex interplay between intrinsic dipoles and dipoles induced by bond formation generates such large work function shifts. Subsequently, we quantify the improvement in contact resistance of organic thin film transistor devices with DTC coated source and drain electrodes. These findings demonstrate that DTC molecules can be employed as universal surface modifiers to produce stable electrodes for electron injection in high performance hybrid organic optoelectronics. PMID:27504721

  12. Photocatalytic performance of Ag doped SnO2 nanoparticles modified with curcumin

    NASA Astrophysics Data System (ADS)

    Vignesh, K.; Hariharan, R.; Rajarajan, M.; Suganthi, A.

    2013-07-01

    Visible light active Ag doped SnO2 nanoparticles modified with curcumin (Cur-Ag-SnO2) have been prepared by a combined precipitation and chemical impregnation route. The optical properties, phase structures and morphologies of the as-prepared nanoparticles were characterized using UV-visible diffuse reflectance spectra (UV-vis-DRS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The surface area was measured by Brunauer. Emmett. Teller (B.E.T) analysis. Compared to bare SnO2, the surface modified photocatalysts (Ag-SnO2 and Cur-Ag-SnO2) showed a red shift in the visible region. The photocatalytic activity was monitored via the degradation of rose bengal (RB) dye and the results revealed that Cur-Ag-SnO2 shows better photocatalytic activity than that of Ag-SnO2 and SnO2. The superior photocatalytic activity of Cur-Ag-SnO2 could be attributed to the effective electron-hole separation by surface modification. The effect of photocatalyst concentration, initial dye concentration and electron scavenger on the photocatalytic activity was examined in detail. Furthermore, the antifungal activity of the photocatalysts and the reusability of Cur-Ag-SnO2 were tested.

  13. Modified embedded-atom potential for B2-MgAg

    NASA Astrophysics Data System (ADS)

    Groh, Sébastien

    2016-08-01

    Interatomic potentials for pure Ag and Mg–Ag alloy have been developed in the framework of the second nearest-neighbors modified embedded-atom method (MEAM). The validity and the transferability of the Ag potential were obtained by calculating physical, mechanical, thermal, and dislocation related properties. Since the {1 1 1}-generalized stacking fault energy curves obtained from first-principle calculations was used to develop the Ag potential, the critical resolved shear stress to move screw dislocations in Ag single crystal is in good agreement with the experimental data. By combining the ability of the potential to predict the surface energies with its accuracy in describing dislocation properties, the potential is thought to be a predictive model for analyzing the fracture properties of Ag. In addition, the performance of the potential was tested under dynamics conditions by predicting the melting temperature, where a good agreement with experimental value was found. The Ag-MEAM potential was then coupled to an existing Mg-MEAM potential to describe the properties of the binary system MgAg. While the heat of formation, the elastic constants, and the (1 1 0) γ-surface of the MgAg compound in the B2 phase were used to parameterize the potential, heat of formation for MgAg alloys with different stoichiometry, thermal properties of the B2-MgAg compound, as well as dislocation related properties in B2-MgAg compound were tested to validate the transferability of the potential. The heat of formation of Mg5Ag2, MgAg, and MgAg3, the elastic constants and the thermal properties of B2-MgAg obtained with the proposed potential align with first-principles and experimental data. In addition, the core structure of both <0 0 1> and <1 1 1> dislocations in {1 1 0} are in agreement with theoretical predictions, and the magnitudes of the critical resolved shear stress obtained at 0 K for both slip systems partially validate the slip behavior of B2-MgAg

  14. Interfacial structure in thin water layers formed by forced dewetting on self-assembled monolayers of omega-terminated alkanethiols on Ag.

    PubMed

    Tiani, Domenic J; Yoo, Heemin; Mudalige, Anoma; Pemberton, Jeanne E

    2008-12-01

    A method for the spectroscopic characterization of interfacial fluid molecular structure near solid substrates is reported. The thickness and interfacial molecular structure of residual ultrathin D20 films remaining after forced dewetting on alkanethiolate self-assembled monolayers (SAMs) of 11 1-mercaptoundecanoic acid (11-MUA), 11-mercaptoundecanol (11-MUD), and undecanethiol (UDT) on Ag are investigated using ellipsometry and surface Raman spectroscopy. The residual film thickness left after withdrawal is greater on hydrophilic SAMs than on hydrophobic SAMs. This behavior is rationalized on the basis of differing degrees of fluid slip within the interfacial region due to different interfacial molecular structure. The v(O-D) regions of surface Raman spectra clearly indicate unique interfacial molecular properties within these films that differ from bulk D20. Although the residual films are created by shear forces and Marangoni flow at the three-phase line during the forced dewetting process, the nature of the films sampled optically must also be considered from the standpoint of thin film stability after dewetting. Thus, the resulting D20 films exist in vastly different morphologies depending on the nature of the water-SAM interactions. Residual D20 is proposed to exist as small nanodroplets on UDT surfaces due tospontaneous rupture of the film after dewetting. In contrast, on 11-MUD and 11-MUA surfaces, these films exist in a metastable state that retains their conformal nature on the underlying modified surface. Analysis of the peak intensity ratios of the so-called "ice-like" to "liquid-like" v(O-D) modes suggests more ice-like D20 character near 11-MUD surfaces, but more liquid-like character near 11-MUA and UDT surfaces. The creation of residual ultrathin films by forced dewetting is thus demonstrated to be a powerful method for characterizing interfacial molecular structure of fluids near a solid substrate under ambient conditions of temperature and

  15. Preparation of vanadium oxide thin films modified with Ag using a hybrid deposition configuration

    NASA Astrophysics Data System (ADS)

    Gonzalez-Zavala, F.; Escobar-Alarcón, L.; Solís-Casados, D. A.; Rivera-Rodríguez, C.; Basurto, R.; Haro-Poniatowski, E.

    2016-04-01

    The application of a hybrid deposition configuration, formed by the interaction of a laser ablation plasma with a flux of atomic vapor, to deposit vanadium oxide thin films modified with different amounts of silver, is reported. The effect of the amount of Ag incorporated in the films on their structural, morphological, compositional and optical properties was studied. The obtained results reveal that films with variable Ag content from 11.7 to 24.6 at.% were obtained. Depending on the silver content, the samples show very different surface morphologies. Optical characterization indicates the presence of nanostructures of Ag. Thin films containing silver exhibit better photocatalytic performances than unmodified V2O5 films. Raman spectra reveal that as the silver content is increased, the signals associated with V2O5 disappear and new modes attributed mainly to silver vanadates appear suggesting the formation of ternary compounds.

  16. Sputtered Ag thin films with modified morphologies: Influence on wetting property

    NASA Astrophysics Data System (ADS)

    Dutheil, P.; Thomann, A. L.; Lecas, T.; Brault, P.; Vayer, M.

    2015-08-01

    Silver thin films with thickness ranging from 3 nm to 33 nm were sputter deposited onto silicon wafers and tungsten layers. Those W layers were previously synthesized in the same DC magnetron sputter deposition system with various experimental conditions (argon pressure, target to substrate distance) in order to stabilize different surface morphologies. SEM observations and AFM images showed that the growth mode of Ag films is similar on Si substrates and on the smoothest W layers, whereas it is modified for rough W layers made of sharp grains. The effect of the W layer morphology on Ag film growth was clearly evidenced when the deposition took place at high temperature. It is seen that performing the deposition onto substrates of various morphologies allows tailoring the wetting property of the Ag deposit.

  17. Modifying the Photoluminescence of Monolayer MoS2 by Metal Deposition

    NASA Astrophysics Data System (ADS)

    Sun, Dezheng; You, Yumeng; Mak, Kin Fai; Zhang, Fan; Hone, James; Bartels, Ludwig; Heinz, Tony

    2013-03-01

    Monolayer MoS2 exhibits strong photoluminescence (PL) due to its direct band gap located at K point. Because of its monolayer thickness, light emission from MoS2 is known to be strongly influenced by interactions with surrounding media. In this study, we have investigated the effect on the photoluminescence of exfoliated monolayers of MoS2 induced by the deposition of gold atoms. The PL from the sample was recorded as a function of amount of gold deposited, up to an effective thickness of about 1 nm. Atomic force microscopy revealed that the gold forms isolated island structures on the surface. A progressive increase in quenching was seen with increasing gold coverage. Deposition of gold on suspended MoS2 samples led to quenching of the PL by more than a factor of 100. Given the low reactivity of gold, we attribute the PL quenching primarily to energy transfer of the photogenerated excitons to the metal clusters. The observed changes in the shape and intensity of emission spectra will be discussed in terms of this mechanism and possible effects of doping induced by the gold deposition.

  18. Ag-modified silicon nanowires substrate for ultrasensitive surface-enhanced raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Shao, Ming-Wang; Zhang, Ming-Liang; Wong, Ning-Bew; Ma, Dorothy Duo-duo; Wang, Hui; Chen, Weiwei; Lee, Shuit-Tong

    2008-12-01

    We report a unique substrate for surface-enhanced raman spectroscopy (SERS) based on silver nanoparticles-embedded silicon nanowires (SiNWs). The SiNWs were prepared by thermal evaporation of SiO powder via oxide-assisted growth, oxide removed with HF, and then used to reduce silver ions to form a highly decorated Ag-embedded surface. Such modified SiNWs substrates yielded ultrahigh SERS sensitivity, which could detect 25μl of 1×10-16M Rhodamine 6G, 1×10-16M crystal violet, and 1×10-14M nicotine in methanol solutions. An Ag-modified SiNW strand could also enable SERS detection of 25μl of 1×10-8mg/ml calf thymus DNA. The possible mechanisms for the ultrahigh SERS sensitivity were discussed.

  19. Controlled preparation of Ag nanoparticle films by a modified photocatalytic method on TiO2 films with Ag seeds for surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Fu, Xin; Pan, Lujun; Li, Shuai; Wang, Qiao; Qin, Jun; Huang, Yingying

    2016-02-01

    Uniform Ag nanoparticle (NP) films were synthesized by a modified photocatalytic method on TiO2 films with Ag seeds for surface-enhanced Raman scattering, which combine the advantages of the spurting method (high nucleation density) and the traditional photocatalytic method (suitable particle size). The Ag seeds were prepared by magnetron sputtering with different time, which would adjust the distribution and transfer of electrons on the surface of TiO2 film in the process of photocatalytic reduction. The distribution and morphology of Ag NP films can be adjusted by the sputtering time and the UV irradiation time. The Raman enhancement of as-prepared Ag NP films was calculated by finite-difference time-domain to validate the experiment data. It is found that the Ag NP films synthesized on TiO2 films with suitable pre-deposited Ag seeds exhibit a much higher Raman enhancement activity than the optimum Ag NP film synthesized directly on the TiO2 film without Ag seeds.

  20. Ag-Modified In₂O₃/ZnO Nanobundles with High Formaldehyde Gas-Sensing Performance.

    PubMed

    Fang, Fang; Bai, Lu; Song, Dongsheng; Yang, Hongping; Sun, Xiaoming; Sun, Hongyu; Zhu, Jing

    2015-01-01

    Ag-modified In2O3/ZnO bundles with micro/nano porous structures have been designed and synthesized with by hydrothermal method continuing with dehydration process. Each bundle consists of nanoparticles, where nanogaps of 10-30 nm are present between the nanoparticles, leading to a porous structure. This porous structure brings high surface area and fast gas diffusion, enhancing the gas sensitivity. Consequently, the HCHO gas-sensing performance of the Ag-modified In2O3/ZnO bundles have been tested, with the formaldehyde-detection limit of 100 ppb (parts per billion) and the response and recover times as short as 6 s and 3 s, respectively, at 300 °C and the detection limit of 100 ppb, response time of 12 s and recover times of 6 s at 100 °C. The HCHO sensing detect limitation matches the health standard limitation on the concentration of formaldehyde for indoor air. Moreover, the strategy to synthesize the nanobundles is just two-step heating and easy to scale up. Therefore, the Ag-modified In2O3/ZnO bundles are ready for industrialization and practical applications. PMID:26287205

  1. PM-IRRAS Studies of DMPC Bilayers Supported on Au(111) Electrodes Modified with Hydrophilic Monolayers of Thioglucose.

    PubMed

    Matyszewska, Dorota; Bilewicz, Renata; Su, ZhangFei; Abbasi, Fatemah; Leitch, J Jay; Lipkowski, Jacek

    2016-02-23

    A phospholipid bilayer composed of 1,2-dimyristoyl-d54-sn-glycero-3-phosphocholine (d54-DMPC) was deposited onto the Au(111) electrode modified with a self-assembled monolayer of 1-thio-β-d-glucose (β-Tg) via the Langmuir-Blodgett and Langmuir-Schaefer (LB-LS) techniques. Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) measurements were used to characterize structural and orientational changes in this model biological membrane on a hydrophilic surface modified gold electrode. The results of the spectroscopic measurements showed that the tilt angle of acyl chains obtained for deuterated DMPC bilayers supported on the β-Tg-modified gold is significantly lower than that reported previously for DMPC bilayers deposited directly on Au(111) electrodes. Moreover, tilt angles of ∼18° were obtained for d54-DMPC bilayers on β-Tg self-assembled monolayers (SAMs) at positive potentials, which are similar to the values calculated for h-DMPC deposited on bare gold in the desorbed state and to those observed for a stack of hydrated DMPC bilayers. This data confirms that the β-thioglucose SAM promotes the formation of a water cushion that separates the phospholipid bilayer from the metal surface. As a result, the DMPC polar heads are not in direct contact with the electrode and can adopt a zigzag configuration, which strengthens the chain-chain interactions and allows for an overall decrease in the tilt of the acyl chains. These novel supported model membranes may be especially useful in studies pertaining to the incorporation of peptides and proteins into phospholipid bilayers. PMID:26829620

  2. Investigation of Ag-TiO2 nanostructures photocatalytic properties prepared by modified dip coating method

    NASA Astrophysics Data System (ADS)

    AlArfaj, Esam

    2016-05-01

    In this article, titanium dioxide and silver nanostructures were deposited on glass substrates using modified sol-gel methods and dip-coating technique. The films were characterised chemically and physically using different techniques (TLC, UV-Vis and XRD) and tested for environmental applications regarding degradation of aromatic hydrocarbons. The photocatalytic activity of the TiO2 nanostructures is tested with different small concentrations of phenol in water and reaction mechanisms discussed. Considerable enhancement is observed in the photodegradation activity of Ag-modified (3 wt.%) TiO2 compared to unmodified TiO2 nanostructures for phenol concentrations within the pseudo-first-order Langmuir-Hinshelwood (LH) model for reaction kinetics. The pseudo-first-order global degradation rate constant increased from <0.005 min-1 for TiO2 to 0.013 min-1 for 3 mol% Ag-modified TiO2. The enhancement is attributed to the incorporation of Ag which promotes the generation of reactive oxygen species and increases the carrier recombination life-time. In addition, Ag has been observed to extend the absorption to the visible region by its surface plasmon resonances and to suppress the anatase-rutile phase transformation. Moreover, TiO2 grain size prepared was found to be 10 nm which maximises the active surface area. For phenol initial concentrations as low as 0.0002 M, saturation trend in the degradation process occurred at 0.00014 M and the reaction rate can be fitted with half-order LH kinetics.

  3. Fabrication of a Polyaniline Ultramicroelectrode via a Self Assembled Monolayer Modified Gold Electrode

    PubMed Central

    Bolat, Gulcin; Kuralay, Filiz; Eroglu, Gunes; Abaci, Serdar

    2013-01-01

    Herein, we report a simple and inexpensive way for the fabrication of an ultramicroelectrode and present its characterization by electrochemical techniques. The fabrication of polyaniline UME involves only two steps: modification of a gold (Au) electrode by self assembled monolayers (SAM) and then electrodeposition of polyaniline film on this thiol-coated Au electrode by using cyclic voltammetry and constant potential electrolysis methods. Two types of self-assembled monolayers (4-mercapto-1-butanol, MB, and 11-mercaptoundecanoic acid, MUA) were used, respectively, to see the effect of chain length on microelectrode formation. Microelectrode fabrication and utility of the surface was investigated by cyclic voltammetric measurements in a redox probe. The thus prepared polyaniline microelectrode was then used for DNA immobilization. Discrimination between double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) was obtained with enhanced electrochemical signals compared to a polyaniline-coated Au electrode. Different modifications on the electrode surfaces were examined using scanning electron microscopy (SEM). PMID:23797740

  4. One pot synthesis of Ag nanoparticle modified ZnO microspheres in ethylene glycol medium and their enhanced photocatalytic performance

    SciTech Connect

    Tian Chungui; Li Wei; Pan Kai; Zhang Qi; Tian Guohui; Zhou Wei; Fu Honggang

    2010-11-15

    Ag nanoparticles (NPs) modified ZnO microspheres (Ag/ZnO microspheres) were prepared by a facile one pot strategy in ethylene glycol (EG) medium. The EG played two important roles in the synthesis: it could act as a reaction media for the formation of ZnO and reduce Ag{sup +} to Ag{sup 0}. A series of the characterizations indicated the successful combination of Ag NPs with ZnO microspheres. It was shown that Ag modification could greatly enhance the photocatalytic efficiency of ZnO microspheres by taking the photodegradation of Rhodamine B as a model reaction. With appropriate ratio of Ag and ZnO, Ag/ZnO microspheres showed the better photocatalytic performance than commercial Degussa P-25 TiO{sub 2}. Photoluminescence and surface photovoltage spectra demonstrated that Ag modification could effectively inhibit the recombination of the photoinduced electron and holes of ZnO. This is responsible for the higher photocatalytic activity of Ag/ZnO composites. -- Graphical abstract: A 'one-pot' strategy was developed for preparing the Ag/ZnO microspheres in ethylene glycol. The composites exhibited superior photocatalytic performance for photodegradation of Rhodamine B dye in water. Display Omitted

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  6. Preparation and characterization of monodispersed PS/Ag composite microspheres through modified electroless plating

    NASA Astrophysics Data System (ADS)

    Ma, Yuehui; Zhang, Qinghua

    2012-07-01

    A modified electroless silver-plating process has been devised for the preparation of monodispersed, polystyrene/silver (PS/Ag) composite microspheres with tunable shell thickness. Tailoring was achieved by altering the concentration of the silver precursor in the plating bath. PS/Ag composite microspheres were characterized by field-emission scanning electron microscopy, ultraviolet-visible absorption, X-ray diffraction and thermogravimetric analysis. The results showed that a dense, stable and uniform silver nanoshell was formed on the surface of PS microspheres in the presence of poly(vinylpyrrolidone) and glucose. The bulk conductivity of the PS/Ag composites increased from 1.16 S/m to 3.57 × 104 S/m, corresponding to a shell thickness of 35-198 nm. The PS/Ag composite microspheres with diameters of ca. 3 μm might have great potential to be used as fillers in anisotropic conductive films because of the uniform diameter, low density and good conductivity of the microspheres.

  7. Two new polyoxometalate-based hybrids consisting of Keggin-type cluster modified by (Ag{sub 4}) group

    SciTech Connect

    Zhao, Xiaofang; Sun, Xiaowei; Han, Zhangang; Zhao, Chuan; Yu, Haitao; Zhai, Xueliang

    2013-11-15

    Two new supramolecular polyoxometalate compounds [Ag{sub 2}(mbpy){sub 3}][Ag(mbpy){sub 2}][PW{sub 12}O{sub 40}] (1) and [Ag{sub 2}(mbpy){sub 3}]{sub 2}[SiW{sub 12}O{sub 40}] (2) (mbpy=4,4'-dimethyl-2,2'-dipyridyl), have been hydrothermally synthesized and characterized by IR, TG, and single-crystal X-ray diffraction techniques. The structural feature of 1–2 is in the cationic moiety of a tetra-core (Ag{sub 4}) cluster through weak Ag…Ag interactions. The silver(I) centers show three-, four- and five-coordinated geometries. In 1 the tetrameric silver atoms in ([Ag{sub 2}(mbpy){sub 3}]{sub 2}){sup 4+} covalently bind to [PW{sub 12}O{sub 40}]{sup 3−} anion via Ag3O bonds, while there is only intermolecular hydrogen bonding between ([Ag{sub 2}(mbpy){sub 3}]{sub 2}){sup 4+} and [SiW{sub 12}O{sub 40}]{sup 4−} in 2. The coordination environments of the tetrameric silver cations have a great influence on the structure richness of the Keggin-based hybrids. The fluorescence properties of compounds 1 and 2 also have been discussed. - Graphical abstract: New polyoxometalate-based hybrids consisting of Keggin-type clusters modified by (Ag{sub 4}) groups had been synthesized and characterized, and their photoluminescence properties were also discussed. Display Omitted - Highlights: • Two Keggin-type polyoxometalates consisting of (Ag{sub 4}) clusters through weak Ag…Ag interactions have been synthesized. • There exist face-to-face and dot-to-face π…π interactions in (Ag-ligand){sub 4} fragment. • The fluorescence properties of (Ag{sub 4}) modified POMs are also discussed.

  8. Characterization and Evaluation of Reverse Osmosis Membranes Modified with Ag2O Nanoparticles to Improve Performance

    NASA Astrophysics Data System (ADS)

    Al-Hobaib, Abdullah S.; AL-Sheetan, Khalid M.; Shaik, Mohammed Rafi; Al-Andis, Naser M.; Al-Suhybani, M. S.

    2015-09-01

    The objective of this work was to prepare and characterize a new and highly efficient modified membrane by in situ interfacial polymerization on porous polysulfone supports. The process used m-phenylenediamine and trimesoyl chloride in hexane, incorporating silver oxide Ag2O nanoparticles of varied concentrations from 0.001 to 0.1 wt%. Ag2O nanoparticles were prepared at different sizes varying between 20 and 50 nm. The modified membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), transmission electron microscopy (TEM), and contact angle measurement. The results showed a smooth membrane surface and average surface roughness from 31 to 74 nm. Moreover, hydrophilicity improved and the contact angle decreased to 41° at 0.009 wt% silver oxide. The performances of the developed membranes were investigated by measuring permeate fluxes and salt rejection capability by passing NaCl solutions (2000 ppm) through the membranes at 225 psi. The results showed that the flux increased from 26 to 40.5 L/m2 h, while the salt rejection was high, at 99 %, with 0.003 wt% Ag2O nanoparticles.

  9. Characterization and Evaluation of Reverse Osmosis Membranes Modified with Ag2O Nanoparticles to Improve Performance.

    PubMed

    Al-Hobaib, Abdullah S; Al-Sheetan, Khalid M; Shaik, Mohammed Rafi; Al-Andis, Naser M; Al-Suhybani, M S

    2015-12-01

    The objective of this work was to prepare and characterize a new and highly efficient modified membrane by in situ interfacial polymerization on porous polysulfone supports. The process used m-phenylenediamine and trimesoyl chloride in hexane, incorporating silver oxide Ag2O nanoparticles of varied concentrations from 0.001 to 0.1 wt%. Ag2O nanoparticles were prepared at different sizes varying between 20 and 50 nm. The modified membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), transmission electron microscopy (TEM), and contact angle measurement. The results showed a smooth membrane surface and average surface roughness from 31 to 74 nm. Moreover, hydrophilicity improved and the contact angle decreased to 41° at 0.009 wt% silver oxide. The performances of the developed membranes were investigated by measuring permeate fluxes and salt rejection capability by passing NaCl solutions (2000 ppm) through the membranes at 225 psi. The results showed that the flux increased from 26 to 40.5 L/m(2) h, while the salt rejection was high, at 99 %, with 0.003 wt% Ag2O nanoparticles. PMID:26428014

  10. Effects of Oxide-Modified Spherical ZnO on Electrical Properties of Ag/ZnO Electrical Contact Material

    NASA Astrophysics Data System (ADS)

    Wei, Zhijun; Zhang, Lingjie; Shen, Tao; Qiao, Zhengyang; Yang, Hui; Fan, Xianping; Chen, Lawson

    2016-07-01

    Silver-zinc oxide (Ag/ZnO) electrical contact material is widely used as contacts of the medium duty switching devices. Effects of modified ZnO on properties of Ag/ZnO electrical contact material were investigated in this work. NiO and CuO were introduced to modify spherical ZnO by a chemical solution nano-coating method. Ag/ZnO contacts prepared using the modified spherical ZnO were produced by powder metallurgy (PM) method in a muffle furnace in temperature ranges from 750 to 900 °C. Results show that electrical conductivity, stability of relative density, and Vickers' hardness of Ag/ZnO electrical contact material can be improved by the addition of NiO because of the formation of NiO solid solution Zn0.2Ni0.8O. The addition of CuO to Ag/ZnO electrical contact material makes arcing energy and mass loss lower. Since this is attractive for a longer service life, using NiO and CuO co-modified ZnO as a second phase may be a promising way to improve properties of Ag/ZnO electrical contact material. Hence, the presented results could also be useful for the design of a new Ag/ZnO electrical contact material.

  11. 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

  12. IMPACT OF POLYCYCLIC AROMATIC HYDROCARBONS OF THE ELECTROCHEMICAL RESPONSES OF A FERRICYNIDE PROBE AT TEMPLATE-MODIFIED SELF ASSEMBLED MONOLAYERS ON GOLD ELECTRODES

    EPA Science Inventory

    The impact of pyrene on the electrochemical response of the ferricyanide probe using Self Assembled Monolayer (SAM)-modified gold electrodes was investigated using Cyclic Voltammetry (CV) and Square Wave Voltammetry (SWV). These results suggest the feasibility of using SAMs, par...

  13. Submicron patterns obtained by thermal-induced reconstruction of self-assembled monolayer of Ag nanoparticles and their application in SERS

    NASA Astrophysics Data System (ADS)

    Ruan, Weidong; Zhou, Tieli; Cui, Yinqiu; Dong, Yujie; Liu, Zhuo; Dong, Fengxia; Wang, Haiyang; Luan, Xintong; Wang, Xu; Song, Wei; Zhao, Bing

    2014-08-01

    The layer-by-layer (LbL) self-assembly technique was employed for the deposition of poly(diallyldimethylammonium chloride) (PDDA) and triangular Ag nanoplates on glass substrates. A thermal-induced reconstruction of these polyelectrolyte-linked nanoparticle (NP) films was presented. Before the reconstruction, triangular Ag nanoplates were distributed uniformly on the surface with an average interval of 50 ± 15 nm. After the reconstruction, the triangular Ag nanoplates accumulated into discrete stacks with an average interval of 90 ± 25 nm. The temperature-dependent experiments were done and the optimal temperature for the formation of the reconstructed patterns was 120 °C. The possible mechanism of the NP movement and stacking was analyzed. Under the experimental conditions, a hydrophobic environment was formed because of the vacuum and heating. As a result the polyelectrolyte-linked Ag NPs preferred to congregate due to the lowered surface energy. Finally the submicron patterns were formed. The ultraviolet-visible (UV-vis) absorption and surface-enhanced Raman scattering (SERS) properties of the films before and after the reconstruction was investigated. The reconstructed films with submicron patterns had better SERS enhancement ability, which was 1300 times to the original films. The reconstruction method of the monolayer films showed great potential in the surface design and related applications. AFM images were obtained to clarify the three dimensional structures of the reconstructed films obtained at 120 °C. As shown in Fig. 2, the Ag NP stacks had an average diameter of 1.0 ± 0.2 μm and an average height of 170 ± 30 nm. The diameter and height of the stacks were shaped by the aggregates of tens of triangular Ag nanoplates. The AFM cross-sectional contour showed the clear intervals of the stacks, which was corresponding to the SEM characterization.XRD patterns of the polyelectrolyte-linked NP films before and after thermal post-treatment are showed in

  14. Electron Transfer Mechanism in Gold Surface Modified with Self-Assembly Monolayers from First Principles

    NASA Astrophysics Data System (ADS)

    Lima, Filipe C. D. A.; Iost, Rodrigo M.; Crespilho, Frank N.; Caldas, Marília J.; Calzolari, Arrigo; Petrilli, Helena M.

    2013-03-01

    We report the investigation of electron tunneling mechanism of peptide ferrocenyl-glycylcystamine self-assembled monolayers (SAMs) onto Au (111) electrode surfaces. Recent experimental investigations showed that electron transfer in peptides can occur across long distances by separating the donor from the acceptor. This mechanism can be further fostered by the presence of electron donor terminations of Fc terminal units on SAMs but the charge transfer mechanism is still not clear. We study the interaction of the peptide ferrocenyl-glycylcystamine on the Au (111) from first principles calculations to evaluate the electron transfer mechanism. For this purpose, we used the Kohn Sham (KS) scheme for the Density Functional Theory (DFT) as implemented in the Quantum-ESPRESSO suit of codes, using Vandebilt ultrasoft pseudopotentials and GGA-PBE exchange correlation functional to evaluate the ground-state atomic and electronic structure of the system. The analysis of KS orbital at the Fermi Energy showed high electronic density localized in Fc molecules and the observation of a minor contribution from the solvent and counter ion. Based on the results, we infer evidences of electron tunneling mechanism from the molecule to the Au(111). We acknowledge FAPESP for grant support. Also, LCCA/USP, RICE and CENAPAD for computational resources.

  15. Electrochemical biosensor modified with dsDNA monolayer for restriction enzyme activity determination.

    PubMed

    Zajda, Joanna; Górski, Łukasz; Malinowska, Elżbieta

    2016-06-01

    A simple and cost effective method for the determination of restriction endonuclease activity is presented. dsDNA immobilized at a gold electrode surface is used as the enzymatic substrate, and an external cationic redox probe is employed in voltammetric measurements for analytical signal generation. The assessment of enzyme activity is based on a decrease of a current signal derived from reduction of methylene blue which is present in the sample solution. For this reason, the covalent attachment of the label molecule is not required which significantly reduces costs of the analysis and simplifies the entire determination procedure. The influence of buffer components on utilized dsDNA/MCH monolayer stability and integrity is also verified. Electrochemical impedance spectroscopy measurements reveal that due to pinhole formation during enzyme activity measurement the presence of any surfactants should be avoided. Additionally, it is shown that the sensitivity of the electrochemical biosensor can be tuned by changing the restriction site location along the DNA length. Under optimal conditions the proposed biosensor exhibits a linear response toward PvuII activity within a range from 0.25 to 1.50 U/μL. PMID:26859430

  16. Modified optical absorption of molecules on metallic nanoparticles at sub-monolayer coverage

    NASA Astrophysics Data System (ADS)

    Darby, Brendan L.; Auguié, Baptiste; Meyer, Matthias; Pantoja, Andres E.; Le Ru, Eric C.

    2016-01-01

    Enhanced optical absorption of molecules in the vicinity of metallic nanostructures is key to a number of surface-enhanced spectroscopies and of great general interest to the fields of plasmonics and nano-optics. However, experimental access to this absorbance has long proven elusive. Here, we present direct measurements of the surface absorbance of dye molecules adsorbed onto silver nanospheres and, crucially, at sub-monolayer concentrations where dye-dye interactions become negligible. With a large detuning from the plasmon resonance, distinct shifts and broadening of the molecular resonances reveal the intrinsic properties of the dye in contact with the metal colloid, in contrast to the often studied strong-coupling regime where the optical properties of the dye molecules cannot be isolated. The observation of these shifts together with the ability to routinely measure them has broad implications in the interpretation of experiments involving resonant molecules on metallic surfaces, such as surface-enhanced spectroscopies and many aspects of molecular plasmonics.

  17. Structural and physical properties of Ag doped poly(dimethylsiloxane) modified silica xerogels

    NASA Astrophysics Data System (ADS)

    Chakrabarti, K.; Whang, C. M.

    2001-12-01

    The purpose of the present work is to study the effect of silver (Ag) incorporation on the structural and physical properties of poly(dimethylsiloxane) (PDMS) modified silica xerogels. PDMS was chosen as the organic component because of its similarity of backbone structure (-Si-O-) with tetraethyl orthosilicate, the inorganic component of organically modified silicates. In the present work silver was incorporated by two routes: (i) directly in the sol and (ii) silver doping was done after preformed porous matrix was obtained. The microstructures, particle size distribution, infrared spectra, and optical coloration have been studied. The utility of two methods has been discussed. It was found that the particle size was much smaller compared with that of classical gels with dispersed Ag particles. For the indirect method of silver doping the particle size distribution was found to follow log-normal distribution function. Upon exposure to humid air the samples change optical state from transparency to opacity. However, this was found to be reversible when treated above 300 °C. This phenomenon may be utilized to fabricate humidity sensor and optical switches.

  18. Mass preparation and novel visible light photocatalytic activity of C and Ag Co-modified ZnO nanocrystals.

    PubMed

    Zhang, Xiao-Yan; Deng, Ya-Juan; Liu, Jin-Ku; Lu, Yi; Yang, Xiao-Hong

    2015-12-01

    A combustion method was developed to synthesize the C and Ag co-modified ZnO NCs to enhance its photocatalytic efficiency and practicability. The results showed that the doped Ag was significant to promote the photocatalytic activity, and the optimum content was 2% molar ratio of Ag to Zn atom. The degradation rate under visible light increased by 150% compared with C-ZnO NCs, while by more 1233.3% than pure ZnO photocatalyst. There were some new little particles with grain size about 10 nm on the C-ZnO NCs surface, which may state for the existence of Ag atoms. The synergy effect of Ag and carbon elements was proposed to explain the mechanism of enhanced photocatalytic performance under visible light irradiation. PMID:26254866

  19. Thermoelectric Generators from AgBiTe and AgSbTe Thin Films Modified by High-Energy Beam

    NASA Astrophysics Data System (ADS)

    Budak, S.; Guner, S.; Muntele, C.; Ila, D.

    2015-06-01

    The ternary chalcogenides AgBiTe2 and AgSbTe2 belong to the family of semiconductors with disordered NaCl cubic structure in which Ag and Sb occupy metal sublattices. Both compounds are very interesting due to their thermoelectric properties. We have grown single-layer AgBiTe and AgSbTe thin films on silicon (Si) and fused silica (Suprasil) substrates using electron beam deposition. High-energy (MeV) Si-ion bombardment was performed on the thin-film samples at five different fluences between 5 × 1013 ions/cm2 and 7 × 1015 ions/cm2. We have measured the thermoelectric efficiency (figure of merit, ZT) of the fabricated thermoelectric devices by measuring the cross-plane thermal conductivity using the third-harmonic (3 ω) method, the cross-plane Seebeck coefficient, and the in-plane electrical conductivity using the van der Pauw method before and after MeV Si-ion bombardment. Rutherford backscattering spectrometry and the Rutherford Universal Manipulation Program (RUMP) simulation package were used to analyze the elemental composition and thickness of the deposited materials on the substrates. The RUMP simulation gave thicknesses for the AgBiTe and AgSbTe thin films of 270 nm and 188 nm, respectively. The figure of merit for AgBiTe started to decrease from the value of 0.37 for the virgin sample after bombardment. We saw similar decreasing behavior for the AgSbTe thin-film system. The figure of merit for AgSbTe started to decrease from the value of 0.88 for the virgin sample after bombardment. MeV Si-ion bombardment caused changes in the thermoelectric properties of the thin films.

  20. Detection of saccharides with a fluorescent sensing device based on a gold film modified with 4-mercaptophenylboronic acid monolayer

    NASA Astrophysics Data System (ADS)

    Chen, Shu-Jen; Chang, Jui-Feng; Cheng, Nai-Jen; Yih, Jeng-Nan; Chiu, Kuo-Chi

    2013-09-01

    An extremely sensitive fluorescent sensor based on a phenylboronic acid monolayer was developed for detecting saccharide molecules. The fluorescent sensor was prepared by assembling a monolayer of 4-mercaptophenylboronic acid (4-MPBA) onto a gold-coated compact disk. The change in the fluorescence of the 4-MPBA monolayer was extremely obvious in basic methanolic buffer containing monosaccharides down to the picomolar level. The fluorescence spectra demonstrated that the 4-MPBA monolayer was sensitive to monosaccharides and disaccharides, and the affinity of the monolayer toward saccharides was in the order of glucose < fructose < mannose < galactose < maltose > lactose > sucrose. Additionally, the fluorescence intensity of 4-MPBA monolayer was restorable after cleaning with weak acid, indicating that the reported fluorescent sensor with the detection limit of glucose down to the picomolar level is reusable for sensing saccharides.

  1. Localized and Continuous Tuning of Monolayer MoS2 Photoluminescence Using a Single Shape-Controlled Ag Nanoantenna.

    PubMed

    Gao, Wei; Lee, Yih Hong; Jiang, Ruibin; Wang, Jianfang; Liu, Tianxi; Ling, Xing Yi

    2016-01-27

    Localized photoluminescence manipulation of 1L-MoS2 is achieved by using single shape-controlled Ag nanoantenna. By varying the antenna morphology, the photoluminescence of 1L-MoS2 is continuously tunable from enhanced (>2-fold) to weakened (>2-fold) states. A heterogeneous optical platform is realized by depositing various antennas on the same 1L-MoS2 , with an unprecedented range of photoluminescence output being observed simultaneously. PMID:26607311

  2. Density functional theory calculations of phenol-modified monolayer silicon nanosheets

    NASA Astrophysics Data System (ADS)

    Spencer, Michelle J. S.; Morishita, Tetsuya; Bassett, Michael R.

    2013-12-01

    Silicon nanosheets are one of most exciting recent discoveries, being a two-dimensional form of silicon that is only nanometers thick, with large lateral dimensions. A single atomic layer silicon nanosheet is known as silicene and can be grown with different surface terminations. It has been shown previously that organo-modified silicene can be synthesised with phenyl groups covalently bonded to both sides of the nanosheet, with hydrogen atoms terminating the undercoordinated silicon atoms. In this work, we use density functional theory calculations and ab initio molecular dynamics simulations to determine the effect of hydroxyl (OH) group substitutions on the phenyl-modified silicene. Different positions of the OH groups on the phenyl rings were modelled including ortho-, meta- and para- substituted positions. We found that the meta-substituted position was favoured, followed by the para- then ortho- substituted positions. Our ab initio MD simulations showed that the phenol groups will freely rotate on the nanosheet, aligning so as to form hydrogen bonds between adjacent phenol groups. The unique properties of this material could be useful for future electronic device applications.

  3. Square Wave Voltammetry of TNT at Gold Electrodes Modified with Self-Assembled Monolayers Containing Aromatic Structures

    PubMed Central

    Trammell, Scott A.; Zabetakis, Dan; Moore, Martin; Verbarg, Jasenka; Stenger, David A.

    2014-01-01

    Square wave voltammetry for the reduction of 2,4,6-trinitrotoluene (TNT) was measured in 100 mM potassium phosphate buffer (pH 8) at gold electrodes modified with self-assembled monolayers (SAMs) containing either an alkane thiol or aromatic ring thiol structures. At 15 Hz, the electrochemical sensitivity (µA/ppm) was similar for all SAMs tested. However, at 60 Hz, the SAMs containing aromatic structures had a greater sensitivity than the alkane thiol SAM. In fact, the alkane thiol SAM had a decrease in sensitivity at the higher frequency. When comparing the electrochemical response between simulations and experimental data, a general trend was observed in which most of the SAMs had similar heterogeneous rate constants within experimental error for the reduction of TNT. This most likely describes a rate limiting step for the reduction of TNT. However, in the case of the alkane SAM at higher frequency, the decrease in sensitivity suggests that the rate limiting step in this case may be electron tunneling through the SAM. Our results show that SAMs containing aromatic rings increased the sensitivity for the reduction of TNT when higher frequencies were employed and at the same time suppressed the electrochemical reduction of dissolved oxygen. PMID:25549081

  4. Nanosecond imaging of microboiling behavior on pulsed-heated au films modified with hydrophilic and hydrophobic self-assembled monolayers.

    PubMed

    Balss, Karin M; Avedisian, C Thomas; Cavicchi, Richard E; Tarlov, Michael J

    2005-11-01

    Fast transient microboiling has been characterized on modified gold microheaters using a novel laser strobe microscopy technique. Microheater surfaces of different hydrophobicity were prepared using self-assembled monolayers of hexadecane thiol (hydrophobic) and 16-mercaptohexadecanol (hydrophilic) as well as the naturally hydrophilic bare gold surface. The microheater was immersed in a pool of water, and a 5-micros voltage pulse to the heater was applied, causing superheating of the water and nucleation of a vapor bubble on the heater surface. Light from a pulsed Nd:Yag laser was configured to illuminate and image the sample through a microscope assembly. The timing of the short duration (7.5 ns) laser flash was varied with respect to the voltage pulse applied to the heater to create a series of images illuminated by the flash of the laser. These images were correlated with the transient resistance change of the heater both during and after the voltage pulse. It was found that hydrophobic surfaces produced a bubble that nucleated at an earlier time, grew more slowly to a smaller maximum size, and collapsed more rapidly than bubbles formed on hydrophilic surfaces. PMID:16262306

  5. Second harmonic generation of chiral-modified silver nanoparticles

    NASA Astrophysics Data System (ADS)

    Tao, Yue; Aldea-Nunzi, Gabriela; Rao Bobbara, Sanyasi; Nunzi, Jean-Michel

    2013-10-01

    Various approaches for the optical detection of chiral compounds have been developed due to their natural optical activity. Since the advantages of second harmonic generation (SHG) on noble-metal nanoparticles (NPs) have been observed, it would be interesting to study the nonlinear phenomena from chiral compounds attached Ag NPs. In the present work, we fabricated chiral-modified Ag NPs based on the self-assembly process of cysteine and Ag, and carried out the investigation on SHG on modified and unmodified Ag NPs. For modified Ag NPs, either L-Cysteine (L-C) or D-Cysteine (D-C), as a pair of enantiomers, was applied on top of the Ag NPs. The resulting chiral-modified monolayers of L-C/Ag NPs and D-C/Ag NPs exhibit a reversed optical rotation difference (ORD) at linearly +/-45° polarization of SH, where no such difference exists for Ag NPs alone. SHG efficiently probes and discriminates L-C from D-C monolayers on the modified Ag NPs, which constitutes a simple and sensitive optical diagnostic of chiral molecules.

  6. Phonon dispersion on Ag (100) surface: A modified analytic embedded atom method study

    NASA Astrophysics Data System (ADS)

    Xiao-Jun, Zhang; Chang-Le, Chen

    2016-01-01

    Within the harmonic approximation, the analytic expression of the dynamical matrix is derived based on the modified analytic embedded atom method (MAEAM) and the dynamics theory of surface lattice. The surface phonon dispersions along three major symmetry directions , and X¯M¯ are calculated for the clean Ag (100) surface by using our derived formulas. We then discuss the polarization and localization of surface modes at points X¯ and M¯ by plotting the squared polarization vectors as a function of the layer index. The phonon frequencies of the surface modes calculated by MAEAM are compared with the available experimental and other theoretical data. It is found that the present results are generally in agreement with the referenced experimental or theoretical results, with a maximum deviation of 10.4%. The agreement shows that the modified analytic embedded atom method is a reasonable many-body potential model to quickly describe the surface lattice vibration. It also lays a significant foundation for studying the surface lattice vibration in other metals. Project supported by the National Natural Science Foundation of China (Grant Nos. 61471301 and 61078057), the Scientific Research Program Funded by Shaanxi Provincial Education Department, China (Grant No. 14JK1301), and the Specialized Research Fund for the Doctoral Program of Higher Education, China (Grant No. 20126102110045).

  7. Demonstrating approaches to chemically modify the surface of Ag nanoparticles in order to influence their cytotoxicity and biodistribution after single dose acute intravenous administration.

    PubMed

    Pang, Chengfang; Brunelli, Andrea; Zhu, Conghui; Hristozov, Danail; Liu, Ying; Semenzin, Elena; Wang, Wenwen; Tao, Wuqun; Liang, Jingnan; Marcomini, Antonio; Chen, Chunying; Zhao, Bin

    2016-03-01

    With the advance in material science and the need to diversify market applications, silver nanoparticles (AgNPs) are modified by different surface coatings. However, how these surface modifications influence the effects of AgNPs on human health is still largely unknown. We have evaluated the uptake, toxicity and pharmacokinetics of AgNPs coated with citrate, polyethylene glycol, polyvinyl pyrolidone and branched polyethyleneimine (Citrate AgNPs, PEG AgNPs, PVP AgNPs and BPEI AgNPs, respectively). Our results demonstrated that the toxicity of AgNPs depends on the intracellular localization that was highly dependent on the surface charge. BPEI AgNPs (ζ potential = +46.5 mV) induced the highest cytotoxicity and DNA fragmentation in Hepa1c1c7. In addition, it showed the highest damage to the nucleus of liver cells in the exposed mice, which is associated with a high accumulation in liver tissues. The PEG AgNPs (ζ potential = -16.2 mV) showed the cytotoxicity, a long blood circulation, as well as bioaccumulation in spleen (34.33 µg/g), which suggest better biocompatibility compared to the other chemically modified AgNPs. Moreover, the adsorption ability with bovine serum albumin revealed that the PEG surface of AgNPs has an optimal biological inertia and can effectively resist opsonization or non-specific binding to protein in mice. The overall results indicated that the biodistribution of AgNPs was significantly dependent on surface chemistry: BPEI AgNPs > Citrate AgNPs = PVP AgNPs > PEG AgNPs. This toxicological data could be useful in supporting the development of safe AgNPs for consumer products and drug delivery applications. PMID:25962681

  8. Fragmentation and reactivity in collisions of protonated diglycine with chemically modified perfluorinated alkylthiolate-self-assembled monolayer surfaces

    SciTech Connect

    Barnes, George L.; Yang Li; Hase, William L.; Young, Kelsey

    2011-03-07

    Direct dynamics simulations are reported for quantum mechanical (QM)/molecular mechanical (MM) trajectories of N-protonated diglycine (gly{sub 2}-H{sup +}) colliding with chemically modified perfluorinated octanethiolate self-assembled monolayer (SAM) surfaces. The RM1 semiempirical theory is used for the QM component of the trajectories. RM1 activation and reaction energies were compared with those determined from higher-level ab initio theories. Two chemical modifications are considered in which a head group (-COCl or -CHO) is substituted on the terminal carbon of a single chain of the SAM. These surfaces are designated as the COCl-SAM and CHO-SAM, respectively. Fragmentation, peptide reaction with the SAM, and covalent linkage of the peptide or its fragments with the SAM surface are observed. Peptide fragmentation via concerted CH{sub 2}-CO bond breakage is the dominant pathway for both surfaces. HCl formation is the dominant species produced by reaction with the COCl-SAM, while for the CHO-SAM a concerted H-atom transfer from the CHO-SAM to the peptide combined with either a H-atom or radical transfer from the peptide to the surface to form singlet reaction products is the dominant pathway. A strong collision energy dependence is found for the probability of peptide fragmentation, its reactivity, and linkage with the SAM. Surface deposition, i.e., covalent linkage between the surface and the peptide, is compared to recent experimental observations of such bonding by Laskin and co-workers [Phys. Chem. Chem. Phys. 10, 1512 (2008)]. Qualitative differences in reactivity are seen between the COCl-SAM and CHO-SAM showing that chemical identity is important for surface reactivity. The probability of reactive surface deposition, which is most closely analogous to experimental observables, peaks at a value of around 20% for a collision energy of 50 eV.

  9. Monolayer magnetism of 3d transition metals in Ag, Au, Pd, and Pt hosts: Systematics of local moment variation

    NASA Astrophysics Data System (ADS)

    McHenry, M. E.; MacLaren, J. M.; Clougherty, D. P.

    1991-11-01

    Electronic and magnetic properties of T/Aun, T/Agn (T=Cr, Mn, Fe, Co, and Ni), Fe/Pdn and Fe/Ptn multilayers and sandwiches have been computed using the layer Korringa-Kohn-Rostoker (LKKR) band-structure technique. Enhanced (as compared with bulk) 2D T magnetism is observed in all Cr, Mn, and Fe/host configurations, consistent with weak coupling between Cr, Mn, and Fe d bands and those of the noble metal (NM) hosts and consequently d bandwidths which are exceeded by the exchange splitting. Fe and Cr moments vary systematically with the number of mediating Ag or Au planes and the Fermi energy of the system. These systematics are explained by considering the variation of the Fermi energy (EF) with composition as well as constraints of charge neutrality and strong (single-band) ferromagnetism. For Fe in Pt and Pd hosts, d-d hybridization leads to a nearly invariant Fe moment as a function of the number of mediating Pd or Pt planes but with large induced moments on the host.

  10. Efficient inverted organic light-emitting devices with self or intentionally Ag-doped interlayer modified cathode

    SciTech Connect

    Liu, Wenbo; Liu, Shihao; Yu, Jing; Zhang, Wei; Wen, Xuemei; Yin, Yongming; Zhang, Letian; Chen, Ping; Xie, Wenfa

    2014-03-03

    Green phosphorescent inverted organic light-emitting devices (IOLEDs) with self or intentionally Ag-doped interlayer modified cathode were demonstrated. The IOLEDs show low driving voltage and high efficiency. For example, the efficiency of inverted bottom-emitting OLED with ITO cathode is comparable with the conventional bottom-emitting OLED with ITO anode. The top-emitting IOLED with Ag cathode shows high current efficiency of 76.4 cd/A which is 2.38 times of that of the conventional bottom-emitting OLED with ITO anode. The results indicate that the electron injection from cathode was observably improved by the Ag-doped interlayer and such interlayer is cathode independent relatively.

  11. Amperometric detection of Sudan I in red chili powder samples using Ag nanoparticles decorated graphene oxide modified glassy carbon electrode.

    PubMed

    Prabakaran, E; Pandian, K

    2015-01-01

    A simple and sensitive electrochemical method was developed to determine the concentration of Sudan I in chili powder based on silver nanoparticles decorated graphene oxide modified glassy carbon electrode (AgNPs@GO/GCE). The voltammetry behaviour of Sudan I on modified GCE was investigated in phosphate buffer medium (PBS) with various pH ranges and the electron transfer properties were studied. It is found that the AgNPs@GO/GCE can catalyse the reduction of azo group, -N=N- followed by electrochemical oxidation of (-)OH group present in Sudan I dye molecule. Quantitative detection of Sudan I present in food products was carried out by amperometry method in which reduction potential was fixed at -0.77 V vs. Ag/AgCl. The amperometry method showed an excellent performance with a sensitivity of 6.83 μA mM(-1) and a detection limit of 11.4 × 10(-7)ML(-1). A linear calibration graph was constructed in the ranging 3.90 × 10(-6) to 3.19 × 10(-5)ML(-1). The method was successfully applied for the determination of Sudan I in red chili powder samples. PMID:25053046

  12. Ag-Modified In2O3/ZnO Nanobundles with High Formaldehyde Gas-Sensing Performance

    PubMed Central

    Fang, Fang; Bai, Lu; Song, Dongsheng; Yang, Hongping; Sun, Xiaoming; Sun, Hongyu; Zhu, Jing

    2015-01-01

    Ag-modified In2O3/ZnO bundles with micro/nano porous structures have been designed and synthesized with by hydrothermal method continuing with dehydration process. Each bundle consists of nanoparticles, where nanogaps of 10–30 nm are present between the nanoparticles, leading to a porous structure. This porous structure brings high surface area and fast gas diffusion, enhancing the gas sensitivity. Consequently, the HCHO gas-sensing performance of the Ag-modified In2O3/ZnO bundles have been tested, with the formaldehyde-detection limit of 100 ppb (parts per billion) and the response and recover times as short as 6 s and 3 s, respectively, at 300 °C and the detection limit of 100 ppb, response time of 12 s and recover times of 6 s at 100 °C. The HCHO sensing detect limitation matches the health standard limitation on the concentration of formaldehyde for indoor air. Moreover, the strategy to synthesize the nanobundles is just two-step heating and easy to scale up. Therefore, the Ag-modified In2O3/ZnO bundles are ready for industrialization and practical applications. PMID:26287205

  13. Growth of Ag nanoparticles using plasma-modified multi-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Tseng, Chun-Hao; Chen, Chuh-Yung

    2008-01-01

    This study presents a novel method for preparing multi-walled carbon nanotubes (MWNTs) grafted with a poly(2-hydroxyethyl methacrylate) (HEMA)-silver complex (CNTs-HEMA-Ag complex) through plasma-induced grafting polymerization. The characteristics of the MWNTs after being grafted with HEMA polymer are monitored by Fourier transform infrared (FT-IR) spectroscopy. The chelating groups in the HEMA polymer grafted on the surface of the CNTs-HEMA are the coordination sites for chelating silver ions, and are further used as nanotemplates for the growing of Ag nanoparticles (quantum dots). Transmission electron microscopy (TEM) reveals that the particle size of Ag nanoparticles on the CNT surfaces increases with the Ag+ chelating concentration, reaction time, and reaction temperature. Moreover, the crystalline phase of Ag nanoparticles is identified by using x-ray diffraction (XRD). In addition, high-resolution x-ray photoelectron spectroscopy (XPS) is used to characterize the functional groups on the surface of the MWNTs after chemical modification through plasma treatment; it demonstrates that the growing amount of the Ag nanoparticles on the nanotubes increases with the Ag+ chelating concentration due to the blocking effect of the Ag particles forming on the MWNTs.

  14. Enhancement of electron injection into a light-emitting polymer from an aluminum oxide cathode modified by a self-assembled monolayer

    NASA Astrophysics Data System (ADS)

    Vaynzof, Yana; Dennes, T. Joseph; Schwartz, Jeffrey; Kahn, Antoine

    2008-09-01

    A self-assembled monolayer (SAM) of octylphosphonate was deposited on an AlOx electrode using the tethering by aggregation and growth (T-BAG) procedure. Ultraviolet photoemission spectroscopy (UPS) measurements showed a decrease in the substrate work function from 3.8to3.3eV. Poly[9,9'-dioctylfluorene-co-bis-N ,N'-(4-butylphenyl)-diphenylamine] (TFB) films spin coated on the bare and the SAM-modified oxide surfaces were investigated by UPS. A shift in molecular levels, corresponding to a reduction in the electron injection barrier, was observed for the SAM-modified electrode. This barrier lowering was confirmed by current-voltage measurements showing a corresponding increase in electron current through the TFB/SAM/AlOx device.

  15. An overwhelmingly selective colorimetric sensor for Ag(+) using a simple modified polyacrylonitrile fiber.

    PubMed

    Xing, Xiaoli; Yang, Huixiao; Tao, Minli; Zhang, Wenqin

    2015-10-30

    A carboxymethyl-dithiocarbamate immobilized polyacrylonitrile fiber colorimetric sensor has been synthesized. This fiber sensor exhibits excellent selectivity and sensitivity for Ag(+) in aqueous solution with a remarkable color change from light pink to red-brown over a wide pH range of 2-12. The sensor responds selectively to Ag(+) in the presence of other ions, including Mg(2+), Al(3+), Ca(2+), Cr(3+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+). The colorimetric sensor has an extremely fast response time (10s) and a low visual limit of detection (5.53×10(-12) mol/L). The fiber sensor also undergoes an obvious color change in the presence of Ag(+) solutions containing EDTA, NaCl or NaBr. Density functional theory optimization reveals that the sensor and Ag(+) interact via a seven-membered ring complexation mechanism. PMID:25967097

  16. Ordered chlorinated monolayer silicene structures

    NASA Astrophysics Data System (ADS)

    Li, Wenbin; Sheng, Shaoxiang; Chen, Jian; Cheng, Peng; Chen, Lan; Wu, Kehui

    2016-04-01

    We report on a systematic experimental study on the chlorination of monatomic silicene layer on Ag(111) by scanning tunneling microscopy. Monolayer silicene on Ag(111) can form 4×4, (√13×√13)R ± 13.9°, and (2√3×2√3)R30° reconstructions due to their different buckling configurations. We found that at low dosage, Cl atoms attach to the upper buckled Si atoms without changing the buckling configuration of the silicene monolayer. However, at high coverage, the global buckling configuration will be significantly changed, resulting in new ordered structures. Interestingly, all monolayer silicene structures, regardless of their initial reconstructions, tend to form a local silicene 1×1 structure at the saturation coverage. The mechanism for chlorination of monolayer silicene is explained.

  17. Modified chitosan encapsulated core-shell Ag Nps for superior antimicrobial and anticancer activity.

    PubMed

    Banerjee, Sovan Lal; Khamrai, Moumita; Sarkar, Kishor; Singha, Nikhil K; Kundu, P P

    2016-04-01

    This investigation reports a one pot synthesis of silver nanoparticles (Ag Nps) using aqueous solution of chitosan-graft-poly(acrylamide) (Cts-g-PAAm) as a reducing agent and polyethylene glycol (PEG) as a stabilizing agent. The as synthesized Ag Nps was characterized by ultra violet-visible (UV-vis), Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis. Field emission scanning electron microscopy (FESEM), dynamic light scattering (DLS) and transmission electron microscopy (TEM) showed that Ag Nps, which were stable upto more than 60 days, were spherical in shape and the particle size was in the range of 5-50 nm. Atomic force microscopy (AFM) image also supported the above obtained result. The prepared Ag Nps exhibited strong antimicrobial activity against different gram positive bacteria (Alkaliphilus, Bascillus substillis, Lysinibascillus) and gram negative bacteria (Enterobacter aerogenus, Vivbrio vulnificus and Escherichia coli) and haemolytic assay revealed its blood compatible nature. The synthesized Ag Nps showed significant cytotoxicity over human cervical HeLa cancer cells and it was found that the inhibitory concentration for 50% cell death (IC50) was 8 μg/ml. PMID:26724687

  18. Changes in the microbiological and chemical characteristics of white bread during storage in paper packages modified with Ag/TiO2-SiO2, Ag/N-TiO2 or Au/TiO2.

    PubMed

    Peter, Anca; Mihaly-Cozmuta, Leonard; Mihaly-Cozmuta, Anca; Nicula, Camelia; Ziemkowska, Wanda; Basiak, Dariusz; Danciu, Virginia; Vulpoi, Adriana; Baia, Lucian; Falup, Anca; Craciun, Grigore; Ciric, Alexandru; Begea, Mihaela; Kiss, Claudia; Vatuiu, Daniela

    2016-04-15

    Microbiological and chemical characteristics of white bread during storage in paper-packages modified with Ag/TiO2-SiO2, Ag/N-TiO2 or Au/TiO2 were investigated. The whiteness and the water retention of the modified packages were slightly superior to those exhibited by the reference sample, as the color of the composite was lighter. The water retention was very good especially for the Ag/TiO2-SiO2-paper. These improvements can be associated with the high specific surface area and with the low agglomeration tendency of Ag nanoparticles in comparison with the Au ones. The preservation activity of the composites for the bread storage is positively influenced by photoactivity and presence of nano-Ag. Packages Ag/TiO2-SiO2-paper and Ag/N-TiO2-paper can find their applicability for extending the shelf life of bread by 2 days as compared with the unmodified paper-package. No influence of the Au/TiO2 on the extending the shelf life of bread was observed. PMID:26617018

  19. Simultaneous Detection of Cadmium, Copper, and Lead using A Carbon Paste Electrode Modified with Carbamoylphosphonic Acid Self-Assembled Monolayer on Mesoporous Silica (SAMMS)

    SciTech Connect

    Yantasee, Wassana ); Lin, Yuehe ); Fryxell, Glen E. ); Busche, Brad J. )

    2004-01-30

    A new sensor was developed for simultaneous detection of cadmium (Cd2+), copper (Cu2+), and lead (Pb2+), based on the voltammetric response at a carbon paste electrode modified with carbamoylphosphonic acid (acetamide phosphonic acid) self-assembled monolayer on mesoporous silica (Ac-Phos SAMMS). The adsorptive stripping voltammetry technique involves preconcentration of the metal ions onto Ac-Phos SAMMS under an open circuit, then electrolysis of the preconcentrated species, followed by a square wave potential sweep towards positive values. Factors affecting the preconcentration process were investigated. The voltammetric responses increased linearly with the preconcentration time from 1 to 30 minutes or with metal ion concentrations ranging from 10 to 200 ppb. The responses also evolved in the same fashion as adsorption isotherm in the pH range of 2-6. The metal detection limits were 10 ppb after 2 minutes preconcentration and improved to 0.5 ppb after 20 minutes preconcentration.

  20. Mediatorless solar energy conversion by covalently bonded thylakoid monolayer on the glassy carbon electrode.

    PubMed

    Lee, Jinhwan; Im, Jaekyun; Kim, Sunghyun

    2016-04-01

    Light reactions of photosynthesis that take place in thylakoid membranes found in plants or cyanobacteria are among the most effective ways of utilizing light. Unlike most researches that use photosystem I or photosystem II as conversion units for converting light to electricity, we have developed a simple method in which the thylakoid monolayer was covalently immobilized on the glassy carbon electrode surface. The activity of isolated thylakoid membrane was confirmed by measuring evolving oxygen under illumination. Glassy carbon surfaces were first modified with partial or full monolayers of carboxyphenyl groups by reductive C-C coupling using 4-aminobenzoic acid and aniline and then thylakoid membrane was bioconjugated through the peptide bond between amine residues of thylakoid and carboxyl groups on the surface. Surface properties of modified surfaces were characterized by cyclic voltammetry, contact angle measurements, and electrochemical impedance spectroscopy. Photocurrent of 230 nA cm(-2) was observed when the thylakoid monolayer was formed on the mixed monolayer of 4-carboxylpheny and benzene at applied potential of 0.4V vs. Ag/AgCl. A small photocurrent resulted when the 4-carboxyphenyl full monolayer was used. This work shows the possibility of solar energy conversion by directly employing the whole thylakoid membrane through simple surface modification. PMID:26625272

  1. Hot compression deformation behavior and a modified physically-based constitutive model of Cu-6 %Ag alloy

    NASA Astrophysics Data System (ADS)

    Meng, Lie; Wang, Menghan; Liu, Xiao; Wang, Fenglin

    2016-04-01

    In order to reveal the flow characteristics of Cu-6 %Ag alloy on the condition of hot deformation, the isothermal compression experiments are carried out at the temperatures of 973-1123 K under strain rates of 0.01-10 s-1. The effects of deformation condition on the hot compression deformation behavior are investigated. The low instability strain (ɛ i) behavior at high strain rate (10 s-1) is discussed in this paper. According to the experiment results and analyses, the deformation twinning and inhomogeneous grains are thought to be the possible reasons for low strain cracking. Then, a modified physically based constitutive model is established. The strain for maximum softening rate (\\varepsilon_{ *} ) is quoted in the constitutive equation which is proved that there is a nearly linear relationship between { ln }\\varepsilon_{ *} and { ln }Z . What's more, the correlation coefficient (R) and the average absolute relative error (AARE) are used to evaluate the accuracy of the established constitutive model. The values of R and AARE are 0.99612 and 3.47 %, respectively, which show that the modified constitutive model can exactly reveal the flow stress of Cu-6 %Ag alloy.

  2. A novel Ag+ cation sensor based on polyamidoamine dendrimer modified with 1,8-naphthalimide derivatives

    NASA Astrophysics Data System (ADS)

    Dodangeh, Mohammad; Gharanjig, Kamaladin; Arami, Mokhtar

    2016-02-01

    In this study, 4-amino-1,8-naphthalimide-conjugated polyamidoamine dendrimer was synthesized and characterized and its potentiality as a cation sensor was investigated. 4-Amino-1,8-naphthalic anhydride reacted with polyamidoamine dendrimer and the product was characterized using FTIR, 1H NMR, 13C NMR and melting point analysis method. The synthesized compound was applied to detect various cations in water media and N,N-dimethylformamide (DMF) via monitoring the quenching of the fluorescence intensity. Furthermore, various metal cations including Cu2 +, Ni2 +, Zn2 +, Pb2 +,Ca2 +, Ba2 +, Cd2 +, Hg2 +, Fe2 +, Fe3 + and Ag+ were tested. The complexes formed between the synthesized compound and metal cations in solution and their effects on Photoinduced Electron Transfer (PET) process were investigated regarding the potential application of the newly-synthesized dendrimer as a colorimetric and fluorescent sensor for such cations. The results clearly confirmed that the 1,8-naphthalimide groups surrounding the central dendrimer core showed strong green fluorescence emission at 553 nm. This effect considerably decreased with the introduction of all cations, except Ag+ where the fluorescence quenching effect was remarkable and more dominant. Therefore, it can be concluded that the synthesized dye has the potentiality of being a highly sensitive and selective fluorescence sensor for Ag+ cation.

  3. Fano Resonance and Spectrally Modified Photoluminescence Enhancement in Monolayer MoS2 Integrated with Plasmonic Nanoantenna Array.

    PubMed

    Lee, Bumsu; Park, Joohee; Han, Gang Hee; Ee, Ho-Seok; Naylor, Carl H; Liu, Wenjing; Johnson, A T Charlie; Agarwal, Ritesh

    2015-05-13

    The manipulation of light-matter interactions in two-dimensional atomically thin crystals is critical for obtaining new optoelectronic functionalities in these strongly confined materials. Here, by integrating chemically grown monolayers of MoS2 with a silver-bowtie nanoantenna array supporting narrow surface-lattice plasmonic resonances, a unique two-dimensional optical system has been achieved. The enhanced exciton-plasmon coupling enables profound changes in the emission and excitation processes leading to spectrally tunable, large photoluminescence enhancement as well as surface-enhanced Raman scattering at room temperature. Furthermore, due to the decreased damping of MoS2 excitons interacting with the plasmonic resonances of the bowtie array at low temperatures stronger exciton-plasmon coupling is achieved resulting in a Fano line shape in the reflection spectrum. The Fano line shape, which is due to the interference between the pathways involving the excitation of the exciton and plasmon, can be tuned by altering the coupling strengths between the two systems via changing the design of the bowties lattice. The ability to manipulate the optical properties of two-dimensional systems with tunable plasmonic resonators offers a new platform for the design of novel optical devices with precisely tailored responses. PMID:25926239

  4. Selective recovery of Ag(I) coordination anion from simulate nickel electrolyte using corn stalk based adsorbent modified by ammonia-thiosemicarbazide.

    PubMed

    Xiong, Ying; Wan, Li; Xuan, Jing; Wang, Yongwei; Xing, Zhiqing; Shan, Weijun; Lou, Zhenning

    2016-01-15

    In nickel electrolyte, Ag(I) was present at trace level concentration (10-20 mg L(-1)) and existed in the form of AgCli(1-i) coordination anion, instead of Ag(+) positive ion usually in several sources. In the present study, TSC-NH3-OCS adsorbent based on natural corn stalk modified by ammonia (NH3)-thiosemicarbazide (TSC) was synthesized and characterized using some instrumental techniques. The TSC-NH3-OCS adsorbent could selectively adsorb Ag(I) as AgCl(i)(1-i) coordination anion from the Ag(I)-Cu(II)-Ni(II) simulate nickel electrolyte, especially in the case of the very high levels of Cu(II) and Ni(II), which significantly outperforms the commercial available resins. The adsorption mechanism was believed to be electrostatic interaction of the protonated bands of AgCl4(3-) with protonated thiol form of the thioamide units by FTIR and XPS analysis. The maximum adsorption capacity in the Ag(I) single and Ag(I)-Cu(II)-Ni(II) ternary system were obtained and calculated as 153.54 and 46.69 mg g(-1), respectively. The reasons that the maximum adsorption capacity of AgCl(i)(1-i) from the single and ternary system varied widely could be explained by adsorption kinetic and thermodynamic results. In addition, three successive sorption/desorption cycle runs from ternary system were performed which indicated that the TSC-NH3-OCS adsorbent has a good performance for recovery Ag(I) from simulate nickel electrolyte. PMID:26368801

  5. A highly sensitive hydrogen peroxide sensor based on (Ag-Au NPs)/poly[o-phenylenediamine] modified glassy carbon electrode.

    PubMed

    Shamsipur, Mojtaba; Karimi, Ziba; Amouzadeh Tabrizi, Mahmoud

    2015-11-01

    Herein, the poly(o-phenylenediamine) decorated with gold-silver nanoparticle (Ag-Au NPs) nanocomposite modified glassy carbon was used for the determination of hydrogen peroxide. Electrochemical experiments indicated that the proposed sensor possesses an excellent sensitivity toward the reduction of hydrogen peroxide. The resulting sensor exhibited a good response to hydrogen peroxide over linear range from 0.2 to 60.0μM with a limit of detection of 0.08μM, good reproducibility, long-term stability and negligible interference from ascorbic acid, uric acid and dopamine. The proposed sensor was successfully applied to the determination of hydrogen peroxide in human serum sample. PMID:26249610

  6. Structural and electrical properties of microwave processed Ag modified KNN-LS ceramics.

    PubMed

    Palei, Prakash; Kumar, Pawan; Agrawal, Dinesh K

    2012-01-01

    Microwave processing steps of 0.95[(K0.5Na0.5)0.94Ag0.06NbO3]-0.05[LiSbO3]/(KNAN-LS) lead free ferroelectric ceramics were optimized for better densification and electrical properties. Calcination temperature and time for single perovskite phase formation were optimized and found to be 850 degrees C for 60 min., respectively. Crystal structural study revealed the presence of mixed structure in the microwave processed (MWP) KNAN-LS ceramics. The sintering of the KNAN-LS ceramics was carried out at 1080 degrees C for 10 min, 20 min and 30 min, respectively, and the sample sintered for 20 min exhibited best properties. PMID:24427858

  7. AC loss in stacks of Bi-2223/Ag tapes modified with ferromagnetic covers at the edges

    NASA Astrophysics Data System (ADS)

    Safran, S.; Gömöry, F.; Gencer, Ali

    2010-10-01

    We investigated the magnetization loss of stacked Bi-2223/Ag tapes with a ferromagnetic cover on the edges. Such modification has been found recently to reduce the AC loss of a single tape; however, the behavior in a coil winding could be different. With experiments and numerical calculations we show that a ferromagnetic cover on the edges of a superconducting tape could reduce its magnetization loss also when the tapes are arranged in a stack. The effect is weaker for larger numbers of tapes but nevertheless remained significant in a stack of four tapes, which was the maximum number studied here. The effects observed experimentally are nicely explained by the results of numerical calculations.

  8. Au-loaded TiO2 and Ag-loaded TiO2 synthesized by modified sol-gel/impregnation method as photocatalysts

    NASA Astrophysics Data System (ADS)

    Ninsonti, Hathaithip; Sriwichai, Saengrawee; Wetchakun, Natda; Kangwansupamonkon, Wiyong; Phanichphant, Sukon

    2016-02-01

    In this work, Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles were synthesized by modified sol-gel method together with impregnation method. The samples were characterized by their physicochemical properties using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy in order to obtain the correlation between structure and photocatalytic properties. XRD results indicated unloaded TiO2, Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles were all in the anatase phase with average crystallite size in the range of 10-13 nm. In addition, XPS analysis confirmed the presence of Au and Ag elements in Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles, respectively. The photocatalytic activities of TiO2, Au-loaded TiO2 and Ag-loaded TiO2 nanoparticles were evaluated through the mineralization of formic acid under UV-light illumination. The results showed that Au-loading and Ag-loading could effectively improve the photocatalytic activities of TiO2. Furthermore, Au-loaded TiO2 exhibited a higher photocatalytic activity than Ag-loaded TiO2.

  9. Antifouling behaviour of silicon surfaces modified with self-assembled monolayers containing both ethylene glycol and charged moieties

    NASA Astrophysics Data System (ADS)

    Ng, Cheuk Chi Albert; Ciampi, Simone; Harper, Jason B.; Gooding, J. Justin

    2010-08-01

    Herein reported is the synthesis of functionalised oligoethylene glycol molecules, with an azido group at one end and an ionisable group at the other end, and their attachment onto alkyne-terminated silicon(100) surfaces using 'click' chemistry. The modified surfaces were characterised using X-ray photoelectron spectroscopy (XPS) and water contact angle goniometry. The antifouling behaviour of these surfaces was assessed and it was shown that while surfaces presenting both charged and ethylene glycol moieties are antifouling, the antifouling effectiveness is influenced by the surface charge as modulated via the pH of the solution.

  10. Immobilization of cellulase on a silica gel substrate modified using a 3-APTES self-assembled monolayer

    DOE PAGESBeta

    Zhang, Dezhi; Hegab, Hisham E.; Lvov, Yuri; Snow, L. Dale; Palmer, James

    2016-01-20

    Cellulase was immobilized onto silica gel surfaces pretreated with (3-aminopropyl) triethoxy-silane (3-APTES), and glutaraldehyde (GA) was used as a cross-linker. A carboxymethyl cellulose sodium salt (CMC) solution was used for activity experiments. Protein assay was performed to determine the mass immobilized and compare with free enzyme. Cellulase was successfully demonstrated to be immobilized on the modified silica gel surface, and no detectable amount of enzyme was stripped off during the hydrolysis of the CMC solution. The specific activity of the immobilized cellulase is 7 ± 2 % compared to the similar amount of free cellulase. Significant activity over multiple reusesmore » was observed. The seventh batch achieved 82 % activity of the initial batch, and the fifteenth batch retained 31 %. Lastly, it was observed that the immobilized cellulase retained 48 % of its initial activity after 4 days, and 22 % even after 14 days.« less

  11. Electrochemical degradation of carbamazepine using modified electrode with graphene-AuAg composite

    NASA Astrophysics Data System (ADS)

    Pogacean, F.; Biris, A. R.; Socaci, C.; Floare-Avram, V.; Rosu, M. C.; Coros, M.; Pruneanu, S.

    2015-12-01

    Carbamazepine is a pharmaceutical drug which has been detected in surface and drinking water primarily due to human usage but also from the accidental disposal of pharmaceuticals into sewers. We have developed a graphene-modified electrode which was tested at the detection and degradation of carbamazepine. The oxidation process was studied by cyclic voltammetry in aqueous and organic solutions. The electrochemical degradation of carbamazepine was performed by polarizing the working electrode at a certain potential, for different times (from 5 to 60 minutes). The degradation efficiency was highly dependent on the type of solution and on the supporting electrolyte.

  12. A self-cleaning coating based on commercial grade polyacrylic latex modified by TiO2/Ag-exchanged-zeolite-A nanocomposite

    NASA Astrophysics Data System (ADS)

    Nosrati, Rahimeh; Olad, Ali; Nofouzi, Katayoon

    2015-08-01

    The commercial grade polyacrylic latex was modified in order to prepare a self-cleaning coating. TiO2/Ag-exchanged-zeolite-A nanocomposite was prepared and used as additive in the matrix of polyacrylic latex to achieve a hydrophilic and photocatalytic coating. FTIR and UV-visible spectroscopy, X-ray diffraction patterns and FESEM were used to characterize the composition and structure of the nanocomposites and coatings. The acrylic coatings, were prepared by using of TiO2/Ag-exchanged-zeolite-A additive, had better UV and visible light absorption, hydrophilic, degradation of organic pollutants, stability in water and antimicrobial properties than pristine commercial grade polyacrylic latex coating. According to the results, the modified polyacrylic based coating containing 0.5 wt% of TiO2/Ag-exchanged-zeolite-A nanocomposite additive with TiO2 to Ag-exchanged-zeolite-A ratio of 1:2 was the best coating considering most of useful properties such as small band gap and low water contact angle. The water contact angle for unmodified polyacrylic latex coating was 68° which was decreased to less than 10° in modified coating after 24 h LED lamp illumination.

  13. TiO2 modified with Ag nanoparticles synthesized via ultrasonic atomization-UV reduction and the use of kinetic models to determine the acetic acid photocatalytic degradation

    NASA Astrophysics Data System (ADS)

    Xu, Yingcao; You, Hong

    2014-12-01

    TiO2 surfaces modified with noble metal nanoparticles have been found to effectively reduce the photogenerated carrier recombination rate and significantly extend the light absorption properties of TiO2, thereby greatly increasing its photocatalytic activity. In this paper, highly ordered, double-sided TiO2 nanotube arrays were prepared using an anodic oxidation method in a home-made reactor using glycerol/water (volume ratio 2:1) and NH4F (0.25 mol/L) as the electrolyte, titanium plates (10 cm × 2 cm × 0.5 mm) as the anode and graphite as the cathode at a constant voltage of 25 V. After a 2-h reaction, anatase TiO2 nanotubes were obtained upon calcination at 450 °C for 4 h. The Ag nanoparticles on the surfaces of the TiO2 were prepared via ultrasonic atomization-ultraviolet light reduction. First, a silver nitrate solution was sputtered into small droplets under ultrasonication. Then, the Ag+ droplets were reduced to Ag nanoparticles. The surface morphologies, structures and elemental compositions were characterized using SEM, EDS, XRD and XPS. The photocatalytic activities were determined in acetic acid solutions (40-200 mg/L), and a mathematical model for catalytic degradation was established based on a hyperbolic model. The SEM results showed that the diameters of the as-prepared Ag/TiO2 are approximately 100 nm and that the lengths are approximately 1.8 μm. The XRD crystal structure analysis shows that the anatase phase of the TiO2 does not change during the Ag modification, and there was a peak from Ag (2 2 0). The XPS determined that the Ag atom percentage was 1.11%. The degradation of acetic acid indicated that Ag/TiO2 has a higher photocatalytic activity than the undoped TiO2.

  14. Study of Ag-Pd bimetallic nanoparticles modified glassy carbon electrode for detection of L-cysteine

    NASA Astrophysics Data System (ADS)

    Murugavelu, M.; Karthikeyan, B.

    2014-11-01

    Ag-Pd bimetallic nanoparticles (Ag-Pd BNPs) as an enhanced sensing material with improved electronic transmission rates in the electrochemical sensing of L-cysteine (L-cys) has been reported. The morphology of Ag-Pd BNPs was characterized with X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and cyclic voltammetry (CV). Oxidation of L-cys on Ag-Pd BNPs is investigated in detail by discussing the effect of the structure and from the electrocatalytic oxidation of L-cys. We found that the Ag-Pd BNPs exhibited high electrocatalytic activity towards L-cys oxidation in neutral condition and could be used for the development of nonenzymatic L-cys sensor. Based on the efficient catalytic ability of Ag-Pd BNPs, the fabricated biosensor exhibited a wide linear range of responses to the L-cys with the concentration detection limit of nearly down to 2 mM with fast response time.

  15. Antifungal activity of Ag:hydroxyapatite thin films synthesized by pulsed laser deposition on Ti and Ti modified by TiO2 nanotubes substrates

    NASA Astrophysics Data System (ADS)

    Eraković, S.; Janković, A.; Ristoscu, C.; Duta, L.; Serban, N.; Visan, A.; Mihailescu, I. N.; Stan, G. E.; Socol, M.; Iordache, O.; Dumitrescu, I.; Luculescu, C. R.; Janaćković, Dj.; Miškovic-Stanković, V.

    2014-02-01

    Hydroxyapatite (HA) is a widely used biomaterial for implant thin films, largely recognized for its excellent capability to chemically bond to hard tissue inducing the osteogenesis without immune response from human tissues. Nowadays, intense research efforts are focused on development of antimicrobial HA doped thin films. In particular, HA doped with Ag (Ag:HA) is expected to inhibit the attachment of microbes and contamination of metallic implant surface. We herewith report on nano-sized HA and Ag:HA thin films synthesized by pulsed laser deposition on pure Ti and Ti modified with 100 nm diameter TiO2 nanotubes (fabricated by anodization of Ti plates) substrates. The HA-based thin films were characterized by SEM, AFM, EDS, FTIR, and XRD. The cytotoxic activity was tested with HEp2 cells against controls. The antifungal efficiency of the deposited layers was tested against the Candida albicans and Aspergillus niger strains. The Ti substrates modified with TiO2 nanotubes covered with Ag:HA thin films showed the highest antifungal activity.

  16. In Situ Photocatalytically Heterostructured ZnO-Ag Nanoparticle Composites as Effective Cathode-Modifying Layers for Air-Processed Polymer Solar Cells.

    PubMed

    Yuan, Kai; Chen, Lie; Chen, Yiwang

    2015-08-10

    A heterostructured semiconductor-metal ZnO-Ag nanoparticle (NP) composite was constructed through a straightforward photocatalytic strategy by using UV irradiation of ZnO NPs and an aqueous solution of Ag precursor. The ZnO-Ag NP composites serve as an effective cathode-modifying layer in polymer solar cells (PSCs) with increased short-circuit current density owing to the light-trapping effect, and improved optical and electrical conductivity properties compared with pure ZnO NPs. The Ag NPs, which are photodeposited in situ on ZnO NPs, can act as effective antennas for incident light to maximize light harvesting and minimize radiative decay or nonradiative losses, consequently resulting in the enhanced photogeneration of excitons in PSCs. Systematic photoelectron and -physical investigations confirm that heterostructured ZnO-Ag NPs can significantly improve charge separation, transport, and collection, as well as lower charge recombination at the cathode interface, leading to a 14.0 % improvement in air-processed device power conversion efficiency. In addition, this processable, cost-effective, and scalable approach is compatible with roll-to-roll manufacturing of large-scale PSCs. PMID:26135916

  17. Dendritic cell vaccine modified by Ag85A gene enhances anti-tumor immunity against bladder cancer.

    PubMed

    Zhang, Pei; Wang, Jinyan; Wang, Danan; Wang, Huan; Shan, Fengping; Chen, Liudan; Hou, Ying; Wang, Enhua; Lu, Chang-Long

    2012-11-01

    The ability of dendritic cells to provide all the signals required for T-cell activation makes them an ideal cancer vaccine platform. With the use of established DC2.4 cell line, originated from C57BL/6 mice and developed by superinfecting GM-CSF transduced bone marrow cells with myc and raf oncogenes, we investigated whether the DC 2.4 cell line transfected with Ag85A gene could enhance immunity against bladder cancer. Both phenotypic and functional analyses of Ag85A-DCs were done with use of FCM and T cell proliferation test. The cytotoxicity of Ag85A-DCs loaded with tumor cell lysate was verified by LDH. Finally, the production of interferon gamma was assayed by both ELISA and FCM. The immunotherapeutic effect of DC vaccine on murine bladder cancer was assessed pharmacologically and pathologically. Our results showed that Ag85A gene transfected DCs expressed high levels of key surface markers such as CD80, CD86 and MHC-II. The CTL primed with MB49 lysate-pulsed Ag85A-DCs elicits higher activity against MB49 tumor cells and upregulated level of IFN-γ production. Furthermore, the significant inhibitive effect on tumor growth in mice was found in the group of Ag85A-DC vaccine. The infiltration of CD4(+) or CD8(+) T cell within established tumor treated by Ag85A-DC vaccine significantly increased as compared with control groups. It is therefore concluded that DCs engineered by Ag85A gene exerts enhanced anti-tumor immunity against bladder cancer and this study might provide a meaningful mode of action with the use of Ag85A engineered DC vaccination in anti-cancer immunotherapy. PMID:22884511

  18. DETECTION OF MOLECULAR MONOLAYERS BY OPTICAL. SECOND HARMONIC GENERATION

    SciTech Connect

    Chen, C. K.; Heinz, T. F.; Ricard, D.; Shen, Y. R.

    1980-12-01

    Second harmonic generation is shown to be sensitive enough to detect molecular monolayers adsorbed on a silver surface. Adsorption of AgCl and pyridine on silver during and after an electrolytic cycle can be easily observed,

  19. Improved performance of Ag-doped TiO2 synthesized by modified sol-gel method as photoanode of dye-sensitized solar cell

    NASA Astrophysics Data System (ADS)

    Gupta, Arun Kumar; Srivastava, Pankaj; Bahadur, Lal

    2016-08-01

    Ag-doped TiO2 with Ag content ranging from 1 to 7 mol% was synthesized by a modified sol-gel route, and its performance as the photoanode of dye-sensitized solar cells (DSSCs) was compared with undoped TiO2 photoanode. Titanium(IV)isopropoxide was used as precursor and hexamethylenetetramine as the capping agent. XRD results show the formation of TiO2 nanoparticles with an average crystallite size of 5 nm (1 % Ag-doped TiO2) and 9 nm (undoped TiO2), respectively. The TiO2 nanopowder was used to prepare its thin film photoelectrode using doctor's blade method. Significant improvement in light-to-energy conversion efficiency was achieved when thin films of 1 % Ag-doped TiO2 were applied as photoanode in DSSC taking N719 as the sensitizer dye. As evidenced by EIS measurements, the electron lifetime of DSSC with Ag-doped TiO2 increased from 1.33 (for undoped TiO2) to 2.05 ms. The short-circuit current density ( J sc), open-circuit voltage ( V oc), fill factor (FF) and the overall energy conversion efficiency ( η) were 1.07 mA cm-2, 0.72 V, 0.73 and 0.40 %, respectively, with the use of 1 % Ag-doped TiO2 photoanode, whereas with undoped TiO2 under similar conditions, J sc = 0.63 mA cm-2, V oc = 0.70 V, fill factor 0.45 and conversion efficiency 0.14 % could be obtained. Therefore, compared with the reference DSSC containing an undoped TiO2 photoanode, the power conversion efficiency of the cell based on Ag-doped TiO2 has been remarkably enhanced by ~70 %. The substantial improvement in the device performance is attributed to the reduced band-gap energy, retarded charge recombination and greater surface coverage of the sensitizing dye over Ag-doped TiO2, which ultimately resulted in improved IPCE, J SC and η values.

  20. Preparation, characterization and electrochemical application of Ag-ZnO nanoplates for voltammetric determination of glutathione and tryptophan using modified carbon paste electrode.

    PubMed

    Beitollahi, Hadi; Gholami, Abbas; Ganjali, Mohammad Reza

    2015-12-01

    Ag-ZnO nanoplates and 2-chlorobenzoyl ferrocene were synthesized and used to construct a modified carbon paste electrode. The electrooxidation of glutathione at the surface of the modified electrode was studied. Under the optimized conditions, the square wave voltammetric (SWV) peak current of glutathione increased linearly with glutathione concentrations in the range of 5.0 × 10(-8) to 2.0 × 10(-4)M with sensitivity of 0.659 μA μM(-1) and method detection limit of 20.0 nM was obtained for glutathione. The prepared modified electrode exhibits a very good resolution between the voltammetric peaks of glutathione and tryptophan which makes it suitable for the detection of glutathione in the presence of tryptophan in real samples. PMID:26354245

  1. Improvement of BCG protective efficacy with a novel chimpanzee adenovirus and a modified vaccinia Ankara virus both expressing Ag85A

    PubMed Central

    Stylianou, E.; Griffiths, K.L.; Poyntz, H.C.; Harrington-Kandt, R.; Dicks, M.D.; Stockdale, L.; Betts, G.; McShane, H.

    2015-01-01

    A replication-deficient chimpanzee adenovirus expressing Ag85A (ChAdOx1.85A) was assessed, both alone and in combination with modified vaccinia Ankara also expressing Ag85A (MVA85A), for its immunogenicity and protective efficacy against a Mycobacterium tuberculosis (M.tb) challenge in mice. Naïve and BCG-primed mice were vaccinated or boosted with ChAdOx1.85A and MVA85A in different combinations. Although intranasally administered ChAdOx1.85A induced strong immune responses in the lungs, it failed to consistently protect against aerosol M.tb challenge. In contrast, ChAdOx1.85A followed by MVA85A administered either mucosally or systemically, induced strong immune responses and was able to improve the protective efficacy of BCG. This vaccination regime has consistently shown superior protection over BCG alone and should be evaluated further. PMID:26478198

  2. Photo-reduction of bromate in drinking water by metallic Ag and reduced graphene oxide (RGO) jointly modified BiVO4 under visible light irradiation.

    PubMed

    Chen, Fei; Yang, Qi; Zhong, Yu; An, Hongxue; Zhao, Jianwei; Xie, Ting; Xu, Qiuxiang; Li, Xiaoming; Wang, Dongbo; Zeng, Guangming

    2016-09-15

    Bromate (BrO3(-)), an oxyhalide disinfection by-product (DBP) in drinking water, has been demonstrated to be carcinogenic and genotoxic. In the current work, metallic Ag and reduced graphene oxide (RGO) co-modified BiVO4 was successfully synthesized by a stepwise chemical method coupling with a photo-deposition process and applied in the photo-reduction of BrO3(-) under visible light irradiation. In this composite, metallic Ag acted as an electron donor or mediator and RGO enhanced the BrO3(-) adsorption onto the surface of catalysts as well as an electron acceptor to restrict the recombination of photo-generated electron-hole pairs. The Ag@BiVO4@RGO composite exhibited greater photo-reduction BrO3(-) performance than pure BiVO4, Ag@BiVO4 and RGO@BiVO4 under identical experimental conditions: initial BrO3(-) concentration 150 μg/L, catalyst dosage 0.5 g/L, pH 7.0 and visible light (λ > 420 nm). The photoluminescence spectra (PL), electron-spin resonance (ESR), photocurrent density (PC) and electrochemical impedance spectroscopy (EIS) measurements indicated that the modified BiVO4 enhanced the photo-generated electrons and separated the electron-hole pairs. The photocatalytic reduction efficiency for BrO3(-) removal decreased with the addition of electron quencher K2S2O8, suggesting that electrons were the primary factor in this photo-reduction process. The declining photo-reduction efficiency of BrO3(-) in tap water should attribute to the consumption of photo-generated electrons by coexisting anions and the adsorption of dissolved organic matter (DOM) on graphene surface. The overall results indicate a promising application potential for photo-reduction in the DBPs removal from drinking water. PMID:27311108

  3. Extracellular polymeric substances (EPS) of freshwater biofilms stabilize and modify CeO2 and Ag nanoparticles.

    PubMed

    Kroll, Alexandra; Behra, Renata; Kaegi, Ralf; Sigg, Laura

    2014-01-01

    Streams are potential receiving compartments for engineered nanoparticles (NP). In streams, NP may remain dispersed or settle to the benthic compartment. Both dispersed and settling NP can accumulate in benthic biofilms called periphyton that are essential to stream ecosystems. Periphytic organisms excrete extracellular polymeric substances (EPS) that interact with any material reaching the biofilms. To understand the interaction of NP with periphyton it is therefore crucial to study the interaction of NP with EPS. We investigated the influence of EPS on the physicochemical properties of selected NP (CeO2, Ag) under controlled conditions at pH 6, 7.6, 8.6 and light or dark exposure. We extracted EPS from five different periphyton communities, characterized the extracts, and exposed CeO2 and carbonate-stabilized Ag NP (0.5 and 5 mg/L, both 25 nm primary particle size) and AgNO3 to EPS (10 mg/L) over two weeks. We measured NP size distribution, shape, primary particle size, surface plasmon resonance, and dissolution. All EPS extracts were composed of biopolymers, building blocks of humic substances, low molecular weight (Mr) acids, and small amphiphilic or neutral compounds in varying concentrations. CeO2 NP were stabilized by EPS independent of pH and light/dark while dissolution increased over time in the dark at pH 6. EPS induced a size increase in Ag NP in the light with decreasing pH and the formation of metallic Ag NP from AgNO3 at the same conditions via EPS-enhanced photoreduction. NP transformation and formation were slower in the extract with the lowest biopolymer and low Mr acid concentrations. Periphytic EPS in combination with naturally varying pH and light/dark conditions influence the properties of the Ag and CeO2 NP tested and thus the exposure conditions within biofilms. Our results indicate that periphytic organisms may be exposed to a constantly changing mixture of engineered and naturally formed Ag NP and Ag+. PMID:25333364

  4. Extracellular Polymeric Substances (EPS) of Freshwater Biofilms Stabilize and Modify CeO2 and Ag Nanoparticles

    PubMed Central

    Kroll, Alexandra; Behra, Renata; Kaegi, Ralf; Sigg, Laura

    2014-01-01

    Streams are potential receiving compartments for engineered nanoparticles (NP). In streams, NP may remain dispersed or settle to the benthic compartment. Both dispersed and settling NP can accumulate in benthic biofilms called periphyton that are essential to stream ecosystems. Periphytic organisms excrete extracellular polymeric substances (EPS) that interact with any material reaching the biofilms. To understand the interaction of NP with periphyton it is therefore crucial to study the interaction of NP with EPS. We investigated the influence of EPS on the physicochemical properties of selected NP (CeO2, Ag) under controlled conditions at pH 6, 7.6, 8.6 and light or dark exposure. We extracted EPS from five different periphyton communities, characterized the extracts, and exposed CeO2 and carbonate-stabilized Ag NP (0.5 and 5 mg/L, both 25 nm primary particle size) and AgNO3 to EPS (10 mg/L) over two weeks. We measured NP size distribution, shape, primary particle size, surface plasmon resonance, and dissolution. All EPS extracts were composed of biopolymers, building blocks of humic substances, low molecular weight (Mr) acids, and small amphiphilic or neutral compounds in varying concentrations. CeO2 NP were stabilized by EPS independent of pH and light/dark while dissolution increased over time in the dark at pH 6. EPS induced a size increase in Ag NP in the light with decreasing pH and the formation of metallic Ag NP from AgNO3 at the same conditions via EPS-enhanced photoreduction. NP transformation and formation were slower in the extract with the lowest biopolymer and low Mr acid concentrations. Periphytic EPS in combination with naturally varying pH and light/dark conditions influence the properties of the Ag and CeO2 NP tested and thus the exposure conditions within biofilms. Our results indicate that periphytic organisms may be exposed to a constantly changing mixture of engineered and naturally formed Ag NP and Ag+. PMID:25333364

  5. A novel glucose biosensor platform based on Ag@AuNPs modified graphene oxide nanocomposite and SERS application.

    PubMed

    Gupta, Vinod Kumar; Atar, Necip; Yola, Mehmet Lütfi; Eryılmaz, Merve; Torul, Hilal; Tamer, Uğur; Boyacı, Ismail Hakkı; Ustündağ, Zafer

    2013-09-15

    This study represents a novel template demonstration of a glucose biosensor based on mercaptophenyl boronic acid (MBA) terminated Ag@AuNPs/graphene oxide (Ag@AuNPs-GO) nanomaterials. The nanocomposites were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) method. The TEM image shows that Ag@AuNPs in the nanocomposite is in the range of diameters of 10-20 nm. The nanocomposite was used for the determination of glucose through the complexation between boronic acid and diol groups of glucose. Thus, a novel glucose biosensor was further fabricated by immobilizing glucose oxidase (GOD) into MBA terminated Ag@AuNPs-GO nanocomposite film (MBA-Ag@AuNPs-GO). The linearity range of glucose was obtained as 2-6mM with detection limit of 0.33 mM. The developed biosensor was also applied successfully for the determination of glucose in blood samples. The concentration value of glucose in blood samples was calculated to be 1.97±0.002 mM from measurements repeated for six times. PMID:23816220

  6. Perforated monolayers

    SciTech Connect

    Regen, S.L.

    1992-12-01

    Goal of this research program is to create ultrathin organic membranes that possess uniform and adjustable pores ( < 7[angstrom] diameter). Such membranes are expected to possess high permeation selectivity (permselectivity) and high permeability, and to provide the basis for energy-efficient methods of molecular separation. Work carried out has demonstrated feasibility of using perforated monolayer''-based composites as molecular sieve membranes. Specifically, composite membranes derived from Langmuir-Blodgett multilayers of the calix[6]arene-based surfactant shown below plus poly[l-(trimethylsilyl)-l-propyne] (PTMSP) were found to exhibit sieving behavior towards He, N[sub 2] and SF[sub 6]. Results of derivative studies that have also been completed are also described in this report.

  7. Ag electrode modified with polyhexamethylene biguanide stabilized silver nanoparticles: a new type of SERS substrates for detection of enzymatically generated thiocholine

    NASA Astrophysics Data System (ADS)

    Tepanov, A. A.; Nechaeva, N. L.; Prokopkina, T. A.; Kudrinskiy, A. A.; Kurochkin, I. N.; Lisichkin, G. V.

    2015-11-01

    The detection of thiocholine is one of the most widespread techniques for estimation of the cholinesterase activity - acetylcholinesterase and butyrylcholinesterase. Both cholinesterases can be inhibited by organophosphates and carbamates and accordingly can be considered for estimation of these pollutants in the environment. In the current work, SERS spectroscopy was applied for the thiocholine detection. The Ag electrodes modified with silver nanoparticles stabilized by polyhexamethylene biguanide were for the first time suggested as SERS-substrates for that purpose. Such electrodes can be applicable for SERS detection of submicromolar concentrations of thiocholine.

  8. Diffusion across the modified polyethylene separator GX in the heat-sterilizable AgO-Zn battery

    NASA Technical Reports Server (NTRS)

    Lutwack, R.

    1973-01-01

    Models of diffusion across an inert membrane have been studied using the computer program CINDA. The models were constructed to simulate various conditions obtained in the consideration of the diffusion of Ag (OH)2 ions in the AgO-Zn battery. The effects on concentrations across the membrane at the steady state and on the fluxout as a function of time were used to examine the consequences of stepwise reducing the number of sources of ions, of stepwise blocking the source and sink surfaces, of varying the magnitude of the diffusion coefficient for a uniform membrane, of varying the diffusion coefficient across the membrane, and of excluding volumes to diffusion.

  9. Destabilization of Ag nanoislands on Ag(100) by adsorbed sulfur

    SciTech Connect

    Shen, Mingmin; Russell, Selena M.; Liu, Da-Jiang; Thiel, Patricia A.

    2011-10-17

    Sulfur accelerates coarsening of Ag nanoislands on Ag(100) at 300 K, and this effect is enhanced with increasing sulfur coverage over a range spanning a few hundredths of a monolayer, to nearly 0.25 monolayers. We propose that acceleration of coarsening in this system is tied to the formation of AgS{sub 2} clusters primarily at step edges. These clusters can transport Ag more efficiently than can Ag adatoms (due to a lower diffusion barrier and comparable formation energy). The mobility of isolated sulfur on Ag(100) is very low so that formation of the complex is kinetically limited at low sulfur coverages, and thus enhancement is minimal. However, higher sulfur coverages force the population of sites adjacent to step edges, so that formation of the cluster is no longer limited by diffusion of sulfur across terraces. Sulfur exerts a much weaker effect on the rate of coarsening on Ag(100) than it does on Ag(111). This is consistent with theory, which shows that the difference between the total energy barrier for coarsening with and without sulfur is also much smaller on Ag(100) than on Ag(111).

  10. Amperometric biosensor of SnO2 thin film modified by Pd, In and Ag nanostructure synthesized by CSP method

    NASA Astrophysics Data System (ADS)

    Hassan, Marwa Abdul Muhsien; Hateef, Areej Adnan; Majeed, Aseel Mustafa Abdul; Al-Jabiry, Ali Jasim Mohammed; Jameel, Sabah; Hussian, Haidar Abdul Razaq Abdul

    2013-10-01

    Palladium, Indium and Silver-doped SnO2 thin film was deposited by chemical spray pyrolysis on ITO and porous silicon substrates to be a fast MgSO4·7H2O amperometric biosensor. The prepared SnO2 films were doped by dipping in palladium chloride PdCl2, indium chloride, InCl3 and silver nitrides AgNO3 dissolved in ethanol C2H5OH. The structural and optical properties of the prepared films were studied. The sensitivity behaviors of SnO2, SnO2: Pd, SnO2: In and SnO2: Ag based on the amperometric biosensor to MgSO4·7H2O salts were investigated at room temperature with different doping.

  11. Control of localized surface plasmon resonance energy in monolayer structures of gold and silver nanoparticles.

    PubMed

    Yokota, Hiroki; Taniguchi, Taichi; Watanabe, Taichi; Kim, DaeGwi

    2015-10-28

    Monolayer structures of Au and Ag nanoparticles (NPs) were fabricated by a dipping method to realize the control of localized surface plasmon resonance (LSPR) energy. The mean inter-particle distance in the monolayer was controlled by changing the concentration of NPs in the colloidal solution used for the monolayer assembly. The extinction-peak energy of the monolayer structure was red-shifted with decreasing inter-particle distance, reflecting plasmon coupling between NPs. PMID:26411840

  12. Preparation and optimization of a bienzymic biosensor based on self-assembled monolayer modified gold electrode for alcohol and glucose detection.

    PubMed

    Asav, Engin; Akyilmaz, Erol

    2010-01-15

    The aim of this project was to develop a bienzymic biosensor, which was based on co-immobilization of alcohol oxidase and glucose oxidase on the same electrode by formation of self-assembled monolayer (SAM) for selective determination of ethanol and glucose. In the biosensor construction the enzymes and the mediator, tetrathiafulvalene (TTF), were immobilized with cross-linking agents glutaraldehyde and cysteamine by forming a self-assembled monolayer (SAM) on a gold disc electrode. Amounts of ethanol and glucose were amperometrically detected by monitoring current values at reduction potential of TTF(+), 0.1V. Decreases in biosensor responses were linearly related to glucose concentrations between 0.1 and 1.0 mM and ethanol concentrations between 1.0 and 10 mM. Limits of detection of the biosensor for ethanol and glucose were calculated to be 0.75 and 0.03 mM, respectively. In the optimization studies of the biosensor some parameters such as optimum pH, optimum temperature, enzyme amount, effect of TTF concentration and duration of SAM formation were investigated. PMID:19819124

  13. Equilibrium adsorption isotherm studies of Cu (II) and Co (II) in high concentration aqueous solutions on Ag-TiO2-modified kaolinite ceramic adsorbents

    NASA Astrophysics Data System (ADS)

    Ajenifuja, E.; Ajao, J. A.; Ajayi, E. O. B.

    2016-03-01

    Photocatalytic ceramic adsorbents were prepared from locally sourced kaolinite clay minerals for the removal of copper and cobalt ions from high concentration aqueous solutions. The minerals were treated with mild acid before modification using silver nanoparticles sources and titanium-oxide nanoparticles. Batch adsorption experiment was carried out on the targeted ions and the results were analyzed by Langmuir and Freundlich equation at different concentrations (100-1000 mg/l). As-received raw materials do not exhibit any adsorption capacity. However, the adsorption isotherms for modified kaolinite clay ceramic adsorbents could be fitted well by the Langmuir model for Cu2+ and Co2+ with correlation coefficient (R) of up to 0.99705. The highest and lowest monolayer coverage (q max) were 93.023 and 30.497 mg/g for Cu2+ and Co2+, respectively. The separation factor (R L ) was less than one (<1), indicating that the adsorption of metal ions on modified ceramic adsorbent is favorable. The highest adsorbent adsorption capacity (K f ) and intensity (n) constants obtained from Freundlich model are 14.401 (Cu2+ on KLN-T) and 6.057 (Co2+ on KLN-T).

  14. Modifying the Surface of a Rashba-Split Pb-Ag Alloy Using Tailored Metal-Organic Bonds.

    PubMed

    Stadtmüller, Benjamin; Seidel, Johannes; Haag, Norman; Grad, Lisa; Tusche, Christian; van Straaten, Gerben; Franke, Markus; Kirschner, Jürgen; Kumpf, Christian; Cinchetti, Mirko; Aeschlimann, Martin

    2016-08-26

    Hybridization-related modifications of the first metal layer of a metal-organic interface are difficult to access experimentally and have been largely neglected so far. Here, we study the influence of specific chemical bonds (as formed by the organic molecules CuPc and PTCDA) on a Pb-Ag surface alloy. We find that delocalized van der Waals or weak chemical π-type bonds are not strong enough to alter the alloy, while localized σ-type bonds lead to a vertical displacement of the Pb surface atoms and to changes in the alloy's surface band structure. Our results provide an exciting platform for tuning the Rashba-type spin texture of surface alloys using organic molecules. PMID:27610875

  15. Highly Sensitive and Selective Surface-Enhanced Raman Spectroscopy Label-free Detection of 3,3',4,4'-Tetrachlorobiphenyl Using DNA Aptamer-Modified Ag-Nanorod Arrays.

    PubMed

    Sun, Kexi; Huang, Qing; Meng, Guowen; Lu, Yilin

    2016-03-01

    An improved label-free approach for highly sensitive and selective detection of 3,3',4,4'-tetrachlorobiphenyl (PCB-77), a type of polychlorinated biphenyl, via surface-enhanced Raman spectroscopy (SERS) using DNA aptamer-modified Ag-nanorod arrays as the effective substrate is reported. The devised system consists of Ag-nanorod (Ag-NR) arrays with the PCB-77 binding aptamers anchored covalently to the Ag surfaces through a thiol linker. The aptamers are made of single-stranded DNA (ssDNA) oligomers, with one end standing on the Ag surface, and upon conjugation with PCB-77, the ssDNA molecules can change their conformation to hairpin loops, so that the Raman intensity of guanines at the other end of the DNA strand increases accordingly. As such, the intensity ratio I(656 cm(-1))/I(733 cm(-1)) increases concomitantly with the increase of the concentration of PCB-77, making the quantitative evaluation of trace amounts of PCB-77 attainable. Moreover, it is found that the DNA aptamer-based Ag-NR arrays can be more responsive with a lower and optimal density of the DNA molecules modified on the substrate surface, and the best sensitivity for detection of PCB-77 can be achieved with the lower detection limit approaching 3.3 × 10(-8) M. This work therefore demonstrates that the design of aptamer-modified Ag-NRs can be used as a practically promising SERS substrate for label-free trace detection of persistent organic pollutants (POPs) in the environment. PMID:26849392

  16. Phonon spectra and temperature variation of bulk properties of Cu, Ag, Au and Pt using Sutton-Chen and modified Sutton-Chen potentials

    NASA Astrophysics Data System (ADS)

    Januszko, A.; Bose, S. K.

    2015-07-01

    Three potentials of the Finnis-Sinclair type are studied with regard to their suitability for predicting bulk thermal and elastic properties of fcc metals Cu, Ag, Au and Pt over a wide temperature range. We start with a particular parametrization of the Finnis-Sinclair model known as the Sutton-Chen potential and a later version of the same, known as the quantum Sutton-Chen potential. The quasiharmonic lattice dynamics method is used to study the temperature variation of the thermodynamic properties. Both models are found to yield poor results for thermal expansion, which can be traced to rapid softening of transverse phonon frequencies with increasing lattice parameter. The form of the Sutton-Chen potential is modified here to seek improvement in the agreement between quasiharmonic calculations and experimental data. It is found that the modified potential better predicts bulk properties in nearly all cases studied. Significant improvement is seen over the Sutton-Chen potential, while lesser but still substantial improvement is observed over the Quantum-Sutton Chen potential.

  17. Photocatalytic Properties of TiO2 Thin Films Modified with Ag and Pt Nanoparticles Deposited by Gas Flow Sputtering.

    PubMed

    Maicu, M; Glöss, D; Frach, Peter; Hecker, D; Gerlach, G; Córdoba, José M

    2015-09-01

    In this work, a gas flow sputtering (GFS) process which allows the production and deposition of metal nanoparticles (NPs) in a vacuum environment is described. Aim of the study is to prove the potential of this technology for the fabrication of new TiO2 films with enhanced photocatalytic properties. For this purpose, Ag and Pt NPs have been produced and deposited on photocatalytic float glass coated with TiO2 thin films by magnetron sputtering. The influence of the process parameters and of the metal amount on the final properties of the particles (quantity, size, size distribution, oxidation state etc.,) was widely investigated. Moreover, the effect of the NPs on the photocatalytic activity of the resulting materials was evaluated for the case of the decomposition of stearic acid (SA) during UV-A irradiation. The reduction of the water contact angle (WCA) during the irradiation period was measured in order to test the photo-induced super-hydrophilicity (PSH). PMID:26716202

  18. Removal of gas phase low-concentration toluene over Mn, Ag and Ce modified HZSM-5 catalysts by periodical operation of adsorption and non-thermal plasma regeneration.

    PubMed

    Wang, Wenzheng; Wang, Honglei; Zhu, Tianle; Fan, Xing

    2015-07-15

    Ag/HZSM-5, Mn/HZSM-5, Ce/HZSM-5, Ag-Mn/HZSM-5 and Ce-Mn/HZSM-5 were prepared by impregnation method. Both their adsorption capacity and catalytic activity were investigated for the removal of gas phase low-concentration toluene by periodical operation of adsorption and non-thermal plasma regeneration. Results show that catalysts loaded with Ag (Ag/HZSM-5 and Ag-Mn/HZSM-5) had larger adsorption capacity for toluene than the other catalysts. And Ag-Mn/HZSM-5 displayed the best catalytic performance for both toluene oxidation by non-thermal plasma and byproducts suppression. On the other hand, the deactivated catalyst can be fully regenerated by calcining in air stream when its adsorption capacity and catalytic activity of the Ag-Mn/HZSM-5 catalyst was found to be decreased after 10 cycles of periodical adsorption and non-thermal regeneration. PMID:25795275

  19. Semifluorinated Alkylphosphonic Acids Form High-Quality Self-Assembled Monolayers on Ag-Coated Yttrium Barium Copper Oxide Tapes and Enable Filamentization of the Tapes by Microcontact Printing.

    PubMed

    Park, Chul Soon; Lee, Han Ju; Lee, Dahye; Jamison, Andrew C; Galstyan, Eduard; Zagozdzon-Wosik, Wanda; Freyhardt, Herbert C; Jacobson, Allan J; Lee, T Randall

    2016-08-30

    A custom-designed semifluorinated phosphonic acid, (9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,16-heptadecafluorohexadecyl)phosphonic acid (F8H8PA), and a normal hexadecylphosphonic acid (H16PA) were synthesized and used to generate self-assembled monolayers (SAMs) on commercially available yttrium barium copper oxide (YBCO) tapes. In this study, we wished to evaluate the effectiveness of these monolayer films as coatings for selectively etching YBCO. Initial films formed by solution deposition and manual stamping using a non-patterned polydimethylsiloxane stamp allowed for a comparison of the film-formation characteristics. The resulting monolayers were characterized by X-ray photoelectron spectroscopy (XPS), contact angle goniometry, and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). To prepare line-patterned (filamentized) YBCO tapes, standard microcontact printing (μ-CP) procedures were used. The stamped patterns on the YBCO tapes were characterized by scanning electron microscopy (SEM) before and after etching to confirm the effectiveness of the patterning process on the YBCO surface and energy-dispersive X-ray spectroscopy (EDX) to obtain the atomic composition of the exposed interface. PMID:27482760

  20. Sensitive Glycoprotein Sandwich Assays by the Synergistic Effect of In Situ Generation of Raman Probes and Plasmonic Coupling of Ag Core-Au Satellite Nanostructures.

    PubMed

    Bi, Xiaoshuang; Li, Xueyuan; Chen, Dong; Du, Xuezhong

    2016-05-01

    Sensitive surface-enhanced Raman scattering (SERS) assays of glycoproteins have been proposed using p-aminothiophenol (PATP)-embedded Ag core-Au satellite nanostructures modified with p-mercaptophenylboronic acid (PMBA) and the self-assembled monolayer of PMBA on a smooth gold-coated wafer. The apparent Raman probe PATP on the surfaces of the Ag cores underwent a photodimerization to generate 4,4'-dimercaptoazobenzene (DMAB) in situ upon excitation of laser, and the in situ generated DMAB acted as the actual Raman probe with considerably strong SERS signals, which was further enhanced by the plasmonic coupling of the Ag core-Au satellite nanostructures due to the synergistic effect. The sandwich assays of glycoproteins showed high sensitivity and excellent selectivity against nonglycoproteins. The Ag core-Au satellite SERS nanostructures can be used for highly sensitive SERS assays of other analytes. PMID:27064515

  1. Simultaneous enzymatic and SERS properties of bifunctional chitosan-modified popcorn-like Au-Ag nanoparticles for high sensitive detection of melamine in milk powder.

    PubMed

    Li, Junrong; Zhang, Guannan; Wang, Lihua; Shen, Aiguo; Hu, Jiming

    2015-08-01

    In this work, we suggest a chitosan-modified popcorn-like Au-Ag nanoparticles (CSPNPs) based assay for high sensitive detection of melamine, in which CSPNPs not only provide with an intrinsic peroxidase-like activity but also act as surface enhanced Raman scattering (SERS) substrates. CSPNPs can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to the charge transfer complex (CTC), which contributes to a tremendous surface-enhanced resonant Raman scattering (SERRS) signals with 632.8 nm laser excitation. The target molecule melamine can generate an additional compound with H2O2, which means the available amount of H2O2 for the oxidation of TMB reduced. Correspondingly, the SERRS intensity of CTC is decreased. The decreased Raman intensity is proportional to the concentration of melamine over a wide range from 10 nM to 50 μM (R(2)=0.989), with a limit of detection (LOD) of 8.51 nM. Moreover, the proposed highly selective method is fully capable of rapid, separation-free detection of melamine in milk powder. PMID:26048843

  2. Structural, thermal, laser damage, photoconductivity, NLO and mechanical properties of modified vertical Bridgman method grown AgGa0.5In0.5Se2 single crystal

    NASA Astrophysics Data System (ADS)

    Vijayakumar, P.; Ramasamy, P.

    2016-08-01

    AgGa0.5In0.5Se2 single crystal was grown using modified vertical Bridgman method. The structural perfection of the AgGa0.5In0.5Se2 single crystal has been analyzed by high-resolution X-ray diffraction rocking curve measurements. The structural and compositional uniformities of AgGa0.5In0.5Se2 were studied using Raman scattering spectroscopy at room temperature. The FWHM of the Γ1 (W1) and Γ5L (Γ15) measured at different regions of the crystal confirms that the composition throughout its length is fairly uniform. Thermal properties of the as-grown crystal, including specific heat, thermal diffusivity and thermal conductivity have been investigated. The multiple shot surface laser damage threshold value was measured using Nd:YAG laser. Photoconductivity measurements with different temperatures have confirmed the positive photoconducting behavior. Second harmonic generation (SHG) on powder samples has been measured using the Kurtz and Perry technique and the results display that AgGa0.5In0.5Se2 is a phase-matchable NLO material. The hardness behavior has been measured using Vickers micro hardness measurement and the indentation size effect has been observed. The classical Meyer's law, propositional resistance model and modified propositional resistance model have been used to analyse the micro hardness behavior.

  3. Disinfection of Escherichia coli Gram negative bacteria using surface modified TiO2: optimization of Ag metallization and depiction of charge transfer mechanism.

    PubMed

    Gomathi Devi, LakshmipathiNaik; Nagaraj, Basavalingaiah

    2014-01-01

    The antibacterial activity of silver deposited TiO2 (Ag-TiO2 ) against Gram negative Escherichia coli bacteria was investigated by varying the Ag metal content from 0.10 to 0.50% on the surface of TiO2 . Ag depositions by the photoreduction method were found to be stable. Surface silver metallization was confirmed by EDAX and XPS studies. Photoluminescence studies show that the charge carrier recombination is less for 0.1% Ag-TiO2 and this catalyst shows superior bactericidal activity under solar light irradiation compared to Sol gel TiO2 (SG-TiO2 ) due to the surface plasmon effect. The energy levels of deposited Ag are dependent on the Ag content and it varies from -4.64 eV to -1.30 eV with respect to the vacuum energy level based on atomic silver to bulk silver deposits. The ability of electron transfer from Ag deposit to O2 depends on the position of the energy levels. The 0.25% and 0.50% Ag depositions showed detrimental effect on bactericidal activity due to the mismatch of energy levels. The effect of the EROS (External generation of the Reactive Oxygen Species by 0.1% Ag-TiO2 ) and IROS (Interior generation of Reactive Oxygen Species within the bacteria) on the bactericidal inactivation is discussed in detail. PMID:24995499

  4. Multifunctional self-assembled monolayers

    SciTech Connect

    Zawodzinski, T.; Bar, G.; Rubin, S.; Uribe, F.; Ferrais, J.

    1996-06-01

    This is the final report of at three year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The specific goals of this research project were threefold: to develop multifunctional self-assembled monolayers, to understand the role of monolayer structure on the functioning of such systems, and to apply this knowledge to the development of electrochemical enzyme sensors. An array of molecules that can be used to attach electrochemically active biomolecules to gold surfaces has been synthesized. Several members of a class of electroactive compounds have been characterized and the factors controlling surface modification are beginning to be characterized. Enzymes have been attached to self-assembled molecules arranged on the gold surface, a critical step toward the ultimate goal of this project. Several alternative enzyme attachment strategies to achieve robust enzyme- modified surfaces have been explored. Several means of juxtaposing enzymes and mediators, electroactive compounds through which the enzyme can exchange electrons with the electrode surface, have also been investigated. Finally, the development of sensitive biosensors based on films loaded with nanoscale-supported gold particles that have surface modified with the self-assembled enzyme and mediator have been explored.

  5. Nucleation and Growth of Cu-Al Intermetallics in Al-Modified Sn-Cu and Sn-Ag-Cu Lead-Free Solder Alloys

    NASA Astrophysics Data System (ADS)

    Reeve, Kathlene N.; Anderson, Iver E.; Handwerker, Carol A.

    2015-03-01

    Lead-free solder alloys Sn-Cu (SC) and Sn-Ag-Cu (SAC) are widely used by the microelectronics industry, but enhanced control of the microstructure is needed to improve solder performance. For such control, nucleation and stability of Cu-Al intermetallic compound (IMC) solidification catalysts were investigated by variation of the Cu (0.7-3.0 wt.%) and Al (0.0-0.4 wt.%) content of SC + Al and SAC + Al alloys, and of SAC + Al ball-grid array (BGA) solder joints. All of the Al-modified alloys produced Cu-Al IMC particles with different morphologies and phases (occasionally non-equilibrium phases). A trend of increasing Cu-Al IMC volume fraction with increasing Al content was established. Because of solidification of non-equilibrium phases in wire alloy structures, differential scanning calorimetry (DSC) experiments revealed delayed, non-equilibrium melting at high temperatures related to quenched-in Cu-Al phases; a final liquidus of 960-1200°C was recorded. During cooling from 1200°C, the DSC samples had the solidification behavior expected from thermodynamic equilibrium calculations. Solidification of the ternary alloys commenced with formation of ternary β and Cu-Al δ phases at 450-550°C; this was followed by β-Sn, and, finally, Cu6Sn5 and Cu-Al γ1. Because of the presence of the retained, high-temperature phases in the alloys, particle size and volume fraction of the room temperature Cu-Al IMC phases were observed to increase when the alloy casting temperature was reduced from 1200°C to 800°C, even though both temperatures are above the calculated liquidus temperature of the alloys. Preliminary electron backscatter diffraction results seemed to show Sn grain refinement in the SAC + Al BGA alloy.

  6. Methods of making monolayers

    DOEpatents

    Alford, Kentin L.; Simmons, Kevin L.; Samuels, William D.; Zemanian, Thomas S.; Liu, Jun; Shin, Yongsoon; Fryxell, Glen E.

    2009-09-15

    The invention pertains to methods of forming monolayers on various surfaces. The surfaces can be selected from a wide array of materials, including, for example, aluminum dioxide, silicon dioxide, carbon and SiC. The substrates can be planar or porous. The monolayer is formed under enhanced pressure conditions. The monolayer contains functionalized molecules, and accordingly functionalizes a surface of the substrate. The properties of the functionalized substrate can enhance the substrate's applicability for numerous purposes including, for example, utilization in extracting contaminants, or incorporation into a polymeric matrix.

  7. Methods of making monolayers

    DOEpatents

    Alford, Kentin L.; Simmons, Kevin L.; Samuels, William D.; Zemanian, Thomas S.; Liu, Jun; Shin, Yongsoon; Fryxell, Glen E.

    2009-12-08

    The invention pertains to methods of forming monolayers on various surfaces. The surfaces can be selected from a wide array of materials, including, for example, aluminum dioxide, silicon dioxide, carbon and SiC. The substrates can be planar or porous. The monolayer is formed under enhanced pressure conditions. The monolayer contains functionalized molecules, and accordingly functionalizes a surface of the substrate. The properties of the functionalized substrate can enhance the substrate's applicability for numerous purposes including, for example, utilization in extracting contaminants, or incorporation into a polymeric matrix.

  8. Monolayer Tungsten Disulfide Laser

    NASA Astrophysics Data System (ADS)

    Ye, Yu; Wong, Zi Jing; Lu, Xiufang; Ni, Xingjie; Zhu, Hanyu; Chen, Xianhui; Wang, Yuan; Zhang, Xiang

    Two-dimensional van der Waals materials have opened a new paradigm for fundamental physics exploration and device applications because of their emerging physical properties. Unlike gapless graphene, monolayer transition-metal dichalcogenides are two-dimensional semiconductors that undergo an indirect-to-direct band gap transition, creating new optical functionalities for next-generation ultra-compact photonics and optoelectronics. Here, we report the realization of a two-dimensional excitonic laser by embedding monolayer tungsten disulfide in a microdisk resonator.

  9. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli; Fabbri, Jason D.; Melosh, Nicholas A.; Hussain, Zahid; Shen, Zhi-Xun

    2012-04-10

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  10. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli; Fabbri, Jason D.; Melosh, Nicholas A.; Hussain, Zahid; Shen, Zhi-Xun

    2013-10-29

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  11. Surface-enhanced Raman scattering of a Ag/oligo(phenyleneethynylene)/Ag sandwich

    NASA Astrophysics Data System (ADS)

    Fletcher, Melissa; Alexson, D. M.; Prokes, Sharka; Glembocki, Orest; Vivoni, Alberto; Hosten, Charles

    2011-02-01

    α,ω-Dithiols are a useful class of compounds in molecular electronics because of their ability to easily adsorb to two metal surfaces, producing a molecular junction. We have prepared Ag nanosphere/oligo(phenyleneethynylene)/Ag sol (AgNS/OPE/Ag sol) and Ag nanowire/oligo(phenyleneethynylene)/Ag sol (AgNW/OPE/Ag sol) sandwiches to simulate the architecture of a molecular electronic device. This was achieved by self-assembly of OPE on the silver nanosurface, deprotection of the terminal sulfur, and deposition of Ag sol atop the monolayer. These sandwiches were then characterized by surface-enhanced Raman scattering (SERS) spectroscopy. The resulting spectra were compared to the bulk spectrum of the dimer and to the Ag nanosurface/OPE SERS spectra. The intensities of the SERS spectra in both systems exhibit a strong dependence on Ag deposition time and the results are also suggestive of intense interparticle coupling of the electromagnetic fields in both the AgNW/OPE/Ag and the AgNS/OPE/Ag systems. Three previously unobserved bands (1219, 1234, 2037 cm -1) arose in the SER spectra of the sandwiches and their presence is attributed to the strong enhancement of the electromagnetic field which is predicted from the COSMOL computational package. The 544 cm -1 disulfide bond which is observed in the spectrum of solid OPE but is absent in the AgNS/OPE/Ag and AgNW/OPE/Ag spectra is indicative of chemisorption of OPE to the nanoparticles through oxidative dissociation of the disulfide bond.

  12. Effects of Ge replacement in GeTe by Ag or Sb on the Seebeck coefficient and carrier concentration modified by local electron imbalance

    NASA Astrophysics Data System (ADS)

    Levin, E. M.; Howard, A.; Straszheim, W. E.

    2015-03-01

    XRD, SEM, EDS, 125Te NMR, Seebeck coefficient, and electrical resistivity of AgxGe50-xTe50 and SbxGe50-xTe50 alloys have been studied. Replacement of Ge in GeTe by Sb significantly increases the Seebeck coefficient, while replacement by Ag decreases it. These effects can be attributed to a change in carrier concentration observed via 125Te NMR spin-lattice relaxation measurements and NMR signal position, which mostly depends on the Knight shift. Variation in carrier concentration in AgxGe50-xTe50 and SbxGe50-xTe50 can be attributed to different electron configurations of valence electrons of Ag (4d105s1) and Sb (5s25p3) compared to that of Ge (4s24p2) resulting in local electron imbalances and changing the concentration of charge carrier (holes) generated by Ge vacancies. In contrast, our 125Te NMR and Seebeck coefficient data for Ag2Sb2Ge46Te50 are similar to those observed for GeTe. This shows that effects from Ag and Sb compensate each other and indicates the existence of [Ag +Sb] pairs. The effects of Ge replacement in GeTe by Ag, Sb, or [Ag +Sb] on rhombohedral lattice distortion also have been analyzed. Interplay between the Seebeck coefficient and electrical resistivity in these alloys results in variation of power factor; the value of 45 mW/cm K2, the highest among known tellurides, was found for Sb2Ge48Te50.

  13. Electrochemical Properties of Organosilane Self Assembled Monolayers on Aluminum 2024

    NASA Technical Reports Server (NTRS)

    Hintze, Paul E.; Calle, Luz Marina

    2004-01-01

    Self assembled monolayers are commonly used to modify surfaces. Within the last 15 years, self assembled monolayers have been investigated as a way to protect from corrosion[1,2] or biofouling.[3] In this study, self assembled monolayers of decitriethoxysilane (C10H21Si(OC2H5)3) and octadecyltriethoxysilane (C18H37Si(OC2H5)3) were formed on aluminum 2024-T3. The modified surfaces and bare Al 2024 were characterized by dynamic water contact angle measurements, x-ray photoelectron spectroscopy (XIPS) and infrared spectroscopy. Electrochemical impedance spectroscopy (EIS) in 0.5 M NaCl was used to characterize the monolayers and evaluate their corrosion protection properties. The advancing water contact angle and infrared measurements show that the mono layers form a surface where the hydrocarbon chains are packed and oriented away from the surface, consistent with what is found in similar systems. The contact angle hysteresis measured in these systems is relatively large, perhaps indicating that the hydrocarbon chains are not as well packed as monolayers formed on other substrates. The results of the EIS measurements were modeled using a Randle's circuit modified by changing the capacitor to a constant phase element. The constant phase element values were found to characterize the monolayer. The capacitance of the monolayer modified surface starts lower than the bare Al 2024, but approaches values similar to the bare Al 2024 within 24 hours as the monolayer is degraded. The n values found for bare Al 2024 quickly approach the value of a true capacitor and are greater than 0.9 within hours after the start of exposure. For the monolayer modified structure, n can stay lower than 0.9 for a longer period of time. In fact, n for the monolayer modified surfaces is different from the bare surface even after the capacitance values have converged. This indicates that the deviation from ideal capacitance is the most sensitive indicator of the presence of the monolayer.

  14. A highly sensitive self assembled monolayer modified copper doped zinc oxide nanofiber interface for detection of Plasmodium falciparum histidine-rich protein-2: Targeted towards rapid, early diagnosis of malaria.

    PubMed

    Brince Paul, K; Kumar, Sanni; Tripathy, Suryasnata; Vanjari, Siva Rama Krishna; Singh, Vikrant; Singh, Shiv Govind

    2016-06-15

    Rapid, ultrasensitive diagnostic/triaging kits for early detection of malarial parasites are critical for prevention of malarial epidemic, especially in developing and tropical countries. Unlike traditional microscopic diagnosis, these kits rely on the detection of antigens specific to malarial parasites. One such antigen which is routinely used in these diagnostic kits is Histidine-rich protein-2; a protein synthesized and released into the blood stream by the parasite Plasmodium falciparum. In this paper, we demonstrate an ultrasensitive nanobiosensor detection platform for Histidine-rich protein-2 having a limit of detection of attogram/ml. This nanobiosensor platform comprises of Mercaptopropylphosphonic acid functionalized copper doped zinc oxide nanofibers synthesized by electrospinning technique. Ultrasensitivity of attogram/ml can be attributed to the complimentary effects of Mercaptopropylphosphonic acid and copper doping in zinc oxide. Mercaptopropylphosphonic acid enhances the functional groups required for immobilizing antibody. Copper doping in zinc oxide not only increases the conductivity of the nanofibers but also pre-concentrates the target analyte onto the Mercaptopropylphosphonic acid treated nanofiber surface due to inherent electric field generated at the copper/zinc oxide heterojunction interface. The impedimetric detection response of copper-doped zinc oxide nanofiber modified electrode shows excellent sensitivity (28.5 kΩ/(gm/ml)/cm(2)) in the detection ranges of 10 ag/ml-10 µg/ml, and a detection limit of 6 attogram/ml. In addition, the proposed biosensor is highly selective to targeted HRP2 protein with a relative standard deviation of 1.9% in the presence of various interference of nonspecific molecules. To the best of our knowledge, this biosensor shows the lowest detection limit of malarial parasites reported in the literature spanning different nanomaterials and different detection mechanisms. Since the nanobiosensor platform is

  15. Reversible Association of Nitro Compounds with p-Nitrothiophenol Modified on Ag Nanoparticles/Graphene Oxide Nanocomposites through Plasmon Mediated Photochemical Reaction.

    PubMed

    Lin, Tsung-Wu; Tasi, Ting-Ti; Chang, Po-Ling; Cheng, Hsiu-Yao

    2016-03-01

    Because localized surface plasmon resonance in nanostructures of noble metals is accompanied by interesting physical effects such as optical near-field enhancement, heat release, and the generation of hot electrons, it has been employed in a wide range of applications, including plasmon-assisted chemical reactions. Here, we use a composite of silver nanoparticles and graphene oxide (Ag@GO) as the catalytic as well as the analytic platform for plasmon-assisted chemical reactions. Through time-dependent surface-enhanced Raman scattering experiments, it is found that p-nitrothiophenol (pNTP) molecules on Ag@GO can be associated with nitro compounds such as nitrobenzene and 1-nitropropane to form azo compounds when aided by the plasmons. Furthermore, the reaction rate can be modulated by varying the wavelength and power of the excitation laser as well as the nitro compounds used. In addition, the aforementioned coupling reaction can be reversed. We demonstrate that the oxidation of azo compounds on Ag@GO using KMnO4 leads to the dissociation of the N═N double bond in the azo compounds and that the rate of bond dissociation can be accelerated significantly via laser irradiation. Furthermore, the pNTP molecules on Ag@GO can be recovered after the oxidation reaction. Finally, we demonstrate that the plasmon-assisted coupling reaction allows for the immobilization of nitro-group-containing fluorophores at specific locations on Ag@GO. PMID:26977529

  16. Direct evidence of metallic bands in a monolayer boron sheet

    NASA Astrophysics Data System (ADS)

    Feng, Baojie; Zhang, Jin; Liu, Ro-Ya; Iimori, Takushi; Lian, Chao; Li, Hui; Chen, Lan; Wu, Kehui; Meng, Sheng; Komori, Fumio; Matsuda, Iwao

    2016-07-01

    The search for metallic boron allotropes has attracted great attention in the past decades and recent theoretical works predict the existence of metallicity in monolayer boron. Here, we synthesize the β12-sheet monolayer boron on a Ag(111) surface and confirm the presence of metallic boron-derived bands using angle-resolved photoemission spectroscopy. The Fermi surface is composed of one electron pocket at the S ¯ point and a pair of hole pockets near the X ¯ point, which is supported by the first-principles calculations. The metallic boron allotrope in β12 sheet opens the way to novel physics and chemistry in material science.

  17. Pentagonal monolayer crystals of carbon, boron nitride, and silver azide

    SciTech Connect

    Yagmurcukardes, M. Senger, R. T.; Sahin, H.; Kang, J.; Torun, E.; Peeters, F. M.

    2015-09-14

    In this study, we present a theoretical investigation of structural, electronic, and mechanical properties of pentagonal monolayers of carbon (p-graphene), boron nitride (p-B{sub 2}N{sub 4} and p-B{sub 4}N{sub 2}), and silver azide (p-AgN{sub 3}) by performing state-of-the-art first principles calculations. Our total energy calculations suggest feasible formation of monolayer crystal structures composed entirely of pentagons. In addition, electronic band dispersion calculations indicate that while p-graphene and p-AgN{sub 3} are semiconductors with indirect bandgaps, p-BN structures display metallic behavior. We also investigate the mechanical properties (in-plane stiffness and the Poisson's ratio) of four different pentagonal structures under uniaxial strain. p-graphene is found to have the highest stiffness value and the corresponding Poisson's ratio is found to be negative. Similarly, p-B{sub 2}N{sub 4} and p-B{sub 4}N{sub 2} have negative Poisson's ratio values. On the other hand, the p-AgN{sub 3} has a large and positive Poisson's ratio. In dynamical stability tests based on calculated phonon spectra of these pentagonal monolayers, we find that only p-graphene and p-B{sub 2}N{sub 4} are stable, but p-AgN{sub 3} and p-B{sub 4}N{sub 2} are vulnerable against vibrational excitations.

  18. Synthesis and characterization of NaX nanozeolite using stem sweep as silica source and application of Ag-modified nanozeolite in electrocatalytic reduction of H2O2.

    PubMed

    Azizi, Seyed Naser; Ghasemi, Shahram; Kavian, Safura

    2014-12-15

    Nanozeolite is one of the three dimensional nanoporous materials consisting of extremely accessible surface area and shorter diffusion pathways. In this study, NaX nanozeolite is synthesized using the hydrothermal method from natural silica source of stem sweep ash (SSA). The synthesized nanoparticles were characterized using X-ray diffraction, scanning electronic microscopy, Brunauer-Emmett-Teller (BET) and FT-IR techniques. The synthesized nanozeolite is used incorporating Ag (I) ions for preparing modified carbon paste electrode (Ag/X-CPE) as an electrochemical sensor for the reduction of H2O2. Electrochemical results demonstrate that nanozeolite provides a promising platform for the development of electrochemical sensors in biosensing and Ag/X-CPE electrode possesses the remarkable catalytic activity toward the H2O2 reduction. Amprometric results show that this sensor could detect H2O2 in linear ranges of 20 µM to 1.76 mM and 1.76-11.76 mM with a detection limit of 9.1 µM at a signal-to-noise ratio of 3 and a response time of 2s. Furthermore, this sensor exhibited good anti-interference and selectivity. PMID:24967881

  19. TiO2-modified Ag-CuO Reactive Air Brazes for Improved Wettability on Mixed Ionic/Electronic Conductors

    SciTech Connect

    Hardy, John S.; Weil, K. Scott; Kim, Jin Yong Y.; Thomsen, Ed C.; Darsell, Jens T.

    2005-03-01

    Mixed ionic/electronic conducting perovskite oxides such as lanthanum strontium cobalt ferrite (LSCF) are strong candidates for potential use in a number of electrochemical devices, including gas separation membranes and solid oxide fuel cells (SOFC). Underlying the excitement over the these novel ceramics is the engineering challenge of effectively incorporating them into practical devices. Taking full advantage of the unique properties of advanced ceramics such as mixed conducting oxides depends in large part on being able to develop reliable joining techniques. Earlier studies have indicated that Ag-CuO reactive air braze (RAB) compositions are effective in joining to LSCF. Meanwhile, it has been found that small additions of as little as 0.5 mol% titanium oxide to Ag-CuO RAB compositions cause a dramatic increase in the wettability of RAB on many oxide ceramic surfaces. Therefore the wettabilty of Ag-CuO-TiO2 brazes on LSCF substrates will be examined and the flexural strength, microstructure, and conductivity of joints in LSCF made using Ag-CuO-TiO2 brazes will be discussed. Long-term aging effects on conductivity and microstructure will also be presented.

  20. Monolayer excitonic laser

    NASA Astrophysics Data System (ADS)

    Ye, Yu; Wong, Zi Jing; Lu, Xiufang; Ni, Xingjie; Zhu, Hanyu; Chen, Xianhui; Wang, Yuan; Zhang, Xiang

    2015-11-01

    Two-dimensional van der Waals materials have opened a new paradigm for fundamental physics exploration and device applications because of their emerging physical properties. Unlike gapless graphene, monolayer transition-metal dichalcogenides (TMDCs) are two-dimensional semiconductors that undergo an indirect-to-direct bandgap transition, creating new optical functionalities for next-generation ultra-compact photonics and optoelectronics. Although the enhancement of spontaneous emission has been reported on TMDC monolayers integrated with photonic crystals and distributed Bragg reflector microcavities, coherent light emission from a TMDC monolayer has not been demonstrated. Here, we report the realization of a two-dimensional excitonic laser by embedding monolayer WS2 in a microdisk resonator. Using a whispering gallery mode with a high quality factor and optical confinement, we observe bright excitonic lasing at visible wavelengths. This demonstration of a two-dimensional excitonic laser marks a major step towards two-dimensional on-chip optoelectronics for high-performance optical communication and computing applications.

  1. Mildly reduced graphene oxide-Ag nanoparticle hybrid films for surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Li, Xiaocheng; Tay, Beng Kang; Li, Junshuai; Tan, Dunlin; Tan, Chong Wei; Liang, Kun

    2012-04-01

    Large-area mildly reduced graphene oxide (MR-GO) monolayer films were self-assembled on SiO2/Si surfaces via an amidation reaction strategy. With the MR-GO as templates, MR-GO-Ag nanoparticle (MR-GO-Ag NP) hybrid films were synthesized by immersing the MR-GO monolayer into a silver salt solution with sodium citrate as a reducing agent under UV illumination. SEM image indicated that Ag NPs with small interparticle gap are uniformly distributed on the MR-GO monolayer. Raman spectra demonstrated that the MR-GO monolayer beneath the Ag NPs can effectively quench the fluorescence signal emitted from the Ag films and dye molecules under laser excitation, resulting in a chemical enhancement (CM). The Ag NPs with narrow gap provided numerous hot spots, which are closely related with electromagnetic mechanism (EM), and were believed to remarkably enhance the Raman signal of the molecules. Due to the co-contribution of the CM and EM effects as well as the coordination mechanism between the MR-GO and Ag NPs, the MR-GO-Ag NP hybrid films showed more excellent Raman signal enhancement performance than that of either Ag films or MR-GO monolayer alone. This will further enrich the application of surface-enhanced Raman scattering in molecule detection.

  2. Temperature dependent effects during Ag deposition on Cu(110)

    SciTech Connect

    Taylor, T.N.; Muenchausen, R.E.; Hoffbauer, M.A.; Denier van der Gon, A.W.; van der Veen, J.F.; FOM-Instituut voor Atoom-en Molecuulfysica, Amsterdam )

    1989-01-01

    The composition, structure, and morphology of ultrathin films grown by Ag deposition on Cu(110) were monitored as a function of temperature using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and medium energy ion scattering (MEIS). Aligned backscattering measurements with 150 keV He ions indicate that the Ag resides on top of the Cu and there is no significant surface compound formation. Measurements with LEED show that the Ag is initially confined to the substrate troughs. Further deposition forces the Ag out of the troughs and results in a split c(2 {times} 4) LEED pattern, which is characteristic of a distorted Ag(111) monolayer template. As verified by both AES and MEIS measurements, postmonolayer deposition of Ag on Cu(110) at 300K leads to a pronounced 3-dimensional clustering. Ion blocking analysis of the Ag clusters show that the crystallites have a (110)-like growth orientation, implying that the Ag monolayer template undergoes a rearrangement. These data are confirmed by low temperature LEED results in the absence of clusters, which indicate that Ag multilayers grow from a Ag--Cu interface where the Ag is captured in the troughs. Changes observed in the film structure and morphology are consistent with a film growth mechanism that is driven by overlayer strain response to the substrate corrugation. 16 refs., 4 figs.

  3. Self-assembly of Epitaxial Monolayers for Vacuum Wafer Bonding.

    NASA Astrophysics Data System (ADS)

    Altfeder, Igor; Huang, Biqin; Appelbaum, Ian; Walker, Barry

    2007-03-01

    Self-assembled epitaxial metal monolayers can be used for hetero-integration of mismatched semiconductors, leading to simultaneously low interfacial resistance and high optical transparency. Lattice-mismatched wafers of Si(100) and Si(111) were bonded at room temperature in situ after vacuum deposition of a single atomic layer of Ag on them. The interfacial resistance was measured to be 3.9x 10-4 ohm. cm^ 2 and the optical transmission of the interface at 2500 nm is approximately 98%. We discuss the important role of electron confinement in ultrathin Ag layers as a possible contributor to the bonding energy.

  4. Self-assembly of epitaxial monolayers for vacuum wafer bonding

    NASA Astrophysics Data System (ADS)

    Altfeder, Igor; Huang, Biqin; Appelbaum, Ian; Walker, B. C.

    2006-11-01

    Self-assembled epitaxial metal monolayers can be used for heterointegration of mismatched semiconductors, leading to simultaneously low interfacial resistance and high optical transparency. Lattice-mismatched wafers of Si(100) and Si(111) were bonded at room temperature in situ after vacuum deposition of a single atomic layer of Ag. The interfacial resistance was measured to be 3.9×10-4Ωcm2 and the optical transmission of the interface at 2500nm is approximately 98%. Electron confinement in ultrathin Ag layers as a possible contributor to the bonding energy.

  5. Polypyrrole growth on YBa{sup 2}Cu{sup 3}O{sup 7-{delta}} modified with a self-assembled monolayer of N-(3-aminopropyl)pyrrole: Hardwiring the `electroactive hot spots` on a superconductor electrode

    SciTech Connect

    Lo, R.K.; Ritchie, J.E.; Zhou, J.P.; Zhao, J.; McDevitt, J.T.; Xu, F.; Mirkin, C.A.

    1996-11-13

    This paper describes a new method for controlling the deposition of conductive polymer systems onto high-T{sup c} superconductor surfaces. This method relies on the spontaneous adsorption of the pyrrole-terminated alkylamine reagent 1 onto YBa{sup 2}Cu{sup 3}O{sup 7-{delta}} prior to polymerization. Large changes in the polymer growth rates and vast improvements in the polymer morphology are obtained with the use of such adsorbed monolayers. As described, the adsorbed monolayer structures promote radically different polymer deposition properties from those observed previously for the more traditional electrode materials (i.e., Au, Pt, etc.). These unusual observations provided valuable insight into the electrochemical characteristics and local surface electroactivity/conductivity properties of oriented cuprate superconductor films. 16 refs., 2 figs.

  6. Plasmon enhanced photoelectrochemical sensing of mercury (II) ions in human serum based on Au@Ag nanorods modified TiO2 nanosheets film.

    PubMed

    Zhang, Yong; Shoaib, Anwer; Li, Jiaojiao; Ji, Muwei; Liu, Jiajia; Xu, Meng; Tong, Bin; Zhang, Jiatao; Wei, Qin

    2016-05-15

    Taking advantages of the monodisperse TiO2 nanosheets (NSs) with high active crystal face exposure and the tunable localized surface plasmon resonance (LSPR) properties of Au@Ag nanorods (NRs), this study demonstrated that TiO2 NSs film with trace amount of Au@Ag NRs modification possess a strong enhancement of photocurrent response, which was remarkably inhibited with the addition of mercury (II) ions (Hg(2+)). Based on the selective decrease of photocurrent with the addition of Hg(2+), a simple photoelectrochemical (PEC) sensor has been assembled. The PEC sensor exhibits wide linear range (0.01-10nM), low detection limit (2.5pM), satisfying selectivity, reproducibility and acceptable stability for Hg(2+) detection. The feasibility of this method for practical application in human serum has been evaluated and the result was satisfactory. This PEC sensing method would provide a potential application for Hg(2+) detection in clinical diagnosis. PMID:26785311

  7. A light-modified ferroelectric resistive switching behavior in Ag/BaMoO{sub 4}/FTO device at ambient temperature

    SciTech Connect

    Zhao, W.X.; Sun, B.; Liu, Y.H.; Wei, L.J.; Li, H.W.; Chen, P.

    2014-12-15

    BaMoO{sub 4} powder was prepared by a facile hydrothermal synthesis. And the BaMoO{sub 4}/FTO device was fabricated by a spin-coated method, in which the thickness of BaMoO{sub 4} layer is about 20 µm. The bipolar resistive switching effect has been observed in Ag/BaMoO{sub 4}/FTO device. Moreover, the resistive switching effect of the device is greatly improved by white light irradiation. The resistive switching behavior is explained by the polarization reversal that changes the charge distribution and modulates the Schottky barriers. - Graphical abstract: We fabricate a resistive switching device based on Ag/BaMoO{sub 4}/FTO, the device shows superior white-light controlled bipolar resistive switching memristive characteristics. - Highlights: • The BaMoO{sub 4} nanosquares powder was prepared by a hydrothermal synthesis. • The resistive switching of the Ag/BaMoO{sub 4}/FTO device was observed for the first time. • It is shown that the resistive switching is greatly improved under the white light irradiation. • The mechanism of resistive switching is attributed to the ferroelectric polarization reversal.

  8. Chemoresponsive Monolayer Transistors

    SciTech Connect

    Guo,X.; Myers, M.; Xiao, S.; Lefenfeld, M.; Steiner, R.; Tulevski, G.; Tang, J.; Baumert, J.; Leibfarth, F.; et al.

    2006-01-01

    This work details a method to make efficacious field-effect transistors from monolayers of polycyclic aromatic hydrocarbons that are able to sense and respond to their chemical environment. The molecules used in this study are functionalized so that they assemble laterally into columns and attach themselves to the silicon oxide surface of a silicon wafer. To measure the electrical properties of these monolayers, we use ultrasmall point contacts that are separated by only a few nanometers as the source and drain electrodes. These contacts are formed through an oxidative cutting of an individual metallic single-walled carbon nanotube that is held between macroscopic metal leads. The molecules assemble in the gap and form transistors with large current modulation and high gate efficiency. Because these devices are formed from an individual stack of molecules, their electrical properties change significantly when exposed to electron-deficient molecules such as tetracyanoquinodimethane (TCNQ), forming the basis for new types of environmental and molecular sensors.

  9. Pt monolayer coating on complex network substrate with high catalytic activity for the hydrogen evolution reaction

    PubMed Central

    Li, Man; Ma, Qiang; Zi, Wei; Liu, Xiaojing; Zhu, Xuejie; Liu, Shengzhong (Frank)

    2015-01-01

    A deposition process has been developed to fabricate a complete-monolayer Pt coating on a large-surface-area three-dimensional (3D) Ni foam substrate using a buffer layer (Ag or Au) strategy. The quartz crystal microbalance, current density analysis, cyclic voltammetry integration, and X-ray photoelectron spectroscopy results show that the monolayer deposition process accomplishes full coverage on the substrate and the deposition can be controlled to a single atomic layer thickness. To our knowledge, this is the first report on a complete-monolayer Pt coating on a 3D bulk substrate with complex fine structures; all prior literature reported on submonolayer or incomplete-monolayer coating. A thin underlayer of Ag or Au is found to be necessary to cover a very reactive Ni substrate to ensure complete-monolayer Pt coverage; otherwise, only an incomplete monolayer is formed. Moreover, the Pt monolayer is found to work as well as a thick Pt film for catalytic reactions. This development may pave a way to fabricating a high-activity Pt catalyst with minimal Pt usage. PMID:26601247

  10. Chemoresponsive monolayer transistors

    PubMed Central

    Guo, Xuefeng; Myers, Matthew; Xiao, Shengxiong; Lefenfeld, Michael; Steiner, Rachel; Tulevski, George S.; Tang, Jinyao; Baumert, Julian; Leibfarth, Frank; Yardley, James T.; Steigerwald, Michael L.; Kim, Philip; Nuckolls, Colin

    2006-01-01

    This work details a method to make efficacious field-effect transistors from monolayers of polycyclic aromatic hydrocarbons that are able to sense and respond to their chemical environment. The molecules used in this study are functionalized so that they assemble laterally into columns and attach themselves to the silicon oxide surface of a silicon wafer. To measure the electrical properties of these monolayers, we use ultrasmall point contacts that are separated by only a few nanometers as the source and drain electrodes. These contacts are formed through an oxidative cutting of an individual metallic single-walled carbon nanotube that is held between macroscopic metal leads. The molecules assemble in the gap and form transistors with large current modulation and high gate efficiency. Because these devices are formed from an individual stack of molecules, their electrical properties change significantly when exposed to electron-deficient molecules such as tetracyanoquinodimethane (TCNQ), forming the basis for new types of environmental and molecular sensors. PMID:16855049

  11. Comparative adherence of granulocytes to endothelial monolayers and nylon fiber.

    PubMed

    MacGregor, R R; Macarak, E J; Kefalides, N A

    1978-03-01

    Adherence of granulocytes to tissue culture monolayers of endothelium averaged 26.2 +/- 1.3% SEM, which was similar to their adherence on 50-mg nylon fiber columns (27.7 +/- 3.6%). In contrast, adherence to epithelial cells, fibroblasts, kidney cells, and plastic Petri dishes without monolayers was only 12.4, 9.9, 11.1, and 4.3%, respectively. Cyclic nucleotides and adherence-modifying plasma factors induced changes of adherence to endothelium similar to those in nylon fiber columns. Adherence of granulocytes in whole blood was the same as for purified granulocytes in Hank's balanced salt solution. Exposure of endothelial monolayers to 0.18% trypsin for 10 min reduced subsequent granulocyte adherence to 25.2% of control values. Incubation of trypsin-treated monolayers with nutrient medium for 4 h did not improve adherence, but values returned to normal or above by 24 h, with or without serum proteins present in the nutrient medium. The similarity of granulocyte adherence to nylon fiber and to endothelial monolayers in vitro suggests that results with the nylon fiber assay reflect in vivo granulocyte-endothelium interaction. Furthermore, the endothelial monolayer offers a new model for studying this cell-cell relationship in vitro. PMID:641148

  12. Acceleration of polarized proton at the AGS

    SciTech Connect

    Lee, Y Y

    1980-01-01

    The unexpected importance of high energy spin effects and the success of the ZGS in correcting many intrinsic and imperfection depolarizing resonances led us to attempt to accelerate polarized protons in the AGS. A collaborative effort is underway by the groups in Argonne, Michigan, Rice, Yale and Brookhaven to improve and modify the AGS to accelerate polarized protons. With the appropriate funding the first polarized proton acceleration at the AGS should be possible by 1983.

  13. Bright white-light emission from Ag/SiO2/CdS-ZnS core/shell/shell plasmon couplers.

    PubMed

    Liao, Chen; Tang, Luping; Gao, Xiaoqin; Xu, Ruilin; Zhang, Huichao; Yu, Yongya; Lu, Changgui; Cui, Yiping; Zhang, Jiayu

    2015-12-28

    Well-defined plasmon couplers (PCs) that comprise a Ag core overcoated with a SiO(2) shell with controlled thickness, followed by a monolayer of CdS-ZnS core-shell quantum dots (QDs) were synthesized to modify the emission from trap-rich CdS-ZnS QDs by adjusting the distance between the QDs and Ag nanoparticles (NPs). When the thickness of the SiO(2) shell was 10 nm, because the shell could effectively suppress the non-radiative energy transfer from the semiconductor QDs to the metal NPs and the localized surface plasmon resonance (LSPR) of the Ag NPs spectrally matched the emission peak of the CdS-ZnS QDs to bring about strong plasmon coupling, optimum enhancements of the surface state emission (SSE) (17 times) and band-edge emission (BEE) (4 times) were simultaneously realized and the SSE to BEE intensity ratio was increased to 55%. As a result, a bright white-light source with 1931 Commission Internationale d'Eclairage (CIE) chromaticity coordinates of (0.32, 0.34) was realized by the superposition of the two emissions. The experimental results from Ag/SiO(2)/CdSe-ZnS and the Ag/SiO(2)/CdS:Mn-ZnS core/shell/shell PCs indicated that suppressing the non-radiative decay rate (k(nr)) was the underlying mechanism for plasmon coupling fluorescence enhancement. PMID:26592756

  14. Bright white-light emission from Ag/SiO2/CdS-ZnS core/shell/shell plasmon couplers

    NASA Astrophysics Data System (ADS)

    Liao, Chen; Tang, Luping; Gao, Xiaoqin; Xu, Ruilin; Zhang, Huichao; Yu, Yongya; Lu, Changgui; Cui, Yiping; Zhang, Jiayu

    2015-12-01

    Well-defined plasmon couplers (PCs) that comprise a Ag core overcoated with a SiO2 shell with controlled thickness, followed by a monolayer of CdS-ZnS core-shell quantum dots (QDs) were synthesized to modify the emission from trap-rich CdS-ZnS QDs by adjusting the distance between the QDs and Ag nanoparticles (NPs). When the thickness of the SiO2 shell was 10 nm, because the shell could effectively suppress the non-radiative energy transfer from the semiconductor QDs to the metal NPs and the localized surface plasmon resonance (LSPR) of the Ag NPs spectrally matched the emission peak of the CdS-ZnS QDs to bring about strong plasmon coupling, optimum enhancements of the surface state emission (SSE) (17 times) and band-edge emission (BEE) (4 times) were simultaneously realized and the SSE to BEE intensity ratio was increased to 55%. As a result, a bright white-light source with 1931 Commission Internationale d'Eclairage (CIE) chromaticity coordinates of (0.32, 0.34) was realized by the superposition of the two emissions. The experimental results from Ag/SiO2/CdSe-ZnS and the Ag/SiO2/CdS:Mn-ZnS core/shell/shell PCs indicated that suppressing the non-radiative decay rate (knr) was the underlying mechanism for plasmon coupling fluorescence enhancement.

  15. Charge transfer and formation of conducting C60 monolayers at C60/noble-metal interfaces

    NASA Astrophysics Data System (ADS)

    Nouchi, Ryo; Kanno, Ikuo

    2005-05-01

    The resistance of a conducting C60 monolayer formed on a polycrystalline Ag film was found to be 0.7±0.1kΩ by in situ resistance measurements. By another series of in situ resistance measurements, the surface scattering cross sections, whose magnitude represents the relative amount of transferred charge, were evaluated as 100Å2 for C60/Au, and 150Å2 for C60/Cu and C60/Ag systems. However, comparison with previous results obtained for monolayers formed on Au and Cu films showed that the resistances of conducting C60 monolayers do not show a simple dependence on the transferred charge. Atomic force microscopy measurements revealed that the grain size of the underlying noble metals also plays an important role.

  16. An epitaxial organic film. The self-assembled monolayer of docosanoic acid on silver(111)

    SciTech Connect

    Samant, M.G.; Brown, C.A.; Gordon, J.G. II )

    1993-04-01

    Docosanoic acid in solution spontaneously forms an ordered self-assembled (SA) monolayer on the silver(111) surface, exposing methyl groups to the atmosphere. The contact wetting angles for water and hexadecane are 116[degrees] and 55[degrees], respectively. Surface X-ray diffraction shows that the in-plane structure of the SA monolayer is p(2 [times] 2). The SA monolayer is present in domains of about 215 A with a mosaic spread of 0.85[degrees]C. The chains within the monolayer are titled at 27 [+-] 1[degrees] from the surface normal toward the near neighbors. We conclude that the carboxylate group is bound nearly normal to specific sites on the Ag surface and that this determines the interchain spacing. The tilt angle is a consequence of this interchain spacing. 17 refs., 6 figs., 1 tab.

  17. Self-assembled monolayers of pyridylthio-functionalized carbon nanotubes used as a support to immobilize cytochrome c

    PubMed Central

    2013-01-01

    Self-assembled monolayers (SAMs) of pyridylthio-functionalized multiwalled carbon nanotubes (pythio-MWNTs) have been constructed on the gold substrate surface, which were used as a support to immobilize cytochrome c (Cyt c). The assembly processes of the SAMs and adsorption of Cyt c were monitored by using quartz crystal microbalance (QCM). Based on the frequency change of the QCM resonator, the surface coverage for the SAMs of pythio-MWNTs was estimated to be about 5.2 μg/cm2, and that of the Cyt c adsorbed was about 0.29 μg/cm2. For the gold electrode modified by the SAMs of pythio-MWNTs-Cyt c, a quasi-reversible redox wave was recorded with the cathodic and anodic potentials at about −0.55 and −0.28 V vs Ag/AgCl, respectively. Compositions and morphologies of the SAMs before and after immobilization of Cyt c were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. PMID:23391460

  18. General synthesis of noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets and the enhanced catalytic activity of Pd-MoS2 for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Yuwen, Lihui; Xu, Fei; Xue, Bing; Luo, Zhimin; Zhang, Qi; Bao, Biqing; Su, Shao; Weng, Lixing; Huang, Wei; Wang, Lianhui

    2014-05-01

    A general and facile method for water-dispersed noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets (NM-MoS2 NSs) has been developed. By using sodium carboxymethyl cellulose as a stabilizer, well-dispersed NM-MoS2 NSs with homogeneously deposited noble metal nanocrystals (NM NCs) can be synthesized in aqueous solutions. Due to the transition from the semiconducting 2H phase to the metallic 1T phase, the chemically exfoliated MoS2 (ce-MoS2) NSs have improved electrochemical activity. The partially metallic nature of the ce-MoS2 NSs and the catalytic activity of the NM NCs synergistically make NM-MoS2 NSs a potential electrochemical catalyst. For the first time, Pd-MoS2 NSs were used as an electrocatalyst for methanol oxidation in alkaline media. The results showed that Pd-MoS2 NSs have enhanced catalytic activity with 2.8-fold anodic peak current mass density compared to a commercial Pd/C catalyst, suggesting potential for application in direct methanol fuel cells (DMFCs).A general and facile method for water-dispersed noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets (NM-MoS2 NSs) has been developed. By using sodium carboxymethyl cellulose as a stabilizer, well-dispersed NM-MoS2 NSs with homogeneously deposited noble metal nanocrystals (NM NCs) can be synthesized in aqueous solutions. Due to the transition from the semiconducting 2H phase to the metallic 1T phase, the chemically exfoliated MoS2 (ce-MoS2) NSs have improved electrochemical activity. The partially metallic nature of the ce-MoS2 NSs and the catalytic activity of the NM NCs synergistically make NM-MoS2 NSs a potential electrochemical catalyst. For the first time, Pd-MoS2 NSs were used as an electrocatalyst for methanol oxidation in alkaline media. The results showed that Pd-MoS2 NSs have enhanced catalytic activity with 2.8-fold anodic peak current mass density compared to a commercial Pd/C catalyst, suggesting potential for application in direct methanol fuel cells (DMFCs

  19. Scanning tunneling microscopy studies of mixed self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Raigoza, Annette Fernandez

    This thesis examines the formation of multicomponent self-assembled mono-layers (SAMs) on the Au(111) surface using scanning tunneling microscopy. Two methods, sequential adsorption and coadsorption, are used to create these mixed SAMs. In the sequential adsorption experiments, a clean Au(111)-on-mica sub-strate is exposed to the first molecular species and then this adsorbate-covered sample is exposed to the second molecular species. Alternately, in the coadsorption experiments, a gold surface is exposed to both adsorbates simultaneously. Exposing a coronene- or dithiocarbamate-covered surface to excess thiol in the vapor phase results in a drastic restructuring of the initial surface. This is primarily driven by the kinetics of the octanethiol monolayer formation process, but the extent to which this happens is dependent on the molecule-molecule and molecule-surface interactions of the adsorbate due to the initial coverage and order of the monolayer. An octanethiolate monolayer is also substantially modified when immersed in a solution containing dithiocarbamate (DTC). Defects in the octanethiol monolayer are prime sites for molecular exchange. A surplus of DTC in the solution drives substitution that can lead to the complete removal of thiol from the surface. When a Au(111) surface is exposed to solutions containing both octanethiol and dithiocarbamate (DTC), both molecular species compete for available ad- sorption sites. At equal octanethiol-to-DTC ratios, molecular exchange hinders octanethiol monolayer formation. Higher octanethiol concentration in solution results in the incorporation of thiol into the resulting monolayer, with a strong dependence on the chain length of the DTC molecules.

  20. Phenomenological Modeling for Langmuir Monolayers

    NASA Astrophysics Data System (ADS)

    Baptiste, Dimitri; Kelly, David; Safford, Twymun; Prayaga, Chandra; Varney, Christopher N.; Wade, Aaron

    Experimentally, Langmuir monolayers have applications in molecular optical, electronic, and sensor devices. Traditionally, Langmuir monolayers are described by a rigid rod model where the rods interact via a Leonard-Jones potential. Here, we propose effective phenomenological models and utilize Monte Carlo simulations to analyze the phase behavior and compare with experimental isotherms. Research reported in this abstract was supported by UWF NIH MARC U-STAR 1T34GM110517-01.

  1. Annealing effect of ultrathin Ag films on Ni /Pt(111)

    NASA Astrophysics Data System (ADS)

    Su, C. W.; Yo, H. Y.; Chen, Y. J.; Shern, C. S.

    2005-06-01

    The epitaxial growth and alloy formation of Ag-capped layer on Ni /Pt(111) surface were investigated using Auger electron spectroscopy, ultraviolet photoelectron spectroscopy, and low-energy electron diffraction. The growth of Ag on one ML Ni /Pt(111) transforms from layer-by-layer mode into three-dimensional island mode after the growth of one atomic monolayer of Ag. The starting temperature for the alloy formation of Ni-Pt is dependent of the thickness of Ni films. The interface compositions after the high-temperature annealing were studied with the depth-profile analysis of Ar ion sputtering.

  2. AGS II

    SciTech Connect

    Palmer, R.B.

    1984-01-01

    Interest in rare K decays, neutrino oscillations and other fields have generated an increasing demand for running, and improved intensity and duty cycle, at the AGS. Current projects include acceleration of polarized protons and light ions (up to mass 32). Future plans are for a booster to increase intensity and allow heavy ions (up to mass 200), and a stretcher to give 100% duty cycle. A later upgrade could yield an average current of 32 ..mu.. amps. 6 figures, 2 tables.

  3. Phase Transitions in Dipalmitoylphosphatidylcholine Monolayers.

    PubMed

    Zuo, Yi Y; Chen, Rimei; Wang, Xianju; Yang, Jinlong; Policova, Zdenka; Neumann, A Wilhelm

    2016-08-23

    A self-assembled phospholipid monolayer at an air-water interface is a well-defined model system for studying surface thermodynamics, membrane biophysics, thin-film materials, and colloidal soft matter. Here we report a study of two-dimensional phase transitions in the dipalmitoylphosphatidylcholine (DPPC) monolayer at the air-water interface using a newly developed methodology called constrained drop surfactometry (CDS). CDS is superior to the classical Langmuir balance in its capacity for rigorous temperature control and leak-proof environments, thus making it an ideal alternative to the Langmuir balance for studying lipid polymorphism. In addition, we have developed a novel Langmuir-Blodgett (LB) transfer technique that allows the direct transfer of lipid monolayers from the droplet surface under well-controlled conditions. This LB transfer technique permits the direct visualization of phase coexistence in the DPPC monolayer. With these technological advances, we found that the two-dimensional phase behavior of the DPPC monolayer is analogous to the three-dimensional phase transition of a pure substance. This study has implications in the fundamental understanding of surface thermodynamics as well as applications such as self-assembled monolayers and pulmonary surfactant biophysics. PMID:27479299

  4. Structure and Function Evolution of Thiolate Monolayers on Gold

    SciTech Connect

    Grant Alvin Edwards

    2006-05-01

    The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (inbred reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

  5. Polymerization and electrochemical blocking of self-assembled alkylthiol monolayers

    SciTech Connect

    Peanasky, J.S.; Willicut, R.J.; Caston, S.L.

    1996-10-01

    Numerous advantages exist for the use of electroactive alkylthiol self-assembled monolayer modified gold electrodes over other monolayer/substrate systems for use as sensors or biosensors. Among these advantages are a wide electrical potential window, large variety of functionality, extensive order within the monolayer, and a vast amount of literature presently describing this system. One weakness is the facile gold-thiolate bond that results in desorption or displacement of the immobilized species from the surface. This is especially true when the {open_quotes}devices{close_quotes} are exposed to organic solutions. This study discusses the usefulness of photopolymerizing unsaturated functionalities located at internal or external positions on the alkyl chain to enhance immobilization of the electroactive species. Discussion focuses on electrochemical blocking by the monolayer before and after polymerization as determined using cyclic voltammetry. Structural changes within the monolayer, as determined by Fourier transform infrared spectroscopy, are related to changes seen electrochemically. Other parameters such as the type of unsaturated functionality, the alkyl chain length, and the exposure of the devices to oxygen are discussed.

  6. Synthesis, Assembly, and Characterization of Monolayer Protected Gold Nanoparticle Films for Protein Monolayer Electrochemistry

    PubMed Central

    Doan, Tran T.; Freeman, Michael H.; Schmidt, Adrienne R.; Nguyen, Natalie D. T.; Leopold, Michael C.

    2011-01-01

    Colloidal gold nanoparticles protected with alkanethiolate ligands called monolayer protected gold clusters (MPCs) are synthesized and subsequently incorporated into film assemblies that serve as adsorption platforms for protein monolayer electrochemistry (PME). PME is utilized as the model system for studying electrochemical properties of redox proteins by confining them to an adsorption platform at a modified electrode, which also serves as a redox partner for electron transfer (ET) reactions. Studies have shown that gold nanoparticle film assemblies of this nature provide for a more homogeneous protein adsorption environment and promote ET without distance dependence compared to the more traditional systems modified with alkanethiol self-assembled monolayers (SAM).1-3 In this paper, MPCs functionalized with hexanethiolate ligands are synthesized using a modified Brust reaction4 and characterized with ultraviolet visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and proton (1H) nuclear magnetic resonance (NMR). MPC films are assembled on SAM modified gold electrode interfaces by using a "dip cycle" method of alternating MPC layers and dithiol linking molecules. Film growth at gold electrode is tracked electrochemically by measuring changes to the double layer charging current of the system. Analogous films assembled on silane modified glass slides allow for optical monitoring of film growth and cross-sectional TEM analysis provides an estimated film thickness. During film assembly, manipulation of the MPC ligand protection as well as the interparticle linkage mechanism allow for networked films, that are readily adaptable, to interface with redox protein having different adsorption mechanism. For example, Pseudomonas aeruginosa azurin (AZ) can be adsorbed hydrophobically to dithiol-linked films of hexanethiolate MPCs and cytochrome c (cyt c) can be immobilized electrostatically at a carboxylic acid modified MPC interfacial layer. In this

  7. Physicochemical properties of the anion-modified surfaces of silver nanostructures

    NASA Astrophysics Data System (ADS)

    Sibbald, Morgan Scot

    Nano-sized structures of silver were prepared, characterized, and then chemically-modified with the adsorption of molecules and ions on the metal surface. Nanostructures prepared as aqueous colloids were found to have highly regular polyhedral shapes by transmission electron microscopy. Electron diffraction techniques indicated that isolated Ag structures were composed of a single crystalline phase or were multiply-twinned, both having a lattice constant of 4.05 A. Adsorption of iodide and bromide ions on the silver surface was monitored by surface-enhanced Raman spectroscopy. A characteristic halide-metal stretching vibration was observed at 112 cmsp{-1} for Isp- and at 156 cmsp{-1} for Brsp-. Extinction spectra of the halide-modified Ag colloids showed a frequency-shift and damping of the surface plasmon resonance band assigned to particle aggregation. This was confirmed using two dimensional arrays of particles in which the surface-modifier caused only damping with no change in the plasmon frequency. Addition of cytochrome c to the halide-modified colloid resulted in the reduction of the protein. Competitive binding of Isp- ions between cytochrome c and the metal necessitated the use of a redox active indophenol dye for quantitative measurements of reduction efficiencies. Two distinct processes were identified: reduction at iodide coverages up to one monolayer on the Ag surface and reduction in the presence of excess Isp- in solution. The latter was characterized by Isp- reacting with silver in a 1:1 stoichiometry to form molecular AgI. The former, which resulted in only 5% reduction of the electron acceptors, was a consequence of partial charge transfer from Isp- to the metal, producing a unique iodide-Ag surface complex different than molecular AgI. Raman spectra of the complex excited at 413 nm and at temperatures less than 150 K contained a strong vibrational progression with a fundamental band at 123 cmsp{-1} and up to six overtones. An excitation profile

  8. Surfactant role of Ag atoms in the growth of Si layers on Si(111)√3×√3-Ag substrates

    SciTech Connect

    Yamagami, Tsuyoshi; Sone, Junki; Nakatsuji, Kan; Hirayama, Hiroyuki

    2014-10-13

    The growth of Si layers on Si(111)√3×√3-Ag substrates was studied for coverages of up to a few mono-layers. Atomically flat islands were observed to nucleate in the growth at 570 K. The top surfaces of the islands were covered in Ag atoms and exhibited a √3×√3 reconstruction with the same surface state dispersions as Si(111)√3×√3-Ag substrates. These results indicate that the Ag atoms on the substrate always hop up to the top of the Si layers.

  9. Monolayer coated aerogels and method of making

    SciTech Connect

    Zemanian, Thomas Samuel; Fryxell, Glen; Ustyugov, Oleksiy A.

    2006-03-28

    Aerogels having a monolayer coating are described. The aerogel and a monolayer forming precursor are provided in a supercritical fluid, whereupon the aerogel and the monolayer forming precursor are reacted in said supercritical fluid to form a covalent bond between the aerogel and the monolayer forming precursor. Suitable aerogels are ceramic oxides such as silica, alumina, aluminosilicate, and combinations thereof. Suitable monolayer forming precursors include alkyl silanes, chlorosilanes, boranes, chloroboranes, germanes, and combinations thereof. The method may also include providing a surface preparation agent such as water, or hydroetching an aerogel to enhance the coating of the monolayer.

  10. Improving the Dielectric Properties of Ethylene-Glycol Alkanethiol Self-Assembled Monolayers

    PubMed Central

    2014-01-01

    Self-assembled monolayers (SAMs) can be formed at the interface between solids and fluids, and are often used to modify the surface properties of the solid. One of the most widely employed SAM systems is exploiting thiol-gold chemistry, which, together with alkane-chain-based molecules, provides a reliable way of SAM formation to modify the surface properties of electrodes. Oligo ethylene-glycol (OEG) terminated alkanethiol monolayers have shown excellent antifouling properties and have been used extensively for the coating of biosensor electrodes to minimize nonspecific binding. Here, we report the investigation of the dielectric properties of COOH-capped OEG monolayers and demonstrate a strategy to improve the dielectric properties significantly by mixing the OEG SAM with small concentrations of 11-mercaptoundecanol (MUD). The monolayer properties and composition were characterized by means of impedance spectroscopy, water contact angle, ellipsometry and X-ray photoelectron spectroscopy. An equivalent circuit model is proposed to interpret the EIS data and to determine the conductivity of the monolayer. We find that for increasing MUD concentrations up to about 5% the resistivity of the SAM steadily increases, which together with a considerable decrease of the phase of the impedance, demonstrates significantly improved dielectric properties of the monolayer. Such monolayers will find widespread use in applications which depend critically on good dielectric properties such as capacitive biosensor. PMID:24447311

  11. Monolayer-induced band shifts at Si(100) and Si(111) surfaces

    SciTech Connect

    Mäkinen, A. J. Kim, Chul-Soo; Kushto, G. P.

    2014-01-27

    We report our study of the interfacial electronic structure of Si(100) and Si(111) surfaces that have been chemically modified with various organic monolayers, including octadecene and two para-substituted benzene derivatives. X-ray photoelectron spectroscopy reveals an upward band shift, associated with the assembly of these organic monolayers on the Si substrates, that does not correlate with either the dipole moment or the electron withdrawing/donating character of the molecular moieties. This suggests that the nature and quality of the self-assembled monolayer and the intrinsic electronic structure of the semiconductor material define the interfacial electronic structure of the functionalized Si(100) and Si(111) surfaces.

  12. Thermodynamic characterisation of Dppc/Polylysine derivatives mixed monolayers

    NASA Astrophysics Data System (ADS)

    Remenyí, J.; Reig, F.; Sospedra, P.; Ortiz, A.; Hudecz, F.

    2004-12-01

    Mixed monolayer of DPPC and a daunomycin-polylysine conjugate, based on a (poly[Lys-(DL-Alam-Glui)] (EAK) core with daunomycin molecules attached through the acid labile cis-aconytil moiety, were studied and thermodynamic parameters associated to this interaction calculated. The same experiments were carried out in parallel with plain polymer and the results obtained indicate that the presence of Daunomycin attached to the lateral chains of polymer backbone modifies the overall surface characteristics of these derivatives.

  13. Aminopropyltrimethoxysilane- and aminopropyltrimethoxysilane-silver-modified montmorillonite for the removal of nitrate ions.

    PubMed

    Gatti, Marcela N; Fernández, Laura G; Sánchez, María P; Parolo, M Eugenia

    2016-10-01

    A natural clay (Mn) modified with γ-aminopropyltrimethoxysilane (Mn-S) and silver (Mn-S-Ag) were evaluated as a potential adsorption media for nitrate removal from water. These materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, zeta-potential, thermogravimetric analysis, scanning electron microscopy and elemental analyses. First, the adsorption capacity of the Mn-S clay for Ag(+) was studied. The cation adsorption capacity was almost three times greater for Mn-S than for Mn because a metal-amino group complex is favored. Second, the nitrate adsorption on Mn-S and Mn-S-Ag was studied as a function of contact time, pH, temperature and adsorbent dosage using batch techniques. In the absence of Ag(+), [Formula: see text] adsorption was high at low pH and the amount of adsorbed nitrate decreased as the pH increased. For the Mn-S, the following monolayer adsorption capacities were obtained: Qmax = 0.80, 0.72 and 0.68 mmol [Formula: see text]/g at pH 3, 5 and 7, respectively, whereas for the Mn-S-Ag the values obtained were: Qmax = 0.77, 0.74 and 0.42 mmol [Formula: see text]/g at pH 3, 5 and 7, respectively. From the results obtained, [Formula: see text] adsorption occurs over [Formula: see text] surface groups without involving the Ag(+) cation in the adsorption process. PMID:26930358

  14. Characterization of heterojunctions via x-ray and uv photoemission spectroscopy: energy level implications for single and mixed monolayer SAMs, cadmium selenide nanoparticle films, and organic semiconductor depositions

    NASA Astrophysics Data System (ADS)

    Graham, Amy L.

    This work has centered on the interface dipoles arising at heterojunctions between metals, semiconductor nanoparticles, self-assembled monolayers, and organic semiconductor materials. Alkanethiol self-assembled monolayers, CdSe nanocrystals, and the organic semiconductors zinc phthalocyanine (ZnPc) and Buckminster fullerene (C60) were the basis of these investigations. UV photoemission spectroscopy has proven to be an invaluable tool to observe the vacuum level shifts for these analyses while using XPS to corroborate surface structure. With a full evaluation of these surfaces, the shifts in the vacuum level, valence ionizations, and core ionizations, the impact of these interfaces, as well as their influence on the subsequent deposition of organic semiconductor layers is established. Alkanethiols possessing varying dipole moments were examined on gold and silver substrates. The viability of these alkanethiols was demonstrated to predictively adjust the work function of these metals as a function of their intrinsic dipole moments projected to surface normal, and established differences between Ag---S and Au---S bonds. The capability of the SAMs to modify the work function of gold provided an opportunity for mixed monolayers of the alkanethiols to produce a precise range of work functions by minimal adjustments of solution concentration, which were examined with a simple point dipole model. Photoemission spectroscopy offers a thorough analysis of CdSe nanoparticle films. Despite a plethora of research on these nanocrystals, there still is controversy on the magnitude of the shift in the valence band with diameter. In our research we found the majority of the valence band shift could be attributed to the interface dipole, ignored previously. Meanwhile, the valence band tethered films was obscured by the sulfur of the thiol tether. Finally, organic semiconductor layers deposited on SAMs on gold exhibited various interface dipole effects at these heterojunctions. Charge

  15. Influence of self-assembled monolayer surface chemistry on Candida antarctica lipase B adsorption and specific activity

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Immobilization of Candida antarctica B lipase was examined on gold surfaces modified with either methyl- or hydroxyl-terminated self-assembled alkylthiol monolayers (SAMs), representing hydrophobic and hydrophilic surfaces, respectively. Lipase adsorption was monitored gravimetrically using a quart...

  16. Electromelting of Confined Monolayer Ice

    NASA Astrophysics Data System (ADS)

    Qiu, Hu; Guo, Wanlin

    2013-05-01

    In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under a perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to the field-induced disruption of the water-wall interaction induced well-ordered network of the hydrogen bond. This electromelting process should add an important new ingredient to the physics of water.

  17. Electromelting of confined monolayer ice.

    PubMed

    Qiu, Hu; Guo, Wanlin

    2013-05-10

    In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under a perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to the field-induced disruption of the water-wall interaction induced well-ordered network of the hydrogen bond. This electromelting process should add an important new ingredient to the physics of water. PMID:23705718

  18. Electronic and geometric structure of the PTCDA/Ag(110) interface probed by angle-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Wießner, M.; Hauschild, D.; Schöll, A.; Reinert, F.; Feyer, V.; Winkler, K.; Krömker, B.

    2012-07-01

    The properties of molecular films are determined by the geometric structure of the first layers near the interface. These are in contact with the substrate and feel the effect of the interfacial bonding, which particularly, for metal substrates, can be substantial. For the model system 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(110), the geometric structure of the first monolayer can be modified by preparation parameters. This leads to significant differences in the electronic structure of the first layer. Here, we show that, by combining angle-resolved photoelectron spectroscopy with low-energy electron diffraction, we cannot only determine the electronic structure of the interfacial layer and the unit cell of the adsorbate superstructure, but also the arrangement of the molecules in the unit cell. Moreover, in bilayer films, we can distinguish the first from the second layer and, thus, study the formation of the second layer and its influence on the buried interface.

  19. First-principles study of the geometry of Ag nanowires growing on a self-assembled Bi nanoline

    NASA Astrophysics Data System (ADS)

    Koga, H.; Ohno, T.

    2007-09-01

    Epitaxial Ag nanowires on a self-assembled Bi nanoline on the Si(001) surface are examined for their geometry and energetic stability at the level of the generalized-gradient approximation. The orientations examined are Ag(001)[100], Ag(110)[100], Ag(111)[110], and Ag(001)[110], where the indices refer to the plane and the direction parallel to the Si(001) surface and the Bi nanoline, respectively. The wires are found to have mostly bulklike structure, except that Ag(001) monolayers undergo extensive reconstruction. The calculated electronic band structure indicates that the Ag wires are metallic wires. Particularly stable among the wires are the Ag(111) wires, having a coincident site lattice interface with the Bi nanoline. The energetic stability generally improves with thickness, indicating that Ag grows through three-dimensional nucleation on the Bi nanoline.

  20. First-principles study of the contractive reconstruction of gold and silver monolayers on gold, silver and aluminum

    SciTech Connect

    Takeuchi, Noboru.

    1990-11-16

    Using first-principles calculations in conjunction with modeling techniques, the author has investigated the structures of Au and Ag monolayers on a number of metal surfaces. Au(100) has a c(26 {times} 68) surface unit cell and the reconstruction has been interpreted as the top layer transforming to a contracted hexagonal-close-packed layer, superimposed on the square lattice of the underlying substrate atoms. Similar reconstructions have been observed on the 5d fcc metals Ir and Pt, but not in the 4d Rh, Pd, and Ag. The author studied the energetics of a monolayer of Au and Ag using first-principles calculations. The author found that it is energetically favorable for both Au and Ag to transform from a square to hexagonal arrangement and to contract to a higher surface density, but Au gains substantially more energy than Ag. This is true both for a monolayer in isolation as well as on top of a jellium surface. The author also calculated the mismatch energy (energy loss when the top layer loses registry with the substrate) for Au and Ag, and found that Ag has a slightly higher mismatch energy. The first-principles results thus offer a strong indication that Au(100) can reconstruct but Ag will not. The reconstruction is further studied with a 2 dimensional Frenkel-Kontorowa model, with parameters extracted from the total energy calculations. The author found that it is indeed energetically favorable for the top layer of Au(100), but not for Ag, to transform to a hexagonal-close-packed structure and contract. 85 refs., 34 figs., 8 tabs.

  1. Mixed multilayered vertical heterostructures utilizing strained monolayer WS2.

    PubMed

    Sheng, Yuewen; Xu, Wenshuo; Wang, Xiaochen; He, Zhengyu; Rong, Youmin; Warner, Jamie H

    2016-02-01

    Creating alternating layers of 2D materials forms vertical heterostructures with diverse electronic and opto-electronic properties. Monolayer WS2 grown by chemical vapour deposition can have inherent strain due to interactions with the substrate. The strain modifies the band structure and properties of monolayer WS2 and can be exploited in a wide range of applications. We demonstrate a non-aqueous transfer method for creating vertical stacks of mixed 2D layers containing a strained monolayer of WS2, with Boron Nitride and Graphene. The 2D materials are all grown by CVD, enabling large area vertical heterostructures to be formed. WS2 monolayers grown by CVD directly on Si substrates with SiO2 surface are easily washed off by water and this makes aqueous based transfer methods challenging for creating vertical stacks on the growth substrate. 2D hexagonal Boron Nitride films are used to provide an insulating layer that limits interactions with a top graphene layer and preserve the strong photoluminescence from the WS2. This transfer method is suitable for layer by layer control of 2D material vertical stacks and is shown to be possible for all CVD grown samples, which opens up pathways for the rapid large scale fabrication of vertical heterostructure systems with atomic thickness depth control and large area coverage. PMID:26758782

  2. Dependence of the band structure of C-60 monolayers on molecularorientations and doping observed by angle resolved photoemission

    SciTech Connect

    Brouet, V.; Yang, W.L.; Zhou, X.J.; Hussain, Z.; Shen, Z.X.

    2008-01-17

    We present angle resolved photoemission studies of C60monolayers deposited on Ag surfaces. The electronic structure of thesemonolayers is derived from the partial filling of the narrow, 6-folddegenerated, C60 conduction band. By comparing the band structure in twomonolayers deposited, respectively, on Ag(111) and Ag(100), we show thatthe molecular degree of freedom, in this case the relative orientationsbetween C60 molecules, is essential to describe the band structure. Wefurther show that the evolution of the band as a function of doping doesnot follow a rigid band-filling picture. Phase separation is observedbetween a metallic and an insulating phase, which might be a result ofstrong correlations.

  3. Plasmon-assisted photocurrent generation from silver nanoparticle monolayers combined with porphyrins via their different chain-length alkylcarboxylates.

    PubMed

    Kakuta, Takayoshi; Kon, Hiroki; Kajikawa, Azusa; Kanaizuka, Katsuhiko; Yagyu, Shigeta; Miyake, Ryosuke; Ishizakil, Manabu; Uruma, Keirei; Togashi, Takanari; Sakamoto, Masatomi; Kurihara, Masato

    2014-06-01

    Three-typed porphyrin derivatives with a different chain-length alkylcarboxylic acid as their peripheral anchor group have been prepared. Anodic photocurrents were observed in a simple system where the porphyrin derivatives were directly anchored on an indium tin oxide (ITO) electrode. Cathodic photocurrents and their plasmon-assisted enhancement appeared from an Ag nanoparticle (Ag NP) composite monolayer combined with the porphyrin derivatives on the ITO electrode. In the photocurrent generation mechanism, Ag NPs played both the roles as photon- and energy-transfer to the porphyrin derivatives. The plasmon-assisted enhancement was affected by the chain-lengths of the peripheral anchor groups. PMID:24738356

  4. Atomistic simulation of the electronic states of adatoms in monolayer MoS{sub 2}

    SciTech Connect

    Chang, Jiwon; Larentis, Stefano; Tutuc, Emanuel; Register, Leonard F.; Banerjee, Sanjay K.

    2014-04-07

    Using an ab initio density functional theory based electronic structure method, we study the effects of adatoms on the electronic properties of monolayer transition metal dichalcogenide Molybdenum-disulfide (MoS{sub 2}). We consider the 1st (Li, Na, K) and 7th (F, Cl, Br) column atoms and metals (Sc, Ti, Ta, Mo, Pd, Pt, Ag, Au). Three high symmetry sites for the adatom on the surface of monolayer MoS{sub 2} are examined as starting points to search for the most energetically stable configuration for each adatom-monolayer MoS{sub 2} system, as well as the type of associated bonding. For the most stable adatom positions, we characterize the emergence of adatom-induced electronic states including any dopant states.

  5. Preparation, characterization, and photocatalytic activity of porous AgBr@Ag and AgBrI@Ag plasmonic photocatalysts

    NASA Astrophysics Data System (ADS)

    Yang, Fan; Tian, Baozhu; Zhang, Jinlong; Xiong, Tianqing; Wang, Tingting

    2014-02-01

    Porous AgBr@Ag and AgBrI@Ag plasmonic photocatalysts were synthesized by a multistep route, including a dealloying method to prepare porous Ag, a transformation from Ag to AgBr and AgBrI, and a photo-reduction process to form Ag nanoparticles on the surface of AgBr and AgBrI. It was found that the porous structure kept unchanged during Ag was transferred into AgBr, AgBrI, AgBr@Ag, and AgBrI@Ag. Both porous AgBr@Ag and porous AgBrI@Ag showed much higher visible-light photocatalytic activity than cubic AgBr@Ag for the degradation of methyl orange, which is because the interconnected pore channels not only provide more reactive sites but also favor the transportation of photo-generated electrons and holes. For AgBrI@Ag, AgBrI solid solution formed at the interface of AgBr and AgI, and the phase junction can effectively separate the photo-generated electrons and holes, favorable to the improvement of photocatalytic activity. The optimal I content for obtaining the highest activity is ∼10 at.%.

  6. Fabrication of Sn-3.5Ag Eutectic Alloy Powder by Annealing Sub-Micrometer Sn@Ag Powder Prepared by Citric Acid-Assisted Ag Immersion Plating.

    PubMed

    Chee, Sang-Soo; Choi, Eun Byeol; Lee, Jong-Hyun

    2015-11-01

    A Sn-3.5Ag eutectic alloy powder has been developed by chemically synthesizing sub-micrometer Sn@Ag powder at room temperature. This synthesis was achieved by first obtaining a sub-micrometer Sn powder for the core using a modified variant of the polyol method, and then coating this with a uniformly thin and continuous Ag layer through immersion plating in 5.20 mM citric acid. The citric acid was found to play multiple roles in the Ag coating process, acting as a chelating agent, a reducing agent and a stabilizer to ensure coating uniformity; and as such, the amount used has an immense influence on the coating quality of the Ag shells. It was later verified by transmission electron microscopy and X-ray diffraction analysis that the coated Ag layer transfers to the Sn core via diffusion to form an Ag3Sn phase at room temperature. Differential scanning calorimetry also revealed that the synthesized Sn@Ag powder is nearly transformed into Sn-3.5Ag eutectic alloy powder upon annealing three times at a temperature of up to 250 degrees C, as evidenced by a single melting peak at 220.5 degrees C. It was inferred from this that Sn-3.5Ag eutectic alloy powder can be successfully prepared through the synthesis of core Sn powders by a modified polyol method, immersion plating using citric acid, and annealing, in that order. PMID:26726525

  7. Uniform Plasmonic Response of Colloidal Ag Patchy Particles Prepared by Swinging Oblique Angle Deposition.

    PubMed

    Bradley, Layne; Zhao, Yiping

    2016-05-17

    The plasmonic property of Ag patchy particles fabricated using a colloid monolayer and oblique angle deposition shows significant variations due to the multidomain nature of the monolayer. A swinging oblique angle deposition method is proposed to create uniform patchy particles. Both numerical calculations and experiment show that when the swinging angle is larger than 90°, the resulting plasmonic patchy particles have similar morphology and demonstrate uniform optical response that does not depend on the monolayer domain orientation. These uniform patchy plasmonic particles have great potential for plasmonic-based applications. PMID:27128221

  8. Structure and Long-Term Stability of Alkylphosphonic Acid Monolayers on SS316L Stainless Steel.

    PubMed

    Kosian, Medea; Smulders, Maarten M J; Zuilhof, Han

    2016-02-01

    Surface modification of stainless steel (SS316L) to improve surface properties or durability is an important avenue of research, as SS316L is widely used in industry and science. We studied, therefore, the formation and stability of a series of organic monolayers on SS316L under industrially relevant conditions. These included acidic (pH 3), basic (pH 11), neutral (Milli-Q water), and physiological conditions [10 mM phosphate-buffered saline (PBS)], as well as dry heating (120 °C). SS316L was modified with alkylphosphonic acids of chain length (CH2)n with n varying between 3 and 18. While alkylphosphonic acids of all chain lengths formed self-assembled monolayers with hydrophobic properties, only monolayers of chain lengths 12-18 formed ordered monolayers, as evidenced by static water contact angle (SCA), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and infrared reflection absorption spectroscopy (IRRAS). A long-term stability study revealed the excellent stability of monolayers with chain lengths 12-18 for up to 30 days in acid, neutral, and physiological solutions, and for up to 7 days under dry heating. Under strong basic conditions a partial breakdown of the monolayer was observed, especially for the shorter chain lengths. Finally, the effect of multivalent surface attachment on monolayer stability was explored by means of a series of divalent bisphosphonic acids. PMID:26771302

  9. Ordered 1,6-bis(2-hydroxyphenyl) pyridine boron complex films grown on Ag(110): From submonolayer to multilayer

    SciTech Connect

    Zhong, D.Y.; Lin, F.; Fuchs, H.; Chi, L.F.; Wang, Y.

    2005-03-15

    Ordered molecular films of a blue-light-emitting material, 1,6-bis(2-hydroxyphenyl) pyridine boron complex [(dppy)BF], grown on the Ag(110) surface by means of organic molecular beam epitaxy, were investigated by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) under an ultrahigh vacuum. Two commensurate structures exist in the monolayer film grown at 300 K, as found by STM. In the monolayer film, two types of hydrogen bonds are formed between the molecules, which, in addition to the molecule-substrate interaction, essentially determine the monolayer structures. The structural evolution of the (dppy)BF films from submonolayer to three monolayers was monitored by LEED in situ and in real time. The results indicate that the growth of the first two monolayers is affected by the periodic potential on the substrate surface, while such a template effect is weakened beyond the second monolayer.

  10. Multifunctional Self-Assembled Monolayers for Organic Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Cernetic, Nathan

    Organic field effect transistors (OFETs) have the potential to reach commercialization for a wide variety of applications such as active matrix display circuitry, chemical and biological sensing, radio-frequency identification devices and flexible electronics. In order to be commercially competitive with already at-market amorphous silicon devices, OFETs need to approach similar performance levels. Significant progress has been made in developing high performance organic semiconductors and dielectric materials. Additionally, a common route to improve the performance metric of OFETs is via interface modification at the critical dielectric/semiconductor and electrode/semiconductor interface which often play a significant role in charge transport properties. These metal oxide interfaces are typically modified with rationally designed multifunctional self-assembled monolayers. As means toward improving the performance metrics of OFETs, rationally designed multifunctional self-assembled monolayers are used to explore the relationship between surface energy, SAM order, and SAM dipole on OFET performance. The studies presented within are (1) development of a multifunctional SAM capable of simultaneously modifying dielectric and metal surface while maintaining compatibility with solution processed techniques (2) exploration of the relationship between SAM dipole and anchor group on graphene transistors, and (3) development of self-assembled monolayer field-effect transistor in which the traditional thick organic semiconductor is replaced by a rationally designed self-assembled monolayer semiconductor. The findings presented within represent advancement in the understanding of the influence of self-assembled monolayers on OFETs as well as progress towards rationally designed monolayer transistors.

  11. Monolayer-Mediated Patterning of Electroceramic Thin Films

    SciTech Connect

    Clem, P.G.; Payne, D.A.

    1998-10-11

    Integrated electroceramic thin film devices on semiconductor and insulator substrates feature a variety of attractive attributes, including high capacitance density, nonvolatile memory, sensor/actuator ability, and other unique electronic and optical properties. The ability to pattern such ceramic materials atop semiconductor substrates, thus, is a critical technology. Patterned oxide thin film devices are typically formed by uniform film deposition followed by somewhat complicated post-deposition ion-beam or chemical etching in a controlled environment. We review here the development of an ambient atmosphere technique which allows selective deposition of electroceramic thin layers without such post-deposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayer to modify the adhesion of subsequently deposited solution-derived electroceramics. The selective fictionalization is achieved through microcontact printing (v-CP) of self-assembled monolayer of the chemical octadecyltrichlorosilane on substrates of technical interest. Subsequent sol-gel deposition of ceramic oxides on these functionalized substrates, followed by lift-off from the monolayer, yields high quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micron- scale dielectric oxide devices have been fabricated using this process, with lateral resolution as fine as 0.5Lm. In this paper, we review the monolayer patterning and electrical behavior of several patterned electroceramic thin films, including Pb(Zr,Ti)03 [PZT], LiNb03, and Ta205. An applied device example is also presented in combination with selective MOCVD deposition of metal electrodes: integrated, fully monolayer-patterned Pt//PZT//PSi(Si(100) ferroelectric memory cells.

  12. Sodium monolayers on thermionic cathodes

    NASA Astrophysics Data System (ADS)

    Almanstötter, Jürgen; Eberhard, Bernd; Günther, Klaus; Hartmann, Thomas

    2002-07-01

    Under certain conditions alkali vapours form dipole monolayers on metallic electrodes that can lower the work function of the bulk material. In this case, the power balance of the electrode, the electrode fall voltage and the electrode loss power can change considerably. To verify this effect a pyrometric technique was adapted and optimized for the diagnostics of tungsten electrodes in high pressure sodium discharges. Using an already verified model of thermally emitting cathodes the effect was observed in a Na DC discharge and the range of existence was investigated. An interpretation of the results is given using a Langmuir description of forming the Na monolayers and first-principles electronic structure calculations using a pseudopotential plane wave method to solve the Kohn-Sham equations of density-functional theory.

  13. Assembly of oriented zeolite monolayers and thin films on polymeric surfaces via hydrogen bonding.

    PubMed

    Zhou, Ming; Liu, Xiufeng; Zhang, Baoquan; Zhu, Huiming

    2008-10-21

    The b-oriented monolayers of microsized silicalite-1 crystals have been manually assembled on glass plate supported poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), chitosan, and poly(methyl methacrylate) (PMMA) thin films via hydrogen bonding with much enhanced binding strength and satisfactory degrees of coverage and close packing. The exerted pressure and rubbing time in the manual assembly do not affect the binding strength of the silicalite-1 monolayer on the glass plate supported polymeric film. This manual assembly has been further applied to fabricate zeolite monolayers on commercially available Plexiglas surfaces and b-oriented multilayered films of silicalite-1 crystals on glass plates. The assembly method established in this study provides a feasible way to produce zeolite monolayers on polymer-modified solid substrates and Plexiglas and to fabricate zeolite-polymer composite membranes by means of the layer-by-layer technique. PMID:18785711

  14. Decorated Ag19 on Pt(111) or the "rare gas necklace".

    PubMed

    Schaub, R; Jödicke, H; Brunet, F; Monot, R; Buttet, J; Harbich, W

    2001-04-16

    Ag19 cluster ions are mass selected and deposited on a Pt(111) surface covered by five monolayers of Kr. Almost monodispersed hexagonal shaped Ag islands are observed after Kr evaporation at 125 K. The identification of the island shape and the exact number of atoms has been successful by decorating the clusters with Kr atoms which can be counted by high resolution scanning tunneling microscopy. PMID:11328030

  15. Seeded growth of robust SERS-active 2D Au@Ag nanoparticulate films

    SciTech Connect

    Baker, Gary A; Dai, Sheng; Hagaman, Edward {Ed} W; Mahurin, Shannon Mark; Zhu, Haoguo; Bao, Lili

    2008-01-01

    We demonstrate herein a novel and versatile solution-based methodology for fabricating self-organized two-dimensional (2D) Au nanoparticle arrays on glass using in situ nucleation at an aminosilane monolayer followed by seeded, electroless growth; subsequent deposition of Ag produced Au{at}Ag core-shell nanoparticulate films which proved highly promising as surface-enhanced Raman scattering (SERS) platforms.

  16. Alloying of Co ultrathin films on Pt(111) with Ag buffer layers

    NASA Astrophysics Data System (ADS)

    Shern, C. S.; Su, C. W.; Wu, Y. E.; Fu, T. Y.

    2000-07-01

    The structure at the interfaces of Co/Ag/Pt(111) was studied by low-energy electron diffraction, ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, and depth profiling. An atomic exchange occurs between Co and Ag before the formation of a Co-Pt alloy. Ag atoms start moving to the top at 425 K when the coverage of Co is one monolayer. The temperature of the complete exchange between Ag atoms and Co atoms is dependent on the thickness of the Ag buffer layer. The Co-Pt alloy develops after the atomic exchange is complete. The especially small surface free energy of Ag and large strain energy in this system are proposed as the driving force for the exchange.

  17. Electrochemical Potential Stabilization of Reconstructed Au(111) Structure by Monolayer Coverage with Graphene.

    PubMed

    Yasuda, Satoshi; Kumagai, Ryota; Nakashima, Koji; Murakoshi, Kei

    2015-09-01

    The electrochemical properties of a monolayer graphene grown on a Au(111) electrode were studied using cyclic voltammetry (CV) and electrochemical scanning tunneling microscopy (EC-STM). CV and EC-STM measurements in 0.1 M H2SO4 aqueous solution revealed that graphene grown on the reconstructed (22 × √3) Au(111) structure effectively inhibited potential-induced structural transitions between reconstructed (22 × √3) and unreconstructed (1 × 1), and the adsorption/desorption of SO4(2-) ions, which are intrinsic behavior of the bare Au(111) surface. The underlying reconstructed structure was significantly stabilized by covering with monolayer graphene over a wide potential range between -0.2 V and +1.35 V vs Ag/AgCl (saturated KCl), which is much wider than that for bare Au(111) (-0.2 to + 0.35 V vs Ag/AgCl (saturated KCl)). Such high stability has not been reported to date; therefore, these results are considered to be important for understanding the fundamentals of surface reconstruction and also serve to open a new branch of electrochemistry related to graphene/metal-electrolyte interfaces. PMID:26279244

  18. Structure and shear response of lipid monolayers

    SciTech Connect

    Dutta, P.; Ketterson, J.B.

    1990-02-01

    Organic monolayers and multilayers are both scientifically fascinating and technologically promising; they are, however, both complex systems and relatively inaccessible to experimental probes. In this Progress Report, we describe our X-ray diffraction studies, which have given us substantial new information about the structures and phase transitions in monolayers on the surface of water; our use of these monolayers as a unique probe of the dynamics of wetting and spreading; and our studies of monolayer mechanical properties using a simple but effective technique available to anyone using the Wilhelmy method to measure surface tension.

  19. Hematite nanoparticle monolayers on mica electrokinetic characteristics.

    PubMed

    Morga, Maria; Adamczyk, Zbigniew; Oćwieja, Magdalena

    2012-11-15

    Electrokinetic properties of α-Fe(2)O(3) (hematite) nanoparticle monolayers on mica were thoroughly characterized using the streaming potential method. Hematite suspensions were obtained by acidic hydrolysis of ferric chloride. The average size of particles (hydrodynamic diameter), determined by dynamic light scattering (DLS) and AFM, was 22 nm (pH=5.5, I=10(-2)M). The hematite monolayers on mica were produced under diffusion-controlled transport from the suspensions of various bulk concentration. The monolayer coverage, quantitatively determined by AFM and SEM, was regulated within broad limits by adjusting the nanoparticle deposition time. This allowed one to uniquely express zeta potential of hematite monolayers, determined by the streaming potential measurements, in terms of the particle coverage. Such dependencies, obtained for various pH, were successfully interpreted in terms of the three-dimensional electrokinetic model. A universal calibrating graph was produced enabling one to determine hematite monolayer coverage from the measured value of the streaming potential. The influence of the ionic strength, varied between 10(-4) and 10(-2)M, on the zeta potential of hematite monolayers was also studied. Additionally, the stability of monolayers (desorption kinetics) was determined under in situ conditions using the streaming potential method. Our experimental data prove that it is feasible to produce uniform and stable hematite particle monolayers of well-controlled coverage. Such monolayers may find practical applications as universal substrates for protein immobilization (biosensors) and in electrocatalytic applications. PMID:22921408

  20. Equilibrating nanoparticle monolayers using wetting films.

    PubMed

    Pontoni, Diego; Alvine, Kyle J; Checco, Antonio; Gang, Oleg; Ocko, Benjamin M; Pershan, Peter S

    2009-01-01

    Monolayers of bimodal gold nanoparticles on silicon are investigated by a combination of microscopy (dry monolayers) and x-ray diffraction (dry and wet monolayers). In the presence of an excess of small particles, the nanoscale packing structure closely resembles the small-particle-rich scenario of the structural crossover transition that has been predicted and also observed with micron-scale hard-sphere colloids. Structural morphology is monitored in situ during monolayer dissolution and reassembly within the thin liquid wetting film. This approach allows investigation of size and solvent effects on nanoparticles in quasi-two-dimensional confinement. PMID:19257214

  1. Facile synthesis of ternary Ag/AgBr-Ag2CO3 hybrids with enhanced photocatalytic removal of elemental mercury driven by visible light.

    PubMed

    Zhang, Anchao; Zhang, Lixiang; Lu, Hao; Chen, Guoyan; Liu, Zhichao; Xiang, Jun; Sun, Lushi

    2016-08-15

    A novel technique for photocatalytic removal of elemental mercury (Hg(0)) using visible-light-driven Ag/AgBr-Ag2CO3 hybrids was proposed. The ternary Ag/AgBr-Ag2CO3 hybrids were synthesized by a simple modified co-precipitation method and characterized by N2 adsorption-desorption, scanning electron microscope (SEM), X-ray diffraction (XRD), UV-vis diffused reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) techniques. The effects of AgBr content, fluorescent lamp (FSL) irradiation, solution temperature, SO2 and NO on Hg(0) removal were investigated in detail. Furthermore, a possible reaction mechanism for higher Hg(0) removal was proposed, and the simultaneous removal of Hg(0), SO2 and NO was studied. The results showed that a high efficiency of Hg(0) removal was obtained by using Ag/AgBr-Ag2CO3 hybrids under fluorescent lamp irradiation. The AgBr content, FSL irradiation, solution temperature, and SO2 all exhibited significant effects on Hg(0) removal, while NO had slight effect on Hg(0) removal. The addition of Ca(OH)2 demonstrated a little impact on Hg(0) removal and could significantly improve the SO2-resistance performance of Ag/AgBr(0.7)-Ag2CO3 hybrid. The characterization results exhibited that hydroxyl radical (OH), superoxide radical (O2(-)), hole (h(+)), and Br(0), were reactive species responsible for removing Hg(0), and the h(+) played a key role in Hg(0) removal. PMID:27135702

  2. Metallurgical characterization of experimental Ag-based soldering alloys

    PubMed Central

    Ntasi, Argyro; Al Jabbari, Youssef S.; Silikas, Nick; Al Taweel, Sara M.; Zinelis, Spiros

    2014-01-01

    Aim To characterize microstructure, hardness and thermal properties of experimental Ag-based soldering alloys for dental applications. Materials and methods Ag12Ga (AgGa) and Ag10Ga5Sn (AgGaSn) were fabricated by induction melting. Six samples were prepared for each alloy and microstructure, hardness and their melting range were determined by, scanning electron microscopy, energy dispersive X-ray (EDX) microanalysis, X-ray diffraction (XRD), Vickers hardness testing and differential scanning calorimetry (DSC). Results Both alloys demonstrated a gross dendritic microstructure while according to XRD results both materials consisted predominately of a Ag-rich face centered cubic phase The hardness of AgGa (61 ± 2) was statistically lower than that of AgGaSn (84 ± 2) while the alloys tested showed similar melting range of 627–762 °C for AgGa and 631–756 °C for AgGaSn. Conclusion The experimental alloys tested demonstrated similar microstructures and melting ranges. Ga and Sn might be used as alternative to Cu and Zn to modify the selected properties of Ag based soldering alloys. PMID:25382945

  3. Molecular Packing of Functionalized Fluorinated Lipids in Langmuir Monolayers

    SciTech Connect

    Landsberg, Michael J.; Ruggles, Jeremy L.; Hussein, Waleed M.; McGeary, Ross P.; Gentle, Ian R.; Hankamer, Ben

    2012-01-20

    Fluorinated amphipaths are a fascinating class of compounds, which, despite significant challenges associated with their syntheses, have found use across a number of areas of biotechnology. Applications range from the in vitro stabilization of membrane proteins to the development of enhanced stability intravenous drug and gene delivery systems. More recently, monolayer-forming fluorinated lipids have found use in the 2D crystallization of detergent-solubilized hydrophobic or partially hydrophobic proteins at the air-water interface. In this study, we investigate the surface properties of a novel suite of monolayer forming, partially fluorinated lipids. These modular lipid structures contain a densely fluorinated insertion in the hydrocarbon tail and a synthetically modifiable headgroup. Analyses of surface-pressure area isotherms and X-ray reflectometry profiles reveal that the lipids spread into fluid monolayers and are more compressible than their non-fluorinated counterparts. Furthermore, the data support a model whereby the partially fluorinated chains of the lipid tails form a film which is fundamentally incompatible with detergents and other destabilizing amphipaths.

  4. Herringbone and triangular patterns of dislocations in Ag, Au, and AgAu alloy films on Ru(0001).

    SciTech Connect

    Thayer, Gayle Echo; de la Figuera, Juan; Bartelt, Norman Charles; Carter, C. Barrington; Hwang, R. Q.; Thurmer, Konrad; Ling, W. L.; Hamilton, John C.; McCarty, Kevin F.

    2008-10-01

    We have studied the dislocation structures that occur in films of Ag, Au, and Ag{sub 0.5}Au{sub 0.5} alloy on a Ru(0001) substrate. Monolayer (ML) films form herringbone phases while films two or more layers thick contain triangular patterns of dislocations. We use scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) to determine how the film composition affects the structure and periodicity of these ordered structures. One layer of Ag forms two different herringbone phases depending on the exact Ag coverage and temperature. Low-energy electron microscopy (LEEM) establishes that a reversible, first-order phase transition occurs between these two phases at a certain temperature. We critically compare our 1 ML Ag structures to conflicting results from an X-ray scattering study [H. Zajonz et al., Phys. Rev. B 67 (2003) 155417]. Unlike Ag, the herringbone phases of Au and AgAu alloy are independent of the exact film coverage. For two layer films in all three systems, none of the dislocations in the triangular networks thread into the second film layer. In all three systems, the in-plane atomic spacing of the second film layer is nearly the same as in the bulk. Film composition does, however, affect the details of the two layer structures. Ag and Au films form interconnected networks of dislocations, which we refer to as 'trigons.' In 2 ML AgAu alloy, the dislocations form a different triangular network that shares features of both trigon and moire structures. Yet another well-ordered structure, with square symmetry, forms at the boundaries of translational trigon domains in 2 ML Ag films but not in Au films.

  5. Synthesis of Ag-coated polystyrene colloids by an improved surface seeding and shell growth technique

    SciTech Connect

    Tian Chungui; Wang Enbo . E-mail: wangenbo@public.cc.jl.cn; Kang Zhenhui; Mao Baodong; Zhang Chao; Lan Yang; Wang Chunlei; Song Yanli

    2006-11-15

    In this paper, an improved surface seeding and shell growth technique was developed to prepare Ag-polystyrene core shell composite. Polyethyleneimine (PEI) could act as the linker between Ag ions (Ag nanoparticles) and polystyrene (PS) colloids and the reducing agent in the formation of Ag nanoparticles. Due to the multi-functional characteristic of PEI, Ag seeds formed in-situ and were immobilized on the surface of PEI-modified PS colloids and no free Ag clusters coexist with the Ag 'seeding' PS colloids in the system. Then, the additional agents could be added into the resulting dispersions straightly to produce a thick Ag nanoshell. The Ag nanoshell with controllable thickness was formed on the surface of PS by the 'one-pot' surface seeding and shell growth method. The Ag-coverage increased gradually with the increasing of mass ratio of AgNO{sub 3}/PS. The optical properties of the Ag-PS colloids could be tailored by changing the coverage of Ag. - Graphical abstract: An improved surface seeding and shell growth technique was developed to prepare Ag-polystyrene core shell composite. The optical properties of the Ag-PS colloids could be tailored by changing the coverage of Ag. Display Omitted.

  6. Mixed multilayered vertical heterostructures utilizing strained monolayer WS2

    NASA Astrophysics Data System (ADS)

    Sheng, Yuewen; Xu, Wenshuo; Wang, Xiaochen; He, Zhengyu; Rong, Youmin; Warner, Jamie H.

    2016-01-01

    Creating alternating layers of 2D materials forms vertical heterostructures with diverse electronic and opto-electronic properties. Monolayer WS2 grown by chemical vapour deposition can have inherent strain due to interactions with the substrate. The strain modifies the band structure and properties of monolayer WS2 and can be exploited in a wide range of applications. We demonstrate a non-aqueous transfer method for creating vertical stacks of mixed 2D layers containing a strained monolayer of WS2, with Boron Nitride and Graphene. The 2D materials are all grown by CVD, enabling large area vertical heterostructures to be formed. WS2 monolayers grown by CVD directly on Si substrates with SiO2 surface are easily washed off by water and this makes aqueous based transfer methods challenging for creating vertical stacks on the growth substrate. 2D hexagonal Boron Nitride films are used to provide an insulating layer that limits interactions with a top graphene layer and preserve the strong photoluminescence from the WS2. This transfer method is suitable for layer by layer control of 2D material vertical stacks and is shown to be possible for all CVD grown samples, which opens up pathways for the rapid large scale fabrication of vertical heterostructure systems with atomic thickness depth control and large area coverage.Creating alternating layers of 2D materials forms vertical heterostructures with diverse electronic and opto-electronic properties. Monolayer WS2 grown by chemical vapour deposition can have inherent strain due to interactions with the substrate. The strain modifies the band structure and properties of monolayer WS2 and can be exploited in a wide range of applications. We demonstrate a non-aqueous transfer method for creating vertical stacks of mixed 2D layers containing a strained monolayer of WS2, with Boron Nitride and Graphene. The 2D materials are all grown by CVD, enabling large area vertical heterostructures to be formed. WS2 monolayers grown by

  7. THE TWO-DIMENSIONAL VALENCE ELECTRONIC STRUCTURE OF A MONOLYAER OF Ag ON Cu(00l)

    SciTech Connect

    Tobin, J.G.; Robey, S.W.; Shirley, D.A.

    1985-05-01

    The metal overlayer system c(10x2)Ag/Cu(001) was studied at coverages near one monolayer with angle-resolved photoemission. The observed spectroscopic features indicate a two-dimensional d-band electronic structure that can be interpreted using a model with planar, hexagonal symmetry in which crystal field effects dominate over spin-orbit effects.

  8. AGS experiments - 1994, 1995, 1996

    SciTech Connect

    Depken, J.C.

    1997-01-01

    This report contains the following information on the Brookhaven AGS Accelerator complex: FY 1996 AGS schedule as run; FY 1997 AGS schedule (working copy); AGS beams 1997; AGS experimental area FY 1994 physics program; AGS experimental area FY 1995 physics program; AGS experimental area FY 1996 physics program; AGS experimental area FY 1997 physics program (in progress); a listing of experiments by number; two-phage summaries of each experiment begin here, also ordered by number; listing of publications of AGS experiments begins here; and listing of AGS experimenters begins here.

  9. New AGS fast extraction system

    SciTech Connect

    Weng, W.T.

    1980-09-01

    Both the high energy physics program and ISA injection require an improved fast extraction system from the AGS. The proposed new system consists of a fast kicker at H5 and an ejector magnet at H10. The H5 kicker is capable of producing 1.2 mrad deflection and rising up to 99% strength in 150 nsec with flat top ripple within +- 1%. It is found that the focusing strengths and positions of UQ3-UQ7 have to be modified to achieve an achromatic condition at the end of 8/sup 0/-bend. Also, the conceptual design of the H5 magnet and the pulser system are discussed.

  10. Stilling Waves with Ordered Molecular Monolayers

    ERIC Educational Resources Information Center

    Vitz, Ed

    2008-01-01

    A demonstration of the damping effect of an oil monolayer on water waves is described. The history of this remarkable demonstration--with a 2000 (or more) year span--and a brief explanation in terms of the properties of water and the monolayer are presented. If a layer of olive oil, one molecule thick (about one-ten millionth of a centimeter), is…

  11. Cell adhesion on a polymerized peptide-amphiphile monolayer.

    PubMed

    Biesalski, Markus A; Knaebel, Alexandra; Tu, Raymond; Tirrell, Matthew

    2006-03-01

    We report the synthesis and characterization of a stable polymerized monolayer of peptide-amphihiles on a planar solid support that promotes mouse fibroblast cell adhesion and spreading. Peptide-amphiphiles consisting of a polymerizable fatty acid attached to a short RGD containing peptide sequence are self-assembled and polymerized at the water-air interface by means of the Langmuir- Blodgett technique. The surface concentration of the peptide-amphiphile is varied by co-spreading the peptide-amphiphile with an analogous non-modified polymerizable amphiphile at the water/air interface, prior to UV light-induced polymerization. The polymerized monolayer is transferred onto a hydrophobized smooth mica surface and the resulting surfaces have been investigated with respect to directing the cell adhesion and spreading of mouse fibroblast cells in a serum-free medium. Fibroblast cells adhere and spread on surfaces exposing the bioactive ligand but do not spread on reference surfaces without peptide. We find a maximum number of adherent cells at rather high peptide surface concentrations of about 10 mol% in the mixed monolayer, equivalent to more than 50 pmol/cm2 peptide on the surface of the film. We attribute this finding to a limited accessibility of the ligands by the integrins. Because of the stability of the polymerized peptide-amphiphile monolayer, these surfaces can be re-seeded multiple times with cells, i.e. adherent cells can be removed from the surface, the surface can be sterilized and cells can be re-attached. PMID:16157369

  12. The structure of percolating lipid monolayers.

    PubMed

    Risović, D; Frka, S; Kozarac, Z

    2012-05-01

    The lattice structure and in plane molecular organization of Langmuir monolayer of amphiphilic material is usually determined from grazing incidence X-ray diffraction (GIXD) or neutron reflectivity. Here we present results of a different approach for determination of monolayer lattice structure based on application of fractal analysis and percolation theory in combination with Brewster angle microscopy. The considerations of compressibility modulus and fractal dimension dynamics provide information on percolation threshold and consequently by application of percolation theory on the lattice structure of a monolayer. We have applied this approach to determine the monolayer lattice structures of single chain and double chain lipids. The compressibility moduli were determined from measured π-A isotherms and fractal dimensions from corresponding BAM images. The monolayer lattice structures of stearic acid, 1-hexadecanol, DPPC and DPPA, obtained in this way conform to the corresponding lattice structures determined previously by other authors using GIXD. PMID:22209411

  13. Binary functionalization of H:Si(111) surfaces by alkyl monolayers with different linker atoms enhances monolayer stability and packing.

    PubMed

    Arefi, Hadi H; Nolan, Michael; Fagas, Giorgos

    2016-05-14

    Alkyl monolayer modified Si forms a class of inorganic-organic hybrid materials with applications across many technologies such as thin-films, fuel/solar-cells and biosensors. Previous studies have shown that the linker atom, through which the monolayer binds to the Si substrate, and any tail group in the alkyl chain, can tune the monolayer stability and electronic properties. In this paper we study the H:Si(111) surface functionalized with binary SAMs: these are composed of alkyl chains that are linked to the surface by two different linker groups. Aiming to enhance SAM stability and increase coverage over singly functionalized Si, we examine with density functional theory simulations that incorporate vdW interactions, a range of linker groups which we denote as -X-(alkyl) with X = CH2, O(H), S(H) or NH(2) (alkyl = C6 and C12 chains). We show how the stability of the SAM can be enhanced by adsorbing alkyl chains with two different linkers, e.g. Si-[C, NH]-alkyl, through which the adsorption energy is increased compared to functionalization with the individual -X-alkyl chains. Our results show that it is possible to improve stability and optimum coverage of alkyl functionalized SAMs linked through a direct Si-C bond by incorporating alkyl chains linked to Si through a different linker group, while preserving the interface electronic structure that determines key electronic properties. This is important since any enhancement in stability and coverage to give more densely packed monolayers will result in fewer defects. We also show that the work function can be tuned within the interval of 3.65-4.94 eV (4.55 eV for bare H:Si(111)). PMID:27109872

  14. Silicene: from monolayer to multilayer — A concise review

    NASA Astrophysics Data System (ADS)

    Li, Hui; Hui-Xia, Fu; Meng, Sheng

    2015-08-01

    Silicene, a newly isolated silicon allotrope with a two-dimensional (2D) honeycomb lattice structure, is predicted to have electronic properties similar to those of graphene, including the existence of signature Dirac fermions. Furthermore, the strong spin-orbit interaction of Si atoms potentially makes silicene an experimentally accessible 2D topological insulator. Since 2012, silicene films have been experimentally synthesized on Ag (111) and other substrates, motivating a burst of research on silicene. We and collaborators have employed STM investigations and first principles calculations to intensively study the structure and electronic properties of silicene films on Ag (111), including monolayer, bilayer, and multilayer silicenes, as well as hydrogenation of silicene. Project supported by the National Natural Science Foundation of China (Grant Nos. 11334011, 11222431, and 11322431), the National Basic Research Program of China (Grant Nos. 2012CB921403, 2013CBA01600, and 2012CB921703), the “Strategic Priority Research Program” of the Chinese Academy of Sciences, and the Hundred Talents Program of Institute of Physics, Chinese Academy of Sciences.

  15. Ionic compound mediated rearrangement of 3, 4, 9, 10-perylene tetracarboxylic dianhydride molecules on Ag(100) surface.

    PubMed

    Guo, Qinmin; Huang, Min; Lu, Shuangzan; Cao, Gengyu

    2015-07-10

    Tailoring of the assembly structure of organic molecular monolayer is of great importance to improve the performance of molecular devices. In this work, a typical ionic compound, namely KCl, was used to mediate the rearrangement of 3, 4, 9, 10-perylene tetracarboxylic dianhydride (PTCDA) monolayer on Ag(100). Combined scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) results indicate that both molecule and molecular superlattice would rotate after the dosing of KCl. The density functional theory calculation shows that KCl would exist in the form of molecules rather than ions on Ag(100) and demonstrates that experimentally observed structural transition induced by KCl molecules is energetically favored. PMID:26080855

  16. Ionic compound mediated rearrangement of 3, 4, 9, 10-perylene tetracarboxylic dianhydride molecules on Ag(100) surface

    NASA Astrophysics Data System (ADS)

    Guo, Qinmin; Huang, Min; Lu, Shuangzan; Cao, Gengyu

    2015-07-01

    Tailoring of the assembly structure of organic molecular monolayer is of great importance to improve the performance of molecular devices. In this work, a typical ionic compound, namely KCl, was used to mediate the rearrangement of 3, 4, 9, 10-perylene tetracarboxylic dianhydride (PTCDA) monolayer on Ag(100). Combined scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) results indicate that both molecule and molecular superlattice would rotate after the dosing of KCl. The density functional theory calculation shows that KCl would exist in the form of molecules rather than ions on Ag(100) and demonstrates that experimentally observed structural transition induced by KCl molecules is energetically favored.

  17. DNA-modified electrodes fabricated using copper-free click chemistry for enhanced protein detection.

    PubMed

    Furst, Ariel L; Hill, Michael G; Barton, Jacqueline K

    2013-12-31

    A method of DNA monolayer formation has been developed using copper-free click chemistry that yields enhanced surface homogeneity and enables variation in the amount of DNA assembled; extremely low-density DNA monolayers, with as little as 5% of the monolayer being DNA, have been formed. These DNA-modified electrodes (DMEs) were characterized visually, with AFM, and electrochemically, and were found to facilitate DNA-mediated reduction of a distally bound redox probe. These low-density monolayers were found to be more homogeneous than traditional thiol-modified DNA monolayers, with greater helix accessibility through an increased surface area-to-volume ratio. Protein binding efficiency of the transcriptional activator TATA-binding protein (TBP) was also investigated on these surfaces and compared to that on DNA monolayers formed with standard thiol-modified DNA. Our low-density monolayers were found to be extremely sensitive to TBP binding, with a signal decrease in excess of 75% for 150 nM protein. This protein was detectable at 4 nM, on the order of its dissociation constant, with our low-density monolayers. The improved DNA helix accessibility and sensitivity of our low-density DNA monolayers to TBP binding reflects the general utility of this method of DNA monolayer formation for DNA-based electrochemical sensor development. PMID:24328347

  18. DNA-modified Electrodes Fabricated using Copper-Free Click Chemistry for Enhanced Protein Detection

    PubMed Central

    Furst, Ariel L.; Hill, Michael G.; Barton, Jacqueline K.

    2014-01-01

    A method of DNA monolayer formation has been developed using copper-free click chemistry that yields enhanced surface homogeneity and enables variation in the amount of DNA assembled; extremely low-density DNA monolayers, with as little as 5% of the monolayer being DNA, have been formed. These DNA-modified electrodes (DMEs) were characterized visually, with AFM, and electrochemically, and were found to facilitate DNA-mediated reduction of a distally bound redox probe. These low-density monolayers were found to be more homogeneous than traditional thiol-modified DNA monolayers, with greater helix accessibility through an increased surface area-to-volume ratio. Protein binding efficiency of the transcriptional activator TATA-binding protein (TBP) was also investigated on these surfaces and compared to that on DNA monolayers formed with standard thiol-modified DNA. Our low-density monolayers were found to be extremely sensitive to TBP binding, with a signal decrease in excess of 75% for 150 nM protein. This protein was detectable at 4 nM, on the order of its dissociation constant, with our low-density monolayers. The improved DNA helix accessibility and sensitivity of our low-density DNA monolayers to TBP binding reflects the general utility of this method of DNA monolayer formation for DNA-based electrochemical sensor development. PMID:24328347

  19. Structure-property Relationships for Methyl-terminated Alkyl Self-assembled Monolayers

    SciTech Connect

    F DelRio; D Rampulla; C Jaye; G Stan; R Gates; D Fischer; R Cook

    2011-12-31

    Structure-property relationships for methyl-terminated alkyl self-assembled monolayers (SAMs) are developed using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and atomic force microscopy (AFM). NEXAFS C K-edge spectra are used to compute the dichroic ratio, which provides a quantitative measure of the molecular structure. AFM data are analyzed with an elastic adhesive contact model, modified by a first-order elastic perturbation method to include substrate effects, to extract the monolayer mechanical properties. Using this approach, the measured mechanical properties are not influenced by the substrate, which allows universal structure-property relationships to be developed for methyl-terminated alkyl SAMs.

  20. A monolayer of hierarchical silver hemi-mesoparticles with tunable surface topographies for highly sensitive surface-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhu, Shuangmei; Fan, Chunzhen; Mao, Yanchao; Wang, Junqiao; He, Jinna; Liang, Erjun; Chao, Mingju

    2016-02-01

    We proposed a facile green synthesis system to synthesize large-scale Ag hemi-mesoparticles monolayer on Cu foil. Ag hemi-mesoparticles have different surface morphologies on their surfaces, including ridge-like, meatball-like, and fluffy-like shapes. In the reaction, silver nitrate was reduced by copper at room temperature in dimethyl sulfoxide via the galvanic displacement reaction. The different surface morphologies of the Ag hemi-mesoparticles were adjusted by changing the reaction time, and the hemi-mesoparticle surface formed fluffy-spherical nanoprotrusions at longer reaction time. At the same time, we explored the growth mechanism of silver hemi-mesoparticles with different surface morphologies. With 4-mercaptobenzoic acid as Raman probe molecules, the fluffy-like silver hemi-mesoparticles monolayer with the best activity of surface enhanced Raman scattering (SERS), the enhancement factor is up to 7.33 × 107 and the detection limit can reach 10-10M. SERS measurements demonstrate that these Ag hemi-mesoparticles can serve as sensitive SERS substrates. At the same time, using finite element method, the distribution of the localized electromagnetic field near the particle surface was simulated to verify the enhanced mechanism. This study helps us to understand the relationship between morphology Ag hemi-mesoparicles and the properties of SERS.

  1. A monolayer of hierarchical silver hemi-mesoparticles with tunable surface topographies for highly sensitive surface-enhanced Raman spectroscopy.

    PubMed

    Zhu, Shuangmei; Fan, Chunzhen; Mao, Yanchao; Wang, Junqiao; He, Jinna; Liang, Erjun; Chao, Mingju

    2016-02-21

    We proposed a facile green synthesis system to synthesize large-scale Ag hemi-mesoparticles monolayer on Cu foil. Ag hemi-mesoparticles have different surface morphologies on their surfaces, including ridge-like, meatball-like, and fluffy-like shapes. In the reaction, silver nitrate was reduced by copper at room temperature in dimethyl sulfoxide via the galvanic displacement reaction. The different surface morphologies of the Ag hemi-mesoparticles were adjusted by changing the reaction time, and the hemi-mesoparticle surface formed fluffy-spherical nanoprotrusions at longer reaction time. At the same time, we explored the growth mechanism of silver hemi-mesoparticles with different surface morphologies. With 4-mercaptobenzoic acid as Raman probe molecules, the fluffy-like silver hemi-mesoparticles monolayer with the best activity of surface enhanced Raman scattering (SERS), the enhancement factor is up to 7.33 × 10(7) and the detection limit can reach 10(-10)M. SERS measurements demonstrate that these Ag hemi-mesoparticles can serve as sensitive SERS substrates. At the same time, using finite element method, the distribution of the localized electromagnetic field near the particle surface was simulated to verify the enhanced mechanism. This study helps us to understand the relationship between morphology Ag hemi-mesoparicles and the properties of SERS. PMID:26896995

  2. Self-assembled monolayers on a ferromagnetic permalloy surface.

    PubMed

    Mattera, Michele; Torres-Cavanillas, Ramón; Prieto-Ruiz, Juan P; Prima-García, Helena; Tatay, Sergio; Forment-Aliaga, Alicia; Coronado, Eugenio

    2015-05-19

    Self-assembled monolayers (SAMs) are nowadays broadly used as surface protectors or modifiers and play a key role in many technological applications. This has motivated the study of their formation in all kind of materials; however, and despite the current interest in molecular spintronics, the study of SAMs on ferromagnetic surfaces remains almost unexplored. In this paper, we report for the first time a methodology for the formation of SAMs of n-alkylphosphonic acids on permalloy in ambient conditions. The formed monolayers have been fully characterized by means of contact angle measurements, atomic force microscopy, X-ray photoelectron spectroscopy, matrix assisted laser desorption ionization time-of-flight mass spectrometry, infrared reflection absorption spectroscopy, and X-ray reflectometry. Additionally, the magnetic stability of the modified permalloy after the solution process required for the SAM formation has been confirmed by magneto-optical Kerr effect magnetometry. Moreover, by means of microcontact printing lithography, very accurate SAM patterns have been transferred onto permalloy surfaces and used as resist mask in a chemical etching process giving rise to submicrometric permalloy surface patterns with potential interest in nanomagnetism, spintronics, and storage technologies. PMID:25919007

  3. Raman characterization of monolayers formed from mixtures of sodium 2-mercaptoethanesulfonate and various aromatic mercapto-derivative bases.

    PubMed

    Kudelski, Andrzej

    2010-04-22

    Metal electrodes covered with organic (mono)layers containing pi-delocalized structures have many potential applications, for example, in construction of bioelectronic elements with high efficiency of electron transfer. In this contribution, a silver surface was modified with mixed monolayers formed from sodium 2-mercaptoethanesulfonate (MES) and four model (stable and easily available) aromatic thiols with strong basic properties: 4,6-diamino-2-mercaptopyrimidine (APY), 1H-1,2,4-triazole-3-thiol (HTR), 4-methyl-1,2,4-triazole-3-thiol (MTR), and 3-amino-1,2,4-triazole-5-thiol (ATR). The structure of the formed monolayers was determined from surface-enhanced Raman scattering (SERS) measurements. These studies showed that, despite significant differences in the molecular structures, MES is a very promising candidate for making mixed monolayers with mercapto-derivative aromatic bases that are relatively homogeneous (without large one-component domains) in broad pH range. At high pH, in a one-component ATR monolayer, a significant amount of molecules are in the anionic form and adopt a flat orientation versus the metal surface. At the same pH, in mixed ATR+MES monolayers, a significantly larger part of ATR molecules than for the respective one-component monolayer is adsorbed in the neutral form with the aromatic ring(s) oriented perpendicularly to the metal surface. Also in the mixed APY+MES and HTR+MES monolayers, a significantly smaller part of HTR or APY molecules than for the respective one-component HTR and APY monolayers is deprotonated. The structure of the MTR monolayer practically does not depend on the pH of the surrounding solution. Increase of the ratio of acidic dissociation and reorientation of ATR molecules from the perpendicular to the parallel orientation is also observed during storage of the respective one-component and mixed monolayers in water, phosphorus buffers, and in the solutions of model peptides (bovine serum albumin or laccase). In some

  4. Effects of irradiated biodegradable polymer in endothelial cell monolayer formation

    NASA Astrophysics Data System (ADS)

    Arbeitman, Claudia R.; del Grosso, Mariela F.; Behar, Moni; García Bermúdez, Gerardo

    2013-11-01

    In this work we study cell adhesion, proliferation and cell morphology of endothelial cell cultured on poly-L-lactide acid (PLLA) modified by heavy ion irradiation. Thin films of PLLA samples were irradiated with sulfur (S) at energies of 75 MeV and gold (Au) at 18 MeV ion-beams. Ion beams were provided by the Tandar (Buenos Aires, Argentina) and Tandetron (Porto Alegre, Brazil) accelerators, respectively. The growth of a monolayer of bovine aortic endothelial cells (BAEC) onto unirradiated and irradiated surfaces has been studied by in vitro techniques in static culture. Cell viability and proliferation increased on modified substrates. But the results on unirradiated samples, indicate cell death (necrosis/apoptosis) with the consequent decrease in proliferation. We analyzed the correlation between irradiation parameters and cell metabolism and morphology.

  5. Morphological transitions in polymer monolayers under compression.

    PubMed

    Srivastava, S; Basu, J K; Sprung, M; Wang, J

    2009-05-01

    We present a systematic investigation of morphological transitions in poly vinylacetate Langmuir monolayers. On compression, the polymer monolayer is converted to a continuous membrane with a thickness of approximately 2-3 nm. Above a certain surface concentration the monolayer, on water, undergoes a morphological transition-buckling, leading to formation of striped patterns of period of lambda(b) approximately 160 nm, as determined from in situ grazing incidence small angle x-ray scattering measurements. The obtained value is much smaller than what has been typically observed for Langmuir monolayers on water or thin films on soft substrates. Using existing theories for buckling of fluidlike films on fluid substrates, we obtain very low values of bending rigidity and Young's modulus of the polymer monolayer compared to that observed earlier for lipid or polymeric monolayers. Since buckling in these monolayers occurs only above a certain surface concentration, we have looked at the possibility that the buckling in these films occurs due to changes in their mechanical properties under compression. Using the model of Huang and Suo of buckling of solidlike films on viscoelastic substrates, we find values of the mechanical properties, which are much closer to the bulk values but still significantly lower. Although the reduction could be along the lines of what has been observed earlier for ultrathin polymer film or surface layers of polymers, the possibility of micromechanical effects also determining the buckling in such polymer monolayers cannot be ruled out. We have provided possible explanation of the buckling of the poly vinylacetate monolayers in terms of the change in isothermal compression modulus with surface concentration. PMID:19425809

  6. Drug induced `softening' in phospholipid monolayers

    NASA Astrophysics Data System (ADS)

    Basak, Uttam Kumar; Datta, Alokmay; Bhattacharya, Dhananjay

    2015-06-01

    Compressibility measurements on Langmuir monolayers of the phospholipid Dimystoryl Phospatidylcholine (DMPC) in pristine form and in the presence of the Non-steroidal Anti-inflammatory Drug (NSAID) Piroxicam at 0.025 drug/lipid (D/L) molecular ratio at different temperatures, show that the monolayer exhibits large increase (and subsequent decrease) in compressibility due to the drug in the vicinity of the Liquid Expanded - Liquid Condensed (LE-LC) phase transition. Molecular dynamics simulations of the lipid monolayer in presence of drug molecules show a disordering of the tail tilt, which is consistent with the above result.

  7. Monolayer coated gold nanoparticles for delivery applications

    PubMed Central

    Rana, Subinoy; Bajaj, Avinash; Mout, Rubul; Rotello, Vincent M.

    2011-01-01

    Gold nanoparticles (AuNPs) provide attractive vehicles for delivery of drugs, genetic materials, proteins, and small molecules. AuNPs feature low core toxicity coupled with the ability to parametrically control particle size and surface properties. In this review, we focus on engineering of the AuNP surface monolayer, highlighting recent advances in tuning monolayer structures for efficient delivery of drugs and biomolecules. This review covers two broad categories of particle functionalization, organic monolayers and biomolecule coatings, and discusses their applications in drug, DNA/RNA, protein and small molecule delivery. PMID:21925556

  8. Selective Amplification of the Primary Exciton in a Mo S2 Monolayer

    NASA Astrophysics Data System (ADS)

    Lee, Hyun Seok; Kim, Min Su; Jin, Youngjo; Han, Gang Hee; Lee, Young Hee; Kim, Jeongyong

    2015-11-01

    Optoelectronics applications for transition-metal dichalcogenides are still limited by weak light absorption and their complex exciton modes are easily perturbed by varying excitation conditions because they are inherent in atomically thin layers. Here, we propose a method of selectively amplifying the primary exciton (A0 ) among the exciton complexes in monolayer Mo S2 via cyclic reexcitation of cavity-free exciton-coupled plasmon propagation. This was implemented by partially overlapping a Ag nanowire on a Mo S2 monolayer separated by a thin Si O2 spacer. Exciton-coupled plasmons in the nanowire enhance the A0 radiation in Mo S2 . The cumulative amplification of emission enhancement by cyclic plasmon traveling reaches approximately twentyfold selectively for the A0 , while excluding other B exciton and multiexciton by significantly reduced band filling, without oscillatory spectra implying plasmonic cavity effects.

  9. Buffer effects of Ag layers on magneto-optical Co/Ge(1 0 0) ultrathin films

    NASA Astrophysics Data System (ADS)

    Su, C. W.; Tsay, J. S.; Yao, Y. D.

    2006-09-01

    Magnetic properties of the Co/Ag/Ge(1 0 0) films grown at room temperature and 200 K were studied by the surface magneto-optical Kerr effect (SMOKE). More than 1.5 monolayer Ag buffer layers not only effectively block the interdiffusion between the capped Co layers and the Ge(1 0 0) substrate but also stabilize the magnetic phase. The temperature and thickness dependence on coercivity measurements show that interactions upon the interfaces are strongly correlated to the microstructures.

  10. Electronic, transport, and optical properties of bulk and mono-layer PdSe2

    DOE PAGESBeta

    Sun, Jifeng; Shi, Hongliang; Siegrist, Theo; Singh, David J.

    2015-10-13

    In this study, the electronic and optical properties of bulk and monolayer PdSe2 are investigated using firstprinciples calculations. Using the modified Becke-Johnson potential, we find semiconductor behavior for both bulk and monolayer PdSe2 with indirect gap values of 0.03 eV for bulk and 1.43 eV for monolayer, respectively. Our sheet optical conductivity results support this observation and show similar anisotropic feature in the 2D plane. We further study the thermoelectric properties of the 2D PdSe2 using Blotzmann transport model and find interestingly high Seebeck coefficients (>200 μV/K) for both p- and n-type up to high doping level (–2 x 1013more » cm2) with an anisotropic character in an electrical conductivity suggesting better thermoelectric performance along y direction in the plane.V« less