Benjamin J Wiley

Duke University, Durham, North Carolina, United States

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Publications (93)949.1 Total impact

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    ABSTRACT: This article describes a room-temperature solution-phase process for the synthesis of copper-silver (Cu-Ag), copper-gold (Cu-Au), and copper-platinum (Cu-Pt) core-shell nanowires (NWs) in which ascorbic acid removes the passivating copper oxide coating from the Cu NWs and reduces noble metal ions onto the Cu NWs while preventing galvanic replacement. Cu-Ag NWs are conductive as printed, and the resulting NW films exhibit optoelectronic properties equivalent to films of Ag NWs with a similar aspect ratio. Unlike Cu NWs, Cu-Ag NWs were resistant to oxidation in dry air at 160°C and under humid conditions (85% RH) at 85°C for 24 h.
    No preview · Article · Nov 2015 · Chemistry of Materials
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    Binay Prasai · Adria R Wilson · Benjamin J. Wiley · Yang Ren · Valeri Petkov
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    ABSTRACT: The extent to which current theoretical modeling alone can reveal real-world metallic nanoparticles (NPs) at the atomic level was scrutinized and demonstrated to be insufficient and how it can be improved by using a pragmatic approach involving straightforward experiments is shown. In particular, 4 to 6 nm in size silica supported Au100-xPdx (x = 30, 46 and 58) explored for catalytic applications is characterized structurally by total scattering experiments including high-energy synchrotron X-ray diffraction (XRD) coupled to atomic pair distribution function (PDF) analysis. Atomic-level models for the NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modeling Sutton-Chen (SC) method. Models are matched against independent experimental data and are demonstrated to be inaccurate unless their theoretical foundation, i.e. the SC method, is supplemented with basic yet crucial information on the length and strength of metal-to-metal bonds and, when necessary, structural disorder in the actual NPs studied. An atomic PDF-based approach for accessing such information and implementing it in theoretical modeling is put forward. For completeness, the approach is concisely demonstrated on 15 nm in size water-dispersed Au particles explored for bio-medical applications and 16 nm in size hexane-dispersed Fe48Pd52 particles explored for magnetic applications as well. It is argued that when "tuned up" against experiments relevant to metals and alloys confined to nanoscale dimensions, such as total scattering coupled to atomic PDF analysis, rather than by mere intuition and/or against data for the respective solids, atomic-level theoretical modeling can provide a sound understanding of the synthesis-structure-property relationships in real-world metallic NPs. Ultimately this can help advance nanoscience and technology a step closer to producing metallic NPs by rational design.
    Full-text · Article · Oct 2015 · Nanoscale
  • Bo Li · Shengrong Ye · Ian E Stewart · Samuel Alvarez · Benjamin J Wiley
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    ABSTRACT: Metal nanowire (NW) networks have the highest performance of any solution-coatable alternative to ITO, but there is as yet no published process for producing NW films with optoelectronic performance that exceeds that of ITO. Here we demonstrate a process for the synthesis and purification of Ag NWs that, when coated from an ink to create a transparent conducting film, exhibit properties which exceed that of ITO. The diameter, and thus optoelectronic performance, of Ag NWs produced by a polyol synthesis can be controlled by adjusting the concentration of bromide. Ag NWs with diameters of 20 nm and aspect ratios up to 2000 were obtained by adding 2.2 mM NaBr to a Ag NW synthesis, but these NWs were contaminated by nanoparticles. Selective precipitation was used to purify the NWs, resulting in a transmittance improvement as large as 4%. At 130.0 Ω sq -1, the transmittance of the purified Ag NW film was 99.1%.
    No preview · Article · Sep 2015 · Nano Letters
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    ABSTRACT: Development of thin-film transparent conductors (TC) based on percolating networks of metal nanowires has leaped forward in recent years, owing to the improvement of nanowire synthetic methods and modeling efforts by several research groups. While silver nanowires are the first commercially viable iteration of this technology, systems based on copper nanowires are not far behind. Here we present an analysis of TCs composed of copper nanowire networks on sheets of polyethylene terephthalate PET that have been treated with various oxide-removing post treatments to improve conductivity. A pseudo-2D rod network modeling approach has been modified to include lognormal distributions in length that more closely reflect experimental data collected from the nanowire TCs. In our analysis, we find that the copper nanowire TCs are capable of achieving comparable electrical performance to silver nanowire TCs with similar dimensions. Lastly, we present a method for more accurately determining the nanowire area coverage in a TC over a large area using Rutherford Backscattering Spectrometry (RBS) to directly measure the metal content in the TCs. These developments will aid research and industry groups alike in the characterization of nanowire based TCs.
    No preview · Article · Jul 2015 · Nanoscale
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    ABSTRACT: A dynamically adjustable colloidal assembly technique is presented, which combines magnetic and acoustic fields to produce a wide range of colloidal structures, ranging from discrete colloidal molecules, to polymer networks and crystals. The structures can be stabilized and dried, making them suitable for the fabrication of advanced materials.
    Full-text · Article · Jul 2015 · Advanced Materials
  • Samuel Alvarez · Shengrong Ye · Patrick F. Flowers · Benjamin J. Wiley
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    ABSTRACT: This article describes the photocatalytic growth of copper nanowires from Cu2O octahedra. When exposed to visible light with an energy greater than the band gap of Cu2O, electrons excited from the valence band to the conduction band within Cu2O octahedra reduce Cu(OH)2- onto the octahedra to form copper nanowires. This phenomenon was used to turn nanowire growth on and off with visible light, as well as pattern the growth of nanowires on a substrate.
    No preview · Article · Jan 2015 · Chemistry of Materials
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    Jialei Du · Zuofeng Chen · Shengrong Ye · Benjamin J. Wiley · Thomas J. Meyer
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    ABSTRACT: Copper metal is in theory a viable oxidative electrocatalyst based on surface oxidation to CuIII and/or CuIV, but its use in water oxidation has been impeded by anodic corrosion. The in situ formation of an efficient interfacial oxygen-evolving Cu catalyst from CuII in concentrated carbonate solutions is presented. The catalyst necessitates use of dissolved CuII and accesses the higher oxidation states prior to decompostion to form an active surface film, which is limited by solution conditions. This observation and restriction led to the exploration of ways to use surface-protected Cu metal as a robust electrocatalyst for water oxidation. Formation of a compact film of CuO on Cu surface prevents anodic corrosion and results in sustained catalytic water oxidation. The Cu/CuO surface stabilization was also applied to Cu nanowire films, which are transparent and flexible electrocatalysts for water oxidation and are an attractive alternative to ITO-supported catalysts for photoelectrochemical applications.
    Full-text · Article · Jan 2015 · Angewandte Chemie International Edition
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    ABSTRACT: There is an ongoing drive to replace the most common transparent conductor, indium tin oxide (ITO), with a material that gives comparable performance, but can be coated from solution at speeds orders of magnitude faster than the sputtering processes used to deposit ITO. Metal nanowires are currently the only alternative to ITO that meets these requirements. This Progress Report summarizes recent advances toward understanding the relationship between the structure of metal nanowires, the electrical and optical properties of metal nanowires, and the properties of a network of metal nanowires. Using the structure–property relationship of metal nanowire networks as a roadmap, this Progress Report describes different synthetic strategies to produce metal nanowires with the desired properties. Practical aspects of processing metal nanowires into high-performance transparent conducting films are discussed, as well as the use of nanowire films in a variety of applications.
    No preview · Article · Dec 2014 · Advanced Materials
  • Zuofeng Chen · Shengrong Ye · Ian E Stewart · Benjamin J Wiley
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    ABSTRACT: Transparent conducting films of solution-synthesized copper nanowires are an attractive alternative to indium tin oxide (ITO) due to the relative abundance of Cu and the low-cost of solution-phase nanowire coating processes. However, there has to date been no way to protect Cu nanowires with a solution-phase process that does not adversely affect the optoelectric performance of Cu nanowire films. This article reports that the electrodeposition of zinc, tin or indium shells onto Cu nanowires, followed by oxidation of these shells, enables the protection of Cu nanowire films against oxidation without decreasing film performance.
    No preview · Article · Sep 2014 · ACS Nano
  • Shengrong Ye · Zuofeng Chen · Yoon-Cheol Ha · Benjamin J Wiley
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    ABSTRACT: This Letter shows that copper nanowires grow through the diffusion-controlled reduction of dihydroxycopper(I), Cu(OH)2-. A combination of potentiostatic coulometry, UV-visible spectroscopy, and thermodynamic calculations was used to determine the species adding to growing Cu nanowires is Cu(OH)2-. Cyclic voltammetry was then used to measure the diffusion coefficient of Cu(OH)2- in the reaction solution. Given the diameter of a Cu nanowire and the diffusion coefficient of Cu(OH)2-, we calculated the dependence of the diffusion-limited growth rate on the concentration of copper ions to be 26 nm s-1 mM-1. Independent measurements of the nanowire growth rate with dark-field optical microscopy yielded 24 nm s-1 mM-1 for the growth rate dependence on the concentration of copper. Dependence of the nanowire growth rate on temperature yielded a low activation energy of 11.5 kJ mol-1, consistent with diffusion-limited growth.
    No preview · Article · Jul 2014 · Nano Letters
  • Ran Long · Shan Zhou · Benjamin J Wiley · Yujie Xiong
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    ABSTRACT: Since the discovery of the role of oxidative etching in shape-controlled metal nanostructure synthesis in 2004, it has become a versatile tool to precisely manipulate the nucleation and growth of metal nanocrystals at the atomic level. Subsequent research has shown that oxidative etching can be used to reshape nanocrystals via atomic addition and subtraction. This research has attracted extensive attention from the community because of its promising practical applications and theoretical value, and as a result, tremendous efforts from numerous research groups have been made to expand and apply this method to their own research. In this review, we first outline the merits of oxidative etching for the controlled synthesis of metal nanocrystals. We then summarize recent progress in the use of oxidative etching to control the morphology of a nanostructure during and after its synthesis, and analyze its specific functions in controlling a variety of nanocrystal parameters. Applications enabled by oxidative etching are also briefly presented to show its practical impact. Finally, we discuss the challenges and opportunities for further development of oxidative etching in nanocrystals synthesis.
    No preview · Article · Jun 2014 · Chemical Society Reviews
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    ABSTRACT: This paper demonstrates that Cu2O nanoparticles form in the early stages of a solution-phase synthesis of copper nanowires, and aggregate to form the seeds from which copper nanowires grow. Removal of ethylenediamine from the synthesis leads to the rapid formation of Cu2O octahedra. These octahedra are introduced as seeds in the same copper nanowire synthesis to improve the yield of copper nanowires from 12% to >55%, and to enable independent control over the length of the nanowires. Transparent conducting films are made from nanowires with different lengths to examine the effect of nanowire aspect ratio on the film performance.
    No preview · Article · May 2014 · Small
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    ABSTRACT: This work describes a process to make anodes for organic solar cells from copper-nickel nanowires with solution-phase processing. Copper nanowire films were coated from solution onto glass and made conductive by dipping them in acetic acid. Acetic acid removes the passivating oxide from the surface of copper nanowires, thereby reducing the contact resistance between nanowires to nearly the same extent as hydrogen annealing. Films of copper nanowires were made as oxidation resistant as silver nanowires under dry and humid conditions by dipping them in an electroless nickel plating solution. Organic solar cells utilizing these completely solution-processed copper-nickel nanowire films exhibited efficiencies of 4.9%.
    Full-text · Article · Apr 2014 · Nanoscale
  • Zuofeng Chen · Shengrong Ye · Adria R. Wilson · Yoon-Cheol Ha · Benjamin J. Wiley
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    ABSTRACT: This article reports the fabrication of copper-platinum core-shell nanowires by electroplating platinum onto copper nanowires, and the first demonstration of their use as a transparent, conducting electrocatalyst for the hydrogen evolution reaction (HER). Cu-Pt core-shell nanowire networks exhibit mass activities up to 8 times higher than carbon-supported Pt nanoparticles for the HER. Electroplating minimizes galvanic replacement, allowing the copper nanowires to retain their conductivity, and eliminating the need for a conductive substrate or overcoat. Cu-Pt core-shell nanowire networks can thus replace more expensive transparent electrodes made from indium tin oxide (ITO) in photoelectrolysis cells and dye sensitized solar cells. Unlike ITO, Cu-Pt core-shell nanowire films retain their conductivity after bending, retain their transmittance during electrochemical reduction, and have consistently high transmittance (>80%) across a wide optical window (300-1800 nm).
    No preview · Article · Apr 2014 · Energy & Environmental Science
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    ABSTRACT: Let the light shine through: A transparent film of copper nanowires was transformed into an electrocatalyst for water oxidation by electrodepostion of Ni or Co onto the surface of the nanowires. These core-shell nanowire networks exhibit electrocatalytic performance equivalent to metal oxide films of similar composition, but are several times more transparent.
    No preview · Article · Apr 2014 · Angewandte Chemie International Edition
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    ABSTRACT: This communication presents a way to produce copper nanowires with aspect ratios as high as 5700 in 30 min, and describes the growth processes responsible for their formation. These nanowires were used to make transparent conducting films with a transmittance >95% at a sheet resistance <100 Ω sq(-1).
    Full-text · Article · Dec 2013 · Chemical Communications
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    ABSTRACT: A metallic nanoparticle positioned over a metal film offers great advantages as a highly controllable system relevant for probing field-enhancement and other plasmonic effects. Because the size and shape of the gap between nanoparticle and film can be controlled to sub-nanometer precision using relatively simple, bottom-up fabrication approaches, the film-coupled nanoparticle geometry has recently been applied to enhancing optical fields, accessing the quantum regime of plasmonics, and the design of surface with controlled reflectance. In the present work, we examine the plasmon modes associated with a silver nanocube positioned above a silver or gold film, separated by an organic, dielectric spacer layer. The film-coupled nanocube is of particular interest due to the formation of waveguide cavity-like modes between the nanocube and film. These modes impart distinctive scattering characteristics to the system that can be used in the creation of controlled reflectance surfaces and other applications. We perform both experimental spectroscopy and numerical simulations of individual nanocubes positioned over a metal film, finding excellent agreement between experiment and simulation. The waveguide mode description serves as a starting point to explain the optical properties observed.
    Full-text · Article · Nov 2013 · Nano Letters
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    ABSTRACT: This article describes the solution-phase synthesis of 4 nm gold nanoparticles with 0.7 atom-thick, 1.9 atom-thick, and 3.8 atom-thick layers of Pd on their surfaces. These well-defined core–shell nanoparticles were deposited on a silica support, calcined, and reduced at 300 °C to create alloyed nanoparticles containing 10.9, 20.2, and 28.5% Pd (w/w). Monometallic Pd nanoparticles sintered during calcination at 300 °C, but no sintering was observed for AuPd nanoparticles. Diffuse reflectance infrared Fourier transform (DRIFT) spectra of adsorbed CO suggests that Au donates d electron density to Pd in the core–shell and alloy structures and confirms the presence of Au and Pd atoms on the surface of the nanoparticles after calcination and reduction. The properties of the AuPd alloy catalysts were tested in the vapor-phase conversion of α-limonene to p-cymene. AuPd nanoparticles containing 20% or more Pd per particle produced p-cymene yields greater than 80%, equivalent to conventional Pd catalysts prepared by incipient wetness and ion exchange methods. Very low yields of p-cymene were obtained from dehydrogenation of p-menthane under equivalent conditions, suggesting that the production of p-cymene from α-limonene proceeds through terpinene intermediates.
    No preview · Article · Aug 2013 · The Journal of Physical Chemistry C
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    ABSTRACT: Metal nanowire films are among the most promising alternatives for next-generation flexible, solution-processed transparent conductors. Breakthroughs in nanowire synthesis and processing have reported low sheet resistance (Rs ≤ 100 Ω/sq) and high optical transparency (%T > 90%). Comparing the merits of the various nanowires and fabrication methods is inexact, because Rs and %T depend on a variety of independent parameters including nanowire length, nanowire diameter, areal density of the nanowires and contact resistance between nanowires. In an effort to account for these fundamental parameters of nanowire thin films, this paper integrates simulations and experimental results to build a quantitatively predictive model. First, by fitting the results from simulations of quasi-2D rod networks to experimental data from well-defined nanowire films, we obtain an effective average contact resistance, which is indicative of the nanowire chemistry and processing methods. Second, this effective contact resistance is used to simulate how the sheet resistance depends on the aspect ratio (L/D) and areal density of monodisperse rods, as well as the effect of mixtures of short and long nanowires on the sheet resistance. Third, by combining our simulations of sheet resistance and an empirical diameter-dependent expression for the optical transmittance, we produced a fully calculated plot of optical transmittance versus sheet resistance. Our predictions for silver nanowires are validated by experimental results for silver nanowire films, where nanowires of L/D > 400 are required for high performance transparent conductors. In contrast to a widely-used approach that employs a single percolative figure of merit, our method integrates simulation and experimental results to enable researchers to independently explore the importance of contact resistance between nanowires, as well as nanowire area fraction and arbitrary distributions in nanowire sizes. To become competitive, metal nanowire systems require a predictive tool to accelerate their design and adoption for specific applications.
    No preview · Article · Aug 2013 · ACS Nano
  • Benjamin John Wiley · Jianfeng Zang · Aaron R. Rathmell · Jianghong Wu · Xuanhe Zhao
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    ABSTRACT: This work demonstrates that metal nanowires in a percolating network can reversibly slide across one another. Reversible sliding allows networks of metal nanowires to maintain electrical contact while being stretched to strains greater than the fracture strain for individual nanowires. This phenomenon was demonstrated by using networks of nanowires as compliant electrodes for a dielectric elastomer actuator. Reversible nanowire sliding enabled actuation to a maximum area strain of 200%, and repetitive cycling of the actuator to an area strain of 25% over 150 times. During actuation, the transmittance of the network increased 4.5 times, from 13% to 58%. Compared to carbon-based compliant electrodes, networks of metal nanowires can actuate across a broader range of optical transmittance. The widely tunable transmittance of nanowire-based actuators allows for their use as a light valve.
    No preview · Article · May 2013 · Nano Letters

Publication Stats

11k Citations
949.10 Total Impact Points


  • 2009-2015
    • Duke University
      • Department of Chemistry
      Durham, North Carolina, United States
  • 2008-2011
    • Harvard University
      • Department of Chemistry and Chemical Biology
      Cambridge, Massachusetts, United States
  • 2004-2008
    • University of Washington Seattle
      • • Department of Chemical Engineering
      • • Department of Chemistry
      • • Department of Bioengineering
      Seattle, Washington, United States
  • 2006
    • University of California, Berkeley
      Berkeley, California, United States
    • University of Minnesota Duluth
      Duluth, Minnesota, United States