Benjamin J Wiley

Duke University, Durham, North Carolina, United States

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Publications (79)751.02 Total impact

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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.
    ACS Nano 09/2014; · 12.03 Impact Factor
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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.
    Advanced Materials 09/2014; · 14.83 Impact Factor
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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.
    Nano letters. 07/2014;
  • 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.
    Chemical Society Reviews 06/2014; · 24.89 Impact Factor
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    ABSTRACT: On page 1771, B. J. Wiley and co-workers report that removal of ethylenediamine from a copper nanowire synthesis leads to the rapid formation of Cu2 O octahedra. These Cu2 O octahedra can be used as seeds in a synthesis to control nanowire aspect ratio. Transparent conducting films are made from nanowires to examine the effect of nanowire aspect ratio on the film performance.
    Small 05/2014; 10(9):1770. · 7.82 Impact Factor
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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%.
    Nanoscale 04/2014; · 6.73 Impact Factor
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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).
    Chemical Communications 12/2013; · 6.38 Impact Factor
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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.
    Nano Letters 11/2013; · 13.03 Impact Factor
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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.
    Angewandte Chemie International Edition 10/2013; · 11.34 Impact Factor
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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.
    The Journal of Physical Chemistry C. 08/2013; 117(34):17557–17566.
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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.
    ACS Nano 08/2013; · 12.03 Impact Factor
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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.
    Nano Letters 05/2013; · 13.03 Impact Factor
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    ABSTRACT: Thin-film metal nanowire networks are being pursued as a viable alternative to the expensive and brittle indium tin oxide (ITO) for transparent conductors. For high performance applications, nanowire networks must exhibit high transmittance at low sheet resistance. Previously, we have used complimentary experimental, simulation and theoretical techniques to explore the effects of filler aspect ratio (L/D), orientation, and size-dispersity on the electrical conductivity of three-dimensional rod-networks in bulk polymer nanocomposites. We adapted our 3D simulation approach and analytical percolation model to study the electrical properties of thin-film rod-networks. By fitting our simulation results to experimental results, we determined the average effective contact resistance between silver nanowires. This contact resistance was then used to quantify how the sheet resistance depends on the aspect ratio of the rods and to show that networks made of nanowires with L/D greater than 100 yield sheet resistances lower than the required 100 Ohm/sq. We also report the critical area fraction of rods required to form a percolated network in thin-film networks and provide an analytical expression for the critical area fraction as a function of L/D.
    03/2013;
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    ABSTRACT: Efficient and tunable absorption is essential for a variety of applications, such as designing controlled-emissivity surfaces for thermophotovoltaic devices, tailoring an infrared spectrum for controlled thermal dissipation and producing detector elements for imaging. Metamaterials based on metallic elements are particularly efficient as absorbing media, because both the electrical and the magnetic properties of a metamaterial can be tuned by structured design. So far, metamaterial absorbers in the infrared or visible range have been fabricated using lithographically patterned metallic structures, making them inherently difficult to produce over large areas and hence reducing their applicability. Here we demonstrate a simple method to create a metamaterial absorber by randomly adsorbing chemically synthesized silver nanocubes onto a nanoscale-thick polymer spacer layer on a gold film, making no effort to control the spatial arrangement of the cubes on the film. We show that the film-coupled nanocubes provide a reflectance spectrum that can be tailored by varying the geometry (the size of the cubes and/or the thickness of the spacer). Each nanocube is the optical analogue of a grounded patch antenna, with a nearly identical local field structure that is modified by the plasmonic response of the metal's dielectric function, and with an anomalously large absorption efficiency that can be partly attributed to an interferometric effect. The absorptivity of large surface areas can be controlled using this method, at scales out of reach of lithographic approaches (such as electron-beam lithography) that are otherwise required to manipulate matter on the nanoscale.
    Nature 12/2012; 492(7427):86-89. · 38.60 Impact Factor
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    ABSTRACT: Nanowires of copper can be coated from liquids to create flexible, transparent conducting films that can potentially replace the dominant transparent conductor, indium tin oxide, in displays, solar cells, organic light-emitting diodes, and electrochromic windows. One issue with these nanowire films is that copper is prone to oxidation. It was hypothesized that the resistance to oxidation could be improved by coating copper nanowires with nickel. This work demonstrates a method for synthesizing copper nanowires with nickel shells as well as the properties of cupronickel nanowires in transparent conducting films. Time- and temperature-dependent sheet resistance measurements indicate that the sheet resistance of copper and silver nanowire films will double after 3 and 36 months at room temperature, respectively. In contrast, the sheet resistance of cupronickel nanowires containing 20 mol % nickel will double in about 400 years. Coating copper nanowires to a ratio of 2:1 Cu:Ni gave them a neutral gray color, making them more suitable for use in displays and electrochromic windows. These properties, and the fact that copper and nickel are 1000 times more abundant than indium or silver, make cupronickel nanowires a promising alternative for the sustainable, efficient production of transparent conductors.
    Nano Letters 05/2012; 12(6):3193-9. · 13.03 Impact Factor
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    ABSTRACT: This article describes how the dimensions of nanowires affect the transmittance and sheet resistance of a random nanowire network. Silver nanowires with independently controlled lengths and diameters were synthesized with a gram-scale polyol synthesis by controlling the reaction temperature and time. Characterization of films composed of nanowires of different lengths but the same diameter enabled the quantification of the effect of length on the conductance and transmittance of silver nanowire films. Finite-difference time-domain calculations were used to determine the effect of nanowire diameter, overlap, and hole size on the transmittance of a nanowire network. For individual nanowires with diameters greater than 50 nm, increasing diameter increases the electrical conductance to optical extinction ratio, but the opposite is true for nanowires with diameters less than this size. Calculations and experimental data show that for a random network of nanowires, decreasing nanowire diameter increases the number density of nanowires at a given transmittance, leading to improved connectivity and conductivity at high transmittance (>90%). This information will facilitate the design of transparent, conducting nanowire films for flexible displays, organic light emitting diodes and thin-film solar cells.
    Nanoscale 03/2012; 4(6):1996-2004. · 6.73 Impact Factor
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    ABSTRACT: We model and experimentally measure the electrical conductivity of two-dimensional networks containing finite, conductive cylinders with aspect ratio ranging from 33 to 333. We have previously used our simulations to explore the effects of cylinder orientation and aspect ratio in three-dimensional composites, and now extend the simulation to consider two-dimensional silver nanowire networks. Preliminary results suggest that increasing the aspect ratio and area fraction of these rods significantly decreases the sheet resistance of the film. For all simulated aspect ratios, this sheet resistance approaches a constant value for high area fractions of rods. This implies that regardless of aspect ratio, there is a limiting minimum sheet resistance that is characteristic of the properties of the nanowires. Experimental data from silver nanowire networks will be incorporated into the simulations to define the contact resistance and corroborate experimentally measured sheet resistances of transparent thin films.
    02/2012;
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    ABSTRACT: This paper reports the quantitative measurement of a full spectrum of mechanical properties of fivefold twinned silver (Ag) nanowires (NWs), including Young's modulus, yield strength, and ultimate tensile strength. In-situ tensile testing of Ag NWs with diameters between 34 and 130 nm was carried out inside a scanning electron microscope (SEM). Young's modulus, yield strength, and ultimate tensile strength all increased as the NW diameter decreased. The maximum yield strength in our tests was found to be 2.64 GPa, which is about 50 times the bulk value and close to the theoretical value of Ag in the 〈110〉 orientation. The size effect in the yield strength is mainly due to the stiffening size effect in the Young's modulus. Yield strain scales reasonably well with the NW surface area, which reveals that yielding of Ag NWs is due to dislocation nucleation from surface sources. Pronounced strain hardening was observed for most NWs in our study. The strain hardening, which has not previously been reported for NWs, is mainly attributed to the presence of internal twin boundaries.
    Physical review. B, Condensed matter 01/2012; 85(4). · 3.77 Impact Factor
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    ABSTRACT: New methods for inducing microscopic particles to assemble into useful macroscopic structures could open pathways for fabricating complex materials that cannot be produced by lithographic methods. Here we demonstrate a colloidal assembly technique that uses two parameters to tune the assembly of over 20 different pre-programmed structures, including kagome, honeycomb and square lattices, as well as various chain and ring configurations. We programme the assembled structures by controlling the relative concentrations and interaction strengths between spherical magnetic and non-magnetic beads, which behave as paramagnetic or diamagnetic dipoles when immersed in a ferrofluid. A comparison of our experimental observations with potential energy calculations suggests that the lowest energy configuration within binary mixtures is determined entirely by the relative dipole strengths and their relative concentrations.
    Nature Communications 01/2012; 3:794. · 10.74 Impact Factor
  • Source
    Aaron R Rathmell, Benjamin J Wiley
    Advanced Materials 09/2011; 23(41):4798-803. · 14.83 Impact Factor

Publication Stats

4k Citations
751.02 Total Impact Points

Institutions

  • 2010–2014
    • Duke University
      • Department of Chemistry
      Durham, North Carolina, United States
  • 2008–2010
    • Harvard University
      • Department of Chemistry and Chemical Biology
      Cambridge, MA, United States
    • Washington University in St. Louis
      • Department of Biomedical Engineering
      Saint Louis, MO, United States
  • 2004–2008
    • University of Washington Seattle
      • Department of Chemistry
      Seattle, WA, United States
  • 2006
    • Technical Institute of Physics and Chemistry
      Peping, Beijing, China
  • 2005
    • Northwestern University
      • Department of Chemistry
      Evanston, IL, United States