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ABSTRACT: Deposition into nanoporous alumina membranes is widely used for nanowire fabrication. Herein using AC electrodeposition ternary Deposition into nanoporous alumina membranes is widely used for nanowire fabrication. Herein using AC electrodeposition ternary
Fe–Co–Ni nanowires are fabricated within the nanoscale-pores of alumina membranes. Using an electrodeposition frequency of Fe–Co–Ni nanowires are fabricated within the nanoscale-pores of alumina membranes. Using an electrodeposition frequency of
1,000Hz, 15Vrms, consistently and repeatably yield nanowire arrays over membranes several cm2 in extent. Electrochemical Impedance Spectroscopy (EIS) is used to explain the effects of AC electrodeposition frequency. 1,000Hz, 15Vrms, consistently and repeatably yield nanowire arrays over membranes several cm2 in extent. Electrochemical Impedance Spectroscopy (EIS) is used to explain the effects of AC electrodeposition frequency.
The impedance of the residual alumina barrier layer, separating the underlying aluminum metal and the nanoporous membrane, The impedance of the residual alumina barrier layer, separating the underlying aluminum metal and the nanoporous membrane,
decreases drastically with electrodeposition frequency facilitating uniform pore-filling of samples several cm2 in area. Anodic polarization studies on thin films having alloy compositions identical to the nanowires display excellent decreases drastically with electrodeposition frequency facilitating uniform pore-filling of samples several cm2 in area. Anodic polarization studies on thin films having alloy compositions identical to the nanowires display excellent
corrosion resistance properties. corrosion resistance properties.
Journal of Materials Science 04/2012; 42(13):4738-4744. · 2.02 Impact Factor
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ABSTRACT: Light-driven, electrically biased pn junction photoelectrochemical (PEC) cells immersed in an electrolyte of CO(2) saturated 1.0 M NaHCO(3) are investigated for use in generating hydrocarbon fuels. The PEC photocathode is comprised of p-type Si nanowire arrays, with and without copper sensitization, while the photoanode is comprised of n-type TiO(2) nanotube array films. Under band gap illumination, the PEC cells convert CO(2) into hydrocarbon fuels, such as methane, along with carbon monoxide and substantial rates of hydrogen generation due to water photoelectrolysis. In addition to traces of C3-C4 hydrocarbons, methane and ethylene were formed at the combined rate of 201.5 nM/cm(2)-hr at an applied potential of -1.5 V vs. Ag/AgCl. The described technique provides a unique approach, utilizing earth abundant materials, for the photocatalytic reduction of CO(2) with subsequent generation of higher order hydrocarbons and syngas constituents of carbon monoxide and hydrogen.
Nanoscale 02/2012; 4(7):2245-50. · 5.91 Impact Factor
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ABSTRACT: Time-resolved emission and absorption spectroscopy are used to study the photoinduced dynamics of forward and back electron transfer processes taking place between a recently synthesized series of donor-(π-spacer)-acceptor organic dyes and semiconductor films. Results are obtained for vertically oriented titania nanotube arrays (inner diameters 36 nm and 70 nm), standard titania nanoparticles (25 nm diameter) and, as a reference, alumina nanoparticle (13 nm diameter) films. The studied dyes contain a triphenylamine group as an electron donor, cyanoacrylic acid part as an electron acceptor, and differ by the substituents in a spacer group that causes a shift of its absorption spectra. Despite a red-shift of the dye absorption band resulting in an improved response to the solar spectrum, smaller electron injection rates and smaller extinction coefficients result in reduced dye sensitized solar cell (DSSC) conversion efficiencies. For the most efficient dye, TPC1, electron injection from the hot locally excited state to titania on a time scale of about 100 fs is suggested, while from the relaxed charge transfer state it proceeds in a non-exponential way with time constants from 1 ps to 50 ps. Our results imply that the latter process involves the trap states below the conduction band edge (or the sub-bandgap tail of the acceptor states), localized close to the dye radical cation, and is accompanied by fast electron recombination to the parent dye's ground state. This process should limit the efficiency of DSSCs made using these types of organic dyes. The residual, slower recombination can be described by a stretched exponential decay with a characteristic time of 0.5 μs and a dispersion parameter of 0.33. Both the electron injection and back electron transfer dynamics are similar in titania nanoparticles and nanotubes. Variations between the two film types are only found in the time resolved emission transients, which are explained in terms of the difference in local electric fields affecting the position of the emission bands.
Physical Chemistry Chemical Physics 02/2012; 14(8):2816-31. · 3.57 Impact Factor
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ABSTRACT: We report on low-cost, all solution fabrication of efficient air-stable nanostructured thin film photovoltaics comprised of n-type Sb(2)S(3) chemically deposited onto TiO(2) nanowire array films, forming coaxial Sb(2)S(3)/TiO(2) nanowire hybrids vertically oriented from the SnO(2):F coated glass substrate, which are then intercalated with poly(3-hexylthiophene) (P3HT) for hole transport and enhanced light absorption.
Chemical Communications 02/2012; 48(22):2818-20. · 6.17 Impact Factor
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ABSTRACT: A rapid solvothermal approach was used to synthesize aligned 1D single-crystal rutile TiO(2) nanowire (NW) arrays on transparent conducting substrates as electrodes for dye-sensitized solar cells. The NW arrays showed a more than 200 times faster charge transport and a factor four lower defect state density than conventional rutile nanoparticle films.
Angewandte Chemie International Edition 02/2012; 51(11):2727-30. · 13.45 Impact Factor
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ABSTRACT: Films of crystalline WO(3) nanosheets oriented perpendicular to tungsten substrates were grown by a surfactant-free hydrothermal method, followed by sintering. The films exhibit photoelectrochemical oxygen evolution at low overpotential.
Chemical Communications 11/2011; 48(5):729-31. · 6.17 Impact Factor
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ABSTRACT: The controlled growth of highly ordered, [211]-oriented FeOOH nanowire arrays on various substrates, such as Pt, W, Ti, and fluoride-doped tin oxide (FTO) glass, was achieved by a solvothermal method in aqueous acetonitrile solutions at 80–120 °C, following by annealing to form α-Fe2O3 nanowires with their [110] direction perpendicular to the substrate. Adjusting the reaction pH and temperature enables control of the nanowire length. In particular, the pH has a dramatic effect on the nanowire growth, with low pH resulting in the growth of longer wires because of the acid-catalyzed hydrolysis of acetonitrile. Photoactive hematite was prepared by diffusing Ti or Sn into the nanowires during thermal annealing. Processing parameters that influenced the photoelectrochemical performance of these nanowire arrays, including the annealing regime, temperature, and length of nanowires, are discussed in detail. The Ti- and Sn-doped one-dimensional [110]-oriented α-Fe2O3 nanowire arrays provide an effective pathway for electron transport, demonstrating increased photocurrents, up to 1.3 mA/cm2 under air mass 1.5 global (AM 1.5G) illumination, in photoelectrochemical water oxidation.
11/2011;
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ABSTRACT: Monodisperse CuInS(2) nanocrystals are produced by injecting mixed metal-oleate precursors into hot organic solvents containing the dissolved sulphur sources. A better understanding of the formation mechanism of CuInS(2) has enabled us to tailor anisotropic shapes in the form of triangular-pyramid, circular cone, and bullet-like rods with tunable crystal phases by varying the synthetic conditions.
Chemical Communications 09/2011; 47(33):9441-3. · 6.17 Impact Factor
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ABSTRACT: High surface area highly ordered nanoporous thin films are the current gold standard for gas sensor use, however the nanostructure of such films is prone to collapse at annealing temperatures as low as 250 °C resulting in formation of a dense layer of limited utility. We report on a templating method used to deposit highly ordered nanoporous platinum (Pt)-doped tin dioxide (SnO(2)) thin films that are crystallized by a 100 °C water vapor hydrothermal treatment, with the low temperature process being compatible with a large variety of substrates including plastic. The resulting highly ordered nanoporous, transparent Pt-SnO(2) thin films are mechanically stable and can be annealed, as desired, at temperatures up to 800 °C for removal of the templating materials and tailoring of gas sensitivities without damage to the nanoporous structure. The synthesis method is general, offering a promising strategy for preparing high performance nanoporous metal oxide crystalline films for applications including gas sensing, photocatalysis, and 3(rd) generation photovoltaics. In our example application of the synthesized materials, we find that these Pt-SnO(2) films exhibit exceptional hydrogen gas sensing behavior, rapidly detecting low-level hydrogen concentrations at room temperature; for example, an eight order of magnitude change in electrical resistance is seen in response to 10 000 ppm H(2), with only minimal sensitivity to humidity.
Nanoscale 08/2011; 3(10):4283-9. · 5.91 Impact Factor
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ABSTRACT: We report on a novel heterojunction WO(3)/BiVO(4) photoanode for photoelectrochemical water splitting. The heterojunction films are prepared by solvothermal deposition of a WO(3) nanorod-array film onto fluorine-doped tin oxide (FTO) coated glass, with subsequent deposition of a low bandgap, 2.4 eV, visible light responding BiVO(4) layer by spin-coating. The heterojunction structure offers enhanced photoconversion efficiency and increased photocorrosion stability. Compared to planar WO(3)/BiVO(4) heterojunction films, the nanorod-array films show significantly improved photoelectrochemical properties due, we believe, to the high surface area and improved separation of the photogenerated charge at the WO(3)/BiVO(4) interface. Synthesis details are discussed, with film morphologies and structures characterized by field emission scanning electron microscopy and X-ray diffraction.
Nano Letters 05/2011; 11(5):1928-33. · 13.20 Impact Factor
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ABSTRACT: Anodization Cu 2 O pH Chloride Fluoride Morphology Annealing Described is the synthesis of various copper oxide nanostructured thin films by anodization of Cu foil in aqueous and ethylene glycol electrolytes containing hydroxide, chloride and/or fluoride ions at room temperature. The nanostructure topology was found to depend on the pH of the anodization electrolyte, KOH concentration, applied voltage and the presence of chloride and fluoride ions. Our results demonstrate the opportunity to grow complex copper oxide nanostructured films possessing sub-micron thick layers by a simple and straightforward electrochemical route. Although no film was observed on the Cu surface when the anodization was carried out at 10 V in KOH solutions with pH≤ 10, various nanoarchitectures were formed upon increasing the electrolyte pH in the presence of chloride ions. Replacing chloride ions with fluoride ions resulted in the formation of highly porous nanoarchitectures. A simple mechanism for the formation of such porous structures is proposed. Anodizing in ethylene glycol-based electrolytes resulted in the formation of leaf-like nanoarchitectures up to 500 nm in thickness. XPS analysis was performed to study the composition of the formed nanoarchitectures. Vacuum annealing of the material at 280 °C resulted in the formation of porous Cu 2 O nanoarchitectures.
Materials Letters 05/2011; · 2.31 Impact Factor
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ABSTRACT: TiO(2) nanotube arrays (NTAs) are modified with PbS nanoparticles by successive ionic layer adsorption and reaction (SILAR) or electrodeposition, with an aim towards tuning the photoelectrochemical cell to the visible region. The PbS modification of the TiO(2) NTAs results in an increase in the visible light adsorption, however the increase in photocurrent is dependent on the modification method. PbS/TiO(2) NTAs prepared by SILAR and electrodeposition show, respectively, photocurrents of 11.02 and 5.72 mA/cm(2). The increase in photocurrent is attributed to enhanced charge separation efficiency and improved electron transport.
ACS Applied Materials & Interfaces 02/2011; 3(3):746-9. · 4.53 Impact Factor
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ABSTRACT: Photocorrosion stable WO(3) nanowire arrays are synthesized by a solvothermal technique on fluorine-doped tin oxide coated glass. WO(3) morphologies of hexagonal and monoclinic structure, ranging from nanowire to nanoflake arrays, are tailored by adjusting solution composition with growth along the (001) direction. Photoelectrochemical measurements of illustrative films show incident photon-to-current conversion efficiencies higher than 60% at 400 nm with a photocurrent of 1.43 mA/cm(2) under AM 1.5G illumination. Our solvothermal film growth technique offers an exciting opportunity for growth of one-dimensional metal oxide nanostructures with practical application in photoelectrochemical energy conversion.
Nano Letters 01/2011; 11(1):203-8. · 13.20 Impact Factor
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Journal of Biomedical Materials Research Part A 01/2011; · 2.63 Impact Factor
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ABSTRACT: Thick-film magnetoelastic sensors vibrate mechanically in response to a time varying magnetic excitation field. The mechanical vibrations of the magnetostrictive magnetoelastic material launch, in turn, a magnetic field by which the sensor can be monitored. Magnetic field telemetry enables contact-less, remote-query operation that has enabled many practical uses of the sensor platform. This paper builds upon a review paper we published in Sensors in 2002 (Grimes, C.A.; et al. Sensors 2002, 2, 294-313), presenting a comprehensive review on the theory, operating principles, instrumentation and key applications of magnetoelastic sensing technology.
Sensors 01/2011; 11(3):2809-44. · 1.74 Impact Factor
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Nano Letters 10/2010; · 13.20 Impact Factor
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ABSTRACT: The functionalized unsymmetrical benzothiazole squaraine organic sensitizers 5-carboxy-2-({3-[(3-hexylbenzothiazol-2(3H)-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene}methyl)-1-hexyl-3,3-dimethyl-3H-indolium (hereafter named as SK-11) and 5-carboxy-2-({3-[(3-hexyl-5-methoxybenzothiazol-2(3H)-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene}methyl)-1-hexyl-3,3-dimethyl-3H-indolium (coded as SK-12) are designed and developed to observe an intense and wider absorption band in the red/NIR wavelength region. DFT/TDDFT calculations have been performed on the two unsymmetrical squaraine sensitizers to gain insight into their electronic and optical properties. The utility of these dyes in solid state dye sensitized solar cells (SS-DSSCs) is demonstrated.
Langmuir 08/2010; 26(16):13486-92. · 4.19 Impact Factor
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ABSTRACT: Solid-state dye-sensitized solar cells (SS-DSCs) offer the potential to make low cost solar power a reality, however their photoconversion efficiency must first be increased. The dyes used are commonly narrow band with high absorption coefficients, while conventional photovoltaic operation requires proper band edge alignment significantly limiting the dyes and charge transporting materials that can be used in combination. We demonstrate a significant enhancement in the light harvesting and photocurrent generation of SS-DSCs due to Förster resonance energy transfer (FRET). TiO(2) nanotube array films are sensitized with red/near IR absorbing SQ-1 acceptor dye, subsequently intercalated with Spiro-OMeTAD blended with a visible light absorbing DCM-pyran donor dye. The calculated Förster radius is 6.1 nm. The donor molecules contribute a FRET-based maximum IPCE of 25% with a corresponding excitation transfer efficiency of approximately 67.5%.
Nano Letters 07/2010; 10(7):2387-94. · 13.20 Impact Factor
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ABSTRACT: It appears that the efficiency of dye-sensitized solar cells (DSSCs) has reached a ceiling due to the limited absorption spectrum of currently available dyes. To achieve new record efficiencies, light absorption must be extended into the near-infrared region of the spectrum without sacrificing performance in the visible region. No single dye has this ability, but there is greater strength in numbers. Forster resonance energy transfer (FRET) may be used to link two or more materials to provide strong absorption across a broad portion of the solar spectrum. This process has been shown to be effective and efficient, and a recent breakthrough in FRET-enhanced DSSCs is presented in this issue. This Perspective explores the background of this topic and considers directions for future development.
ACS Nano 03/2010; 4(3):1253-8. · 10.77 Impact Factor
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ABSTRACT: The past several decades have seen a significant rise in atmospheric carbon dioxide levels resulting from the combustion of hydrocarbon fuels. A solar energy based technology to recycle carbon dioxide into readily transportable hydrocarbon fuel (i.e., a solar fuel) would help reduce atmospheric CO2 levels and partly fulfill energy demands within the present hydrocarbon based fuel infrastructure. We review the present status of carbon dioxide conversion techniques, with particular attention to a recently developed photocatalytic process to convert carbon dioxide and water vapor into hydrocarbon fuels using sunlight.
ACS Nano 02/2010; 4(3):1259-78. · 10.77 Impact Factor
