Roger J. Mortimer

Loughborough University, Loughborough, England, United Kingdom

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Publications (100)348.14 Total impact

  • D. M. Haspel · M. A. Ashworth · L. Wu · G. D. Wilcox · R. J. Mortimer

    No preview · Article · Nov 2015 · Transactions of the Institute of Metal Finishing
  • Adriana S. Ribeiro · Roger J. Mortimer

    No preview · Chapter · Sep 2015
  • Paul M. S. Monk · David R. Rosseinsky · Roger J. Mortimer
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    ABSTRACT: Bipyridilium species are electrochromic. These compounds have several trivial, non-IUPAC names. By far the most common is ‘viologen’. Electrochromism occurs in bipyridilium species because, in contrast to the bipyridilium dications, radical cations display an intense colour. The colours of viologen radical cations species change with concentration. For viologens with short alkyl chains, the radical cation is monomeric in solution and has a blue colour becoming blue purple when the solution is more concentrated. By comparison, aryl-substituted viologens generally form a solid green or dark-red deposit. Most viologen species can operate as a type-1 electrochrome. Type-2 electrochromes are in solution when colourless but are solid in their coloured forms. The exemplar devices are described in more or less the order of their appearance in patents or as marketable products: the Philips device, ICI device, IBM device, Gentex device, NTERA Device, NanoChromics cell, and the Grätzel device.
    No preview · Chapter · Jul 2015
  • David R. Rosseinsky · Roger J. Mortimer

    No preview · Chapter · Jul 2015
  • J. Wang · G. D. Wilcox · R. J. Mortimer · C. Liu · M. A. Ashworth
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    ABSTRACT: The control of interfacial microstructural stability is of utmost importance to the reliability of liquid solder interconnects in high temperature electronic assemblies. This is primarily due to excessive intermetallic compounds (IMCs) that can form and continuously grow during high temperature operation, which renders conventional barrier metallisations inadequate. With the intention of reducing such excessive IMC growth, electrically conducting, NbOx containing Ni coatings were developed using electrodeposition and were assessed as solder diffusion barrier layers in terms of their electrical conductivity and barrier property. The present work adopts a novel electrochemical route to produce Ni-NbOx composite coatings of good uniformity, compactness and purity, from non-aqueous glycol-based electrolytes consisting of NiCl2 and NbCl5 as metal precursors. The effects of cathodic current density and NaBH4 concentrations on the surface morphology, composition and thickness of the coatings were examined. Increased NaBH4 concentrations were found to elevate the maximum deposit thickness (above 10 μm), although these led to a reduction in the co-deposited Nb content. The composite coatings generally exhibited good electrical conductivity. The reaction between a liquid 52In-48Sn solder and Ni-NbOx, with Nb contents up to 6 at.%, was studied at 200°C. The results indicate that, Ni-NbOx with sufficient layer thickness and higher Nb content, offered longer service lifetime. Nb enrichment was generally observed at or close to the reaction front after high temperature storage which suggests evident effectiveness of the enhanced diffusion barrier characteristics. A mechanism for the role of Nb as a barrier performance enhancer was postulated.
    No preview · Article · Apr 2015 · ECS Transactions
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    ABSTRACT: The copolymerisation of 3,3′″ Dihexyl-2,2′:5′,2″:5″,2′″-quaterthiophene (DHQT) and (R)-(-)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-α-phenylglycinate (DNBP) was successfully performed electrochemically in acetonitrile (CH3CN) containing tetrabutylammonium tetrafluoroborate ((C4H9)4NBF4) by direct oxidation of monomer mixtures in different feed ratios. Copolymerisation improved the properties of the films of both polymers PDHQT and PDNBP, in respect to the adhesion of PDHQT onto ITO/glass surface and the chromatic contrast of these electrochromic materials. PDHQT, PDNBP and P(DHQT-co-DNBP) films were characterised by FTIR spectroscopy, fluorescence spectroscopy, Scanning Electron Microscopy (SEM) and spectroelectrochemical techniques. Solutions of PDHQT and its copolymers with DNBP (independently of the feed ratio) in N-methylpyrrolidone are fluorescent with emission bands at 555 and 585 nm when excited at 375 nm. Reversible changes in the hue and saturation occur in all the copolymer films from yellow or orange in the reduced state to green or blue in the oxidised state, but were dependent on the proportion of the comonomers used to prepare the copolymers. These changes are more significant for P(DHQT-co-DNBP) films deposited onto ITO/glass with 1:5 feed ratio, as shown by the track of the CIE 1931 xy chromaticity coordinates and by the electrochromic parameters in which this film (thickness 0.8±0.2 μm) presented chromatic contrast (Δ%T) at 660 nm of 62%, coloration efficiency (η) of 266 cm2 C−1 and stability to redox cycling (Δ%T=17% at the 1000th cycle). Therefore, these copolymers are potentially applicable in displays and optoelectronic devices as electrochromic and fluorescent materials.
    Full-text · Article · Mar 2015 · Solar Energy Materials and Solar Cells
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    ABSTRACT: The control of interfacial microstructural stability is of utmost importance to the reliability of liquid solder interconnects in high temperature electronic assemblies. This is primarily due to excessive intermetallic compounds (IMCs) that can form and continuously grow during high temperature operation, which renders conventional barrier metallizations inadequate.With the intention of reducing such excessive IMC growth, electrically conducting, NbOx containing Ni coatings were developed using electrodeposition and were assessed as solder diffusion barrier layers in terms of their electrical conductivity and barrier property. The present work adopts a novel electrochemical route to produce Ni-NbOx composite coatings of good uniformity, compactness and purity, from nonaqueous glycol-based electrolytes consisting of NiCl2 and NbCl5 as metal precursors. The effects of cathodic current density and NaBH4 concentrations on the surface morphology, composition and thickness of the coatings were examined. Increased NaBH4 concentrations were found to elevate the maximum deposit thickness (above 10 μm), although these led to a reduction in the co-deposited Nb content. The composite coatings generally exhibited good electrical conductivity. The reaction between a liquid 52In-48Sn solder and Ni-NbOx, with Nb contents up to 6 at.%, was studied at 200°C. The results indicate that, Ni-NbOx with sufficient layer thickness and higher Nb content, offered longer service lifetime. Nb enrichment was generally observed at or close to the reaction front after high temperature storage which suggests evident effectiveness of the enhanced diffusion barrier characteristics. A mechanism for the role of Nb as a barrier performance enhancer was postulated.
    Preview · Article · Jan 2015 · Journal of The Electrochemical Society
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    ABSTRACT: Stainless steels are used in an array of applications where their ability to take on colour is of aesthetic value. Although thermal colouring (heat tinting) is known, particularly in terms of its effect on welds, the surface development of thermally coloured stainless steel has not been considered in detail. This paper demonstrates the colour development of a bright annealed 304 stainless steel with time at temperature. The colour development has been quantified using colour spectrophotoscopy and the colour related to the growth of surface oxide features by scanning electron microscopy and the chemical profiles by X-ray photoelectron spectroscopy (XPS). There is a clear development of both the oxide thickness and chemistry, with increasing time with small nodules being the main features seen across the surface of the samples with time. The oxides have been shown to comprise of an outer iron rich oxide and an inner chromium/iron spinel layer.
    No preview · Article · Jan 2015 · Materials at High Temperatures
  • M. A. Ashworth · D. Haspel · L. Wu · G. D. Wilcox · R. J. Mortimer
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    ABSTRACT: Since the ‘cracked oxide theory’ was proposed by Tu in 1994,1 there has only been a limited number of studies that have sought to investigate the effect of the Sn oxide on whisker growth. The current study has used electrochemical oxidation to produce oxide films, which has enabled the effect of the surface oxide thickness on whisker growth to be established. The effect of oxide thickness on whisker growth has been investigated for tin electrodeposits on both Cu and brass substrates. The influence of applied oxidation potential on the thickness of the Sn oxide film has been investigated using x-ray photoelectron spectroscopy (XPS) for potassium bicarbonate–carbonate and borate buffer electrolyte solutions. Whisker growth from electrochemically oxidised Sn-Cu deposits on Cu and Sn deposits on brass has been investigated and compared with samples left to develop a native air-formed oxide. XPS studies show that the thickness of the electrochemically formed Sn oxide film is dependent on the applied oxidation potential and the total charge passed. Subsequent whisker growth studies demonstrate that electrochemically oxidised Sn-Cu deposits on Cu and Sn deposits on brass are significantly less susceptible to whisker growth than those having a native oxide film. For Sn deposits on brass, the electrochemically formed Sn oxide greatly reduces Zn oxide formation at the surface of the tin deposit, which results in whisker mitigation. For Sn-Cu deposits on Cu, the reduction in whisker growth must simply derive from the increased thickness of the Sn oxide, i.e. the Sn oxide film has an important role in stemming the development of whiskers.
    No preview · Article · Jan 2015 · Journal of Electronic Materials
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    ABSTRACT: Electrochromic thin-film ‘hydrous nickel oxide’ (nickel hydroxide) was deposited on fluorine-doped tin oxide (FTO)/glass substrates by galvanostatic electrochemical reduction at −0.1 mA cm−2 for 100, 400 and 800 s from aqueous 0.01 mol dm−3 nickel nitrate solution. Following transfer to aqueous 0.1 mol dm−3 potassium hydroxide, the transmittance and absorbance changes, colouration efficiencies and stability to multiple potential cycling were measured on reversibly electrochemically switching the transmissive light green (essentially ‘bleached’) ‘hydrous nickel oxide’ to the deep brown (‘coloured’) nickel oxyhydroxide redox state. The ‘hydrous nickel oxide’ (as deposited) films showed excellent transmittance modulation, achieving a maximum Δ%T of 83.2 at 432 nm, for the highest deposition time (800 s) studied. Colouration efficiency (CE) values were ∼30 cm2 C−1, with response times of 12.0 s (colouration) and 9.5 s (‘bleaching’). Using the Commission Internationale de l’Eclairage (CIE) system of colorimetry, the colour stimuli at rest, and on dynamically reversibly switching between the electrochromic redox states were calculated from in situ visible spectra recorded under electrochemical control. Reversible changes in hue and saturation occur, as shown by the track of the CIE 1931 xy chromaticity coordinates, together with a sharp decrease in luminance on oxidation. CIELAB L*a*b* coordinates were also used to quantify the colour of the electrochromic films. A combination of a low L*, and positive a* and b* values, quantified the perceived deep brown ‘coloured’ state.
    No preview · Article · Dec 2014 · Journal of Solid State Electrochemistry
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    ABSTRACT: Electroplated tin finishes are widely used in the electronics industry due to their excellent solderability, electrical conductivity and corrosion resistance. However, the spontaneous growth of tin whiskers during service can result in localised electrical shorting or other harmful effects. Until recently, the growth of tin whiskers was successfully mitigated by alloying the tin with lead. However, restriction in the use of lead in electronics as a result of EU legislation (RoHS) has led to renewed interest in finding a successful alternative mitigation strategy.
    Preview · Article · Nov 2014 · Microelectronics Reliability
  • C. J. Stuttle · M. A. Ashworth · G. D. Wilcox · R. J. Mortimer
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    ABSTRACT: In the present investigations electrochemical oxidation has allowed for the removal of tin from coated copper substrates permitting scanning electron microscopy to be employed to assess intermetallic compound distribution and morphology. It was shown that the initial growth of intermetallic compound was not uniform, with its distribution dependent upon the grain structure of the copper substrate, and the grain orientation and distribution within the tin coating. After a period of further nucleation and coarsening, the intermetallic compound forms an almost complete layer along the interface. It is thought this uniform layer of intermetallic compound, formed soon after deposition, may be responsible for this specific electrodeposited tin system having a low whiskering propensity.
    No preview · Article · Sep 2014 · Transactions of the Institute of Metal Finishing
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    ABSTRACT: Ni-NbOx nano-composite coatings on Cu, from glycol-based electrolytes consisting of NbCl5, NiCl2 center dot 6H(2)O and propylene glycol. The effects of both cathodic current density and metal electrodeposition bath concentrations on the surface morphology and composition of the coating were examined. The highest relative metal percentage of co-deposited Nb was 14.3 at% obtained at a current density of 400 mA/cm(2). Scanning transmission electron microscopy (STEM) revealed a nanocrystalline FCC Ni structure without any significant lattice distortion, as well as an as-yet-unidentified compound. STEM X-ray mapping suggests Nb and O were uniformly distributed in the Ni matrix, without any significant phase segregation, which is consistent with XPS compositional depth profiling. Also, according to the XPS spectra, a 0.7 eV shift to lower binding energy for the Nb (V) species may suggest the partial chemical reduction of Nb2O5 due to possible Ni-Nb bonding. It is thus proposed that a Ni-NbOx deposit was formed by two parallel electrochemical reduction routes: 1) deposition of Ni metal; 2) deposition of a Ni-Nb-O compound as nano-clusters.
    No preview · Article · May 2014 · Journal of The Electrochemical Society
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    ABSTRACT: Polyaniline (PAni) was modified with chitosan and/or organophilic clay (Nanomer I-24) by in situ polymerisation using p-toluenesulfonic acid (PTSA) as dopant agent. These materials were characterised by FTIR spectroscopy, thermal analysis, scanning electron microscopy, d.c. electrical conductivity and spectroelectrochemical measurements. All samples maintained the electrical and electrochromic properties inherent to the PAni. Also, the addition of clay to the samples improved thermal stability and the modification of the PAni with chitosan provided the formation of homogeneous films with good adhesion onto ITO/glass electrodes as compared with pristine PAni. Using the CIE (Commission Internationale de l'Eclairage) system of colorimetry the colour stimuli of the PAni and PAni hybrid films deposited onto ITO/glass were calculated from in situ visible spectra recorded simultaneously to the cyclic voltammograms. Reversible changes in the hue and saturation occur in the films of all samples from yellow in the reduced state to blue in the oxidised state, but the change is much more significant for the PAni-chitosan-clay, as shown by the track of the CIE 1931 xy chromaticity coordinates. For the PAni-chitosan-clay film, the CIELAB 1976 colour space coordinates for a D55 illuminant were L* = 67, a* = −27 and b* = 51, and L* = 17, a* = −22 and b* = −5, respectively for the film in the reduced and oxidised states. These materials showed good electrochromic properties and could be applied in the assembly of electrochromic devices.
    Full-text · Article · Mar 2014 · RSC Advances
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    ABSTRACT: The synthesis and fluorescence characterization of a new pyrrole derivative (PyPDG) containing the electron donor-acceptor dansyl substituent is reported. The effects of temperature and solvent polarity on the steady-state fluorescence of this compound are investigated. Our results show that PyPDG exhibits desirable fluorescent properties which makes it a promising candidate to be used as the photoactive material in optical thermometry and thermography applications. Further, the electrochemical and emission properties of polymeric films obtained from the oxidation polymerization of PyPDG are also analyzed.
    Full-text · Article · Mar 2014 · Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy
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    ABSTRACT: Aerosol-assisted chemical vapor deposition (AACVD) was used for the first time in the preparation of thin-film electrochromic nickel(II) oxide (NiO). The as-deposited films were cubic NiO, with an octahedral-like grain structure, and an optical band gap that decreased from 3.61 to 3.48 eV on increase in film thickness (in the range 500-1000 nm). On oxidative voltammetric cycling in aqueous KOH (0.1 mol dm(-3)) electrolyte, the morphology gradually changed to an open porous NiO structure. The electrochromic properties of the films were investigated as a function of film thickness, following 50, 100, and 500 conditioning oxidative voltammetric cycles in aqueous KOH (0.1 mol dm(-3)). Light modulation of the films increased with the number of conditioning cycles. The maximum coloration efficiency (CE) for the NiO (transmissive light green, the "bleached" state) to NiOOH (deep brown, the colored state) electrochromic process was found to be 56.3 cm(2) C(-1) (at 450 nm) for films prepared by AACVD for 15 min followed by 100 "bleached"-to-colored conditioning oxidative voltammetric cycles. Electrochromic response times were <10 s and generally longer for the coloration than the bleaching process. The films showed good stability when tested for up to 10 000 color/bleach cycles. Using the CIE (Commission Internationale de l'Eclairage) system of colorimetry the color stimuli of the electrochromic NiO films and the changes that take place on reversibly oxidatively switching to the NiOOH form were calculated from in situ visible spectra recorded under electrochemical control. Reversible changes in the hue and saturation occur on oxidation of the NiO (transmissive light green) form to the NiOOH (deep brown) form, as shown by the track of the CIE 1931 xy chromaticity coordinates. As the NiO film is oxidized, a sharp decrease in luminance was observed. CIELAB L*a*b* coordinates were also used to quantify the electrochromic color states. A combination of a low L* and positive a* and b* values quantified the perceived deep brown colored state.
    No preview · Article · Jun 2013 · ACS Applied Materials & Interfaces
  • Roger J. Mortimer · Thomas S. Varley
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    ABSTRACT: Prototype electrochromic devices (ECDs) based on anodically-colouring thin-film Prussian blue (PB) or Ruthenium purple (RP) and cathodically-colouring aqueous solution-phase di-n-heptyl viologen are described. The initial (‘off’) state of each ECD is set with the PB (or RP) in the colourless reduced form and the di-n-heptyl viologen as the colourless di-cation. Switching the ECDs to the coloured state (‘on’), forms on oxidation the coloured mixed-valence PB (or RP), with simultaneous reduction of the di-n-heptyl viologen di-cation to form the purplish-red di-n-heptyl viologen radical cation dimer salt as a thin film. The overall perceived reversible colour changes were colourless to deep blue/purple for the PB/di-n-heptyl viologen ECDs and colourless to pinkish-purple for the RP/di-n-heptyl viologen ECDs. Using the Commission Internationale de l'Eclairage (CIE) system of colorimetry, the colour stimuli of the ECDs were calculated from in situ visible region spectra recorded under electrochemical control, the depth of colour being controlled by the di-n-heptyl viologen concentration. For the coloured states of the PB/di-n-heptyl viologen ECDs, the CIELAB 1976 colour space coordinates for a D55 illuminant were L⁎=60, a*=22 and b*=−47, and L*=39, a*=47 and b*=−55, respectively for 5 and 10 mmol dm−3 di-n-heptyl viologen solution concentrations. For the RP/di-n-heptyl viologen ECDs, the coordinates were L*=70, a*=31 and b*=−27, and L*=63, a*=44 and b*=−34, respectively for 5 and 10 mmol dm−3 di-n-heptyl viologen solution concentrations. L* quantifies the lightness, with +a*, −a*, +b* and −b* respectively giving the red, green, yellow and blue directions away from the achromatic point (0, 0).
    No preview · Article · Feb 2013 · Solar Energy Materials and Solar Cells
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    ABSTRACT: Prussian-blue (PB) film for electro-chromism can be electro-deposited on to an electrode (usually tin-doped indium oxide/glass) either directly from a PB colloid or from ferric ferricyanide in a two-electrode electro-chemical cell by applying a reductive potential. Alternatively, a “sacrificial” electron-producing silver flag electrode in the solution, when connected to the PB-receiving electrode, can effect the required reductive deposition. A silver spot, here innovatively applied as silver paint directly onto the deposition electrode, produces PB film on immersion in the iron(III)(III) solution, obviating the separate counter-electrode method.
    No preview · Article · Dec 2012 · Journal of Solid State Electrochemistry
  • Roger J. Mortimer · Thomas S. Varley
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    ABSTRACT: The fabrication, in situ spectroelectrochemistry and colour measurement of hybrid electrochromic devices (ECDs) based on a surface-confined metal hexacyanometallate – Prussian blue (PB, containing the iron(III) hexacyanoferrate(II) chromophore) – and aqueous solution-phase methyl viologen (N,N′-dimethyl-4,4′-bipyridylium) are described. In the ECDs, the initial (‘off’) bleached state is set with PB in its reduced form and the methyl viologen as the di-cation. Switching to the coloured state (‘on’), forms the mixed-valence iron(III) hexacyanoferrate(II) chromophore upon oxidation of iron(II) hexacyanoferrate(II), with simultaneous reduction of the methyl viologen di-cation to form a mixture of the radical cation monomer/dimer. Using the Commission Internationale de l'Eclairage (CIE) system of colorimetry, the colour stimulus of such ECDs and the changes that take place on reversibly switching between the colourless and coloured states have been calculated from in situ visible region spectra recorded under electrochemical control. The concentration of the solution-phase methyl viologen and its diffusion to the cathode controlled both the proportion of surface-confined (reduced) PB that is switched to the blue form and the overall ECD changes. For the ECDs' ‘on’ states, the CIELAB 1976 colour space coordinates for a D55 illuminant were L⁎=60, a⁎=3 and b⁎=−46, and L⁎=49, a⁎=9 and b⁎=−59, respectively for 5 and 10 mM methyl viologen solution concentrations. The low a⁎ and high (negative) b⁎ chromaticity coordinates quantified the overall ECD colour stimulus of the ‘on’ state as being deep blue, with a broad absorption across the visible spectral region. CIELAB 1976 colour space coordinates showed that the ECDs were fully transparent and nearly colourless in the ‘off’ states, with L⁎=100, a⁎=1 and b⁎=1. The changes in the transparency were 83.0% (5 mM methyl viologen) and 93.1% (10 mM methyl viologen) between the ‘off’ (bleached) and ‘on’ (coloured) states of the ECDs.
    No preview · Article · Apr 2012 · Solar Energy Materials and Solar Cells
  • Roger J. Mortimer · Thomas S. Varley
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    ABSTRACT: A novel color-reinforcing electrochromic device (ECD) is described in which the anode and cathode reactions simultaneously exhibit reversible colorless to intense purple changes. Under coloration, the mixed-valence iron(III) hexacyanoruthenate(II) chromophore is formed on oxidation of iron(II) hexacyanoruthenate(II), with simultaneous reduction of the methyl viologen dication to form a mixture of the radical cation monomer/dimer. Using the CIE (Commission Internationale de l'Eclairage) system of colorimetry, the color stimulus of such ECDs and the changes that take place on reversibly switching between the colored and colorless states have been calculated from in situ visible spectra recorded under electrochemical control. On ECD color switching, with the excellent color-matching between the two purple states, sharp and reversible changes in the hue and saturation occur, as shown by the minimal hysteresis of the track of the CIE 1931 xy chromaticity coordinates. Extrapolation of the xy track to the color locus gave a complementary wavelength (λc) of 565 (±5) nm in close agreement with values obtained for the individual electrochromic materials. The concentration of the solution-phase methyl viologen and its diffusion to the cathode controlled both the proportion of surface-confined Ruthenium purple (RP) that is switched to the intense purple form and the overall ECD changes. For the ECDs' "on" states, the CIELAB 1976 color space coordinates were L* = 86, a* = 9, and b* =-15, and L* = 79, a* = 15, and b* =-22, respectively, for 5 and 10 mmol dm-3 methyl viologen solution concentrations. CIELAB 1976 color space coordinates showed that the ECDs were fully transparent and colorless in the "off" states, with L* = 100, a* = 0, and b* = 0. Switching times, as estimated for 95% of the total absorbance change, were 4 and 10 s respectively, for coloration and bleaching for the 5 mmol dm-3 methyl viologen ECD, and 8 and 16 s for the 10 mmol dm-3 methyl viologen ECD.
    No preview · Article · Aug 2011 · Chemistry of Materials

Publication Stats

3k Citations
348.14 Total Impact Points

Institutions

  • 1991-2015
    • Loughborough University
      • Department of Chemistry
      Loughborough, England, United Kingdom
  • 2005-2006
    • University of Florida
      • Department of Chemistry
      Gainesville, FL, United States
  • 1990-2002
    • University of Birmingham
      • School of Chemistry
      Birmingham, England, United Kingdom
  • 1999
    • University of Oxford
      • Inorganic Chemistry Laboratory
      Oxford, England, United Kingdom
  • 1996
    • University of Reading
      Reading, England, United Kingdom
  • 1983
    • University of Exeter
      Exeter, England, United Kingdom