| 1. |
- Doherty, Walter J, et al.
(författare)
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Electrochemical copolymerization and spectroelectrochemical characterization of 3,4-ethylenedioxythiophene and 3,4-ethylenedioxythiophene-methanol copolymers on indium-tin oxide
- 2006
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:13, s. 4418-4424
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Tidskriftsartikel (refereegranskat)abstract
- This work describes the electrochemical copolymerization and spectroelectrochemical characterization of 3,4-ethylenedioxythiophene (EDOT) with a commonly used EDOT derivative: 2,3-dihydrothieno[3,4b]-l,4-dioxyn-2-yl methanol (EDTM), on indium-tin oxide (ITO) electrodes, as a function of the EDTM/EDOT comonomer feed ratio. The potential of initial polymerization and the degree of optical contrast between reduced and oxidized states increased steadily with increasing proportions of EDTM. Reactivity ratios were determined by spectroscopic characterization of the copolymer film and by monitoring the depletion of monomer from the starting solution by liquid chromatography, following the formation of relatively thick PEDOT/PEDTM films. Average reactivity ratios of 1.5 ±0.2 and 0.4 ±0.3 were obtained for EDOT and EDTM, respectively, demonstrating preferential deposition of EDOT on ITO electrode surfaces. Significant differences were noted at low and high degrees of conversion, indicating changes in copolymer composition with film thickness. These results have real significance for the characterization of electron-transfer rates for the first monolayer of PEDOT/ PEDTM on ITO, determined by a new mode of potential-modulated attenuated total reflectance spectroelectrochemistry. © 2006 American Chemical Society.
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| 2. |
- Doherty, Walter J, et al.
(författare)
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Potential-modulated, attenuated total reflectance spectroscopy of poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxythiophene methanol) copolymer films on indium-tin oxide
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:10, s. 4900-4907
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Tidskriftsartikel (refereegranskat)abstract
- We report the first application of a potential-modulated spectroelectrochemical ATR (PM-ATR) instrument utilizing multiple internal reflections at an optically transparent electrode to study the charge-transfer kinetics and electrochromic response of adsorbed films. A sinusoidally modulated potential waveform was applied to an indium-tin oxide (ITO) electrode while simultaneously monitoring the optical reflectivity of thin (2-6 equivalent monolayers) copolymer films of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4ethylenedioxythiophene methanol) (PEDTM), previously characterized in our laboratory.1 At high modulation frequencies the measured response of the polymer film is selective toward the fastest electrochromic processes in the film, presumably those occurring within the first adsorbed monolayer. Quantitative determination of the electrochromic switching rate, derived from the frequency response of the attenuated reflectivity, shows a linear decrease in the rate, from 11 × 103 s-1 to × 103 s -1, with increasing proportions of PEDTM in the copolymer, suggesting that interactions between the methanol substituent on EDTM and the ITO surface slow the switching process by limiting the rate of conformational change in the polymer film. © 2006 American Chemical Society.
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| 3. |
- Doherty, Walter J, et al.
(författare)
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Conducting polymer growth in porous sol-gel thin films : Formation of nanoelectrode arrays and mediated electron transfer to sequestered macromolecules
- 2005
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 17:14, s. 3652-3660
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Tidskriftsartikel (refereegranskat)abstract
- The templated electrochemical growth of poly(3,4-ethylenedioxythiophene) (PEDOT) into porous sol-gel (PSG) films and PEDOT-mediated electron transfer to ferrocene-modified dendrimers encapsulated within these sol-gel matrices, were analyzed. The conditions needed to optimize PEDOT electropolymerization within the PSG films such that barely emergent PEDOT features protrude from a PSG thin film surface, were also described. It was observed that oxidation/reduction of the encapsulated Fc-PAMAM units could be voltammetrically detected after PEDOT growth into the sol-gel film. The results show that up to ca. 20% of these Fc-PAMAM units became electrochemically active, with high rates of electron transfer, when EDTM was conjugated to the Fc-PAMAM dendrimer.
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| 4. |
- Doherty, Walter J, et al.
(författare)
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Electronic structure of Li-intercalated oligopyridines : A comparative study by photoelectron spectroscopy
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:9
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Tidskriftsartikel (refereegranskat)abstract
- The role of nitrogen in the charge transfer and storage capacity of lithium-intercalated heterocyclic oligophenylenes was investigated using photoelectron spectroscopy. The development of new occupied states at low binding energies in the valence band region, as well as core level chemical shifts at both carbon and nitrogen sites, demonstrates partial charge transfer from lithium atoms to the organic component during formation of the intercalated compound. In small compounds, i.e., biphenyl and bipyridine derivatives, the position of the nitrogen heteroatom significantly affects the spacing between gap states in the Li-intercalated film, yet it has minimal effects on the charge storage capacity. In larger, branched systems, the presence of nitrogen in the aromatic system significantly enhances the charge storage capacity while the Li-N bond strength at high intercalation levels is significantly weakened relative to the nitrogen-free derivative. These observations have strong implications towards improved deintercalation processes in organic electrodes in lithium-ion batteries. © 2007 American Institute of Physics.
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| 5. |
- Doherty, Walter J, et al.
(författare)
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Layer-by-layer deposition of copper phthalocyanine from aqueous solution : Molecular orientation, ordering parameters, and electronic structure
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:6, s. 2724-2729
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Tidskriftsartikel (refereegranskat)abstract
- Highly ordered, multilayer films composed of alternating, oppositely charged, polyionic copper phthalocyanines were prepared on HOPG [0001] substrates via layer-by-layer deposition from aqueous solution and characterized by scanning force microscopy and photoelectron spectroscopies. In films of up to four layers, individual layers alternate. Angle-resolved ultraviolet photoelectron spectra are consistent with a molecular orientation parallel to the substrate surface and indicate that structural order is reduced with film thickness © 2007 American Chemical Society.
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| 6. |
- Doherty, Walter J, et al.
(författare)
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Molecular ordering in monolayers of an alkyl-Substituted perylene-bisimide dye by attenuated total reflectance ultraviolet-visible spectroscopy
- 2005
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 59:10, s. 1248-1256
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Tidskriftsartikel (refereegranskat)abstract
- Surface-relative orientational parameters were determined for monolayer films of N, N'-ditridecylperylenetetracarboxylic dianhydridediimide (C 13-PTCDI) in terms of the relative electronic transition dipole strengths, providing a three-dimensional view of the absorption dipole distribution. In order to obtain a macroscopically ordered film, C 13-PTCDI was deposited by (1) horizontal Langmuir-Blodgett (LB) transfer onto methyl- and phenyl-silanized glass, and (2) vapor deposition onto oriented films of poly(tetrafluoroethylene) (PTFE) on glass. Films of LB-deposited C13-PTCDI were found to be completely Isotropic prior to annealing. After annealing, these films remained isotropic in the plane of the substrate while the out-of-plane anisotropy was significantly enhanced. In contrast, films of C13-PTCDI vapor deposited onto oriented poly(tetrafluoroethylene) (PTFE)-modified substrates yielded films with a high degree of both in- and out-of-plane anisotropy. Atomic force microscopy (AFM) images of both the LB- and vapor-deposited films show substantial differences in film morphology and long-range order. These results demonstrate that molecular orientation in C13-PTCDI films can be controlled by varying substrate surface chemistry and post-deposition processing. © 2005 Society for Applied Spectroscopy.
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| 7. |
- Gorgoi, M, et al.
(författare)
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The high kinetic energy photoelectron spectroscopy facility at BESSY progress and first results
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 601:1-2, s. 48-53
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectroscopy at high kinetic energy is a research field that receives an increasing interest due to the possibility of studying bulk properties of materials and deeply buried interfaces. Recently the high kinetic energy electron (HIKE) spectroscopy facility at BESSY in Berlin has become operative at the bending magnet beamline KMC-1. The first results show very good performance. Electron spectra have been recorded using X-ray energies from 2 keV up to 12 keV. Using back-scattering conditions in the crystal monochromator, very high-resolution has been achieved for photon energies around 2, 6 and 8 keV. In the latter case, spectra with a resolving power from the monochromator of >= 80 000 have been achieved and it has been possible to perform electron spectroscopy with resolving power of >= 60 000, yielding a total instrument resolution of about 150 meV as determined directly from spectra. This paper describes the facility and reports some of the first results. (C) 2009 Elsevier B.V. All rights reserved.
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| 8. |
- J Doherty, Walter, et al.
(författare)
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Selective hydrogen bond disruption in adenine monolayer films by reaction with water
- 2009
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 174:1-3, s. 107-109
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution X-ray photoelectron spectroscopy of two-dimensional films of adenine on a highly oriented pyrolitic graphite [0 0 0 1] surface reveal bonding changes induced by exposure to water. The hydrogen-bond interactions between adenine molecules were replaced by adenine-water hydrogen bonds in a stepwise pattern. This reaction destroyed the film network and changed the chemical state of the nitrogen sites. The reaction with water molecules affected both the donor and acceptor states of the oxygen atoms, as compared to those in water. (C) 2009 Elsevier B.V. All rights reserved.
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