W. P. Gomes

Simon Fraser University, Burnaby, British Columbia, Canada

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Publications (114)188.27 Total impact

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    A.Vervaet, W.P.Gomes, F.Cardon
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    ABSTRACT: Only recently, has some attention been paid to InP as a semiconductor elec. trode material, especially in view of its possible applications for solar energy conversion purposes [ 1--3]. Impedance measurements on n- and p-InP electrodes have led to the determination of the flat-band potential and hence of the position of the band edges at the electrode surface [ 3,4]. In the present communication, some results on electrochemical and photoelectrochemi.cal reactions at the nand p-InP single crystal electrodes are reported.
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    A.Vervaet, W.P.Gomes, F.Cardon
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    A.Vervaet, W.P.Gomes, F.Cardon
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    Dataset: scannen0008
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    Dataset: scannen0005
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    Dataset: scannen0002
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    Dataset: scannen0007
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    Dataset: scannen0004
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    Dataset: scannen0006
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    Dataset: scannen0003
  • M. J. Madou, F. Cardon, W. P. Gomes
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    ABSTRACT: Cyclic-voltammetric electrochemical studies were performed on n- and p-type GaP single crystal electrodes in indifferent aqueous electrolytes. The n-type GaP cathode was observed to show quasi-metallic behaviour and the p-type cathode to be a stable photoelectrode. In this connection some thermodynamic considerations are held. It was found that the potentiodynamic current-voltage characteristics exhibited additional currents as compared to the potentiostatic curves. The additional currents were attributed to surface redox reactions and reactions with oxidation products accumulated at the surface.Es wurden zyklische Strom-Potential-Kurven am n- und p-Typ GaP in indifferenten wäßrigen Elektrolyten registriert. Es zeigte sich, daß die n-leitende GaP-Kathode metallartige Eigenschaften hat und daß die p-leitende Kathode eine stabile Photo-Elektrode ist. In diesem Zusammenhang werden einige thermodynamische Daten diskutiert. Im Vergleich zu den stationären Strom-Spannungs-Kurven wurden in den zyklischen Strom-Spannungs-Kurven zusätzliche Ströme beobachtet. Diese zusätzlichen Ströme wurden Oberflächenredoxreaktionen und Reaktionen mit Oxydationsprodukten an der Oberfläche zugeschrieben.
    05/2010; 82(8):819 - 823. DOI:10.1002/bbpc.19780820812
  • R. A. L. Vanden Berghe, W. P. Gomes
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    ABSTRACT: The anodic behaviour in darkness of the n-type semiconductors ZnO, CdS and CdSe in contact with solutions of indifferent electrolyte and of one-equivalent reducing agents was studied by capacity and current measurements. The same group of strong reducing agents appeared to be able to inject electrons into the conduction band of the three electrodes investigated. Making use of the capacity results and of literature data on redox potentials, an energy diagram was constructed in order to compare the position of the band edges of the semiconductors with that of the redox levels in the electrolyte. A relationship was found between the relative energetic height of these levels and the injection behaviour. The results indicate that the filled energy levels in the redox electrolyte are spread over a rather wide energy range.Das anodische Dunkelverhalten der n-Halbleiter ZnO, CdS und CdSe, die mit Lösungen von indifferentem Elektrolyt und von Reduktionsmitteln, die pro Molekül ein Elektron abgeben können, in Berührung standen, wurde durch Kapazitäts- und Strommessungen untersucht. Dieselbe Gruppe starker Reduktionsmittel konnte anscheinend Elektronen in das Leitungsband der drei untersuchten Elektroden injizieren. Mit Hilfe der gemessenen Kapazitäten und Literaturwerten der Redoxpotentiale wurde ein Energiediagramm aufgestellt, um die Lagen der Bandkanten in den Halbleitern und der Redoxniveaus im Elektrolyt zu vergleichen. Zwischen der relativen Höhe der Energieniveaus und dem Injektionsverhalten wurde ein Zusammenhang gefunden. Die Ergebnisse weisen darauf hin, daß sich die gefüllten Energieniveaus im Redox-Elektrolyt über einen ziemlich weiten Energiebereich erstrecken.
    05/2010; 76(6):481 - 485. DOI:10.1002/bbpc.19720760605
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    ABSTRACT: The anodic behaviour of CdS in contact with an indifferent electrolyte was studied in darkness and under illumination by current-voltage, capacity-voltage and analytical measurements. Marked effects of surface pretreatment on the current and the capacity were observed. The results suggest that pre-breakdown phenomena are involved in the dark current mechanism as well as in some anomalies observed in the photocurrent under band-gap illumination. Photo-effects were also found at wavelengths up to 800 nm and ascribed to the presence of localised electron levels in the space charge region. Surface and sub-surface imperfections appear to play an important role in the electrochemical behaviour of the CdS anode.Das anodische Verhalten des Cadmiumsulfids, das mit Lösungen von indifferentem Elektrolyt in Berührung stand, wurde im Dunkeln und unter Belichtung durch Strom-Spannungs-, Kapazitt-Spannungs- und analytische Messungen untersucht. Ausgeprgte Effekte der Oberflchenvorbehandlung auf den Strom und auf die Kapazitt wurden beobachtet. Die Ergebnisse deuten darauf hin, daß Vordurchschlagerscheinungen auftreten beim Dunkelstrommechanismus und bei gewissen Anomalien, beobachtet am Photostrom unter Bestrahlung mit Licht von Energie, der Bandlücke entsprechend. Photoeffekte wurden auch mit Licht von Wellenlngen bis 800 nm gefunden und der Anwesenheit lokalisierter Elektronenterme im Raumladungsgebiet zugeschrieben. Es ergibt sich, daß Oberflchen- und Randschichtdefekte beim elektrochemischen Verhalten der CdS-Anode eine wichtige Rolle spielen.
    05/2010; 77(4):289 - 293. DOI:10.1002/bbpc.19730770415
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    ABSTRACT: The anodic dark current at the single crystal CdS/indifferent electrolyte interface was studied on different crystal faces of several samples as a function of applied voltage, of pretreatment of the crystal, of electrolyte composition and of temperature. The results indicate that electron tunneling from surface states located at about 0.12 eV below the conduction band edge into the crystal constitutes the rate-determining step of the electrode reaction. The observed activation energy of 0.42 eV is interpreted on the basis of an equilibrium between the surface states and the solution. The influence of preliminary etching on the current is attributed to changes in the number of surface states.Der anodische Dunkelstrom durch die Phasengrenze zwischen einem CdS-Einkristall und einem indifferenten Elektrolyten wurde auf verschiedenen Kristalloberflächen mehrerer Spezimes in Abhängigkeit von der angelegten Spannung, der Vorbehandlung des Kristalls, der Zusammensetzung des Elektrolyten und der Temperatur untersucht. Die Ergebnisse weisen darauf hin, daß ein Tunnelvorgang von Elektronen aus Oberflächenzuständen lokalisiert auf etwa 0,12 eV unter der Leitungsbandkante zum Kristallinneren der geschwindigkeitsbestimmende Teilschritt der Elektrodenreaktion ist. Die gemessene Aktivierungsenergie von 0,42 eV wird auf Grund eines Gleichgewichts zwischen den Oberflächenzuständen und der Lösung gedeutet. Der Einfluß vorangehender Ätzung auf den Strom wird Veränderungen der Zahl von Oberflächenzuständen zugeschrieben.
    05/2010; 78(4):331 - 335. DOI:10.1002/bbpc.19740780406
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 04/2010; 22(16). DOI:10.1002/chin.199116014
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 02/2010; 27(9). DOI:10.1002/chin.199609019
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    ABSTRACT: The influence of the light intensity (L) and the concentration (y) of the Fe(CN)64 ion on the stabilization of n-GaP photoelectrodes was studied in alkaline medium by means of the rotating ring-disk technique. The steady-state stabilization ratio increased with increasing y or decreasing L. A kinetic model, involving surface intermediates, is proposed in order to explain the experimental results.
    01/2010; 89(3). DOI:10.1002/bscb.19800890305
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    ABSTRACT: In this paper, the etching behaviour of germanium in hydrogen peroxide solutions is described. Electrochemical experiments showed that the etching process is most probably purely chemical. The etch rate was found to depend upon the H2O2 concentration, the pH value, the amount of KCl in the solution and , in some cases, upon the rotation rate. Based on all of these findings, possible etching mechanisms for Ge in H2O2 are discussed on a molecular level.
    ECS Transactions 04/2007; 6(2). DOI:10.1149/1.2731205
  • I. M. Huygens, W. P. Gomes, K. Strubbe
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    ABSTRACT: Luminescence measurements in aqueous solutions were performed upon n-GaN layers grown on sapphire substrates and on Si substrates. Photoluminescence (PL) measurements at n- and n- electrodes show an identical emission band centered at 2.20 eV (the well-known yellow luminescence band), showing that the same deep acceptor level is present in both materials. Additional reddish luminescence is observed when the holes are injected from the solution [electroluminescence (EL)], which may be ascribed to the occurrence of radiative (near) surface recombination. From an analysis of the potential dependence of both the PL and EL intensity of the 2.20-eV band, it may be concluded that this band possesses a significant contribution from the (near) surface.
    12/2005; 153(1):G72-G77. DOI:10.1149/1.2135218
  • I. M. Huygens, W. P. Gomes, K. Strubbe
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    ABSTRACT: Photocurrent multiplication (‘photocurrent doubling’) effects were studied at n-GaN electrodes in 1M H2SO4 solutions containing formic acid. The photocurrent multiplication factor f was measured as a function of different parameters. It was found that f increases with increasing formic acid concentration, reaching a limiting value at high concentrations. Surprisingly, this limiting value for f was found to depend upon the extent of photoanodic etching prior to performing the photocurrent multiplication measurements: it increased from about 1.05 for ‘new’ electrodes to a maximum of 1.3 for etched electrodes. This suggests that somehow, intrinsic surface states are involved in the photo-oxidation of formic acid, the concentration of which changes due to etching. Further, it appeared that n-GaN dissolves photoanodically in 1M H2SO4 solutions containing formic acid, even at very high concentrations. A mechanism, accounting for all of the experimental findings was proposed.
    Electrochimica Acta 05/2005; 50(14):2919-2926. DOI:10.1016/j.electacta.2004.11.041 · 4.09 Impact Factor

Publication Stats

845 Citations
188.27 Total Impact Points

Institutions

  • 2010
    • Simon Fraser University
      • Department of Physics
      Burnaby, British Columbia, Canada
  • 1971–2010
    • Ghent University
      • • Department of Inorganic and Physical Chemistry
      • • Department of Solid-state Physics
      Gand, Flemish, Belgium
  • 1996
    • Utrecht University
      Utrecht, Utrecht, Netherlands