XPS and EXAFS Studies of the Reactions of Co(III) Ammine Complexes with GaAs Surfaces

Bruce J. Tufts, Sharon R. Lunt, Gordon M. Miskelly, Michael J. Sailor, Patrick G. Santangelo, Nathan S. Lewis, Lawrence A. Roe, Keith O. Hodgson, Ian L. Abrahams, Catherine E. Caley

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Abstract

The chemisorption of Co(Il) and Co(III) complexes onto GaAs surfaces has been investigated by X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy, and radiotracer techniques. XPS of (lOO)-oriented-GaAs single crystals exposed to aqueous (pH > 10) [CoIII(NH3)5X]n+ (X = NH3, Br-, HO-) solutions indicated the deposition of a Co(II)-oxo overlayer of approximate stoichiometry Co(OH)2, with a coverage of (0.2-2.4) ⨯ 10-8 mol of Co/cm2 projected area of GaAs. The reaction stoichiometry between Co(IlI) and GaAs was confirmed by quantitative chemical and X-ray fluorescence analysis, as well as by XPS analysis. X-ray absorption spectroscopy indicated that the oxidation state of the adsorbed Co (from either Co(III) or Co(II) complexes) from aqueous pH = 12 electrolytes was Co(II). Extended X-ray absorption fine structure (EXAFS) spectroscopy at 298 K in contact with aqueous 0.010 KOH indicated that the Co had (6 ± 1) O or N scatterers at (2.08 ± 0.05) Å and (7 ± 1) Co (or possibly Ga or As) scatterers at (3.13 ± 0.05) Å. EXAFS and XPS methods also indicated that exposure of the Co-GaAs surfaces to 1.0 M KOH-0.8 M Se2--0.1 M Se22- for photoelectrochemical measurements yielded a new Co surface phase, with an approximate composition of CoSe1.8.

Original languageEnglish
Pages (from-to)5123-5136
Number of pages14
JournalJournal of the American Chemical Society
Volume112
Issue number13
DOIs
Publication statusPublished - Jan 1990

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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    Tufts, B. J., Lunt, S. R., Miskelly, G. M., Sailor, M. J., Santangelo, P. G., Lewis, N. S., Roe, L. A., Hodgson, K. O., Abrahams, I. L., & Caley, C. E. (1990). XPS and EXAFS Studies of the Reactions of Co(III) Ammine Complexes with GaAs Surfaces. Journal of the American Chemical Society, 112(13), 5123-5136. https://doi.org/10.1021/ja00169a021