XPS and EXAFS studies of the reactions of Co(III) ammine complexes with GaAs surfaces

The chemisorption of Co(II) 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 (100)-oriented n-GaAs single crystals exposed to aqueous (pH > 10) (Co{sup III}(NH{sub 3}){sub 5}X){sup n+} (X = NH{sub 3}, Br{sup {minus}}, HO{sup {minus}}) solutions indicated the deposition of a Co(II)-oxo overlayer of approximate stoichiometry Co(OH){sub 2}, with a coverage of (0.2-2.4) {times} 10{sup {minus}8} mol of Co/cm{sup 2} projected area of GaAs. The reaction stoichiometry between Co(III) 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).