Tufts, Bruce John (1991) Electrochemical and surface chemical studies of n-GaAs photoanodes. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:04112011-141342746
The electrochemical response of n-type gallium arsenide (n-GaAs) pbotoanodes was monitored while in contact with aqueous basic selenide electrolytes before and after exposme to separate aqueous 0.010 M solutions of transition metal ions. Representative members of the transition metal complexes included RuCl_3•xH_2O, RhCl_3•xH_2O, IrCl_3•xH_2), OsCl_3•xH_2O, [Co(lll)(NH_3)_6](Br)_3, [Ru(III)(NH_3)_5(Cl)](Cl)_2, and [Ru(II)(NH_3)_5(OH_2)](Cl)_2. Several members of this group were shown to yield improved current-voltage (I-V) characteristics at the n-GaAs/KOH – Se^(-/2-)(aq) junction. A comparison of the current-voltage properties for p-type and n^+-type GaAs electrodes in the ~ as well as for 10% Sn-doped In_2O_3 electrodes, demonstrated that the source of the improved I-V response following metal ion exposure was a large decrease in the overpotentials, at a given current density, required for selenide oxidation. An extensive surface analytic study revealed that Co(III) ammine complexes became adsorbed on GaAs surfaces from solutions of pH > 9 by a redox reaction involving sacrificial oxidation of the GaAs substrate. The product in all cases was an amorphous Co(OH)_2 surface layer. The stoichiometry of the redox reaction involves one equivalent of GaAs per six equivalent Co(III) species. Following immersion into the KOH – Se^(-/2)(aq) electrolyte, the Co(OH)_2 surface layer was converted to a CoSe_2-like phase that is believed to be the active electrocatalyst responsible for the reduced overpotential dependence following Co(III) ammine treatment. Finally, the surface composition of n-GaAs electrodes that had been specifically etched to produce either a clean, a metallic arsenic covered, or a uniformly oxidized surface were probed by high resolution XPS and were correlated with the n-GaAs I-V properties in aqueous and non-aqueous electrolytes.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Thesis Availability:||Restricted to Caltech community only|
|Defense Date:||18 March 1991|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||11 Apr 2011 22:05|
|Last Modified:||26 Dec 2012 04:33|
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