Oxidation of ordered Pt-Sn surface alloys by O2

Dmitri I. Jerdev, Bruce E. Koel

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

We have studied the oxidation of two, ordered Pt-Sn surface alloys at 380-425 K using moderately high pressures of oxygen (O2) at Po2=2×10-2 Torr. Under these conditions, the surface oxygen concentration increased to a maximum oxygen uptake of ΘO=1.2 ML (1ML=1.505×1015 atom/cm2) for the (2×2)-Sn/Pt(1 1 1) alloy (with ΘSn=0.25) and ΘO=1.4 ML for the (√3×√3)R30°-Sn/Pt(1 1 1) alloy (with ΘSn=0.33). Oxygen accumulation was accompanied by a shift in the Sn(3d5/2) XPS peak from 484.9 to 485.5 eV, with most of the pre-alloyed tin oxidized to a "quasimetallic" state (a form more reduced than SnO). In addition, an oxidic state of Sn (with composition SnO or SnOx, where x<2) is formed. No change occurred in the Pt(4f) peaks, suggesting that no "Pt oxide" phase was formed under these conditions. On the (2×2)-Sn/Pt(1 1 1) alloy, oxygen uptake to ΘO=0.5 ML was achieved instantly (in less than 10 s) and then occurred more slowly until a saturation uptake was reached. Two kinetic regions for oxygen uptake exceeding ΘO=0.5 ML were distinguished, with apparent activation energies Eapp of 14 and 20 kcal/mol for oxygen concentrations of ΘO=0.5-0.8 and 0.8-1.0 ML, respectively. The oxygen uptake curve for the (√3×√3)R30°-Sn/Pt(1 1 1) alloy also displayed two distinct regions. In the first region, with ΘO≥0.4 ML, Eapp was 9 kcal/mol. In the second region, with ΘO≥0.4 ML, oxidation proceeded with Eapp=17 kcal/mol. Overall, these results are consistent with previous studies on bulk Pt-Sn alloys, but new information is obtained on the role of alloy surface structure in controlling the initial stages of oxidation kinetics.

Original languageEnglish (US)
Pages (from-to)106-114
Number of pages9
JournalSurface Science
Volume492
Issue number1-2
DOIs
StatePublished - Oct 10 2001
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

Keywords

  • Chemisorption
  • Isotopic exchange/traces
  • Surface diffusion
  • Thermal desorption

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