Surface recoiling, XPS and UPS study of chemisorption of H2, O2 and H2O on lanthanum

Ranjit Kumar, Moshe H. Mintz, J. Wayne Rabalais

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32 Scopus citations


Chemisorption of H2, O2 and H2O on polycrystalline lanthanum is characterized by X-ray and UV photoelectron spectroscopy (XPS and UPS) and surface recoiling (SR) of adsorbate atoms. The SR technique using a pulsed 3 keV Ar+ source and time-of-flight detection of both neutrals and ions is demonstrated to have outer-monolayer sensitivity and the capability of directly detecting adsorbate hydrogen. The high sensitivity of SR (particularly to surface hydrogen) coupled with the chemical state information from XPS and UPS provides an excellent combination for monitoring adsorbates. Reaction of H2 with La forms the dihydride compound, reaching saturation on the surface after ∼ 50 L exposure and in the outer ∼ 20 Å after ∼ 2000 L. Reaction with O2 is consistent with the formation of La2O3 at exposures ≲ 10 L. The results suggest that during the initial stages of reaction with H2O, oxide and hydride are formed followed by hydroxide formation beginning at ∼ 35 L. The saturation level exhibits a ratio OH/O ∼ 0.4.

Original languageEnglish
Pages (from-to)37-47
Number of pages11
JournalSurface Science
Issue number1
StatePublished - 2 Nov 1984
Externally publishedYes

ASJC Scopus subject areas

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


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