USE OF SIMS FOR STUDIES OF ADSORPTION ON WELL-DEFINED METAL-SURFACES (1) COMBINED XPS-LEED-SIMS STUDIES OF O2, CO, H2O, AND H-2 ON NI (100)

We have investigated the potential of SIMS for providing information on substrate-adsorbate geometry and substrate-adsorbate elemental and chemical composition by studying adsorption on Ni (100) while simultaneously monitoring by XPS and LEED. H//2, CO, O//2, and H//2O were studied. We find no obvious dependence in SIMS ion cluster distributions on specific adsorbate geometry. We find a strong direct dependence on chemical composition. Distinction between molecular and dissociative adsorption of CO and H//2O is easy, as is distinction between chemisorbed O and oxide. The ability to detect H is important. Thus low coverages of H on Ni (100) are easily detected, and distinction of O from OH is of great assistance to XPS which cannot distinguish these species on the basis of O(1s) bond energies. We conclude that SIMS is a very useful adjunct to electron spectroscopy but that, at least for the systems we have studied, sputtered ion cluster distributions are not relatable in any simple way to adsorbate-substrate geometry.