Use of SIMS for studies of adsorption on well-defined metal surfaces (1) Combined XPS/LEED/SIMS studies of O2, CO, H2O, and H2 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. H2, CO, O2, and H2O 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 H2O 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.