ELECTRONIC-STRUCTURE MODIFICATION AND THE ADSORPTION SITE OF OXYGEN ON ALKALI (CS) COVERED SURFACES STUDIED BY NORMAL EXIT LI- ION SPECTROSCOPY

Electronic-structure change of Ni(lll) surfaces with low and high Cs p recoverages upon exposure to oxygen has been studied by normal exit Li - ion spectroscopy. It is shown that for low Cs coverages the Li- yiel d from Ni sites decreases mon rapidly than front Cs; while for Cs cove rages near 1 monolayer (ML), both the yields show a maximum at low O e xposures, which is explained as the extension of alkali valence-electr on wave functions further towards the vacuum. The results also provide the first direct evidence that oxygen atoms lie above the Cs sites fo r Cs coverages near I ML and low O exposures.