Coverage and adsorption-site dependence of core-level binding energies for tin and lead on Al(111) and Ni(111)

Abstract Thin layers (0.2–10 monolayers) of Pb and Sn were prepared on Al(111) and Ni(111) surfaces and characterized by means of LEED, AES, UPS and work-function measurements. The binding energy of the shallow Sn 4d and Pb 5d core-levels was investigated with respect to coverage and adsorption-site-dependent changes. On Al(111) the Sn and Pb monolayers exhibit ordered, two-domain, aligned but not in registry structures. For these layers core-level binding energies were found identical to those of the bulk metals. On Ni(111), Pb gives rise to a 3 × 3 structure, followed then by a 4 × 4 structure at higher coverages. The Pb 5d core-level binding energies shift continuously to higher values. A final shift of 0.42 eV is reached after about 2 monolayers. Sn on Ni(111) exhibits two welll separated peaks lying at 23.70 and 23.97 eV for the 4d 5 2 line. These two lines can be correlated with two different adsorption sites which have to be assumed for the ( 3 × 3 )R30° and the (2 × 2) structure found at different coverages. The binding energy shifts are discussed in a model based on a Born-Haber cycle.