DIFFERENCES IN THE CS 4D AND 5P SURFACE AND INTERFACE CORE-LEVEL SHIFTS

Core-level binding energy shifts of Cs induced by changes in the surroundings of the Cs atoms are measured for two different Cs core levels, 5p and 4d, and are found to be different for these two levels. The surface core-level shift of Cs is found to differ by 25 meV between the two levels. In the case of the Cs core-level shifts between bulk Cs atoms and Cs atoms at an interface between Cs and an Al(111) surface the difference between the two levels is found to be as large as 60 meV. The implications of these results for the precision of the Z + 1 approximation are discussed.