CORE-LEVEL PHOTOEMISSION FROM ALKALI-METALS ON RU(001)

We report soft-x-ray photoemission results on the core-level binding energies of Li, Na, K, and Cs adsorbed on Ru(001). For all four alkali metals, the saturated alkali-metalRu interface core level and the second- (surface-) layer core-level binding energies differ by as much as 0.851.25 eV. Surface versus bulklike core-level shifts are reported for Li, K, and Cs, which are 0.55 eV for Li and 0.25 eV for the other two. For increasing coverages of Li, Na, and K in direct contact with Ru, there are significant decreases in the core-level binding energies, the total shift ranging from -1.25 eV for Li to -0.80 eV for K; the shift for Cs is small and the reasons for the deviation are discussed. A comparison between our observations and the prediction from the thermodynamic model of Johannson and Martensson is also given. © 1990 The American Physical Society.