UNIFIED BEHAVIOR OF ALKALI CORE-LEVEL BINDING-ENERGY SHIFTS INDUCED BY SP METALS

Thin overlayers of Na, K, Rb, and Cs on different sp-metal substrates have been investigated using photoelectron spectroscopy. The alkali co re levels show clearly resolved binding-energy shifts between the surf ace layer, the intermediate layer(s), and the interface layer. The mag nitude of these shifts depends on sp metal and on alkali metal. The la yer-resolved core-level binding-energy shifts are well reproduced by m odels based on a thermodynamical description. For three-layer alkali f ilms the core-level binding energy of the intermediate layer is found to exhibit a small but significant shift between different sp-metal su bstrates. A simple relationship between the core-level binding-energy shift for the interface layer and the difference in r(s) value between the sp substrate and the adsorbate is shown to exist.