ALKALI-METAL ADSORPTION ON AL(111)

The submonolayer adsorption of Na, Y, Rb, and Cs on the Al(111) surfac e at 100 K and at room temperature is investigated by high resolution core level spectroscopy and low energy electron diffraction. It is fou nd that the first alkali atoms on the surface adsorb at surface defect s. At higher coverages, up to approximately one third of the maximum s ubmonolayer coverage, alkali atoms adsorbed at defects coexist with a dispersed phase. At higher coverages island formation is found to occu r for the majority of the systems. It is argued that all of the ordere d structures formed at room temperature involve a disruption of the Al (111) surface in contrast to the situation at 100 K where the alkali a toms adsorb as adatoms.