ALKALI-METAL ADSORPTION ON AL(111) AND AL(100)

Up to the beginning of this decade the physical properties of alkali-metal adsorbates on metal substrates were seemingly soundly explained and drew no special attention aside from their known technological importance related to catalysis and the dramatic lowering of the work function which they induce. Surprisingly, however, recent experimental and theoretical work has turned this situation around with reports of most unexpected behavior. We discuss density-functional theory calculations for Na and K adsorbates on aluminum where new adsorbate geometries are predicted. The interplay and competition of the adsorbate-substrate and the adsorbate-adsorbate interactions is shown to give rise to interesting geometry changes (e.g. hollow, on-top, and substitutional sites) and to a condensation phase transition of the (initially, mutually repelling) alkali adatoms into islands.