Alkali metal adsorption on ZnO (0001); anomalous behaviour of sodium

Abstract
Adsorption of the metals caesium, potassium and calcium onto an atomically clean ZnO (0001) surface gives rise to stable ( square root 3* square root 3) surface structures containing about one-third of a monolayer of the alkali metal. Similar treatment with sodium also produces this surface structure on annealing but now with no detectable sodium on the surface.