Stability of oxygen adsorption sites and ultrathin aluminum oxide films on Al( 1 1 1 )
First-principles density-functional calculations are used to study oxygen adsorption and incorporation, and properties of (two O-layer) Al2O3 film in different sites at the Al(111) surface. For a monolayer (ML) of O chemisorbed in the on-surface hcp hollows the most stable O-(1×1) subsurface structure is found in tetrahedral sites below the topmost Al atomic plane. A ML of subsurface oxygen atoms induces a very large (37%) increase in the mean interplanar distance of the topmost Al layers. The stability of the structures formed by the incorporated O atoms is almost independent of the type of the on-surface O-layer. It is suggested that the sizeable work-function change appearing for some of the structures allows to discriminate between different kinds of oxygen incorporation. The stability of the ultrathin Al2O3 film on the Al(111) surface is very little dependent on the geometry of the oxygen ML at the film/substrate interface.