Abstract
The structural and electronic properties of oxygen atoms adsorbed in on-surface and subsurface sites at the Al(111) surface are investigated from first principles using the density functional theory within the generalized gradient approximation and a supercell approach for a range of oxygen coverages in some cases in two layers. For on-surface adsorption the binding energy increases with Θ, predicting formation of islands in agreement with earlier calculations and experiments. The most stable subsurface adsorption site is found for the structure, i.e., in tetrahedral sites 1.92 Å below the topmost, 25% relaxed, Al atomic plane and 0.4 eV/atom higher in energy than the most preferred energy state in the on-surface fcc hollow site. The adsorption of O has a significant effect on surface buckling relaxation. Oxygen atoms adsorbed in subsurface octahedral sites induce very large (60%) outward relaxation of the topmost layer spacing, which points to the weakening of metal-metal bonds between the two outer Al layers. For the simultaneous subsurface and on-surface adsorption at the binding energy in the subsurface site is 0.2 eV/atom lower than the binding energy in over-surface fcc hollow sites. The sizable work-function changes for different structures are presented and discussed.
- Received 5 May 2000
DOI:https://doi.org/10.1103/PhysRevB.63.085405
©2001 American Physical Society