The bond geometries of Rb atoms in two different (√3 x √3)R30° structures, formed by adsorption on Al(111) at 100 and 300K, were determined by low energy electron diffraction. Adsorption at 300K led to occupation by Rb atoms of a quasi-substitutional, six-fold coordinate site formed by displacing every third Al atom in the first layer of the substrate. Adsorption at 100K led to occupation of an on-top site on a rumpled Al layer in which the vibrational amplitudes of Al atoms were anomalously large. An irreversible, order-preserving phase transition from the 100K to the 300K structure occurred on annealing.

Enhanced Surface Vibrations and Reconstruction of the Al(111) Surface Induced by Rb Adsorption. M.M.Nielsen, J.Burchhardt, D.L.Adams, E.Lundgren, J.N.Andersen: Physical Review Letters, 1994, 72, 3370-3