ROTATIONAL RECONSTRUCTION OF SAPPHIRE(0001)

The structure of the (root 31 x root 31)R +/- 9 degrees reconstructed phase on sapphire (0001) surface is investigated by means of a simulat ion based on the energy minimization. The interaction between Al adato ms is described with the semi-empirical many-body Sutton-Chen potentia l, corrected for the charge transfer between the metallic overlayer an d the substrate. The interactions between the Al adatoms and sapphire substrate are described with a simple three-dimensional potential fiel d which has the hexagonal periodicity of sapphire surface. Our energy analysis gave evidence that the structure which is observed at room te mperature is in fact a frozen high-temperature structure. In accordanc e with the X-ray scattering, a hexagonal domain pattern separated by d omain walls has been found. The Al adatoms, distributed in two monolay ers, are ordered and isomorphic to metallic Al(111) in the domains and disordered in the domain walls. The main reason for the rotational re construction is the lattice misfit between the metallic Al and sapphir e. (C) 1997 Elsevier Science B.V.