Formation processes of an ordered mixed structure: Cu(0 0 1)-(22×2)R45°-Li,Mg

The formation processes of a (22×2)R45° structure formed by the coadsorption of Li and Mg on Cu(0 0 1) at room temperature, whose structure has been determined [Surf. Sci. 493 (2001) 91], are examined by low-energy electron diffraction (LEED). By depositing Mg atoms on the Li pre-adsorbed (2×1) surface, a sequence of LEED patterns (2×1)→c(4×4)→(22×2)R45° was observed. The c(4×4) LEED pattern is proved to be due to the coexistence of the (2×1)-Li and (22×2)R45°-Li,Mg structures. On the other hand, when Li was adsorbed on the Mg pre-adsorbed surface, a disordered surface was formed until the (22×2)R45°-Li,Mg structure appeared at Li coverage of about 0.22. Different formation processes of the (22×2)R45° structure in the two adsorption sequences are discussed at the atomic level.