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

The formation processes of a (2√2 × √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) → (2√2 × √2)R45° was observed. The c(4 × 4) LEED pattern is proved to be due to the coexistence of the (2 × 1)-Li and (2√2 × √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 (2√2 × √2)R45°-Li,Mg structure appeared at Li coverage of about 0.22. Different formation processes of the (2√2 × √2)R45° structure in the two adsorption sequences are discussed at the atomic level.