Annealing effects and structural evolution of Si/Cu(1 1 1) ultrathin films

The surface structure and compositions of the Si/Cu(1 1 1) system have been systematically investigated. As Si atoms are deposited on a Cu(1 1 1) surface, a sqrt(3) × sqrt(3) R 30 ° structure is observed for up to 2 monolayers. The surface structure changes to be 1 × 1 for thicker films. As the annealing temperature increases, most Si atoms diffuse into the Cu(1 1 1) substrate. The residual Si atoms in the top layer form an ordered surface alloy that lies on a Cu-rich surface. A structural phase diagram is successfully established for Si/Cu(1 1 1) films thinner than 5 monolayers at temperatures up to 600 K. The phase diagram can be divided into three regions. In region I for low coverage or at high temperatures, the films exhibit sqrt(3) × sqrt(3) R 30 ° structure. In regions II and III, 1 × 1 and disordered surface structure are resolved, respectively.