NEW RESULTS ON THE REACTION OF SI(111) WITH MG

The reaction of Si{111}7 x 7 with Mg is studied with low-energy electron diffraction (LEED) and Auger-electron spectroscopy (AES). In contrast to Vandre, Incoccia and Kaindl [Surf. Sci. 225 (1990) 233], who reported the formation of a square-root 3 x square-root 3-30-degrees superstructure for deposition on the room-temperature substrate and the formation of a 3 x 3 superstructure upon thermal annealing, we observe the formation of a 2/3 square-root 3 x 2/3 square-root 3-30-degrees superstructure for slow-rate deposition on the room-temperature substrate and the formation of a 3 x 1 superstructure upon thermal annealing of the Mg/Si 1 x 1 phase. The 2/3 square-root 3 x 2/3 square-root 3-30-degrees phase is probably SiMg2 with about 2% strain, while the 3 x 1 phase is equal to the 3 x 1 phases produced by adsorption of Li, Na or Ag on Si{111}7 x 7 as reported by Fan and Ignatiev [Phys. Rev. B 41 (1990) 3592].