Mg-induced Si(111)-(3x2) reconstruction studied by scanning tunneling microscopy

Using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED), a Mg-induced Si(Ill)-(3x2) reconstruction formed by annealing of deposited Mg submonolayers is studied. The STM observations reveal that the Mg-Si(lll) surface, which shows up in LEED as a (3 x 1) structure, actually has local (3 x 2) and c(6 x 2) periodicity. It is found that the formation of the Si(111)-(3 x 2)-Mg phase involves considerable Si-atom redistribution, caused by the difference in the top Si-atom density of the Si(111)-(7 x 7) and Si(111)-(3 x 2)-Mg surfaces. From the Si mass transport balance, the top Si-atom density in the (3 x 2)-Mg phase is determined to be 4/3 ML. We conclude that the top Si layer has a (3 x 1) structure similar to that of the Si(lll)(3 x 1) reconstructions induced by the alkali metals Li and Na, while the double periodicity is associated with the Mg adsorbate structure. (C) 1998 Elsevier Science B.V. All rights reserved.