One monolayer of gold on an Si(111) surface: surface phases and phase transitions

The formation and atomic structure of the surface phases induced by Au coverages of about one monolayer have been studied using RHEED and STM. From the comparison of one-beam RHEED intensity rocking curves and STM images, we have found that the alpha root 3-Au, beta root 3-Au, 2 root 21-Au and 6 x 6-Au surfaces have similar atomic structures, which are different from the structure of high-temperature gamma root 3-Au phase at the same Au coverage. To obtain the atomic structure perpendicular to the surface, the one-beam RHEED intensity rocking curves have been analyzed by RHEED dynamical calculations and thereby the interlayer distances and atomic densities of surface parallel layers have been determined. A possible mechanism of phase transitions and surface ordering is proposed and discussed. (C) 1999 Elsevier Science B.V. All rights reserved.