We have used medium-energy ion scattering to investigate the geometric structure of the Si(111)-(√3 × √3 )R30°-Au surface. Several drastically different models have been proposed which vary in both Au coverage and location of the Au atoms relative to the Si substrate. Our results provide several rigid constraints on acceptable models of this surface. We measure a Au coverage of 0.84±0.05 monolayer and argue that the nominal Au coverage for this surface should be 1.0 monolayer. Furthermore, the Au atoms are not located in Si bulk sites and the Si lattice in the surface region is severely distorted.

• Received 8 August 1990

DOI:https://doi.org/10.1103/PhysRevB.42.9233