Surface-sensitive x-ray standing-wave study of Si(111)3×3-Ag

By combining the surface sensitivity of low-energy elastic photoelectrons with the position sensitivity of the x-ray standing-wave technique, we have determined both the Ag and Si atomic heights at the Si(111)$\sqrt{3}$\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$-Ag interface. Our data give evidence that the Si(111)$\sqrt{3}$\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$-Ag surface consists of a missing Si top-layer reconstruction, with Ag adatoms terminating the structure. The perpendicular height of the Ag layer and the first Si layer supports the honeycomb-chained-trimer model proposed for this interface. \textcopyright{} 1996 The American Physical Society.