Atomic bond configuration of Ge(111)-(√3 × √3 )R30°-Au: A low-energy electron-diffraction study

We determined the bond geometry of the Ge(111)-(√3 × √3 )R30°-Au surface by means of low-energy electron diffraction. The resulting lateral parameters are in excellent agreement with values recently obtained by a surface x-ray-diffraction study while perpendicular parameters differ substantially from them. The Au/Ge(111)-(√3 × √3 )R30° surface consists of a (√3 × √3 )R30° net of Au atoms which replace the topmost Ge atoms and form trimers. The Au-Au bond length is 2.81±0.07 Å. The Ge atoms in the second layer are laterally displaced from their bulk positions by 0.5 Å, resulting in a Au-Ge bond length of 2.50±0.14 Å. The missing top Ge layer and the displacement of second-layer Ge atoms lead to distortions in deeper Ge layers, most notably a buckling in the third and fourth Ge layers with a magnitude of about 0.2 Å.