ATOMIC BOND CONFIGURATION OF GE(111)-(ROOT-3X-ROOT-3)R30-DEGREES-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. The Ge atoms in the second layer are laterally displaced from their bulk positions by 0.5, resulting in a Au-Ge bond length of 2.50±0.14. 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. © 1995 The American Physical Society.