Atomic bond configuration of Ge(111)-( sqrt 3 x sqrt 3 )R30 degrees-Au: A low-energy electron-diffraction study.

Abstract

We determined the bond geometry of the Ge(111)-(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{}-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)-(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} surface consists of a (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} net of Au atoms which replace the topmost Ge atoms and form trimers. The Au-Au bond length is 2.81\ifmmode\pm\else\textpm\fi{}0.07 \AA{}. The Ge atoms in the second layer are laterally displaced from their bulk positions by 0.5 \AA{}, resulting in a Au-Ge bond length of 2.50\ifmmode\pm\else\textpm\fi{}0.14 \AA{}. 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 \AA{}.