Geometry of the Ge(111)-Au(√3 × √3 )<i>R</i>30° reconstruction

Abstract

A structure model for the Ge(111)-Au(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} surface reconstruction is proposed based on scanning tunneling microscopy (STM) and photoelectron spectroscopy on the Ge 3d and Au 4f core lines. The basic unit is a ${\mathrm{Au}}_{3}$Ge molecule binding in one-third of the ${\mathit{T}}_{1}$ substrate sites with a gold trimer pointing out of the surface. This leaves two-thirds of a monolayer of unoccupied ${\mathit{T}}_{1}$ sites which make up a hexagonal honeycomb pattern. Two types of STM images have been obtained which are explained within this model, where either the trimers or the substrate Ge atoms are probed depending on the specific tip conditions in combination with the sample bias voltage. Furthermore, small insets of a metallic (1\ifmmode\times\else\texttimes\fi{}1) structure are found at low gold coverage together with a distorted (2\ifmmode\times\else\texttimes\fi{}2) surface structure.