GEOMETRY OF THE GE(111)-AU(ROOT-3X-ROOT-3)R 30-DEGREES RECONSTRUCTION

A structure model for the Ge(111)-Au(root 3X root 3)R30 degrees surfac e reconstruction is proposed based on scanning tunneling microscopy (S TM) and photoelectron spectroscopy on the Ge 3d and Au 4f core lines. The basic unit is a Au3Ge molecule binding in one-third of the T-1 sub strate sites with a gold trimer pointing out of the surface. This leav es two-thirds of a monolayer of unoccupied T-1 sites which make up a h exagonal honeycomb pattern. Two types of STM images have been obtained which are explained within this model, where either the trimers or th e substrate Ge atoms are probed depending on the specific tip conditio ns in combination with the sample bias voltage. Furthermore, small ins ets of a metallic (1X1) structure are found at low gold coverage toget her with a distorted (2X2) surface structure.