STM STUDY OF THE ADSORPTION OF SINGLE C-60 MOLECULES ON THE GE(111)-C(2X8) SURFACE

The interaction of isolated C-60 molecules with the Ge(111)-c(2 x 8) s urface is studied using scanning tunneling microscopy. Following room temperature deposition, the C-60 molecules seem to be randomly distrib uted on the surface. However, in most cases the adatom arrangement of the c(2 x 8) structure is perturbed close to the C-60 molecules. A rat her typical defect is the shift of a part of a Ge adatom row by one su rface lattice constant. We present strong evidence that a large number of these defects is produced upon C-60 adsorption. We show that in mo st cases the defective adatom arrangement in the vicinity of the C-60 must be accompanied by unsaturated Ge surface atoms, which exhibit a h alf-filled dangling bond state, underneath the molecules. We propose t hat the C-60-substrate bond is mediated by a charge transfer from thes e substrate dangling bond states to the C-60 molecules.