INITIAL-STAGES OF OXIDATION OF GE(111)-C(2X8) STUDIED BY SCANNING TUNNELING MICROSCOPY

The reaction of oxygen with the Ge(111)-c(2 X 8) surface has been studied with use of a scanning tunneling microscope. Atomically resolved images of the same area before and after oxygen exposure reveal that, on a room-temperature surface, the primary nucleation sites are the boundaries between domains of different orientations of the c(2 X 8) reconstruction. Point defects and disordered adatom regions can also act as nucleation sites. The c(2 X 8) reconstructed terraces themselves and, unexpectedly, the step risers between terraces are found to be relatively unreactive. At elevated sample temperatures, the surface unreconstructs due to adatom mobility. At these elevated temperatures, the oxide nucleates homogeneously and pins the surface in a disordered adatom configuration. This suggests that facilitated oxidation at elevated sample temperatures is primarily due to degradation of the c(2 X 8) reconstruction. Spectroscopic data from I-V curves are also presented and compared with known electronic spectra.