New model of the initial stages of Si(111)-(7 x 7) oxidation.

By combining scanning tunneling microscopy (STM) and ultraviolet photoelectron spectroscopy, we show that the adsorption of single O 2 molecules on Si(111)-(7 3 7) produces essentially molecular sites, seen as bright individual sites in STM topographs, which are stable at room temperature. Atomresolved STM studies also reveal that these molecular sites react very efficiently with further O 2 and H 2O molecules. This is shown to account for the saturation at low exposure of the molecular site density and for the apparent decay lifetime of these molecular sites. [S0031-9007(96)00224-4]