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Imaging and Manipulation of Initial Oxidation Product on Si(111)-(7×7)

The initial reaction of an O2 molecule with Si(111)-(7×7) was studied using a scanning tunneling microscope at 10 K. The reacted site shows a characteristic dark feature which is ascribed to a metastable product with one oxygen atom bonded on top of a Si adatom and another inserted into a back bond. The dark site appears asymmetric with respect to the surface mirror plane, possibly reflecting the location of the inserted oxygen atom. No evidence for molecular chemisorption was obtained even at 10 K. The atomic-scale manipulation of the initial oxidation product was demonstrated.