Thermal dissociation of CO molecules and carbon incorporation on the Si(111)-(7 x 7) surface

Incorporation of carbon (C) atoms in the Si(111)-(7 x 7) surface is investigated by using scanning tunneling microscopy and density-functional theory calculations. C atoms are supplied through thermal dissociation of CO molecules adsorbed on the Si(111)-(7 x 7) surface. One C atom can be incorporated substitutionally below the Si adatoms of the (7 x 7) structure. However, the stable (7 x 7) surface can accommodate only a very small amount of C atoms and the surplus C atoms are swept away to the step edges in the form of silicon-carbon clusters, restoring the clean Si(111)-(7 x 7) structure on the flat terrace. In contrast to the B-induced root 3 x root 3 reconstruction, high density C atoms do not induce a single crystalline root 3 x root 3 reconstruction over a wide area of Si(111).