INTERACTION OF SN ATOMS WITH THE INTRINSIC DANGLING-BOND STATES OF SI(111)-(7X7)

At the initial stages of room-temperature deposition we have observed the preferential adsorption of the individual Sn atoms on the Si cente r-adatom (T-1) sites on Si(111)-(7 x 7) using scanning tunneling micro scopy. A spectroscopic analysis of changes in the energy spectrum of s urface states around the Fermi level (E(f)) suggests that covalent bon ding occurs between individual Sn and Si adatoms. This results in a su rface metal-insulator transition due to the removal of Si adatom surfa ce states at E(f) while preserving the (7 x 7) sub-lattice. An energy- level scheme is proposed to explain this behavior.