Initial Stage of Ag Condensation on Si(111)7×7

Using scanning tunneling microscopy and spectroscopy we have investigated the growth of a ⅓ - monolayer Ag film on Si(111)7×{}7 at substrate temperatures of 90 and 130^∘{}C. An Ag-induced subunit has been identified on top of three dangling bonds of the second atomic layer, which may be considered as the critical nucleus of Ag condensation. At 130^∘{}C Ag mostly condenses in the form of triangularshaped flat islands of equal size, which are preferentially located on faulted halves of the 7×{}7 unit cells and are explained by a close-packed structure of Ag atoms. On the Ag islands the local density of states near the Fermi level is reduced compared to the uncovered 7×{}7 unit cells.